Sample records for x-band traveling wave

  1. K-Band Traveling-Wave Tube Amplifier

    NASA Technical Reports Server (NTRS)

    Force, Dale A.; Simons, Rainee N.; Peterson, Todd T.; Spitsen, Paul C.

    2010-01-01

    A new space-qualified, high-power, high-efficiency, K-band traveling-wave tube amplifier (TWTA) will provide high-rate, high-capacity, direct-to-Earth communications for science data and video gathered by the Lunar Reconnaissance Orbiter (LRO) during its mission. Several technological advances were responsible for the successful demonstration of the K-band TWTA.

  2. A Novel Ku-Band/Ka-Band and Ka-Band/E-Band Multimode Waveguide Couplers for Power Measurement of Traveling-Wave Tube Amplifier Harmonic Frequencies

    NASA Technical Reports Server (NTRS)

    Wintucky, Edwin G.; Simons, Rainee N.

    2015-01-01

    This paper presents the design, fabrication and test results for a novel waveguide multimode directional coupler (MDC). The coupler, fabricated from two dissimilar frequency band waveguides, is capable of isolating power at the second harmonic frequency from the fundamental power at the output port of a traveling-wave tube (TWT) amplifier. Test results from proof-of-concept demonstrations are presented for a Ku-band/Ka-band MDC and a Ka-band/E-band MDC. In addition to power measurements at harmonic frequencies, a potential application of the MDC is in the design of a satellite borne beacon source for atmospheric propagation studies at millimeter-wave (mm-wave) frequencies (Ka-band and E-band).

  3. High-Power, High-Efficiency Ka-Band Space Traveling-Wave Tube

    NASA Technical Reports Server (NTRS)

    Krawczyk, Richard; Wilson, Jeffrey; Simons, Rainee; Williams, Wallace; Bhasin, Kul; Robbins, Neal; Dibb, Daniel; Menninger, William; Zhai, Xiaoling; Benton, Robert; hide

    2007-01-01

    The L-3 Communications Model 999H traveling-wave tube (TWT) has been demonstrated to generate an output power of 144 W at 60-percent overall efficiency in continuous-wave operation over the frequency band from 31.8 to 32.3 GHz. The best TWT heretofore commercially available for operation in the affected frequency band is characterized by an output power of only 35 W and an efficiency of 50 percent. Moreover, whereas prior TWTs are limited to single output power levels, it has been shown that the output power of the Model 999H can be varied from 54 to 144 W. A TWT is a vacuum electronic device used to amplify microwave signals. TWTs are typically used in free-space communication systems because they are capable of operating at power and efficiency levels significantly higher than those of solid-state devices. In a TWT, an electron beam is generated by an electron gun consisting of a cathode, focusing electrodes, and an anode. The electrons pass through a hole in the anode and are focused into a cylindrical beam by a stack of periodic permanent magnets and travel along the axis of an electrically conductive helix, along which propagates an electromagnetic wave that has been launched by an input signal that is to be amplified. The beam travels within the helix at a velocity close to the phase velocity of the electromagnetic wave. The electromagnetic field decelerates some of the electrons and accelerates others, causing the beam to become formed into electron bunches, which further interact with the electromagnetic wave in such a manner as to surrender kinetic energy to the wave, thereby amplifying the wave. The net result is to amplify the input signal by a factor of about 100,000. After the electrons have passed along the helix, they impinge on electrodes in a collector. The collector decelerates the electrons in such a manner as to recover most of the remaining kinetic energy and thereby significantly increase the power efficiency of the TWT.

  4. X-band preamplifier filter

    NASA Technical Reports Server (NTRS)

    Manshadi, F.

    1986-01-01

    A low-loss bandstop filter designed and developed for the Deep Space Network's 34-meter high-efficiency antennas is described. The filter is used for protection of the X-band traveling wave masers from the 20-kW transmitter signal. A combination of empirical and theoretical techniques was employed as well as computer simulation to verify the design before fabrication.

  5. The modification of X and L band radar signals by monomolecular sea slicks

    NASA Technical Reports Server (NTRS)

    Huehnerfuss, H.; Alpers, W.; Cross, A.; Garrett, W. D.; Keller, W. C.; Plant, W. J.; Schuler, D. L.; Lange, P. A.; Schlude, F.

    1983-01-01

    One methyl oleate and two oleyl alcohol surface films were produced on the surface of the North Sea under comparable oceanographic and meteorological conditions in order to investigate their influence on X and L band radar backscatter. Signals are backscattered in these bands primarily by surface waves with lengths of about 2 and 12 cm, respectively, and backscattered power levels in both bands were reduced by the slicks. The reduction was larger at X band than at L band, however, indicating that shorter waves are more intensely damped by the surface films. The oleyl alcohol film caused greater attenuation of short gravity waves than the film of methyl oleate, thus demonstrating the importance of the physicochemical properties of films on the damping of wind-generated gravity capillary waves. Finally, these experiments indicate a distinct dependence of the degree of damping on the angle between wind and waves. Wind-generated waves traveling in the wind direction are more intensely damped by surface films than are waves traveling at large angles to the wind.

  6. Electronic Power Conditioner for Ku-band Travelling Wave Tube

    NASA Astrophysics Data System (ADS)

    Kowstubha, Palle; Krishnaveni, K.; Ramesh Reddy, K.

    2017-04-01

    A highly sophisticated regulated power supply is known as electronic power conditioner (EPC) is required to energise travelling wave tubes (TWTs), which are used as RF signal amplifiers in satellite payloads. The assembly consisting of TWT and EPC together is known as travelling wave tube amplifier (TWTA). EPC is used to provide isolated and conditioned voltage rails with tight regulation to various electrodes of TWT and makes its RF performance independent of solar bus variations which are caused due to varying conditions of eclipse and sunlit. The payload mass and their power consumption is mainly due to the existence of TWTAs that represent about 35 % of total mass and about 70-90 % (based on the type of satellite application) of overall dc power consumption. This situation ensures a continuous improvement in the design of TWTAs and their associated EPCs to realize more efficient and light products. Critical technologies involved in EPCs are design and configuration, closed loop regulation, component and material selection, energy limiting of high voltage (HV) outputs and potting of HV card etc. This work addresses some of these critical technologies evolved in realizing and testing the state of art of EPC and it focuses on the design of HV supply with a HV and high power capability, up to 6 kV and 170 WRF, respectively required for a space TWTA. Finally, an experimental prototype of EPC with a dc power of 320 W provides different voltages required by Ku-band TWT in open loop configuration.

  7. Novel high-gain, improved-bandwidth, finned-ladder V-band Traveling-Wave Tube slow-wave circuit design

    NASA Technical Reports Server (NTRS)

    Kory, Carol L.; Wilson, Jeffrey D.

    1994-01-01

    The V-band frequency range of 59-64 GHz is a region of the millimeter-wave spectrum that has been designated for inter-satellite communications. As a first effort to develop a high-efficiency V-band Traveling-Wave Tube (TWT), variations on a ring-plane slow-wave circuit were computationally investigated to develop an alternative to the more conventional ferruled coupled-cavity circuit. The ring-plane circuit was chosen because of its high interaction impedance, large beam aperture, and excellent thermal dissipation properties. Despite these advantages, however, low bandwidth and high voltage requirements have, until now, prevented its acceptance outside the laboratory. In this paper, the three-dimensional electrodynamic simulation code MAFIA (solution of MAxwell's Equation by the Finite-Integration-Algorithm) is used to investigate methods of increasing the bandwidth and lowering the operating voltage of the ring-plane circuit. Calculations of frequency-phase dispersion, beam on-axis interaction impedance, attenuation and small-signal gain per wavelength were performed for various geometric variations and loading distributions of the ring-plane TWT slow-wave circuit. Based on the results of the variations, a circuit termed the finned-ladder TWT slow-wave circuit was designed and is compared here to the scaled prototype ring-plane and a conventional ferruled coupled-cavity TWT circuit over the V-band frequency range. The simulation results indicate that this circuit has a much higher gain, significantly wider bandwidth, and a much lower voltage requirement than the scaled ring-plane prototype circuit, while retaining its excellent thermal dissipation properties. The finned-ladder circuit has a much larger small-signal gain per wavelength than the ferruled coupled-cavity circuit, but with a moderate sacrifice in bandwidth.

  8. Traveling-Wave Maser for 32 GHz

    NASA Technical Reports Server (NTRS)

    Shell, James; Clauss, Robert

    2009-01-01

    The figure depicts a traveling-wave ruby maser that has been designed (though not yet implemented in hardware) to serve as a low-noise amplifier for reception of weak radio signals in the frequency band of 31.8 to 32.3 GHz. The design offers significant improvements over previous designs of 32-GHz traveling-wave masers. In addition, relative to prior designs of 32-GHz amplifiers based on high-electron-mobility transistors, this design affords higher immunity to radio-frequency interference and lower equivalent input noise temperature. In addition to the basic frequency-band and low-noise requirements, the initial design problem included a requirement for capability of operation in a closed-cycle helium refrigerator at a temperature .4 K and a requirement that the design be mechanically simplified, relative to prior designs, in order to minimize the cost of fabrication and assembly. Previous attempts to build 32- GHz traveling-wave masers involved the use of metallic slow-wave structures comprising coupled transverse electromagnetic (TEM)-mode resonators that were subject to very tight tolerances and, hence, were expensive to fabricate and assemble. Impedance matching for coupling signals into and out of these earlier masers was very difficult. A key feature of the design is a slow-wave structure, the metallic portions of which would be mechanically relatively simple in that, unlike in prior slow-wave structures, there would be no internal metal steps, irises, or posts. The metallic portions of the slow-wave structure would consist only of two rectangular metal waveguide arms. The arms would contain sections filled with the active material (ruby) alternating with evanescent-wave sections. This structure would be transparent in both the signal-frequency band (the aforementioned range of 31.8 to 32.3 GHz) and the pump-frequency band (65.75 to 66.75 GHz), and would impose large slowing factors in both frequency bands. Resonant ferrite isolators would be placed in the

  9. Beam Measurement of 11.424 GHz X-Band Linac for Compton Scattering X-ray Source

    NASA Astrophysics Data System (ADS)

    Natsui, Takuya; Mori, Azusa; Masuda, Hirotoshi; Uesaka, Mitsuru; Sakamoto, Fumito

    2010-11-01

    An inverse Compton scattering X-ray source for medical applications, consisting of an X-band (11.424 GHz) linac and Q-switched Nd:YAG laser, is currently being developed at the University of Tokyo. This system uses an X-band 3.5-cell thermionic cathode RF gun for electron beam generation. We can obtain a multi-bunch electron beam with this gun. The beam is accelerated to 30 MeV by a traveling-wave accelerating tube. So far, we have verified stable beam generation (around 2.3 MeV) by using the newly designed RF gun and we have succeeded in beam transportation to a beam dump.

  10. Study on W-band sheet-beam traveling-wave tube based on flat-roofed sine waveguide

    NASA Astrophysics Data System (ADS)

    Fang, Shuanzhu; Xu, Jin; Jiang, Xuebing; Lei, Xia; Wu, Gangxiong; Li, Qian; Ding, Chong; Yu, Xiang; Wang, Wenxiang; Gong, Yubin; Wei, Yanyu

    2018-05-01

    A W-band sheet electron beam (SEB) traveling-wave tube (TWT) based on flat-roofed sine waveguide slow-wave structure (FRSWG-SWS) is proposed. The sine wave of the metal grating is replaced by a flat-roofed sine wave around the electron beam tunnel. The slow-wave characteristics including the dispersion properties and interaction impedance have been investigated by using the eigenmode solver in the 3-D electromagnetic simulation software Ansoft HFSS. Through calculations, the FRSWG SWS possesses the larger average interaction impedance than the conventional sine waveguide (SWG) SWS in the frequency range of 86-110 GHz. The beam-wave interaction was studied and particle-in-cell simulation results show that the SEB TWT can produce output power over 120 W within the bandwidth ranging from 90 to 100 GHz, and the maximum output power is 226 W at typical frequency 94 GHz, corresponding electron efficiency of 5.89%.

  11. Progress towards 3-cell superconducting traveling wave cavity cryogenic test

    NASA Astrophysics Data System (ADS)

    Kostin, R.; Avrakhov, P.; Kanareykin, A.; Yakovlev, V.; Solyak, N.

    2017-12-01

    This paper describes a superconducting L-band travelling wave cavity for electron linacs as an alternative to the 9-cell superconducting standing wave Tesla type cavity. A superconducting travelling wave cavity may provide 20-40% higher accelerating gradient by comparison with conventional cavities. This feature arises from an opportunity to use a smaller phase advance per cell which increases the transit time factor and affords the opportunity to use longer cavities because of its significantly smaller sensitivity to manufacturing errors. Two prototype superconducting travelling wave cavities were designed and manufactured for a high gradient travelling wave demonstration at cryogenic temperature. This paper presents the main milestones achieved towards this test.

  12. Travelling-wave resonant four-wave mixing breaks the limits of cavity-enhanced all-optical wavelength conversion.

    PubMed

    Morichetti, Francesco; Canciamilla, Antonio; Ferrari, Carlo; Samarelli, Antonio; Sorel, Marc; Melloni, Andrea

    2011-01-01

    Wave mixing inside optical resonators, while experiencing a large enhancement of the nonlinear interaction efficiency, suffers from strong bandwidth constraints, preventing its practical exploitation for processing broad-band signals. Here we show that such limits are overcome by the new concept of travelling-wave resonant four-wave mixing (FWM). This approach combines the efficiency enhancement provided by resonant propagation with a wide-band conversion process. Compared with conventional FWM in bare waveguides, it exhibits higher robustness against chromatic dispersion and propagation loss, while preserving transparency to modulation formats. Travelling-wave resonant FWM has been demonstrated in silicon-coupled ring resonators and was exploited to realize a 630-μm-long wavelength converter operating over a wavelength range wider than 60 nm and with 28-dB gain with respect to a bare waveguide of the same physical length. Full compatibility of the travelling-wave resonant FWM with optical signal processing applications has been demonstrated through signal retiming and reshaping at 10 Gb s(-1).

  13. Travelling-wave resonant four-wave mixing breaks the limits of cavity-enhanced all-optical wavelength conversion

    PubMed Central

    Morichetti, Francesco; Canciamilla, Antonio; Ferrari, Carlo; Samarelli, Antonio; Sorel, Marc; Melloni, Andrea

    2011-01-01

    Wave mixing inside optical resonators, while experiencing a large enhancement of the nonlinear interaction efficiency, suffers from strong bandwidth constraints, preventing its practical exploitation for processing broad-band signals. Here we show that such limits are overcome by the new concept of travelling-wave resonant four-wave mixing (FWM). This approach combines the efficiency enhancement provided by resonant propagation with a wide-band conversion process. Compared with conventional FWM in bare waveguides, it exhibits higher robustness against chromatic dispersion and propagation loss, while preserving transparency to modulation formats. Travelling-wave resonant FWM has been demonstrated in silicon-coupled ring resonators and was exploited to realize a 630-μm-long wavelength converter operating over a wavelength range wider than 60 nm and with 28-dB gain with respect to a bare waveguide of the same physical length. Full compatibility of the travelling-wave resonant FWM with optical signal processing applications has been demonstrated through signal retiming and reshaping at 10 Gb s−1 PMID:21540838

  14. Space-Qualified Traveling-Wave Tube

    NASA Technical Reports Server (NTRS)

    Wilson, Jeffrey D.; Krawczyk, Richard; Simons, Rainee N.; Williams, Wallace D.; Robbins, Neal R.; Dibb, Daniel R.; Menninger, William L.; Zhai, Xiaoling; Benton, Robert T.

    2010-01-01

    The L-3 Communications Electron Technologies, Inc. Model 999HA traveling-wave tube (TWT), was developed for use as a high-power microwave amplifier for high-rate transmission of data and video signals from deep space to Earth (see figure). The 999HA is a successor to the 999H a non-space qualified TWT described in High-Power, High-Efficiency Ka-Band Traveling-Wave Tube (LEW-17900-1), NASA Tech Briefs, Vol. 31, No. 2 (February 2007), page 32. Operating in the 31.8-to-32.3 GHz frequency band, the 999HA has been shown to generate 252 W of continuous- wave output power at 62 percent overall power efficiency a 75-percent increase in output power over the 999H. The mass of the 999HA is 35 percent less than that of the 999H. Moreover, taking account of the elimination of a Faraday cage that is necessary for operation of the 999H but is obviated by a redesign of high-voltage feed-throughs for the 999HA, the overall reduction in mass becomes 57 percent with an 82 percent reduction in volume. Through a series of rigorous tests, the 999HA has been qualified for operation aboard spacecraft with a lifetime exceeding seven years. Offspring of the 999HA will fly on the Kepler and Lunar Reconnaissance Orbiter missions.

  15. Traveling-Wave Tube Amplifier Second Harmonic as Millimeter-Wave Beacon Source for Atmospheric Propagation Studies

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Wintucky, Edwin G.

    2014-01-01

    This paper presents the design and test results of a CW millimeter-wave satellite beacon source, based on the second harmonic from a traveling-wave tube amplifier and utilizes a novel waveguide multimode directional coupler. A potential application of the beacon source is for investigating the atmospheric effects on Q-band (37 to 42 GHz) and V/W-band (71 to 76 GHz) satellite-to-ground signals.

  16. Traveling-Wave Tube Amplifier Second Harmonic as Millimeter-Wave Beacon Source for Atmospheric Propagation Studies

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Wintucky, Edwin G.

    2014-01-01

    This paper presents the design and test results of a CW millimeter-wave satellite beacon source, based on the second harmonic from a traveling-wave tube amplifier and utilizes a novel waveguide multimode directional coupler. A potential application of the beacon source is for investigating the atmospheric effects on Q-band (37-42 GHz) and V/W-band (71- 76 GHz) satellite-to-ground signals.

  17. Traveling-Wave Tube Amplifier Second Harmonic as Millimeter-Wave Beacon Source for Atmospheric Propagation Studies

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Wintucky, Edwin G.

    2014-01-01

    The design and test results of a novel waveguide multimode directional coupler for a CW millimeter-wave satellite beacon source are presented. The coupler separates the second harmonic power from the fundamental output power of a traveling-wave tube amplifier. A potential application of the beacon source is for investigating the atmospheric effects on Q-band (37 to 42 GHz) and VW-band (71 to 76 GHz) satellite-to-ground signals.

  18. X-Band wave radar system for monitoring and risk management of the coastal infrastructures

    NASA Astrophysics Data System (ADS)

    Ludeno, Giovanni; Soldovieri, Francesco; Serafino, Francesco

    2017-04-01

    The presence of the infrastructures in coastal region entails an increase of the sea level and the shift of the sediment on the bottom with a continuous change of the coastline. In order to preserve the coastline, it has been necessary to resort the use of applications coastal engineering, as the construction of the breakwaters for preventing the coastal erosion. In this frame, the knowledge of the sea state parameters, as wavelength, period and significant wave height and of surface current and bathymetry can be used for the harbor operations and to prevent environmental disasters. In the last years, the study of the coastal phenomena and monitoring of the sea waves impact on the coastal infrastructures through the analysis of images acquired by marine X-band radars is of great interest [1-3]. The possibility to observe the sea surface from radar images is due to the fact that the X-band electromagnetic waves interact with the sea capillary waves (Bragg resonance), which ride on the gravity waves. However, the image acquired by a X-band radar is not the direct representation of the sea state, but it represents the sea surface as seen by the radar. Accordingly, to estimate the sea state parameters as, direction, wavelength, period of dominant waves, the significant wave height as well as the bathymetry and surface current, through a time stack of radar data are required advanced data processing procedures. In particular, in the coastal areas due to the non-uniformity of sea surface current and bathymetry fields is necessary a local analysis of the sea state parameters. In order to analyze the data acquired in coastal area an inversion procedure defined "Local Method" is adopted, which is based on the spatial partitioning of the investigated area in partially overlapping sub-areas. In addition, the analysis of the sea spectrum of each sub-area allows us to retrieve the local sea state parameters. In particular, this local analysis allows us to detect the reflected

  19. The new wave-ring helical (WRH) slow-wave structure for traveling wave tube amplifiers

    NASA Astrophysics Data System (ADS)

    Panahi, Nasser; Saviz, S.; Ghorannevis, M.

    2017-12-01

    In this paper, the new slow-wave structure called wave-ring helix to enhance the power of the traveling wave tubes is introduced. In this new structure, without increasing the length and radius of the helix, the wave motion path can be increased to radiofrequency wave in phase with the electron beam. The results show that in the special frequency range the output power and gain are greater than conventional helix. In this paper, optimization results are presented in cold and hot tests on the new structure. The software CST is used in S-band frequency range.

  20. Traveling-wave photodetector

    DOEpatents

    Hietala, V.M.; Vawter, G.A.

    1993-12-14

    The traveling-wave photodetector of the present invention combines an absorptive optical waveguide and an electrical transmission line, in which optical absorption in the waveguide results in a photocurrent at the electrodes of the electrical transmission line. The optical waveguide and electrical transmission line of the electrically distributed traveling-wave photodetector are designed to achieve matched velocities between the light in the optical waveguide and electrical signal generated on the transmission line. This velocity synchronization provides the traveling-wave photodetector with a large electrical bandwidth and a high quantum efficiency, because of the effective extended volume for optical absorption. The traveling-wave photodetector also provides large power dissipation, because of its large physical size. 4 figures.

  1. Traveling-wave photodetector

    DOEpatents

    Hietala, Vincent M.; Vawter, Gregory A.

    1993-01-01

    The traveling-wave photodetector of the present invention combines an absorptive optical waveguide and an electrical transmission line, in which optical absorption in the waveguide results in a photocurrent at the electrodes of the electrical transmission line. The optical waveguide and electrical transmission line of the electrically distributed traveling-wave photodetector are designed to achieve matched velocities between the light in the optical waveguide and electrical signal generated on the transmission line. This velocity synchronization provides the traveling-wave photodetector with a large electrical bandwidth and a high quantum efficiency, because of the effective extended volume for optical absorption. The traveling-wave photodetector also provides large power dissipation, because of its large physical size.

  2. Analysis of X-band radar images for the detection of the reflected and diffracted waves in coastal zones

    NASA Astrophysics Data System (ADS)

    Ludeno, Giovanni; Natale, Antonio; Soldovieri, Francesco; Vicinanza, Diego; Serafino, Francesco

    2014-05-01

    The observation of nearshore waves and the knowledge of the sea state parameters can play a crucial role for the safety of harbors and ocean engineering. In the last two decades, different algorithms for the estimation of sea state parameters, surface currents and bathymetry from X-band radar data have been developed and validated [1, 2]. The retrieval of ocean wave parameters such as significant height, period, direction and wavelength of the dominant wave is based on the spectral analysis of data sequences collected by nautical X-band radars [3]. In particular, the reconstruction of the wave motion is carried out through the inversion procedure explained in [1-3], which exploits the dispersion relationship to define a band pass filter used to separate the energy associated with the ocean waves from the background noise. It is worth to note that the shape of such a band pass filter depends upon the value of both the surface currents and bathymetry; in our reconstruction algorithm these parameters are estimated through the (Normalized Scalar Product) procedure [1], which outperforms other existing methods (e.g., the Least Squares) [4]. From the reconstructed wave elevation sequences we can get the directional spectrum that provides useful information (i.e., wavelength, period, direction and amplitude) relevant to the main waves contributing to the wave motion. Of course, in coastal zones a number of diffraction and reflection phenomena can be observed, due to sea-waves impinging obstacles as jetties, breakwaters and boats. In the present paper we want to show the capability to detect reflected and diffracted sea-waves offered by the processing of X-band radar data. Further details relevant to the obtained results will be provided in the full paper and at the conference time. References [1] F. Serafino, C. Lugni, F. Soldovieri, "A novel strategy for the surface current determination from marine X-Band radar data", IEEE Geosci. and Remote Sensing Letters, vol. 7, no

  3. 200 MW S-band traveling wave resonant ring development at IHEP

    NASA Astrophysics Data System (ADS)

    Zhou, Zu-Sheng; Chi, Yun-Long; Git, Meng-Ping; Pei, Guo-Xi

    2010-03-01

    The resonant-ring is a traveling wave circuit, which is used to produce high peak power with comparatively smaller stored energy. The application to be considered is its use as a high power simulator mainly for testing the klystron ceramic output window, as well as for high power microwave transmission devices. This paper describes the principle of a resonant ring and introduces the structure and property of the newly constructed traveling wave resonant ring at IHEP. Our goal is to produce a 200 MW class resonant ring at 2.856 GHz with a pulse length of 2 μs and repetition rate of 25 Hz. The installation, commissioning and testing of the ring have been completed and a peak power of 200 MW at 3 μs has been achieved. The conditioning results show that all the parameters of the resonant ring reach the design goals.

  4. An X-band phase-locked relativistic backward wave oscillator

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wu, Y.; Science and Technology on High Power Microwave Laboratory, Mianyang 621900; Li, Z. H.

    2015-08-15

    For the purpose of coherent high power microwave combining at high frequency band, an X-band phase-locked relativistic backward wave oscillator is presented and investigated. The phase-locking of the oscillator is accomplished by modulation of the electron beam before it reaches the oscillator. To produce a bunched beam with an acceptable injected RF power requirement, an overmoded input cavity is employed to provide initial density modulation. And a buncher cavity is introduced to further increase the modulation depth. When the beam enters the oscillator, the modulation depth is enough to lock the frequency and phase of the output microwave generated bymore » the oscillator. Particle-in-cell simulation shows that an input power of 90 kW is sufficient to lock the frequency and phase of 1.5 GW output microwave with locking bandwidth of 60 MHz.« less

  5. G-band harmonic multiplying gyrotron traveling-wave amplifier with a mode-selective circuit

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Yeh, Y. S.; Chen, Chang-Hong; Wang, Z. W.

    Harmonic multiplying gyrotron traveling-wave amplifiers (gyro-TWAs) permit for magnetic field reduction and frequency multiplication. A high-order-mode harmonic multiplying gyro-TWA with large circuit dimensions and low ohmic loss can achieve a high average power. By amplifying a fundamental harmonic TE{sub 01} drive wave, the second harmonic component of the beam current initiates a TE{sub 02} wave to be amplified. Wall losses can suppress some competing modes because they act as an effective sink of the energy of the modes. However, such wall losses do not suppress all competing modes as the fields are contracted in the copper section in the gyro-TWA.more » An improved mode-selective circuit, using circular waveguides with the specified radii, can provide the rejection points within the frequency range to suppress the competing modes. The simulated results reveal that the mode-selective circuit can provide an attenuation of more than 10 dB to suppress the competing modes (TE{sub 21}, TE{sub 51}, TE{sub 22}, and TE{sub 03}). A G-band second harmonic multiplying gyro-TWA with the mode-selective circuit is predicted to yield a peak output power of 50 kW at 198.8 GHz, corresponding to a saturated gain of 55 dB at an interaction efficiency of 10%. The full width at half maximum bandwidth is 5 GHz.« less

  6. X-band RF gun and linac for medical Compton scattering X-ray source

    NASA Astrophysics Data System (ADS)

    Dobashi, Katsuhito; Uesaka, Mitsuru; Fukasawa, Atsushi; Sakamoto, Fumito; Ebina, Futaro; Ogino, Haruyuki; Urakawa, Junji; Higo, Toshiyasu; Akemoto, Mitsuo; Hayano, Hitoshi; Nakagawa, Keiichi

    2004-12-01

    Compton scattering hard X-ray source for 10-80 keV are under construction using the X-band (11.424 GHz) electron linear accelerator and YAG laser at Nuclear Engineering Research laboratory, University of Tokyo. This work is a part of the national project on the development of advanced compact medical accelerators in Japan. National Institute for Radiological Science is the host institute and U.Tokyo and KEK are working for the X-ray source. Main advantage is to produce tunable monochromatic hard (10-80 keV) X-rays with the intensities of 108-1010 photons/s (at several stages) and the table-top size. Second important aspect is to reduce noise radiation at a beam dump by adopting the deceleration of electrons after the Compton scattering. This realizes one beamline of a 3rd generation SR source at small facilities without heavy shielding. The final goal is that the linac and laser are installed on the moving gantry. We have designed the X-band (11.424 GHz) traveling-wave-type linac for the purpose. Numerical consideration by CAIN code and luminosity calculation are performed to estimate the X-ray yield. X-band thermionic-cathode RF-gun and RDS(Round Detuned Structure)-type X-band accelerating structure are applied to generate 50 MeV electron beam with 20 pC microbunches (104) for 1 microsecond RF macro-pulse. The X-ray yield by the electron beam and Q-switch Nd:YAG laser of 2 J/10 ns is 107 photons/RF-pulse (108 photons/sec at 10 pps). We design to adopt a technique of laser circulation to increase the X-ray yield up to 109 photons/pulse (1010 photons/s). 50 MW X-band klystron and compact modulator have been constructed and now under tuning. The construction of the whole system has started. X-ray generation and medical application will be performed in the early next year.

  7. Simulation and development of novel slow-wave structures for miniaturized THz-band vacuum-tube devices

    NASA Astrophysics Data System (ADS)

    Benedik, Andrey I.; Karetnikova, Tatiana A.; Torgashov, Roman A.; Terentyuk, Artem G.; Rozhnev, Andrey G.; Torgashov, Gennadiy V.; Ryskin, Nikita M.

    2018-04-01

    Microfabricated vacuum-tube millimeter- and THz-band sources are of great interest for numerous applications such as communications, radar, sensors, imaging, etc. Recently, miniaturized sheet-beam traveling-wave tubes for sub-THz and THz operation have attracted a considerable interest. In this paper, we present the results of modeling and development of slow-wave structures (SWS) for medium power (10-100 W) traveling-wave tube (TWT) amplifiers and backwardwave oscillators (BWO) in near-THz frequency band. Different types of SWSs are considered, such as double-vane SWS for TWT with a sheet electron beam, a folded-waveguide SWS, and novel planar SWSs on dielectric substrates.

  8. The existence of minimum speed of traveling wave solutions to a non-KPP isothermal diffusion system

    NASA Astrophysics Data System (ADS)

    Chen, Xinfu; Liu, Guirong; Qi, Yuanwei

    2017-08-01

    The reaction-diffusion system at =axx - abn ,bt = Dbxx + abn, where n ≥ 1 and D > 0, arises from many real-world chemical reactions. Whereas n = 1 is the KPP type nonlinearity, which is much studied and very important results obtained in literature not only in one dimensional spatial domains, but also multi-dimensional spaces, but n > 1 proves to be much harder. One of the interesting features of the system is the existence of traveling wave solutions. In particular, for the traveling wave solution a (x , t) = a (x - vt), b (x , t) = b (x - vt), where v > 0, if we fix lim x → - ∞ ⁡ (a , b) = (0 , 1) it was proved by many authors with different bounds v* (n , D) > 0 such that a traveling wave solution exists for any v ≥v* when n > 1. For the latest progress, see [7]. That is, the traveling wave problem exhibits the mono-stable phenomenon for traveling wave of scalar equation ut =uxx + f (u) with f (0) = f (1) = 0, f (u) > 0 in (0 , 1) and, u = 0 is unstable and u = 1 is stable. A natural and significant question is whether, like the scalar case, there exists a minimum speed. That is, whether there exists a minimum speed vmin > 0 such that traveling wave solution of speed v exists iff v ≥vmin? This is an open question, in spite of many works on traveling wave of the system in last thirty years. This is duo to the reason, unlike the KPP case, the minimum speed cannot be obtained through linear analysis at equilibrium points (a , b) = (0 , 1) and (a , b) = (1 , 0). In this work, we give an affirmative answer to this question.

  9. Complete multipactor suppression in an X-band dielectric-loaded accelerating structure

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Jing, C.; Gold, S. H.; Fischer, Richard

    2016-05-09

    Multipactor is a major issue limiting the gradient of rf-driven Dielectric-Loaded Accelerating (DLA) structures. Theoretical models have predicted that an axial magnetic field applied to DLA structures may completely block the multipactor discharge. However, previous attempts to demonstrate this magnetic field effect in an X-band traveling-wave DLA structure were inconclusive, due to the axial variation of the applied magnetic field, and showed only partial suppression of the multipactor loading [Jing et al., Appl. Phys. Lett. 103, 213503 (2013)]. The present experiment has been performed under improved conditions with a uniform axial magnetic field extending along the length of an X-bandmore » standing-wave DLA structure. Multipactor loading began to be continuously reduced starting from 3.5 kG applied magnetic field and was completely suppressed at 8 kG. Dependence of multipactor suppression on the rf gradient inside the DLA structure was also measured.« less

  10. Studying Nearshore Ocean Waves Using X-Band Radar

    NASA Astrophysics Data System (ADS)

    Laughlin, B.; Bland, R. W.

    2014-12-01

    In January of 2010, ocean waves generated by an unusually large storm caused major erosion damage to the San Francisco coastline, with an erosion "hot spot" partially collapsing a four-lane throughway and threatening important infrastructure. Every winter, swells from the northwest approach San Francisco's Ocean Beach by passing over the southern limb of the San Francisco Bar, an ebb-tidal delta seaward of the Golden Gate Bridge. Refraction of approaching wave-fronts causes focusing of wave energy at the southern end of Ocean Beach where the S.F. Bar meets the coast, possibly explaining the location of the 2010 hot spot. In 2011 an x-band radar system was installed on a site near the erosion hot spot, at an elevation of 13 m above low tide, about 40 m back from the high-tide line. The radar system collects images of wave crests out to 3 km from the scanner. Study of these images when offshore buoys report a single NW swell shows two swell patterns arriving at Ocean Beach, separated in direction by about 30 degrees, and producing a quilted interference pattern, as seen in the accompanying figure. We interpret these swells as following two different paths around the Bar. Preliminary ray-tracing studies tend to confirm this interpretation. To enhance these images we have employed two techniques. The first technique, which is concerned with identification and visualization of swells in the region of interest, involves iteration over possible swell periods: scans taken at integral multiples of a given period are added together, with the sharpest image determining the swell period (see figure) and providing an enhanced image for further analysis. The second technique involves displacement of images in time by phase incrementation in k-space, with subsequent addition of images. We will present results concerning the stability of the relative phase of the two swells, and the applicability to models for propagation of waves. Establishment of a tested propagation model would

  11. Superconducting traveling wave accelerators

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Farkas, Z.D.

    1984-11-01

    This note considers the applicability of superconductivity to traveling wave accelerators. Unlike CW operation of a superconducting standing wave or circulating wave accelerator section, which requires improvement factors (superconductor conductivity divided by copper conductivity) of about 10/sup 6/ in order to be of practical use, a SUperconducting TRaveling wave Accelerator, SUTRA, operating in the pulsed mode requires improvement factors as low as about 10/sup 3/, which are attainable with niobium or lead at 4.2K, the temperature of liquid helium at atmospheric pressure. Changing from a copper traveling wave accelerator to SUTRA achieves the following. (1) For a given gradient SUTRAmore » reduces the peak and average power requirements typically by a factor of 2. (2) SUTRA reduces the peak power still further because it enables us to increase the filling time and thus trade pulse width for gradient. (3) SUTRA makes possible a reasonably long section at higher frequencies. (4) SUTRA makes possible recirculation without additional rf average power. 8 references, 6 figures, 1 table.« less

  12. Traveling-Wave Tubes

    NASA Technical Reports Server (NTRS)

    Kory, Carol L.

    1998-01-01

    The traveling-wave tube (TWT) is a vacuum device invented in the early 1940's used for amplification at microwave frequencies. Amplification is attained by surrendering kinetic energy from an electron beam to a radio frequency (RF) electromagnetic wave. The demand for vacuum devices has been decreased largely by the advent of solid-state devices. However, although solid state devices have replaced vacuum devices in many areas, there are still many applications such as radar, electronic countermeasures and satellite communications, that require operating characteristics such as high power (Watts to Megawatts), high frequency (below 1 GHz to over 100 GHz) and large bandwidth that only vacuum devices can provide. Vacuum devices are also deemed irreplaceable in the music industry where musicians treasure their tube-based amplifiers claiming that the solid-state and digital counterparts could never provide the same "warmth" (3). The term traveling-wave tube includes both fast-wave and slow-wave devices. This article will concentrate on slow-wave devices as the vast majority of TWTs in operation fall into this category.

  13. Design, construction and evaluation of a 12.2 GHz, 4.0 kW-CW coupled-cavity traveling wave tube

    NASA Technical Reports Server (NTRS)

    Ayers, W. R.; Harman, W. A.

    1973-01-01

    An analytical and experimental program to study design techniques and to utilize these techniques to optimize the performance of an X-band 4 kW, CW traveling wave tube ultimately intended for satellite-borne television broadcast transmitters is described. The design is based on the coupled-cavity slow-wave circuit with velocity resynchronization to maximize the conversion efficiency. The design incorporates a collector which is demountable from the tube. This was done to facilitate multistage depressed collector experiments employing a NASA designed axisymmetric, electrostatic collector for linear beam microwave tubes after shipment of the tubes to NASA.

  14. Traveling wave device for combining or splitting symmetric and asymmetric waves

    DOEpatents

    Möbius, Arnold; Ives, Robert Lawrence

    2005-07-19

    A traveling wave device for the combining or splitting of symmetric and asymmetric traveling wave energy includes a feed waveguide for traveling wave energy, the feed waveguide having an input port and a launching port, a reflector for coupling wave energy between the feed waveguide and a final waveguide for the collection and transport of wave energy to or from the reflector. The power combiner has a launching port for symmetrical waves which includes a cylindrical section coaxial to the feed waveguide, and a launching port for asymmetric waves which includes a sawtooth rotated about a central axis.

  15. Concentric traveling ionospheric disturbances triggered by the launch of a SpaceX Falcon 9 rocket

    NASA Astrophysics Data System (ADS)

    Lin, Charles C. H.; Shen, Ming-Hsueh; Chou, Min-Yang; Chen, Chia-Hung; Yue, Jia; Chen, Po-Cheng; Matsumura, Mitsuru

    2017-08-01

    We report the first observation of concentric traveling ionospheric disturbances (CTIDs) triggered by the launch of a SpaceX Falcon 9 rocket on 17 January 2016. The rocket-triggered ionospheric disturbances show shock acoustic wave signature in the time rate change (time derivative) of total electron content (TEC), followed by CTIDs in the 8-15 min band-pass filtering of TEC. The CTIDs propagated northward with phase velocity of 241-617 m/s and reached distances more than 1000 km away from the source on the rocket trajectory. The wave characteristics of CTIDs with periods of 10.5-12.7 min and wavelength 200-400 km agree well with the gravity wave dispersion relation. The optimal wave source searching and gravity wave ray tracing technique suggested that the CTIDs have multiple sources which are originated from 38-120 km altitude before and after the ignition of the second-stage rocket, 200 s after the rocket was launched.

  16. Waveguide Multimode Directional Coupler for Harvesting Harmonic Power from the Output of Traveling-Wave Tube Amplifiers

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Wintucky, Edwin G.

    2017-01-01

    This paper presents the design, fabrication, and test results for a novel waveguide multimode directional coupler (MDC). The coupler fabricated from dissimilar frequency band waveguides, is capable of isolating power at the 2nd harmonic frequency from the fundamental power at the output port of traveling-wave tube amplifiers. Test results from proof-of-concept demonstrations are presented for Ku/Ka-band and Ka/E-band MDCs, which demonstrate sufficient power in the 2nd harmonic for a space borne beacon source for mm-wave atmospheric propagation studies.

  17. Generalized thermoelastic wave band gaps in phononic crystals without energy dissipation

    NASA Astrophysics Data System (ADS)

    Wu, Ying; Yu, Kaiping; Li, Xiao; Zhou, Haotian

    2016-01-01

    We present a theoretical investigation of the thermoelastic wave propagation in the phononic crystals in the context of Green-Nagdhi theory by taking thermoelastic coupling into account. The thermal field is assumed to be steady. Thermoelastic wave band structures of 3D and 2D are derived by using the plane wave expansion method. For the 2D problem, the anti-plane shear mode is not affected by the temperature difference. Thermoelastic wave bands of the in-plane x-y mode are calculated for lead/silicone rubber, aluminium/silicone rubber, and aurum/silicone rubber phononic crystals. The new findings in the numerical results indicate that the thermoelastic wave bands are composed of the pure elastic wave bands and the thermal wave bands, and that the thermal wave bands can serve as the low boundary of the first band gap when the filling ratio is low. In addition, for the lead/silicone rubber phononic crystals the effects of lattice type (square, rectangle, regular triangle, and hexagon) and inclusion shape (circle, oval, and square) on the normalized thermoelastic bandwidth and the upper/lower gap boundaries are analysed and discussed. It is concluded that their effects on the thermoelastic wave band structure are remarkable.

  18. The variability, structure and energy conversion of the northern hemisphere traveling waves simulated in a Mars general circulation model

    NASA Astrophysics Data System (ADS)

    Wang, Huiqun; Toigo, Anthony D.

    2016-06-01

    Investigations of the variability, structure and energetics of the m = 1-3 traveling waves in the northern hemisphere of Mars are conducted with the MarsWRF general circulation model. Using a simple, annually repeatable dust scenario, the model reproduces many general characteristics of the observed traveling waves. The simulated m = 1 and m = 3 traveling waves show large differences in terms of their structures and energetics. For each representative wave mode, the geopotential signature maximizes at a higher altitude than the temperature signature, and the wave energetics suggests a mixed baroclinic-barotropic nature. There is a large contrast in wave energetics between the near-surface and higher altitudes, as well as between the lower latitudes and higher latitudes at high altitudes. Both barotropic and baroclinic conversions can act as either sources or sinks of eddy kinetic energy. Band-pass filtered transient eddies exhibit strong zonal variations in eddy kinetic energy and various energy transfer terms. Transient eddies are mainly interacting with the time mean flow. However, there appear to be non-negligible wave-wave interactions associated with wave mode transitions. These interactions include those between traveling waves and thermal tides and those among traveling waves.

  19. High Power RF Testing of A 3-Cell Superconducting Traveling Wave Accelerating Structure

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kanareykin, Alex; Kostin, Romna; Avrakhov, Pavel

    Euclid Techlabs has completed the Phase II SBIR project, entitled “High Power RF Testing of a 3-Cell Superconducting Traveling Wave Accelerating Structure” under Grant #DE-SC0006300. In this final technical report, we summarize the major achievements of Phase I of the project and review the details of Phase II of the project. The accelerating gradient in a superconducting structure is limited mainly by quenching, i.e., by the maximum surface RF magnetic field. Various techniques have been developed to increase the gradient. A traveling wave accelerating SC structure with a feedback waveguide was suggested to allow an increased transit time factor andmore » ultimately, a maximum gradient that is 22%-24% higher than in the best of the time standing wave SRF cavity solution. The proposed structure has an additional benefit in that it can be fabricated much longer than the standing wave ones that are limited by the field flatness factor. Taken together, all of these factors will result in a significant overall length and, correspondingly cost reduction of the SRF based linear collider ILC or SRF technology based FELs. In Phase I of this project, a 3-cell L-band SC traveling wave cavity was designed. Cavity shape, surface field ratios, inter-cell coupling coefficients, accelerating field flatness have been reviewed with the analysis of tuning issues. Moreover, the technological aspects of SC traveling wave accelerating structure fabrication have been studied. As the next step in the project, the Phase II experimental program included engineering design, manufacturing, surface processing and high gradient testing. Euclid Techlabs, LLC contracted AES, Inc. to manufacture two niobium cavities. Euclid Techlabs cold tested traveling wave regime in the cavity, and the results showed very good agreement with mathematical model specially developed for superconducting traveling wave cavity performance analysis. Traveling wave regime was adjusted by amplitude and phase

  20. Traveling-Wave Membrane Photomixers

    NASA Technical Reports Server (NTRS)

    Wyss, R. A.; Martin, S. C.; Nakamura, B. J.; Neto, A.; Pasqualini, D.; Siegel, P. H.; Kadow, C.; Gossard, A. C.

    2001-01-01

    Traveling-wave photomixers have superior performance when compared with lumped area photomixers in the 1 to 3 THz frequency range. Their large active area and distributed gain mechanism assure high thermal damage threshold and elimination of the capacitive frequency roll-off. However, the losses experienced by the radio frequency wave traveling along the coplanar strips waveguide (due to underlying semi-infinite GaAs substrate) were a serious drawback. In this paper we present device designs and an experimental setup that make possible the realization of photomixers on membranes which eliminate the losses.

  1. Theory of multiwave mixing within the superconducting kinetic-inductance traveling-wave amplifier

    NASA Astrophysics Data System (ADS)

    Erickson, R. P.; Pappas, D. P.

    2017-03-01

    We present a theory of parametric mixing within the coplanar waveguide (CPW) of a superconducting nonlinear kinetic-inductance traveling-wave (KIT) amplifier engineered with periodic dispersion loadings. This is done by first developing a metamaterial band theory of the dispersion-engineered KIT using a Floquet-Bloch construction and then applying it to the description of mixing of the nonlinear RF traveling waves. Our theory allows us to calculate signal gain versus signal frequency in the presence of a frequency stop gap, based solely on loading design. We present results for both three-wave mixing (3WM), with applied dc bias, and four-wave mixing (4WM), without dc. Our theory predicts an intrinsic and deterministic origin to undulations of 4WM signal gain with signal frequency, apart from extrinsic sources, such as impedance mismatch, and shows that such undulations are absent from 3WM signal gain achievable with dc. Our theory is extensible to amplifiers based on Josephson junctions in a lumped LC-ladder transmission line (TWPA).

  2. Experimental study of an X-band phase-locked relativistic backward wave oscillator

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wu, Y.; Science and Technology on High Power Microwave Laboratory, Mianyang 621900; Li, Z. H.

    2015-11-15

    To achieve high power microwave combined with high frequency band, an X-band phase-locked relativistic backward wave oscillator (RBWO) is proposed and investigated theoretically and experimentally using a modulated electron beam. In the device, an overmoded input cavity and a buncher cavity are employed to premodulate the electron beam. Particle-in-cell simulation shows that an input power of 90 kW is sufficient to lock the frequency and phase of 1.5 GW output microwave with the locking bandwidth of 60 MHz. Moreover, phase and frequency locking of an RBWO has been accomplished experimentally with an output power of 1.5 GW. The fluctuation of the relative phase differencemore » between output microwave and input RF signal is less than ±20° with the locking duration of about 50 ns. The input RF power required to lock the oscillator is only 90 kW.« less

  3. The noisy edge of traveling waves

    PubMed Central

    Hallatschek, Oskar

    2011-01-01

    Traveling waves are ubiquitous in nature and control the speed of many important dynamical processes, including chemical reactions, epidemic outbreaks, and biological evolution. Despite their fundamental role in complex systems, traveling waves remain elusive because they are often dominated by rare fluctuations in the wave tip, which have defied any rigorous analysis so far. Here, we show that by adjusting nonlinear model details, noisy traveling waves can be solved exactly. The moment equations of these tuned models are closed and have a simple analytical structure resembling the deterministic approximation supplemented by a nonlocal cutoff term. The peculiar form of the cutoff shapes the noisy edge of traveling waves and is critical for the correct prediction of the wave speed and its fluctuations. Our approach is illustrated and benchmarked using the example of fitness waves arising in simple models of microbial evolution, which are highly sensitive to number fluctuations. We demonstrate explicitly how these models can be tuned to account for finite population sizes and determine how quickly populations adapt as a function of population size and mutation rates. More generally, our method is shown to apply to a broad class of models, in which number fluctuations are generated by branching processes. Because of this versatility, the method of model tuning may serve as a promising route toward unraveling universal properties of complex discrete particle systems. PMID:21187435

  4. Cortical travelling waves: mechanisms and computational principles

    PubMed Central

    Muller, Lyle; Chavane, Frédéric; Reynolds, John

    2018-01-01

    Multichannel recording technologies have revealed travelling waves of neural activity in multiple sensory, motor and cognitive systems. These waves can be spontaneously generated by recurrent circuits or evoked by external stimuli. They travel along brain networks at multiple scales, transiently modulating spiking and excitability as they pass. Here, we review recent experimental findings that have found evidence for travelling waves at single-area (mesoscopic) and whole-brain (macroscopic) scales. We place these findings in the context of the current theoretical understanding of wave generation and propagation in recurrent networks. During the large low-frequency rhythms of sleep or the relatively desynchronized state of the awake cortex, travelling waves may serve a variety of functions, from long-term memory consolidation to processing of dynamic visual stimuli. We explore new avenues for experimental and computational understanding of the role of spatiotemporal activity patterns in the cortex. PMID:29563572

  5. High Efficiency Traveling-Wave Tube Power Amplifier for Ka-Band Software Defined Radio on International Space Station-A Platform for Communications Technology Development

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Force, Dale A.; Kacpura, Thomas J.

    2013-01-01

    The design, fabrication and RF performance of the output traveling-wave tube amplifier (TWTA) for a space based Ka-band software defined radio (SDR) is presented. The TWTA, the SDR and the supporting avionics are integrated to forms a testbed, which is currently located on an exterior truss of the International Space Station (ISS). The SDR in the testbed communicates at Ka-band frequencies through a high-gain antenna directed to NASA s Tracking and Data Relay Satellite System (TDRSS), which communicates to the ground station located at White Sands Complex. The application of the testbed is for demonstrating new waveforms and software designed to enhance data delivery from scientific spacecraft and, the waveforms and software can be upgraded and reconfigured from the ground. The construction and the salient features of the Ka-band SDR are discussed. The testbed is currently undergoing on-orbit checkout and commissioning and is expected to operate for 3 to 5 years in space.

  6. Oversized 250 GHz Traveling Wave Tube with a Photonic Band-Gap Structure

    NASA Astrophysics Data System (ADS)

    Rosenzweig, Guy; Shapiro, Michael A.; Temkin, Richard J.

    2017-10-01

    The challenge in manufacturing traveling wave tubes (TWTs) at high frequencies is that the sizes of the structures scale with, and are much smaller than, the wavelength. We have designed and are building a 250 GHz TWT that uses an oversized structure to overcome fabrication and power handling issues that result from the small dimensions. Using a photonic band-gap (PBG) structure, we succeeded to design the TWT with a beam tunnel diameter of 0.72 mm. The circuit consists of metal plates with the beam tunnel drilled down their center. Twelve posts are protruding on one side of each plate in a triangular array and corresponding sockets are drilled on the other side. The posts of each plate are inserted into the sockets of an adjacent plate, forming a PBG lattice. The vacuum spacing between adjacent plates forms the `PBG cavity''. The full structure is a series of PBG coupled cavities, with microwave power coupling through the beam tunnel. The PBG lattice provides confinement of microwave power in each of the cavities and can be tuned to give the right amount of diffraction per cavity so that no sever is needed to suppress oscillations in the operating mode. CST PIC simulations predict over 38 dB gain with 67 W peak power, using a 30 kV, 310 mA electron beam, 0.6 mm in diameter. Research supported by the AFOSR Program on Plasma and Electro-Energetic Physics and by the NIH National Institute of Biomedical Imaging and Bioengineering.

  7. High-Efficiency K-Band Space Traveling-Wave Tube Amplifier for Near-Earth High Data Rate Communications

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Force, Dale A.; Spitsen, Paul C.; Menninger, William L.; Robbins, Neal R.; Dibb, Daniel R.; Todd, Phillip

    2010-01-01

    The RF performance of a new K-Band helix conduction cooled traveling-wave tube amplifier (TWTA) is presented in this paper. A total of three such units were manufactured, tested and delivered. The first unit is currently flying onboard NASA s Lunar Reconnaissance Orbiter (LRO) spacecraft and has flawlessly completed over 2000 orbits around the Moon. The second unit is a proto-flight model. The third unit will fly onboard NASA s International Space Station (ISS) as a very compact and lightweight transmitter package for the Communications, Navigation and Networking Reconfigurable Testbed (CoNNeCT), which is scheduled for launch in 2011. These TWTAs were characterized over the frequencies 25.5 to 25.8 GHz. The saturated RF output power is >40 W and the saturated RF gain is >46 dB. The saturated AM-to- PM conversion is 3.5 /dB and the small signal gain ripple is 0.46 dB peak-to-peak. The overall efficiency of the TWTA, including that of the electronic power conditioner (EPC) is as high as 45 percent.

  8. High-Efficiency K-Band Space Traveling-Wave Tube Amplifier for Near-Earth High Data Rate Communications

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Force, Dale A.; Spitsen, Paul C.; Menninger, William L.; Robbins, Neal R.; Dibb, Daniel R.; Todd, Phillip C.

    2010-01-01

    The RF performance of a new K-Band helix conduction cooled traveling-wave tube amplifier (TWTA), is presented in this paper. A total of three such units were manufactured, tested and delivered. The first unit is currently flying onboard NASA's Lunar Reconnaissance Orbiter (LRO) spacecraft and has flawlessly completed over 2000 orbits around the Moon. The second unit is a proto-flight model. The third unit will fly onboard NASA's International Space Station (ISS) as a very compact and lightweight transmitter package for the Communications, Navigation and Networking Reconfigurable Testbed (CoNNeCT), which is scheduled for launch in 2011. These TWTAs were characterized over the frequencies 25.5 to 25.8 GHz. The saturated RF output power is greater than 40 W and the saturated RF gain is greater than 46 dB. The saturated AM-to-PM conversion is 3.5 /dB and the small signal gain ripple is 0.46 dB peak-to-peak. The overall efficiency of the TWTA, including that of the electronic power conditioner (EPC) is as high as 45%.

  9. Traveling Theta Waves in the Human Hippocampus

    PubMed Central

    Zhang, Honghui

    2015-01-01

    The hippocampal theta oscillation is strongly correlated with behaviors such as memory and spatial navigation, but we do not understand its specific functional role. One hint of theta's function came from the discovery in rodents that theta oscillations are traveling waves that allow parts of the hippocampus to simultaneously exhibit separate oscillatory phases. Because hippocampal theta oscillations in humans have different properties compared with rodents, we examined these signals directly using multielectrode recordings from neurosurgical patients. Our findings confirm that human hippocampal theta oscillations are traveling waves, but also show that these oscillations appear at a broader range of frequencies compared with rodents. Human traveling waves showed a distinctive pattern of spatial propagation such that there is a consistent phase spread across the hippocampus regardless of the oscillations' frequency. This suggests that traveling theta oscillations are important functionally in humans because they coordinate phase coding throughout the hippocampus in a consistent manner. SIGNIFICANCE STATEMENT We show for the first time in humans that hippocampal theta oscillations are traveling waves, moving along the length of the hippocampus in a posterior–anterior direction. The existence of these traveling theta waves is important for understanding hippocampal neural coding because they cause neurons at separate positions in the hippocampus to experience different theta phases simultaneously. The theta phase that a neuron measures is a key factor in how that cell represents behavioral information. Therefore, the existence of traveling theta waves indicates that, to fully understand how a hippocampal neuron represents information, it is vital to also account for that cell's location in addition to conventional measures of neural activity. PMID:26354915

  10. X-Band RF Gun Development

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Vlieks, Arnold; Dolgashev, Valery; Tantawi, Sami

    In support of the MEGa-ray program at LLNL and the High Gradient research program at SLAC, a new X-band multi-cell RF gun is being developed. This gun, similar to earlier guns developed at SLAC for Compton X-ray source program, will be a standing wave structure made of 5.5 cells operating in the pi mode with copper cathode. This gun was designed following criteria used to build SLAC X-band high gradient accelerating structures. It is anticipated that this gun will operate with surface electric fields on the cathode of 200 MeV/m with low breakdown rate. RF will be coupled into themore » structure through a final cell with symmetric duel feeds and with a shape optimized to minimize quadrupole field components. In addition, geometry changes to the original gun, operated with Compton X-ray source, will include a wider RF mode separation, reduced surface electric and magnetic fields.« less

  11. Electron wind in strong wave guide fields

    NASA Astrophysics Data System (ADS)

    Krienen, F.

    1985-03-01

    The X-ray activity observed near highly powered waveguide structures is usually caused by local electric discharges originating from discontinuities such as couplers, tuners or bends. In traveling waves electrons move in the direction of the power flow. Seed electrons can multipactor in a traveling wave, the moving charge pattern is different from the multipactor in a resonant structure and is self-extinguishing. The charge density in the wave guide will modify impedance and propagation constant of the wave guide. The radiation level inside the output wave guide of the SLAC, 50 MW, S-band, klystron is estimated. Possible contributions of radiation to window failure are discussed.

  12. Ku-Band Traveling Wave Slot Array Using Simple Scanning Control

    NASA Technical Reports Server (NTRS)

    Host, Nicholas K.; Chen, Chi-Chih; Volakis, John L.; Miranda, Felix A.

    2015-01-01

    This paper introduces a feeding concept aimed at simplifying the backend (phase shifters) of traditional phased arrays. As an alternative to traditional phased arrays, we employ a traveling wave array (TWA) using a single feedline whose propagation constant is controlled via a single, small mechanical movement without a need for phase shifters to enable scanning. Specifically, a dielectric plunger is positioned within a parallel plate waveguide (PPW) transmission line (TL) that feeds the TWA. By adjusting the position of the dielectric plunger within the PPW feeding the TWA, beam steering is achieved. A 20 element array is designed at 13GHz shown to give stable realized gain across the angular range of -25 deg. less than or equal to theta less than or equal to 25 deg. A proof of concept array is fabricated and measured to demonstrate and validate the concept's operation.

  13. Dual traveling wave rotary ultrasonic motor with single active vibrator

    NASA Astrophysics Data System (ADS)

    An, Dawei; Yang, Ming; Zhuang, Xiaoqi; Yang, Tianyue; Meng, Fan; Dong, Zhaopeng

    2017-04-01

    Traveling wave rotary ultrasonic motor with double vibrators can improve the output performance effectively. However, the rotor has to be energized through a slip ring, which increases the complexity and reduces the reliability. Inheriting the concept of two traveling waves propagating in the stator and rotor, a dual traveling wave rotary ultrasonic motor energized only in the stator is proposed. By analyzing the oscillatory differential equation and the contact particles motion, a traveling wave is found in the rotor and the drive mechanism of dual traveling wave is studied. With the resonant rotor adopted, the consistent eigenfrequencies are calculated by finite element method and verified by an impedance analyzer. The performance experiment presents that the dual traveling wave rotary ultrasonic motor is superior to the motor with single traveling wave. The no-load speed is 60 rpm and the stalling torque is 0.85 Nm. Additionally, compared with a reported motor with double vibrators, the proposed motor presents the better output performance and the simpler design.

  14. Beam Dynamics a Integrated Plane Wave Transformer Photoinjector at S- and X- band

    NASA Astrophysics Data System (ADS)

    Rosenzweig, J. B.; Ding, X.; Pellegrini, X.; Serafini, L.; Yu, D.

    1997-05-01

    The beam dynamics of an integrated S-band rf photoinjector based on the plane wave transformer concept, proposed as part of an SBIR collaboration between UCLA and DULY Research, are studied. The intial design, which calls for an 11.5 cell structure run at a peak on-axis accelerating field of 60 MV/m, and has a compact solenoid around the intial 2.5 cells, is based on the recently developed theory of emittance compensation(L.Serafini, and J.B. Rosenzweig, submitted to Physical Review E.). It calls for matching the beam onto an envelope which is a generalized Brillouin flow, producing a beam which diminishes in transverse size as the square root of the accelerating beam energy. This condition produces a minimized emittance, which for the S-band case is 1 mm-rad at at charge of 1 nC. This design is also scaled to produce nearly identical performance at X-band, giving an injector appropriate to running an FEL at the SLAC NLCTA. It is noted that these designs are insensitive to rf emittance increase, allowign a choice of injection phase, and the option to compress the emitted pulse.

  15. Ku-Band Traveling Wave Slot Array Using Simple Scanning Control

    NASA Technical Reports Server (NTRS)

    Host, Nicholas K.; Chen, Chi-Chih; Volakis, John L.; Miranda, Felix A.

    2015-01-01

    This poster introduces a feeding concept aimed at simplifying the backend (phase shifters) of traditional phased arrays. As an alternative to traditional phased arrays, we employ a traveling wave array (TWA) using a single feedline whose propagation constant is controlled via a single, small mechanical movement without a need for phase shifters to enable scanning. Specifically, a dielectric plunger is positioned within a parallel plate waveguide (PPW) transmission line (TL) that feeds the TWA. By adjusting the position of the dielectric plunger within the PPW feeding the TWA, beam steering is achieved. A 20-element array is designed at 13 gigaherz shown to give stable realized gain across the angular range of minus 25 degrees less than or equal to theta and less than or equal to 25 degrees. A proof of concept array is fabricated and measured to demonstrate and validate the concept's operation.

  16. Nonlinear ultrasonic imaging with X wave

    NASA Astrophysics Data System (ADS)

    Du, Hongwei; Lu, Wei; Feng, Huanqing

    2009-10-01

    X wave has a large depth of field and may have important application in ultrasonic imaging to provide high frame rate (HFR). However, the HFR system suffers from lower spatial resolution. In this paper, a study of nonlinear imaging with X wave is presented to improve the resolution. A theoretical description of realizable nonlinear X wave is reported. The nonlinear field is simulated by solving the KZK nonlinear wave equation with a time-domain difference method. The results show that the second harmonic field of X wave has narrower mainlobe and lower sidelobes than the fundamental field. In order to evaluate the imaging effect with X wave, an imaging model involving numerical calculation of the KZK equation, Rayleigh-Sommerfeld integral, band-pass filtering and envelope detection is constructed to obtain 2D fundamental and second harmonic images of scatters in tissue-like medium. The results indicate that if X wave is used, the harmonic image has higher spatial resolution throughout the entire imaging region than the fundamental image, but higher sidelobes occur as compared to conventional focus imaging. A HFR imaging method with higher spatial resolution is thus feasible provided an apodization method is used to suppress sidelobes.

  17. Design, fabrication, and high-gradient testing of an X -band, traveling-wave accelerating structure milled from copper halves

    NASA Astrophysics Data System (ADS)

    Argyropoulos, Theodoros; Catalan-Lasheras, Nuria; Grudiev, Alexej; Mcmonagle, Gerard; Rodriguez-Castro, Enrique; Syrachev, Igor; Wegner, Rolf; Woolley, Ben; Wuensch, Walter; Zha, Hao; Dolgashev, Valery; Bowden, Gorden; Haase, Andrew; Lucas, Thomas Geoffrey; Volpi, Matteo; Esperante-Pereira, Daniel; Rajamäki, Robin

    2018-06-01

    A prototype 11.994 GHz, traveling-wave accelerating structure for the Compact Linear Collider has been built, using the novel technique of assembling the structure from milled halves. The use of milled halves has many advantages when compared to a structure made from individual disks. These include the potential for a reduction in cost, because there are fewer parts, as well as a greater freedom in choice of joining technology because there are no rf currents across the halves' joint. Here we present the rf design and fabrication of the prototype structure, followed by the results of the high-power test and post-test surface analysis. During high-power testing the structure reached an unloaded gradient of 100 MV /m at a rf breakdown rate of less than 1.5 ×10-5 breakdowns /pulse /m with a 200 ns pulse. This structure has been designed for the CLIC testing program but construction from halves can be advantageous in a wide variety of applications.

  18. The Influence of Drift Gas Composition on the Separation Mechanism in Traveling Wave Ion Mobility Spectrometry: Insight from Electrodynamic Simulations

    PubMed Central

    May, Jody C.; McLean, John A.

    2013-01-01

    The influence of three different drift gases (helium, nitrogen, and argon) on the separation mechanism in traveling wave ion mobility spectrometry is explored through ion trajectory simulations which include considerations for ion diffusion based on kinetic theory and the electrodynamic traveling wave potential. The model developed for this work is an accurate depiction of a second-generation commercial traveling wave instrument. Three ion systems (cocaine, MDMA, and amphetamine) whose reduced mobility values have previously been measured in different drift gases are represented in the simulation model. The simulation results presented here provide a fundamental understanding of the separation mechanism in traveling wave, which is characterized by three regions of ion motion: (1) ions surfing on a single wave, (2) ions exhibiting intermittent roll-over onto subsequent waves, and (3) ions experiencing a steady state roll-over which repeats every few wave cycles. These regions of ion motion are accessed through changes in the gas pressure, wave amplitude, and wave velocity. Resolving power values extracted from simulated arrival times suggest that momentum transfer in helium gas is generally insufficient to access regions (2) and (3) where ion mobility separations occur. Ion mobility separations by traveling wave are predicted to be effectual for both nitrogen and argon, with slightly lower resolving power values observed for argon as a result of band-broadening due to collisional scattering. For the simulation conditions studied here, the resolving power in traveling wave plateaus between regions (2) and (3), with further increases in wave velocity contributing only minor improvements in separations. PMID:23888124

  19. The Influence of Drift Gas Composition on the Separation Mechanism in Traveling Wave Ion Mobility Spectrometry: Insight from Electrodynamic Simulations.

    PubMed

    May, Jody C; McLean, John A

    2003-06-01

    The influence of three different drift gases (helium, nitrogen, and argon) on the separation mechanism in traveling wave ion mobility spectrometry is explored through ion trajectory simulations which include considerations for ion diffusion based on kinetic theory and the electrodynamic traveling wave potential. The model developed for this work is an accurate depiction of a second-generation commercial traveling wave instrument. Three ion systems (cocaine, MDMA, and amphetamine) whose reduced mobility values have previously been measured in different drift gases are represented in the simulation model. The simulation results presented here provide a fundamental understanding of the separation mechanism in traveling wave, which is characterized by three regions of ion motion: (1) ions surfing on a single wave, (2) ions exhibiting intermittent roll-over onto subsequent waves, and (3) ions experiencing a steady state roll-over which repeats every few wave cycles. These regions of ion motion are accessed through changes in the gas pressure, wave amplitude, and wave velocity. Resolving power values extracted from simulated arrival times suggest that momentum transfer in helium gas is generally insufficient to access regions (2) and (3) where ion mobility separations occur. Ion mobility separations by traveling wave are predicted to be effectual for both nitrogen and argon, with slightly lower resolving power values observed for argon as a result of band-broadening due to collisional scattering. For the simulation conditions studied here, the resolving power in traveling wave plateaus between regions (2) and (3), with further increases in wave velocity contributing only minor improvements in separations.

  20. Travelling wave effects in large space structures

    NASA Technical Reports Server (NTRS)

    Vonflotow, A.

    1983-01-01

    Several aspects of travelling waves in Large Space Structures(LSS) are discussed. The dynamic similarity among LSS's, electric power systems, microwave circuits and communications network is noted. The existence of time lag between actuation and response is illuminated with the aid of simple examples, and their prediction is demonstrated. To prevent echoes, communications lines have matched terminations; this idea is applied to the design of dampers of one dimensional structures. Periodic structures act as mechanical band pass filters. Implications of this behavior are examined on a simple example. It is noted that the implication is twofold; continuum models of periodic lattice structures may err considerably; on the other hand, it is possible to design favorable transmission (and resonance) characteristics into the structure.

  1. Traveling-Wave Tube Efficiency Enhancement

    NASA Technical Reports Server (NTRS)

    Dayton, James A., Jr.

    2011-01-01

    Traveling-wave tubes (TWT's) are used to amplify microwave communication signals on virtually all NASA and commercial spacecraft. Because TWT's are a primary power user, increasing their power efficiency is important for reducing spacecraft weight and cost. NASA Glenn Research Center has played a major role in increasing TWT efficiency over the last thirty years. In particular, two types of efficiency optimization algorithms have been developed for coupled-cavity TWT's. The first is the phase-adjusted taper which was used to increase the RF power from 420 to 1000 watts and the RF efficiency from 9.6% to 22.6% for a Ka-band (29.5 GHz) TWT. This was a record efficiency at this frequency level. The second is an optimization algorithm based on simulated annealing. This improved algorithm is more general and can be used to optimize efficiency over a frequency bandwidth and to provide a robust design for very high frequency TWT's in which dimensional tolerance variations are significant.

  2. Full Spectrum Conversion Using Traveling Pulse Wave Quantization

    DTIC Science & Technology

    2017-03-01

    Full Spectrum Conversion Using Traveling Pulse Wave Quantization Michael S. Kappes Mikko E. Waltari IQ-Analog Corporation San Diego, California...temporal-domain quantization technique called Traveling Pulse Wave Quantization (TPWQ). Full spectrum conversion is defined as the complete...pulse width measurements that are continuously generated hence the name “traveling” pulse wave quantization. Our TPWQ-based ADC is composed of a

  3. Simulation of radar backscattering from snowpack at X-band and Ku-band

    NASA Astrophysics Data System (ADS)

    Gay, Michel; Phan, Xuan-Vu; Ferro-Famil, Laurent

    2016-04-01

    This paper presents a multilayer snowpack electromagnetic backscattering model, based on Dense Media Radiative Transfer (DMRT). This model is capable of simulating the interaction of electromagnetic wave (EMW) at X-band and Ku-band frequencies with multilayer snowpack. The air-snow interface and snow-ground backscattering components are calculated using the Integral Equation Model (IEM) by [1], whereas the volume backscattering component is calculated based on the solution of Vector Radiative Transfer (VRT) equation at order 1. Case study has been carried out using measurement data from NoSREx project [2], which include SnowScat data in X-band and Ku-band, TerraSAR-X acquisitions and snowpack stratigraphic in-situ measurements. The results of model simulations show good agreement with the radar observations, and therefore allow the DMRT model to be used in various applications, such as data assimilation [3]. [1] A.K. Fung and K.S. Chen, "An update on the iem surface backscattering model," Geoscience and Remote Sensing Letters, IEEE, vol. 1, no. 2, pp. 75 - 77, april 2004. [2] J. Lemmetyinen, A. Kontu, J. Pulliainen, A. Wiesmann, C. Werner, T. Nagler, H. Rott, and M. Heidinger, "Technical assistance for the deployment of an x- to ku-band scatterometer during the nosrex ii experiment," Final Report, ESA ESTEC Contract No. 22671/09/NL/JA., 2011. [3] X. V. Phan, L. Ferro-Famil, M. Gay, Y. Durand, M. Dumont, S. Morin, S. Allain, G. D'Urso, and A. Girard, "3d-var multilayer assimilation of x-band sar data into a detailed snowpack model," The Cryosphere Discussions, vol. 7, no. 5, pp. 4881-4912, 2013.

  4. Linearized traveling wave amplifier with hard limiter characteristics

    NASA Technical Reports Server (NTRS)

    Kosmahl, H. G. (Inventor)

    1986-01-01

    A dynamic velocity taper is provided for a traveling wave tube with increased linearity to avoid intermodulation of signals being amplified. In a traveling wave tube, the slow wave structure is a helix including a sever. A dynamic velocity taper is provided by gradually reducing the spacing between the repeating elements of the slow wave structure which are the windings of the helix. The reduction which takes place coincides with the ouput point of helix. The spacing between the repeating elements of the slow wave structure is ideally at an exponential rate because the curve increases the point of maximum efficiency and power, at an exponential rate. A coupled cavity traveling wave tube having cavities is shown. The space between apertured discs is gradually reduced from 0.1% to 5% at an exponential rate. Output power (or efficiency) versus input power for a commercial tube is shown.

  5. Major dust storms and westward traveling waves on Mars

    NASA Astrophysics Data System (ADS)

    Wang, Huiqun

    2017-04-01

    Westward traveling waves are observed during major dust storm periods in northern fall and winter. The close correlation in timing makes westward traveling wave one of the signature responses of the Martian atmosphere to major dust storms. Westward traveling waves are dominated by zonal wave number m = 1 in the middle atmosphere and are typically characterized by long wave period. They are associated with significant temperature perturbations near the edge of the north polar vortex. Their wind signals extend to the low latitudes and the southern hemisphere. Their eddy momentum and heat fluxes exhibit complex patterns on a global scale in the middle atmosphere.

  6. Boundary mediated position control of traveling waves

    NASA Astrophysics Data System (ADS)

    Martens, Steffen; Ziepke, Alexander; Engel, Harald

    Reaction control is an essential task in biological systems and chemical process industry. Often, the excitable medium supporting wave propagation exhibits an irregular shape and/or is limited in size. In particular, the analytic treatment of wave phenomena is notoriously difficult due to the spatial modulation of the domain's. Recently, we have provided a first systematic treatment by applying asymptotic perturbation analysis leading to an approximate description that involves a reduction of dimensionality; the 3D RD equation with spatially dependent NFBCs on the reactants reduces to a 1D reaction-diffusion-advection equation. Here, we present a novel method to control the position ϕ (t) of traveling waves in modulated domains according to a prespecified protocol of motion. Given this protocol, the ``optimal'' geometry of reactive domains Q (x) is found as the solution of the perturbatively derived equation of motion. Noteworthy, such a boundary control can be expressed in terms of the uncontrolled wave profile and its propagation velocity, rendering detailed knowledge of the reaction kinetics unnecessary. German Science Foundation DFG through the SFB 910 ''Control of Self-Organizing Nonlinear Systems''.

  7. Controlling spiral waves and turbulent states in cardiac tissue by traveling wave perturbations

    NASA Astrophysics Data System (ADS)

    Wang, Peng-Ye; Xie, Ping

    2000-03-01

    We propose a traveling wave perturbation method to control the spatiotemporal dynamics in cardiac tissue. With a two-variable model we demonstrate that the method can successfully suppress the wave instability (alternans in action potential duration) in the one-dimensional case and convert spiral waves and turbulent states to the normal traveling wave state in the two-dimensional case. An experimental scheme is suggested which may provide a new design for a cardiac defibrillator.

  8. Revisiting the difference between traveling-wave and standing-wave thermoacoustic engines - A simple analytical model for the standing-wave one

    NASA Astrophysics Data System (ADS)

    Yasui, Kyuichi; Kozuka, Teruyuki; Yasuoka, Masaki; Kato, Kazumi

    2015-11-01

    There are two major categories in a thermoacoustic prime-mover. One is the traveling-wave type and the other is the standing-wave type. A simple analytical model of a standing-wave thermoacoustic prime-mover is proposed at relatively low heat-flux for a stack much shorter than the acoustic wavelength, which approximately describes the Brayton cycle. Numerical simulations of Rott's equations have revealed that the work flow (acoustic power) increases by increasing of the amplitude of the particle velocity (| U|) for the traveling-wave type and by increasing cosΦ for the standing-wave type, where Φ is the phase difference between the particle velocity and the acoustic pressure. In other words, the standing-wave type is a phase-dominant type while the traveling-wave type is an amplitude-dominant one. The ratio of the absolute value of the traveling-wave component (| U|cosΦ) to that of the standing-wave component (| U|sinΦ) of any thermoacoustic engine roughly equals the ratio of the absolute value of the increasing rate of | U| to that of cosΦ. The different mechanism between the traveling-wave and the standing-wave type is discussed regarding the dependence of the energy efficiency on the acoustic impedance of a stack as well as that on ωτα, where ω is the angular frequency of an acoustic wave and τα is the thermal relaxation time. While the energy efficiency of the traveling-wave type at the optimal ωτα is much higher than that of the standing-wave type, the energy efficiency of the standing-wave type is higher than that of the traveling-wave type at much higher ωτα under a fixed temperature difference between the cold and the hot ends of the stack.

  9. rf traveling-wave electron gun for photoinjectors

    NASA Astrophysics Data System (ADS)

    Schaer, Mattia; Citterio, Alessandro; Craievich, Paolo; Reiche, Sven; Stingelin, Lukas; Zennaro, Riccardo

    2016-07-01

    The design of a photoinjector, in particular that of the electron source, is of central importance for free electron laser (FEL) machines where a high beam brightness is required. In comparison to standard designs, an rf traveling-wave photocathode gun can provide a more rigid beam with a higher brightness and a shorter pulse. This is illustrated by applying a specific optimization procedure to the SwissFEL photoinjector, for which a brightness improvement up to a factor 3 could be achieved together with a double gun output energy compared to the reference setup foreseeing a state-of-the-art S-band rf standing-wave gun. The higher brightness is mainly given by a (at least) double peak current at the exit of the gun which brings benefits for both the beam dynamics in the linac and the efficiency of the FEL process. The gun design foresees an innovative coaxial rf coupling at both ends of the structure which allows a solenoid with integrated bucking coil to be placed around the cathode in order to provide the necessary focusing right after emission.

  10. Mechanism of travelling-wave transport of particles

    NASA Astrophysics Data System (ADS)

    Kawamoto, Hiroyuki; Seki, Kyogo; Kuromiya, Naoyuki

    2006-03-01

    Numerical and experimental investigations have been carried out on transport of particles in an electrostatic travelling field. A three-dimensional hard-sphere model of the distinct element method was developed to simulate the dynamics of particles. Forces applied to particles in the model were the Coulomb force, the dielectrophoresis force on polarized dipole particles in a non-uniform field, the image force, gravity and the air drag. Friction and repulsion between particle-particle and particle-conveyer were included in the model to replace initial conditions after mechanical contacts. Two kinds of experiments were performed to confirm the model. One was the measurement of charge of particles that is indispensable to determine the Coulomb force. Charge distribution was measured from the locus of free-fallen particles in a parallel electrostatic field. The averaged charge of the bulk particle was confirmed by measurement with a Faraday cage. The other experiment was measurements of the differential dynamics of particles on a conveyer consisting of parallel electrodes to which a four-phase travelling electrostatic wave was applied. Calculated results agreed with measurements, and the following characteristics were clarified. (1) The Coulomb force is the predominant force to drive particles compared with the other kinds of forces, (2) the direction of particle transport did not always coincide with that of the travelling wave but changed partially. It depended on the frequency of the travelling wave, the particle diameter and the electric field, (3) although some particles overtook the travelling wave at a very low frequency, the motion of particles was almost synchronized with the wave at the low frequency and (4) the transport of some particles was delayed to the wave at medium frequency; the majority of particles were transported backwards at high frequency and particles were not transported but only vibrated at very high frequency.

  11. Stability of post-fertilization traveling waves

    NASA Astrophysics Data System (ADS)

    Flores, Gilberto; Plaza, Ramón G.

    This paper studies the stability of a family of traveling wave solutions to the system proposed by Lane et al. [D.C. Lane, J.D. Murray, V.S. Manoranjan, Analysis of wave phenomena in a morphogenetic mechanochemical model and an application to post-fertilization waves on eggs, IMA J. Math. Appl. Med. Biol. 4 (4) (1987) 309-331], to model a pair of mechanochemical phenomena known as post-fertilization waves on eggs. The waves consist of an elastic deformation pulse on the egg's surface, and a free calcium concentration front. The family is indexed by a coupling parameter measuring contraction stress effects on the calcium concentration. This work establishes the spectral, linear and nonlinear orbital stability of these post-fertilization waves for small values of the coupling parameter. The usual methods for the spectral and evolution equations cannot be applied because of the presence of mixed partial derivatives in the elastic equation. Nonetheless, exponential decay of the directly constructed semigroup on the complement of the zero eigenspace is established. We show that small perturbations of the waves yield solutions to the nonlinear equations decaying exponentially to a phase-modulated traveling wave.

  12. Lateralization of Travelling Wave Response in the Hearing Organ of Bushcrickets

    PubMed Central

    Palghat Udayashankar, Arun; Kössl, Manfred; Nowotny, Manuela

    2014-01-01

    Travelling waves are the physical basis of frequency discrimination in many vertebrate and invertebrate taxa, including mammals, birds, and some insects. In bushcrickets (Tettigoniidae), the crista acustica is the hearing organ that has been shown to use sound-induced travelling waves. Up to now, data on mechanical characteristics of sound-induced travelling waves were only available along the longitudinal (proximal-distal) direction. In this study, we use laser Doppler vibrometry to investigate in-vivo radial (anterior-posterior) features of travelling waves in the tropical bushcricket Mecopoda elongata. Our results demonstrate that the maximum of sound-induced travelling wave amplitude response is always shifted towards the anterior part of the crista acustica. This lateralization of the travelling wave response induces a tilt in the motion of the crista acustica, which presumably optimizes sensory transduction by exerting a shear motion on the sensory cilia in this hearing organ. PMID:24465889

  13. Coupled Transmission Line Based Slow Wave Structures for Traveling Wave Tubes Applications

    NASA Astrophysics Data System (ADS)

    Zuboraj, Md. Rashedul Alam

    High power microwave devices especially Traveling Wave Tubes (TWTs) and Backward Wave Oscillators (BWOs) are largely dependent on Slow Wave Structures for efficient beam to RF coupling. In this work, a novel approach of analyzing SWSs is proposed and investigated. Specifically, a rigorous study of helical geometries is carried out and a novel SWS "Half-Ring-Helix" is designed. This Half-Ring-Helix circuit achieves 27% miniaturization and delivers 10dB more gain than conventional helices. A generalization of the helix structures is also proposed in the form of Coupled Transmission Line (CTL). It is demonstrated that control of coupling among the CTLs leads to new propagation properties. With this in mind, a novel geometry referred to as "Curved Ring-Bar" is introduced. This geometry is shown to deliver 1MW power across a 33% bandwidth. Notably, this is the first demonstration of MW power TWT across large bandwidth. The CTL is further expanded to enable engineered propagation characteristics. This is done by introducing CTLs having non-identical transmission lines and CTLs with as many as four transmission lines in the same slow wave structure circuit. These non-identical CTLs are demonstrated to generate fourth order dispersion curves. Building on the property of CTLs, a `butterfly' slow wave structure is developed and demonstrated to provide degenerate band edge (DBE) mode. This mode are known to provide large feld enhancement that can be exploited to design high power backward wave oscillators.

  14. X-Band, 17-Watt Solid-State Power Amplifier

    NASA Technical Reports Server (NTRS)

    Mittskus, Anthony; Stone, Ernest; Boger, William; Burgess, David; Honda, Richard; Nuckolls, Carl

    2005-01-01

    An advanced solid-state power amplifier that can generate an output power of as much as 17 W at a design operating frequency of 8.4 GHz has been designed and constructed as a smaller, lighter, less expensive alternative to traveling-wave-tube X-band amplifiers and to prior solid-state X-band power amplifiers of equivalent output power. This amplifier comprises a monolithic microwave integrated circuit (MMIC) amplifier module and a power-converter module integrated into a compact package (see Figure 1). The amplifier module contains an input variable-gain amplifier (VGA), an intermediate driver stage, a final power stage, and input and output power monitors (see Figure 2). The VGA and the driver amplifier are 0.5-m GaAs-based metal semiconductor field-effect transistors (MESFETs). The final power stage contains four parallel high-efficiency, GaAs-based pseudomorphic high-electron-mobility transistors (PHEMTs). The gain of the VGA is voltage-variable over a range of 10 to 24 dB. To provide for temperature compensation of the overall amplifier gain, the gain-control voltage is generated by an operational-amplifier circuit that includes a resistor/thermistor temperature-sensing network. The driver amplifier provides a gain of 14 dB to an output power of 27 dBm to drive the four parallel output PHEMTs, each of which is nominally capable of putting out as much as 5 W. The driver output is sent to the input terminals of the four parallel PHEMTs through microstrip power dividers; the outputs of these PHEMTs are combined by microstrip power combiners (which are similar to the microstrip power dividers) to obtain the final output power of 17 W.

  15. Traveling-wave induction launchers

    NASA Technical Reports Server (NTRS)

    Elliott, David G.

    1989-01-01

    An analysis of traveling-wave induction launchers shows that induction is a feasible method of producing armature current and that efficient accelerators can be built without sliding contacts or arcs. In a traveling-wave induction launcher the armature current is induced by a slip speed between the armature and a traveling magnetic field. At 9 m/s slip speed a 9 kg projectile with an aluminum armature weighing 25 percent of the total mass can be accelerated to 3000 m/s in a 5 m-long barrel with a total ohmic loss in the barrel coils and armature of 4 percent of the launch kinetic energy and with an average armature temperature rise of 220 deg C, but a peak excitation frequency of 8600 Hz is required. With a 2 kg launch mass the ohmic loss is 7 percent. A launcher system optimized for rotating generators would have a peak frequency of 4850 Hz; with an aluminum armature weighing 33 percent of the launch mass and a slip speed of 30 m/s the total ohmic loss in the generators, cables, and accelerator would be 43 percent of the launch kinetic energy, and the average armature temperature rise would be 510 deg C.

  16. Enhancing Variable Friction Tactile Display Using an Ultrasonic Travelling Wave.

    PubMed

    Ghenna, Sofiane; Vezzoli, Eric; Giraud-Audine, Christophe; Giraud, Frederic; Amberg, Michel; Lemaire-Semail, Betty

    2017-01-01

    In Variable Friction Tactile Displays, an ultrasonic standing wave can be used to reduce the friction coefficient between a user's finger sliding and a vibrating surface. However, by principle, the effect is limited by a saturation due to the contact mechanics, and very low friction levels require very high vibration amplitudes. Besides, to be effective, the user's finger has to move. We present a device which uses a travelling wave rather than a standing wave. We present a control that allows to realize such a travelling wave in a robust way, and thus can be implemented on various plane surfaces. We show experimentally that the force produced by the travelling wave has two superimposed contributions. The first one is equal to the friction reduction produced by a standing of the same vibration amplitude. The second produces a driving force in the opposite direction of the travelling wave. As a result, the modulation range of the tangential force on the finger can be extended to zero and even negative values. Moreover, the effect is dependant on the relative direction of exploration with regards to the travelling wave, which is perceivable and confirmed by a psycho-physical study.

  17. High Power and Efficiency Space Traveling-Wave Tube Amplifiers With Reduced Size and Mass for NASA Missions

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Wilson, Jeffrey D.; Force, Dale A.

    2008-01-01

    Recent advances in high power and efficiency space traveling-wave tube amplifiers (TWTAs) for NASA s space-to-Earth communications are presented in this paper. The RF power and efficiency of a new K-Band amplifier are 40 W and 50 percent and that of a new Ka-Band amplifier are 200 W and 60 percent. An important figure-of-merit, which is defined as the ratio of the RF power output to the mass (W/kg) of a TWT has improved by a factor of ten over the previous generation Ka-Band devices.

  18. Sequentially pulsed traveling wave accelerator

    DOEpatents

    Caporaso, George J [Livermore, CA; Nelson, Scott D [Patterson, CA; Poole, Brian R [Tracy, CA

    2009-08-18

    A sequentially pulsed traveling wave compact accelerator having two or more pulse forming lines each with a switch for producing a short acceleration pulse along a short length of a beam tube, and a trigger mechanism for sequentially triggering the switches so that a traveling axial electric field is produced along the beam tube in synchronism with an axially traversing pulsed beam of charged particles to serially impart energy to the particle beam.

  19. Permanent magnet focused X-band photoinjector

    DOEpatents

    Yu, David U. L.; Rosenzweig, James

    2002-09-10

    A compact high energy photoelectron injector integrates the photocathode directly into a multicell linear accelerator with no drift space between the injection and the linac. High electron beam brightness is achieved by accelerating a tightly focused electron beam in an integrated, multi-cell, X-band rf linear accelerator (linac). The photoelectron linac employs a Plane-Wave-Transformer (PWT) design which provides strong cell-to-cell coupling, easing manufacturing tolerances and costs.

  20. Traveling-wave synchronous coil gun

    NASA Technical Reports Server (NTRS)

    Elliott, David G.

    1991-01-01

    An outline is presented of the coilgun concept, excitation, switching, brush commutation, power supply, and performance. It is shown that a traveling-wave synchronous coilgun permits independent adjustment of the magnetic field and armature current for high velocity at low armature mass fraction. Magnetic field energy is transferred from the rear of the wave to the front without passing through the power supply. Elaborate switching is required.

  1. TerraSAR-X Measurements of Wind Fields, Ocean Waves and Currents

    NASA Astrophysics Data System (ADS)

    Lehner, S.; Schulz-Stellenfleth, J.; Brusch, S.

    2008-01-01

    TerraSAR-X is a new german X-band radar satellite launched on June 15, 2007. In this mission an operational spaceborne synthetic aperture radar (SAR) system with very high spatial resolution is set up producing remote sensing products for commercial and scientific use. TerraSAR-X is a scientific and technological continuation of the successful Space Shuttle missions SIR-C/X and SRTM.The spacecraft is equipped with a phased array X-band SAR, which can operate in different polarisations and has furthermore beam stearing capabilities. In addition the system has a split antenna mode, which is able to provide along track interferometric information. The instrument is designed for multiple imaging modes like Stripmap, Spotlight and ScanSAR.Due to its polarimetric and interferometric capabilities as well as the high spatial resolution of up to 1 m, the TerraSAR-X sensor is a very interesting tool for oceanography. The presentation will give an overview of several applications, which are of both scientific and commercial interest, like e.g. current and ocean wave measurements, monitoring of morphodynamical processes or high resolution wind field retrieval. The potential as well as limitations of the instrument will be summarized and compared with existing sensors. Necessary steps to translate existing C-band SAR inversion algorithms for wind and wave measurements to X-band will be discussed. A strategy will be outlined to achieve this by a combination of theoretical investigations and the use of existing experimental data acquired by both airborne and groundbased X-band radar. First results on the adaption of existing C-band wind retrieval algorithms will be presented. Wind and ocean wave parameter retrievals will be presented, e.g., based on TerraSAR-X scenes taken over the English channel.

  2. Vacillations induced by interference of stationary and traveling planetary waves

    NASA Technical Reports Server (NTRS)

    Salby, Murry L.; Garcia, Rolando R.

    1987-01-01

    The interference pattern produced when a traveling planetary wave propagates over a stationary forced wave is explored, examining the interference signature in a variety of diagnostics. The wave field is first restricted to a diatomic spectrum consisting of two components: a single stationary wave and a single monochromatic traveling wave. A simple barotropic normal mode propagating over a simple stationary plane wave is considered, and closed form solutions are obtained. The wave fields are then restricted spatially, providing more realistic structures without sacrificing the advantages of an analytical solution. Both stationary and traveling wave fields are calculated numerically with the linearized Primitive Equations in a realistic basic state. The mean flow reaction to the fluctuating eddy forcing which results from interference is derived. Synoptic geopotential behavior corresponding to the combined wave and mean flow fields is presented, and the synoptic signature in potential vorticity on isentropic surfaces is examined.

  3. Superconducting magnets for traveling-wave maser application. Technical documentary report, Oct 1960--Mar 1962

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Okwit, S.; Siegel, K.; Smith, J.G.

    1962-09-01

    Results of an investigation to determine the feasibility of incorporating superconducting magnet techniques in the design of traveling-wave maser systems are reported. Several different types of magnet configurations were investigated: isomagnets, Helmholtz coils, modified Helmholtz coils, air-core solenoids, and magnetic end-loaded air-core solenoids. The magnetic end-loaded air-core solenoid was found to be the best configuration for the S-band maser under consideration. This technique yielded relatively large regions of field homogeneity with relatively small aspect ratios (length of solenoid/diameter of solenoid). Several small-scale models of full-length superconducting magnets and foreshortened end-loaded superconducting magnets were constructed using un-annealed niobium wire. Measurements havemore » shown that these magnets were adequate for traveling-wave maser applications that require magnetic fields up to 2,200 G and marginal for magnetic fields up to 2,500 G.« less

  4. Synthesis, growth and characterization of ZnO microtubes using a traveling-wave mode microwave system

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Al-Naser, Qusay A.H.; Zhou, Jian, E-mail: jianzhou@whut.edu.cn; Wang, Han

    Highlights: • ZnO microtubes were successfully synthesized within 15 min. • Introducing a design of a traveling-wave mode microwave system. • Growth temperature of ZnO microtubes becomes predominant between 1350 °C and 1400 °C. • ZnO microtube showed a strong ultraviolet and a weak and broad green emission. • ZnO microtube is composed only of ZnO with high crystallinity. - Abstract: Field emission scanning electron microscopy (FESEM) investigation reveals that zinc oxide (ZnO) microtubes have been successfully synthesized via a traveling-wave mode microwave system. These products are hexagonal tubular crystals with an average diameter of 60 μm and 250 μmmore » in length, having a well faceted end and side surfaces. The wall thickness of the ZnO tubes is about 3–5 μm. The influence of reaction temperature on the formation of crystalline ZnO hexagonal tubes is studied. Room temperature photoluminescence (PL) spectra have also been examined to explore the optical property which exhibits strong ultraviolet emission at 377.422 nm and a weak and broad green emission band at 587.548 nm. X-ray diffraction (XRD) and energy dispersive spectrometer (EDS) show that the product is composed only of ZnO with high crystallinity. The presented synthesis method possesses several advantages, which would be significant to the deeper study and wide applications of ZnO tubes in the future.« less

  5. An Improved X-Band Maser System for Deep Space Network Applications

    NASA Astrophysics Data System (ADS)

    Britcliffe, M.; Hanson, T.; Fernandez, J.

    2000-01-01

    An 8450-MHz (X-band) maser system utilizing a commercial Gifford--McMahon (GM) closed-cycle cryocooler (CCR) was designed, fabricated, and demonstrated. The CCR system was used to cool a maser operating at 8450 MHz. The prototype GM CCR system meets or exceeds all Deep Space Network requirements for maser performance. The two-stage GM CCR operates at 4.2 K; for comparison, the DSN's current three-stage cryocooler, which uses a Joule--Thompson cooling stage in addition to GM cooling, operates at 4.5 K. The new CCR withstands heat loads of 1.5 W at 4.2 K as compared to 1 W at 4.5 K for the existing DSN cryocooler used for cooling masers. The measured noise temperature, T_e, of the maser used for these tests is defined at the ambient connection to the antenna feed system. The T_e measured 5.0 K at a CCR temperature of 4.5 K, about 1.5 K higher than the noise temperature of a typical DSN Block II-A X-band traveling-wave maser (TWM). Reducing the temperature of the CCR significantly lowers the maser noise temperature and increases maser gain and bandwidth. The new GM CCR gives future maser systems significant operational advantages, including reduced maintenance time and logistics requirements. The results of a demonstration of this new system are presented. Advantages of using a GM-cooled maser and the effects of the reduced CCR temperature on maser performance are discussed.

  6. A Discrete Velocity Kinetic Model with Food Metric: Chemotaxis Traveling Waves.

    PubMed

    Choi, Sun-Ho; Kim, Yong-Jung

    2017-02-01

    We introduce a mesoscopic scale chemotaxis model for traveling wave phenomena which is induced by food metric. The organisms of this simplified kinetic model have two discrete velocity modes, [Formula: see text] and a constant tumbling rate. The main feature of the model is that the speed of organisms is constant [Formula: see text] with respect to the food metric, not the Euclidean metric. The uniqueness and the existence of the traveling wave solution of the model are obtained. Unlike the classical logarithmic model case there exist traveling waves under super-linear consumption rates and infinite population pulse-type traveling waves are obtained. Numerical simulations are also provided.

  7. A Low Cost Traveling Wave Tube for Wireless Communications

    NASA Technical Reports Server (NTRS)

    Vancil, Bernard Kenneth; Wintucky, Edwin G.; Williams, W. D. (Technical Monitor)

    2002-01-01

    Demand for high data rate wireless communications is pushing up amplifier power, bandwidth and frequency requirements. Some systems are using vacuum electron devices again because solid-state power amplifiers are not able to efficiently meet the new requirements. The traveling wave tube is the VED of choice because of its excellent broadband capability as well as high power efficiency and frequency. But TWTs are very expensive on a per watt basis below about 200 watts of output power. We propose a new traveling wave tube that utilizes cathode ray tube construction technology and electrostatic focusing. We believe the tube can be built in quantity for under $1,000 each. We discuss several traveling wave tube slow wave circuits that lend themselves to the new construction. We will present modeling results and data on prototype devices.

  8. Control of spiral waves and turbulent states in a cardiac model by travelling-wave perturbations

    NASA Astrophysics Data System (ADS)

    Wang, Peng-Ye; Xie, Ping; Yin, Hua-Wei

    2003-06-01

    We propose a travelling-wave perturbation method to control the spatiotemporal dynamics in a cardiac model. It is numerically demonstrated that the method can successfully suppress the wave instability (alternans in action potential duration) in the one-dimensional case and convert spiral waves and turbulent states to the normal travelling wave states in the two-dimensional case. An experimental scheme is suggested which may provide a new design for a cardiac defibrillator.

  9. Body-wave traveltime and amplitude shifts from asymptotic travelling wave coupling

    USGS Publications Warehouse

    Pollitz, F.

    2006-01-01

    We explore the sensitivity of finite-frequency body-wave traveltimes and amplitudes to perturbations in 3-D seismic velocity structure relative to a spherically symmetric model. Using the approach of coupled travelling wave theory, we consider the effect of a structural perturbation on an isolated portion of the seismogram. By convolving the spectrum of the differential seismogram with the spectrum of a narrow window taper, and using a Taylor's series expansion for wavenumber as a function of frequency on a mode dispersion branch, we derive semi-analytic expressions for the sensitivity kernels. Far-field effects of wave interactions with the free surface or internal discontinuities are implicitly included, as are wave conversions upon scattering. The kernels may be computed rapidly for the purpose of structural inversions. We give examples of traveltime sensitivity kernels for regional wave propagation at 1 Hz. For the direct SV wave in a simple crustal velocity model, they are generally complicated because of interfering waves generated by interactions with the free surface and the Mohorovic??ic?? discontinuity. A large part of the interference effects may be eliminated by restricting the travelling wave basis set to those waves within a certain range of horizontal phase velocity. ?? Journal compilation ?? 2006 RAS.

  10. Analysis of the hot-cavity mode composition of an X-band overmoded relativistic backward wave oscillators

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Yuan, Yuzhang; Zhang, Jun; Zhong, Huihuang

    Overmoded RBWO (Relativistic Backward Wave Oscillators) is utilized more and more often for its high power capacity. However, both sides of SWS (Slow Wave Structure) of overmoded RBWO consist multi TM{sub 0n} modes; in order to achieve the design of reflector, it is essential to make clear of the mode composition of TM{sub 0n}. NUDT (National University of Defence Technology) had done research of the output mode composition in overmoded O-type Cerenkov HPM (High Power Microwave) Oscillators in detail, but in the area where the electron beam exists, the influence of electron beam must be taken into account. Hot-cavity dispersionmore » equation is figured out in this article first, and then analyzes the hot-cavity mode composition of an X-band overmoded RBWO tentatively. The results show that in collimating hole, the hot-cavity mode analysis is more accurate.« less

  11. An integrated sea monitoring system based on a X-band wave radar to support the removal activities of the Costa Concordia wreck.

    NASA Astrophysics Data System (ADS)

    Gozzini, Bernardo; Serafino, Francesco; Lugni, Claudio; Antonini, Andrea; Costanza, Letizia; Orlandi, Andrea; Arturi, Daniele; Ludeno, Giovanni; Natale, Antonio; Soldovieri, Francesco; Ortolani, Alberto; Brandini, Carlo

    2013-04-01

    The planning and management of different types of operations at sea requires a number of sea state data as much in real-time as possible, for rapid and effective response to different situations. This need is particularly strong in emergency management practices, in accidents due to man-made or natural causes, that require the planning of civil protection activities (such as search-and-rescue, cleaning of pollution, ship recovery), transport planning etc. The use of X-band radar technology nowadays provides great advantages over traditional in-situ and satellite-based techniques for sea state measuring, to update information on waves and currents over a sea area with high spatial and temporal resolution. Other advantages include a good spatial coverage around the area of interest, the flexibility of use, the capacity to provide, on-demand and when necessary, complementary information (possible oil spills detection, integration with VTS, etc.). X-band coastal radars (so-called "wave-radars") are widely used in the monitoring of large marine areas, in integration with in-situ measurements, satellites and other radar types (HF), as a key element of the observational component of present operational oceanography systems. Outside of these systems, the use of this technology to support emergency management practices is very promising for both the quality and quantity of available parameters, and for an easy integration with all other available monitoring and forecasting tools. A case study particularly relevant is offered by the presence of the Costa Concordia ship near the Giglio Island. The management of this disaster has requested at an early stage a large number of data to support the monitoring of marine environment around the ship, e.g. to optimally plan water samples. In the next and present phase, to support the highly risky and costly activities linked to the wreck removal, which are extremely sea-state dependent, the installation of a wave-radar allows to

  12. Microfabricated Millimeter-Wave High-Power Vacuum Electronic Amplifiers

    DTIC Science & Technology

    2015-01-01

    Applications filed 2012). In spite of the challenges, high power sources of electromagnetic radiation are needed in the mmW bands for advanced DoD...Research Laboratory is demonstrating and developing millimeter-wave vacuum electronic traveling wave tube amplifiers at W- and G- band in the 10’ s to 100... s of watts power range at several percent instantaneous bandwidth. Keywords: Traveling wave tube; millimeter wave; vacuum electron device

  13. Existence and exponential stability of traveling waves for delayed reaction-diffusion systems

    NASA Astrophysics Data System (ADS)

    Hsu, Cheng-Hsiung; Yang, Tzi-Sheng; Yu, Zhixian

    2018-03-01

    The purpose of this work is to investigate the existence and exponential stability of traveling wave solutions for general delayed multi-component reaction-diffusion systems. Following the monotone iteration scheme via an explicit construction of a pair of upper and lower solutions, we first obtain the existence of monostable traveling wave solutions connecting two different equilibria. Then, applying the techniques of weighted energy method and comparison principle, we show that all solutions of the Cauchy problem for the considered systems converge exponentially to traveling wave solutions provided that the initial perturbations around the traveling wave fronts belong to a suitable weighted Sobolev space.

  14. Traveling waves in an optimal velocity model of freeway traffic.

    PubMed

    Berg, P; Woods, A

    2001-03-01

    Car-following models provide both a tool to describe traffic flow and algorithms for autonomous cruise control systems. Recently developed optimal velocity models contain a relaxation term that assigns a desirable speed to each headway and a response time over which drivers adjust to optimal velocity conditions. These models predict traffic breakdown phenomena analogous to real traffic instabilities. In order to deepen our understanding of these models, in this paper, we examine the transition from a linear stable stream of cars of one headway into a linear stable stream of a second headway. Numerical results of the governing equations identify a range of transition phenomena, including monotonic and oscillating travelling waves and a time- dependent dispersive adjustment wave. However, for certain conditions, we find that the adjustment takes the form of a nonlinear traveling wave from the upstream headway to a third, intermediate headway, followed by either another traveling wave or a dispersive wave further downstream matching the downstream headway. This intermediate value of the headway is selected such that the nonlinear traveling wave is the fastest stable traveling wave which is observed to develop in the numerical calculations. The development of these nonlinear waves, connecting linear stable flows of two different headways, is somewhat reminiscent of stop-start waves in congested flow on freeways. The different types of adjustments are classified in a phase diagram depending on the upstream and downstream headway and the response time of the model. The results have profound consequences for autonomous cruise control systems. For an autocade of both identical and different vehicles, the control system itself may trigger formations of nonlinear, steep wave transitions. Further information is available [Y. Sugiyama, Traffic and Granular Flow (World Scientific, Singapore, 1995), p. 137].

  15. Traveling waves in an optimal velocity model of freeway traffic

    NASA Astrophysics Data System (ADS)

    Berg, Peter; Woods, Andrew

    2001-03-01

    Car-following models provide both a tool to describe traffic flow and algorithms for autonomous cruise control systems. Recently developed optimal velocity models contain a relaxation term that assigns a desirable speed to each headway and a response time over which drivers adjust to optimal velocity conditions. These models predict traffic breakdown phenomena analogous to real traffic instabilities. In order to deepen our understanding of these models, in this paper, we examine the transition from a linear stable stream of cars of one headway into a linear stable stream of a second headway. Numerical results of the governing equations identify a range of transition phenomena, including monotonic and oscillating travelling waves and a time- dependent dispersive adjustment wave. However, for certain conditions, we find that the adjustment takes the form of a nonlinear traveling wave from the upstream headway to a third, intermediate headway, followed by either another traveling wave or a dispersive wave further downstream matching the downstream headway. This intermediate value of the headway is selected such that the nonlinear traveling wave is the fastest stable traveling wave which is observed to develop in the numerical calculations. The development of these nonlinear waves, connecting linear stable flows of two different headways, is somewhat reminiscent of stop-start waves in congested flow on freeways. The different types of adjustments are classified in a phase diagram depending on the upstream and downstream headway and the response time of the model. The results have profound consequences for autonomous cruise control systems. For an autocade of both identical and different vehicles, the control system itself may trigger formations of nonlinear, steep wave transitions. Further information is available [Y. Sugiyama, Traffic and Granular Flow (World Scientific, Singapore, 1995), p. 137].

  16. Asymptotic traveling wave solution for a credit rating migration problem

    NASA Astrophysics Data System (ADS)

    Liang, Jin; Wu, Yuan; Hu, Bei

    2016-07-01

    In this paper, an asymptotic traveling wave solution of a free boundary model for pricing a corporate bond with credit rating migration risk is studied. This is the first study to associate the asymptotic traveling wave solution to the credit rating migration problem. The pricing problem with credit rating migration risk is modeled by a free boundary problem. The existence, uniqueness and regularity of the solution are obtained. Under some condition, we proved that the solution of our credit rating problem is convergent to a traveling wave solution, which has an explicit form. Furthermore, numerical examples are presented.

  17. Suppressing wall turbulence by means of a transverse traveling wave

    PubMed

    Du; Karniadakis

    2000-05-19

    Direct numerical simulations of wall-bounded flow reveal that turbulence production can be suppressed by a transverse traveling wave. Flow visualizations show that the near-wall streaks are eliminated, in contrast to other turbulence-control techniques, leading to a large shear stress reduction. The traveling wave can be induced by a spanwise force that is confined within the viscous sublayer; it has its maximum at the wall and decays exponentially away from it. We demonstrate the application of this approach in salt water, using arrays of electromagnetic tiles that produce the required traveling wave excitation at a high efficiency.

  18. Traveling waves in a spring-block chain sliding down a slope

    NASA Astrophysics Data System (ADS)

    Morales, J. E.; James, G.; Tonnelier, A.

    2017-07-01

    Traveling waves are studied in a spring slider-block model. We explicitly construct front waves (kinks) for a piecewise-linear spinodal friction force. Pulse waves are obtained as the matching of two traveling fronts with identical speeds. Explicit formulas are obtained for the wavespeed and the wave form in the anticontinuum limit. The link with localized waves in a Burridge-Knopoff model of an earthquake fault is briefly discussed.

  19. Traveling waves in a spring-block chain sliding down a slope.

    PubMed

    Morales, J E; James, G; Tonnelier, A

    2017-07-01

    Traveling waves are studied in a spring slider-block model. We explicitly construct front waves (kinks) for a piecewise-linear spinodal friction force. Pulse waves are obtained as the matching of two traveling fronts with identical speeds. Explicit formulas are obtained for the wavespeed and the wave form in the anticontinuum limit. The link with localized waves in a Burridge-Knopoff model of an earthquake fault is briefly discussed.

  20. Traveling waves and chaos in thermosolutal convection

    NASA Technical Reports Server (NTRS)

    Deane, A. E.; Toomre, J.; Knobloch, E.

    1987-01-01

    Numerical experiments on two-dimensional thermosolutal convection reveal oscillations in the form of traveling, standing, modulated, and chaotic waves. Transitions between these wave forms and steady convection are investigated and compared with theory. Such rich nonlinear behavior is possible in fluid layers of wide horizontal extent, and provides an explanation for waves observed in recent laboratory experiments with binary fluid mixtures.

  1. Tuning gain and bandwidth of traveling wave tubes using metamaterial beam-wave interaction structures

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Lipton, Robert, E-mail: lipton@math.lsu.edu; Polizzi, Anthony, E-mail: polizzi@math.lsu.edu

    We employ metamaterial beam-wave interaction structures for tuning the gain and bandwidth of short traveling wave tubes. The interaction structures are made from metal rings of uniform cross section, which are periodically deployed along the length of the traveling wave tube. The aspect ratio of the ring cross sections is adjusted to control both gain and bandwidth. The frequency of operation is controlled by the filling fraction of the ring cross section with respect to the size of the period cell.

  2. Tympanal travelling waves in migratory locusts.

    PubMed

    Windmill, James F C; Göpfert, Martin C; Robert, Daniel

    2005-01-01

    Hearing animals, including many vertebrates and insects, have the capacity to analyse the frequency composition of sound. In mammals, frequency analysis relies on the mechanical response of the basilar membrane in the cochlear duct. These vibrations take the form of a slow vibrational wave propagating along the basilar membrane from base to apex. Known as von Békésy's travelling wave, this wave displays amplitude maxima at frequency-specific locations along the basilar membrane, providing a spatial map of the frequency of sound--a tonotopy. In their structure, insect auditory systems may not be as sophisticated at those of mammals, yet some are known to perform sound frequency analysis. In the desert locust, this analysis arises from the mechanical properties of the tympanal membrane. In effect, the spatial decomposition of incident sound into discrete frequency components involves a tympanal travelling wave that funnels mechanical energy to specific tympanal locations, where distinct groups of mechanoreceptor neurones project. Notably, observed tympanal deflections differ from those predicted by drum theory. Although phenomenologically equivalent, von Békésy's and the locust's waves differ in their physical implementation. von Békésy's wave is born from interactions between the anisotropic basilar membrane and the surrounding incompressible fluids, whereas the locust's wave rides on an anisotropic membrane suspended in air. The locust's ear thus combines in one structure the functions of sound reception and frequency decomposition.

  3. Travelling waves and spatial hierarchies in measles epidemics

    NASA Astrophysics Data System (ADS)

    Grenfell, B. T.; Bjørnstad, O. N.; Kappey, J.

    2001-12-01

    Spatio-temporal travelling waves are striking manifestations of predator-prey and host-parasite dynamics. However, few systems are well enough documented both to detect repeated waves and to explain their interaction with spatio-temporal variations in population structure and demography. Here, we demonstrate recurrent epidemic travelling waves in an exhaustive spatio-temporal data set for measles in England and Wales. We use wavelet phase analysis, which allows for dynamical non-stationarity-a complication in interpreting spatio-temporal patterns in these and many other ecological time series. In the pre-vaccination era, conspicuous hierarchical waves of infection moved regionally from large cities to small towns; the introduction of measles vaccination restricted but did not eliminate this hierarchical contagion. A mechanistic stochastic model suggests a dynamical explanation for the waves-spread via infective `sparks' from large `core' cities to smaller `satellite' towns. Thus, the spatial hierarchy of host population structure is a prerequisite for these infection waves.

  4. Multi-Band (K- Q- and E-Band) Multi-Tone Millimeter-Wave Frequency Synthesizer for Radio Wave Propagation Studies

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Wintucky, Edwin G.

    2014-01-01

    This paper presents the design and test results of a multi-band multi-tone millimeter-wave frequency synthesizer, based on a solid-state frequency comb generator. The intended application of the synthesizer is in a space-borne transmitter for radio wave atmospheric studies at K-band (18 to 26.5 GHz), Q-band (37 to 42 GHz), and E-band (71 to 76 GHz). These studies would enable the design of robust multi-Gbps data rate space-to-ground satellite communication links. Lastly, the architecture for a compact multi-tone beacon transmitter, which includes a high frequency synthesizer, a polarizer, and a conical horn antenna, has been investigated for a notional CubeSat based space-to-ground radio wave propagation experiment.

  5. Stability of planar traveling waves in a Keller-Segel equation on an infinite strip domain

    NASA Astrophysics Data System (ADS)

    Chae, Myeongju; Choi, Kyudong; Kang, Kyungkeun; Lee, Jihoon

    2018-07-01

    We consider a simplified model of tumor angiogenesis, described by a Keller-Segel equation on the two dimensional domain (x , y) ∈ R ×Sλ where Sλ is the circle of perimeter λ. It is known that the system allows planar traveling wave solutions of an invading type. In case that λ is sufficiently small, we establish the nonlinear stability of traveling wave solutions in the absence of chemical diffusion if the initial perturbation is sufficiently small in some weighted Sobolev space. When chemical diffusion is present, it can be shown that the system is linearly stable. Lastly, we prove that any solution with our front condition eventually becomes planar under certain regularity conditions.

  6. Acousto-optic modulation of a photonic crystal nanocavity with Lamb waves in microwave K band

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Tadesse, Semere A.; School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455; Li, Huan

    2015-11-16

    Integrating nanoscale electromechanical transducers and nanophotonic devices potentially can enable acousto-optic devices to reach unprecedented high frequencies and modulation efficiency. Here, we demonstrate acousto-optic modulation of a photonic crystal nanocavity using Lamb waves with frequency up to 19 GHz, reaching the microwave K band. The devices are fabricated in suspended aluminum nitride membrane. Excitation of acoustic waves is achieved with interdigital transducers with period as small as 300 nm. Confining both acoustic wave and optical wave within the thickness of the membrane leads to improved acousto-optic modulation efficiency in these devices than that obtained in previous surface acoustic wave devices. Ourmore » system demonstrates a scalable optomechanical platform where strong acousto-optic coupling between cavity-confined photons and high frequency traveling phonons can be explored.« less

  7. Theta and Alpha Oscillations Are Traveling Waves in the Human Neocortex.

    PubMed

    Zhang, Honghui; Watrous, Andrew J; Patel, Ansh; Jacobs, Joshua

    2018-06-01

    Human cognition requires the coordination of neural activity across widespread brain networks. Here, we describe a new mechanism for large-scale coordination in the human brain: traveling waves of theta and alpha oscillations. Examining direct brain recordings from neurosurgical patients performing a memory task, we found contiguous clusters of cortex in individual patients with oscillations at specific frequencies within 2 to 15 Hz. These oscillatory clusters displayed spatial phase gradients, indicating that they formed traveling waves that propagated at ∼0.25-0.75 m/s. Traveling waves were relevant behaviorally because their propagation correlated with task events and was more consistent when subjects performed the task well. Human traveling theta and alpha waves can be modeled by a network of coupled oscillators because the direction of wave propagation correlated with the spatial orientation of local frequency gradients. Our findings suggest that oscillations support brain connectivity by organizing neural processes across space and time. Copyright © 2018 Elsevier Inc. All rights reserved.

  8. Dispersion-Engineered Traveling Wave Kinetic Inductance Parametric Amplifier

    NASA Technical Reports Server (NTRS)

    Zmuidzinas, Jonas (Inventor); Day, Peter K. (Inventor)

    2014-01-01

    A traveling wave kinetic inductance parametric amplifier comprises a superconducting transmission line and a dispersion control element. The transmission line can include periodic variations of its dimension along its length. The superconducting material can include a high normal state resistivity material. In some instances the high normal state resistivity material includes nitrogen and a metal selected from the group consisting of titanium, niobium and vanadium. The traveling wave kinetic inductance parametric amplifier is expected to exhibit a noise temperature below 100 mK/GHz.

  9. Modification of wave propagation and wave travel-time by the presence of magnetic fields in the solar network atmosphere

    NASA Astrophysics Data System (ADS)

    Nutto, C.; Steiner, O.; Schaffenberger, W.; Roth, M.

    2012-02-01

    Context. Observations of waves at frequencies above the acoustic cut-off frequency have revealed vanishing wave travel-times in the vicinity of strong magnetic fields. This detection of apparently evanescent waves, instead of the expected propagating waves, has remained a riddle. Aims: We investigate the influence of a strong magnetic field on the propagation of magneto-acoustic waves in the atmosphere of the solar network. We test whether mode conversion effects can account for the shortening in wave travel-times between different heights in the solar atmosphere. Methods: We carry out numerical simulations of the complex magneto-atmosphere representing the solar magnetic network. In the simulation domain, we artificially excite high frequency waves whose wave travel-times between different height levels we then analyze. Results: The simulations demonstrate that the wave travel-time in the solar magneto-atmosphere is strongly influenced by mode conversion. In a layer enclosing the surface sheet defined by the set of points where the Alfvén speed and the sound speed are equal, called the equipartition level, energy is partially transferred from the fast acoustic mode to the fast magnetic mode. Above the equipartition level, the fast magnetic mode is refracted due to the large gradient of the Alfvén speed. The refractive wave path and the increasing phase speed of the fast mode inside the magnetic canopy significantly reduce the wave travel-time, provided that both observing levels are above the equipartition level. Conclusions: Mode conversion and the resulting excitation and propagation of fast magneto-acoustic waves is responsible for the observation of vanishing wave travel-times in the vicinity of strong magnetic fields. In particular, the wave propagation behavior of the fast mode above the equipartition level may mimic evanescent behavior. The present wave propagation experiments provide an explanation of vanishing wave travel-times as observed with multi

  10. Apparatus and method for measuring and imaging traveling waves

    DOEpatents

    Telschow, Kenneth L.; Deason, Vance A.

    2001-01-01

    An apparatus is provided for imaging traveling waves in a medium. The apparatus includes a vibration excitation source configured to impart traveling waves within a medium. An emitter is configured to produce two or more wavefronts, at least one wavefront modulated by a vibrating medium. A modulator is configured to modulate another wavefront in synchronization with the vibrating medium. A sensing media is configured to receive in combination the modulated one wavefront and the another wavefront and having a detection resolution within a limited bandwidth. The another wavefront is modulated at a frequency such that a difference frequency between the one wavefront and the another wavefront is within a response range of the sensing media. Such modulation produces an image of the vibrating medium having an output intensity that is substantially linear with small physical variations within the vibrating medium for all vibration frequencies above the sensing media's response bandwidth. A detector is configured to detect an image of traveling waves in the vibrating medium resulting from interference between the modulated one wavefront and the another wavefront when combined in association with the sensing media. The traveling wave can be used to characterize certain material properties of the medium. Furthermore, a method is provided for imaging and characterizing material properties according to the apparatus.

  11. Phononic band gap and wave propagation on polyvinylidene fluoride-based acoustic metamaterials

    NASA Astrophysics Data System (ADS)

    Oltulu, Oral; Simsek, Sevket; Mamedov, Amirullah M.; Ozbay, Ekmel

    2016-12-01

    In the present work, the acoustic band structure of a two-dimensional phononic crystal (PC) containing an organic ferroelectric (PVDF-polyvinylidene fluoride) and topological insulator (SnTe) was investigated by the plane-wave-expansion (PWE) method. Two-dimensional PC with square lattices composed of SnTe cylindrical rods embedded in the PVDF matrix is studied to find the allowed and stop bands for the waves of certain energy. Phononic band diagram ω = ω(k) for a 2D PC, in which non-dimensional frequencies ωa/2πc (c-velocity of wave) were plotted vs. the wavevector k along the Г-X-M-Г path in the square Brillouin zone shows five stop bands in the frequency range between 10 and 110 kHz. The ferroelectric properties of PVDF and the unusual properties of SnTe as a topological material give us the ability to control the wave propagation through the PC over a wide frequency range of 103-106 Hz. SnTe is a discrete component that allows conducting electricity on its surface but shows insulator properties through its bulk volume. Tin telluride is considered as an acoustic topological insulator as the extension of topological insulators into the field of "topological phononics".

  12. Bistable traveling waves for a competitive-cooperative system with nonlocal delays

    NASA Astrophysics Data System (ADS)

    Tian, Yanling; Zhao, Xiao-Qiang

    2018-04-01

    This paper is devoted to the study of bistable traveling waves for a competitive-cooperative reaction and diffusion system with nonlocal time delays. The existence of bistable waves is established by appealing to the theory of monotone semiflows and the finite-delay approximations. Then the global stability of such traveling waves is obtained via a squeezing technique and a dynamical systems approach.

  13. Three-dimensional simulation of helix traveling-wave tube cold-test characteristics using MAFIA

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kory, C.L.

    1996-12-31

    A critically important step in the traveling-wave tube (TWT) design process is the cold-testing of the slow-wave circuit for dispersion, beam interaction impedance and RF losses. Experimental cold-tests can be very time-consuming and expensive, thus limiting the freedom to examine numerous variations to the test circuit. This makes the need for computational methods crucial as they can lower cost, reduce tube development time and allow the freedom to introduce novel and improved designs. The cold-test parameters have been calculated for a C-Band Northrop-Grumman helix TWT slow-wave circuit using MAFIA, the three-dimensional electromagnetic finite-integration computer code. Measured and simulated cold-test datamore » for the Northrop-Grumman helix TWT including dispersion, impedance and attenuation will be presented. Close agreement between simulated and measured values of the dispersion, impedance and attenuation has been obtained.« less

  14. Miniature traveling wave tube and method of making

    NASA Technical Reports Server (NTRS)

    Kosmahl, Henry G. (Inventor)

    1989-01-01

    It is an object of the invention to provide a miniature traveling wave tube which will have most of the advantages of solid state circuitry but with higher efficiency and without being highly sensitive to temperature and various types of electromagnetic radiation and subatomic particles as are solid state devices. The traveling wave tube which is about 2.5 cm in length includes a slow wave circuit (SWS) comprising apertured fins with a top cover which is insulated from the fins by strips or rungs of electrically insulating, dielectric material. Another object of the invention is to construct a SWS of extremely small size by employing various grooving or etching methods and by providing insulating strips or rungs by various deposition and masking techniques.

  15. Parallel traveling-wave MRI: a feasibility study.

    PubMed

    Pang, Yong; Vigneron, Daniel B; Zhang, Xiaoliang

    2012-04-01

    Traveling-wave magnetic resonance imaging utilizes far fields of a single-piece patch antenna in the magnet bore to generate radio frequency fields for imaging large-size samples, such as the human body. In this work, the feasibility of applying the "traveling-wave" technique to parallel imaging is studied using microstrip patch antenna arrays with both the numerical analysis and experimental tests. A specific patch array model is built and each array element is a microstrip patch antenna. Bench tests show that decoupling between two adjacent elements is better than -26-dB while matching of each element reaches -36-dB, demonstrating excellent isolation performance and impedance match capability. The sensitivity patterns are simulated and g-factors are calculated for both unloaded and loaded cases. The results on B 1- sensitivity patterns and g-factors demonstrate the feasibility of the traveling-wave parallel imaging. Simulations also suggest that different array configuration such as patch shape, position and orientation leads to different sensitivity patterns and g-factor maps, which provides a way to manipulate B(1) fields and improve the parallel imaging performance. The proposed method is also validated by using 7T MR imaging experiments. Copyright © 2011 Wiley-Liss, Inc.

  16. Skin friction drag reduction in turbulent flow using spanwise traveling surface waves

    NASA Astrophysics Data System (ADS)

    Musgrave, Patrick F.; Tarazaga, Pablo A.

    2017-04-01

    A major technological driver in current aircraft and other vehicles is the improvement of fuel efficiency. One way to increase the efficiency is to reduce the skin friction drag on these vehicles. This experimental study presents an active drag reduction technique which decreases the skin friction using spanwise traveling waves. A novel method is introduced for generating traveling waves which is low-profile, non-intrusive, and operates under various flow conditions. This wave generation method is discussed and the resulting traveling waves are presented. These waves are then tested in a low-speed wind tunnel to determine their drag reduction potential. To calculate the drag reduction, the momentum integral method is applied to turbulent boundary layer data collected using a pitot tube and traversing system. The skin friction coefficients are then calculated and the drag reduction determined. Preliminary results yielded a drag reduction of ≍ 5% for 244Hz traveling waves. Thus, this novel wave generation method possesses the potential to yield an easily implementable, non-invasive drag reduction technology.

  17. Wide Band Gyrotron Traveling Wave Amplifier Analysis.

    DTIC Science & Technology

    1987-12-01

    phase versus frequency characteristics. It is in these aspects that the gyrotron amplifier effort has been less than successful. A C-band gyro- TWT ...proposals were made several years ago, no experimental results have yet been reported. Another concept for increasing the bandwidth of the gyro- TWT is to...including dielectric loading of the waveguide [24], helix loaded waveguide (25]-[26], and disc-loaded waveguide [26]-(27). No experimental results on

  18. Existence and Stability of Traveling Waves for Degenerate Reaction-Diffusion Equation with Time Delay

    NASA Astrophysics Data System (ADS)

    Huang, Rui; Jin, Chunhua; Mei, Ming; Yin, Jingxue

    2018-01-01

    This paper deals with the existence and stability of traveling wave solutions for a degenerate reaction-diffusion equation with time delay. The degeneracy of spatial diffusion together with the effect of time delay causes us the essential difficulty for the existence of the traveling waves and their stabilities. In order to treat this case, we first show the existence of smooth- and sharp-type traveling wave solutions in the case of c≥c^* for the degenerate reaction-diffusion equation without delay, where c^*>0 is the critical wave speed of smooth traveling waves. Then, as a small perturbation, we obtain the existence of the smooth non-critical traveling waves for the degenerate diffusion equation with small time delay τ >0 . Furthermore, we prove the global existence and uniqueness of C^{α ,β } -solution to the time-delayed degenerate reaction-diffusion equation via compactness analysis. Finally, by the weighted energy method, we prove that the smooth non-critical traveling wave is globally stable in the weighted L^1 -space. The exponential convergence rate is also derived.

  19. Existence and Stability of Traveling Waves for Degenerate Reaction-Diffusion Equation with Time Delay

    NASA Astrophysics Data System (ADS)

    Huang, Rui; Jin, Chunhua; Mei, Ming; Yin, Jingxue

    2018-06-01

    This paper deals with the existence and stability of traveling wave solutions for a degenerate reaction-diffusion equation with time delay. The degeneracy of spatial diffusion together with the effect of time delay causes us the essential difficulty for the existence of the traveling waves and their stabilities. In order to treat this case, we first show the existence of smooth- and sharp-type traveling wave solutions in the case of c≥c^* for the degenerate reaction-diffusion equation without delay, where c^*>0 is the critical wave speed of smooth traveling waves. Then, as a small perturbation, we obtain the existence of the smooth non-critical traveling waves for the degenerate diffusion equation with small time delay τ >0. Furthermore, we prove the global existence and uniqueness of C^{α ,β }-solution to the time-delayed degenerate reaction-diffusion equation via compactness analysis. Finally, by the weighted energy method, we prove that the smooth non-critical traveling wave is globally stable in the weighted L^1-space. The exponential convergence rate is also derived.

  20. Absolute instabilities of travelling wave solutions in a Keller-Segel model

    NASA Astrophysics Data System (ADS)

    Davis, P. N.; van Heijster, P.; Marangell, R.

    2017-11-01

    We investigate the spectral stability of travelling wave solutions in a Keller-Segel model of bacterial chemotaxis with a logarithmic chemosensitivity function and a constant, sublinear, and linear consumption rate. Linearising around the travelling wave solutions, we locate the essential and absolute spectrum of the associated linear operators and find that all travelling wave solutions have parts of the essential spectrum in the right half plane. However, we show that in the case of constant or sublinear consumption there exists a range of parameters such that the absolute spectrum is contained in the open left half plane and the essential spectrum can thus be weighted into the open left half plane. For the constant and sublinear consumption rate models we also determine critical parameter values for which the absolute spectrum crosses into the right half plane, indicating the onset of an absolute instability of the travelling wave solution. We observe that this crossing always occurs off of the real axis.

  1. Low-voltage harmonic multiplying gyrotron traveling-wave amplifier in G band

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Yeh, Y. S.; Guo, Y. W.; Kao, B. H.

    Harmonic multiplying operation in a gyrotron traveling-wave amplifier (gyro-TWA) permits for magnetic field reduction and frequency multiplication. Lowering a beam voltage is an important step toward miniaturization of a harmonic multiplying gyro-TWA. However, the additional degree of freedom that is provided by the multitude cyclotron harmonics in a low-voltage harmonic multiplying gyro-TWA still easily generates various competing modes. An improved mode-selective circuit, using circular waveguides with various radii, can provide the rejection points within the frequency range to suppress competing modes. Simulated results reveal that the mode-selective circuit can provide an attenuation of more than 14 dB to suppress the competingmore » modes. Furthermore, the performance of the gyro-TWA is analyzed for studying the sensitivity of the saturated output power and full width at half maximum bandwidth of the gyro-TWA to the beam voltage and the magnetic field. A stable low-voltage harmonic multiplying gyro-TWA with the mode-selective circuit is predicted to yield a peak output power of 24 kW at 200.4 GHz, corresponding to a saturated gain of 56 dB at an interaction efficiency of 20%. The full width at half maximum bandwidth is 3.0 GHz.« less

  2. Traveling waves in a magnetized Taylor-Couette flow.

    PubMed

    Liu, Wei; Goodman, Jeremy; Ji, Hantao

    2007-07-01

    We investigate numerically a traveling wave pattern observed in experimental magnetized Taylor-Couette flow at low magnetic Reynolds number. By accurately modeling viscous and magnetic boundaries in all directions, we reproduce the experimentally measured wave patterns and their amplitudes. Contrary to previous claims, the waves are shown to be transiently amplified disturbances launched by viscous boundary layers, rather than globally unstable magnetorotational modes.

  3. Traveling wave solutions in a chain of periodically forced coupled nonlinear oscillators

    NASA Astrophysics Data System (ADS)

    Duanmu, M.; Whitaker, N.; Kevrekidis, P. G.; Vainchtein, A.; Rubin, J. E.

    2016-06-01

    Motivated by earlier studies of artificial perceptions of light called phosphenes, we analyze traveling wave solutions in a chain of periodically forced coupled nonlinear oscillators modeling this phenomenon. We examine the discrete model problem in its co-traveling frame and systematically obtain the corresponding traveling waves in one spatial dimension. Direct numerical simulations as well as linear stability analysis are employed to reveal the parameter regions where the traveling waves are stable, and these waves are, in turn, connected to the standing waves analyzed in earlier work. We also consider a two-dimensional extension of the model and demonstrate the robust evolution and stability of planar fronts. Our simulations also suggest the radial fronts tend to either annihilate or expand and flatten out, depending on the phase value inside and the parameter regime. Finally, we observe that solutions that initially feature two symmetric fronts with bulged centers evolve in qualitative agreement with experimental observations of phosphenes.

  4. Traveling wave solutions in a chain of periodically forced coupled nonlinear oscillators

    DOE PAGES

    Duanmu, M.; Whitaker, N.; Kevrekidis, P. G.; ...

    2016-02-27

    Artificial perceptions of light called phosphenes were motivated by earlier studies. We analyze traveling wave solutions in a chain of periodically forced coupled nonlinear oscillators modeling this phenomenon. We examine the discrete model problem in its co-traveling frame and systematically obtain the corresponding traveling waves in one spatial dimension. Direct numerical simulations as well as linear stability analysis are employed to reveal the parameter regions where the traveling waves are stable, and these waves are, in turn, connected to the standing waves analyzed in earlier work. We also consider a two-dimensional extension of the model and demonstrate the robust evolutionmore » and stability of planar fronts. Moreover, our simulations also suggest the radial fronts tend to either annihilate or expand and flatten out, depending on the phase value inside and the parameter regime. Finally, we observe that solutions that initially feature two symmetric fronts with bulged centers evolve in qualitative agreement with experimental observations of phosphenes.« less

  5. Traveling wave solutions in a chain of periodically forced coupled nonlinear oscillators

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Duanmu, M.; Whitaker, N.; Kevrekidis, P. G.

    Artificial perceptions of light called phosphenes were motivated by earlier studies. We analyze traveling wave solutions in a chain of periodically forced coupled nonlinear oscillators modeling this phenomenon. We examine the discrete model problem in its co-traveling frame and systematically obtain the corresponding traveling waves in one spatial dimension. Direct numerical simulations as well as linear stability analysis are employed to reveal the parameter regions where the traveling waves are stable, and these waves are, in turn, connected to the standing waves analyzed in earlier work. We also consider a two-dimensional extension of the model and demonstrate the robust evolutionmore » and stability of planar fronts. Moreover, our simulations also suggest the radial fronts tend to either annihilate or expand and flatten out, depending on the phase value inside and the parameter regime. Finally, we observe that solutions that initially feature two symmetric fronts with bulged centers evolve in qualitative agreement with experimental observations of phosphenes.« less

  6. Decomposing variations of geopotential height in the troposphere and stratosphere into stationary and travelling waves

    NASA Astrophysics Data System (ADS)

    Guryanov, Vladimir; Eliseev, Alexey

    2016-07-01

    The ERA-Interim geopotential height in the Northern Hemisphere from November to March, 1992-2015 in the layer from between pressure levels 1000 mb and 1 mb is expanded into stationary and travelling zonal waves with zonal wavenumbers, k, from 1 to 10, and with periods, T, from 2 to 156 days (the so called Hayashi spectra). Among the studied waves, the largest amplitude is attained by the stationary and travelling waves with zonal wavenumber k=1 and with periods from 3 to 4 weeks in the upper stratosphere over the latitudinal belt 60-70oN. The stationary waves with k from 1 to 3 and with T from 2 to 3 weeks are most pronounced in the stratosphere. In turn, the largest amplitudes of the travelling waves with zonal wavenumbers k ≥ 5 are found in the troposphere. The dominant periods of the latter waves are about 1 week or slightly higher, and this dominant period basically decrease with increasing wavenumber. In the upper stratosphere, the eastward travelling waves generally dominate over westward ones. The only exception is the longest zonal mode with k=1, for which the amplitude of the westward travelling wave is larger than that for the eastward one. The period of the travelling waves dominating in the upper stratosphere is close to 3 weeks. In the upper troposphere, the amplitudes of the eastward waves with k from 4 to 10 is several-fold larger than those for their westward counterparts. The latter is reflected in the larger average wavenumber of the eastward travelling wave in comparison to that of the westarward one. The period of the gravest of the dominant travelling waves in the upper troposphere is close to one week, and it decreases to 2-4 days for the dominant travelling waves with k=8-10.

  7. Snakes mimic earthworms: propulsion using rectilinear travelling waves

    PubMed Central

    Marvi, Hamidreza; Bridges, Jacob; Hu, David L.

    2013-01-01

    In rectilinear locomotion, snakes propel themselves using unidirectional travelling waves of muscular contraction, in a style similar to earthworms. In this combined experimental and theoretical study, we film rectilinear locomotion of three species of snakes, including red-tailed boa constrictors, Dumeril's boas and Gaboon vipers. The kinematics of a snake's extension–contraction travelling wave are characterized by wave frequency, amplitude and speed. We find wave frequency increases with increasing body size, an opposite trend than that for legged animals. We predict body speed with 73–97% accuracy using a mathematical model of a one-dimensional n-linked crawler that uses friction as the dominant propulsive force. We apply our model to show snakes have optimal wave frequencies: higher values increase Froude number causing the snake to slip; smaller values decrease thrust and so body speed. Other choices of kinematic variables, such as wave amplitude, are suboptimal and appear to be limited by anatomical constraints. Our model also shows that local body lifting increases a snake's speed by 31 per cent, demonstrating that rectilinear locomotion benefits from vertical motion similar to walking. PMID:23635494

  8. Multiple branches of travelling waves for the Gross–Pitaevskii equation

    NASA Astrophysics Data System (ADS)

    Chiron, David; Scheid, Claire

    2018-06-01

    Explicit solitary waves are known to exist for the Kadomtsev–Petviashvili-I (KP-I) equation in dimension 2. We first address numerically the question of their Morse index. The results confirm that the lump solitary wave has Morse index one and that the other explicit solutions correspond to excited states. We then turn to the 2D Gross–Pitaevskii (GP) equation, which in some long wave regime converges to the KP-I equation. Numerical simulations have already shown that a branch of travelling waves of GP converges to a ground state of KP-I, expected to be the lump. In this work, we perform numerical simulations showing that other explicit solitary waves solutions to the KP-I equation give rise to new branches of travelling waves of GP corresponding to excited states.

  9. X-band inverse class-F GaN internally-matched power amplifier

    NASA Astrophysics Data System (ADS)

    Zhao, Bo-Chao; Lu, Yang; Han, Wen-Zhe; Zheng, Jia-Xin; Zhang, Heng-Shuang; Ma, Pei-jun; Ma, Xiao-Hua; Hao, Yue

    2016-09-01

    An X-band inverse class-F power amplifier is realized by a 1-mm AlGaN/GaN high electron mobility transistor (HEMT). The intrinsic and parasitic components inside the transistor, especially output capacitor Cds, influence the harmonic impedance heavily at the X-band, so compensation design is used for meeting the harmonic condition of inverse class-F on the current source plane. Experiment results show that, in the continuous-wave mode, the power amplifier achieves 61.7% power added efficiency (PAE), which is 16.3% higher than the class-AB power amplifier realized by the same kind of HEMT. To the best of our knowledge, this is the first inverse class-F GaN internally-matched power amplifier, and the PAE is quite high at the X-band. Project supported by the National High Technology Research and Development Program of China (Grant No. 2015AA016801).

  10. Sensitivity enhancement of traveling wave MRI using free local resonators: an experimental demonstration.

    PubMed

    Zhang, Xiaoliang

    2017-04-01

    Traveling wave MR uses the far fields in signal excitation and reception, therefore its acquisition efficiency is low in contrast to the conventional near field magnetic resonance (MR). Here we show a simple and efficient method based on the local resonator to improving sensitivity of traveling wave MR technique. The proposed method utilizes a standalone or free local resonator to amplify the radio frequency magnetic fields in the interested target. The resonators have no wire connections to the MR system and thus can be conveniently placed to any place around imaging simples. A rectangular loop L/C resonator to be used as the free local resonator was tuned to the proton Larmor frequency at 7T. Traveling wave MR experiments with and without the wireless free local resonator were performed on a living rat using a 7T whole body MR scanner. The signal-to-noise ratio (SNR) or sensitivity of the images acquired was compared and evaluated. In vivo 7T imaging results show that traveling wave MR with a wireless free local resonator placed near the head of a living rat achieves at least 10-fold SNR gain over the images acquired on the same rat using conventional traveling wave MR method, i.e. imaging with no free local resonators. The proposed free local resonator technique is able to enhance the MR sensitivity and acquisition efficiency of traveling wave MR at ultrahigh fields in vivo . This method can be a simple solution to alleviating low sensitivity problem of traveling wave MRI.

  11. Development of a W-band Serpentine Waveguide Amplifier based on a UV-LIGA Microfabricated Copper Circuit

    DTIC Science & Technology

    2013-03-01

    beam tunnel [5,6] for a high - power , wideband W- band traveling-wave tube (TWT) amplifier. UV-LIGA is also a promising technique at higher...wide- band , high - power operation of the amplifier [7, 8]. The interaction circuit consists of two traveling-wave stages separated by a power ...technique produces monolithic all-copper circuits, integrated with electron beam tunnel, suitable for high - power continuous-wave operation [1]. We

  12. Giant amplification in degenerate band edge slow-wave structures interacting with an electron beam

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Othman, Mohamed A. K.; Veysi, Mehdi; Capolino, Filippo

    2016-03-15

    We propose a new amplification regime based on a synchronous operation of four degenerate electromagnetic (EM) modes in a slow-wave structure and the electron beam, referred to as super synchronization. These four EM modes arise in a Fabry-Pérot cavity when degenerate band edge (DBE) condition is satisfied. The modes interact constructively with the electron beam resulting in superior amplification. In particular, much larger gains are achieved for smaller beam currents compared to conventional structures based on synchronization with only a single EM mode. We demonstrate giant gain scaling with respect to the length of the slow-wave structure compared to conventionalmore » Pierce type single mode traveling wave tube amplifiers. We construct a coupled transmission line model for a loaded waveguide slow-wave structure exhibiting a DBE, and investigate the phenomenon of giant gain via super synchronization using the Pierce model generalized to multimode interaction.« less

  13. Traveling wave tube and method of manufacture

    NASA Technical Reports Server (NTRS)

    Vancil, Bernard K. (Inventor)

    2004-01-01

    A traveling wave tube includes a glass or other insulating envelope having a plurality of substantially parallel glass rods supported therewithin which in turn support an electron gun, a collector and an intermediate slow wave structure. The slow wave structure itself provides electrostatic focussing of a central electron beam thereby eliminating the need for focussing magnetics and materially decreasing the cost of construction as well as enabling miniaturization. The slow wave structure advantageously includes cavities along the electron beam through which the r.f. energy is propagated, or a double, interleaved ring loop structure supported by dielectric fins within a ground plane cylinder disposed coaxially within the glass envelope.

  14. Traveling wave in a three-dimensional array of conformist and contrarian oscillators

    NASA Astrophysics Data System (ADS)

    Hoang, Danh-Tai; Jo, Junghyo; Hong, Hyunsuk

    2015-03-01

    We consider a system of conformist and contrarian oscillators coupled locally in a three-dimensional cubic lattice and explore collective behavior of the system. The conformist oscillators attractively interact with the neighbor oscillators and therefore tend to be aligned with the neighbors' phase. The contrarian oscillators interact repulsively with the neighbors and therefore tend to be out of phase with them. In this paper, we investigate whether many peculiar dynamics that have been observed in the mean-field system with global coupling can emerge even with local coupling. In particular, we pay attention to the possibility that a traveling wave may arise. We find that the traveling wave occurs due to coupling asymmetry and not by global coupling; this observation confirms that the global coupling is not essential to the occurrence of a traveling wave in the system. The traveling wave can be a mechanism for the coherent rhythm generation of the circadian clock or of hormone secretion in biological systems under local coupling.

  15. The sleep slow oscillation as a traveling wave.

    PubMed

    Massimini, Marcello; Huber, Reto; Ferrarelli, Fabio; Hill, Sean; Tononi, Giulio

    2004-08-04

    During much of sleep, virtually all cortical neurons undergo a slow oscillation (<1 Hz) in membrane potential, cycling from a hyperpolarized state of silence to a depolarized state of intense firing. This slow oscillation is the fundamental cellular phenomenon that organizes other sleep rhythms such as spindles and slow waves. Using high-density electroencephalogram recordings in humans, we show here that each cycle of the slow oscillation is a traveling wave. Each wave originates at a definite site and travels over the scalp at an estimated speed of 1.2-7.0 m/sec. Waves originate more frequently in prefrontal-orbitofrontal regions and propagate in an anteroposterior direction. Their rate of occurrence increases progressively reaching almost once per second as sleep deepens. The pattern of origin and propagation of sleep slow oscillations is reproducible across nights and subjects and provides a blueprint of cortical excitability and connectivity. The orderly propagation of correlated activity along connected pathways may play a role in spike timing-dependent synaptic plasticity during sleep.

  16. Band gaps and localization of surface water waves over large-scale sand waves with random fluctuations

    NASA Astrophysics Data System (ADS)

    Zhang, Yu; Li, Yan; Shao, Hao; Zhong, Yaozhao; Zhang, Sai; Zhao, Zongxi

    2012-06-01

    Band structure and wave localization are investigated for sea surface water waves over large-scale sand wave topography. Sand wave height, sand wave width, water depth, and water width between adjacent sand waves have significant impact on band gaps. Random fluctuations of sand wave height, sand wave width, and water depth induce water wave localization. However, random water width produces a perfect transmission tunnel of water waves at a certain frequency so that localization does not occur no matter how large a disorder level is applied. Together with theoretical results, the field experimental observations in the Taiwan Bank suggest band gap and wave localization as the physical mechanism of sea surface water wave propagating over natural large-scale sand waves.

  17. Input and output compensation for the cochlear traveling wave delay in wide-band ABR recordings: implications for small acoustic tumor detection.

    PubMed

    Don, Manuel; Elberling, Claus; Maloff, Erin

    2009-02-01

    The Stacked ABR (auditory brainstem response) attempts at the output of the auditory periphery to compensate for the temporal dispersion of neural activation caused by the cochlear traveling wave in response to click stimulation. Compensation can also be made at the input by using a chirp stimulus. It has been demonstrated that the Stacked ABR is sensitive to small tumors that are often missed by standard ABR latency measures. Because a chirp stimulus requires only a single data acquisition run whereas the Stacked ABR requires six, we try to evaluate some indirect evidence justifying the use of a chirp for small tumor detection. We compared the sensitivity and specificity of different Stacked ABRs formed by aligning the derived-band ABRs according to (1) the individual's peak latencies, (2) the group mean latencies, and (3) the modeled latencies used to develop a chirp. For tumor detection with a chosen sensitivity of 95%, a relatively high specificity of 85% may be achieved with a chirp. It appears worthwhile to explore the actual use of a chirp because significantly shorter test and analysis times might be possible.

  18. Comparing the Robustness of High-Frequency Traveling-Wave Tube Slow-Wave Circuits

    NASA Technical Reports Server (NTRS)

    Chevalier, Christine T.; Wilson, Jeffrey D.; Kory, Carol L.

    2007-01-01

    A three-dimensional electromagnetic field simulation software package was used to compute the cold-test parameters, phase velocity, on-axis interaction impedance, and attenuation, for several high-frequency traveling-wave tube slow-wave circuit geometries. This research effort determined the effects of variations in circuit dimensions on cold-test performance. The parameter variations were based on the tolerances of conventional micromachining techniques.

  19. Exact traveling wave solutions of modified KdV-Zakharov-Kuznetsov equation and viscous Burgers equation.

    PubMed

    Islam, Md Hamidul; Khan, Kamruzzaman; Akbar, M Ali; Salam, Md Abdus

    2014-01-01

    Mathematical modeling of many physical systems leads to nonlinear evolution equations because most physical systems are inherently nonlinear in nature. The investigation of traveling wave solutions of nonlinear partial differential equations (NPDEs) plays a significant role in the study of nonlinear physical phenomena. In this article, we construct the traveling wave solutions of modified KDV-ZK equation and viscous Burgers equation by using an enhanced (G '/G) -expansion method. A number of traveling wave solutions in terms of unknown parameters are obtained. Derived traveling wave solutions exhibit solitary waves when special values are given to its unknown parameters. 35C07; 35C08; 35P99.

  20. Traveling waves in the discrete fast buffered bistable system.

    PubMed

    Tsai, Je-Chiang; Sneyd, James

    2007-11-01

    We study the existence and uniqueness of traveling wave solutions of the discrete buffered bistable equation. Buffered excitable systems are used to model, among other things, the propagation of waves of increased calcium concentration, and discrete models are often used to describe the propagation of such waves across multiple cells. We derive necessary conditions for the existence of waves, and, under some restrictive technical assumptions, we derive sufficient conditions. When the wave exists it is unique and stable.

  1. Orbital stability of periodic traveling wave solutions for the Kawahara equation

    NASA Astrophysics Data System (ADS)

    de Andrade, Thiago Pinguello; Cristófani, Fabrício; Natali, Fábio

    2017-05-01

    In this paper, we investigate the orbital stability of periodic traveling waves for the Kawahara equation. We prove that the periodic traveling wave, under certain conditions, minimizes a convenient functional by using an adaptation of the method developed by Grillakis et al. [J. Funct. Anal. 74, 160-197 (1987)]. The required spectral properties to ensure the orbital stability are obtained by knowing the positiveness of the Fourier transform of the associated periodic wave established by Angulo and Natali [SIAM J. Math. Anal. 40, 1123-1151 (2008)].

  2. C (G)-Band & X (I) - Band Noncoherent Radar Transponder Performance Specification Standard

    DTIC Science & Technology

    2002-04-01

    TRAINING RANGE NEVADA TEST SITE STANDARD 262-02 ELECTRONIC TRAJECTORY MEASUREMENTS GROUP C (G) – BAND & X (I) – BAND NONCOHERENT RADAR...Date 00 Apr 2002 Report Type N/A Dates Covered (from... to) - Title and Subtitle C (G)-Band & X (I) - Band Noncoherent Radar Transponder...Number of Pages 157 i STANDARD 262-02 C (G) – BAND & X (I) – BAND NONCOHERENT RADAR TRANSPONDER PERFORMANCE SPECIFICATION STANDARD APRIL 2002 Prepared by

  3. Block 3 X-band receiver-exciter

    NASA Technical Reports Server (NTRS)

    Johns, C. E.

    1987-01-01

    The development of an X-band exciter, for use in the X-Band Uplink Subsystem, was completed. The exciter generates the drive signal for the X-band transmitter and also generates coherent test signals for the S- and X-band Block 3 translator and a Doppler reference signal for the Doppler extractor system. In addition to the above, the exciter generates other reference signals that are described. Also presented is an overview of the exciter design and some test data taken on the prototype. A brief discussion of the Block 3 Doppler extractor is presented.

  4. Modified method of simplest equation: Powerful tool for obtaining exact and approximate traveling-wave solutions of nonlinear PDEs

    NASA Astrophysics Data System (ADS)

    Vitanov, Nikolay K.

    2011-03-01

    We discuss the class of equations ∑i,j=0mAij(u){∂iu}/{∂ti}∂+∑k,l=0nBkl(u){∂ku}/{∂xk}∂=C(u) where Aij( u), Bkl( u) and C( u) are functions of u( x, t) as follows: (i) Aij, Bkl and C are polynomials of u; or (ii) Aij, Bkl and C can be reduced to polynomials of u by means of Taylor series for small values of u. For these two cases the above-mentioned class of equations consists of nonlinear PDEs with polynomial nonlinearities. We show that the modified method of simplest equation is powerful tool for obtaining exact traveling-wave solution of this class of equations. The balance equations for the sub-class of traveling-wave solutions of the investigated class of equations are obtained. We illustrate the method by obtaining exact traveling-wave solutions (i) of the Swift-Hohenberg equation and (ii) of the generalized Rayleigh equation for the cases when the extended tanh-equation or the equations of Bernoulli and Riccati are used as simplest equations.

  5. Design and cold test of period-tapered double-ridge-loaded folded waveguide slow wave structure for Ka band TWTs

    NASA Astrophysics Data System (ADS)

    Lu, Zhigang; Su, Zhicheng; Wei, Yanyu

    2018-05-01

    A double-ridge-loaded folded waveguide (DRL-FW) travelling wave tube (TWT) based on period-tapered structure is proposed. Through analysing the dispersion characteristics of the DRL-FW slow wave structure (SWS), the physical mechanism of the band-edge oscillation is obtained. Period-tapered SWS is proposed and analysed for verifying the feasibility in suppressing upper-band-edge oscillation and increasing the output power. Then the electromagnetic characteristics and the beam-wave interaction of TWT based on the period-tapered DRL-FW SWS are investigated. The calculation results predict that it potentially could provide continuous wave power over 600W from 29 GHz to 32 GHz without upper-band-edge oscillation. The bandwidth expands from 29-31GHz to 29-32GHz and electron efficiency is increased from more than 8.3% to more than 11%, while the range of operating voltage expands from 22kV-22.5kV to 22kV-24kV. The corresponding saturated gain can reach over 36.8 dB. In addition, we have carried out experimental tests on the transmission characteristics of period-tapered DRL-FW SWS. The cold test results show that the voltage stand-wave ratio (VSWR) is below 1.8 in the range of 29-32GHz. Good transmission characteristics greatly reduce the risk of reflection wave oscillation, thus improving the stability of DRL-FW TWT.

  6. An Investigation of Traveling-Wave Electrophoresis using a Trigonometric Potential

    NASA Astrophysics Data System (ADS)

    Vopal, James

    Traveling-wave electrophoresis, a technique for microfluidic separations in lab-on-achip devices, is investigated using a trigonometric model that naturally incorporates the spatial periodicity of the device. Traveling-wave electrophoresis can be used to separate high-mobility ions from low-mobility ions in forensic and medical applications, with a separation threshold that can be tuned for specific applications by simply choosing the traveling wave frequency. Our simulations predict plateaus in the average ion velocity verses the mobility, plateaus that correspond to Farey fractions and yield Devil's staircases for non-zero discreteness values. The plateaus indicate that ions with different mobilities can travel with the same average velocity. To determine the conditions for chaos, Lyapunov exponents and contact maps are employed. Through the use of contact maps, the chaotic trajectories are determined to be either narrowband or broadband. Narrowband chaotic trajectories are exhibited in the plateaus of the average velocity, while broadband chaotic trajectories are exhibited where the average velocity varies nonmonotonically with the mobility. Narrowband chaos will be investigated in future work incorporating the role of diffusion. The results of this and future work can be used to develop new tools for electrophoretic separation.

  7. Emergence of traveling waves in the spreading of dengue fever

    NASA Astrophysics Data System (ADS)

    Bianco, Simone; Faatz, Andrea; Cummings, Derek; Shaw, Leah

    2010-03-01

    Dengue fever is a multistrain mosquito-borne subtropical disease that exhibits complex oscillatory outbreaks. Epidemiological data from Thailand displays traveling waves of infection originating in Bangkok, the largest population center (Cummings et al., Nature 427: 344, 2004). We present a multistrain metapopulation model in which traveling wave like behavior results from migration coupling between heterogeneous regions. The region with the highest effective person-to-person contact rate leads the dynamics. A stochastic version of the model will also be presented.

  8. Traveling wave to a reaction-hyperbolic system for axonal transport

    NASA Astrophysics Data System (ADS)

    Huang, Feimin; Li, Xing; Zhang, Yinglong

    2017-07-01

    In this paper, we study a class of nonlinear reaction-hyperbolic systems modeling the neuronal signal transfer in neuroscience. This reaction-hyperbolic system can be regarded as n × n (n ≥ 2) hyperbolic system with relaxation. We first prove the existence of traveling wave by Gershgorin circle theorem and mathematically describe the neuronal signal transport. Then for a special case n = 2, we show the traveling wave is nonlinearly stable, and obtain the convergence rate simultaneously by a weighted estimate.

  9. Traveling wave solutions to a reaction-diffusion equation

    NASA Astrophysics Data System (ADS)

    Feng, Zhaosheng; Zheng, Shenzhou; Gao, David Y.

    2009-07-01

    In this paper, we restrict our attention to traveling wave solutions of a reaction-diffusion equation. Firstly we apply the Divisor Theorem for two variables in the complex domain, which is based on the ring theory of commutative algebra, to find a quasi-polynomial first integral of an explicit form to an equivalent autonomous system. Then through this first integral, we reduce the reaction-diffusion equation to a first-order integrable ordinary differential equation, and a class of traveling wave solutions is obtained accordingly. Comparisons with the existing results in the literature are also provided, which indicates that some analytical results in the literature contain errors. We clarify the errors and instead give a refined result in a simple and straightforward manner.

  10. An 'X-banded' Tidbinbilla interferometer

    NASA Technical Reports Server (NTRS)

    Batty, Michael J.; Gardyne, R. G.; Gay, G. J.; Jauncy, David L.; Gulkis, S.; Kirk, A.

    1986-01-01

    The recent upgrading of the Tidbinbilla two-element interferometer to simultaneous S-band (2.3 GHz) and X-band (8.4 GHz) operation has provided a powerful new astronomical facility for weak radio source measurement in the Southern Hemisphere. The new X-band system has a minimum fringe spacing of 38 arcsec, and about the same positional measurement capability (approximately 2 arcsec) and sensitivity (1 s rms noise of 10 mJy) as the previous S-band system. However, the far lower confusion limit will allow detection and accurate positional measurements for sources as weak as a few millijanskys. This capability will be invaluable for observations of radio stars, X-ray sources and other weak, compact radio sources.

  11. Monostable traveling waves for a time-periodic and delayed nonlocal reaction-diffusion equation

    NASA Astrophysics Data System (ADS)

    Li, Panxiao; Wu, Shi-Liang

    2018-04-01

    This paper is concerned with a time-periodic and delayed nonlocal reaction-diffusion population model with monostable nonlinearity. Under quasi-monotone or non-quasi-monotone assumptions, it is known that there exists a critical wave speed c_*>0 such that a periodic traveling wave exists if and only if the wave speed is above c_*. In this paper, we first prove the uniqueness of non-critical periodic traveling waves regardless of whether the model is quasi-monotone or not. Further, in the quasi-monotone case, we establish the exponential stability of non-critical periodic traveling fronts. Finally, we illustrate the main results by discussing two types of death and birth functions arising from population biology.

  12. Synchronization of Large Josephson-Junction Arrays by Traveling Electromagnetic Waves

    NASA Astrophysics Data System (ADS)

    Galin, M. A.; Borodianskyi, E. A.; Kurin, V. V.; Shereshevskiy, I. A.; Vdovicheva, N. K.; Krasnov, V. M.; Klushin, A. M.

    2018-05-01

    Mutual synchronization of many Josephson junctions is required for superradiant enhancement of the emission power. However, the larger the junction array is, the more difficult is the synchronization, especially when the array size becomes much larger than the emitted wavelength. Here, we study experimentally Josephson emission from such larger-than-the-wavelength Nb /NbSi /Nb junction arrays. For one of the arrays we observe a clear superradiant enhancement of emission above a threshold number of active junctions. The arrays exhibit strong geometrical resonances, seen as steps in current-voltage characteristics. However, radiation patterns of the arrays have forward-backward asymmetry, which is inconsistent with the solely geometrical resonance (standing-wave) mechanism of synchronization. We argue that the asymmetry provides evidence for an alternative mechanism of synchronization mediated by unidirectional traveling-wave propagation along the array (such as a surface plasmon). In this case, emission occurs predominantly in the direction of propagation of the traveling wave. Our conclusions are supported by numerical modeling of Josephson traveling-wave antenna. We argue that such a nonresonant mechanism of synchronization opens a possibility for phase locking of very large arrays of oscillators.

  13. The occurrence and wave properties of H+-, He+-, and O+-band EMIC waves observed by the Van Allen Probes

    NASA Astrophysics Data System (ADS)

    Saikin, A. A.; Zhang, J.-C.; Allen, R. C.; Smith, C. W.; Kistler, L. M.; Spence, H. E.; Torbert, R. B.; Kletzing, C. A.; Jordanova, V. K.

    2015-09-01

    We perform a statistical study of electromagnetic ion cyclotron (EMIC) waves detected by the Van Allen Probes mission to investigate the spatial distribution of their occurrence, wave power, ellipticity, and normal angle. The Van Allen Probes have been used which allow us to explore the inner magnetosphere (1.1 to 5.8 RE). Magnetic field measurements from the Electric and Magnetic Field Instrument Suite and Integrated Science on board the Van Allen Probes are used to identify EMIC wave events for the first 22 months of the mission operation (8 September 2012 to 30 June 2014). EMIC waves are examined in H+, He+, and O+ bands. Over 700 EMIC wave events have been identified over the three different wave bands (265 H+-band events, 438 He+-band events, and 68 O+-band events). EMIC wave events are observed between L = 2-8, with over 140 EMIC wave events observed below L = 4. Results show that H+-band EMIC waves have two peak magnetic local time (MLT) occurrence regions: prenoon (09:00 < MLT ≤ 12:00) and afternoon (15:00 < MLT ≤ 17:00) sectors. He+-band EMIC waves feature an overall stronger dayside occurrence. O+-band EMIC waves have one peak region located in the morning sector at lower L shells (L < 4). He+-band EMIC waves average the highest wave power overall (>0.1 nT2/Hz), especially in the afternoon sector. Ellipticity observations reveal that linearly polarized EMIC waves dominate in lower L shells.

  14. Waveguide Multimode Directional Coupler for Harvesting Harmonic Power from the Output of Traveling-Wave Tube Amplifiers

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Wintucky, Edwin G.

    2017-01-01

    The paper presents the design, fabrication, and test results for a novel waveguide multimode directional coupler (MDC). The coupler fabricated from dissimilar frequency band waveguides, is capable of isolating power at the 2nd harmonic frequency from the fundamental power at the output port of a high power traveling-wave tube amplifier. The major advantage of the MDC is significantly lower insertion loss compared to a diplexer. The presentation slides for the paper that was approved is attached. The tracking number for the paper that was approved is TN 37015.

  15. Generation of Highly Oblique Lower Band Chorus Via Nonlinear Three-Wave Resonance

    DOE PAGES

    Fu, Xiangrong; Gary, Stephen Peter; Reeves, Geoffrey D.; ...

    2017-09-05

    Chorus in the inner magnetosphere has been observed frequently at geomagnetically active times, typically exhibiting a two-band structure with a quasi-parallel lower band and an upper band with a broad range of wave normal angles. But recent observations by Van Allen Probes confirm another type of lower band chorus, which has a large wave normal angle close to the resonance cone angle. It has been proposed that these waves could be generated by a low-energy beam-like electron component or by temperature anisotropy of keV electrons in the presence of a low-energy plateau-like electron component. This paper, however, presents an alternativemore » mechanism for generation of this highly oblique lower band chorus. Through a nonlinear three-wave resonance, a quasi-parallel lower band chorus wave can interact with a mildly oblique upper band chorus wave, producing a highly oblique quasi-electrostatic lower band chorus wave. This theoretical analysis is confirmed by 2-D electromagnetic particle-in-cell simulations. Furthermore, as the newly generated waves propagate away from the equator, their wave normal angle can further increase and they are able to scatter low-energy electrons to form a plateau-like structure in the parallel velocity distribution. As a result, the three-wave resonance mechanism may also explain the generation of quasi-parallel upper band chorus which has also been observed in the magnetosphere.« less

  16. Fully- and weakly-nonlinear biperiodic traveling waves in shallow water

    NASA Astrophysics Data System (ADS)

    Hirakawa, Tomoaki; Okamura, Makoto

    2018-04-01

    We directly calculate fully nonlinear traveling waves that are periodic in two independent horizontal directions (biperiodic) in shallow water. Based on the Riemann theta function, we also calculate exact periodic solutions to the Kadomtsev-Petviashvili (KP) equation, which can be obtained by assuming weakly-nonlinear, weakly-dispersive, weakly-two-dimensional waves. To clarify how the accuracy of the biperiodic KP solution is affected when some of the KP approximations are not satisfied, we compare the fully- and weakly-nonlinear periodic traveling waves of various wave amplitudes, wave depths, and interaction angles. As the interaction angle θ decreases, the wave frequency and the maximum wave height of the biperiodic KP solution both increase, and the central peak sharpens and grows beyond the height of the corresponding direct numerical solutions, indicating that the biperiodic KP solution cannot qualitatively model direct numerical solutions for θ ≲ 45^\\circ . To remedy the weak two-dimensionality approximation, we apply the correction of Yeh et al (2010 Eur. Phys. J. Spec. Top. 185 97-111) to the biperiodic KP solution, which substantially improves the solution accuracy and results in wave profiles that are indistinguishable from most other cases.

  17. PZT Thin Film Piezoelectric Traveling Wave Motor

    NASA Technical Reports Server (NTRS)

    Shen, Dexin; Zhang, Baoan; Yang, Genqing; Jiao, Jiwei; Lu, Jianguo; Wang, Weiyuan

    1995-01-01

    With the development of micro-electro-mechanical systems (MEMS), its various applications are attracting more and more attention. Among MEMS, micro motors, electrostatic and electromagnetic, are the typical and important ones. As an alternative approach, the piezoelectric traveling wave micro motor, based on thin film material and integrated circuit technologies, circumvents many of the drawbacks of the above mentioned two types of motors and displays distinct advantages. In this paper we report on a lead-zirconate-titanate (PZT) piezoelectric thin film traveling wave motor. The PZT film with a thickness of 150 micrometers and a diameter of 8 mm was first deposited onto a metal substrate as the stator material. Then, eight sections were patterned to form the stator electrodes. The rotor had an 8 kHz frequency power supply. The rotation speed of the motor is 100 rpm. The relationship of the friction between the stator and the rotor and the structure of the rotor on rotation were also studied.

  18. Stability analysis of a two-stage tapered gyrotron traveling-wave tube amplifier with distributed losses

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hung, C. L.; Lian, Y. H.; Cheng, N. H.

    2012-11-15

    The two-stage tapered gyrotron traveling-wave tube (gyro-TWT) amplifier has achieved wide bandwidth in the millimeter wave range. However, possible oscillations in each stage limit this amplifier's operating beam current and thus its output power. To further enhance the amplifier's stability, distributed losses are applied to the interaction circuit of the two-stage tapered gyro-TWT. A self-consistent particle-tracing code is used for analyzing the beam-wave interactions. The stability analysis includes the effects of the wall losses and the length of each stage on the possible oscillations. Simulation results reveal that the distributed-loss method effectively stabilizes all the oscillations in the two stages.more » Under stable operating conditions, the device is predicted to produce a peak power of 60 kW with an efficiency of 29% and a saturated gain of 52 dB in the Ka-band. The 3-dB bandwidth is 5.7 GHz, which is approximately 16% of the center frequency.« less

  19. A tapered multi-gap multi-aperture pseudospark-sourced electron gun based X-band slow wave oscillator

    NASA Astrophysics Data System (ADS)

    Kumar, N.; Lamba, R. P.; Hossain, A. M.; Pal, U. N.; Phelps, A. D. R.; Prakash, R.

    2017-11-01

    The experimental study of a tapered, multi-gap, multi-aperture pseudospark-sourced electron gun based X-band plasma assisted slow wave oscillator is presented. The designed electron gun is based on the pseudospark discharge concept and has been used to generate a high current density and high energy electron beam simultaneously. The distribution of apertures has been arranged such that the field penetration potency inside the backspace of the hollow-cathode is different while passing through the tapered gap region. This leads to non-concurrent ignition of the discharge through all the channels which is, in general, quite challenging in the case of multi-aperture plasma cathode electron gun geometries. Multiple and successive hollow cathode phases are reported from this electron gun geometry, which have been confirmed using simulations. This geometry also has led to the achievement of ˜71% fill factor inside the slow wave oscillator for an electron beam of energy of 20 keV and a beam current density in the range of 115-190 A/cm2 at a working argon gas pressure of 18 Pa. The oscillator has generated broadband microwave output in the frequency range of 10-11.7 GHz with a peak power of ˜10 kW for ˜50 ns.

  20. Coupled effects of chemotaxis and growth on traveling bacterial waves.

    PubMed

    Yan, Zhifeng; Bouwer, Edward J; Hilpert, Markus

    2014-08-01

    Traveling bacterial waves are capable of improving contaminant remediation in the subsurface. It is fairly well understood how bacterial chemotaxis and growth separately affect the formation and propagation of such waves. However, their interaction is not well understood. We therefore perform a modeling study to investigate the coupled effects of chemotaxis and growth on bacterial migration, and examine their effects on contaminant remediation. We study the waves by using different initial electron acceptor concentrations for different bacteria and substrate systems. Three types of traveling waves can occur: a chemotactic wave due to the biased movement of chemotactic bacteria resulting from metabolism-generated substrate concentration gradients; a growth/decay/motility wave due to a dynamic equilibrium between bacterial growth, decay and random motility; and an integrated wave due to the interaction between bacterial chemotaxis and growth. Chemotaxis hardly enhances the bacterial propagation if it is too weak to form a chemotactic wave or its wave speed is less than half of the growth/decay/motility wave speed. However, chemotaxis significantly accelerates bacterial propagation once its wave speed exceeds the growth/decay/motility wave speed. When convection occurs, it speeds up the growth/decay/motility wave but slows down or even eliminates the chemotactic wave due to the dispersion. Bacterial survival proves particularly important for bacterial propagation. Therefore we develop a conceptual model to estimate the speed of growth/decay/motility waves. Copyright © 2014 Elsevier B.V. All rights reserved.

  1. Traveling waves in discretized Balitsky Kovchegov evolution

    NASA Astrophysics Data System (ADS)

    Marquet, C.; Peschanski, R.; Soyez, G.; Bialas, A.

    2006-02-01

    We study the asymptotic solutions of a version of the Balitsky-Kovchegov evolution with discrete steps in rapidity. We derive a closed iterative equation in momentum space. We show that it possesses traveling-wave solutions and extract their properties. We find no evidence for chaotic behaviour due to discretization.

  2. X-Band CubeSat Communication System Demonstration

    NASA Technical Reports Server (NTRS)

    Altunc, Serhat; Kegege, Obadiah; Bundick, Steve; Shaw, Harry; Schaire, Scott; Bussey, George; Crum, Gary; Burke, Jacob C.; Palo, Scott; O'Conor, Darren

    2015-01-01

    Today's CubeSats mostly operate their communications at UHF- and S-band frequencies. UHF band is presently crowded, thus downlink communications are at lower data rates due to bandwidth limitations and are unreliable due to interference. This research presents an end-to-end robust, innovative, compact, efficient and low cost S-band uplink and X-band downlink CubeSat communication system demonstration between a balloon and a Near Earth Network (NEN) ground system. Since communication systems serve as umbilical cords for space missions, demonstration of this X-band communication system is critical for successfully supporting current and future CubeSat communication needs. This research has three main objectives. The first objective is to design, simulate, and test a CubeSat S- and X-band communication system. Satellite Tool Kit (STK) dynamic link budget calculations and HFSS Simulations and modeling results have been used to trade the merit of various designs for small satellite applications. S- and X-band antennas have been tested in the compact antenna test range at Goddard Space Flight Center (GSFC) to gather radiation pattern data. The second objective is simulate and test a CubeSat compatible X-band communication system at 12.5Mbps including S-band antennas, X-band antennas, Laboratory for Atmospheric and Space Physics (LASP) /GSFC transmitter and an S-band receiver from TRL-5 to TRL-8 by the end of this effort. Different X-band communication system components (antennas, diplexers, etc.) from GSFC, other NASA centers, universities, and private companies have been investigated and traded, and a complete component list for the communication system baseline has been developed by performing analytical and numerical analysis. This objective also includes running simulations and performing trades between different X-band antenna systems to optimize communication system performance. The final objective is to perform an end-to-end X-band CubeSat communication system

  3. Traveling-wave piezoelectric linear motor part II: experiment and performance evaluation.

    PubMed

    Ting, Yung; Li, Chun-Chung; Chen, Liang-Chiang; Yang, Chieh-Min

    2007-04-01

    This article continues the discussion of a traveling-wave piezoelectric linear motor. Part I of this article dealt with the design and analysis of the stator of a traveling-wave piezoelectric linear motor. In this part, the discussion focuses on the structure and modeling of the contact layer and the carriage. In addition, the performance analysis and evaluation of the linear motor also are dealt with in this study. The traveling wave is created by stator, which is constructed by a series of bimorph actuators arranged in a line and connected to form a meander-line structure. Analytical and experimental results of the performance are presented and shown to be almost in agreement. Power losses due to friction and transmission are studied and found to be significant. Compared with other types of linear motors, the motor in this study is capable of supporting heavier loads and provides a larger thrust force.

  4. A High Efficiency, Miniaturized Ka Band Traveling Wave Tube Based on a Novel Finned Ladder RF Circuit Design

    NASA Technical Reports Server (NTRS)

    Wintucky, E. G.; Wilson, J. D.; Vaden, K. R.; Force, D. A.; Freeman, J. C.; Lesny, G. G.; Kory, C. L.; Chevalier, C. T.; Ebihara, B.; Dayton, J. A.; hide

    2001-01-01

    Space communications architectures are being planned to meet the high rate data distribution requirements of future NASA Enterprise missions. These will require the use of traveling wave tube amplifiers (TWTAs) to provide the high frequency, RF (radio frequency) power and efficiency needed for many of the communications links. A program addressing these requirements is currently underway at NASA Glenn Research Center (GRC) for the development of a high efficiency, 20 watt, 32 GHz TWT of reduced size and weight that is based on a novel high gain n circuit design, termed the 'finned ladder'.

  5. Spike-like solitary waves in incompressible boundary layers driven by a travelling wave.

    PubMed

    Feng, Peihua; Zhang, Jiazhong; Wang, Wei

    2016-06-01

    Nonlinear waves produced in an incompressible boundary layer driven by a travelling wave are investigated, with damping considered as well. As one of the typical nonlinear waves, the spike-like wave is governed by the driven-damped Benjamin-Ono equation. The wave field enters a completely irregular state beyond a critical time, increasing the amplitude of the driving wave continuously. On the other hand, the number of spikes of solitary waves increases through multiplication of the wave pattern. The wave energy grows in a sequence of sharp steps, and hysteresis loops are found in the system. The wave energy jumps to different levels with multiplication of the wave, which is described by winding number bifurcation of phase trajectories. Also, the phenomenon of multiplication and hysteresis steps is found when varying the speed of driving wave as well. Moreover, the nature of the change of wave pattern and its energy is the stability loss of the wave caused by saddle-node bifurcation.

  6. Long-range traveling waves of activity triggered by local dichoptic stimulation in V1 of behaving monkeys

    PubMed Central

    Yang, Zhiyong; Heeger, David J.; Blake, Randolph

    2014-01-01

    Traveling waves of cortical activity, in which local stimulation triggers lateral spread of activity to distal locations, have been hypothesized to play an important role in cortical function. However, there is conflicting physiological evidence for the existence of spreading traveling waves of neural activity triggered locally. Dichoptic stimulation, in which the two eyes view dissimilar monocular patterns, can lead to dynamic wave-like fluctuations in visual perception and therefore, provides a promising means for identifying and studying cortical traveling waves. Here, we used voltage-sensitive dye imaging to test for the existence of traveling waves of activity in the primary visual cortex of awake, fixating monkeys viewing dichoptic stimuli. We find clear traveling waves that are initiated by brief, localized contrast increments in one of the monocular patterns and then, propagate at speeds of ∼30 mm/s. These results demonstrate that under an appropriate visual context, circuitry in visual cortex in alert animals is capable of supporting long-range traveling waves triggered by local stimulation. PMID:25343785

  7. Analysis of limited-diffractive and limited-dispersive X-waves generated by finite radial waveguides

    NASA Astrophysics Data System (ADS)

    Fuscaldo, Walter; Pavone, Santi C.; Valerio, Guido; Galli, Alessandro; Albani, Matteo; Ettorre, Mauro

    2016-05-01

    In this work, we analyze the spatial and temporal features of electromagnetic X-waves propagating in free space and generated by planar radiating apertures. The performance of ideal X-waves is discussed and compared to practical cases where the important effects related to the finiteness of the radiating aperture and the wavenumber dispersion are taken into account. In particular, a practical device consisting of a radial waveguide loaded with radiating slots aligned along a spiral path is considered for the practical case in the millimeter-wave range. A common mathematical framework is defined for a precise comparison of the spatiotemporal properties and focusing capabilities of the generated X-wave. It is clearly shown that the fractional bandwidth of the radiating aperture has a key role in the longitudinal confinement of an X-wave in both ideal and practical cases. In addition, the finiteness of the radiating aperture as well as the wavenumber dispersion clearly affect both the transverse and the longitudinal profiles of the generated radiation as it travels beyond the depth-of-field of the generated X-wave. Nevertheless, the spatiotemporal properties of the X-wave are preserved even in this "dispersive-finite" case within a defined region and duration related to the nondiffractive range and fractional bandwidth of the spectral components of the generated X-wave. The proposed analysis may open new perspectives for the efficient generation of X-waves over finite radiating apertures at millimeter waves where the dispersive behavior of realistic devices is no longer negligible.

  8. Ultra High Power and Efficiency Space Traveling-Wave Tube Amplifier Power Combiner with Reduced Size and Mass for NASA Missions

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Wintucky, Edwin G.; Wilson, Jeffrey D.; Force, Dale A.

    2009-01-01

    In the 2008 International Microwave Symposium (IMS) Digest version of our paper, recent advances in high power and efficiency space traveling-wave tube amplifiers (TWTAs) for NASA s space-to-Earth communications are presented. The RF power and efficiency of a new K-Band amplifier are 40 W and 50 percent and that of a new Ka-Band amplifier are 200 W and 60 percent. An important figure-of-merit, which is defined as the ratio of the RF power output to the mass (W/kg) of a TWT, has improved by a factor of ten over the previous generation Ka-Band devices. In this extended paper, a high power, high efficiency Ka-band combiner for multiple TWTs, based on a novel hybrid magic-T waveguide circuit design, is presented. The measured combiner efficiency is as high as 90 percent. In addition, at the design frequency of 32.05 GHz, error-free uncoded BPSK/QPSK data transmission at 8 megabits per second (Mbps), which is typical for deep space communications is demonstrated. Furthermore, QPSK data transmission at 622 Mbps is demonstrated with a low bit error rate of 2.4x10(exp -8), which exceeds the deep space state-of-the-art data rate transmission capability by more than two orders of magnitude. A potential application of the TWT combiner is in deep space communication systems for planetary exploration requiring transmitter power on the order of a kilowatt or higher.

  9. A Model for Measured Traveling Waves at End-Diastole in Human Heart Wall by Ultrasonic Imaging Method

    NASA Astrophysics Data System (ADS)

    Bekki, Naoaki; Shintani, Seine A.; Ishiwata, Shin'ichi; Kanai, Hiroshi

    2016-04-01

    We observe traveling waves, measured by the ultrasonic noninvasive imaging method, in a longitudinal beam direction from the apex to the base side on the interventricular septum (IVS) during the period from the end-diastole to the beginning of systole for a healthy human heart wall. We present a possible phenomenological model to explain part of one-dimensional cardiac behaviors for the observed traveling waves around the time of R-wave of echocardiography (ECG) in the human heart. Although the observed two-dimensional patterns of traveling waves are extremely complex and no one knows yet the exact solutions for the traveling homoclinic plane wave in the one-dimensional complex Ginzburg-Landau equation (CGLE), we numerically find that part of the one-dimensional homoclinic dynamics of the phase and amplitude patterns in the observed traveling waves is similar to that of the numerical homoclinic plane-wave solutions in the CGLE with periodic boundary condition in a certain parameter space. It is suggested that part of the cardiac dynamics of the traveling waves on the IVS can be qualitatively described by the CGLE model as a paradigm for understanding biophysical nonlinear phenomena.

  10. Impedance of strip-traveling waves on an elastic half space - Asymptotic solution

    NASA Technical Reports Server (NTRS)

    Crandall, S. H.; Nigam, A. K.

    1973-01-01

    The dynamic normal-load distribution across a strip that is required to maintain a plane progressive wave along its length is studied for the case where the strip is of infinite length and lies on the surface of a homogeneous isotropic elastic half space. This configuration is proposed as a preliminary idealized model for analyzing the dynamic interaction between soils and flexible foundations. The surface load distribution across the strip and the motion of the strip are related by a pair of dual integral equations. An asymptotic solution is obtained for the limiting case of small wavelength. The nature of this solution depends importantly on the propagation velocity of the strip-traveling wave in comparison with the Rayleigh wave speed, the shear wave speed and the dilatational wave speed. When the strip-traveling wave propagates faster than the Rayleigh wave speed, a pattern of trailing Rayleigh waves is shed from the strip. The limiting amplitude of the trailing waves is provided by the asymptotic solution.

  11. Traveling wave solutions of the nonlinear Schrödinger equation

    NASA Astrophysics Data System (ADS)

    Akbari-Moghanjoughi, M.

    2017-10-01

    In this paper, we investigate the traveling soliton and the periodic wave solutions of the nonlinear Schrödinger equation (NLSE) with generalized nonlinear functionality. We also explore the underlying close connection between the well-known KdV equation and the NLSE. It is remarked that both one-dimensional KdV and NLSE models share the same pseudoenergy spectrum. We also derive the traveling wave solutions for two cases of weakly nonlinear mathematical models, namely, the Helmholtz and the Duffing oscillators' potentials. It is found that these models only allow gray-type NLSE solitary propagations. It is also found that the pseudofrequency ratio for the Helmholtz potential between the nonlinear periodic carrier and the modulated sinusoidal waves is always in the range 0.5 ≤ Ω/ω ≤ 0.537285 regardless of the potential parameter values. The values of Ω/ω = {0.5, 0.537285} correspond to the cnoidal waves modulus of m = {0, 1} for soliton and sinusoidal limits and m = 0.5, respectively. Moreover, the current NLSE model is extended to fully NLSE (FNLSE) situation for Sagdeev oscillator pseudopotential which can be derived using a closed set of hydrodynamic fluid equations with a fully integrable Hamiltonian system. The generalized quasi-three-dimensional traveling wave solution is also derived. The current simple hydrodynamic plasma model may also be generalized to two dimensions and other complex situations including different charged species and cases with magnetic or gravitational field effects.

  12. Applications of exact traveling wave solutions of Modified Liouville and the Symmetric Regularized Long Wave equations via two new techniques

    NASA Astrophysics Data System (ADS)

    Lu, Dianchen; Seadawy, Aly R.; Ali, Asghar

    2018-06-01

    In this current work, we employ novel methods to find the exact travelling wave solutions of Modified Liouville equation and the Symmetric Regularized Long Wave equation, which are called extended simple equation and exp(-Ψ(ξ))-expansion methods. By assigning the different values to the parameters, different types of the solitary wave solutions are derived from the exact traveling wave solutions, which shows the efficiency and precision of our methods. Some solutions have been represented by graphical. The obtained results have several applications in physical science.

  13. Phase transition of traveling waves in bacterial colony pattern

    NASA Astrophysics Data System (ADS)

    Wakano, Joe Yuichiro; Komoto, Atsushi; Yamaguchi, Yukio

    2004-05-01

    Depending on the growth condition, bacterial colonies can exhibit different morphologies. Many previous studies have used reaction diffusion equations to reproduce spatial patterns. They have revealed that nonlinear reaction term can produce diverse patterns as well as nonlinear diffusion coefficient. Typical reaction term consists of nutrient consumption, bacterial reproduction, and sporulation. Among them, the functional form of sporulation rate has not been biologically investigated. Here we report experimentally measured sporulation rate. Then, based on the result, a reaction diffusion model is proposed. One-dimensional simulation showed the existence of traveling wave solution. We study the wave form as a function of the initial nutrient concentration and find two distinct types of solution. Moreover, transition between them is very sharp, which is analogous to phase transition. The velocity of traveling wave also shows sharp transition in nonlinear diffusion model, which is consistent with the previous experimental result. The phenomenon can be explained by separatrix in reaction term dynamics. Results of two-dimensional simulation are also shown and discussed.

  14. Optimal Design of a Traveling-Wave Kinetic Inductance Amplifier Operated in Three-Wave Mixing Mode

    NASA Astrophysics Data System (ADS)

    Erickson, Robert; Bal, Mustafa; Ku, Ksiang-Sheng; Wu, Xian; Pappas, David

    In the presence of a DC bias, an injected pump, of frequency fP, and a signal, of frequency fS, undergo parametric three-way mixing (3WM) within a traveling-wave kinetic inductance (KIT) amplifier, producing an idler product of frequency fI =fP -fS . Periodic frequency stops are engineered into the coplanar waveguide of the device to enhance signal amplification. With fP placed just above the first frequency stop gap, 3WM broadband signal gain is achieved with maximum gain at fS =fP / 2 . Within a theory of the dispersion of traveling waves in the presence of these engineered loadings, which accounts for this broadband signal gain, we show how an optimal frequency-stop design may be constructed to achieve maximum signal amplification. The optimization approach we describe can be applied to the design of other nonlinear traveling-wave parametric amplifiers. This work was supported by the Army Research Office and the Laboratory for Physical Sciences under EAO221146, EAO241777, and the NIST Quantum Initiative. RPE acknowledges Grant 60NANB14D024 from the US Department of Commerce, NIST.

  15. X-band Uplink Ground Systems Development

    NASA Technical Reports Server (NTRS)

    Johns, C. E.

    1984-01-01

    The development of the X-band exciter and Doppler extractor equipment for the X-band uplink was completed. Stability measurements were made on the exciter and Doppler reference signals and the results are presented.

  16. Existence, Uniqueness and Asymptotic Stability of Time Periodic Traveling Waves for a Periodic Lotka-Volterra Competition System with Diffusion

    PubMed Central

    Zhao, Guangyu; Ruan, Shigui

    2011-01-01

    We study the existence, uniqueness, and asymptotic stability of time periodic traveling wave solutions to a periodic diffusive Lotka-Volterra competition system. Under certain conditions, we prove that there exists a maximal wave speed c* such that for each wave speed c ≤ c*, there is a time periodic traveling wave connecting two semi-trivial periodic solutions of the corresponding kinetic system. It is shown that such a traveling wave is unique modulo translation and is monotone with respect to its co-moving frame coordinate. We also show that the traveling wave solutions with wave speed c < c* are asymptotically stable in certain sense. In addition, we establish the nonexistence of time periodic traveling waves for nonzero speed c > c*. PMID:21572575

  17. Metastable state en route to traveling-wave synchronization state

    NASA Astrophysics Data System (ADS)

    Park, Jinha; Kahng, B.

    2018-02-01

    The Kuramoto model with mixed signs of couplings is known to produce a traveling-wave synchronized state. Here, we consider an abrupt synchronization transition from the incoherent state to the traveling-wave state through a long-lasting metastable state with large fluctuations. Our explanation of the metastability is that the dynamic flow remains within a limited region of phase space and circulates through a few active states bounded by saddle and stable fixed points. This complex flow generates a long-lasting critical behavior, a signature of a hybrid phase transition. We show that the long-lasting period can be controlled by varying the density of inhibitory/excitatory interactions. We discuss a potential application of this transition behavior to the recovery process of human consciousness.

  18. Parametric traveling wave amplifier with a low pump frequency

    NASA Astrophysics Data System (ADS)

    Marchenko, V. F.; Streltsov, A. M.; Zhmurov, S. E.

    1983-01-01

    Consideration is given to the model of a parametric traveling wave amplifier with a cubic nonlinearity in the form of an LF filter with MOS varactors. The operation of the amplifier is analyzed with allowance for wave damping and nonlinearity saturation, and the nonlinear mode of operation is examined. Experimental results are discussed, with emphasis on the amplitude-frequency response characteristics.

  19. Numerical Study of Periodic Traveling Wave Solutions for the Predator-Prey Model with Landscape Features

    NASA Astrophysics Data System (ADS)

    Yun, Ana; Shin, Jaemin; Li, Yibao; Lee, Seunggyu; Kim, Junseok

    We numerically investigate periodic traveling wave solutions for a diffusive predator-prey system with landscape features. The landscape features are modeled through the homogeneous Dirichlet boundary condition which is imposed at the edge of the obstacle domain. To effectively treat the Dirichlet boundary condition, we employ a robust and accurate numerical technique by using a boundary control function. We also propose a robust algorithm for calculating the numerical periodicity of the traveling wave solution. In numerical experiments, we show that periodic traveling waves which move out and away from the obstacle are effectively generated. We explain the formation of the traveling waves by comparing the wavelengths. The spatial asynchrony has been shown in quantitative detail for various obstacles. Furthermore, we apply our numerical technique to the complicated real landscape features.

  20. High-frequency homogenization for travelling waves in periodic media.

    PubMed

    Harutyunyan, Davit; Milton, Graeme W; Craster, Richard V

    2016-07-01

    We consider high-frequency homogenization in periodic media for travelling waves of several different equations: the wave equation for scalar-valued waves such as acoustics; the wave equation for vector-valued waves such as electromagnetism and elasticity; and a system that encompasses the Schrödinger equation. This homogenization applies when the wavelength is of the order of the size of the medium periodicity cell. The travelling wave is assumed to be the sum of two waves: a modulated Bloch carrier wave having crystal wavevector [Formula: see text] and frequency ω 1 plus a modulated Bloch carrier wave having crystal wavevector [Formula: see text] and frequency ω 2 . We derive effective equations for the modulating functions, and then prove that there is no coupling in the effective equations between the two different waves both in the scalar and the system cases. To be precise, we prove that there is no coupling unless ω 1 = ω 2 and [Formula: see text] where Λ =(λ 1 λ 2 …λ d ) is the periodicity cell of the medium and for any two vectors [Formula: see text] the product a ⊙ b is defined to be the vector ( a 1 b 1 , a 2 b 2 ,…, a d b d ). This last condition forces the carrier waves to be equivalent Bloch waves meaning that the coupling constants in the system of effective equations vanish. We use two-scale analysis and some new weak-convergence type lemmas. The analysis is not at the same level of rigour as that of Allaire and co-workers who use two-scale convergence theory to treat the problem, but has the advantage of simplicity which will allow it to be easily extended to the case where there is degeneracy of the Bloch eigenvalue.

  1. Flow control by means of a traveling curvature wave in fishlike escape responses.

    PubMed

    Liu, Geng; Yu, Yong-Liang; Tong, Bing-Gang

    2011-11-01

    Fish usually bend their bodies into a ''C'' shape and then beat their tails one or more times to escape from predators (in nature) or stimuli (in experiments). The maneuvering behavior, i.e., the C-shape bending and the return flapping, is called C-start. In this paper, the escaping performance of fishlike C-start motions has been numerically investigated for a flow physics study by the use of a two-dimensional deformable foil bending and stretching quickly. The C-start motions, performed in the quiescent water and based on prescribed deforming modes, are predicted by a numerical method coupling the two-dimensional incompressible Navier-Stokes equations and the deforming body dynamic equations. It has been found earlier that a typical C-start motion consists of (1) a main C-shape bending and (2) a rearward travelling curvature wave which was seldom mentioned in previous studies. In order to reveal the flow control mechanism of the traveling curvature wave in a fish's C-start motion, two kinds of C-start flows with different deforming modes, namely the integrated mode (IM, a C-shape bending plus a travelling curvature wave) and the basic mode (BM, a C-shape bending only) are analyzed and compared in detail. According to the numerical results, it shows that if proper values of the travelling curvature wave parameters are chosen, the foil's escaping maneuverability presented in the IM is much better than that in the BM, i.e. the turn angle and the speed of the center of mass at the end of a C-start in the IM is almost twice as large as those in the BM. Further study shows that the travelling curvature wave not only can enhance the thrust and the centripetal force but also increase the propulsive efficiency. These results suggest that an efficient travelling curvature wave is of great significance in the flow control of a C-start motion. Finally, a parametric study finds that the phase difference between the C-shape bending and the travelling curvature wave (i.e., the

  2. Chaotic operation and chaos control of travelling wave ultrasonic motor.

    PubMed

    Shi, Jingzhuo; Zhao, Fujie; Shen, Xiaoxi; Wang, Xiaojie

    2013-08-01

    The travelling wave ultrasonic motor, which is a nonlinear dynamic system, has complex chaotic phenomenon with some certain choices of system parameters and external inputs, and its chaotic characteristics have not been studied until now. In this paper, the preliminary study of the chaos phenomenon in ultrasonic motor driving system has been done. The experiment of speed closed-loop control is designed to obtain several groups of time sampling data sequence of the amplitude of driving voltage, and phase-space reconstruction is used to analyze the chaos characteristics of these time sequences. The largest Lyapunov index is calculated and the result is positive, which shows that the travelling wave ultrasonic motor has chaotic characteristics in a certain working condition Then, the nonlinear characteristics of travelling wave ultrasonic motor are analyzed which includes Lyapunov exponent map, the bifurcation diagram and the locus of voltage relative to speed based on the nonlinear chaos model of a travelling wave ultrasonic motor. After that, two kinds of adaptive delay feedback controllers are designed in this paper to control and suppress chaos in USM speed control system. Simulation results show that the method can control unstable periodic orbits, suppress chaos in USM control system. Proportion-delayed feedback controller was designed following and arithmetic of fuzzy logic was used to adaptively adjust the delay time online. Simulation results show that this method could fast and effectively change the chaos movement into periodic or fixed-point movement and make the system enter into stable state from chaos state. Finally the chaos behavior was controlled. Copyright © 2013 Elsevier B.V. All rights reserved.

  3. Development of a 75-watt 60-GHz traveling-wave tube for intersatellite communications

    NASA Technical Reports Server (NTRS)

    Rousseau, A. L.; Tammaru, I.; Vaszari, J. P.

    1988-01-01

    This program covers the initial design and development of a 75 watt, 60 GHz traveling-wave tube for intersatellite communications. The objective frequency band was 59 to 64 GHz, with a minimum tube gain of 35 dB. The objective overall efficiency at saturation was 40 percent. The tube, designated the 961H, used a coupled-cavity interaction circuit with periodic permanent magnet beam focusing to minimize the weight. For efficiency enhancement, it incorporated a four-stage depressed collector capable of radiation cooling in space. The electron gun had a low-temperature (type-M) cathode and an isolated anode. Two tubes were built and tested; one feasibility model with a single-stage collector and one experimental model that incorporated the multistage collector.

  4. Study on monostable and bistable reaction-diffusion equations by iteration of travelling wave maps

    NASA Astrophysics Data System (ADS)

    Yi, Taishan; Chen, Yuming

    2017-12-01

    In this paper, based on the iterative properties of travelling wave maps, we develop a new method to obtain spreading speeds and asymptotic propagation for monostable and bistable reaction-diffusion equations. Precisely, for Dirichlet problems of monostable reaction-diffusion equations on the half line, by making links between travelling wave maps and integral operators associated with the Dirichlet diffusion kernel (the latter is NOT invariant under translation), we obtain some iteration properties of the Dirichlet diffusion and some a priori estimates on nontrivial solutions of Dirichlet problems under travelling wave transformation. We then provide the asymptotic behavior of nontrivial solutions in the space-time region for Dirichlet problems. These enable us to develop a unified method to obtain results on heterogeneous steady states, travelling waves, spreading speeds, and asymptotic spreading behavior for Dirichlet problem of monostable reaction-diffusion equations on R+ as well as of monostable/bistable reaction-diffusion equations on R.

  5. Exciter For X-Band Transmitter And Receiver

    NASA Technical Reports Server (NTRS)

    Johns, Carl E.

    1989-01-01

    Report describes developmental X-band exciter for X-band uplink subsystem of Deep Space Network. X-band transmitter-exciting signal expected to have fractional frequency stability of 5.2 X 10 to negative 15th power during 1,000-second integration period. Generates coherent test signals for S- and X-band Block III translator of Deep Space Network, Doppler-reference signal for associated Doppler-extractor system, first-local-oscillator signal for associated receiver, and reference signal for associated ranging subsystem. Tests of prototype exciter show controlling and monitoring and internal phase-correcting loops perform according to applicable design criteria. Measurements of stability of frequency and of single-sideband noise spectral density of transmitter-exciting signal made subsequently.

  6. Theory of a Traveling Wave Feed for a Planar Slot Array Antenna

    NASA Technical Reports Server (NTRS)

    Rengarajan, Sembiam

    2012-01-01

    Planar arrays of waveguide-fed slots have been employed in many radar and remote sensing applications. Such arrays are designed in the standing wave configuration because of high efficiency. Traveling wave arrays can produce greater bandwidth at the expense of efficiency due to power loss in the load or loads. Traveling wave planar slot arrays may be designed with a long feed waveguide consisting of centered-inclined coupling slots. The feed waveguide is terminated in a matched load, and the element spacing in the feed waveguide is chosen to produce a beam squinted from the broadside. The traveling wave planar slot array consists of a long feed waveguide containing resonant-centered inclined coupling slots in the broad wall, coupling power into an array of stacked radiating waveguides orthogonal to it. The radiating waveguides consist of longitudinal offset radiating slots in a standing wave configuration. For the traveling wave feed of a planar slot array, one has to design the tilt angle and length of each coupling slot such that the amplitude and phase of excitation of each radiating waveguide are close to the desired values. The coupling slot spacing is chosen for an appropriate beam squint. Scattering matrix parameters of resonant coupling slots are used in the design process to produce appropriate excitations of radiating waveguides with constraints placed only on amplitudes. Since the radiating slots in each radiating waveguide are designed to produce a certain total admittance, the scattering (S) matrix of each coupling slot is reduced to a 2x2 matrix. Elements of each 2x2 S-matrix and the amount of coupling into the corresponding radiating waveguide are expressed in terms of the element S11. S matrices are converted into transmission (T) matrices, and the T matrices are multiplied to cascade the coupling slots and waveguide sections, starting from the load end and proceeding towards the source. While the use of non-resonant coupling slots may provide an

  7. Energy band gap and spectroscopic studies in Mn{sub 1-x}Cu{sub x}WO{sub 4} (0 ≤ x ≤ 0.125)

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Mal, Priyanath; Rambabu, P.; Turpu, G. R.

    2016-05-06

    A study on the effect of nonmagnetic Cu{sup 2+} substitution at Mn{sup 2+} site on the structural and energy band gap of the MnWO{sub 4} is reported. Convenient solid state reaction route has been adopted for the synthesis of Mn{sub 1-x}Cu{sub x}WO{sub 4}. X-ray diffraction (XRD) pattern showed high crystalline quality of the prepared samples. Raman spectroscopic studies were carried out to understand the structural aspects of the doping. 15 Raman active modes were identified out of 18, predicted for wolframite type monoclinic structure of MnWO{sub 4}. UV-visible diffuse reflectance spectra were recorded and analyzed to get energy band gapmore » of the studied system and are found in the range of 2.5 eV to 2.04 eV with a systematic decrease with the increase in Cu{sup 2+} concentration. Energy band gap values are verified by Density Functional Theory calculations based on projector augmented wave (PAW) method. The calculated values are in good agreement with the experimental data.« less

  8. Stable operating regime for traveling wave devices

    DOEpatents

    Carlsten, Bruce E.

    2000-01-01

    Autophase stability is provided for a traveling wave device (TWD) electron beam for amplifying an RF electromagnetic wave in walls defining a waveguide for said electromagnetic wave. An off-axis electron beam is generated at a selected energy and has an energy noise inherently arising from electron gun. The off-axis electron beam is introduced into the waveguide. The off-axis electron beam is introduced into the waveguide at a second radius. The waveguide structure is designed to obtain a selected detuning of the electron beam. The off-axis electron beam has a velocity and the second radius to place the electron beam at a selected distance from the walls defining the waveguide, wherein changes in a density of the electron beam due to the RF electromagnetic wave are independent of the energy of the electron beam to provide a concomitant stable operating regime relative to the energy noise.

  9. Traveling waves and conservation laws for highly nonlinear wave equations modeling Hertz chains

    NASA Astrophysics Data System (ADS)

    Przedborski, Michelle; Anco, Stephen C.

    2017-09-01

    A highly nonlinear, fourth-order wave equation that models the continuum theory of long wavelength pulses in weakly compressed, homogeneous, discrete chains with a general power-law contact interaction is studied. For this wave equation, all solitary wave solutions and all nonlinear periodic wave solutions, along with all conservation laws, are derived. The solutions are explicitly parameterized in terms of the asymptotic value of the wave amplitude in the case of solitary waves and the peak of the wave amplitude in the case of nonlinear periodic waves. All cases in which the solution expressions can be stated in an explicit analytic form using elementary functions are worked out. In these cases, explicit expressions for the total energy and total momentum for all solutions are obtained as well. The derivation of the solutions uses the conservation laws combined with an energy analysis argument to reduce the wave equation directly to a separable first-order differential equation that determines the wave amplitude in terms of the traveling wave variable. This method can be applied more generally to other highly nonlinear wave equations.

  10. Traveling waves in a delayed SIR model with nonlocal dispersal and nonlinear incidence

    NASA Astrophysics Data System (ADS)

    Zhang, Shou-Peng; Yang, Yun-Rui; Zhou, Yong-Hui

    2018-01-01

    This paper is concerned with traveling waves of a delayed SIR model with nonlocal dispersal and a general nonlinear incidence. The existence and nonexistence of traveling waves of the system are established respectively by Schauder's fixed point theorem and two-sided Laplace transform. It is also shown that the spread speed c is influenced by the dispersal rate of the infected individuals and the delay τ.

  11. Computer program for analysis of coupled-cavity traveling wave tubes

    NASA Technical Reports Server (NTRS)

    Connolly, D. J.; Omalley, T. A.

    1977-01-01

    A flexible, accurate, large signal computer program was developed for the design of coupled cavity traveling wave tubes. The program is written in FORTRAN IV for an IBM 360/67 time sharing system. The beam is described by a disk model and the slow wave structure by a sequence of cavities, or cells. The computational approach is arranged so that each cavity may have geometrical or electrical parameters different from those of its neighbors. This allows the program user to simulate a tube of almost arbitrary complexity. Input and output couplers, severs, complicated velocity tapers, and other features peculiar to one or a few cavities may be modeled by a correct choice of input data. The beam-wave interaction is handled by an approach in which the radio frequency fields are expanded in solutions to the transverse magnetic wave equation. All significant space harmonics are retained. The program was used to perform a design study of the traveling-wave tube developed for the Communications Technology Satellite. Good agreement was obtained between the predictions of the program and the measured performance of the flight tube.

  12. Flow control by means of a traveling curvature wave in fishlike escape responses

    NASA Astrophysics Data System (ADS)

    Liu, Geng; Yu, Yong-Liang; Tong, Bing-Gang

    2011-11-01

    Fish usually bend their bodies into a ‘‘C’’ shape and then beat their tails one or more times to escape from predators (in nature) or stimuli (in experiments). The maneuvering behavior, i.e., the C-shape bending and the return flapping, is called C-start. In this paper, the escaping performance of fishlike C-start motions has been numerically investigated for a flow physics study by the use of a two-dimensional deformable foil bending and stretching quickly. The C-start motions, performed in the quiescent water and based on prescribed deforming modes, are predicted by a numerical method coupling the two-dimensional incompressible Navier-Stokes equations and the deforming body dynamic equations. It has been found earlier that a typical C-start motion consists of (1) a main C-shape bending and (2) a rearward travelling curvature wave which was seldom mentioned in previous studies. In order to reveal the flow control mechanism of the traveling curvature wave in a fish's C-start motion, two kinds of C-start flows with different deforming modes, namely the integrated mode (IM, a C-shape bending plus a travelling curvature wave) and the basic mode (BM, a C-shape bending only) are analyzed and compared in detail. According to the numerical results, it shows that if proper values of the travelling curvature wave parameters are chosen, the foil's escaping maneuverability presented in the IM is much better than that in the BM, i.e. the turn angle and the speed of the center of mass at the end of a C-start in the IM is almost twice as large as those in the BM. Further study shows that the travelling curvature wave not only can enhance the thrust and the centripetal force but also increase the propulsive efficiency. These results suggest that an efficient travelling curvature wave is of great significance in the flow control of a C-start motion. Finally, a parametric study finds that the phase difference between the C-shape bending and the travelling curvature wave (i

  13. Traveling waves in a continuum model of 1D schools

    NASA Astrophysics Data System (ADS)

    Oza, Anand; Kanso, Eva; Shelley, Michael

    2017-11-01

    We construct and analyze a continuum model of a 1D school of flapping swimmers. Our starting point is a delay differential equation that models the interaction between a swimmer and its upstream neighbors' wakes, which is motivated by recent experiments in the Applied Math Lab at NYU. We coarse-grain the evolution equations and derive PDEs for the swimmer density and variables describing the upstream wake. We study the equations both analytically and numerically, and find that a uniform density of swimmers destabilizes into a traveling wave. Our model makes a number of predictions about the properties of such traveling waves, and sheds light on the role of hydrodynamics in mediating the structure of swimming schools.

  14. Exact traveling wave solutions for system of nonlinear evolution equations.

    PubMed

    Khan, Kamruzzaman; Akbar, M Ali; Arnous, Ahmed H

    2016-01-01

    In this work, recently deduced generalized Kudryashov method is applied to the variant Boussinesq equations, and the (2 + 1)-dimensional breaking soliton equations. As a result a range of qualitative explicit exact traveling wave solutions are deduced for these equations, which motivates us to develop, in the near future, a new approach to obtain unsteady solutions of autonomous nonlinear evolution equations those arise in mathematical physics and engineering fields. It is uncomplicated to extend this method to higher-order nonlinear evolution equations in mathematical physics. And it should be possible to apply the same method to nonlinear evolution equations having more general forms of nonlinearities by utilizing the traveling wave hypothesis.

  15. On Traveling Waves in Lattices: The Case of Riccati Lattices

    NASA Astrophysics Data System (ADS)

    Dimitrova, Zlatinka

    2012-09-01

    The method of simplest equation is applied for analysis of a class of lattices described by differential-difference equations that admit traveling-wave solutions constructed on the basis of the solution of the Riccati equation. We denote such lattices as Riccati lattices. We search for Riccati lattices within two classes of lattices: generalized Lotka-Volterra lattices and generalized Holling lattices. We show that from the class of generalized Lotka-Volterra lattices only the Wadati lattice belongs to the class of Riccati lattices. Opposite to this many lattices from the Holling class are Riccati lattices. We construct exact traveling wave solutions on the basis of the solution of Riccati equation for three members of the class of generalized Holling lattices.

  16. Range-dependence of acoustic channel with traveling sinusoidal surface wave.

    PubMed

    Choo, Youngmin; Seong, Woojae; Lee, Keunhwa

    2014-04-01

    Range-dependence of time-varying acoustic channels caused by a traveling surface wave is investigated through water tank experiments and acoustic propagation analysis schemes. As the surface wave travels, surface reflected signals fluctuate and the fluctuation varies with source-receiver horizontal range. Amplitude fluctuations of surface reflected signals increase with increasing horizontal range whereas the opposite occurs in delay fluctuations. The scattered pressure field at a fixed time shows strong dependence on the receiver position because of caustics and shadow zones formed by the surface. The Doppler shifts of surface reflected signals also depend on the horizontal range. Comparison between measurement data and model results indicates the Doppler shift relies on the delay fluctuation under current experimental conditions.

  17. Traveling waves and their tails in locally resonant granular systems

    DOE PAGES

    Xu, H.; Kevrekidis, P. G.; Stefanov, A.

    2015-04-22

    In the present study, we revisit the theme of wave propagation in locally resonant granular crystal systems, also referred to as mass-in-mass systems. We use three distinct approaches to identify relevant traveling waves. In addition, the first consists of a direct solution of the traveling wave problem. The second one consists of the solution of the Fourier tranformed variant of the problem, or, more precisely, of its convolution reformulation (upon an inverse Fourier transform) in real space. Finally, our third approach will restrict considerations to a finite domain, utilizing the notion of Fourier series for important technical reasons, namely themore » avoidance of resonances, which will be discussed in detail. All three approaches can be utilized in either the displacement or the strain formulation. Typical resulting computations in finite domains result in the solitary waves bearing symmetric non-vanishing tails at both ends of the computational domain. Importantly, however, a countably infinite set of anti-resonance conditions is identified for which solutions with genuinely rapidly decaying tails arise.« less

  18. Traveling waves and their tails in locally resonant granular systems

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Xu, H.; Kevrekidis, P. G.; Stefanov, A.

    In the present study, we revisit the theme of wave propagation in locally resonant granular crystal systems, also referred to as mass-in-mass systems. We use three distinct approaches to identify relevant traveling waves. In addition, the first consists of a direct solution of the traveling wave problem. The second one consists of the solution of the Fourier tranformed variant of the problem, or, more precisely, of its convolution reformulation (upon an inverse Fourier transform) in real space. Finally, our third approach will restrict considerations to a finite domain, utilizing the notion of Fourier series for important technical reasons, namely themore » avoidance of resonances, which will be discussed in detail. All three approaches can be utilized in either the displacement or the strain formulation. Typical resulting computations in finite domains result in the solitary waves bearing symmetric non-vanishing tails at both ends of the computational domain. Importantly, however, a countably infinite set of anti-resonance conditions is identified for which solutions with genuinely rapidly decaying tails arise.« less

  19. A mass filter based on an accelerating traveling wave.

    PubMed

    Wiedenbeck, Michael; Kasemset, Bodin; Kasper, Manfred

    2008-01-01

    We describe a novel mass filtering concept based on the acceleration of a pulsed ion beam through a stack of electrostatic plates. A precisely controlled traveling wave generated within such an ion guide will induce a mass-selective ion acceleration, with mass separation ultimately accomplished via a simple energy-filtering system. Crucial for successful filtering is that the velocity with which the traveling wave passes through the ion guide must be dynamically controlled in order to accommodate the acceleration of the target ion species. Mass selection is determined by the velocity and acceleration with which the wave traverses the ion guide, whereby the target species will acquire a higher kinetic energy than all other lighter as well as heaver species. Finite element simulations of this design demonstrate that for small masses a mass resolution M/DeltaM approximately 1000 can be achieved within an electrode stack containing as few as 20 plates. Some of the possible advantages and drawbacks which distinguish this concept from established mass spectrometric technologies are discussed.

  20. Comparison of actinide production in traveling wave and pressurized water reactors

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Osborne, A.G.; Smith, T.A.; Deinert, M.R.

    The geopolitical problems associated with civilian nuclear energy production arise in part from the accumulation of transuranics in spent nuclear fuel. A traveling wave reactor is a type of breed-burn reactor that could, if feasible, reduce the overall production of transuranics. In one possible configuration, a cylinder of natural or depleted uranium would be subjected to a fast neutron flux at one end. The neutrons would transmute the uranium, producing plutonium and higher actinides. Under the right conditions, the reactor could become critical, at which point a self-stabilizing fission wave would form and propagate down the length of the reactormore » cylinder. The neutrons from the fission wave would burn the fissile nuclides and transmute uranium ahead of the wave to produce additional fuel. Fission waves in uranium are driven largely by the production and fission of {sup 239}Pu. Simulations have shown that the fuel burnup can reach values greater than 400 MWd/kgIHM, before fission products poison the reaction. In this work we compare the production of plutonium and minor actinides produced in a fission wave to that of a UOX fueled light water reactor, both on an energy normalized basis. The nuclide concentrations in the spent traveling wave reactor fuel are computed using a one-group diffusion model and are verified using Monte Carlo simulations. In the case of the pressurized water reactor, a multi-group collision probability model is used to generate the nuclide quantities. We find that the traveling wave reactor produces about 0.187 g/MWd/kgIHM of transuranics compared to 0.413 g/MWd/kgIHM for a pressurized water reactor running fuel enriched to 4.95 % and burned to 50 MWd/kgIHM. (authors)« less

  1. 0.22 THz wideband sheet electron beam traveling wave tube amplifier: Cold test measurements and beam wave interaction analysis

    NASA Astrophysics Data System (ADS)

    Baig, Anisullah; Gamzina, Diana; Barchfeld, Robert; Domier, Calvin; Barnett, Larry R.; Luhmann, Neville C.

    2012-09-01

    In this paper, we describe micro-fabrication, RF measurements, and particle-in-cell (PIC) simulation modeling analysis of the 0.22 THz double-vane half period staggered traveling wave tube amplifier (TWTA) circuit. The TWTA slow wave structure comprised of two sections separated by two sever ports loaded by loss material, with integrated broadband input/output couplers. The micro-metallic structures were fabricated using nano-CNC milling and diffusion bonded in a three layer process. The 3D optical microscopy and SEM analysis showed that the fabrication error was within 2-3 μm and surface roughness was measured within 30-50 nm. The RF measurements were conducted with an Agilent PNA-X network analyzer employing WR5.1 T/R modules with a frequency range of 178-228 GHz. The in-band insertion loss (S21) for both the short section and long section (separated by a sever) was measured as ˜-5 dB while the return loss was generally around ˜-15 dB or better. The measurements matched well with the S-matrix simulation analysis that predicted a 3 dB bandwidth of ˜45 GHz with an operating frequency at 220 GHz. However, the measured S21 was ˜3 dB less than the design values, and is attributed to surface roughness and alignment issues. The confirmation measurements were conducted over the full frequency band up to 270 GHz employing a backward wave oscillator (BWO) scalar network analyzer setup employing a BWO in the frequency range 190 GHz-270 GHz. PIC simulations were conducted for the realistic TWT output power performance analysis with incorporation of corner radius of 127 μm, which is inevitably induced by nano-machining. Furthermore, the S21 value in both sections of the TWT structure was reduced to correspond to the measurements by using a degraded conductivity of 10% International Annealed Copper Standard. At 220 GHz, for an elliptic sheet electron beam of 20 kV and 0.25 A, the average output power of the tube was predicted to be reduced from 90 W (for ideal

  2. A three-dimensional finite-element thermal/mechanical analytical technique for high-performance traveling wave tubes

    NASA Technical Reports Server (NTRS)

    Bartos, Karen F.; Fite, E. Brian; Shalkhauser, Kurt A.; Sharp, G. Richard

    1991-01-01

    Current research in high-efficiency, high-performance traveling wave tubes (TWT's) has led to the development of novel thermal/ mechanical computer models for use with helical slow-wave structures. A three-dimensional, finite element computer model and analytical technique used to study the structural integrity and thermal operation of a high-efficiency, diamond-rod, K-band TWT designed for use in advanced space communications systems. This analysis focused on the slow-wave circuit in the radiofrequency section of the TWT, where an inherent localized heating problem existed and where failures were observed during earlier cold compression, or 'coining' fabrication technique that shows great potential for future TWT development efforts. For this analysis, a three-dimensional, finite element model was used along with MARC, a commercially available finite element code, to simulate the fabrication of a diamond-rod TWT. This analysis was conducted by using component and material specifications consistent with actual TWT fabrication and was verified against empirical data. The analysis is nonlinear owing to material plasticity introduced by the forming process and also to geometric nonlinearities presented by the component assembly configuration. The computer model was developed by using the high efficiency, K-band TWT design but is general enough to permit similar analyses to be performed on a wide variety of TWT designs and styles. The results of the TWT operating condition and structural failure mode analysis, as well as a comparison of analytical results to test data are presented.

  3. A three-dimensional finite-element thermal/mechanical analytical technique for high-performance traveling wave tubes

    NASA Technical Reports Server (NTRS)

    Shalkhauser, Kurt A.; Bartos, Karen F.; Fite, E. B.; Sharp, G. R.

    1992-01-01

    Current research in high-efficiency, high-performance traveling wave tubes (TWT's) has led to the development of novel thermal/mechanical computer models for use with helical slow-wave structures. A three-dimensional, finite element computer model and analytical technique used to study the structural integrity and thermal operation of a high-efficiency, diamond-rod, K-band TWT designed for use in advanced space communications systems. This analysis focused on the slow-wave circuit in the radiofrequency section of the TWT, where an inherent localized heating problem existed and where failures were observed during earlier cold compression, or 'coining' fabrication technique that shows great potential for future TWT development efforts. For this analysis, a three-dimensional, finite element model was used along with MARC, a commercially available finite element code, to simulate the fabrication of a diamond-rod TWT. This analysis was conducted by using component and material specifications consistent with actual TWT fabrication and was verified against empirical data. The analysis is nonlinear owing to material plasticity introduced by the forming process and also to geometric nonlinearities presented by the component assembly configuration. The computer model was developed by using the high efficiency, K-band TWT design but is general enough to permit similar analyses to be performed on a wide variety of TWT designs and styles. The results of the TWT operating condition and structural failure mode analysis, as well as a comparison of analytical results to test data are presented.

  4. The occurrence, spatial distribution, and wave properties of hydrogen-, helium-, and oxygen-band EMIC waves observed by the Van Allen Probes

    NASA Astrophysics Data System (ADS)

    Saikin, A.; Zhang, J.; Allen, R. C.; Smith, C. W.; Kistler, L. M.; Spence, H. E.; Torbert, R. B.; Kletzing, C.; Jordanova, V.

    2014-12-01

    Electromagnetic ion cyclotron (EMIC) waves play an important role in the overall dynamics of the Earth's magnetosphere, including the energization and loss of particles. We perform a statistical study of EMIC waves detected by the Van Allen Probes mission to investigate their occurrence, spatial distribution, and properties (e.g., wave power, normal angle, and ellipticity). Magnetic field measurements from the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) onboard Van Allen Probes are used to identify EMIC wave events from the beginning of the mission (September, 2012) to the present. EMIC waves are examined in hydrogen, helium and oxygen bands. So far, about 280 EMIC wave events have been identified over the three different bands. Preliminary results show that hydrogen-band EMIC waves have been primarily observed in the dusk sector, while helium-band EMIC waves have been observed in all Magnetic Local Times (MLTs). Particularly, the Van Allen Probes provide a better resolution of lower frequencies (0.2-0.9 Hz), within which oxygen-band EMIC waves can occur in the inner magnetosphere. This allows us to obtain better insight into the characteristics of this previously largely unavailable band of EMIC waves, and allows for comparisons amongst EMIC waves in different bands.

  5. Weierstrass traveling wave solutions for dissipative Benjamin, Bona, and Mahony (BBM) equation

    NASA Astrophysics Data System (ADS)

    Mancas, Stefan C.; Spradlin, Greg; Khanal, Harihar

    2013-08-01

    In this paper the effect of a small dissipation on waves is included to find exact solutions to the modified Benjamin, Bona, and Mahony (BBM) equation by viscosity. Using Lyapunov functions and dynamical systems theory, we prove that when viscosity is added to the BBM equation, in certain regions there still exist bounded traveling wave solutions in the form of solitary waves, periodic, and elliptic functions. By using the canonical form of Abel equation, the polynomial Appell invariant makes the equation integrable in terms of Weierstrass ℘ functions. We will use a general formalism based on Ince's transformation to write the general solution of dissipative BBM in terms of ℘ functions, from which all the other known solutions can be obtained via simplifying assumptions. Using ODE (ordinary differential equations) analysis we show that the traveling wave speed is a bifurcation parameter that makes transition between different classes of waves.

  6. Extraction of body waves from seismic ambient noise

    NASA Astrophysics Data System (ADS)

    Kim, Eun Mi; Kang, Tae Seob; Kim, Tae Sung

    2014-05-01

    Ambient noise cross-correlation is used in seismology to obtain the part of the surface waves and applied to the theoretical researches and various experiments. Obtaining the part of body waves from the ambient noise correlation is difficult to recognize because of the feature decreasing body waves along the travel path. However, the travel times of body waves detected from temporal and spacial events occurrence involve uncertainty of the epicenter and accompany temporal-spacial restriction. On the other hand, ambient noise is always occurred and is obtained at the all stations. So it can be applied to research of the internal earth when the case of extracting the body waves using the cross-correlation is possible. This study shows that body waves can be observed by analyzing the ambient noise recorded seismic data in South Korea. Using 42 broad-band three components stations located on the South Korea. The data removed the mean and trend are filtered high-frequency band(0.5-2Hz). The noise correlations were calculated for all combinations of radial, transverse and veltical components, which required rotation of the horizontal components for each station pair according to the azimuth at each station of the great-circle between the two stations. Removing the part of broad-band signals effected by occurring event, the part of standard deviations more than three times are removed. And it applied spectral whitening to reduce effects of the surface waves. After data processing, all ambient noise signals are cross-correlated and temporal stacked. We found the signals propagating from one station to another station, this signals can be interpreted as the body waves distinguished surface travel-time in high-frequency band.From this analysis, we can extract the body waves using ambient noise cross correlation of continuous data at the stations.

  7. Simulation studies on the standing and traveling wave thermoacoustic prime movers

    NASA Astrophysics Data System (ADS)

    Skaria, Mathew; Rasheed, K. K. Abdul; Shafi, K. A.; Kasthurirengan, S.; Behera, Upendra

    2014-01-01

    Thermoacoustic systems have been a focus of recent research due to its structural simplicity, high reliability due to absence of moving parts, and can be driven by low grade energy such as fuel, gas, solar energy, waste heat etc. There has been extensive research on both standing wave and traveling wave systems. Towards the development of such systems, simulations can be carried out by several methods such as (a) solving the energy equation, (b) enthalpy flow model, (c) DeltaEC, a free software available from LANL, USA (d) Computational Fluid Dynamics (CFD) etc. We present here the simulation studies of standing wave and traveling wave thermoacoustic prime movers using CFD and DeltaEC. The CFD analysis is carried out using Fluent 6.3.26, incorporating the necessary boundary conditions with different working fluids at different operating pressures. The results obtained by CFD are compared with those obtained using DeltaEC. Also, the CFD simulation of the thermoacoustically driven refrigerator is presented.

  8. Simulation studies on the standing and traveling wave thermoacoustic prime movers

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Skaria, Mathew; Rasheed, K. K. Abdul; Shafi, K. A.

    Thermoacoustic systems have been a focus of recent research due to its structural simplicity, high reliability due to absence of moving parts, and can be driven by low grade energy such as fuel, gas, solar energy, waste heat etc. There has been extensive research on both standing wave and traveling wave systems. Towards the development of such systems, simulations can be carried out by several methods such as (a) solving the energy equation, (b) enthalpy flow model, (c) DeltaEC, a free software available from LANL, USA (d) Computational Fluid Dynamics (CFD) etc. We present here the simulation studies of standingmore » wave and traveling wave thermoacoustic prime movers using CFD and DeltaEC. The CFD analysis is carried out using Fluent 6.3.26, incorporating the necessary boundary conditions with different working fluids at different operating pressures. The results obtained by CFD are compared with those obtained using DeltaEC. Also, the CFD simulation of the thermoacoustically driven refrigerator is presented.« less

  9. Evans function computation for the stability of travelling waves

    NASA Astrophysics Data System (ADS)

    Barker, B.; Humpherys, J.; Lyng, G.; Lytle, J.

    2018-04-01

    In recent years, the Evans function has become an important tool for the determination of stability of travelling waves. This function, a Wronskian of decaying solutions of the eigenvalue equation, is useful both analytically and computationally for the spectral analysis of the linearized operator about the wave. In particular, Evans-function computation allows one to locate any unstable eigenvalues of the linear operator (if they exist); this allows one to establish spectral stability of a given wave and identify bifurcation points (loss of stability) as model parameters vary. In this paper, we review computational aspects of the Evans function and apply it to multidimensional detonation waves. This article is part of the theme issue `Stability of nonlinear waves and patterns and related topics'.

  10. Broadening of effective photonic band gaps in biological chiral structures: From intrinsic narrow band gaps to broad band reflection spectra

    NASA Astrophysics Data System (ADS)

    Vargas, W. E.; Hernández-Jiménez, M.; Libby, E.; Azofeifa, D. E.; Solis, Á.; Barboza-Aguilar, C.

    2015-09-01

    Under normal illumination with non-polarized light, reflection spectra of the cuticle of golden-like and red Chrysina aurigans scarabs show a structured broad band of left-handed circularly polarized light. The polarization of the reflected light is attributed to a Bouligand-type left-handed chiral structure found through the scarab's cuticle. By considering these twisted structures as one-dimensional photonic crystals, a novel approach is developed from the dispersion relation of circularly polarized electromagnetic waves traveling through chiral media, to show how the broad band characterizing these spectra arises from an intrinsic narrow photonic band gap whose spectral position moves through visible and near-infrared wavelengths.

  11. Dutch X-band SLAR calibration

    NASA Technical Reports Server (NTRS)

    Groot, J. S.

    1990-01-01

    In August 1989 the NASA/JPL airborne P/L/C-band DC-8 SAR participated in several remote sensing campaigns in Europe. Amongst other test sites, data were obtained of the Flevopolder test site in the Netherlands on August the 16th. The Dutch X-band SLAR was flown on the same date and imaged parts of the same area as the SAR. To calibrate the two imaging radars a set of 33 calibration devices was deployed. 16 trihedrals were used to calibrate a part of the SLAR data. This short paper outlines the X-band SLAR characteristics, the experimental set-up and the calibration method used to calibrate the SLAR data. Finally some preliminary results are given.

  12. The occurrence and wave properties of H⁺-, He⁺-, and O⁺-band EMIC waves observed by the Van Allen Probes

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Saikin, A. A.; Zhang, J. -C.; Allen, R. C.

    2015-09-26

    We perform a statistical study of electromagnetic ion cyclotron (EMIC) waves detected by the Van Allen Probes mission to investigate the spatial distribution of their occurrence, wave power, ellipticity, and normal angle. The Van Allen Probes have been used which allow us to explore the inner magnetosphere (1.1 to 5.8 RE). Magnetic field measurements from the Electric and Magnetic Field Instrument Suite and Integrated Science on board the Van Allen Probes are used to identify EMIC wave events for the first 22 months of the mission operation (8 September 2012 to 30 June 2014). EMIC waves are examined in H⁺-,more » He⁺-, and O⁺-bands. Over 700 EMIC wave events have been identified over the three different wave bands (265 H⁺-band events, 438 He⁺-band events, and 68 O⁺-band events). EMIC wave events are observed between L = 2 – 8, with over 140 EMIC wave events observed below L = 4. The results show that H⁺-band EMIC waves have two peak magnetic local time (MLT) occurrence regions: pre-noon (09:00 < MLT ≤ 12:00) and afternoon (15:00 < MLT ≤ 17:00) sectors. He⁺-band EMIC waves feature an overall stronger dayside occurrence. O⁺-band EMIC waves have one peak region located in the morning sector at lower L shells (L < 4). He⁺-band EMIC waves average the highest wave power overall (>0.1 nT²/Hz), especially in the afternoon sector. Ellipticity observations reveal that linearly polarized EMIC waves dominate in lower L shells.« less

  13. Critical Points and Traveling Wave in Locomotion: Experimental Evidence and Some Theoretical Considerations.

    PubMed

    Saltiel, Philippe; d'Avella, Andrea; Tresch, Matthew C; Wyler, Kuno; Bizzi, Emilio

    2017-01-01

    The central pattern generator (CPG) architecture for rhythm generation remains partly elusive. We compare cat and frog locomotion results, where the component unrelated to pattern formation appears as a temporal grid, and traveling wave respectively. Frog spinal cord microstimulation with N-methyl-D-Aspartate (NMDA), a CPG activator, produced a limited set of force directions, sometimes tonic, but more often alternating between directions similar to the tonic forces. The tonic forces were topographically organized, and sites evoking rhythms with different force subsets were located close to the constituent tonic force regions. Thus CPGs consist of topographically organized modules. Modularity was also identified as a limited set of muscle synergies whose combinations reconstructed the EMGs. The cat CPG was investigated using proprioceptive inputs during fictive locomotion. Critical points identified both as abrupt transitions in the effect of phasic perturbations, and burst shape transitions, had biomechanical correlates in intact locomotion. During tonic proprioceptive perturbations, discrete shifts between these critical points explained the burst durations changes, and amplitude changes occurred at one of these points. Besides confirming CPG modularity, these results suggest a fixed temporal grid of anchoring points, to shift modules onsets and offsets. Frog locomotion, reconstructed with the NMDA synergies, showed a partially overlapping synergy activation sequence. Using the early synergy output evoked by NMDA at different spinal sites, revealed a rostrocaudal topographic organization, where each synergy is preferentially evoked from a few, albeit overlapping, cord regions. Comparing the locomotor synergy sequence with this topography suggests that a rostrocaudal traveling wave would activate the synergies in the proper sequence for locomotion. This output was reproduced in a two-layer model using this topography and a traveling wave. Together our results

  14. Simulation of Noise in a Traveling Wave Tube

    NASA Astrophysics Data System (ADS)

    Verboncoeur, J. P.; Christenson, P. J.; Smith, H. B.

    1999-11-01

    Low frequency noise, manifested as close-in sidebands, has long been a significant limit to the performance of many traveling wave tubes. In this study, we investigate oscillations in the gun region due to the presence of plasma formed by electron-impact ionization of a background gas. The gun region of a coupled-cavity traveling wave tube is modeled using the two-dimensional XOOPIC particle-in-cell Monte Carlo collision code (J. P. Verboncoeur et al. Comput. Phys. Comm.) 87, 199-211 (1995). (available via the web: http://ptsg.eecs.berkeley.edu). The beam is 20.5 kV, 2.8 A, in near-confined flow in a solenoidal magnetic field with peak axial value of 0.263 T. Beam scalloping leads to trapping of plasma generated via electron-impact ionization of a background gas. The trapped plasma periodically leaves the system rapidly, and the density begins regenerating at a slow rate, leading to characteristic sawtooth oscillations. Plasma electrons are observed to exit the system axially about 20 ns before the ions exit primarily radially.

  15. On traveling waves in beams

    NASA Technical Reports Server (NTRS)

    Leonard, Robert W; Budiansky, Bernard

    1954-01-01

    The basic equations of Timoshenko for the motion of vibrating nonuniform beams, which allow for effects of transverse shear deformation and rotary inertia, are presented in several forms, including one in which the equations are written in the directions of the characteristics. The propagation of discontinuities in moment and shear, as governed by these equations, is discussed. Numerical traveling-wave solutions are obtained for some elementary problems of finite uniform beams for which the propagation velocities of bending and shear discontinuities are taken to be equal. These solutions are compared with modal solutions of Timoshenko's equations and, in some cases, with exact closed solutions. (author)

  16. Mariner Venus Mercury 1973 S/X-band experiment

    NASA Technical Reports Server (NTRS)

    Levy, G. S.

    1977-01-01

    The S/X-band experiment on the Mariner Venus/Mercury 1973 spacecraft constituted a unique opportunity to demonstrate the capability of an X-band downlink coherent with the normal S-band downlink. This was both a technological and scientific experiment, and the results indicated that it was successful in both cases. Analysis of the tracking data shows that the new S/X data type was capable of reducing the miss distance at the planet Mercury by 80% (post-processed data). The use of S/X electron content was demonstrated by comparison with Faraday rotation data. An X-band turnaround telemetry experiment showed the feasibility of a planetary X-band link. In the science area, the model atmospheric environment of Venus was refined. The ionosphere of the planet was measured to a higher accuracy than before, and the value of the dual-frequency link for measuring the scale size of turbulence was demonstrated. The estimate of the scale size was increased from 100 m to above 5 km.

  17. A programmable ultra-low noise X-band exciter.

    PubMed

    MacMullen, A; Hoover, L R; Justice, R D; Callahan, B S

    2001-07-01

    A programmable ultra-low noise X-band exciter has been developed using commercial off-the-shelf components. Its phase noise is more than 10 dB below the best available microwave synthesizers. It covers a 7% frequency band with 0.1-Hz resolution. The X-band output at +23 dBm is a combination of signals from an X-band sapphire-loaded cavity oscillator (SLCO), a low noise UHF frequency synthesizer, and special-purpose frequency translation and up-conversion circuitry.

  18. X-band uplink ground systems development: Part 2

    NASA Technical Reports Server (NTRS)

    Johns, C. E.

    1987-01-01

    The prototype X-band exciter testing has been completed. Stability and single-sideband phase noise measurements have been made on the X-band exciter signal (7.145-7.235 GHz) and on the coherent X- and S-band receiver test signals (8.4-8.5 GHz and 2.29-2.3 GHz) generated within the exciter equipment. Outputs are well within error budgets.

  19. Ferruleless coupled-cavity traveling-wave tube cold-test characteristics simulated with micro-SOS

    NASA Technical Reports Server (NTRS)

    Schroeder, Dana L.; Wilson, Jeffrey D.

    1993-01-01

    The three-dimensional, electromagnetic circuit analysis code, Micro-SOS, can be used to reduce expensive and time consuming experimental 'cold-testing' of traveling-wave tube (TWT) circuits. The frequency-phase dispersion and beam interaction impedance characteristics of a ferruleless coupled-cavity traveling-wave tube slow-wave circuit were simulated using the code. Computer results agree closely with experimental data. Variations in the cavity geometry dimensions of period length and gap-to-period ratio were modeled. These variations can be used in velocity taper designs to reduce the radiofrequency (RF) phase velocity in synchronism with the decelerating electron beam. Such circuit designs can result in enhanced TWT power and efficiency.

  20. Enhanced traveling wave amplification of co-planar slow wave structure by extended phase-matching

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Palm, Andrew; Sirigiri, Jagadishwar; Shin, Young-Min, E-mail: yshin@niu.edu

    2015-09-15

    The electron beam co-propagating with slow waves in a staggered double grating array (SDGA) efficiently amplifies millimeter and sub-millimeter waves over a wide spectrum. Our theoretical and numerical analyses show that the power amplification in the fundamental passband is enhanced by the extended beam-wave phase-matching. Particle-in-cell simulations on the SDGA slow wave structure, designed with 10.4 keV and 50–100 mA sheet beam, indicate that maintaining beam-wave synchronization along the entire length of the circuit improves the gain by 7.3% leading to a total gain of 28 dB, corresponding to 62 W saturated power at the middle of operating band, and a 3-dB bandwidthmore » of 7 GHz with 10.5% at V-band (73.5 GHz center frequency) with saturated peak power reaching 80 W and 28 dB at 71 GHz. These results also show a reasonably good agreement with analytic calculations based on Pierce small signal gain theory.« less

  1. On a `time' reparametrization in relativistic electrodynamics with travelling waves

    NASA Astrophysics Data System (ADS)

    Fiore, Gaetano

    2018-01-01

    We briefly report on our method [23] of simplifying the equations of motion of charged particles in an electromagnetic (EM) field that is the sum of a plane travelling wave and a static part; it is based on changes of the dependent variables and the independent one (light-like coordinate ξ instead of time t). We sketch its application to a few cases of extreme laser-induced accelerations, both in vacuum and in plane problems at the vacuum-plasma interface, where we are able to reduce the system of the (Lorentz-Maxwell and continuity) partial differential equations into a family of decoupled systems of Hamilton equations in 1 dimension. Since Fourier analysis plays no role, the method can be applied to all kind of travelling waves, ranging from almost monochromatic to socalled "impulses".

  2. A high frequency GaAlAs travelling wave electro-optic modulator at 0.82 micrometers

    NASA Technical Reports Server (NTRS)

    Chorey, Christopher M.; Ferendeci, Altan; Bhasin, Kul B.

    1988-01-01

    Experimental GaAlAs modulators operating at 0.82 micrometers using a Mach-Zehnder interferometer configuration were designed and fabricated. Coplanar 50 ohm travelling wave microwave electrodes were used to obtain a bandwidth length product of 11.95 GHz-cm. The design, fabrication and dc performance of the GaAlAs travelling wave modulator is presented.

  3. Numerical simulation of single bubble dynamics under acoustic travelling waves.

    PubMed

    Ma, Xiaojian; Huang, Biao; Li, Yikai; Chang, Qing; Qiu, Sicong; Su, Zheng; Fu, Xiaoying; Wang, Guoyu

    2018-04-01

    The objective of this paper is to apply CLSVOF method to investigate the single bubble dynamics in acoustic travelling waves. The Naiver-Stokes equation considering the acoustic radiation force is proposed and validated to capture the bubble behaviors. And the CLSVOF method, which can capture the continuous geometric properties and satisfies mass conservation, is applied in present work. Firstly, the regime map, depending on the dimensionless acoustic pressure amplitude and acoustic wave number, is constructed to present different bubble behaviors. Then, the time evolution of the bubble oscillation is investigated and analyzed. Finally, the effect of the direction and the damping coefficient of acoustic wave propagation on the bubble behavior are also considered. The numerical results show that the bubble presents distinct oscillation types in acoustic travelling waves, namely, volume oscillation, shape oscillation, and splitting oscillation. For the splitting oscillation, the formation of jet, splitting of bubble, and the rebound of sub-bubbles may lead to substantial increase in pressure fluctuations on the boundary. For the shape oscillation, the nodes and antinodes of the acoustic pressure wave contribute to the formation of the "cross shape" of the bubble. It should be noted that the direction of the bubble translation and bubble jet are always towards the direction of wave propagation. In addition, the damping coefficient causes bubble in shape oscillation to be of asymmetry in shape and inequality in size, and delays the splitting process. Copyright © 2017 Elsevier B.V. All rights reserved.

  4. Tunnel pressure waves - A smartphone inquiry on rail travel

    NASA Astrophysics Data System (ADS)

    Müller, Andreas; Hirth, Michael; Kuhn, Jochen

    2016-02-01

    When traveling by rail, you might have experienced the following phenomenon: The train enters a tunnel, and after some seconds a noticeable pressure change occurs, as perceived by your ears or even by a rapid wobbling of the train windows. The basic physics is that pressure waves created by the train travel down the tunnel, are reflected at its other end, and travel back until they meet the train again. Here we will show (i) how this effect can be well understood as a kind of large-scale outdoor case of a textbook paradigm, and (ii) how, e.g., a prediction of the tunnel length from the inside of a moving train on the basis of this model can be validated by means of a mobile phone measurement.

  5. RF breakdown in "cold" slow wave structures operating at travelling wave mode of TM01

    NASA Astrophysics Data System (ADS)

    Yuan, Yuzhang; Zhang, Jun; Zhong, Huihuang; Zhang, Dian; Bai, Zhen; Zhu, Danni

    2018-01-01

    RF breakdown experiments and simulations in "cold" slow wave structures (SWSs) are executed. All the SWSs are designed as traveling wave structures, which operate at the π/2 mode of TM01 waves. The experimental results indicate that the input microwave energy is mainly absorbed, not reflected by the RF breakdown process in traveling wave SWSs. Both larger magnitude of Es-max and more numbers of periods of SWSs aggravate the microwave absorption in the breakdown process and bring about a shorter transmission pulse width. We think that the critical surface E-field of the multi-period SWSs is 1 MV/cm. However, little correlation between RF breakdown effects and Bext is observed in the experiments. The simulation conditions are coincident with the experimental setup. Explosive emissions of electrons in the rounded corner of SWSs together with the ionization of the gas layer close to it supply the breakdown plasma. The gas layer consists of water vapor and hydrogen gas and has a pressure of 1 Pa. Different kinds of circumstances of SWSs are simulated. We mainly concern about the characteristic of the plasma and its influence on microwave power. Comprehensive simulation results are obtained. The simulation results match the experimental results basically and are helpful in explaining the RF breakdown phenomenon physically.

  6. A new traveling wave ultrasonic motor using thick ring stator with nested PZT excitation.

    PubMed

    Chen, Weishan; Shi, Shengjun; Liu, Yingxiang; Li, Pei

    2010-05-01

    To avoid the disadvantages of conventional traveling wave ultrasonic motors--lower efficiency PZT working mode of d(31), fragility of the PZT element under strong excitation, fatigue of the adhesive layer under harsh environmental conditions, and low volume of the PZT material in the stator--a new type of traveling wave ultrasonic motor is presented in this paper. Here we implement the stator by nesting 64 PZT stacks in 64 slots specifically cut in a thick metal ring and 64 block springs nested within another 64 slots to produce preloading on the PZT stacks. In this new design, the d33 mode of the PZT is used to excite the flexural vibrations of the stator, and fragility of the PZT ceramics and fatigue of the adhesive layer are no longer an issue. The working principle, FEM simulation, fabrication, and performance measurements of a prototype motor were demonstrated to validate the proposed ideas. Typical output of the prototype motor is no-load speed of 15 rpm and maximum torque of 7.96 N x m. Further improvement will potentially enhance its features by increasing the accuracy in fabrication and adopting appropriate frictional material into the interface between the stator and the rotor.

  7. Spin-wave stiffness in the Dzyaloshinskii-Moriya helimagnets Mn1 -xFexSi

    NASA Astrophysics Data System (ADS)

    Grigoriev, S. V.; Altynbaev, E. V.; Siegfried, S.-A.; Pschenichnyi, K. A.; Menzel, D.; Heinemann, A.; Chaboussant, G.

    2018-01-01

    The small-angle neutron scattering is used to measure the spin-wave stiffness in the field-polarized state of the Dzyaloshinskii-Moriya helimagnets Mn1 -xFexSi with x =0.03 , 0.06, 0.09, and 0.10. The Mn1 -xFexSi compounds are helically ordered below Tc and show a helical fluctuation regime above Tc in a wide range up to TDM. The critical temperatures Tc and TDM decrease with x and tend to 0 at x =0.11 and 0.17, respectively. We have found that the spin-wave stiffness A change weakly with temperature for each individual Fe-doped compound. On the other hand, the spin-wave stiffness A decreases with x duplicating the TDM dependence on x , rather than Tc(x ) . These findings classify the thermal phase transition in all Mn1 -xFexSi compounds as an abrupt change in the spin state caused, most probably, by the features of an electronic band structure. Moreover, the criticality in these compounds is not related to the value of the ferromagnetic interaction but demonstrates the remarkable role of the Dzyaloshinskii-Moriya interaction as a factor destabilizing the magnetic order.

  8. A rod type linear ultrasonic motor utilizing longitudinal traveling waves: proof of concept

    NASA Astrophysics Data System (ADS)

    Wang, Liang; Wielert, Tim; Twiefel, Jens; Jin, Jiamei; Wallaschek, Jörg

    2017-08-01

    This paper proposes a non-resonant linear ultrasonic motor utilizing longitudinal traveling waves. The longitudinal traveling waves in the rod type stator are generated by inducing longitudinal vibrations at one end of the waveguide and eliminating reflections at the opposite end by a passive damper. Considering the Poisson’s effect, the stator surface points move on elliptic trajectories and the slider is driven forward by friction. In contrast to many other flexural traveling wave linear ultrasonic motors, the driving direction of the proposed motor is identical to the wave propagation direction. The feasibility of the motor concept is demonstrated theoretically and experimentally. First, the design and operation principle of the motor are presented in detail. Then, the stator is modeled utilizing the transfer matrix method and verified by experimental studies. In addition, experimental parameter studies are carried out to identify the motor characteristics. Finally, the performance of the proposed motor is investigated. Overall, the results indicate very dynamic drive characteristics. The motor prototype achieves a maximum mean velocity of 115 mm s-1 and a maximum load of 0.25 N. Thereby, the start-up and shutdown times from the maximum speed are lower than 5 ms.

  9. Availability analysis of the traveling-wave maser amplifiers in the deep space network. Part 1: The 70-meter antennas

    NASA Technical Reports Server (NTRS)

    Issa, T. N.

    1992-01-01

    The results of the reliability and availability analyses of the individual S- and X-band traveling-wave maser (TWM) assemblies and their operational configurations in the 70-meter antennas of NASA's Deep Space Network (DSN) are described. For the period 1990 through 1991, the TWM availability parameters for the Telemetry Data System are: mean time between failures (MTBF), 930 hr; mean time to restore services (MTTRS), 1.4 hr; and the average availability, 99.85 percent. In previously published articles, the performance analysis of the TWM assemblies was confined to the determination of the parameters specified above. However, as the mean down time (MDT) for the repair of TWM's increases, the levels of the TWM operational availabilities and MTTRS are adversely affected. A more comprehensive TWM availability analysis is presented to permit evaluation of both MTBF and MDT effects. Performance analysis of the TWM assemblies, based on their station monthly failure reports, indicates that the TWM's required MTBF and MDT levels of 3000 hr and 36 to 48 hr, respectively, have been achieved by the TWM's only at the Canberra Deep Space Station (DSS 43). The Markov Process technique is employed to develop suitable availability measures for the S- and X-band TWM configurations when each is operated in a two-assembly standby mode. The derived stochastic expressions allow for the evaluation of those configurations' simultaneous availability for the Antenna Microwave Subsystem. The application of these expressions to demonstrate the impact of various levels of TWM maintainability (or MDT) on their configurations' operational availabilities is presented for each of the 70-m antenna stations.

  10. Measuring the band structures of periodic beams using the wave superposition method

    NASA Astrophysics Data System (ADS)

    Junyi, L.; Ruffini, V.; Balint, D.

    2016-11-01

    Phononic crystals and elastic metamaterials are artificially engineered periodic structures that have several interesting properties, such as negative effective stiffness in certain frequency ranges. An interesting property of phononic crystals and elastic metamaterials is the presence of band gaps, which are bands of frequencies where elastic waves cannot propagate. The presence of band gaps gives this class of materials the potential to be used as vibration isolators. In many studies, the band structures were used to evaluate the band gaps. The presence of band gaps in a finite structure is commonly validated by measuring the frequency response as there are no direct methods of measuring the band structures. In this study, an experiment was conducted to determine the band structure of one dimension phononic crystals with two wave modes, such as a bi-material beam, using the frequency response at only 6 points to validate the wave superposition method (WSM) introduced in a previous study. A bi-material beam and an aluminium beam with varying geometry were studied. The experiment was performed by hanging the beams freely, exciting one end of the beams, and measuring the acceleration at consecutive unit cells. The measured transfer function of the beams agrees with the analytical solutions but minor discrepancies. The band structure was then determined using WSM and the band structure of one set of the waves was found to agree well with the analytical solutions. The measurements taken for the other set of waves, which are the evanescent waves in the bi-material beams, were inaccurate and noisy. The transfer functions at additional points of one of the beams were calculated from the measured band structure using WSM. The calculated transfer function agrees with the measured results except at the frequencies where the band structure was inaccurate. Lastly, a study of the potential sources of errors was also conducted using finite element modelling and the errors in

  11. Modeling Multi-Bunch X-band Photoinjector Challenges

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Marsh, R A; Anderson, S G; Gibson, D J

    An X-band test station is being developed at LLNL to investigate accelerator optimization for future upgrades to mono-energetic gamma-ray technology at LLNL. The test station will consist of a 5.5 cell X-band rf photoinjector, single accelerator section, and beam diagnostics. Of critical import to the functioning of the LLNL X-band system with multiple electron bunches is the performance of the photoinjector. In depth modeling of the Mark 1 LLNL/SLAC X-band rf photoinjector performance will be presented addressing important challenges that must be addressed in order to fabricate a multi-bunch Mark 2 photoinjector. Emittance performance is evaluated under different nominal electronmore » bunch parameters using electrostatic codes such as PARMELA. Wake potential is analyzed using electromagnetic time domain simulations using the ACE3P code T3P. Plans for multi-bunch experiments and implementation of photoinjector advances for the Mark 2 design will also be discussed.« less

  12. Kinetic Monte Carlo simulations of travelling pulses and spiral waves in the lattice Lotka-Volterra model.

    PubMed

    Makeev, Alexei G; Kurkina, Elena S; Kevrekidis, Ioannis G

    2012-06-01

    Kinetic Monte Carlo simulations are used to study the stochastic two-species Lotka-Volterra model on a square lattice. For certain values of the model parameters, the system constitutes an excitable medium: travelling pulses and rotating spiral waves can be excited. Stable solitary pulses travel with constant (modulo stochastic fluctuations) shape and speed along a periodic lattice. The spiral waves observed persist sometimes for hundreds of rotations, but they are ultimately unstable and break-up (because of fluctuations and interactions between neighboring fronts) giving rise to complex dynamic behavior in which numerous small spiral waves rotate and interact with each other. It is interesting that travelling pulses and spiral waves can be exhibited by the model even for completely immobile species, due to the non-local reaction kinetics.

  13. Nonlinear travelling waves in rotating Hagen–Poiseuille flow

    NASA Astrophysics Data System (ADS)

    Pier, Benoît; Govindarajan, Rama

    2018-03-01

    The dynamics of viscous flow through a rotating pipe is considered. Small-amplitude stability characteristics are obtained by linearizing the Navier–Stokes equations around the base flow and solving the resulting eigenvalue problems. For linearly unstable configurations, the dynamics leads to fully developed finite-amplitude perturbations that are computed by direct numerical simulations of the complete Navier–Stokes equations. By systematically investigating all linearly unstable combinations of streamwise wave number k and azimuthal mode number m, for streamwise Reynolds numbers {{Re}}z ≤slant 500 and rotational Reynolds numbers {{Re}}{{Ω }} ≤slant 500, the complete range of nonlinear travelling waves is obtained and the associated flow fields are characterized.

  14. A novel traveling wave piezoelectric actuated tracked mobile robot utilizing friction effect

    NASA Astrophysics Data System (ADS)

    Wang, Liang; Shu, Chengyou; Jin, Jiamei; Zhang, Jianhui

    2017-03-01

    A novel traveling wave piezoelectric-actuated tracked mobile robot with potential application to robotic rovers was proposed and investigated in this study. The proposed tracked mobile robot is composed of a parallelogram-frame-structure piezoelectric transducer with four rings and a metal track. Utilizing the converse piezoelectric and friction effects, traveling waves were propagated in the rings and then the metal track was actuated by the piezoelectric transducer. Compared with traditional tracked mechanisms, the proposed tracked mobile robot has a simpler and more compact structure without lubricant, which eliminates the problem of lubricant volatilization and deflation, thus, it could be operated in the vacuum environment. Dynamic characteristics were simulated and measured to reveal the mechanism of actuating track of the piezoelectric transducer. Experimental investigations of the traveling wave piezoelectric-actuated tracked mobile robot were then carried out, and the results indicated that the robot prototype with a pair of exciting voltages of 460 Vpp is able to achieve a maximum velocity of 57 mm s-1 moving on the foam plate and possesses the obstacle crossing capability with a maximum height of 27 mm. The proposed tracked mobile robot exhibits potential to be the driving system of robotic rovers.

  15. Feasibility of Traveling Wave Direct Energy Conversion of Fission Reaction Fragments

    NASA Technical Reports Server (NTRS)

    Tarditi, A. G.; George, J. A.; Miley, G. H.; Scott, J. H.

    2013-01-01

    Fission fragment direct energy conversion has been considered in the past for the purpose of increasing nuclear power plant efficiency and for advanced space propulsion. Since the fragments carry electric charge (typically in the order of 20 e) and have 100 MeV-range kinetic energy, techniques utilizing very high-voltage DC electrodes have been considered. This study is focused on a different approach: the kinetic energy of the charged fission fragments is converted into alternating current by means of a traveling wave coupling scheme (Traveling Wave Direct Energy Converter, TWDEC), thereby not requiring the utilization of high voltage technology. A preliminary feasibility analysis of the concept is introduced based on a conceptual level study and on a particle simulation model of the beam dynamics.

  16. SPREADING SPEEDS AND TRAVELING WAVES FOR NON-COOPERATIVE INTEGRO-DIFFERENCE SYSTEMS

    PubMed Central

    Wang, Haiyan; Castillo-Chavez, Carlos

    2014-01-01

    The study of spatially explicit integro-difference systems when the local population dynamics are given in terms of discrete-time generations models has gained considerable attention over the past two decades. These nonlinear systems arise naturally in the study of the spatial dispersal of organisms. The brunt of the mathematical research on these systems, particularly, when dealing with cooperative systems, has focused on the study of the existence of traveling wave solutions and the characterization of their spreading speed. Here, we characterize the minimum propagation (spreading) speed, via the convergence of initial data to wave solutions, for a large class of non cooperative nonlinear systems of integro-difference equations. The spreading speed turns out to be the slowest speed from a family of non-constant traveling wave solutions. The applicability of these theoretical results is illustrated through the explicit study of an integro-difference system with local population dynamics governed by Hassell and Comins’ non-cooperative competition model (1976). The corresponding integro-difference nonlinear systems that results from the redistribution of individuals via a dispersal kernel is shown to satisfy conditions that guarantee the existence of minimum speeds and traveling waves. This paper is dedicated to Avner Friedman as we celebrate his immense contributions to the fields of partial differential equations, integral equations, mathematical biology, industrial mathematics and applied mathematics in general. His leadership in the mathematical sciences and his mentorship of students and friends over several decades has made a huge difference in the personal and professional lives of many, including both of us. PMID:24899868

  17. Excitation of O+ Band EMIC Waves Through H+ Ring Velocity Distributions: Van Allen Probe Observations

    NASA Astrophysics Data System (ADS)

    Yu, Xiongdong; Yuan, Zhigang; Huang, Shiyong; Yao, Fei; Wang, Dedong; Funsten, Herbert O.; Wygant, John R.

    2018-02-01

    A typical case of electromagnetic ion cyclotron (EMIC) emissions with both He+ band and O+ band waves was observed by Van Allen Probe A on 14 July 2014. These emissions occurred in the morning sector on the equator inside the plasmasphere, in which region O+ band EMIC waves prefer to appear. Through property analysis of these emissions, it is found that the He+ band EMIC waves are linearly polarized and propagating quasi-parallelly along the background magnetic field, while the O+ band ones are of linear and left-hand polarization and propagating obliquely with respect to the background magnetic field. Using the in situ observations of plasma environment and particle data, excitation of these O+ band EMIC waves has been investigated with the linear growth theory. The calculated linear growth rate shows that these O+ band EMIC waves can be locally excited by ring current protons with ring velocity distributions. The comparison of the observed wave spectral intensity and the calculated growth rate suggests that the density of H+ rings providing the free energy for the instability has decreased after the wave grows. Therefore, this paper provides a direct observational evidence to the excitation mechanism of O+ band EMIC waves: ring current protons with ring distributions provide the free energy supporting the instability in the presence of rich O+ in the plasmasphere.

  18. Collective transport for active matter run-and-tumble disk systems on a traveling-wave substrate

    DOE PAGES

    Sándor, Csand; Libál, Andras; Reichhardt, Charles; ...

    2017-01-17

    Here, we examine numerically the transport of an assembly of active run-and-tumble disks interacting with a traveling-wave substrate. We show that as a function of substrate strength, wave speed, disk activity, and disk density, a variety of dynamical phases arise that are correlated with the structure and net flux of disks. We find that there is a sharp transition into a state in which the disks are only partially coupled to the substrate and form a phase-separated cluster state. This transition is associated with a drop in the net disk flux, and it can occur as a function of themore » substrate speed, maximum substrate force, disk run time, and disk density. Since variation of the disk activity parameters produces different disk drift rates for a fixed traveling-wave speed on the substrate, the system we consider could be used as an efficient method for active matter species separation. Within the cluster phase, we find that in some regimes the motion of the cluster center of mass is in the opposite direction to that of the traveling wave, while when the maximum substrate force is increased, the cluster drifts in the direction of the traveling wave. This suggests that swarming or clustering motion can serve as a method by which an active system can collectively move against an external drift.« less

  19. Collective transport for active matter run-and-tumble disk systems on a traveling-wave substrate

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Sándor, Csand; Libál, Andras; Reichhardt, Charles

    Here, we examine numerically the transport of an assembly of active run-and-tumble disks interacting with a traveling-wave substrate. We show that as a function of substrate strength, wave speed, disk activity, and disk density, a variety of dynamical phases arise that are correlated with the structure and net flux of disks. We find that there is a sharp transition into a state in which the disks are only partially coupled to the substrate and form a phase-separated cluster state. This transition is associated with a drop in the net disk flux, and it can occur as a function of themore » substrate speed, maximum substrate force, disk run time, and disk density. Since variation of the disk activity parameters produces different disk drift rates for a fixed traveling-wave speed on the substrate, the system we consider could be used as an efficient method for active matter species separation. Within the cluster phase, we find that in some regimes the motion of the cluster center of mass is in the opposite direction to that of the traveling wave, while when the maximum substrate force is increased, the cluster drifts in the direction of the traveling wave. This suggests that swarming or clustering motion can serve as a method by which an active system can collectively move against an external drift.« less

  20. A synopsis of X-band radar-derived results from New River Inlet, NC (May 2012): Wave transformation, bathymetry, and tidal currents

    NASA Astrophysics Data System (ADS)

    Honegger, D. A.; Haller, M. C.; Diaz Mendez, G. M.; Pittman, R.; Catalan, P. A.

    2012-12-01

    Land-based X-band marine radar observations were collected as part of the month-long DARLA-MURI / RIVET-DRI field experiment at New River Inlet, NC in May 2012. Here we present a synopsis of preliminary results utilizing microwave radar backscatter time series collected from an antenna located 400 m inside the inlet mouth and with a footprint spanning 1000 m beyond the ebb shoals. Two crucial factors in the forcing and constraining of nearshore numerical models are accurate bathymetry and offshore variability in the wave field. Image time series of radar backscatter from surface gravity waves can be utilized to infer these parameters over a large swath and during times of poor optical visibility. Presented are radar-derived wavenumber vector maps obtained from the Plant et al. (2008) algorithm and bathymetric estimates as calculated using Holman et al. (JGR, in review). We also evaluate the effects of tidal currents on the wave directions and depth inversion accuracy. In addition, shifts in the average wave breaking patterns at tidal frequencies shed light on depth- (and possibly current-) induced breaking as a function of tide level and tidal current velocity, while shifts over longer timescales imply bedform movement during the course of the experiment. Lastly, lowpass filtered radar image time series of backscatter intensity are shown to identify the structure and propagation of tidal plume fronts and multiscale ebb jets at the offshore shoal boundary.

  1. The Direct Digital Modulation of Traveling Wave Tubes

    NASA Technical Reports Server (NTRS)

    Radhamohan, Ranjan S.

    2004-01-01

    Traveling wave tube (TWT) technology, first described by Rudolf Kompfner in the early 1940s, has been a key component of space missions from the earliest communication satellites in the 1960s to the Cassini probe today. TWTs are essentially signal amplifiers that have the special capability of operating at microwave frequencies. The microwave frequency range, which spans from approximately 500 MHz to 300 GHz, is shared by many technologies including cellular phones, satellite television, space communication, and radar. TWT devices are superior in reliability, weight, and efficiency to solid-state amplifiers at the high power and frequency levels required for most space missions. TWTs have three main components -an electron gun, slow wave structure, and collector. The electron gun generates an electron beam that moves along the length of the tube axis, inside of the slow wave circuit. At the same time, the inputted signal is slowed by its travel through the coils of the helical slow wave circuit. The interaction of the electron beam and this slowed signal produces a transfer of kinetic energy to the signal, and in turn, amplification. At the end of its travel, the spent electron beam moves into the collector where its remaining energy is dissipated as heat or harnessed for reuse. TWTs can easily produce gains in the tens of decibels, numbers that are suitable for space missions. To date, however, TWTs have typically operated at fixed levels of gain. This gain is determined by various, unchanging, physical factors of the tube. Traditionally, to achieve varying gain, an input signal s amplitude has had to first be modulated by a separate device before being fed into the TWT. This is not always desirable, as significant distortion can occur in certain situations. My mentor, Mr. Dale Force, has proposed an innovative solution to this problem called direct digital modulation . The testing and implementation of this solution is the focus of my summer internship. The

  2. Analytical approximation and numerical simulations for periodic travelling water waves

    NASA Astrophysics Data System (ADS)

    Kalimeris, Konstantinos

    2017-12-01

    We present recent analytical and numerical results for two-dimensional periodic travelling water waves with constant vorticity. The analytical approach is based on novel asymptotic expansions. We obtain numerical results in two different ways: the first is based on the solution of a constrained optimization problem, and the second is realized as a numerical continuation algorithm. Both methods are applied on some examples of non-constant vorticity. This article is part of the theme issue 'Nonlinear water waves'.

  3. Pulsed Traveling-wave Quadrature Squeezing Using Quasi-phase Matched Lithium Niobate Crystals

    NASA Astrophysics Data System (ADS)

    Chen, Chao-Hsiang

    Interests in generating higher quantum noise squeezing in order to develop methods to enhance optical measurement below the shot-noise limit in various applications has grown in recent years. The noise suppression from squeezing can improve the SNR in coherent optical systems when the returning signal power is weak, such as optical coherence tomography, LADAR, confocal microscopy and low-light coherent imaging. Unlike the generation of squeezing with a continuous wave, which is currently developed mainly for gravitational wave detection in LIGO project, the study of pulsed-traveling waves is focused on industrial, medical and other commercial interests. This dissertation presents the experimental results of pulsed traveling wave squeezing. The intention of the study is to explore the possibility of using quasi-phase matched crystals to generate the highest possible degree of quadrature squeezing. In order to achieve this goal, efforts to test the various effects from spatial Gaussian modes and relative beam waist placement for the second-harmonic pump were carried out in order to further the understanding of limiting factors to pulsed traveling wave squeezing. 20mm and 30mm-long periodically poled lithium noibate (PPLN) crystals were used in the experiment to generate a squeezed vacuum state. A maximum of 4.2+/-0.2dB quadrature squeezing has been observed, and the measured anti-squeezing exceeds 20dB.The phase sensitive amplification (PSA) gain and de-gain performance were also measured to compare the results of measured squeezing. The PPLN crystals can produce high conversion efficiency of second-harmonic generation (SHG) without a cavity. When a long PPLN crystal is used in a squeezer, the beam propagation in the nonlinear medium does not follow the characteristics in thin crystals. Instead, it is operated under the long-crystal criteria, which the crystal length is multiple times longer than the Rayleigh range of the injected beam i n the crystals. Quasi

  4. The Effects of Hydrogen Band EMIC Waves on Ring Current H+ Ions

    NASA Astrophysics Data System (ADS)

    Wang, Zhiqiang; Zhai, Hao; Gao, Zhuxiu

    2017-12-01

    Hydrogen band electromagnetic ion cyclotron (EMIC) waves have received much attention recently because they are found to frequently span larger spatial areas than the other band EMIC waves. Using test particle simulations, we study the nonlinear effects of hydrogen band EMIC waves on ring current H+ ions. A dimensionless parameter R is used to characterize the competition between wave-induced and adiabatic motions. The results indicate that there are three regimes of wave-particle interactions for typical 35 keV H+ ions at L = 5: diffusive (quasi-linear) behavior when αeq ≤ 35° (R ≥ 2.45), the nonlinear phase trapping when 35° < αeq < 50° (0.75 < R < 2.45), and both the nonlinear phase bunching and phase trapping when αeq ≥ 50° (R ≤ 0.75). The phase trapping can transport H+ ions toward large pitch angle, while the phase bunching has the opposite effect. The phase-trapped H+ ions can be significantly accelerated (from 35 keV to over 500 keV) in about 4 min and thus contribute to the formation of high energy components of ring current ions. The results suggest that the effect of hydrogen band EMIC waves is not ignorable in the nonlinear acceleration and resonance scattering of ring current H+ ions.

  5. Observations of Radar Backscatter at Ku and C Bands in the Presence of Large Waves during the Surface Wave Dynamics Experiment

    NASA Technical Reports Server (NTRS)

    Nghiem, S. V.; Li, Fuk K.; Lou, Shu-Hsiang; Neumann, Gregory; McIntosh, Robert E.; Carson, Steven C.; Carswell, James R.; Walsh, Edward J.; Donelan, Mark A.; Drennan, William M.

    1995-01-01

    Ocean radar backscatter in the presence of large waves is investigated using data acquired with the Jet Propulsion Laboratory NUSCAT radar at Ku band for horizontal and vertical polarizations and the University of Massachusetts CSCAT radar at C band for vertical polarization during the Surface Wave Dynamics Experiment. Off-nadir backscatter data of ocean surfaces were obtained in the presence of large waves with significant wave height up to 5.6 m. In moderate-wind cases, effects of large waves are not detectable within the measurement uncertainty and no noticeable correlation between backscatter coefficients and wave height is found. Under high-wave light-wind conditions, backscatter is enhanced significantly at large incidence angles with a weaker effect at small incidence angles. Backscatter coefficients in the wind speed range under consideration are compared with SASS-2 (Ku band), CMOD3-H1 (C band), and Plant's model results which confirm the experimental observations. Variations of the friction velocity, which can give rise to the observed backscatter behaviors in the presence of large waves, are presented.

  6. Designing broad phononic band gaps for in-plane modes

    NASA Astrophysics Data System (ADS)

    Li, Yang Fan; Meng, Fei; Li, Shuo; Jia, Baohua; Zhou, Shiwei; Huang, Xiaodong

    2018-03-01

    Phononic crystals are known as artificial materials that can manipulate the propagation of elastic waves, and one essential feature of phononic crystals is the existence of forbidden frequency range of traveling waves called band gaps. In this paper, we have proposed an easy way to design phononic crystals with large in-plane band gaps. We demonstrated that the gap between two arbitrarily appointed bands of in-plane mode can be formed by employing a certain number of solid or hollow circular rods embedded in a matrix material. Topology optimization has been applied to find the best material distributions within the primitive unit cell with maximal band gap width. Our results reveal that the centroids of optimized rods coincide with the point positions generated by Lloyd's algorithm, which deepens our understandings on the formation mechanism of phononic in-plane band gaps.

  7. Basilar-membrane interference patterns from multiple internal reflection of cochlear traveling waves.

    PubMed

    Shera, Christopher A; Cooper, Nigel P

    2013-04-01

    At low stimulus levels, basilar-membrane (BM) mechanical transfer functions in sensitive cochleae manifest a quasiperiodic rippling pattern in both amplitude and phase. Analysis of the responses of active cochlear models suggests that the rippling is a mechanical interference pattern created by multiple internal reflection within the cochlea. In models, the interference arises when reverse-traveling waves responsible for stimulus-frequency otoacoustic emissions (SFOAEs) reflect off the stapes on their way to the ear canal, launching a secondary forward-traveling wave that combines with the primary wave produced by the stimulus. Frequency-dependent phase differences between the two waves then create the rippling pattern measurable on the BM. Measurements of BM ripples and SFOAEs in individual chinchilla ears demonstrate that the ripples are strongly correlated with the acoustic interference pattern measured in ear-canal pressure, consistent with a common origin involving the generation of SFOAEs. In BM responses to clicks, the ripples appear as temporal fine structure in the response envelope (multiple lobes, waxing and waning). Analysis of the ripple spacing and response phase gradients provides a test for the role of fast- and slow-wave modes of reverse energy propagation within the cochlea. The data indicate that SFOAE delays are consistent with reverse slow-wave propagation but much too long to be explained by fast waves.

  8. Towards band structure and band offset engineering of monolayer Mo(1-x)W(x)S2 via Strain

    NASA Astrophysics Data System (ADS)

    Kim, Joon-Seok; Ahmad, Rafia; Pandey, Tribhuwan; Rai, Amritesh; Feng, Simin; Yang, Jing; Lin, Zhong; Terrones, Mauricio; Banerjee, Sanjay K.; Singh, Abhishek K.; Akinwande, Deji; Lin, Jung-Fu

    2018-01-01

    Semiconducting transition metal dichalcogenides (TMDs) demonstrate a wide range of optoelectronic properties due to their diverse elemental compositions, and are promising candidates for next-generation optoelectronics and energy harvesting devices. However, effective band offset engineering is required to implement practical structures with desirable functionalities. Here, we explore the pressure-induced band structure evolution of monolayer WS2 and Mo0.5W0.5S2 using hydrostatic compressive strain applied in a diamond anvil cell (DAC) apparatus and theoretical calculations, in order to study the modulation of band structure and explore the possibility of band alignment engineering through different compositions. Higher W composition in Mo(1-x)W(x)S2 contributes to a greater pressure-sensitivity of direct band gap opening, with a maximum value of 54 meV GPa-1 in WS2. Interestingly, while the conduction band minima (CBMs) remains largely unchanged after the rapid gap increase, valence band maxima (VBMs) significantly rise above the initial values. It is suggested that the pressure- and composition-engineering could introduce a wide variety of band alignments including type I, type II, and type III heterojunctions, and allow to construct precise structures with desirable functionalities. No structural transition is observed during the pressure experiments, implying the pressure could provide selective modulation of band offset.

  9. Theoretical band structure of the superconducting antiperovskite oxide Sr3-xSnO

    NASA Astrophysics Data System (ADS)

    Ikeda, Atsutoshi; Fukumoto, Toshiyuki; Oudah, Mohamed; Hausmann, Jan Niklas; Yonezawa, Shingo; Kobayashi, Shingo; Sato, Masatoshi; Tassel, Cédric; Takeiri, Fumitaka; Takatsu, Hiroshi; Kageyama, Hiroshi; Maeno, Yoshiteru

    2018-05-01

    In order to investigate the position of the strontium deficiency in superconductive Sr3-xSnO, we synthesized and measured X-ray-diffraction patterns of Sr3-xSnO (x ∼ 0.5). Because no clear peaks originating from superstructures were observed, strontium deficiency is most likely to be randomly distributed. We also performed first-principles band-structure calculations on Sr3-xSnO (x = 0, 0.5) using two methods: full-potential linearized-augmented plane-wave plus local orbitals method and the Korringa-Kohn-Rostoker Green function method combined with the coherent potential approximation. We revealed that the Fermi energy of Sr3-xSnO in case of x ∼ 0.5 is about 0.8 eV below the original Fermi energy of the stoichiometric Sr3SnO, where the mixing of the valence p and conduction d orbitals are considered to be small.

  10. The flaky porous Fe3O4 with tunable dimensions for enhanced microwave absorption performance in X and C bands.

    PubMed

    Zhao, Huanqin; Cheng, Yan; Liu, Wei; Yang, Zhihong; Zhang, Baoshan; Ji, Guangbin; Du, Youwei

    2018-07-20

    Special electric and magnetic characteristics make Fe 3 O 4 widely applied in the electromagnetic (EM) wave absorption region. However, for pure Fe 3 O 4 , it is still a challenge to simultaneously obtain high absorption intensity and broadband absorption at a low thickness, owing to its low dielectric property. As we realized, flake configuration and the porous structure have obviously promote the EM wave absorption property. Because the former can lead to multi-reflection between flakes and the latter is conductive to interface polarization, flaky Fe 3 O 4 with a porous and coarse surface was designed to overcome the deficiency of traditional Fe 3 O 4 particles. The experimental results demonstrate that the flaky configuration is conductive to enhancing the dielectric coefficient and optimizing impedance matching. Moreover, the complex permittivity rises with the aspect ratio of the sheet. Under a suitable dimension, the flaky Fe 3 O 4 could acquire targeted EM wave absorption capacity in the X band (8-12 GHz). In detail, the maximum reflection loss (RL) could reach a strong intensity of -49 dB at 2.05 mm. The effective absorption bandwidth (EAB) with RL below -10 dB is 4.32 (7.52-11.84) GHz, which is almost equivalent to the whole X band (8-12 GHz). Even more exciting, when regulating the thickness between 2.05 and 3.05 mm, the EAB could cover the entire C and X bands (4-12 GHz). This study provides a good reference for the future development of other ferromagnetic materials toward specific microwave bands.

  11. Whole body traveling wave magnetic resonance imaging at high field strength: homogeneity, efficiency, and energy deposition as compared with traditional excitation mechanisms.

    PubMed

    Zhang, Bei; Sodickson, Daniel K; Lattanzi, Riccardo; Duan, Qi; Stoeckel, Bernd; Wiggins, Graham C

    2012-04-01

    In 7 T traveling wave imaging, waveguide modes supported by the scanner radiofrequency shield are used to excite an MR signal in samples or tissue which may be several meters away from the antenna used to drive radiofrequency power into the system. To explore the potential merits of traveling wave excitation for whole-body imaging at 7 T, we compare numerical simulations of traveling wave and TEM systems, and juxtapose full-wave electrodynamic simulations using a human body model with in vivo human traveling wave imaging at multiple stations covering the entire body. The simulated and in vivo traveling wave results correspond well, with strong signal at the periphery of the body and weak signal deep in the torso. These numerical results also illustrate the complicated wave behavior that emerges when a body is present. The TEM resonator simulation allowed comparison of traveling wave excitation with standard quadrature excitation, showing that while the traveling wave B +1 per unit drive voltage is much less than that of the TEM system, the square of the average B +1 compared to peak specific absorption rate (SAR) values can be comparable in certain imaging planes. Both systems produce highly inhomogeneous excitation of MR signal in the torso, suggesting that B(1) shimming or other parallel transmission methods are necessary for 7 T whole body imaging. Copyright © 2011 Wiley-Liss, Inc.

  12. Spatiotemporal optical dark X solitary waves.

    PubMed

    Baronio, Fabio; Chen, Shihua; Onorato, Miguel; Trillo, Stefano; Wabnitz, Stefan; Kodama, Yuji

    2016-12-01

    We introduce spatiotemporal optical dark X solitary waves of the (2+1)D hyperbolic nonlinear Schrödinger equation (NLSE), which rules wave propagation in a self-focusing and normally dispersive medium. These analytical solutions are derived by exploiting the connection between the NLSE and a well-known equation of hydrodynamics, namely the type II Kadomtsev-Petviashvili (KP-II) equation. As a result, families of shallow water X soliton solutions of the KP-II equation are mapped into optical dark X solitary wave solutions of the NLSE. Numerical simulations show that optical dark X solitary waves may propagate for long distances (tens of nonlinear lengths) before they eventually break up, owing to the modulation instability of the continuous wave background. This finding opens a novel path for the excitation and control of X solitary waves in nonlinear optics.

  13. Traveling wave solution of driven nonlinear Schrödinger equation

    NASA Astrophysics Data System (ADS)

    Akbari-Moghanjoughi, M.

    2017-09-01

    The traveling solitary and cnoidal wave solutions of the one dimensional driven nonlinear Schrödinger equation with a generalized form of nonlinearity are presented in this paper. We examine the modulation of nonlinear solitary excitations in two known weakly nonlinear models of classic oscillators, namely, the Helmholtz and Duffing oscillators and envelope structure formations for different oscillator and driver parameters. It is shown that two distinct regimes of subcritical and supercritical modulations may occur for nonlinear excitations with propagation speeds v <√{4 F0 } and v >√{4 F0 } , respectively, in which F0 is the driver force strength. The envelope soliton and cnoidal waves in these regimes are observed to be fundamentally different. The effect of pseudoenergy on the structure of the modulated envelope excitations is studied in detail for both sub- and supercritical modulation types. The current model for traveling envelope excitations may be easily extended to pseudopotentials with full nonlinearity relevant to more realistic gases, fluids, and plasmas.

  14. Power and Efficiency Optimized in Traveling-Wave Tubes Over a Broad Frequency Bandwidth

    NASA Technical Reports Server (NTRS)

    Wilson, Jeffrey D.

    2001-01-01

    A traveling-wave tube (TWT) is an electron beam device that is used to amplify electromagnetic communication waves at radio and microwave frequencies. TWT's are critical components in deep space probes, communication satellites, and high-power radar systems. Power conversion efficiency is of paramount importance for TWT's employed in deep space probes and communication satellites. A previous effort was very successful in increasing efficiency and power at a single frequency (ref. 1). Such an algorithm is sufficient for narrow bandwidth designs, but for optimal designs in applications that require high radiofrequency power over a wide bandwidth, such as high-density communications or high-resolution radar, the variation of the circuit response with respect to frequency must be considered. This work at the NASA Glenn Research Center is the first to develop techniques for optimizing TWT efficiency and output power over a broad frequency bandwidth (ref. 2). The techniques are based on simulated annealing, which has the advantage over conventional optimization techniques in that it enables the best possible solution to be obtained (ref. 3). Two new broadband simulated annealing algorithms were developed that optimize (1) minimum saturated power efficiency over a frequency bandwidth and (2) simultaneous bandwidth and minimum power efficiency over the frequency band with constant input power. The algorithms were incorporated into the NASA coupled-cavity TWT computer model (ref. 4) and used to design optimal phase velocity tapers using the 59- to 64-GHz Hughes 961HA coupled-cavity TWT as a baseline model. In comparison to the baseline design, the computational results of the first broad-band design algorithm show an improvement of 73.9 percent in minimum saturated efficiency (see the top graph). The second broadband design algorithm (see the bottom graph) improves minimum radiofrequency efficiency with constant input power drive by a factor of 2.7 at the high band edge (64

  15. Self-consistent inclusion of space-charge in the traveling wave tube

    NASA Technical Reports Server (NTRS)

    Freeman, Jon C.

    1987-01-01

    It is shown how the complete field of the electron beam may be incorporated into the transmission line model theory of the traveling wave tube (TWT). The fact that the longitudinal component of the field due to the bunched beam is not used when formulating the beam-to-circuit coupling equation is not well-known. The fundamental partial differential equation for the traveling wave field is developed and compared with the older (now standard) one. The equation can be solved numerically using the same algorithms, but now the coefficients can be updated continuously as the calculation proceeds down the tube. The coefficients in the older equations are primarily derived from preliminary measurements and some trial and error. The newer coefficients can be found by a recursive method, since each has a well defined physical interpretation and can be calculated once a reasonable first trial solution is postulated. The results of the new expression were compared with those of the older forms, as well as to a field theory model to show the ease in which a reasonable fit to the field prediction is obtained. A complete summary of the existing transmission line modeling of the TWT is given to explain the somewhat vague ideas and techniques in the general area of drifting carrier-traveling circuit wave interactions. The basic assumptions and inconsistencies of the existing theory and areas of confusion in the general literature are examined and hopefully cleared up.

  16. Lexical access and evoked traveling alpha waves

    PubMed Central

    Zauner, Andrea; Gruber, Walter; Himmelstoß, Nicole Alexandra; Lechinger, Julia; Klimesch, Wolfgang

    2014-01-01

    Retrieval from semantic memory is usually considered within a time window around 300–600 ms. Here we suggest that lexical access already occurs at around 100 ms. This interpretation is based on the finding that semantically rich and frequent words exhibit a significantly shorter topographical latency difference between the site with the shortest P1 latency (leading site) and that with the longest P1 latency (trailing site). This latency difference can be described in terms of an evoked traveling alpha wave as was already shown in earlier studies. PMID:24486978

  17. Acoustic tweezing of particles using decaying opposing travelling surface acoustic waves (DOTSAW).

    PubMed

    Ng, Jia Wei; Devendran, Citsabehsan; Neild, Adrian

    2017-10-11

    Surface acoustic waves offer a versatile and biocompatible method of manipulating the location of suspended particles or cells within microfluidic systems. The most common approach uses the interference of identical frequency, counter propagating travelling waves to generate a standing surface acoustic wave, in which particles migrate a distance less than half the acoustic wavelength to their nearest pressure node. The result is the formation of a periodic pattern of particles. Subsequent displacement of this pattern, the prerequisite for tweezing, can be achieved by translation of the standing wave, and with it the pressure nodes; this requires changing either the frequency of the pair of waves, or their relative phase. Here, in contrast, we examine the use of two counterpropagating traveling waves of different frequency. The non-linearity of the acoustic forces used to manipulate particles, means that a small frequency difference between the two waves creates a substantially different force field, which offers significant advantages. Firstly, this approach creates a much longer range force field, in which migration takes place across multiple wavelengths, and causes particles to be gathered together in a single trapping site. Secondly, the location of this single trapping site can be controlled by the relative amplitude of the two waves, requiring simply an attenuation of one of the electrical drive signals. Using this approach, we show that by controlling the powers of the opposing incoherent waves, 5 μm particles can be migrated laterally across a fluid flow to defined locations with an accuracy of ±10 μm.

  18. Development of an X-band 25 watt traveling-wave tube

    NASA Technical Reports Server (NTRS)

    Roberts, L. A.; Knight, R. I.

    1972-01-01

    The development of a 25 watt high efficiency travelingwave tube at 8.5 GHz for space communications and telemetry applications is reported. Described is the design basis for the tube, which is known as the WJ-3703. Because of the combined high efficiency and high frequency requirements, the helix and body dimensions are very small and require special techniques for various assembly and construction procedures. These are described in detail. Measurement results of focusing tests and RF operation are given, but only pulsed RF performance of the tubes was obtained.

  19. Microscale anechoic architecture: acoustic diffusers for ultra low power microparticle separation via traveling surface acoustic waves.

    PubMed

    Behrens, Jan; Langelier, Sean; Rezk, Amgad R; Lindner, Gerhard; Yeo, Leslie Y; Friend, James R

    2015-01-07

    We present a versatile and very low-power traveling SAW microfluidic sorting device able to displace and separate particles of different diameter in aqueous suspension; the travelling wave propagates through the fluid bulk and diffuses via a Schröder diffuser, adapted from its typical use in concert hall acoustics to be the smallest such diffuser to be suitable for microfluidics. The effective operating power range is two to three orders of magnitude less than current SAW devices, uniquely eliminating the need for amplifiers, and by using traveling waves to impart forces directly upon suspended microparticles, they can be separated by size.

  20. Reconfigurable wave band structure of an artificial square ice

    DOE PAGES

    lacocca, Ezio; Gliga, Sebastian; Stamps, Robert L.; ...

    2016-04-18

    Artificial square ices are structures composed of magnetic nanoelements arranged on the sites of a twodimensional square lattice, such that there are four interacting magnetic elements at each vertex, leading to geometrical frustration. Using a semianalytical approach, we show that square ices exhibit a rich spin-wave band structure that is tunable both by external magnetic fields and the magnetization configuration of individual elements. Internal degrees of freedom can give rise to equilibrium states with bent magnetization at the element edges leading to characteristic excitations; in the presence of magnetostatic interactions these form separate bands analogous to impurity bands in semiconductors.more » Full-scale micromagnetic simulations corroborate our semianalytical approach. Our results show that artificial square ices can be viewed as reconfigurable and tunable magnonic crystals that can be used as metamaterials for spin-wave-based applications at the nanoscale.« less

  1. Reconfigurable wave band structure of an artificial square ice

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    lacocca, Ezio; Gliga, Sebastian; Stamps, Robert L.

    Artificial square ices are structures composed of magnetic nanoelements arranged on the sites of a twodimensional square lattice, such that there are four interacting magnetic elements at each vertex, leading to geometrical frustration. Using a semianalytical approach, we show that square ices exhibit a rich spin-wave band structure that is tunable both by external magnetic fields and the magnetization configuration of individual elements. Internal degrees of freedom can give rise to equilibrium states with bent magnetization at the element edges leading to characteristic excitations; in the presence of magnetostatic interactions these form separate bands analogous to impurity bands in semiconductors.more » Full-scale micromagnetic simulations corroborate our semianalytical approach. Our results show that artificial square ices can be viewed as reconfigurable and tunable magnonic crystals that can be used as metamaterials for spin-wave-based applications at the nanoscale.« less

  2. An X-Band Gun Test Area at SLAC

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Limborg-Deprey, C.; Adolphsen, C.; Chu, T.S.

    The X-Band Test Area (XTA) is being assembled in the NLCTA tunnel at SLAC to serve as a test facility for new RF guns. The first gun to be tested will be an upgraded version of the 5.6 cell, 200 MV/m peak field X-band gun designed at SLAC in 2003 for the Compton Scattering experiment run in ASTA. This new version includes some features implemented in 2006 on the LCLS gun such as racetrack couplers, increased mode separation and elliptical irises. These upgrades were developed in collaboration with LLNL since the same gun will be used in an injector formore » a LLNL Gamma-ray Source. Our beamline includes an X-band acceleration section which takes the electron beam up to 100 MeV and an electron beam measurement station. Other X-Band guns such as the UCLA Hybrid gun will be characterized at our facility.« less

  3. X-SAR: The X-band synthetic aperture radar on board the Space Shuttle

    NASA Technical Reports Server (NTRS)

    Werner, Marian U.

    1993-01-01

    The X-band synthetic aperture radar (X-SAR) is the German/Italian contribution to the NASA/JPL Shuttle Radar Lab missions as part of the preparation for the Earth Observation System (EOS) program. The Shuttle Radar Lab is a combination of several radars: an L-band (1.2 GHz) and a C-band (5.3 GHz) multipolarization SAR known as SIR-C (Shuttle Imaging Radar); and an X-band (9.6 GHz) vertically polarized SAR which will be operated synchronously over the same target areas to deliver calibrated multifrequency and multipolarization SAR data at multiple incidence angles from space. A joint German/Italian project office at DARA (German Space Agency) is responsible for the management of the X-SAR project. The space hardware has been developed and manufactured under industrial contract by Dornier and Alenia Spazio. Besides supporting all the technical and scientific tasks, DLR, in cooperation with ASI (Agencia Spaziale Italiano) is responsible for mission operation, calibration, and high precision SAR processing. In addition, DLR developed an airborne X-band SAR to support the experimenters with campaigns to prepare for the missions. The main advantage of adding a shorter wavelength (3 cm) radar to the SIR-C radars is the X-band radar's weaker penetration into vegetation and soil and its high sensitivity to surface roughness and associated phenomena. The performance of each of the three radars is comparable with respect to radiometric and geometric resolution.

  4. Angular-spectrum representation of nondiffracting X waves

    NASA Astrophysics Data System (ADS)

    Fagerholm, Juha; Friberg, Ari T.; Huttunen, Juhani; Morgan, David P.; Salomaa, Martti M.

    1996-10-01

    We derive the nondiffracting X waves, first discussed within acoustics by Lu and Greenleaf [IEEE Trans. Ultrason. Ferroelec. Freq. Contr. 39, 19 (1992)], using the general mathematical formalism based on an angular spectrum of plane waves. This serves to provide a unified treatment of not only the fundamental zeroth-order X waves of Lu and Greenleaf, but also of the lesser-known higher-order derivative X waves, first discussed here in terms of a single, universal, angular spectrum. The characteristic crossed (letter-X-like) shape and the special properties of the X waves, as well as of their angular-spectrum representation, are discussed and illustrated in detail. Asymptotically, for increasing order, the appearance of the X waves is found to transform into a triangular wedgelike waveform.

  5. Lamb wave band gaps in a double-sided phononic plate

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Chen, Tian-Ning; Yu, Kun-Peng; Wang, Xiao-Peng

    2013-02-01

    In this paper, we report on the theoretical investigation of the propagation characteristics of Lamb wave in a phononic crystal structure constituted by a square array of cylindrical stubs deposited on both sides of a thin homogeneous plate. The dispersion relations, the power transmission spectra, and the displacement fields of the eigenmodes are studied by using the finite-element method. We investigate the evolution of band gaps in the double-sided phononic plate with stub height on both sides arranged from an asymmetrical distribution to a symmetrical distribution gradually. Numerical results show that as the double stubs in a unit cell arranged more symmetrically on both sides, band width shifts, new band gaps appear, and the bands become flat due to localized resonant modes which couple with plate modes. Specially, more band gaps and flat bands can be found in the symmetrical system as a result of local resonances of the stubs which interact in a stronger way with the plate modes. Moreover, the symmetrical double-sided plate exhibits lower and smaller band gap than that of the asymmetrical plate. These propagation properties of elastic or acoustic waves in the double-sided plate can potentially be utilized to generate filters, slow the group velocity, low-frequency sound insulation, and design acoustic sensors.

  6. Advanced mobile satellite communications system using Ka and MM-wave bands in Japan's R and D satellite project

    NASA Technical Reports Server (NTRS)

    Isobe, Shunkichi; Ohmori, Shingo; Hamamoto, Naokazu; Yamamoto, Minoru

    1991-01-01

    Communications Research Laboratory (CRL) studied an advanced mobile satellite communications system using Ka and millimeter-wave bands in the R&D Satellite project. The project started in 1990 and the satellite will be launched in 1997. On-board multi-beam interconnecting is one of basic functions to realize one-hop connection among Very Small Aperture Terminals (VSATs), mobile, and hand-held terminals in future mobile satellite communications system. An Intermediate Frequency (IF) filter bank and regenerative transponder are suitable for this function. The transponder configuration of an advanced mobile communications mission of the R&D Satellite for experiment is shown. High power transmitters of Ka and millimeter-wave bands, a 3x3 IF filter band and Single Channel Per Carrier/Time Division Multiplexing (SCPC/TDM) regenerative MODEMS, which will be boarded on the R&D Satellite, are being developed for the purpose of studying the feasibility of advanced mobile communications system.

  7. Nonlinear Bloch waves in metallic photonic band-gap filaments

    NASA Astrophysics Data System (ADS)

    Kaso, Artan; John, Sajeev

    2007-11-01

    We demonstrate the occurrence of nonlinear Bloch waves in metallic photonic crystals (PCs). These periodically structured filaments are characterized by an isolated optical pass band below an effective plasma gap. The pass band occurs in a frequency range where the metallic filament exhibits a negative, frequency-dependent dielectric function and absorption loss. The metallic losses are counterbalanced by gain in two models of inhomogeneously broadened nonlinear oscillators. In the first model, we consider close-packed quantum dots that fill the void regions of a two-dimensional (2D) metallic PC, and whose inhomogeneously broadened emission spectrum spans the original optical pass band of the bare filament. In the second model, we consider thin (10 50 nm) layers of inhomogeneously broadened two-level resonators, with large dipole oscillator strength, that cover the interior surfaces of 2D metallic (silver and tungsten) PCs. These may arise from localized surface plasmon resonances due to small metal particles or an otherwise rough metal surface. For simplicity, we treat electromagnetic modes with electric field perpendicular to the plane of metal periodicity. In both models, a pumping threshold of the resonators is found, above which periodic nonlinear solutions of Maxwell’s equations with purely real frequency within the optical pass band emerge. These nonlinear Bloch waves exhibit a laserlike input pumping to output amplitude characteristic. For strong surface resonances, these nonlinear waves may play a role in light emission from a hot tungsten (suitably microstructured) filament.

  8. Multi-Band Multi-Tone Tunable Millimeter-Wave Frequency Synthesizer For Satellite Beacon Transmitter

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Wintucky, Edwin G.

    2016-01-01

    This paper presents the design and test results of a multi-band multi-tone tunable millimeter-wave frequency synthesizer, based on a solid-state frequency comb generator. The intended application of the synthesizer is in a satellite beacon transmitter for radio wave propagation studies at K-band (18 to 26.5 GHz), Q-band (37 to 42 GHz), and E-band (71 to 76 GHz). In addition, the architecture for a compact beacon transmitter, which includes the multi-tone synthesizer, polarizer, horn antenna, and power/control electronics, has been investigated for a notional space-to-ground radio wave propagation experiment payload on a small satellite. The above studies would enable the design of robust high throughput multi-Gbps data rate future space-to-ground satellite communication links.

  9. Travelling Wave Solutions in Multigroup Age-Structured Epidemic Models

    NASA Astrophysics Data System (ADS)

    Ducrot, Arnaut; Magal, Pierre; Ruan, Shigui

    2010-01-01

    Age-structured epidemic models have been used to describe either the age of individuals or the age of infection of certain diseases and to determine how these characteristics affect the outcomes and consequences of epidemiological processes. Most results on age-structured epidemic models focus on the existence, uniqueness, and convergence to disease equilibria of solutions. In this paper we investigate the existence of travelling wave solutions in a deterministic age-structured model describing the circulation of a disease within a population of multigroups. Individuals of each group are able to move with a random walk which is modelled by the classical Fickian diffusion and are classified into two subclasses, susceptible and infective. A susceptible individual in a given group can be crisscross infected by direct contact with infective individuals of possibly any group. This process of transmission can depend upon the age of the disease of infected individuals. The goal of this paper is to provide sufficient conditions that ensure the existence of travelling wave solutions for the age-structured epidemic model. The case of two population groups is numerically investigated which applies to the crisscross transmission of feline immunodeficiency virus (FIV) and some sexual transmission diseases.

  10. NASA Researcher Adjusts a Travelling Magnetic Wave Plasma Engine

    NASA Image and Video Library

    1964-02-21

    Raymond Palmer, of the Electromagnetic Propulsion Division’s Plasma Flow Section, adjusts the traveling magnetic wave plasma engine being operated in the Electric Power Conversion at the National Aeronautics and Space Administration (NASA) Lewis Research Center. During the 1960s Lewis researchers were exploring several different methods of creating electric propulsion systems, including the traveling magnetic wave plasma engine. The device operated similarly to alternating-current motors, except that a gas, not a solid, was used to conduct the electricity. A magnetic wave induced a current as it passed through the plasma. The current and magnetic field pushed the plasma in one direction. Palmer and colleague Robert Jones explored a variety of engine configurations in the Electric Propulsion Research Building. The engine is seen here mounted externally on the facility’s 5-foot diameter and 16-foot long vacuum tank. The four magnetic coils are seen on the left end of the engine. The researchers conducted two-minute test runs with varying configurations and used of both argon and xenon as the propellant. The Electric Propulsion Research Building was built in 1942 as the Engine Propeller Research Building, often called the Prop House. It contained four test cells to study large reciprocating engines with their propellers. After World War II, the facility was modified to study turbojet engines. By the 1960s, the facility was modified again for electric propulsion research and given its current name.

  11. Expression for time travel based on diffusive wave theory: applicability and considerations

    NASA Astrophysics Data System (ADS)

    Aguilera, J. C.; Escauriaza, C. R.; Passalacqua, P.; Gironas, J. A.

    2017-12-01

    Prediction of hydrological response is of utmost importance when dealing with urban planning, risk assessment, or water resources management issues. With the advent of climate change, special care must be taken with respect to variations in rainfall and runoff due to rising temperature averages. Nowadays, while typical workstations have adequate power to run distributed routing hydrological models, it is still not enough for modeling on-the-fly, a crucial ability in a natural disaster context, where rapid decisions must be made. Semi-distributed time travel models, which compute a watershed's hydrograph without explicitly solving the full shallow water equations, appear as an attractive approach to rainfall-runoff modeling since, like fully distributed models, also superimpose a grid on the watershed, and compute runoff based on cell parameter values. These models are heavily dependent on the travel time expression for an individual cell. Many models make use of expressions based on kinematic wave theory, which is not applicable in cases where watershed storage is important, such as mild slopes. This work presents a new expression for concentration times in overland flow, based on diffusive wave theory, which considers not only the effects of storage but also the effects on upstream contribution. Setting upstream contribution equal to zero gives an expression consistent with previous work on diffusive wave theory; on the other hand, neglecting storage effects (i.e.: diffusion,) is shown to be equivalent to kinematic wave theory, currently used in many spatially distributed time travel models. The newly found expression is shown to be dependent on plane discretization, particularly when dealing with very non-kinematic cases. This is shown to be the result of upstream contribution, which gets larger downstream, versus plane length. This result also provides some light on the limits on applicability of the expression: when a certain kinematic threshold is reached, the

  12. Low-noise kinetic inductance traveling-wave amplifier using three-wave mixing

    NASA Astrophysics Data System (ADS)

    Vissers, M. R.; Erickson, R. P.; Ku, H.-S.; Vale, Leila; Wu, Xian; Hilton, G. C.; Pappas, D. P.

    2016-01-01

    We have fabricated a wide-bandwidth, high dynamic range, low-noise cryogenic amplifier based on a superconducting kinetic inductance traveling-wave device. The device was made from NbTiN and consisted of a long, coplanar waveguide on a silicon chip. By adding a DC current and an RF pump tone, we are able to generate parametric amplification using three-wave mixing (3WM). The devices exhibit gain of more than 15 dB across an instantaneous bandwidth from 4 to 8 GHz. The total usable gain bandwidth, including both sides of the signal-idler gain region, is more than 6 GHz. The noise referred to the input of the devices approaches the quantum limit, with less than 1 photon excess noise. We compare these results directly to the four-wave mixing amplification mode, i.e., without DC-biasing. We find that the 3WM mode allows operation with the pump at lower RF power and at frequencies far from the signal. We have used this knowledge to redesign the amplifiers to utilize primarily 3WM amplification, thereby allowing for direct integration into large scale qubit and detector applications.

  13. Low-noise kinetic inductance traveling-wave amplifier using three-wave mixing

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Vissers, M. R.; Erickson, R. P.; Ku, H.-S.

    We have fabricated a wide-bandwidth, high dynamic range, low-noise cryogenic amplifier based on a superconducting kinetic inductance traveling-wave device. The device was made from NbTiN and consisted of a long, coplanar waveguide on a silicon chip. By adding a DC current and an RF pump tone, we are able to generate parametric amplification using three-wave mixing (3WM). The devices exhibit gain of more than 15 dB across an instantaneous bandwidth from 4 to 8 GHz. The total usable gain bandwidth, including both sides of the signal-idler gain region, is more than 6 GHz. The noise referred to the input of the devices approachesmore » the quantum limit, with less than 1 photon excess noise. We compare these results directly to the four-wave mixing amplification mode, i.e., without DC-biasing. We find that the 3WM mode allows operation with the pump at lower RF power and at frequencies far from the signal. We have used this knowledge to redesign the amplifiers to utilize primarily 3WM amplification, thereby allowing for direct integration into large scale qubit and detector applications.« less

  14. Scaling EUV and X-ray Thomson sources to optical free-electron laser operation with traveling-wave Thomson scattering (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Steiniger, Klaus; Albach, Daniel; Debus, Alexander; Loeser, Markus; Pausch, Richard; Roeser, Fabian; Schramm, Ulrich; Siebold, Matthias; Bussmann, Michael

    2017-05-01

    Traveling-Wave Thomson-Scattering (TWTS) allows for the realization of optical free-electron lasers (OFELs) from the interaction of short, high-power laser pulses with brilliant relativistic electron bunches. The laser field provides the optical undulator which is traversed by the electrons. In order to achieve coherent amplification of radiation through electron microbunching the interaction between electrons and laser must be maintained over hundreds to thousands of undulator periods. Traveling-Wave Thomson-Scattering is the only scattering geometry so far allowing for the realization of optical undulators of this length which is at the same time scalable from extreme ultraviolet to X-ray photon energies. TWTS is also applicable for the realization of incoherent high peak brightness hard X-ray to gamma-ray sources which can provide orders of magnitude higher photon output than classic head-on Thomson sources. In contrast to head-on Thomson sources TWTS employs a side-scattering geometry where laser and electron propagation direction of motion enclose an angle. Tilting the laser pulse front with respect to the wave front by half of this interaction angle optimizes electron and laser pulse overlap. In the side-scattering geometry the tilt of the pulse-front compensates the spatial offset between electrons and laser pulse-front which would be present otherwise for an electron bunch far from the interaction point where it overlaps with the laser pulse center. Thus the laser pulse-front tilt ensures continuous overlap between laser pulse and electrons while these traverse the laser pulse cross-sectional area. This allows to control the interaction distance in TWTS by the laser pulse width rather than laser pulse duration as is the case for head-on Thomson scattering. Utilizing petawatt class laser pulses with millimeter to centimeter scale width allows for the realization of compact optical undulators with thousands of periods. When laser pulses for TWTS are prepared

  15. Frequency modulation and compression of optical pulses in an optical fibre with a travelling refractive-index wave

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zolotovskii, I O; Lapin, V A; Sementsov, D I

    2016-01-31

    We have studied the conditions for spectral broadening, frequency modulation and compression (both temporal and spectral) of Gaussian pulses propagating in a fibre with a travelling refractive-index wave. Analytical expressions have been derived for the dependences of pulse duration, chirp and spectral width on the distance travelled through the fibre, parameters of the fibre and radiation launched into it. Based on the numerical analysis we have studied the behaviour of these characteristics by changing the coefficient of the refractive-index modulation and other parameters of the travelling refractive-index wave. (nonlinear optical phenomena)

  16. Performances estimation of a rotary traveling wave ultrasonic motor based on two-dimension analytical model.

    PubMed

    Ming, Y; Peiwen, Q

    2001-03-01

    The understanding of ultrasonic motor performances as a function of input parameters, such as the voltage amplitude, driving frequency, the preload on the rotor, is a key to many applications and control of ultrasonic motor. This paper presents performances estimation of the piezoelectric rotary traveling wave ultrasonic motor as a function of input voltage amplitude and driving frequency and preload. The Love equation is used to derive the traveling wave amplitude on the stator surface. With the contact model of the distributed spring-rigid body between the stator and rotor, a two-dimension analytical model of the rotary traveling wave ultrasonic motor is constructed. Then the performances of stead rotation speed and stall torque are deduced. With MATLAB computational language and iteration algorithm, we estimate the performances of rotation speed and stall torque versus input parameters respectively. The same experiments are completed with the optoelectronic tachometer and stand weight. Both estimation and experiment results reveal the pattern of performance variation as a function of its input parameters.

  17. Spatial gradients of protein-level time delays set the pace of the traveling segmentation clock waves

    PubMed Central

    Ay, Ahmet; Holland, Jack; Sperlea, Adriana; Devakanmalai, Gnanapackiam Sheela; Knierer, Stephan; Sangervasi, Sebastian; Stevenson, Angel; Özbudak, Ertuğrul M.

    2014-01-01

    The vertebrate segmentation clock is a gene expression oscillator controlling rhythmic segmentation of the vertebral column during embryonic development. The period of oscillations becomes longer as cells are displaced along the posterior to anterior axis, which results in traveling waves of clock gene expression sweeping in the unsegmented tissue. Although various hypotheses necessitating the inclusion of additional regulatory genes into the core clock network at different spatial locations have been proposed, the mechanism underlying traveling waves has remained elusive. Here, we combined molecular-level computational modeling and quantitative experimentation to solve this puzzle. Our model predicts the existence of an increasing gradient of gene expression time delays along the posterior to anterior direction to recapitulate spatiotemporal profiles of the traveling segmentation clock waves in different genetic backgrounds in zebrafish. We validated this prediction by measuring an increased time delay of oscillatory Her1 protein production along the unsegmented tissue. Our results refuted the need for spatial expansion of the core feedback loop to explain the occurrence of traveling waves. Spatial regulation of gene expression time delays is a novel way of creating dynamic patterns; this is the first report demonstrating such a control mechanism in any tissue and future investigations will explore the presence of analogous examples in other biological systems. PMID:25336742

  18. The flaky porous Fe3O4 with tunable dimensions for enhanced microwave absorption performance in X and C bands

    NASA Astrophysics Data System (ADS)

    Zhao, Huanqin; Cheng, Yan; Liu, Wei; Yang, Zhihong; Zhang, Baoshan; Ji, Guangbin; Du, Youwei

    2018-07-01

    Special electric and magnetic characteristics make Fe3O4 widely applied in the electromagnetic (EM) wave absorption region. However, for pure Fe3O4, it is still a challenge to simultaneously obtain high absorption intensity and broadband absorption at a low thickness, owing to its low dielectric property. As we realized, flake configuration and the porous structure have obviously promote the EM wave absorption property. Because the former can lead to multi-reflection between flakes and the latter is conductive to interface polarization, flaky Fe3O4 with a porous and coarse surface was designed to overcome the deficiency of traditional Fe3O4 particles. The experimental results demonstrate that the flaky configuration is conductive to enhancing the dielectric coefficient and optimizing impedance matching. Moreover, the complex permittivity rises with the aspect ratio of the sheet. Under a suitable dimension, the flaky Fe3O4 could acquire targeted EM wave absorption capacity in the X band (8–12 GHz). In detail, the maximum reflection loss (RL) could reach a strong intensity of ‑49 dB at 2.05 mm. The effective absorption bandwidth (EAB) with RL below ‑10 dB is 4.32 (7.52–11.84) GHz, which is almost equivalent to the whole X band (8–12 GHz). Even more exciting, when regulating the thickness between 2.05 and 3.05 mm, the EAB could cover the entire C and X bands (4–12 GHz). This study provides a good reference for the future development of other ferromagnetic materials toward specific microwave bands.

  19. Quantum information processing with a travelling wave of light

    NASA Astrophysics Data System (ADS)

    Serikawa, Takahiro; Shiozawa, Yu; Ogawa, Hisashi; Takanashi, Naoto; Takeda, Shuntaro; Yoshikawa, Jun-ichi; Furusawa, Akira

    2018-02-01

    We exploit quantum information processing on a traveling wave of light, expecting emancipation from thermal noise, easy coupling to fiber communication, and potentially high operation speed. Although optical memories are technically challenging, we have an alternative approach to apply multi-step operations on traveling light, that is, continuous-variable one-way computation. So far our achievement includes generation of a one-million-mode entangled chain in time-domain, mode engineering of nonlinear resource states, and real-time nonlinear feedforward. Although they are implemented with free space optics, we are also investigating photonic integration and performed quantum teleportation with a passive liner waveguide chip as a demonstration of entangling, measurement, and feedforward. We also suggest a loop-based architecture as another model of continuous-variable computing.

  20. Impurity-Band Model for GaP1-xNx

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Fluegel, B.; Zhang, Y.; Geisz, J. F.

    2005-11-01

    Low-temperature absorption studies on free-standing GaP1-xNx films provide direct experimental evidence that the host conduction-band minimum (CBM) near X1C does not plunge downward with increased nitrogen doping, contrary to what has been suggested recently; rather, it remains stationary for x up to 0.1%. This fact, combined with the results of earlier studies of the CBM at ..GAMMA.. and conduction-band edge near L, confirms that the giant bandgap lowering observed in GaP1-xNx results from a CBM that evolves purely from nitrogen impurity bands.

  1. Computational methods and traveling wave solutions for the fourth-order nonlinear Ablowitz-Kaup-Newell-Segur water wave dynamical equation via two methods and its applications

    NASA Astrophysics Data System (ADS)

    Ali, Asghar; Seadawy, Aly R.; Lu, Dianchen

    2018-05-01

    The aim of this article is to construct some new traveling wave solutions and investigate localized structures for fourth-order nonlinear Ablowitz-Kaup-Newell-Segur (AKNS) water wave dynamical equation. The simple equation method (SEM) and the modified simple equation method (MSEM) are applied in this paper to construct the analytical traveling wave solutions of AKNS equation. The different waves solutions are derived by assigning special values to the parameters. The obtained results have their importance in the field of physics and other areas of applied sciences. All the solutions are also graphically represented. The constructed results are often helpful for studying several new localized structures and the waves interaction in the high-dimensional models.

  2. Traveling wave linear accelerator with RF power flow outside of accelerating cavities

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Dolgashev, Valery A.

    A high power RF traveling wave accelerator structure includes a symmetric RF feed, an input matching cell coupled to the symmetric RF feed, a sequence of regular accelerating cavities coupled to the input matching cell at an input beam pipe end of the sequence, one or more waveguides parallel to and coupled to the sequence of regular accelerating cavities, an output matching cell coupled to the sequence of regular accelerating cavities at an output beam pipe end of the sequence, and output waveguide circuit or RF loads coupled to the output matching cell. Each of the regular accelerating cavities hasmore » a nose cone that cuts off field propagating into the beam pipe and therefore all power flows in a traveling wave along the structure in the waveguide.« less

  3. Ultralow drive voltage silicon traveling-wave modulator.

    PubMed

    Baehr-Jones, Tom; Ding, Ran; Liu, Yang; Ayazi, Ali; Pinguet, Thierry; Harris, Nicholas C; Streshinsky, Matt; Lee, Poshen; Zhang, Yi; Lim, Andy Eu-Jin; Liow, Tsung-Yang; Teo, Selin Hwee-Gee; Lo, Guo-Qiang; Hochberg, Michael

    2012-05-21

    There has been great interest in the silicon platform as a material system for integrated photonics. A key challenge is the development of a low-power, low drive voltage, broadband modulator. Drive voltages at or below 1 Vpp are desirable for compatibility with CMOS processes. Here we demonstrate a CMOS-compatible broadband traveling-wave modulator based on a reverse-biased pn junction. We demonstrate operation with a drive voltage of 0.63 Vpp at 20 Gb/s, a significant improvement in the state of the art, with an RF energy consumption of only 200 fJ/bit.

  4. Lexical access and evoked traveling alpha waves.

    PubMed

    Zauner, Andrea; Gruber, Walter; Himmelstoß, Nicole Alexandra; Lechinger, Julia; Klimesch, Wolfgang

    2014-05-01

    Retrieval from semantic memory is usually considered within a time window around 300-600ms. Here we suggest that lexical access already occurs at around 100ms. This interpretation is based on the finding that semantically rich and frequent words exhibit a significantly shorter topographical latency difference between the site with the shortest P1 latency (leading site) and that with the longest P1 latency (trailing site). This latency difference can be described in terms of an evoked traveling alpha wave as was already shown in earlier studies. Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.

  5. Internal waves, Andaman Sea

    NASA Image and Video Library

    1994-09-30

    STS068-236-044 (30 September-11 October 1994) --- These internal waves in the Andaman Sea, west of Burma, were photographed from 115 nautical miles above Earth by the crew of the Space Shuttle Endeavour during the Space Radar Laboratory 2 (SRL-2) mission. The internal waves smooth out some of the capillary waves at the surface in bands and travel along the density discontinuity at the bottom of the mixed layer depth. There is little evidence of the internal waves at the surface. They are visible in the Space Shuttle photography because of sunglint, which reflects off the water.

  6. Searches for continuous gravitational waves from Scorpius X-1 and XTE J1751-305 in LIGO's sixth science run

    NASA Astrophysics Data System (ADS)

    Meadors, G. D.; Goetz, E.; Riles, K.; Creighton, T.; Robinet, F.

    2017-02-01

    Scorpius X-1 (Sco X-1) and x-ray transient XTE J1751-305 are low-mass x-ray binaries (LMXBs) that may emit continuous gravitational waves detectable in the band of ground-based interferometric observatories. Neutron stars in LMXBs could reach a torque-balance steady-state equilibrium in which angular momentum addition from infalling matter from the binary companion is balanced by angular momentum loss, conceivably due to gravitational-wave emission. Torque balance predicts a scale for detectable gravitational-wave strain based on observed x-ray flux. This paper describes a search for Sco X-1 and XTE J1751-305 in LIGO science run 6 data using the TwoSpect algorithm, based on searching for orbital modulations in the frequency domain. While no detections are claimed, upper limits on continuous gravitational-wave emission from Sco X-1 are obtained, spanning gravitational-wave frequencies from 40 to 2040 Hz and projected semimajor axes from 0.90 to 1.98 light-seconds. These upper limits are injection validated, equal any previous set in initial LIGO data, and extend over a broader parameter range. At optimal strain sensitivity, achieved at 165 Hz, the 95% confidence level random-polarization upper limit on dimensionless strain h0 is approximately 1.8 ×10-24. The closest approach to the torque-balance limit, within a factor of 27, is also at 165 Hz. Upper limits are set in particular narrow frequency bands of interest for J1751-305. These are the first upper limits known to date on r -mode emission from this XTE source. The TwoSpect method will be used in upcoming searches of Advanced LIGO and Virgo data.

  7. Technique Developed for Optimizing Traveling-Wave Tubes

    NASA Technical Reports Server (NTRS)

    Wilson, Jeffrey D.

    1999-01-01

    A traveling-wave tube (TWT) is an electron beam device that is used to amplify electromagnetic communication waves at radio and microwave frequencies. TWT s are critical components in deep-space probes, geosynchronous communication satellites, and high-power radar systems. Power efficiency is of paramount importance for TWT s employed in deep-space probes and communications satellites. Consequently, increasing the power efficiency of TWT s has been the primary goal of the TWT group at the NASA Lewis Research Center over the last 25 years. An in-house effort produced a technique (ref. 1) to design TWT's for optimized power efficiency. This technique is based on simulated annealing, which has an advantage over conventional optimization techniques in that it enables the best possible solution to be obtained (ref. 2). A simulated annealing algorithm was created and integrated into the NASA TWT computer model (ref. 3). The new technique almost doubled the computed conversion power efficiency of a TWT from 7.1 to 13.5 percent (ref. 1).

  8. Extended adiabatic blast waves and a model of the soft X-ray background. [interstellar matter

    NASA Technical Reports Server (NTRS)

    Cox, D. P.; Anderson, P. R.

    1981-01-01

    An analytical approximation is generated which follows the development of an adiabatic spherical blast wave in a homogeneous ambient medium of finite pressure. An analytical approximation is also presented for the electron temperature distribution resulting from coulomb collisional heating. The dynamical, thermal, ionization, and spectral structures are calculated for blast waves of energy E sub 0 = 5 x 10 to the 50th power ergs in a hot low-density interstellar environment. A formula is presented for estimating the luminosity evolution of such explosions. The B and C bands of the soft X-ray background, it is shown, are reproduced by such a model explosion if the ambient density is about .000004 cm, the blast radius is roughly 100 pc, and the solar system is located inside the shocked region. Evolution in a pre-existing cavity with a strong density gradient may, it is suggested, remove both the M band and OVI discrepancies.

  9. Defining a relationship between incident wave parameters and morphologic evolution of shoals on ebb tidal deltas using long term X-band radar observation from RIOS

    NASA Astrophysics Data System (ADS)

    Humberston, J. L.; McNinch, J.; Lippmann, T. C.

    2016-12-01

    The morphology of tidal inlet ebb-shoals varies dynamically over time, particularly in response to large wave events. Understanding which wave qualities most influence shoals' evolution would support advancements in sediment bypassing models as well as targeted maintenance dredging for hydrographic purposes. Unfortunately, shallow and rapidly changing bathymetry, turbid waters and ambiguous wave speeds resulting from multiple shoaling and de-shoaling areas limits many traditional surveying techniques from obtaining the spatial and temporal resolution necessary to effectively characterize shoal development. The Radar Inlet Observing System (RIOS) is a uniquely designed mobile X-band radar system that can be deployed to inlet environments and, using roof-mounted solar panels and an automatically triggered highly efficient diesel generator, run automated hourly collections and wirelessly stream data for up to several months at a time in nearly all weather and water conditions. During 2015 and early 2016, RIOS was deployed to St. Augustine Inlet, FL., New River Inlet, N.C., and Oregon Inlet, N.C. for periods of one to six months to allow for measureable shoal evolution. During deployments, ten minute collections (at 1 Hz) were conducted every hour and the data gridded to a 5m alongshore/cross-shore grid. Raw intensity returns were time-averaged and analyzed to define three metrics of shoal evolution: movement direction, movement velocity and inferred bathymetry. For each location and time period, wave frequencies, wave directions and significant wave heights were collected from the nearest wave-buoy. Time lapse videos of shoal positions were inspected and used in concert with cross-correlations values from each pair of shoal and wave parameters to determine the incident wave qualities most strongly relating to shoal evolution. Preliminary results suggest wave height, more than frequency, controls shoal movement. Wave direction and size collaboratively appear to direct

  10. Design, fabrication, and characterization of a valveless magnetic travelling-wave micropump

    NASA Astrophysics Data System (ADS)

    Yu, Huawei; Ye, Weixiang; Zhang, Wei; Yue, Zhao; Liu, Guohua

    2015-06-01

    In this paper, we propose a valveless magnetic micropump for lab-on-a-chip and microfluidic applications. The micropump, based on polydimethylsiloxane (PDMS) and polymethylmethacrylate (PMMA), consists primarily of a saw-toothed microchannel, two substrates, and two integrated NdFeB permanent magnetic arrays. The travelling wave beneath the top wall of the elastic microchannel can be induced by the proper magnetic pole orientation arrangement of these magnetic arrays, and the liquid particles are then transported along with the travelling wave in the microchannel. Appropriate geometry of the saw-toothed microchannel was also studied for optimizing the performance of the micropump. Experimental characterization of the micropump has been performed in terms of the frequency response of the flow rate and backpressure. The results demonstrate that this micropump is capable of reliably generating a maximum flow rate of 342.4 μL min-1 and operating against a high backpressure of 1.67 kPa.

  11. Delivery and application of precise timing for a traveling wave powerline fault locator system

    NASA Technical Reports Server (NTRS)

    Street, Michael A.

    1990-01-01

    The Bonneville Power Administration (BPA) has successfully operated an in-house developed powerline fault locator system since 1986. The BPA fault locator system consists of remotes installed at cardinal power transmission line system nodes and a central master which polls the remotes for traveling wave time-of-arrival data. A power line fault produces a fast rise-time traveling wave which emanates from the fault point and propagates throughout the power grid. The remotes time-tag the traveling wave leading edge as it passes through the power system cardinal substation nodes. A synchronizing pulse transmitted via the BPA analog microwave system on a wideband channel sychronizes the time-tagging counters in the remote units to a different accuracy of better than one microsecond. The remote units correct the raw time tags for synchronizing pulse propagation delay and return these corrected values to the fault locator master. The master then calculates the power system disturbance source using the collected time tags. The system design objective is a fault location accuracy of 300 meters. BPA's fault locator system operation, error producing phenomena, and method of distributing precise timing are described.

  12. The soft X-ray background as a supernova blast wave viewed from inside - Solar abundance models

    NASA Technical Reports Server (NTRS)

    Edgar, R. J.

    1986-01-01

    A model of the soft X-ray background is presented in which the sun is assumed to be inside an active supernova blast wave. The blast wave evolves in a preexisting cavity. The broad band surface brightnesses is explained by such a blast wave with an explosion energy of E sub approximately 5 x 10 to the 50th power ergs and radius 80 to 100 pc, using solar abundances. An approach to treating the problem of large anisotropies in the ambient medium is also explored, accommodating the observed anticorrelation between the soft X-ray surface brightness and the 21 cm column density. It is found that only for post shock temperatures below 10 to the 6 power K a shock propagating into a density enhancement will be dimmer than a similar shock in a lower density region.

  13. Banded Structures in Electron Pitch Angle Diffusion Coefficients from Resonant Wave Particle Interactions

    NASA Technical Reports Server (NTRS)

    Tripathi, A. K.; Singhal, R. P.; Khazanov, G. V.; Avanov, L. A.

    2016-01-01

    Electron pitch angle (D (alpha)) and momentum (D(pp)) diffusion coefficients have been calculated due to resonant interactions with electrostatic electron cyclotron harmonic (ECH) and whistler mode chorus waves. Calculations have been performed at two spatial locations L = 4.6 and 6.8 for electron energies 10 keV. Landau (n = 0) resonance and cyclotron harmonic resonances n = +/-1, +/-2,...+/-5 have been included in the calculations. It is found that diffusion coefficient versus pitch angle (alpha) profiles show large dips and oscillations or banded structures. The structures are more pronounced for ECH and lower band chorus (LBC) and particularly at location 4.6. Calculations of diffusion coefficients have also been performed for individual resonances. It is noticed that the main contribution of ECH waves in pitch angle diffusion coefficient is due to resonances n = +1 and n = +2. A major contribution to momentum diffusion coefficients appears from n = +2. However, the banded structures in D alpha and Dpp coefficients appear only in the profile of diffusion coefficients for n = +2. The contribution of other resonances to diffusion coefficients is found to be, in general, quite small or even negligible. For LBC and upper band chorus waves, the banded structures appear only in Landau resonance. The Dpp diffusion coefficient for ECH waves is one to two orders smaller than D alpha coefficients. For chorus waves, Dpp coefficients are about an order of magnitude smaller than D alpha coefficients for the case n does not = 0. In case of Landau resonance, the values of Dpp coefficient are generally larger than the values of D alpha coefficients particularly at lower energies. As an aid to the interpretation of results, we have also determined the resonant frequencies. For ECH waves, resonant frequencies have been estimated for wave normal angle 89 deg and harmonic resonances n = +1, +2, and +3, whereas for whistler mode waves, the frequencies have been calculated for angle

  14. A 2x2 W-Band Reference Time-Shifted Phase-Locked Transmitter Array in 65nm CMOS Technology

    NASA Technical Reports Server (NTRS)

    Tang, Adrian; Virbila, Gabriel; Hsiao, Frank; Wu, Hao; Murphy, David; Mehdi, Imran; Siegel, P. H.; Chang, M-C. Frank

    2013-01-01

    This paper presents a complete 2x2 phased array transmitter system operating at W-band (90-95 GHz) which employs a PLL reference time-shifting approach instead of using traditional mm-wave phase shifters. PLL reference shifting enables a phased array to be distributed over multiple chips without the need for coherent mm-wave signal distribution between chips. The proposed phased array transmitter system consumes 248 mW per array element when implemented in a 65 nm CMOS technology.

  15. Discrete-State Simulated Annealing For Traveling-Wave Tube Slow-Wave Circuit Optimization

    NASA Technical Reports Server (NTRS)

    Wilson, Jeffrey D.; Bulson, Brian A.; Kory, Carol L.; Williams, W. Dan (Technical Monitor)

    2001-01-01

    Algorithms based on the global optimization technique of simulated annealing (SA) have proven useful in designing traveling-wave tube (TWT) slow-wave circuits for high RF power efficiency. The characteristic of SA that enables it to determine a globally optimized solution is its ability to accept non-improving moves in a controlled manner. In the initial stages of the optimization, the algorithm moves freely through configuration space, accepting most of the proposed designs. This freedom of movement allows non-intuitive designs to be explored rather than restricting the optimization to local improvement upon the initial configuration. As the optimization proceeds, the rate of acceptance of non-improving moves is gradually reduced until the algorithm converges to the optimized solution. The rate at which the freedom of movement is decreased is known as the annealing or cooling schedule of the SA algorithm. The main disadvantage of SA is that there is not a rigorous theoretical foundation for determining the parameters of the cooling schedule. The choice of these parameters is highly problem dependent and the designer needs to experiment in order to determine values that will provide a good optimization in a reasonable amount of computational time. This experimentation can absorb a large amount of time especially when the algorithm is being applied to a new type of design. In order to eliminate this disadvantage, a variation of SA known as discrete-state simulated annealing (DSSA), was recently developed. DSSA provides the theoretical foundation for a generic cooling schedule which is problem independent, Results of similar quality to SA can be obtained, but without the extra computational time required to tune the cooling parameters. Two algorithm variations based on DSSA were developed and programmed into a Microsoft Excel spreadsheet graphical user interface (GUI) to the two-dimensional nonlinear multisignal helix traveling-wave amplifier analysis program TWA3

  16. Crosstalk effect and its mitigation in Aqua MODIS middle wave infrared bands

    NASA Astrophysics Data System (ADS)

    Sun, Junqiang; Madhavan, Sriharsha; Wang, Menghua

    2017-09-01

    The MODerate-resolution Imaging Spectroradiometer (MODIS) is one of the primary instruments in the National Aeronautics and Space Administration (NASA) Earth Observing System (EOS). The first MODIS instrument was launched in December 1999 on-board the Terra spacecraft. A follow on MODIS was launched on an afternoon orbit in 2002 and is aboard the Aqua spacecraft. Both MODIS instruments are very akin, has 36 bands, among which bands 20 to 25 are Middle Wave Infrared (MWIR) bands covering a wavelength range from approximately 3.750 μm to 4.515 μm. It was found that there was severe contamination in these bands early in mission but the effect has not been characterized and mitigated at the time. The crosstalk effect induces strong striping in the Earth View (EV) images and causes significant retrieval errors in the EV Brightness Temperature (BT) in these bands. An algorithm using a linear approximation derived from on-orbit lunar observations has been developed to correct the crosstalk effect and successfully applied to mitigate the effect in both Terra and Aqua MODIS Long Wave Infrared (LWIR) Photovoltaic (PV) bands. In this paper, the crosstalk effect in the Aqua MWIR bands is investigated and characterized by deriving the crosstalk coefficients using the scheduled Aqua MODIS lunar observations for the MWIR bands. It is shown that there are strong crosstalk contaminations among the five MWIR bands and they also have significant crosstalk contaminations from Short Wave Infrared (SWIR) bands. The crosstalk correction algorithm previously developed is applied to correct the crosstalk effect in these bands. It is demonstrated that the crosstalk correction successfully reduces the striping in the EV images and improves the accuracy of the EV BT in the five bands as was done similarly for LWIR PV bands. The crosstalk correction algorithm should thus be applied to improve both the image quality and radiometric accuracy of the Aqua MODIS MWIR bands Level 1B (L1B) products.

  17. Wide forbidden band induced by the interference of different transverse acoustic standing-wave modes

    NASA Astrophysics Data System (ADS)

    Tao, Zhiyong; He, Weiyu; Xiao, Yumeng; Wang, Xinlong

    2008-03-01

    A non-Bragg nature forbidden band is experimentally observed in an axially symmetric hard-walled duct with a periodically varying cross section. Unlike the familiar Bragg ones, the observed bandgap is found to result from the interference of sound wave modes having different transverse standing-wave profiles, the so-called non-Bragg resonance. The experiments also show that the non-Bragg band can be comparably wider than the Bragg one; furthermore, the sound transmission loss within the band can be much more effective, exhibiting the great significance of the non-Bragg resonance in wave propagation in periodic waveguides.

  18. X-Band Rapid-Scan Electron Paramagnetic Resonance of Radiation-Induced Defects in Tooth Enamel

    PubMed Central

    Yu, Zhelin; Romanyukha, Alexander; Eaton, Sandra S.; Eaton, Gareth R.

    2015-01-01

    X-band rapid-scan electron paramagnetic resonance (EPR) spectra from tooth enamel samples irradiated with doses of 0.5, 1 and 10 Gy had substantially improved signal-to-noise relative to conventional continuous wave EPR. The radiation-induced signal in 60 mg of a tooth enamel sample irradiated with a 0.5 Gy dose was readily characterized in spectra recorded with 34 min data acquisition times. The coefficient of variance of the calculated dose for a 1 Gy irradiated sample, based on simulation of the first-derivative spectra for three replicates as the sum of native and radiation-induced signals, was 3.9% for continuous wave and 0.4% for rapid scan. PMID:26207683

  19. X/X/Ka-band prime focus feed antenna for the Mars Observer beacon spacecraft

    NASA Technical Reports Server (NTRS)

    Stanton, P.; Reilly, H.; Esquivel, M.

    1988-01-01

    The results of an X/X/Ka-band feed design concept demonstration are presented. The purpose is to show the feasibility of adding a Ka-band beacon to the Mars Observer spacecraft. Scale model radiation patterns were made and analyzed.

  20. On exact traveling-wave solutions for local fractional Korteweg-de Vries equation.

    PubMed

    Yang, Xiao-Jun; Tenreiro Machado, J A; Baleanu, Dumitru; Cattani, Carlo

    2016-08-01

    This paper investigates the Korteweg-de Vries equation within the scope of the local fractional derivative formulation. The exact traveling wave solutions of non-differentiable type with the generalized functions defined on Cantor sets are analyzed. The results for the non-differentiable solutions when fractal dimension is 1 are also discussed. It is shown that the exact solutions for the local fractional Korteweg-de Vries equation characterize the fractal wave on shallow water surfaces.

  1. Power System Transient Diagnostics Based on Novel Traveling Wave Detection

    NASA Astrophysics Data System (ADS)

    Hamidi, Reza Jalilzadeh

    Modern electrical power systems demand novel diagnostic approaches to enhancing the system resiliency by improving the state-of-the-art algorithms. The proliferation of high-voltage optical transducers and high time-resolution measurements provide opportunities to develop novel diagnostic methods of very fast transients in power systems. At the same time, emerging complex configuration, such as multi-terminal hybrid transmission systems, limits the applications of the traditional diagnostic methods, especially in fault location and health monitoring. The impedance-based fault-location methods are inefficient for cross-bounded cables, which are widely used for connection of offshore wind farms to the main grid. Thus, this dissertation first presents a novel traveling wave-based fault-location method for hybrid multi-terminal transmission systems. The proposed method utilizes time-synchronized high-sampling voltage measurements. The traveling wave arrival times (ATs) are detected by observation of the squares of wavelet transformation coefficients. Using the ATs, an over-determined set of linear equations are developed for noise reduction, and consequently, the faulty segment is determined based on the characteristics of the provided equation set. Then, the fault location is estimated. The accuracy and capabilities of the proposed fault location method are evaluated and also compared to the existing traveling-wave-based method for a wide range of fault parameters. In order to improve power systems stability, auto-reclosing (AR), single-phase auto-reclosing (SPAR), and adaptive single-phase auto-reclosing (ASPAR) methods have been developed with the final objectives of distinguishing between the transient and permanent faults to clear the transient faults without de-energization of the solid phases. However, the features of the electrical arcs (transient faults) are severely influenced by a number of random parameters, including the convection of the air and plasma

  2. Stability and instability of periodic travelling wave solutions for the critical Korteweg-de Vries and nonlinear Schrödinger equations

    NASA Astrophysics Data System (ADS)

    Angulo Pava, Jaime; Natali, Fábio M. Amorin

    2009-04-01

    In this paper we establish new results about the existence, stability, and instability of periodic travelling wave solutions related to the critical Korteweg-de Vries equation ut+5u4ux+u=0, and the critical nonlinear Schrödinger equation ivt+v+|v=0. The periodic travelling wave solutions obtained in our study tend to the classical solitary wave solutions in the infinite wavelength scenario. The stability approach is based on the theory developed by Angulo & Natali in [J. Angulo, F. Natali, Positivity properties of the Fourier transform and the stability of periodic travelling wave solutions, SIAM J. Math. Anal. 40 (2008) 1123-1151] for positive periodic travelling wave solutions associated to dispersive evolution equations of Korteweg-de Vries type. The instability approach is based on an extension to the periodic setting of arguments found in Bona & Souganidis & Strauss [J.L. Bona, P.E. Souganidis, W.A. Strauss, Stability and instability of solitary waves of Korteweg-de Vries type, Proc. Roy. Soc. London Ser. A 411 (1987) 395-412]. Regarding the critical Schrödinger equation stability/instability theories similar to the critical Korteweg-de Vries equation are obtained by using the classical Grillakis & Shatah & Strauss theory in [M. Grillakis, J. Shatah, W. Strauss, Stability theory of solitary waves in the presence of symmetry II, J. Funct. Anal. 94 (1990) 308-348; M. Grillakis, J. Shatah, W. Strauss, Stability theory of solitary waves in the presence of symmetry I, J. Funct. Anal. 74 (1987) 160-197]. The arguments presented in this investigation have prospects for the study of the stability of periodic travelling wave solutions of other nonlinear evolution equations.

  3. Standard Observing Bands: Is Now the Time to Replace S/X with X/Ka?

    NASA Technical Reports Server (NTRS)

    Jacobs, C. S.; Lanyi, G. E.; Naudet, C. J.

    2004-01-01

    In this paper we will argue that the VLBI community should be developing a road map to transition from S/X to simultaneous X and Ka-band (32 GHz) observations. There are both negative and positive reasons for planning such a transition. On the negative side, we will outline concerns that S-band observations may be headed toward obsolescence. On the positive side, we will refer to evidence that X/Ka has potential for providing a more stable reference frame than S/X. We will propose timetables for a transition to X/Ka observing starting from the current status of X/Ka and plans that are now taking shape. First X/Ka fringes were obtained in 2001 with the Deep Space Network. Future plans will be discussed including a proposed X/Ka-band upgrade to the VLBA. Lastly, we will consider the need for a period of overlap between S/X and X/Ka so that the long and rich history of astrometric and geodetic VLBI is not compromised.

  4. Traveling waves in Hall-magnetohydrodynamics and the ion-acoustic shock structure

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hagstrom, George I.; Hameiri, Eliezer

    Hall-magnetohydrodynamics (HMHD) is a mixed hyperbolic-parabolic partial differential equation that describes the dynamics of an ideal two fluid plasma with massless electrons. We study the only shock wave family that exists in this system (the other discontinuities being contact discontinuities and not shocks). We study planar traveling wave solutions and we find solutions with discontinuities in the hydrodynamic variables, which arise due to the presence of real characteristics in Hall-MHD. We introduce a small viscosity into the equations and use the method of matched asymptotic expansions to show that solutions with a discontinuity satisfying the Rankine-Hugoniot conditions and also anmore » entropy condition have continuous shock structures. The lowest order inner equations reduce to the compressible Navier-Stokes equations, plus an equation which implies the constancy of the magnetic field inside the shock structure. We are able to show that the current is discontinuous across the shock, even as the magnetic field is continuous, and that the lowest order outer equations, which are the equations for traveling waves in inviscid Hall-MHD, are exactly integrable. We show that the inner and outer solutions match, which allows us to construct a family of uniformly valid continuous composite solutions that become discontinuous when the diffusivity vanishes.« less

  5. High Power Broadband Millimeter Wave TWTs

    NASA Astrophysics Data System (ADS)

    James, Bill G.

    1998-04-01

    In the early 1980's the requirement for high power broadband millimeter wave sources encouraged the development of microwave vacuum device amplifiers for radar and communication systems. Many government funded programs were implemented for the development of high power broadband millimeter wave amplifiers that would meet the needs of the high power community. The tube design capable of meeting these goals was the slow wave coupled cavity traveling wave device, which had a proven technology base at the lower frequencies (X Band). However scaling this technology to the millimeter frequencies had severe shortcomings in both thermal and manufacturing design. These shortcomings were overcome with the development of the Ladder Circuit technology. In conjunction with the circuit development high power electron beam systems had to be developed for the generation of high rf powers. These beam systems had to be capable of many megawatts of beam power density and high current densities. The cathode technology required to be capable of operating at current densities of 10 amperes per square centimeter at long pulse lengths and high duty cycle. Since the introduction of the Ladder Circuit technology a number of high power broadband millimeter wave amplifiers have been developed and deployed in operating radar and communication systems. Broadband millimeter wave sources have been manufactured in the frequency range from 27 GHz to 100 GHz with power levels ranging from 100 watts CW to 10 kilowatts Peak at W band over a 2 GHz bandwidth. Also a 50 kW peak power and 10 kW average power device at Ka band with 2 GHz bandwidth has been developed. Today the power levels achieved by these devices are nearing the limits of this technology; therefore to gain a significant increase in power at the millimeter wave frequencies, other technologies will have to be considered, particularly fast wave devices. This paper will briefly review the ladder circuit technology and present the designs of

  6. Exact traveling wave solutions of the KP-BBM equation by using the new approach of generalized (G'/G)-expansion method.

    PubMed

    Alam, Md Nur; Akbar, M Ali

    2013-01-01

    The new approach of the generalized (G'/G)-expansion method is an effective and powerful mathematical tool in finding exact traveling wave solutions of nonlinear evolution equations (NLEEs) in science, engineering and mathematical physics. In this article, the new approach of the generalized (G'/G)-expansion method is applied to construct traveling wave solutions of the Kadomtsev-Petviashvili-Benjamin-Bona-Mahony (KP-BBM) equation. The solutions are expressed in terms of the hyperbolic functions, the trigonometric functions and the rational functions. By means of this scheme, we found some new traveling wave solutions of the above mentioned equation.

  7. Orbital stability of periodic traveling-wave solutions for the log-KdV equation

    NASA Astrophysics Data System (ADS)

    Natali, Fábio; Pastor, Ademir; Cristófani, Fabrício

    2017-09-01

    In this paper we establish the orbital stability of periodic waves related to the logarithmic Korteweg-de Vries equation. Our motivation is inspired in the recent work [3], in which the authors established the well-posedness and the linear stability of Gaussian solitary waves. By using the approach put forward recently in [20] to construct a smooth branch of periodic waves as well as to get the spectral properties of the associated linearized operator, we apply the abstract theories in [13] and [25] to deduce the orbital stability of the periodic traveling waves in the energy space.

  8. Characterization of edge oscillation in a traveling-wave field-effect transistor.

    PubMed

    Narahara, Koichi

    2013-07-01

    In this study, we characterize the oscillating pulse edges developed in a traveling-wave field-effect transistor (TWFET). Recently, it has been found that a stable shock front can develop on a TWFET, which can travel in one direction only. Once the reflected pulse edge at the far end is transmitted to the input, the shock front develops and begins to travel on the device again. This process establishes a permanent edge oscillation. This paper discusses the device setup necessary to excite such oscillations and how pulse edges oscillate on a TWFET. By applying the phase reduction scheme to the transmission equations of a TWFET, we obtain phase sensitivity, which appropriately explains the measured spatial dependence of the locking range in frequency. Moreover, multiple oscillating edges can develop simultaneously, which are mutually synchronized. The dynamics of these multiple edges are also described.

  9. Three-Dimensional Simulation of Traveling-Wave Tube Cold-Test Characteristics Using MAFIA

    NASA Technical Reports Server (NTRS)

    Kory, Carol L.; Wilson, Jeffrey D.

    1995-01-01

    The three-dimensional simulation code MAFIA was used to compute the cold-test parameters - frequency-phase dispersion, beam on-axis interaction impedance, and attenuation - for two types of traveling-wave tube (TWT) slow-wave circuits. The potential for this electromagnetic computer modeling code to reduce the time and cost of TWT development is demonstrated by the high degree of accuracy achieved in calculating these parameters. Generalized input files were developed for ferruled coupled-cavity and TunneLadder slow-wave circuits. These files make it easy to model circuits of arbitrary dimensions. The utility of these files was tested by applying each to a specific TWT slow-wave circuit and comparing the results with experimental data. Excellent agreement was obtained.

  10. Noninvasive in vivo imaging reveals differences between tectorial membrane and basilar membrane traveling waves in the mouse cochlea

    PubMed Central

    Lee, Hee Yoon; Raphael, Patrick D.; Park, Jesung; Ellerbee, Audrey K.; Applegate, Brian E.; Oghalai, John S.

    2015-01-01

    Sound is encoded within the auditory portion of the inner ear, the cochlea, after propagating down its length as a traveling wave. For over half a century, vibratory measurements to study cochlear traveling waves have been made using invasive approaches such as laser Doppler vibrometry. Although these studies have provided critical information regarding the nonlinear processes within the living cochlea that increase the amplitude of vibration and sharpen frequency tuning, the data have typically been limited to point measurements of basilar membrane vibration. In addition, opening the cochlea may alter its function and affect the findings. Here we describe volumetric optical coherence tomography vibrometry, a technique that overcomes these limitations by providing depth-resolved displacement measurements at 200 kHz inside a 3D volume of tissue with picometer sensitivity. We studied the mouse cochlea by imaging noninvasively through the surrounding bone to measure sound-induced vibrations of the sensory structures in vivo, and report, to our knowledge, the first measures of tectorial membrane vibration within the unopened cochlea. We found that the tectorial membrane sustains traveling wave propagation. Compared with basilar membrane traveling waves, tectorial membrane traveling waves have larger dynamic ranges, sharper frequency tuning, and apically shifted positions of peak vibration. These findings explain discrepancies between previously published basilar membrane vibration and auditory nerve single unit data. Because the tectorial membrane directly overlies the inner hair cell stereociliary bundles, these data provide the most accurate characterization of the stimulus shaping the afferent auditory response available to date. PMID:25737536

  11. Cloud-based design of high average power traveling wave linacs

    NASA Astrophysics Data System (ADS)

    Kutsaev, S. V.; Eidelman, Y.; Bruhwiler, D. L.; Moeller, P.; Nagler, R.; Barbe Welzel, J.

    2017-12-01

    The design of industrial high average power traveling wave linacs must accurately consider some specific effects. For example, acceleration of high current beam reduces power flow in the accelerating waveguide. Space charge may influence the stability of longitudinal or transverse beam dynamics. Accurate treatment of beam loading is central to the design of high-power TW accelerators, and it is especially difficult to model in the meter-scale region where the electrons are nonrelativistic. Currently, there are two types of available codes: tracking codes (e.g. PARMELA or ASTRA) that cannot solve self-consistent problems, and particle-in-cell codes (e.g. Magic 3D or CST Particle Studio) that can model the physics correctly but are very time-consuming and resource-demanding. Hellweg is a special tool for quick and accurate electron dynamics simulation in traveling wave accelerating structures. The underlying theory of this software is based on the differential equations of motion. The effects considered in this code include beam loading, space charge forces, and external magnetic fields. We present the current capabilities of the code, provide benchmarking results, and discuss future plans. We also describe the browser-based GUI for executing Hellweg in the cloud.

  12. Band gap bowing in NixMg1−xO

    PubMed Central

    Niedermeier, Christian A.; Råsander, Mikael; Rhode, Sneha; Kachkanov, Vyacheslav; Zou, Bin; Alford, Neil; Moram, Michelle A.

    2016-01-01

    Epitaxial transparent oxide NixMg1−xO (0 ≤ x ≤ 1) thin films were grown on MgO(100) substrates by pulsed laser deposition. High-resolution synchrotron X-ray diffraction and high-resolution transmission electron microscopy analysis indicate that the thin films are compositionally and structurally homogeneous, forming a completely miscible solid solution. Nevertheless, the composition dependence of the NixMg1−xO optical band gap shows a strong non-parabolic bowing with a discontinuity at dilute NiO concentrations of x < 0.037. Density functional calculations of the NixMg1−xO band structure and the density of states demonstrate that deep Ni 3d levels are introduced into the MgO band gap, which significantly reduce the fundamental gap as confirmed by optical absorption spectra. These states broaden into a Ni 3d-derived conduction band for x > 0.074 and account for the anomalously large band gap narrowing in the NixMg1−xO solid solution system. PMID:27503808

  13. Traveling wave solutions and conservation laws for nonlinear evolution equation

    NASA Astrophysics Data System (ADS)

    Baleanu, Dumitru; Inc, Mustafa; Yusuf, Abdullahi; Aliyu, Aliyu Isa

    2018-02-01

    In this work, the Riccati-Bernoulli sub-ordinary differential equation and modified tanh-coth methods are used to reach soliton solutions of the nonlinear evolution equation. We acquire new types of traveling wave solutions for the governing equation. We show that the equation is nonlinear self-adjoint by obtaining suitable substitution. Therefore, we construct conservation laws for the equation using new conservation theorem. The obtained solutions in this work may be used to explain and understand the physical nature of the wave spreads in the most dispersive medium. The constraint condition for the existence of solitons is stated. Some three dimensional figures for some of the acquired results are illustrated.

  14. Time-domain theory of gyrotron traveling wave amplifiers operating at grazing incidence

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ginzburg, N. S., E-mail: ginzburg@appl.sci-nnov.ru; Nizhny Novgorod State University, Gagarin Ave., 23, 603950 Nizhny Novgorod; Sergeev, A. S.

    Time-domain theory of the gyrotron traveling wave tube (gyro-TWT) operating at grazing incidence has been developed. The theory is based on a description of wave propagation by a parabolic equation. The results of the simulations are compared with experimental results of the observation of subnanosecond pulse amplification in a gyro-TWT consisting of three gain sections separated by severs. The theory developed can also be used successfully for a description of amplification of monochromatic signals.

  15. Short-arc orbit determination using coherent X-band ranging data

    NASA Technical Reports Server (NTRS)

    Thurman, S. W.; Mcelrath, T. P.; Pollmeier, V. M.

    1992-01-01

    The use of X-band frequencies in ground-spacecraft and spacecraft-ground telecommunication links for current and future robotic interplanetary missions makes it possible to perform ranging measurements of greater accuracy than previously obtained. It is shown that ranging data of sufficient accuracy, when acquired from multiple stations, can sense the geocentric angular position of a distant spacecraft. The application of high-accuracy S/X-band and X-band ranging to orbit determination with relatively short data arcs is investigated in planetary approach and encounter scenarios. Actual trajectory solutions for the Ulysses spacecraft constructed from S/X-band ranging and Doppler data are presented; error covariance calculations are used to predict the performance of X-band ranging and Doppler data. The Ulysses trajectory solutions indicate that the aim point for the spacecraft's February 1992 Jupiter encounter was predicted to a geocentric accuracy of 0.20 to 0.23/microrad. Explicit modeling of range bias parameters for each station pass is shown to largely remove systematic ground system calibration errors and transmission media effects from the Ulysses range measurements, which would otherwise corrupt the angle finding capabilities of the data. The Ulysses solutions were found to be reasonably consistent with the theoretical results, which suggest that angular accuracies of 0.08 to 0.1/microrad are achievable with X-band ranging.

  16. Traveling-Wave Tube Amplifier Model to Predict High-Order Modulation Intersymbol Interference

    NASA Technical Reports Server (NTRS)

    Kory, Carol L.; Andro, Monty; Williams, W. D. (Technical Monitor)

    2001-01-01

    Demands for increased data rates in satellite communications necessitate higher order modulation schemes, larger system bandwidth, and minimum distortion of the modulated signal as it is passed through the traveling wave tube amplifier (TWTA). One type of distortion that the TWTA contributes to is intersymbol interference (ISI), and this becomes particularly disruptive with wide-band, complex modulation schemes. It is suspected that in addition to the dispersion of the TWT, frequency dependent reflections due to mismatches within the TWT are a significant contributor to ISI. To experimentally investigate the effect of these mismatches within the physical TWT on ISI would be prohibitively expensive, as it would require manufacturing numerous amplifiers in addition to the acquisition of the required digital hardware. In an attempt to develop a more accurate model to correlate IS1 with the TWTA and the operational signal, a fully three-dimensional (3D), time-dependent, TWT interaction model has been developed using the electromagnetic particle-in-cell (PIC) code MAFIA (solution of Maxwell's equations by the Finite-Integration-Algorithm). The model includes a user defined slow-wave circuit with a spatially tapered region of loss to implement a sever, and spatially varied geometry (such as helical pitch) to implement a phase velocity taper. The model also includes user defined input/output coupling and an electron beam contained by solenoidal, electrostatic, or periodic permanent magnet (PPM) focusing allowing standard or novel TWTs to be investigated. This model comprehensively takes into account the effects of frequency dependent nonlinear distortions (MAM and AMPM); gain ripple due to frequency dependent reflections at the input/output coupling, severs, and mismatches from dynamic pitch variations; drive induced oscillations; harmonic generation; intermodulation products; and backward waves.

  17. Some new traveling wave exact solutions of the (2+1)-dimensional Boiti-Leon-Pempinelli equations.

    PubMed

    Qi, Jian-ming; Zhang, Fu; Yuan, Wen-jun; Huang, Zi-feng

    2014-01-01

    We employ the complex method to obtain all meromorphic exact solutions of complex (2+1)-dimensional Boiti-Leon-Pempinelli equations (BLP system of equations). The idea introduced in this paper can be applied to other nonlinear evolution equations. Our results show that all rational and simply periodic traveling wave exact solutions of the equations (BLP) are solitary wave solutions, the complex method is simpler than other methods, and there exist some rational solutions ur,2 (z) and simply periodic solutions us,2-6(z) which are not only new but also not degenerated successively by the elliptic function solutions. We believe that this method should play an important role for finding exact solutions in the mathematical physics. For these new traveling wave solutions, we give some computer simulations to illustrate our main results.

  18. Periodic wave, breather wave and travelling wave solutions of a (2 + 1)-dimensional B-type Kadomtsev-Petviashvili equation in fluids or plasmas

    NASA Astrophysics Data System (ADS)

    Hu, Wen-Qiang; Gao, Yi-Tian; Jia, Shu-Liang; Huang, Qian-Min; Lan, Zhong-Zhou

    2016-11-01

    In this paper, a (2 + 1)-dimensional B-type Kadomtsev-Petviashvili equation is investigated, which has been presented as a model for the shallow water wave in fluids or the electrostatic wave potential in plasmas. By virtue of the binary Bell polynomials, the bilinear form of this equation is obtained. With the aid of the bilinear form, N -soliton solutions are obtained by the Hirota method, periodic wave solutions are constructed via the Riemann theta function, and breather wave solutions are obtained according to the extended homoclinic test approach. Travelling waves are constructed by the polynomial expansion method as well. Then, the relations between soliton solutions and periodic wave solutions are strictly established, which implies the asymptotic behaviors of the periodic waves under a limited procedure. Furthermore, we obtain some new solutions of this equation by the standard extended homoclinic test approach. Finally, we give a generalized form of this equation, and find that similar analytical solutions can be obtained from the generalized equation with arbitrary coefficients.

  19. A finite volume method and experimental study of a stator of a piezoelectric traveling wave rotary ultrasonic motor.

    PubMed

    Bolborici, V; Dawson, F P; Pugh, M C

    2014-03-01

    Piezoelectric traveling wave rotary ultrasonic motors are motors that generate torque by using the friction force between a piezoelectric composite ring (or disk-shaped stator) and a metallic ring (or disk-shaped rotor) when a traveling wave is excited in the stator. The motor speed is proportional to the amplitude of the traveling wave and, in order to obtain large amplitudes, the stator is excited at frequencies close to its resonance frequency. This paper presents a non-empirical partial differential equations model for the stator, which is discretized using the finite volume method. The fundamental frequency of the discretized model is computed and compared to the experimentally-measured operating frequency of the stator of Shinsei USR60 piezoelectric motor. Copyright © 2013 Elsevier B.V. All rights reserved.

  20. A doubly curved reflector X-band antenna with integrated IFF array

    NASA Astrophysics Data System (ADS)

    Alia, F.; Barbati, S.

    Primary radar antennas and Identification Friend or Foe (IFF) antennas must rotate with the same speed and synchronism, so that the target echo and IFF transponder mark will appear to the operator at the same time and at the same angular direction. A doubly-curved reflector antenna with a six-element microstrip array integrated in the reflector surface is presented to meet this requirement. The main antenna operates at X-band for low angle search radar, while the secondary antenna operates at L-band for IFF functions. The new configuration minimizes masking of the X-band radiated energy as a result of the IFF L-band elements. In fact, the only effect of the microstrip array on the X-band radiation pattern is the presence of several sidelobes in the + or - 90 deg angular region. The proposed new solution is compared to three other L-band/X-band integrated antenna configurations, and is found to be more advantageous with respect to masking, mechanical aspects, and production costs.

  1. Banded structures in electron pitch angle diffusion coefficients from resonant wave-particle interactions

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Tripathi, A. K., E-mail: aktrip2001@yahoo.co.in; Singhal, R. P., E-mail: rpsiitbhu@yahoo.com; Khazanov, G. V., E-mail: George.V.Khazanov@nasa.gov

    2016-04-15

    Electron pitch angle (D{sub αα}) and momentum (D{sub pp}) diffusion coefficients have been calculated due to resonant interactions with electrostatic electron cyclotron harmonic (ECH) and whistler mode chorus waves. Calculations have been performed at two spatial locations L = 4.6 and 6.8 for electron energies ≤10 keV. Landau (n = 0) resonance and cyclotron harmonic resonances n = ±1, ±2, … ±5 have been included in the calculations. It is found that diffusion coefficient versus pitch angle (α) profiles show large dips and oscillations or banded structures. The structures are more pronounced for ECH and lower band chorus (LBC) and particularly at location 4.6. Calculations of diffusionmore » coefficients have also been performed for individual resonances. It is noticed that the main contribution of ECH waves in pitch angle diffusion coefficient is due to resonances n = +1 and n = +2. A major contribution to momentum diffusion coefficients appears from n = +2. However, the banded structures in D{sub αα} and D{sub pp} coefficients appear only in the profile of diffusion coefficients for n = +2. The contribution of other resonances to diffusion coefficients is found to be, in general, quite small or even negligible. For LBC and upper band chorus waves, the banded structures appear only in Landau resonance. The D{sub pp} diffusion coefficient for ECH waves is one to two orders smaller than D{sub αα} coefficients. For chorus waves, D{sub pp} coefficients are about an order of magnitude smaller than D{sub αα} coefficients for the case n ≠ 0. In case of Landau resonance, the values of D{sub pp} coefficient are generally larger than the values of D{sub αα} coefficients particularly at lower energies. As an aid to the interpretation of results, we have also determined the resonant frequencies. For ECH waves, resonant frequencies have been estimated for wave normal angle 89° and harmonic resonances n = +1, +2, and

  2. Banded Structures in Electron Pitch Angle Diffusion Coefficients from Resonant Wave-Particle Interactions

    NASA Technical Reports Server (NTRS)

    Tripathi, A. K.; Singhal, R. P.; Khazanov, G. V.; Avanov, L. A.

    2016-01-01

    Electron pitch angle (D(sub (alpha alpha))) and momentum (D(sub pp)) diffusion coefficients have been calculated due to resonant interactions with electrostatic electron cyclotron harmonic (ECH) and whistler mode chorus waves. Calculations have been performed at two spatial locations L=4.6 and 6.8 for electron energies less than or equal to 10 keV. Landau (n=0) resonance and cyclotron harmonic resonances n= +/- 1, +/-2, ... +/-5 have been included in the calculations. It is found that diffusion coefficient versus pitch angle (alpha) profiles show large dips and oscillations or banded structures. The structures are more pronounced for ECH and lower band chorus (LBC) and particularly at location 4.6. Calculations of diffusion coefficients have also been performed for individual resonances. It is noticed that the main contribution of ECH waves in pitch angle diffusion coefficient is due to resonances n=+1 and n=+2. A major contribution to momentum diffusion coefficients appears from n=+2. However, the banded structures in D(sub alpha alpha) and D(sub pp) coefficients appear only in the profile of diffusion coefficients for n=+2. The contribution of other resonances to diffusion coefficients is found to be, in general, quite small or even negligible. For LBC and upper band chorus waves, the banded structures appear only in Landau resonance. The D(sub pp) diffusion coefficient for ECH waves is one to two orders smaller than D(sub alpha alpha) coefficients. For chorus waves, D(sub pp) coefficients are about an order of magnitude smaller than D(sub alpha alpha) coefficients for the case n does not equal 0. In case of Landau resonance, the values of D(sub pp) coefficient are generally larger than the values of D(sub alpha alpha) coefficients particularly at lower energies. As an aid to the interpretation of results, we have also determined the resonant frequencies. For ECH waves, resonant frequencies have been estimated for wave normal angle 89 deg and harmonic resonances

  3. FOUR WAVE MIXING SPECTROSCOPY OF THE NO_3 tilde{B} ^2E' - tilde{X} ^2A_2' transition

    NASA Astrophysics Data System (ADS)

    Fukushima, Masaru; Ishiwata, Takashi

    2014-06-01

    The tilde{B} ^2E' - tilde{X} ^2A_2' electronic transition of NO_3 generated in a supersonic free jet expansion was investigated by four wave mixing ( 4WM ) spectroscopy. The degenerated 4WM and laser induced fluorescence ( LIF ) spectra around the 0_0^0 band region were measured simultaneously. The D4WM spectrum shows broad band features for the 0_0^0 band similar to that of the LIF spectrum. The broad 0_0^0 band does not consist of one sub-band, but of several bands. The intensity distribution of the sub-bands of the D4WM spectrum is similar, but not identical to that of the LIF spectrum.

  4. Energy Flux in the Cochlea: Evidence Against Power Amplification of the Traveling Wave.

    PubMed

    van der Heijden, Marcel; Versteegh, Corstiaen P C

    2015-10-01

    Traveling waves in the inner ear exhibit an amplitude peak that shifts with frequency. The peaking is commonly believed to rely on motile processes that amplify the wave by inserting energy. We recorded the vibrations at adjacent positions on the basilar membrane in sensitive gerbil cochleae and tested the putative power amplification in two ways. First, we determined the energy flux of the traveling wave at its peak and compared it to the acoustic power entering the ear, thereby obtaining the net cochlear power gain. For soft sounds, the energy flux at the peak was 1 ± 0.6 dB less than the middle ear input power. For more intense sounds, increasingly smaller fractions of the acoustic power actually reached the peak region. Thus, we found no net power amplification of soft sounds and a strong net attenuation of intense sounds. Second, we analyzed local wave propagation on the basilar membrane. We found that the waves slowed down abruptly when approaching their peak, causing an energy densification that quantitatively matched the amplitude peaking, similar to the growth of sea waves approaching the beach. Thus, we found no local power amplification of soft sounds and strong local attenuation of intense sounds. The most parsimonious interpretation of these findings is that cochlear sensitivity is not realized by amplifying acoustic energy, but by spatially focusing it, and that dynamic compression is realized by adjusting the amount of dissipation to sound intensity.

  5. Inflatable Antenna for CubeSat: Extension of the Previously Developed S-Band Design to the X-Band

    NASA Technical Reports Server (NTRS)

    Babuscia, Alessandra; Choi, Thomas; Cheung, Kar-Ming; Thangavelautham, Jekan; Ravichandran, Mithun; Chandra, Aman

    2015-01-01

    The inflatable antenna for CubeSat is a 1 meter antenna reflector designed with one side reflective Mylar, another side clear Mylar with a patch antenna at the focus. The development of this technology responds to the increasing need for more capable communication systems to allow CubeSats to operate autonomously in interplanetary missions. An initial version of the antenna for the S-Band was developed and tested in both anechoic chamber and vacuum chamber. Recent developments in transceivers and amplifiers for CubeSat at X-band motivated the extension from the S-Band to the X-Band. This paper describes the process of extending the design of the antenna to the X-Band focusing on patch antenna redesign, new manufacturing challenges and initial results of experimental tests.

  6. Wave-function-based approach to quasiparticle bands: Insight into the electronic structure of c-ZnS

    NASA Astrophysics Data System (ADS)

    Stoyanova, A.; Hozoi, L.; Fulde, P.; Stoll, H.

    2011-05-01

    Ab initio wave-function-based methods are employed for the study of quasiparticle energy bands of zinc-blende ZnS, with focus on the Zn 3d “semicore” states. The relative energies of these states with respect to the top of the S 3p valence bands appear to be poorly described as compared to experimental values not only within the local density approximation (LDA), but also when many-body corrections within the GW approximation are applied to the LDA or LDA + U mean-field solutions [T. Miyake, P. Zhang, M. L. Cohen, and S. G. Louie, Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.74.245213 74, 245213 (2006)]. In the present study, we show that for the accurate description of the Zn 3d states a correlation treatment based on wave-function methods is needed. Our study rests on a local Hamiltonian approach which rigorously describes the short-range polarization and charge redistribution effects around an extra hole or electron placed into the valence respective conduction bands of semiconductors and insulators. The method also facilitates the computation of electron correlation effects beyond relaxation and polarization. The electron correlation treatment is performed on finite clusters cut off the infinite system. The formalism makes use of localized Wannier functions and embedding potentials derived explicitly from prior periodic Hartree-Fock calculations. The on-site and nearest-neighbor charge relaxation lead to corrections of several eV to the Hartree-Fock band energies and gap. Corrections due to long-range polarization are of the order of 1.0 eV. The dispersion of the Hartree-Fock bands is only slightly affected by electron correlations. We find the Zn 3d “semicore” states to lie ~9.0 eV below the top of the S 3p valence bands, in very good agreement with values from valence-band x-ray photoemission.

  7. Evanescent waves and deaf bands in sonic crystals

    NASA Astrophysics Data System (ADS)

    Romero-García, V.; Garcia-Raffi, L. M.; Sánchez-Pérez, J. V.

    2011-12-01

    The properties of sonic crystals (SC) are theoretically investigated in this work by solving the inverse problem k(ω) using the extended plane wave expansion (EPWE). The solution of the resulting eigenvalue problem gives the complex band structure which takes into account both the propagating and the evanescent modes. In this work we show the complete mathematical formulation of the EPWE for SC and the supercell approximation for its use in both a complete SC and a SC with defects. As an example we show a novel interpretation of the deaf bands in a complete SC in good agreement with multiple scattering simulations.

  8. Survey of upper band chorus and ECH waves: Implications for the diffuse aurora

    NASA Astrophysics Data System (ADS)

    Meredith, Nigel; Horne, Richard; Thorne, Richard; Anderson, Roger

    2010-05-01

    The origin of the diffuse aurora has been a source of controversy for many years. More recently the question has taken a new significance in view of the associated changes in atmospheric chemistry which may affect the middle atmosphere. Here we use CRRES data to assess the importance of upper band chorus and electron cyclotron harmonic (ECH) waves in the production of the diffuse aurora. Both wave modes increase with increasing geomagnetic activity, suggesting they are related to periods of enhanced convection and/or substorm activity. They are confined to the near-equatorial region which excludes the pre-noon sector from the wave survey. During active conditions intense ECH waves and upper band chorus, with amplitudes exceeding 1 mVm-1, are observed in the region 4 < L < 7 from 2100 to 0600 MLT approximately 20% and 6% of the time respectively. This suggests that both wave modes can put electrons on strong diffusion, but only during active conditions and not at all local times. Scattering rates fall below the strong diffusion limit at other times when the wave amplitudes are weaker. Fluxes of low energy electrons (100 eV < E < 30 keV) also increase with increasing geomagnetic activity in approximately the same region of geospace as the waves, suggesting that these electrons are responsible for the generation of the waves. The patterns of the upper band chorus, ECH waves and low energy electrons are similar to the global morphology of the diffuse aurora, suggesting that both wave modes play significant roles in the production of the diffuse aurora.

  9. Traveling wave solutions of the Boussinesq equation via the new approach of generalized (G'/G)-expansion method.

    PubMed

    Alam, Md Nur; Akbar, M Ali; Roshid, Harun-Or-

    2014-01-01

    Exact solutions of nonlinear evolution equations (NLEEs) play a vital role to reveal the internal mechanism of complex physical phenomena. In this work, the exact traveling wave solutions of the Boussinesq equation is studied by using the new generalized (G'/G)-expansion method. Abundant traveling wave solutions with arbitrary parameters are successfully obtained by this method and the wave solutions are expressed in terms of the hyperbolic, trigonometric, and rational functions. It is shown that the new approach of generalized (G'/G)-expansion method is a powerful and concise mathematical tool for solving nonlinear partial differential equations in mathematical physics and engineering. 05.45.Yv, 02.30.Jr, 02.30.Ik.

  10. Piezoelectric parametric effects on wave vibration and contact mechanics of traveling wave ultrasonic motor.

    PubMed

    Zhang, Dongsheng; Wang, Shiyu; Xiu, Jie

    2017-11-01

    Elastic wave quality determines the operating performance of traveling wave ultrasonic motor (TWUM). The time-variant circumferential force from the shrink of piezoelectric ceramic is one of the factors that distort the elastic wave. The distorted waveshape deviates from the ideal standard sinusoidal fashion and affects the contact mechanics and driving performance. An analytical dynamic model of ring ultrasonic motor is developed. Based on this model, the piezoelectric parametric effects on the wave distortion and contact mechanics are examined. Multi-scale method is employed to obtain unstable regions and distorted wave response. The unstable region is verified by Floquét theory. Since the waveshape affects the contact mechanism, a contact model involving the distorted waveshape and normal stiffness of the contact layer is established. The contact model is solved by numerical calculation. The results verify that the deformation of the contact layer deviates from sinusoidal waveshape and the pressure distribution is changed, which influences the output characteristics directly. The surface speed within the contact region is averaged such that the rotor speed decreases for lower torque and increases for larger torque. The effects from different parametric strengths, excitation frequencies and pre-pressures on pressure distribution and torque-speed relation are compared. Copyright © 2017 Elsevier B.V. All rights reserved.

  11. Chemical trends of the luminescence in wide band gap II 1-xMn xVI semimagnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Benecke, C.; Busse, W.; Gumlich, H.-E.

    1990-04-01

    Time resolved emission and excitation spectroscopy is used to investigate the Mn correlated luminescence in wide band gap II-VI compounds, i.e. Zn 1-xMn xS, Cd 1-xMn xSe, Zn 1-xMn xTe and Cd 1-xMn xTe. Additional Information has been obtained with CdxZnyMnzTe( x+ y+ z=1) in checking the luminescence by variation of the ratio of the cations Cd and Zn. Generally speaking, at least two distinct emissions bands can be observed for each II 1- xMn xVI compound. One emissions band is attributed to the internal transition 4T 1(G)→ 6A 1(S) of the 3d 5 electron of the Mn 2+ on regular metal sites with energies of about ≈2 eV. The other emission band is found to occur in the near infrared range of about ≈1.3 eV. This emission band is tentatively interpreted as a transition of Mn 2+ ions on interstitial sites or in small Mn chalcogenide clusters, both interpretations assuming cubic symmetry. This model is supported by the existence of low energy excitation bands and by the great similarity of the shape of the two emission bands which lead to comparable Huang-Rhys factors and effective phonon energies. Also the established trend in the experimental data of the II-VI compounds under consideration confirm this interpretation. For both the IR and the yellow Mn 2+ center, the Racah parameters B and C and the crystal field parameter Dq are determined on the basis of experimental data. As a result, the energy of both the emission and the excitation bands is predominantly determined by the sorrounding anions. These bands shift to higher energies when the anions are changed in the fixed order: Te→Se→S. Regularly, there is also a spectral shift when Zn is replaced by Cd, which is smaller than the shift due to the variation of onions.

  12. X-band ultralow-noise maser amplifier performance

    NASA Technical Reports Server (NTRS)

    Glass, G. W.; Ortiz, G. G.; Johnson, D. L.

    1994-01-01

    Noise temperature measurements of an 8440-MHz ultralow noise maser amplifier (ULNA) have been performed at subatmospheric, liquid-helium temperatures. The traveling-wave maser was operated while immersed in a liquid helium bath. The lowest input noise temperature measured was 1.43 +/- 0.16 K at a physical temperature of 1.60 K. At this physical temperature, the observed gain per centimeter of ruby was 4.9 dB/cm. The amplifier had a 3-dB bandwidth of 76 MHz.

  13. Traveling waves for the mass in mass model of granular chains

    DOE PAGES

    Kevrekidis, Panayotis G.; Stefanov, Atanas G.; Xu, Haitao

    2016-06-03

    In this work, we consider the mass in mass (or mass with mass) system of granular chains, namely, a granular chain involving additionally an internal (or, respectively, external) resonator. For these chains, we rigorously establish that under suitable “anti-resonance” conditions connecting the mass of the resonator and the speed of the wave, bell-shaped traveling-wave solutions continue to exist in the system, in a way reminiscent of the results proven for the standard granular chain of elastic Hertzian contacts. Finally, we also numerically touch upon settings, where the conditions do not hold, illustrating, in line also with recent experimental work, thatmore » non-monotonic waves bearing non-vanishing tails may exist in the latter case.« less

  14. Traveling waves for the mass in mass model of granular chains

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kevrekidis, Panayotis G.; Stefanov, Atanas G.; Xu, Haitao

    In this work, we consider the mass in mass (or mass with mass) system of granular chains, namely, a granular chain involving additionally an internal (or, respectively, external) resonator. For these chains, we rigorously establish that under suitable “anti-resonance” conditions connecting the mass of the resonator and the speed of the wave, bell-shaped traveling-wave solutions continue to exist in the system, in a way reminiscent of the results proven for the standard granular chain of elastic Hertzian contacts. Finally, we also numerically touch upon settings, where the conditions do not hold, illustrating, in line also with recent experimental work, thatmore » non-monotonic waves bearing non-vanishing tails may exist in the latter case.« less

  15. A novel contact model of piezoelectric traveling wave rotary ultrasonic motors with the finite volume method.

    PubMed

    Renteria-Marquez, I A; Renteria-Marquez, A; Tseng, B T L

    2018-06-06

    The operating principle of the piezoelectric traveling wave rotary ultrasonic motor is based on two energy conversion processes: the generation of the stator traveling wave and the rectification of the stator movement through the stator-rotor contact mechanism. This paper presents a methodology to model in detail the stator-rotor contact interface of these motors. A contact algorithm that couples a model of the stator which is discretized with the finite volume method and an analytical model of the rotor is presented. The outputs of the proposed model are the normal and tangential force distribution produced at the stator-rotor contact interface, contact length, height and shape of the stator traveling wave and rotor speed. The torque-speed characteristic of the USR60 is calculated with the proposed model, and the results of the model are compared versus the real torque-speed of the motor. A good agreement between the proposed model results and the torque-speed characteristic of the USR60 was observed. Copyright © 2018 Elsevier B.V. All rights reserved.

  16. Low-current traveling wave tube for use in the microwave power module

    NASA Technical Reports Server (NTRS)

    Palmer, Raymond W.; Ramins, Peter; Force, Dale A.; Dayton, James A.; Ebihara, Ben T.; Gruber, Robert P.

    1993-01-01

    The results of a traveling-wave-tube/multistage depressed-collector (TWT-MDC) design study in support of the Advanced Research Projects Agency/Department of Defense (ARPA/DOD) Microwave Power Module (MPM) Program are described. The study stressed the possible application of dynamic and other tapers to the RF output circuit of the MPM traveling wave tube as a means of increasing the RF and overall efficiencies and reducing the required beam current (perveance). The results indicate that a highly efficient, modified dynamic velocity taper (DVT) circuit can be designed for the broadband MPM application. The combination of reduced cathode current (lower perveance) and increased RF efficiency leads to (1) a substantially higher overall efficiency and reduction in the prime power to the MPM, and (2) substantially reduced levels of MDC and MPM heat dissipation, which simplify the cooling problems. However, the selected TWT circuit parameters need to be validated by cold test measurements on actual circuits.

  17. Toward broad-band x-ray detected ferromagnetic resonance in longitudinal geometry

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ollefs, K.; European Synchrotron Radiation Facility; Meckenstock, R.

    2015-06-14

    An ultrahigh-vacuum-compatible setup for broad-band X-ray detected ferromagnetic resonance (XFMR) in longitudinal geometry is introduced which relies on a low-power, continuous-wave excitation of the ferromagnetic sample. A simultaneous detection of the conventional ferromagnetic resonance via measuring the reflected microwave power and the XFMR signal of the X-ray absorption is possible. First experiments on the Fe and Co L{sub 3}-edges of a permalloy film covered with Co nanostripes as well as the Fe and Ni K-edges of a permalloy film are presented and discussed. Two different XFMR signals are found, one of which is independent of the photon energy and thereforemore » does not provide element-selective information. The other much weaker signal is element-selective, and the dynamic magnetic properties could be detected for Fe and Co separately. The dependence of the latter XFMR signal on the photon helicity of the synchrotron light is found to be distinct from the usual x-ray magnetic circular dichroism effect.« less

  18. Generation of powerful microwave pulses by channel power summation of two X-band phase-locked relativistic backward wave oscillators

    NASA Astrophysics Data System (ADS)

    Xiao, Renzhen; Deng, Yuqun; Chen, Changhua; Shi, Yanchao; Sun, Jun

    2018-03-01

    We demonstrate both theoretically and experimentally the possibility of the generation of powerful microwave pulses by channel power summation of two X-band phase-locked relativistic backward wave oscillators (RBWOs). A modulated electron beam induced by an external signal can lead the microwave field with an arbitrary initial phase to the same equilibrium phase, which is determined by the initial phase of the external signal. A high-current dual-beam accelerator was built to drive the two RBWOs. An external signal was divided into two channels with an adjusted relative phase and injected into the two RBWOs through two TE10-TEM mode converters. The generated microwaves were combined with a power combiner consisting of two TM01-TE11 serpentine mode converters with a common output. In the experiments, as the input power for each channel was 150 kW, the two RBWOs output 3.1 GW and 3.7 GW, respectively, the jitter of the relative phase of two output microwaves was about 20°, and the summation power from the power combiner is 6.2 GW, corresponding to a combination efficiency of 91%.

  19. Comparison of Walking and Traveling-Wave Piezoelectric Motors as Actuators in Kinesthetic Haptic Devices.

    PubMed

    Olsson, Pontus; Nysjo, Fredrik; Carlbom, Ingrid B; Johansson, Stefan

    2016-01-01

    Piezoelectric motors offer an attractive alternative to electromagnetic actuators in portable haptic interfaces: they are compact, have a high force-to-volume ratio, and can operate with limited or no gearing. However, the choice of a piezoelectric motor type is not obvious due to differences in performance characteristics. We present our evaluation of two commercial, operationally different, piezoelectric motors acting as actuators in two kinesthetic haptic grippers, a walking quasi-static motor and a traveling wave ultrasonic motor. We evaluate each gripper's ability to display common virtual objects including springs, dampers, and rigid walls, and conclude that the walking quasi-static motor is superior at low velocities. However, for applications where high velocity is required, traveling wave ultrasonic motors are a better option.

  20. Electromagnetic waves in a topological insulator thin film stack: helicon-like wave mode and photonic band structure.

    PubMed

    Inoue, Jun-ichi

    2013-09-09

    We theoretically explore the electromagnetic modes specific to a topological insulator superlattice in which topological and conventional insulator thin films are stacked periodically. In particular, we obtain analytic formulas for low energy mode that corresponds to a helicon wave, as well as those for photonic bands. We illustrate that the system can be modeled as a stack of quantum Hall layers whose conductivity tensors alternately change signs, and then we analyze the photonic band structures. This subject is a natural extension of a previous study by Tselis et al., which took into consideration a stack of identical quantum Hall layers but their discussion was limited into a low energy mode. Thus we provide analytic formulas for photonic bands and compare their features between the two systems. Our central findings in the topological insulator superlattice are that a low energy mode corresponding to a helicon wave has linear dispersion instead of the conventional quadratic form, and that a robust gapless photonic band appears although the system considered has spacial periodicity. In addition, we demonstrate that the photonic bands agree with the numerically calculated transmission spectra.

  1. Wave propagation in axially moving periodic strings

    NASA Astrophysics Data System (ADS)

    Sorokin, Vladislav S.; Thomsen, Jon Juel

    2017-04-01

    The paper deals with analytically studying transverse waves propagation in an axially moving string with periodically modulated cross section. The structure effectively models various relevant technological systems, e.g. belts, thread lines, band saws, etc., and, in particular, roller chain drives for diesel engines by capturing both their spatial periodicity and axial motion. The Method of Varying Amplitudes is employed in the analysis. It is shown that the compound wave traveling in the axially moving periodic string comprises many components with different frequencies and wavenumbers. This is in contrast to non-moving periodic structures, for which all components of the corresponding compound wave feature the same frequency. Due to this "multi-frequency" character of the wave motion, the conventional notion of frequency band-gaps appears to be not applicable for the moving periodic strings. Thus, for such structures, by frequency band-gaps it is proposed to understand frequency ranges in which the primary component of the compound wave attenuates. Such frequency band-gaps can be present for a moving periodic string, but only if its axial velocity is lower than the transverse wave speed, and, the higher the axial velocity, the narrower the frequency band-gaps. The revealed effects could be of potential importance for applications, e.g. they indicate that due to spatial inhomogeneity, oscillations of axially moving periodic chains always involve a multitude of frequencies.

  2. Hybrid density functional study of band alignment in ZnO-GaN and ZnO-(Ga(1-x)Zn(x))(N(1-x)O(x))-GaN heterostructures.

    PubMed

    Wang, Zhenhai; Zhao, Mingwen; Wang, Xiaopeng; Xi, Yan; He, Xiujie; Liu, Xiangdong; Yan, Shishen

    2012-12-05

    The band alignment in ZnO-GaN and related heterostructures is crucial for uses in solar harvesting technology. Here, we report our density functional calculations of the band alignment and optical properties of ZnO-GaN and ZnO-(Ga(1-x)Zn(x))(N(1-x)O(x))-GaN heterostructures using a Heyd-Scuseria-Ernzerhof (HSE) hybrid functional. We found that the conventional GGA functionals underestimate not only the band gap but also the band offset of these heterostructures. Using the hybrid functional calculations, we show that the (Ga(1-x)Zn(x))(N(1-x)O(x)) solid solution has a direct band gap of about 2.608 eV, in good agreement with the experimental data. More importantly, this solid solution forms type-II band alignment with the host materials. A GaN-(Ga(1-x)Zn(x))(N(1-x)O(x))-ZnO core-shell solar cell model is presented to improve the visible light absorption ability and carrier collection efficiency.

  3. Demonstration of 1024x1024 pixel dual-band QWIP focal plane array

    NASA Astrophysics Data System (ADS)

    Gunapala, S. D.; Bandara, S. V.; Liu, J. K.; Mumolo, J. M.; Ting, D. Z.; Hill, C. J.; Nguyen, J.; Rafol, S. B.

    2010-04-01

    QWIPs are well known for their stability, high pixel-pixel uniformity and high pixel operability which are quintessential parameters for large area imaging arrays. In this paper we report the first demonstration of the megapixel-simultaneously-readable and pixel-co-registered dual-band QWIP focal plane array (FPA). The dual-band QWIP device was developed by stacking two multi-quantum-well stacks tuned to absorb two different infrared wavelengths. The full width at half maximum (FWHM) of the mid-wave infrared (MWIR) band extends from 4.4 - 5.1 μm and FWHM of the long-wave infrared (LWIR) band extends from 7.8 - 8.8 μm. Dual-band QWIP detector arrays were hybridized with direct injection 30 μm pixel pitch megapixel dual-band simultaneously readable CMOS read out integrated circuits using the indium bump hybridization technique. The initial dual-band megapixel QWIP FPAs were cooled to 68K operating temperature. The preliminary data taken from the first megapixel QWIP FPA has shown system NE▵T of 27 and 40 mK for MWIR and LWIR bands respectively.

  4. Actuating mechanism and design of a cylindrical traveling wave ultrasonic motor using cantilever type composite transducer.

    PubMed

    Liu, Yingxiang; Chen, Weishan; Liu, Junkao; Shi, Shengjun

    2010-04-02

    Ultrasonic motors (USM) are based on the concept of driving the rotor by a mechanical vibration excited on the stator via piezoelectric effect. USM exhibit merits such as simple structure, quick response, quiet operation, self-locking when power off, nonelectromagnetic radiation and higher position accuracy. A cylindrical type traveling wave ultrasonic motor using cantilever type composite transducer was proposed in this paper. There are two cantilevers on the outside surface of cylinder, four longitudinal PZT ceramics are set between the cantilevers, and four bending PZT ceramics are set on each outside surface of cantilevers. Two degenerate flexural vibration modes spatially and temporally orthogonal to each other in the cylinder are excited by the composite transducer. In this new design, a single transducer can excite a flexural traveling wave in the cylinder. Thus, elliptical motions are achieved on the teeth. The actuating mechanism of proposed motor was analyzed. The stator was designed with FEM. The two vibration modes of stator were degenerated. Transient analysis was developed to gain the vibration characteristic of stator, and results indicate the motion trajectories of nodes on the teeth are nearly ellipses. The study results verify the feasibility of the proposed design. The wave excited in the cylinder isn't an ideal traveling wave, and the vibration amplitudes are inconsistent. The distortion of traveling wave is generated by the deformation of bending vibration mode of cylinder, which is caused by the coupling effect between the cylinder and transducer. Analysis results also prove that the objective motions of nodes on the teeth are three-dimensional vibrations. But, the vibration in axial direction is minute compared with the vibrations in circumferential and radial direction. The results of this paper can guide the development of this new type of motor.

  5. Actuating Mechanism and Design of a Cylindrical Traveling Wave Ultrasonic Motor Using Cantilever Type Composite Transducer

    PubMed Central

    Liu, Yingxiang; Chen, Weishan; Liu, Junkao; Shi, Shengjun

    2010-01-01

    Background Ultrasonic motors (USM) are based on the concept of driving the rotor by a mechanical vibration excited on the stator via piezoelectric effect. USM exhibit merits such as simple structure, quick response, quiet operation, self-locking when power off, nonelectromagnetic radiation and higher position accuracy. Principal Findings A cylindrical type traveling wave ultrasonic motor using cantilever type composite transducer was proposed in this paper. There are two cantilevers on the outside surface of cylinder, four longitudinal PZT ceramics are set between the cantilevers, and four bending PZT ceramics are set on each outside surface of cantilevers. Two degenerate flexural vibration modes spatially and temporally orthogonal to each other in the cylinder are excited by the composite transducer. In this new design, a single transducer can excite a flexural traveling wave in the cylinder. Thus, elliptical motions are achieved on the teeth. The actuating mechanism of proposed motor was analyzed. The stator was designed with FEM. The two vibration modes of stator were degenerated. Transient analysis was developed to gain the vibration characteristic of stator, and results indicate the motion trajectories of nodes on the teeth are nearly ellipses. Conclusions The study results verify the feasibility of the proposed design. The wave excited in the cylinder isn't an ideal traveling wave, and the vibration amplitudes are inconsistent. The distortion of traveling wave is generated by the deformation of bending vibration mode of cylinder, which is caused by the coupling effect between the cylinder and transducer. Analysis results also prove that the objective motions of nodes on the teeth are three-dimensional vibrations. But, the vibration in axial direction is minute compared with the vibrations in circumferential and radial direction. The results of this paper can guide the development of this new type of motor. PMID:20368809

  6. Generating synchrony from the asynchronous: compensation for cochlear traveling wave delays by the dendrites of individual brainstem neurons

    PubMed Central

    McGinley, Matthew J.; Liberman, M. Charles; Bal, Ramazan; Oertel, Donata

    2012-01-01

    Broadband transient sounds, such as clicks and consonants, activate a traveling wave in the cochlea. This wave evokes firing in auditory nerve fibers that are tuned to high frequencies several milliseconds earlier than in fibers tuned to low frequencies. Despite this substantial traveling wave delay, octopus cells in the brainstem receive broadband input and respond to clicks with submillisecond temporal precision. The dendrites of octopus cells lie perpendicular to the tonotopically organized array of auditory nerve fibers, placing the earliest arriving inputs most distally and the latest arriving closest to the soma. Here, we test the hypothesis that the topographic arrangement of synaptic inputs on dendrites of octopus cells allows octopus cells to compensate the traveling wave delay. We show that in mice the full cochlear traveling wave delay is 1.6 ms. Because the dendrites of each octopus cell spread across about one third of the tonotopic axis, a click evokes a soma directed sweep of synaptic input lasting 0.5 ms in individual octopus cells. Morphologically and biophysically realistic, computational models of octopus cells show that soma-directed sweeps with durations matching in vivo measurements result in the largest and sharpest somatic excitatory postsynaptic potentials (EPSPs). A low input resistance and activation of a low-voltage-activated potassium conductance that are characteristic of octopus cells are important determinants of sweep sensitivity. We conclude that octopus cells have dendritic morphologies and biophysics tailored to accomplish the precise encoding of broadband transient sounds. PMID:22764237

  7. Ballistic-electron-emission spectroscopy of Al{sub x}Ga{sub 1{minus}x}As/GaAs heterostructures: Conduction-band offsets, transport mechanisms, and band-structure effects

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    OShea, J.J.; Brazel, E.G.; Rubin, M.E.

    1997-07-01

    We report an extensive investigation of semiconductor band-structure effects in single-barrier Al{sub x}Ga{sub 1{minus}x}As/GaAs heterostructures using ballistic-electron-emission spectroscopy (BEES). The transport mechanisms in these single-barrier structures were studied systematically as a function of temperature and Al composition over the full compositional range (0{le}x{le}1). The initial ({Gamma}) BEES thresholds for Al{sub x}Ga{sub 1{minus}x}As single barriers with 0{le}x{le}0.42 were extracted using a model which includes the complete transmission probability of the metal-semiconductor interface and the semiconductor heterostructure. Band offsets measured by BEES are in good agreement with previous measurements by other techniques which demonstrates the accuracy of this technique. BEES measurements atmore » 77 K give the same band-offset values as at room temperature. When a reverse bias is applied to the heterostructures, the BEES thresholds shift to lower voltages in good agreement with the expected bias-induced band-bending. In the indirect band-gap regime ({ital x}{gt}0.45), spectra show a weak ballistic-electron-emission microscopy current contribution due to intervalley scattering through Al{sub x}Ga{sub 1{minus}x}As {ital X} valley states. Low-temperature spectra show a marked reduction in this intervalley current component, indicating that intervalley phonon scattering at the GaAs/Al{sub x}Ga{sub 1{minus}x}As interface produces a significant fraction of this{ital X} valley current. A comparison of the BEES thresholds with the expected composition dependence of the Al{sub x}Ga{sub 1{minus}x}As {Gamma}, {ital L}, and {ital X} points yields good agreement over the entire composition range. {copyright} {ital 1997} {ital The American Physical Society}« less

  8. Existence and numerical simulation of periodic traveling wave solutions to the Casimir equation for the Ito system

    NASA Astrophysics Data System (ADS)

    Abbasbandy, S.; Van Gorder, R. A.; Hajiketabi, M.; Mesrizadeh, M.

    2015-10-01

    We consider traveling wave solutions to the Casimir equation for the Ito system (a two-field extension of the KdV equation). These traveling waves are governed by a nonlinear initial value problem with an interesting nonlinearity (which actually amplifies in magnitude as the size of the solution becomes small). The nonlinear problem is parameterized by two initial constant values, and we demonstrate that the existence of solutions is strongly tied to these parameter values. For our interests, we are concerned with positive, bounded, periodic wave solutions. We are able to classify parameter regimes which admit such solutions in full generality, thereby obtaining a nice existence result. Using the existence result, we are then able to numerically simulate the positive, bounded, periodic solutions. We elect to employ a group preserving scheme in order to numerically study these solutions, and an outline of this approach is provided. The numerical simulations serve to illustrate the properties of these solutions predicted analytically through the existence result. Physically, these results demonstrate the existence of a type of space-periodic structure in the Casimir equation for the Ito model, which propagates as a traveling wave.

  9. Sea Surface Scattering of Radar Signals in Ku- and C-Bands: the Role of Breaking Waves

    NASA Astrophysics Data System (ADS)

    Voronovich, A.; Zavorotny, V.

    2001-05-01

    A small-slope approximation (SSA) is used for numerical calculations of a radar backscattering cross section of the ocean surface for both Ku- and C-bands for wind speeds ranging from 5 m/s to 15 m/s as a function of an incident angle. Both the lowest order of the SSA and the one that includes the next-order correction to it are considered. The initial calculations were made assuming Gaussian statistics of sea surface and the Elfouhaily et al. surface-height spectrum for fully developed seas (T. Elfouhaily et al., J. Geophys. Res., vol.102, pp.15,781-15,796 (1997)). Empirical scattering models CMOD2-I3 and SASS-II are used for comparison. Theoretical calculations are in good overall agreement with the experiment, being within a 2 dB accuracy on average with a 3 dB maximal discrepancy. The only exception is HH-polarization in the upwind direction where discrepancies reach 5.7 dB for an incidence angle of 60{° }. Note that the SSA allows controlling the accuracy of calculations by comparing the results of the lowest order approximation with corrections originated from higher order terms. The discrepancy between our calculations and empirical data for HH polarization appears to be significantly larger then accuracy of the calculations. Hence, the reason for it should be attributed to the inadequate sea-roughness model. We have checked a hypothesis that steep waves are responsible for this effect. We assumed that the contribution from steep waves could be evaluated in the geometric optics approximation. This allowed us to retrieve the probability density function of large slopes based on comparison of theoretical calculations and experimental data for Ku-band at HH polarization. It was found that in the upwind direction this function could be approximated by a simple relationship: \\[ \\text{Log}_{10}P(a_{x},0) = -2.84 + 0.097ṡ U + 1.33ṡ a_{x}, \\] where U is wind speed in m/s and ax>0.8 is the appropriate slope. Note that such large slopes cannot belong to steady

  10. Effects of discrete-electrode arrangement on traveling-wave electroosmotic pumping

    NASA Astrophysics Data System (ADS)

    Liu, Weiyu; Shao, Jinyou; Ren, Yukun; Wu, Yupan; Wang, Chunhui; Ding, Haitao; Jiang, Hongyuan; Ding, Yucheng

    2016-09-01

    Traveling-wave electroosmotic (TWEO) pumping arises from the action of an imposed traveling-wave (TW) electric field on its own induced charge in the diffuse double layer, which is formed on top of an electrode array immersed in electrolyte solutions. Such a traveling field can be merely realized in practice by a discrete electrode array upon which the corresponding voltages of correct phase are imposed. By employing the theory of linear and weakly nonlinear double-layer charging dynamics, a physical model incorporating both the nonlinear surface capacitance of diffuse layer and Faradaic current injection is developed herein in order to quantify the changes in TWEO pumping performance from a single-mode TW to discrete electrode configuration. Benefiting from the linear analysis, we investigate the influence of using discrete electrode array to create the TW signal on the resulting fluid motion, and several approaches are suggested to improve the pumping performance. In the nonlinear regime, our full numerical analysis considering the intervening isolation spacing indicates that a practical four-phase discrete electrode configuration of equal electrode and gap width exhibits stronger nonlinearity than expected from the idealized pump applied with a single-mode TW in terms of voltage-dependence of the ideal pumping frequency and peak flow rate, though it has a much lower pumping performance. For model validation, pumping of electrolytes by TWEO is achieved over a confocal spiral four-phase electrode array covered by an insulating microchannel; measurement of flow velocity indicates the modified nonlinear theory considering moderate Faradaic conductance is indeed a more accurate physical description of TWEO. These results offer useful guidelines for designing high-performance TWEO microfluidic pumps with discrete electrode array.

  11. Solar Supergranulation Revealed as a Superposition of Traveling Waves

    NASA Technical Reports Server (NTRS)

    Gizon, L.; Duvall, T. L., Jr.; Schou, J.; Oegerle, William (Technical Monitor)

    2002-01-01

    40 years ago two new solar phenomena were described: supergranulation and the five-minute solar oscillations. While the oscillations have since been explained and exploited to determine the properties of the solar interior, the supergranulation has remained unexplained. The supergranules, appearing as convective-like cellular patterns of horizontal outward flow with a characteristic diameter of 30 Mm and an apparent lifetime of 1 day, have puzzling properties, including their apparent superrotation and the minute temperature variations over the cells. Using a 60-day sequence of data from the MDI (Michelson-Doppler Imager) instrument onboard the SOHO (Solar and Heliospheric Observatory) spacecraft, we show that the supergranulation pattern is formed by a superposition of traveling waves with periods of 5-10 days. The wave power is anisotropic with excess power in the direction of rotation and toward the equator, leading to spurious rotation rates and north-south flows as derived from correlation analyses. These newly discovered waves could play an important role in maintaining differential rotation in the upper convection zone by transporting angular momentum towards the equator.

  12. Temperature effects on the band gaps of Lamb waves in a one-dimensional phononic-crystal plate (L).

    PubMed

    Cheng, Y; Liu, X J; Wu, D J

    2011-03-01

    This study investigates the temperature-tuned band gaps of Lamb waves in a one-dimensional phononic-crystal plate, which is formed by alternating strips of ferroelectric ceramic Ba(0.7)Sr(0.3)TiO(3) and epoxy. The sensitive and continuous temperature-tunability of Lamb wave band gaps is demonstrated using the analyses of the band structures and the transmission spectra. The width and position of Lamb wave band gaps shift prominently with variation of temperature in the range of 26 °C-50 °C. For example, the width of the second band gap increases from 0.066 to 0.111 MHz as the temperature is increased from 26 °C to 50 °C. The strong shift promises that the structure could be suitable for temperature-tuned multi-frequency Lamb wave filters. © 2011 Acoustical Society of America

  13. System Identification of Mistuned Bladed Disks from Traveling Wave Response Measurements

    NASA Technical Reports Server (NTRS)

    Feiner, D. M.; Griffin, J. H.; Jones, K. W.; Kenyon, J. A.; Mehmed, O.; Kurkov, A. P.

    2003-01-01

    A new approach to modal analysis is presented. By applying this technique to bladed disk system identification methods, one can determine the mistuning in a rotor based on its response to a traveling wave excitation. This allows system identification to be performed under rotating conditions, and thus expands the applicability of existing mistuning identification techniques from integrally bladed rotors to conventional bladed disks.

  14. Traveling-wave solutions in continuous chains of unidirectionally coupled oscillators

    NASA Astrophysics Data System (ADS)

    Glyzin, S. D.; Kolesov, A. Yu; Rozov, N. Kh

    2017-12-01

    Proposed is a mathematical model of a continuous annular chain of unidirectionally coupled generators given by certain nonlinear advection-type hyperbolic boundary value problem. Such problems are constructed by a limit transition from annular chains of unidirectionally coupled ordinary differential equations with an unbounded increase in the number of links. It is shown that any preassigned finite number of stable periodic motions of the traveling-wave type can coexist in the model.

  15. Traveling and Standing Waves in Coupled Pendula and Newton's Cradle

    NASA Astrophysics Data System (ADS)

    García-Azpeitia, Carlos

    2016-12-01

    The existence of traveling and standing waves is investigated for chains of coupled pendula with periodic boundary conditions. The results are proven by applying topological methods to subspaces of symmetric solutions. The main advantage of this approach comes from the fact that only properties of the linearized forces are required. This allows to cover a wide range of models such as Newton's cradle, the Fermi-Pasta-Ulam lattice, and the Toda lattice.

  16. Narrow-band search of continuous gravitational-wave signals from Crab and Vela pulsars in Virgo VSR4 data

    NASA Astrophysics Data System (ADS)

    Aasi, J.; Abbott, B. P.; Abbott, R.; Abbott, T.; Abernathy, M. R.; Acernese, F.; Ackley, K.; Adams, C.; Adams, T.; Adams, T.; Addesso, P.; Adhikari, R. X.; Adya, V.; Affeldt, C.; Agathos, M.; Agatsuma, K.; Aggarwal, N.; Aguiar, O. D.; Ain, A.; Ajith, P.; Alemic, A.; Allen, B.; Allocca, A.; Amariutei, D.; Anderson, S. B.; Anderson, W. G.; Arai, K.; Araya, M. C.; Arceneaux, C.; Areeda, J. S.; Ashton, G.; Ast, S.; Aston, S. M.; Astone, P.; Aufmuth, P.; Aulbert, C.; Aylott, B. E.; Babak, S.; Baker, P. T.; Baldaccini, F.; Ballardin, G.; Ballmer, S. W.; Barayoga, J. C.; Barbet, M.; Barclay, S.; Barish, B. C.; Barker, D.; Barone, F.; Barr, B.; Barsotti, L.; Barsuglia, M.; Bartlett, J.; Barton, M. A.; Bartos, I.; Bassiri, R.; Basti, A.; Batch, J. C.; Bauer, Th. S.; Baune, C.; Bavigadda, V.; Behnke, B.; Bejger, M.; Belczynski, C.; Bell, A. S.; Bell, C.; Benacquista, M.; Bergman, J.; Bergmann, G.; Berry, C. P. L.; Bersanetti, D.; Bertolini, A.; Betzwieser, J.; Bhagwat, S.; Bhandare, R.; Bilenko, I. A.; Billingsley, G.; Birch, J.; Biscans, S.; Bitossi, M.; Biwer, C.; Bizouard, M. A.; Blackburn, J. K.; Blackburn, L.; Blair, C. D.; Blair, D.; Bloemen, S.; Bock, O.; Bodiya, T. P.; Boer, M.; Bogaert, G.; Bojtos, P.; Bond, C.; Bondu, F.; Bonelli, L.; Bonnand, R.; Bork, R.; Born, M.; Boschi, V.; Bose, Sukanta; Bradaschia, C.; Brady, P. R.; Braginsky, V. B.; Branchesi, M.; Brau, J. E.; Briant, T.; Bridges, D. O.; Brillet, A.; Brinkmann, M.; Brisson, V.; Brooks, A. F.; Brown, D. A.; Brown, D. D.; Brown, N. M.; Buchman, S.; Buikema, A.; Bulik, T.; Bulten, H. J.; Buonanno, A.; Buskulic, D.; Buy, C.; Cadonati, L.; Cagnoli, G.; Calderón Bustillo, J.; Calloni, E.; Camp, J. B.; Cannon, K. C.; Cao, J.; Capano, C. D.; Carbognani, F.; Caride, S.; Caudill, S.; Cavaglià, M.; Cavalier, F.; Cavalieri, R.; Cella, G.; Cepeda, C.; Cesarini, E.; Chakraborty, R.; Chalermsongsak, T.; Chamberlin, S. J.; Chao, S.; Charlton, P.; Chassande-Mottin, E.; Chen, Y.; Chincarini, A.; Chiummo, A.; Cho, H. S.; Cho, M.; Chow, J. H.; Christensen, N.; Chu, Q.; Chua, S.; Chung, S.; Ciani, G.; Clara, F.; Clark, J. A.; Cleva, F.; Coccia, E.; Cohadon, P.-F.; Colla, A.; Collette, C.; Colombini, M.; Cominsky, L.; Constancio, M.; Conte, A.; Cook, D.; Corbitt, T. R.; Cornish, N.; Corsi, A.; Costa, C. A.; Coughlin, M. W.; Coulon, J.-P.; Countryman, S.; Couvares, P.; Coward, D. M.; Cowart, M. J.; Coyne, D. C.; Coyne, R.; Craig, K.; Creighton, J. D. E.; Creighton, T. D.; Cripe, J.; Crowder, S. G.; Cumming, A.; Cunningham, L.; Cuoco, E.; Cutler, C.; Dahl, K.; Canton, T. Dal; Damjanic, M.; Danilishin, S. L.; D'Antonio, S.; Danzmann, K.; Dartez, L.; Dattilo, V.; Dave, I.; Daveloza, H.; Davier, M.; Davies, G. S.; Daw, E. J.; Day, R.; DeBra, D.; Debreczeni, G.; Degallaix, J.; De Laurentis, M.; Deléglise, S.; Del Pozzo, W.; Denker, T.; Dent, T.; Dereli, H.; Dergachev, V.; De Rosa, R.; DeRosa, R. T.; DeSalvo, R.; Dhurandhar, S.; Díaz, M.; Di Fiore, L.; Di Lieto, A.; Di Palma, I.; Di Virgilio, A.; Dojcinoski, G.; Dolique, V.; Dominguez, E.; Donovan, F.; Dooley, K. L.; Doravari, S.; Douglas, R.; Downes, T. P.; Drago, M.; Driggers, J. C.; Du, Z.; Ducrot, M.; Dwyer, S.; Eberle, T.; Edo, T.; Edwards, M.; Edwards, M.; Effler, A.; Eggenstein, H.-B.; Ehrens, P.; Eichholz, J.; Eikenberry, S. S.; Essick, R.; Etzel, T.; Evans, M.; Evans, T.; Factourovich, M.; Fafone, V.; Fairhurst, S.; Fan, X.; Fang, Q.; Farinon, S.; Farr, B.; Farr, W. M.; Favata, M.; Fays, M.; Fehrmann, H.; Fejer, M. M.; Feldbaum, D.; Ferrante, I.; Ferreira, E. C.; Ferrini, F.; Fidecaro, F.; Fiori, I.; Fisher, R. P.; Flaminio, R.; Fournier, J.-D.; Franco, S.; Frasca, S.; Frasconi, F.; Frei, Z.; Freise, A.; Frey, R.; Fricke, T. T.; Fritschel, P.; Frolov, V. V.; Fuentes-Tapia, S.; Fulda, P.; Fyffe, M.; Gair, J. R.; Gammaitoni, L.; Gaonkar, S.; Garufi, F.; Gatto, A.; Gehrels, N.; Gemme, G.; Gendre, B.; Genin, E.; Gennai, A.; Gergely, L. Á.; Ghosh, S.; Giaime, J. A.; Giardina, K. D.; Giazotto, A.; Gleason, J.; Goetz, E.; Goetz, R.; Gondan, L.; González, G.; Gordon, N.; Gorodetsky, M. L.; Gossan, S.; Goßler, S.; Gouaty, R.; Gräf, C.; Graff, P. B.; Granata, M.; Grant, A.; Gras, S.; Gray, C.; Greco, G.; Greenhalgh, R. J. S.; Gretarsson, A. M.; Groot, P.; Grote, H.; Grunewald, S.; Guidi, G. M.; Guido, C. J.; Guo, X.; Gushwa, K.; Gustafson, E. K.; Gustafson, R.; Hacker, J.; Hall, E. D.; Hammond, G.; Hanke, M.; Hanks, J.; Hanna, C.; Hannam, M. D.; Hanson, J.; Hardwick, T.; Harms, J.; Harry, G. M.; Harry, I. W.; Hart, M.; Hartman, M. T.; Haster, C.-J.; Haughian, K.; Hee, S.; Heidmann, A.; Heintze, M.; Heinzel, G.; Heitmann, H.; Hello, P.; Hemming, G.; Hendry, M.; Heng, I. S.; Heptonstall, A. W.; Heurs, M.; Hewitson, M.; Hild, S.; Hoak, D.; Hodge, K. A.; Hofman, D.; Hollitt, S. E.; Holt, K.; Hopkins, P.; Hosken, D. J.; Hough, J.; Houston, E.; Howell, E. J.; Hu, Y. M.; Huerta, E.; Hughey, B.; Husa, S.; Huttner, S. H.; Huynh, M.; Huynh-Dinh, T.; Idrisy, A.; Indik, N.; Ingram, D. R.; Inta, R.; Islas, G.; Isler, J. C.; Isogai, T.; Iyer, B. R.; Izumi, K.; Jacobson, M.; Jang, H.; Jaranowski, P.; Jawahar, S.; Ji, Y.; Jiménez-Forteza, F.; Johnson, W. W.; Jones, D. I.; Jones, R.; Jonker, R. J. G.; Ju, L.; Haris, K.; Kalogera, V.; Kandhasamy, S.; Kang, G.; Kanner, J. B.; Kasprzack, M.; Katsavounidis, E.; Katzman, W.; Kaufer, H.; Kaufer, S.; Kaur, T.; Kawabe, K.; Kawazoe, F.; Kéfélian, F.; Keiser, G. M.; Keitel, D.; Kelley, D. B.; Kells, W.; Keppel, D. G.; Key, J. S.; Khalaidovski, A.; Khalili, F. Y.; Khazanov, E. A.; Kim, C.; Kim, K.; Kim, N. G.; Kim, N.; Kim, Y.-M.; King, E. J.; King, P. J.; Kinzel, D. L.; Kissel, J. S.; Klimenko, S.; Kline, J.; Koehlenbeck, S.; Kokeyama, K.; Kondrashov, V.; Korobko, M.; Korth, W. Z.; Kowalska, I.; Kozak, D. B.; Kringel, V.; Krishnan, B.; Królak, A.; Krueger, C.; Kuehn, G.; Kumar, A.; Kumar, P.; Kuo, L.; Kutynia, A.; Landry, M.; Lantz, B.; Larson, S.; Lasky, P. D.; Lazzarini, A.; Lazzaro, C.; Lazzaro, C.; Le, J.; Leaci, P.; Leavey, S.; Lebigot, E.; Lebigot, E. O.; Lee, C. H.; Lee, H. K.; Lee, H. M.; Leonardi, M.; Leong, J. R.; Leroy, N.; Letendre, N.; Levin, Y.; Levine, B.; Lewis, J.; Li, T. G. F.; Libbrecht, K.; Libson, A.; Lin, A. C.; Littenberg, T. B.; Lockerbie, N. A.; Lockett, V.; Logue, J.; Lombardi, A. L.; Lorenzini, M.; Loriette, V.; Lormand, M.; Losurdo, G.; Lough, J.; Lubinski, M. J.; Lück, H.; Lundgren, A. P.; Lynch, R.; Ma, Y.; Macarthur, J.; MacDonald, T.; Machenschalk, B.; MacInnis, M.; Macleod, D. M.; Magaña-Sandoval, F.; Magee, R.; Mageswaran, M.; Maglione, C.; Mailand, K.; Majorana, E.; Maksimovic, I.; Malvezzi, V.; Man, N.; Mandel, I.; Mandic, V.; Mangano, V.; Mangano, V.; Mansell, G. L.; Mantovani, M.; Marchesoni, F.; Marion, F.; Márka, S.; Márka, Z.; Markosyan, A.; Maros, E.; Martelli, F.; Martellini, L.; Martin, I. W.; Martin, R. M.; Martynov, D.; Marx, J. N.; Mason, K.; Masserot, A.; Massinger, T. J.; Matichard, F.; Matone, L.; Mavalvala, N.; Mazumder, N.; Mazzolo, G.; McCarthy, R.; McClelland, D. E.; McCormick, S.; McGuire, S. C.; McIntyre, G.; McIver, J.; McLin, K.; McWilliams, S.; Meacher, D.; Meadors, G. D.; Meidam, J.; Meinders, M.; Melatos, A.; Mendell, G.; Mercer, R. A.; Meshkov, S.; Messenger, C.; Meyers, P. M.; Mezzani, F.; Miao, H.; Michel, C.; Middleton, H.; Mikhailov, E. E.; Milano, L.; Miller, A.; Miller, J.; Millhouse, M.; Minenkov, Y.; Ming, J.; Mirshekari, S.; Mishra, C.; Mitra, S.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.; Moe, B.; Moggi, A.; Mohan, M.; Mohanty, S. D.; Mohapatra, S. R. P.; Moore, B.; Moraru, D.; Moreno, G.; Morriss, S. R.; Mossavi, K.; Mours, B.; Mow-Lowry, C. M.; Mueller, C. L.; Mueller, G.; Mukherjee, S.; Mullavey, A.; Munch, J.; Murphy, D.; Murray, P. G.; Mytidis, A.; Nagy, M. F.; Nardecchia, I.; Nash, T.; Naticchioni, L.; Nayak, R. K.; Necula, V.; Nedkova, K.; Nelemans, G.; Neri, I.; Neri, M.; Newton, G.; Nguyen, T.; Nielsen, A. B.; Nissanke, S.; Nitz, A. H.; Nocera, F.; Nolting, D.; Normandin, M. E. N.; Nuttall, L. K.; Ochsner, E.; O'Dell, J.; Oelker, E.; Ogin, G. H.; Oh, J. J.; Oh, S. H.; Ohme, F.; Oppermann, P.; Oram, R.; O'Reilly, B.; Ortega, W.; O'Shaughnessy, R.; Osthelder, C.; Ottaway, D. J.; Ottens, R. S.; Overmier, H.; Owen, B. J.; Padilla, C.; Pai, A.; Pai, S.; Palashov, O.; Palomba, C.; Pal-Singh, A.; Pan, H.; Pankow, C.; Pannarale, F.; Pant, B. C.; Paoletti, F.; Papa, M. A.; Paris, H.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Patrick, Z.; Pedraza, M.; Pekowsky, L.; Pele, A.; Penn, S.; Perreca, A.; Phelps, M.; Pichot, M.; Piergiovanni, F.; Pierro, V.; Pillant, G.; Pinard, L.; Pinto, I. M.; Pitkin, M.; Poeld, J.; Poggiani, R.; Post, A.; Poteomkin, A.; Powell, J.; Prasad, J.; Predoi, V.; Premachandra, S.; Prestegard, T.; Price, L. R.; Prijatelj, M.; Principe, M.; Privitera, S.; Prodi, G. A.; Prokhorov, L.; Puncken, O.; Punturo, M.; Puppo, P.; Pürrer, M.; Qin, J.; Quetschke, V.; Quintero, E.; Quiroga, G.; Quitzow-James, R.; Raab, F. J.; Rabeling, D. S.; Rácz, I.; Radkins, H.; Raffai, P.; Raja, S.; Rajalakshmi, G.; Rakhmanov, M.; Ramirez, K.; Rapagnani, P.; Raymond, V.; Razzano, M.; Re, V.; Reed, C. M.; Regimbau, T.; Rei, L.; Reid, S.; Reitze, D. H.; Reula, O.; Ricci, F.; Riles, K.; Robertson, N. A.; Robie, R.; Robinet, F.; Rocchi, A.; Rolland, L.; Rollins, J. G.; Roma, V.; Romano, R.; Romanov, G.; Romie, J. H.; Rosińska, D.; Rowan, S.; Rüdiger, A.; Ruggi, P.; Ryan, K.; Sachdev, S.; Sadecki, T.; Sadeghian, L.; Saleem, M.; Salemi, F.; Sammut, L.; Sandberg, V.; Sanders, J. R.; Sannibale, V.; Santiago-Prieto, I.; Sassolas, B.; Sathyaprakash, B. S.; Saulson, P. R.; Savage, R.; Sawadsky, A.; Scheuer, J.; Schilling, R.; Schmidt, P.; Schnabel, R.; Schofield, R. M. S.; Schreiber, E.; Schuette, D.; Schutz, B. F.; Scott, J.; Scott, S. M.; Sellers, D.; Sengupta, A. S.; Sentenac, D.; Sequino, V.; Serafinelli, R.; Sergeev, A.; Serna, G.; Sevigny, A.; Shaddock, D. A.; Shah, S.; Shahriar, M. S.; Shaltev, M.; Shao, Z.; Shapiro, B.; Shawhan, P.; Shoemaker, D. H.; Sidery, T. L.; Siellez, K.; Siemens, X.; Sigg, D.; Silva, A. D.; Simakov, D.; Singer, A.; Singer, L.; Singh, R.; Sintes, A. M.; Slagmolen, B. J. J.; Smith, J. R.; Smith, M. R.; Smith, R. J. E.; Smith-Lefebvre, N. D.; Son, E. J.; Sorazu, B.; Souradeep, T.; Staley, A.; Stebbins, J.; Steinke, M.; Steinlechner, J.; Steinlechner, S.; Steinmeyer, D.; Stephens, B. C.; Steplewski, S.; Stevenson, S.; Stone, R.; Strain, K. A.; Straniero, N.; Strigin, S.; Sturani, R.; Stuver, A. L.; Summerscales, T. Z.; Sutton, P. J.; Swinkels, B.; Szczepanczyk, M.; Szeifert, G.; Tacca, M.; Talukder, D.; Tanner, D. B.; Tápai, M.; Tarabrin, S. P.; Taracchini, A.; Taylor, R.; Tellez, G.; Theeg, T.; Thirugnanasambandam, M. P.; Thomas, M.; Thomas, P.; Thorne, K. A.; Thorne, K. S.; Thrane, E.; Tiwari, V.; Tomlinson, C.; Tonelli, M.; Torres, C. V.; Torrie, C. I.; Travasso, F.; Traylor, G.; Tse, M.; Tshilumba, D.; Ugolini, D.; Unnikrishnan, C. S.; Urban, A. L.; Usman, S. A.; Vahlbruch, H.; Vajente, G.; Vajente, G.; Valdes, G.; Vallisneri, M.; van Bakel, N.; van Beuzekom, M.; van den Brand, J. F. J.; van den Broeck, C.; van der Sluys, M. V.; van Heijningen, J.; van Veggel, A. A.; Vass, S.; Vasúth, M.; Vaulin, R.; Vecchio, A.; Vedovato, G.; Veitch, J.; Veitch, J.; Veitch, P. J.; Venkateswara, K.; Verkindt, D.; Vetrano, F.; Viceré, A.; Vincent-Finley, R.; Vinet, J.-Y.; Vitale, S.; Vo, T.; Vocca, H.; Vorvick, C.; Vousden, W. D.; Vyatchanin, S. P.; Wade, A. R.; Wade, L.; Wade, M.; Walker, M.; Wallace, L.; Walsh, S.; Wang, H.; Wang, M.; Wang, X.; Ward, R. L.; Warner, J.; Was, M.; Weaver, B.; Wei, L.-W.; Weinert, M.; Weinstein, A. J.; Weiss, R.; Welborn, T.; Wen, L.; Wessels, P.; Westphal, T.; Wette, K.; Whelan, J. T.; White, D. J.; Whiting, B. F.; Wilkinson, C.; Williams, L.; Williams, R.; Williamson, A. R.; Willis, J. L.; Willke, B.; Wimmer, M.; Winkler, W.; Wipf, C. C.; Wittel, H.; Woan, G.; Worden, J.; Xie, S.; Yablon, J.; Yakushin, I.; Yam, W.; Yamamoto, H.; Yancey, C. C.; Yang, Q.; Yvert, M.; ZadroŻny, A.; Zanolin, M.; Zendri, J.-P.; Zhang, Fan; Zhang, L.; Zhang, M.; Zhang, Y.; Zhao, C.; Zhou, M.; Zhu, X. J.; Zucker, M. E.; Zuraw, S.; Zweizig, J.; LIGO Scientific Collaboration; Virgo Collaboration

    2015-01-01

    In this paper we present the results of a coherent narrow-band search for continuous gravitational-wave signals from the Crab and Vela pulsars conducted on Virgo VSR4 data. In order to take into account a possible small mismatch between the gravitational-wave frequency and two times the star rotation frequency, inferred from measurement of the electromagnetic pulse rate, a range of 0.02 Hz around two times the star rotational frequency has been searched for both the pulsars. No evidence for a signal has been found and 95% confidence level upper limits have been computed assuming both that polarization parameters are completely unknown and that they are known with some uncertainty, as derived from x-ray observations of the pulsar wind torii. For Vela the upper limits are comparable to the spin-down limit, computed assuming that all the observed spin-down is due to the emission of gravitational waves. For Crab the upper limits are about a factor of 2 below the spin-down limit, and represent a significant improvement with respect to past analysis. This is the first time the spin-down limit is significantly overcome in a narrow-band search.

  17. Narrow-Band Search of Continuous Gravitational-Wave Signals from Crab and Vela Pulsars in Virgo VSR4 Data

    NASA Technical Reports Server (NTRS)

    Aasi, J.; Abbott, B. P.; Abbott, R.; Abbott, T.; Abernathy, M. R.; Acernese, F.; Ackley, K.; Adams, C.; Adams, T.; Adams, T.; hide

    2015-01-01

    In this paper we present the results of a coherent narrow-band search for continuous gravitational-wave signals from the Crab and Vela pulsars conducted on Virgo VSR4 data. In order to take into account a possible small mismatch between the gravitational wave frequency and two times the star rotation frequency, inferred from measurement of the electromagnetic pulse rate, a range of 0.02 Hz around two times the star rotational frequency has been searched for both the pulsars. No evidence for a signal has been found and 95% confidence level upper limits have been computed both assuming polarization parameters are completely unknown and that they are known with some uncertainty, as derived from X-ray observations of the pulsar wind torii. For Vela the upper limits are comparable to the spin-down limit, computed assuming that all the observed spin-down is due to the emission of gravitational waves. For Crab the upper limits are about a factor of two below the spin-down limit, and represent a significant improvement with respect to past analysis. This is the first time the spin-down limit is significantly overcome in a narrow-band search.

  18. A traveling wave ultrasonic motor of high torque.

    PubMed

    Chen, Y; Liu, Q L; Zhou, T Y

    2006-12-22

    A traveling wave ultrasonic motor of high torque with a new configuration is proposed in this paper. In the new design, a part of the motor serves as the stator. The rotor is the vibrator consisting of a toothed metal ring with piezoelectric ceramic bonded, which generates ultrasonic vibration. The rotor is in contact with the shell of motor and is driven by the friction between the rotor and the stator. This configuration not only removes the rotor in a conventional type of traveling wave ultrasonic motor but also changes the interaction between the rotor and the stator of the motor so that it improves the output performance of the motor. Although an electric brush is added to the ultrasonic motor, it is easy to be fabricated because of the low speed of motor. The finite element method was used to compute the vibration modes of an ultrasonic motor with a diameter of 100mm to optimize the design of the motor. A 9th mode was chosen as the operation mode with a resonance frequency about 25 kHz. According to the design, a prototype was fabricated. Its performance was measured. The rotation speed-torque curves for various frequencies were obtained. The result shows that its stall torque is greater than 4 Nm within a range of 400 Hz. This ultrasonic motor was used to drive the window glass of a mobile car and the result was satisfactory. In the further the research on the friction material between the stator and the rotor is under way to improve the efficiency of the ultrasonic motor.

  19. Characterizing Global Flood Wave Travel Times to Optimize the Utility of Near Real-Time Satellite Remote Sensing Products

    NASA Astrophysics Data System (ADS)

    Allen, G. H.; David, C. H.; Andreadis, K. M.; Emery, C. M.; Famiglietti, J. S.

    2017-12-01

    Earth observing satellites provide valuable near real-time (NRT) information about flood occurrence and magnitude worldwide. This NRT information can be used in early flood warning systems and other flood management applications to save lives and mitigate flood damage. However, these NRT products are only useful to early flood warning systems if they are quickly made available, with sufficient time for flood mitigation actions to be implemented. More specifically, NRT data latency, or the time period between the satellite observation and when the user has access to the information, must be less than the time it takes a flood to travel from the flood observation location to a given downstream point of interest. Yet the paradigm that "lower latency is always better" may not necessarily hold true in river systems due to tradeoffs between data latency and data quality. Further, the existence of statistical breaks in the global distribution of flood wave travel time (i.e. a jagged statistical distribution) would represent preferable latencies for river-observation NRT remote sensing products. Here we present a global analysis of flood wave velocity (i.e. flow celerity) and travel time. We apply a simple kinematic wave model to a global hydrography dataset and calculate flow wave celerity and travel time during bankfull flow conditions. Bankfull flow corresponds to the condition of maximum celerity and thus we present the "worst-case scenario" minimum flow wave travel time. We conduct a similar analysis with respect to the time it takes flood waves to reach the next downstream city, as well as the next downstream reservoir. Finally, we conduct these same analyses, but with regards to the technical capabilities of the planned Surface Water and Ocean Topography (SWOT) satellite mission, which is anticipated to provide waterbody elevation and extent measurements at an unprecedented spatial and temporal resolution. We validate these results with discharge records from paired

  20. Small X-Band Oscillator Antennas

    NASA Technical Reports Server (NTRS)

    Lee, Richard Q.; Miranda, Felix A.; Clark, Eric B.; Wilt, David M.; Mueller, Carl H.; Kory, Carol L.; Lambert, Kevin M.

    2009-01-01

    A small, segmented microstrip patch antenna integrated with an X-band feedback oscillator on a high-permittivity substrate has been built and tested. This oscillator antenna is a prototype for demonstrating the feasibility of such devices as compact, low-power-consumption building blocks of advanced, lightweight, phased antenna arrays that would generate steerable beams for communication and remotesensing applications.

  1. Manipulating Traveling Brain Waves with Electric Fields: From Theory to Experiment.

    NASA Astrophysics Data System (ADS)

    Gluckman, Bruce J.

    2004-03-01

    Activity waves in disinhibited neocortical slices have been used as a biological model for epileptic seizure propagation [1]. Such waves have been mathematically modeled with integro-differential equations [2] representing non-local reaction diffusion dynamics of an excitable medium with an excitability threshold. Stability and propagation speed of traveling pulse solutions depend strongly on the threshold in the following manner: propagation speed should decrease with increased threshold over a finite range, beyond which the waves become unstable. Because populations of neurons can be polarized with an applied electric field that effectively shifts their threshold for action potential initiation [3], we predicted, and have experimentally verified, that electric fields could be used globally or locally to speed up, slow down and even block wave propagation. [1] Telfeian and Conners, Epilepsia, 40, 1499-1506, 1999. [2] Pinto and Ermentrout, SIAM J. App. Math, 62, 206-225, 2001. [3] Gluckman, et. al. J Neurophysiol. 76, 4202-5, 1996.

  2. 50 Gb/s hybrid silicon traveling-wave electroabsorption modulator.

    PubMed

    Tang, Yongbo; Chen, Hui-Wen; Jain, Siddharth; Peters, Jonathan D; Westergren, Urban; Bowers, John E

    2011-03-28

    We have demonstrated a traveling-wave electroabsorption modulator based on the hybrid silicon platform. For a device with a 100 μm active segment, the small-signal electro/optical response renders a 3 dB bandwidth of around 42 GHz and its modulation efficiency reaches 23 GHz/V. A dynamic extinction ratio of 9.8 dB with a driving voltage swing of only 2 V was demonstrated at a transmission rate of 50 Gb/s. This represents a significant improvement for modulators compatible with integration of silicon-based photonic integrated circuits.

  3. Direct EUV/X-Ray Modulation of the Ionosphere During the August 2017 Total Solar Eclipse

    NASA Astrophysics Data System (ADS)

    Mrak, Sebastijan; Semeter, Joshua; Drob, Douglas; Huba, J. D.

    2018-05-01

    The great American total solar eclipse of 21 August 2017 offered a fortuitous opportunity to study the response of the atmosphere and ionosphere using a myriad of ground instruments. We have used the network of U.S. Global Positioning System receivers to examine perturbations in maps of ionospheric total electron content (TEC). Coherent large-scale variations in TEC have been interpreted by others as gravity wave-induced traveling ionospheric disturbances. However, the solar disk had two active regions at that time, one near the center of the disk and one at the edge, which resulted in an irregular illumination pattern in the extreme ultraviolet (EUV)/X-ray bands. Using detailed EUV occultation maps calculated from the National Aeronautics and Space Administration Solar Dynamics Observatory Atmospheric Imaging Assembly images, we show excellent agreement between TEC perturbations and computed gradients in EUV illumination. The results strongly suggest that prominent large-scale TEC disturbances were consequences of direct EUV modulation, rather than gravity wave-induced traveling ionospheric disturbances.

  4. Traveling-Wave Tube Cold-Test Circuit Optimization Using CST MICROWAVE STUDIO

    NASA Technical Reports Server (NTRS)

    Chevalier, Christine T.; Kory, Carol L.; Wilson, Jeffrey D.; Wintucky, Edwin G.; Dayton, James A., Jr.

    2003-01-01

    The internal optimizer of CST MICROWAVE STUDIO (MWS) was used along with an application-specific Visual Basic for Applications (VBA) script to develop a method to optimize traveling-wave tube (TWT) cold-test circuit performance. The optimization procedure allows simultaneous optimization of circuit specifications including on-axis interaction impedance, bandwidth or geometric limitations. The application of Microwave Studio to TWT cold-test circuit optimization is described.

  5. Refinement and Pattern Formation in Neural Circuits by the Interaction of Traveling Waves with Spike-Timing Dependent Plasticity

    PubMed Central

    Bennett, James E. M.; Bair, Wyeth

    2015-01-01

    Traveling waves in the developing brain are a prominent source of highly correlated spiking activity that may instruct the refinement of neural circuits. A candidate mechanism for mediating such refinement is spike-timing dependent plasticity (STDP), which translates correlated activity patterns into changes in synaptic strength. To assess the potential of these phenomena to build useful structure in developing neural circuits, we examined the interaction of wave activity with STDP rules in simple, biologically plausible models of spiking neurons. We derive an expression for the synaptic strength dynamics showing that, by mapping the time dependence of STDP into spatial interactions, traveling waves can build periodic synaptic connectivity patterns into feedforward circuits with a broad class of experimentally observed STDP rules. The spatial scale of the connectivity patterns increases with wave speed and STDP time constants. We verify these results with simulations and demonstrate their robustness to likely sources of noise. We show how this pattern formation ability, which is analogous to solutions of reaction-diffusion systems that have been widely applied to biological pattern formation, can be harnessed to instruct the refinement of postsynaptic receptive fields. Our results hold for rich, complex wave patterns in two dimensions and over several orders of magnitude in wave speeds and STDP time constants, and they provide predictions that can be tested under existing experimental paradigms. Our model generalizes across brain areas and STDP rules, allowing broad application to the ubiquitous occurrence of traveling waves and to wave-like activity patterns induced by moving stimuli. PMID:26308406

  6. Refinement and Pattern Formation in Neural Circuits by the Interaction of Traveling Waves with Spike-Timing Dependent Plasticity.

    PubMed

    Bennett, James E M; Bair, Wyeth

    2015-08-01

    Traveling waves in the developing brain are a prominent source of highly correlated spiking activity that may instruct the refinement of neural circuits. A candidate mechanism for mediating such refinement is spike-timing dependent plasticity (STDP), which translates correlated activity patterns into changes in synaptic strength. To assess the potential of these phenomena to build useful structure in developing neural circuits, we examined the interaction of wave activity with STDP rules in simple, biologically plausible models of spiking neurons. We derive an expression for the synaptic strength dynamics showing that, by mapping the time dependence of STDP into spatial interactions, traveling waves can build periodic synaptic connectivity patterns into feedforward circuits with a broad class of experimentally observed STDP rules. The spatial scale of the connectivity patterns increases with wave speed and STDP time constants. We verify these results with simulations and demonstrate their robustness to likely sources of noise. We show how this pattern formation ability, which is analogous to solutions of reaction-diffusion systems that have been widely applied to biological pattern formation, can be harnessed to instruct the refinement of postsynaptic receptive fields. Our results hold for rich, complex wave patterns in two dimensions and over several orders of magnitude in wave speeds and STDP time constants, and they provide predictions that can be tested under existing experimental paradigms. Our model generalizes across brain areas and STDP rules, allowing broad application to the ubiquitous occurrence of traveling waves and to wave-like activity patterns induced by moving stimuli.

  7. Travelling wave solutions of the homogeneous one-dimensional FREFLO model

    NASA Astrophysics Data System (ADS)

    Huang, B.; Hong, J. Y.; Jing, G. Q.; Niu, W.; Fang, L.

    2018-01-01

    Presently there is quite few analytical studies in traffic flows due to the non-linearity of the governing equations. In the present paper we introduce travelling wave solutions for the homogeneous one-dimensional FREFLO model, which are expressed in the form of series and describe the procedure that vehicles/pedestrians move with a negative velocity and decelerate until rest, then accelerate inversely to positive velocities. This method is expect to be extended to more complex situations in the future.

  8. Travelling-wave solutions of a weakly nonlinear two-dimensional higher-order Kadomtsev-Petviashvili dynamical equation for dispersive shallow-water waves

    NASA Astrophysics Data System (ADS)

    Seadawy, Aly R.

    2017-01-01

    The propagation of three-dimensional nonlinear irrotational flow of an inviscid and incompressible fluid of the long waves in dispersive shallow-water approximation is analyzed. The problem formulation of the long waves in dispersive shallow-water approximation lead to fifth-order Kadomtsev-Petviashvili (KP) dynamical equation by applying the reductive perturbation theory. By using an extended auxiliary equation method, the solitary travelling-wave solutions of the two-dimensional nonlinear fifth-order KP dynamical equation are derived. An analytical as well as a numerical solution of the two-dimensional nonlinear KP equation are obtained and analyzed with the effects of external pressure flow.

  9. ON THE PROBLEM OF PARTICLE GROUPINGS IN A TRAVELING WAVE LINEAR ACCELERATOR

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhileyko, G.I.

    1957-01-01

    A linear accelerator with traveling'' waves may be used for the production of especially short electron momenta, although in many cases the grouping capacity of the accelerator is not sufficient. Theoretically the case is derived in which grouping of the electrons takes place in the accelerator itself. (With 3 illustrations and 1 Slavic Reference). (TCO)

  10. Temporal change in shallow subsurface P- and S-wave velocities and S-wave anisotropy inferred from coda wave interferometry

    NASA Astrophysics Data System (ADS)

    Yamamoto, M.; Nishida, K.; Takeda, T.

    2012-12-01

    Recent progresses in theoretical and observational researches on seismic interferometry reveal the possibility to detect subtle change in subsurface seismic structure. This high sensitivity of seismic interferometry to the medium properties may thus one of the most important ways to directly observe the time-lapse behavior of shallow crustal structure. Here, using the coda wave interferometry, we show the co-seismic and post-seismic changes in P- and S-wave velocities and S-wave anisotropy associated with the 2011 off the Pacific coast of Tohoku earthquake (M9.0). In this study, we use the acceleration data recorded at KiK-net stations operated by NIED, Japan. Each KiK-net station has a borehole whose typical depth is about 100m, and two three-component accelerometers are installed at the top and bottom of the borehole. To estimate the shallow subsurface P- and S-wave velocities and S-wave anisotropy between two sensors and their temporal change, we select about 1000 earthquakes that occurred between 2004 and 2012, and extract body waves propagating between borehole sensors by computing the cross-correlation functions (CCFs) of 3 x 3 component pairs. We use frequency bands of 2-4, 4-8, 8-16 Hz in our analysis. Each averaged CCF shows clear wave packets traveling between borehole sensors, and their travel times are almost consistent with those of P- and S-waves calculated from the borehole log data. Until the occurrence of the 2011 Tohoku earthquake, the estimated travel time at each station is rather stable with time except for weak seasonal/annual variation. On the other hand, the 2011 Tohoku earthquake and its aftershocks cause sudden decrease in the S-wave velocity at most of the KiK-net stations in eastern Japan. The typical value of S-wave velocity changes, which are measured by the time-stretching method, is about 5-15%. After this co-seismic change, the S-wave velocity gradually recovers with time, and the recovery continues for over one year following the

  11. Calculation of the X-Ray emission K and L 2,3 bands of metallic magnesium and aluminum with allowance for multielectron effects

    NASA Astrophysics Data System (ADS)

    Ovcharenko, R. E.; Tupitsyn, I. I.; Savinov, E. P.; Voloshina, E. N.; Dedkov, Yu. S.; Shulakov, A. S.

    2014-01-01

    A procedure is proposed to calculate the shape of the characteristic X-ray emission bands of metals with allowance for multielectron effects. The effects of the dynamic screening of a core vacancy by conduction electrons and the Auger effect in the valence band are taken into account. The dynamic screening of a core vacancy, which is known to be called the MND (Mahan-Nozeieres-De Dominics) effect, is taken into account by an ab initio band calculation of crystals using the PAW (projected augmented waves) method. The Auger effect is taken into account by a semiempirical method using the approximation of a quadratic dependence of the level width in the valence band on the difference between the level energy and the Fermi energy. The proposed calculation procedure is used to describe the X-ray emission K and L 2,3 bands of metallic magnesium and aluminum crystals. The calculated spectra agree well with the experimental bands both near the Fermi level and in the low-energy part of the spectra in all cases.

  12. Validation of attenuation, beam blockage, and calibration estimation methods using two dual polarization X band weather radars

    NASA Astrophysics Data System (ADS)

    Diederich, M.; Ryzhkov, A.; Simmer, C.; Mühlbauer, K.

    2011-12-01

    The amplitude a of radar wave reflected by meteorological targets can be misjudged due to several factors. At X band wavelength, attenuation of the radar beam by hydro meteors reduces the signal strength enough to be a significant source of error for quantitative precipitation estimation. Depending on the surrounding orography, the radar beam may be partially blocked when scanning at low elevation angles, and the knowledge of the exact amount of signal loss through beam blockage becomes necessary. The phase shift between the radar signals at horizontal and vertical polarizations is affected by the hydrometeors that the beam travels through, but remains unaffected by variations in signal strength. This has allowed for several ways of compensating for the attenuation of the signal, and for consistency checks between these variables. In this study, we make use of several weather radars and gauge network measuring in the same area to examine the effectiveness of several methods of attenuation and beam blockage corrections. The methods include consistency checks of radar reflectivity and specific differential phase, calculation of beam blockage using a topography map, estimating attenuation using differential propagation phase, and the ZPHI method proposed by Testud et al. in 2000. Results show the high effectiveness of differential phase in estimating attenuation, and potential of the ZPHI method to compensate attenuation, beam blockage, and calibration errors.

  13. MODELING THE MULTI-BAND AFTERGLOW OF GRB 130831A: EVIDENCE FOR A SPINNING-DOWN MAGNETAR DOMINATED BY GRAVITATIONAL WAVE LOSSES?

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhang, Q.; Zong, H. S.; Huang, Y. F., E-mail: zonghs@nju.edu.cn, E-mail: hyf@nju.edu.cn

    2016-06-01

    The X-ray afterglow of GRB 130831A shows an “internal plateau” with a decay slope of ∼0.8, followed by a steep drop at around 10{sup 5} s with a slope of ∼6. After the drop, the X-ray afterglow continues with a much shallower decay. The optical afterglow exhibits two segments of plateaus separated by a luminous optical flare, followed by a normal decay with a slope basically consistent with that of the late-time X-ray afterglow. The decay of the internal X-ray plateau is much steeper than what we expect in the simplest magnetar model. We propose a scenario in which themore » magnetar undergoes gravitational-wave-driven r-mode instability, and the spin-down is dominated by gravitational wave losses up to the end of the steep plateau, so that such a relatively steep plateau can be interpreted as the internal emission of the magnetar wind and the sharp drop can be produced when the magnetar collapses into a black hole. This scenario also predicts an initial X-ray plateau lasting for hundreds of seconds with an approximately constant flux which is compatible with observation. Assuming that the magnetar wind has a negligible contribution in the optical band, we interpret the optical afterglow as the forward shock emission by invoking the energy injection from a continuously refreshed shock following the prompt emission phase. It is shown that our model can basically describe the temporal evolution of the multi-band afterglow of GRB 130831A.« less

  14. Modeling the Multi-band Afterglow of GRB 130831A: Evidence for a Spinning-down Magnetar Dominated by Gravitational Wave Losses?

    NASA Astrophysics Data System (ADS)

    Zhang, Q.; Huang, Y. F.; Zong, H. S.

    2016-06-01

    The X-ray afterglow of GRB 130831A shows an “internal plateau” with a decay slope of ˜0.8, followed by a steep drop at around 105 s with a slope of ˜6. After the drop, the X-ray afterglow continues with a much shallower decay. The optical afterglow exhibits two segments of plateaus separated by a luminous optical flare, followed by a normal decay with a slope basically consistent with that of the late-time X-ray afterglow. The decay of the internal X-ray plateau is much steeper than what we expect in the simplest magnetar model. We propose a scenario in which the magnetar undergoes gravitational-wave-driven r-mode instability, and the spin-down is dominated by gravitational wave losses up to the end of the steep plateau, so that such a relatively steep plateau can be interpreted as the internal emission of the magnetar wind and the sharp drop can be produced when the magnetar collapses into a black hole. This scenario also predicts an initial X-ray plateau lasting for hundreds of seconds with an approximately constant flux which is compatible with observation. Assuming that the magnetar wind has a negligible contribution in the optical band, we interpret the optical afterglow as the forward shock emission by invoking the energy injection from a continuously refreshed shock following the prompt emission phase. It is shown that our model can basically describe the temporal evolution of the multi-band afterglow of GRB 130831A.

  15. Internal Waves, Western Indian Ocean

    NASA Image and Video Library

    1991-12-01

    STS044-79-077 (24 Nov.-1 Dec. 1991) --- This photograph, captured from the Earth-orbiting Space Shuttle Atlantis, shows sunglint pattern in the western tropical Indian Ocean. Several large internal waves reflect around a shallow area on the sea floor. NASA scientists studying the STS-44 photography believe the shallow area to be a sediment (a submerged mountain) on top of the Mascarene Plateau, located northeast of Madagascar at approximately 5.6 degrees south latitude and 55.7 degrees east longitude. Internal waves are similar to surface ocean waves, except that they travel inside the water column along the boundary between water layers of different density. At the surface, their passage is marked on the sea surface by bands of smooth and rough water. These bands appear in the sunglint pattern as areas of brighter or darker water. NASA scientists point out that, when the waves encounter an obstacle, such as a near-surface seamount, they bend or refract around the obstacle in the same manner as surface waves bend around an island or headland.

  16. Unraveling the excitation mechanisms of highly oblique lower-band chorus waves

    DOE PAGES

    Li, Wen; Mourenas, D.; Artemyev, A. V.; ...

    2016-08-17

    Excitation mechanisms of highly oblique, quasi-electrostatic lower band chorus waves are investigated using Van Allen Probes observations near the equator of the Earth's magnetosphere. Linear growth rates are evaluated based on in situ, measured electron velocity distributions and plasma conditions and compared with simultaneously observed wave frequency spectra and wave normal angles. Accordingly, two distinct excitation mechanisms of highly oblique lower band chorus have been clearly identified for the first time. The first mechanism relies on cyclotron resonance with electrons possessing both a realistic temperature anisotropy at keV energies and a plateau at 100–500 eV in the parallel velocity distribution.more » The second mechanism corresponds to Landau resonance with a 100–500 eV beam. In both cases, a small low-energy beam-like component is necessary for suppressing an otherwise dominating Landau damping. In conclusion, our new findings suggest that small variations in the electron distribution could have important impacts on energetic electron dynamics.« less

  17. A Ka-band radial relativistic backward wave oscillator with GW-class output power

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhu, Jiaxin; Zhang, Xiaoping, E-mail: zhangxiaoping@nudt.edu.cn; Dang, Fangchao

    A novel radial relativistic backward wave oscillator with a reflector is proposed and designed to generate GW-level high power microwaves at Ka-band. The segmented radial slow wave structure and the reflector are matched to enhance interaction efficiency. We choose the volume wave TM{sub 01} mode as the working mode due to the volume wave characteristic. The main structural parameters of the novel device are optimized by particle-in-cell simulation. High power microwaves with power of 2 GW and a frequency of 29.4 GHz are generated with 30% efficiency when the electron beam voltage is 383 kV, the beam current is 17 kA, and themore » guiding magnetic field is only 0.6 T. Simultaneously, the highest electric field in the novel Ka-band device is just about 960 kV/cm in second slow wave structure.« less

  18. Valence band offsets of Sc x Ga1-x N/AlN and Sc x Ga1-x N/GaN heterojunctions

    NASA Astrophysics Data System (ADS)

    Tsui, H. C. L.; Goff, L. E.; Palgrave, R. G.; Beere, H. E.; Farrer, I.; Ritchie, D. A.; Moram, M. A.

    2016-07-01

    The valence band offsets of Sc x Ga1-x N/AlN heterojunctions were measured by x-ray photoelectron spectroscopy (XPS) and were found to increase from 0.42 eV to 0.95 eV as the Sc content x increased from 0 to 0.15. The increase in valence band offset with increasing x is attributed to the corresponding increase in spontaneous polarization of the wurtzite structure. The Sc x Ga1-x N/AlN heterojunction is type I, similar to other III-nitride-based heterojunctions. The data also indicate that a type II staggered heterojunction, which can enhance spatial charge separation, could be formed if Sc x Ga1-x N is grown on GaN.

  19. W-Band Transmission MeasurementS and X-Band Dielectric Properties Measurements for a Radome Material Sample

    NASA Technical Reports Server (NTRS)

    Cravey, Robin L.; Tiemsin, Pacita I.

    1997-01-01

    This paper describes measurements which were performed on a sample of radome material in the Electromagnetic Properties Measurements Laboratory (EPML). The purpose of the measurements described in this paper was to determine the one-way transmission loss through the flat panel of radome material for a frequency range of 84 to 94 GHz, for varying incidence angles. The panel, which was manufactured by Norton Performance Plastics Corporation, was provided to the EPML by TRW. The size of the panel is 40 in x 36 in x 0.422 in and consists of a foam material with one side coated with a smooth white coating (this side will be referred to as the front side). The dielectric properties of the foam material from the inside of the panel were also determined at X-band (8.2-12.4 GHz). The W-band free space measurements are presented first, followed by the X-band dielectric properties measurements.

  20. Nitrogen-related intermediate band in P-rich GaN xP yAs 1-x-y alloys

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zelazna, K.; Gladysiewicz, M.; Polak, M. P.

    The electronic band structure of phosphorus-rich GaN xP yAs 1-x-y alloys (x ~ 0.025 and y ≥ 0.6) is studied experimentally using optical absorption, photomodulated transmission, contactless electroreflectance, and photoluminescence. Here, it is shown that incorporation of a few percent of N atoms has a drastic effect on the electronic structure of the alloys. The change of the electronic band structure is very well described by the band anticrossing (BAC) model in which localized nitrogen states interact with the extended states of the conduction band of GaAsP host. The BAC interaction results in the formation of a narrow intermediate bandmore » (E - band in BAC model) with the minimum at the Γ point of the Brillouin zone resulting in a change of the nature of the fundamental band gap from indirect to direct. The splitting of the conduction band by the BAC interaction is further confirmed by a direct observation of the optical transitions to the E + band using contactless electroreflectance spectroscopy.« less

  1. Nitrogen-related intermediate band in P-rich GaN xP yAs 1-x-y alloys

    DOE PAGES

    Zelazna, K.; Gladysiewicz, M.; Polak, M. P.; ...

    2017-11-16

    The electronic band structure of phosphorus-rich GaN xP yAs 1-x-y alloys (x ~ 0.025 and y ≥ 0.6) is studied experimentally using optical absorption, photomodulated transmission, contactless electroreflectance, and photoluminescence. Here, it is shown that incorporation of a few percent of N atoms has a drastic effect on the electronic structure of the alloys. The change of the electronic band structure is very well described by the band anticrossing (BAC) model in which localized nitrogen states interact with the extended states of the conduction band of GaAsP host. The BAC interaction results in the formation of a narrow intermediate bandmore » (E - band in BAC model) with the minimum at the Γ point of the Brillouin zone resulting in a change of the nature of the fundamental band gap from indirect to direct. The splitting of the conduction band by the BAC interaction is further confirmed by a direct observation of the optical transitions to the E + band using contactless electroreflectance spectroscopy.« less

  2. Travel distance as factor in follow-up visit compliance in postlaparoscopic adjustable gastric banding population.

    PubMed

    DeNino, Walter F; Osler, Turner; Evans, Ellen G; Forgione, Patrick M

    2010-01-01

    Despite the 2008 "American Association of Clinical Endocrinologists, The Obesity Society, and American Society for Metabolic and Bariatric Surgery Medical Guidelines for Clinical Practice for the Perioperative Nutritional, Metabolic, and Nonsurgical Support of the Bariatric Surgery Patient," consensus does not exist for postoperative care in laparoscopic adjustable gastric banding (LAGB) patients (grade D evidence). It has been suggested that regular follow-up is related to better outcomes, specifically greater weight loss. The aim of the present study was to investigate the effects of travel distance to the clinic on the adherence to follow-up visits and weight loss in a cohort of LAGB patients in the setting of a rural, university-affiliated teaching hospital in the United States. A retrospective chart review was performed of all consecutive LAGB patients for a 1-year period. Linear regression analysis was used to identify the relationships between appointment compliance and the distance traveled and between the amount of weight loss and the distance traveled. Linear regression analysis was performed to investigate the effect of the travel distance to the clinic on the percentage of follow-up visits postoperatively. This effect was not significant (P = .4). Linear regression analysis was also performed to elucidate the effect of the travel distance to the clinic on the amount of weight loss. This effect was significant (P = .04). The travel distance to the clinic did not seem to be a significant predictor of compliance in a cohort of LAGB patients with ≤ 1 year of follow-up in a rural setting. However, a weak relationship was found between the travel distance to the clinic and weight loss, with patients who traveled further seeming to lose slightly more weight. Copyright © 2010 American Society for Metabolic and Bariatric Surgery. Published by Elsevier Inc. All rights reserved.

  3. Design and performance verification of advanced multistage depressed collectors. [traveling wave tubes for ECM

    NASA Technical Reports Server (NTRS)

    Kosmahl, H.; Ramins, P.

    1975-01-01

    Design and performance of a small size, 4-stage depressed collector are discussed. The collector and a spent beam refocusing section preceding it are intended for efficiency enhancement of octave bandwidth, high CW power traveling wave tubes for use in ECM.

  4. Donders is dead: cortical traveling waves and the limits of mental chronometry in cognitive neuroscience.

    PubMed

    Alexander, David M; Trengove, Chris; van Leeuwen, Cees

    2015-11-01

    An assumption nearly all researchers in cognitive neuroscience tacitly adhere to is that of space-time separability. Historically, it forms the basis of Donders' difference method, and to date, it underwrites all difference imaging and trial-averaging of cortical activity, including the customary techniques for analyzing fMRI and EEG/MEG data. We describe the assumption and how it licenses common methods in cognitive neuroscience; in particular, we show how it plays out in signal differencing and averaging, and how it misleads us into seeing the brain as a set of static activity sources. In fact, rather than being static, the domains of cortical activity change from moment to moment: Recent research has suggested the importance of traveling waves of activation in the cortex. Traveling waves have been described at a range of different spatial scales in the cortex; they explain a large proportion of the variance in phase measurements of EEG, MEG and ECoG, and are important for understanding cortical function. Critically, traveling waves are not space-time separable. Their prominence suggests that the correct frame of reference for analyzing cortical activity is the dynamical trajectory of the system, rather than the time and space coordinates of measurements. We illustrate what the failure of space-time separability implies for cortical activation, and what consequences this should have for cognitive neuroscience.

  5. Study of transmission line attenuation in broad band millimeter wave frequency range.

    PubMed

    Pandya, Hitesh Kumar B; Austin, M E; Ellis, R F

    2013-10-01

    Broad band millimeter wave transmission lines are used in fusion plasma diagnostics such as electron cyclotron emission (ECE), electron cyclotron absorption, reflectometry and interferometry systems. In particular, the ECE diagnostic for ITER will require efficient transmission over an ultra wide band, 100 to 1000 GHz. A circular corrugated waveguide transmission line is a prospective candidate to transmit such wide band with low attenuation. To evaluate this system, experiments of transmission line attenuation were performed and compared with theoretical loss calculations. A millimeter wave Michelson interferometer and a liquid nitrogen black body source are used to perform all the experiments. Atmospheric water vapor lines and continuum absorption within this band are reported. Ohmic attenuation in corrugated waveguide is very low; however, there is Bragg scattering and higher order mode conversion that can cause significant attenuation in this transmission line. The attenuation due to miter bends, gaps, joints, and curvature are estimated. The measured attenuation of 15 m length with seven miter bends and eighteen joints is 1 dB at low frequency (300 GHz) and 10 dB at high frequency (900 GHz), respectively.

  6. Nonlinear waves in subwavelength waveguide arrays: evanescent bands and the "phoenix soliton".

    PubMed

    Peleg, Or; Segev, Mordechai; Bartal, Guy; Christodoulides, Demetrios N; Moiseyev, Nimrod

    2009-04-24

    We formulate wave propagation in arrays of subwavelength waveguides with sharp index contrasts and demonstrate the collapse of bands into evanescent modes and lattice solitons with superluminal phase velocity. We find a self-reviving soliton ("phoenix soliton") comprised of coupled forward- and backward-propagating light, originating solely from evanescent bands. In the linear regime, all Bloch waves comprising this beam decay, whereas a proper nonlinearity assembles them into a propagating self-trapped beam. Finally, we simulate the dynamics of such a beam and observe breakup into temporal pulses, indicating a new kind of slow-light gap solitons, trapped in time and in one transverse dimension.

  7. Traveling-Wave Solutions of the Kolmogorov-Petrovskii-Piskunov Equation

    NASA Astrophysics Data System (ADS)

    Pikulin, S. V.

    2018-02-01

    We consider quasi-stationary solutions of a problem without initial conditions for the Kolmogorov-Petrovskii-Piskunov (KPP) equation, which is a quasilinear parabolic one arising in the modeling of certain reaction-diffusion processes in the theory of combustion, mathematical biology, and other areas of natural sciences. A new efficiently numerically implementable analytical representation is constructed for self-similar plane traveling-wave solutions of the KPP equation with a special right-hand side. Sufficient conditions for an auxiliary function involved in this representation to be analytical for all values of its argument, including the endpoints, are obtained. Numerical results are obtained for model examples.

  8. Band alignment of SiO2/(AlxGa1-x)2O3 (0 ≤ x ≤ 0.49) determined by X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Feng, Zhaoqing; Feng, Qian; Zhang, Jincheng; Li, Xiang; Li, Fuguo; Huang, Lu; Chen, Hong-Yan; Lu, Hong-Liang; Hao, Yue

    2018-03-01

    In this work, we report the investigation of the band alignment of SiO2/(AlxGa1-x)2O3 (0 ≤ x ≤ 0.49) utilizing the high resolution X-ray photoelectron spectroscopy (XPS) measurements. The single crystallinity and orientation of β-(AlxGa1-x)2O3 films grown on sapphire by pulsed laser deposition were studied with the high resolution X-ray diffraction. The Ga 2p3/2 and Si 2p core-level spectra as well as valence band spectra were used in the analysis of band alignment. As the mole fraction x of Al increases from 0 to 0.49, the bandgap and conduction band offset values of SiO2/(AlxGa1-x)2O3 increases from 4.9 to 5.6 eV and from 1.5 to 2.1 eV, respectively, while that of valence band offset decreases from 2.2 to 0.9 eV. From the results obtained, the energy band diagram of the studied SiO2/(AlxGa1-x)2O3 (0 ≤ x ≤ 0.49) interfaces is found to be of type I. Energy band lineups of SiO2/(AlxGa1-x)2O3 were thus determined which can be used as for Ga2O3 based power device technology.

  9. Banded whistlers observed on OGO-4

    NASA Technical Reports Server (NTRS)

    Paymar, E. M.

    1972-01-01

    Inspection of broadband VLF records from OGO-4 shows that some whistlers exhibit a banded structure in which one or more bands of frequencies are missing from the whistler's spectrum. The phenomenon is commonly observed by satellites on midlatitude field lines at all local times and at various longitudes around the world. The dispersion of banded whistlers (BW) is of several tens of sec to the 1/2 power, indicating that they originated in the opposite hemisphere and are propagating downward at the satellite. BW are generally spread in time (tenths of seconds) rather than sharply defined and tend to occur at random. The frequency spacing of the bands may be either uniform or irregular, and may vary radically between successive events. Several possible explanations for BW are considered. In particular, an analysis of the interaction of plane electromagnetic waves traveling in an anisotropic plasma with a field aligned slab of enhanced ionization is presented with promising results.

  10. Simulation of TunneLadder traveling-wave tube cold-test characteristics: Implementation of the three-dimensional, electromagnetic circuit analysis code micro-SOS

    NASA Technical Reports Server (NTRS)

    Kory, Carol L.; Wilson, Jeffrey D.

    1993-01-01

    The three-dimensional, electromagnetic circuit analysis code, Micro-SOS, can be used to reduce expensive time-consuming experimental 'cold-testing' of traveling-wave tube (TWT) circuits. The frequency-phase dispersion characteristics and beam interaction impedance of a TunneLadder traveling-wave tube slow-wave structure were simulated using the code. When reasonable dimensional adjustments are made, computer results agree closely with experimental data. Modifications to the circuit geometry that would make the TunneLadder TWT easier to fabricate for higher frequency operation are explored.

  11. The electronic band structure of Ge1-x Sn x in the full composition range: indirect, direct, and inverted gaps regimes, band offsets, and the Burstein-Moss effect

    NASA Astrophysics Data System (ADS)

    Polak, M. P.; Scharoch, P.; Kudrawiec, R.

    2017-05-01

    A comprehensive and detailed study of the composition dependence of lattice constants, band gaps and band offsets has been performed for bulk Ge1-x Sn x alloy in the full composition range using state-of-the-art density functional theory methods. A spectral weight approach to band unfolding has been applied as a means of distinguishing the indirect and direct band gaps from folded supercell band structures. In this way, four characteristic regions of the band gap character have been identified for Ge1-x Sn x alloy: an indirect band gap (x  <  6.5%), a direct band gap (6.5%  <  x  <  25%) and an inverse band gap (x  >  25%) with inverse spin-orbit split-off for 45%  <  x  <  85%. In general, it has been observed that the bowing parameters of band edges (Γ and L-point in conduction band (CBΓ and CB L ), valence band (VB), and spin-orbit (SO) band) are rather large ({{b}\\text{C{{\\text{B}} Γ }}}   =  2.43  ±  0.06 eV, {{b}\\text{C{{\\text{B}}L}}}   =  0.64  ±  0.04 eV, {{b}\\text{VB}}   =  -0.59  ±  0.04 eV, and {{b}\\text{SO}}   =  -0.49  ±  0.05 eV). This indicates that Ge1-x Sn x behaves like a highly mismatched group IV alloy. The composition dependence of lattice constant shows negligible bowing (b a   =  -0.083 Å). Obtained results have been compared with available experimental data. The origin of band gap reduction and large bowing has been analyzed and conclusions have been drawn regarding the relationship between experimental and theoretical results. It is shown that due to the low DOS at the Γ-point, a significant filling of CB by electrons in the direct gap regime may easily take place. Therefore, the Burstein-Moss effect should be considered when comparing experimental data with theoretical predictions as has already been shown for other intrinsic n-type narrow gap semiconductors (e.g. InN).

  12. Evaluation of band alignment of α-Ga2O3/α-(Al x Ga1‑ x )2O3 heterostructures by X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Uchida, Takayuki; Jinno, Riena; Takemoto, Shu; Kaneko, Kentaro; Fujita, Shizuo

    2018-04-01

    The band alignment at an α-Ga2O3/α-(Al x Ga1‑ x )2O3 heterointerface, with different Al compositions (x), grown on a c-plane sapphire substrate was evaluated by X-ray photoelectron spectroscopy. The experimental results show that the heterointerface has the type-I band discontinuity with the valence band offsets of 0.090, 0.12, and 0.14 eV, and the conduction band offsets of 0.34, 0.79, and 1.87 eV, for x values of 0.1, 0.4, and 0.8, respectively. The small band offset for the valence band is attributed to the fact that the valence band of oxides is constituted by the localized O 2p level, which is dominated by the nature of oxygen atoms. The type-I band discontinuity is desirable for a variety of heterostructure devices.

  13. Dual-band and high-efficiency polarization converter based on metasurfaces at microwave frequencies

    NASA Astrophysics Data System (ADS)

    Liu, Yajun; Xia, Song; Shi, Hongyu; Zhang, Anxue; Xu, Zhuo

    2016-06-01

    We present a dual-band and high-efficiency polarization converter in microwave regime. The proposed converter can convert a linearly polarized wave to its cross-polarized wave for two distinct bands: Ku (11.5-20.0 GHz) and Ka (28.8-34.0 GHz). It can also convert the linearly polarized wave to a circularly polarized wave at four other frequencies. The experimental results are in good agreement with simulation results for both frequency bands. The polarization conversion ratio is above 0.94 for the Ku-band and 0.90 for the Ka-band. Furthermore, the converter can achieve dual-band and high-efficiency polarization conversion over angles of incidence up to 45°. The converter is also polarization-selective in that only the x- and y-polarized waves can be converted. The physical mechanism of the dual-band polarization conversion effect is interpreted via decomposed electric field components that couple with different plasmon resonance modes of the structure.

  14. Angle-resolved spin wave band diagrams of square antidot lattices studied by Brillouin light scattering

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Gubbiotti, G.; Tacchi, S.; Montoncello, F.

    2015-06-29

    The Brillouin light scattering technique has been exploited to study the angle-resolved spin wave band diagrams of squared Permalloy antidot lattice. Frequency dispersion of spin waves has been measured for a set of fixed wave vector magnitudes, while varying the wave vector in-plane orientation with respect to the applied magnetic field. The magnonic band gap between the two most dispersive modes exhibits a minimum value at an angular position, which exclusively depends on the product between the selected wave vector magnitude and the lattice constant of the array. The experimental data are in very good agreement with predictions obtained bymore » dynamical matrix method calculations. The presented results are relevant for magnonic devices where the antidot lattice, acting as a diffraction grating, is exploited to achieve multidirectional spin wave emission.« less

  15. Resolving Structural Isomers of Monosaccharide Methyl Glycosides Using Drift Tube and Traveling Wave Ion Mobility Mass Spectrometry

    PubMed Central

    Li, Hongli; Giles, Kevin; Bendiak, Brad; Kaplan, Kimberly; Siems, William F.; Hill, Herbert H.

    2013-01-01

    Monosaccharide structural isomers including sixteen methyl-D-glycopyranosides and four methyl-N-acetylhexosamines were subjected to ion mobility measurements by electrospray ion mobility mass spectrometry. Two ion mobility-MS systems were employed: atmospheric pressure drift tube ion mobility time-of-flight mass spectrometry and a Synapt G2 HDMS system which incorporates a low pressure traveling wave ion mobility separator. All the compounds were investigated as [M+Na]+ ions in the positive mode. A majority of the monosaccharide structural isomers exhibited different mobility drift times in either system, depending on differences in their anomeric and stereochemical configurations. In general, drift time patterns (relative drift times of isomers) matched between the two instruments. Higher resolving power was observed using the atmospheric pressure drift tube. Collision cross section values of monosaccharide structural isomers were directly calculated from the atmospheric pressure ion mobility experiments and a collision cross section calibration curve was made for the traveling wave ion mobility instrument. Overall, it was demonstrated that ion mobility-mass spectrometry using either drift tube or traveling wave ion mobility is a valuable technique for resolving subtle variations in stereochemistry among the sodium adducts of monosaccharide methyl glycosides. PMID:22339760

  16. Characterization and Applications of Micro- and Nano- Ferrites at Microwave and Millimeter Waves

    NASA Astrophysics Data System (ADS)

    Chao, Liu

    -type barium micro- and nano-ferrite. A new fabrication process using ferrite composite is proposed to integrate the Y-junction circulator into the semiconductor substrate. Theoretical design of a high gain Traveling Wave Tube (TWT) amplifier using a metamaterial (MTM) structure and cold-test of the MTM structure are also included in this dissertation. An SWS working around 6 GHz below the X-band waveguide TE10 cutoff frequency is fabricated.

  17. Investigating Holey Metamaterial Effects in Terahertz Traveling-Wave Tube Amplifier

    NASA Technical Reports Server (NTRS)

    Starinshak, David P.; Wilson, Jeffrey D.; Chevalier, Christine T.

    2007-01-01

    Applying subwavelength holes to a novel traveling-wave tube amplifier is investigated. Plans to increase the on-axis impedance are discussed as well as optimization schemes to achieve this goal. Results suggest that an array of holes alone cannot significantly change the on-axis electric field in the vicinity of the electron beam. However, models of a beam tunnel with corrugated walls show promise in maximizing the amplifier s on-axis impedance. Additional work is required on the subject, and suggestions are made to determine research directions.

  18. The effect of inhibition on the existence of traveling wave solutions for a neural field model of human seizure termination.

    PubMed

    González-Ramírez, L R; Kramer, M A

    2018-06-01

    In this paper we study the influence of inhibition on an activity-based neural field model consisting of an excitatory population with a linear adaptation term that directly regulates the activity of the excitatory population. Such a model has been used to replicate traveling wave data as observed in high density local field potential recordings (González-Ramírez et al. PLoS Computational Biology, 11(2), e1004065, 2015). In this work, we show that by adding an inhibitory population to this model we can still replicate wave properties as observed in human clinical data preceding seizure termination, but the parameter range over which such waves exist becomes more restricted. This restriction depends on the strength of the inhibition and the timescale at which the inhibition acts. In particular, if inhibition acts on a slower timescale relative to excitation then it is possible to still replicate traveling wave patterns as observed in the clinical data even with a relatively strong effect of inhibition. However, if inhibition acts on the same timescale as the excitation, or faster, then traveling wave patterns with the desired characteristics cease to exist when the inhibition becomes sufficiently strong.

  19. High Band Technology Program (HiTeP)

    DTIC Science & Technology

    2005-03-01

    clock distribution circuit. One Receiver Memory module receives 60MHz reference sine wave and distributes 60MHz clock signals to all Receiver Memory...Diagram UNCLASSIFIED 23 in N00014-99-C-0314 Integrated Defense Systems Final Report 1 March 2005 .. 4.ran FibreXpress Fibre-Channel PMC "Motrl Medea FCR...the Electrically Short Crossed-Notch (ESCN). It is shorter than traditional traveling wave notch antennas. The 2X ECSN fin length is approximately 1.2

  20. Influence of High Speed Repetition of Pulsed Streamer Discharge Produced by Polarity-Reversed Traveling Wave on NO Oxidation

    NASA Astrophysics Data System (ADS)

    Matsuda, Eiji; Kadowaki, Kazunori; Nishimoto, Sakae; Kitani, Isamu

    This paper describes experimental results of NO removal from a simulated exhausted gas using a barrier-type plasma reactor subjected to reciprocal traveling wave voltage pulses. A pulse-forming cable was charged and then grounded at one end without any resistance, so that a traveling wave reciprocated along the cable with a change in its polarity because the traveling wave was negatively reflected at the grounded-end. Transient discharge light between point-plane electrodes with a glass barrier was observed using a gated image-intensifier. Photographs of the transient discharge light indicated that many streamer channels extended widely in the gap at the initial stage in the voltage oscillation, while only an intense discharge channel was observed at the latter stage. NO removal tests were carried out using the reciprocal pulse generator and a coaxial plasma reactor with a cylindrical glass-barrier. Results indicated that the discharges at the first and the second polarity reversals contributed largely to the oxidation reaction from NO into NO2, whereas the contribution of the subsequent discharges in the latter stage to NO removal was small.

  1. Photonic band structures solved by a plane-wave-based transfer-matrix method.

    PubMed

    Li, Zhi-Yuan; Lin, Lan-Lan

    2003-04-01

    Transfer-matrix methods adopting a plane-wave basis have been routinely used to calculate the scattering of electromagnetic waves by general multilayer gratings and photonic crystal slabs. In this paper we show that this technique, when combined with Bloch's theorem, can be extended to solve the photonic band structure for 2D and 3D photonic crystal structures. Three different eigensolution schemes to solve the traditional band diagrams along high-symmetry lines in the first Brillouin zone of the crystal are discussed. Optimal rules for the Fourier expansion over the dielectric function and electromagnetic fields with discontinuities occurring at the boundary of different material domains have been employed to accelerate the convergence of numerical computation. Application of this method to an important class of 3D layer-by-layer photonic crystals reveals the superior convergency of this different approach over the conventional plane-wave expansion method.

  2. Traveling wave and exact solutions for the perturbed nonlinear Schrödinger equation with Kerr law nonlinearity

    NASA Astrophysics Data System (ADS)

    Akram, Ghazala; Mahak, Nadia

    2018-06-01

    The nonlinear Schrödinger equation (NLSE) with the aid of three order dispersion terms is investigated to find the exact solutions via the extended (G'/G2)-expansion method and the first integral method. Many exact traveling wave solutions, such as trigonometric, hyperbolic, rational, soliton and complex function solutions, are characterized with some free parameters of the problem studied. It is corroborated that the proposed techniques are manageable, straightforward and powerful tools to find the exact solutions of nonlinear partial differential equations (PDEs). Some figures are plotted to describe the propagation of traveling wave solutions expressed by the hyperbolic functions, trigonometric functions and rational functions.

  3. Traveling-wave device with mass flux suppression

    DOEpatents

    Swift, Gregory W.; Backhaus, Scott N.; Gardner, David L.

    2000-01-01

    A traveling-wave device is provided with the conventional moving pistons eliminated. Acoustic energy circulates in a direction through a fluid within a torus. A side branch may be connected to the torus for transferring acoustic energy into or out of the torus. A regenerator is located in the torus with a first heat exchanger located on a first side of the regenerator downstream of the regenerator relative to the direction of the circulating acoustic energy; and a second heat exchanger located on an upstream side of the regenerator. The improvement is a mass flux suppressor located in the torus to minimize time-averaged mass flux of the fluid. In one embodiment, the device further includes a thermal buffer column in the torus to thermally isolate the heat exchanger that is at the operating temperature of the device.

  4. Approximation of traveling wave solutions in wall-bounded flows using resolvent modes

    NASA Astrophysics Data System (ADS)

    McKeon, Beverley; Graham, Michael; Moarref, Rashad; Park, Jae Sung; Sharma, Ati; Willis, Ashley

    2014-11-01

    Significant recent attention has been devoted to computing and understanding exact traveling wave solutions of the Navier-Stokes equations. These solutions can be interpreted as the state-space skeleton of turbulence and are attractive benchmarks for studying low-order models of wall turbulence. Here, we project such solutions onto the velocity response (or resolvent) modes supplied by the gain-based resolvent analysis outlined by McKeon & Sharma (JFM, 2010). We demonstrate that in both pipe (Pringle et al., Phil. Trans. R. Soc. A, 2009) and channel (Waleffe, JFM, 2001) flows, the solutions can be well-described by a small number of resolvent modes. Analysis of the nonlinear forcing modes sustaining these solutions reveals the importance of small amplitude forcing, consistent with the large amplifications admitted by the resolvent operator. We investigate the use of resolvent modes as computationally cheap ``seeds'' for the identification of further traveling wave solutions. The support of AFOSR under Grants FA9550-09-1-0701, FA9550-12-1-0469, FA9550-11-1-0094 and FA9550-14-1-0042 (program managers Rengasamy Ponnappan, Doug Smith and Gregg Abate) is gratefully acknowledged.

  5. Hybrid functional study of band structures of GaAs1-xNx and GaSb1-xNx alloys

    NASA Astrophysics Data System (ADS)

    Virkkala, Ville; Havu, Ville; Tuomisto, Filip; Puska, Martti J.

    2012-02-01

    Band structures of GaAs1-xNx and GaSb1-xNx alloys are studied in the framework of the density functional theory within the hybrid functional scheme (HSE06). We find that the scheme gives a clear improvement over the traditional (semi)local functionals in describing, in a qualitative agreement with experiments, the bowing of electron energy band gap in GaAs1-xNx alloys. In the case of GaSb1-xNx alloys, the hybrid functional used makes the study of band structures possible ab initio without any empirical parameter fitting. We explain the trends in the band gap reductions in the two materials that result mainly from the positions of the nitrogen-induced states with respect to the bottoms of the bulk conduction bands.

  6. Investigating Dielectric and Metamaterial Effects in a Terahertz Traveling-Wave Tube Amplifier

    NASA Technical Reports Server (NTRS)

    Starinshak, David P.; Wilson, Jeffrey D.

    2008-01-01

    Adding material enhancements to a terahertz traveling-wave tube amplifier is investigated. Isotropic dielectrics, negative-index metamaterials, and anisotropic crystals are simulated, and plans to increase the efficiency of the device are discussed. Early results indicate that adding dielectric to the curved sections of the serpentine-shaped slow-wave circuit produce optimal changes in the cold-test characteristics of the device and a minimal drop in operating frequency. Additional results suggest that materials with simultaneously small relative permittivities and electrical conductivities are best suited for increasing the efficiency of the device. More research is required on the subject, and recommendations are given to determine the direction.

  7. Superconducting magnet for a Ku-band maser.

    NASA Technical Reports Server (NTRS)

    Berwin, R.; Wiebe, E.; Dachel, P.

    1972-01-01

    A superconducting magnet to provide a uniform magnetic field of up to 8000 G in a 1.14-cm gap for the 15.3-GHz (Ku-band) traveling wave maser is described. The magnet operates in a persistent mode in the vacuum environment of a closed-cycle helium refrigerator (4.5 K). The features of a superconducting switch, which has both leads connected to 4.5 K heat stations and thereby does not receive heat generated by the magnet charging leads, are described.

  8. X-Ray Standing Waves on Surfaces

    DTIC Science & Technology

    1993-01-01

    dependent distributional changes of iodine on Pt 6.3 X-ray standing wave study of a Langmuir - Blodgett multilayer film 7. Conclusions 8. Acknowledgments...4B. 6.3 X-ray standing wave study of a Langmuir - Blodgett multilayer film As mentioned previously the total external reflection condition occurs...for a Zn atom layer embedded in the top arachidate bilayer of a Langmuir - Blodgett (LB) multilayer film which was deposited on the surface of a gold

  9. High power broadband millimeter wave TWTs

    NASA Astrophysics Data System (ADS)

    James, Bill G.

    1999-05-01

    In the early 1980's the requirement for high power broadband millimeter wave sources encouraged the development of microwave vacuum device amplifiers for radar and communication systems. Many government funded programs were implemented for the development of high power broadband millimeter wave amplifiers that would meet the needs of the high power community. The tube design capable of meeting these goals was the slow wave coupled cavity traveling wave device, which had a proven technology base at the lower frequencies (X Band). However scaling this technology to the millimeter frequencies had severe shortcomings in both thermal and manufacturing design. These shortcomings were overcome with the development of the Ladder Circuit technology. In conjunction with the circuit development high power electron beam systems had to be developed for the generation of high rf powers. These beam systems had to be capable of many megawatts of beam power density and high current densities. The cathode technology required to be capable of operating at current densities of 10 amperes per square centimeter at long pulse lengths and high duty cycle. Since the introduction of the Ladder Circuit technology a number of high power broadband millimeter wave amplifiers have been developed using this technology, and have been deployed in operating radar and communication systems. Broadband millimeter wave sources have been manufactured in the frequency range from 27 GHz to 100 GHz with power levels ranging from 100 watts to 50 kilowatts. Today the power levels achieved by these devices are nearing the limits of this technology; therefore to gain a significant increase in power at the millimeter wave frequencies other technologies will have to be considered particularly fast wave devices. This paper will briefly review the ladder circuit technology and present the designs of a number of broadband high power devices developed at Ka and W band. The discussion will include the beam systems

  10. Simulating nonlinear steady-state traveling waves on the falling liquid film entrained by a gas flow

    NASA Astrophysics Data System (ADS)

    Tsvelodub, O. Yu; Bocharov, A. A.

    2017-09-01

    The article is devoted to the simulation of nonlinear waves on a liquid film flowing under gravity in the known stress field at the interface. The paper studies nonlinear waves on a liquid film, flowing under the action of gravity in a known stress field at the interface. In the case of small Reynolds numbers the problem is reduced to the consideration of solutions of the nonlinear integral-differential equation for film thickness deviation from the undisturbed level. The periodic and soliton steady-state traveling solutions of this equation have been numerically found. The analysis of branching of new families of steady-state traveling solutions has been performed. In particular, it is shown that this model equation has solutions in the form of solitons-humps.

  11. Wave propagation in relaxed micromorphic continua: modeling metamaterials with frequency band-gaps

    NASA Astrophysics Data System (ADS)

    Madeo, A.; Neff, P.; Ghiba, I. D.; Placidi, L.; Rosi, G.

    2015-09-01

    In this paper, the relaxed micromorphic model proposed in Ghiba et al. (Math Mech Solids, 2013), Neff et al. (Contin Mech Thermodyn, 2013) has been used to study wave propagation in unbounded continua with microstructure. By studying dispersion relations for the considered relaxed medium, we are able to disclose precise frequency ranges (band-gaps) for which propagation of waves cannot occur. These dispersion relations are strongly nonlinear so giving rise to a macroscopic dispersive behavior of the considered medium. We prove that the presence of band-gaps is related to a unique elastic coefficient, the so-called Cosserat couple modulus μ c , which is also responsible for the loss of symmetry of the Cauchy force stress tensor. This parameter can be seen as the trigger of a bifurcation phenomenon since the fact of slightly changing its value around a given threshold drastically changes the observed response of the material with respect to wave propagation. We finally show that band-gaps cannot be accounted for by classical micromorphic models as well as by Cosserat and second gradient ones. The potential fields of application of the proposed relaxed model are manifold, above all for what concerns the conception of new engineering materials to be used for vibration control and stealth technology.

  12. A coupler for parasitic mode diagnosis in an X-band triaxial klystron amplifier

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Ju, Jin-chuan; Zhang, Jun; Qi, Zu-min; Zhong, Hui-huang

    2017-10-01

    The traditional methods of parasitic mode excitation diagnosis in an X-band triaxial klystron amplifier (TKA) meet two difficulties: limited installation space and vacuum sealing. In order to solve these issues, a simple and compact coupler with good sealing performance, which can prevent air flow between the main and the auxiliary waveguides, is proposed and investigated experimentally. The coupler is designed with the aperture diffraction theory and the finite-different time-domain (FDTD) method. The designed coupler consists of a main coaxial waveguide (for microwave transmission) and a rectangular auxiliary waveguide (for parasitic mode diagnosis). The entire coupler structure has been fabricated by macromolecule polymer which is transparent to microwave signal in frequency range of X-band. The metal coating of about 200 microns has been performed through electroplating technique to ensure that the device operates well at high power. A small aperture is made in the metal coating. Hence, microwave can couple through the hole and the wave-transparent medium, whereas air flow is blocked by the wave-transparent medium. The coupling coefficient is analyzed and simulated with CST software. The coupler model is also included in particle-in-cell (PIC) simulation with CHIPIC software and the associated parasitic mode excitation is studied. A frequency component of 11.46 GHz is observed in the FFT of the electric field of the drift tube and its corresponding competition mode appears as TE61 mode according to the electric field distribution. Besides, a frequency component of 10.8 GHz is also observed in the FFT of the electric field. After optimization of TE61 mode suppression, an experiment of the TKA with the designed coupler is carried out and the parasitic mode excitation at 10.8 GHz is observed through the designed coupler.

  13. Traveling wave ultrasonic motor: coupling effects in free stator.

    PubMed

    Frayssignes, H; Briot, R

    2003-03-01

    Generally a stator of traveling wave ultrasonic motor (TWUM) consists of piezoelectric transducers (annular plate or rods) coupled by the way of a metallic ring. These transducers divided into halves are excited independently by two electrical signals with different phases of about 90 degrees. So an elastic traveling wave propagates along the circumference of the ring and a rotor pressed on this vibrating surface is then driven by the stator via contact forces. Many difficulties appear in developing TWUM because the contact between the stator and the rotor via a frictional material is very important. However that may be, the first stage consists in obtaining a vibrating stator with optimum characteristics with two symmetrical phases. The aim of this paper is to discuss some coupling effects in a free stator through an enhanced equivalent circuit model. A simple experimental method based on impedance measurements is performed to estimate the coupling characteristics at a low driving voltage. This paper reports results obtained with the free stator of the well known piezoelectric ultrasonic motor "USR60" by Shinsei Co. Ltd. Since the stator behaves as an elastic body, interactions between the two electrical inputs might be described by the introduction of a coupling oscillator. The comparison of experimental and theoretical results leads to validate the new equivalent circuit of the free stator. The presence of coupling impedance could imply a change of electrical supply condition to optimize the TWUM efficiency. The effects of unbalanced features for each electrical input and the applicability of the proposed model to actual operating condition are discussed in the paper. Copyright 2002 Elsevier Science B.V.

  14. Global paths of time-periodic solutions of the Benjamin-Ono equation connecting arbitrary traveling waves

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ambrose, David M.; Wilkening, Jon

    2008-12-11

    We classify all bifurcations from traveling waves to non-trivial time-periodic solutions of the Benjamin-Ono equation that are predicted by linearization. We use a spectrally accurate numerical continuation method to study several paths of non-trivial solutions beyond the realm of linear theory. These paths are found to either re-connect with a different traveling wave or to blow up. In the latter case, as the bifurcation parameter approaches a critical value, the amplitude of the initial condition grows without bound and the period approaches zero. We propose a conjecture that gives the mapping from one bifurcation to its counterpart on the othermore » side of the path of non-trivial solutions. By experimentation with data fitting, we identify the form of the exact solutions on the path connecting two traveling waves, which represents the Fourier coefficients of the solution as power sums of a finite number of particle positions whose elementary symmetric functions execute simple orbits in the complex plane (circles or epicycles). We then solve a system of algebraic equations to express the unknown constants in the new representation in terms of the mean, a spatial phase, a temporal phase, four integers (enumerating the bifurcation at each end of the path) and one additional bifurcation parameter. We also find examples of interior bifurcations from these paths of already non-trivial solutions, but we do not attempt to analyze their algebraic structure.« less

  15. Traveling waves in a spatially-distributed Wilson-Cowan model of cortex: From fronts to pulses

    NASA Astrophysics Data System (ADS)

    Harris, Jeremy D.; Ermentrout, Bard

    2018-04-01

    Wave propagation in excitable media has been studied in various biological, chemical, and physical systems. Waves are among the most common evoked and spontaneous organized activity seen in cortical networks. In this paper, we study traveling fronts and pulses in a spatially-extended version of the Wilson-Cowan equations, a neural firing rate model of sensory cortex having two population types: Excitatory and inhibitory. We are primarily interested in the case when the local or space-clamped dynamics has three fixed points: (1) a stable down state; (2) a saddle point with stable manifold that acts as a threshold for firing; (3) an up state having stability that depends on the time scale of the inhibition. In the case when the up state is stable, we look for wave fronts, which transition the media from a down to up state, and when the up state is unstable, we are interested in pulses, a transient increase in firing that returns to the down state. We explore the behavior of these waves as the time and space scales of the inhibitory population vary. Some interesting findings include bistability between a traveling front and pulse, fronts that join the down state to an oscillation or spatiotemporal pattern, and pulses which go through an oscillatory instability.

  16. Recent developments in guided wave travel time tomography

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zon, Tim van; Volker, Arno

    The concept of predictive maintenance using permanent sensors that monitor the integrity of an installation is an interesting addition to the current method of periodic inspections. Guided wave tomography had been developed to create a map of the wall thickness using the travel times of guided waves. It can be used for both monitoring and for inspection of pipe-segments that are difficult to access, for instance at the location of pipe-supports. An important outcome of the tomography is the minimum remaining wall thickness, as this is critical in the scheduling of a replacement of the pipe-segment. In order to improvemore » the sizing accuracy we have improved the tomography scheme. A number of major improvements have been realized allowing to extend the application envelope to pipes with a larger wall thickness and to larger distances between the transducer rings. Simulation results indicate that the sizing accuracy has improved and that is now possible to have a spacing of 8 meter between the source-ring and the receiver-ring. Additionally a reduction of the number of sensors required might be possible as well.« less

  17. Study of transmission line attenuation in broad band millimeter wave frequency range

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Pandya, Hitesh Kumar B.; Austin, M. E.; Ellis, R. F.

    2013-10-15

    Broad band millimeter wave transmission lines are used in fusion plasma diagnostics such as electron cyclotron emission (ECE), electron cyclotron absorption, reflectometry and interferometry systems. In particular, the ECE diagnostic for ITER will require efficient transmission over an ultra wide band, 100 to 1000 GHz. A circular corrugated waveguide transmission line is a prospective candidate to transmit such wide band with low attenuation. To evaluate this system, experiments of transmission line attenuation were performed and compared with theoretical loss calculations. A millimeter wave Michelson interferometer and a liquid nitrogen black body source are used to perform all the experiments. Atmosphericmore » water vapor lines and continuum absorption within this band are reported. Ohmic attenuation in corrugated waveguide is very low; however, there is Bragg scattering and higher order mode conversion that can cause significant attenuation in this transmission line. The attenuation due to miter bends, gaps, joints, and curvature are estimated. The measured attenuation of 15 m length with seven miter bends and eighteen joints is 1 dB at low frequency (300 GHz) and 10 dB at high frequency (900 GHz), respectively.« less

  18. Tonotopically Ordered Traveling Waves in the Hearing Organs of Bushcrickets in-vivo

    NASA Astrophysics Data System (ADS)

    Udayashankar, Arun Palghat; Kössl, Manfred; Nowotny, Manuela

    2011-11-01

    Experimental investigation of auditory mechanics in the mammalian cochlea has been difficult to address in-vivo due to its secure housing inside the temporal bone. Here we studied the easily accessible hearing organ of bushcrickets, located in their forelegs, known as the crista acustica. A characteristic feature of the organ is that it is lined with an array of auditory receptors in a tonotopic fashion with lower frequencies processed at the proximal part and higher frequencies at the distal part of the foreleg. Each receptor cell is associated with so called cap cells. The cap cells, graded in size, are directly involved in the mechanics of transduction along with the part of the acoustic trachea that supports the cap cells. Functional similarities between the crista acustica and the vertebrate cochlea such as frequency selectivity and distortion product otoacoustic emissions have been well documented. In this study we used laser Doppler vibrometry to study the mechanics of the organ and observed sound induced traveling waves (TW) along it's length. Frequency representation was tonotopic with TW propagating from the high frequency to the low frequency region of the organ similar to the situation in the cochlea. Traveling wave velocity increased monotonically from 4 to 12 m/s for a frequency range of 6 to 60 kHz, reflecting a smaller topographic spread (organ length: 1 mm) compared to the guinea pig cochlea (organ length: 18 mm). The wavelength of the traveling wave decreased monotonically from 0.67 mm to 0.27 mm for the same frequency range. Vibration velocity of the organ reached noise threshold levels (10 μm/s) at 30 dB SPL for a frequency of 21 kHz. A small non-linear compression (73 dB increase in velocity for an 80 dB increase in SPL) was also observed at the 21 kHz. Our results indicate that bushcrickets can be a good model system for exploration of auditory mechanics in-vivo.

  19. First-principle study of effect of variation of `x' on the band alignment in CZTS1-xSex

    NASA Astrophysics Data System (ADS)

    Ghemud, Vipul; Kshirsagar, Anjali

    2018-04-01

    The present work concentrates on the electronic structure study of CZTS1-xSex alloy with x ranging from 0 to 1. For the alloy study, we have carried out first-principles calculations employing generalized gradient approximation for structural optimization and further hybrid functional approach to compare the optical band gap with that obtained from the experiments. A systematic increase in the lattice parameters with lowering of band gap from 1.52eV to 1.04eV is seen with increasing Se concentration from 0 to 100%, however the lowering of valence band edge and conduction band edge is not linear with the concentration variation. Our results indicate that the lowering of band gap is a result increased Cu:d and Se:p hybridization with increasing `x'.

  20. First narrow-band search for continuous gravitational waves from known pulsars in advanced detector data

    NASA Astrophysics Data System (ADS)

    Abbott, B. P.; Abbott, R.; Abbott, T. D.; Acernese, F.; Ackley, K.; Adams, C.; Adams, T.; Addesso, P.; Adhikari, R. X.; Adya, V. B.; Affeldt, C.; Afrough, M.; Agarwal, B.; Agathos, M.; Agatsuma, K.; Aggarwal, N.; Aguiar, O. D.; Aiello, L.; Ain, A.; Allen, B.; Allen, G.; Allocca, A.; Altin, P. A.; Amato, A.; Ananyeva, A.; Anderson, S. B.; Anderson, W. G.; Angelova, S. V.; Antier, S.; Appert, S.; Arai, K.; Araya, M. C.; Areeda, J. S.; Arnaud, N.; Arun, K. G.; Ascenzi, S.; Ashton, G.; Ast, M.; Aston, S. M.; Astone, P.; Atallah, D. V.; Aufmuth, P.; Aulbert, C.; AultONeal, K.; Austin, C.; Avila-Alvarez, A.; Babak, S.; Bacon, P.; Bader, M. K. M.; Bae, S.; Baker, P. T.; Baldaccini, F.; Ballardin, G.; Ballmer, S. W.; Banagiri, S.; Barayoga, J. C.; Barclay, S. E.; Barish, B. C.; Barker, D.; Barkett, K.; Barone, F.; Barr, B.; Barsotti, L.; Barsuglia, M.; Barta, D.; Bartlett, J.; Bartos, I.; Bassiri, R.; Basti, A.; Batch, J. C.; Bawaj, M.; Bayley, J. C.; Bazzan, M.; Bécsy, B.; Beer, C.; Bejger, M.; Belahcene, I.; Bell, A. S.; Berger, B. K.; Bergmann, G.; Bero, J. J.; Berry, C. P. L.; Bersanetti, D.; Bertolini, A.; Betzwieser, J.; Bhagwat, S.; Bhandare, R.; Bilenko, I. A.; Billingsley, G.; Billman, C. R.; Birch, J.; Birney, R.; Birnholtz, O.; Biscans, S.; Biscoveanu, S.; Bisht, A.; Bitossi, M.; Biwer, C.; Bizouard, M. A.; Blackburn, J. K.; Blackman, J.; Blair, C. D.; Blair, D. G.; Blair, R. M.; Bloemen, S.; Bock, O.; Bode, N.; Boer, M.; Bogaert, G.; Bohe, A.; Bondu, F.; Bonilla, E.; Bonnand, R.; Boom, B. A.; Bork, R.; Boschi, V.; Bose, S.; Bossie, K.; Bouffanais, Y.; Bozzi, A.; Bradaschia, C.; Brady, P. R.; Branchesi, M.; Brau, J. E.; Briant, T.; Brillet, A.; Brinkmann, M.; Brisson, V.; Brockill, P.; Broida, J. E.; Brooks, A. F.; Brown, D. A.; Brown, D. D.; Brunett, S.; Buchanan, C. C.; Buikema, A.; Bulik, T.; Bulten, H. J.; Buonanno, A.; Buskulic, D.; Buy, C.; Byer, R. L.; Cabero, M.; Cadonati, L.; Cagnoli, G.; Cahillane, C.; Calderón Bustillo, J.; Callister, T. A.; Calloni, E.; Camp, J. B.; Canizares, P.; Cannon, K. C.; Cao, H.; Cao, J.; Capano, C. D.; Capocasa, E.; Carbognani, F.; Caride, S.; Carney, M. F.; Casanueva Diaz, J.; Casentini, C.; Caudill, S.; Cavaglià, M.; Cavalier, F.; Cavalieri, R.; Cella, G.; Cepeda, C. B.; Cerdá-Durán, P.; Cerretani, G.; Cesarini, E.; Chamberlin, S. J.; Chan, M.; Chao, S.; Charlton, P.; Chase, E.; Chassande-Mottin, E.; Chatterjee, D.; Cheeseboro, B. D.; Chen, H. Y.; Chen, X.; Chen, Y.; Cheng, H.-P.; Chia, H.; Chincarini, A.; Chiummo, A.; Chmiel, T.; Cho, H. S.; Cho, M.; Chow, J. H.; Christensen, N.; Chu, Q.; Chua, A. J. K.; Chua, S.; Chung, A. K. W.; Chung, S.; Ciani, G.; Ciolfi, R.; Cirelli, C. E.; Cirone, A.; Clara, F.; Clark, J. A.; Clearwater, P.; Cleva, F.; Cocchieri, C.; Coccia, E.; Cohadon, P.-F.; Cohen, D.; Colla, A.; Collette, C. G.; Cominsky, L. R.; Constancio, M.; Conti, L.; Cooper, S. J.; Corban, P.; Corbitt, T. R.; Cordero-Carrión, I.; Corley, K. R.; Cornish, N.; Corsi, A.; Cortese, S.; Costa, C. A.; Coughlin, M. W.; Coughlin, S. B.; Coulon, J.-P.; Countryman, S. T.; Couvares, P.; Covas, P. B.; Cowan, E. E.; Coward, D. M.; Cowart, M. J.; Coyne, D. C.; Coyne, R.; Creighton, J. D. E.; Creighton, T. D.; Cripe, J.; Crowder, S. G.; Cullen, T. J.; Cumming, A.; Cunningham, L.; Cuoco, E.; Dal Canton, T.; Dálya, G.; Danilishin, S. L.; D'Antonio, S.; Danzmann, K.; Dasgupta, A.; Da Silva Costa, C. F.; Dattilo, V.; Dave, I.; Davier, M.; Davis, D.; Daw, E. J.; Day, B.; De, S.; DeBra, D.; Degallaix, J.; De Laurentis, M.; Deléglise, S.; Del Pozzo, W.; Demos, N.; Denker, T.; Dent, T.; De Pietri, R.; Dergachev, V.; De Rosa, R.; DeRosa, R. T.; De Rossi, C.; DeSalvo, R.; de Varona, O.; Devenson, J.; Dhurandhar, S.; Díaz, M. C.; Di Fiore, L.; Di Giovanni, M.; Di Girolamo, T.; Di Lieto, A.; Di Pace, S.; Di Palma, I.; Di Renzo, F.; Doctor, Z.; Dolique, V.; Donovan, F.; Dooley, K. L.; Doravari, S.; Dorrington, I.; Douglas, R.; Dovale Álvarez, M.; Downes, T. P.; Drago, M.; Dreissigacker, C.; Driggers, J. C.; Du, Z.; Ducrot, M.; Dupej, P.; Dwyer, S. E.; Edo, T. B.; Edwards, M. C.; Effler, A.; Eggenstein, H.-B.; Ehrens, P.; Eichholz, J.; Eikenberry, S. S.; Eisenstein, R. A.; Essick, R. C.; Estevez, D.; Etienne, Z. B.; Etzel, T.; Evans, M.; Evans, T. M.; Factourovich, M.; Fafone, V.; Fair, H.; Fairhurst, S.; Fan, X.; Farinon, S.; Farr, B.; Farr, W. M.; Fauchon-Jones, E. J.; Favata, M.; Fays, M.; Fee, C.; Fehrmann, H.; Feicht, J.; Fejer, M. M.; Fernandez-Galiana, A.; Ferrante, I.; Ferreira, E. C.; Ferrini, F.; Fidecaro, F.; Finstad, D.; Fiori, I.; Fiorucci, D.; Fishbach, M.; Fisher, R. P.; Fitz-Axen, M.; Flaminio, R.; Fletcher, M.; Fong, H.; Font, J. A.; Forsyth, P. W. F.; Forsyth, S. S.; Fournier, J.-D.; Frasca, S.; Frasconi, F.; Frei, Z.; Freise, A.; Frey, R.; Frey, V.; Fries, E. M.; Fritschel, P.; Frolov, V. V.; Fulda, P.; Fyffe, M.; Gabbard, H.; Gadre, B. U.; Gaebel, S. M.; Gair, J. R.; Gammaitoni, L.; Ganija, M. R.; Gaonkar, S. G.; Garcia-Quiros, C.; Garufi, F.; Gateley, B.; Gaudio, S.; Gaur, G.; Gayathri, V.; Gehrels, N.; Gemme, G.; Genin, E.; Gennai, A.; George, D.; George, J.; Gergely, L.; Germain, V.; Ghonge, S.; Ghosh, Abhirup; Ghosh, Archisman; Ghosh, S.; Giaime, J. A.; Giardina, K. D.; Giazotto, A.; Gill, K.; Glover, L.; Goetz, E.; Goetz, R.; Gomes, S.; Goncharov, B.; González, G.; Gonzalez Castro, J. M.; Gopakumar, A.; Gorodetsky, M. L.; Gossan, S. E.; Gosselin, M.; Gouaty, R.; Grado, A.; Graef, C.; Granata, M.; Grant, A.; Gras, S.; Gray, C.; Greco, G.; Green, A. C.; Gretarsson, E. M.; Groot, P.; Grote, H.; Grunewald, S.; Gruning, P.; Guidi, G. M.; Guo, X.; Gupta, A.; Gupta, M. K.; Gushwa, K. E.; Gustafson, E. K.; Gustafson, R.; Halim, O.; Hall, B. R.; Hall, E. D.; Hamilton, E. Z.; Hammond, G.; Haney, M.; Hanke, M. M.; Hanks, J.; Hanna, C.; Hannam, M. D.; Hannuksela, O. A.; Hanson, J.; Hardwick, T.; Harms, J.; Harry, G. M.; Harry, I. W.; Hart, M. J.; Haster, C.-J.; Haughian, K.; Healy, J.; Heidmann, A.; Heintze, M. C.; Heitmann, H.; Hello, P.; Hemming, G.; Hendry, M.; Heng, I. S.; Hennig, J.; Heptonstall, A. W.; Heurs, M.; Hild, S.; Hinderer, T.; Ho, W. C. G.; Hoak, D.; Hofman, D.; Holt, K.; Holz, D. E.; Hopkins, P.; Horst, C.; Hough, J.; Houston, E. A.; Howell, E. J.; Hreibi, A.; Hu, Y. M.; Huerta, E. A.; Huet, D.; Hughey, B.; Husa, S.; Huttner, S. H.; Huynh-Dinh, T.; Indik, N.; Inta, R.; Intini, G.; Isa, H. N.; Isac, J.-M.; Isi, M.; Iyer, B. R.; Izumi, K.; Jacqmin, T.; Jani, K.; Jaranowski, P.; Jawahar, S.; Jiménez-Forteza, F.; Johnson, W. W.; Jones, D. I.; Jones, R.; Jonker, R. J. G.; Ju, L.; Junker, J.; Kalaghatgi, C. V.; Kalogera, V.; Kamai, B.; Kandhasamy, S.; Kang, G.; Kanner, J. B.; Kapadia, S. J.; Karki, S.; Karvinen, K. S.; Kasprzack, M.; Katolik, M.; Katsavounidis, E.; Katzman, W.; Kaufer, S.; Kawabe, K.; Kéfélian, F.; Keitel, D.; Kemball, A. J.; Kennedy, R.; Kent, C.; Key, J. S.; Khalili, F. Y.; Khan, I.; Khan, S.; Khan, Z.; Khazanov, E. A.; Kijbunchoo, N.; Kim, Chunglee; Kim, J. C.; Kim, K.; Kim, W.; Kim, W. S.; Kim, Y.-M.; Kimbrell, S. J.; King, E. J.; King, P. J.; Kinley-Hanlon, M.; Kirchhoff, R.; Kissel, J. S.; Kleybolte, L.; Klimenko, S.; Knowles, T. D.; Koch, P.; Koehlenbeck, S. M.; Koley, S.; Kondrashov, V.; Kontos, A.; Korobko, M.; Korth, W. Z.; Kowalska, I.; Kozak, D. B.; Krämer, C.; Kringel, V.; Krishnan, B.; Królak, A.; Kuehn, G.; Kumar, P.; Kumar, R.; Kumar, S.; Kuo, L.; Kutynia, A.; Kwang, S.; Lackey, B. D.; Lai, K. H.; Landry, M.; Lang, R. N.; Lange, J.; Lantz, B.; Lanza, R. K.; Lartaux-Vollard, A.; Lasky, P. D.; Laxen, M.; Lazzarini, A.; Lazzaro, C.; Leaci, P.; Leavey, S.; Lee, C. H.; Lee, H. K.; Lee, H. M.; Lee, H. W.; Lee, K.; Lehmann, J.; Lenon, A.; Leonardi, M.; Leroy, N.; Letendre, N.; Levin, Y.; Li, T. G. F.; Linker, S. D.; Littenberg, T. B.; Liu, J.; Lo, R. K. L.; Lockerbie, N. A.; London, L. T.; Lord, J. E.; Lorenzini, M.; Loriette, V.; Lormand, M.; Losurdo, G.; Lough, J. D.; Lovelace, G.; Lück, H.; Lumaca, D.; Lundgren, A. P.; Lynch, R.; Ma, Y.; Macas, R.; Macfoy, S.; Machenschalk, B.; MacInnis, M.; Macleod, D. M.; Magaña Hernandez, I.; Magaña-Sandoval, F.; Magaña Zertuche, L.; Magee, R. M.; Majorana, E.; Maksimovic, I.; Man, N.; Mandic, V.; Mangano, V.; Mansell, G. L.; Manske, M.; Mantovani, M.; Marchesoni, F.; Marion, F.; Márka, S.; Márka, Z.; Markakis, C.; Markosyan, A. S.; Markowitz, A.; Maros, E.; Marquina, A.; Martelli, F.; Martellini, L.; Martin, I. W.; Martin, R. M.; Martynov, D. V.; Mason, K.; Massera, E.; Masserot, A.; Massinger, T. J.; Masso-Reid, M.; Mastrogiovanni, S.; Matas, A.; Matichard, F.; Matone, L.; Mavalvala, N.; Mazumder, N.; McCarthy, R.; McClelland, D. E.; McCormick, S.; McCuller, L.; McGuire, S. C.; McIntyre, G.; McIver, J.; McManus, D. J.; McNeill, L.; McRae, T.; McWilliams, S. T.; Meacher, D.; Meadors, G. D.; Mehmet, M.; Meidam, J.; Mejuto-Villa, E.; Melatos, A.; Mendell, G.; Mercer, R. A.; Merilh, E. L.; Merzougui, M.; Meshkov, S.; Messenger, C.; Messick, C.; Metzdorff, R.; Meyers, P. M.; Miao, H.; Michel, C.; Middleton, H.; Mikhailov, E. E.; Milano, L.; Miller, A. L.; Miller, B. B.; Miller, J.; Millhouse, M.; Milovich-Goff, M. C.; Minazzoli, O.; Minenkov, Y.; Ming, J.; Mishra, C.; Mitra, S.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.; Moffa, D.; Moggi, A.; Mogushi, K.; Mohan, M.; Mohapatra, S. R. P.; Montani, M.; Moore, C. J.; Moraru, D.; Moreno, G.; Morriss, S. R.; Mours, B.; Mow-Lowry, C. M.; Mueller, G.; Muir, A. W.; Mukherjee, Arunava; Mukherjee, D.; Mukherjee, S.; Mukund, N.; Mullavey, A.; Munch, J.; Muñiz, E. A.; Muratore, M.; Murray, P. G.; Napier, K.; Nardecchia, I.; Naticchioni, L.; Nayak, R. K.; Neilson, J.; Nelemans, G.; Nelson, T. J. N.; Nery, M.; Neunzert, A.; Nevin, L.; Newport, J. M.; Newton, G.; Ng, K. K. Y.; Nguyen, T. T.; Nichols, D.; Nielsen, A. B.; Nissanke, S.; Nitz, A.; Noack, A.; Nocera, F.; Nolting, D.; North, C.; Nuttall, L. K.; Oberling, J.; O'Dea, G. D.; Ogin, G. H.; Oh, J. J.; Oh, S. H.; Ohme, F.; Okada, M. A.; Oliver, M.; Oppermann, P.; Oram, Richard J.; O'Reilly, B.; Ormiston, R.; Ortega, L. F.; O'Shaughnessy, R.; Ossokine, S.; Ottaway, D. J.; Overmier, H.; Owen, B. J.; Pace, A. E.; Page, J.; Page, M. A.; Pai, A.; Pai, S. A.; Palamos, J. R.; Palashov, O.; Palomba, C.; Pal-Singh, A.; Pan, Howard; Pan, Huang-Wei; Pang, B.; Pang, P. T. H.; Pankow, C.; Pannarale, F.; Pant, B. C.; Paoletti, F.; Paoli, A.; Papa, M. A.; Parida, A.; Parker, W.; Pascucci, D.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Patil, M.; Patricelli, B.; Pearlstone, B. L.; Pedraza, M.; Pedurand, R.; Pekowsky, L.; Pele, A.; Penn, S.; Perez, C. J.; Perreca, A.; Perri, L. M.; Pfeiffer, H. P.; Phelps, M.; Piccinni, O. J.; Pichot, M.; Piergiovanni, F.; Pierro, V.; Pillant, G.; Pinard, L.; Pinto, I. M.; Pirello, M.; Pitkin, M.; Poe, M.; Poggiani, R.; Popolizio, P.; Porter, E. K.; Post, A.; Powell, J.; Prasad, J.; Pratt, J. W. W.; Pratten, G.; Predoi, V.; Prestegard, T.; Prijatelj, M.; Principe, M.; Privitera, S.; Prodi, G. A.; Prokhorov, L. G.; Puncken, O.; Punturo, M.; Puppo, P.; Pürrer, M.; Qi, H.; Quetschke, V.; Quintero, E. A.; Quitzow-James, R.; Raab, F. J.; Rabeling, D. S.; Radkins, H.; Raffai, P.; Raja, S.; Rajan, C.; Rajbhandari, B.; Rakhmanov, M.; Ramirez, K. E.; Ramos-Buades, A.; Rapagnani, P.; Raymond, V.; Razzano, M.; Read, J.; Regimbau, T.; Rei, L.; Reid, S.; Reitze, D. H.; Ren, W.; Reyes, S. D.; Ricci, F.; Ricker, P. M.; Rieger, S.; Riles, K.; Rizzo, M.; Robertson, N. A.; Robie, R.; Robinet, F.; Rocchi, A.; Rolland, L.; Rollins, J. G.; Roma, V. J.; Romano, R.; Romel, C. L.; Romie, J. H.; Rosińska, D.; Ross, M. P.; Rowan, S.; Rüdiger, A.; Ruggi, P.; Rutins, G.; Ryan, K.; Sachdev, S.; Sadecki, T.; Sadeghian, L.; Sakellariadou, M.; Salconi, L.; Saleem, M.; Salemi, F.; Samajdar, A.; Sammut, L.; Sampson, L. M.; Sanchez, E. J.; Sanchez, L. E.; Sanchis-Gual, N.; Sandberg, V.; Sanders, J. R.; Sassolas, B.; Sathyaprakash, B. S.; Saulson, P. R.; Sauter, O.; Savage, R. L.; Sawadsky, A.; Schale, P.; Scheel, M.; Scheuer, J.; Schmidt, J.; Schmidt, P.; Schnabel, R.; Schofield, R. M. S.; Schönbeck, A.; Schreiber, E.; Schuette, D.; Schulte, B. W.; Schutz, B. F.; Schwalbe, S. G.; Scott, J.; Scott, S. M.; Seidel, E.; Sellers, D.; Sengupta, A. S.; Sentenac, D.; Sequino, V.; Sergeev, A.; Shaddock, D. A.; Shaffer, T. J.; Shah, A. A.; Shahriar, M. S.; Shaner, M. B.; Shao, L.; Shapiro, B.; Shawhan, P.; Sheperd, A.; Shoemaker, D. H.; Shoemaker, D. M.; Siellez, K.; Siemens, X.; Sieniawska, M.; Sigg, D.; Silva, A. D.; Singer, L. P.; Singh, A.; Singhal, A.; Sintes, A. M.; Slagmolen, B. J. J.; Smith, B.; Smith, J. R.; Smith, R. J. E.; Somala, S.; Son, E. J.; Sonnenberg, J. A.; Sorazu, B.; Sorrentino, F.; Souradeep, T.; Spencer, A. P.; Srivastava, A. K.; Staats, K.; Staley, A.; Steinke, M.; Steinlechner, J.; Steinlechner, S.; Steinmeyer, D.; Stevenson, S. P.; Stone, R.; Stops, D. J.; Strain, K. A.; Stratta, G.; Strigin, S. E.; Strunk, A.; Sturani, R.; Stuver, A. L.; Summerscales, T. Z.; Sun, L.; Sunil, S.; Suresh, J.; Sutton, P. J.; Swinkels, B. L.; Szczepańczyk, M. J.; Tacca, M.; Tait, S. C.; Talbot, C.; Talukder, D.; Tanner, D. B.; Tápai, M.; Taracchini, A.; Tasson, J. D.; Taylor, J. A.; Taylor, R.; Tewari, S. V.; Theeg, T.; Thies, F.; Thomas, E. G.; Thomas, M.; Thomas, P.; Thorne, K. A.; Thrane, E.; Tiwari, S.; Tiwari, V.; Tokmakov, K. V.; Toland, K.; Tonelli, M.; Tornasi, Z.; Torres-Forné, A.; Torrie, C. I.; Töyrä, D.; Travasso, F.; Traylor, G.; Trinastic, J.; Tringali, M. C.; Trozzo, L.; Tsang, K. W.; Tse, M.; Tso, R.; Tsukada, L.; Tsuna, D.; Tuyenbayev, D.; Ueno, K.; Ugolini, D.; Unnikrishnan, C. S.; Urban, A. L.; Usman, S. A.; Vahlbruch, H.; Vajente, G.; Valdes, G.; van Bakel, N.; van Beuzekom, M.; van den Brand, J. F. J.; Van Den Broeck, C.; Vander-Hyde, D. C.; van der Schaaf, L.; van Heijningen, J. V.; van Veggel, A. A.; Vardaro, M.; Varma, V.; Vass, S.; Vasúth, M.; Vecchio, A.; Vedovato, G.; Veitch, J.; Veitch, P. J.; Venkateswara, K.; Venugopalan, G.; Verkindt, D.; Vetrano, F.; Viceré, A.; Viets, A. D.; Vinciguerra, S.; Vine, D. J.; Vinet, J.-Y.; Vitale, S.; Vo, T.; Vocca, H.; Vorvick, C.; Vyatchanin, S. P.; Wade, A. R.; Wade, L. E.; Wade, M.; Walet, R.; Walker, M.; Wallace, L.; Walsh, S.; Wang, G.; Wang, H.; Wang, J. Z.; Wang, W. H.; Wang, Y. F.; Ward, R. L.; Warner, J.; Was, M.; Watchi, J.; Weaver, B.; Wei, L.-W.; Weinert, M.; Weinstein, A. J.; Weiss, R.; Wen, L.; Wessel, E. K.; Weßels, P.; Westerweck, J.; Westphal, T.; Wette, K.; Whelan, J. T.; Whiting, B. F.; Whittle, C.; Wilken, D.; Williams, D.; Williams, R. D.; Williamson, A. R.; Willis, J. L.; Willke, B.; Wimmer, M. H.; Winkler, W.; Wipf, C. C.; Wittel, H.; Woan, G.; Woehler, J.; Wofford, J.; Wong, K. W. K.; Worden, J.; Wright, J. L.; Wu, D. S.; Wysocki, D. M.; Xiao, S.; Yamamoto, H.; Yancey, C. C.; Yang, L.; Yap, M. J.; Yazback, M.; Yu, Hang; Yu, Haocun; Yvert, M.; ZadroŻny, A.; Zanolin, M.; Zelenova, T.; Zendri, J.-P.; Zevin, M.; Zhang, L.; Zhang, M.; Zhang, T.; Zhang, Y.-H.; Zhao, C.; Zhou, M.; Zhou, Z.; Zhu, S. J.; Zhu, X. J.; Zucker, M. E.; Zweizig, J.; LIGO Scientific Collaboration; Virgo Collaboration

    2017-12-01

    Spinning neutron stars asymmetric with respect to their rotation axis are potential sources of continuous gravitational waves for ground-based interferometric detectors. In the case of known pulsars a fully coherent search, based on matched filtering, which uses the position and rotational parameters obtained from electromagnetic observations, can be carried out. Matched filtering maximizes the signal-to-noise (SNR) ratio, but a large sensitivity loss is expected in case of even a very small mismatch between the assumed and the true signal parameters. For this reason, narrow-band analysis methods have been developed, allowing a fully coherent search for gravitational waves from known pulsars over a fraction of a hertz and several spin-down values. In this paper we describe a narrow-band search of 11 pulsars using data from Advanced LIGO's first observing run. Although we have found several initial outliers, further studies show no significant evidence for the presence of a gravitational wave signal. Finally, we have placed upper limits on the signal strain amplitude lower than the spin-down limit for 5 of the 11 targets over the bands searched; in the case of J1813-1749 the spin-down limit has been beaten for the first time. For an additional 3 targets, the median upper limit across the search bands is below the spin-down limit. This is the most sensitive narrow-band search for continuous gravitational waves carried out so far.

  1. Determination of band offset using continuous-wave two-photon excitation in a ZnSe quantum-well waveguide structure

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wagner, H. P.; Kuhnelt, M.; Wenisch, H.

    2001-06-15

    We investigate exciton subband transitions in a ZnSe/Zn{sub 1{minus}x}Mg{sub x}S{sub y}Se{sub 1{minus}y} multiple-quantum-well grown by molecular beam epitaxy waveguide structure by photoluminescence excitation and two-photon excitation spectroscopy. A continuous-wave two-photon absorption is realized by an efficient waveguide coupling scheme within the cryostat. From the energetic position of the 1s and 2p exciton transitions exciton binding energies of 33 and 38 meV are deduced for heavy and light-hole excitons, respectively. With these values we are able to determine the strain free and dimensionless conduction-band-offset parameter to Q{sub c}=0.3{+-}0.1.

  2. V x In (2–x) S 3 Intermediate Band Absorbers Deposited by Atomic Layer Deposition

    DOE PAGES

    McCarthy, Robert F.; Weimer, Matthew S.; Haasch, Richard T.; ...

    2016-03-21

    Substitutional alloys of several thin film semiconductors have been proposed as intermediate band (IB) materials for use in next-generation photovoltaics, which aim to utilize a larger fraction of the solar spectrum without sacrificing significant photovoltage. Here, we demonstrate a novel approach to IB material growth, namely atomic layer deposition (ALD), to enable unique control over substitutional-dopant location and density. Two new ALD processes for vanadium sulfide incorporation are introduced, one of which incorporates a vanadium (III) amidinate previously untested for ALD. We synthesize the first thin film V xIn (2-x)S 3 intermediate band semiconductors, using this process, and further demonstratemore » that the V:In ratio, and therefore intraband gap density of states, can be finely tuned according to the ALD dosing schedule. Deposition on a crystalline In 2S 3 underlayer promotes the growth of a tetragonal β-In 2S 3-like phase V xIn (2-x)S 3, which exhibits a distinct sub-band gap absorption peak with onset near 1.1 eV in agreement with computational predictions. But, the V xIn (2-x)S 3 films lack the lower energy transition predicted for a partially filled IB, and photoelectrochemical devices reveal a photocurrent response only from illumination with energy sufficient to span the parent band-gap.« less

  3. Inter-band optoelectronic properties in quantum dot structure of low band gap III-V semiconductors

    NASA Astrophysics Data System (ADS)

    Dey, Anup; Maiti, Biswajit; Chanda Sarkar, Debasree

    2014-04-01

    A generalized theory is developed to study inter-band optical absorption coefficient (IOAC) and material gain (MG) in quantum dot structures of narrow gap III-V compound semiconductor considering the wave-vector (k→) dependence of the optical transition matrix element. The band structures of these low band gap semiconducting materials with sufficiently separated split-off valance band are frequently described by the three energy band model of Kane. This has been adopted for analysis of the IOAC and MG taking InAs, InSb, Hg1-xCdxTe, and In1-xGaxAsyP1-y lattice matched to InP, as example of III-V compound semiconductors, having varied split-off energy band compared to their bulk band gap energy. It has been found that magnitude of the IOAC for quantum dots increases with increasing incident photon energy and the lines of absorption are more closely spaced in the three band model of Kane than those with parabolic energy band approximations reflecting the direct the influence of energy band parameters. The results show a significant deviation to the MG spectrum of narrow-gap materials having band nonparabolicity compared to the parabolic band model approximations. The results reflect the important role of valence band split-off energies in these narrow gap semiconductors.

  4. Performance of a first generation X-band photoelectron rf gun

    DOE PAGES

    Limborg-Deprey, C.; Adolphsen, C.; McCormick, D.; ...

    2016-05-04

    Building more compact accelerators to deliver high brightness electron beams for the generation of high flux, highly coherent radiation is a priority for the photon science community. A relatively straightforward reduction in footprint can be achieved by using high-gradient X-band (11.4 GHz) rf technology. To this end, an X-band injector consisting of a 5.5 cell rf gun and a 1-m long linac has been commissioned at SLAC. It delivers an 85 MeV electron beam with peak brightness somewhat better than that achieved in S-band photoinjectors, such as the one developed for the Linac Coherent Light Source (LCLS). The X-band rfmore » gun operates with up to a 200 MV/m peak field on the cathode, and has been used to produce bunches of a few pC to 1.2 nC in charge. Notably, bunch lengths as short as 120 fs rms have been measured for charges of 5 pC (~3×10 7 electrons), and normalized transverse emittances as small as 0.22 mm-mrad have been measured for this same charge level. Bunch lengths as short as 400 (250) fs rms have been achieved for electron bunches of 100 (20) pC with transverse normalized emittances of 0.7 (0.35) mm-mrad. As a result, we report on the performance and the lessons learned from the operation and optimization of this first generation X-band gun.« less

  5. Performance of a first generation X-band photoelectron rf gun

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Limborg-Deprey, C.; Adolphsen, C.; McCormick, D.

    Building more compact accelerators to deliver high brightness electron beams for the generation of high flux, highly coherent radiation is a priority for the photon science community. A relatively straightforward reduction in footprint can be achieved by using high-gradient X-band (11.4 GHz) rf technology. To this end, an X-band injector consisting of a 5.5 cell rf gun and a 1-m long linac has been commissioned at SLAC. It delivers an 85 MeV electron beam with peak brightness somewhat better than that achieved in S-band photoinjectors, such as the one developed for the Linac Coherent Light Source (LCLS). The X-band rfmore » gun operates with up to a 200 MV/m peak field on the cathode, and has been used to produce bunches of a few pC to 1.2 nC in charge. Notably, bunch lengths as short as 120 fs rms have been measured for charges of 5 pC (~3×10 7 electrons), and normalized transverse emittances as small as 0.22 mm-mrad have been measured for this same charge level. Bunch lengths as short as 400 (250) fs rms have been achieved for electron bunches of 100 (20) pC with transverse normalized emittances of 0.7 (0.35) mm-mrad. As a result, we report on the performance and the lessons learned from the operation and optimization of this first generation X-band gun.« less

  6. Performance of computer-designed small-size multistage depressed collectors for a high-perveance traveling wave tube

    NASA Technical Reports Server (NTRS)

    Ramins, P.

    1984-01-01

    Computer designed axisymmetric 2.4-cm-diameter three-, four-, and five-stage depressed collectors were evaluated in conjunction with an octave bandwidth, high-perveance, and high-electronic-efficiency, griddled-gun traveling wave tube (TWT). Spent-beam refocusing was used to condition the beam for optimum entry into the depressed collectors. Both the TWT and multistage depressed collector (MDC) efficiencies were measured, as well as the MDC current, dissipated thermal power, and DC input power distributions, for the TWT operating both at saturation over its bandwidth and over its full dynamic range. Relatively high collector efficiencies were obtained, leading to a very substantial improvement in the overall TWT efficiency. In spite of large fixed TWT body losses (due largely to the 6 to 8 percent beam interception), average overall efficiencies of 45 to 47 percent (for three to five collector stages) were obtained at saturation across the 2.5-, to 5.5-GHz operating band. For operation below saturation the collector efficiencies improved steadily, leading to reasonable ( 20 percent) overall efficiencies as far as 6 dB below saturation.

  7. Artificial cochlea and acoustic black hole travelling waves observation: Model and experimental results

    NASA Astrophysics Data System (ADS)

    Foucaud, Simon; Michon, Guilhem; Gourinat, Yves; Pelat, Adrien; Gautier, François

    2014-07-01

    An inhomogeneous fluid structure waveguide reproducing passive behaviour of the inner ear is modelled with the help of the Wentzel-Kramers-Brillouin method. A physical setup is designed and built. Experimental results are compared with a good correlation to theoretical ones. The experimental setup is a varying width plate immersed in fluid and terminated with an acoustic black hole. The varying width plate provides a spatial repartition of the vibration depending on the excitation frequency. The acoustic black hole is made by decreasing the plate's thickness with a quadratic profile and by covering this region with a thin film of viscoelastic material. Such a termination attenuates the flexural wave reflection at the end of the waveguide, turning standing waves into travelling waves.

  8. Design studies of the Ku-band, wide-band Gyro-TWT amplifier

    NASA Astrophysics Data System (ADS)

    Jung, Sang Wook; Lee, Han Seul; Jang, Kwong Ho; Choi, Jin Joo; Hong, Yong Jun; Shin, Jin Woo; So, Jun Ho; Won, Jong Hyo

    2014-02-01

    This paper reports a Ku-band, wide band Gyrotron-Traveling-wave-tube(Gyro-TWT) that is currently being developed at Kwangwoon University. The Gyro-TWT has a two stage linear tapered interaction circuit to obtain a wide operating bandwidth. The linearly-tapered interaction circuit and nonlinearly-tapered magnetic field gives the Gyro-TWT a wide operating bandwidth. The Gyro-TWT bandwidth is 23%. The 2d-Particle-in-cell(PIC) and MAGIC2d code simulation results are 17.3 dB and 24.34 kW, respectively for the maximum saturated output power. A double anode MIG was simulated with E-Gun code. The results were 0.7 for the transvers to the axial beam velocity ratio (=alpha) and a 2.3% axial velocity spread at 50 kV and 4 A. A magnetic field profile simulation was performed by using the Poisson code to obtain the grazing magnetic field of the entire interaction circuit with Poisson code.

  9. Tropical-forest biomass estimation at X-Band from the spaceborne TanDEM-X interferometer

    Treesearch

    R. Treuhaft; F. Goncalves; J.R. dos Santos; M. Keller; M. Palace; S.N. Madsen; F. Sullivan; P.M.L.A. Graca

    2014-01-01

    This letter reports the sensitivity of X-band interferometric synthetic aperture radar (InSAR) data from the first dual-spacecraft radar interferometer, TanDEM-X, to variations in tropical-forest aboveground biomass (AGB). It also reports the first tropical-forest AGB estimates fromTanDEM-X data. Tropical forests account for...

  10. Impact localization in dispersive waveguides based on energy-attenuation of waves with the traveled distance

    NASA Astrophysics Data System (ADS)

    Alajlouni, Sa'ed; Albakri, Mohammad; Tarazaga, Pablo

    2018-05-01

    An algorithm is introduced to solve the general multilateration (source localization) problem in a dispersive waveguide. The algorithm is designed with the intention of localizing impact forces in a dispersive floor, and can potentially be used to localize and track occupants in a building using vibration sensors connected to the lower surface of the walking floor. The lower the wave frequencies generated by the impact force, the more accurate the localization is expected to be. An impact force acting on a floor, generates a seismic wave that gets distorted as it travels away from the source. This distortion is noticeable even over relatively short traveled distances, and is mainly caused by the dispersion phenomenon among other reasons, therefore using conventional localization/multilateration methods will produce localization error values that are highly variable and occasionally large. The proposed localization approach is based on the fact that the wave's energy, calculated over some time window, decays exponentially as the wave travels away from the source. Although localization methods that assume exponential decay exist in the literature (in the field of wireless communications), these methods have only been considered for wave propagation in non-dispersive media, in addition to the limiting assumption required by these methods that the source must not coincide with a sensor location. As a result, these methods cannot be applied to the indoor localization problem in their current form. We show how our proposed method is different from the other methods, and that it overcomes the source-sensor location coincidence limitation. Theoretical analysis and experimental data will be used to motivate and justify the pursuit of the proposed approach for localization in a dispersive medium. Additionally, hammer impacts on an instrumented floor section inside an operational building, as well as finite element model simulations, are used to evaluate the performance of

  11. Travelling Wave Pulse Coupled Oscillator (TWPCO) Using a Self-Organizing Scheme for Energy-Efficient Wireless Sensor Networks.

    PubMed

    Al-Mekhlafi, Zeyad Ghaleb; Hanapi, Zurina Mohd; Othman, Mohamed; Zukarnain, Zuriati Ahmad

    2017-01-01

    Recently, Pulse Coupled Oscillator (PCO)-based travelling waves have attracted substantial attention by researchers in wireless sensor network (WSN) synchronization. Because WSNs are generally artificial occurrences that mimic natural phenomena, the PCO utilizes firefly synchronization of attracting mating partners for modelling the WSN. However, given that sensor nodes are unable to receive messages while transmitting data packets (due to deafness), the PCO model may not be efficient for sensor network modelling. To overcome this limitation, this paper proposed a new scheme called the Travelling Wave Pulse Coupled Oscillator (TWPCO). For this, the study used a self-organizing scheme for energy-efficient WSNs that adopted travelling wave biologically inspired network systems based on phase locking of the PCO model to counteract deafness. From the simulation, it was found that the proposed TWPCO scheme attained a steady state after a number of cycles. It also showed superior performance compared to other mechanisms, with a reduction in the total energy consumption of 25%. The results showed that the performance improved by 13% in terms of data gathering. Based on the results, the proposed scheme avoids the deafness that occurs in the transmit state in WSNs and increases the data collection throughout the transmission states in WSNs.

  12. Travelling Wave Pulse Coupled Oscillator (TWPCO) Using a Self-Organizing Scheme for Energy-Efficient Wireless Sensor Networks

    PubMed Central

    Hanapi, Zurina Mohd; Othman, Mohamed; Zukarnain, Zuriati Ahmad

    2017-01-01

    Recently, Pulse Coupled Oscillator (PCO)-based travelling waves have attracted substantial attention by researchers in wireless sensor network (WSN) synchronization. Because WSNs are generally artificial occurrences that mimic natural phenomena, the PCO utilizes firefly synchronization of attracting mating partners for modelling the WSN. However, given that sensor nodes are unable to receive messages while transmitting data packets (due to deafness), the PCO model may not be efficient for sensor network modelling. To overcome this limitation, this paper proposed a new scheme called the Travelling Wave Pulse Coupled Oscillator (TWPCO). For this, the study used a self-organizing scheme for energy-efficient WSNs that adopted travelling wave biologically inspired network systems based on phase locking of the PCO model to counteract deafness. From the simulation, it was found that the proposed TWPCO scheme attained a steady state after a number of cycles. It also showed superior performance compared to other mechanisms, with a reduction in the total energy consumption of 25%. The results showed that the performance improved by 13% in terms of data gathering. Based on the results, the proposed scheme avoids the deafness that occurs in the transmit state in WSNs and increases the data collection throughout the transmission states in WSNs. PMID:28056020

  13. DTWT (Dispersive Tsunami Wave Tool): a new tool for computing the complete dispersion of tsunami travel time.

    NASA Astrophysics Data System (ADS)

    Reymond, Dominique

    2017-04-01

    We present a tool for computing the complete arrival times of the dispersed wave-train of a tsunami. The calculus is made using the exact formulation of the tsunami dispersion (and without approximations), at any desired periods between one hour or more (concerning the gravity waves propagation) until 10s (the highly dispersed mode). The computation of the travel times is based on the a summation of the necessary time for a tsunami to cross all the elementary blocs of a grid of bathymetry following a path between the source and receiver at a given period. In addition the source dimensions and the focal mechanism are taken into account to adjust the minimum travel time to the different possible points of emission of the source. A possible application of this tool is to forecast the arrival time of late arrivals of tsunami waves that could produce the resonnance of some bays and sites at higher frequencies than the gravity mode. The theoretical arrival times are compared to the observed ones and to the results obtained by TTT (P. Wessel, 2009) and the ones obtained by numerical simulations. References: Wessel, P. (2009). Analysis of oberved and predicted tsunami travel times for the Pacic and Indian oceans. Pure Appl. Geophys., 166:301-324.

  14. Performance of a Wideband Cadmium Ferrite Microstrip Patch Antenna in the X-Band Region

    NASA Astrophysics Data System (ADS)

    Bhongale, S. R.; Ingavale, H. R.; Shinde, T. J.; Vasambekar, P. N.

    2018-01-01

    Magnesium-substituted cadmium ferrites with the chemical composition Mg x Cd1- x Fe2O4 ( x = 0, 0.4 and 0.8) were prepared by an oxalate co-precipitation method under microwave sintering technique. The structural properties of ferrites were studied by x-ray diffraction, Fourier transform infrared spectroscopy and field emission scanning electron microscope techniques. The scattering parameters such as reflection coefficient ( S 11) and transmission coefficient ( S 21) at microwave frequencies of palletized ferrites were measured by using a vector network analyzer. The software module 85071E followed by scattering parameters was used to determine the electromagnetic properties of the ferrites. The values determined for electromagnetic parameters such as the real part of permittivity ( ɛ'), permeability ( μ'), dielectric loss tangent (tan δ e) and magnetic loss tangent (tan δ m) of synthesized ferrites were used to design rectangular microstrip patch antennas. The performance of magnesium-substituted Cd ferrites as substrate for microstrip patch antennas was investigated. The antenna parameters such as return loss, bandwidth, voltage standing wave ratio, Smith chart and radiation pattern were studied. It is found that the Cd ferrite has applicability as a substrate for wideband antennas in the X-band region.

  15. Application of the nudged elastic band method to the point-to-point radio wave ray tracing in IRI modeled ionosphere

    NASA Astrophysics Data System (ADS)

    Nosikov, I. A.; Klimenko, M. V.; Bessarab, P. F.; Zhbankov, G. A.

    2017-07-01

    Point-to-point ray tracing is an important problem in many fields of science. While direct variational methods where some trajectory is transformed to an optimal one are routinely used in calculations of pathways of seismic waves, chemical reactions, diffusion processes, etc., this approach is not widely known in ionospheric point-to-point ray tracing. We apply the Nudged Elastic Band (NEB) method to a radio wave propagation problem. In the NEB method, a chain of points which gives a discrete representation of the radio wave ray is adjusted iteratively to an optimal configuration satisfying the Fermat's principle, while the endpoints of the trajectory are kept fixed according to the boundary conditions. Transverse displacements define the radio ray trajectory, while springs between the points control their distribution along the ray. The method is applied to a study of point-to-point ionospheric ray tracing, where the propagation medium is obtained with the International Reference Ionosphere model taking into account traveling ionospheric disturbances. A 2-dimensional representation of the optical path functional is developed and used to gain insight into the fundamental difference between high and low rays. We conclude that high and low rays are minima and saddle points of the optical path functional, respectively.

  16. Conjugate observations of electromagnetic ion cyclotron waves associated with traveling convection vortex events

    NASA Astrophysics Data System (ADS)

    Kim, Hyomin; Clauer, C. Robert; Gerrard, Andrew J.; Engebretson, Mark J.; Hartinger, Michael D.; Lessard, Marc R.; Matzka, Jürgen; Sibeck, David G.; Singer, Howard J.; Stolle, Claudia; Weimer, Daniel R.; Xu, Zhonghua

    2017-07-01

    We report on simultaneous observations of electromagnetic ion cyclotron (EMIC) waves associated with traveling convection vortex (TCV) events caused by transient solar wind dynamic pressure (Pd) impulse events. The Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft located near the magnetopause observed radial fluctuations of the magnetopause, and the GOES spacecraft measured sudden compressions of the magnetosphere in response to sudden increases in Pd. During the transient events, EMIC waves were observed by interhemispheric conjugate ground-based magnetometer arrays as well as the GOES spacecraft. The spectral structures of the waves appear to be well correlated with the fluctuating motion of the magnetopause, showing compression-associated wave generation. In addition, the wave features are remarkably similar in conjugate hemispheres in terms of bandwidth, quasiperiodic wave power modulation, and polarization. Proton precipitation was also observed by the DMSP spacecraft during the wave events, from which the wave source region is estimated to be 72°-74° in magnetic latitude, consistent with the TCV center. The confluence of space-borne and ground instruments including the interhemispheric, high-latitude, fluxgate/induction coil magnetometer array allows us to constrain the EMIC source region while also confirming the relationship between EMIC waves and the TCV current system.

  17. Status of experiments at LLNL on high-power X-band microwave generators

    NASA Astrophysics Data System (ADS)

    Houck, Timothy L.; Westenskow, Glen A.

    1994-05-01

    The Microwave Source Facility at the Lawrence Livermore National Laboratory (LLNL) is studying the application of induction accelerator technology to high-power microwave generators suitable for linear collider power sources. We report on the results of two experiments, both using the Choppertron's 11.4 GHz modulator and a 5-MeV, 1-kA induction beam. The first experimental configuration has a single traveling-wave output structure designed to produce in excess of 300 MW in a single fundamental waveguide. This output structure consists of 12 individual cells, the first two incorporating de-Q-ing circuits to dampen higher order resonant modes. The second experiment studies the feasibility of enhancing beam to microwave power conversion by accelerating a modulated beam with induction cells. Referred to as the `reacceleration experiment,' this experiment consists of three traveling-wave output structures designed to produce about 125 MW per output and two induction cells located between the outputs. Status of current and planned experiments are presented.

  18. Generalized three-dimensional simulation of ferruled coupled-cavity traveling-wave-tube dispersion and impedance characteristics

    NASA Technical Reports Server (NTRS)

    Maruschek, Joseph W.; Kory, Carol L.; Wilson, Jeffrey D.

    1993-01-01

    The frequency-phase dispersion and Pierce on-axis interaction impedance of a ferruled, coupled-cavity, traveling-wave tube (TWT), slow-wave circuit were calculated using the three-dimensional simulation code Micro-SOS. The utilization of the code to reduce costly and time-consuming experimental cold tests is demonstrated by the accuracy achieved in calculating these parameters. A generalized input file was developed so that ferruled coupled-cavity TWT slow-wave circuits of arbitrary dimensions could be easily modeled. The practicality of the generalized input file was tested by applying it to the ferruled coupled-cavity slow-wave circuit of the Hughes Aircraft Company model 961HA TWT and by comparing the results with experimental results.

  19. Use of acoustic wave travel-time measurements to probe the near-surface layers of the Sun

    NASA Technical Reports Server (NTRS)

    Jefferies, S. M.; Osaki, Y.; Shibahashi, H.; Duvall, T. L., Jr.; Harvey, J. W.; Pomerantz, M. A.

    1994-01-01

    The variation of solar p-mode travel times with cyclic frequency nu is shown to provide information on both the radial variation of the acoustic potential and the depth of the effective source of the oscillations. Observed travel-time data for waves with frequency lower than the acoustic cutoff frequency for the solar atmosphere (approximately equals 5.5 mHz) are inverted to yield the local acoustic cutoff frequency nu(sub c) as a function of depth in the outer convection zone and lower atmosphere of the Sun. The data for waves with nu greater than 5.5 mHz are used to show that the source of the p-mode oscillations lies approximately 100 km beneath the base of the photosphere. This depth is deeper than that determined using a standard mixing-length calculation.

  20. Travelling wave ultrasonic motors, Part I: Working principle and mathematical modelling of the stator

    NASA Astrophysics Data System (ADS)

    Hagedorn, P.; Wallaschek, J.

    1992-05-01

    Travelling wave ultrasonic motors have recently been attracting considerable attention: they may possibly soon replace—at least in certain areas—small electromagnetic motors. This development has been made possible by recent advances in power electronics, material research and digital control, which allow utilization of the piezoelectric effect for low power motors. In these motors the mechanical energy is generated with frequencies of the order of 40 kHz via piezo-elements producing bending waves in a stator, which has approximately the form of a circular plate. The rotor is then driven by the stator via contact forces, and with an extremely simple mechanism frequency reductions of 1:40 000 and more are obtained between the stator vibration and the rotor motion. As a consequence, one can work in the 40 kHz range on the electrical side, while a low frequency rotation is obtained on the mechanical side, as is desirable for many applications. In the present paper, which is the first of a series, the working principle of travelling wave ultrasonic motors is reviewed, and the main phenomena are mathematically modelled. In further papers a detailed mathematical description of the stator vibration and a first model of the contact problem will be given.

  1. Multi-band filter design with less total film thickness for short-wave infrared

    NASA Astrophysics Data System (ADS)

    Yan, Yung-Jhe; Chien, I.-Pen; Chen, Po-Han; Chen, Sheng-Hui; Tsai, Yi-Chun; Ou-Yang, Mang

    2017-08-01

    A multi-band pass filter array was proposed and designed for short wave infrared applications. The central wavelength of the multi-band pass filters are located about 905 nm, 950 nm, 1055 nm and 1550 nm. In the simulation of an optical interference band pass filter, high spectrum performance (high transmittance ratio between the pass band and stop band) relies on (1) the index gap between the selected high/low-index film materials, with a larger gap correlated to higher performance, and (2) sufficient repeated periods of high/low-index thin-film layers. When determining high and low refractive index materials, spectrum performance was improved by increasing repeated periods. Consequently, the total film thickness increases rapidly. In some cases, a thick total film thickness is difficult to process in practice, especially when incorporating photolithography liftoff. Actually the maximal thickness of the photoresist being able to liftoff will bound the total film thickness of the band pass filter. For the application of the short wave infrared with the wavelength range from 900nm to 1700nm, silicone was chosen as a high refractive index material. Different from other dielectric materials used in the visible range, silicone has a higher absorptance in the visible range opposite to higher transmission in the short wave infrared. In other words, designing band pass filters based on silicone as a high refractive index material film could not obtain a better spectrum performance than conventional high index materials like TiO2 or Ta2O5, but also its material cost would reduce about half compared to the total film thickness with the conventional material TiO2. Through the simulation and several experimental trials, the total film thickness below 4 um was practicable and reasonable. The fabrication of the filters was employed a dual electric gun deposition system with ion assisted deposition after the lithography process. Repeating four times of lithography and deposition

  2. Clamped seismic metamaterials: ultra-low frequency stop bands

    NASA Astrophysics Data System (ADS)

    Achaoui, Y.; Antonakakis, T.; Brûlé, S.; Craster, R. V.; Enoch, S.; Guenneau, S.

    2017-06-01

    The regularity of earthquakes, their destructive power, and the nuisance of ground vibration in urban environments, all motivate designs of defence structures to lessen the impact of seismic and ground vibration waves on buildings. Low frequency waves, in the range 1-10 Hz for earthquakes and up to a few tens of Hz for vibrations generated by human activities, cause a large amount of damage, or inconvenience; depending on the geological conditions they can travel considerable distances and may match the resonant fundamental frequency of buildings. The ultimate aim of any seismic metamaterial, or any other seismic shield, is to protect over this entire range of frequencies; the long wavelengths involved, and low frequency, have meant this has been unachievable to date. Notably this is scalable and the effects also hold for smaller devices in ultrasonics. There are three approaches to obtaining shielding effects: bragg scattering, locally resonant sub-wavelength inclusions and zero-frequency stop-band media. The former two have been explored, but the latter has not and is examined here. Elastic flexural waves, applicable in the mechanical vibrations of thin elastic plates, can be designed to have a broad zero-frequency stop-band using a periodic array of very small clamped circles. Inspired by this experimental and theoretical observation, all be it in a situation far removed from seismic waves, we demonstrate that it is possible to achieve elastic surface (Rayleigh) wave reflectors at very large wavelengths in structured soils modelled as a fully elastic layer periodically clamped to bedrock. We identify zero frequency stop-bands that only exist in the limit of columns of concrete clamped at their base to the bedrock. In a realistic configuration of a sedimentary basin 15 m deep we observe a zero frequency stop-band covering a broad frequency range of 0-30 Hz.

  3. The excitonic photoluminescence mechanism and lasing action in band-gap-tunable CdS(1-x)Se(x) nanostructures.

    PubMed

    Dai, Jun; Zhou, Pengxia; Lu, Junfeng; Zheng, Hongge; Guo, Jiyuan; Wang, Fang; Gu, Ning; Xu, Chunxiang

    2016-01-14

    Bandgap tunable semiconductor materials have wide application in integrated-optoelectronic and communication devices. The CdS1-xSex ternary semiconductor materials covering green-red bands have been reported previously, but their basic band-gap and optical properties crucial to the performance of the CdS1-xSex-based optoelectronic devices have not been deeply understood. In this paper, we theoretically simulated and discussed the feasibility of bandgap-tunable CdS1-xSex nanomaterials for designing wavelength tunable microlasers. Then we fabricated the CdS1-xSex nanobelts with their band gap ranging from 2.4 to 1.74 eV by adjusting the composition ratio x in the vapor-phase-transport growth process. The temperature-dependent photoluminescence and exciton-related optical constants of the CdS1-xSex nanobelts were carefully demonstrated. Finally, the wavelength-tunable Fabry-Perot lasing in CdS1-xSex nanobelts was obtained, and the Fabry-Perot lasing mechanism was numerically simulated by the FDTD method. The systematic results on the mechanism of the tunable band gap, exciton properties and lasing of the CdS1-xSex nanostructure help us deeply understand the intrinsic optical properties of this material, and will build a strong foundation for future application of green-red wavelength-tunable CdS1-xSex microlasers.

  4. Inverted S-Shaped Compact Antenna for X-Band Applications

    PubMed Central

    Samsuzzaman, M.; Islam, M. T.

    2014-01-01

    A novel probe-fed compact inverted S-shaped multifrequency patch antenna is designed. By employing two rectangular slots that change the conventional rectangular patch into an inverted S-shaped patch, the antenna is able to operate in triple frequency in the X-band. The performance criteria of the proposed design have been experimentally verified by fabricating a printed prototype. The measured results show that the −10 dB impedance bandwidth of the proposed antenna at lower band is 5.02% (8.69–9.14 GHz), at middle band is 9.13% (10.47–11.48 GHz), and at upper band is 3.79% (11.53–11.98 GHz). Two elliptical slots are introduced in the ground plane to increase the peak gain. The antenna is excited by a simple probe feeding mechanism. The overall antenna dimension is  0.52λ × 0.60λ × 0.046λ at a lower resonance frequency of 9.08 GHz. The antenna configuration and parametric investigation are conducted with the help of the high frequency structural simulator, and a good agreement is achieved between the simulated and measured data. The stable gain, omnidirectional radiation pattern, and consistent radiation efficiency in the achieved operating band make the proposed antenna a suitable candidate for X-band applications. PMID:24895656

  5. Dual-polarization 8.45 GHz traveling-wave maser

    NASA Technical Reports Server (NTRS)

    Quinn, R. B.

    1987-01-01

    An 8.5 GHz dual-channel, dual-polarization traveling-wave maser (TWM) amplifier was installed in the XKR solar system radar cone at DSS 14. The TWM is based on the Blk IIA 8.45 GHz maser structure, with two of the four maser stages being used for each channel, and each maser half then followed by a high-performance GaAs FET amplifier to achieve the desired net gain. A shortened low-noise input waveguide and an orthogonal-mode junction which is cooled to 4.5 K feeds each amplifier chain. The rotation of an external polarizer permits the polarization of each channel to be defined as either linear or circular. A circular waveguide switch was also developed to provide for noise calibration and to protect the maser from incident transmitter power.

  6. Three-Dimensional Simulation of Traveling-Wave Tube Cold-Test Characteristics Using CST MICROWAVE STUDIO

    NASA Technical Reports Server (NTRS)

    Chevalier, Christine T.; Herrmann, Kimberly A.; Kory, Carol L.; Wilson, Jeffrey D.; Cross, Andrew W.; Santana , Samuel

    2003-01-01

    The electromagnetic field simulation software package CST MICROWAVE STUDIO (MWS) was used to compute the cold-test parameters - frequency-phase dispersion, on-axis impedance, and attenuation - for a traveling-wave tube (TWT) slow-wave circuit. The results were compared to experimental data, as well as to results from MAFIA, another three-dimensional simulation code from CST currently used at the NASA Glenn Research Center (GRC). The strong agreement between cold-test parameters simulated with MWS and those measured experimentally demonstrates the potential of this code to reduce the time and cost of TWT development.

  7. Reactive-Diffusive-Advective Traveling Waves in a Family of Degenerate Nonlinear Equations.

    PubMed

    Sánchez-Garduño, Faustino; Pérez-Velázquez, Judith

    This paper deals with the analysis of existence of traveling wave solutions (TWS) for a diffusion-degenerate (at D (0) = 0) and advection-degenerate (at h '(0) = 0) reaction-diffusion-advection (RDA) equation. Diffusion is a strictly increasing function and the reaction term generalizes the kinetic part of the Fisher-KPP equation. We consider different forms of the convection term h ( u ): (1)   h '( u ) is constant k , (2)   h '( u ) = ku with k > 0, and (3) it is a quite general form which guarantees the degeneracy in the advective term. In Case 1, we prove that the task can be reduced to that for the corresponding equation, where k = 0, and then previous results reported from the authors can be extended. For the other two cases, we use both analytical and numerical tools. The analysis we carried out is based on the restatement of searching TWS for the full RDA equation into a two-dimensional dynamical problem. This consists of searching for the conditions on the parameter values for which there exist heteroclinic trajectories of the ordinary differential equations (ODE) system in the traveling wave coordinates. Throughout the paper we obtain the dynamics by using tools coming from qualitative theory of ODE.

  8. Reactive-Diffusive-Advective Traveling Waves in a Family of Degenerate Nonlinear Equations

    PubMed Central

    Sánchez-Garduño, Faustino

    2016-01-01

    This paper deals with the analysis of existence of traveling wave solutions (TWS) for a diffusion-degenerate (at D(0) = 0) and advection-degenerate (at h′(0) = 0) reaction-diffusion-advection (RDA) equation. Diffusion is a strictly increasing function and the reaction term generalizes the kinetic part of the Fisher-KPP equation. We consider different forms of the convection term h(u): (1)  h′(u) is constant k, (2)  h′(u) = ku with k > 0, and (3) it is a quite general form which guarantees the degeneracy in the advective term. In Case 1, we prove that the task can be reduced to that for the corresponding equation, where k = 0, and then previous results reported from the authors can be extended. For the other two cases, we use both analytical and numerical tools. The analysis we carried out is based on the restatement of searching TWS for the full RDA equation into a two-dimensional dynamical problem. This consists of searching for the conditions on the parameter values for which there exist heteroclinic trajectories of the ordinary differential equations (ODE) system in the traveling wave coordinates. Throughout the paper we obtain the dynamics by using tools coming from qualitative theory of ODE. PMID:27689131

  9. Band structure engineering for solar energy applications: Zinc oxide(1-x) selenium(x) films and devices

    NASA Astrophysics Data System (ADS)

    Mayer, Marie Annette

    New technologies motivate the development of new semiconducting materials, for which structural, electrical and chemical properties are not well understood. In addition to new materials systems, there are huge opportunities for new applications, especially in solar energy conversion. In this dissertation I explore the role of band structure engineering of semiconducting oxides for solar energy. Due to the abundance and electrochemical stability of oxides, the appropriate modification could make them appealing for applications in both photovoltaics and photoelectrochemical hydrogen production. This dissertation describes the design, synthesis and evaluation of the alloy ZnO1-xSe x for these purposes. I review several methods of band structure engineering including strain, quantum confinement and alloying. A detailed description of the band anticrossing (BAC) model for highly mismatched alloys is provided, including the derivation of the BAC model as well as recent work and potential applications. Thin film ZnOxSe1-x samples are grown by pulsed laser deposition (PLD). I describe in detail the effect of growth conditions (temperature, pressure and laser fluence) on the chemistry, structure and optoelectronic properties of ZnOxSe1-x. The films are grown using different combinations of PLD conditions and characterized with a variety of techniques. Phase pure films with low roughness and high crystallinity were obtained at temperatures below 450¢ªC, pressures less than 10-4 Torr and laser fluences on the order of 1.5 J/cm 2. Electrical conduction was still observed despite heavy concentrations of grain boundaries. The band structure of ZnO1-xSex is then examined in detail. The bulk electron affinity of a ZnO thin film was measured to be 4.5 eV by pinning the Fermi level with native defects. This is explained in the framework of the amphoteric defect model. A shift in the ZnO1-xSe x valence band edge with x is observed using synchrotron x-ray absorption and emission

  10. Multiple scattering and stop band characteristics of flexural waves on a thin plate with circular holes

    NASA Astrophysics Data System (ADS)

    Wang, Zuowei; Biwa, Shiro

    2018-03-01

    A numerical procedure is proposed for the multiple scattering analysis of flexural waves on a thin plate with circular holes based on the Kirchhoff plate theory. The numerical procedure utilizes the wave function expansion of the exciting as well as scattered fields, and the boundary conditions at the periphery of holes are incorporated as the relations between the expansion coefficients of exciting and scattered fields. A set of linear algebraic equations with respect to the wave expansion coefficients of the exciting field alone is established by the numerical collocation method. To demonstrate the applicability of the procedure, the stop band characteristics of flexural waves are analyzed for different arrangements and concentrations of circular holes on a steel plate. The energy transmission spectra of flexural waves are shown to capture the detailed features of the stop band formation of regular and random arrangements of holes. The increase of the concentration of holes is found to shift the dips of the energy transmission spectra toward higher frequencies as well as deepen them. The hexagonal hole arrangement can form a much broader stop band than the square hole arrangement for flexural wave transmission. It is also demonstrated that random arrangements of holes make the transmission spectrum more complicated.

  11. Ex situ themo-catalytic upgrading of biomass pyrolysis vapors using a traveling wave microwave reactor

    USDA-ARS?s Scientific Manuscript database

    Microwave heating offers a number of advantages over conventional heating methods, such as, rapid and volumetric heating, precise temperature control, energy efficiency and lower temperature gradient. In this article we demonstrate the use of 2450 MHz microwave traveling wave reactor to heat the cat...

  12. Ultra wideband surface wave communications

    NASA Astrophysics Data System (ADS)

    Lacomb, Julie Anne

    Ultra Wideband (UWB), an impulse carrier waveform, was applied at HF-VHF frequencies to utilize surface wave propagation. UWB involves the propagation of transient pulses rather than continuous waves which makes the system easier to implement, inexpensive, low power and small. Commercial UWB for wireless personal area networks is 3.1 to 10.6 GHz band as approved by the FCC with ranges up to 12 ft. The use of surface wave propagation (instead of commercial SHF UWB) extends the communication range. Surface wave is a means of propagation where the wave is guided by the surface of the Earth. Surface wave is efficient at low frequencies, VLF to HF. The UWB HF channel was modeled and also experimentally characterized. The Federal Communications Commission (FCC) defines UWB as a signal with either a fractional bandwidth of 20% of the center frequency or a bandwidth of 500MHz. Designing an antenna to operate over the 20% bandwidth requirement of UWB is one of the greatest challenges. Two different antenna designs are presented, a spoke top antenna and a traveling wave antenna with photonic bandgap. These designs were implemented at the commercial UWB frequencies (3.1--10.6 GHz) due to availability of modeling tools for the higher frequencies, the reduced antenna size and the availability of measurement facilities. The spoke top was optimum for replication of the time domain input signal. The traveling wave antenna with photonic bandgap demonstrated increased impedance bandwidth of the antenna.

  13. Hardware system of X-wave generator with simple driving pulses

    NASA Astrophysics Data System (ADS)

    Li, Xu; Li, Yaqin; Xiao, Feng; Ding, Mingyue; Yuchi, Ming

    2013-03-01

    The limited diffraction beams such as X-wave have the properties of larger depth of field. Thus, it has the potential to generate ultra-high frame rate ultrasound images. However, in practice, the real-time generation of X-wave ultrasonic field requires complex and high-cost system, especially the precise and specific voltage time distribution part for the excitation of each distinct array element. In order to simplify the hardware realization of X-wave, based on the previous works, X-wave excitation signals were decomposed and expressed as the superposition of a group of simple driving pulses, such as rectangular and triangular waves. The hardware system for the X-wave generator was also designed. The generator consists of a computer for communication with the circuit, universal serial bus (USB) based micro-controller unit (MCU) for data transmission, field programmable gate array (FPGA) based Direct Digital Synthesizer(DDS), 12-bit digital-to-analog (D/A) converter and a two stage amplifier.The hardware simulation results show that the designed system can generate the waveforms at different radius approximating the theoretical X-wave excitations with a maximum error of 0.49% triggered by the quantification of amplitude data.

  14. Acceleration of ions and neutrals by a traveling electrostatic wave

    NASA Astrophysics Data System (ADS)

    Lee, K. H.; Lee, L. C.; Wong, A. Y.

    2018-02-01

    We propose a new scheme for accelerating a weakly ionized gas by externally imposing a sinusoidal electrostatic (ES) potential in a tubular system. The weakly ionized gas consists of three fluid components: neutral hydrogen fluid ( H ), positively charged fluid ( H + ), and negatively charged fluids ( H - and/or e - ), as an example. The sinusoidal ES potential is imposed on a series of conductive meshes in the tubular system, and its phase varies with time and space to mimic a traveling ES wave. The charged fluids are trapped and accelerated by the sinusoidal ES potential, while the neutral fluid is accelerated through neutral-ion collisions. The neutral fluid can be accelerated to the wave phase velocity in a few neutral-ion collision times. The whole device remains charge-neutral, and there is no build-up of space charge. The acceleration scheme can be applied to, for example, the propulsion of glider in the air, partially ionized plasma in a chamber, spacecraft, and wind tunnel.

  15. Computer Aided Design of Ka-Band Waveguide Power Combining Architectures for Interplanetary Spacecraft

    NASA Technical Reports Server (NTRS)

    Vaden, Karl R.

    2006-01-01

    Communication systems for future NASA interplanetary spacecraft require transmitter power ranging from several hundred watts to kilowatts. Several hybrid junctions are considered as elements within a corporate combining architecture for high power Ka-band space traveling-wave tube amplifiers (TWTAs). This report presents the simulated transmission characteristics of several hybrid junctions designed for a low loss, high power waveguide based power combiner.

  16. Novel modeling technique for the stator of traveling wave ultrasonic motors.

    PubMed

    Pons, José L; Rodríguez, Humberto; Ceres, Ramón; Calderón, Leopoldo

    2003-11-01

    Traveling wave ultrasonic motors (TWUM) are a promising type of piezoelectric transducers, which are based on the friction transmission of mechanical propagating waves. These waves are excited on the stator by using high Q piezoelectric ceramics. This article presents a modeling strategy, which allows for a quick and precise modal and forced analysis of the stator of TWUM. First-order shear deformation laminated plate theory is applied to annular subdomains (super-elements) of the stator. In addition to shear deformations, the model takes into account the effect of rotary inertia, the stiffness contribution of the teeth, and the linear varying thickness of the stator. Moreover, the formulation considers a more realistic function for the electric field inside the piezoelectric ceramic, i.e., a linear function, instead of the generally assumed constant electric field. The Ritz method is used to find an approximated solution for the dynamic equations. Finally, the modal response is obtained and compared against the results from classical simplified models and the finite element method. Thus, the high accuracy and short computation times of the novel strategy were demonstrated.

  17. A Novel Multimode Waveguide Coupler for Accurate Power Measurement of Traveling Wave Tube Harmonic Frequencies

    NASA Technical Reports Server (NTRS)

    Wintucky, Edwin G.; Simons, Rainee N.

    2014-01-01

    This paper presents the design, fabrication and test results for a novel waveguide multimode directional coupler (MDC). The coupler fabricated from two dissimilar waveguides is capable of isolating the power at the second harmonic frequency from the fundamental power at the output port of a traveling-wave tube (TWT). In addition to accurate power measurements at harmonic frequencies, a potential application of the MDC is in the design of a beacon source for atmospheric propagation studies at millimeter-wave frequencies.

  18. Collapse of a nanoscopic void triggered by a spherically symmetric traveling sound wave.

    PubMed

    Hołyst, Robert; Litniewski, Marek; Garstecki, Piotr

    2012-05-01

    Molecular-dynamics simulations of the Lennard-Jones fluid (up to 10(7) atoms) are used to analyze the collapse of a nanoscopic bubble. The collapse is triggered by a traveling sound wave that forms a shock wave at the interface. The peak temperature T(max) in the focal point of the collapse is approximately ΣR(0)(a), where Σ is the surface density of energy injected at the boundary of the container of radius R(0) and α ≈ 0.4-0.45. For Σ = 1.6 J/m(2) and R(0) = 51 nm, the shock wave velocity, which is proportional to √Σ, reaches 3400 m/s (4 times the speed of sound in the liquid); the pressure at the interface, which is proportional to Σ, reaches 10 GPa; and T(max) reaches 40,000 K. The Rayleigh-Plesset equation together with the time of the collapse can be used to estimate the pressure at the front of the shock wave.

  19. The electromagnetic-trait imaging computation of traveling wave method in breast tumor microwave sensor system.

    PubMed

    Tao, Zhi-Fu; Han, Zhong-Ling; Yao, Meng

    2011-01-01

    Using the difference of dielectric constant between malignant tumor tissue and normal breast tissue, breast tumor microwave sensor system (BRATUMASS) determines the detected target of imaging electromagnetic trait by analyzing the properties of target tissue back wave obtained after near-field microwave radicalization (conelrad). The key of obtained target properties relationship and reconstructed detected space is to analyze the characteristics of the whole process from microwave transmission to back wave reception. Using traveling wave method, we derive spatial transmission properties and the relationship of the relation detected points distances, and valuate the properties of each unit by statistical valuation theory. This chapter gives the experimental data analysis results.

  20. Monte Carlo simulation for kinetic chemotaxis model: An application to the traveling population wave

    NASA Astrophysics Data System (ADS)

    Yasuda, Shugo

    2017-02-01

    A Monte Carlo simulation of chemotactic bacteria is developed on the basis of the kinetic model and is applied to a one-dimensional traveling population wave in a microchannel. In this simulation, the Monte Carlo method, which calculates the run-and-tumble motions of bacteria, is coupled with a finite volume method to calculate the macroscopic transport of the chemical cues in the environment. The simulation method can successfully reproduce the traveling population wave of bacteria that was observed experimentally and reveal the microscopic dynamics of bacterium coupled with the macroscopic transports of the chemical cues and bacteria population density. The results obtained by the Monte Carlo method are also compared with the asymptotic solution derived from the kinetic chemotaxis equation in the continuum limit, where the Knudsen number, which is defined by the ratio of the mean free path of bacterium to the characteristic length of the system, vanishes. The validity of the Monte Carlo method in the asymptotic behaviors for small Knudsen numbers is numerically verified.

  1. Simultaneous S- and X-band uplink-downlink performance at DSS 13

    NASA Technical Reports Server (NTRS)

    Freiley, A. J.

    1988-01-01

    The Deep Space Station 13 26-meter antenna with the second generation S/X feedcone was tested to determine the dual S- and X-band (2.1 to 2.3 GHz and 7.1 to 8.5 GHz) transmit and receive performance. Measurements were conducted using the 20 kW transmitters at S- and X-band while simultaneously receiving S- and X-band. This system proved to be very quiet compared with the other DSN antennas. Under normal tracking configurations, no noise burst or intermodulation product (IMP) activity was detectable to the -175 dBm level. To prove the instrumentation's ability to detect such phenomena, an IMP generator was introduced onto the system with positive, verifiable results. The IMP occurred at the -162 dBm level, accompanied by moderate noise burst activity, and was readily repeatable. The measurement also showed the possible need for additional fourth channel filtering in the system to reduce the effect of the transmitter power on the low noise amplifiers.

  2. Solving complex band structure problems with the FEAST eigenvalue algorithm

    NASA Astrophysics Data System (ADS)

    Laux, S. E.

    2012-08-01

    With straightforward extension, the FEAST eigenvalue algorithm [Polizzi, Phys. Rev. B 79, 115112 (2009)] is capable of solving the generalized eigenvalue problems representing traveling-wave problems—as exemplified by the complex band-structure problem—even though the matrices involved are complex, non-Hermitian, and singular, and hence outside the originally stated range of applicability of the algorithm. The obtained eigenvalues/eigenvectors, however, contain spurious solutions which must be detected and removed. The efficiency and parallel structure of the original algorithm are unaltered. The complex band structures of Si layers of varying thicknesses and InAs nanowires of varying radii are computed as test problems.

  3. A dynamic model of the piezoelectric traveling wave rotary ultrasonic motor stator with the finite volume method.

    PubMed

    Renteria Marquez, I A; Bolborici, V

    2017-05-01

    This manuscript presents a method to model in detail the piezoelectric traveling wave rotary ultrasonic motor (PTRUSM) stator response under the action of DC and AC voltages. The stator is modeled with a discrete two dimensional system of equations using the finite volume method (FVM). In order to obtain accurate results, a model of the stator bridge is included into the stator model. The model of the stator under the action of DC voltage is presented first, and the results of the model are compared versus a similar model using the commercial finite element software COMSOL Multiphysics. One can observe that there is a difference of less than 5% between the displacements of the stator using the proposed model and the one with COMSOL Multiphysics. After that, the model of the stator under the action of AC voltages is presented. The time domain analysis shows the generation of the traveling wave in the stator surface. One can use this model to accurately calculate the stator surface velocities, elliptical motion of the stator surface and the amplitude and shape of the stator traveling wave. A system of equations discretized with the finite volume method can easily be transformed into electrical circuits, because of that, FVM may be a better choice to develop a model-based control strategy for the PTRUSM. Copyright © 2017 Elsevier B.V. All rights reserved.

  4. Vibration band gaps for elastic metamaterial rods using wave finite element method

    NASA Astrophysics Data System (ADS)

    Nobrega, E. D.; Gautier, F.; Pelat, A.; Dos Santos, J. M. C.

    2016-10-01

    Band gaps in elastic metamaterial rods with spatial periodic distribution and periodically attached local resonators are investigated. New techniques to analyze metamaterial systems are using a combination of analytical or numerical method with wave propagation. One of them, called here wave spectral element method (WSEM), consists of combining the spectral element method (SEM) with Floquet-Bloch's theorem. A modern methodology called wave finite element method (WFEM), developed to calculate dynamic behavior in periodic acoustic and structural systems, utilizes a similar approach where SEM is substituted by the conventional finite element method (FEM). In this paper, it is proposed to use WFEM to calculate band gaps in elastic metamaterial rods with spatial periodic distribution and periodically attached local resonators of multi-degree-of-freedom (M-DOF). Simulated examples with band gaps generated by Bragg scattering and local resonators are calculated by WFEM and verified with WSEM, which is used as a reference method. Results are presented in the form of attenuation constant, vibration transmittance and frequency response function (FRF). For all cases, WFEM and WSEM results are in agreement, provided that the number of elements used in WFEM is sufficient to convergence. An experimental test was conducted with a real elastic metamaterial rod, manufactured with plastic in a 3D printer, without local resonance-type effect. The experimental results for the metamaterial rod with band gaps generated by Bragg scattering are compared with the simulated ones. Both numerical methods (WSEM and WFEM) can localize the band gap position and width very close to the experimental results. A hybrid approach combining WFEM with the commercial finite element software ANSYS is proposed to model complex metamaterial systems. Two examples illustrating its efficiency and accuracy to model an elastic metamaterial rod unit-cell using 1D simple rod element and 3D solid element are

  5. A continuous high-throughput bioparticle sorter based on 3D traveling-wave dielectrophoresis.

    PubMed

    Cheng, I-Fang; Froude, Victoria E; Zhu, Yingxi; Chang, Hsueh-Chia; Chang, Hsien-Chang

    2009-11-21

    We present a high throughput (maximum flow rate approximately 10 microl/min or linear velocity approximately 3 mm/s) continuous bio-particle sorter based on 3D traveling-wave dielectrophoresis (twDEP) at an optimum AC frequency of 500 kHz. The high throughput sorting is achieved with a sustained twDEP particle force normal to the continuous through-flow, which is applied over the entire chip by a single 3D electrode array. The design allows continuous fractionation of micron-sized particles into different downstream sub-channels based on differences in their twDEP mobility on both sides of the cross-over. Conventional DEP is integrated upstream to focus the particles into a single levitated queue to allow twDEP sorting by mobility difference and to minimize sedimentation and field-induced lysis. The 3D electrode array design minimizes the offsetting effect of nDEP (negative DEP with particle force towards regions with weak fields) on twDEP such that both forces increase monotonically with voltage to further increase the throughput. Effective focusing and separation of red blood cells from debris-filled heterogeneous samples are demonstrated, as well as size-based separation of poly-dispersed liposome suspensions into two distinct bands at 2.3 to 4.6 microm and 1.5 to 2.7 microm, at the highest throughput recorded in hand-held chips of 6 microl/min.

  6. Ultrabroadband Design for Linear Polarization Conversion and Asymmetric Transmission Crossing X- and K- Band

    PubMed Central

    Zhang, Linbo; Zhou, Peiheng; Chen, Haiyan; Lu, Haipeng; Xie, Haiyan; Zhang, Li; Li, En; Xie, Jianliang; Deng, Longjiang

    2016-01-01

    In this work, a high-efficiency and broadband reflective converter using ultrathin planar metamaterial (MM) composed of single-layered SRR is firstly realized. Numerical and experimental results demonstrate that the cross-polarization conversion reflectance above 0.84 is achieved from 8.6 to 18.6 GHz for linearly polarized (LP) incident waves under normal incidence. Subsequently, a multi-layered MM based on SRR enables a dramatic improvement of the recently demonstrated asymmetric transmission (AT) effect. Theoretical and measured results present that strong one-way transmission of two orthogonally polarized waves crossing C- and K- band has been observed. These two separated AT pass-bands have a function of selective polarization filter, which can be switched on/off by changing the polarization state of incident waves. The physical mechanisms are elucidated by taking advantage of electric fields and current distributions. Considering the broad bandwidth and the dual band, we believe that these two structures will be beneficial for designing polarization-controlled and selective transmission converter. PMID:27658929

  7. Ultrabroadband Design for Linear Polarization Conversion and Asymmetric Transmission Crossing X- and K- Band.

    PubMed

    Zhang, Linbo; Zhou, Peiheng; Chen, Haiyan; Lu, Haipeng; Xie, Haiyan; Zhang, Li; Li, En; Xie, Jianliang; Deng, Longjiang

    2016-09-23

    In this work, a high-efficiency and broadband reflective converter using ultrathin planar metamaterial (MM) composed of single-layered SRR is firstly realized. Numerical and experimental results demonstrate that the cross-polarization conversion reflectance above 0.84 is achieved from 8.6 to 18.6 GHz for linearly polarized (LP) incident waves under normal incidence. Subsequently, a multi-layered MM based on SRR enables a dramatic improvement of the recently demonstrated asymmetric transmission (AT) effect. Theoretical and measured results present that strong one-way transmission of two orthogonally polarized waves crossing C- and K- band has been observed. These two separated AT pass-bands have a function of selective polarization filter, which can be switched on/off by changing the polarization state of incident waves. The physical mechanisms are elucidated by taking advantage of electric fields and current distributions. Considering the broad bandwidth and the dual band, we believe that these two structures will be beneficial for designing polarization-controlled and selective transmission converter.

  8. Traveling wave ultrasonic motor using polymer-based vibrator

    NASA Astrophysics Data System (ADS)

    Wu, Jiang; Mizuno, Yosuke; Tabaru, Marie; Nakamura, Kentaro

    2016-01-01

    With the characteristics of low density, low elastic modulus, and low mechanical loss, poly(phenylene sulfide) (PPS) is a promising material for fabricating lightweight ultrasonic motors (USMs). For the first time, we used PPS to fabricate an annular elastomer with teeth and glued a piece of piezoelectric-ceramic annular disk to the bottom of the elastomer to form a vibrator. To explore for a material suitable for the rotor surface coming in contact with the PPS-based vibrator, several disk-shaped rotors made of different materials were fabricated to form traveling wave USMs. The polymer-based USM rotates successfully as the conventional metal-based USMs. The experimental results show that the USM with the aluminum rotor has the largest torque, which indicates that aluminum is the most suitable for the rotor surface among the tested materials.

  9. Travelling wave solutions and conservation laws for the Korteweg-de Vries-Bejamin-Bona-Mahony equation

    NASA Astrophysics Data System (ADS)

    Simbanefayi, Innocent; Khalique, Chaudry Masood

    2018-03-01

    In this work we study the Korteweg-de Vries-Benjamin-Bona-Mahony (KdV-BBM) equation, which describes the two-way propagation of waves. Using Lie symmetry method together with Jacobi elliptic function expansion and Kudryashov methods we construct its travelling wave solutions. Also, we derive conservation laws of the KdV-BBM equation using the variational derivative approach. In this method, we begin by computing second-order multipliers for the KdV-BBM equation followed by a derivation of the respective conservation laws for each multiplier.

  10. Intercomparison of attenuation correction algorithms for single-polarized X-band radars

    NASA Astrophysics Data System (ADS)

    Lengfeld, K.; Berenguer, M.; Sempere Torres, D.

    2018-03-01

    Attenuation due to liquid water is one of the largest uncertainties in radar observations. The effects of attenuation are generally inversely proportional to the wavelength, i.e. observations from X-band radars are more affected by attenuation than those from C- or S-band systems. On the other hand, X-band radars can measure precipitation fields in higher temporal and spatial resolution and are more mobile and easier to install due to smaller antennas. A first algorithm for attenuation correction in single-polarized systems was proposed by Hitschfeld and Bordan (1954) (HB), but it gets unstable in case of small errors (e.g. in the radar calibration) and strong attenuation. Therefore, methods have been developed that restrict attenuation correction to keep the algorithm stable, using e.g. surface echoes (for space-borne radars) and mountain returns (for ground radars) as a final value (FV), or adjustment of the radar constant (C) or the coefficient α. In the absence of mountain returns, measurements from C- or S-band radars can be used to constrain the correction. All these methods are based on the statistical relation between reflectivity and specific attenuation. Another way to correct for attenuation in X-band radar observations is to use additional information from less attenuated radar systems, e.g. the ratio between X-band and C- or S-band radar measurements. Lengfeld et al. (2016) proposed such a method based isotonic regression of the ratio between X- and C-band radar observations along the radar beam. This study presents a comparison of the original HB algorithm and three algorithms based on the statistical relation between reflectivity and specific attenuation as well as two methods implementing additional information of C-band radar measurements. Their performance in two precipitation events (one mainly convective and the other one stratiform) shows that a restriction of the HB is necessary to avoid instabilities. A comparison with vertically pointing

  11. Slip-stick excitation and travelling waves excite silo honking

    NASA Astrophysics Data System (ADS)

    Vriend, Nathalie; Warburton, Kasia; Porte, Elze

    2016-11-01

    Industrial storage silos filled with PET-particles can create a sound upon discharge. The sound forms a nuisance for the environment when the structure starts to act as a loudspeaker and may ultimately result in structural failure. This work investigates the phenomenon experimentally-the deployment of a microphone, an accelerometer and high-speed imaging on a laboratory set-up reveal the driving mechanism for the structural resonance: stick-slip at the wall. Particle image velocimetry shows an asymmetric, upwards travelling wave (at 50 m/s) which contains the dynamic "slip"-region. The frequency of the mechanical motion of the grains is successfully correlated to the frequency of the emitted sound. Friction models are explored to describe and quantify the frictional interaction between the grains and the wall.

  12. Unimodal dynamical systems: Comparison principles, spreading speeds and travelling waves

    NASA Astrophysics Data System (ADS)

    Yi, Taishan; Chen, Yuming; Wu, Jianhong

    Reaction diffusion equations with delayed nonlinear reaction terms are used as prototypes to motivate an appropriate abstract formulation of dynamical systems with unimodal nonlinearity. For such non-monotone dynamical systems, we develop a general comparison principle and show how this general comparison principle, coupled with some existing results for monotone dynamical systems, can be used to establish results on the asymptotic speeds of spread and travelling waves. We illustrate our main results by an integral equation which includes a nonlocal delayed reaction diffusion equation and a nonlocal delayed lattice differential system in an unbounded domain, with the non-monotone nonlinearities including the Ricker birth function and the Mackey-Glass hematopoiesis feedback.

  13. The effect of traveling wave shapes in the maneuver control and efficiency of an underwater robot propelled by an undulating fin

    NASA Astrophysics Data System (ADS)

    Liu, Hanlin; Curet, Oscar

    2016-11-01

    Effective control of propulsive undulating fins has the potential to enhance the maneuverability and efficiency of underwater vehicles allowing them to navigate in more complex environments. Aquatic animals using this type of propulsion are able to perform complex maneuvers by sending different traveling waves along one or multiple elongated fins. Recent work has investigated the propulsive forces, the hydrodynamics and the efficiency of an undulating ribbon fin. However, it is still not understood how different traveling wave shapes along the fin can be used to control the hydrodynamic forces and torques to perform different maneuvers. In this work, we study the effect of traveling wave shapes on the hydrodynamic forces and torques, swimming speed, maneuver control and propulsive performance of an underwater vehicle propelled by an undulating fin. The underwater robot propels by actuating a fin that is composed of sixteen independent rays interconnected with a flexible membrane. The hull contains all the electronics, batteries, motors and sensors. The underwater vehicle was tested in a water tank-flume facility. In a series of experiments, we measured the motion of the vessel and the power consumption for different traveling wave patterns. In addition, we measured the flow around the fin using Particle Image Velocimetry. We present the results concerning the power distribution along the fin, propulsive efficiency, free-swimming speed and pitch control based on different fin kinematics. National Science Foundation under Grant No. 1420774.

  14. Monitoring deformation at the Geysers Geothermal Field, California using C-band and X-band interferometric synthetic aperture radar

    DOE PAGES

    Vasco, D. W.; Rutqvist, Jonny; Ferretti, Alessandro; ...

    2013-06-07

    In this study, we resolve deformation at The Geysers Geothermal Field using two distinct sets of interferometric synthetic aperture radar (InSAR) data. The first set of observations utilize archived European Space Agency C-band synthetic aperture radar data from 1992 through 1999 to image the long-term and large-scale subsidence at The Geysers. The peak range velocity of approximately 50 mm/year agrees with previous estimates from leveling and global positioning system observations. Data from a second set of measurements, acquired by TerraSAR-X satellites, extend from May 2011 until April 2012 and overlap the C-band data spatially but not temporally. These X-band data,more » analyzed using a combined permanent and distributed scatterer algorithm, provide a higher density of scatterers (1122 per square kilometer) than do the C-band data (12 per square kilometer). The TerraSAR-X observations resolve 1 to 2 cm of deformation due to water injection into a Northwest Geysers enhanced geothermal system well, initiated on October 2011. Lastly, the temporal variation of the deformation is compatible with estimates from coupled numerical modeling.« less

  15. The Celestial Reference Frame at X/Ka-band (8.4/32 GHz)

    NASA Technical Reports Server (NTRS)

    Jacobs, C. S.; Clark, J. E.; Heflin, M. B.; Skjerve, L. J.; Sovers, O. J.; Garcia-Miro, C.; Moll, V. E.; Horiuchi, S.

    2011-01-01

    A celestial reference frame at X/Ka-band (8.4/32 GHz) has been constructed using fifty-one 24-hour sessions with the Deep Space Network. We report on observations which have detected 436 sources covering the full 24 hours of right ascension and declinations down to -45 deg. Comparison of this X/Ka-band frame to the S/X-band (2.3/8.4 GHz) ICRF2 shows wRMS agreement of 200 micro-arcsec in a cos delta and 290 micro-arcsec in delta. There is evidence for zonal errors at the 100 micro-arcsec level. Known errors include limited SNR, lack of phase calibration, troposphere mismodelling, and limited southern geometry. The motivations for extending the ICRF to frequencies above 8 GHz are to access more compact source morphology for improved frame stability, to provide calibrators for phase referencing, and to support spacecraft navigation at Ka-band.

  16. Two-dimensional wide-band-gap nitride semiconductors: Single-layer 1 T -X N2 (X =S ,Se , and Te )

    NASA Astrophysics Data System (ADS)

    Lin, Jia-He; Zhang, Hong; Cheng, Xin-Lu; Miyamoto, Yoshiyuki

    2016-11-01

    Recently, the two-dimensional (2D) semiconductors arsenene and antimonene, with band gaps larger than 2.0 eV, have attracted tremendous interest, especially for potential applications in optoelectronic devices with a photoresponse in the blue and UV range. Motivated by this exciting discovery, types of highly stable wide-band-gap 2D nitride semiconductors were theoretically designed. We propose single-layer 1 T -X N2 (X =S , Se, and Te) via first-principles simulations. We compute 1 T -X N2 (X =S , Se, and Te) with indirect band gaps of 2.825, 2.351, and 2.336 eV, respectively. By applying biaxial strain, they are able to induce the transition from a wide-band-gap semiconductor to a metal, and the range of absorption spectra of 1 T -X N2 (X =S , Se, and Te) obviously extend from the ultraviolet region to the blue-purple light region. With an underlying graphene, we find that 1 T -X N2 can completely shield the light absorption of graphene in the range of 1-1.6 eV. Our research paves the way for optoelectronic devices working under blue or UV light, and mechanical sensors based on these 2D crystals.

  17. Wave Processes in Arctic Seas, Observed from TerraSAR-X

    DTIC Science & Technology

    2015-09-30

    in order to improve wave models as well as ice models applicable to a changing Arctic wave/ and ice climate . This includes observation and...fields retrieved from the TS-X image swaths. 4. “Wave Climate and Wave Mixing in the Marginal Ice Zones of Arctic Seas, Observations and Modelling”, by...1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. “Wave Processes in Arctic Seas, Observed from TerraSAR-X

  18. Theoretical analysis on lower band cascade as a mechanism for multiband chorus in the Earth's magnetosphere

    NASA Astrophysics Data System (ADS)

    Gao, Xinliang; Lu, Quanming; Wang, Shaojie; Wang, Shui

    2018-05-01

    Whistler-mode waves play a crucial role in controlling electron dynamics in the Earth's Van Allen radiation belt, which is increasingly important for spacecraft safety. Using THEMIS waveform data, Gao et al. [X. L. Gao, Q. Lu, J. Bortnik, W. Li, L. Chen, and S. Wang, Geophys. Res. Lett., 43, 2343-2350, 2016] have reported two multiband chorus events, wherein upper-band chorus appears at harmonics of lower-band chorus. They proposed that upper-band harmonic waves are excited through the nonlinear coupling between the electromagnetic and electrostatic components of lower-band chorus, a second-order effect called "lower band cascade". However, the theoretical explanation of lower band cascade was not thoroughly explained in the earlier work. In this paper, based on a cold plasma assumption, we have obtained the explicit nonlinear driven force of lower band cascade through a full nonlinear theoretical analysis, which includes both the ponderomotive force and coupling between electrostatic and electromagnetic components of the pump whistler wave. Moreover, we discover the existence of an efficient energy-transfer (E-t) channel from lower-band to upper-band whistler-mode waves during lower band cascade for the first time, which is also confirmed by PIC simulations. For lower-band whistler-mode waves with a small wave normal angle (WNA), the E-t channel is detected when the driven upper-band wave nearly satisfies the linear dispersion relation of whistler mode. While, for lower-band waves with a large WNA, the E-t channel is found when the lower-band wave is close to its resonant frequency, and the driven upper-band wave becomes quasi-electrostatic. Through this efficient channel, the harmonic upper band of whistler waves is generated through energy cascade from the lower band, and the two-band spectral structure of whistler waves is then formed. Both two types of banded whistler-mode spectrum have also been successfully reproduced by PIC simulations.

  19. Stabilization of domain walls between traveling waves by nonlinear mode coupling in Taylor-Couette flow.

    PubMed

    Heise, M; Hoffmann, Ch; Abshagen, J; Pinter, A; Pfister, G; Lücke, M

    2008-02-15

    We present a new mechanism that allows the stable existence of domain walls between oppositely traveling waves in pattern-forming systems far from onset. It involves a nonlinear mode coupling that results directly from the nonlinearities in the underlying momentum balance. Our work provides the first observation and explanation of such strongly nonlinearly driven domain walls that separate structured states by a phase generating or annihilating defect. Furthermore, the influence of a symmetry breaking externally imposed flow on the wave domains and the domain walls is studied. The results are obtained for vortex waves in the Taylor-Couette system by combining numerical simulations of the full Navier-Stokes equations and experimental measurements.

  20. Improved Design/Reduction of Manufacturing Costs of Space-Traveling Wave Tiube Amplifiers Final Report CRADA No. TC-0461-93

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Shang, C. C.; Drasco, M.

    The purpose of the CRADA was to develop new microwave codes for analyzing both slow-,vave structures and beam-wave interactions of traveling wave tube amplifiers (TWTA), the microwave power source for satellite and radar communication systems. The scope of work also included testing and improving power modules through measurements and simulation.

  1. Study of travelling wave solutions for some special-type nonlinear evolution equations

    NASA Astrophysics Data System (ADS)

    Song, Junquan; Hu, Lan; Shen, Shoufeng; Ma, Wen-Xiu

    2018-07-01

    The tanh-function expansion method has been improved and used to construct travelling wave solutions of the form U={\\sum }j=0n{a}j{\\tanh }jξ for some special-type nonlinear evolution equations, which have a variety of physical applications. The positive integer n can be determined by balancing the highest order linear term with the nonlinear term in the evolution equations. We improve the tanh-function expansion method with n = 0 by introducing a new transform U=-W\\prime (ξ )/{W}2. A nonlinear wave equation with source terms, and mKdV-type equations, are considered in order to show the effectiveness of the improved scheme. We also propose the tanh-function expansion method of implicit function form, and apply it to a Harry Dym-type equation as an example.

  2. Fluid film force control in lubricated journal bearings by means of a travelling wave generated with a piezoelectric actuators' system

    NASA Astrophysics Data System (ADS)

    Iula, Antonio; Lamberti, Nicola; Savoia, Alessandro; Caliano, Giosue

    2012-05-01

    In this work an experimental evaluation of the possiblity to influence and control the fluid film forces in the gap of a lubricated journal bearing by means of a rotating travelling wave is carried out. The travellig wave is generated by two power actuators opportunely positioned on the outer surface of the bearing and electrically driven with a phase shift of 90°. Each transducer is designed to work at the natural frequency of the radial nonaxisymmetrical mode 0-5 (23.6 kHz). Experimental results show that the travelling wave is capable to control the motion of an oil drop on the inner surface of the bearing and that it is capable to put in rotation a rotor layed on the drop oil via the viscous forces in the oil drop itself.

  3. Energy transport in weakly nonlinear wave systems with narrow frequency band excitation.

    PubMed

    Kartashova, Elena

    2012-10-01

    A novel discrete model (D model) is presented describing nonlinear wave interactions in systems with small and moderate nonlinearity under narrow frequency band excitation. It integrates in a single theoretical frame two mechanisms of energy transport between modes, namely, intermittency and energy cascade, and gives the conditions under which each regime will take place. Conditions for the formation of a cascade, cascade direction, conditions for cascade termination, etc., are given and depend strongly on the choice of excitation parameters. The energy spectra of a cascade may be computed, yielding discrete and continuous energy spectra. The model does not require statistical assumptions, as all effects are derived from the interaction of distinct modes. In the example given-surface water waves with dispersion function ω(2)=gk and small nonlinearity-the D model predicts asymmetrical growth of side-bands for Benjamin-Feir instability, while the transition from discrete to continuous energy spectrum, excitation parameters properly chosen, yields the saturated Phillips' power spectrum ~g(2)ω(-5). The D model can be applied to the experimental and theoretical study of numerous wave systems appearing in hydrodynamics, nonlinear optics, electrodynamics, plasma, convection theory, etc.

  4. Detection of traveling ionospheric disturbances induced by atmospheric gravity waves using the global positioning system

    NASA Technical Reports Server (NTRS)

    Bassiri, Sassan; Hajj, George A.

    1993-01-01

    Natural and man-made events like earthquakes and nuclear explosions launch atmospheric gravity waves (AGW) into the atmosphere. Since the particle density decreases exponentially with height, the gravity waves increase exponentially in amplitude as they propagate toward the upper atmosphere and ionosphere. As atmospheric gravity waves approach the ionospheric heights, the neutral particles carried by gravity waves collide with electrons and ions, setting these particles in motion. This motion of charged particles manifests itself by wave-like fluctuations and disturbances that are known as traveling ionospheric disturbances (TID). The perturbation in the total electron content due to TID's is derived analytically from first principles. Using the tilted dipole magnetic field approximation and a Chapman layer distribution for the electron density, the variations of the total electron content versus the line-of-sight direction are numerically analyzed. The temporal variation associated with the total electron content measurements due to AGW's can be used as a means of detecting characteristics of the gravity waves. As an example, detection of tsunami generated earthquakes from their associated atmospheric gravity waves using the Global Positioning System is simulated.

  5. Design of 6 MeV X-band electron linac for dual-head gantry radiotherapy system

    NASA Astrophysics Data System (ADS)

    Shin, Seung-wook; Lee, Seung-Hyun; Lee, Jong-Chul; Kim, Huisu; Ha, Donghyup; Ghergherehchi, Mitra; Chai, Jongseo; Lee, Byung-no; Chae, Moonsik

    2017-12-01

    A compact 6 MeV electron linac is being developed at Sungkyunkwan University, in collaboration with the Korea atomic energy research institute (KAERI). The linac will be used as an X-ray source for a dual-head gantry radiotherapy system. X-band technology has been employed to satisfy the size requirement of the dual-head gantry radiotherapy machine. Among the several options available, we selected a pi/2-mode, standing-wave, side-coupled cavity. This choice of radiofrequency (RF) cavity design is intended to enhance the shunt impedance of each cavity in the linac. An optimum structure of the RF cavity with a high-performance design was determined by applying a genetic algorithm during the optimization procedure. This paper describes the detailed design process for a single normal RF cavity and the entire structure, including the RF power coupler and coupling cavity, as well as the beam dynamics results.

  6. Narrow-band erbium-doped fibre linear–ring laser

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kolegov, A A; Sofienko, G S; Minashina, L A

    2014-01-31

    We have demonstrated a narrow-band linear – ring fibre laser with an output power of 15 mW at a wavelength of 1.55 μm and an emission bandwidth less than 5 kHz. The laser frequency is stabilised by an unpumped active fibre section and fibre Bragg grating. The fibre laser operates in a travelling wave mode, which allows the spatial hole burning effect to be avoided. At a certain pump power level, the laser switches from continuous mode to repetitivepulse operation, corresponding to relaxation oscillations. (control of laser radiation parameters)

  7. Simultaneous large band gaps and localization of electromagnetic and elastic waves in defect-free quasicrystals.

    PubMed

    Yu, Tianbao; Wang, Zhong; Liu, Wenxing; Wang, Tongbiao; Liu, Nianhua; Liao, Qinghua

    2016-04-18

    We report numerically large and complete photonic and phononic band gaps that simultaneously exist in eight-fold phoxonic quasicrystals (PhXQCs). PhXQCs can possess simultaneous photonic and phononic band gaps over a wide range of geometric parameters. Abundant localized modes can be achieved in defect-free PhXQCs for all photonic and phononic polarizations. These defect-free localized modes exhibit multiform spatial distributions and can confine simultaneously electromagnetic and elastic waves in a large area, thereby providing rich selectivity and enlarging the interaction space of optical and elastic waves. The simulated results based on finite element method show that quasiperiodic structures formed of both solid rods in air and holes in solid materials can simultaneously confine and tailor electromagnetic and elastic waves; these structures showed advantages over the periodic counterparts.

  8. Radiation from a current filament driven by a traveling wave

    NASA Technical Reports Server (NTRS)

    Levine, D. M.; Meneghini, R.

    1976-01-01

    Solutions are presented for the electromagnetic fields radiated by an arbitrarily oriented current filament located above a perfectly conducting ground plane and excited by a traveling current wave. Both an approximate solution, valid in the fraunhofer region of the filament and predicting the radiation terms in the fields, and an exact solution, which predicts both near and far field components of the electromagnetic fields, are presented. Both solutions apply to current waveforms which propagate along the channel but are valid regardless of the actual waveshape. The exact solution is valid only for waves which propagate at the speed of light, and the approximate solution is formulated for arbitrary velocity of propagation. The spectrum-magnitude of the fourier transform-of the radiated fields is computed by assuming a compound exponential model for the current waveform. The effects of channel orientation and length, as well as velocity of propagation of the current waveform and location of the observer, are discussed. It is shown that both velocity of propagation and an effective channel length are important in determining the shape of the spectrum.

  9. Time-Dependent Traveling Wave Tube Model for Intersymbol Interference Investigations

    NASA Technical Reports Server (NTRS)

    Kory, Carol L.; Andro, Monty; Downey, Alan (Technical Monitor)

    2001-01-01

    For the first time, a computational model has been used to provide a direct description of the effects of the traveling wave tube (TWT) on modulated digital signals. The TWT model comprehensively takes into account the effects of frequency dependent AM/AM and AM/PM conversion, gain and phase ripple; drive-induced oscillations; harmonic generation; intermodulation products; and backward waves. Thus, signal integrity can be investigated in the presence of these sources of potential distortion as a function of the physical geometry of the high power amplifier and the operational digital signal. This method promises superior predictive fidelity compared to methods using TWT models based on swept-amplitude and/or swept-frequency data. The fully three-dimensional (3D), time-dependent, TWT interaction model using the electromagnetic code MAFIA is presented. This model is used to investigate assumptions made in TWT black-box models used in communication system level simulations. In addition, digital signal performance, including intersymbol interference (ISI), is compared using direct data input into the MAFIA model and using the system level analysis tool, SPW.

  10. A nonlinear analysis of the terahertz serpentine waveguide traveling-wave amplifier

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Li, Ke, E-mail: like.3714@163.com; Cao, Miaomiao, E-mail: mona486@yeah.net; Institute of Electronics, University of Chinese Academy of Sciences, Beijing 100190

    A nonlinear model for the numerical simulation of terahertz serpentine waveguide traveling-wave tube (SW-TWT) is described. In this model, the electromagnetic wave transmission in the SW is represented as an infinite set of space harmonics to interact with an electron beam. Analytical expressions for axial electric fields in axisymmetric interaction gaps of SW-TWTs are derived and compared with the results from CST simulation. The continuous beam is treated as discrete macro-particles with different initial phases. The beam-tunnel field equations, space-charge field equations, and motion equations are combined to solve the beam-wave interaction. The influence of backward wave and relativistic effectmore » is also considered in the series of equations. The nonlinear model is used to design a 340 GHz SW-TWT. Several favorable comparisons of model predictions with results from a 3-D Particle-in-cell simulation code CHIPIC are presented, in which the output power versus beam voltage and interaction periods are illustrated. The relative error of the predicted output power is less than 15% in the 3 dB bandwidth and the relative error of the saturated length is less than 8%.The results show that the 1-D nonlinear analysis model is appropriate to solve the terahertz SW-TWT operation characteristics.« less

  11. 2D Traveling Wave Array Employing a Trapezoidal Dielectric Wedge for Beam Steering

    NASA Technical Reports Server (NTRS)

    Host, Nicholas K.; Chen, Chi-Chih; Volakis, John L.; Miranada, Felix A.

    2014-01-01

    This presentation addresses the progress made so far in the development of an antenna array with reconfigurable transmission line feeds connecting each element in series. In particular, 2D traveling wave array employing trapezoidal Dielectric Wedge for Beam Steering will be discussed. The presentation includes current status of the effort and suggested future work. The work is being done as part of the NASA Office of the Chief Technologist's Space Technology Research Fellowship (NSTRF).

  12. Inelastic ponderomotive scattering of electrons at a high-intensity optical travelling wave in vacuum

    NASA Astrophysics Data System (ADS)

    Kozák, M.; Eckstein, T.; Schönenberger, N.; Hommelhoff, P.

    2018-02-01

    In the early days of quantum mechanics Kapitza and Dirac predicted that matter waves would scatter off the optical intensity grating formed by two counter-propagating light waves. This interaction, driven by the ponderomotive potential of the optical standing wave, was both studied theoretically and demonstrated experimentally for atoms and electrons. In the original version of the experiment, only the transverse momentum of particles was varied, but their energy and longitudinal momentum remained unchanged after the interaction. Here, we report on the generalization of the Kapitza-Dirac effect. We demonstrate that the energy of sub-relativistic electrons is strongly modulated on the few-femtosecond timescale via the interaction with a travelling wave created in vacuum by two colliding laser pulses at different frequencies. This effect extends the possibilities of temporal control of freely propagating particles with coherent light and can serve the attosecond ballistic bunching of electrons, or for the acceleration of neutral atoms or molecules by light.

  13. Control of Ge1-x-ySixSny layer lattice constant for energy band alignment in Ge1-xSnx/Ge1-x-ySixSny heterostructures

    NASA Astrophysics Data System (ADS)

    Fukuda, Masahiro; Watanabe, Kazuhiro; Sakashita, Mitsuo; Kurosawa, Masashi; Nakatsuka, Osamu; Zaima, Shigeaki

    2017-10-01

    The energy band alignment of Ge1-xSnx/Ge1-x-ySixSny heterostructures was investigated, and control of the valence band offset at the Ge1-xSnx/Ge1-x-ySixSny heterointerface was achieved by controlling the Si and Sn contents in the Ge1-x-ySixSny layer. The valence band offset in the Ge0.902Sn0.098/Ge0.41Si0.50Sn0.09 heterostructure was evaluated to be as high as 330 meV, and its conduction band offset was estimated to be 150 meV by considering the energy bandgap calculated from the theoretical prediction. In addition, the formation of the strain-relaxed Ge1-x-ySixSny layer was examined and the crystalline structure was characterized. The epitaxial growth of a strain-relaxed Ge0.64Si0.21Sn0.15 layer with the degree of strain relaxation of 55% was examined using a virtual Ge substrate. Moreover, enhancement of the strain relaxation was demonstrated by post-deposition annealing, where a degree of strain relaxation of 70% was achieved after annealing at 400 °C. These results indicate the possibility for enhancing the indirect-direct crossover with a strained and high-Sn-content Ge1-xSnx layer on a strain-relaxed Ge1-x-ySixSny layer, realizing preferable carrier confinement by type-I energy band alignment with high conduction and valence band offsets.

  14. A novel sandwich-type traveling wave piezoelectric tracked mobile system.

    PubMed

    Wang, Liang; Shu, Chengyou; Zhang, Quan; Jin, Jiamei

    2017-03-01

    In this paper, a novel sandwich-type traveling wave piezoelectric tracked mobile system was proposed, designed, fabricated and experimentally investigated. The proposed system exhibits the advantages of simple structure, high mechanical integration, lack of electromagnetic interference, and lack of lubrication requirement, and hence shows potential application to robotic rovers for planetary exploration. The tracked mobile system is comprised of a sandwich actuating mechanism and a metal track. The actuating mechanism includes a sandwich piezoelectric transducer and two annular parts symmetrically placed at either end of the transducer, while the metal track is tensioned along the outer surfaces of the annular parts. Traveling waves with the same rotational direction are generated in the two annular parts, producing the microscopic elliptical motions of the surface particles on the annular parts. In this situation, if the pre-load is applied properly, the metal track can be driven by friction force to achieve bidirectional movement. At first, the finite element method was adopted to conduct the modal analysis and harmonic response analysis of the actuating mechanism, and the vibration characteristics were measured to confirm the operating principle. Then the optimal driving frequency of the system prototype, namely 35.1kHz, was measured by frequency sensitivity experiments. At last, the mechanical motion characteristics of the prototype were investigated experimentally. The results show that the average motion speeds of the prototype in dual directions were as 72mm/s and 61.5mm/s under the excitation voltage of 500V RMS , respectively. The optimal loading weights of the prototype in bi-directions were 0.32kg and 0.24kg with a maximum speed of 59.5mm/s and 61.67mm/s at the driving voltage of 300V RMS , respectively. Copyright © 2016 Elsevier B.V. All rights reserved.

  15. Asymptotics of QCD traveling waves with fluctuations and running coupling effects

    NASA Astrophysics Data System (ADS)

    Beuf, Guillaume

    2008-09-01

    Extending the Balitsky-Kovchegov (BK) equation independently to running coupling or to fluctuation effects due to pomeron loops is known to lead in both cases to qualitative changes of the traveling-wave asymptotic solutions. In this paper we study the extension of the forward BK equation, including both running coupling and fluctuations effects, extending the method developed for the fixed coupling case [E. Brunet, B. Derrida, A.H. Mueller, S. Munier, Phys. Rev. E 73 (2006) 056126, cond-mat/0512021]. We derive the exact asymptotic behavior in rapidity of the probabilistic distribution of the saturation scale.

  16. Non-cooperative Fisher-KPP systems: traveling waves and long-time behavior

    NASA Astrophysics Data System (ADS)

    Girardin, Léo

    2018-01-01

    This paper is concerned with non-cooperative parabolic reaction-diffusion systems which share structural similarities with the scalar Fisher-KPP equation. These similarities make it possible to prove, among other results, an extinction and persistence dichotomy and, when persistence occurs, the existence of a positive steady state, the existence of traveling waves with a half-line of possible speeds and a positive minimal speed and the equality between this minimal speed and the spreading speed for the Cauchy problem. Non-cooperative KPP systems can model various phenomena where the following three mechanisms occur: local diffusion in space, linear cooperation and superlinear competition.

  17. Visible-light absorption and large band-gap bowing of GaN 1-xSb x from first principles

    DOE PAGES

    Sheetz, R. Michael; Richter, Ernst; Andriotis, Antonis N.; ...

    2011-08-01

    Applicability of the Ga(Sb x)N 1-x alloys for practical realization of photoelectrochemical water splitting is investigated using first-principles density functional theory incorporating the local density approximation and generalized gradient approximation plus the Hubbard U parameter formalism. Our calculations reveal that a relatively small concentration of Sb impurities is sufficient to achieve a significant narrowing of the band gap, enabling absorption of visible light. Theoretical results predict that Ga(Sb x)N 1-x alloys with 2-eV band gaps straddle the potential window at moderate to low pH values, thus indicating that dilute Ga(Sb x)N 1-x alloys could be potential candidates for splitting watermore » under visible light irradiation.« less

  18. A wave-bending structure at Ka-band using 3D-printed metamaterial

    NASA Astrophysics Data System (ADS)

    Wu, Junqiang; Liang, Min; Xin, Hao

    2018-03-01

    Three-dimensional printing technologies enable metamaterials of complex structures with arbitrary inhomogeneity. In this work, a 90° wave-bending structure at the Ka-band (26.5-40 GHz) based on 3D-printed metamaterials is designed, fabricated, and measured. The wave-bending effect is realized through a spatial distribution of varied effective dielectric constants. Based on the effective medium theory, different effective dielectric constants are accomplished by special, 3D-printable unit cells, which allow different ratios of dielectric to air at the unit cell level. In contrast to traditional, metallic-structure-included metamaterial designs, the reported wave-bending structure here is all dielectric and implemented by the polymer-jetting technique, which features rapid, low-cost, and convenient prototyping. Both simulation and experiment results demonstrate the effectiveness of the wave-bending structure.

  19. Travelling waves in somitogenesis: Collective cellular properties emerge from time-delayed juxtacrine oscillation coupling.

    PubMed

    Tomka, Tomas; Iber, Dagmar; Boareto, Marcelo

    2018-04-24

    The sculpturing of the vertebrate body plan into segments begins with the sequential formation of somites in the presomitic mesoderm (PSM). The rhythmicity of this process is controlled by travelling waves of gene expression. These kinetic waves emerge from coupled cellular oscillators and sweep across the PSM. In zebrafish, the oscillations are driven by autorepression of her genes and are synchronized via Notch signalling. Mathematical modelling has played an important role in explaining how collective properties emerge from the molecular interactions. Increasingly more quantitative experimental data permits the validation of those mathematical models, yet leads to increasingly more complex model formulations that hamper an intuitive understanding of the underlying mechanisms. Here, we review previous efforts, and design a mechanistic model of the her1 oscillator, which represents the experimentally viable her7;hes6 double mutant. This genetically simplified system is ideally suited to conceptually recapitulate oscillatory entrainment and travelling wave formation, and to highlight open questions. It shows that three key parameters, the autorepression delay, the juxtacrine coupling delay, and the coupling strength, are sufficient to understand the emergence of the collective period, the collective amplitude, and the synchronization of neighbouring Her1 oscillators. Moreover, two spatiotemporal time delay gradients, in the autorepression and in the juxtacrine signalling, are required to explain the collective oscillatory dynamics and synchrony of PSM cells. The highlighted developmental principles likely apply more generally to other developmental processes, including neurogenesis and angiogenesis. Copyright © 2018. Published by Elsevier Ltd.

  20. SALSA3D: A Tomographic Model of Compressional Wave Slowness in the Earth’s Mantle for Improved Travel-Time Prediction and Travel-Time Prediction Uncertainty

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ballard, Sanford; Hipp, James R.; Begnaud, Michael L.

    The task of monitoring the Earth for nuclear explosions relies heavily on seismic data to detect, locate, and characterize suspected nuclear tests. In this study, motivated by the need to locate suspected explosions as accurately and precisely as possible, we developed a tomographic model of the compressional wave slowness in the Earth’s mantle with primary focus on the accuracy and precision of travel-time predictions for P and Pn ray paths through the model. Path-dependent travel-time prediction uncertainties are obtained by computing the full 3D model covariance matrix and then integrating slowness variance and covariance along ray paths from source tomore » receiver. Path-dependent travel-time prediction uncertainties reflect the amount of seismic data that was used in tomography with very low values for paths represented by abundant data in the tomographic data set and very high values for paths through portions of the model that were poorly sampled by the tomography data set. The pattern of travel-time prediction uncertainty is a direct result of the off-diagonal terms of the model covariance matrix and underscores the importance of incorporating the full model covariance matrix in the determination of travel-time prediction uncertainty. In addition, the computed pattern of uncertainty differs significantly from that of 1D distance-dependent travel-time uncertainties computed using traditional methods, which are only appropriate for use with travel times computed through 1D velocity models.« less