Advanced specialty fiber designs for high power fiber lasers

NASA Astrophysics Data System (ADS)

Gu, Guancheng

The output power of fiber lasers has increased rapidly over the last decade. There are two major limiting factors, namely nonlinear effects and transverse mode instability, prohibiting the power scaling capability of fiber lasers. The nonlinear effects, originating from high optical intensity, primarily limit the peak power scaling. The mode instability, on the other hand, arises from quantum-defect driven heating, causing undesired mode coupling once the power exceeds the threshold and degradation of beam quality. The mode instability has now become the bottleneck for average output power scaling of fiber lasers. Mode area scaling is the most effective way to mitigate nonlinear effects. However, the use of large mode area may increase the tendency to support multiple modes in the core, resulting in lower mode instability threshold. Therefore, it is critical to maintain single mode operation in a large mode area fiber. Sufficient higher order mode suppression can lead to effective single-transverse-mode propagation. In this dissertation, we explore the feasibility of using specialty fiber to construct high power fiber lasers with robust single-mode output. The first type of fiber discussed is the resonantly-enhanced leakage channel fiber. Coherent reflection at the fiber outer boundary can lead to additional confinement especially for highly leaky HOM, leading to lower HOM losses than what are predicted by conventional finite element mothod mode solver considering infinite cladding. In this work, we conducted careful measurements of HOM losses in two leakage channel fibers (LCF) with circular and rounded hexagonal boundary shapes respectively. Impact on HOM losses from coiling, fiber boundary shapes and coating indexes were studied in comparison to simulations. This work demonstrates the limit of the simulation method commonly used in the large-mode-area fiber designs and the need for an improved approach. More importantly, this work also demonstrates that a deviation from circular fiber outer shape may be an effective method to mitigate HOM loss reduction from coherent reflection from fiber outer boundary. In an all-solid photonic bandgap fiber, modes are only guided due to anti-resonance of cladding photonic crystal lattice. This provides strongly mode-dependent guidance, leading to very high differential mode losses, which is essential for lasing far from the gain peak and suppression of stimulated Raman scattering. We will show that all-solid photonic bandgap fibers with effective mode area of 920microm2 can be made with excellent higher order mode suppression. We then demonstrate a 50microm-core-diameter Yb-doped all-solid photonic bandgap fiber laser. 75W output power has been generated with a diffraction-limited beam and an efficiency of 70% relative to the launched pump power. We have also experimentally confirmed that a robust single-mode regime exists near the high frequency edge of the bandgap. It is well known that incorporation of additional smaller cores in the cladding can be used to resonantly out-couple higher-order modes from a main core to suppress higher-order-mode propagation in the main core. Using a novel design with multiple coupled smaller cores in the cladding, we further scaled up the mode area and have successfully demonstrated a single-mode photonic bandgap fiber with record effective mode area of 2650microm2. Detailed numeric studies have been conducted for multiple cladding designs. For the optimal designs, the simulated minimum higher-order-mode losses are well over two orders of magnitudes higher than that of fundamental mode when expressed in dBs. We have also experimentally validated one of the designs. M 2<1.08 across the transmission band was demonstrated. Lowering quantum defect heating is another approach to mitigate mode instability. Highly-efficient high-power fiber lasers operating at wavelength below 1020nm are critical for tandem-pumping in >10kW fiber lasers to provide high pump brightness and low thermal loading. Using an ytterbium-doped-phosphosilicate double-clad leakage-channel fiber with 50microm core and 420microm cladding, we have achieved 70% optical-to-optical efficiency at 1018nm. The much larger cladding than those in previous reports demonstrates the much lower required pump brightness, a key for efficient kW operation. The demonstrated 1018nm fiber laser has ASE suppression of 41dB. This is higher than previous reports and further demonstrates the advantages of the fiber used. Limiting factors to efficiency are also systematically studied.

Quantum Devices Bonded Beneath a Superconducting Shield: Part 2

NASA Astrophysics Data System (ADS)

McRae, Corey Rae; Abdallah, Adel; Bejanin, Jeremy; Earnest, Carolyn; McConkey, Thomas; Pagel, Zachary; Mariantoni, Matteo

The next-generation quantum computer will rely on physical quantum bits (qubits) organized into arrays to form error-robust logical qubits. In the superconducting quantum circuit implementation, this architecture will require the use of larger and larger chip sizes. In order for on-chip superconducting quantum computers to be scalable, various issues found in large chips must be addressed, including the suppression of box modes (due to the sample holder) and the suppression of slot modes (due to fractured ground planes). By bonding a metallized shield layer over a superconducting circuit using thin-film indium as a bonding agent, we have demonstrated proof of concept of an extensible circuit architecture that holds the key to the suppression of spurious modes. Microwave characterization of shielded transmission lines and measurement of superconducting resonators were compared to identical unshielded devices. The elimination of box modes was investigated, as well as bond characteristics including bond homogeneity and the presence of a superconducting connection.

Decentralized control experiments on the JPL flexible spacecraft

NASA Technical Reports Server (NTRS)

Ozguner, U.; Ossman, K.; Donne, J.; Boesch, M.; Ahmed, A.

1990-01-01

Decentralized control experiments were successfully demonstrated for the JPL/AFAL Flexible Structure. A simulation package using MATRIXx showed strong correlation between the simulations and experimental result, while providing a means for test and debug of the various control strategies. Implementation was simplified by a modular software design that was easily transported from the simulation environment to the experimental environment. Control designs worked well for suppression of the dominant modes of the structure. Static decentralized output feedback dampened the excited modes of the structure, but sometimes excited higher order modes upon startup of the controller. A second-order frequency shaping controller helped to eliminate excitation of the higher order modes by attenuating high frequencies in the control effort. However, it also resulted in slightly longer settling times.

Low-loss single-mode hollow-core fiber with anisotropic anti-resonant elements.

PubMed

Habib, Md Selim; Bang, Ole; Bache, Morten

2016-04-18

A hollow-core fiber using anisotropic anti-resonant tubes in the cladding is proposed for low loss and effectively single-mode guidance. We show that the loss performance and higher-order mode suppression is significantly improved by using symmetrically distributed anisotropic anti-resonant tubes in the cladding, elongated in the radial direction, when compared to using isotropic, i.e. circular, anti-resonant tubes. The effective single-mode guidance of the proposed fiber is achieved by enhancing the coupling between the cladding modes and higher-order-core modes by suitably engineering the anisotropic anti-resonant elements. With a silica-based fiber design aimed at 1.06 µm, we show that the loss extinction ratio between the higher-order core modes and the fundamental core mode can be more than 1000 in the range 1.0-1.65 µm, while the leakage loss of the fundamental core mode is below 15 dB/km in the same range.

Two-mode elliptical-core weighted fiber sensors for vibration analysis

NASA Technical Reports Server (NTRS)

Vengsarkar, Ashish M.; Murphy, Kent A.; Fogg, Brian R.; Miller, William V.; Greene, Jonathan A.; Claus, Richard O.

1992-01-01

Two-mode, elliptical-core optical fibers are demonstrated in weighted, distributed and selective vibration-mode-filtering applications. We show how appropriate placement of optical fibers on a vibrating structure can lead to vibration mode filtering. Selective vibration-mode suppression on the order of 10 dB has been obtained using tapered two-mode, circular-core fibers with tapering functions that match the second derivatives of the modes of vibration to be enhanced. We also demonstrate the use of chirped, two-mode gratings in fibers as spatial modal sensors that are equivalents of shaped piezoelectric sensors.

Design of dual-mode optical fibres for the FTTH applications

NASA Astrophysics Data System (ADS)

Chen, Ming-Yang; Li, Yu-Rong; Zhang, Yin; Zhu, Yuan-Feng; Zhang, Yong-Kang; Zhou, Jun

2011-01-01

We present in this article a proposal and design for dual-mode optical fibres for fibre-to-the-home applications. High-order modes in the fibre can be effectively suppressed by the connection of the fibre with standard single-mode optical fibres at the two ends of the fibre. The alignment tolerance at the splicing process is presented. In particular, a low bending loss operation with low splice loss is demonstrated using the proposed technique.

Broadband single-mode operation of standard optical fibers by using a sub-wavelength optical wire filter.

PubMed

Jung, Yongmin; Brambilla, Gilberto; Richardson, David J

2008-09-15

We report the use of a sub-wavelength optical wire (SOW) with a specifically designed transition region as an efficient tool to filter higher-order modes in multimode waveguides. Higher-order modes are effectively suppressed by controlling the transition taper profile and the diameter of the sub-wavelength optical wire. As a practical example, single-mode operation of a standard telecom optical fiber over a broad spectral window (400 approximately 1700 nm) was demonstrated with a 1microm SOW. The ability to obtain robust and stable single-mode operation over a very broad range of wavelengths offers new possibilities for mode control within fiber devices and is relevant to a range of application sectors including high performance fiber lasers, sensors, photolithography, and optical coherence tomography systems.

MHD control experiments in the Extrap T2R Reversed Field Pinch

NASA Astrophysics Data System (ADS)

Marrelli, L.; Bolzonella, T.; Brunsell, P.; Cecconello, M.; Drake, J.; Franz, P.; Gregoratto, D.; Manduchi, G.; Martin, P.; Ortolani, S.; Paccagnella, R.; Piovesan, P.; Spizzo, G.; Yadikin, D.; Zanca, P.

2004-11-01

We report here on MHD active control experiments performed in the Extrap T2R device, which has been recently equipped with a set of 32 feedback controlled saddle coils couples. Experiments aiming at selectively exciting a resonant resistive instability in order to actively induce Quasi Single Helicity states will be presented. Open loop experiments have in fact shown that a spectrum with one dominant mode can be excited in a high aspect ratio device like T2R. In addition, evidences of controlled braking of tearing modes, which spontaneously rotate in T2R, have been gathered, allowing the determination of a threshold for mode wall locking. Different feedback control schemes have been implemented. In particular, mode suppression schemes proved successful in delaying resistive wall modes growth and in increasing the discharge duration: this suggests a hybrid mode control scenario, in which RWM are suppressed and QSH is induced. Radiation imaging and internal magnetic field reconstructions performed with the ORBIT code will be presented.

Cladding pumped Yb-doped HOM power amplifier with high gain

NASA Astrophysics Data System (ADS)

Abedin, Kazi S.; Ahmad, Raja; DeSantolo, Anthony M.; Nicholson, Jeffrey W.; Westbrook, Paul S.; Headley, Clifford; DiGiovanni, David J.

2018-02-01

Higher-order mode (HOM) fibers have been engineered to allow propagation of linearly polarized symmetric modes LP0,N in a robust way. Compared with the fundamental mode LP(0,1), HOMs exhibits an effective area that can be larger by over two order magnitude, and thus propagating light in these modes could greatly suppress the effect of nonlinear effects. HOM fibers could also be doped with rare earth ions in order to amplify light propagating in these modes, which offers the enormous potential for generating high-intensity pulses. Excitation of HOM gain fiber using cladding pumping with multimode pump source is attractive for ytterbium based amplifiers, because of the availability of low-cost multimode pump diodes in the 975nm wavelength range. One problem associated with cladding pumping which leads to excitation of the large doped core (over 100 μm diameter) is that it could result in a large amount of amplifiedspontaneous- emission (ASE) noise, particularly when the input signal is weak. Optimization of amplifier design is critical in order to suppress ASE and achieve high gain and pump-to-signal conversion efficiency. We conducted numerical modeling of a cladding pumped HOM-amplifier, which revealed that this problem could be mitigated by using a relatively long gain-fiber that allowed reabsorption of the forward propagating ASE resulting in a further amplification of the signal. We demonstrate efficient amplification of a LP0,10 mode with an effective area 3140μm2 in an Yb-doped HOM amplifier cladding pumped at 975nm. We have successfully obtained a 20.2dB gain for 0.95 W 1064 nm input seed signal to more than 105W.

Collective Beam Instabilities in the Taiwan Light Source

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

Chao, Alex W.

2002-08-12

The storage ring at Taiwan Light Source has experienced a strong collective instability since 1994. Various cures have been attempted to suppress this instability, including the use of damping antenna, tunable rf plungers, different filling patterns, and rf gap voltage modulation. So far these cures have improved the beam intensity, but the operation remains to be limited by the instability. The dominant phenomenon is the longitudinal coupled bunch instability. The major source of longitudinal impedance is from rf cavities of Doris type. The high-order modes of the cavity were numerically analyzed using a 3-D code GdfidL. The correlation of themore » observed phenomenon in user operation with high-order modes of rf cavities will be presented. Results of various attempts to suppress beam instabilities will be summarized. Proposed cures for beam instabilities will be discussed.« less

Investigation of violin mode Q for wires of various materials

NASA Astrophysics Data System (ADS)

Dawid, Daryush J.; Kawamura, Seiji

1997-12-01

The Q factors of violin modes for wires of various materials have been measured in order to determine which would be most suitable for use in the suspension of test masses in the initial laser interferometer gravitational wave observatory (LIGO) interferometers. A "guitar" type apparatus was employed to measure violin mode Qs, and losses due to clamping and other practical sources were successfully suppressed below the level of intrinsic wire losses. Steel music wire was found to give the highest extrapolated Q factors under LIGO conditions among the wires we tested. This extrapolated Q sets a target for the LIGO suspension which can be attained if all the losses other than the intrinsic wire loss are successfully suppressed. The measured Qs for the steel, tungsten, and titanium wire, which were approximately frequency independent for the first two to three modes, were found to be roughly proportional to the square root of the tension in the wire. This is consistent with the theory of violin mode losses due to frequency-independent intrinsic wire losses.

Suppression and nonlinear excitation of parasitic modes in second harmonic gyrotrons operating in a very high order mode

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

Nusinovich, Gregory S.; Pu, Ruifeng; Granatstein, Victor L.

2015-07-06

In recent years, there was an active development of high-power, sub-terahertz (sub-THz) gyrotrons for numerous applications. For example, a 0.67 THz gyrotron delivering more than 200 kW with about 20% efficiency was developed. This record high efficiency was achieved because the gyrotron operated in a high-order TE{sub 31,8}-mode with the power of ohmic losses less than 10% of the power of outgoing radiation. That gyrotron operated at the fundamental cyclotron resonance, and a high magnetic field of about 27 T was created by a pulse solenoid. For numerous applications, it is beneficial to use gyrotrons at cyclotron harmonics which can operate inmore » available cryomagnets with fields not exceeding 15 T. However, typically, the gyrotron operation at harmonics faces severe competition from parasitic modes at the fundamental resonance. In the present paper, we consider a similar 0.67 THz gyrotron designed for operation in the same TE{sub 31,8}-mode, but at the second harmonic. We focus on two nonlinear effects typical for interaction between the fundamental and second harmonic modes, viz., the mode suppression and the nonlinear excitation of the mode at the fundamental harmonic by the second harmonic oscillations. Our study includes both the analytical theory and numerical simulations performed with the self-consistent code MAGY. The simulations show that stable second harmonic operation in the TE{sub 31,8} mode is possible with only modest sacrifice of efficiency and power.« less

Suppressing turbulence of self-propelling rods by strongly coupled passive particles.

PubMed

Su, Yen-Shuo; Wang, Hao-Chen; I, Lin

2015-03-01

The strong turbulence suppression, mainly for large-scale modes, of two-dimensional self-propelling rods, by increasing the long-range coupling strength Γ of low-concentration passive particles, is numerically demonstrated. It is found that large-scale collective rod motion in forms of swirls or jets is mainly contributed from well-aligned dense patches, which can push small poorly aligned rod patches and uncoupled passive particles. The more efficient momentum transfer and dissipation through increasing passive particle coupling leads to the formation of a more ordered and slowed down network of passive particles, which competes with coherent dense active rod clusters. The frustration of active rod alignment ordering and coherent motion by the passive particle network, which interrupt the inverse cascading of forming large-scale swirls, is the key for suppressing collective rod motion with scales beyond the interpassive distance, even in the liquid phase of passive particles. The loosely packed active rods are weakly affected by increasing passive particle coupling due to the weak rod-particle interaction. They mainly contribute to the small-scale modes and high-speed motion.

Transverse single-mode edge-emitting lasers based on coupled waveguides.

PubMed

Gordeev, Nikita Yu; Payusov, Alexey S; Shernyakov, Yuri M; Mintairov, Sergey A; Kalyuzhnyy, Nikolay A; Kulagina, Marina M; Maximov, Mikhail V

2015-05-01

We report on the transverse single-mode emission from InGaAs/GaAs quantum well edge-emitting lasers with broadened waveguide. The lasers are based on coupled large optical cavity (CLOC) structures where high-order vertical modes of the broad active waveguide are suppressed due to their resonant tunneling into a coupled single-mode passive waveguide. The CLOC lasers have shown stable Gaussian-shaped vertical far-field profiles with a reduced divergence of ∼22° FWHM (full width at half-maximum) in CW (continuous-wave) operation.

Guiding and amplification properties of rod-type photonic crystal fibers with sectioned core doping

NASA Astrophysics Data System (ADS)

Selleri, S.; Poli, F.; Passaro, D.; Cucinotta, A.; Lægsgaard, J.; Broeng, J.

2009-05-01

Rod-type photonic crystal fibers are large mode area double-cladding fibers with an outer diameter of few millimeters which can provide important advantages for high-power lasers and amplifiers. Numerical studies have recently demonstrated the guidance of higher-order modes in these fibers, which can worsen the output beam quality of lasers and amplifiers. In the present analysis a sectioned core doping has been proposed for Ybdoped rod-type photonic crystal fibers, with the aim to improve the higher-order mode suppression. A full-vector modal solver based on the finite element method has been applied to properly design the low refractive index ring in the fiber core, which can provide an increase of the differential overlap between the fundamental and the higher-order mode. Then, the gain competition among the guided modes along the Yb-doped rod-type fibers has been investigated with a spatial and spectral amplifier model. Simulation results have shown the effectiveness of the sectioned core doping in worsening the higher-order mode overlap on the doped area, thus providing an effective single-mode behavior of the Yb-doped rod-type photonic crystal fibers.

Multipole surface plasmons in metallic nanohole arrays

NASA Astrophysics Data System (ADS)

Nishida, Munehiro; Hatakenaka, Noriyuki; Kadoya, Yutaka

2015-06-01

The quasibound electromagnetic modes for the arrays of nanoholes perforated in thin gold film are analyzed both numerically by the rigorous coupled wave analysis (RCWA) method and semianalytically by the coupled mode method. It is shown that when the size of the nanohole occupies a large portion of the unit cell, the surface plasmon polaritons (SPPs) at both sides of the film are combined by the higher order waveguide modes of the holes to produce multipole surface plasmons: coupled surface plasmon modes with multipole texture on the elec-tric field distributions. Further, it is revealed that the multipole texture either enhances or suppresses the couplings between SPPs depending on their diffraction orders and also causes band inversion and reconstruction in the coupled SPP band structure. Due to the multipole nature of the quasibound modes, multiple dark modes coexist to produce a variety of Fano resonance structures on the transmission and reflection spectra.

Suppressing Anomalous Localized Waffle Behavior in Least Squares Wavefront Reconstructors

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

Gavel, D

2002-10-08

A major difficulty with wavefront slope sensors is their insensitivity to certain phase aberration patterns, the classic example being the waffle pattern in the Fried sampling geometry. As the number of degrees of freedom in AO systems grows larger, the possibility of troublesome waffle-like behavior over localized portions of the aperture is becoming evident. Reconstructor matrices have associated with them, either explicitly or implicitly, an orthogonal mode space over which they operate, called the singular mode space. If not properly preconditioned, the reconstructor's mode set can consist almost entirely of modes that each have some localized waffle-like behavior. In thismore » paper we analyze the behavior of least-squares reconstructors with regard to their mode spaces. We introduce a new technique that is successful in producing a mode space that segregates the waffle-like behavior into a few ''high order'' modes, which can then be projected out of the reconstructor matrix. This technique can be adapted so as to remove any specific modes that are undesirable in the final reconstructor (such as piston, tip, and tilt for example) as well as suppress (the more nebulously defined) localized waffle behavior.« less

Modeling thermo-optic effect in large mode area double cladding photonic crystal fibers

NASA Astrophysics Data System (ADS)

Coscelli, Enrico; Cucinotta, Annamaria

2014-02-01

The impact of thermally-induced refractive index changes on the single-mode (SM) properties of large mode area (LMA) photonic crystal fibers are thoroughly investigated by means of a full-vector modal solver with integrated thermal model. Three photonic crystal fiber designs are taken into account, namely the 19-cell core fiber, the large-pitch fiber (LPF) and the distributed modal filtering (DMF) fiber, to assess the effects of the interplay between thermal effects and the high-order mode (HOM) suppression mechanisms exploited in order to obtain effectively SM guiding. The results have shown significant differences in the way the SM regime is changed by the increase of heat load, providing useful hints for the design of LMA fibers for high power lasers.

Multiphoton endoscopy based on a mode-filtered single-mode fiber

NASA Astrophysics Data System (ADS)

Moon, Sucbei; Liu, Gangjun; Chen, Zhongping

2011-03-01

We present a new low-nonlinearity fiber of mode-filtered large-core fiber for flexible beam delivery of intense pulsed light aiming at multi-photon endoscopy application. A multimode fiber of a large core diameter (20 μm) equips a mode filtering means in the middle of the fiber link to suppress the high-order modes selectively. A large effective core area of ~200 μm2 has been achieved at 0.8-μm and 1.0-μm bands. This is 8 times larger than the core area of a conventional SMF used for those spectral bands. Various advantages of our large-mode area fiber will be demonstrated and discussed in this report.

Approximate analytical solutions of a pair of coupled anharmonic oscillators

NASA Astrophysics Data System (ADS)

Alam, Nasir; Mandal, Swapan; Öhberg, Patrik

2015-02-01

The Hamiltonian and the corresponding equations of motion involving the field operators of two quartic anharmonic oscillators indirectly coupled via a linear oscillator are constructed. The approximate analytical solutions of the coupled differential equations involving the non-commuting field operators are solved up to the second order in the anharmonic coupling. In the absence of nonlinearity these solutions are used to calculate the second order variances and hence the squeezing in pure and in mixed modes. The higher order quadrature squeezing and the amplitude squared squeezing of various field modes are also investigated where the squeezing in pure and in mixed modes are found to be suppressed. Moreover, the absence of a nonlinearity prohibits the higher order quadrature and higher ordered amplitude squeezing of the input coherent states. It is established that the mere coupling of two oscillators through a third one is unable to produce any squeezing effects of input coherent light, but the presence of a nonlinear interaction may provide squeezed states and other nonclassical phenomena.

Excitation of Higher Order Modes of Cylindrical Dielectric Resonator Antenna using Dual-slot feed

NASA Astrophysics Data System (ADS)

Ojha, A. K.; Praveen Kumar, A. V.

2018-03-01

Excitation of the higher order modes (HOM) of a cylindrical dielectric resonator antenna(DRA) of high relative permittivity, using dual feed scheme is investigated. The feed scheme uses a pair of narrow slots and is chosen on the basis of the field distribution of the desired DRA modes. Numerical studies using ANSYS HFSS show that the dual-feed excited a combination of two HOMs, which are identified as HEM21δ and TM01δ. The mixed-up nature is further verified through studying the radiation pattern of the DRA which shows azimuthal asymmetry and low gain. It is suggested that if one of the HOM is suppressed, better antenna performance can be achieved.

Suppression of the asymmetric modes for experimentally achieving gigawatt-level radiation from a Ku-band Cerenkov type oscillator

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

Zhang, Hua; Shu, Ting, E-mail: mrtingshu@qq.com; Ju, Jinchuan

2014-08-15

We present the analysis and suppression of asymmetric modes in a Ku-band Cerenkov-type oscillator numerically and experimentally. The asymmetric modes generated in the initial experiments were identified to be HE{sub 11}, HE{sub 21}, and HE{sub 31} modes, respectively, by analyzing of the dispersion relationships, the simulation results and the experiment phenomenon. The factors, such as the cathode emission uniformity, the diode voltage, guiding magnetic field, and the concentricity play key roles in the excitation and suppression of these asymmetric modes. In the improved experiments, the asymmetric modes were suppressed effectively. In the improved experiments the asymmetric modes are suppressed effectively,more » and the designed TM{sub 01} mode microwave is generated at a frequency of 13.76 GHz with a power of 1.1 GW, which is in good agreement with numerically predications.« less

Distributed feedback interband cascade lasers with top grating and corrugated sidewalls

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

Xie, Feng; Stocker, Michael; Pham, John

Distributed feedback (DFB) interband cascade lasers (ICLs) with a 1st order top surface grating were designed and fabricated. Partially corrugated sidewalls were implemented to suppress high order lateral modes. The DFB ICLs have 4 mm long and 4.5 mu m wide ridge waveguides and are mounted epi-up on AlN submounts. We demonstrated a continuous-wave (CW) DFB ICL, from a first wafer which has a large detuning of the gain peak from the DFB wavelength, with a side mode suppression ratio of 30 dB. With proper matching of grating feedback and the gain peak wavelength for the second wafer, a DFBmore » ICL was demonstrated with a maximum CW output power and a maximum wall plug efficiency reaching 42 mW and 2%, respectively, at 25 degrees C. The lasing wavelengths of both lasers are around 3.3 mu m at 25 degrees C. Published by AIP Publishing.« less

Mode locking and island suppression by resonant magnetic perturbations in Rutherford regime

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

Huang, Wenlong; Zhu, Ping, E-mail: pzhu@ustc.edu.cn

We demonstrate in theory that tearing mode locking and magnetic island suppression by resonant magnetic perturbations (RMPs) can correspond to different states of a same dynamic system governed by the torque balance and the nonlinear island evolution in the Rutherford regime. In particular, mode locking corresponds to the exact steady state of this system. A new exact analytic solution has been obtained for such a steady state, which quantifies the dependence of the locked mode island width on RMP amplitude in different plasma regimes. Furthermore, two different branches of mode locking have been revealed with the new analytic solution andmore » the branch with suppressed island width turns out to be unstable in general. On the other hand, the system also admits stable states of island suppression achieved through the RMP modulation of tearing mode rotational frequency. When the RMP amplitude is above a certain threshold, the island suppression is transient until the tearing mode eventually gets locked. When the RMP amplitude is below the mode locking threshold, the island can be suppressed in a steady state on time-average, along with transient oscillations in rotational frequency and island width due to the absence of mode locking.« less

Realtime speckle sensing and suppression with project 1640 at Palomar

NASA Astrophysics Data System (ADS)

Vasisht, Gautam; Cady, Eric; Zhai, Chengxing; Lockhart, Thomas; Oppenheimer, Ben

2014-08-01

Palomar's Project 1640 (P1640) is the first stellar coronagraph to regularly use active coronagraphic wavefront control (CWFC). For this it has a hierarchy of offset wavefront sensors (WFS), the most important of which is the higher-order WFS (called CAL), which tracks quasi-static modes between 2-35 cycles-per-aperture. The wavefront is measured in the coronagraph at 0.01 Hz rates, providing slope targets to the upstream Palm 3000 adaptive optics (AO) system. The CWFC handles all non-common path distortions up to the coronagraphic focal plane mask, but does not sense second order modes between the WFSs and the science integral field unit (IFU); these modes determine the system's current limit. We have two CWFC operating modes: (1) P-mode, where we only control phases, generating double-sided darkholes by correcting to the largest controllable spatial frequencies, and (2) E-mode, where we can control amplitudes and phases, generating single-sided dark-holes in specified regions-of-interest. We describe the performance and limitations of both these modes, and discuss the improvements we are considering going forward.

Effect of magnet/slot combination on triple-frequency magnetic force and vibration of permanent magnet motors

NASA Astrophysics Data System (ADS)

Huo, Mina; Wang, Shiyu; Xiu, Jie; Cao, Shuqian

2013-10-01

The relationship between magnet/slot combination and magnetic forces including unbalanced magnetic force (UMF) and cogging torque (CT) of permanent magnet (PM) motors is investigated by using superposition principle and mechanical and magnetic symmetries. The results show that magnetic force can be produced by all magnets passing a single slot, by all slots passing a single magnet, or by eccentricity, which respectively correspond to three frequency components. The results further show that net force/torque can be classified into three typical cases: UMF is suppressed and CT is excited, UMF excited and CT suppressed, and UMF and CT both suppressed, and consequently possible vibrations include three unique groups: rotational modes, translational modes, and balanced modes. The conclusion that combinations with the greatest common divisor (GCD) greater than unity can avoid UMF is mathematically verified, and at the same time lower CT harmonics are preliminarily addressed by the typical excitations. The above findings can create simple guidelines for the suppression of certain UMF and/or CT by using suitable combinations, which in turn can present approach to yield a more desirable response in high performance applications. The superposition effect and predicted relationship are verified by the transient magnetic Finite Element method. Since this work is motivated by symmetries, comparisons are made in order to give further insight into the inner force and vibration behaviors of general rotary power-transmission systems.

Flutter suppression digital control law design and testing for the AFW wind tunnel model

NASA Technical Reports Server (NTRS)

Mukhopadhyay, Vivek

1994-01-01

The design of a control law for simultaneously suppressing the symmetric and antisymmetric flutter modes of a sting mounted fixed-in-roll aeroelastic wind-tunnel model is described. The flutter suppression control law was designed using linear quadratic Gaussian theory, and it also involved control law order reduction, a gain root-locus study, and use of previous experimental results. A 23 percent increase in the open-loop flutter dynamic pressure was demonstrated during the wind-tunnel test. Rapid roll maneuvers at 11 percent above the symmetric flutter boundary were also performed when the model was in a free-to-roll configuration.

Optical frequency shot-noise suppression in electron beams: Three-dimensional analysis

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

Nause, A.; Dyunin, E.; Gover, A.

2010-05-15

A predicted effect of current shot-noise suppression at optical-frequencies in a drifting charged-particle-beam and the corresponding process of particles self-ordering are analyzed in a one-dimensional (1D) model and verified by three-dimensional numerical simulations. The analysis confirms the prediction of a 1D single mode Langmuir plasma wave model of longitudinal plasma oscillation in the beam, and it defines the regime of beam parameters in which this effect takes place. The suppression of relativistic beam shot noise can be utilized to enhance the coherence of free electron lasers and of any coherent radiation device using an electron beam.

Flutter suppression digital control law design and testing for the AFW wind tunnel model

NASA Technical Reports Server (NTRS)

Mukhopadhyay, Vivek

1992-01-01

Design of a control law for simultaneously suppressing the symmetric and antisymmetric flutter modes of a sting mounted fixed-in-roll aeroelastic wind tunnel model is described. The flutter suppression control law was designed using linear quadratic Gaussian theory, and involved control law order reduction, a gain root-locus study and use of previous experimental results. A 23 percent increase in the open-loop flutter dynamic pressure was demonstrated during the wind tunnel test. Rapid roll maneuvers at 11 percent above the symmetric flutter boundary were also performed when the model was in a free-to-roll configuration.

Flutter suppression digital control law design and testing for the AFW wind-tunnel model

NASA Technical Reports Server (NTRS)

Mukhopadhyay, Vivek

1992-01-01

Design of a control law for simultaneously suppressing the symmetric and antisymmetric flutter modes of a string mounted fixed-in-roll aeroelastic wind tunnel model is described. The flutter suppression control law was designed using linear quadratic Gaussian theory and involved control law order reduction, a gain root-locus study, and the use of previous experimental results. A 23 percent increase in open-loop flutter dynamic pressure was demonstrated during the wind tunnel test. Rapid roll maneuvers at 11 percent above the symmetric flutter boundary were also performed when the model was in a free-to-roll configuration.

Smooth and flat phase-locked Kerr frequency comb generation by higher order mode suppression

PubMed Central

Huang, S.-W.; Liu, H.; Yang, J.; Yu, M.; Kwong, D.-L.; Wong, C. W.

2016-01-01

High-Q microresonator is perceived as a promising platform for optical frequency comb generation, via dissipative soliton formation. In order to achieve a higher quality factor and obtain the necessary anomalous dispersion, multi-mode waveguides were previously implemented in Si3N4 microresonators. However, coupling between different transverse mode families in multi-mode waveguides results in periodic disruption of dispersion and quality factor, and consequently causes perturbation to dissipative soliton formation and amplitude modulation to the corresponding spectrum. Careful choice of pump wavelength to avoid the mode crossing region is thus critical in conventional Si3N4 microresonators. Here, we report a novel design of Si3N4 microresonator in which single-mode operation, high quality factor, and anomalous dispersion are attained simultaneously. The novel microresonator is consisted of uniform single-mode waveguides in the semi-circle region, to eliminate bending induced mode coupling, and adiabatically tapered waveguides in the straight region, to avoid excitation of higher order modes. The intrinsic quality factor of the microresonator reaches 1.36 × 106 while the group velocity dispersion remains to be anomalous at −50 fs2/mm. With this novel microresonator, we demonstrate that broadband phase-locked Kerr frequency combs with flat and smooth spectra can be generated by pumping at any resonances in the optical C-band. PMID:27181420

Lattice gauge action suppressing near-zero modes of H{sub W}

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

Fukaya, Hidenori; Hashimoto, Shoji; Kaneko, Takashi

2006-11-01

We propose a lattice action including unphysical Wilson fermions with a negative mass m{sub 0} of the order of the inverse lattice spacing. With this action, the exact zero mode of the Hermitian Wilson-Dirac operator H{sub W}(m{sub 0}) cannot appear and near-zero modes are strongly suppressed. By measuring the spectral density {rho}({lambda}{sub W}), we find a gap near {lambda}{sub W}=0 on the configurations generated with the standard and improved gauge actions. This gap provides a necessary condition for the proof of the exponential locality of the overlap-Dirac operator by Hernandez, Jansen, and Luescher. Since the number of near-zero modes ismore » small, the numerical cost to calculate the matrix sign function of H{sub W}(m{sub 0}) is significantly reduced, and the simulation including dynamical overlap fermions becomes feasible. We also introduce a pair of twisted mass pseudofermions to cancel the unwanted higher mode effects of the Wilson fermions. The gauge coupling renormalization due to the additional fields is then minimized. The topological charge measured through the index of the overlap-Dirac operator is conserved during continuous evolutions of gauge field variables.« less

Effects of sputtering mode on the microstructure and ionic conductivity of yttria-stabilized zirconia films

NASA Astrophysics Data System (ADS)

Yeh, Tsung-Her; Lin, Ruei-De; Cherng, Bo-Ruei; Cherng, Jyh-Shiarn

2018-05-01

The microstructure and ionic conductivity of reactively sputtered yttria-stabilized zirconia (YSZ) films are systematically studied. Those films were reactively sputtered in various sputtering modes using a closed-loop controlled system with plasma emission monitoring. A transition-mode sputtering corresponding to 45% of target poisoning produces a microstructure with ultrafine crystallites embedded in an amorphous matrix, which undergoes an abnormal grain growth upon annealing at 800 °C. At 500 °C, the measured ionic conductivity of this annealed film is higher, by about a half order of magnitude, than those of its poisoned-mode counterparts, which are in turn significantly higher than that of the YSZ bulk by about two orders of magnitude. The abnormally-grown ultra-large grain size of the film deposited in the transition mode and then annealed is believed to be responsible for the former comparison due to the suppression of the grain boundary blocking effect, while the latter comparison can be attributed to the interface effect.

Shaped pupil coronagraphy for WFIRST: high-contrast broadband testbed demonstration

NASA Astrophysics Data System (ADS)

Cady, Eric; Balasubramanian, Kunjithapatham; Gersh-Range, Jessica; Kasdin, Jeremy; Kern, Brian; Lam, Raymond; Mejia Prada, Camilo; Moody, Dwight; Patterson, Keith; Poberezhskiy, Ilya; Riggs, A. J. Eldorado; Seo, Byoung-Joon; Shi, Fang; Tang, Hong; Trauger, John; Zhou, Hanying; Zimmerman, Neil

2017-09-01

The Shaped Pupil Coronagraph (SPC) is one of the two operating modes of the WFIRST coronagraph instrument. The SPC provides starlight suppression in a pair of wedge-shaped regions over an 18% bandpass, and is well suited for spectroscopy of known exoplanets. To demonstrate this starlight suppression in the presence of expected onorbit input wavefront disturbances, we have recently built a dynamic testbed at JPL analogous to the WFIRST flight instrument architecture, with both Hybrid Lyot Coronagraph (HLC) and SPC architectures and a Low Order Wavefront Sensing and Control (LOWFS/C) subsystem to apply, sense, and correct dynamic wavefront disturbances. We present our best up-to-date results of the SPC mode demonstration from the testbed, in both static and dynamic conditions, along with model comparisons. HLC results will be reported separately.

Perturbative two- and three-loop coefficients from large β Monte Carlo

NASA Astrophysics Data System (ADS)

Lepage, G. P.; Mackenzie, P. B.; Shakespeare, N. H.; Trottier, H. D.

Perturbative coefficients for Wilson loops and the static quark self-energy are extracted from Monte Carlo simulations at large β on finite volumes, where all the lattice momenta are large. The Monte Carlo results are in excellent agreement with perturbation theory through second order. New results for third order coefficients are reported. Twisted boundary conditions are used to eliminate zero modes and to suppress Z3 tunneling.

Perturbative two- and three-loop coefficients from large b Monte Carlo

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

G.P. Lepage; P.B. Mackenzie; N.H. Shakespeare

1999-10-18

Perturbative coefficients for Wilson loops and the static quark self-energy are extracted from Monte Carlo simulations at large {beta} on finite volumes, where all the lattice momenta are large. The Monte Carlo results are in excellent agreement with perturbation theory through second order. New results for third order coefficients are reported. Twisted boundary conditions are used to eliminate zero modes and to suppress Z{sub 3} tunneling.

Adaptive and nonadaptive feedback control of global instabilities with application to a heated 2-D jet

NASA Astrophysics Data System (ADS)

Monkewitz, Peter A.; Mingori, D. L.

1992-04-01

Close to the onset of self-excited fluid oscillations the generic complex Ginzburg-Landau is proposed as the lowest order model for the plant. Its linear part which provides the stability boundaries is derived from first principles for both doubly-infinite and semi-infinite flow domains. Concentrating on a single global mode, the model is further simplified to the Stuart-Landau equation. For this latter model, a methodology is developed for the design of single-input single-output controllers. The so designed controllers have been implemented on a self-excited, heated two-dimensional jet with one hot wire as sensor and an acoustic speaker as actuator, and are shown to be effective within their limitations in suppressing or enhancing limit-cycle oscillations. Finally, the effect of of a controller designed to suppress the most unstable global mode on other modes is investigated experimentally in the wake of a cylinder at low Reynolds number, where an encouraging semi-quantitative correspondence to the Ginzburg-Landau model is found.

The Thermal Regulation of Gravitational Instabilities in Protoplanetary Disks. IV. Simulations with Envelope Irradiation

NASA Astrophysics Data System (ADS)

Cai, Kai; Durisen, Richard H.; Boley, Aaron C.; Pickett, Megan K.; Mejía, Annie C.

2008-02-01

It is generally thought that protoplanetary disks embedded in envelopes are more massive and thus more susceptible to gravitational instabilities (GIs) than exposed disks. We present three-dimensional radiative hydrodynamic simulations of protoplanetary disks with the presence of envelope irradiation. For a disk with a radius of 40 AU and a mass of 0.07 M⊙ around a young star of 0.5 M⊙, envelope irradiation tends to weaken and even suppress GIs as the irradiating flux is increased. The global mass transport induced by GIs is dominated by lower order modes, and irradiation preferentially suppresses higher order modes. As a result, gravitational torques and mass inflow rates are actually increased by mild irradiation. None of the simulations produce dense clumps or rapid cooling by convection, arguing against direct formation of giant planets by disk instability, at least in irradiated disks. However, dense gas rings and radial mass concentrations are produced, and these might be conducive to accelerated planetary core formation. Preliminary results from a simulation of a massive embedded disk with physical characteristics similar to one of the disks in the embedded source L1551 IRS 5 indicate a long radiative cooling time and no fragmentation. The GIs in this disk are dominated by global two- and three-armed modes.

Drag reduction by polymers in turbulent channel flows: Energy redistribution between invariant empirical modes.

PubMed

De Angelis, Elisabetta; Casciola, Carlo M; L'vov, Victor S; Piva, Renzo; Procaccia, Itamar

2003-05-01

We address the phenomenon of drag reduction by a dilute polymeric additive to turbulent flows, using direct numerical simulations (DNS) of the FENE-P model of viscoelastic flows. It had been amply demonstrated that these model equations reproduce the phenomenon, but the results of DNS were not analyzed so far with the goal of interpreting the phenomenon. In order to construct a useful framework for the understanding of drag reduction we initiate in this paper an investigation of the most important modes that are sustained in the viscoelastic and Newtonian turbulent flows, respectively. The modes are obtained empirically using the Karhunen-Loéve decomposition, allowing us to compare the most energetic modes in the viscoelastic and Newtonian flows. The main finding of the present study is that the spatial profile of the most energetic modes is hardly changed between the two flows. What changes is the energy associated with these modes, and their relative ordering in the decreasing order from the most energetic to the least. Modes that are highly excited in one flow can be strongly suppressed in the other, and vice versa. This dramatic energy redistribution is an important clue to the mechanism of drag reduction as is proposed in this paper. In particular, there is an enhancement of the energy containing modes in the viscoelastic flow compared to the Newtonian one; drag reduction is seen in the energy containing modes rather than the dissipative modes, as proposed in some previous theories.

Supermode-noise-free eighth-order femtosecond soliton from a backward dark-optical-comb-injection mode-locked semiconductor optical amplifier fiber laser.

PubMed

Lin, Gong-Ru; Pan, Ci-Ling; Chiu, I-Hsiang

2006-03-15

A backward dark-optical-comb-injection mode-locked semiconductor optical amplifier fiber laser (SOAFL) with a femtosecond pulse width and an ultrahigh supermode-noise suppressing ratio (SMSR) is primarily demonstrated. The mode-locked SOAFL pulse with a spectral linewidth of 0.45 nm is shortened from 15 to 8.6 ps under chirp compensation in a 420 m long dispersion-compensated fiber, corresponding to a time-bandwidth product of 0.48. The eighth-order soliton is obtained by the nonlinearly soliton's compression of the chirp-compensated SOAFL pulse in a 112 m long single-mode fiber at an input peak power of 51 W, providing the pulse width, the linewidth, and the nearly transform-limited time-bandwidth product are <200 fs, 13.8 nm, and 0.34, respectively. The phase noise and integrated timing jitter at an offset frequency below 1 MHz are -105 dBc/Hz and 0.8 ps, respectively. An ultrahigh pulse-compression ratio of 43 and a SMSR of 87 dB for the eighth-order SOAFL soliton are reported.

Parametric instability in the high power era of Advanced LIGO

NASA Astrophysics Data System (ADS)

Hardwick, Terra; Blair, Carl; Kennedy, Ross; Evans, Matthew; Fritschel, Peter; LIGO Virgo Scientific Collaboration

2017-01-01

After the first direct detections of gravitational waves, Advanced LIGO aims to increase its detection rate during the upcoming science runs through a series of detector improvements, including increased optical power. Higher circulating power increases the likelihood for three-mode parametric instabilities (PIs), in which mechanical modes of the mirrors scatter light into higher-order optical modes in the cavity and the resulting optical modes reinforce the mechanical modes via radiation pressure. Currently, LIGO uses two PI mitigation methods: thermal tuning to change the cavity g-factor and effectively decrease the frequency overlap between mechanical and optical modes, and active damping of mechanical modes with electrostatic actuation. While the combined methods provide stability at the current operating power, there is evidence that these will be insufficient for the next planned power increase; future suppression methods including acoustic mode dampers and dynamic g-factor modulation are discussed.

Eigenspace techniques for active flutter suppression

NASA Technical Reports Server (NTRS)

Garrard, W. L.

1982-01-01

Mathematical models to be used in the control system design were developed. A computer program, which takes aerodynamic and structural data for the ARW-2 aircraft and converts these data into state space models suitable for use in modern control synthesis procedures, was developed. Reduced order models of inboard and outboard control surface actuator dynamics and a second order vertical wind gust model were developed. An analysis of the rigid body motion of the ARW-2 was conducted. The deletion of the aerodynamic lag states in the rigid body modes resulted in more accurate values for the eigenvalues associated with the plunge and pitch modes than were obtainable if the lag states were retained.

Selective suppression of CARS signal with three-beam competing stimulated Raman scattering processes.

PubMed

Choi, Dae Sik; Rao, B Jayachander; Kim, Doyeon; Shim, Sang-Hee; Rhee, Hanju; Cho, Minhaeng

2018-06-14

Coherent Raman scattering spectroscopy and microscopy are useful methods for studying the chemical and biological structures of molecules with Raman-active modes. In particular, coherent anti-Stokes Raman scattering (CARS) microscopy, which is a label-free method capable of imaging structures by displaying the vibrational contrast of the molecules, has been widely used. However, the lack of a technique for switching-off the CARS signal has prevented the development of the super-resolution Raman imaging method. Here, we demonstrate that a selective suppression of the CARS signal is possible by using a three-beam double stimulated Raman scattering (SRS) scheme; the three beams are the pump, Stokes, and depletion lights in order of frequency. Both pump-Stokes and pump-depletion beam pairs can generate SRS processes by tuning their beat frequencies to match two different vibrational modes, then two CARS signals induced by pump-Stokes-pump and pump-depletion-pump interactions can be generated, where the two CARS signals are coupled with each other because they both involve interactions with the common pump beam. Herein, we show that as the intensity of the depletion beam is increased, one can selectively suppress the pump-Stokes-pump CARS signal because the pump-depletion SRS depletes the pump photons. A detailed theoretical description of the coupled differential equations for the three incident fields and the generated CARS signal fields is presented. Taking benzene as a molecular system, we obtained a maximum CARS suppression efficiency of about 97% with our experimental scheme, where the ring breathing mode of the benzene is associated with pump-Stokes-pump CARS, while the C-H stretching mode is associated with the competing pump-depletion SRS process. We anticipate that this selective switching-off scheme will be of use in developing super-resolution label-free CARS microscopy.

Single-Mode VCSELs

NASA Astrophysics Data System (ADS)

Larsson, Anders; Gustavsson, Johan S.

The only active transverse mode in a truly single-mode VCSEL is the fundamental mode with a near Gaussian field distribution. A single-mode VCSEL produces a light beam of higher spectral purity, higher degree of coherence and lower divergence than a multimode VCSEL and the beam can be more precisely shaped and focused to a smaller spot. Such beam properties are required in many applications. In this chapter, after discussing applications of single-mode VCSELs, we introduce the basics of fields and modes in VCSELs and review designs implemented for single-mode emission from VCSELs in different materials and at different wavelengths. This includes VCSELs that are inherently single-mode as well as inherently multimode VCSELs where higher-order modes are suppressed by mode selective gain or loss. In each case we present the current state-of-the-art and discuss pros and cons. At the end, a specific example with experimental results is provided and, as a summary, the most promising designs based on current technologies are identified.

Active sources in the cutoff of centrifugal fans to reduce the blade tones at higher-order duct mode frequencies

NASA Astrophysics Data System (ADS)

Neise, W.; Koopmann, G. H.

1991-01-01

A previously developed (e.g., Neise and Koopmann, 1984; Koopmann et al., 1988) active noise control technique in which the unwanted acoustic signals from centrifugal fans are suppressed by placing two externally driven sources near the cutoff of the casing was applied to the frequency region where not only plane sound waves are propagational in the fan ducts but also higher-order acoustic modes. Using a specially designed fan noise testing facility, the performance of two fans (280-mm impeller diam and 508 mm diam) was monitored with static pressure taps mounted peripherally around the inlet nozzle. Experimental results show that the aerodynamically generated source pressure field around the cutoff is too complex to be successfully counterimaged by only two active sources introduced in this region. It is suggested that, for an efficient application of this noise control technique in the higher-order mode frequency regime, it is neccessary to use an active source involving larger number of individually driven loudspeakers.

Acoustic mode measurements in the inlet of a model turbofan using a continuously rotating rake

NASA Astrophysics Data System (ADS)

Heidelberg, Laurence J.; Hall, David G.

1993-01-01

Comprehensive measurements of the spinning acoustic mode structure in the inlet of the Advanced Ducted Propeller (ADP) have been completed. These measurements were taken using a unique and previously untried method which was first proposed by T.G. Sofrin. A continuously rotating microphone system was employed. The ADP model was designed and built by Pratt & Whitney and tested in the NASA Lewis 9- by 15-foot Anechoic Wind Tunnel. Three inlet configurations were tested with cut-on and cutoff stator vane sets. The cutoff stator was designed to suppress all modes at the blade passing frequency. Rotating rake measurements indicate that several extraneous circumferential modes were active. The mode orders suggest that their source was an interaction between the rotor and small interruptions in the casing tip treatment. The cut-on stator produced the expected circumferential modes plus higher levels of the unexpected modes seen with the cutoff stator.

Acoustic Mode Measurements in the Inlet of a Model Turbofan Using a Continuously Rotating Rake

NASA Technical Reports Server (NTRS)

Heidelberg, Laurence J.; Hall, David G.

1992-01-01

Comprehensive measurements of the spinning acoustic mode structure in the inlet of the Advanced Ducted Propeller (ADP) have been completed. These measurements were taken using a unique and previously untried method which was first proposed by T.G. Sofrin. A continuously rotating microphone system was employed. The ADP model was designed and built by Pratt & Whitney and tested in the NASA Lewis 9- by 15-foot Anechoic Wind Tunnel. Three inlet configurations were tested with cut-on and cutoff stator vane sets. The cutoff stator was designed to suppress all modes at the blade passing frequency. Rotating rake measurements indicate that several extraneous circumferential modes were active. The mode orders suggest that their source was an interaction between the rotor and small interruptions in the casing tip treatment. The cut-on stator produced the expected circumferential modes plus higher levels of the unexpected modes seen with the cutoff stator.

Elimination of the asymmetric modes in a Ka-band super overmoded coaxial Cerenkov oscillator

NASA Astrophysics Data System (ADS)

Bai, Zhen; Zhang, Jun; Zhong, Huihuang; Zhao, Xuelong; Yang, Fuxiang

2017-12-01

The issue of asymmetric modes output of a Ka-band super overmoded coaxial Cerenkov oscillator is analyzed in this paper. Due to serious passband overlapping in a super overmoded coaxial slow wave structure (SWS), the asymmetric competition mode EH11 can hardly be suppressed thoroughly by the methods adopted in moderately overmoded devices, especially in the startup of oscillation. If the output structures reflect the asymmetric modes, the asymmetric mode competition in SWS will be aggravated and the normal operation state will be destroyed. In order to solve this problem, a taper waveguide is inserted at a specific position to achieve the destructive interference of the reflected TM11, and a special support structure is designed to avoid reflection of TE11. With these methods, asymmetric mode competition can be successfully eliminated, and the oscillator is capable of achieving a steady fundamental mode operation performance.

Hybrid PD and effective multi-mode positive position feedback control for slewing and vibration suppression of a smart flexible manipulator

NASA Astrophysics Data System (ADS)

Lou, Jun-qiang; Wei, Yan-ding; Yang, Yi-ling; Xie, Feng-ran

2015-03-01

A hybrid control strategy for slewing and vibration suppression of a smart flexible manipulator is presented in this paper. It consists of a proportional derivative controller to realize motion control, and an effective multi-mode positive position feedback (EMPPF) controller to suppress the multi-mode vibration. Rather than treat each mode equally as the standard multi-mode PPF, the essence of the EMPPF is that control forces of different modes are applied according to the mode parameters of the respective modes, so the vibration modes with less vibration energy receive fewer control forces. Stability conditions for the close loop system are established through stability analysis. Optimal parameters of the EMPPF controller are obtained using the method of root locus analysis. The performance of the proposed strategy is demonstrated by simulation and experiments. Experimental results show that the first two vibration modes of the manipulator are effectively suppressed. The setting time of the setup descends approximately 55%, reaching 3.12 s from 5.67 s.

Experimental study on parasitic mode suppression using FeSiAl in relativistic klystron amplifier

NASA Astrophysics Data System (ADS)

Zhang, Zehai

2015-03-01

Experimental study of parasitic mode suppression using electromagnetic attenuate material FeSiAl in an S-band Relativistic Klystron Amplifier (RKA) is presented in this paper. The FeSiAl powder is coated and sintered onto the inner surface of a drift tube which locates between the input and the middle cavity of the RKA. Cold tests show that the attenuate rate of the tube against parasitic mode TE11 is about 50%. Experiments carried out on the Torch-01 accelerator present that the tube is effective in suppressing the parasitic mode. Two typical outputs are obtained. When the diode voltage is on a moderate level, the RKA operates well and the parasitic mode is totally suppressed. The pulse length of the High Power Microwave (HPM) almost equals the electron beam pulse length and the HPM average output power is about 300 MW, with a power efficiency of 10%. When the diode voltage is on a higher level, the output power and efficiency rise but the parasitic mode oscillation occurred and the pulse length is shortened. By contrast, the parasitic mode oscillation is too strong for the RKA to operate normally with un-sintered drift tube. The experimental study implies that FeSiAl is effective in suppressing the parasitic mode oscillation in a certain extent. However, total suppression needs a deeper attenuate rate and further investigation.

Experimental study on parasitic mode suppression using FeSiAl in Relativistic Klystron Amplifier.

PubMed

Zhang, Zehai

2015-03-01

Experimental study of parasitic mode suppression using electromagnetic attenuate material FeSiAl in an S-band Relativistic Klystron Amplifier (RKA) is presented in this paper. The FeSiAl powder is coated and sintered onto the inner surface of a drift tube which locates between the input and the middle cavity of the RKA. Cold tests show that the attenuate rate of the tube against parasitic mode TE11 is about 50%. Experiments carried out on the Torch-01 accelerator present that the tube is effective in suppressing the parasitic mode. Two typical outputs are obtained. When the diode voltage is on a moderate level, the RKA operates well and the parasitic mode is totally suppressed. The pulse length of the High Power Microwave (HPM) almost equals the electron beam pulse length and the HPM average output power is about 300 MW, with a power efficiency of 10%. When the diode voltage is on a higher level, the output power and efficiency rise but the parasitic mode oscillation occurred and the pulse length is shortened. By contrast, the parasitic mode oscillation is too strong for the RKA to operate normally with un-sintered drift tube. The experimental study implies that FeSiAl is effective in suppressing the parasitic mode oscillation in a certain extent. However, total suppression needs a deeper attenuate rate and further investigation.

Simultaneous transmission of wired and wireless signals based on double sideband carrier suppression

NASA Astrophysics Data System (ADS)

Bitew, Mekuanint Agegnehu; Shiu, Run-Kai; Peng, Peng-Chun; Wang, Cheng-Hao; Chen, Yan-Ming

2017-11-01

In this paper, we proposed and experimentally demonstrated simultaneous transmission of wired and wireless signals based on double sideband optical carrier suppression. By properly adjusting the bias point of the dual-output mach-zehnder modulator (MZM), a central carrier in one output port and a pair of first-order sidebands in another output port are generated. The pair of first-order sidebands are fed into a second MZM to generate second-order order sidebands. A wired signal is embedded on the central carrier while a wireless signal is embedded on the second-order sidebands. Unlike other schemes, we did not use optical filter to separate the carrier from the optical sidebands. The measured bit error rate (BER) and eye-diagrams after a 25 km single-mode-fiber (SMF) transmission proved that the proposed scheme is successful for both wired and wireless signals transmission. Moreover, the power penalty at the BER of 10-9 is 0.3 and 0.7 dB for wired and wireless signals, respectively.

Suppression of Higher Order Modes in an Array of Cavities Using Waveguides

NASA Astrophysics Data System (ADS)

Shashkov, Ya. V.; Sobenin, N. P.; Bazyl, D. S.; Kaminskiy, V. I.; Mitrofanov, A. A.; Zobov, M. M.

An application of additional harmonic cavities operating at multiplies of the main RF system frequency of 400 MHz is currently under discussionin the framework of the High Luminosity LHC upgrade program [1,2]. A structure consisting of two 800 MHz single cell superconducting cavities with grooved beam pipes coupled by drift tubes has been suggested for implementation. However, it is desirable to increase the number of single cells installed in one cryomodule in order to decrease the number of transitions between "warm" and "cold" parts of the collider vacuum chamber. Unfortunately, it can lead to the appearance of higher order modes (HOM) trapped between the cavities. In order to solve this problem the methods of HOM damping with rectangular waveguides connected to the drift tubes were investigated and compared. We describe the results obtained for arrays of 2, 4 and 8 cavitiesin this paper.

60-GHz Millimeter-wave Over Fiber with Directly Modulated Dual-mode Laser Diode

PubMed Central

Tsai, Cheng-Ting; Lin, Chi-Hsiang; Lin, Chun-Ting; Chi, Yu-Chieh; Lin, Gong-Ru

2016-01-01

A directly modulated dual-mode laser diode (DMLD) with third-order intermodulation distortion (IMD3) suppression is proposed for a 60-GHz millimeter-wave over fiber (MMWoF) architecture, enabling new fiber-wireless communication access to cover 4-km single-mode-fiber (SMF) and 3-m wireless 16-QAM OFDM transmissions. By dual-mode injection-locking, the throughput degradation of the DMLD is mitigated with saturation effect to reduce its threshold, IMD3 power and relative intensity noise to 7.7 mA, −85 dBm and −110.4 dBc/Hz, respectively, providing huge spurious-free dynamic range of 85.8 dB/Hz2/3. This operation suppresses the noise floor of the DMLD carried QPSK-OFDM spectrum by 5 dB. The optical receiving power is optimized to restrict the power fading effect for improving the bit error rate to 1.9 × 10−3 and the receiving power penalty to 1.1 dB. Such DMLD based hybrid architecture for 60-GHz MMW fiber-wireless access can directly cover the current optical and wireless networks for next-generation indoor and short-reach mobile communications. PMID:27297267

Direct visualization of the in-plane leakage of high-order transverse modes in vertical-cavity surface-emitting lasers mediated by oxide-aperture engineering

NASA Astrophysics Data System (ADS)

Ledentsov, N.; Shchukin, V. A.; Kropp, J.-R.; Burger, S.; Schmidt, F.; Ledentsov, N. N.

2016-03-01

Oxide-confined apertures in vertical cavity surface emitting laser (VCSEL) can be engineered such that they promote leakage of the transverse optical modes from the non- oxidized core region to the selectively oxidized periphery of the device. The reason of the leakage is that the VCSEL modes in the core can be coupled to tilted modes in the periphery if the orthogonality between the core mode and the modes at the periphery is broken by the oxidation-induced optical field redistribution. Three-dimensional modeling of a practical VCSEL design reveals i) significantly stronger leakage losses for high-order transverse modes than that of the fundamental one as high-order modes have a higher field intensity close to the oxide layers and ii) narrow peaks in the far-field profile generated by the leaky component of the optical modes. Experimental 850-nm GaAlAs leaky VCSELs produced in the modeled design demonstrate i) single-mode lasing with the aperture diameters up to 5μm with side mode suppression ratio >20dB at the current density of 10kA/cm2; and ii) narrow peaks tilted at 37 degrees with respect to the vertical axis in excellent agreement with the modeling data and confirming the leaky nature of the modes and the proposed mechanism of mode selection. The results indicate that in- plane coupling of VCSELs, VCSELs and p-i-n photodiodes, VCSEL and delay lines is possible allowing novel photonic integrated circuits. We show that the approach enables design of oxide apertures, air-gap apertures, devices created by impurity-induced intermixing or any combinations of such designs through quantitative evaluation of the leaky emission.

Experimental study on parasitic mode suppression using FeSiAl in relativistic klystron amplifier

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

Zhang, Zehai

2015-03-15

Experimental study of parasitic mode suppression using electromagnetic attenuate material FeSiAl in an S-band Relativistic Klystron Amplifier (RKA) is presented in this paper. The FeSiAl powder is coated and sintered onto the inner surface of a drift tube which locates between the input and the middle cavity of the RKA. Cold tests show that the attenuate rate of the tube against parasitic mode TE{sub 11} is about 50%. Experiments carried out on the Torch-01 accelerator present that the tube is effective in suppressing the parasitic mode. Two typical outputs are obtained. When the diode voltage is on a moderate level,more » the RKA operates well and the parasitic mode is totally suppressed. The pulse length of the High Power Microwave (HPM) almost equals the electron beam pulse length and the HPM average output power is about 300 MW, with a power efficiency of 10%. When the diode voltage is on a higher level, the output power and efficiency rise but the parasitic mode oscillation occurred and the pulse length is shortened. By contrast, the parasitic mode oscillation is too strong for the RKA to operate normally with un-sintered drift tube. The experimental study implies that FeSiAl is effective in suppressing the parasitic mode oscillation in a certain extent. However, total suppression needs a deeper attenuate rate and further investigation.« less

Neural adaptive control for vibration suppression in composite fin-tip of aircraft.

PubMed

Suresh, S; Kannan, N; Sundararajan, N; Saratchandran, P

2008-06-01

In this paper, we present a neural adaptive control scheme for active vibration suppression of a composite aircraft fin tip. The mathematical model of a composite aircraft fin tip is derived using the finite element approach. The finite element model is updated experimentally to reflect the natural frequencies and mode shapes very accurately. Piezo-electric actuators and sensors are placed at optimal locations such that the vibration suppression is a maximum. Model-reference direct adaptive neural network control scheme is proposed to force the vibration level within the minimum acceptable limit. In this scheme, Gaussian neural network with linear filters is used to approximate the inverse dynamics of the system and the parameters of the neural controller are estimated using Lyapunov based update law. In order to reduce the computational burden, which is critical for real-time applications, the number of hidden neurons is also estimated in the proposed scheme. The global asymptotic stability of the overall system is ensured using the principles of Lyapunov approach. Simulation studies are carried-out using sinusoidal force functions of varying frequency. Experimental results show that the proposed neural adaptive control scheme is capable of providing significant vibration suppression in the multiple bending modes of interest. The performance of the proposed scheme is better than the H(infinity) control scheme.

Tuning the resonance frequencies and mode shapes in a large range multi-degree of freedom micromirror.

PubMed

Morrison, Jessica; Imboden, Matthias; Bishop, David J

2017-04-03

The ability to actively shift the primary resonance of a 2D scanning micromirror allows the user to set the scanning direction, set the scanning frequency, and lift otherwise degenerate modes in a symmetrically designed system. In most cases, resonant scanning micromirrors require frequency stability in order to perform imaging and projection functions properly. This paper suggests a method to tune the tip and tilt resonant frequencies in real time while actively suppressing or allowing degeneracy of the two modes in a symmetric electrothermal micromirror. We show resonant frequency tuning with a range of degeneracy separation of 470 Hz or by approximately ±15% and controllable coupling.

Mode-filtered large-core fiber for optical coherence tomography

PubMed Central

Moon, Sucbei; Chen, Zhongping

2013-01-01

We have investigated the use of multimode fiber in optical coherence tomography (OCT) with a mode filter that selectively suppresses the power of the high-order modes (HOMs). A large-core fiber (LCF) that has a moderate number of guiding modes was found to be an attractive alternative to the conventional single-mode fiber for its large mode area and the consequentially wide Rayleigh range of the output beam if the HOMs of the LCF were efficiently filtered out by a mode filter installed in the middle. For this, a simple mode filtering scheme of a fiber-coil mode filter was developed in this study. The LCF was uniformly coiled by an optimal bend radius with a fiber winder, specially devised for making a low-loss mode filter. The feasibility of the mode-filtered LCF in OCT imaging was tested with a common-path OCT system. It has been successfully demonstrated that our mode-filtered LCF can provide a useful imaging or sensing probe without an objective lens that greatly simplifies the structure of the probing optics. PMID:23207399

Observation of Wakefield Suppression in a Photonic-Band-Gap Accelerator Structure

DOE PAGES

Simakov, Evgenya I.; Arsenyev, Sergey A.; Buechler, Cynthia E.; ...

2016-02-10

We report experimental observation of higher order mode (HOM) wakefield suppression in a room-temperature traveling-wave photonic band gap (PBG) accelerating structure at 11.700 GHz. It has been long recognized that PBG structures have potential for reducing long-range wakefields in accelerators. The first ever demonstration of acceleration in a room-temperature PBG structure was conducted in 2005. Since then, the importance of PBG accelerator research has been recognized by many institutions. However, the full experimental characterization of the wakefield spectrum and demonstration of wakefield suppression when the accelerating structure is excited by an electron beam has not been performed to date. Wemore » conducted an experiment at the Argonne Wakefield Accelerator (AWA) test facility and observed wakefields excited by a single high charge electron bunch when it passes through a PBG accelerator structure. Lastly, excellent HOM suppression properties of the PBG accelerator were demonstrated in the beam test.« less

Increased electron temperature turbulence during suppression of edge localized mode by resonant magnetic perturbations in the DIII-D tokamak

NASA Astrophysics Data System (ADS)

Sung, C.; Wang, G.; Rhodes, T. L.; Smith, S. P.; Osborne, T. H.; Ono, M.; McKee, G. R.; Yan, Z.; Groebner, R. J.; Davis, E. M.; Zeng, L.; Peebles, W. A.; Evans, T. E.

2017-11-01

The first observation of increased electron temperature turbulence during edge localized mode (ELM) suppression by resonant magnetic perturbations (RMPs) is presented. These are long wavelength fluctuations (kθρs ≤ 0.2, where kθ = poloidal wavenumber and ρs = ion sound gyroradius) observed during H-mode plasmas on the DIII-D. This increase occurs only after ELMs are suppressed and are not observed during the initial RMP application. The T˜ e/Te increases ( >60%) are coincident with changes in normalized density and electron temperature gradients in the region from the top of the pedestal outward to the upper portion of the steep edge gradient. Density turbulence (kθρs ≤ 0.4) in this location was also observed to increase only after ELM suppression. These results are significant since they indicate that increased gradient-driven turbulent transport is one possible mechanism to regulate and maintain ELM-free H-mode operation. Investigation of linear stability of drift wave instabilities using the CGYRO code [Candy et al., J. Comput. Phys. 324, 73 (2016)] shows that the dominant mode moves closer to the electron mode branch from the ion mode branch only after ELMs are suppressed, correlated with the increased turbulence. The increased turbulence during ELM suppression, rather than with the initial RMP application, indicates that the often observed RMP induced "density pump-out" cannot be attributed to long wavelength edge turbulence level changes.

Exploring the effect of nested capillaries on core-cladding mode resonances in hollow-core antiresonant fibers

NASA Astrophysics Data System (ADS)

Provino, Laurent; Taunay, Thierry

2018-02-01

Optimal suppression of higher-order modes (HOMs) in hollow-core antiresonant fibers comprising a single ring of thin-walled capillaries was previously studied, and can be achieved when the condition on the capillary-tocore diameter ratio is satisfied (d/D ≍ 0.68). Here we report on the conditions for maximizing the leakage losses of HOMs in hollow-core nested antiresonant node-less fibers, while preserving low confinement loss for the fundamental mode. Using an analytical model based on coupled capillary waveguides, as well as full-vector finite element modeling, we show that optimal d/D value leading to high leakage losses of HOMs, is strongly correlated to the size of nested capillaries. We also show that extremely high value of degree of HOM suppression (˜1200) at the resonant coupling is almost unchanged on a wide range of nested capillary diameter dN ested values. These results thus suggest the possibility of designing antiresonant fibers with nested elements, which show optimal guiding performances in terms of the HOM loss compared to that of the fundamental mode, for clearly defined paired values of the ratios dN ested/d and d/D. These can also tend towards a single-mode behavior only when the dimensionless parameter dN ested/d is less than 0.30, with identical wall thicknesses for all of the capillaries.

Design, test, and evaluation of three active flutter suppression controllers

NASA Technical Reports Server (NTRS)

Adams, William M., Jr.; Christhilf, David M.; Waszak, Martin R.; Mukhopadhyay, Vivek; Srinathkumar, S.

1992-01-01

Three control law design techniques for flutter suppression are presented. Each technique uses multiple control surfaces and/or sensors. The first method uses traditional tools (such as pole/zero loci and Nyquist diagrams) for producing a controller that has minimal complexity and which is sufficiently robust to handle plant uncertainty. The second procedure uses linear combinations of several accelerometer signals and dynamic compensation to synthesize the model rate of the critical mode for feedback to the distributed control surfaces. The third technique starts with a minimum-energy linear quadratic Gaussian controller, iteratively modifies intensity matrices corresponding to input and output noise, and applies controller order reduction to achieve a low-order, robust controller. The resulting designs were implemented digitally and tested subsonically on the active flexible wing wind-tunnel model in the Langley Transonic Dynamics Tunnel. Only the traditional pole/zero loci design was sufficiently robust to errors in the nominal plant to successfully suppress flutter during the test. The traditional pole/zero loci design provided simultaneous suppression of symmetric and antisymmetric flutter with a 24-percent increase in attainable dynamic pressure. Posttest analyses are shown which illustrate the problems encountered with the other laws.

Optimization of the structural and control system for LSS with reduced-order model

NASA Technical Reports Server (NTRS)

Khot, N. S.

1989-01-01

The objective is the simultaneous design of the structural and control system for space structures. The minimum weight of the structure is the objective function, and the constraints are placed on the closed loop distribution of the frequencies and the damping parameters. The controls approach used is linear quadratic regulator with constant feedback. A reduced-order control system is used. The effect of uncontrolled modes is taken into consideration by the model error sensitivity suppression (MESS) technique which modified the weighting parameters for the control forces. For illustration, an ACOSS-FOUR structure is designed for a different number of controlled modes with specified values for the closed loop damping parameters and frequencies. The dynamic response of the optimum designs for an initial disturbance is compared.

10th order laterally coupled GaN-based DFB laser diodes with V-shaped surface gratings

NASA Astrophysics Data System (ADS)

Kang, J. H.; Wenzel, H.; Hoffmann, V.; Freier, E.; Sulmoni, L.; Unger, R.-S.; Einfeldt, S.; Wernicke, T.; Kneissl, M.

2018-02-01

Single longitudinal mode operation of laterally coupled distributed feedback (DFB) laser diodes (LDs) based on GaN containing 10th-order surface Bragg gratings with V-shaped grooves is demonstrated using i-line stepper lithography and inductively coupled plasma etching. A threshold current of 82 mA, a slope efficiency of 1.7 W/A, a single peak emission at 404.5 nm with a full width at half maximum of 0.04 nm and a side mode suppression ratio of > 23 dB at an output power of about 46 mW were achieved under pulsed operation. The shift of the lasing wavelength of DFB LDs with temperature was around three times smaller than that of conventional ridge waveguide LDs.

100-mW high-power three-section tunable distributed Bragg reflector laser diodes with a real refractive-index-guided self-aligned structure

NASA Astrophysics Data System (ADS)

Takayama, Toru; Mochida, Atsunori; Orita, Kenji; Tamura, Satoshi; Ohnishi, Toshikazu; Yuri, Masaaki; Shimizu, Hirokazu

2002-05-01

High-power (>100mW) 820 nm-band distributed Bragg reflector (DBR) laser diodes (LDs) with stable fundamental transverse mode operation and continuous wavelength tuning characteristics have been developed. To obtain high-power LDs with a stable fundamental transverse mode in 820 nm wavelength range, an AlGaAs narrow stripe (2.0 micrometers ) real refractive-index-guided self-aligned (RISA) structure is utilized. In the RISA structure, the index step between inside and outside the stripe region ((Delta) n) can be precisely controlled in the order of 10-3). To maintain a stable fundamental transverse mode up to an output power over 100 mW, (Delta) n is designed to be 4x10-3. Higher-order transverse modes are effectively suppressed by a narrow stripe geometry. Further, to achieve continuous wavelength tuning capability, the three-section LD structure, which consists of the active (700micrometers ), phase control (300micrometers ), and DBR(500micrometers ) sections, is incorporated. Our DBR LDs show a maximum output power over 200mW with a stable fundamental transverse mode, and wavelength tuning characteristics ((Delta) (lambda) ~2nm) under 100 mW CW operation.

Criteria for Neoclassical Tearing Modes Suppression in KSTAR

NASA Astrophysics Data System (ADS)

Park, Y. S.; Hwang, Y. S.

2007-11-01

In KSTAR, neoclassical tearing modes(NTMs) will be suppressed by using 170GHz electron cyclotron current drive(ECCD) system with steering mirrors that align the current deposition to NTM locations. As an initial stage of NTM suppression study, 1 MW ECCD power will be used to suppress m/n = 3/2 and 2/1 NTMs. To confirm the feasibility of successful suppression of the modes under the proposed KSTAR environment, modified Rutherford equation(MRE) which encapsulates stability of NTMs is constructed for the target equilibrium of KSTAR. The geometric coefficients in MRE are obtained by comparing saturated sizes of NTMs from ISLAND code [1] with the amounts of local bootstrap currents from ONETWO. Parameters related to the operation of ECCD are analyzed by TORAY-GA linear ray-tracing code. Due to the small ECCD power available at the initial stage of KSTAR, condition of the optimum ECCD modulation is considered in the analysis to maximize suppression performance. From the analyses, criteria such as the minimum ECCD power required for complete suppression of the modes and the optimum conditions of EC wave launch angle and modulation duty factor are derived for the successful NTM suppression in KSTAR. [1] C.N. Nguyen, G. Bateman and A.H. Kritz, Phys. Plasmas 11 3460 (2004)

Stimulated neutrino transformation through turbulence

DOE PAGES

Patton, Kelly M.; Kneller, James P.; McLaughlin, Gail C.

2014-04-30

We derive an analytical solution for the flavor evolution of a neutrino through a turbulent density profile which is found to accurately predict the amplitude and transition wavelength of numerical solutions on a case-by-case basis. The evolution is seen to strongly depend upon those Fourier modes in the turbulence which are approximately the same as the splitting between neutrino eigenvalues. Transitions are strongly enhanced by those Fourier modes in the turbulence which are approximately the same as the splitting between neutrino eigenvalues. Lastly, we also find a suppression of transitions due to the long wavelength modes when the ratio ofmore » their amplitude and the wavenumber is of order, or greater than, the first root of the Bessel function J 0.« less

Vibration suppression in flexible structures via the sliding-mode control approach

NASA Technical Reports Server (NTRS)

Drakunov, S.; Oezguener, Uemit

1994-01-01

Sliding mode control became very popular recently because it makes the closed loop system highly insensitive to external disturbances and parameter variations. Sliding algorithms for flexible structures have been used previously, but these were based on finite-dimensional models. An extension of this approach for differential-difference systems is obtained. That makes if possible to apply sliding-mode control algorithms to the variety of nondispersive flexible structures which can be described as differential-difference systems. The main idea of using this technique for dispersive structures is to reduce the order of the controlled part of the system by applying an integral transformation. We can say that transformation 'absorbs' the dispersive properties of the flexible structure as the controlled part becomes dispersive.

Measurement of Branching Ratios for Non-leptonic Cabibbo-suppressed Decays of the Charmed-Strange Baryon Ξ c +

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

Vazquez Jauregui, Eric

2008-08-01

We studied several Ξ c + decay modes, most of them with a hyperon in the final state, and determined their branching ratios. The data used in this analysis come from the fixed target experiment SELEX, a multi-stage spectrometer with high acceptance for forward interactions, that took data during 1996 and 1997 at Fermilab with 600 GeV=c (mainly Σ -, π -) and 540 GeV/c (mainly p) beams incident on copper and carbon targets. The thesis mainly details the first observation of two Cabibbo-suppressed decay modes, Ξ c + → Σ +π -π + and Ξ c + → Σmore » -π +π +. The branching ratios of the decays relative to the Cabibbo-favored Ξ c + → Σ -π +π + are measured to be: Γ(Ξ c + → Σ -π +π +)/Γ(Ξ c + → Ξ -π +π +) = 0.184 ± 0.086. Systematic studies have been performed in order to check the stability of the measurements varying all cuts used in the selection of events over a wide interval and we do not observe evidence of any trend, so the systematic error is negligible in the final results because the quadrature sum of the total error is not affected. The branching ratios for the same decay modes of the Λ c + are measured to check the methodology of the analysis. The branching ratio of the decay mode Λ c + → Σ +π -π + is measured relative to Λ c + → pK - π +, while the one of the decay mode Λ c + → Σ -π +π +is relative to Λ c +→ Σ +π -π +, as they have been reported earlier. The results for the control modes are: Γ(Λ c +→ Σ +π -π +)/Γ(Λ c + → pK - π +) = 0.716 ± 0.144 and Γ(Λ c +→ Σ -π +π +)/Γ(Λ c + → Σ +π -π +) = 0.382 ± 0.104. The branching ratio of the decay mode Ξ c + → pK - π + relative to Ξ c + → Ξ -π +π + is considered as another control mode, the measured value is Γ(Ξ c + → pK -π +)/Γ(Ξ c + → Ξ -π +π +) = 0.194 ± 0.054. Systematic studies have been also performed for the control modes and all systematic variations are also small compared to the statistical error. We also report the first observation of two more decay modes, the Cabibbo-suppressed decay Ξ c + → Σ - K +π + and the doubly Cabibbo-suppressed decay Ξ c + → Σ +K +π -, but their branching ratios have not been measured up to now.« less

Femtosecond wavelength tunable semiconductor optical amplifier fiber laser mode-locked by backward dark-optical-comb injection at 10 GHz.

PubMed

Lin, Gong-Ru; Chiu, I-Hsiang

2005-10-31

Femtosecond nonlinear pulse compression of a wavelength-tunable, backward dark-optical-comb injection harmonic-mode-locked semiconductor optical amplifier based fiber laser (SOAFL) is demonstrated for the first time. Shortest mode-locked SOAFL pulsewidth of 15 ps at 1 GHz is generated, which can further be compressed to 180 fs after linear chirp compensation, nonlinear soliton compression, and birefringent filtering. A maximum pulsewidth compression ratio for the compressed eighth-order SOAFL soliton of up to 80 is reported. The pedestal-free eighth-order soliton can be obtained by injecting the amplified pulse with peak power of 51 W into a 107.5m-long single-mode fiber (SMF), providing a linewidth and time-bandwidth product of 13.8 nm and 0.31, respectively. The tolerance in SMF length is relatively large (100-300 m) for obtaining <200fs SOAFL pulsewidth at wavelength tuning range of 1530-1560 nm. By extending the repetition frequency of dark-optical-comb up to 10 GHz, the mode-locked SOAFL pulsewidth can be slightly shortened from 5.4 ps to 3.9 ps after dispersion compensating, and further to 560 fs after second-order soliton compression. The lasing linewidth, time-bandwidth product and pulsewidth suppressing ratio of the SOAFL soliton become 4.5 nm, 0.33, and 10, respectively.

Feedback stabilization of resistive wall modes in a reversed-field pinch

NASA Astrophysics Data System (ADS)

Brunsell, P. R.; Yadikin, D.; Gregoratto, D.; Paccagnella, R.; Liu, Y. Q.; Cecconello, M.; Drake, J. R.; Manduchi, G.; Marchiori, G.

2005-09-01

An array of saddle coils having Nc=16 equally spaced positions along the toroidal direction has been installed for feedback control of resistive wall modes (RWMs) on the EXTRAP T2R reversed-field pinch [P. R. Brunsell, H. Bergsaker, M. Cecconello et al., Plasma Phys. Controlled Fusion 43, 1457 (2001)]. Using feedback, multiple nonresonant RWMs are simultaneously suppressed for three to four wall times. Feedback stabilization of RWMs results in a significant prolongation of the discharge duration. This is linked to a better sustainment of the plasma and tearing mode toroidal rotation with feedback. Due to the limited number of coils in the toroidal direction, pairs of modes with toroidal mode numbers n ,n' that fulfill the condition ∣n-n'∣=Nc are coupled by the feedback action from the discrete coil array. With only one unstable mode in a pair of coupled modes, the suppression of the unstable mode is successful. If two modes are unstable in a coupled pair, two possibilities exist: partial suppression of both modes or, alternatively, complete stabilization of one target mode while the other is left unstable.

Performance analysis of higher mode spoof surface plasmon polariton for terahertz sensing

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

Yao, Haizi; Tu, Wanli; Zhong, Shuncong, E-mail: zhongshuncong@hotmail.com

2015-04-07

We investigated the spoof surface plasmon polaritons (SSPPs) on 1D grooved metal surface for terahertz sensing of refractive index of the filling analyte through a prism-coupling attenuated total reflection setup. From the dispersion relation analysis and the finite element method-based simulation, we revealed that the dispersion curve of SSPP got suppressed as the filling refractive index increased, which cause the coupling resonance frequency redshifting in the reflection spectrum. The simulated results for testing various refractive indexes demonstrated that the incident angle of terahertz radiation has a great effect on the performance of sensing. Smaller incident angle will result in amore » higher sensitive sensing with a narrower detection range. In the meanwhile, the higher order mode SSPP-based sensing has a higher sensitivity with a narrower detection range. The maximum sensitivity is 2.57 THz/RIU for the second-order mode sensing at 45° internal incident angle. The proposed SSPP-based method has great potential for high sensitive terahertz sensing.« less

Design and fabrication of elliptical-core few-mode fiber for MIMO-less data transmission.

PubMed

Liang, Junpeng; Mo, Qi; Fu, Songnian; Tang, Ming; Shum, P; Liu, Deming

2016-07-01

We propose a design strategy of elliptical core few-mode fiber (e-FMF) that supports three spatial modes with enhanced mode spacing between LP_11a and LP_11b, to suppress intra-mode coupling during mode-division multiplexing (MDM) transmission. Our theoretical investigations show that there exist two optimization regimes for the e-FMF, as a comparison with traditional circular core FMF(c-FMF). At the regime of three-mode operation, there occurs a trade-off between mode spacing and bending-induced loss. Meanwhile, in terms of five-mode regime, a trade-off between mode spacing and high-order mode crosstalk happens. Finally, we fabricate 7.94 km e-FMF with the optimal parameters, based on the commercial fiber manufacture facility. The primary characterizations at 1550 nm show that three spatial modes of e-FMF can be transmitted with a loss less than 0.3 dB/km. Meanwhile, -22.44  dB crosstalk between LP_11a and LP_11b is observed, even when the 2 km e-FMF is under stress-induced strong perturbation.

Suppression of the asymmetric competition mode in the relativistic Ku-band coaxial transit-time oscillator

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

Ling, Junpu; He, Juntao; Zhang, Jiande

2014-10-15

A relativistic Ku-band coaxial transit-time oscillator has been proposed in our previous work. In the experiments, we find that the asymmetric competition mode in the device limits the microwave power with the increase of the input electric power. For solving such a problem, the methods for analysis and suppression of the asymmetric competition mode in the device are investigated theoretically and experimentally. It is shown that the structure and the material of the collector, the concentricity, and the electron emission uniformity play an important part in the suppression of the asymmetric competition mode in the relativistic Ku-band transit-time oscillator. Inmore » the subsequent experiments, the asymmetric mode was suppressed effectively. At a low guiding magnetic field of 0.7 T, a microwave pulse with power of 1 GW, frequency of 14.3 GHz close to the simulation one, and efficiency of 20% was generated.« less

Using multi-ring structure for suppression of mode competition in stable single-longitudinal-mode erbium fiber laser

NASA Astrophysics Data System (ADS)

Yeh, Chien-Hung; Huang, Tzu-Jung; Yang, Zi-Qing; Chow, Chi-Wai

2017-12-01

In this demonstration, a stable and tunable single-longitudinal-mode (SLM) erbium-doped fiber (EDF) laser with multiple-ring configuration is proposed and investigated. The proposed compound-ring structure can create different free spectrum ranges (FSRs) to result in the mode-filter effect based on the Vernier effect for suppressing the other modes. Additionally, the output stabilization of power and wavelength in the proposed EDF multiple-ring laser are also discussed.

Rare top quark decays at a 100 TeV proton-proton collider: t → bWZ and t→ hc

NASA Astrophysics Data System (ADS)

Papaefstathiou, Andreas; Tetlalmatzi-Xolocotzi, Gilberto

2018-03-01

We investigate extremely rare top quark decays at a future proton-proton collider with centre-of-mass energy of 100 TeV. We focus on two decay modes: radiative decay with a Z boson, t → b WZ, and flavour-changing neutral decay with a Higgs boson, t → h c, the former being kinematically suppressed with a branching ratio of O(10^{-6}) (Altarelli et al., Phys Lett B 502:125-132, 2001), and the latter highly loop-suppressed, with a branching ratio of O(10^{-15}) (Aguilar-Saavedra, Acta Phys Polon B 35:2695-2710, 2004). We find that t → b WZ will be very challenging to observe in top quark pair production, even within well-motivated beyond-the-standard model scenarios. For the mode t→ h c we find a stronger sensitivity than that obtained by any future LHC measurement by at least one order of magnitude.

Negative Gaussian curvature induces significant suppression of thermal conduction in carbon crystals.

PubMed

Zhang, Zhongwei; Chen, Jie; Li, Baowen

2017-09-28

From the mathematic category of surface Gaussian curvature, carbon allotropes can be classified into three types: zero curvature, positive curvature, and negative curvature. By performing Green-Kubo equilibrium molecular dynamics simulations, we found that surface curvature has a significant impact on the phonon vibration and thermal conductivity (κ) of carbon crystals. When curving from zero curvature to negative or positive curvature structures, κ is reduced by several orders of magnitude. Interestingly, we found that κ of negatively curved carbon crystals exhibits a monotonic dependence on curvature. Through phonon mode analysis, we show that curvature induces remarkable phonon softening in phonon dispersion, which results in the reduction of phonon group velocity and flattening of phonon band structure. Furthermore, the curvature was found to induce phonon mode hybridization, leading to the suppression of phonon relaxation time. Our study provides physical insight into thermal transport in curvature materials, and will be valuable in the modulation of phonon activity through surface curvature.

Study on Misalignment Angle Compensation during Scale Factor Matching for Two Pairs of Accelerometers in a Gravity Gradient Instrument

PubMed Central

Huang, Xiangqing; Deng, Zhongguang; Xie, Yafei; Fan, Ji; Hu, Chenyuan

2018-01-01

A method for automatic compensation of misalignment angles during matching the scale factors of two pairs of the accelerometers in developing the rotating accelerometer gravity gradient instrument (GGI) is proposed and demonstrated in this paper. The purpose of automatic scale factor matching of the four accelerometers in GGI is to suppress the common mode acceleration of the moving-based platforms. However, taking the full model equation of the accelerometer into consideration, the other two orthogonal axes which is the pendulous axis and the output axis, will also sense the common mode acceleration and reduce the suppression performance. The coefficients from the two axes to the output are δO and δP respectively, called the misalignment angles. The angle δO, coupling with the acceleration along the pendulous axis perpendicular to the rotational plane, will not be modulated by the rotation and gives little contribution to the scale factors matching. On the other hand, because of coupling with the acceleration along the centripetal direction in the rotating plane, the angle δP would produce a component with 90 degrees phase delay relative to the scale factor component. Hence, the δP component coincides exactly with the sensitive direction of the orthogonal accelerometers. To improve the common mode acceleration rejection, the misalignment angle δP is compensated by injecting a trimming current, which is proportional to the output of an orthogonal accelerometer, into the torque coil of the accelerometer during the scale factor matching. The experimental results show that the common linear acceleration suppression achieved three orders after the scale factors balance and five orders after the misalignment angles compensation, which is almost down to the noise level of the used accelerometers of 1~2 × 10−7 g/√Hz (1 g ≈ 9.8 m/s2). PMID:29670021

Study on Misalignment Angle Compensation during Scale Factor Matching for Two Pairs of Accelerometers in a Gravity Gradient Instrument.

PubMed

Huang, Xiangqing; Deng, Zhongguang; Xie, Yafei; Fan, Ji; Hu, Chenyuan; Tu, Liangcheng

2018-04-18

A method for automatic compensation of misalignment angles during matching the scale factors of two pairs of the accelerometers in developing the rotating accelerometer gravity gradient instrument (GGI) is proposed and demonstrated in this paper. The purpose of automatic scale factor matching of the four accelerometers in GGI is to suppress the common mode acceleration of the moving-based platforms. However, taking the full model equation of the accelerometer into consideration, the other two orthogonal axes which is the pendulous axis and the output axis, will also sense the common mode acceleration and reduce the suppression performance. The coefficients from the two axes to the output are δ O and δ P respectively, called the misalignment angles. The angle δ O , coupling with the acceleration along the pendulous axis perpendicular to the rotational plane, will not be modulated by the rotation and gives little contribution to the scale factors matching. On the other hand, because of coupling with the acceleration along the centripetal direction in the rotating plane, the angle δ P would produce a component with 90 degrees phase delay relative to the scale factor component. Hence, the δ P component coincides exactly with the sensitive direction of the orthogonal accelerometers. To improve the common mode acceleration rejection, the misalignment angle δ P is compensated by injecting a trimming current, which is proportional to the output of an orthogonal accelerometer, into the torque coil of the accelerometer during the scale factor matching. The experimental results show that the common linear acceleration suppression achieved three orders after the scale factors balance and five orders after the misalignment angles compensation, which is almost down to the noise level of the used accelerometers of 1~2 × 10 −7 g/√Hz (1 g ≈ 9.8 m/s²).

Physics of thermal transport and increased electron temperature turbulence in the edge pedestal of ELM-free, H-mode regimes on DIII-D

NASA Astrophysics Data System (ADS)

Sung, Choongki

2017-10-01

It has been observed, for the first time, that suppression of Edge Localized Modes (ELMs) in tokamak plasmas is accompanied by an increase in electron temperature turbulence. A correlation electron cyclotron emission technique has been utilized to quantify the observed increase: 40% increase in Quiescent H-mode (QH-mode) and 70% increase in 3D field ELM suppressed H-mode. Since reliable ELM-free H-mode operation is essential for future burning plasma experiments, it is crucial to develop a validated predictive capability for these plasmas. Linear stability analysis using TGLF has provided an explanation for the observations and has indicated that the underlying physical mechanisms are different in the two regimes. In QH-mode, profile gradients and the associated linear growth rate are decreased compared to ELMing H-mode. However, the ExB shearing rate is reduced by an even greater factor such that turbulent transport is no longer suppressed by flow shear. In contrast, during 3D field ELM suppressed H-mode, gradients are increased and TGLF predicts that a large increase in linear growth rate is primarily responsible for the increased turbulence. Power balance analysis using ONETWO is also consistent with the changes in electron thermal transport being due to the increased turbulence. These new findings are significant since they i) provide a physics explanation of these changes via TGLF analysis and enable validation of the model in the key pedestal region, and ii) support the hypothesis that turbulent transport partially replaces ELM-dominated transport during ELM-free operation. These results form a basis to develop a predictive understanding of pedestal regulation in ELM suppressed regimes. Supported by the US DOE under DE-FG02-08ER54984, DE-FC02-04ER54698.

Active flutter suppression using dipole filters

NASA Technical Reports Server (NTRS)

Srinathkumar, S.; Waszak, Martin R.

1992-01-01

By using traditional control concepts of gain root locus, the active suppression of a flutter mode of a flexible wing is examined. It is shown that the attraction of the unstable mode towards a critical system zero determines the degree to which the flutter mode can be stabilized. For control situations where the critical zero is adversely placed in the complex plane, a novel compensation scheme called a 'Dipole' filter is proposed. This filter ensures that the flutter mode is stabilized with acceptable control energy. The control strategy is illustrated by designing flutter suppression laws for an active flexible wing (AFW) wind-tunnel model, where minimal control effort solutions are mandated by control rate saturation problems caused by wind-tunnel turbulence.

The simulation on diode-clamped five-level converters common-mode voltage suppression with zero-vector PWM strategy

NASA Astrophysics Data System (ADS)

Zhang, Yonggao; Gao, Yanli; Long, Lizhong

2012-04-01

More and more researchers have great concern on the issue of Common-mode voltage (CMV) in high voltage large power converter. A novel common-mode voltage suppression scheme based on zero-vector PWM strategy (ZVPWM) is present in this paper. Taking a diode-clamped five-level converter as example, the principle of zero vector PWM common-mode voltage (ZCMVPWM) suppression method is studied in detail. ZCMVPWM suppression strategy is including four important parts, which are locating the sector of reference voltage vector, locating the small triangular sub-sector of reference voltage vector, reference vector synthesis, and calculating the operating time of vector. The principles of four important pars are illustrated in detail and the corresponding MATLAB models are established. System simulation and experimental results are provided. It gives some consultation value for the development and research of multi-level converters.

Manipulation and control of instabilities for surfactant-laden liquid film flowing down an inclined plane using a deformable solid layer

NASA Astrophysics Data System (ADS)

Tomar, Dharmendra S.; Sharma, Gaurav

2018-01-01

We analyzed the linear stability of surfactant-laden liquid film with a free surface flowing down an inclined plane under the action of gravity when the inclined plane is coated with a deformable solid layer. For a flow past a rigid incline and in the presence of inertia, the gas-liquid (GL) interface is prone to the free surface instability and the presence of surfactant is known to stabilize the free surface mode when the Marangoni number increases above a critical value. The rigid surface configuration also admits a surfactant induced Marangoni mode which remains stable for film flows with a free surface. This Marangoni mode was observed to become unstable for a surfactant covered film flow past a flexible inclined plane in a creeping flow limit when the wall is made sufficiently deformable. In view of these observations, we investigate the following two aspects. First, what is the effect of inertia on Marangoni mode instability induced by wall deformability? Second, and more importantly, whether it is possible to use a deformable solid coating to obtain stable flow for the surfactant covered film for cases when the Marangoni number is below the critical value required for stabilization of free surface instability. In order to explore the first question, we continued the growth rates for the Marangoni mode from the creeping flow limit to finite Reynolds numbers (Re) and observed that while the increase in Reynolds number has a small stabilizing effect on growth rates, the Marangoni mode still remains unstable for finite Reynolds numbers as long as the wall is sufficiently deformable. The Marangoni mode remains the dominant mode for zero and small Reynolds numbers until the GL mode also becomes unstable with the increase in Re. Thus, for a given set of parameters and beyond a critical Re, there is an exchange of dominant mode of instability from the Marangoni to free surface GL mode. With respect to the second important aspect, our results clearly demonstrate that for cases when the stabilizing contribution of surfactant is not sufficient for suppressing GL mode instability, a deformable solid coating could be employed to suppress free surface instability without triggering Marangoni or liquid-solid interfacial modes. Specifically, we have shown that for a given solid thickness, as the shear modulus of the solid layer decreases (i.e., the solid becomes more deformable) the GL mode instability is suppressed. With further decrease in shear modulus, the Marangoni and liquid-solid interfacial modes become unstable. Thus, there exists a stability window in terms of shear modulus where the surfactant-laden film flow remains stable even when the Marangoni number is below the critical value required for free surface instability suppression. Further, when the Marangoni number is greater than the critical value so that the GL mode remains stable in the rigid limit or with the deformable wall, the increase in wall deformability or solid thickness triggers Marangoni mode instability and, thus, renders a stable flow configuration into an unstable one. Thus, we show that the soft solid layer can be used to manipulate and control the stability of surfactant-laden film flows.

Cooperative Couplings between Octahedral Rotations and Ferroelectricity in Perovskites and Related Materials

NASA Astrophysics Data System (ADS)

Gu, Teng; Scarbrough, Timothy; Yang, Yurong; Íñiguez, Jorge; Bellaiche, L.; Xiang, H. J.

2018-05-01

The structure of AB O 3 perovskites is dominated by two types of unstable modes, namely, the oxygen octahedral rotation (AFD) and ferroelectric (FE) mode. It is generally believed that such AFD and FE modes tend to compete and suppress each other. Here we use first-principles methods to show that a dual nature of the FE-AFD coupling, which turns from competitive to cooperative as the AFD mode strengthens, occurs in numerous perovskite oxides. We provide a unified model of such a dual interaction by introducing novel high-order coupling terms and explain the atomistic origin of the resulting new form of ferroelectricity in terms of universal steric mechanisms. We also predict that such a novel form of ferroelectricity leads to atypical behaviors, such as an enhancement of all the three Cartesian components of the electric polarization under hydrostatic pressure and compressive epitaxial strain.

Efficient single-mode operation of a cladding-pumped ytterbium-doped helical-core fiber laser.

PubMed

Wang, P; Cooper, L J; Sahu, J K; Clarkson, W A

2006-01-15

A novel approach to achieving robust single-spatial-mode operation of cladding-pumped fiber lasers with multimode cores is reported. The approach is based on the use of a fiber geometry in which the core has a helical trajectory within the inner cladding to suppress laser oscillation on higher-order modes. In a preliminary proof-of-principle study, efficient single-mode operation of a cladding-pumped ytterbium-doped helical-core fiber laser with a 30 microm diameter core and a numerical aperture of 0.087 has been demonstrated. The laser yielded 60.4 W of output at 1043 nm in a beam with M2 < 1.4 for 92.6 W launched pump power from a diode stack at 976 nm. The slope efficiency at pump powers well above threshold was approximately 84%, which compares favorably with the slope efficiencies achievable with conventional straight-core Yb-doped double-clad fiber lasers.

Suppression of large edge-localized modes in high-confinement DIII-D plasmas with a stochastic magnetic boundary.

PubMed

Evans, T E; Moyer, R A; Thomas, P R; Watkins, J G; Osborne, T H; Boedo, J A; Doyle, E J; Fenstermacher, M E; Finken, K H; Groebner, R J; Groth, M; Harris, J H; La Haye, R J; Lasnier, C J; Masuzaki, S; Ohyabu, N; Pretty, D G; Rhodes, T L; Reimerdes, H; Rudakov, D L; Schaffer, M J; Wang, G; Zeng, L

2004-06-11

A stochastic magnetic boundary, produced by an applied edge resonant magnetic perturbation, is used to suppress most large edge-localized modes (ELMs) in high confinement (H-mode) plasmas. The resulting H mode displays rapid, small oscillations with a bursty character modulated by a coherent 130 Hz envelope. The H mode transport barrier and core confinement are unaffected by the stochastic boundary, despite a threefold drop in the toroidal rotation. These results demonstrate that stochastic boundaries are compatible with H modes and may be attractive for ELM control in next-step fusion tokamaks.

Active control for vibration suppression in a flexible beam using a modal domain optical fiber sensor

NASA Technical Reports Server (NTRS)

Cox, D. E.; Lindner, D. K.

1991-01-01

An account is given of the use of a modal-domain (MD) fiber-optic sensor as an active control system component for vibration suppression, whose output is proportional to the integral of the axial strain along the optical fiber. When an MD sensor is attached to, or embedded in, a flexible structure, it senses the strain in the structure along its gage length. On the basis of the present integration of the sensor model into a flexible-structure model, it becomes possible to design a control system with a dynamic compensator which adds damping to the low-order modes of the flexible structure. This modeling procedure has been experimentally validated.

Generation of Higher Order Modes in a Rectangular Duct

NASA Technical Reports Server (NTRS)

Gerhold, Carl H.; Cabell, Randolph H.; Brown, Donald E.

2004-01-01

Advanced noise control methodologies to reduce sound emission from aircraft engines take advantage of the modal structure of the noise in the duct. This noise is caused by the interaction of rotor wakes with downstream obstructions such as exit guide vanes. Mode synthesis has been accomplished in circular ducts and current active noise control work has made use of this capability to cancel fan noise. The goal of the current effort is to examine the fundamental process of higher order mode propagation through an acoustically treated, curved duct. The duct cross-section is rectangular to permit greater flexibility in representation of a range of duct curvatures. The work presented is the development of a feedforward control system to generate a user-specified modal pattern in the duct. The multiple-error, filtered-x LMS algorithm is used to determine the magnitude and phase of signal input to the loudspeakers to produce a desired modal pattern at a set of error microphones. Implementation issues, including loudspeaker placement and error microphone placement, are discussed. Preliminary results from a 9-3/8 inch by 21 inch duct, using 12 loudspeakers and 24 microphones, are presented. These results demonstrate the ability of the control system to generate a user-specified mode while suppressing undesired modes.

All-fiber-based selective mode multiplexer and demultiplexer for weakly-coupled mode-division multiplexed systems

NASA Astrophysics Data System (ADS)

Igarashi, Koji; Park, Kyung Jun; Tsuritani, Takahiro; Morita, Itsuro; Kim, Byoung Yoon

2018-02-01

We show all-fiber-based selective mode multiplexers and demultiplexers for weakly-coupled mode-division multiplexed systems. We fabricate a set of six-mode multiplexer and demultiplexer based on fiber mode selective couplers, and experimentally evaluate the performance for the six-mode dual-polarization (DP) quadrature phase shift keying (QPSK) optical signals. In the mode multiplexer and demultiplexer, the mode couplings between the lower three modes and the higher three modes are suppressed to be less than -20 dB, which enables us to apply partial 6 ×6 MIMO equalizers even for the six-mode demultiplexing. For the six-mode DP-QPSK signals, the penalty of optical signal-to-noise ratio by replacing the full 12 ×12MIMO to the partial 6 ×6 MIMO is suppressed by less than 1 dB.

Superimposed coherent terahertz wave radiation from mono-energetically bunched multi-beam

DOE PAGES

Shin, Young -Min; Fermi National Accelerator Lab.

2012-06-27

Intense coherent radiation is obtained from multiple electron beams monochromatically bunched over the wide higher-order-mode (HOM) spectral band in the THz regime. The overmoded waveguide corrugated by dielectric-implanted staggered gratings superimposes evanescent waves emitted from the low energy electron beams. The dispersion and transmission simulations of the three-beam slow wave structure show that the first two fundamental modes (more » $$TE_{10}$$ and $$TE_{20}$$) are considerably suppressed ($$\\sim-50$$ dB) below the multi-beam resonating mode ($$TE_{30}$$) at the THz regime (0.8–1.24 THz). The theoretical calculations and particle-in-cell simulations show that with significantly higher interaction impedance and power growth rate radiation of the $$TE_{30}$$ mode is $$\\sim$$23 dBm and $$\\sim$$50 dBm stronger than the $$TE_{10}$$ and $$TE_{20}$$ modes around 1 THz, respectively. As a result, this highly selective HOM multi-beam interaction has potential applications for power THz sources and high intensity accelerators.« less

Effect of ripple taper on band-gap overlap in a coaxial Bragg structure operating at terahertz frequency

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

Ding Xueyong; Li Hongfan; Lv Zhensu

Based on the mode-coupling method, numerical analysis is presented to demonstrate the influence of ripple taper on band-gap overlap in a coaxial Bragg structure operating at terahertz frequency. Results show that the interval between the band-gaps of the competing mode and the desired working mode is narrowed by use of positive-taper ripples, but is expanded if negative-taper ripples are employed, and the influence of the negative-taper ripples is obviously more advantageous than the positive-taper ripples; the band-gap overlap of modes can be efficiently separated by use of negative-taper ripples. The residual side-lobes of the frequency response in a coaxial Braggmore » structure with ripple taper also can be effectively suppressed by employing the windowing-function technique. These peculiarities provide potential advantage in constructing a coaxial Bragg cavity with high quality factor for single higher-order-mode operation of a high-power free-electron maser in the terahertz frequency range.« less

Design, analysis, and testing of high frequency passively damped struts

NASA Technical Reports Server (NTRS)

Yiu, Y. C.; Davis, L. Porter; Napolitano, Kevin; Ninneman, R. Rory

1993-01-01

Objectives of the research are: (1) to develop design requirements for damped struts to stabilize control system in the high frequency cross-over and spill-over range; (2) to design, fabricate and test viscously damped strut and viscoelastically damped strut; (3) to verify accuracy of design and analysis methodology of damped struts; and (4) to design and build test apparatus, and develop data reduction algorithm to measure strut complex stiffness. In order to meet the stringent performance requirements of the SPICE experiment, the active control system is used to suppress the dynamic responses of the low order structural modes. However, the control system also inadvertently drives some of the higher order modes unstable in the cross-over and spill-over frequency range. Passive damping is a reliable and effective way to provide damping to stabilize the control system. It also improves the robustness of the control system. Damping is designed into the SPICE testbed as an integral part of the control-structure technology.

Suppression of an acoustic mode by an elastic mode of a liquid-filled spherical shell resonator.

PubMed

Lonzaga, Joel B; Raymond, Jason L; Mobley, Joel; Gaitan, D Felipe

2011-02-01

The purpose of this paper is to report on the suppression of an approximately radial (radially symmetric) acoustic mode by an elastic mode of a water-filled, spherical shell resonator. The resonator, which has a 1-in. wall thickness and a 9.5-in. outer diameter, was externally driven by a small transducer bolted to the external wall. Experiments showed that for the range of drive frequencies (19.7-20.6 kHz) and sound speeds in water (1520-1570 m/s) considered in this paper, a nonradial (radially nonsymmetric) mode was also excited, in addition to the radial mode. Furthermore, as the sound speed in the liquid was changed, the resonance frequency of the nonradial mode crossed with that of the radial one and the amplitude of the latter was greatly reduced near the crossing point. The crossing of the eigenfrequency curves of these two modes was also predicted theoretically. Further calculations demonstrated that while the radial mode is an acoustic one associated with the interior fluid, the nonradial mode is an elastic one associated with the shell. Thus, the suppression of the radial acoustic mode is apparently caused by the overlapping with the nonradial elastic mode near the crossing point.

Mode competition and hopping in optomechanical nano-oscillators

NASA Astrophysics Data System (ADS)

Zhang, Xingwang; Lin, Tong; Tian, Feng; Du, Han; Zou, Yongchao; Chau, Fook Siong; Zhou, Guangya

2018-04-01

We investigate the inter-mode nonlinear interaction in the multi-mode optomechanical nano-oscillator which consists of coupled silicon nanocantilevers, where the integrated photonic crystal nanocavities provide the coupling between the optical and mechanical modes. Due to the self-saturation and cross-saturation of the mechanical gain, the inter-mode competition is observed, which leads to the bistable operation of the optomechanical nano-oscillator: only one of the mechanical modes can oscillate at any one time, and the oscillation of one mode extremely suppresses that of the other with a side mode suppression ratio (SMSR) up to 40 dB. In the meantime, mode hopping, i.e., the optomechanical oscillation switches from one mode to the other, is also observed and found to be able to be provoked by excitation laser fluctuations.

Suppression of type-I ELMs with reduced RMP coil set on DIII-D

DOE PAGES

Orlov, Dmitriy M.; Moyer, Richard A.; Evans, Todd E.; ...

2016-02-19

Recent experiments on DIII-D have demonstrated that having a toroidally-monochromatic spectral content of edge-resonant magnetic perturbations (RMPs) is not a necessary condition for suppression of Edge Localized Modes (ELMs). Robust ELM suppression has been reproducibly obtained on DIII-D during experiments in which various non-axisymmetric coil loops were turned off pseudo-randomly producing a variety of n=1, n=2, and n=3 spectral contributions. It was shown that RMP ELM suppression could be achieved with as few as 5 out of 12 internal coil loops (I-coils) on DIII-D at similar coil currents and with good plasma confinement. Linear MHD plasma response (M3DC1, IPEC, MARS)more » and vacuum (SURFMN, TRIP3D) modeling have been performed in order to understand the effects of the perturbation spectrum on the plasma response and ELM suppression. The results suggest that reduction of the dominant n=3 perturbation field is compensated by increased n=2 field in the plasma that may lead to RMP ELM suppression at lower levels of n=3 perturbative magnetic flux from the I-coils. These results provide additional confidence that ITER may be capable of RMP ELM suppression in the event of multiple internal coil failures.« less

Optical Add-Drop Filters Based on Photonic Crystal Ring Resonators

DTIC Science & Technology

2007-02-19

34 Appl. Phys. Lett. 81,2499-2501 (2002). 17. V. Dinesh Kumar , T. Srinivas, A. Selvarajan, "Investigation of ring resonators in photonic crystal...No.4 / opncs EXPRESS 1824 Kumar et al. [17], where a large single quasi-rectangular ring was introduced as the frequency selective dropping elements...were introduced by Kumar et al. as well, in order to suppress the counter propagating modes which can cause spurious dips in the transmission spectrum

Quantitative Surface Analysis of a Binary Drug Mixture—Suppression Effects in the Detection of Sputtered Ions and Post-Ionized Neutrals

NASA Astrophysics Data System (ADS)

Karras, Gabriel; Lockyer, Nicholas P.

2014-05-01

A systematic mass spectrometric study of two of the most common analgesic drugs, paracetamol and ibuprofen, is reported. The drugs were studied by means of secondary ion mass spectrometry (SIMS) and secondary neutral mass spectrometry (SNMS) using laser post-ionization (LPI) both in pure samples and in a two-component mixture. Ion suppression within the two-component system observed in SIMS mode is ameliorated using LPI under room temperature analysis. However, suppression effects are apparent in LPI mode on performing the analysis at cryogenic temperatures, which we attribute to changes in the desorption characteristics of sputtered molecules, which influences the subsequent post-ionization efficiency. This suggests different mechanisms of ion suppression in SIMS and LPI modes.

Weakly-coupled 4-mode step-index FMF and demonstration of IM/DD MDM transmission.

PubMed

Hu, Tao; Li, Juhao; Ge, Dawei; Wu, Zhongying; Tian, Yu; Shen, Lei; Liu, Yaping; Chen, Su; Li, Zhengbin; He, Yongqi; Chen, Zhangyuan

2018-04-02

Weakly coupled-mode division multiplexing (MDM) over few-mode fibers (FMF) for short-reach transmission has attracted great interest, which can avoid multiple-input-multiple-output digital signal processing (MIMO-DSP) by greatly suppressing modal crosstalk. In this paper, step-index FMF supporting 4 linearity polarization (LP) modes for MIMO-free transmission is designed and fabricated for the first time, to our knowledge. Modal crosstalk of the fiber is suppressed by increasing the mode effective refractive index differences. The same fabrication method as standard single-mode fiber is adopted so that it is practical and cost-effective. The mode multiplexer/demultiplexer (MUX/DEMUX) consists of cascaded mode-selective couplers (MSCs), which are designed and fabricated by tapering the proposed FMF with single-mode fiber (SMF). The mode MUX and DEMUX achieve very low modal crosstalk not only for the multiplexing/demultiplexing but also for the coupling to/from the FMF. Based on the fabricated FMF and mode MUX/DEMUX, we successfully demonstrate the first simultaneous 4-modes (LP 01 , LP 11 , LP 21 & LP 31 ) 10-km FMF transmission with 10-Gb/s intensity modulation and MIMO-free direct detection (IM/DD). The modal crosstalk of the whole transmission link is successfully suppressed to less than -16.5 dB. The experimental results indicate that FMF with simple step-index structure supporting 4 weakly-coupled modes is feasible.

Single-mode annular chirally-coupled core fibers for fiber lasers

NASA Astrophysics Data System (ADS)

Zhang, Haitao; Hao, He; He, Linlu; Gong, Mali

2018-03-01

Chirally-coupled core (CCC) fiber can transmit single fundamental mode and effectively suppresses higher-order mode (HOM) propagation, thus improve the beam quality. However, the manufacture of CCC fiber is complicated due to its small side core. To decrease the manufacture difficulty in China, a novel fiber structure is presented, defined as annular chirally-coupled core (ACCC) fiber, replacing the small side core by a larger side annulus. In this paper, we designed the fiber parameters of this new structure, and demonstrated that the new structure has a similar property of single mode with traditional CCC fiber. Helical coordinate system was introduced into the finite element method (FEM) to analyze the mode field in the fiber, and the beam propagation method (BPM) was employed to analyze the influence of the fiber parameters on the mode loss. Based on the result above, the fiber structure was optimized for efficient single-mode transmission, in which the core diameter is 35 μm with beam quality M2 value of 1.04 and an optical to optical conversion efficiency of 84%. In this fiber, fundamental mode propagates in an acceptable loss, while the HOMs decay rapidly.

Transverse mode selection in vertical-cavity surface-emitting lasers via deep impurity-induced disordering

NASA Astrophysics Data System (ADS)

O'Brien, Thomas R.; Kesler, Benjamin; Dallesasse, John M.

2017-02-01

Top emission 850-nm vertical-cavity surface-emitting lasers (VCSELs) demonstrating transverse mode selection via impurity-induced disordering (IID) are presented. The IID apertures are fabricated via closed ampoule zinc diffusion. A simple 1-D plane wave model based on the intermixing of Group III atoms during IID is presented to optimize the mirror loss of higher-order modes as a function of IID strength and depth. In addition, the impact of impurity diffusion into the cap layer of the lasers is shown to improve contact resistance. Further investigation of the mode-dependent characteristics of the device imply an increase in the thermal impedance associated with the fraction of IID contained within the oxide aperture. The optimization of the ratio of the IID aperture to oxide aperture is experimentally determined. Single fundamental mode output of 1.6 mW with 30 dBm side mode suppression ratio is achieved by a 3.0 μm oxide-confined device with an IID aperture of 1.3 μm indicating an optimal IID aperture size of 43% of the oxide aperture.

Stabilization of time domain acoustic boundary element method for the exterior problem avoiding the nonuniqueness.

PubMed

Jang, Hae-Won; Ih, Jeong-Guon

2013-03-01

The time domain boundary element method (TBEM) to calculate the exterior sound field using the Kirchhoff integral has difficulties in non-uniqueness and exponential divergence. In this work, a method to stabilize TBEM calculation for the exterior problem is suggested. The time domain CHIEF (Combined Helmholtz Integral Equation Formulation) method is newly formulated to suppress low order fictitious internal modes. This method constrains the surface Kirchhoff integral by forcing the pressures at the additional interior points to be zero when the shortest retarded time between boundary nodes and an interior point elapses. However, even after using the CHIEF method, the TBEM calculation suffers the exponential divergence due to the remaining unstable high order fictitious modes at frequencies higher than the frequency limit of the boundary element model. For complete stabilization, such troublesome modes are selectively adjusted by projecting the time response onto the eigenspace. In a test example for a transiently pulsating sphere, the final average error norm of the stabilized response compared to the analytic solution is 2.5%.

Suppression of the noise-induced effects in an electrostatic micro-plate using an adaptive back-stepping sliding mode control.

PubMed

Nwagoum Tuwa, Peguy Roussel; Woafo, P

2018-01-01

In this work, an adaptive backstepping sliding mode control approach is applied through the piezoelectric layer in order to control and to stabilize an electrostatic micro-plate. The mathematical model of the system by taking into account the small fluctuations in the gap considered as bounded noise is carried out. The accuracy of the proposed modal equation is proven using the method of lines. By using both approaches, the effects of noise are presented. It is found that they lead to pull-in instability as well as to random chaos. A suitable backstepping approach to improve the tracking performance is integrated to the adaptive sliding mode control in order to eliminate chattering phenomena and reinforce the robustness of the system in presence of uncertainties and external random disturbances. It is proved that all the variables of the closed-loop system are bounded and the system can follow the given reference signals as close as possible. Numerical simulations are provided to show the effectiveness of proposed controller. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.

Assessing the Importance of the Evaporation-Wind Feedback Mechanism in the Modulation of Simulated Madden-Julian Oscillations

NASA Technical Reports Server (NTRS)

Colon, Edward; Lindesay, James; Suarez, Max J.

1998-01-01

An examination of simulated Madden-Julian Oscillation (MJO) response to active and suppressed air-sea interactions is made using an aquaplanet model employing a realistic representation of the hydrologic cyle. In general, the evaporation-wind feedback (EWF) results from a coupling between tropical zonal surface wind stresses and evaporation anomalies. Recent observational and theoretical studies have questioned the significance of EWF in sustaining the predominantly wavenumber 1 eastward propagating mode commonly attributed to the interaction between large scale convergence and cumulus-scale convection (conditional instability of the second kind, CISK). To ascertain the nature of the EWF dependence on lower boundary conditions and thus quantify its effect on MJO development, a series of numerical experiments were conducted employing various zonally symmetric sea surface temperature (SST) distributions with active and suppressed EWF mechanisms. Results suggest that a correlation exists between tropical SSTs and the efficacy of the EWF in vertically redistributing heat acquired through surface wind stresses. It has been determined that the removal of the EWF is not a crucial factor in the dampening of the simulated MJO at high equatorial SSTs. The additional energy fed into the developing convective mode by the EWF selectively amplifies higher order wave modes in all numerical experiments thus boosting overall variances in oscillatory responses.

Search for multipolar instability in URu2Si2 studied by ultrasonic measurements under pulsed magnetic field

NASA Astrophysics Data System (ADS)

Yanagisawa, T.; Mombetsu, S.; Hidaka, H.; Amitsuka, H.; Cong, P. T.; Yasin, S.; Zherlitsyn, S.; Wosnitza, J.; Huang, K.; Kanchanavatee, N.; Janoschek, M.; Maple, M. B.; Aoki, D.

2018-04-01

The elastic properties of URu2Si2 in the high magnetic field region above 40 T, over a wide temperature range from 1.5 to 120 K, were systematically investigated by means of high-frequency ultrasonic measurements. The investigation was performed at high magnetic fields to better investigate the innate bare 5 f -electron properties, since the unidentified electronic thermodynamic phase of unknown origin, the so-called "hidden order" (HO), and associated hybridization of conduction and f electrons (c -f hybridization) are suppressed at high magnetic fields. From the three different transverse modes we find contrasting results; both the Γ4(B2 g) and Γ5(Eg) symmetry modes C66 and C44 show elastic softening that is enhanced above 30 T, while the characteristic softening of the Γ3(B1 g) symmetry mode (C11-C12)/2 is suppressed in high magnetic fields. These results underscore the presence of a hybridization-driven Γ3(B1 g) lattice instability in URu2Si2 . However, the results from this work cannot be explained by using existing crystalline electric field schemes applied to the quadrupolar susceptibility in a local 5 f2 configuration. Instead, we present an analysis based on a band Jahn-Teller effect.

Effects of spatiotemporal variation of soil salinity on fine root distribution in different plant configuration modes in new reclamation coastal saline field.

PubMed

Jiang, Hong; Du, Hongyu; Bai, Yingying; Hu, Yue; Rao, Yingfu; Chen, Chong; Cai, Yongli

2016-04-01

In order to study the effects of salinity on plant fine roots, we considered three different plant configuration modes (tree stand model (TSM), shrub stand model (SSM), and tree-shrub stand model (TSSM)). Soil samples were collected with the method of soil drilling. Significant differences of electrical conductivity (EC) in the soil depth of 0-60 cm were observed among the three modes (p < 0.05). In the above three modes, the variation of soil salinity among various soil layers and monthly variation of soil salinity were the highest in SSM and reached 2.30 and 2.23 mS/cm (EC1:5), respectively. Due to the effect of salinity, fine root biomass (FRB) showed significant differences in different soil depths (p < 0.05). More than 60% of FRB was concentrated in the soil depth above 30 cm. FRB showed exponential decline with soil depth (p < 0.05). FRB showed spatial heterogeneity in the 40-cm soil depth. In the above three modes, compared with FRB, specific root length (SRL) and fine root length density (FRLD) showed the similar changing trend. Fine roots showed significant seasonal differences among different modes (p < 0.05). FRB showed the bimodal variation and was the highest in July. However, we found that the high content of salts had obvious inhibitory effect on the distribution of FRB. Therefore, the salinity should be below 1.5 mS/cm, which was suitable for the growth of plant roots. Among the three modes, TSSM had the highest FRB, SRL, and FRLD and no obvious soil salt accumulation was observed. The results indicated that fine root biomass was affected by high salt and that TSSM had the strong effects of salt suppression and control. In our study, TSSM may be the optimal configuration mode for salt suppression and control in saline soil.

Study of Uneven Fills to Cure the Coupled-Bunch Instability in SRRC

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

Chao, Alex W.

2002-08-12

The performance of the 1.5-GeV storage ring light source TLS in SRRC has been limited by a longitudinal coupled-bunch beam instability. To improve the performance of the TLS, the beam instability has to be suppressed. One possible way considered for the TLS to suppress its coupled-bunch instability uses uneven filling patterns according to the theory of Prabhakar[1]. By knowing the harmful high-order-modes (HOMs), a special filling pattern can be designed to utilize either mode coupling or Landau damping to cure beam instability. In TLS the HOMs are contributed from the Doris RF cavity installed in the storage ring. The HOMsmore » of a 3-D Doris cavity was numerically analyzed. Filling patterns with equal bunch current according to theory had been calculated to cure the most harmful HOM. A longitudinal particle tracking program was used to simulate the coupled-bunch beam instability with both the uniform filling and the special designed filling. Filling pattern with unequal bunch current was also studied. The results of the simulation were discussed and compared to the theory.« less

Effect of ionization suppression by trace impurities in mobile phase water on the accuracy of quantification by high-performance liquid chromatography/mass spectrometry.

PubMed

Herath, H M D R; Shaw, P N; Cabot, P; Hewavitharana, A K

2010-06-15

The high-performance liquid chromatography (HPLC) column is capable of enrichment/pre-concentration of trace impurities in the mobile phase during the column equilibration, prior to sample injection and elution. These impurities elute during gradient elution and result in significant chromatographic peaks. Three types of purified water were tested for their impurity levels, and hence their performances as mobile phase, in HPLC followed by total ion current (TIC) mode of MS. Two types of HPLC-grade water produced 3-4 significant peaks in solvent blanks while LC/MS-grade water produced no peaks (although peaks were produced by LC/MS-grade water also after a few days of standing). None of the three waters produced peaks in HPLC followed by UV-Vis detection. These peaks, if co-eluted with analyte, are capable of suppressing or enhancing the analyte signal in a MS detector. As it is not common practice to run solvent blanks in TIC mode, when quantification is commonly carried out using single ion monitoring (SIM) or single or multiple reaction monitoring (SRM or MRM), the effect of co-eluting impurities on the analyte signal and hence on the accuracy of the results is often unknown to the analyst. Running solvent blanks in TIC mode, regardless of the MS mode used for quantification, is essential in order to detect this problem and to take subsequent precautions. Copyright (c) 2010 John Wiley & Sons, Ltd.

Design and measurement of a TE{sub 13} input converter for high order mode gyrotron travelling wave amplifiers

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

Wang, Yan; Liu, Guo, E-mail: liuguo@uestc.edu.cn; Shu, Guoxiang

2016-03-15

A technique to launch a circular TE{sub 13} mode to interact with the helical electron beam of a gyrotron travelling wave amplifier is proposed and verified by simulation and cold test in this paper. The high order (HOM) TE{sub 13} mode is excited by a broadband Y-type power divider with the aid of a cylindrical waveguide system. Using grooves and convex strips loaded at the lateral planes of the output cylindrical waveguide, the electric fields of the potential competing TE{sub 32} and TE{sub 71} modes are suppressed to allow the transmission of the dominant TE{sub 13} mode. The converter performancemore » for different structural dimensions of grooves and convex strips is studied in detail and excellent results have been achieved. Simulation predicts that the average transmission is ∼−1.8 dB with a 3 dB bandwidth of 7.2 GHz (91.5–98.7 GHz) and port reflection is less than −15 dB. The conversion efficiency to the TE{sub 32} and TE{sub 71} modes are, respectively, under −15 dB and −24 dB in the operating frequency band. Such an HOM converter operating at W-band has been fabricated and cold tested with the radiation boundary. Measurement from the vector network analyzer cold test and microwave simulations show a good reflection performance for the converter.« less

Three-dimensional equilibria and island energy transport due to resonant magnetic perturbation edge localized mode suppression on DIII-D

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

King, J. D.; Strait, Edward J.; Nazikian, Raffi

2015-11-01

Experiments in the DIII-D tokamak show that the plasma responds to resonant magnetic perturbations (RMP) with toroidal mode numbers of n = 2 and n = 3 without field line reconnection, consistent with resistive magnetohydrodynamic predictions (MHD), while a strong nonlinear bifurcation is apparent when edge localized modes (ELM) are suppressed. The magnetic response associated with this bifurcation is localized to the high field side (HFS) of the machine and exhibits a dominant n = 1 component despite the application of a constant amplitude, slowly toroidally rotating, n = 2 applied field. The n = 1 mode is born lockedmore » to the vacuum vessel wall, while the n = 2 mode is entrained to the rotating field. Based on these magnetic response measurements, and Thomson scattering measurements of flattening of the electron temperature profile it is likely that these modes are magnetic island chains near the H-mode pedestal. The reduction in ∇T e occurs near the q = 4 and 5 rational surfaces, suggesting five unique islands are possible (m = 8, 9 or 10 for n = 2) and (m = 4 or 5 for n = 1). In all cases, the island width is estimated to be 2 ~ 3 cm. The Chang-Callen calculated confinement degradation due to the presence of an individual island of this size is 8 ~ 12%, which is close to the 13 ~ 14% measured between the ELMing and suppressed states. This suggests that edge tearing modes may alter the pedestal causing peeling ballooning stability during resonant magnetic perturbation (RMP) induced ELM suppression.« less

Far-field emission characteristics and linewidth measurements of surface micro-machined MEMS tunable VCSELs

NASA Astrophysics Data System (ADS)

Paul, Sujoy; Gierl, Christian; Gründl, Tobias; Zogal, Karolina; Meissner, Peter; Amann, Markus-Christian; Küppers, Franko

2013-03-01

In this paper, we demonstrate for the first time the far-field experimental results and the linewidth characteris- tics for widely tunable surface-micromachined micro-electro-mechanical system (MEMS) vertical-cavity surface- emitting lasers (VCSELs) operating at 1550 nm. The fundamental Gaussian mode emission is confirmed by optimizing the radius of curvature of top distributed Bragg reflector (DBR) membrane and by choosing an ap- propriate diameter of circular buried tunnel junctions (BTJs) so that only the fundamental Gaussian mode can sustain. For these VCSELs, a mode-hop free continuous tuning over 100 nm has already been demonstrated, which is achieved by electro-thermal tuning of the MEMS mirror. The fiber-coupled optical power of 2mW over the entire tuning range has been reported. The singlemode laser emission has more than 40 dB of side-mode suppression ratio (SMSR). The smallest linewidth achieved with these of MEMS tunable VCSELs is 98MHz which is one order of magnitude higher than that of fixed-wavelength VCSELs.

Acoustic theory of axisymmetric multisectioned ducts. [reduction of turbofan engine noise

NASA Technical Reports Server (NTRS)

Zorumski, W. E.

1974-01-01

Equations are developed for the acoustic field in a duct system which is made up of a number of connected circular and annular ducts. These equations are suitable for finding the acoustic field inside of and radiated from an aircraft turbofan engine. Acoustic modes are used as generalized coordinates in order to develop a set of matrix equations for the acoustic field. Equations for these modes are given for circular and annular ducts with uniform flow. Modal source equations are derived for point acoustic sources. General equations for mode transmission and reflection are developed and detailed equations are derived for ducts with multiple sections of acoustic treatment and for ducts with circumferential splitter rings. The general theory is applied to the special case of a uniform area circular duct with multisection liners and it is shown that the mode reflection effects are proportional to differences of the acoustic admittances of adjacent liners. A numerical example is given which shows that multisection liners may provide greater noise suppression than uniform liners.

Revealing spatio-spectral electroencephalographic dynamics of musical mode and tempo perception by independent component analysis.

PubMed

Lin, Yuan-Pin; Duann, Jeng-Ren; Feng, Wenfeng; Chen, Jyh-Horng; Jung, Tzyy-Ping

2014-02-28

Music conveys emotion by manipulating musical structures, particularly musical mode- and tempo-impact. The neural correlates of musical mode and tempo perception revealed by electroencephalography (EEG) have not been adequately addressed in the literature. This study used independent component analysis (ICA) to systematically assess spatio-spectral EEG dynamics associated with the changes of musical mode and tempo. Empirical results showed that music with major mode augmented delta-band activity over the right sensorimotor cortex, suppressed theta activity over the superior parietal cortex, and moderately suppressed beta activity over the medial frontal cortex, compared to minor-mode music, whereas fast-tempo music engaged significant alpha suppression over the right sensorimotor cortex. The resultant EEG brain sources were comparable with previous studies obtained by other neuroimaging modalities, such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET). In conjunction with advanced dry and mobile EEG technology, the EEG results might facilitate the translation from laboratory-oriented research to real-life applications for music therapy, training and entertainment in naturalistic environments.

ALON® Components With Tunable Dielectric Properties for High Power Accelerator Applications

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

Goldman, Lee M; Jha, Santosh K; Lobur, Nicole

There are challenges in linear particle accelerators associated with the need to suppress “higher order modes” (HOMs). HOMs are detrimental to accelerator operation as they are a source of beam instability. The absorption/suppression of HOMs and dissipation of the energy of higher order modes is vital to the function of these accelerators. Surmet has identified ALON® Optical Ceramic (Aluminum Oxynitride), a hard, durable ceramic that is fabricated through conventional powder processing techniques, as a potential material for HOM absorber. In this Phase I program, Surmet has produced new ALON-composite HOM absorber materials that function at both ambient and cryogenic temperatures.more » The composite materials were developed and evaluated in collaboration with Thomas Jefferson National Labs. Success in this Phase I and the potential Phase II will demonstrate the utility of ALON composite components for RF absorbing applications and lay the groundwork for commercialization of such products, with applications in basic science, medical and digital electronics industries.« less

Renormalization of dijet operators at order 1 /Q 2 in soft-collinear effective theory

NASA Astrophysics Data System (ADS)

Goerke, Raymond; Inglis-Whalen, Matthew

2018-05-01

We make progress towards resummation of power-suppressed logarithms in dijet event shapes such as thrust, which have the potential to improve high-precision fits for the value of the strong coupling constant. Using a newly developed formalism for Soft-Collinear Effective Theory (SCET), we identify and compute the anomalous dimensions of all the operators that contribute to event shapes at order 1 /Q 2. These anomalous dimensions are necessary to resum power-suppressed logarithms in dijet event shape distributions, although an additional matching step and running of observable-dependent soft functions will be necessary to complete the resummation. In contrast to standard SCET, the new formalism does not make reference to modes or λ-scaling. Since the formalism does not distinguish between collinear and ultrasoft degrees of freedom at the matching scale, fewer subleading operators are required when compared to recent similar work. We demonstrate how the overlap subtraction prescription extends to these subleading operators.

Asymmetric dual-loop feedback to suppress spurious tones and reduce timing jitter in self-mode-locked quantum-dash lasers emitting at 155 μm

NASA Astrophysics Data System (ADS)

Asghar, Haroon; McInerney, John G.

2017-09-01

We demonstrate an asymmetric dual-loop feedback scheme to suppress external cavity side-modes induced in self-mode-locked quantum-dash lasers with conventional single and dual-loop feedback. In this letter, we achieved optimal suppression of spurious tones by optimizing the length of second delay time. We observed that asymmetric dual-loop feedback, with large (~8x) disparity in cavity lengths, eliminates all external-cavity side-modes and produces flat RF spectra close to the main peak with low timing jitter compared to single-loop feedback. Significant reduction in RF linewidth and reduced timing jitter was also observed as a function of increased second feedback delay time. The experimental results based on this feedback configuration validate predictions of recently published numerical simulations. This interesting asymmetric dual-loop feedback scheme provides simplest, efficient and cost effective stabilization of side-band free optoelectronic oscillators based on mode-locked lasers.

Gain media edge treatment to suppress amplified spontaneous emission in a high power laser

DOEpatents

Hackel, Lloyd A [Livermore, CA; Soules, Thomas F [Livermore, CA; Fochs, Scott N [Livermore, CA; Rotter, Mark D [San Ramon, CA; Letts, Stephan A [San Ramon, CA

2011-02-22

A novel method and apparatus for suppressing ASE and/or parasitic oscillation modes in a laser is introduced. By roughening one or more peripheral edges of a solid-state crystal or ceramic laser gain media and by bonding such edges to a predetermined electromagnetic absorbing material arranged adjacent to the entire outer surface of the peripheral edges of the roughened laser gain media, ASE, parasitic oscillation modes and/or residual pump energy can be effectively suppressed.

Terahertz vibrational modes of the rigid crystal phase of succinonitrile.

PubMed

Nickel, Daniel V; Delaney, Sean P; Bian, Hongtao; Zheng, Junrong; Korter, Timothy M; Mittleman, Daniel M

2014-04-03

Succinonitrile (N ≡ C-CH2-CH2-C ≡ N), an orientationally disordered molecular plastic crystal at room temperature, exhibits rich phase behavior including a solid-solid phase transition at 238 K. In cooling through this phase transition, the high-temperature rotational disorder of the plastic crystal phase is frozen out, forming a rigid crystal that is both spatially and orientationally ordered. Using temperature-dependent terahertz time-domain spectroscopy, we characterize the vibrational modes of this low-temperature crystalline phase for frequencies from 0.3 to 2.7 THz and temperatures ranging from 20 to 220 K. Vibrational modes are observed at 1.122 and 2.33 THz at 90 K. These modes are assigned by solid-state density functional theory simulations, corresponding respectively to the translation and rotation of the molecules along and about their crystallographic c-axis. In addition, we observe a suppression of the phonon modes as the concentration of dopants, in this case a lithium salt (LiTFSI), increases, indicating the importance of doping-induced disorder in these ionic conductors.

Surfing gravitational waves: can bigravity survive growing tensor modes?

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

Amendola, Luca; Könnig, Frank; Martinelli, Matteo

The theory of bigravity offers one of the simplest possibilities to describe a massive graviton while having self-accelerating cosmological solutions without a cosmological constant. However, it has been shown recently that bigravity is affected by early-time fast growing modes on the tensor sector. Here we argue that we can only trust the linear analysis up to when perturbations are in the linear regime and use a cut-off to stop the growing of the metric perturbations. This analysis, although more consistent, still leads to growing tensor modes that are unacceptably large for the theory to be compatible with measurements of themore » cosmic microwave background (CMB), both in temperature and polarization spectra. In order to suppress the growing modes and make the model compatible with CMB spectra, we find it necessary to either fine-tune the initial conditions, modify the theory or set the cut-off for the tensor perturbations of the second metric much lower than unity. Initial conditions such that the growing mode is sufficiently suppresed can be achieved in scenarios in which inflation ends at the GeV scale.« less

Interface width effect on the classical Rayleigh-Taylor instability in the weakly nonlinear regime

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

Wang, L. F.; State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Beijing 100083; Ye, W. H.

2010-05-15

In this paper, the interface width effects (i.e., the density gradient effects or the density transition layer effects) on the Rayleigh-Taylor instability (RTI) in the weakly nonlinear (WN) regime are investigated by numerical simulation (NS). It is found that the interface width effects dramatically influence the linear growth rate in the linear growth regime and the mode coupling process in the WN growth regime. First, the interface width effects decrease the linear growth rate of the RTI, particularly for the short perturbation wavelengths. Second, the interface width effects suppress (reduce) the third-order feedback to the fundamental mode, which induces themore » nonlinear saturation amplitude (NSA) to exceed the classical prediction, 0.1lambda. The wider the density transition layer is, the larger the NSA is. The NSA in our NS can reach a half of its perturbation wavelength. Finally, the interface width effects suppress the generation and the growth of the second and the third harmonics. The ability to suppress the harmonics' growth increases with the interface width but decreases with the perturbation wavelength. On the whole, in the WN regime, the interface width effects stabilize the RTI, except for an enhancement of the NSA, which is expected to improve the understanding of the formation mechanism for the astrophysical jets, and for the jetlike long spikes in the high energy density physics.« less

Effective squeezing enhancement via measurement-induced non-Gaussian operation and its application to the dense coding scheme

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

Kitagawa, Akira; Takeoka, Masahiro; Sasaki, Masahide

2005-08-15

We study the measurement-induced non-Gaussian operation on the single- and two-mode Gaussian squeezed vacuum states with beam splitters and on-off type photon detectors, with which mixed non-Gaussian states are generally obtained in the conditional process. It is known that the entanglement can be enhanced via this non-Gaussian operation on the two-mode squeezed vacuum state. We show that, in the range of practical squeezing parameters, the conditional outputs are still close to Gaussian states, but their second order variances of quantum fluctuations and correlations are effectively suppressed and enhanced, respectively. To investigate an operational meaning of these states, especially entangled states,more » we also evaluate the quantum dense coding scheme from the viewpoint of the mutual information, and we show that non-Gaussian entangled state can be advantageous compared with the original two-mode squeezed state.« less

Test of the multiquark structure of a1(1420 ) in strong two-body decays

NASA Astrophysics Data System (ADS)

Gutsche, Thomas; Ivanov, Mikhail A.; Körner, Jürgen G.; Lyubovitskij, Valery E.; Xu, Kai

2017-12-01

We present an analysis of strong two-body decays of the a1(1420 ) with JP C=1++ recently reported by the COMPASS Collaboration at CERN. Following the interpretation of the COMPASS Collaboration that the a1 is an unusual state with a four-quark q q ¯s s ¯ structure we consider two possible configurations for this state—hadronic molecular and color diquark-antidiquark structures. We find that the dominant decay mode of the a1 is the decay into K and K*. In particular, we calculate that the four decay modes a1→V P with V P =K*±K∓, K*0K¯0, K¯*0K0 together give a dominant contribution to the measured total width of about 150 MeV. The observational mode a1→f0(980 )+π0 is significantly suppressed by one order of magnitude.

Numerical design and analysis of parasitic mode oscillations for 95 GHz gyrotron beam tunnel

NASA Astrophysics Data System (ADS)

Kumar, Nitin; Singh, Udaybir; Yadav, Vivek; Kumar, Anil; Sinha, A. K.

2013-05-01

The beam tunnel, equipped with the high lossy ceramics, is designed for 95 GHz gyrotron. The geometry of the beam tunnel is optimized considering the maximum RF absorption (ideally 100%) and the suppression of parasitic oscillations. The excitation of parasitic modes is a concerning problem for high frequency, high power gyrotrons. Considering the problem of parasitic mode excitation in beam tunnel, a detail analysis is performed for the suppression of these kinds of modes. Trajectory code EGUN and CST Microwave Studio are used for the simulations of electron beam trajectory and electromagnetic analysis, respectively.

Compensation for large tensor modes with iso-curvature perturbations in CMB anisotropies

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

Kawasaki, Masahiro; Yokoyama, Shuichiro, E-mail: kawasaki@icrr.u-tokyo.ac.jp, E-mail: shu@icrr.u-tokyo.ac.jp

Recently, BICEP2 has reported the large tensor-to-scalar ratio r = 0.2{sup +0.07}{sub −0.05} from the observation of the cosmic microwave background (CMB) B-mode at degree-scales. Since tensor modes induce not only CMB B-mode but also the temperature fluctuations on large scales, to realize the consistent temperature fluctuations with the Planck result we should consider suppression of scalar perturbations on corresponding large scales. To realize such a suppression, we consider anti-correlated iso-curvature perturbations which could be realized in the simple curvaton model.

On magnetothermal instability in cluster cooling flows

NASA Technical Reports Server (NTRS)

Balbus, Steven A.

1991-01-01

Lagrangian techniques appropriate to a local calculation are used to show that a weak ordered magnetic field can result in a generic condensational mode in cluster cooling flows. However, thermal instability appears possible only if the conductivity is well below its Spitzer value, for all nonradial wavenumbers. Wavenumbers not subject to conductive damping are subject to buoyant oscillations. It is shown that when instability is present, lateral magnetic confinement of high thermal pressure regions in the plasma by radial magnetic field lines is responsible in at least equal measure with radially directed magnetic tension for the suppression of oscillations and the reappearance of local condensational modes. The general importance of even very modest magnetic fields for destabilizing thermal time scale perturbations is emphasized.

Mode selective generation of guided waves by systematic optimization of the interfacial shear stress profile

NASA Astrophysics Data System (ADS)

Yazdanpanah Moghadam, Peyman; Quaegebeur, Nicolas; Masson, Patrice

2015-01-01

Piezoelectric transducers are commonly used in structural health monitoring systems to generate and measure ultrasonic guided waves (GWs) by applying interfacial shear and normal stresses to the host structure. In most cases, in order to perform damage detection, advanced signal processing techniques are required, since a minimum of two dispersive modes are propagating in the host structure. In this paper, a systematic approach for mode selection is proposed by optimizing the interfacial shear stress profile applied to the host structure, representing the first step of a global optimization of selective mode actuator design. This approach has the potential of reducing the complexity of signal processing tools as the number of propagating modes could be reduced. Using the superposition principle, an analytical method is first developed for GWs excitation by a finite number of uniform segments, each contributing with a given elementary shear stress profile. Based on this, cost functions are defined in order to minimize the undesired modes and amplify the selected mode and the optimization problem is solved with a parallel genetic algorithm optimization framework. Advantages of this method over more conventional transducers tuning approaches are that (1) the shear stress can be explicitly optimized to both excite one mode and suppress other undesired modes, (2) the size of the excitation area is not constrained and mode-selective excitation is still possible even if excitation width is smaller than all excited wavelengths, and (3) the selectivity is increased and the bandwidth extended. The complexity of the optimal shear stress profile obtained is shown considering two cost functions with various optimal excitation widths and number of segments. Results illustrate that the desired mode (A0 or S0) can be excited dominantly over other modes up to a wave power ratio of 1010 using an optimal shear stress profile.

Breaking the glass ceiling: hollow OmniGuide fibers

NASA Astrophysics Data System (ADS)

Johnson, Steven G.; Ibanescu, Mihai; Skorobogatiy, Maksim A.; Weisberg, Ori; Engeness, Torkel D.; Soljacic, Marin; Jacobs, Steven A.; Joannopoulos, John D.; Fink, Yoel

2002-04-01

We argue that OmniGuide fibers, which guide light within a hollow core by concentric multilayer films having the property of omnidirectional reflection, have the potential to lift several physical limitations of silica fibers. We show how the strong confinement in OmniGuide fibers greatly suppresses the properties of the cladding materials: even if highly lossy and nonlinear materials are employed, both the intrinsic losses and nonlinearities of silica fibers can be surpassed by orders of magnitude. This feat, impossible to duplicate in an index-guided fiber with existing materials, would open up new regimes for long-distance propagation and dense wavelength-division multiplexing (DWDM). The OmniGuide-fiber modes bear a strong analogy to those of hollow metallic waveguides; from this analogy, we are able to derive several general scaling laws with core radius. Moreover, there is strong loss discrimination between guided modes, depending upon their degree of confinement in the hollow core: this allows large, ostensibly multi-mode cores to be used, with the lowest-loss TE01 mode propagating in an effectively single-mode fashion. Finally, because this TE01 mode is a cylindrically symmetrical ('azimuthally' polarized) singlet state, it is immune to polarization-mode dispersion (PMD), unlike the doubly-degenerate linearly-polarized modes in silica fibers that are vulnerable to birefringence.

Photonic spectra of a Bragg microresonator with a ferroelectric resonator layer

NASA Astrophysics Data System (ADS)

Fedorova, Irina V.; Eliseeva, Svetlana V.; Sementsov, Dmitrij I.

2018-05-01

Transmission spectra of a photonic crystal resonator structure have been obtained where the Bragg dielectric mirrors contain a finite number of periods with an inverted order of layers and the resonator layer is made of a ferroelectric with a permittivity many times exceeding the permittivity of the layers in Bragg mirrors. Almost a complete transmission suppression was detected not only in the photonic band gap (except for a narrow region of the defect mode), but also outside the forbidden band.

Definition of experiments to investigate fire suppressants in microgravity

NASA Technical Reports Server (NTRS)

Reuther, James J.

1990-01-01

Defined and justified here are the conceptual design and operation of a critical set of experiments expected to yield information on suppressants and on suppressant delivery systems under realistic spacecraft-fire conditions (smoldering). Specific experiment parameters are provided on the solid fuel (carbon), oxidants (habitable spacecraft atmospheres), fuel/oxidant supply, mixing mode, and rate (quiescent and finite; ventilated and replenishable), ignition mode, event, and reignition tendency, fire-zone size, fire conditions, lifetime, and consequences (toxicity), suppressants (CO2, H2O, N2) and suppressant delivery systems, and diagnostics. Candidate suppressants were identified after an analysis of how reduced gravity alters combustion, and how these alterations may influence the modes, mechanisms, and capacities of terrestrial agents to suppress unwanted combustion, or fire. Preferred spacecraft suppression concepts included the local, near-quiescent application of a gas, vapor, or mist that has thermophysical fire-suppression activity and is chemically inert under terrestrial (normal gravity) combustion conditions. The scale, number, and duration (about 1 hour) of the proposed low-gravity experiments were estimated using data not only on the limitations imposed by spacecraft-carrier (Shuttle or Space Station Freedom) accommodations, but also data on the details and experience of standardized smolder-suppression experiments at normal gravity. Deliberately incorporated into the conceptual design was sufficient interchangeability for the prototype experimental package to fly either on Shuttle now or Freedom later. This flexibility is provided by the design concept of up to 25 modular fuel canisters within a containment vessel, which permits both integration into existing low-gravity in-space combustion experiments and simultaneous testing of separate experiments to conserve utilities and time.

Suppression criteria of parasitic mode oscillations in a gyrotron beam tunnel

NASA Astrophysics Data System (ADS)

Kumar, Nitin; Singh, Udaybir; Singh, T. P.; Sinha, A. K.

2011-02-01

This paper presents the design criteria of the parasitic mode oscillations suppression for a periodic, ceramic, and copper loaded gyrotron beam tunnel. In such a type of beam tunnel, the suppression of parasitic mode oscillations is an important design problem. A method of beam-wave coupling coefficient and its mathematical formulation are presented. The developed design criteria are used in the beam tunnel design of a 42 GHz gyrotron to be developed for the Indian TOKAMAK system. The role of the thickness and the radius of the beam tunnel copper rings to obtain the developed design criteria are also discussed. The commercially available electromagnetic code CST and the electron trajectory code EGUN are used for the simulations.

Effects of planar shear on the three-dimensional instability in flow past a circular cylinder

NASA Astrophysics Data System (ADS)

Park, Doohyun; Yang, Kyung-Soo

2018-03-01

A Floquet stability analysis has been carried out in order to investigate how a planar shear in wake flow affects the three-dimensional (3D) instability in the near-wake region. We consider a circular cylinder immersed in a freestream with planar shear. The cylinder was implemented in a Cartesian grid system by means of an immersed boundary method. Planar shear tends to promote the primary instability, known as Hopf bifurcation where steady flow bifurcates into time-periodic flow, in the sense that its critical Reynolds number decreases with increasing planar shear. The effects of planar shear on the 3D instability are different depending on the type of 3D instability. The flow asymmetry caused by the planar shear suppresses a QP-type mode but generates a C-type mode. The conventional A and B modes are stabilized by the planar shear, whereas mode C is intensified with increasing shear. The criticality of each 3D mode is discussed, and the neutral stability curves for each 3D mode are presented. The current Floquet results have been validated by using direct numerical simulation for some selected cases of flow parameters.

Three-dimensional equilibria and island energy transport due to resonant magnetic perturbation edge localized mode suppression on DIII-D

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

King, J. D.; Strait, E. J.; Nazikian, R.

In this research, we conducted experiments in the DIII-D tokamak that show that the plasma responds to resonant magnetic perturbations (RMPs) with toroidalmode numbers of n=2 and n=3 without field line reconnection, consistent with resistive magnetohydrodynamic predictions, while a strong nonlinear bifurcation is apparent when edge localized modes(ELMs) are suppressed. The magnetic response associated with this bifurcation is localized to the high field side of the machine and exhibits a dominant n=1 component despite the application of a constant amplitude, slowly toroidally rotating, n=2 applied field. The n=1 mode is born locked to the vacuum vessel wall, while the n=2more » mode is entrained to the rotating field. Based on these magnetic response measurements and Thomson scattering measurements of flattening of the electron temperature profile, it is likely that these modes are magnetic island chains near the H-mode pedestal. The reduction in ∇Te occurs near the q=4 and 5 rational surfaces, suggesting five unique islands are possible (m=8, 9, or 10 for n=2) and (m=4 or 5 for n=1). In all cases, the island width is estimated to be 2–3 cm. The Chang-Callen calculated confinement degradation due to the presence of an individual island of this size is 8%–12%, which is close to the 13%–14% measured between the ELMs and suppressed states. In conclusion, this suggests that edge tearing modes may alter the pedestal causing peeling-ballooning stability during RMP induced ELM suppression.« less

Three-dimensional equilibria and island energy transport due to resonant magnetic perturbation edge localized mode suppression on DIII-D

DOE PAGES

King, J. D.; Strait, E. J.; Nazikian, R.; ...

2015-11-16

In this research, we conducted experiments in the DIII-D tokamak that show that the plasma responds to resonant magnetic perturbations (RMPs) with toroidalmode numbers of n=2 and n=3 without field line reconnection, consistent with resistive magnetohydrodynamic predictions, while a strong nonlinear bifurcation is apparent when edge localized modes(ELMs) are suppressed. The magnetic response associated with this bifurcation is localized to the high field side of the machine and exhibits a dominant n=1 component despite the application of a constant amplitude, slowly toroidally rotating, n=2 applied field. The n=1 mode is born locked to the vacuum vessel wall, while the n=2more » mode is entrained to the rotating field. Based on these magnetic response measurements and Thomson scattering measurements of flattening of the electron temperature profile, it is likely that these modes are magnetic island chains near the H-mode pedestal. The reduction in ∇Te occurs near the q=4 and 5 rational surfaces, suggesting five unique islands are possible (m=8, 9, or 10 for n=2) and (m=4 or 5 for n=1). In all cases, the island width is estimated to be 2–3 cm. The Chang-Callen calculated confinement degradation due to the presence of an individual island of this size is 8%–12%, which is close to the 13%–14% measured between the ELMs and suppressed states. In conclusion, this suggests that edge tearing modes may alter the pedestal causing peeling-ballooning stability during RMP induced ELM suppression.« less

Design and test of three active flutter suppression controllers

NASA Technical Reports Server (NTRS)

Christhilf, David M.; Waszak, Martin R.; Adams, William M.; Srinathkumar, S.; Mukhopadhyay, Vivek

1991-01-01

Three flutter suppression control law design techniques are presented. Each uses multiple control surfaces and/or sensors. The first uses linear combinations of several accelerometer signals together with dynamic compensation to synthesize the modal rate of the critical mode for feedback to distributed control surfaces. The second uses traditional tools (pole/zero loci and Nyquist diagrams) to develop a good understanding of the flutter mechanism and produce a controller with minimal complexity and good robustness to plant uncertainty. The third starts with a minimum energy Linear Quadratic Gaussian controller, applies controller order reduction, and then modifies weight and noise covariance matrices to improve multi-variable robustness. The resulting designs were implemented digitally and tested subsonically on the Active Flexible Wing (AFW) wind tunnel model. Test results presented here include plant characteristics, maximum attained closed-loop dynamic pressure, and Root Mean Square control surface activity. A key result is that simultaneous symmetric and antisymmetric flutter suppression was achieved by the second control law, with a 24 percent increase in attainable dynamic pressure.

Active control of multiple resistive wall modes

NASA Astrophysics Data System (ADS)

Brunsell, P. R.; Yadikin, D.; Gregoratto, D.; Paccagnella, R.; Liu, Y. Q.; Bolzonella, T.; Cecconello, M.; Drake, J. R.; Kuldkepp, M.; Manduchi, G.; Marchiori, G.; Marrelli, L.; Martin, P.; Menmuir, S.; Ortolani, S.; Rachlew, E.; Spizzo, G.; Zanca, P.

2005-12-01

A two-dimensional array of saddle coils at Mc poloidal and Nc toroidal positions is used on the EXTRAP T2R reversed-field pinch (Brunsell P R et al 2001 Plasma Phys. Control. Fusion 43 1457) to study active control of resistive wall modes (RWMs). Spontaneous growth of several RWMs with poloidal mode number m = 1 and different toroidal mode number n is observed experimentally, in agreement with linear MHD modelling. The measured plasma response to a controlled coil field and the plasma response computed using the linear circular cylinder MHD model are in quantitive agreement. Feedback control introduces a linear coupling of modes with toroidal mode numbers n, n' that fulfil the condition |n - n'| = Nc. Pairs of coupled unstable RWMs are present in feedback experiments with an array of Mc × Nc = 4 × 16 coils. Using intelligent shell feedback, the coupled modes are generally not controlled even though the field is suppressed at the active coils. A better suppression of coupled modes may be achieved in the case of rotating modes by using the mode control feedback scheme with individually set complex gains. In feedback with a larger array of Mc × Nc = 4 × 32 coils, the coupling effect largely disappears, and with this array, the main internal RWMs n = -11, -10, +5, +6 are all simultaneously suppressed throughout the discharge (7 8 wall times). With feedback there is a two-fold extension of the pulse length, compared to discharges without feedback.

Gain media edge treatment to suppress amplified spontaneous emission in a high power laser

DOEpatents

Hackel, Lloyd A.; Soules, Thomas F.; Fochs, Scott N.; Rotter, Mark D.; Letts, Stephan A.

2008-12-09

A novel method and apparatus for suppressing ASE and parasitic oscillation modes in a high average power laser is introduced. By roughening one or more peripheral edges of a solid-state crystal or ceramic laser gain media and by bonding such edges using a substantially high index bonding elastomer or epoxy to a predetermined electromagnetic absorbing arranged adjacent to the entire outer surface of the peripheral edges of the roughened laser gain media, ASE and parasitic oscillation modes can be effectively suppressed.

Demonstration of suppressed phonon tunneling losses in phononic bandgap shielded membrane resonators for high-Q optomechanics.

PubMed

Tsaturyan, Yeghishe; Barg, Andreas; Simonsen, Anders; Villanueva, Luis Guillermo; Schmid, Silvan; Schliesser, Albert; Polzik, Eugene S

2014-03-24

Dielectric membranes with exceptional mechanical and optical properties present one of the most promising platforms in quantum opto-mechanics. The performance of stressed silicon nitride nanomembranes as mechanical resonators notoriously depends on how their frame is clamped to the sample mount, which in practice usually necessitates delicate, and difficult-to-reproduce mounting solutions. Here, we demonstrate that a phononic bandgap shield integrated in the membrane's silicon frame eliminates this dependence, by suppressing dissipation through phonon tunneling. We dry-etch the membrane's frame so that it assumes the form of a cm-sized bridge featuring a 1-dimensional periodic pattern, whose phononic density of states is tailored to exhibit one, or several, full band gaps around the membrane's high-Q modes in the MHz-range. We quantify the effectiveness of this phononic bandgap shield by optical interferometry measuring both the suppressed transmission of vibrations, as well as the influence of frame clamping conditions on the membrane modes. We find suppressions up to 40 dB and, for three different realized phononic structures, consistently observe significant suppression of the dependence of the membrane's modes on sample clamping-if the mode's frequency lies in the bandgap. As a result, we achieve membrane mode quality factors of 5 × 10(6) with samples that are tightly bolted to the 8 K-cold finger of a cryostat. Q × f -products of 6 × 10(12) Hz at 300 K and 14 × 10(12) Hz at 8 K are observed, satisfying one of the main requirements for optical cooling of mechanical vibrations to their quantum ground-state.

Nonlinear simulations of particle source effects on edge localized mode

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

Huang, J.; Tang, C. J.; Key Laboratory of High Energy Density Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610064

2015-12-15

The effects of particle source (PS) with different intensities and located positions on Edge Localized Mode (ELM) are systematically studied with BOUT++ code. The results show the ELM size strongly decreases with increasing the PS intensity once the PS is located in the middle or bottom of the pedestal. The effects of PS on ELM depend on the located position of PS. When it is located at the top of the pedestal, peeling-ballooning (P-B) modes can extract more free energy from the pressure gradient and grow up to be a large filament at the initial crash phase and the broadeningmore » of mode spectrum can be suppressed by PS, which leads to more energy loss. When it is located in the middle or bottom of the pedestal, the extraction of free energy by P-B modes can be suppressed, and a small filament is generated. During the turbulence transport phase, the broader mode spectrum suppresses the turbulence transport when PS is located in the middle, while the zonal flow plays an important role in damping the turbulence transport when PS is located at the bottom.« less

Effect of heating on the suppression of tearing modes in tokamaks.

PubMed

Classen, I G J; Westerhof, E; Domier, C W; Donné, A J H; Jaspers, R J E; Luhmann, N C; Park, H K; van de Pol, M J; Spakman, G W; Jakubowski, M W

2007-01-19

The suppression of (neoclassical) tearing modes is of great importance for the success of future fusion reactors like ITER. Electron cyclotron waves can suppress islands, both by driving noninductive current in the island region and by heating the island, causing a perturbation to the Ohmic plasma current. This Letter reports on experiments on the TEXTOR tokamak, investigating the effect of heating, which is usually neglected. The unique set of tools available on TEXTOR, notably the dynamic ergodic divertor to create islands with a fully known driving term, and the electron cyclotron emission imaging diagnostic to provide detailed 2D electron temperature information, enables a detailed study of the suppression process and a comparison with theory.

Smooth adaptive sliding mode vibration control of a flexible parallel manipulator with multiple smart linkages in modal space

NASA Astrophysics Data System (ADS)

Zhang, Quan; Li, Chaodong; Zhang, Jiantao; Zhang, Jianhui

2017-12-01

This paper addresses the dynamic model and active vibration control of a rigid-flexible parallel manipulator with three smart links actuated by three linear ultrasonic motors. To suppress the vibration of three flexible intermediate links under high speed and acceleration, multiple Lead Zirconium Titanate (PZT) sensors and actuators are collocated mounted on each link, forming a smart structure which can achieve self-sensing and self-actuating. The dynamic characteristics and equations of the flexible link incorporated with the PZT sensors and actuator are analyzed and formulated. The smooth adaptive sliding mode based active vibration control is proposed to suppress the vibration of the smart links, and the first and second modes of the three links are targeted to be suppressed in modal space to avoid the spillover phenomenon. Simulations and experiments are implemented to validate the effectiveness of the smart structures and the proposed control laws. Experimental results show that the vibration of the first mode around 92 Hz and the second mode around 240 Hz of the three smart links are reduced respectively by 64.98%, 59.47%, 62.28%, and 45.80%, 36.79%, 33.33%, which further verify the multi-mode vibration control ability of the smooth adaptive sliding mode control law.

Copper-tuned magnetic order and excitations in iron-based superconductors Fe1+yTe1-xSex

NASA Astrophysics Data System (ADS)

Wen, Jinsheng; Xu, Zhijun; Xu, Guangyong; Lumsden, Mark; Matsuda, Masaaki; Valdivia, Patrick; Bourret, Edith; Lee, Dunghai; Gu, Genda; Tranquada, John; Birgeneau, Robert

2012-02-01

We report neutron scattering results on the Cu-substitution effects in the iron-based superconductors, Fe1+yTe1-xSex. In the parent compound, it is found that Cu drives the low-temperature magnetic ground state from long-range commensurate antiferromagnetic order in Fe1.06TeCu0.04 to short-range incommensurate order in FeTeCu0.1. In the former sample, the structural and magnetic ordering temperature is 40 K; in FeTeCu0.1, the structural phase transition is not obvious and a transition to the spin-glass state is found at 22 K. Cu suppresses superconductivity in FeTe0.5Se0.5---Tc is reduced to 7 K with a 2% Cu doping, and no superconductivity is found in the 10% Cu-doped sample. In the meantime, the intensity and energy of the resonance mode are suppressed in the 2% Cu-doped sample, while there is no resonance in the non-superconducting sample. Besides, the low-temperature magnetic excitation spectra are distinct for these two samples, with the superconducting one having an ``hour-glass" shape and the other one having a ``waterfall" shape. Our results provide further insights on the interplay between magnetism and superconductivity in the iron-based superconductors.

Frequency-tunable Pre-stabilized Lasers for LISA via Sideband-locking

NASA Technical Reports Server (NTRS)

Livas, Jeffrey C.; Thorpe, James I.; Numata, Kenji; Mitryk, Shawn; Mueller, Guido; Wand, Vinzenz

2008-01-01

Laser frequency noise mitigation is one of the most challenging aspects of the LISA interferometric measurement system. The unstabilized frequency fluctuations must be suppressed by roughly twelve orders of magnitude in order to achieve stability sufficient for gravitational wave detection. This enormous suppression will be achieved through a combination of stabilization and common-mode rejection. The stabilization component will itself be achieved in two stages: pre-stabilization to a local optical cavity followed by arm-locking to some combination of the inter-spacecraft distances. In order for these two stabilization stages to work simultaneously, the lock-point of the pre-stabilization loop must be frequency tunable. The current baseline stabilization technique, locking to an optical cavity, does not provide tunability between cavity resonances, which are typically spaced by 100s of MHz. Here we present a modification to the traditional Pound-Drever-Hall cavity locking technique that allows the laser to be locked to a cavity resonance with an adjustable frequency offset. This technique requires no modifications to the optical cavity itself, thus preserving the stability of the frequency reference. We present measurements of the system performance and demonstrate that we can meet implement the first two stages of stabilization.

Initial evaluation of commercially available InGaAsP DFB laser diodes for use in high-speed digital fiber optic transceivers

NASA Technical Reports Server (NTRS)

Cook, Anthony L.; Hendricks, Herbert D.

1990-01-01

NASA has been pursuing the development of high-speed fiber-optic transceivers for use in a number of space data system applications. Current efforts are directed toward a high-performance all-integrated-circuit transceiver operating up to the 3-5 Gb/s range. Details of the evaluation and selection of candidate high-speed optical sources to be used in the space-qualified high-performance transceiver are presented. Data on the performance of commercially available DFB (distributed feedback) lasers are presented, and their performance relative to each other and to their structural design with regard to their use in high-performance fiber-optic transceivers is discussed. The DFB lasers were obtained from seven commercial manufacturers. The data taken on each laser included threshold current, differential quantum efficiency, CW side mode suppression radio, wavelength temperature coefficient, threshold temperature coefficient, natural linewidth, and far field pattern. It was found that laser diodes with buried heterostructures and first-order gratings had, in general, the best CW operating characteristics. The modulated characteristics of the DFB laser diodes are emphasized. Modulated linewidth, modulated side mode suppression ratio, and frequency response are discussed.

Development of robust and multi-mode control of tearing in DIII-D

DOE PAGES

Welander, A. S.; La Haye, R.J.; Humphreys, D. A.; ...

2016-06-02

Neoclassical tearing modes (NTMs) are instabilities that can produce undesirable magnetic islands in tokamak plasmas. They can be stabilized by applying electron cyclotron current drive (ECCD) at the island. The NTM control system on DIII-D can now control multiple modes. Each of 6 mirrors that reflect ECCD beams into the plasma can be assigned to different surfaces in the plasma where NTMs are unstable. The control system then steers the mirrors to keep the beams aimed at the surfaces. The system routinely stabilizes one NTM preemptively and has now also been used to control two modes in the same discharge.more » With the “catch-and-subdue” function, ECCD-generating gyrotrons can be turned on when NTMs appear and off after suppression. Newly triggered NTMs can be promptly suppressed if mode onset is detected early and ECCD immediately applied. Early mode detection is achieved in this paper by spectral analysis of Mirnov probes with a band-pass filter for the expected mode frequency. Targeted surfaces are tracked by equilibrium reconstructions (that include measurements of the motional Stark effect). The ECCD position is tracked by ray-tracing using the TORBEAM code. Several techniques are being explored for fine-tuning alignment when NTMs occur. One method adjusts ECCD alignment in steps until the island decays fast enough. A second method sweeps the alignment to find the optimum. A third method pulses gyrotrons and uses electron cyclotron emission to compare where the resulting temperature pulses are relative to temperature fluctuations from a rotating NTM. NTM control in ITER is expected to use active profile regulation to maximize controllability, followed by repeated catch-and-subdue actions if modes are retriggered, in order to maintain island size below the disruptive threshold while maximizing confinement and fusion gain. Between events, real-time tracking will be performed to maintain alignment and readiness for subsequent catch-andsubdue actions. Methods for active probing of stability boundaries will be studied as possible diagnostics for the profile regulation. Finally, selected elements of this ITER NTM control vision will be discussed and assessed.« less

A Demonstration of a Versatile Low-order Wavefront Sensor Tested on Multiple Coronographs

NASA Astrophysics Data System (ADS)

Singh, Garima; Lozi, Julien; Jovanovic, Nemanja; Guyon, Olivier; Baudoz, Pierre; Martinache, Frantz; Kudo, Tomoyuki

2017-09-01

Detecting faint companions in close proximity to stars is one of the major goals of current/planned ground- and space-based high-contrast imaging instruments. High-performance coronagraphs can suppress the diffraction features and gain access to companions at small angular separation. However, the uncontrolled pointing errors degrade the coronagraphic performance by leaking starlight around the coronagraphic focal-plane mask, preventing the detection of companions at small separations. A Lyot-stop low-order wavefront sensor (LLOWFS) was therefore introduced to calibrate and measure these aberrations for focal-plane phase mask coronagraphs. This sensor quantifies the variations in wavefront error decomposed into a few Zernike modes by reimaging the diffracted starlight rejected by a reflective Lyot stop. The technique was tested with several coronagraphs on the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system at the Subaru Telescope. The wavefront was decomposed into 15 and 35 Zernike modes with an occulting and focal-plane phase mask coronagraph, respectively, which were used to drive a closed-loop correction in the laboratory. Using a 2000-actuator deformable mirror, a closed-loop pointing stability between 10-3-10-4 λ/D was achieved in the laboratory in H-band, with sub nanometer residuals for the other Zernike modes (Noll index > 4). On-sky, the low-order control of 10+ Zernike modes for the phase-induced amplitude apodization and the vector vortex coronagraphs was demonstrated, with a closed-loop pointing stability of {10}-4λ /D under good seeing and {10}-3λ /D under moderate seeing conditions readily achievable.

Excitation of parasitic waves in forward-wave amplifiers with weak guiding fields.

PubMed

Nusinovich, G S; Romero-Talamás, C A; Han, Y

2012-12-01

To produce high-power coherent electromagnetic radiation at frequencies from microwaves up to terahertz, the radiation sources should have interaction circuits of large cross sections, i.e., the sources should operate in high-order modes. In such devices, the excitation of higher-order parasitic modes near cutoff where the group velocity is small and, hence, start currents are low can be a serious problem. The problem is especially severe in the sources of coherent, phase-controlled radiation, i.e., the amplifiers or phase-locked oscillators. This problem was studied earlier [Nusinovich, Sinitsyn, and Antonsen, Phys. Rev. E 82, 046404 (2010)] for the case of electron focusing by strong guiding magnetic fields. For many applications it is desirable to minimize these focusing fields. Therefore in this paper we analyze the problem of excitation of parasitic modes near cutoff in forward-wave amplifiers with weak focusing fields. First, we study the large-signal operation of such a device with a signal wave only. Then, we analyze the self-excitation conditions of parasitic waves near cutoff in the presence of the signal wave. It is shown that the main effect is the suppression of the parasitic wave in large-signal regimes. At the same time, there is a region of device parameters where the presence of signal waves can enhance excitation of parasitic modes. The role of focusing fields in such effects is studied.

Lattice and beam optics design for suppression of CSR-induced emittance growth at the KEK-ERL test facility

NASA Astrophysics Data System (ADS)

Shimada, M.; Yokoya, K.; Suwada, T.; Enomoto, A.

2007-06-01

The lattice and beam optics of the arc section of the KEK-ERL test facility, having an energy of 200 MeV, were optimized to efficiently suppress emittance growth based on a simulation using a particle-tracking method taking coherent synchrotron radiation effects into account. The lattice optimization in the arc section was performed under two conditions: a high-current mode with a bunch charge of 76.9 pC without bunch compression, and a short-bunch mode with bunch compression, producing a final bunch length of around 0.1 ps. The simulation results showed that, in the high-current mode, emittance growth was efficiently suppressed by keeping a root-mean-square (rms) bunch length of 1 ps at a bunch charge of 76.9 pC, and in the short-bunch mode, emittance growth was kept within permissible limits with a maximum allowable bunch charge of 23.1 pC at an rms bunch length of 0.1 ps.

Testing models with a nonminimal Higgs sector through the decay t-->q+WZ

NASA Astrophysics Data System (ADS)

Díaz Cruz, J. L.; López Falcón, D. A.

2000-03-01

We study the contribution of the charged Higgs boson to the rare decay of the top quark t-->q+WZ (q=d,s,b) in models with Higgs sectors that include doublets and triplets. Higgs doublets are needed to couple a charged Higgs boson with quarks, whereas the Higgs triplets are required to generate the nonstandard vertex HWZ at the tree level. It is found that within a model that respects the custodial SU(2)c symmetry and avoids flavor-changing neutral current (FCNC) by imposing discrete symmetries, the decay mode t-->b+WZ can reach a branching ratio (BR) of order 10-2, whereas the decay modes t-->(d,s)+WZ, can reach a similar BR in models where FCNC are suppressed by flavor symmetries.

Control of edge localized modes by pedestal deposited impurity in the HL-2A tokamak

NASA Astrophysics Data System (ADS)

Zhang, Y. P.; Mazon, D.; Zou, X. L.; Zhong, W. L.; Gao, J. M.; Zhang, K.; Sun, P.; Dong, C. F.; Cui, Z. Y.; Liu, Yi; Shi, Z. B.; Yu, D. L.; Cheng, J.; Jiang, M.; Xu, J. Q.; Isobe, M.; Xiao, G. L.; Chen, W.; Song, S. D.; Bai, X. Y.; Zhang, P. F.; Yuan, G. L.; Ji, X. Q.; Li, Y. G.; Zhou, Y.; Delpech, L.; Ekedahl, A.; Giruzzi, G.; Hoang, T.; Peysson, Y.; Song, X. M.; Song, X. Y.; Li, X.; Ding, X. T.; Dong, J. Q.; Yang, Q. W.; Xu, M.; Duan, X. R.; Liu, Y.; the HL-2A Team

2018-04-01

Effect of the pedestal deposited impurity on the edge-localized mode (ELM) behaviour has been observed and intensively investigated in the HL-2A tokamak. Impurities have been externally seeded by a newly developed laser blow-off (LBO) system. Both mitigation and suppression of ELMs have been realized by LBO-seeded impurity. Measurements have shown that the LBO-seeded impurity particles are mainly deposited in the pedestal region. During the ELM mitigation phase, the pedestal density fluctuation is significantly increased, indicating that the ELM mitigation may be achieved by the enhancement of the pedestal transport. The transition from ELM mitigation to ELM suppression was triggered when the number of the LBO-seeded impurity exceeds a threshold value. During the ELM suppression phase, a harmonic coherent mode (HCM) is excited by the LBO-seeded impurity, and the pedestal density fluctuation is significantly decreased, the electron density is continuously increased, implying that HCM may reduce the pedestal turbulence, suppress ELMs, increase the pedestal pressure, thus extending the Peeling-Ballooning instability limit. It has been found that the occurance of the ELM mitigation and ELM suppression closely depends on the LBO laser spot diameter.

Suppression of electron temperature gradient turbulence via negative magnetic shear in NSTX.

PubMed

Yuh, H Y; Kaye, S M; Levinton, F M; Mazzucato, E; Mikkelsen, D R; Smith, D R; Bell, R E; Hosea, J C; LeBlanc, B P; Peterson, J L; Park, H K; Lee, W

2011-02-04

Negative magnetic shear is found to suppress electron turbulence and improve electron thermal transport for plasmas in the National Spherical Torus Experiment (NSTX). Sufficiently negative magnetic shear results in a transition out of a stiff profile regime. Density fluctuation measurements from high-k microwave scattering are verified to be the electron temperature gradient (ETG) mode by matching measured rest frequency and linear growth rate to gyrokinetic calculations. Fluctuation suppression under negligible E×B shear conditions confirm that negative magnetic shear alone is sufficient for ETG suppression. Measured electron temperature gradients can significantly exceed ETG critical gradients with ETG mode activity reduced to intermittent bursts, while electron thermal diffusivity improves to below 0.1 electron gyro-Bohms.

Modes of targets in water excited and identified using radiation pressure of modulated focused ultrasound

NASA Astrophysics Data System (ADS)

Daniel, Timothy; Fortuner, Auberry; Abawi, Ahmad; Kirsteins, Ivars; Marston, Philip

2016-11-01

The modulated radiation pressure (MRP) of ultrasound has been widely used to selectively excite low frequency modes of fluid objects. We previously used MRP to excite less compliant metallic object in water including the low frequency modes of a circular metal plate in water. A larger focused ultrasonic transducer allows us to drive modes of larger more-realistic targets. In our experiments solid targets are suspended by strings or supported on sand and the modulated ultrasound is focused on the target's surface. Target sound emissions were recorded and a laser vibrometer was used to measure the surface velocity of the target to give the magnitude of the target response. The source transducer was driven with a doublesideband suppressed carrier voltage as in. By varying the modulation frequency and monitoring target response, resonant frequencies can be measured and compared to finite element models. We also demonstrate the radiation torque of a focused first-order acoustic vortex beam associated with power absorption in the Stokes layer adjacent to a sphere. Funded by ONR.

Supermode noise suppression with mutual injection locking for coupled optoelectronic oscillator.

PubMed

Dai, Jian; Liu, Anni; Liu, Jingliang; Zhang, Tian; Zhou, Yue; Yin, Feifei; Dai, Yitang; Liu, Yuanan; Xu, Kun

2017-10-30

The coupled optoelectronic oscillator (COEO) is typically used to generate high frequency spectrally pure microwave signal with serious sidemodes noise. We propose and experimentally demonstrate a simple scheme for supermode suppression with mutual injection locking between the COEO (master oscillator with multi-modes oscillation) and the embedded free-running oscillator (slave oscillator with single-mode oscillation). The master and slave oscillators share the same electrical feedback path, which means that the mutually injection-locked COEO brings no additional hardware complexity. Owing to the mode matching and mutually injection locking effect, 9.999 GHz signal has been successfully obtained by the mutually injection-locked COEO with the phase noise about -117 dBc/Hz at 10 kHz offset frequency. Besides, the supermode noise can be significantly suppressed more than 50 dB to below -120 dBc.

Convective-core Overshoot and Suppression of Oscillations: Constraints from Red Giants in NGC 6811

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

Arentoft, T.; Brogaard, K.; Jessen-Hansen, J.

Using data from the NASA spacecraft Kepler , we study solar-like oscillations in red giant stars in the open cluster NGC 6811. We determine oscillation frequencies, frequency separations, period spacings of mixed modes, and mode visibilities for eight cluster giants. The oscillation parameters show that these stars are helium-core-burning red giants. The eight stars form two groups with very different oscillation power spectra; the four stars with the lowest Δ ν values display rich sets of mixed l = 1 modes, while this is not the case for the four stars with higher Δ ν . For the four starsmore » with lowest Δ ν , we determine the asymptotic period spacing of the mixed modes, Δ P , which together with the masses we derive for all eight stars suggest that they belong to the so-called secondary clump. Based on the global oscillation parameters, we present initial theoretical stellar modeling that indicates that we can constrain convective-core overshoot on the main sequence and in the helium-burning phase for these ∼2 M {sub ⊙} stars. Finally, our results indicate less mode suppression than predicted by recent theories for magnetic suppression of certain oscillation modes in red giants.« less

Pedestal bifurcation and resonant field penetration at the threshold of edge-localized mode suppression in the DIII-D Tokamak.

PubMed

Nazikian, R; Paz-Soldan, C; Callen, J D; deGrassie, J S; Eldon, D; Evans, T E; Ferraro, N M; Grierson, B A; Groebner, R J; Haskey, S R; Hegna, C C; King, J D; Logan, N C; McKee, G R; Moyer, R A; Okabayashi, M; Orlov, D M; Osborne, T H; Park, J-K; Rhodes, T L; Shafer, M W; Snyder, P B; Solomon, W M; Strait, E J; Wade, M R

2015-03-13

Rapid bifurcations in the plasma response to slowly varying n=2 magnetic fields are observed as the plasma transitions into and out of edge-localized mode (ELM) suppression. The rapid transition to ELM suppression is characterized by an increase in the toroidal rotation and a reduction in the electron pressure gradient at the top of the pedestal that reduces the perpendicular electron flow there to near zero. These events occur simultaneously with an increase in the inner-wall magnetic response. These observations are consistent with strong resonant field penetration of n=2 fields at the onset of ELM suppression, based on extended MHD simulations using measured plasma profiles. Spontaneous transitions into (and out of) ELM suppression with a static applied n=2 field indicate competing mechanisms of screening and penetration of resonant fields near threshold conditions. Magnetic measurements reveal evidence for the unlocking and rotation of tearinglike structures as the plasma transitions out of ELM suppression.

Pedestal Bifurcation and Resonant Field Penetration at the Threshold of Edge-Localized Mode Suppression in the DIII-D Tokamak

DOE PAGES

Nazikian, Raffi; Paz-Soldan, Carlos; Callen, James D.; ...

2015-03-12

Rapid bifurcations in the plasma response to slowly varying n=2 magnetic fields are observed as the plasma transitions into and out of edge localized mode (ELM) suppression. The rapid transition to ELM suppression is characterized by an increase in the toroidal rotation and a reduction in the electron pressure gradient at the top of the pedestal which reduces the perpendicular electron flow to near zero. These events occur simultaneously with an increase in the inner wall magnetic response. These observations are consistent strong resonant field penetration of n=2 fields at the onset of ELM suppression, based on extended MHD simulationsmore » using measured plasma profiles. Spontaneous transitions into (and out of) ELM suppression with a static applied n=2 field indicate competing mechanisms of screening and penetration of resonant fields near threshold conditions. Magnetic measurements reveal evidence for the unlocking and rotation of tearing-like structures as the plasma transitions out of ELM suppression.« less

The effect of periodic wavy profile on suppressing window multipactor under arbitrary electromagnetic mode

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

Chang, C., E-mail: chang@slac.stanford.edu; Key Laboratory of Physical Electronics and Devices of the Ministry of Education, Xi'an Jiaotong University, Xi'an, Shaanxi 710049; Liu, Y. S.

2015-01-05

The three-dimensional periodic ripple profile with each unit of rotational symmetric surface is proposed to suppress multipactor for arbitrary electromagnetic mode with any polarization. The field distribution and multipactor electron dynamics on the wavy surface are studied to illustrate the multipactor inhibition mechanism. High power microwave experiment was conducted to demonstrate the effect of wavy surface on significantly improving the window power capacity.

Magneto-Rayleigh-Taylor instability driven by a rotating magnetic field

NASA Astrophysics Data System (ADS)

Duan, Shuchao; Xie, Weiping; Cao, Jintao; Li, Ding

2018-04-01

In this paper, we analyze theoretically the magneto-Rayleigh-Taylor instability driven by a rotating magnetic field. Slab configurations of finite thickness are treated both with and without using the Wenzel-Kramers-Brillouin approximation. Regardless of the slab thickness, the directional rotation of the driving magnetic field contributes to suppressing these instabilities. The two factors of the finite thickness and directional rotation of the magnetic field cooperate to enhance suppression, with the finite thickness playing a role only when the orientation of the magnetic field is time varying. The suppression becomes stronger as the driving magnetic field rotates faster, and all modes are suppressed, in contrast to the case of a non-rotating magnetic field, for which the vertical mode cannot be suppressed. This implies that the dynamically alternate configuration of a Theta-pinch and a Z-pinch may be applicable to the concept of Theta-Z liner inertial fusion.

The relationships between edge localized modes suppression, pedestal profiles and lithium wall coatings in NSTX

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

Boyle, D. P.; Maingi, R.; Snyder, P. B.

2011-01-01

Recently in the National Spherical Torus Experiment (NSTX), increasing lithium wall coatings suppressed edge localized modes (ELMs), gradually but not quite monotonically. This work details profile and stability analysis as ELMs disappeared throughout the lithium scan. While the quantity of lithium deposited between discharges did not uniquely determine the presence of ELMs, profile analysis demonstrated that lithium was correlated with wider density and pressure pedestals with peak gradients farther from the separatrix. Moreover, the ELMy and ELM-free discharges were cleanly separated by their density and pedestal widths and peak gradient locations. Ultimately, ELMs were only suppressed when lithium caused themore » density pedestal to widen and shift inward. These changes in the density gradient were directly reflected in the pressure gradient and calculated bootstrap current. This supports the theory that ELMs in NSTX are caused by peeling and/or ballooning modes, as kink/peeling modes are stabilized when the edge current and pressure gradient shift away from the separatrix. Edge stability analysis using ELITE corroborated this picture, as reconstructed equilibria from ELM-free discharges were generally farther from their kink/peeling stability boundaries than ELMy discharges. We conclude that density profile control provided by lithium is the key first step to ELM suppression in NSTX.« less

Effects of Sheared Flow on Microinstabilities and Transport in Plasmas

NASA Astrophysics Data System (ADS)

H, Sanuki; K, Itoh; A, Fujisawa; J, Q. Dong

2005-02-01

Theoretical and experimental studies associated with electric field effects on the stability and transport are briefly surveyed. The effects of radial electric field on the suppression and/or enhancement of various microinstabilities such as drift waves, flute mode and temperature gradient modes are discussed. The suppression of flow shear on the electron temperature gradient mode in plasmas with slightly hollow density profiles is investigated by solving the gyrokinetic integral eigenvalue equation. Comparison between theoretical predictions and experimental observations based on the HIBP measurements with high temporal and spatial resolutions is made in bumpy tori and heliotron (CHS) devices.

Passive broadband targeted energy transfers and control of self-excited vibrations

NASA Astrophysics Data System (ADS)

Lee, Young S.

This work consists of the three main parts---Nonlinear energy pumping (that is, passive broadband targeted energy transfers---TETs), and its applications to theoretical and experimental suppression of aeroelastic instabilities. In the first part, nonlinear energy pumping (or TETs) in coupled oscillators is studied. The system is composed of a primary linear subsystem coupled through an essentially nonlinear stiffness and a linear viscous damper to an additional mass (which is called, as a whole, a nonlinear energy sink---NES). By considering the linear damping as a perturbation to the system, periodic solutions of the underlying Hamiltonian system are formulated by means of the non-smooth temporal transformation and solved numerically by a shooting method. The special periodic orbits, which are corresponding to the impulsive initial conditions for the primary subsystem, bear their importance as baits for initiating localized transfers of a significant portion of energy to the NES. The second part theoretically deals with suppression of limit cycle oscillations (LCOs) in self-excited systems by means of passive energy localizations. As a pilot scheme, suppression or even complete elimination of the LCO in a van der Pol (VDP) oscillator coupled with two types of NESS---grounded and ungrounded---is studied. Computational parametric study proves the efficacy of LCO elimination by means of passive nonlinear energy pumping from the VDP oscillator to appropriately designed NESs. The numerical study of the transient dynamics of the system showed that the dynamical mechanism for LCO suppression is a series of 1:1 and 1:3 transient resonance captures, with the damped transient dynamics following closely corresponding resonant manifolds of the underlying Hamiltonian system. It is through the TRCs that energy gets transferred from the VDP oscillator to the NES, thus causing LCO suppression. By performing an additional bifurcation analysis of the steady state responses through a numerical continuation of equilibria and periodic solutions, the parameter dependence and bifurcations of the steady-state solutions are examined. It is also proved that a Hopf bifurcation is the global dynamical mechanism for generation and elimination of the LCOs in the configurations considered. The bifurcation analysis revealed that it is possible to design grounded or ungrounded NESs that robustly and completely eliminate the LCO instability of the system. This should be possible when the system parameters are chosen such that a subcritical Hopf bifurcation occurs, thus assuring the existence of a unique global trivial attractor of the dynamics in the parameter ranges of interest. Then, triggering mechanisms of aeroelastic instability is investigated for a two-DOF rigid wing model in subsonic flow with cubic nonlinear stiffnesses at the support. Based on the observation of the instability triggering, a single-degree-of-freedom (SDOF) NES is applied to the wing model. The NES is attached at an offset from the elastic axis for its additional interaction with the pitch mode, as well as being parallel with the heave mode, primarily to hinder initial triggering of the heave mode by the flow. It is shown that it is feasible to partially or even completely suppress aeroelastic instabilities of the wing by passively transferring vibration energy from the wing to the NES in a one-way irreversible fashion. Moreover, this aeroelastic instability suppression is performed by partially or completely eliminating the triggering mechanists for aeroelastic suppression. Through numerical parametric studies three main mechanisms for suppressing aeroelastic instability are identified: (i) Recurring burst-out and suppression; (ii) intermediate suppression; (iii) complete elimination of instability. In general, the relative occurrence of one of the two limit point cycle (LPC) bifurcations with respect to the Hopf bifurcation decides whether or not the suppression mechanisms are robust. In order to improve robustness of instability suppression, several types of multi-DOF NES configurations are introduced. In the last part, experimental suppression of aeroelastic instability by means of targeted energy transfers is investigated. In order to gain insights into the experiments, theoretical triggering mechanism of the aeroelastic instability in the nonlinear aeroelastic test apparatus (NATA) in a low-speed wind tunnel at Texas A&M University is studied. Finally, experimental results are presented in connection to the theoretical investigation, and all the predictions on the instability suppression mechanisms are demonstrated experimentally. It is also revealed that the dry friction affects only the robustness of an instability suppression by changing the unstable trivial equilibrium into an equilibrium set. (Abstract shortened by UMI.)

Quasiparticle Coherence, Collective Modes, and Competing Order in Cuprate Superconductors

NASA Astrophysics Data System (ADS)

Hinton, James Patrick

In recent years, the study of cuprate superconductors has been dominated by the investigation of normal state properties. Of particular interest is the nature of interactions between superconductivity and other incipient orders which emerge above the superconducting transition temperature, Tc. The discovery of charge density wave (CDW) correlations in YBa2Cu3O6+x (YBCO) and HgBa2CuO 4+d (Hg-1201) has established that some form of charge order is ubiquitous in the cuprates. In this work, we explore the non-equilibrium dynamics of systems which sit near the boundary between superconductivity and competing orders. Ultrafast pump-probe spectroscopy is ideally suited to the study of competing order. Exciting the sample with an optical pulse perturbs the system from equilibrium, altering the balance between the co-existing orders. The return to equilibrium is then monitored by a time-delayed probe pulse, revealing multiple decay processes as well as collective excitations. We first apply this technique to Hg-1201, conducting a detailed study of the phase diagram. At temperatures near Tc, the pump pulse induces a non-equilibrium quasiparticle population. At Tc we observe a doping-dependent peak in the relaxation time of these quasiparticles which we associate with a divergence in the coherence time of the fluctuating CDW. Using heterodyne probing in the transient grating geometry, we are able to disentangle the transient reflectivity components associated with superconductivity and the pseudogap, domonstrating competition across the phase diagram. We also discuss the observation of a sharp transition in the nature of the pseudogap signal at ˜ 11% doping. In YBCO, we explore the temperature and doping dependence of coherent oscillations excited by the pump pulse. We associate these oscillations with the excitation of the CDW amplitude mode, and model their temperature dependence within the framework of a Landau model of competing orders. We conclude with an investigation of pseudogap dynamics in the electron doped compound Nd2-xCexCuO4+d as a function of temperature and doping. Near optimal doping, we observe the impulsive excitation of a critically damped mode, with time-temperature scaling consistent with quantum-critical fluctuations. This mode competes with superconductivity in a dynamical fashion, such that the suppression of this mode below T c can be lifted via photo-evaporation of the superconducting condensate.

MiRNA-Target Interaction Reveals Cell-Specific Post-Transcriptional Regulation in Mammalian Cell Lines

PubMed Central

Kulkarni, Varun; Naqvi, Afsar Raza; Uttamani, Juhi Raju; Nares, Salvador

2016-01-01

MicroRNAs are 18–22 nucleotides long, non-coding RNAs that bind transcripts with complementary sequences leading to either mRNA degradation or translational suppression. However, the inherent differences in preferred mode of miRNA regulation among cells of different origin have not been examined. In our previous transcriptome profiling studies, we observed that post-transcriptional regulation can differ substantially depending on the cell in context. Here we examined mechanistic differences in the regulation of a let-7a targeted (wild type) or resistant (mutant) engineered renilla transcript across various mammalian cell lines of diverse origin. Dual luciferase assays show that compared to mutant (mut), the reporter gene containing wild type (wt) let-7a binding sites was efficiently suppressed upon transfection in various cell lines. Importantly, the strength of miRNA regulation varied across the cell lines. Total RNA analysis demonstrates that wt renilla mRNA was expressed to similar or higher levels compared to mut suggesting that translation repression is a predominant mode of miRNA regulation. Nonetheless, transcript degradation was observed in some cell lines. Ago-2 immunoprecipitation show that miRNA repressed renilla mRNA are associated with functional mi-RISC (miRNA-RNA induced silencing complex). Given the immense potential of miRNA as a therapeutic option, these findings highlight the necessity to thoroughly examine the mode of mRNA regulation in order to achieve the beneficial effects in targeting cells. PMID:26761000

Status of Electron Bernstein Wave (EBW) Research on NSTX and CDX-U

NASA Astrophysics Data System (ADS)

Taylor, G.; Efthimion, P. C.; Jones, B. M.; Wilson, J. R.; Wilgen, J. B.; Bell, G. L.; Bigelow, T. S.; Rasmussen, D. A.; Ram, A. K.; Bers, A.; Harvey, R. W.

2002-11-01

Recent studies of EBWs, via mode conversion (MC) to X-mode electromagnetic radiation on the CDX-U and NSTX spherical torus (ST) plasmas, support the use of EBWs to measure the Te profile and allow local heating and current drive in ST plasmas. An in-vessel antenna with a local adjustable limiter has successfully controlled the density scale length at the MC layer in CDX-U increasing the MC by an order of magnitude to ˜ 100%. A similar technique on NSTX has so far increased MC efficiency fivefold to ˜ 50%. Both results are in good agreement with theoretical predictions. Experiments focused on achieving >= 80% MC on NSTX are planned for the coming year. Ray tracing and Fokker-Planck modeling support the design of a ˜ 1 MW EBW heating and current drive system for NSTX that will assist plasma startup, locally heat electrons, drive non-inductive current and may suppress tearing modes or other MHD that limit high β operation.

Interaction of rotating helical magnetic field with the HIST spherical torus plasmas

NASA Astrophysics Data System (ADS)

Kikuchi, Yusuke; Sugahara, Masato; Yamada, Satoshi; Yoshikawa, Tatsuya; Fukumoto, Naoyuki; Nagata, Masayoshi

2006-10-01

The physical mechanism of current drive by co-axial helicity injection (CHI) has been experimentally investigated on both spheromak and spherical torus (ST) configurations on the HIST device [1]. It has been observed that the n = 1 kink mode rotates toroidally with a frequency of 10-20 kHz in the ExB direction. It seems that the induced toroidal current by CHI strongly relates with the observed rotating kink mode. On the other hand, it is well known that MHD instabilities can be controlled or even suppressed by an externally applied helical magnetic field in tokamak devices. Therefore, we have started to install two sets of external helical coils in order to produce a rotating helical magnetic field on HIST. Mode structures of the generated rotating helical magnetic field and preliminary experimental results of the interaction of the rotating helical magnetic field with the HIST plasmas will be shown in the conference. [1] M. Nagata, et al., Physics of Plasmas 10, 2932 (2003)

Modeling and control for vibration suppression of a flexible smart structure

NASA Technical Reports Server (NTRS)

Dosch, J.; Leo, D.; Inman, D.

1993-01-01

Theoretical and experimental results of the modeling and control of a flexible ribbed antenna are presented. The antenna consists of eight flexible ribs which constitutes a smart antenna in the sense that the actuator and sensors are an integral part of the structure. The antenna exhibits closely space and repeated modes, thus multi-input multi-output (MIMO) control is necessary for controllability and observability of the structure. The structure also exhibits mode localization phenomenon and contains post buckled members making an accurate finite element model of the structure difficult to obtain. An identified MIMO minimum order model of the antenna is synthesized from identified single-input single-output (SISO) transfer functions curve fit in the frequency domain. The identified model is used to design a positive position feedback (PPF) controller that increases damping in all of the modes in the targeted frequency range. Due to the accuracy of the open loop model of the antenna, the closed loop response predicted by the identified model correlates well wtih experimental results.

Magnetic field amplification by the r-mode instability

NASA Astrophysics Data System (ADS)

Chugunov, A. I.; Friedman, J. L.; Lindblom, L.; Rezzolla, L.

2017-12-01

We discuss the magnetic field enhancement by unstable r-modes (driven by the gravitational radiation reaction force) in rotating stars. In the absence of a magnetic field, gravitational radiation exponentially increases the r-mode amplitude α, and accelerates differential rotation (secular motion of fluid elements). For a magnetized star, differential rotation enhances the magnetic field energy. Rezzolla et al (2000-2001) argued that if the magnetic energy grows faster than the gravitational radiation reaction force pumps energy into the r-modes, then the r-mode instability is suppressed. Chugunov (2015) demonstrated that without gravitational radiation, differential rotation can be treated as a degree of freedom decoupled from the r-modes and controlled by the back reaction of the magnetic field. In particular, the magnetic field windup does not damp r-modes. Here we discuss the effect of the back reaction of the magnetic field on differential rotation of unstable r-modes, and show that it limits the generated magnetic field and the magnetic energy growth rate preventing suppression of the r-mode instability by magnetic windup at low saturation amplitudes, α ≪ 1, predicted by current models.

An integrated parity-time symmetric wavelength-tunable single-mode microring laser

PubMed Central

Liu, Weilin; Li, Ming; Guzzon, Robert S.; Norberg, Erik J.; Parker, John S.; Lu, Mingzhi; Coldren, Larry A.; Yao, Jianping

2017-01-01

Mode control in a laser cavity is critical for a stable single-mode operation of a ring laser. In this study we propose and experimentally demonstrate an electrically pumped parity-time (PT)-symmetric microring laser with precise mode control, to achieve wavelength-tunable single-mode lasing with an improved mode suppression ratio. The proposed PT-symmetric laser is implemented based on a photonic integrated circuit consisting of two mutually coupled active microring resonators. By incorporating multiple semiconductor optical amplifiers in the microring resonators, the PT-symmetry condition can be achieved by a precise manipulation of the interplay between the gain and loss in the two microring resonators, and the incorporation of phase modulators in the microring resonators enables continuous wavelength tuning. Single-mode lasing at 1,554.148 nm with a sidemode suppression ratio exceeding 36 dB is demonstrated and the lasing wavelength is continuously tunable from 1,553.800 to 1,554.020 nm. PMID:28497784

An integrated parity-time symmetric wavelength-tunable single-mode microring laser.

PubMed

Liu, Weilin; Li, Ming; Guzzon, Robert S; Norberg, Erik J; Parker, John S; Lu, Mingzhi; Coldren, Larry A; Yao, Jianping

2017-05-12

Mode control in a laser cavity is critical for a stable single-mode operation of a ring laser. In this study we propose and experimentally demonstrate an electrically pumped parity-time (PT)-symmetric microring laser with precise mode control, to achieve wavelength-tunable single-mode lasing with an improved mode suppression ratio. The proposed PT-symmetric laser is implemented based on a photonic integrated circuit consisting of two mutually coupled active microring resonators. By incorporating multiple semiconductor optical amplifiers in the microring resonators, the PT-symmetry condition can be achieved by a precise manipulation of the interplay between the gain and loss in the two microring resonators, and the incorporation of phase modulators in the microring resonators enables continuous wavelength tuning. Single-mode lasing at 1,554.148 nm with a sidemode suppression ratio exceeding 36 dB is demonstrated and the lasing wavelength is continuously tunable from 1,553.800 to 1,554.020 nm.

Surface effects on the red giant branch

NASA Astrophysics Data System (ADS)

Ball, W. H.; Themeßl, N.; Hekker, S.

2018-05-01

Individual mode frequencies have been detected in thousands of individual solar-like oscillators on the red giant branch (RGB). Fitting stellar models to these mode frequencies, however, is more difficult than in main-sequence stars. This is partly because of the uncertain magnitude of the surface effect: the systematic difference between observed and modelled frequencies caused by poor modelling of the near-surface layers. We aim to study the magnitude of the surface effect in RGB stars. Surface effect corrections used for main-sequence targets are potentially large enough to put the non-radial mixed modes in RGB stars out of order, which is unphysical. Unless this can be circumvented, model-fitting of evolved RGB stars is restricted to the radial modes, which reduces the number of available modes. Here, we present a method to suppress gravity modes (g-modes) in the cores of our stellar models, so that they have only pure pressure modes (p-modes). We show that the method gives unbiased results and apply it to three RGB solar-like oscillators in double-lined eclipsing binaries: KIC 8410637, KIC 9540226 and KIC 5640750. In all three stars, the surface effect decreases the model frequencies consistently by about 0.1-0.3 μHz at the frequency of maximum oscillation power νmax, which agrees with existing predictions from three-dimensional radiation hydrodynamics simulations. Though our method in essence discards information about the stellar cores, it provides a useful step forward in understanding the surface effect in RGB stars.

Frequency noise suppression of a single mode laser with an unbalanced fiber interferometer for subnanometer interferometry.

PubMed

Šmíd, Radek; Čížek, Martin; Mikel, Břetislav; Číp, Ondřej

2015-01-12

We present a method of noise suppression of laser diodes by an unbalanced Michelson fiber interferometer. The unstabilized laser source is represented by compact planar waveguide external cavity laser module, ORIONTM (Redfern Integrated Optics, Inc.), working at 1540.57 nm with a 1.5-kHz linewidth. We built up the unbalanced Michelson interferometer with a 2.09 km-long arm based on the standard telecommunication single-mode fiber (SMF-28) spool to suppress the frequency noise by the servo-loop control by 20 dB to 40 dB within the Fourier frequency range, remaining the tuning range of the laser frequency.

Differential BPFs with Multiple Transmission Zeros Based on Terminated Coupled Lines

NASA Astrophysics Data System (ADS)

Niu, Yiming; Yang, Guo; Wu, Wen

2018-04-01

Differential bandpass filters (BPFs) named Filter A and Filter B based on Terminated Coupled Lines (TCLs) are proposed in this letter. The TCLs contributes to not only three poles in differential-mode (DM) for wideband filtering response but also multiple zeros in both DM and common-mode (CM) offering wide DM out-of-band rejection and good CM suppression. Fabricated filters centred at 3.5 GHz with wide DM passband and wideband CM suppression have been designed and measured. The filters improved the noise suppression capability of the communication and radiometer systems. The simulated and measured results are in good agreement.

Control of atomic transition rates via laser-light shaping

NASA Astrophysics Data System (ADS)

Jáuregui, R.

2015-04-01

A modular systematic analysis of the feasibility of modifying atomic transition rates by tailoring the electromagnetic field of an external coherent light source is presented. The formalism considers both the center of mass and internal degrees of freedom of the atom, and all properties of the field: frequency, angular spectrum, and polarization. General features of recoil effects for internal forbidden transitions are discussed. A comparative analysis of different structured light sources is explicitly worked out. It includes spherical waves, Gaussian beams, Laguerre-Gaussian beams, and propagation invariant beams with closed analytical expressions. It is shown that increments in the order of magnitude of the transition rates for Gaussian and Laguerre-Gaussian beams, with respect to those obtained in the paraxial limit, require waists of the order of the wavelength, while propagation invariant modes may considerably enhance transition rates under more favorable conditions. For transitions that can be naturally described as modifications of the atomic angular momentum, this enhancement is maximal (within propagation invariant beams) for Bessel modes, Mathieu modes can be used to entangle the internal and center-of-mass involved states, and Weber beams suppress this kind of transition unless they have a significant component of odd modes. However, if a recoil effect of the transition with an adequate symmetry is allowed, the global transition rate (center of mass and internal motion) can also be enhanced using Weber modes. The global analysis presented reinforces the idea that a better control of the transitions between internal atomic states requires both a proper control of the available states of the atomic center of mass, and shaping of the background electromagnetic field.

Vortex coronagraphs for the Habitable Exoplanet Imaging Mission concept: theoretical performance and telescope requirements

NASA Astrophysics Data System (ADS)

Ruane, Garreth; Mawet, Dimitri; Mennesson, Bertrand; Jewell, Jeffrey; Shaklan, Stuart

2018-01-01

The Habitable Exoplanet Imaging Mission concept requires an optical coronagraph that provides deep starlight suppression over a broad spectral bandwidth, high throughput for point sources at small angular separation, and insensitivity to temporally varying, low-order aberrations. Vortex coronagraphs are a promising solution that performs optimally on off-axis, monolithic telescopes and may also be designed for segmented telescopes with minor losses in performance. We describe the key advantages of vortex coronagraphs on off-axis telescopes such as (1) unwanted diffraction due to aberrations is passively rejected in several low-order Zernike modes relaxing the wavefront stability requirements for imaging Earth-like planets from <10 to >100 pm rms, (2) stars with angular diameters >0.1 λ / D may be sufficiently suppressed, (3) the absolute planet throughput is >10 % , even for unfavorable telescope architectures, and (4) broadband solutions (Δλ / λ > 0.1) are readily available for both monolithic and segmented apertures. The latter make use of grayscale apodizers in an upstream pupil plane to provide suppression of diffracted light from amplitude discontinuities in the telescope pupil without inducing additional stroke on the deformable mirrors. We set wavefront stability requirements on the telescope, based on a stellar irradiance threshold set at an angular separation of 3 ± 0.5λ / D from the star, and discuss how some requirements may be relaxed by trading robustness to aberrations for planet throughput.

Suppressed Superconductivity on the Surface of Superconducting RF Quality Niobium for Particle Accelerating Cavities

NASA Astrophysics Data System (ADS)

Sung, Z. H.; Polyanskii, A. A.; Lee, P. J.; Gurevich, A.; Larbalestier, D. C.

2011-03-01

Significant performance degradation of superconducting RF (radio frequency) niobium cavities in high RF field is strongly associated with the breakdown of superconductivity on localized multi-scale surface defects lying within the 40 nm penetration depth. These defects may be on the nanometer scale, like grain boundaries and dislocations or even at the much larger scale of surface roughness and welding pits. By combining multiple superconducting characterization techniques including magneto-optical (MO) imaging and direct transport measurement with non-contact characterization of the surface topology using scanning confocal microscopy, we were able to show clear evidence of suppression of surface superconductivity at chemically treated RF-quality niobium. We found that pinning of vortices along GBs is weaker than pinning of vortices in the grains, which may indicate suppressed superfluid density on GBs. We also directly measured the local magnetic characteristics of BCP-treated Nb sample surface using a micro-Hall sensor in order to further understanding of the effect of surface topological features on the breakdown of superconducting state in RF mode.

Resolution to the B→πK puzzle

NASA Astrophysics Data System (ADS)

Li, Hsiang-Nan; Mishima, Satoshi; Sanda, A. I.

2005-12-01

We calculate the important next-to-leading-order contributions to the B→πK, ππ decays from the vertex corrections, the quark loops, and the magnetic penguins in the perturbative QCD approach. It is found that the latter two reduce the leading-order penguin amplitudes by about 10% and modify only the B→πK branching ratios. The main effect of the vertex corrections is to increase the small color-suppressed tree amplitude by a factor of 3, which then resolves the large difference between the direct CP asymmetries of the B0→π∓K± and B±→π0K± modes. The puzzle from the large B0→π0π0 branching ratio still remains.

Magnetic field amplification via protostellar disc dynamos

NASA Astrophysics Data System (ADS)

Dyda, S.; Lovelace, R. V. E.; Ustyugova, G. V.; Koldoba, A. V.; Wasserman, I.

2018-06-01

We numerically investigate the generation of a magnetic field in a protostellar disc via an αΩ-dynamo and the resulting magnetohydrodynamic (MHD) driven outflows. We find that for small values of the dimensionless dynamo parameter αd, the poloidal field grows exponentially at a rate σ ∝ Ω _K √{α _d}, before saturating to a value ∝ √{α _d}. The dynamo excites dipole and octupole modes, but quadrupole modes are suppressed, because of the symmetries of the seed field. Initial seed fields too weak to launch MHD outflows are found to grow sufficiently to launch winds with observationally relevant mass fluxes of the order of 10^{-9} M_{⊙} yr^{-1} for T Tauri stars. This suggests that αΩ-dynamos may be responsible for generating magnetic fields strong enough to launch observed outflows.

A Balanced Tri-band PD Based on Microstrip-slotline Transition Structure Embedded Complementary Split-ring Resonators

NASA Astrophysics Data System (ADS)

Chen, Lei; Li, Xiao Yan; Wei, Feng

2017-12-01

A balanced tri-band equal power divider (PD) is proposed based on a balanced stepped-impedance microstrip-slotline transition structure in this paper. Multi-band differential-mode (DM) responses can be realized by embedding multiple complementary split-ring resonators (CSRRs) into the slotline resonator. It is found that a high and wideband common-mode (CM) suppression can be achieved. Moreover, the center frequencies of the DM passbands are independent from the CM ones, which significantly simplifies the design procedure. In order to validate its practicalbility, a balanced PD with three DM passbands centred at 1.57, 2.5 and 3.5 GHz is fabricated and a good agreement between the simulated and measured results is observed. To our best knowledge, a balanced tri-band PD is the first ever reported.

RMP ELM Suppression in DIII-D Plasmas with ITER Similar Shapes and Collisionalities

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

Evans, T.E.; Fenstermacher, M. E.; Moyer, R.A.

2008-01-01

Large Type-I edge localized modes (ELMs) are completely eliminated with small n = 3 resonant magnetic perturbations (RMP) in low average triangularity, = 0.26, plasmas and in ITER similar shaped (ISS) plasmas, = 0.53, with ITER relevant collisionalities ve 0.2. Significant differences in the RMP requirements and in the properties of the ELM suppressed plasmas are found when comparing the two triangularities. In ISS plasmas, the current required to suppress ELMs is approximately 25% higher than in low average triangularity plasmas. It is also found that the width of the resonant q95 window required for ELM suppression is smaller inmore » ISS plasmas than in low average triangularity plasmas. An analysis of the positions and widths of resonant magnetic islands across the pedestal region, in the absence of resonant field screening or a self-consistent plasma response, indicates that differences in the shape of the q profile may explain the need for higher RMP coil currents during ELM suppression in ISS plasmas. Changes in the pedestal profiles are compared for each plasma shape as well as with changes in the injected neutral beam power and the RMP amplitude. Implications of these results are discussed in terms of requirements for optimal ELM control coil designs and for establishing the physics basis needed in order to scale this approach to future burning plasma devices such as ITER.« less

Increased electron temperature turbulence during suppression of edge localized mode by resonant magnetic perturbations in the DIII-D tokamak [Increased electron temperature turbulence during edge localized mode (ELM) suppression by resonant magnetic perturbations (RMPs) in the DIII-D tokamak

DOE PAGES

Sung, Choongki; Wang, G.; Rhodes, Terry L.; ...

2017-11-16

We report the first observation of increased edge electron temperature turbulence correlated with changes in gradients and the ELM suppression time which occurs after the application of resonant magnetic perturbations (RMP) on DIII-D H-mode plasmas. This increase (T ~ e/T e approximately doubles) occurs in the region extending from the top of the pedestal outward to the upper part of the edge steep gradient region. This is significant as it is consistent with increased turbulence driven transport potentially replacing some part of the edge localized mode (ELM) driven transport. However, temperature turbulence does not change with the initial RMP applicationmore » while ELMs are still present, indicating the turbulence changes are not causative in the development of ELM suppression or initial profile evolution with RMP – but rather a response to these effects. This temperature turbulence is broadband and long wavelength, k θρ s < 0.5, where k θ = poloidal wavenumber, ρ s = ion sound gyroradius. As has been reported previously, long wavelength density turbulence (k θρ s < 1.0) in the same location also increases after ELMs were suppressed by the RMP. Since the decrease of the density starts nearly immediately with RMP application, these results suggest that the so-called RMP “density pump-out” is not linked to these long wavelength turbulent transport changes. Comparison with linear stability analysis finds both consistencies and inconsistencies in this important region.« less

Increased electron temperature turbulence during suppression of edge localized mode by resonant magnetic perturbations in the DIII-D tokamak [Increased electron temperature turbulence during edge localized mode (ELM) suppression by resonant magnetic perturbations (RMPs) in the DIII-D tokamak

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

Sung, Choongki; Wang, G.; Rhodes, Terry L.

We report the first observation of increased edge electron temperature turbulence correlated with changes in gradients and the ELM suppression time which occurs after the application of resonant magnetic perturbations (RMP) on DIII-D H-mode plasmas. This increase (T ~ e/T e approximately doubles) occurs in the region extending from the top of the pedestal outward to the upper part of the edge steep gradient region. This is significant as it is consistent with increased turbulence driven transport potentially replacing some part of the edge localized mode (ELM) driven transport. However, temperature turbulence does not change with the initial RMP applicationmore » while ELMs are still present, indicating the turbulence changes are not causative in the development of ELM suppression or initial profile evolution with RMP – but rather a response to these effects. This temperature turbulence is broadband and long wavelength, k θρ s < 0.5, where k θ = poloidal wavenumber, ρ s = ion sound gyroradius. As has been reported previously, long wavelength density turbulence (k θρ s < 1.0) in the same location also increases after ELMs were suppressed by the RMP. Since the decrease of the density starts nearly immediately with RMP application, these results suggest that the so-called RMP “density pump-out” is not linked to these long wavelength turbulent transport changes. Comparison with linear stability analysis finds both consistencies and inconsistencies in this important region.« less

Active control for stabilization of neoclassical tearing modesa)

NASA Astrophysics Data System (ADS)

Humphreys, D. A.; Ferron, J. R.; La Haye, R. J.; Luce, T. C.; Petty, C. C.; Prater, R.; Welander, A. S.

2006-05-01

This work describes active control algorithms used by DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] to stabilize and maintain suppression of 3/2 or 2/1 neoclassical tearing modes (NTMs) by application of electron cyclotron current drive (ECCD) at the rational q surface. The DIII-D NTM control system can determine the correct q-surface/ECCD alignment and stabilize existing modes within 100-500ms of activation, or prevent mode growth with preemptive application of ECCD, in both cases enabling stable operation at normalized beta values above 3.5. Because NTMs can limit performance or cause plasma-terminating disruptions in tokamaks, their stabilization is essential to the high performance operation of ITER [R. Aymar et al., ITER Joint Central Team, ITER Home Teams, Nucl. Fusion 41, 1301 (2001)]. The DIII-D NTM control system has demonstrated many elements of an eventual ITER solution, including general algorithms for robust detection of q-surface/ECCD alignment and for real-time maintenance of alignment following the disappearance of the mode. This latter capability, unique to DIII-D, is based on real-time reconstruction of q-surface geometry by a Grad-Shafranov solver using external magnetics and internal motional Stark effect measurements. Alignment is achieved by varying either the plasma major radius (and the rational q surface) or the toroidal field (and the deposition location). The requirement to achieve and maintain q-surface/ECCD alignment with accuracy on the order of 1cm is routinely met by the DIII-D Plasma Control System and these algorithms. We discuss the integrated plasma control design process used for developing these and other general control algorithms, which includes physics-based modeling and testing of the algorithm implementation against simulations of actuator and plasma responses. This systematic design/test method and modeling environment enabled successful mode suppression by the NTM control system upon first-time use in an experimental discharge.

Thermal transport dynamics in the quasi-single helicity state

NASA Astrophysics Data System (ADS)

McKinney, I. J.; Terry, P. W.

2017-06-01

A dynamical model describing oscillations between multiple and single helicity configurations in the quasi-single helicity (QSH) state of the reversed field pinch [P. W. Terry and G. G. Whelan, Plasma Phys. Controlled Fusion 56, 094003 (2014)] is extended to include electron temperature profile dynamics. It is shown that QSH dynamics is linked to the electron temperature profile because the suppression of mode coupling between tearing modes proposed to underlie QSH also suppresses magnetic-fluctuation-induced thermal transport. Above the threshold of dominant-mode shear that marks the transition to QSH, the model produces temperature-gradient steepening in the strong shear region. Oscillations of the dominant and secondary mode amplitudes give rise to oscillations of the temperature gradient. The phasing and amplitude of temperature gradient oscillations relative to those of the dominant mode are in agreement with experiment. This provides further evidence that the model, while heuristic, captures key physical aspects of the QSH state.

Dual-mass vibratory rate gyroscope with suppressed translational acceleration response and quadrature-error correction capability

NASA Technical Reports Server (NTRS)

Clark, William A. (Inventor); Juneau, Thor N. (Inventor); Lemkin, Mark A. (Inventor); Roessig, Allen W. (Inventor)

2001-01-01

A microfabricated vibratory rate gyroscope to measure rotation includes two proof-masses mounted in a suspension system anchored to a substrate. The suspension has two principal modes of compliance, one of which is driven into oscillation. The driven oscillation combined with rotation of the substrate about an axis perpendicular to the substrate results in Coriolis acceleration along the other mode of compliance, the sense-mode. The sense-mode is designed to respond to Coriolis accelerationwhile suppressing the response to translational acceleration. This is accomplished using one or more rigid levers connecting the two proof-masses. The lever allows the proof-masses to move in opposite directions in response to Coriolis acceleration. The invention includes a means for canceling errors, termed quadrature error, due to imperfections in implementation of the sensor. Quadrature-error cancellation utilizes electrostatic forces to cancel out undesired sense-axis motion in phase with drive-mode position.

Grating enhanced solid-state laser amplifiers

DOEpatents

Erlandson, Alvin C.; Britten, Jerald A.

2010-11-09

A novel method and apparatus for suppressing ASE and parasitic oscillation modes in a high average power laser is introduced. Such an invention, as disclosed herein, uses diffraction gratings to increase gain, stored energy density, and pumping efficiency of solid-state laser gain media, such as, but not limited to rods, disks and slabs. By coupling predetermined gratings to solid-state gain media, such as crystal or ceramic laser gain media, ASE and parasitic oscillation modes can be effectively suppressed.

Electrophysiological evidence for speech-specific audiovisual integration.

PubMed

Baart, Martijn; Stekelenburg, Jeroen J; Vroomen, Jean

2014-01-01

Lip-read speech is integrated with heard speech at various neural levels. Here, we investigated the extent to which lip-read induced modulations of the auditory N1 and P2 (measured with EEG) are indicative of speech-specific audiovisual integration, and we explored to what extent the ERPs were modulated by phonetic audiovisual congruency. In order to disentangle speech-specific (phonetic) integration from non-speech integration, we used Sine-Wave Speech (SWS) that was perceived as speech by half of the participants (they were in speech-mode), while the other half was in non-speech mode. Results showed that the N1 obtained with audiovisual stimuli peaked earlier than the N1 evoked by auditory-only stimuli. This lip-read induced speeding up of the N1 occurred for listeners in speech and non-speech mode. In contrast, if listeners were in speech-mode, lip-read speech also modulated the auditory P2, but not if listeners were in non-speech mode, thus revealing speech-specific audiovisual binding. Comparing ERPs for phonetically congruent audiovisual stimuli with ERPs for incongruent stimuli revealed an effect of phonetic stimulus congruency that started at ~200 ms after (in)congruence became apparent. Critically, akin to the P2 suppression, congruency effects were only observed if listeners were in speech mode, and not if they were in non-speech mode. Using identical stimuli, we thus confirm that audiovisual binding involves (partially) different neural mechanisms for sound processing in speech and non-speech mode. © 2013 Published by Elsevier Ltd.

Global analysis of charmless B decays into two vector mesons in soft-collinear effective theory

NASA Astrophysics Data System (ADS)

Wang, Chao; Zhou, Si-Hong; Li, Ying; Lü, Cai-Dian

2017-10-01

Under the framework of soft-collinear effective theory, we analyze the charmless B →V V decays in a global way at leading power in 1 /mb and leading order in αs with V denoting a light vector meson. In the flavor SU(3) symmetry, decay amplitudes for the 28 decay modes are expressed in terms of eight nonperturbative parameters. We fit these eight nonperturbative parameters with 35 experimental results. Annihilation contributions are neglected due to power suppression in the mb→∞ limit, so we include in the fit the nonperturbative charm penguins, which will play an important role in understanding the direct C P asymmetries. Charming penguins are also responsible for the large transverse polarizations of penguin-dominated and color-suppressed decays. With the best-fitted parameters, we calculate all possible physical observables of 28 decay modes, including branching fractions, direct C P asymmetries, and the complete set of polarization observables. Most of our results are compatible with the present experimental data when available, while others can be examined on the ongoing LHCb experiment and the forthcoming Belle II experiment. Moreover, the agreements and differences with results in QCD factorization and perturbative QCD approach are also discussed. A few observables are suggested to discriminate between these different approaches.

The detection and characterization of high frequency and high wavenumber solar oscillations. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Fernandes, David Neil

1992-01-01

Doppler shift measurements of the Na D(sub 1) absorption line have revealed solar oscillations in a new regime of frequency and wavenumber. Oscillations of vertical velocities in the temperature minimum and low chromosphere of the Sun are observed with frequencies ranging up to 9.5 mHz. There is no evidence for chromospheric modes of 3 minute period. This indicates that the chromosphere does not form a good cavity for acoustic waves. The fundamental-modes appear with wavenumbers up to 5.57 M per m (equivalent spherical harmonic degree, 3877). The frequencies lie below the predicted values at wavenumbers above 1 M per m. The values are in agreement with previous measurements that exist for wavenumbers up to 2.67 M per m. Spatial maps of velocity power show that high wavenumber oscillations are suppressed in active regions. The shape of the power depression indicates that wave motion is affected in the layer of atmosphere where the measurement is made. The f-modes are suppressed in the same way as p-modes, indicating that the mechanism for wave suppression affects velocity fluctuations. Mode frequencies are not affected by the magnetic fields by more than 50 micro Hz, the precision of the measurement.

Frequency Noise Suppression of a Single Mode Laser with an Unbalanced Fiber Interferometer for Subnanometer Interferometry

PubMed Central

Šmíd, Radek; Čížek, Martin; Mikel, Břetislav; Číp, Ondřej

2015-01-01

We present a method of noise suppression of laser diodes by an unbalanced Michelson fiber interferometer. The unstabilized laser source is represented by compact planar waveguide external cavity laser module, ORIONTM (Redfern Integrated Optics, Inc.), working at 1540.57 nm with a 1.5-kHz linewidth. We built up the unbalanced Michelson interferometer with a 2.09 km-long arm based on the standard telecommunication single-mode fiber (SMF-28) spool to suppress the frequency noise by the servo-loop control by 20 dB to 40 dB within the Fourier frequency range, remaining the tuning range of the laser frequency. PMID:25587980

Majorana-assisted nonlocal electron transport through a floating topological superconductor

NASA Astrophysics Data System (ADS)

Ulrich, Jascha; Hassler, Fabian

2015-08-01

The nonlocal nature of the fermionic mode spanned by a pair of Majorana bound states in a one-dimensional topological superconductor has inspired many proposals aiming at demonstrating this property in transport. In particular, transport through the mode from a lead attached to the left bound state to a lead attached to the right will result in current cross correlations. For ideal zero modes on a grounded superconductor, the cross correlations are however completely suppressed in favor of purely local Andreev reflection. In order to obtain a nonvanishing cross correlation, previous studies have required the presence of an additional global charging energy. Adding nonlocal terms in the form of a global charging energy to the Hamiltonian when testing the intrinsic nonlocality of the Majorana modes seems to be conceptually troublesome. Here, we show that a floating superconductor allows observing nonlocal current correlations in the absence of charging energy. We show that the noninteracting and the Coulomb-blockade regime have the same peak conductance e2/h but different shot-noise power; whereas the shot noise is sub-Poissonian in the Coulomb-blockade regime in the large-bias limit, Poissonian shot noise is generically obtained in the noninteracting case.

In-plane modal frequencies and mode shapes of two stay cables interconnected by uniformly distributed cross-ties

NASA Astrophysics Data System (ADS)

Jing, Haiquan; He, Xuhui; Zou, Yunfeng; Wang, Hanfeng

2018-03-01

Stay cables are important load-bearing structural elements of cable-stayed bridges. Suppressing the large vibrations of the stay cables under the external excitations is of worldwide concern for the bridge engineers and researchers. Over the past decade, the use of crosstie has become one of the most practical and effective methods. Extensive research has led to a better understanding of the mechanics of cable networks, and the effects of different parameters, such as length ratio, mass-tension ratio, and segment ratio on the effectiveness of the crosstie have been investigated. In this study, uniformly distributed elastic crossties serve to replace the traditional single, or several cross-ties, aiming to delay "mode localization." A numerical method is developed by replacing the uniformly distributed, discrete elastic cross-tie model with an equivalent, continuously distributed, elastic cross-tie model in order to calculate the modal frequencies and mode shapes of the cable-crosstie system. The effectiveness of the proposed method is verified by comparing the elicited results with those obtained using the previous method. The uniformly distributed elastic cross-ties are shown to significantly delay "mode localization."

Photoactuation behavior of styrene-b-isoprene-b-styrene filled with covalently modified carbon nanotubes

NASA Astrophysics Data System (ADS)

Mosnáček, Jaroslav; Ilčíková, Markéta; Chorvát, Dušan; Czaniková, Klaudia; Krupa, Igor

2012-07-01

Styrene-b-isoprene-b-styrene (Kraton) was used as polymer matrix for preparation of multiwall carbon nanotubes (MWCNT) based nanocomposites. In order to suppress aggregation of the he carbon nanotubes and to improve the interations with the Kraton matrix, the MWCNT were modified with cholesteryl molecules and/or polystyrene chains. The effect of the modification on the composite materials was evaluated by using DMTA. The nanocomposite materials were thermoformed to achieve Braille text elements and their elastic response to light (photoactuation) was tested by atomic force microscopy in a contact mode.

Object Localization Does Not Imply Awareness of Object Category at the Break of Continuous Flash Suppression

PubMed Central

Kobylka, Florian; Persike, Malte; Meinhardt, Günter

2017-01-01

In continuous flash suppression (CFS), a dynamic noise masker, presented to one eye, suppresses conscious perception of a test stimulus, presented to the other eye, until the suppressed stimulus comes to awareness after few seconds. But what do we see breaking the dominance of the masker in the transition period? We addressed this question with a dual-task in which observers indicated (i) whether the test object was left or right of the fixation mark (localization) and (ii) whether it was a face or a house (categorization). As done recently Stein et al. (2011a), we used two experimental varieties to rule out confounds with decisional strategy. In the terminated mode, stimulus and masker were presented for distinct durations, and the observers were asked to give both judgments at the end of the trial. In the self-paced mode, presentation lasted until the observers responded. In the self-paced mode, b-CFS durations for object categorization were about half a second longer than for object localization. In the terminated mode, correct categorization rates were consistently lower than correct detection rates, measured at five duration intervals ranging up to 2 s. In both experiments we observed an upright face advantage compared to inverted faces and houses, as concurrently reported in b-CFS studies. Our findings reveal that more time is necessary to enable observers judging the nature of the object, compared to judging that there is “something other” than the noise which can be localized, but not recognized. This suggests gradual transitions in the first break of CFS. Further, the results imply that suppression is such that no cues to object identity are conveyed in potential “leaks” of CFS (Gelbard-Sagiv et al., 2016). PMID:28663728

Investigation of single lateral mode for 852nm diode lasers with ridge waveguide design

NASA Astrophysics Data System (ADS)

Liu, Chu; Guan, Baolu; Mi, Guoxin; Liao, Yiru; Liu, Zhenyang; Li, Jianjun; Xu, Chen

2016-11-01

852nm Narrow linewidth lasers can be widely used in the field of ultra-fine spectrum measurement, Cs atomic clock control, satellite and optical fiber communication and so on. Furthermore, the stability of the single lateral mode is a very important condition to guarantee the narrow linewidth lasers. Here we investigate experimentally the influence of the narrow ridge structure and asymmetrical waveguide design on the stability single lateral mode of an 852nm diode laser. According to the waveguide theoretical analysis, ridge mesa etch depth (Δη , related to the refractive index difference of parallel to the junction) and ridge mesa width (the narrower the more control force to low order mode) are the main elements for lateral modes. In this paper, we designed different structures to investigate and verify major factors for lateral mode by experiment, and to confirm our thought. Finally, the 5μm mesa ridge laser, 800nm etch depth, with groove structure obtains excellent steady single lateral mode output by 150mA operating current and 30°C temperature. The optical spectrum FWHM is 0.5nm and side mode suppression ratio is 27dBm with uncoated. The laser with 1mm cavity length showed the threshold current of 50mA, a lasing wavelength of λ = 852.6nm, slope efficiency of above 0.7mW/mA. We accomplished single lateral mode of ridge waveguide edge-emitting lasers which can also be used as a laser source in the ultra-narrow linewidth external cavity laser system.

ELM suppression in helium plasmas with 3D magnetic fields

DOE PAGES

Evans, T. E.; Loarte, A.; Orlov, D. M.; ...

2017-06-21

Experiments in DIII-D, using non-axisymmetric magnetic perturbation fields in high-purity low toroidal rotation, 4He plasmas have resulted in Type-I edge localized mode (ELM) suppression and mitigation. Suppression is obtained in plasmas with zero net input torque near the L–H power threshold using either electron cyclotron resonant heating (ECRH) or balanced co- and counter-I p neutral beam injection (NBI) resulting in conditions equivalent to those expected in ITER's non-active operating phase. In low-power ECRH H-modes, periods with uncontrolled density and impurity radiation excursions are prevented by applying n = 3 non-axisymmetric magnetic perturbation fields. ELM suppression results from a reduction andmore » an outward shift of the electron pressure gradient peak compared to that in the high-power ELMing phase. Here, the change in the electron pressure gradient peak is primarily due to a drop in the pedestal temperature rather than the pedestal density.« less

ELM suppression in helium plasmas with 3D magnetic fields

NASA Astrophysics Data System (ADS)

Evans, T. E.; Loarte, A.; Orlov, D. M.; Grierson, B. A.; Knölker, M. M.; Lyons, B. C.; Cui, L.; Gohil, P.; Groebner, R. J.; Moyer, R. A.; Nazikian, R.; Osborne, T. H.; Unterberg, E. A.

2017-08-01

Experiments in DIII-D, using non-axisymmetric magnetic perturbation fields in high-purity low toroidal rotation, 4He plasmas have resulted in Type-I edge localized mode (ELM) suppression and mitigation. Suppression is obtained in plasmas with zero net input torque near the L-H power threshold using either electron cyclotron resonant heating (ECRH) or balanced co- and counter-I p neutral beam injection (NBI) resulting in conditions equivalent to those expected in ITER’s non-active operating phase. In low-power ECRH H-modes, periods with uncontrolled density and impurity radiation excursions are prevented by applying n  =  3 non-axisymmetric magnetic perturbation fields. ELM suppression results from a reduction and an outward shift of the electron pressure gradient peak compared to that in the high-power ELMing phase. The change in the electron pressure gradient peak is primarily due to a drop in the pedestal temperature rather than the pedestal density.

Bi-dimensional empirical mode decomposition based fringe-like pattern suppression in polarization interference imaging spectrometer

NASA Astrophysics Data System (ADS)

Ren, Wenyi; Cao, Qizhi; Wu, Dan; Jiang, Jiangang; Yang, Guoan; Xie, Yingge; Wang, Guodong; Zhang, Sheqi

2018-01-01

Many observers using interference imaging spectrometer were plagued by the fringe-like pattern(FP) that occurs for optical wavelengths in red and near-infrared region. It brings us more difficulties in the data processing such as the spectrum calibration, information retrieval, and so on. An adaptive method based on the bi-dimensional empirical mode decomposition was developed to suppress the nonlinear FP in polarization interference imaging spectrometer. The FP and corrected interferogram were separated effectively. Meanwhile, the stripes introduced by CCD mosaic was suppressed. The nonlinear interferogram background removal and the spectrum distortion correction were implemented as well. It provides us an alternative method to adaptively suppress the nonlinear FP without prior experimental data and knowledge. This approach potentially is a powerful tool in the fields of Fourier transform spectroscopy, holographic imaging, optical measurement based on moire fringe, etc.

Electro-opto-mechanical radio-frequency oscillator driven by guided acoustic waves in standard single-mode fiber

NASA Astrophysics Data System (ADS)

London, Yosef; Diamandi, Hilel Hagai; Zadok, Avi

2017-04-01

An opto-electronic radio-frequency oscillator that is based on forward scattering by the guided acoustic modes of a standard single-mode optical fiber is proposed and demonstrated. An optical pump wave is used to stimulate narrowband, resonant guided acoustic modes, which introduce phase modulation to a co-propagating optical probe wave. The phase modulation is converted to an intensity signal at the output of a Sagnac interferometer loop. The intensity waveform is detected, amplified, and driven back to modulate the optical pump. Oscillations are achieved at a frequency of 319 MHz, which matches the resonance of the acoustic mode that provides the largest phase modulation of the probe wave. Oscillations at the frequencies of competing acoustic modes are suppressed by at least 40 dB. The linewidth of the acoustic resonance is sufficiently narrow to provide oscillations at a single longitudinal mode of the hybrid cavity. Competing longitudinal modes are suppressed by at least 38 dB as well. Unlike other opto-electronic oscillators, no radio-frequency filtering is required within the hybrid cavity. The frequency of oscillations is entirely determined by the fiber opto-mechanics.

Mode transition coordinated control for a compound power-split hybrid car

NASA Astrophysics Data System (ADS)

Wang, Chen; Zhao, Zhiguo; Zhang, Tong; Li, Mengna

2017-03-01

With a compound power-split transmission directly connected to the engine in hybrid cars, dramatic fluctuations in engine output torque result in noticeable jerks when the car is in mode transition from electric drive mode to hybrid drive mode. This study designed a mode transition coordinated control strategy, and verified that strategy's effectiveness with both simulations and experiments. Firstly, the mode transition process was analyzed, and ride comfort issues during the mode transition process were demonstrated. Secondly, engine ripple torque was modeled using the measured cylinder pumping pressure when the engine was not in operation. The complete dynamic plant model of the power-split hybrid car was deduced, and its effectiveness was validated by a comparison of experimental and simulation results. Thirdly, a coordinated control strategy was designed to determine the desired engine torque, motor torque, and the moment of fuel injection. Active damping control with two degrees of freedom, based on reference output shaft speed estimation, was designed to mitigate driveline speed oscillations. Carrier torque estimation based on transmission kinematics and dynamics was used to suppress torque disturbance during engine cranking. The simulation and experimental results indicate that the proposed strategy effectively suppressed vehicle jerks and improved ride comfort during mode transition.

Advanced feedback control methods in EXTRAP T2R reversed field pinch

NASA Astrophysics Data System (ADS)

Yadikin, D.; Brunsell, P. R.; Paccagnella, R.

2006-07-01

Previous experiments in the EXTRAP T2R reversed field pinch device have shown the possibility of suppression of multiple resistive wall modes (RWM). A feedback system has been installed in EXTRAP T2R having 100% coverage of the toroidal surface by the active coil array. Predictions based on theory and the previous experimental results show that the number of active coils should be sufficient for independent stabilization of all unstable RWMs in the EXTRAP T2R. Experiments using different feedback schemes are performed, comparing the intelligent shell, the fake rotating shell, and the mode control with complex feedback gains. Stabilization of all unstable RWMs throughout the discharge duration of td≈10τw is seen using the intelligent shell feedback scheme. Mode rotation and the control of selected Fourier harmonics is obtained simultaneously using the mode control scheme with complex gains. Different sensor signals are studied. A feedback system with toroidal magnetic field sensors could have an advantage of lower feedback gain needed for the RWM suppression compared to the system with radial magnetic field sensors. In this study, RWM suppression is demonstrated, using also the toroidal field component as a sensor signal in the feedback system.

Forbidden phonon: Dynamical signature of bond symmetry breaking in the iron chalcogenides

DOE PAGES

Fobes, David M.; Zaliznyak, Igor A.; Tranquada, John M.; ...

2016-09-01

Investigation of the inelastic neutron scattering spectra in Fe 1+yTe 1₋xSe x near a signature wave vector Q=(1,0,0) for the bond-order wave (BOW) formation of parent compound Fe 1+yTe reveals an acoustic-phonon-like dispersion present in all structural phases. While a structural Bragg peak accompanies the mode in the low-temperature phase of Fe 1+yTe, it is absent in the high-temperature tetragonal phase, where Bragg scattering at this Q is forbidden by symmetry. Notably, this mode is also observed in superconducting FeTe 0.55Se 0.45, where structural and magnetic transitions are suppressed, and no BOW has been observed. Lastly, the presence of thismore » “forbidden” phonon indicates that the lattice symmetry is dynamically or locally broken by magneto-orbital BOW fluctuations, which are strongly coupled to lattice in these materials.« less

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

Lu, Chenyang; Niu, Liangliang; Chen, Nanjun

A grand challenge in material science is to understand the correlation between intrinsic properties and defect dynamics. Radiation tolerant materials are in great demand for safe operation and advancement of nuclear and aerospace systems. Unlike traditional approaches that rely on microstructural and nanoscale features to mitigate radiation damage, this study demonstrates enhancement of radiation tolerance with the suppression of void formation by two orders magnitude at elevated temperatures in equiatomic single-phase concentrated solid solution alloys, and more importantly, reveals its controlling mechanism through a detailed analysis of the depth distribution of defect clusters and an atomistic computer simulation. The enhancedmore » swelling resistance is attributed to the tailored interstitial defect cluster motion in the alloys from a long-range one-dimensional mode to a short-range three-dimensional mode, which leads to enhanced point defect recombination. Finally, the results suggest design criteria for next generation radiation tolerant structural alloys.« less

10 W single-mode Er/Yb co-doped all-fiber amplifier with suppressed Yb-ASE

NASA Astrophysics Data System (ADS)

Sobon, G.; Sliwinska, D.; Abramski, K. M.; Kaczmarek, P.

2014-02-01

In this work we demonstrate a single-frequency, single-mode all-fiber master oscillator power amplifier (MOPA) source, based on erbium-ytterbium co-doped double-clad fiber emitting 10 W of continuous wave power at 1565 nm. In the power amplifier stage, the amplified spontaneous emission from Yb3+ ions (Yb-ASE) is forced to recirculate in a loop resonator in order to provide stable lasing at 1060 nm. The generated signal acts as an additional pump source for the amplifier and is reabsorbed by the Yb3+ ions in the active fiber, allowing an increase in the efficiency and boosting the output power. The feedback loop also protects the amplifier from parasitic lasing or self-pulsing at a wavelength of 1 μm. This allows one to significantly scale the output power in comparison to a conventional setup without any Yb-ASE control.

Enhancing radiation tolerance by controlling defect mobility and migration pathways in multicomponent single-phase alloys

NASA Astrophysics Data System (ADS)

Lu, Chenyang; Niu, Liangliang; Chen, Nanjun; Jin, Ke; Yang, Taini; Xiu, Pengyuan; Zhang, Yanwen; Gao, Fei; Bei, Hongbin; Shi, Shi; He, Mo-Rigen; Robertson, Ian M.; Weber, William J.; Wang, Lumin

2016-12-01

A grand challenge in material science is to understand the correlation between intrinsic properties and defect dynamics. Radiation tolerant materials are in great demand for safe operation and advancement of nuclear and aerospace systems. Unlike traditional approaches that rely on microstructural and nanoscale features to mitigate radiation damage, this study demonstrates enhancement of radiation tolerance with the suppression of void formation by two orders magnitude at elevated temperatures in equiatomic single-phase concentrated solid solution alloys, and more importantly, reveals its controlling mechanism through a detailed analysis of the depth distribution of defect clusters and an atomistic computer simulation. The enhanced swelling resistance is attributed to the tailored interstitial defect cluster motion in the alloys from a long-range one-dimensional mode to a short-range three-dimensional mode, which leads to enhanced point defect recombination. The results suggest design criteria for next generation radiation tolerant structural alloys.

Structural phase transition and phonon instability in Cu 12Sb 4S 13

DOE PAGES

May, Andrew F.; Delaire, Olivier A.; Niedziela, Jennifer L.; ...

2016-02-08

In this study, a structural phase transition has been discovered in the synthetic tetrahedrite Cu 12Sb 4S 13 at approximately 88 K. Upon cooling, the material transforms from its known cubic symmetry to a tetragonal unit cell that is characterized by an in-plane ordering that leads to a doubling of the unit cell volume. Specific heat capacity measurements demonstrate a hysteresis of more than two degrees in the associated anomaly. A similar hysteresis was observed in powder x-ray diffraction measurements, which also indicate a coexistence of the two phases, and together these results suggest a first-order transition. This structural transitionmore » coincides with a recently-reported metal-insulator transition, and the structural instability is related to the very low thermal conductivity κ in these materials. Inelastic neutron scattering was used to measure the phonon density of states in Cu 12Sb 4S 13 and Cu 10Zn 2Sb 4S 13, both of which possess a localized, low-energy phonon mode associated with strongly anharmonic copper displacements that suppress κ. In Cu 12Sb 4S 13, signatures of the phase transition are observed in the temperature dependence of the localized mode, which disappears at the structural transition. In contrast, in the cubic Zn-doped material, the mode is at slightly higher-energy but observable for all temperatures, though it softens upon cooling.« less

Piezoelectric control of columns prone to instabilities and nonlinear modal interaction

NASA Astrophysics Data System (ADS)

Sridharan, Srinivasan; Kim, Sunjung

2008-06-01

This paper attempts to unravel the issues of piezoelectric control of structures prone to nonlinear static and dynamic instabilities. A simple yet typical example is considered, namely the problem of a simply supported axially compressed imperfect column on an elastic softening foundation. Here the significant nonlinearity arises from the softening foundation. The column is so designed as to have coincident critical loads for the first two modes of buckling. Piezoelectric actuators/sensors are deemed to be attached to a column in regions of maximum strain at several locations along the length of the column. The issues involved in (i) enhancing the static buckling load, (ii) suppression of vibrations as the column is compressed to a load close to its dynamic instability load and (iii) enhancing the dynamic instability load are investigated and discussed. It is shown that there is a premium price to pay for enhancing the buckling capacity of the column, be it static or dynamic. The paper concludes by alluding to the possibility of a failure of patch control if a higher-order shortwave mode happens to be the governing principal mode of the structure.

Guided wave imaging of oblique reflecting interfaces in pipes using common-source synthetic focusing

NASA Astrophysics Data System (ADS)

Sun, Zeqing; Sun, Anyu; Ju, Bing-Feng

2018-04-01

Cross-mode-family mode conversion and secondary reflection of guided waves in pipes complicate the processing of guided waves signals, and can cause false detection. In this paper, filters operating in the spectral domain of wavenumber, circumferential order and frequency are designed to suppress the signal components of unwanted mode-family and unwanted traveling direction. Common-source synthetic focusing is used to reconstruct defect images from the guided wave signals. Simulations of the reflections from linear oblique defects and a semicircle defect are separately implemented. Defect images, which are reconstructed from the simulation results under different excitation conditions, are comparatively studied in terms of axial resolution, reflection amplitude, detectable oblique angle and so on. Further, the proposed method is experimentally validated by detecting linear cracks with various oblique angles (10-40°). The proposed method relies on the guided wave signals that are captured during 2-D scanning of a cylindrical area on the pipe. The redundancy of the signals is analyzed to reduce the time-consumption of the scanning process and to enhance the practicability of the proposed method.

Which hadronic decay modes are good for {eta}{sub b} searching: Double J/{psi} or something else?

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

Jia Yu

2008-09-01

It has been controversial whether {eta}{sub b} can be discovered in Tevatron Run 2 through the decay {eta}{sub b}{yields}J/{psi}J/{psi} followed by J/{psi}{yields}{mu}{sup +}{mu}{sup -}. I clear this controversy by an explicit calculation which predicts Br[{eta}{sub b}{yields}J/{psi}J/{psi}] to be of order 10{sup -8}. It is concluded that observing {eta}{sub b} through this decay mode in Tevatron Run 2 may be rather unrealistic. The {eta}{sub b} may be observed in the forthcoming CERN LHC experiments through the 4-lepton channel, if the background events can be significantly reduced by imposing some kinematical cuts. By some rough but plausible considerations, I find that themore » analogous decay processes {eta}{sub b}{yields}VV, D*D* also have very suppressed branching ratios; nevertheless it may be worth looking for {eta}{sub b} at LHC and Super B factory through the decay modes {eta}{sub b}{yields}K{sub S}K{sup {+-}}{pi}{sup {+-}}, D*D.« less

Resistive wall mode feedback control in EXTRAP T2R with improved steady-state error and transient response

NASA Astrophysics Data System (ADS)

Brunsell, P. R.; Olofsson, K. E. J.; Frassinetti, L.; Drake, J. R.

2007-10-01

Experiments in the EXTRAP T2R reversed field pinch [P. R. Brunsell, H. Bergsåker, M. Cecconello et al., Plasma Phys. Control. Fusion 43, 1457 (2001)] on feedback control of m =1 resistive wall modes (RWMs) are compared with simulations using the cylindrical linear magnetohydrodynamic model, including the dynamics of the active coils and power amplifiers. Stabilization of the main RWMs (n=-11,-10,-9,-8,+5,+6) is shown using modest loop gains of the order G ˜1. However, other marginally unstable RWMs (n=-2,-1,+1,+2) driven by external field errors are only partially canceled at these gains. The experimental system stability limit is confirmed by simulations showing that the latency of the digital controller ˜50μs is degrading the system gain margin. The transient response is improved with a proportional-plus-derivative controller, and steady-state error is improved with a proportional-plus-integral controller. Suppression of all modes is obtained at high gain G ˜10 using a proportional-plus-integral-plus-derivative controller.

Observing Exoplanets with High-dispersion Coronagraphy. II. Demonstration of an Active Single-mode Fiber Injection Unit

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

Mawet, D.; Ruane, G.; Xuan, W.

2017-04-01

High-dispersion coronagraphy (HDC) optimally combines high-contrast imaging techniques such as adaptive optics/wavefront control plus coronagraphy to high spectral resolution spectroscopy. HDC is a critical pathway toward fully characterizing exoplanet atmospheres across a broad range of masses from giant gaseous planets down to Earth-like planets. In addition to determining the molecular composition of exoplanet atmospheres, HDC also enables Doppler mapping of atmosphere inhomogeneities (temperature, clouds, wind), as well as precise measurements of exoplanet rotational velocities. Here, we demonstrate an innovative concept for injecting the directly imaged planet light into a single-mode fiber, linking a high-contrast adaptively corrected coronagraph to a high-resolutionmore » spectrograph (diffraction-limited or not). Our laboratory demonstration includes three key milestones: close-to-theoretical injection efficiency, accurate pointing and tracking, and on-fiber coherent modulation and speckle nulling of spurious starlight signal coupling into the fiber. Using the extreme modal selectivity of single-mode fibers, we also demonstrated speckle suppression gains that outperform conventional image-based speckle nulling by at least two orders of magnitude.« less

A model for the selective amplification of spatially coherent waves in a centrifugal compressor on the verge of rotating stall

NASA Technical Reports Server (NTRS)

Lawless, Patrick B.; Fleeter, Sanford

1993-01-01

A simple model for the stability zones of a low speed centrifugal compressor is developed, with the goal of understanding the driving mechanism for the changes in stalling behavior predicted for, and observed in, the Purdue Low Speed Centrifugal Research Compressor Facility. To this end, earlier analyses of rotating stall suppression in centrifugal compressors are presented in a reduced form that preserves the essential parameters of the model that affect the stalling behavior of the compressor. The model is then used to illuminate the relationship between compressor geometry, expected mode shape, and regions of amplification for weak waves which are indicative of the susceptibility of the system to rotating stall. The results demonstrate that increasing the stagger angle of the diffuser vanes, and consequently the diffusion path length, results in the compressor moving towards a condition where higher-order spatial modes are excited during stall initiation. Similarly, flow acceleration in the diffuser section caused by an increase in the number of diffuser vanes also results in the excitation of higher modes.

Observing Exoplanets with High-dispersion Coronagraphy. II. Demonstration of an Active Single-mode Fiber Injection Unit

NASA Astrophysics Data System (ADS)

Mawet, D.; Ruane, G.; Xuan, W.; Echeverri, D.; Klimovich, N.; Randolph, M.; Fucik, J.; Wallace, J. K.; Wang, J.; Vasisht, G.; Dekany, R.; Mennesson, B.; Choquet, E.; Delorme, J.-R.; Serabyn, E.

2017-04-01

High-dispersion coronagraphy (HDC) optimally combines high-contrast imaging techniques such as adaptive optics/wavefront control plus coronagraphy to high spectral resolution spectroscopy. HDC is a critical pathway toward fully characterizing exoplanet atmospheres across a broad range of masses from giant gaseous planets down to Earth-like planets. In addition to determining the molecular composition of exoplanet atmospheres, HDC also enables Doppler mapping of atmosphere inhomogeneities (temperature, clouds, wind), as well as precise measurements of exoplanet rotational velocities. Here, we demonstrate an innovative concept for injecting the directly imaged planet light into a single-mode fiber, linking a high-contrast adaptively corrected coronagraph to a high-resolution spectrograph (diffraction-limited or not). Our laboratory demonstration includes three key milestones: close-to-theoretical injection efficiency, accurate pointing and tracking, and on-fiber coherent modulation and speckle nulling of spurious starlight signal coupling into the fiber. Using the extreme modal selectivity of single-mode fibers, we also demonstrated speckle suppression gains that outperform conventional image-based speckle nulling by at least two orders of magnitude.

Sidelobe Suppression Mode Performance of ATCRBS with Various Antennas.

DOT National Transportation Integrated Search

1975-02-01

The SLS mode performance of terminal and enroute ATCRBS using existing and various improved antennas in the presence of perfectly dielectric flat ground are investigated theoretically. Necessary analytical expressions for various quantities character...

Improved sidelobe suppression mode performance on ATCRBS with various antennas

DOT National Transportation Integrated Search

1975-02-01

The SLS mode performance of terminal and enroute ATCRBS using existing and various improved antennas in the presence of perfectly dielectric flat ground are investigated theoretically. Necessary analytical expressions for various quantities character...

780nm-range VCSEL array for laser printer system and other applications at Ricoh

NASA Astrophysics Data System (ADS)

Jikutani, Naoto; Itoh, Akihiro; Harasaka, Kazuhiro; Sasaki, Toshihide; Sato, Shunichi

2016-03-01

A 780 nm-range 40 channels vertical-cavity surface-emitting laser (VCSEL) array was developed as a writing light source for printers. A 15° off missoriented GaAs substrate, an aluminum-free GaInAsP/GaInP compressively-strained multiple quantum well and an anisotropic-shape transverse-mode filter were employed to control polarization characteristics. The anisotropic-shape transverse-mode filter also suppressed higher transverse-mode and enabled high-power single-mode operation. Thus, orthogonal-polarization suppression-ratio (OPSR) of over 22 dB and side-mode suppression-ratio (SMSR) of 30 dB were obtained at operation power of 3mW at same time for wide oxide-aperture range below 50 μm2. Moreover, a thermal resistance was reduced for 38% by increasing a thickness of high thermal conductivity layer (3λ/4-AlAs layer) near a cavity. By this structure, a peak-power increased to 1.3 times. Moreover, a power-fall caused by self-heating at pulse-rise was decreased to 10% and the one caused by a thermal-crosstalk between channels was decreased to 46%. The VCSEL array was mounted in a ceramic package with a tilted seal glass to prevent optical-crosstalk caused by other channels. Thus, we achieved stable-output and high-quality beam characteristics for long-duration pulse drive.

Phonon Dispersion and the Competition between Pairing and Charge Order

NASA Astrophysics Data System (ADS)

Costa, N. C.; Blommel, T.; Chiu, W.-T.; Batrouni, G.; Scalettar, R. T.

2018-05-01

The Holstein model describes the interaction between fermions and a collection of local (dispersionless) phonon modes. In the dilute limit, the phonon degrees of freedom dress the fermions, giving rise to polaron and bipolaron formation. At higher densities, the phonons mediate collective superconducting (SC) and charge-density wave (CDW) phases. Quantum Monte Carlo (QMC) simulations have considered both these limits but have not yet focused on the physics of more general phonon spectra. Here we report QMC studies of the role of phonon dispersion on SC and CDW order in such models. We quantify the effect of finite phonon bandwidth and curvature on the critical temperature Tcdw for CDW order and also uncover several novel features of diagonal long-range order in the phase diagram, including a competition between charge patterns at momenta q =(π ,π ) and q =(0 ,π ) which lends insight into the relationship between Fermi surface nesting and the wave vector at which charge order occurs. We also demonstrate SC order at half filling in situations where a nonzero bandwidth sufficiently suppresses Tcdw.

Narrow-band injection seeding of a terahertz frequency quantum cascade laser: Selection and suppression of longitudinal modes

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

Nong, Hanond, E-mail: Nong.Hanond@rub.de; Markmann, Sergej; Hekmat, Negar

2014-09-15

A periodically poled lithium niobate (PPLN) crystal with multiple poling periods is used to generate tunable narrow-bandwidth THz pulses for injection seeding a quantum cascade laser (QCL). We demonstrate that longitudinal modes of the quantum cascade laser close to the gain maximum can be selected or suppressed according to the seed spectrum. The QCL emission spectra obtained by electro-optic sampling from the quantum cascade laser, in the most favorable case, shows high selectivity and amplification of the longitudinal modes that overlap the frequency of the narrow-band seed. Proper selection of the narrow-band THz seed from the PPLN crystal discretely tunesmore » the longitudinal mode emission of the quantum cascade laser. Moreover, the THz wave build-up within the laser cavity is studied as a function of the round-trip time. When the seed frequency is outside the maximum of the gain spectrum the laser emission shifts to the preferential longitudinal mode.« less

Mode suppression means for gyrotron cavities

DOEpatents

Chodorow, Marvin; Symons, Robert S.

1983-08-09

In a gyrotron electron tube of the gyro-klystron or gyro-monotron type, having a cavity supporting an electromagnetic mode with circular electric field, spurious resonances can occur in modes having noncircular electric field. These spurious resonances are damped and their frequencies shifted by a circular groove in the cavity parallel to the electric field.

Suppressing interfacial water signals to assist the peak assignment of the N⁺-H stretching mode in sum frequency generation vibrational spectroscopy.

PubMed

Nguyen, Khoi Tan; Nguyen, Anh V

2015-11-21

Amines are one of the common functional groups of interest due to their abundant presence in natural proteins, surfactants and other chemicals. However, their accurate spectral assignment of vibrational modes, critical to interpreting SFG signals for characterizing various bio-interfaces such as protein-membrane interaction and surfactant adsorption, still remains elusive. Herein we present a systematic study to identify and justify the correct peak assignment of the N(+)-H stretching mode at the air-water interface. We used three special surfactants: hexadecylamine (a primary amine without counterions), dodecylamine hydrochloride (a primary amine with counterions) and hexadecyltrimethylammonium bromide as a control (the N(+)-H stretching mode is absent in this quarternary amine). We suppressed the SFG interfacial water signals using saturated NaCl solutions. Our designed experiments resolved the current controversy and concluded that the 3080 cm(-1) peak is from the N(+)-H vibrations, while the 3330 cm(-1) peak is not due to ammonium species but rather originates from the interfacial water vibrational modes or the backbone amide modes.

Characteristics of the surface plasma wave in a self-gravitating magnetized dusty plasma slab

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

Lee, Myoung-Jae; Jung, Young-Dae, E-mail: ydjung@hanyang.ac.kr; Department of Applied Physics and Department of Bionanotechnology, Hanyang University, Ansan, Kyunggi-Do 15588

2015-11-15

The dispersion properties of surface dust ion-acoustic waves in a self-gravitating magnetized dusty plasma slab are investigated. The dispersion relation is derived by using the low-frequency magnetized dusty dielectric function and the surface wave dispersion integral for the slab geometry. We find that the self-gravitating effect suppresses the frequency of surface dust ion-acoustic wave for the symmetric mode in the long wavelength regime, whereas it hardly changes the frequency for the anti-symmetric mode. As the slab thickness and the wave number increase, the surface wave frequency slowly decreases for the symmetric mode but increases significantly for the anti-symmetric mode. Themore » influence of external magnetic field is also investigated in the case of symmetric mode. We find that the strength of the magnetic field enhances the frequency of the symmetric-mode of the surface plasma wave. The increase of magnetic field reduces the self-gravitational effect and thus the self-gravitating collapse may be suppressed and the stability of dusty objects in space is enhanced.« less

Magnetic and velocity fluctuations from nonlinearly coupled tearing modes in the reversed field pinch with and without the reversal surface

NASA Astrophysics Data System (ADS)

Craig, D.; Martin, D.; Den Hartog, D. J.; Nornberg, M. D.; Reusch, J. A.

2017-08-01

We investigate the role of poloidal mode number m = 0 fluctuations on m = 1 velocity and magnetic field fluctuations in the Reversed Field Pinch (RFP). Removing the m = 0 resonant surface in the Madison Symmetric Torus (MST), results in suppressed m = 0 activity without a reduction in m = 1 magnetic activity. However, the m = 1 velocity fluctuations and fluctuation-induced mean emf are reduced as m = 0 modes are suppressed. Velocity fluctuations are measured directly using fast Doppler spectroscopy. Similar results are seen in visco-resistive MHD simulation with the DEBS code. An artificial line-averaged velocity diagnostic is developed for DEBS simulations to facilitate direct comparisons with experimental measurements. The sensitivity of the m = 1 velocity fluctuations and corresponding emf to changes in m = 0 mode activity is a feature of tearing modes in the nonlinear regime with a spectrum of interacting modes. These results have implications for RFP sustainment strategies and inform our understanding of the role of magnetic turbulence in astrophysical contexts.

High power experimental studies of hybrid photonic band gap accelerator structures

DOE PAGES

Zhang, JieXi; Munroe, Brian J.; Xu, Haoran; ...

2016-08-31

This paper reports the first high power tests of hybrid photonic band gap (PBG) accelerator structures. Three hybrid PBG (HPBG) structures were designed, built and tested at 17.14 GHz. Each structure had a triangular lattice array with 60 inner sapphire rods and 24 outer copper rods sandwiched between copper disks. The dielectric PBG band gap map allows the unique feature of overmoded operation in a TM 02 mode, with suppression of both lower order modes, such as the TM 11 mode, as well as higher order modes. The use of sapphire rods, which have negligible dielectric loss, required inclusion ofmore » the dielectric birefringence in the design. The three structures were designed to sequentially reduce the peak surface electric field. Simulations showed relatively high surface fields at the triple point as well as in any gaps between components in the clamped assembly. The third structure used sapphire rods with small pin extensions at each end and obtained the highest gradient of 19 MV/m, corresponding to a surface electric field of 78 MV/m, with a breakdown probability of 5×10 –1 per pulse per meter for a 100-ns input power pulse. Operation at a gradient above 20 MV/m led to runaway breakdowns with extensive light emission and eventual damage. For all three structures, multipactor light emission was observed at gradients well below the breakdown threshold. As a result, this research indicated that multipactor triggered at the triple point limited the operational gradient of the hybrid structure.« less

Dynamic divertor control using resonant mixed toroidal harmonic magnetic fields during ELM suppression in DIII-D

NASA Astrophysics Data System (ADS)

Jia, M.; Sun, Y.; Paz-Soldan, C.; Nazikian, R.; Gu, S.; Liu, Y. Q.; Abrams, T.; Bykov, I.; Cui, L.; Evans, T.; Garofalo, A.; Guo, W.; Gong, X.; Lasnier, C.; Logan, N. C.; Makowski, M.; Orlov, D.; Wang, H. H.

2018-05-01

Experiments using Resonant Magnetic Perturbations (RMPs), with a rotating n = 2 toroidal harmonic combined with a stationary n = 3 toroidal harmonic, have validated predictions that divertor heat and particle flux can be dynamically controlled while maintaining Edge Localized Mode (ELM) suppression in the DIII-D tokamak. Here, n is the toroidal mode number. ELM suppression over one full cycle of a rotating n = 2 RMP that was mixed with a static n = 3 RMP field has been achieved. Prominent heat flux splitting on the outer divertor has been observed during ELM suppression by RMPs in low collisionality regime in DIII-D. Strong changes in the three dimensional heat and particle flux footprint in the divertor were observed during the application of the mixed toroidal harmonic magnetic perturbations. These results agree well with modeling of the edge magnetic field structure using the TOP2D code, which takes into account the plasma response from the MARS-F code. These results expand the potential effectiveness of the RMP ELM suppression technique for the simultaneous control of divertor heat and particle load required in ITER.

Semiclassical electron transport at the edge of a two-dimensional topological insulator: Interplay of protected and unprotected modes

NASA Astrophysics Data System (ADS)

Khalaf, E.; Skvortsov, M. A.; Ostrovsky, P. M.

2016-03-01

We study electron transport at the edge of a generic disordered two-dimensional topological insulator, where some channels are topologically protected from backscattering. Assuming the total number of channels is large, we consider the edge as a quasi-one-dimensional quantum wire and describe it in terms of a nonlinear sigma model with a topological term. Neglecting localization effects, we calculate the average distribution function of transmission probabilities as a function of the sample length. We mainly focus on the two experimentally relevant cases: a junction between two quantum Hall (QH) states with different filling factors (unitary class) and a relatively thick quantum well exhibiting quantum spin Hall (QSH) effect (symplectic class). In a QH sample, the presence of topologically protected modes leads to a strong suppression of diffusion in the other channels already at scales much shorter than the localization length. On the semiclassical level, this is accompanied by the formation of a gap in the spectrum of transmission probabilities close to unit transmission, thereby suppressing shot noise and conductance fluctuations. In the case of a QSH system, there is at most one topologically protected edge channel leading to weaker transport effects. In order to describe `topological' suppression of nearly perfect transparencies, we develop an exact mapping of the semiclassical limit of the one-dimensional sigma model onto a zero-dimensional sigma model of a different symmetry class, allowing us to identify the distribution of transmission probabilities with the average spectral density of a certain random-matrix ensemble. We extend our results to other symmetry classes with topologically protected edges in two dimensions.

CW injection locking for long-term stability of frequency combs

NASA Astrophysics Data System (ADS)

Williams, Charles; Quinlan, Franklyn; Delfyett, Peter J.

2009-05-01

Harmonically mode-locked semiconductor lasers with external ring cavities offer high repetition rate pulse trains while maintaining low optical linewidth via long cavity storage times. Continuous wave (CW) injection locking further reduces linewidth and stabilizes the optical frequencies. The output can be stabilized long-term with the help of a modified Pound-Drever-Hall feedback loop. Optical sidemode suppression of 36 dB has been shown, as well as RF supermode noise suppression of 14 dB for longer than 1 hour. In addition to the injection locking of harmonically mode-locked lasers requiring an external frequency source, recent work shows the viability of the injection locking technique for regeneratively mode-locked lasers, or Coupled Opto-Electronic Oscillators (COEO).

Experimental Characterization of Electron-Beam-Driven Wakefield Modes in a Dielectric-Woodpile Cartesian Symmetric Structure

NASA Astrophysics Data System (ADS)

Hoang, P. D.; Andonian, G.; Gadjev, I.; Naranjo, B.; Sakai, Y.; Sudar, N.; Williams, O.; Fedurin, M.; Kusche, K.; Swinson, C.; Zhang, P.; Rosenzweig, J. B.

2018-04-01

Photonic structures operating in the terahertz (THz) spectral region enable the essential characteristics of confinement, modal control, and electric field shielding for very high gradient accelerators based on wakefields in dielectrics. We report here an experimental investigation of THz wakefield modes in a three-dimensional photonic woodpile structure. Selective control in exciting or suppressing of wakefield modes with a nonzero transverse wave vector is demonstrated by using drive beams of varying transverse ellipticity. Additionally, we show that the wakefield spectrum is insensitive to the offset position of strongly elliptical beams. These results are consistent with analytic theory and three-dimensional simulations and illustrate a key advantage of wakefield systems with Cartesian symmetry: the suppression of transverse wakes by elliptical beams.

Measurement of the Branching Ratio Lambda_c+ -> p pi+ pi- (in Spanish)

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

Lopez-Hinojosa, Guillermo; /San Luis Potosi U.

2008-03-01

The confirmation of the Cabibbo-suppressed charm baryon decay mode {Lambda}{sub c}{sup +} {yields} p{pi}{sup +}{pi}{sup -} is reported. All data analyzed are from SELEX, a fixed target experiment at Fermilab that took data during 1996 and 1997, mainly with a 600 GeV/c {Sigma}{sup -} beam. The branching ratio of the Cabibbo-suppressed decay mode {Lambda}{sub c}{sup +} {yields} p{pi}{sup +}{pi}{sup -} relative to the Cabibbo-favored mode {Lambda}{sub c}{sup +} {yields} pK{sup -}{pi}{sup +} is measured to be: {Gamma}({Lambda}{sub c}{sup +} {yields} p{pi}{sup +}{pi}{sup -})/{Gamma}({Lambda}{sub c}{sup +} {yields} pK{sup -}{pi}{sup +}) = 0.103 {+-} 0.022.

1700 nm and 1800 nm band tunable thulium doped mode-locked fiber lasers.

PubMed

Emami, Siamak Dawazdah; Dashtabi, Mahdi Mozdoor; Lee, Hui Jing; Arabanian, Atoosa Sadat; Rashid, Hairul Azhar Abdul

2017-10-06

This paper presents short wavelength operation of tunable thulium-doped mode-locked lasers with sweep ranges of 1702 to 1764 nm and 1788 to 1831 nm. This operation is realized by a combination of the partial amplified spontaneous emission suppression method, the bidirectional pumping mechanism and the nonlinear polarization rotation (NPR) technique. Lasing at emission bands lower than the 1800 nm wavelength in thulium-doped fiber lasers is achieved using mode confinement loss in a specially designed photonic crystal fiber (PCF). The enlargement of the first outer ring air holes around the core region of the PCF attenuates emissions above the cut-off wavelength and dominates the active region. This amplified spontaneous emission (ASE) suppression using our presented PCF is applied to a mode-locked laser cavity and is demonstrated to be a simple and compact solution to widely tunable all-fiber lasers.

Suppression of Alfven Modes on the National Spherical Torus Experiment Upgrade with Outboard Beam Injection [Suppression of Alfven Modes on the NSTX-U with Outboard Beam Injection

DOE PAGES

Fredrickson, E. D.; Belova, E. V.; Battaglia, D. J.; ...

2017-06-29

In this paper we present data from experiments on the National Spherical Torus Experiment Upgrade, where it is shown for the first time that small amounts of high pitch-angle beam ions can strongly suppress the counterpropagating global Alfven eigenmodes (GAE). GAE have been implicated in the redistribution of fast ions and modification of the electron power balance in previous experiments on NSTX. The ability to predict the stability of Alfven modes, and developing methods to control them, is important for fusion reactors like the International Tokamak Experimental Reactor, which are heated by a large population of nonthermal, super-Alfvenic ions consistingmore » of fusion generated alpha's and beam ions injected for current profile control. We present a qualitative interpretation of these observations using an analytic model of the Doppler-shifted ion-cyclotron resonance drive responsible for GAE instability which has an important dependence on k(perpendicular to rho L). A quantitative analysis of this data with the HYM stability code predicts both the frequencies and instability of the GAE prior to, and suppression of the GAE after the injection of high pitch-angle beam ions.« less

The Relationships Between ELM Suppression, Pedestal Profiles, and Lithium Wall Coatings in NSTX

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

D.P. Boyle, R. Maingi, P.B. Snyder, J. Manickam, T.H. Osborne, R.E. Bell, B.P. LeBlanc, and the NSTX Team

2012-08-17

Recently in the National Spherical Torus Experiment (NSTX), increasing lithium wall coatings suppressed edge localized modes (ELMs), gradually but not quite monotonically. This work details profile and stability analysis as ELMs disappeared throughout the lithium scan. While the quantity of lithium deposited between discharges did not uniquely determine the presence of ELMs, profile analysis demonstrated that lithium was correlated to wider density and pressure pedestals with peak gradients farther from the separatrix. Moreover, the ELMy and ELM-free discharges were cleanly separated by their density and pedestal widths and peak gradient locations. Ultimately, ELMs were only suppressed when lithium caused themore » density pedestal to widen and shift inward. These changes in the density gradient were directly reflected in the pressure gradient and calculated bootstrap current. This supports the theory that ELMs in NSTX are caused by peeling and/or ballooning modes, as kink/peeling modes are stabilized when the edge current and pressure gradient shift away from the separatrix. Edge stability analysis using ELITE corroborated this picture, as reconstructed equilibria from ELM-free discharges were generally farther from their kink/peeling stability boundaries than ELMy discharges. We conclude that density profile control provided by lithium is the key first step to ELM suppression in NSTX« less

Simplified adaptive control of an orbiting flexible spacecraft

NASA Astrophysics Data System (ADS)

Maganti, Ganesh B.; Singh, Sahjendra N.

2007-10-01

The paper presents the design of a new simple adaptive system for the rotational maneuver and vibration suppression of an orbiting spacecraft with flexible appendages. A moment generating device located on the central rigid body of the spacecraft is used for the attitude control. It is assumed that the system parameters are unknown and the truncated model of the spacecraft has finite but arbitrary dimension. In addition, only the pitch angle and its derivative are measured and elastic modes are not available for feedback. The control output variable is chosen as the linear combination of the pitch angle and the pitch rate. Exploiting the hyper minimum phase nature of the spacecraft, a simple adaptive control law is derived for the pitch angle control and elastic mode stabilization. The adaptation rule requires only four adjustable parameters and the structure of the control system does not depend on the order of the truncated spacecraft model. For the synthesis of control system, the measured output error and the states of a third-order command generator are used. Simulation results are presented which show that in the closed-loop system adaptive output regulation is accomplished in spite of large parameter uncertainties and disturbance input.

One- and two-dimensional antenna arrays for microwave wireless power transfer (MWPT) systems and dual-antenna transceivers

NASA Astrophysics Data System (ADS)

Lin, Yo-Sheng; Hu, Chun-Hao; Chang, Chi-Ho; Tsao, Ping-Chang

2018-06-01

In this work, we demonstrate novel one-dimensional (1D) and two-dimensional (2D) antenna arrays for both microwave wireless power transfer (MWPT) systems and dual-antenna transceivers. The antenna array can be used as the MWPT receiving antenna of an integrated MWPT and Bluetooth (BLE) communication module (MWPT-BLE module) for smart CNC (computer numerical control) spindle incorporated with the cloud computing system SkyMars. The 2D antenna array has n rows of 1 × m 1D array, and each array is composed of multiple (m) differential feeding antenna elements. Each differential feeding antenna element is a differential feeding structure with a microstrip antenna stripe. The stripe length is shorter than one wavelength to minimise the antenna area and to prevent being excited to a high-order mode. That is, the differential feeding antenna element can suppress the even mode. The mutual coupling between the antenna elements can be suppressed, and the isolation between the receiver and the transmitter can be enhanced. An inclination angle of the main beam aligns with the broadside, and the main beam is further concentrated and shrunk at the elevation direction. Moreover, if more differential feeding antenna elements are used, antenna gain and isolation can be further enhanced. The excellent performance of the proposed antenna arrays indicates that they are suitable for both MWPT systems and dual-antenna transceivers.

Interface-facilitated energy transport in coupled Frenkel-Kontorova chains

NASA Astrophysics Data System (ADS)

Su, Rui-Xia; Yuan, Zong-Qiang; Wang, Jun; Zheng, Zhi-Gang

2016-04-01

The role of interface couplings on the energy transport of two coupled Frenkel-Kontorova (FK) chains is explored through numerical simulations. In general, it is expected that the interface couplings result in the suppression of heat conduction through the coupled system due to the additional interface phonon-phonon scattering. In the present paper, it is found that the thermal conductivity increases with increasing intensity of interface interactions for weak inter-chain couplings, whereas the heat conduction is suppressed by the interface interaction in the case of strong inter-chain couplings. Based on the phonon spectral energy density method, we demonstrate that the enhancement of energy transport results from the excited phonon modes (in addition to the intrinsic phonon modes), while the strong interface phonon-phonon scattering results in the suppressed energy transport.

Suppression of Alfvénic modes through modification of the fast ion distribution

NASA Astrophysics Data System (ADS)

Fredrickson, Eric

2017-10-01

Experiments on NSTX-U have shown for the first time that small amounts of high pitch-angle, low ρL beam ions can strongly suppress the counter-propagating Global Alfvén Eigenmodes (GAE) [1]. GAE have been implicated in the redistribution of fast ions and modification of the electron power balance in previous experiments on NSTX. The ability to predict the stability of Alfvén modes, and development of methods to control them, is important for fusion reactors like ITER, which like NSTX, will be heated with a large population of non-thermal, super-Alfvénic ions (unlike the normal operation of conventional tokamaks). The suppression of the GAE by adding a small population of high-pitch resonant fast ions is qualitatively consistent with an analytic model of the Doppler-shifted ion-cyclotron resonance drive responsible for GAE instability [2]. The model predicts that fast ions with k⊥ρL <1.9 are stabilizing, which is in good agreement with the experimental observations. A quantitative analysis was done using the HYM stability code [3] of one of the nearly 100 identified examples of GAE suppression. The simulations find remarkable agreement with the observed mode numbers and frequencies of the unstable GAE prior to suppression. Adding the population of high pitch-angle, low ρL beam ions to the HYM fast ion distribution function predicts complete suppression of the GAE. TRANSP/NUBEAM calculations for the example analyzed with HYM suggest that the additional beam source increases the population of resonant fast ions with k⊥ρL <1.9 by roughly a factor of four. Work supported by U.S. DOE Contract DE-AC02-09CH11466.

Localization enhanced and degraded topological order in interacting p -wave wires

NASA Astrophysics Data System (ADS)

Kells, G.; Moran, N.; Meidan, D.

2018-02-01

We numerically study the effect of disorder on the stability of the many-body zero mode in a Kitaev chain with local interactions. Our numerical procedure allows us to resolve the position space and multiparticle structure of the zero modes, as well as providing estimates for the mean energy splitting between pairs of states of opposite fermion parity, over the full many-body spectrum. We find that the parameter space of a clean system can be divided into regions where interaction induced decay transitions are suppressed (region I) and where they are not (region II). In region I we observe that disorder has an adverse effect on the zero mode, which extends further into the bulk and is accompanied by an increased energy splitting between pairs of states of opposite parity. Conversely region II sees a more intricate effect of disorder, showing an enhancement of localization at the system's end accompanied by a reduction in the mean pairwise energy splitting. We discuss our results in the context of the many-body localization (MBL). We show that while the mechanism that drives the MBL transition also contributes to the fock-space localization of the many-body zero modes, measures that characterize the degree of MBL do not necessarily correlate with an enhancement of the zero mode or an improved stability of the topological region.

Higher-order vibrational mode frequency tuning utilizing fishbone-shaped microelectromechanical systems resonator

NASA Astrophysics Data System (ADS)

Suzuki, Naoya; Tanigawa, Hiroshi; Suzuki, Kenichiro

2013-04-01

Resonators based on microelectromechanical systems (MEMS) have received considerable attention for their applications for wireless equipment. The requirements for this application include small size, high frequency, wide bandwidth and high portability. However, few MEMS resonators with wide-frequency tuning have been reported. A fishbone-shaped resonator has a resonant frequency with a maximum response that can be changed according to the location and number of several exciting electrodes. Therefore, it can be expected to provide wide-frequency tuning. The resonator has three types of electrostatic forces that can be generated to deform a main beam. We evaluate the vibrational modes caused by each exciting electrodes by comparing simulated results with measured ones. We then successfully demonstrate the frequency tuning of the first to fifth resonant modes by using the algorithm we propose here. The resulting frequency tuning covers 178 to 1746 kHz. In addition, we investigate the suppression of the anchor loss to enhance the Q-factor. An experiment shows that tapered-shaped anchors provide a higher Q-factor than rectangular-shaped anchors. The Q-factor of the resonators supported by suspension beams is also discussed. Because the suspension beams cause complicated vibrational modes for higher frequencies, the enhancement of the Q-factor for high vibrational modes cannot be obtained here. At present, the tapered-anchor resonators are thought to be most suitable for frequency tuning applications.

Ultrashort, high power, and ultralow noise mode-locked optical pulse generation using quantum-dot semiconductor lasers

NASA Astrophysics Data System (ADS)

Choi, Myoung-Taek

This dissertation explores various aspects and potential of optical pulse generation based on active, passive, and hybrid mode-locked quantum dot semiconductor lasers with target applications such as optical interconnect and high speed signal processing. Design guidelines are developed for the single mode operation with suppressed reflection from waveguide discontinuities. The device fabrication procedure is explained, followed by characteristics of FP laser, SOA, and monolithic two-section devices. Short pulse generation from an external cavity mode-locked QD two-section diode laser is studied. High quality, sub-picosecond (960 fs), high peak power (1.2 W) pulse trains are obtained. The sign and magnitude of pulse chirp were measured for the first time. The role of the self-phase modulation and the linewidth enhancement factor in QD mode-locked lasers is addressed. The noise performance of two-section mode-locked lasers and a SOA-based ring laser was investigated. Significant reduction of the timing jitter under hybrid mode-locked operation was achieved owing to more than one order of magnitude reduction of the linewidth in QD gain media. Ultralow phase noise performance (integrated timing jitter of a few fs at a 10 GHz repetition rate) was demonstrated from an actively mode-locked unidirectional ring laser. These results show that quantum dot mode-locked lasers are strong competitors to conventional semiconductor lasers in noise performance. Finally we demonstrated an opto-electronic oscillator (OEO) and coupled opto-electronic oscillators (COEO) which have the potential for both high purity microwave and low noise optical pulse generation. The phase noise of the COEO is measured by the photonic delay line frequency discriminator method. Based on this study we discuss the prospects of the COEO as a low noise optical pulse source.

Design of bent waveguide semiconductor lasers using nonlinear equivalent chirp

NASA Astrophysics Data System (ADS)

Li, Lianyan; Shi, Yuechun; Zhang, Yunshan; Chen, Xiangfei

2018-01-01

Reconstruction equivalent chirp (REC) technique is widely used in the design and fabrication of semiconductor laser arrays and tunable lasers with low cost and high wavelength accuracy. Bent waveguide is a promising method to suppress the zeroth order resonance, which is an intrinsic problem in REC technique. However, it may introduce basic grating chirp and deteriorate the single longitudinal mode (SLM) property of the laser. A nonlinear equivalent chirp pattern is proposed in this paper to compensate the grating chirp and improve the SLM property. It will benefit the realization of low-cost Distributed feedback (DFB) semiconductor laser arrays with accurate lasing wavelength.

Turbofan aft duct suppressor study

NASA Technical Reports Server (NTRS)

Syed, A. A.; Motsinger, R. E.; Fiske, G. H.; Joshi, M. C.; Kraft, R. E.

1983-01-01

Suppressions due to acoustic treatment in the annular exhaust duct of a model fan were theoretically predicted and compared with measured suppressions. The predictions are based on the modal analysis of sound propagation in a straight annular flow duct with segmented treatment. Modal distributions of the fan noise source (fan-stator interaction only) were measured using in-duct modal probes. The flow profiles were also measured in the vicinity of the modal probes. The acoustic impedance of the single degree of freedom treatment was measured in the presence of grazing flow. The measured values of mode distribution of the fan noise source, the flow velocity profile and the acoustic impedance of the treatment in the duct were used as input to the prediction program. The predicted suppressions, under the assumption of uniform flow in the duct, compared well with the suppressions measured in the duct for all test conditions. The interaction modes generated by the rotor-stator interaction spanned a cut-off ratio range from nearly 1 to 7.

Design of Microstrip Bandpass Filters Using SIRs with Even-Mode Harmonics Suppression for Cellular Systems

NASA Astrophysics Data System (ADS)

Theerawisitpong, Somboon; Suzuki, Toshitatsu; Morita, Noboru; Utsumi, Yozo

The design of microstrip bandpass filters using stepped-impedance resonators (SIRs) is examined. The passband center frequency for the WCDMA-FDD (uplink band) Japanese cellular system is 1950MHz with a 60-MHz bandwidth. The SIR physical characteristic can be designed using a SIR characteristic chart based on second harmonic suppression. In our filter design, passband design charts were obtained through the design procedure. Tchebycheff and maximally flat bandpass filters of any bandwidth and any number of steps can be designed using these passband design charts. In addition, sharp skirt characteristics in the passband can be realized by having two transmission zeros at both adjacent frequency bands by using open-ended quarter-wavelength stubs at input and output ports. A new even-mode harmonics suppression technique is proposed to enable a wide rejection band having a high suppression level. The unloaded quality factor of the resonator used in the proposed filters is greater than 240.

A fuzzy neural network sliding mode controller for vibration suppression in robotically assisted minimally invasive surgery.

PubMed

Sang, Hongqiang; Yang, Chenghao; Liu, Fen; Yun, Jintian; Jin, Guoguang

2016-12-01

It is very important for robotically assisted minimally invasive surgery to achieve a high-precision and smooth motion control. However, the surgical instrument tip will exhibit vibration caused by nonlinear friction and unmodeled dynamics, especially when the surgical robot system is attempting low-speed, fine motion. A fuzzy neural network sliding mode controller (FNNSMC) is proposed to suppress vibration of the surgical robotic system. Nonlinear friction and modeling uncertainties are compensated by a Stribeck model, a radial basis function (RBF) neural network and a fuzzy system, respectively. Simulations and experiments were performed on a 3 degree-of-freedom (DOF) minimally invasive surgical robot. The results demonstrate that the FNNSMC is effective and can suppress vibrations at the surgical instrument tip. The proposed FNNSMC can provide a robust performance and suppress the vibrations at the surgical instrument tip, which can enhance the quality and security of surgical procedures. Copyright © 2016 John Wiley & Sons, Ltd.

Post-inscription tuning of multicore fiber Bragg gratings

NASA Astrophysics Data System (ADS)

Lindley, Emma Y.; Min, Seong-sik; Leon-Saval, Sergio G.; Bland-Hawthorn, Joss

2016-07-01

Fiber Bragg gratings are used in astronomy for their ability to suppress narrow atmospheric emission lines of temporally varying brightness before the light is dispersed. These gratings can only operate in a single-mode fiber as the suppressed wavelength depends on mode velocity in the core. Recent experiments with fibers containing multiple single-moded cores have demonstrated the potential for inscribing identical gratings across all cores in a single pass. We have already improved the uniformity of gratings in 7-core fibers via modifications to the writing process; further progress can be achieved by tuning the gratings of the outer and inner cores relative to one another. Our eventual goal is to make the entire fiber suppress one wavelength to a depth of 30 dB or greater. By coating the fiber in a heat-conductive material with a high expansion coefficient, we can examine the effects of temperature and strain on the spectral response of each core. In this paper we present methods and results from experiments concerning the post-write tuning of gratings in multicore fibers.

Effects of Density and Impurity on Edge Localized Modes in Tokamaks

NASA Astrophysics Data System (ADS)

Zhu, Ping

2017-10-01

Plasma density and impurity concentration are believed to be two of the key elements governing the edge tokamak plasma conditions. Optimal levels of plasma density and impurity concentration in the edge region have been searched for in order to achieve the desired fusion gain and divertor heat/particle load mitigation. However, how plasma density or impurity would affect the edge pedestal stability may have not been well known. Our recent MHD theory modeling and simulations using the NIMROD code have found novel effects of density and impurity on the dynamics of edge-localized modes (ELMs) in tokamaks. First, previous MHD analyses often predict merely a weak stabilizing effect of toroidal flow on ELMs in experimentally relevant regimes. We find that the stabilizing effects on the high- n ELMs from toroidal flow can be significantly enhanced with the increased edge plasma density. Here n denotes the toroidal mode number. Second, the stabilizing effects of the enhanced edge resistivity due to lithium-conditioning on the low- n ELMs in the high confinement (H-mode) discharges in NSTX have been identified. Linear stability analysis of the experimentally constrained equilibrium suggests that the change in the equilibrium plasma density and pressure profiles alone due to lithium-conditioning may not be sufficient for a complete suppression of the low- n ELMs. The enhanced resistivity due to the increased effective electric charge number Zeff after lithium-conditioning provides additional stabilization of the low- n ELMs. These new effects revealed in our theory analyses may help further understand recent ELM experiments and suggest new control schemes for ELM suppression and mitigation in future experiments. They may also pose additional constraints on the optimal levels of plasma density and impurity concentration in the edge region for H-mode tokamak operation. Supported by National Magnetic Confinement Fusion Science Program of China Grants 2014GB124002 and 2015GB101004, the 100 Talent Program of the Chinese Academy of Sciences, and U.S. Department of Energy Grants DE-FG02-86ER53218 and DE-FC02-08ER54975.

Competition and coexistence of polar and non-polar states in Sr1-x Ca x TiO3: an investigation using pressure dependent Raman spectroscopy

NASA Astrophysics Data System (ADS)

Tyagi, Shekhar; Sharma, Gaurav; Sathe, Vasant G.

2018-03-01

The competition and cooperation between ferroelectric and anti-ferro-distortion (AFD) instabilities are studied using pressure dependent Raman spectroscopy on polycrystalline powder samples of Sr1-x Ca x TiO3(x  =  0.0, 0.06, 0.25, 0.35). For x  =  0.0 composition, a broad polar mode is detected in the Raman spectra above 6 GPa, while for x  =  0.06 composition, the polar modes appear well above 9 GPa where the AFD modes showed strong suppression. In x  =  0.25 and 0.35 composition, the application of small pressure resulted in the appearance of strong AFD modes suppressing the polar modes. At elevated pressures, re-entrant polar modes are observed along with the broad AFD modes and some new peaks are also observed, signifying the lowering of local symmetry. The reappearance of polar modes is found to be related to pressure induced symmetry disorder at local level, suggesting its electronic origin. The re-entrant polar modes observed at higher pressure values are found to be significantly broad and asymmetric in nature, signifying the development of ferroelectric micro regions/nano domains coexisting with AFD. The lower symmetry at local length scale provides a conducive atmosphere for coexisting AFD and FE instabilities.

Tunable orbital angular momentum mode filter based on optical geometric transformation.

PubMed

Huang, Hao; Ren, Yongxiong; Xie, Guodong; Yan, Yan; Yue, Yang; Ahmed, Nisar; Lavery, Martin P J; Padgett, Miles J; Dolinar, Sam; Tur, Moshe; Willner, Alan E

2014-03-15

We present a tunable mode filter for spatially multiplexed laser beams carrying orbital angular momentum (OAM). The filter comprises an optical geometric transformation-based OAM mode sorter and a spatial light modulator (SLM). The programmable SLM can selectively control the passing/blocking of each input OAM beam. We experimentally demonstrate tunable filtering of one or multiple OAM modes from four multiplexed input OAM modes with vortex charge of ℓ=-9, -4, +4, and +9. The measured output power suppression ratio of the propagated modes to the blocked modes exceeds 14.5 dB.

Parasitic Effects of Grounding Paths on Common-Mode EMI Filter's Performance in Power Electronics Systems

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

Wang, Shuo; Maillet, Yoann; Wang, Fei

2010-01-01

High-frequency common-mode (CM) electromagnetic-interference (EMI) noise is difficult to suppress in electronics systems. EMI filters are used to suppress CM noise, but their performance is greatly affected by the parasitic effects of the grounding paths. In this paper, the parasitic effects of the grounding paths on an EMI filter's performance are investigated in a motor-drive system. The effects of the mutual inductance between two grounding paths are explored. Guidelines for the grounding of CM EMI filters are derived. Simulations and experiments are finally carried out to verify the theoretical analysis.

Readout circuit with novel background suppression for long wavelength infrared focal plane arrays

NASA Astrophysics Data System (ADS)

Xie, L.; Xia, X. J.; Zhou, Y. F.; Wen, Y.; Sun, W. F.; Shi, L. X.

2011-02-01

In this article, a novel pixel readout circuit using a switched-capacitor integrator mode background suppression technique is presented for long wavelength infrared focal plane arrays. This circuit can improve dynamic range and signal-to-noise ratio by suppressing the large background current during integration. Compared with other background suppression techniques, the new background suppression technique is less sensitive to the process mismatch and has no additional shot noise. The proposed circuit is theoretically analysed and simulated while taking into account the non-ideal characteristics. The result shows that the background suppression non-uniformity is ultra-low even for a large process mismatch. The background suppression non-uniformity of the proposed circuit can also remain very small with technology scaling.

Design and simulation of a novel E-mode GaN MIS-HEMT based on a cascode connection for suppression of electric field under gate and improvement of reliability

NASA Astrophysics Data System (ADS)

Li, Weiyi; Zhang, Zhili; Fu, Kai; Yu, Guohao; Zhang, Xiaodong; Sun, Shichuang; Song, Liang; Hao, Ronghui; Fan, Yaming; Cai, Yong; Zhang, Baoshun

2017-07-01

We proposed a novel AlGaN/GaN enhancement-mode (E-mode) high electron mobility transistor (HEMT) with a dual-gate structure and carried out the detailed numerical simulation of device operation using Silvaco Atlas. The dual-gate device is based on a cascode connection of an E-mode and a D-mode gate. The simulation results show that electric field under the gate is decreased by more than 70% compared to that of the conventional E-mode MIS-HEMTs (from 2.83 MV/cm decreased to 0.83 MV/cm). Thus, with the discussion of ionized trap density, the proposed dual-gate structure can highly improve electric field-related reliability, such as, threshold voltage stability. In addition, compared with HEMT with field plate structure, the proposed structure exhibits a simplified fabrication process and a more effective suppression of high electric field. Project supported by the Key Technologies Support Program of Jiangsu Province (No. BE2013002-2) and the National Key Scientific Instrument and Equipment Development Projects of China (No. 2013YQ470767).

Tunable zero-line modes via magnetic field in bilayer graphene

NASA Astrophysics Data System (ADS)

Wang, Ke; Qiao, Zhenhua

Zero-line modes appear in bilayer graphene at the internal boundary between two opposite vertical electrostatic confinements. These one-dimensional modes are metallic along the boundary and exhibit quantized conductance in the absence of inter-valley scattering. However, experimental results show that the conductance is around 0.5 e2/h rather than quantized. This observation can be explained from our numerical results, which suggest that the scattering between zero-line mode and bound states and the presence of atomic scale disorders that provide inter-valley scattering can effectively reduce the conductance to about 0.5 e2/h. We further find that out-of-plane magnetic field can strongly suppress these scattering mechanisms and gives rise to nearly quantized conductance. On one hand, the presence of magnetic field makes bound states become Landau levels, which reduces the scattering between zero-line mode and bound states. On the other hand, the wave function distributions of oppositely propagating zero-line modes at different valleys are spatially separated, which can strongly suppress the inter-valley scattering. Specifically speaking, the conductance can be increased to 3.2 e2/h at 8 T even when the atomic Anderson type disorders are considered.

External amplitude and frequency modulation of a terahertz quantum cascade laser using metamaterial/graphene devices.

PubMed

Kindness, S J; Jessop, D S; Wei, B; Wallis, R; Kamboj, V S; Xiao, L; Ren, Y; Braeuninger-Weimer, P; Aria, A I; Hofmann, S; Beere, H E; Ritchie, D A; Degl'Innocenti, R

2017-08-09

Active control of the amplitude and frequency of terahertz sources is an essential prerequisite for exploiting a myriad of terahertz applications in imaging, spectroscopy, and communications. Here we present a optoelectronic, external modulation technique applied to a terahertz quantum cascade laser which holds the promise of addressing a number of important challenges in this research area. A hybrid metamaterial/graphene device is implemented into an external cavity set-up allowing for optoelectronic tuning of feedback into a quantum cascade laser. We demonstrate powerful, all-electronic, control over the amplitude and frequency of the laser output. Full laser switching is performed by electrostatic gating of the metamaterial/graphene device, demonstrating a modulation depth of 100%. External control of the emission spectrum is also achieved, highlighting the flexibility of this feedback method. By taking advantage of the frequency dispersive reflectivity of the metamaterial array, different modes of the QCL output are selectively suppressed using lithographic tuning and single mode operation of the multi-mode laser is enforced. Side mode suppression is electrically modulated from ~6 dB to ~21 dB, demonstrating active, optoelectronic modulation of the laser frequency content between multi-mode and single mode operation.

Plasma Density Effects on Toroidal Flow Stabilization of Edge Localized Modes

NASA Astrophysics Data System (ADS)

Cheng, Shikui; Zhu, Ping; Banerjee, Debabrata

2016-10-01

Recent EAST experiments have demonstrated mitigation and suppression of edge localized modes (ELMs) with toroidal rotation flow in higher collisionality regime, suggesting potential roles of plasma density. In this work, the effects of plasma density on the toroidal flow stabilization of the high- n edge localized modes have been extensively studied in linear calculations for a circular-shaped limiter H-mode tokamak, using the initial-value extended MHD code NIMROD. In the single MHD model, toroidal flow has a weak stabilizing effects on the high- n modes. Such a stabilization, however, can be significantly enhanced with the increase in plasma density. Furthermore, our calculations show that the enhanced stabilization of high- n modes from toroidal flow with higher edge plasma density persists in the 2-fluid MHD model. These findings may explain the ELM mitigation and suppression by toroidal rotation in higher collisionality regime due to the enhancement of plasma density obtained in EAST experiment. Supported by the National Magnetic Confinement Fusion Program of China under Grant Nos. 2014GB124002 and 2015GB101004, the 100 Talent Program and the President International Fellowship Initiative of Chinese Academy of Sciences.

Virtual Deformation Control of the X-56A Model with Simulated Fiber Optic Sensors

NASA Technical Reports Server (NTRS)

Suh, Peter M.; Chin, Alexander W.; Mavris, Dimitri N.

2014-01-01

A robust control law design methodology is presented to stabilize the X-56A model and command its wing shape. The X-56A was purposely designed to experience flutter modes in its flight envelope. The methodology introduces three phases: the controller design phase, the modal filter design phase, and the reference signal design phase. A mu-optimal controller is designed and made robust to speed and parameter variations. A conversion technique is presented for generating sensor strain modes from sensor deformation mode shapes. The sensor modes are utilized for modal filtering and simulating fiber optic sensors for feedback to the controller. To generate appropriate virtual deformation reference signals, rigid-body corrections are introduced to the deformation mode shapes. After successful completion of the phases, virtual deformation control is demonstrated. The wing is deformed and it is shown that angle-ofattack changes occur which could potentially be used to an advantage. The X-56A program must demonstrate active flutter suppression. It is shown that the virtual deformation controller can achieve active flutter suppression on the X-56A simulation model.

Virtual Deformation Control of the X-56A Model with Simulated Fiber Optic Sensors

NASA Technical Reports Server (NTRS)

Suh, Peter M.; Chin, Alexander Wong

2013-01-01

A robust control law design methodology is presented to stabilize the X-56A model and command its wing shape. The X-56A was purposely designed to experience flutter modes in its flight envelope. The methodology introduces three phases: the controller design phase, the modal filter design phase, and the reference signal design phase. A mu-optimal controller is designed and made robust to speed and parameter variations. A conversion technique is presented for generating sensor strain modes from sensor deformation mode shapes. The sensor modes are utilized for modal filtering and simulating fiber optic sensors for feedback to the controller. To generate appropriate virtual deformation reference signals, rigid-body corrections are introduced to the deformation mode shapes. After successful completion of the phases, virtual deformation control is demonstrated. The wing is deformed and it is shown that angle-of-attack changes occur which could potentially be used to an advantage. The X-56A program must demonstrate active flutter suppression. It is shown that the virtual deformation controller can achieve active flutter suppression on the X-56A simulation model.

Reexamining X-mode suppression and fine structure in artificial E region field-aligned plasma density irregularities

NASA Astrophysics Data System (ADS)

Miceli, R. J.; Hysell, D. L.; Munk, J.; McCarrick, M.; Huba, J. D.

2013-09-01

Artificial field-aligned plasma density irregularities (FAIs) were generated in the E region of the ionosphere above the High Frequency Active Auroral Research Program facility during campaigns in May and August of 2012 and observed using a 30 MHz coherent scatter radar imager in Homer, Alaska. The purpose of this ionospheric modification experiment was to measure the threshold pump power required to excite thermal parametric instabilities by O-mode heating and to investigate the suppression of the FAIs by simultaneous X-mode heating. We find that the threshold pump power for irregularity excitation was consistent with theoretical predictions and increased by approximately a factor of 2 when X-mode heating was present. A modified version of the Another Model of the Ionosphere (SAMI2) ionospheric model was used to simulate the threshold experiments and suggested that the increase was entirely due to enhanced D region absorption associated with X-mode heating. Additionally, a remarkable degree of fine structure possibly caused by natural gradient drift instability in the heater-modified volume was observed in experiments performed during geomagnetically active conditions.

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.

Transient-Switch-Signal Suppressor

NASA Technical Reports Server (NTRS)

Bozeman, Richard J., Jr.

1995-01-01

Circuit delays transmission of switch-opening or switch-closing signal until after preset suppression time. Used to prevent transmission of undesired momentary switch signal. Basic mode of operation simple. Beginning of switch signal initiates timing sequence. If switch signal persists after preset suppression time, circuit transmits switch signal to external circuitry. If switch signal no longer present after suppression time, switch signal deemed transient, and circuit does not pass signal on to external circuitry, as though no transient switch signal. Suppression time preset at value large enough to allow for damping of underlying pressure wave or other mechanical transient.

Coronal Seismology of Flare-Excited Standing Slow-Mode Waves Observed by SDO/AIA

NASA Astrophysics Data System (ADS)

Wang, Tongjiang; Ofman, Leon; Davila, Joseph M.

2016-05-01

Flare-excited longitudinal intensity oscillations in hot flaring loops have been recently detected by SDO/AIA in 94 and 131 Å bandpasses. Based on the interpretation in terms of a slow-mode wave, quantitative evidence of thermal conduction suppression in hot (>9 MK) loops has been obtained for the first time from measurements of the polytropic index and phase shift between the temperature and density perturbations (Wang et al. 2015, ApJL, 811, L13). This result has significant implications in two aspects. One is that the thermal conduction suppression suggests the need of greatly enhanced compressive viscosity to interpret the observed strong wave damping. The other is that the conduction suppression provides a reasonable mechanism for explaining the long-duration events where the thermal plasma is sustained well beyond the duration of impulsive hard X-ray bursts in many flares, for a time much longer than expected by the classical Spitzer conductive cooling. In this study, we model the observed standing slow-mode wave in Wang et al. (2015) using a 1D nonlinear MHD code. With the seismology-derived transport coefficients for thermal conduction and compressive viscosity, we successfully simulate the oscillation period and damping time of the observed waves. Based on the parametric study of the effect of thermal conduction suppression and viscosity enhancement on the observables, we discuss the inversion scheme for determining the energy transport coefficients by coronal seismology.

Singly Cabibbo-suppressed hadronic decays of Λc+

NASA Astrophysics Data System (ADS)

Cheng, Hai-Yang; Kang, Xian-Wei; Xu, Fanrong

2018-04-01

We study singly Cabibbo-suppressed two-body hadronic decays of the charmed baryon Λc+, namely, Λc+→Λ K+,p π0,p η ,n π+,Σ0K+,Σ+K0 . We use the measured rate of Λc+→p ϕ to fix the effective Wilson coefficient a2 for naive color-suppressed modes and the effective number of color Nceff. We rely on the current-algebra approach to evaluate W -exchange and nonfactorizable internal W -emission amplitudes, that is, the commutator terms for the S wave and the pole terms for the P wave. Our prediction for Λc+→p η is in excellent agreement with the BESIII measurement. The p η (p π0) mode has a large (small) rate because of a large constructive (destructive) interference between the factorizable and nonfactorizable amplitudes for both S and P waves. Some of the SU(3) relations such as M (Λc+→n π+)=√{2 }M (Λc+→p π0) derived under the assumption of sextet dominance are not valid for decays with factorizable terms. Our calculation indicates that the branching fraction of Λc+→n π+ is about 3.5 times larger than that of Λc+→p π0 . Decay asymmetries are found to be negative for all singly Cabibbo-suppressed modes and range from -0.56 to -0.96 .

Numerical Analysis of the Effects of Normalized Plasma Pressure on RMP ELM Suppression in DIII-D

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

Orlov, D. M.; Moyer, R.A.; Evans, T. E.

2010-01-01

The effect of normalized plasma pressure as characterized by normalized pressure parameter (beta(N)) on the suppression of edge localized modes (ELMs) using resonant magnetic perturbations (RMPs) is studied in low-collisionality (nu* <= 0.2) H-mode plasmas with low-triangularity ( = 0.25) and ITER similar shapes ( = 0.51). Experimental results have suggested that ELM suppression by RMPs requires a minimum threshold in plasma pressure as characterized by beta(N). The variations in the vacuum field topology with beta(N) due to safety factor profile and island overlap changes caused by variation of the Shafranov shift and pedestal bootstrap current are examined numerically withmore » the field line integration code TRIP3D. The results show very small differences in the vacuum field structure in terms of the Chirikov (magnetic island overlap) parameter, Poincare sections and field line loss fractions. These differences do not appear to explain the observed threshold in beta(N) for ELM suppression. Linear peeling-ballooning stability analysis with the ELITE code suggests that the ELMs which persist during the RMPs when beta(N) is below the observed threshold are not type I ELMs, because the pedestal conditions are deep within the stable regime for peeling-ballooning modes. These ELMs have similarities to type III ELMs or low density ELMs.« less

Carbon Nanotube-Poly(vinylalcohol) Nanocomposite Film Devices: Applications for Femtosecond Fiber Laser Mode Lockers and Optical Amplifier Noise Suppressors

NASA Astrophysics Data System (ADS)

Sakakibara, Youichi; Rozhin, Aleksey G.; Kataura, Hiromichi; Achiba, Yohji; Tokumoto, Madoka

2005-04-01

We fabricated single-wall carbon nanotube (SWNT)/poly(vinylalcohol) (PVA) nanocomposite freestanding films and examined their application in devices in which the saturable absorption of SWNTs at near-infrared optical telecommunication wavelengths can be utilized. In a passively mode-locked fiber laser, we integrated a 30-μm-thick SWNT/PVA film into a fiber connection adaptor with the film sandwiched by a pair of fiber ferrules. A ring fiber laser with a SWNT/PVA saturable absorber was operated very easily in the mode-locked short-pulse mode with a pulse width of about 500 fs. Reproducible stable device performance was confirmed. In examining noise suppression for optical amplifiers, mixed light of semiconductor amplified spontaneous emission (ASE) source and 370 fs laser pulses was passed through a 100-μm-thick SWNT/PVA film. The transmission loss of the femtosecond pulse light was smaller than that of the ASE light. This proved that the SWNT/PVA film has the ability to suppress ASE noise.

PRAXIS: low thermal emission high efficiency OH suppressed fibre spectrograph

NASA Astrophysics Data System (ADS)

Content, Robert; Bland-Hawthorn, Joss; Ellis, Simon; Gers, Luke; Haynes, Roger; Horton, Anthony; Lawrence, Jon; Leon-Saval, Sergio; Lindley, Emma; Min, Seong-Sik; Shortridge, Keith; Staszak, Nick; Trinh, Christopher; Xavier, Pascal; Zhelem, Ross

2014-07-01

PRAXIS is a second generation instrument that follows on from GNOSIS, which was the first instrument using fibre Bragg gratings for OH suppression to be deployed on a telescope. The Bragg gratings reflect the NIR OH lines while being transparent to the light between the lines. This gives in principle a much higher signal-noise ratio at low resolution spectroscopy but also at higher resolutions by removing the scattered wings of the OH lines. The specifications call for high throughput and very low thermal and detector noise so that PRAXIS will remain sky noise limited even with the low sky background levels remaining after OH suppression. The optical and mechanical designs are presented. The optical train starts with fore-optics that image the telescope focal plane on an IFU which has 19 hexagonal microlenses each feeding a multi-mode fibre. Seven of these fibres are attached to a fibre Bragg grating OH suppression system while the others are reference/acquisition fibres. The light from each of the seven OH suppression fibres is then split by a photonic lantern into many single mode fibres where the Bragg gratings are imprinted. Another lantern recombines the light from the single mode fibres into a multi-mode fibre. A trade-off was made in the design of the IFU between field of view and transmission to maximize the signal-noise ratio for observations of faint, compact objects under typical seeing. GNOSIS used the pre-existing IRIS2 spectrograph while PRAXIS will use a new spectrograph specifically designed for the fibre Bragg grating OH suppression and optimised for 1.47 μm to 1.7 μm (it can also be used in the 1.09 μm to 1.26 μm band by changing the grating and refocussing). This results in a significantly higher transmission due to high efficiency coatings, a VPH grating at low incident angle and optimized for our small bandwidth, and low absorption glasses. The detector noise will also be lower thanks to the use of a current generation HAWAII-2RG detector. Throughout the PRAXIS design, from the fore-optics to the detector enclosure, special care was taken at every step along the optical path to reduce thermal emission or stop it leaking into the system. The spectrograph design itself was particularly challenging in this aspect because practical constraints required that the detector and the spectrograph enclosures be physically separate with air at ambient temperature between them. At present, the instrument uses the GNOSIS fibre Bragg grating OH suppression unit. We intend to soon use a new OH suppression unit based on multicore fibre Bragg gratings which will allow an increased field of view per fibre. Theoretical calculations show that the gain in interline sky background signal-noise ratio over GNOSIS may very well be as high as 9 with the GNOSIS OH suppression unit and 17 with the multicore fibre OH suppression unit.

Corrosion and erosion monitoring in plates and pipes using constant group velocity Lamb wave inspection.

PubMed

Nagy, Peter B; Simonetti, Francesco; Instanes, Geir

2014-09-01

Recent improvements in tomographic reconstruction techniques generated a renewed interest in short-range ultrasonic guided wave inspection for real-time monitoring of internal corrosion and erosion in pipes and other plate-like structures. Emerging evidence suggests that in most cases the fundamental asymmetric A0 mode holds a distinct advantage over the earlier market leader fundamental symmetric S0 mode. Most existing A0 mode inspections operate at relatively low inspection frequencies where the mode is highly dispersive therefore very sensitive to variations in wall thickness. This paper examines the potential advantages of increasing the inspection frequency to the so-called constant group velocity (CGV) point where the group velocity remains essentially constant over a wide range of wall thickness variation, but the phase velocity is still dispersive enough to allow accurate wall thickness assessment from phase angle measurements. This paper shows that in the CGV region the crucial issue of temperature correction becomes especially simple, which is particularly beneficial when higher-order helical modes are also exploited for tomography. One disadvantage of working at such relatively high inspection frequency is that, as the slower A0 mode becomes faster and less dispersive, the competing faster S0 mode becomes slower and more dispersive. At higher inspection frequencies these modes cannot be separated any longer based on their vibration polarization only, which is mostly tangential for the S0 mode while mostly normal for the A0 at low frequencies, as the two modes become more similar as the frequency increases. Therefore, we propose a novel method for suppressing the unwanted S0 mode based on the Poisson effect of the material by optimizing the angle of inclination of the equivalent transduction force of the Electromagnetic Acoustic Transducers (EMATs) used for generation and detection purposes. Copyright © 2014 Elsevier B.V. All rights reserved.

Pogo suppression on space shuttle - early studies

NASA Technical Reports Server (NTRS)

Rubin, S.; Wagner, R. G.; Payne, J. G.

1973-01-01

Preliminary studies for pogo prevention on the shuttle vehicle are reported. The importance of the effect of oscillatory outflow from a hydroelastic tank is displayed in terms of excitation of normal modes for a structure containing that tank assuming its outlet is closed. Evaluation of an approximate propulsion frequency response at undamped feedline resonance reveals the conditions for which the contribution of tank outflow is destabilizing and also provides a criterion for identifying those structural modes which are of potential significance for system stability. Various finite-element and normal-mode models for hydraulic feedlines are evaluated relative to accuracy of admittances of a long line. A procedure is recommended for modeling a feed system to minimize the required number of second-order equations. Specific recommendations are made for the analytical estimation of pump cavitation compliance and a first estimate for the shuttle pumps is given. Weakness in past practices of pump testing are identified and a new three-phase program is proposed. Finally results of numerical studies on the early vehicle configuration are presented. It is concluded that an accumulator between the boost and main pump offers promise of higher effectiveness than one at the engine inlet.

Lasers with intra-cavity phase elements

NASA Astrophysics Data System (ADS)

Gulses, A. Alkan; Kurtz, Russell; Islas, Gabriel; Anisimov, Igor

2018-02-01

Conventional laser resonators yield multimodal output, especially at high powers and short cavity lengths. Since highorder modes exhibit large divergence, it is desirable to suppress them to improve laser quality. Traditionally, such modal discriminations can be achieved by simple apertures that provide absorptive loss for large diameter modes, while allowing the lower orders, such as the fundamental Gaussian, to pass through. However, modal discrimination may not be sufficient for short-cavity lasers, resulting in multimodal operation as well as power loss and overheating in the absorptive part of the aperture. In research to improve laser mode control with minimal energy loss, systematic experiments have been executed using phase-only elements. These were composed of an intra-cavity step function and a diffractive out-coupler made of a computer-generated hologram. The platform was a 15-cm long solid-state laser that employs a neodymium-doped yttrium orthovanadate crystal rod, producing 1064 nm multimodal laser output. The intra-cavity phase elements (PEs) were shown to be highly effective in obtaining beams with reduced M-squared values and increased output powers, yielding improved values of radiance. The utilization of more sophisticated diffractive elements is promising for more difficult laser systems.

Harmonically mode-locked erbium-doped waveguide laser

NASA Astrophysics Data System (ADS)

Fanto, Michael L.; Malowicki, John E.; Bussjager, Rebecca J.; Johns, Steven T.; Vettese, Elizabeth K.; Hayduk, Michael J.

2004-08-01

The generation of ultrastable picosecond pulses in the 1550 nm range is required for numerous applications that include photonic analog-to-digital converter systems and high-bit rate optical communication systems. Mode-locked erbium-doped fiber ring lasers (EDFLs) are typically used to generate pulses at this wavelength. In addition to timing stability and output power, the physical size of the laser cavity is of primary importance to the Air Force. The length of the erbium (Er)-doped fiber used as the gain medium may be on the order of meters or even tens of meters which adds complexity to packaging. However, with the recent advancements in the production of multi-component glasses, higher doping concentrations can be achieved as compared to silicate glasses. Even more recent is the introduction of Er-doped multi-component glass waveguides, thus allowing the overall footprint of the gain medium to be reduced. We have constructed a novel harmonically mode-locked fiber ring laser using the Er-doped multi-component glass waveguide as the gain medium. The performance characteristics of this Er-doped waveguide laser (EDWL) including pulse width, spectral width, harmonic suppression, optical output power, laser stability and single sideband residual phase noise will be discussed in this paper.

Suppressed phase variations in a high amplitude rapidly oscillating Ap star pulsating in a distorted quadrupole mode

NASA Astrophysics Data System (ADS)

Holdsworth, Daniel L.; Saio, H.; Bowman, D. M.; Kurtz, D. W.; Sefako, R. R.; Joyce, M.; Lambert, T.; Smalley, B.

2018-05-01

We present the results of a multisite photometric observing campaign on the rapidly oscillating Ap (roAp) star 2MASS 16400299-0737293 (J1640; V = 12.7). We analyse photometric B data to show the star pulsates at a frequency of 151.93 d-1 (1758.45 μHz; P = 9.5 min) with a peak-to-peak amplitude of 20.68 mmag, making it one of the highest amplitude roAp stars. No further pulsation modes are detected. The stellar rotation period is measured at 3.674 7 ± 0.000 5 d, and we show that rotational modulation due to spots is in antiphase between broad-band and B observations. Analysis and modelling of the pulsation reveals this star to be pulsating in a distorted quadrupole mode, but with a strong spherically symmetric component. The pulsational phase variation in this star is suppressed, leading to the conclusion that the contribution of ℓ > 2 components dictate the shape of phase variations in roAp stars that pulsate in quadrupole modes. This is only the fourth time such a strong pulsation phase suppression has been observed, leading us to question the mechanisms at work in these stars. We classify J1640 as an A7 Vp SrEu(Cr) star through analysis of classification resolution spectra.

Room temperature continuous wave, monolithic tunable THz sources based on highly efficient mid-infrared quantum cascade lasers

PubMed Central

Lu, Quanyong; Wu, Donghai; Sengupta, Saumya; Slivken, Steven; Razeghi, Manijeh

2016-01-01

A compact, high power, room temperature continuous wave terahertz source emitting in a wide frequency range (ν ~ 1–5 THz) is of great importance to terahertz system development for applications in spectroscopy, communication, sensing, and imaging. Here, we present a strong-coupled strain-balanced quantum cascade laser design for efficient THz generation based on intracavity difference frequency generation. Room temperature continuous wave emission at 3.41 THz with a side-mode suppression ratio of 30 dB and output power up to 14 μW is achieved with a wall-plug efficiency about one order of magnitude higher than previous demonstrations. With this highly efficient design, continuous wave, single mode THz emissions with a wide frequency tuning range of 2.06–4.35 THz and an output power up to 4.2 μW are demonstrated at room temperature from two monolithic three-section sampled grating distributed feedback-distributed Bragg reflector lasers. PMID:27009375

Enhancing radiation tolerance by controlling defect mobility and migration pathways in multicomponent single-phase alloys

DOE PAGES

Lu, Chenyang; Niu, Liangliang; Chen, Nanjun; ...

2016-12-15

A grand challenge in material science is to understand the correlation between intrinsic properties and defect dynamics. Radiation tolerant materials are in great demand for safe operation and advancement of nuclear and aerospace systems. Unlike traditional approaches that rely on microstructural and nanoscale features to mitigate radiation damage, this study demonstrates enhancement of radiation tolerance with the suppression of void formation by two orders magnitude at elevated temperatures in equiatomic single-phase concentrated solid solution alloys, and more importantly, reveals its controlling mechanism through a detailed analysis of the depth distribution of defect clusters and an atomistic computer simulation. The enhancedmore » swelling resistance is attributed to the tailored interstitial defect cluster motion in the alloys from a long-range one-dimensional mode to a short-range three-dimensional mode, which leads to enhanced point defect recombination. Finally, the results suggest design criteria for next generation radiation tolerant structural alloys.« less

Faraday spectroscopy of ultracold atoms guided in hollow core optical fibers

NASA Astrophysics Data System (ADS)

Fatemi, Fredrik; Pechkis, Joseph

2013-05-01

We have performed spatially and temporally resolved magnetometry using Faraday spectroscopy of ultracold rubidium atoms confined in hollow core optical fibers. We first guide 105 Rb atoms into a 3-cm-long, 100-micron-core hollow fiber using blue-detuned hollow waveguide modes. Inside the fiber, the atoms are exposed to an optical pumping pulse, and the Larmor precession is monitored by the polarization rotation of a probe laser beam detuned by 50 GHz. The intense guide beams can perturb the detected Larmor precession frequencies, but we show that by confining the atoms to the intensity null of higher order blue-detuned hollow modes, these perturbations are reduced by over 95% compared to red-detuned guides. By adjusting the guide beam detuning and polarization, the deleterious effects of both photon scattering and frequency shifts can be suppressed such that multiple magnetic field measurements with sensitivity of 30 nT per sampling pulse can be obtained throughout the length of the fiber in a single loading cycle. Work supported by ONR and DARPA.

Lattice dynamics and thermal transport in multiferroic CuCrO2

NASA Astrophysics Data System (ADS)

Bansal, Dipanshu; Niedziela, Jennifer L.; May, Andrew F.; Said, Ayman; Ehlers, Georg; Abernathy, Douglas L.; Huq, Ashfia; Kirkham, Melanie; Zhou, Haidong; Delaire, Olivier

2017-02-01

Inelastic neutron and x-ray scattering measurements of phonons and spin waves were performed in the delafossite compound CuCrO2 over a wide range of temperature, and complemented with first-principles lattice dynamics simulations. The phonon dispersions and density of states are well reproduced by our density functional calculations, and reveal a strong anisotropy of Cu vibrations, which exhibit low-frequency modes of large amplitude parallel to the basal plane of the layered delafossite structure. The low frequency in-plane modes also show a systematic temperature dependence of neutron and x-ray scattering intensities. In addition, we find that spin fluctuations persist above 300 K, far above the Néel temperature for long-range antiferromagnetic order, TN≃24 K . Our modeling of the thermal conductivity, based on our phonon measurements and simulations, reveals a significant anisotropy and indicates that spin fluctuations above TN constitute an important source of phonon scattering, considerably suppressing the thermal conductivity compared to that of the isostructural but nonmagnetic compound CuAlO2.

Design, implementation and flight testing of PIF autopilots for general aviation aircraft

NASA Technical Reports Server (NTRS)

Broussard, J. R.

1983-01-01

The designs of Proportional-Integrated-Filter (PIF) auto-pilots for a General Aviation (NAVION) aircraft are presented. The PIF autopilot uses the sampled-data regulator and command generator tracking to determine roll select, pitch select, heading select, altitude select and localizer/glideslope capture and hold autopilot modes. The PIF control law uses typical General Aviation sensors for state feedback, command error integration for command tracking, digital complementary filtering and analog prefiltering for sensor noise suppression, a control filter for computation delay accommodation and the incremental form to eliminate trim values in implementation. Theoretical developments described in detail, were needed to combine the sampled-data regulator with command generator tracking for use as a digital flight control system. The digital PIF autopilots are evaluated using closed-loop eigenvalues and linear simulations. The implementation of the PIF autopilots in a digital flight computer using a high order language (FORTRAN) is briefly described. The successful flight test results for each PIF autopilot mode is presented.

Room temperature continuous wave, monolithic tunable THz sources based on highly efficient mid-infrared quantum cascade lasers.

PubMed

Lu, Quanyong; Wu, Donghai; Sengupta, Saumya; Slivken, Steven; Razeghi, Manijeh

2016-03-24

A compact, high power, room temperature continuous wave terahertz source emitting in a wide frequency range (ν~1-5 THz) is of great importance to terahertz system development for applications in spectroscopy, communication, sensing, and imaging. Here, we present a strong-coupled strain-balanced quantum cascade laser design for efficient THz generation based on intracavity difference frequency generation. Room temperature continuous wave emission at 3.41 THz with a side-mode suppression ratio of 30 dB and output power up to 14 μW is achieved with a wall-plug efficiency about one order of magnitude higher than previous demonstrations. With this highly efficient design, continuous wave, single mode THz emissions with a wide frequency tuning range of 2.06-4.35 THz and an output power up to 4.2 μW are demonstrated at room temperature from two monolithic three-section sampled grating distributed feedback-distributed Bragg reflector lasers.

Effects of alloy composition and Si-doping on vacancy defect formation in (InxGa1-x)2O3 thin films

NASA Astrophysics Data System (ADS)

Prozheeva, V.; Hölldobler, R.; von Wenckstern, H.; Grundmann, M.; Tuomisto, F.

2018-03-01

Various nominally undoped and Si-doped (InxGa1-x)2O3 thin films were grown by pulsed laser deposition in a continuous composition spread mode on c-plane α-sapphire and (100)-oriented MgO substrates. Positron annihilation spectroscopy in the Doppler broadening mode was used as the primary characterisation technique in order to investigate the effect of alloy composition and dopant atoms on the formation of vacancy-type defects. In the undoped samples, we observe a Ga2O3-like trend for low indium concentrations changing to In2O3-like behaviour along with the increase in the indium fraction. Increasing indium concentration is found to suppress defect formation in the undoped samples at [In] > 70 at. %. Si doping leads to positron saturation trapping in VIn-like defects, suggesting a vacancy concentration of at least mid-1018 cm-3 independent of the indium content.

Ping-pong modes and higher-periodicity multipactor

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

Kishek, R. A.

Multipactor is a vacuum discharge driven by secondary electron emission. Multiple period multipactors have long been known to exist but have been studied less extensively. In a period-n multipactor, electrons undergo multiple impacts in one rf period, with the synchronous phase alternating periodically between multiple values. A novel resonant form is proposed that combines one- and two-surface impacts within a single period, provided the total transit time is an odd number of rf half-periods and the product of secondary yields exceeds unity. For low fD products, the simplest such mode is shown to significantly increase the upper electric field boundarymore » of the multipacting region and lead to overlap of higher-order bands. The results agree nicely with 3-D particle-in-cell code simulations. An alternative, map-based method is introduced for analyzing higher-periodicity multipactor. Practical implications of the findings are discussed, including consequences for multipactor suppression strategies using a dc magnetic field.« less

Cavity Quantum Acoustic Device in the Multimode Strong Coupling Regime

NASA Astrophysics Data System (ADS)

Moores, Bradley A.; Sletten, Lucas R.; Viennot, Jeremie J.; Lehnert, K. W.

2018-06-01

We demonstrate an acoustical analog of a circuit quantum electrodynamics system that leverages acoustic properties to enable strong multimode coupling in the dispersive regime while suppressing spontaneous emission to unconfined modes. Specifically, we fabricate and characterize a device that comprises a flux tunable transmon coupled to a 300 μ m long surface acoustic wave resonator. For some modes, the qubit-cavity coupling reaches 6.5 MHz, exceeding the cavity loss rate (200 kHz), qubit linewidth (1.1 MHz), and the cavity free spectral range (4.8 MHz), placing the device in both the strong coupling and strong multimode regimes. With the qubit detuned from the confined modes of the cavity, we observe that the qubit linewidth strongly depends on its frequency, as expected for spontaneous emission of phonons, and we identify operating frequencies where this emission rate is suppressed.

Distinguishing among potential mechanisms of singleton suppression.

PubMed

Gaspelin, Nicholas; Luck, Steven J

2018-04-01

Previous research has revealed that people can suppress salient stimuli that might otherwise capture visual attention. The present study tests between 3 possible mechanisms of visual suppression. According to first-order feature suppression models , items are suppressed on the basis of simple feature values. According to second-order feature suppression models , items are suppressed on the basis of local discontinuities within a given feature dimension. According to global-salience suppression models , items are suppressed on the basis of their dimension-independent salience levels. The current study distinguished among these models by varying the predictability of the singleton color value. If items are suppressed by virtue of salience alone, then it should not matter whether the singleton color is predictable. However, evidence from probe processing and eye movements indicated that suppression is possible only when the color values are predictable. Moreover, the ability to suppress salient items developed gradually as participants gained experience with the feature that defined the salient distractor. These results are consistent with first-order feature suppression models, and are inconsistent with the other models of suppression. In other words, people primarily suppress salient distractors on the basis of their simple features and not on the basis of salience per se. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

ELM Suppression and Pedestal Structure in I-Mode Plasmas

NASA Astrophysics Data System (ADS)

Walk, John

2013-10-01

The I-mode regime is characterized by the formation of a temperature pedestal and enhanced energy confinement (H98 up to 1.2), without an accompanying density pedestal or drop in particle transport. Unlike ELMy H-modes, I-mode operation appears to have naturally-occurring suppression of large ELMs in addition to its highly favorable scalings of pedestal structure (and therefore overall performance). Instead, continuous Weakly Coherent Modes help to regulate density. Extensive study of the ELMy H-mode has led to the development of the EPED model, which utilizes calculations of coupled peeling-ballooning MHD modes and kinetic-ballooning mode (KBM) stability limits to predict the pedestal structure preceding an ELM crash. We apply similar tools to the structure and ELM stability of I-mode pedestals. Peeling-ballooning MHD calculations are completed using the ELITE code, showing I-mode pedestals to be generally MHD-stable. Under certain conditions, intermittent ELMs are observed in I-mode at reduced field, typically triggered by sawtooth crashes; modification of the temperature pedestal (and therefore the pressure profile stability) by sawtooth heat pulses is being examined in ELITE. Modeled stability to KBM turbulence in I-mode and ELMy H-mode suggests that typical I-modes are stable against KBM turbulence. Measured I-mode pedestals are significantly wider (more stable) than the width scaling with the square root of poloidal beta characteristic of the KBM-limited pedestals in ELMy H-mode. Finally, we explore scalings of pedestal structure with engineering parameters compared to ELMy H-modes on C-Mod. In particular, we focus on scalings of the pressure pedestal with heating power (and its relation to the favorable scaling of confinement with power in I-mode) and on relationships between heat flux and pedestal temperature gradients. This work is supported by DOE agreement DE-FC02-99ER54512. Theory work at General Atomics is supported by DOE agreement DE-FG02-99ER54309.

Analysis of Tospovirus NSs Proteins in Suppression of Systemic Silencing.

PubMed

Hedil, Marcio; Sterken, Mark G; de Ronde, Dryas; Lohuis, Dick; Kormelink, Richard

2015-01-01

RNA silencing is a sequence-specific gene regulation mechanism that in plants also acts antiviral. In order to counteract antiviral RNA silencing, viruses have evolved RNA silencing suppressors (RSS). In the case of tospoviruses, the non-structural NSs protein has been identified as the RSS. Although the tomato spotted wilt virus (TSWV) tospovirus NSs protein has been shown to exhibit affinity to long and small dsRNA molecules, its ability to suppress the non-cell autonomous part of RNA silencing has only been studied to a limited extent. Here, the NSs proteins of TSWV, groundnut ringspot virus (GRSV) and tomato yellow ring virus (TYRV), representatives for three distinct tospovirus species, have been studied on their ability and strength to suppress local and systemic silencing. A system has been developed to quantify suppression of GFP silencing in Nicotiana benthamiana 16C lines, to allow a comparison of relative RNA silencing suppressor strength. It is shown that NSs of all three tospoviruses are suppressors of local and systemic silencing. Unexpectedly, suppression of systemic RNA silencing by NSsTYRV was just as strong as those by NSsTSWV and NSsGRSV, even though NSsTYRV was expressed in lower amounts. Using the system established, a set of selected NSsTSWV gene constructs mutated in predicted RNA binding domains, as well as NSs from TSWV isolates 160 and 171 (resistance breakers of the Tsw resistance gene), were analyzed for their ability to suppress systemic GFP silencing. The results indicate another mode of RNA silencing suppression by NSs that acts further downstream the biogenesis of siRNAs and their sequestration. The findings are discussed in light of the affinity of NSs for small and long dsRNA, and recent mutant screen of NSsTSWV to map domains required for RSS activity and triggering of Tsw-governed resistance.

Analysis of Tospovirus NSs Proteins in Suppression of Systemic Silencing

PubMed Central

Hedil, Marcio; Sterken, Mark G.; de Ronde, Dryas; Lohuis, Dick; Kormelink, Richard

2015-01-01

RNA silencing is a sequence-specific gene regulation mechanism that in plants also acts antiviral. In order to counteract antiviral RNA silencing, viruses have evolved RNA silencing suppressors (RSS). In the case of tospoviruses, the non-structural NSs protein has been identified as the RSS. Although the tomato spotted wilt virus (TSWV) tospovirus NSs protein has been shown to exhibit affinity to long and small dsRNA molecules, its ability to suppress the non-cell autonomous part of RNA silencing has only been studied to a limited extent. Here, the NSs proteins of TSWV, groundnut ringspot virus (GRSV) and tomato yellow ring virus (TYRV), representatives for three distinct tospovirus species, have been studied on their ability and strength to suppress local and systemic silencing. A system has been developed to quantify suppression of GFP silencing in Nicotiana benthamiana 16C lines, to allow a comparison of relative RNA silencing suppressor strength. It is shown that NSs of all three tospoviruses are suppressors of local and systemic silencing. Unexpectedly, suppression of systemic RNA silencing by NSsTYRV was just as strong as those by NSsTSWV and NSsGRSV, even though NSsTYRV was expressed in lower amounts. Using the system established, a set of selected NSsTSWV gene constructs mutated in predicted RNA binding domains, as well as NSs from TSWV isolates 160 and 171 (resistance breakers of the Tsw resistance gene), were analyzed for their ability to suppress systemic GFP silencing. The results indicate another mode of RNA silencing suppression by NSs that acts further downstream the biogenesis of siRNAs and their sequestration. The findings are discussed in light of the affinity of NSs for small and long dsRNA, and recent mutant screen of NSsTSWV to map domains required for RSS activity and triggering of Tsw-governed resistance. PMID:26275304

Incipient ferroelectricity of water molecules confined to nano-channels of beryl

NASA Astrophysics Data System (ADS)

Gorshunov, B. P.; Torgashev, V. I.; Zhukova, E. S.; Thomas, V. G.; Belyanchikov, M. A.; Kadlec, C.; Kadlec, F.; Savinov, M.; Ostapchuk, T.; Petzelt, J.; Prokleška, J.; Tomas, P. V.; Pestrjakov, E. V.; Fursenko, D. A.; Shakurov, G. S.; Prokhorov, A. S.; Gorelik, V. S.; Kadyrov, L. S.; Uskov, V. V.; Kremer, R. K.; Dressel, M.

2016-09-01

Water is characterized by large molecular electric dipole moments and strong interactions between molecules; however, hydrogen bonds screen the dipole-dipole coupling and suppress the ferroelectric order. The situation changes drastically when water is confined: in this case ordering of the molecular dipoles has been predicted, but never unambiguously detected experimentally. In the present study we place separate H2O molecules in the structural channels of a beryl single crystal so that they are located far enough to prevent hydrogen bonding, but close enough to keep the dipole-dipole interaction, resulting in incipient ferroelectricity in the water molecular subsystem. We observe a ferroelectric soft mode that causes Curie-Weiss behaviour of the static permittivity, which saturates below 10 K due to quantum fluctuations. The ferroelectricity of water molecules may play a key role in the functioning of biological systems and find applications in fuel and memory cells, light emitters and other nanoscale electronic devices.

Strong quantum squeezing of mechanical resonator via parametric amplification and coherent feedback

NASA Astrophysics Data System (ADS)

You, Xiang; Li, Zongyang; Li, Yongmin

2017-12-01

A scheme to achieve strong quantum squeezing of a mechanical resonator in a membrane-in-the-middle optomechanical system is developed. To this end, simultaneous linear and nonlinear coupling between the mechanical resonator and the cavity modes is applied. A two-tone driving light field, comprising unequal red-detuned and blue-detuned sidebands, helps in generating a coherent feedback force through the linear coupling with the membrane resonator. Another driving light field with its amplitude modulated at twice the mechanical frequency drives the mechanical parametric amplification through a second-order coupling with the resonator. The combined effect produces strong quantum squeezing of the mechanical state. The proposed scheme is quite robust to excess second-order coupling observed in coherent feedback operations and can suppress the fluctuations in the mechanical quadrature to far below the zero point and achieve strong squeezing (greater than 10 dB) for realistic parameters.

Using nonequilibrium dynamics to probe competing orders in a Mott-Peierls system

DOE PAGES

Wang, Y.; Moritz, B.; Chen, C. -C.; ...

2016-02-24

Competition between ordered phases, and their associated phase transitions, are significant in the study of strongly correlated systems. Here, we examine one aspect, the nonequilibrium dynamics of a photoexcited Mott-Peierls system, using an effective Peierls-Hubbard model and exact diagonalization. Near a transition where spin and charge become strongly intertwined, we observe antiphase dynamics and a coupling-strength-dependent suppression or enhancement in the static structure factors. The renormalized bosonic excitations coupled to a particular photoexcited electron can be extracted, which provides an approach for characterizing the underlying bosonic modes. The results from this analysis for different electronic momenta show an uneven softeningmore » due to a stronger coupling near k F. As a result, this behavior reflects the strong link between the fermionic momenta, the coupling vertices, and ultimately, the bosonic susceptibilities when multiple phases compete for the ground state of the system.« less

Optical single sideband millimeter-wave signal generation and transmission using 120° hybrid coupler

NASA Astrophysics Data System (ADS)

Zheng, Zhiwei; Peng, Miao; Zhou, Hui; Chen, Ming; Jiang, Leyong; Tan, Li; Dai, Xiaoyu; Xiang, Yuanjiang

2018-03-01

We propose a novel 60 GHz optical single sideband (OSSB) millimeter-wave (mm-wave) signal generation scheme using 120° hybrid coupler based on external integrated Mach-Zehnder modulator (MZM). The proposed scheme shows that the bit error ratio (BER) performance is improved by suppressing the +2nd-order sideband. Meanwhile, the transmission distance is extended as only the optical +1st-order sideband is modulated by using 5 Gbit/s baseband signal while the carrier is blank, owing to the elimination of walk-off effect suffered from fiber dispersion. The simulation results demonstrated that the eye diagrams of the generated 60 GHz OSSB signal keep open and clear after 100 km standard single-mode fiber (SSMF). In addition, the proposed scheme can achieve 2 dB receiver sensitivity improvements than the conventional 90° hybrid coupler when transmitted over 100 km SSMF at a BER of 10-9.

Design and experimental validation of a flutter suppression controller for the active flexible wing

NASA Technical Reports Server (NTRS)

Waszak, Martin R.; Srinathkumar, S.

1992-01-01

The synthesis and experimental validation of an active flutter suppression controller for the Active Flexible Wing wind tunnel model is presented. The design is accomplished with traditional root locus and Nyquist methods using interactive computer graphics tools and extensive simulation based analysis. The design approach uses a fundamental understanding of the flutter mechanism to formulate a simple controller structure to meet stringent design specifications. Experimentally, the flutter suppression controller succeeded in simultaneous suppression of two flutter modes, significantly increasing the flutter dynamic pressure despite modeling errors in predicted flutter dynamic pressure and flutter frequency. The flutter suppression controller was also successfully operated in combination with another controller to perform flutter suppression during rapid rolling maneuvers.

Model-Based Self-Tuning Multiscale Method for Combustion Control

NASA Technical Reports Server (NTRS)

Le, Dzu, K.; DeLaat, John C.; Chang, Clarence T.; Vrnak, Daniel R.

2006-01-01

A multi-scale representation of the combustor dynamics was used to create a self-tuning, scalable controller to suppress multiple instability modes in a liquid-fueled aero engine-derived combustor operating at engine-like conditions. Its self-tuning features designed to handle the uncertainties in the combustor dynamics and time-delays are essential for control performance and robustness. The controller was implemented to modulate a high-frequency fuel valve with feedback from dynamic pressure sensors. This scalable algorithm suppressed pressure oscillations of different instability modes by as much as 90 percent without the peak-splitting effect. The self-tuning logic guided the adjustment of controller parameters and converged quickly toward phase-lock for optimal suppression of the instabilities. The forced-response characteristics of the control model compare well with those of the test rig on both the frequency-domain and the time-domain.

Phase-modulated decoupling and error suppression in qubit-oscillator systems.

PubMed

Green, Todd J; Biercuk, Michael J

2015-03-27

We present a scheme designed to suppress the dominant source of infidelity in entangling gates between quantum systems coupled through intermediate bosonic oscillator modes. Such systems are particularly susceptible to residual qubit-oscillator entanglement at the conclusion of a gate period that reduces the fidelity of the target entangling operation. We demonstrate how the exclusive use of discrete shifts in the phase of the field moderating the qubit-oscillator interaction is sufficient to both ensure multiple oscillator modes are decoupled and to suppress the effects of fluctuations in the driving field. This approach is amenable to a wide variety of technical implementations including geometric phase gates in superconducting qubits and the Molmer-Sorensen gate for trapped ions. We present detailed example protocols tailored to trapped-ion experiments and demonstrate that our approach has the potential to enable multiqubit gate implementation with a significant reduction in technical complexity relative to previously demonstrated protocols.

A comparison of oncogene-induced senescence and replicative senescence: implications for tumor suppression and aging.

PubMed

Nelson, David M; McBryan, Tony; Jeyapalan, Jessie C; Sedivy, John M; Adams, Peter D

2014-06-01

Cellular senescence is a stable proliferation arrest associated with an altered secretory pathway, the senescence-associated secretory phenotype. However, cellular senescence is initiated by diverse molecular triggers, such as activated oncogenes and shortened telomeres, and is associated with varied and complex physiological endpoints, such as tumor suppression and tissue aging. The extent to which distinct triggers activate divergent modes of senescence that might be associated with different physiological endpoints is largely unknown. To begin to address this, we performed gene expression profiling to compare the senescence programs associated with two different modes of senescence, oncogene-induced senescence (OIS) and replicative senescence (RS [in part caused by shortened telomeres]). While both OIS and RS are associated with many common changes in gene expression compared to control proliferating cells, they also exhibit substantial differences. These results are discussed in light of potential physiological consequences, tumor suppression and aging.

Accuracy versus convergence rates for a three dimensional multistage Euler code

NASA Technical Reports Server (NTRS)

Turkel, Eli

1988-01-01

Using a central difference scheme, it is necessary to add an artificial viscosity in order to reach a steady state. This viscosity usually consists of a linear fourth difference to eliminate odd-even oscillations and a nonlinear second difference to suppress oscillations in the neighborhood of steep gradients. There are free constants in these differences. As one increases the artificial viscosity, the high modes are dissipated more and the scheme converges more rapidly. However, this higher level of viscosity smooths the shocks and eliminates other features of the flow. Thus, there is a conflict between the requirements of accuracy and efficiency. Examples are presented for a variety of three-dimensional inviscid solutions over isolated wings.

Validation of the model for ELM suppression with 3D magnetic fields using low torque ITER baseline scenario discharges in DIII-D

DOE PAGES

Moyer, Richard A.; Paz-Soldan, Carlos; Nazikian, Raffi; ...

2017-09-18

Here, experiments have been executed in the DIII-D tokamak to extend suppression of Edge Localized Modes (ELMs) with Resonant Magnetic Perturbations (RMPs) to ITER-relevant levels of beam torque. The results support the hypothesis for RMP ELM suppression based on transition from an ideal screened response to a tearing response at a resonant surface that prevents expansion of the pedestal to an unstable width.

Observation of Trapped-Electron Mode Microturbulence in Improved Confinement Reversed-Field Pinch Plasmas

NASA Astrophysics Data System (ADS)

Duff, James R.

This is a dissertation for the completion of a Doctorate of Philosophy in Physics degree granted at the University of Wisconsin-Madison. Density fluctuations in the large-density-gradient region of improved confinement Madison Sym- metric Torus (MST) RFP plasmas exhibit multiple features that are characteristic of the trapped- electron mode (TEM). In fusion relevant plasmas, thermal transport is a key avenue of research in order to achieve a burning plasma. In the reversed field pinch (RFP) magnetic geometry, the dy- namics of conventional plasma discharges are primarily governed by magnetic stochasticity stem- ming from multiple long-wavelength tearing modes, that sustain the RFP discharge but have an adverse effect on the plasma confinement. Using inductive current profile control, these tearing modes are reduced, and global confinement is increased to that expected for comparable tokamak plasma. Under these conditions with certain plasma equilibria, new short-wavelength fluctuations distinct from global tearing modes appear in the spectrum at frequencies f 50 kHz that have normalized perpendicular wavenumbers k⊥rhos ≤ 0.2, and propagate in the electron diamagnetic drift direction. By adjusting the plasma current or the inductive suppression, there are observable variations in the spectral features. They exhibit a critical-gradient threshold, and the fluctuation amplitude increases with a local density gradient dependent parameter. These characteristics are consistent with the predictions of unstable TEMs based on gyrokinetic analysis using the GENE code. This thesis represents the first observation and description of TEM-like instabilities in the RFP geometry.

Suppression of energetic particle driven instabilities with HHFW heating

DOE PAGES

Fredrickson, E. D.; Taylor, G.; Bertelli, N.; ...

2015-01-01

In plasmas in the National Spherical Torus Experiment (NSTX) [Ono et al., Nucl. Fusion 40 (2000) 557] heated with neutral beams, the beam ions typically excite Energetic Particle Modes (EPMs or fishbones), and Toroidal, Global or Compressional Alfvén Eigenmodes (TAE, GAE, CAE). These modes can redistribute the energetic beam ions, altering the beam driven current profile and the plasma heating profile, or they may affect electron thermal transport or cause losses of the beam ions. In this paper we present experimental results where these instabilities, driven by the super-thermal beam ions, are suppressed with the application of High Harmonic Fastmore » Wave heating.« less

Myopotential inhibition of a bipolar pacemaker caused by electrode insulation defect.

PubMed Central

Amikam, S; Peleg, H; Lemer, J; Riss, E

1977-01-01

A patient is described in whom myopotentials orginating from the anterior abdominal wall muscle suppressed the implanted demand pacemaker despite its bipolar mode of action. This phenomenon was shown by simultaneous recording of the electrocardiogram the electromyogram. At operation, a defect in the insulation of a previously repaired epicardial electrode was found lying in close proximity to these muscles. After repair of the insulation defect, normal pacemaker function was restored. It is suggested that the myopotentials leaked into the pacing system through the insulation defect, thereby suppressing the demand unit, which maintained its bipolar mode of pacing throughout. Images PMID:145229

Raman-Suppressing Coupling for Optical Parametric Oscillator

NASA Technical Reports Server (NTRS)

Savchenkov, Anatoliy; Maleki, Lute; Matsko, Andrey; Rubiola, Enrico

2007-01-01

A Raman-scattering-suppressing input/ output coupling scheme has been devised for a whispering-gallery-mode optical resonator that is used as a four-wave-mixing device to effect an all-optical parametric oscillator. Raman scattering is undesired in such a device because (1) it is a nonlinear process that competes with the desired nonlinear four-wave conversion process involved in optical parametric oscillation and (2) as such, it reduces the power of the desired oscillation and contributes to output noise. The essence of the present input/output coupling scheme is to reduce output loading of the desired resonator modes while increasing output loading of the undesired ones.

[An EMD based time-frequency distribution and its application in EEG analysis].

PubMed

Li, Xiaobing; Chu, Meng; Qiu, Tianshuang; Bao, Haiping

2007-10-01

Hilbert-Huang transform (HHT) is a new time-frequency analytic method to analyze the nonlinear and the non-stationary signals. The key step of this method is the empirical mode decomposition (EMD), with which any complicated signal can be decomposed into a finite and small number of intrinsic mode functions (IMF). In this paper, a new EMD based method for suppressing the cross-term of Wigner-Ville distribution (WVD) is developed and is applied to analyze the epileptic EEG signals. The simulation data and analysis results show that the new method suppresses the cross-term of the WVD effectively with an excellent resolution.

Clockwork inflation

NASA Astrophysics Data System (ADS)

Kehagias, Alex; Riotto, Antonio

2017-04-01

We investigate the recently proposed clockwork mechanism delivering light degrees of freedom with suppressed interactions and show, with various examples, that it can be efficiently implemented in inflationary scenarios to generate flat inflaton potentials and small density perturbations without fine-tunings. We also study the clockwork graviton in de Sitter and, interestingly, we find that the corresponding clockwork charge is site-dependent. As a consequence, the amount of tensor modes is generically suppressed with respect to the standard cases where the clockwork set-up is not adopted. This point can be made a virtue in resurrecting models of inflation which were supposed to be ruled out because of the excessive amount of tensor modes from inflation.

Josephson current through a quantum dot molecule with a Majorana zero mode and Andreev bound states

NASA Astrophysics Data System (ADS)

Tang, Han-Zhao; Zhang, Ying-Tao; Liu, Jian-Jun

2018-04-01

Based on the Green's function method, we investigate the interplay between Majorana zero mode (MZM) and Andreev bound states (ABSs) in a quantum dot molecule side coupled to a topological superconducting nanowire with a pair of MZMs forming a Josephson junction. Since the strong electron-hole asymmetry induced by the nanowire with a topologically non-trivial phase, the MZM suppress the ABSs. The suppression induced by the MZM is robust against the Coulomb repulsion. The interplay between the MZM and the ABSs in Josephson junction presents a feasible experimental means for distinguish between the presence of MZM and ABSs.

Study of Cabibbo suppressed decays of the Ds+ charmed-strange meson involving a KS0

NASA Astrophysics Data System (ADS)

Link, J. M.; Yager, P. M.; Anjos, J. C.; Bediaga, I.; Castromonte, C.; Machado, A. A.; Magnin, J.; Massafferri, A.; de Miranda, J. M.; Pepe, I. M.; Polycarpo, E.; Dos Reis, A. C.; Carrillo, S.; Casimiro, E.; Cuautle, E.; Sánchez-Hernández, A.; Uribe, C.; Vázquez, F.; Agostino, L.; Cinquini, L.; Cumalat, J. P.; Frisullo, V.; O'Reilly, B.; Segoni, I.; Stenson, K.; Tucker, R. S.; Butler, J. N.; Cheung, H. W. K.; Chiodini, G.; Gaines, I.; Garbincius, P. H.; Garren, L. A.; Gottschalk, E.; Kasper, P. H.; Kreymer, A. E.; Kutschke, R.; Wang, M.; Benussi, L.; Bianco, S.; Fabbri, F. L.; Zallo, A.; Reyes, M.; Cawlfield, C.; Kim, D. Y.; Rahimi, A.; Wiss, J.; Gardner, R.; Kryemadhi, A.; Chung, Y. S.; Kang, J. S.; Ko, B. R.; Kwak, J. W.; Lee, K. B.; Cho, K.; Park, H.; Alimonti, G.; Barberis, S.; Boschini, M.; Cerutti, A.; D'Angelo, P.; Dicorato, M.; Dini, P.; Edera, L.; Erba, S.; Inzani, P.; Leveraro, F.; Malvezzi, S.; Menasce, D.; Mezzadri, M.; Moroni, L.; Pedrini, D.; Pontoglio, C.; Prelz, F.; Rovere, M.; Sala, S.; Davenport, T. F.; Arena, V.; Boca, G.; Bonomi, G.; Gianini, G.; Liguori, G.; Lopes Pegna, D.; Merlo, M. M.; Pantea, D.; Ratti, S. P.; Riccardi, C.; Vitulo, P.; Göbel, C.; Otalora, J.; Hernandez, H.; Lopez, A. M.; Mendez, H.; Paris, A.; Quinones, J.; Ramirez, J. E.; Zhang, Y.; Wilson, J. R.; Handler, T.; Mitchell, R.; Engh, D.; Hosack, M.; Johns, W. E.; Luiggi, E.; Nehring, M.; Sheldon, P. D.; Vaandering, E. W.; Webster, M.; Sheaff, M.; Focus Collaboration

2008-02-01

We study the decay of Ds+ mesons into final states involving a KS0 and report the discovery of Cabibbo suppressed decay modes Ds+ →KS0π-π+π+ (179 ± 36 events) and Ds+ →KS0π+ (113 ± 26 events). The branching fraction ratios for the new modes are Γ (Ds+ →KS0π-π+π+)/Γ (Ds+ →KS0K-π+π+) = 0.18 ± 0.04 ± 0.05 and Γ (Ds+ →KS0π+)/Γ (Ds+ →KS0K+) = 0.104 ± 0.024 ± 0.014.

Study of Cabibbo suppressed decays of the Ds+ charmed-strange meson involving a KS0

NASA Astrophysics Data System (ADS)

FOCUS Collaboration; Link, J. M.; Yager, P. M.; Anjos, J. C.; Bediaga, I.; Castromonte, C.; Machado, A. A.; Magnin, J.; Massafferri, A.; de Miranda, J. M.; Pepe, I. M.; Polycarpo, E.; Dos Reis, A. C.; Carrillo, S.; Casimiro, E.; Cuautle, E.; Sánchez-Hernández, A.; Uribe, C.; Vázquez, F.; Agostino, L.; Cinquini, L.; Cumalat, J. P.; Frisullo, V.; O'Reilly, B.; Segoni, I.; Stenson, K.; Tucker, R. S.; Butler, J. N.; Cheung, H. W. K.; Chiodini, G.; Gaines, I.; Garbincius, P. H.; Garren, L. A.; Gottschalk, E.; Kasper, P. H.; Kreymer, A. E.; Kutschke, R.; Wang, M.; Benussi, L.; Bianco, S.; Fabbri, F. L.; Zallo, A.; Reyes, M.; Cawlfield, C.; Kim, D. Y.; Rahimi, A.; Wiss, J.; Gardner, R.; Kryemadhi, A.; Chung, Y. S.; Kang, J. S.; Ko, B. R.; Kwak, J. W.; Lee, K. B.; Cho, K.; Park, H.; Alimonti, G.; Barberis, S.; Boschini, M.; Cerutti, A.; D'Angelo, P.; Dicorato, M.; Dini, P.; Edera, L.; Erba, S.; Inzani, P.; Leveraro, F.; Malvezzi, S.; Menasce, D.; Mezzadri, M.; Moroni, L.; Pedrini, D.; Pontoglio, C.; Prelz, F.; Rovere, M.; Sala, S.; Davenport, T. F.; Arena, V.; Boca, G.; Bonomi, G.; Gianini, G.; Liguori, G.; Lopes Pegna, D.; Merlo, M. M.; Pantea, D.; Ratti, S. P.; Riccardi, C.; Vitulo, P.; Göbel, C.; Otalora, J.; Hernandez, H.; Lopez, A. M.; Mendez, H.; Paris, A.; Quinones, J.; Ramirez, J. E.; Zhang, Y.; Wilson, J. R.; Handler, T.; Mitchell, R.; Engh, D.; Hosack, M.; Johns, W. E.; Luiggi, E.; Nehring, M.; Sheldon, P. D.; Vaandering, E. W.; Webster, M.; Sheaff, M.

2008-02-01

We study the decay of Ds+ mesons into final states involving a KS0 and report the discovery of Cabibbo suppressed decay modes Ds+→KS0πππ (179±36 events) and Ds+→KS0π (113±26 events). The branching fraction ratios for the new modes are Γ(Ds+→KS0πππ)Γ(Ds+→KS0Kππ)=0.18±0.04±0.05 and Γ(Ds+→KS0π)Γ(Ds+→KS0K)=0.104±0.024±0.014.

Impact of a primordial magnetic field on cosmic microwave background B modes with weak lensing

NASA Astrophysics Data System (ADS)

Yamazaki, Dai G.

2018-05-01

We discuss the manner in which the primordial magnetic field (PMF) suppresses the cosmic microwave background (CMB) B mode due to the weak-lensing (WL) effect. The WL effect depends on the lensing potential (LP) caused by matter perturbations, the distribution of which at cosmological scales is given by the matter power spectrum (MPS). Therefore, the WL effect on the CMB B mode is affected by the MPS. Considering the effect of the ensemble average energy density of the PMF, which we call "the background PMF," on the MPS, the amplitude of MPS is suppressed in the wave number range of k >0.01 h Mpc-1 . The MPS affects the LP and the WL effect in the CMB B mode; however, the PMF can damp this effect. Previous studies of the CMB B mode with the PMF have only considered the vector and tensor modes. These modes boost the CMB B mode in the multipole range of ℓ>1000 , whereas the background PMF damps the CMB B mode owing to the WL effect in the entire multipole range. The matter density in the Universe controls the WL effect. Therefore, when we constrain the PMF and the matter density parameters from cosmological observational data sets, including the CMB B mode, we expect degeneracy between these parameters. The CMB B mode also provides important information on the background gravitational waves, inflation theory, matter density fluctuations, and the structure formations at the cosmological scale through the cosmological parameter search. If we study these topics and correctly constrain the cosmological parameters from cosmological observations, including the CMB B mode, we need to correctly consider the background PMF.

Evaluating Cognitive Action Control Using Eye-Movement Analysis: An Oculomotor Adaptation of the Simon Task.

PubMed

Duprez, Joan; Houvenaghel, Jean-François; Naudet, Florian; Dondaine, Thibaut; Auffret, Manon; Robert, Gabriel; Drapier, Dominique; Argaud, Soizic; Vérin, Marc; Sauleau, Paul

2016-01-01

Cognitive action control has been extensively studied using conflict tasks such as the Simon task. In most recent studies, this process has been investigated in the light of the dual route hypothesis and more specifically of the activation-suppression model using distributional analyses. Some authors have suggested that cognitive action control assessment is not specific to response modes. In this study we adapted the Simon task, using oculomotor responses instead of manual responses, in order to evaluate whether the resolution of conflict induced by a two-dimensional stimulus yielded similar results to what is usually reported in tasks with manual responses. Results obtained from 43 young healthy participants revealed the typical congruence effect, with longer reaction times (RT) and lesser accuracy in the incongruent condition. Conditional accuracy functions (CAF) also revealed a higher proportion of fast errors in the incongruent condition and delta plots confirmed that conflict resolution was easier, as the time taken to respond increased. These results are very similar to what has been reported in the literature. Furthermore, our observations are in line with the assumptions of the activation-suppression model, in which automatic activation in conflict situations is captured in the fastest responses and selective inhibition of cognitive action control needs time to build up. Altogether, our results suggest that conflict resolution has core mechanisms whatever the response mode, manual or oculomotor. Using oculomotor responses in such tasks could be of interest when investigating cognitive action control in patients with severe motor disorders.

Physics of increased edge electron temperature and density turbulence during ELM-free QH-mode operation on DIII-D

NASA Astrophysics Data System (ADS)

Sung, C.; Rhodes, T. L.; Staebler, G. M.; Yan, Z.; McKee, G. R.; Smith, S. P.; Osborne, T. H.; Peebles, W. A.

2018-05-01

For the first time, we report increased edge electron temperature and density turbulence levels ( T˜ e and n˜ e) in Edge Localized Mode free Quiescent H-mode (ELM-free QH-mode) plasmas as compared to the ELMing time period. ELMs can severely damage plasma facing components in fusion plasma devices due to their large transient energy transport, making ELM-free operation a highly sought after goal. The QH-mode is a candidate for this goal as it is ELM-free for times limited only by hardware constraints. It is found that the driving gradients decrease during the QH-mode compared to the ELMing phase, however, a significant decrease in the ExB shearing rate is also observed that taken together is consistent with the increased turbulence. These results are significant as the prediction and control of ELM-free H-mode regimes are crucial for the operation of future fusion devices such as ITER. The changes in the linear growth rates calculated by CGYRO [Candy et al., J. Comput. Phys. 324, 73 (2016)] and the measured ExB shearing rate between ELMing and QH-mode phases are qualitatively consistent with these turbulence changes. Comparison with ELMing and 3D fields ELM suppressed H-mode finds a similar increase in T˜ e and n˜ e, however, with distinctly different origins, the increased driving gradients rather than the changes in the ExB shearing rate in 3D fields ELM suppressed the H-mode. However, linear gyrokinetic calculation results are generally consistent with the increased turbulence in both ELM-controlled discharges.

Connection between plasma response and resonant magnetic perturbation (RMP) edge localized mode (ELM) suppression in DIII-D [Connection between plasma response and RMP ELM suppression in DIII-D

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

Wingen, Andreas; Ferraro, Nathaniel M.; Shafer, Morgan W.

Calculations of the plasma response to applied non-axisymmetric fields in several DIII-D discharges show that predicted displacements depend strongly on the edge current density. This result is found using both a linear two-fluid-MHD model (M3D-C1) and a nonlinear ideal-MHD model (VMEC). Furthermore, it is observed that the probability of a discharge being edge localized mode (ELM)-suppressed is most closely related to the edge current density, as opposed to the pressure gradient. It is found that discharges with a stronger kink response are closer to the peeling–ballooning stability limit in ELITE simulations and eventually cross into the unstable region, causing ELMsmore » to reappear. Thus for effective ELM suppression, the RMP has to prevent the plasma from generating a large kink response, associated with ELM instability. Experimental observations are in agreement with the finding; discharges which have a strong kink response in the MHD simulations show ELMs or ELM mitigation during the RMP phase of the experiment, while discharges with a small kink response in the MHD simulations are fully ELM suppressed in the experiment by the applied resonant magnetic perturbation. The results are cross-checked against modeled 3D ideal MHD equilibria using the VMEC code. The procedure of constructing optimal 3D equilibria for diverted H-mode discharges using VMEC is presented. As a result, kink displacements in VMEC are found to scale with the edge current density, similar to M3D-C1, but the displacements are smaller. A direct correlation in the flux surface displacements to the bootstrap current is shown.« less

Connection between plasma response and resonant magnetic perturbation (RMP) edge localized mode (ELM) suppression in DIII-D [Connection between plasma response and RMP ELM suppression in DIII-D

DOE PAGES

Wingen, Andreas; Ferraro, Nathaniel M.; Shafer, Morgan W.; ...

2015-09-03

Calculations of the plasma response to applied non-axisymmetric fields in several DIII-D discharges show that predicted displacements depend strongly on the edge current density. This result is found using both a linear two-fluid-MHD model (M3D-C1) and a nonlinear ideal-MHD model (VMEC). Furthermore, it is observed that the probability of a discharge being edge localized mode (ELM)-suppressed is most closely related to the edge current density, as opposed to the pressure gradient. It is found that discharges with a stronger kink response are closer to the peeling–ballooning stability limit in ELITE simulations and eventually cross into the unstable region, causing ELMsmore » to reappear. Thus for effective ELM suppression, the RMP has to prevent the plasma from generating a large kink response, associated with ELM instability. Experimental observations are in agreement with the finding; discharges which have a strong kink response in the MHD simulations show ELMs or ELM mitigation during the RMP phase of the experiment, while discharges with a small kink response in the MHD simulations are fully ELM suppressed in the experiment by the applied resonant magnetic perturbation. The results are cross-checked against modeled 3D ideal MHD equilibria using the VMEC code. The procedure of constructing optimal 3D equilibria for diverted H-mode discharges using VMEC is presented. As a result, kink displacements in VMEC are found to scale with the edge current density, similar to M3D-C1, but the displacements are smaller. A direct correlation in the flux surface displacements to the bootstrap current is shown.« less

Dynamic ELM and divertor control using resonant toroidal multi-mode magnetic fields in DIII-D and EAST

NASA Astrophysics Data System (ADS)

Sun, Youwen

2017-10-01

A rotating n = 2 Resonant Magnetic Perturbation (RMP) field combined with a stationary n = 3 RMP field has validated predictions that access to ELM suppression can be improved, while divertor heat and particle flux can also be dynamically controlled in DIII-D. Recent observations in the EAST tokamak indicate that edge magnetic topology changes, due to nonlinear plasma response to magnetic perturbations, play a critical role in accessing ELM suppression. MARS-F code MHD simulations, which include the plasma response to the RMP, indicate the nonlinear transition to ELM suppression is optimized by configuring the RMP coils to drive maximal edge stochasticity. Consequently, mixed toroidal multi-mode RMP fields, which produce more densely packed islands over a range of additional rational surfaces, improve access to ELM suppression, and further spread heat loading on the divertor. Beneficial effects of this multi-harmonic spectrum on ELM suppression have been validated in DIII-D. Here, the threshold current required for ELM suppression with a mixed n spectrum, where part of the n = 3 RMP field is replaced by an n = 2 field, is smaller than the case with pure n = 3 field. An important further benefit of this multi-mode approach is that significant changes of 3D particle flux footprint profiles on the divertor are found in the experiment during the application of a rotating n = 2 RMP field superimposed on a static n = 3 RMP field. This result was predicted by modeling studies of the edge magnetic field structure using the TOP2D code which takes into account plasma response from MARS-F code. These results expand physics understanding and potential effectiveness of the technique for reliably controlling ELMs and divertor power/particle loading distributions in future burning plasma devices such as ITER. Work supported by USDOE under DE-FC02-04ER54698 and NNSF of China under 11475224.

Tensor to scalar ratio and large scale power suppression from pre-slow roll initial conditions

NASA Astrophysics Data System (ADS)

Lello, Louis; Boyanovsky, Daniel

2014-05-01

We study the corrections to the power spectra of curvature and tensor perturbations and the tensor-to-scalar ratio r in single field slow roll inflation with standard kinetic term due to initial conditions imprinted by a ``fast-roll'' stage prior to slow roll. For a wide range of initial inflaton kinetic energy, this stage lasts only a few e-folds and merges smoothly with slow-roll thereby leading to non-Bunch-Davies initial conditions for modes that exit the Hubble radius during slow roll. We describe a program that yields the dynamics in the fast-roll stage while matching to the slow roll stage in a manner that is independent of the inflationary potentials. Corrections to the power spectra are encoded in a ``transfer function'' for initial conditions Script Tα(k), Script Pα(k) = PBDα(k)Script Tα(k), implying a modification of the ``consistency condition'' for the tensor to scalar ratio at a pivot scale k0: r(k0) = -8nT(k0) [Script TT(k0)/Script TScript R(k0)]. We obtain Script Tα(k) to leading order in a Born approximation valid for modes of observational relevance today. A fit yields Script Tα(k) = 1+Aαk-pcos [2πωk/Hsr+varphiα], with 1.5lesssimplesssim2, ω simeq 1 and Hsr the Hubble scale during slow roll inflation, where curvature and tensor perturbations feature the same p,ω for a wide range of initial conditions. These corrections lead to both a suppression of the quadrupole and oscillatory features in both PR(k) and r(k0) with a period of the order of the Hubble scale during slow roll inflation. The results are quite general and independent of the specific inflationary potentials, depending solely on the ratio of kinetic to potential energy κ and the slow roll parameters epsilonV, ηV to leading order in slow roll. For a wide range of κ and the values of epsilonV ηV corresponding to the upper bounds from Planck, we find that the low quadrupole is consistent with the results from Planck, and the oscillations in r(k0) as a function of k0 could be observable if the modes corresponding to the quadrupole and the pivot scale crossed the Hubble radius very few (2-3) e-folds after the onset of slow roll. We comment on possible impact on the recent BICEP2 results.

Experimental Performance of a Single-Mode Ytterbium-doped Fiber Ring Laser with Intracavity Modulator

NASA Technical Reports Server (NTRS)

Numata, Kenji; Camp, Jordan

2012-01-01

We have developed a linearly polarized Ytterbium-doped fiber ring laser with a single longitudinal mode output at 1064 run. A fiber-coupled intracavity phase modulator ensured mode-hop free operation and allowed fast frequency tuning. The fiber laser was locked with high stability to an iodine-stabilized laser, showing a frequency noise suppression of a factor approx 10 (exp 5) at 1 mHz

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

Superconductivity induced by flexural modes in non-σh-symmetric Dirac-like two-dimensional materials: A theoretical study for silicene and germanene

NASA Astrophysics Data System (ADS)

Fischetti, Massimo V.; Polley, Arup

2018-04-01

In two-dimensional crystals that lack symmetry under reflections on the horizontal plane of the lattice (non-σh-symmetric), electrons can couple to flexural modes (ZA phonons) at first order. We show that in materials of this type that also exhibit a Dirac-like electron dispersion, the strong coupling can result in electron pairing mediated by these phonons, as long as the flexural modes are not damped or suppressed by additional interactions with a supporting substrate or gate insulator. We consider several models: The weak-coupling limit, which is applicable only in the case of gapped and parabolic materials, like stanene and HfSe2, thanks to the weak coupling; the full gap-equation, solved using the constant-gap approximation and considering statically screened interactions; its extensions to energy-dependent gap and to dynamic screening. We argue that in the case of silicene and germanene superconductivity mediated by this process can exhibit a critical temperature of a few degrees K, or even a few tens of degrees K when accounting for the effect of a high-dielectric-constant environment. We conclude that the electron/flexural-modes coupling should be included in studies of possible superconductivity in non-σh-symmetric two-dimensional crystals, even if alternative forms of coupling are considered.

Assessment of Fiber Chromatic Dispersion Based on Elimination of Second-Order Harmonics in Optical OFDM Single Sideband Modulation Using Mach Zehnder Modulator

NASA Astrophysics Data System (ADS)

Patel, Dhananjay; Singh, Vinay Kumar; Dalal, U. D.

2016-07-01

This work addresses the analytical and numerical investigations of the transmission performance of an optical Single Sideband (SSB) modulation technique generated by a Mach Zehnder Modulator (MZM) with a 90° and 120° hybrid coupler. It takes into account the problem of chromatic dispersion in single mode fibers in Passive Optical Networks (PON), which severely degrades the performance of the system. Considering the transmission length of the fiber, the SSB modulation generated by maintaining a phase shift of π/2 between the two electrodes of the MZM provides better receiver sensitivity. However, the power of higher-order harmonics generated due to the nonlinearity of the MZM is directly proportional to the modulation index, making the SSB look like a quasi-double sideband (DSB) and causing power fading due to chromatic dispersion. To eliminate one of the second-order harmonics, the SSB signal based on an MZM with a 120° hybrid coupler is simulated. An analytical model of conventional SSB using 90° and 120° hybrid couplers is established. The latter suppresses unwanted (upper/lower) first-order and second-order (lower/upper) sidebands. For the analysis, a varying quadrature amplitude modulation (QAM) Orthogonal Frequency Division Multiplexing (OFDM) signal with a data rate of 5 Gb/s is upconverted using both of the SSB techniques and is transmitted over a distance of 75 km in Single Mode Fiber (SMF). The simulation results show that the SSB with 120° hybrid coupler proves to be more immune to chromatic dispersion as compared to the conventional SSB technique. This is in tandem with the theoretical analysis presented in the article.

Elevation or Suppression? The Resolved Star Formation Main Sequence of Galaxies with Two Different Assembly Modes

NASA Astrophysics Data System (ADS)

Liu, Qing; Wang, Enci; Lin, Zesen; Gao, Yulong; Liu, Haiyang; Berhane Teklu, Berzaf; Kong, Xu

2018-04-01

We investigate the spatially resolved star formation main sequence in star-forming galaxies using Integral Field Spectroscopic observations from the Mapping Nearby Galaxies at the Apache Point Observatory survey. We demonstrate that the correlation between the stellar mass surface density (Σ*) and star formation rate surface density (ΣSFR) holds down to the sub-galactic scale, leading to the sub-galactic main sequence (SGMS). By dividing galaxies into two populations based on their recent mass assembly modes, we find the resolved main sequence in galaxies with the “outside-in” mode is steeper than that in galaxies with the “inside-out” mode. This is also confirmed on a galaxy-by-galaxy level, where we find the distributions of SGMS slopes for individual galaxies are clearly separated for the two populations. When normalizing and stacking the SGMS of individual galaxies on one panel for the two populations, we find that the inner regions of galaxies with the “inside-out” mode statistically exhibit a suppression in star formation, with a less significant trend in the outer regions of galaxies with the “outside-in” mode. In contrast, the inner regions of galaxies with “outside-in” mode and the outer regions of galaxies with “inside-out” mode follow a slightly sublinear scaling relation with a slope ∼0.9, which is in good agreement with previous findings, suggesting that they are experiencing a universal regulation without influences of additional physical processes.

Cavity Quantum Acoustic Device in the Multimode Strong Coupling Regime.

PubMed

Moores, Bradley A; Sletten, Lucas R; Viennot, Jeremie J; Lehnert, K W

2018-06-01

We demonstrate an acoustical analog of a circuit quantum electrodynamics system that leverages acoustic properties to enable strong multimode coupling in the dispersive regime while suppressing spontaneous emission to unconfined modes. Specifically, we fabricate and characterize a device that comprises a flux tunable transmon coupled to a 300  μm long surface acoustic wave resonator. For some modes, the qubit-cavity coupling reaches 6.5 MHz, exceeding the cavity loss rate (200 kHz), qubit linewidth (1.1 MHz), and the cavity free spectral range (4.8 MHz), placing the device in both the strong coupling and strong multimode regimes. With the qubit detuned from the confined modes of the cavity, we observe that the qubit linewidth strongly depends on its frequency, as expected for spontaneous emission of phonons, and we identify operating frequencies where this emission rate is suppressed.

Suppression of the cooperative Jahn-Teller distortion and its effect on the Raman octahedra-rotation modes of TbM n1 -xF exO3

NASA Astrophysics Data System (ADS)

Vilarinho, R.; Passos, D. J.; Queirós, E. C.; Tavares, P. B.; Almeida, A.; Weber, M. C.; Guennou, M.; Kreisel, J.; Moreira, J. Agostinho

2018-04-01

This work reports the changes in structure and lattice dynamics induced by substituting the Jahn-Teller-active M n3 + ion by the Jahn-Teller-inactive F e3 + in TbM n1 -xF exO3 over the full composition range. The structural analysis reveals that the amplitude of the cooperative Jahn-Teller distortion decreases linearly from x =0 (pure TbMn O3 ) to x =0.5 , where it is completely suppressed. We then correlate this evolution with the behavior of the Raman modes across the solid solution. In particular, we show that the Raman modes associated with the rotation of octahedra, whose wave number is commonly considered to scale linearly with the tilt angles in orthorhombic Pnma perovskites, are also sensitive to the amplitude of the Jahn-Teller distortion.

Analytical and numerical treatment of resistive drift instability in a plasma slab

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

Mirnov, V. V., E-mail: vvmirnov@wisc.edu; Sauppe, J. P.; Hegna, C. C.

An analytic approach combining the effect of equilibrium diamagnetic flows and the finite ionsound gyroradius associated with electron−ion decoupling and kinetic Alfvén wave dispersion is derived to study resistive drift instabilities in a plasma slab. Linear numerical computations using the NIMROD code are performed with cold ions and hot electrons in a plasma slab with a doubly periodic box bounded by two perfectly conducting walls. A linearly unstable resistive drift mode is observed in computations with a growth rate that is consistent with the analytic dispersion relation. The resistive drift mode is expected to be suppressed by magnetic shear inmore » unbounded domains, but the mode is observed in numerical computations with and without magnetic shear. In the slab model, the finite slab thickness and the perfectly conducting boundary conditions are likely to account for the lack of suppression.« less

Gutzwiller charge phase diagram of cuprates, including electron–phonon coupling effects

DOE PAGES

Markiewicz, R. S.; Seibold, G.; Lorenzana, J.; ...

2015-02-01

Besides significant electronic correlations, high-temperature superconductors also show a strong coupling of electrons to a number of lattice modes. Combined with the experimental detection of electronic inhomogeneities and ordering phenomena in many high-T c compounds, these features raise the question as to what extent phonons are involved in the associated instabilities. Here we address this problem based on the Hubbard model including a coupling to phonons in order to capture several salient features of the phase diagram of hole-doped cuprates. Charge degrees of freedom, which are suppressed by the large Hubbard U near half-filling, are found to become active atmore » a fairly low doping level. We find that possible charge order is mainly driven by Fermi surface nesting, with competition between a near-(π, π) order at low doping and antinodal nesting at higher doping, very similar to the momentum structure of magnetic fluctuations. The resulting nesting vectors are generally consistent with photoemission and tunneling observations, evidence for charge density wave order in YBa₂Cu₃O 7-δ including Kohn anomalies, and suggestions of competition between one- and two-q-vector nesting.« less

Enhancement of elliptic flow can signal a first-order phase transition in high-energy heavy-ion collisions

NASA Astrophysics Data System (ADS)

Nara, Yasushi; Niemi, Harri; Ohnishi, Akira; Steinheimer, Jan; Luo, Xiaofeng; Stöcker, Horst

2018-02-01

The beam energy dependence of the elliptic flow, v2, is studied in mid-central Au+Au collisions in the energy range of 3≤ √{s_{NN}} ≤ 30 GeV within the microscopic transport model JAM. The results of three different modes of JAM are compared; cascade-, hadronic mean field-, and a new mode with modified equations of state, with a first-order phase transition and with a crossover transition. The standard hadronic mean field suppresses the elliptic flow v2, while the inclusion of the effects of a first-order phase transition (and also of a crossover transition) does enhance the elliptic flow at √{s_{NN}} < 30 GeV. This is due to the high sensitivity of v2 on the early, compression stage, pressure gradients of the systems created in high-energy heavy-ion collisions. The enhancement or suppression of the scaled energy flow, dubbed "elliptic flow", v2= <(px2-py2)/pT2 >, is understood as being due to out-of-plane flow, py > px, i.e. v2 < 0, dubbed out of plane - "squeeze-out", which occurs predominantly in the early, compression stage. Subsequently, the in-plane flow dominates, px > py, in the expansion stage, v2 > 0. The directed flow, v1(y) = < px(y)/pT(y)>, dubbed "bounce-off", is an independent measure of the pressure, which quickly builds up the transverse momentum transfer in the reaction plane. When the spectator matter leaves the participant fireball region, where the highest compression occurs, a hard expansion leads to larger v2. A combined analysis of the three transverse flow coefficients, radial v0 ˜ v_{\\perp}-, directed v1- and elliptic v2- flow of nucleons, in the beam energy range 3≤√{s_{NN}} ≤ 10 GeV, distinguishes the different compression and expansion scenarios: a characteristic dependence on the early stage equation of state is observed. The enhancement of both the elliptic and the transverse radial flow and the simultaneous collapse of the directed flow of nucleons offers a clear signature if a first-order phase transition is realized at the highest baryon densities created in high-energy heavy-ion collisions.

Edge-localized mode avoidance and pedestal structure in I-mode plasmas

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

Walk, J. R., E-mail: jrwalk@psfc.mit.edu; Hughes, J. W.; Hubbard, A. E.

I-mode is a high-performance tokamak regime characterized by the formation of a temperature pedestal and enhanced energy confinement, without an accompanying density pedestal or drop in particle and impurity transport. I-mode operation appears to have naturally occurring suppression of large Edge-Localized Modes (ELMs) in addition to its highly favorable scalings of pedestal structure and overall performance. Extensive study of the ELMy H-mode has led to the development of the EPED model, which utilizes calculations of coupled peeling-ballooning MHD modes and kinetic-ballooning mode (KBM) stability limits to predict the pedestal structure preceding an ELM crash. We apply similar tools to themore » structure and ELM stability of I-mode pedestals. Analysis of I-mode discharges prepared with high-resolution pedestal data from the most recent C-Mod campaign reveals favorable pedestal scalings for extrapolation to large machines—pedestal temperature scales strongly with power per particle P{sub net}/n{sup ¯}{sub e}, and likewise pedestal pressure scales as the net heating power (consistent with weak degradation of confinement with heating power). Matched discharges in current, field, and shaping demonstrate the decoupling of energy and particle transport in I-mode, increasing fueling to span nearly a factor of two in density while maintaining matched temperature pedestals with consistent levels of P{sub net}/n{sup ¯}{sub e}. This is consistent with targets for increased performance in I-mode, elevating pedestal β{sub p} and global performance with matched increases in density and heating power. MHD calculations using the ELITE code indicate that I-mode pedestals are strongly stable to edge peeling-ballooning instabilities. Likewise, numerical modeling of the KBM turbulence onset, as well as scalings of the pedestal width with poloidal beta, indicates that I-mode pedestals are not limited by KBM turbulence—both features identified with the trigger for large ELMs, consistent with the observed suppression of large ELMs in I-mode.« less

Edge-localized mode avoidance and pedestal structure in I-mode plasmasa)

NASA Astrophysics Data System (ADS)

Walk, J. R.; Hughes, J. W.; Hubbard, A. E.; Terry, J. L.; Whyte, D. G.; White, A. E.; Baek, S. G.; Reinke, M. L.; Theiler, C.; Churchill, R. M.; Rice, J. E.; Snyder, P. B.; Osborne, T.; Dominguez, A.; Cziegler, I.

2014-05-01

I-mode is a high-performance tokamak regime characterized by the formation of a temperature pedestal and enhanced energy confinement, without an accompanying density pedestal or drop in particle and impurity transport. I-mode operation appears to have naturally occurring suppression of large Edge-Localized Modes (ELMs) in addition to its highly favorable scalings of pedestal structure and overall performance. Extensive study of the ELMy H-mode has led to the development of the EPED model, which utilizes calculations of coupled peeling-ballooning MHD modes and kinetic-ballooning mode (KBM) stability limits to predict the pedestal structure preceding an ELM crash. We apply similar tools to the structure and ELM stability of I-mode pedestals. Analysis of I-mode discharges prepared with high-resolution pedestal data from the most recent C-Mod campaign reveals favorable pedestal scalings for extrapolation to large machines—pedestal temperature scales strongly with power per particle Pnet/n ¯e, and likewise pedestal pressure scales as the net heating power (consistent with weak degradation of confinement with heating power). Matched discharges in current, field, and shaping demonstrate the decoupling of energy and particle transport in I-mode, increasing fueling to span nearly a factor of two in density while maintaining matched temperature pedestals with consistent levels of Pnet/n ¯e. This is consistent with targets for increased performance in I-mode, elevating pedestal βp and global performance with matched increases in density and heating power. MHD calculations using the ELITE code indicate that I-mode pedestals are strongly stable to edge peeling-ballooning instabilities. Likewise, numerical modeling of the KBM turbulence onset, as well as scalings of the pedestal width with poloidal beta, indicates that I-mode pedestals are not limited by KBM turbulence—both features identified with the trigger for large ELMs, consistent with the observed suppression of large ELMs in I-mode.

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

Moyer, Richard A.; Paz-Soldan, Carlos; Nazikian, Raffi

Here, experiments have been executed in the DIII-D tokamak to extend suppression of Edge Localized Modes (ELMs) with Resonant Magnetic Perturbations (RMPs) to ITER-relevant levels of beam torque. The results support the hypothesis for RMP ELM suppression based on transition from an ideal screened response to a tearing response at a resonant surface that prevents expansion of the pedestal to an unstable width.

Observation of improved and degraded confinement with driven flow on the LAPD

NASA Astrophysics Data System (ADS)

Schaffner, David

2012-10-01

External continuous control over azimuthal flow and flow shear has been achieved in a linear plasma device for the first time allowing for a careful study of the effect of flow shear on pressure-gradient-driven turbulence and transport in the edge of the Large Plasma Device (LAPD). The flow is controlled using biasable iris-like limiters situated axially between the cathode source and main plasma chamber. LAPD rotates spontaneously in the ion diamagnetic direction (IDD); positive limiter bias first reduces, then minimizes (producing a near-zero shear state), and finally reverses the flow into the electron diamagnetic direction (EDD). Degradation of particle confinement is observed in the minimum shearing state and reduction in turbulent particle flux is observed with increasing shearing in both flow directions. Near-complete suppression of turbulent particle flux is observed for shearing rates comparable to the turbulent autocorrelation rate measured in the minimum shear state. Turbulent flux suppression is dominated by amplitude reduction in low-frequency (>10kHz) density fluctuations and a reduction in the radial correlation length. An increase in fluctuations for the highest shearing states is observed with the emergence of a coherent mode which does not lead to net particle transport. Magnetic field is varied in order to explore whether and how field effects transport modification. Calculations of transport equations are used to predict density profiles given source and temperature profiles and can show the level of transport predicted to be necessary in order to produce the experimental density profiles observed. Finally, the variations of density fluctuations and radial correlation length are fit well with power-laws and compare favorably to simple models of shear suppression of transport.

Flutter suppression for the Active Flexible Wing - Control system design and experimental validation

NASA Technical Reports Server (NTRS)

Waszak, M. R.; Srinathkumar, S.

1992-01-01

The synthesis and experimental validation of a control law for an active flutter suppression system for the Active Flexible Wing wind-tunnel model is presented. The design was accomplished with traditional root locus and Nyquist methods using interactive computer graphics tools and with extensive use of simulation-based analysis. The design approach relied on a fundamental understanding of the flutter mechanism to formulate understanding of the flutter mechanism to formulate a simple control law structure. Experimentally, the flutter suppression controller succeeded in simultaneous suppression of two flutter modes, significantly increasing the flutter dynamic pressure despite errors in the design model. The flutter suppression controller was also successfully operated in combination with a rolling maneuver controller to perform flutter suppression during rapid rolling maneuvers.

Dampers for Stationary Labyrinth Seals

NASA Technical Reports Server (NTRS)

El-Aini, Yehia; Mitchell, William; Roberts, Lawrence; Montgomery, Stuart; Davis, Gary

2011-01-01

Vibration dampers have been invented that are incorporated as components within the stationary labyrinth seal assembly. These dampers are intended to supplement other vibration-suppressing features of labyrinth seals in order to reduce the incidence of high-cycle-fatigue failures, which have been known to occur in the severe vibratory environments of jet engines and turbopumps in which labyrinth seals are typically used. A vibration damper of this type includes several leaf springs and/or a number of metallic particles (shot) all held in an annular seal cavity by a retaining ring. The leaf springs are made of a spring steel alloy chosen, in conjunction with design parameters, to maintain sufficient preload to ensure effectiveness of damping at desired operating temperatures. The cavity is vented via a small radial gap between the retaining ring and seal housing. The damping mechanism is complex. In the case of leaf springs, the mechanism is mainly friction in the slippage between the seal housing and individual dampers. In the case of a damper that contains shot, the damping mechanism includes contributions from friction between individual particles, friction between particles and cavity walls, and dissipation of kinetic energy of impact. The basic concept of particle/shot vibration dampers has been published previously; what is new here is the use of such dampers to suppress traveling-wave vibrations in labyrinth seals. Damping effectiveness depends on many parameters, including, but not limited to, coefficient of friction, mode shape, and frequency and amplitude of vibrational modes. In tests, preloads of the order of 6 to 15 lb (2.72 to 6.8 kilograms) per spring damper were demonstrated to provide adequate damping levels. Effectiveness of shot damping of vibrations having amplitudes from 20 to 200 times normal terrestrial gravitational acceleration (196 to 1,960 meters per square second) and frequencies up to 12 kHz was demonstrated for shot sizes from 0.032 to 0.062 in. (0.8 to 1.6 millimeters) at fill levels of from 70 to 95 percent.

Development of an Experimental Rig for Investigation of Higher Order Modes in Ducts

NASA Technical Reports Server (NTRS)

Gerhold, Carl H.; Cabell, Randolph H.; Brown, Martha C.

2006-01-01

Continued progress to reduce fan noise emission from high bypass ratio engine ducts in aircraft increasingly relies on accurate description of the sound propagation in the duct. A project has been undertaken at NASA Langley Research Center to investigate the propagation of higher order modes in ducts with flow. This is a two-pronged approach, including development of analytic models (the subject of a separate paper) and installation of a laboratory-quality test rig. The purposes of the rig are to validate the analytical models and to evaluate novel duct acoustic liner concepts, both passive and active. The dimensions of the experimental rig test section scale to between 25% and 50% of the aft bypass ducts of most modern engines. The duct is of rectangular cross section so as to provide flexibility to design and fabricate test duct liner samples. The test section can accommodate flow paths that are straight through or offset from inlet to discharge, the latter design allowing investigation of the effect of curvature on sound propagation and duct liner performance. The maximum air flow rate through the duct is Mach 0.3. Sound in the duct is generated by an array of 16 high-intensity acoustic drivers. The signals to the loudspeaker array are generated by a multi-input/multi-output feedforward control system that has been developed for this project. The sound is sampled by arrays of flush-mounted microphones and a modal decomposition is performed at the frequency of sound generation. The data acquisition system consists of two arrays of flush-mounted microphones, one upstream of the test section and one downstream. The data are used to determine parameters such as the overall insertion loss of the test section treatment as well as the effect of the treatment on a modal basis such as mode scattering. The methodology used for modal decomposition is described, as is a description of the mode generation control system. Data are presented which demonstrate the performance of the controller to generate the desired mode while suppressing all other cut on modes in the duct.

Comparative study of A-site order in the lead-free bismuth titanates M{sub 1/2}Bi{sub 1/2}TiO{sub 3} (M=Li, Na, K, Rb, Cs, Ag, Tl) from first-principles

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

Gröting, Melanie, E-mail: groeting@mm.tu-darmstadt.de; Albe, Karsten, E-mail: albe@mm.tu-darmstadt.de

2014-05-01

We investigate the possibility of enhancing chemical order in the relaxor ferroelectric Na{sub 1/2}Bi{sub 1/2}TiO{sub 3} upon substitution of Na{sup +} by other monovalent cations M{sup +} using total energy calculations based on density functional theory. All chemically available monovalent cations M{sup +}, which are Li, Na, Ag, K, Tl, Rb and Cs, are considered and an analysis of the structurally relaxed structures in terms of symmetry-adapted distortion modes is given in order to quantify the chemically induced structural distortions. We demonstrate that the replacement of Na{sup +} by other monovalent cations can hardly alter the tendency of chemical ordermore » with respect to Na{sub 1/2}Bi{sub 1/2}TiO{sub 3}. Only Tl{sub 1/2}Bi{sub 1/2}TiO{sub 3} and Ag{sub 1/2}Bi{sub 1/2}TiO{sub 3} show enhanced tendency for chemical ordering. Both heavy metals behave similar to the light alkali metals in terms of structural relaxations and relative stabilities of the ordered configurations. Although a comparison of the Goldschmidt factors of components (M TiO{sub 3}){sup −} reveals for Tl a value above the upper stability limit for perovskites, the additional lone-pair effect of Tl{sup +} stabilizes the ordered structure. - Graphical abstract: Amplitudes of chemically induced distortion modes in different ordered perovskites M{sub 1/2}Bi{sub 1/2}TiO{sub 3} and visualisation of atomic displacements associated with distortion mode X{sup +}{sub 1} in the 001-ordered compounds Li{sub 1/2}Bi{sub 1/2}TiO{sub 3} and Cs{sub 1/2}Bi{sub 1/2}TiO{sub 3}. Due to a substantial size mismatch between bismuth (green) and caesium (dark blue), incorporation of the latter leads to enhanced displacements of oxygen atoms (red) and suppresses displacements of titanium (silver) as compared to lithium (light blue) or other smaller monovalent cations. - Highlights: • Lead-free A-site mixed bismuth titanates M{sub 1/2}Bi{sub 1/2}TiO{sub 3} are studied by first-principles calculations. • Investigation of chemical ordering tendency for M=Li, Na, K, Rb, Cs, Ag, and Tl. • Group theoretical analysis of different ordered structures. • Ag and Tl compounds are the most promising candidates for study of chemical order dependent ferroelectric properties.« less

Deficient Suppression of Default Mode Regions during Working Memory in Individuals with Early Psychosis and at Clinical High-Risk for Psychosis

PubMed Central

Fryer, Susanna L.; Woods, Scott W.; Kiehl, Kent A.; Calhoun, Vince D.; Pearlson, Godfrey D.; Roach, Brian J.; Ford, Judith M.; Srihari, Vinod H.; McGlashan, Thomas H.; Mathalon, Daniel H.

2013-01-01

Background: The default mode network (DMN) is a set of brain regions typically activated at rest and suppressed during extrinsic cognition. Schizophrenia has been associated with deficient DMN suppression, though the extent to which DMN dysfunction predates psychosis onset is unclear. This study examined DMN suppression during working memory (WM) performance in youth at clinical high-risk (CHR) for psychosis, early schizophrenia (ESZ) patients, and healthy controls (HC). We hypothesized that the DMN would show load-dependent suppression during WM retrieval in HC but not in ESZ, with CHR participants showing an intermediate pattern. Methods: fMRI data were collected from CHR (n = 32), ESZ (n = 22), and HC (n = 54) participants, ages 12–30. DMN regions were defined via seed-based connectivity analysis of resting-state fMRI data from an independent HC sample. Load-dependent deactivations of these DMN regions in response to WM probes were interrogated. Results: Healthy controls showed linear load-dependent increases in DMN deactivation. Significant Group-by-Load interactions were observed in DMN regions including medial prefrontal and lateral posterior parietal cortices. Group-by-Load effects in posterior DMN nodes resulted from less suppression at higher WM loads in ESZ relative to HC, with CHR differing from neither group. In medial prefrontal cortex, suppression of activity at higher WM loads was significantly diminished in both CHR and ESZ groups, relative to HC. In addition, investigation of dorsolateral prefrontal cortex (DLPFC) activations revealed that ESZ activated right DLPFC significantly more than HC, with CHR differing from neither group. Conclusion: While HC showed WM load-dependent modulation of DMN suppression, CHR individuals had deficient higher-load DMN suppression that was similar to, but less pronounced than, the distributed suppression deficits evident in ESZ patients. These results suggest that DMN dysregulation associated with schizophrenia predates psychosis onset. PMID:24032017

Deficient Suppression of Default Mode Regions during Working Memory in Individuals with Early Psychosis and at Clinical High-Risk for Psychosis.

PubMed

Fryer, Susanna L; Woods, Scott W; Kiehl, Kent A; Calhoun, Vince D; Pearlson, Godfrey D; Roach, Brian J; Ford, Judith M; Srihari, Vinod H; McGlashan, Thomas H; Mathalon, Daniel H

2013-01-01

The default mode network (DMN) is a set of brain regions typically activated at rest and suppressed during extrinsic cognition. Schizophrenia has been associated with deficient DMN suppression, though the extent to which DMN dysfunction predates psychosis onset is unclear. This study examined DMN suppression during working memory (WM) performance in youth at clinical high-risk (CHR) for psychosis, early schizophrenia (ESZ) patients, and healthy controls (HC). We hypothesized that the DMN would show load-dependent suppression during WM retrieval in HC but not in ESZ, with CHR participants showing an intermediate pattern. fMRI data were collected from CHR (n = 32), ESZ (n = 22), and HC (n = 54) participants, ages 12-30. DMN regions were defined via seed-based connectivity analysis of resting-state fMRI data from an independent HC sample. Load-dependent deactivations of these DMN regions in response to WM probes were interrogated. Healthy controls showed linear load-dependent increases in DMN deactivation. Significant Group-by-Load interactions were observed in DMN regions including medial prefrontal and lateral posterior parietal cortices. Group-by-Load effects in posterior DMN nodes resulted from less suppression at higher WM loads in ESZ relative to HC, with CHR differing from neither group. In medial prefrontal cortex, suppression of activity at higher WM loads was significantly diminished in both CHR and ESZ groups, relative to HC. In addition, investigation of dorsolateral prefrontal cortex (DLPFC) activations revealed that ESZ activated right DLPFC significantly more than HC, with CHR differing from neither group. While HC showed WM load-dependent modulation of DMN suppression, CHR individuals had deficient higher-load DMN suppression that was similar to, but less pronounced than, the distributed suppression deficits evident in ESZ patients. These results suggest that DMN dysregulation associated with schizophrenia predates psychosis onset.

3D metamaterial absorber for attomole molecular detection (Conference Presentation)

NASA Astrophysics Data System (ADS)

Tanaka, Takuo; Ishikawa, Atsushi

2016-09-01

3D Metamaterial absorber was used for a background-suppressed surface-enhanced molecular detection technique. By utilizing the resonant coupling of plasmonic modes of a metamaterial absorber and infrared (IR) vibrational modes of a self-assembled monolayer (SAM), attomole level molecular sensitivity was experimentally demonstrated. IR absorption spectroscopy of molecular vibrations is of importance in chemical, material, medical science and so on, since it provides essential information of the molecular structure, composition, and orientation. In the vibrational spectroscopic techniques, in addition to the weak signals from the molecules, strong background degrades the signal-to-noise ratio, and suppression of the background is crucial for the further improvement of the sensitivity. Here, we demonstrate low-background resonant Surface enhanced IR absorption (SEIRA) by using the metamaterial IR absorber that offers significant background suppression as well as plasmonic enhancement. The fabricated metamaterial consisted of 1D array of Au micro-ribbons on a thick Au film separated by a transparent gap layer made of MgF2. The surface structures were designed to exhibit an anomalous IR absorption at 3000 cm-1, which spectrally overlapped with C-H stretching vibrational modes. 16-Mercaptohexadecanoic acid (16-MHDA) was used as a test molecule, which formed a 2-nm thick SAM with their thiol head-group chemisorbed on the Au surface. In the FTIR measurements, the symmetric and asymmetric C-H stretching modes were clearly observed as reflection peaks within a broad plasmonic absorption of the metamaterial.

Branching ratio and polarization of B→ρ(ω)ρ(ω) decays in perturbative QCD approach

NASA Astrophysics Data System (ADS)

Li, Ying; Lü, Cai-Dian

2006-01-01

In this work, we calculate the branching ratios, polarization fractions and CP asymmetry parameters of decay modes B→ρ(ω)ρ(ω) in the perturbative QCD approach, which is based on kT factorization. After calculation, we find that the branching ratios of B0→ρ+ρ-, B+→ρ+ρ0, and B+→ρ+ω are at the order of 10-5, and their longitudinal polarization fractions are more than 90%. The above results agree with BaBar’s measurements. We also calculate the branching ratios and polarization fractions of B0→ρ0ρ0, B0→ρ0ω, and B0→ωω decays. We find that their longitudinal polarization fractions are suppressed to 60-80% due to a small color suppressed tree contribution. The dominant penguin and nonfactorization tree contributions equally contribute to the longitudinal and transverse polarization, which will be tested in the future experiments. We predict the CP asymmetry of B0→ρ+ρ- and B+→ρ+ρ0, which will be measured in B factories.

DSP-based CSO cancellation technique for RoF transmission system implemented by using directly modulated laser.

PubMed

Kim, Byung Gon; Bae, Sung Hyun; Kim, Hoon; Chung, Yun C

2017-05-29

We propose and demonstrate a simple composite second-order (CSO) cancellation technique based on the digital signal processing (DSP) for the radio-over-fiber (RoF) transmission system implemented by using directly modulated lasers (DMLs). When the RoF transmission system is implemented by using DMLs, its performance could be limited by the CSO distortions caused by the interplay between the DML's chirp and fiber's chromatic dispersion. We present the theoretical analysis of these nonlinear distortions and show that they can be suppressed at the receiver by using a simple DSP. To verify the effectiveness of the proposed technique, we demonstrate the transmission of twenty-four 100-MHz filtered orthogonal frequency-division multiplexing (f-OFDM) signals in 64 quadrature amplitude modulation (QAM) format over 20 km of the standard single-mode fiber (SSMF). The results show that, by using the proposed technique, we can suppress the CSO distortion components by >10 dB and achieve the error-vector magnitude performance better than 6% even after the 20-km long SSMF transmission.

Integrated arc suppression unit for defect reduction in PVD applications

NASA Astrophysics Data System (ADS)

Li, Jason; Narasimhan, Murali K.; Pavate, Vikram; Loo, David; Rosenblum, Steve; Trubell, Larry; Scholl, Richard; Seamons, Scott; Hagerty, Chris; Ramaswami, Sesh

1997-09-01

Arcing between the target and plasma during PVD deposition causes substantial damage to the target and splats and other contamination on the deposited films. Arc-related damages and defects are frequently encountered in microelectronics manufacturing and contributes largely to reduced wafer yields. Arcing is caused largely by the charge buildup at the contaminated sites on the target surface that contains either nonconducting inclusions or nodules. Arc suppression is a key issue for defect reduction, yield improvement and for reliable high quality metallization. An Integrated Arc Suppression Unit (IASU) has been designed for Endura HP PVDTM sputtering sources. The integrated design reduces cable length from unit to source and reduces electrical energy stored in the cable. Active arc handling mode, proactive arc prevention mode, and passive by-pass arc counting mode are incorporated into the same unit. The active mode is designed to quickly respond to chamber conditions, like a large chamber voltage drop, that signals a arc. The self run mode is designed to proactively prevent arc formation by pulsing and reversing target voltage at 50 kHz. The design of the IASU, also called mini small package arc repression circuit--low energy unit (mini Sparc-le), has been optimized for various DC magnetron sources, plasma stability, chamber impedance, power matching, CE MARK test, and power dissipation. Process characterization with Ti, TiN and Al sputtering indicates that the unit has little adverse impact on film properties. Mini Sparc-le unit has been shown here to significantly reduce splats occurrence in Al sputtering. Marathon test of the unit with Ti/TiN test demonstrated the unit's reliability and its ability to reduce sensitivity of defects to target characteristics.

Turbofan aft duct suppressor study. Contractor's data report of mode probe signal data

NASA Technical Reports Server (NTRS)

Fiske, G. H.; Motsinger, R. E.; Syed, A. A.; Joshi, M. C.; Kraft, R. E.

1983-01-01

Acoustic modal distributions were measured in a fan test model having an annular exhaust duct for comparison with theoretically predicted acoustic suppression values. This report contains the amplitude and phase data of the acoustic signals sensed by the transducers of the two mode probes employed in the measurement. Each mode probe consisted of an array of 12 transducers sensing the acoustic field at three axial positions and four radial positions.

Multi-resonant electromagnetic shunt in base isolation for vibration damping and energy harvesting

NASA Astrophysics Data System (ADS)

Pei, Yalu; Liu, Yilun; Zuo, Lei

2018-06-01

This paper investigates multi-resonant electromagnetic shunts applied to base isolation for dual-function vibration damping and energy harvesting. Two multi-mode shunt circuit configurations, namely parallel and series, are proposed and optimized based on the H2 criteria. The root-mean-square (RMS) value of the relative displacement between the base and the primary structure is minimized. Practically, this will improve the safety of base-isolated buildings subjected the broad bandwidth ground acceleration. Case studies of a base-isolated building are conducted in both the frequency and time domains to investigate the effectiveness of multi-resonant electromagnetic shunts under recorded earthquake signals. It shows that both multi-mode shunt circuits outperform traditional single mode shunt circuits by suppressing the first and the second vibration modes simultaneously. Moreover, for the same stiffness ratio, the parallel shunt circuit is more effective at harvesting energy and suppressing vibration, and can more robustly handle parameter mistuning than the series shunt circuit. Furthermore, this paper discusses experimental validation of the effectiveness of multi-resonant electromagnetic shunts for vibration damping and energy harvesting on a scaled-down base isolation system.

Investigation on the oscillation modes in a thermoacoustic Stirling prime mover: mode stability and mode transition

NASA Astrophysics Data System (ADS)

Yu, Z. B.; Li, Q.; Chen, X.; Guo, F. Z.; Xie, X. J.; Wu, J. H.

2003-12-01

The purpose of this paper is to investigate the stability of oscillation modes in a thermoacoustic Stirling prime mover, which is a combination of looped tube and resonator. Two modes, with oscillation frequencies of 76 and 528 Hz, have been observed, stabilities of which are widely different. The stability of the high frequency mode (HFM) is affected by low frequency mode (LFM) strongly. Once the LFM is excited when the HFM is present, the HFM will be gradually slaved and suppressed by the LFM. The details of the transition from HFM to LFM have been described. The two stability curves of the two modes have been measured. Mean pressure Pm is an important control parameter influencing the mode stability in the tested system.

Electro-optic guided-mode resonance tuning suppressible by optically induced screening in a vertically coupled hybrid GaN/Si microring resonator

NASA Astrophysics Data System (ADS)

Thubthimthong, B.; Sasaki, T.; Hane, K.

2018-02-01

GaN as a nanophotonic material has gained much attention in recent years. Using the hybrid GaN/Si platform, we report the electro-optic tuning of guided-mode resonance in a vertically coupled hybrid GaN/Si microring resonator operating in the 1.5 μm window with up to a 6 dB extinction ratio and a 1.5 MHz modulation frequency (test equipment limit). The electro-optic tuning could be optically suppressed by electron-hole-originated screening induced by an ultraviolet excitation at 325 nm. Our work may benefit in externally intervenable optical interconnects for uninterrupted secure photonic networks.

Suppression of Even-Order Photodiode Nonlinearities in Multioctave Photonic Links

NASA Astrophysics Data System (ADS)

Hastings, Alexander S.; Urick, Vincent J.; Sunderman, Christopher; Diehl, John F.; McKinney, Jason D.; Tulchinsky, David A.; Devgan, Preetpaul S.; Williams, Keith J.

2008-08-01

A balanced photonic receiver is demonstrated to suppress photodiode-generated even-order nonlinearities in a photonic link. This result is especially important for multioctave analog applications. Experimental results are presented for a high-frequency (2-30 MHz) link exhibiting 33-dB suppression of the second harmonic, resulting in an output intercept point of 99 dBm due to second-order intermodulation distortion at 26-mA average photocurrent.

Cloaks for suppression or enhancement of scattering of diffuse photon density waves

NASA Astrophysics Data System (ADS)

Renthlei, Lalruatfela; Ramakrishna, S. Anantha; Wanare, Harshawardhan

2018-07-01

Enhancement of wave-like characteristics of heavily damped diffuse photon density waves in a random medium by amplification can induce strongly localised resonances. These resonances can be used to either suppress or enhance scattering from an inhomogeneity in the random medium by cloaking the inhomogeneous region by a shell of random medium with the correct levels of absorption or amplification. A spherical core-shell structure consisting of a shell of a random amplifying medium is shown to enhance or suppress specific resonant modes. A shell with an absorbing random medium is also shown to suppress scattering which can also be used for cloaking the core region.

Resolving the Mystery of Transport Within Internal Transport Barriers

NASA Astrophysics Data System (ADS)

Staebler, G. M.

2013-10-01

The Trapped Gyro-Landau Fluid (TGLF) quasilinear model, which is calibrated to approximate non-linear gyro-kinetic turbulence simulations, is now able to predict the electron density, electron and ion temperatures and ion toroidal rotation simultaneously for internal transport barrier (ITB) discharges in excellent agreement with data from the DIII-D tokamak. This is a strong validation of gyro-kinetic theory of ITBs, requiring multiple instabilities responsible for transport in different channels at different scales. Inside the ITB, the ion energy transport is observed to be reduced to the neoclassical level which is consistent with the theory of turbulence suppression by E × B velocity shear acting on low wavenumber turbulence. The electron energy transport is observed to be far above the neoclassical level which is consistent with electron energy transport due to high wavenumber electron temperature gradient (ETG) modes. Since the ETG modes do not produce particle and ion momentum transport, and low wavenumber modes are suppressed, these channels are expected to be reduced to the neoclassical level in striking disagreement with experimental measurements. A possible resolution of this conundrum was found in 2005 when gyro-kinetic turbulence simulations showed that the parallel velocity shear driven Kelvin-Helmholtz (KH) mode can arrest the suppression of transport by the shear in the E × B velocity Doppler shift at high toroidal flow shear. The success of TGLF in predicting ITB transport is due to the inclusion of ion gyro-radius scale modes that become dominant at high E × B shear and to recent improvements to TGLF that allow the KH mode to be faithfully modeled. The resolution of this long-standing mystery of the missing particle and momentum transport in an ITB is the result of the steady advances in gyro-kinetic simulations and quasilinear modeling. Supported by the US Department of Energy under DE-FG02-95ER54309.

76 FR 14341 - Special Conditions: Boeing Model 747-8/-8F Airplanes, Interaction of Systems and Structures

Federal Register 2010, 2011, 2012, 2013, 2014

2011-03-16

... Suppression (OAMS) system to the fly-by- wire (FBW) flight control system to reduce, but not eliminate, the... control flutter modes but do not completely suppress them. The use of the OAMS system is a novel and... characteristic and provides the necessary standards that permit the use of such active flutter control systems...

Measurements of branching fraction ratios and CP-asymmetries in suppressed B -→ D(→ K +π -)K - and B -→ D(→ K +π -)π - decays

DOE PAGES

Aaltonen, T.

2011-08-01

We report the first reconstruction in hadron collisions of the suppressed decays B -→ D(→ K +π -)K - and B -→ D(→ K +π -)π - decays, sensitive to the CKM phase {gamma}, using data from 7 fb -1 of integrated luminosity collected by the CDF II detector at the Tevatron collider. We reconstruct a signal for the B -→ D(→ K +π -)K - suppressed mode with a significance of 3.2 standard deviations, and measure the ratios of the suppressed to favored branching fractions R(K) = [22.0 ± 8.6(stat) ± 2.6(syst)] x 10 -3, R +(K) = [42.6more » ± 13.7(stat) ± 2.8(syst)] x 10 -3, R -(K) = [3.8 ± 10.3(stat) ± 2.7(syst)] x 10 -3 as well as the direct CP-violating asymmetry A(K) = -0.82±0.44(stat)±0.09(syst) of this mode. Corresponding quantities for B - → D(→ K +π -)π - decay are also reported.« less

Second generation OH suppression filters using multicore fibers

NASA Astrophysics Data System (ADS)

Haynes, R.; Birks, T. A.; Bland-Hawthorn, J.; Cruz, J. L.; Diez, A.; Ellis, S. C.; Haynes, D.; Krämer, R. G.; Mangan, B. J.; Min, S.; Murphy, D. F.; Nolte, S.; Olaya, J. C.; Thomas, J. U.; Trinh, C. Q.; Tünnermann, A.; Voigtländer, Christian

2012-09-01

Ground based near-infrared observations have long been plagued by poor sensitivity when compared to visible observations as a result of the bright narrow line emission from atmospheric OH molecules. The GNOSIS instrument recently commissioned at the Australian Astronomical Observatory uses Photonic Lanterns in combination with individually printed single mode fibre Bragg gratings to filter out the brightest OH-emission lines between 1.47 and 1.70μm. GNOSIS, reported in a separate paper in this conference, demonstrates excellent OH-suppression, providing very “clean” filtering of the lines. It represents a major step forward in the goal to improve the sensitivity of ground based near-infrared observation to that possible at visible wavelengths, however, the filter units are relatively bulky and costly to produce. The 2nd generation fibre OH-Suppression filters based on multicore fibres are currently under development. The development aims to produce high quality, cost effective, compact and robust OH-Suppression units in a single optical fibre with numerous isolated single mode cores that replicate the function and performance of the current generation of “conventional” photonic lantern based devices. In this paper we present the early results from the multicore fibre development and multicore fibre Bragg grating imprinting process.

Passive and Active Stabilization of Liquid Bridges in Low Gravity

NASA Technical Reports Server (NTRS)

Marston, Philip L.; Thiessen, David B.; Marr-Lyon, Mark J.; Wei, Wei; Niederhaus, Charles E.; Truong, Duc K.

2001-01-01

Tests are planned in the low gravity environment of the International Space Station (ISS) of new methods for the suppression of the capillary instability of liquid bridges. Our suppression methods are unusual in that they are not limited to liquid bridges having very special properties and may impact a variety of low-gravity and earth-based technologies. There are two main approaches to be investigated: (1) Passive Acoustic Stabilization (PAS); and (2) Active Electrostatic Stabilization (AES). In PAS, the suppression of the mode growth is accomplished by placing the bridge in an acoustic field having the appropriate properties such that the acoustic radiation pressure automatically pulls outward on the thinnest portion of the bridge. In AES, the bridge deformation is sensed optically and counteracted by actively adjusting the electrostatic Maxwell stresses via two ring electrodes concentric with the slightly conducting bridge to offset the growth of the unstable mode. While the present work emphasizes cylindrical bridges, the methods need not be restricted to that case. The methods to be explored are relevant to the suppression of capillary instabilities in floating zone crystal growth, breakup of liquid jets and columns, bubbles, and annular films as well as the management of coolants or propellants in low-gravity.

Relative humidity sensor based on a few-mode microfiber knot resonator by mitigating group index difference

NASA Astrophysics Data System (ADS)

Anh Le, Duy Duong; Lee, Seungmin; Han, Young-Geun

2017-04-01

A few-mode microfiber knot resonator (FM-MKR) incorporating a polyvinyl alcohol (PVA) is investigated for measurement of relative humidity (RH). Two modes, such as HE11 and HE12, are excited and interfered in a nonadiabatically tapered structure of the single-mode fiber (SMF). After making a tie with the few-mode microfiber, the FM-MKR is fabricated. In the FM-MKR, two modes, such as HE11 and HE12, must be circulated within the optical knot and cross-coupled independently with a phase delay. By optimizing the diameter of the microfiber, the difference of group effective refractive indices between two modes is dramatically suppressed resulting in the improvement of RH sensitivity of the proposed FM-MKR.

Selective coherent perfect absorption of subradiant mode in ultrathin bi-layer metamaterials via antisymmetric excitation

NASA Astrophysics Data System (ADS)

Tan, Wei; Zhang, Caihong; Li, Chun; Zhou, Xiaoying; Jia, Xiaoqing; Feng, Zheng; Su, Juan; Jin, Biaobing

2017-05-01

We demonstrate that the subradiant mode in ultrathin bi-layer metamaterials can be exclusively excited under two-antisymmetric-beam illumination (or equivalently, at a node of the standing wave field), while the superradiant mode is fully suppressed due to their different mode symmetry. Coherent perfect absorption (CPA) with the Lorentzian lineshape can be achieved corresponding to the subradiant mode. A theoretical model is established to distinguish the different behaviors of these two modes and to elucidate the CPA condition. Terahertz ultrathin bi-layer metamaterials on flexible polyimide substrates are fabricated and tested, exhibiting excellent agreement with theoretical predictions. This work provides physical insight into how to selectively excite the antisymmetric subradiant mode via coherence incidence.

Gyro-Landau-Fluid Theory and Simulations of Edge-Localized-Modes

NASA Astrophysics Data System (ADS)

Xu, X. Q.

2012-10-01

We report on the theory and simulations of edge-localized-modes (ELMs) using a gyro-Landau-fluid (GLF) extension of the BOUT++ code. Consistent with the two-fluid model (including 1st order FLR corrections), large ELMs, which are low-to-intermediate toroidal mode number (n) peeling-ballooning (P-B) modes, are suppressed by finite Larmor radius (FLR) effects as the ion temperature increases, while small ELMs (at intermediate n's) remain unstable. This result is good news for high ion temperatures in ITER due to the large stabilizing effects of FLR. Because the FLR effects are proportional to both Ti and n, the maximum growth rate is inversely proportional to Ti and the P-B mode is stabilized at high n. Nonlinear gyro-fluid simulations show results similar to those from the two-fluid model, namely that the P-B modes trigger magnetic reconnection, which drives the collapse of the pedestal pressure. Hyper-resistivity limits the radial spreading of ELMs by facilitating magnetic reconnection. The gyro-fluid ion model further limits the radial spreading of ELMs due to FLR-corrected nonlinear ExB convection of the ion gyro-center density. A gyro-fluid ETG model is being developed to self-consistently calculate the hyper-resistivity. Zonal magnetic fields arise from an ELM event and finite beta drift-wave turbulence when electron inertia effects are included. These lead to current generation and self-consistent current transport as a result of ExB convection in the generalized Ohm's law. Because edge plasmas have significant spatial inhomogeneities and complicated boundary conditions, we have developed a fast non-Fourier method for the computation of Landau-fluid closure terms based on an accurate and tunable approximation. The accuracy and the fast computational scaling of the method are demonstrated.

Millimeter-Wave Gyroklystron Amplifier Experiment Using a Relativistic Electron Beam

DTIC Science & Technology

1990-03-08

Qint to 400 for the TE1 l1 mode, while assisting in suppressing other competing modes [7]. The length of these slots is three times the nominal cavity...frequency by tranverse compression by means of separate clamps. However, cavity deformation affects both the center frequency and the value 5 of Q...amplifier operation was limited by the excitation of parasitic oscillation of the competing TE1 12 mode, as predicted by theory [7]. Despite this

Single mode levitation and translation

NASA Technical Reports Server (NTRS)

Barmatz, Martin B. (Inventor); Allen, James L. (Inventor)

1988-01-01

A single frequency resonance mode is applied by a transducer to acoustically levitate an object within a chamber. This process allows smooth movement of the object and suppression of unwanted levitation modes that would urge the object to a different levitation position. A plunger forms one end of the chamber, and the frequency changes as the plunger moves. Acoustic energy is applied to opposite sides of the chamber, with the acoustic energy on opposite sides being substantially 180 degrees out of phase.

Single-mode temperature and polarisation-stable high-speed 850nm vertical cavity surface emitting lasers

NASA Astrophysics Data System (ADS)

Nazaruk, D. E.; Blokhin, S. A.; Maleev, N. A.; Bobrov, M. A.; Kuzmenkov, A. G.; Vasil'ev, A. P.; Gladyshev, A. G.; Pavlov, M. M.; Blokhin, A. A.; Kulagina, M. M.; Vashanova, K. A.; Zadiranov, Yu M.; Fefelov, A. G.; Ustinov, V. M.

2014-12-01

A new intracavity-contacted design to realize temperature and polarization-stable high-speed single-mode 850 nm vertical cavity surface emitting lasers (VCSELs) grown by molecular-beam epitaxy is proposed. Temperature dependences of static and dynamic characteristics of the 4.5 pm oxide aperture InGaAlAs VCSEL were investigated in detail. Due to optimal gain-cavity detuning and enhanced carrier localization in the active region the threshold current remains below 0.75 mA for the temperature range within 20-90°C, while the output power exceeds 1 mW up to 90°C. Single-mode operation with side-mode suppression ratio higher than 30 dB and orthogonal polarization suppression ratio more than 18 dB was obtained in the whole current and temperature operation range. Device demonstrates serial resistance less than 250 Ohm, which is rather low for any type of single-mode short- wavelength VCSELs. VCSEL demonstrates temperature robust high-speed operation with modulation bandwidth higher than 13 GHz in the entire temperature range of 20-90°C. Despite high resonance frequency the high-speed performance of developed VCSELs was limited by the cut-off frequency of the parasitic low pass filter created by device resistances and capacitances. The proposed design is promising for single-mode high-speed VCSEL applications in a wide spectral range.

Experimental study on discretely modulated continuous-variable quantum key distribution

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

Shen Yong; Zou Hongxin; Chen Pingxing

2010-08-15

We present a discretely modulated continuous-variable quantum key distribution system in free space by using strong coherent states. The amplitude noise in the laser source is suppressed to the shot-noise limit by using a mode cleaner combined with a frequency shift technique. Also, it is proven that the phase noise in the source has no impact on the final secret key rate. In order to increase the encoding rate, we use broadband homodyne detectors and the no-switching protocol. In a realistic model, we establish a secret key rate of 46.8 kbits/s against collective attacks at an encoding rate of 10more » MHz for a 90% channel loss when the modulation variance is optimal.« less

Robust 2-Qubit Gates in a Linear Ion Crystal Using a Frequency-Modulated Driving Force

NASA Astrophysics Data System (ADS)

Leung, Pak Hong; Landsman, Kevin A.; Figgatt, Caroline; Linke, Norbert M.; Monroe, Christopher; Brown, Kenneth R.

2018-01-01

In an ion trap quantum computer, collective motional modes are used to entangle two or more qubits in order to execute multiqubit logical gates. Any residual entanglement between the internal and motional states of the ions results in loss of fidelity, especially when there are many spectator ions in the crystal. We propose using a frequency-modulated driving force to minimize such errors. In simulation, we obtained an optimized frequency-modulated 2-qubit gate that can suppress errors to less than 0.01% and is robust against frequency drifts over ±1 kHz . Experimentally, we have obtained a 2-qubit gate fidelity of 98.3(4)%, a state-of-the-art result for 2-qubit gates with five ions.

Optimal locations and orientations of piezoelectric transducers on cylindrical shell based on gramians of contributed and undesired Rayleigh-Ritz modes using genetic algorithm

NASA Astrophysics Data System (ADS)

Biglar, Mojtaba; Mirdamadi, Hamid Reza; Danesh, Mohammad

2014-02-01

In this study, the active vibration control and configurational optimization of a cylindrical shell are analyzed by using piezoelectric transducers. The piezoelectric patches are attached to the surface of the cylindrical shell. The Rayleigh-Ritz method is used for deriving dynamic modeling of cylindrical shell and piezoelectric sensors and actuators based on the Donnel-Mushtari shell theory. The major goal of this study is to find the optimal locations and orientations of piezoelectric sensors and actuators on the cylindrical shell. The optimization procedure is designed based on desired controllability and observability of each contributed and undesired mode. Further, in order to limit spillover effects, the residual modes are taken into consideration. The optimization variables are the positions and orientations of piezoelectric patches. Genetic algorithm is utilized to evaluate the optimal configurations. In this article, for improving the maximum power and capacity of actuators for amplitude depreciation of negative velocity feedback strategy, we have proposed a new control strategy, called "Saturated Negative Velocity Feedback Rule (SNVF)". The numerical results show that the optimization procedure is effective for vibration reduction, and specifically, by locating actuators and sensors in their optimal locations and orientations, the vibrations of cylindrical shell are suppressed more quickly.

High-brightness-solar-pumped Nd:YAG laser design

NASA Astrophysics Data System (ADS)

Lando, Mordechai; Jenkins, David G.; Bernstein, Hana; O'Gallagher, Joseph J.; Winston, Roland; Lewandowski, Allan

1995-06-01

We have designed a Nd:YAG laser to be pumped by the High-Flux Solar Furnace (HFSF) at the National Renewable Energy Laboratory. Based on the unique features of the HFSF, the design objectives are high brightness and superior efficiency in primary mirror area utilization. The HFSF has a primary mirror of 11.5 m2 and a 1.85 f-number. With such a high f-number, the target is set off-axis and does not block incoming solar flux. Moreover, large f-number enables concentration which approaches the theoretical limit, and a two- dimensional non-imaging concentrator deposits the solar flux onto the internal part of a 10 mm diameter laser rod. For high brightness, we plan a wide low-loss fundamental mode and a laser rod aperture that suppresses high order modes. To get a fundamental mode, of up to a 2.5 mm waist, we have designed a convex-concave resonator, following well-known g1g2 equals 0.5 design for resonators with internal beam focusing. We have used the edge ray principle to design the concentrator, and ray traced the deposited power inside the laser rod. A 1.3% Nd doping level supports a maximal power deposition inside a 5 mm diameter.

Single-molecule electronics: Cooling individual vibrational modes by the tunneling current.

PubMed

Lykkebo, Jacob; Romano, Giuseppe; Gagliardi, Alessio; Pecchia, Alessandro; Solomon, Gemma C

2016-03-21

Electronic devices composed of single molecules constitute the ultimate limit in the continued downscaling of electronic components. A key challenge for single-molecule electronics is to control the temperature of these junctions. Controlling heating and cooling effects in individual vibrational modes can, in principle, be utilized to increase stability of single-molecule junctions under bias, to pump energy into particular vibrational modes to perform current-induced reactions, or to increase the resolution in inelastic electron tunneling spectroscopy by controlling the life-times of phonons in a molecule by suppressing absorption and external dissipation processes. Under bias the current and the molecule exchange energy, which typically results in heating of the molecule. However, the opposite process is also possible, where energy is extracted from the molecule by the tunneling current. Designing a molecular "heat sink" where a particular vibrational mode funnels heat out of the molecule and into the leads would be very desirable. It is even possible to imagine how the vibrational energy of the other vibrational modes could be funneled into the "cooling mode," given the right molecular design. Previous efforts to understand heating and cooling mechanisms in single molecule junctions have primarily been concerned with small models, where it is unclear which molecular systems they correspond to. In this paper, our focus is on suppressing heating and obtaining current-induced cooling in certain vibrational modes. Strategies for cooling vibrational modes in single-molecule junctions are presented, together with atomistic calculations based on those strategies. Cooling and reduced heating are observed for two different cooling schemes in calculations of atomistic single-molecule junctions.

Mode switching in a multi-wavelength distributed feedback quantum cascade laser using an external micro-cavity

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

Sidler, Meinrad; Institute for Quantum Electronics, ETH Zurich, Wolfgang-Pauli-Strasse 16, 8093 Zurich; Rauter, Patrick

2014-02-03

We demonstrate a multi-wavelength distributed feedback (DFB) quantum cascade laser (QCL) operating in a lensless external micro-cavity and achieve switchable single-mode emission at three distinct wavelengths selected by the DFB grating, each with a side-mode suppression ratio larger than 30 dB. Discrete wavelength tuning is achieved by modulating the feedback experienced by each mode of the multi-wavelength DFB QCL, resulting from a variation of the external cavity length. This method also provides a post-fabrication control of the lasing modes to correct for fabrication inhomogeneities, in particular, related to the cleaved facets position.

A wind-tunnel investigation of a B-52 model flutter suppression system

NASA Technical Reports Server (NTRS)

Redd, L. T.; Gilman, J., Jr.; Cooley, D. E.; Sevart, F. D.

1974-01-01

Flutter modeling techniques have been successfully extended to the difficult case of the active suppression of flutter. The demonstration was conducted in a transonic dynamics tunnel using a 1/30 scale, elastic, dynamic model of a Boeing B-52 control configured vehicle. The results from the study show that with the flutter suppression system operating there is a substantial increase in the damping associated with the critical flutter mode. The results also show good correlation between the damping characteristics of the model and the aircraft.

NASA Instep/mdmsc Jitter Suppression Experiment (JITTER)

NASA Technical Reports Server (NTRS)

White, Edward V.

1992-01-01

The objectives are the following: (1) to develop and demonstrate in-space performance of both passive and active damping systems for suppression of micro-amplitude vibration on an actual application structure and operate despite uncertain dynamics and uncertain disturbance characteristics; and (2) to correlate ground and in-space performance - the performance metric is vibration attenuation. The goals are to achieve vibration suppression equivalent to 5 percent passive damping in selected models and 15 percent active damping in selected modes. Various aspects of this experiment are presented in viewgraph form.

Parietal EEG alpha suppression time of memory retrieval reflects memory load while the alpha power of memory maintenance is a composite of the visual process according to simultaneous and successive Sternberg memory tasks.

PubMed

Okuhata, Shiho; Kusanagi, Takuya; Kobayashi, Tetsuo

2013-10-25

The present study investigated EEG alpha activity during visual Sternberg memory tasks using two different stimulus presentation modes to elucidate how the presentation mode affected parietal alpha activity. EEGs were recorded from 10 healthy adults during the Sternberg tasks in which memory items were presented simultaneously and successively. EEG power and suppression time (ST) in the alpha band (8-13Hz) were computed for the memory maintenance and retrieval phases. The alpha activity differed according to the presentation mode during the maintenance phase but not during the retrieval phase. Results indicated that parietal alpha power recorded during the maintenance phase did not reflect the memory load alone. In contrast, ST during the retrieval phase increased with the memory load for both presentation modes, indicating a serial memory scanning process, regardless of the presentation mode. These results indicate that there was a dynamic transition in the memory process from the maintenance phase, which was sensitive to external factors, toward the retrieval phase, during which the process converged on the sequential scanning process, the Sternberg task essentially required. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

Impurity confinement and transport in high confinement regimes without edge localized modes on DIII-D [Impurity confinement and transport in high confinement regimes without ELMs on DIII-D

DOE PAGES

Grierson, Brian A.; Burrell, Keith H.; Nazikian, Raffi M.; ...

2015-04-17

Here, impurity transport in the DIII-D tokamak is investigated in stationary high confinement (H-mode) regimes without edge localized modes (ELMs). In plasmas maintained by resonant magnetic perturbation (RMP) ELM-suppression and QH-mode the confinement time of fluorine (Z=9) is equivalent to that in ELMing discharges with 40 Hz ELMs. For selected discharges with impurity injection the impurity particle confinement time compared to the energy confinement time is in the range of τ p/τ e ≈ 2 $-$ 3. In QH-mode operation the impurity confinement time is shown to be smaller for intense, coherent magnetic and density fluctuations of the edge harmonicmore » oscillation than weaker fluctuations. Transport coefficients are derived from the time evolution of the impurity density profile and compared to neoclassical and turbulent transport models NEO and TGLF. Neoclassical transport of fluorine is found to be small compared to the experimental values. In the ELMing and RMP ELM-suppressed plasma the impurity transport is affected by the presence of tearing modes. For radii larger than the mode radius the TGLF diffusion coefficient is smaller than the experimental value by a factor of 2-3, while the convective velocity is within error estimates. Low levels of diffusion are observed for radii smaller than the tearing mode radius. In the QH-mode plasma investigated, the TGLF diffusion coefficient higher inside of ρ = 0.4 and lower outside of 0.4 than the experiment, and the TGLF convective velocity is more negative by a factor of approximately 1.7.« less

Broadband mode conversion via gradient index metamaterials

PubMed Central

Wang, HaiXiao; Xu, YaDong; Genevet, Patrice; Jiang, Jian-Hua; Chen, HuanYang

2016-01-01

We propose a design for broadband waveguide mode conversion based on gradient index metamaterials (GIMs). Numerical simulations demonstrate that the zeroth order of transverse magnetic mode or the first order of transverse electric mode (TM0/TE1) can be converted into the first order of transverse magnetic mode or the second order of transverse electric mode (TM1/TE2) for a broadband of frequencies. As an application, an asymmetric propagation is achieved by integrating zero index metamaterials inside the GIM waveguide. PMID:27098456

Metamaterial absorber for molecular detection and identification (Conference Presentation)

NASA Astrophysics Data System (ADS)

Tanaka, Takuo

2017-03-01

Metamaterial absorber was used for a background-suppressed surface-enhanced molecular detection technique. By utilizing the resonant coupling between plasmonic modes of a metamaterial absorber and infrared (IR) vibrational modes of a self-assembled monolayer (SAM), attomole level molecular sensitivity was experimentally demonstrated. IR absorption spectroscopy of molecular vibrations is of importance in chemical, material, medical science and so on, since it provides essential information of the molecular structure, composition, and orientation. In the vibrational spectroscopic techniques, in addition to the weak signals from the molecules, strong background degrades the signal-to-noise ratio, and suppression of the background is crucial for the further improvement of the sensitivity. Here, we demonstrate low-background resonant Surface enhanced IR absorption (SEIRA) by using the metamaterial IR absorber that offers significant background suppression as well as plasmonic enhancement. By using mask-less laser lithography technique, metamaterial absorber which consisted of 1D array of Au micro-ribbons on a thick Au film separated by a transparent gap layer made of MgF2 was fabricated. This metamaterial structure was designed to exhibit an anomalous IR absorption at 3000 cm-1, which spectrally overlapped with C-H stretching vibrational modes. 16-Mercaptohexadecanoic acid (16-MHDA) was used as a test molecule, which formed a 2-nm thick SAM with their thiol head-group chemisorbed on the Au surface. In the FTIR measurements, the symmetric and asymmetric C-H stretching modes were clearly observed as reflection peaks within a broad plasmonic absorption of the metamaterial, and 1.8 attomole molecular sensitivity was experimentally demonstrated.

Mode coupling in hybrid square-rectangular lasers for single mode operation

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

Ma, Xiu-Wen; Huang, Yong-Zhen, E-mail: yzhuang@semi.ac.cn; Yang, Yue-De

Mode coupling between a square microcavity and a Fabry-Pérot (FP) cavity is proposed and demonstrated for realizing single mode lasers. The modulations of the mode Q factor as simulation results are observed and single mode operation is obtained with a side mode suppression ratio of 46 dB and a single mode fiber coupling loss of 3.2 dB for an AlGaInAs/InP hybrid laser as a 300-μm-length and 1.5-μm-wide FP cavity connected to a vertex of a 10-μm-side square microcavity. Furthermore, tunable single mode operation is demonstrated with a continuous wavelength tuning range over 10 nm. The simple hybrid structure may shed light on practicalmore » applications of whispering-gallery mode microcavities in large-scale photonic integrated circuits and optical communication and interconnection.« less

Photonic-band-gap gyrotron amplifier with picosecond pulses.

PubMed

Nanni, Emilio A; Jawla, Sudheer; Lewis, Samantha M; Shapiro, Michael A; Temkin, Richard J

2017-12-04

We report the amplification of 250 GHz pulses as short as 260 ps without observation of pulse broadening using a photonic-band-gap circuit gyrotron traveling-wave-amplifier. The gyrotron amplifier operates with a device gain of 38 dB and an instantaneous bandwidth of 8 GHz. The operational bandwidth of the amplifier can be tuned over 16 GHz by adjusting the operating voltage of the electron beam and the magnetic field. The amplifier uses a 30 cm long photonic-band-gap interaction circuit to confine the desired TE 03 -like operating mode while suppressing lower order modes which can result in undesired oscillations. The circuit gain is >55 dB for a beam voltage of 23 kV and a current of 700 mA. These results demonstrate the wide bandwidths and a high gain achievable with gyrotron amplifiers. The amplification of picosecond pulses of variable lengths, 260-800 ps, shows good agreement with the theory using the coupled dispersion relation and the gain-spectrum of the amplifier as measured with quasi-CW input pulses.

Photonic-band-gap gyrotron amplifier with picosecond pulses

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

Nanni, Emilio A.; Jawla, Sudheer; Lewis, Samantha M.

Here, we report the amplification of 250 GHz pulses as short as 260 ps without observation of pulse broadening using a photonic-band-gap circuit gyrotron traveling-wave-amplifier. The gyrotron amplifier operates with a device gain of 38 dB and an instantaneous bandwidth of 8 GHz. The operational bandwidth of the amplifier can be tuned over 16 GHz by adjusting the operating voltage of the electron beam and the magnetic field. The amplifier uses a 30 cm long photonic-band-gap interaction circuit to confine the desired TE 03-like operating mode while suppressing lower order modes which can result in undesired oscillations. The circuit gainmore » is >55 dB for a beam voltage of 23 kV and a current of 700 mA. These results demonstrate the wide bandwidths and a high gain achievable with gyrotron amplifiers. The amplification of picosecond pulses of variable lengths, 260–800 ps, shows good agreement with the theory using the coupled dispersion relation and the gain-spectrum of the amplifier as measured with quasi-CW input pulses.« less

Photonic-band-gap gyrotron amplifier with picosecond pulses

DOE PAGES

Nanni, Emilio A.; Jawla, Sudheer; Lewis, Samantha M.; ...

2017-12-05

Here, we report the amplification of 250 GHz pulses as short as 260 ps without observation of pulse broadening using a photonic-band-gap circuit gyrotron traveling-wave-amplifier. The gyrotron amplifier operates with a device gain of 38 dB and an instantaneous bandwidth of 8 GHz. The operational bandwidth of the amplifier can be tuned over 16 GHz by adjusting the operating voltage of the electron beam and the magnetic field. The amplifier uses a 30 cm long photonic-band-gap interaction circuit to confine the desired TE 03-like operating mode while suppressing lower order modes which can result in undesired oscillations. The circuit gainmore » is >55 dB for a beam voltage of 23 kV and a current of 700 mA. These results demonstrate the wide bandwidths and a high gain achievable with gyrotron amplifiers. The amplification of picosecond pulses of variable lengths, 260–800 ps, shows good agreement with the theory using the coupled dispersion relation and the gain-spectrum of the amplifier as measured with quasi-CW input pulses.« less

Thermoelectric unipolar spin battery in a suspended carbon nanotube.

PubMed

Cao, Zhan; Fang, Tie-Feng; He, Wan-Xiu; Luo, Hong-Gang

2017-04-26

A quantum dot formed in a suspended carbon nanotube exposed to an external magnetic field is predicted to act as a thermoelectric unipolar spin battery which generates pure spin current. The built-in spin flip mechanism is a consequence of the spin-vibration interaction resulting from the interplay between the intrinsic spin-orbit coupling and the vibrational modes of the suspended carbon nanotube. On the other hand, utilizing thermoelectric effect, the temperature difference between the electron and the thermal bath to which the vibrational modes are coupled provides the driving force. We find that both magnitude and direction of the generated pure spin current are dependent on the strength of spin-vibration interaction, the sublevel configuration in dot, the temperatures of electron and thermal bath, and the tunneling rate between the dot and the pole. Moreover, in the linear response regime, the kinetic coefficient is non-monotonic in the temperature T and it reaches its maximum when [Formula: see text] is about one phonon energy. The existence of a strong intradot Coulomb interaction is irrelevant for our spin battery, provided that high-order cotunneling processes are suppressed.

Plasmonic distributed feedback lasers at telecommunications wavelengths.

PubMed

Marell, Milan J H; Smalbrugge, Barry; Geluk, Erik Jan; van Veldhoven, Peter J; Barcones, Beatrix; Koopmans, Bert; Nötzel, Richard; Smit, Meint K; Hill, Martin T

2011-08-01

We investigate electrically pumped, distributed feedback (DFB) lasers, based on gap-plasmon mode metallic waveguides. The waveguides have nano-scale widths below the diffraction limit and incorporate vertical groove Bragg gratings. These metallic Bragg gratings provide a broad bandwidth stop band (~500 nm) with grating coupling coefficients of over 5000/cm. A strong suppression of spontaneous emission occurs in these Bragg grating cavities, over the stop band frequencies. This strong suppression manifests itself in our experimental results as a near absence of spontaneous emission and significantly reduced lasing thresholds when compared to similar length Fabry-Pérot waveguide cavities. Furthermore, the reduced threshold pumping requirements permits us to show strong line narrowing and super linear light current curves for these plasmon mode devices even at room temperature.

Clockwork seesaw mechanisms

NASA Astrophysics Data System (ADS)

Park, Seong Chan; Shin, Chang Sub

2018-01-01

We propose new mechanisms for small neutrino masses based on clockwork mechanism. The Standard Model neutrinos and lepton number violating operators communicate through the zero mode of clockwork gears, one of the two couplings of the zero mode is exponentially suppressed by clockwork mechanism. Including all known examples for the clockwork realization of the neutrino masses, different types of models are realized depending on the profile and chirality of the zero mode fermion. Each type of realization would have phenomenologically distinctive features with the accompanying heavy neutrinos.

Utilizing wheel-ring architecture for stable and selectable single-longitudinal-mode erbium fiber laser

NASA Astrophysics Data System (ADS)

Yeh, Chien-Hung; Yang, Zi-Qing; Huang, Tzu-Jung; Chow, Chi-Wai

2018-03-01

To achieve a steady single-longitudinal-mode (SLM) erbium-doped fiber (EDF) laser, the wheel-ring architecture is proposed in the laser cavity. According to Vernier effect, the proposed wheel-ring can produce three different free spectrum ranges (FSRs) to serve as the mode-filter for suppressing the densely multi-longitudinal-mode (MLM). Here, to complete wavelength-tunable EDF laser, an optical tunable bandpass filter (OTBF) is utilized inside the cavity for tuning arbitrarily. In addition, the entire output performances of the proposed EDF wheel-ring laser are also discussed and analyzed experimentally.

Observable cosmological vector mode in the dark ages

NASA Astrophysics Data System (ADS)

Saga, Shohei

2016-09-01

The second-order vector mode is inevitably induced from the coupling of first-order scalar modes in cosmological perturbation theory and might hinder a possible detection of primordial gravitational waves from inflation through 21 cm lensing observations. Here, we investigate the weak lensing signal in 21 cm photons emitted by neutral hydrogen atoms in the dark ages induced by the second-order vector mode by decomposing the deflection angle of the 21 cm lensing signal into the gradient and curl modes. The curl mode is a good tracer of the cosmological vector and tensor modes since the scalar mode does not induce the curl one. By comparing angular power spectra of the 21 cm lensing curl mode induced by the second-order vector mode and primordial gravitational waves whose amplitude is parametrized by the tensor-to-scalar ratio r , we find that the 21 cm curl mode from the second-order vector mode dominates over that from primordial gravitational waves on almost all scales if r ≲10-5. If we use the multipoles of the power spectrum up to ℓmax=1 05 and 1 06 in reconstructing the curl mode from 21 cm temperature maps, the signal-to-noise ratios of the 21 cm curl mode from the second-order vector mode achieve S /N ≈0.46 and 73, respectively. Observation of 21 cm radiation is, in principle, a powerful tool to explore not only the tensor mode but also the cosmological vector mode.

Singlemode 1.1 μm InGaAs quantum well microstructured photonic crystal VCSEL

NASA Astrophysics Data System (ADS)

Stevens, Renaud; Gilet, Philippe; Larrue, Alexandre; Grenouillet, Laurent; Olivier, Nicolas; Grosse, Philippe; Gilbert, Karen; Teysseyre, Raphael; Chelnokov, Alexei

2008-02-01

In this article, we present our results on long wavelength (1.1 μm) single-mode micro-structured photonic crystal strained InGaAs quantum wells VCSELs for optical interconnection applications. Single fundamental mode roomtemperature continuous-wave lasing operation was demonstrated for devices designed and processed with a number of different two-dimensional etched patterns. The conventional epitaxial structure was grown by Molecular Beam Epitaxy (MBE) and contains fully doped GaAs/AlGaAs DBRs, one oxidation layer and three strained InGaAs quantum wells. The holes were etched half-way through the top-mirror following various designs (triangular and square lattices) and with varying hole's diameters and pitches. At room temperature and in continuous wave operation, micro-structured 50 µm diameter mesa VCSELs with 10 μm oxidation aperture exhibited more than 1 mW optical power, 2 to 5 mA threshold currents and more than 30 dB side mode suppression ratio at a wavelength of 1090 nm. These structures show slight power reduction but similar electrical performances than unstructured devices. Systematic static electrical, optical and spectral characterization was performed on wafer using an automated probe station. Numerical modeling using the MIT Photonic-Bands (MPB [1]) package of the transverse modal behaviors in the photonic crystal was performed using the plane wave method in order to understand the index-guiding effects of the chosen patterns, and to further optimize the design structures for mode selection at extended wavelength range.

Tensor perturbations during inflation in a spatially closed Universe

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

Bonga, Béatrice; Gupt, Brajesh; Yokomizo, Nelson, E-mail: bpb165@psu.edu, E-mail: bgupt@gravity.psu.edu, E-mail: yokomizo@gravity.psu.edu

2017-05-01

In a recent paper [1], we studied the evolution of the background geometry and scalar perturbations in an inflationary, spatially closed Friedmann-Lemaȋtre-Robertson-Walker (FLRW) model having constant positive spatial curvature and spatial topology S{sup 3}. Due to the spatial curvature, the early phase of slow-roll inflation is modified, leading to suppression of power in the scalar power spectrum at large angular scales. In this paper, we extend the analysis to include tensor perturbations. We find that, similarly to the scalar perturbations, the tensor power spectrum also shows suppression for long wavelength modes. The correction to the tensor spectrum is limited tomore » the very long wavelength modes, therefore the resulting observable CMB B-mode polarization spectrum remains practically the same as in the standard scenario with flat spatial sections. However, since both the tensor and scalar power spectra are modified, there are scale dependent corrections to the tensor-to-scalar ratio that leads to violation of the standard slow-roll consistency relation.« less

Effects of transport coefficients on excitation of flare-induced standing slow-mode waves

NASA Astrophysics Data System (ADS)

Wang, Tongjiang; Ofman, Leon; Davila, Joseph

2017-08-01

The flare-excited longitudinal intensity oscillations in hot flaring loops have been recently detected by SDO/AIA, and interpreted as the slow-mode standing waves. By means of the seismology technique we have, for the first time, determined the transport coefficients in the hot (>9 MK) flare plasma, and found that thermal conductivity is suppressed by at least 3 times and viscosity coefficient is enhanced by a factor of 15 as the upper limit (Wang et al. 2015, ApJL, 811, L13). In this presentation, we first discuss possible causes for conduction suppression and viscosity enhancements. Then we use the nonlinear MHD simulations to validate the seismology method that is based on linear analytical analysis, and demonstrate the inversion scheme for determining transport coefficients using numerical parametric study. Finally, we show how the seismologically-determined transport coefficients are crucial for understanding the excitation of the observed standing slow-mode waves in coronal loops and the heating of the loop plasma by a footpoint flare.

Suppression law of quantum states in a 3D photonic fast Fourier transform chip

PubMed Central

Crespi, Andrea; Osellame, Roberto; Ramponi, Roberta; Bentivegna, Marco; Flamini, Fulvio; Spagnolo, Nicolò; Viggianiello, Niko; Innocenti, Luca; Mataloni, Paolo; Sciarrino, Fabio

2016-01-01

The identification of phenomena able to pinpoint quantum interference is attracting large interest. Indeed, a generalization of the Hong–Ou–Mandel effect valid for any number of photons and optical modes would represent an important leap ahead both from a fundamental perspective and for practical applications, such as certification of photonic quantum devices, whose computational speedup is expected to depend critically on multi-particle interference. Quantum distinctive features have been predicted for many particles injected into multimode interferometers implementing the Fourier transform over the optical modes. Here we develop a scalable approach for the implementation of the fast Fourier transform algorithm using three-dimensional photonic integrated interferometers, fabricated via femtosecond laser writing technique. We observe the suppression law for a large number of output states with four- and eight-mode optical circuits: the experimental results demonstrate genuine quantum interference between the injected photons, thus offering a powerful tool for diagnostic of photonic platforms. PMID:26843135

Dual-mode characteristics of the Buneman instability in a bounded slab plasma

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

Hong, Woo-Pyo; Jung, Young-Dae, E-mail: ydjung@hanyang.ac.kr; Department of Applied Physics and Department of Bionanotechnology, Hanyang University, Ansan, Kyunggi-Do 426-791

2015-06-15

The dual-mode characteristics of the Buneman instability are investigated in a slab plasma, including the geometric effects. The dual symmetric and anti-symmetric dispersion modes of the Buneman instability are obtained by the plasma dielectric function with the spectral reflection conditions for the slab geometry. The result shows that the magnitudes of the growth rate for the symmetric mode are always greater than those for the anti-symmetric mode. It is also found that the geometric effect suppresses the position of the maximum growth rate for the Buneman instability in bounded slab plasmas since the maximum conditions for the symmetric and anti-symmetricmore » modes of the Buneman instability are given by 0.60« less

High power and single mode quantum cascade lasers.

PubMed

Bismuto, Alfredo; Bidaux, Yves; Blaser, Stéphane; Terazzi, Romain; Gresch, Tobias; Rochat, Michel; Muller, Antoine; Bonzon, Christopher; Faist, Jerome

2016-05-16

We present a single mode quantum cascade laser with nearly 1 W optical power. A buried distributed feedback reflector is used on the back section for wavelength selection. The laser is 6 mm long, 3.5 μm wide, mounted episide-up and the laser facets are left uncoated. Laser emission is centered at 4.68 μm. Single-mode operation with a side mode suppression ratio of more than 30 dB is obtained in whole range of operation. Farfield measurements prove a symmetric, single transverse-mode emission in TM00-mode with typical divergences of 41° and 33° in the vertical and horizontal direction respectively. This work shows the potential for simple fabrication of high power lasers compatible with standard DFB processing.

Suppressing explosive synchronization by contrarians

NASA Astrophysics Data System (ADS)

Zhang, Xiyun; Guan, Shuguang; Zou, Yong; Chen, Xiaosong; Liu, Zonghua

2016-01-01

Explosive synchronization (ES) has recently received increasing attention and studies have mainly focused on the conditions of its onset so far. However, its inverse problem, i.e. the suppression of ES, has not been systematically studied so far. As ES is usually considered to be harmful in certain circumstances such as the cascading failure of power grids and epileptic seizure, etc., its suppression is definitely important and deserves to be studied. We here study this inverse problem by presenting an efficient approach to suppress ES from a first-order to second-order transition, without changing the intrinsic network structure. We find that ES can be suppressed by only changing a small fraction of oscillators into contrarians with negative couplings and the critical fraction for the transition from the first order to the second order increases with both the network size and the average degree. A brief theory is presented to explain the underlying mechanism. This finding underlines the importance of our method to improve the understanding of neural interactions underlying cognitive processes.

Hybrid propulsion for launch vehicle boosters: A program status update

NASA Technical Reports Server (NTRS)

Carpenter, R. L.; Boardman, T. A.; Claflin, S. E.; Harwell, R. J.

1995-01-01

Results obtained in studying the origin and suppression of large-amplitude pressure oscillations in a 24 in. diameter hybrid motor using a liquid oxygen/hydroxylterminated polybutadiene/polycyclopentadiene propellant system are discussed. Tests conducted with liquid oxygen flow rates varying from 10 to 40 lbm/sec were designed to gauge the effectiveness of various vaporization chamber flow fields, injector designs, and levels of heat addition in suppressing high-frequency longitudinal mode oscillations. Longitudinal acoustic modes did not arise in any tests. However, initial testing revealed the presence of high-amplitude, sinusoidal, nonacoustic oscillations persisting throughout the burn durations. Analysis showed this to be analogous to chug mode instability in liquid rocket engines brought about by a coupling of motor combustion processes and the liquid oxygen feed system. Analytical models were developed and verified by test data to predict the amplitude and frequency of feed-system-coupled combustion pressure oscillations. Subsequent testing showed that increasing the feed system impedance eliminated the bulk mode instability. This paper documents the work completed to date in performance of the Hybrid Propulsion Technology for Launch Vehicle Boosters Program (NAS8-39942) sponsored by NASA's George C. Marshall Space Flight Center.

Stabilizing effect of resistivity towards ELM-free H-mode discharge in lithium-conditioned NSTX

NASA Astrophysics Data System (ADS)

Banerjee, Debabrata; Zhu, Ping; Maingi, Rajesh

2017-07-01

Linear stability analysis of the national spherical torus experiment (NSTX) Li-conditioned ELM-free H-mode equilibria is carried out in the context of the extended magneto-hydrodynamic (MHD) model in NIMROD. The purpose is to investigate the physical cause behind edge localized mode (ELM) suppression in experiment after the Li-coating of the divertor and the first wall of the NSTX tokamak. Besides ideal MHD modeling, including finite-Larmor radius effect and two-fluid Hall and electron diamagnetic drift contributions, a non-ideal resistivity model is employed, taking into account the increase of Z eff after Li-conditioning in ELM-free H-mode. Unlike an earlier conclusion from an eigenvalue code analysis of these equilibria, NIMROD results find that after reduced recycling from divertor plates, profile modification is necessary but insufficient to explain the mechanism behind complete ELMs suppression in ideal two-fluid MHD. After considering the higher plasma resistivity due to higher Z eff, the complete stabilization could be explained. A thorough analysis of both pre-lithium ELMy and with-lithium ELM-free cases using ideal and non-ideal MHD models is presented, after accurately including a vacuum-like cold halo region in NIMROD to investigate ELMs.

Incipient ferroelectricity of water molecules confined to nano-channels of beryl

PubMed Central

Gorshunov, B. P.; Torgashev, V. I.; Zhukova, E. S.; Thomas, V. G.; Belyanchikov, M. A.; Kadlec, C.; Kadlec, F.; Savinov, M.; Ostapchuk, T.; Petzelt, J.; Prokleška, J.; Tomas, P. V.; Pestrjakov, E. V.; Fursenko, D. A.; Shakurov, G. S.; Prokhorov, A. S.; Gorelik, V. S.; Kadyrov, L. S.; Uskov, V. V.; Kremer, R. K.; Dressel, M.

2016-01-01

Water is characterized by large molecular electric dipole moments and strong interactions between molecules; however, hydrogen bonds screen the dipole–dipole coupling and suppress the ferroelectric order. The situation changes drastically when water is confined: in this case ordering of the molecular dipoles has been predicted, but never unambiguously detected experimentally. In the present study we place separate H2O molecules in the structural channels of a beryl single crystal so that they are located far enough to prevent hydrogen bonding, but close enough to keep the dipole–dipole interaction, resulting in incipient ferroelectricity in the water molecular subsystem. We observe a ferroelectric soft mode that causes Curie–Weiss behaviour of the static permittivity, which saturates below 10 K due to quantum fluctuations. The ferroelectricity of water molecules may play a key role in the functioning of biological systems and find applications in fuel and memory cells, light emitters and other nanoscale electronic devices. PMID:27687693

Perturbative expansions from Monte Carlo simulations at weak coupling: Wilson loops and the static-quark self-energy

NASA Astrophysics Data System (ADS)

Trottier, H. D.; Shakespeare, N. H.; Lepage, G. P.; MacKenzie, P. B.

2002-05-01

Perturbative coefficients for Wilson loops and the static-quark self-energy are extracted from Monte Carlo simulations at weak coupling. The lattice volumes and couplings are chosen to ensure that the lattice momenta are all perturbative. Twisted boundary conditions are used to eliminate the effects of lattice zero modes and to suppress nonperturbative finite-volume effects due to Z(3) phases. Simulations of the Wilson gluon action are done with both periodic and twisted boundary conditions, and over a wide range of lattice volumes (from 34 to 164) and couplings (from β~9 to β~60). A high precision comparison is made between the simulation data and results from finite-volume lattice perturbation theory. The Monte Carlo results are shown to be in excellent agreement with perturbation theory through second order. New results for third-order coefficients for a number of Wilson loops and the static-quark self-energy are reported.

Scattering of a longitudinal Bessel beam by a sphere embedded in an isotropic elastic solid.

PubMed

Leão-Neto, J P; Lopes, J H; Silva, G T

2017-11-01

The scattering of a longitudinal Bessel beam of arbitrary order by a sphere embedded in an isotropic solid matrix is theoretically analyzed. The spherical inclusion can be made of a viscoelastic, elastic, or fluid-filled isotropic material. In the analysis, the absorbing, scattering, and extinction efficiency factors are obtained, e.g., the corresponding power per characteristic beam intensity per sphere's cross-section area. Furthermore, the extended optical theorem, which expresses the extinction efficiency in terms of an integral of the longitudinal scattering function is derived. Several features of zeroth- and first-order Bessel beams scattering in solids are illustrated considering a polymer adhesive (cured) sphere embedded in a stainless steel matrix. For instance, omnidirectional scattering can be achieved by choosing specific values of the half-cone angle of the Bessel beam, which is the beam's geometrical parameter. Additionally, it is demonstrated that mode suppression leads to lower absorption inside the inclusion when compared to plane wave scattering results.

Local Turbulence Suppression and Shear Flow Dynamics During qmin-Triggered Internal Transport Barriers on DIII-D

NASA Astrophysics Data System (ADS)

Shafer, M. W.; McKee, G. R.; Schlossberg, D. J.; Austin, M. E.; Burrell, K. H.

2008-11-01

Long-wavelength turbulence (kρi< 1) is locally suppressed simultaneously with a rapid but transient increase in local poloidal flow shear at the appearance of low-order rational qmin surfaces in negative central shear discharges. At these events, reductions in energy transport are observed and Internal Transport Barriers (ITBs) may form. Application of off-axis ECH slows the q-profile evolution and increases ρqmin, both of which enhance turbulence measurements using a new high-sensitivity large-area (8x,8) 2D BES array. The measured transient turbulence suppression is localized to the low-order rational surface (qmin= 2, 5/2, 3, etc.). Measured poloidal flow shear transiently exceeds the turbulence decorrelation rate, which is consistent with shear suppression. The localized suppression zone propagates radially outward, nearly coincident with the low-order surface.

Investigation on the effect of MR elastomer based adaptive vibration absorbers on the radiated sound from circular elastic plates

NASA Astrophysics Data System (ADS)

Hemmatian, M.; Sedaghati, R.

2016-04-01

This study aims to investigate the effect of using magnetorheological elastomer (MRE)-based adaptive tuned vibration absorbers (ATVA) on the sound transmission in an elastic plate. Sound transmission loss (STL) of an elastic circular thin plate is analytically studied. The plate is excited by a plane acoustic wave as an incident sound and the displacement of the plate is calculated using corresponding mode shapes of the system for clamped boundary condition. Rayleigh integral approach is used to express the transmitted sound pressure in terms of the plate's displacement modal amplitude. In order to increase sound transmission loss of the plate, the MRE-based ATVA is considered. The basic idea is to be able to change the stiffness of the ATVA by varying magnetic field in order to reduce the transmitted acoustic energy of the host structure in a wide frequency range. Here, a MRE-based ATVA under the shear mode consisting of an oscillator mass, magnetic conductor, coils and MRE is investigated. In order to predict the viscoelastic characteristics of the field-dependent MRE based on the applied magnetic field, the double pole model is used. Finally, MRE-based ATVAs are integrated with the plate to absorb the plate energy with the aim of decreasing the transmitted sound power. Results show that plate with integrated MRE-based ATVAs suppresses the axisymmetric vibration of the plate and thus considerably improves the STL. Parametric studies on the influence of the position of MRE-based ATVAs and the effects of applied current on their performance are also presented.

Room temperature, single mode emission from two-section coupled cavity InGaAs/AlGaAs/GaAs quantum cascade laser

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

Pierściński, K., E-mail: kamil.pierscinski@ite.waw.pl; Pierścińska, D.; Pluska, M.

2015-10-07

Room temperature, single mode, pulsed emission from two-section coupled cavity InGaAs/AlGaAs/GaAs quantum cascade laser fabricated by focused ion beam processing is demonstrated and analyzed. The single mode emission is centered at 1059.4 cm{sup −1} (9.44 μm). A side mode suppression ratio of 43 dB was achieved. The laser exhibits a peak output power of 15 mW per facet at room temperature. The stable, single mode emission is observed within temperature tuning range, exhibiting shift at rate of 0.59 nm/K.

Low-Loss Hollow Waveguide Fibers for Mid-Infrared Quantum Cascade Laser Sensing Applications

PubMed Central

Patimisco, Pietro; Spagnolo, Vincenzo; Vitiello, Miriam S.; Scamarcio, Gaetano; Bledt, Carlos M.; Harrington, James A.

2013-01-01

We report on single mode optical transmission of hollow core glass waveguides (HWG) coupled with an external cavity mid-IR quantum cascade lasers (QCLs). The QCL mode results perfectly matched to the hybrid HE11 waveguide mode and the higher losses TE-like modes have efficiently suppressed by the deposited inner dielectric coating. Optical losses down to 0.44 dB/m and output beam divergence of ∼5 mrad were measured. Using a HGW fiber with internal core size of 300 μm we obtained single mode laser transmission at 10.54 μm and successful employed it in a quartz enhanced photoacoustic gas sensor setup. PMID:23337336

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

Lykkebo, Jacob; Solomon, Gemma C., E-mail: gsolomon@nano.ku.dk; Romano, Giuseppe

Electronic devices composed of single molecules constitute the ultimate limit in the continued downscaling of electronic components. A key challenge for single-molecule electronics is to control the temperature of these junctions. Controlling heating and cooling effects in individual vibrational modes can, in principle, be utilized to increase stability of single-molecule junctions under bias, to pump energy into particular vibrational modes to perform current-induced reactions, or to increase the resolution in inelastic electron tunneling spectroscopy by controlling the life-times of phonons in a molecule by suppressing absorption and external dissipation processes. Under bias the current and the molecule exchange energy, whichmore » typically results in heating of the molecule. However, the opposite process is also possible, where energy is extracted from the molecule by the tunneling current. Designing a molecular “heat sink” where a particular vibrational mode funnels heat out of the molecule and into the leads would be very desirable. It is even possible to imagine how the vibrational energy of the other vibrational modes could be funneled into the “cooling mode,” given the right molecular design. Previous efforts to understand heating and cooling mechanisms in single molecule junctions have primarily been concerned with small models, where it is unclear which molecular systems they correspond to. In this paper, our focus is on suppressing heating and obtaining current-induced cooling in certain vibrational modes. Strategies for cooling vibrational modes in single-molecule junctions are presented, together with atomistic calculations based on those strategies. Cooling and reduced heating are observed for two different cooling schemes in calculations of atomistic single-molecule junctions.« less

Simple model of inhibition of chain-branching combustion processes

NASA Astrophysics Data System (ADS)

Babushok, Valeri I.; Gubernov, Vladimir V.; Minaev, Sergei S.; Miroshnichenko, Taisia P.

2017-11-01

A simple kinetic model has been suggested to describe the inhibition and extinction of flame propagation in reaction systems with chain-branching reactions typical for hydrocarbon systems. The model is based on the generalised model of the combustion process with chain-branching reaction combined with the one-stage reaction describing the thermal mode of flame propagation with the addition of inhibition reaction steps. Inhibitor addition suppresses the radical overshoot in flame and leads to the change of reaction mode from the chain-branching reaction to a thermal mode of flame propagation. With the increase of inhibitor the transition of chain-branching mode of reaction to the reaction with straight-chains (non-branching chain reaction) is observed. The inhibition part of the model includes a block of three reactions to describe the influence of the inhibitor. The heat losses are incorporated into the model via Newton cooling. The flame extinction is the result of the decreased heat release of inhibited reaction processes and the suppression of radical overshoot with the further decrease of the reaction rate due to the temperature decrease and mixture dilution. A comparison of the results of modelling laminar premixed methane/air flames inhibited by potassium bicarbonate (gas phase model, detailed kinetic model) with the results obtained using the suggested simple model is presented. The calculations with the detailed kinetic model demonstrate the following modes of combustion process: (1) flame propagation with chain-branching reaction (with radical overshoot, inhibitor addition decreases the radical overshoot down to the equilibrium level); (2) saturation of chemical influence of inhibitor, and (3) transition to thermal mode of flame propagation (non-branching chain mode of reaction). The suggested simple kinetic model qualitatively reproduces the modes of flame propagation with the addition of the inhibitor observed using detailed kinetic models.

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

Pan, Huilin; Yang, Jiayue; Zhang, Dong

The effect of antisymmetric C–H stretching excitation of CH{sub 4} on the dynamics and reactivity of the O({sup 1}D) + CH{sub 4} → OH + CD{sub 3} reaction at the collision energy of 6.10 kcal/mol has been investigated using the crossed-beam and time-sliced velocity map imaging techniques. The antisymmetric C–H stretching mode excited CH{sub 4} molecule was prepared by direct infrared excitation. From the measured images of the CH{sub 3} products with the infrared laser on and off, the product translational energy and angular distributions were derived for both the ground and vibrationally excited reactions. Experimental results show that themore » vibrational energy of the antisymmetric stretching excited CH{sub 4} reagent is channeled exclusively into the vibrational energy of the OH co-products and, hence, the OH products from the excited-state reaction are about one vibrational quantum hotter than those from the ground-state reaction, and the product angular distributions are barely affected by the vibrational excitation of the CH{sub 4} reagent. The reactivity was found to be suppressed by the antisymmetric stretching excitation of CH{sub 4} for all observed CH{sub 3} vibrational states. The degree of suppression is different for different CH{sub 3} vibrational states: the suppression is about 40%–60% for the ground state and the umbrella mode excited CH{sub 3} products, while for the CH{sub 3} products with one quantum symmetric stretching mode excitation, the suppression is much less pronounced. In consequence, the vibrational state distribution of the CH{sub 3} product from the excited-state reaction is considerably different from that of the ground-state reaction.« less

The development and optimisation of 3D black-blood R2* mapping of the carotid artery wall.

PubMed

Yuan, Jianmin; Graves, Martin J; Patterson, Andrew J; Priest, Andrew N; Ruetten, Pascal P R; Usman, Ammara; Gillard, Jonathan H

2017-12-01

To develop and optimise a 3D black-blood R 2 * mapping sequence for imaging the carotid artery wall, using optimal blood suppression and k-space view ordering. Two different blood suppression preparation methods were used; Delay Alternating with Nutation for Tailored Excitation (DANTE) and improved Motion Sensitive Driven Equilibrium (iMSDE) were each combined with a three-dimensional (3D) multi-echo Fast Spoiled GRadient echo (ME-FSPGR) readout. Three different k-space view-order designs: Radial Fan-beam Encoding Ordering (RFEO), Distance-Determined Encoding Ordering (DDEO) and Centric Phase Encoding Order (CPEO) were investigated. The sequences were evaluated through Bloch simulation and in a cohort of twenty volunteers. The vessel wall Signal-to-Noise Ratio (SNR), Contrast-to-Noise Ratio (CNR) and R 2 *, and the sternocleidomastoid muscle R 2 * were measured and compared. Different numbers of acquisitions-per-shot (APS) were evaluated to further optimise the effectiveness of blood suppression. All sequences resulted in comparable R 2 * measurements to a conventional, i.e. non-blood suppressed sequence in the sternocleidomastoid muscle of the volunteers. Both Bloch simulations and volunteer data showed that DANTE has a higher signal intensity and results in a higher image SNR than iMSDE. Blood suppression efficiency was not significantly different when using different k-space view orders. Smaller APS achieved better blood suppression. The use of blood-suppression preparation methods does not affect the measurement of R 2 *. DANTE prepared ME-FSPGR sequence with a small number of acquisitions-per-shot can provide high quality black-blood R 2 * measurements of the carotid vessel wall. Copyright © 2017 Elsevier Inc. All rights reserved.

Higher-order mode photonic crystal based nanofluidic sensor

NASA Astrophysics Data System (ADS)

Peng, Wang; Chen, Youping; Ai, Wu

2017-01-01

A higher-order photonic crystal (PC) based nanofluidic sensor, which worked at 532 nm, was designed and demonstrated. A systematical and detailed method for sculpturing a PC sensor for a given peak wavelength value (PWV) and specified materials was illuminated. It was the first time that the higher order mode was used to design PC based nanofluidic sensor, and the refractive index (RI) sensitivity of this sensor had been verified with FDTD simulation software from Lumerical. The enhanced electrical field of higher order mode structure was mostly confined in the channel area, where the enhance field is wholly interacting with the analytes in the channels. The comparison of RI sensitivity between fundamental mode and higher order mode shows the RI variation of higher order mode is 124.5 nm/RIU which is much larger than the fundamental mode. The proposed PC based nanofluidic structure pioneering a novel style for future optofluidic design.

Measurements of branching fraction ratios and CP-asymmetries in suppressed B{sup -}{yields}D({yields}K{sup +}{pi}{sup -})K{sup -} and B{sup -}{yields}D({yields}K{sup +}{pi}{sup -}){pi}{sup -} decays

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

Aaltonen, T.; Brucken, E.; Devoto, F.

2011-11-01

We report the first reconstruction in hadron collisions of the suppressed decays B{sup -}{yields}D({yields}K{sup +}{pi}{sup -})K{sup -} and B{sup -}{yields}D({yields}K{sup +}{pi}{sup -}){pi}{sup -}, sensitive to the Cabibbo-Kobayashi-Maskawa phase {gamma}, using data from 7 fb{sup -1} of integrated luminosity collected by the CDF II detector at the Tevatron collider. We reconstruct a signal for the B{sup -}{yields}D({yields}K{sup +}{pi}{sup -})K{sup -} suppressed mode with a significance of 3.2 standard deviations, and measure the ratios of the suppressed to favored branching fractions R(K)=[22.0{+-}8.6(stat){+-}2.6(syst)]x10{sup -3}, R{sup +}(K)=[42.6{+-}13.7(stat){+-}2.8(syst)]x10{sup -3}, R{sup -}(K)=[3.8{+-}10.3(stat){+-}2.7(syst)]x10{sup -3} as well as the direct CP-violating asymmetry A(K)=-0.82{+-}0.44(stat){+-}0.09(syst) of this mode. Corresponding quantitiesmore » for B{sup -}{yields}D({yields}K{sup +}{pi}{sup -}){pi}{sup -} decay are also reported.« less

A BABAR sensitivity study on the search for the invisible decay of J/psi in B+/- mesons going to K*+/- J/psi

NASA Astrophysics Data System (ADS)

Cheaib, Racha

We present a sensitivity study on the search for J/psi → nu nu in B+/- → K*+/- J/psi using data from the BABAR experiment at the SLAC National Accelerator Laboratory. The decay is highly suppressed in the Standard Model and thus is a possible window for new physics such as supersymmetry and dark matter. Hadronic tag reconstruction is employed for the analysis, where one B is fully reconstructed using hadronic decay modes. The remaining tracks and clusters are attributed to the signal B on which the B+/- → K*+/- J/psi cut-based signal selection is applied. The associated K* is allowed to decay via two modes, Mode 1: K* +/- → K0S pi+/- and Mode 2: K* +/- → K+/- pi 0. The approach is to reconstruct a K*+/- candidate, the only signature in a signal event, and calculate the recoiling mass. The data is left blinded in the signal region and only a range of the branching fraction limits is calculated to determine the sensitivity. The result for Mode 1 is an upper limit, at the 90% confidence level, on B (J/psi → nunu) of 9.13 x 10-2 using the Barlow method and 11.10 x 10-2 using the Feldmann-Cousins method. The upper limit for Mode 2, also at the 90% CL, is estimated to be 2.49 x 10-2 and 2.98 x 10-2 using Barlow and Feldmann-Cousins respectively. The branching fractions thus yield a sensitivity of order 10-2. Although the result is not an improvement on the current J/psi → nu nu limits, this method can be extended to other cc¯ quarkonium modes and could further yield a much better result with data from the newly approved SuperB experiment, the extension of BABAR to higher luminosities.

Impact of toroidal and poloidal mode spectra on the control of non-axisymmetric fields in tokamaks

NASA Astrophysics Data System (ADS)

Lanctot, Matthew J.

2016-10-01

In several tokamaks, non-axisymmetric magnetic field studies show applied n=2 fields can lead to disruptive n=1 locked modes, suggesting nonlinear mode coupling. A multimode plasma response to n=2 fields can be observed in H-mode plasmas, in contrast to the single-mode response found in Ohmic plasmas. These effects highlight a role for n >1 error field correction in disruption avoidance, and identify additional degrees of freedom for 3D field optimization at high plasma pressure. In COMPASS, EAST, and DIII-D Ohmic plasmas, n=2 magnetic reconnection thresholds in otherwise stable discharges are readily accessed at edge safety factors q 3 and low density. Similar to previous studies, the thresholds are correlated with the ``overlap'' field for the dominant linear ideal MHD plasma mode calculated with the IPEC code. The overlap field measures the plasma-mediated coupling of the external field to the resonant field. Remarkably, the critical overlap fields are similar for n=1 and 2 fields with m >nq fields dominating the drive for resonant fields. Complementary experiments in RFX-Mod show fields with m 1 control, including the need for multiple rows of coils to control selected plasma parameters for specific functions (e.g., rotation control or ELM suppression). Optimal multi-harmonic (n=1 and n=2) error field control may be achieved using control algorithms that continuously respond to time-varying 3D field sources and plasma parameters. Supported by the US DOE under DE-FC02-04ER54698.

Fast ion transport during applied 3D magnetic perturbations on DIII-D

DOE PAGES

Van Zeeland, Michael A.; Ferraro, Nathaniel M.; Grierson, Brian A.; ...

2015-06-26

In this paper, measurements show fast ion losses correlated with applied three-dimensional (3D) fields in a variety of plasmas ranging from L-mode to resonant magnetic perturbation (RMP) edge localized mode (ELM) suppressed H-mode discharges. In DIII-D L-mode discharges with a slowly rotatingmore » $n=2$ magnetic perturbation, scintillator detector loss signals synchronized with the applied fields are observed to decay within one poloidal transit time after beam turn-off indicating they arise predominantly from prompt loss orbits. Full orbit following using M3D-C1 calculations of the perturbed fields and kinetic profiles reproduce many features of the measured losses and points to the importance of the applied 3D field phase with respect to the beam injection location in determining the overall impact on prompt beam ion loss. Modeling of these results includes a self-consistent calculation of the 3D perturbed beam ion birth profiles and scrape-off-layer ionization, a factor found to be essential to reproducing the experimental measurements. Extension of the simulations to full slowing down timescales, including fueling and the effects of drag and pitch angle scattering, show the applied $n=3$ RMPs in ELM suppressed H-mode plasmas can induce a significant loss of energetic particles from the core. With the applied $n=3$ fields, up to 8.4% of the injected beam power is predicted to be lost, compared to 2.7% with axisymmetric fields only. These fast ions, originating from minor radii $$\\rho >0.7$$ , are predicted to be primarily passing particles lost to the divertor region, consistent with wide field-of-view infrared periscope measurements of wall heating in $n=3$ RMP ELM suppressed plasmas. Edge fast ion $${{\\text{D}}_{\\alpha}}$$ (FIDA) measurements also confirm a large change in edge fast ion profile due to the $n=3$ fields, where the effect was isolated by using short 50 ms RMP-off periods during which ELM suppression was maintained yet the fast ion profile was allowed to recover. Finally, the role of resonances between fast ion drift motion and the applied 3D fields in the context of selectively targeting regions of fast ion phase space is also discussed.« less

Experimental generalized quantum suppression law in Sylvester interferometers

NASA Astrophysics Data System (ADS)

Viggianiello, Niko; Flamini, Fulvio; Innocenti, Luca; Cozzolino, Daniele; Bentivegna, Marco; Spagnolo, Nicolò; Crespi, Andrea; Brod, Daniel J.; Galvão, Ernesto F.; Osellame, Roberto; Sciarrino, Fabio

2018-03-01

Photonic interference is a key quantum resource for optical quantum computation, and in particular for so-called boson sampling devices. In interferometers with certain symmetries, genuine multiphoton quantum interference effectively suppresses certain sets of events, as in the original Hong–Ou–Mandel effect. Recently, it was shown that some classical and semi-classical models could be ruled out by identifying such suppressions in Fourier interferometers. Here we propose a suppression law suitable for random-input experiments in multimode Sylvester interferometers, and verify it experimentally using 4- and 8-mode integrated interferometers. The observed suppression occurs for a much larger fraction of input–output combinations than what is observed in Fourier interferometers of the same size, and could be relevant to certification of boson sampling machines and other experiments relying on bosonic interference, such as quantum simulation and quantum metrology.

Electron cyclotron maser instability in the solar corona - The role of superthermal tails

NASA Technical Reports Server (NTRS)

Vlahos, L.; Sharma, R. R.

1985-01-01

The effect of a superthermal component of electrons on the loss-cone-driven electron cyclotron maser instability is analyzed. It is found that for a superthermal tail with temperature about 10 KeV, the first harmonic (X- and O-mode) is suppressed for n(t)/n(r) of about 1 (n/t/ and n/r/ are the densities of superthermal tail and loss-cone electrons) and the second harmonic (X- and O-modes) is suppressed for n(t)/n(r) less than about 0.1. A qualitative discussion on the formation of superthermal tails is presented and it is suggested that superthermal tails play an important role on the observed or available power, at microwave frequencies, from the electron cyclotron maser instability in the solar corona.

New measurements of Cabibbo-suppressed decays of mesons with the CLEO-c detector.

PubMed

Rubin, P; Cawlfield, C; Eisenstein, B I; Karliner, I; Kim, D; Lowrey, N; Naik, P; Sedlack, C; Selen, M; White, E J; Wiss, J; Shepherd, M R; Besson, D; Pedlar, T K; Cronin-Hennessy, D; Gao, K Y; Gong, D T; Hietala, J; Kubota, Y; Klein, T; Lang, B W; Poling, R; Scott, A W; Smith, A; Dobbs, S; Metreveli, Z; Seth, K K; Tomaradze, A; Zweber, P; Ernst, J; Severini, H; Dytman, S A; Love, W; Mehrabyan, S; Savinov, V; Aquines, O; Li, Z; Lopez, A; Mendez, H; Ramirez, J; Xin, B; Huang, G S; Miller, D H; Pavlunin, V; Sanghi, B; Shipsey, I P J; Adams, G S; Anderson, M; Cummings, J P; Danko, I; Napolitano, J; He, Q; Insler, J; Muramatsu, H; Park, C S; Thorndike, E H; Coan, T E; Gao, Y S; Liu, F; Stroynowski, R; Artuso, M; Blusk, S; Butt, J; Li, J; Menaa, N; Mountain, R; Nisar, S; Randrianarivony, K; Redjimi, R; Sia, R; Skwarnicki, T; Stone, S; Wang, J C; Zhang, K; Csorna, S E; Bonvicini, G; Cinabro, D; Dubrovin, M; Lincoln, A; Asner, D M; Edwards, K W; Briere, R A; Brock, I; Chen, J; Ferguson, T; Tatishvili, G; Vogel, H; Watkins, M E; Rosner, J L; Adam, N E; Alexander, J P; Berkelman, K; Cassel, D G; Duboscq, J E; Ecklund, K M; Ehrlich, R; Fields, L; Gibbons, L; Gray, R; Gray, S W; Hartill, D L; Heltsley, B K; Hertz, D; Jones, C D; Kandaswamy, J; Kreinick, D L; Kuznetsov, V E; Mahlke-Krüger, H; Meyer, T O; Onyisi, P U E; Patterson, J R; Peterson, D; Phillips, E A; Pivarski, J; Riley, D; Ryd, A; Sadoff, A J; Schwarthoff, H; Shi, X; Stroiney, S; Sun, W M; Wilksen, T; Weinberger, M; Athar, S B; Avery, P; Breva-Newell, L; Patel, R; Potlia, V; Stoeck, H; Yelton, J

2006-03-03

Using of data collected with the CLEO-c detector, we report on first observations and measurements of Cabibbo-suppressed decays of D mesons in the following six decay modes: pi+ pi- pi0 pi0, pi+ pi+ pi- pi- pi0, pi+ pi0 pi0, pi+ pi+ pi- pi0, eta pi0, and omega pi+ pi-. Improved branching fraction measurements in eight other multipion decay modes are also presented. The measured D --> pi pi rates allow us to extract the ratio of isospin amplitudes A(DeltaI = (3/2) / A(DeltaI = (1/2)) = 0.420 +/- 0.014(stat) +/- 0.016(syst) and the strong phase shift of delta1 = (86.4 +/- 2.8 +/- 3.3) degrees, which is quite large and now more precisely determined.

Investigation of Supercurrent in the Quantum Hall Regime in Graphene Josephson Junctions

NASA Astrophysics Data System (ADS)

Draelos, Anne W.; Wei, Ming Tso; Seredinski, Andrew; Ke, Chung Ting; Mehta, Yash; Chamberlain, Russell; Watanabe, Kenji; Taniguchi, Takashi; Yamamoto, Michihisa; Tarucha, Seigo; Borzenets, Ivan V.; Amet, François; Finkelstein, Gleb

2018-06-01

In this study, we examine multiple encapsulated graphene Josephson junctions to determine which mechanisms may be responsible for the supercurrent observed in the quantum Hall (QH) regime. Rectangular junctions with various widths and lengths were studied to identify which parameters affect the occurrence of QH supercurrent. We also studied additional samples where the graphene region is extended beyond the contacts on one side, making that edge of the mesa significantly longer than the opposite edge. This is done in order to distinguish two potential mechanisms: (a) supercurrents independently flowing along both non-contacted edges of graphene mesa, and (b) opposite sides of the mesa being coupled by hybrid electron-hole modes flowing along the superconductor/graphene boundary. The supercurrent appears suppressed in extended junctions, suggesting the latter mechanism.

Resurgence of oscillation in coupled oscillators under delayed cyclic interaction

NASA Astrophysics Data System (ADS)

Bera, Bidesh K.; Majhi, Soumen; Ghosh, Dibakar

2017-07-01

This paper investigates the emergence of amplitude death and revival of oscillations from the suppression states in a system of coupled dynamical units interacting through delayed cyclic mode. In order to resurrect the oscillation from amplitude death state, we introduce asymmetry and feedback parameter in the cyclic coupling forms as a result of which the death region shrinks due to higher asymmetry and lower feedback parameter values for coupled oscillatory systems. Some analytical conditions are derived for amplitude death and revival of oscillations in two coupled limit cycle oscillators and corresponding numerical simulations confirm the obtained theoretical results. We also report that the death state and revival of oscillations from quenched state are possible in the network of identical coupled oscillators. The proposed mechanism has also been examined using chaotic Lorenz oscillator.

Experimental demonstration of 24-Gb/s CAP-64QAM radio-over-fiber system over 40-GHz mm-wave fiber-wireless transmission.

PubMed

Zhang, Junwen; Yu, Jianjun; Chi, Nan; Li, Fan; Li, Xinying

2013-11-04

We propose and demonstrate a novel CAP-ROF system based on multi-level carrier-less amplitude and phase modulation (CAP) 64QAM with high spectrum efficiency for mm-wave fiber-wireless transmission. The performance of novel CAP modulation with high order QAM, for the first time, is investigated in the mm-wave fiber-wireless transmission system. One I/Q modulator is used for mm-wave generation and base-band signal modulation based on optical carrier suppression (OCS) and intensity modulation. Finally, we demonstrated a 24-Gb/s CAP-64QAM radio-over-fiber (ROF) system over 40-km stand single-mode-fiber (SMMF) and 1.5-m 38-GHz wireless transmission. The system operation factors are also experimentally investigated.

Functional Based Adaptive and Fuzzy Sliding Controller for Non-Autonomous Active Suspension System

NASA Astrophysics Data System (ADS)

Huang, Shiuh-Jer; Chen, Hung-Yi

In this paper, an adaptive sliding controller is developed for controlling a vehicle active suspension system. The functional approximation technique is employed to substitute the unknown non-autonomous functions of the suspension system and release the model-based requirement of sliding mode control algorithm. In order to improve the control performance and reduce the implementation problem, a fuzzy strategy with online learning ability is added to compensate the functional approximation error. The update laws of the functional approximation coefficients and the fuzzy tuning parameters are derived from the Lyapunov theorem to guarantee the system stability. The proposed controller is implemented on a quarter-car hydraulic actuating active suspension system test-rig. The experimental results show that the proposed controller suppresses the oscillation amplitude of the suspension system effectively.

Integrated optical gyroscope using active Long-range surface plasmon-polariton waveguide resonator

PubMed Central

Zhang, Tong; Qian, Guang; Wang, Yang-Yang; Xue, Xiao-Jun; Shan, Feng; Li, Ruo-Zhou; Wu, Jing-Yuan; Zhang, Xiao-Yang

2014-01-01

Optical gyroscopes with high sensitivity are important rotation sensors for inertial navigation systems. Here, we present the concept of integrated resonant optical gyroscope constructed by active long-range surface plasmon-polariton (LRSPP) waveguide resonator. In this gyroscope, LRSPP waveguide doped gain medium is pumped to compensate the propagation loss, which has lower pump noise than that of conventional optical waveguide. Peculiar properties of single-polarization of LRSPP waveguide have been found to significantly reduce the polarization error. The metal layer of LRSPP waveguide is electro-optical multiplexed for suppression of reciprocal noises. It shows a limited sensitivity of ~10−4 deg/h, and a maximum zero drift which is 4 orders of magnitude lower than that constructed by conventional single-mode waveguide. PMID:24458281

Dispersion of speckle suppression efficiency for binary DOE structures: spectral domain and coherent matrix approaches.

PubMed

Lapchuk, Anatoliy; Prygun, Olexandr; Fu, Minglei; Le, Zichun; Xiong, Qiyuan; Kryuchyn, Andriy

2017-06-26

We present the first general theoretical description of speckle suppression efficiency based on an active diffractive optical element (DOE). The approach is based on spectral analysis of diffracted beams and a coherent matrix. Analytical formulae are obtained for the dispersion of speckle suppression efficiency using different DOE structures and different DOE activation methods. We show that a one-sided 2D DOE structure has smaller speckle suppression range than a two-sided 1D DOE structure. Both DOE structures have sufficient speckle suppression range to suppress low-order speckles in the entire visible range, but only the two-sided 1D DOE can suppress higher-order speckles. We also show that a linear shift 2D DOE in a laser projector with a large numerical aperture has higher effective speckle suppression efficiency than the method using switching or step-wise shift DOE structures. The generalized theoretical models elucidate the mechanism and practical realization of speckle suppression.

Local suppression of the hidden-order phase by impurities in URu2Si2

NASA Astrophysics Data System (ADS)

Pezzoli, Maria E.; Graf, Matthias J.; Haule, Kristjan; Kotliar, Gabriel; Balatsky, Alexander V.

2011-06-01

We consider the effects of impurities on the enigmatic hidden order (HO) state of the heavy-fermion material URu2Si2. In particular, we focus on local effects of Rh impurities as a tool to probe the suppression of the HO state. To study local properties, we introduce a lattice free energy, where the time invariant HO order parameter Ψ and local antiferromagnetic (AFM) order parameter M are competing orders. Near each Rh atom, the HO order parameter is suppressed, creating a hole in which local AFM order emerges as a result of competition. These local holes are created in the fabric of the HO state like in a Swiss cheese and “filled” with droplets of AFM order. We compare our analysis with recent NMR results on U(RhxRu1-x)2Si2 and find good agreement with the data.

Low-bending loss and single-mode operation in few-mode optical fiber

NASA Astrophysics Data System (ADS)

Yin, Ping; Wang, Hua; Chen, Ming-Yang; Wei, Jin; Cai, Zhi-Min; Li, Lu-Ming; Yang, Ji-Hai; Zhu, Yuan-Feng

2016-10-01

The technique of eliminating the higher-order modes in a few-mode optical fiber is proposed. The fiber is designed with a group of defect modes in the cladding. The higher-order modes in the fiber can be eliminated by bending the fiber to induce strong coupling between the defect modes and the higher-order modes. Numerical simulation shows the bending losses of the LP01 mode are lower than 1.5×10-4 dB/turn for the wavelength shorter than 1.625 μm. The proposed fiber can be bent multiple turns at small bending radius which are preferable for FTTH related applications.

Application of transmission loss concept in the evaluation of an acoustic filter for liquid-borne transverse resonance modes in a duct of circular cross section

NASA Technical Reports Server (NTRS)

Iwanicki, L. R.; Chang, Y. M.

1980-01-01

The transmission loss concept is used in the evaluation of an acoustic filter for liquid-borne transverse modes. Tests are conducted to determine the nature of filter element designs required to suppress transverse modes, to verify the presence of transverse modes in the test assembly, to define the acoustic wave incident, and to establish data recording, processing and analysis techniques providing transmission wave filter data. The first, second, and third tangential modes, and the first radial mode are found at frequencies of 2150, 3330, 4420, and 4110 Hz, respectively, and peaks of the tangential modes recede while the radial mode peak remains, demonstrating agreement with theoretical nodal patterns. The present design is found applicable to a liquid-oxygen system, and allows the easy-to-fabricate filter to fit within the available space envelope.

Range side lobe inversion for chirp-encoded dual-band tissue harmonic imaging.

PubMed

Shen, Che-Chou; Peng, Jun-Kai; Wu, Chi

2014-02-01

Dual-band (DB) harmonic imaging is performed by transmitting and receiving at both fundamental band (f0) and second-harmonic band (2f0). In our previous work, particular chirp excitation has been developed to increase the signal- to-noise ratio in DB harmonic imaging. However, spectral overlap between the second-order DB harmonic signals results in range side lobes in the pulse compression. In this study, a novel range side lobe inversion (RSI) method is developed to alleviate the level of range side lobes from spectral overlap. The method is implemented by firing an auxiliary chirp to change the polarity of the range side lobes so that the range side lobes can be suppressed in the combination of the original chirp and the auxiliary chirp. Hydrophone measurements show that the RSI method reduces the range side lobe level (RSLL) and thus increases the quality of pulse compression in DB harmonic imaging. With the signal bandwidth of 60%, the RSLL decreases from -23 dB to -36 dB and the corresponding compression quality improves from 78% to 94%. B-mode images also indicate that the magnitude of range side lobe is suppressed by 7 dB when the RSI method is applied.

Son of IXION: A Steady State Centrifugally Confined Plasma for Fusion*

NASA Astrophysics Data System (ADS)

Hassam, Adil

1996-11-01

A magnetic confinement scheme in which the inertial, u.grad(u), forces effect parallel confinement is proposed. The basic geometry is mirror-like as far as the poloidal field goes or, more simply, multipole (FM-1) type. The rotation is toroidal in this geometry. A supersonic rotation can effect complete parallel confinement, with the usual magnetic mirror force rendered irrelevant. The rotation shear, in addition, aids in the suppression of the flute mode. This suppression is not complete which indicates the addition of a toroidal field, at maximum of the order of the poloidal field. We show that at rotation in excess of Mach 3, the parallel particle and heat losses can be minimized to below the Lawson breakeven point. The crossfield transport can be expected to be better than tokamaks on account of the large velocity shear. Other advantages of the scheme are that it is steady state and disruption free. An exploratory experiment that tests equilibrium, parallel detachment, and MHD stability is proposed. The concept resembles earlier (Geneva, 1958) experiments on "homopolar generators" and a mirror configuration called IXION. Ixion, Greek mythological king, was forever strapped to a rotating, flaming wheel. *Work supported by DOE

Fractional order integration and fuzzy logic based filter for denoising of echocardiographic image.

PubMed

Saadia, Ayesha; Rashdi, Adnan

2016-12-01

Ultrasound is widely used for imaging due to its cost effectiveness and safety feature. However, ultrasound images are inherently corrupted with speckle noise which severely affects the quality of these images and create difficulty for physicians in diagnosis. To get maximum benefit from ultrasound imaging, image denoising is an essential requirement. To perform image denoising, a two stage methodology using fuzzy weighted mean and fractional integration filter has been proposed in this research work. In stage-1, image pixels are processed by applying a 3 × 3 window around each pixel and fuzzy logic is used to assign weights to the pixels in each window, replacing central pixel of the window with weighted mean of all neighboring pixels present in the same window. Noise suppression is achieved by assigning weights to the pixels while preserving edges and other important features of an image. In stage-2, the resultant image is further improved by fractional order integration filter. Effectiveness of the proposed methodology has been analyzed for standard test images artificially corrupted with speckle noise and real ultrasound B-mode images. Results of the proposed technique have been compared with different state-of-the-art techniques including Lsmv, Wiener, Geometric filter, Bilateral, Non-local means, Wavelet, Perona et al., Total variation (TV), Global Adaptive Fractional Integral Algorithm (GAFIA) and Improved Fractional Order Differential (IFD) model. Comparison has been done on quantitative and qualitative basis. For quantitative analysis different metrics like Peak Signal to Noise Ratio (PSNR), Speckle Suppression Index (SSI), Structural Similarity (SSIM), Edge Preservation Index (β) and Correlation Coefficient (ρ) have been used. Simulations have been done using Matlab. Simulation results of artificially corrupted standard test images and two real Echocardiographic images reveal that the proposed method outperforms existing image denoising techniques reported in the literature. The proposed method for denoising of Echocardiographic images is effective in noise suppression/removal. It not only removes noise from an image but also preserves edges and other important structure. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Standardization and performance evaluation of "modified" and "ultrasensitive" versions of the Abbott RealTime HIV-1 assay, adapted to quantify minimal residual viremia.

PubMed

Amendola, Alessandra; Bloisi, Maria; Marsella, Patrizia; Sabatini, Rosella; Bibbò, Angela; Angeletti, Claudio; Capobianchi, Maria Rosaria

2011-09-01

Numerous studies investigating clinical significance of HIV-1 minimal residual viremia (MRV) suggest potential utility of assays more sensitive than those routinely used to monitor viral suppression. However currently available methods, based on different technologies, show great variation in detection limit and input plasma volume, and generally suffer from lack of standardization. In order to establish new tools suitable for routine quantification of minimal residual viremia in patients under virological suppression, some modifications were introduced into standard procedure of the Abbott RealTime HIV-1 assay leading to a "modified" and an "ultrasensitive" protocols. The following modifications were introduced: calibration curve extended towards low HIV-1 RNA concentration; 4 fold increased sample volume by concentrating starting material; reduced volume of internal control; adoption of "open-mode" software for quantification. Analytical performances were evaluated using the HIV-1 RNA Working Reagent 1 for NAT assays (NIBSC). Both tests were applied to clinical samples from virologically suppressed patients. The "modified" and the "ultrasensitive" configurations of the assay reached a limit of detection of 18.8 (95% CI: 11.1-51.0 cp/mL) and 4.8 cp/mL (95% CI: 2.6-9.1 cp/mL), respectively, with high precision and accuracy. In clinical samples from virologically suppressed patients, "modified" and "ultrasensitive" protocols allowed to detect and quantify HIV RNA in 12.7% and 46.6%, respectively, of samples resulted "not-detectable", and in 70.0% and 69.5%, respectively, of samples "detected <40 cp/mL" in the standard assay. The "modified" and "ultrasensitive" assays are precise and accurate, and easily adoptable in routine diagnostic laboratories for measuring MRV. Copyright © 2011 Elsevier B.V. All rights reserved.

Multi-octave analog photonic link with improved second- and third-order SFDRs

NASA Astrophysics Data System (ADS)

Tan, Qinggui; Gao, Yongsheng; Fan, Yangyu; He, You

2018-03-01

The second- and third-order spurious free dynamic ranges (SFDRs) are two key performance indicators for a multi-octave analogy photonic link (APL). The linearization methods for either second- or third-order intermodulation distortion (IMD2 or IMD3) have been intensively studied, but the simultaneous suppression for the both were merely reported. In this paper, we propose an APL with improved second- and third-order SFDRs for multi-octave applications based on two parallel DPMZM-based sub-APLs. The IMD3 in each sub-APL is suppressed by properly biasing the DPMZM, and the IMD2 is suppressed by balanced detecting the two sub-APLs. The experiment demonstrates significant suppression ratios for both the IMD2 and IMD3 after linearization in the proposed link, and the measured second- and third-order SFDRs with the operating frequency from 6 to 40 GHz are above 91 dB ṡHz 1 / 2 and 116 dB ṡHz 2 / 3, respectively.

Two-body open charm decays of Z{sup +}(4430)

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

Liu Xiang; Centro de Fisica Teorica, Departamento de Fisica, Universidade de Coimbra, P-3004-516, Coimbra; Zhang Bo

2008-06-01

The two-body open charm decays Z{sup +}(4430){yields}D{sup +}D*{sup 0}, D*{sup +}D{sup 0}, D*{sup +}D*{sup 0} occur through the rescattering mechanism and their branching ratios are strongly suppressed if Z{sup +}(4430) is a D{sub 1}D* molecular state. In contrast, Z{sup +}(4430) falls apart into these modes easily with large phase space and they become the main decay modes if Z{sup +}(4430) is a tetraquark state. Experimental search of these two-body open charm modes and the hidden charm mode {chi}{sub cJ}{rho} will help distinguish different theoretical schemes.

Spinal cord stimulation for the treatment of chronic back pain patients: 500-Hz vs. 1000-Hz burst stimulation.

PubMed

Van Havenbergh, Tony; Vancamp, Tim; Van Looy, Pieter; Vanneste, Sven; De Ridder, Dirk

2015-01-01

Spinal cord stimulation is a commonly used, safe, and effective procedure applied for medically intractable failed back surgery syndrome, as well as other neuropathic pain syndromes. Recently, a novel stimulation paradigm called burst stimulation has been developed that is paresthesia-free and has a more pronounced suppressive effect on neuropathic pain. Fifteen patients who were being treated with burst spinal cord stimulation for failed back surgery syndrome participated in an open-label trial to verify whether their pain suppression could be further ameliorated by changing the burst pattern. Burst stimulation with packets of five electrical pulses delivered at 500 Hz with 1000-μsec pulse width 40 times per second was changed to burst mode delivering five spikes at 1000 Hz with 500-μsec pulse width 40 times a second. As the amplitudes did not differ between the two groups, the total delivery of current to the spinal cord was not different between the two modes of burst stimulation. Scores on visual analog scales for pain and paresthesia, the Pain Catastrophizing Scale, the Pain Vigilance and Awareness Questionnaire, and the Short Form 36 quality of life measurement were compared between the two modes of burst stimulation. [Correction added on 06 Feb 2015, after first online publication: this paragraph has been revised to signify the comparison of amplitudes between two groups] No statistically significant differences were found between the two modes of stimulation. The results suggest that increasing the frequency from 500 to 1000 Hz while keeping the pulse width constant does not add any extra benefit in suppressing pain. Further studies should verify whether increasing the frequency above 1000 Hz has a similar lack of effect. © 2014 International Neuromodulation Society.

Stabilized single-longitudinal-mode erbium fibre laser employing silicon-micro-ring resonator and saturable absorber

NASA Astrophysics Data System (ADS)

Hsu, Yung; Yeh, Chien-Hung; Chow, Chi-Wai; Chang, Yuan-Chia; Cheng, Hao-Yun

2018-07-01

In the paper, a wavelength-tunable erbium-doped fiber (EDF) ring laser with stable single-longitudinal-mode (SLM) oscillation is proposed and investigated. Here, a silicon-micro-ring-resonator can be applied in a laser cavity for tuning wavelength in the C-band range. To complete the SLM oscillation, an unpumped EDF-based saturable absorber is used to act as ultra-narrowband filter for suppressing other oscillation modes. Additionally, the output stabilities of power and wavelength in the proposed EDF ring laser are also executed and discussed.

Widely tunable semiconductor lasers with three interferometric arms.

PubMed

Su, Guan-Lin; Wu, Ming C

2017-09-04

We present a comprehensive study for a new three-branch widely tunable semiconductor laser based on a self-imaging, lossless multi-mode interference (MMI) coupler. We have developed a general theoretical framework that is applicable to all types of interferometric lasers. Our analysis showed that the three-branch laser offers high side-mode suppression ratios (SMSRs) while maintaining a wide tuning range and a low threshold modal gain of the lasing mode. We also present the design rules for tuning over the dense-wavelength division multiplexing grid over the C-band.

Bend compensated large-mode-area fibers: achieving robust single-modedness with transformation optics.

PubMed

Fini, John M; Nicholson, Jeffrey W

2013-08-12

Fibers with symmetric bend compensated claddings are proposed, and demonstrate performance much better than conventional designs. These fibers can simultaneously achieve complete HOM suppression, negligible bend loss, and mode area >1000 square microns. The robust single-modedness of these fibers offers a path to overcoming mode instability limits on high-power amplifiers and lasers. The proposed designs achieve many of the advantages of our previous (asymmetric) bend compensation strategy in the regime of moderately large area, and are much easier to fabricate and utilize.

Higher order mode of a microstripline fed cylindrical dielectric resonator antenna

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

Kumar, A. V. Praveen, E-mail: praveen.kumar@pilani.bits-pilani.ac.in

2016-03-09

A microstrip transmission line can be used to excite the broadside radiating mode of a cylindrical dielectric resonator antenna (CDRA). The same is found to excite considerably well a higher order mode (HOM) as well. However unlike the broadside mode, the higher order mode gives distorted radiation pattern which makes this mode less useful for practical applications. The cause of distortion in the HOM radiation and the dependence of HOM coupling on the microstrip feed line are explored using HFSS simulations.

Effect of electrode biasing on m/n  =  2/1 tearing modes in J-TEXT experiments

NASA Astrophysics Data System (ADS)

Liu, Hai; Hu, Qiming; Chen, Zhipeng; Yu, Q.; Zhu, Lizhi; Cheng, Zhifeng; Zhuang, Ge; Chen, Zhongyong

2017-01-01

The effects of electrode biasing (EB) on the m/n  =  2/1 tearing mode have been experimentally studied in J-TEXT tokamak discharges, where m and n are the poloidal and toroidal mode numbers. It is found that for a negative bias voltage, the mode amplitude is reduced, and the mode frequency is increased accompanied by the increased toroidal plasma rotation speed in the counter-I p direction. For a positive bias voltage, the mode frequency is decreased together with the change of the rotation velocity towards the co-I p direction, and the mode amplitude is increased. Statistic results show that the variations in the toroidal rotation speed, the 2/1 mode frequency and its amplitude linearly depend on the bias voltage. The threshold voltages for complete suppression and locking of the mode are found. The experimental results suggest that applied electrode biasing is a possible method for the avoidance of mode locking and disruption.

Mode Behavior in Ultralarge Ring Lasers

NASA Astrophysics Data System (ADS)

Hurst, Robert B.; Dunn, Robert W.; Schreiber, K. Ulrich; Thirkettle, Robert J.; MacDonald, Graeme K.

2004-04-01

Contrary to expectations based on mode spacing, single-mode operation in very large He-Ne ring lasers may be achieved at intracavity power levels up to ~0.15 times the saturation intensity for the He-Ne transition. Homogeneous line broadening at a high total gas pressure of 4-6 Torr allows a single-peaked gain profile that suppresses closely spaced multiple modes. At startup, decay of initial multiple modes may take tens of seconds. The single remaining mode in each direction persists metastably as the cavity is detuned by many times the mode frequency spacing. A theoretical explanation requires the gain profile to be concave down and to satisfy an inequality related to slope and saturation at the operating frequency. Calculated metastable frequency ranges are greater than 150 MHz at 6 Torr and depend strongly on pressure. Examples of unusual stable mode configurations are shown, with differently numbered modes in the two directions and with multiple modes at a spacing of ~100 MHz.

Mode behavior in ultralarge ring lasers.

PubMed

Hurst, Robert B; Dunn, Robert W; Schreiber, K Ulrich; Thirkettle, Robert J; MacDonald, Graeme K

2004-04-10

Contrary to expectations based on mode spacing, single-mode operation in very large He-Ne ring lasers may be achieved at intracavity power levels up to approximately0.15 times the saturation intensity for the He-Ne transition. Homogeneous line broadening at a high total gas pressure of 4-6 Torr allows a single-peaked gain profile that suppresses closely spaced multiple modes. At startup, decay of initial multiple modes may take tens of seconds. The single remaining mode in each direction persists metastably as the cavity is detuned by many times the mode frequency spacing. A theoretical explanation requires the gain profile to be concave down and to satisfy an inequality related to slope and saturation at the operating frequency. Calculated metastable frequency ranges are > 150 MHz at 6 Torr and depend strongly on pressure. Examples of unusual stable mode configurations are shown, with differently numbered modes in the two directions and with multiple modes at a spacing of approximately 100 MHz.

Mode control in a high gain relativistic klystron amplifier with 3 GW output power

NASA Astrophysics Data System (ADS)

Wu, Yang; Xie, Hong-Quan; Xu, Zhou

2014-01-01

Higher mode excitation is very serious in the relativistic klystron amplifier, especially for the high gain relativistic amplifier working at tens of kilo-amperes. The mechanism of higher mode excitation is explored in the PIC simulation and it is shown that insufficient separation of adjacent cavities is the main cause of higher mode excitation. So RF lossy material mounted on the drift tube wall is adopted to suppress higher mode excitation. A high gain S-band relativistic klystron amplifier is designed for the beam current of 13 kA and the voltage of 1 MV. PIC simulation shows that the output power is 3.2 GW when the input power is only 2.8 kW.

Mean and oscillating plasma flows and turbulence interactions across the L-H confinement transition.

PubMed

Conway, G D; Angioni, C; Ryter, F; Sauter, P; Vicente, J

2011-02-11

A complex interaction between turbulence driven E × B zonal flow oscillations, i.e., geodesic acoustic modes (GAMs), the turbulence, and mean equilibrium flows is observed during the low to high (L-H) plasma confinement mode transition in the ASDEX Upgrade tokamak. Below the L-H threshold at low densities a limit-cycle oscillation forms with competition between the turbulence level and the GAM flow shearing. At higher densities the cycle is diminished, while in the H mode the cycle duration becomes too short to sustain the GAM, which is replaced by large amplitude broadband flow perturbations. Initially GAM amplitude increases as the H-mode transition is approached, but is then suppressed in the H mode by enhanced mean flow shear.

Discrete mode laser diodes for FTTH/PON applications up to 10 Gbit/s

NASA Astrophysics Data System (ADS)

O'Carroll, John; Phelan, Richard; Kelly, Brian; Byrne, Diarmuid; Latkowski, Sylwester; Anandarajah, Prince M.; Barry, Liam P.

2012-06-01

Discrete Mode Laser Diodes (DMLDs) present an economic approach with a focus on high volume manufacturability of single mode lasers using a single step fabrication process. We report on a DMLD designed for operation in the 1550 nm window with high Side Mode Suppression Ratio (SMSR) over a wide temperature tuning range of -20 °C < T < 95 °C. Direct modulation rates as high as 10 Gbit/s are demonstrated at both 1550 nm and 1310 nm. Transmission experiments were also carried out over single mode fibre at both wavelengths. Using dispersion pre-compensation transmission from 0 to 60 km is demonstrated at 1550 nm with a maximum power penalty measured at 60 km of 3.6 dB.

Continuous tuning of two-section, single-mode terahertz quantum-cascade lasers by fiber-coupled, near-infrared illumination

NASA Astrophysics Data System (ADS)

Hempel, Martin; Röben, Benjamin; Niehle, Michael; Schrottke, Lutz; Trampert, Achim; Grahn, Holger T.

2017-05-01

The dynamical tuning due to rear facet illumination of single-mode, terahertz (THz) quantum-cascade lasers (QCLs) which employ distributed feedback gratings are compared to the tuning of single-mode QCLs based on two-section cavities. The THz QCLs under investigation emit in the range of 3 to 4.7 THz. The tuning is achieved by illuminating the rear facet of the QCL with a fiber-coupled light source emitting at 777 nm. Tuning ranges of 5.0 and 11.9 GHz under continuous-wave and pulsed operation, respectively, are demonstrated for a single-mode, two-section cavity QCL emitting at about 3.1 THz, which exhibits a side-mode suppression ratio better than -25 dB.

Boundary control of anti-symmetric vibration of satellite with flexible appendages in planar motion with exponential stability

NASA Astrophysics Data System (ADS)

Rad, Hossein Kaviani; Salarieh, Hassan; Alasty, Aria; Vatankhah, Ramin

2018-06-01

In this research, we have investigated the planar maneuver of a flexible satellite with appendages anti-symmetric vibration. The hybrid governing equations are comprised of coupled partial and ordinary differential equations which are derived by employing Hamilton's principle. In this paper, control goals are the tracking desired pitch angle along with the flexible appendages vibration suppression simultaneously by using only one control torque which is applied to the central hub. The boundary control is proposed to fulfill these control aims; furthermore, this boundary control ensures that spillover instability phenomenon is eliminated, and in-domain sensors and actuators implement are excluded. Indeed, the proposed boundary control is able to stabilize an infinite number of vibration modes, which is one of the important benefits of the proposed control when it is considered that different factors including external disturbances and even the satellite maneuver can excite the various vibration modes of the flexible appendages and consequently the excitement of the high order vibration modes will be possible. Lyapunov's direct method is used to prove the exponential stability; moreover, this Proof is achieved in absence of any damping effect in modeling the vibrations of flexible appendages. In addition, the procedure for finding the boundary control coefficients which ensures the exponential stability is provided. Eventually, numerical simulations are presented to illustrate the effectiveness of the proposed boundary control.

Metasurface-assisted orbital angular momentum carrying Bessel-Gaussian Laser: proposal and simulation.

PubMed

Zhou, Nan; Wang, Jian

2018-05-23

Bessel-Gaussian beams have distinct properties of suppressed diffraction divergence and self-reconstruction. In this paper, we propose and simulate metasurface-assisted orbital angular momentum (OAM) carrying Bessel-Gaussian laser. The laser can be regarded as a Fabry-Perot cavity formed by one partially transparent output plane mirror and the other metasurface-based reflector mirror. The gain medium of Nd:YVO 4 enables the lasing wavelength at 1064 nm with a 808 nm laser serving as the pump. The sub-wavelength structure of metasurface facilitates flexible spatial light manipulation. The compact metasurface-based reflector provides combined phase functions of an axicon and a spherical mirror. By appropriately selecting the size of output mirror and inserting mode-selection element in the laser cavity, different orders of OAM-carrying Bessel-Gaussian lasing modes are achievable. The lasing Bessel-Gaussian 0 , Bessel-Gaussian 01 + , Bessel-Gaussian 02 + and Bessel-Gaussian 03 + modes have high fidelities of ~0.889, ~0.889, ~0.881 and ~0.879, respectively. The metasurface fabrication tolerance and the dependence of threshold power and output lasing power on the length of gain medium, beam radius of pump and transmittance of output mirror are also discussed. The obtained results show successful implementation of metasurface-assisted OAM-carrying Bessel-Gaussian laser with favorable performance. The metasurface-assisted OAM-carrying Bessel-Gaussian laser may find wide OAM-enabled communication and non-communication applications.

Transmission of laser pulses with high output beam quality using step-index fibers having large cladding

DOEpatents

Yalin, Azer P; Joshi, Sachin

2014-06-03

An apparatus and method for transmission of laser pulses with high output beam quality using large core step-index silica optical fibers having thick cladding, are described. The thick cladding suppresses diffusion of modal power to higher order modes at the core-cladding interface, thereby enabling higher beam quality, M.sup.2, than are observed for large core, thin cladding optical fibers. For a given NA and core size, the thicker the cladding, the better the output beam quality. Mode coupling coefficients, D, has been found to scale approximately as the inverse square of the cladding dimension and the inverse square root of the wavelength. Output from a 2 m long silica optical fiber having a 100 .mu.m core and a 660 .mu.m cladding was found to be close to single mode, with an M.sup.2=1.6. Another thick cladding fiber (400 .mu.m core and 720 .mu.m clad) was used to transmit 1064 nm pulses of nanosecond duration with high beam quality to form gas sparks at the focused output (focused intensity of >100 GW/cm.sup.2), wherein the energy in the core was <6 mJ, and the duration of the laser pulses was about 6 ns. Extending the pulse duration provided the ability to increase the delivered pulse energy (>20 mJ delivered for 50 ns pulses) without damaging the silica fiber.

Mode switching and linear stability analysis of resonant acoustic flows

NASA Astrophysics Data System (ADS)

Panickar, Praveen

Resonant acoustic flows occur in a wide variety of practical, aerospace-related applications and are a rich source of complex flow-physics. The primary concern associated with these types of flows is the high-amplitude fluctuating pressures associated with the resonant tones that could lead to sonic fatigue failure of sensitive components in the vicinity of such flows. However, before attempting to devise methods to suppress the resonant tones, it is imperative to understand the physics governing these flows in the hope that such an understanding will lead to more robust and effective suppression techniques. To this end, an in-depth study of various resonant acoustic flows was undertaken in this thesis, the main aim being to bring about a better understanding of such flows by revealing physically relevant information. Starting with the resonant acoustic mechanism in underexpanded jets from two-dimensional nozzles, it was shown that, for a variety of flow situations (geometries, shock-cell structures and orientations) in such jets, the nonlinear interaction density acted as a faithful precursor to a, hitherto unpredictable, spanwise instability mode switch. Following this, a study of the occurrence of, previously undocumented and theoretically unexpected, helical instabilities in subsonic impinging jets was undertaken. Using metrics from linear stability analysis, it was shown that the presence of the helical modes was justified. The results from this study on impinging jets are directly applicable to modern Stationary Take-Off and Vertical Landing (STOVL) aircraft that have twin, closely spaced exhausts. Finally, a novel technique that yielded dramatic suppression of resonant acoustic tones using high frequency excitation, in subsonic flows over open cavities, was investigated. Linear stability calculations of the experimentally measured baseline and excited velocity profiles showed that the instability of the high frequency excitation corresponded to a spatially decaying mode, which in turn lead to the resonance suppression associated with this mechanism. The experimental results showed good agreement with linear stability calculations for the measured mean velocity profiles. It is hoped that the work presented in this thesis will further the understanding of resonant acoustic flows and provide insights that can lead to better control techniques in the future.

Hadronic decays of B →a1(1260 )b1(1235 ) in the perturbative QCD approach

NASA Astrophysics Data System (ADS)

Jing, Hao-Yang; Liu, Xin; Xiao, Zhen-Jun

2017-12-01

We calculate the branching ratios and polarization fractions of the B →a1b1 decays in the perturbative QCD(pQCD) approach at leading order, where a1(b1) stands for the axial-vector a1(1260 )[b1(1235 )] state. By combining the phenomenological analyses with the perturbative calculations, we find the following results: (a) the large decay rates around 10-5 to 10-6 of the B →a1b1 decays dominated by the longitudinal polarization(except for the B+→b1+a10 mode) are predicted and basically consistent with those in the QCD factorization(QCDF) within errors, which are expected to be tested by the Large Hadron Collider and Belle-II experiments. The large B0→a10b10 branching ratio could provide hints to help explore the mechanism of the color-suppressed decays. (b) the rather different QCD behaviors between the a1 and b1 mesons result in the destructive(constructive) contributions in the nonfactorizable spectator diagrams with a1(b1) emission. Therefore, an interesting pattern of the branching ratios appears for the color-suppressed B0→a10a10,a10b10, and b10b10 modes in the pQCD approach, BR (B0→b10b10)>BR (B0→a10b10)≳BR (B0→a10a10), which is different from BR (B0→b10b10)˜BR (B0→a10b10)≳BR (B0→a10a10) in the QCDF and would be verified at future experiments. (c) the large naive factorization breaking effects are observed in these B →a1b1 decays. Specifically, the large nonfactorizable spectator(weak annihilation) amplitudes contribute to the B0→b1+a1-(B+→a1+b10andB+→b1+a10) mode(s), which demand confirmations via the precise measurements. Furthermore, the different phenomenologies shown among B →a1b1, B →a1a1, and B →b1b1 decays are also expected to be tested stringently, which could shed light on the typical QCD dynamics involved in these modes, even further distinguish those two popular pQCD and QCDF approaches.

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

Cheaib, Racha

The flavour changing neutral current (FCNC) process,more » $B^+$ → $K^+ τ^+ τ^-$ highly suppressed in the Standard Model (SM). This decay is forbidden at tree level and only occurs at lowest order via one-loop diagrams.$B^+$ → $K^+ τ^+ τ^-$ thus has the potential to provide a stringent test of the SM and a fertile ground for new physics searches. Contributions due to virtual particles in the loop allow one to probe, at relatively low energies, new physics at large mass scales. We search for the rare FCNC process $B^+$ → $K^+ τ^+ τ^-$ using data collected by the BaBaR detector at the SLAC National Accelerator Laboratory. The BaBaR data sample corresponds to a total integrated luminosity, at the energy of the Τ(4S) resonance, of 424.4 $fb^-1$ and 471 million $$B\\bar{B}$$ pairs. For this search, hadronic $$B_{tag}$$ reconstruction is employed, where one B is exclusively reconstructed via one of many possible hadronic modes. The remaining decay products in an event are then attributed to the signal B, on which the search for $B^+$ → $K^+ τ^+ τ^-$ is performed. Each τ is required to decay leptonically, into either an electron or a muon and the lepton neutrinos. Furthermore, a multi-variate analysis technique (neural network) is used to select for signal events and suppress dominant background modes. No significant signal is observed. The resulting branching fraction is measured to be $$\\beta(B^+$$ → $K^+ τ^+)$ = $$1.31^{0:66}_{-0:61}$$(stat.) $$^{+0:35}_{-0:25}$$(sys.) x 10$$^{-3}$$, which is consistent with zero at the 1.9σ level, with an upper limit of 2.25 x 10$$^{-3}$$, at the 90% confidence level.« less

Controllable all-fiber generation/conversion of circularly polarized orbital angular momentum beams using long period fiber gratings

NASA Astrophysics Data System (ADS)

Han, Ya; Liu, Yan-Ge; Wang, Zhi; Huang, Wei; Chen, Lei; Zhang, Hong-Wei; Yang, Kang

2018-01-01

Mode-division multiplexing (MDM) is a promising technology for increasing the data-carrying capacity of a single few-mode optical fiber. The flexible mode manipulation would be highly desired in a robust MDM network. Recently, orbital angular momentum (OAM) modes have received wide attention as a new spatial mode basis. In this paper, we firstly proposed a long period fiber grating (LPFG) system to realize mode conversions between the higher order LP core modes in four-mode fiber. Based on the proposed system, we, for the first time, demonstrate the controllable all-fiber generation and conversion of the higher order LP core modes to the first and second order circularly polarized OAM beams with all the combinations of spin and OAM. Therefore, the proposed LPFG system can be potentially used as a controllable higher order OAM beam switch and a physical layer of the translating protocol from the conventional LP modes communication to the OAM modes communication in the future mode carrier telecommunication system and light calculation protocols.

Parametric effects on pinch-off modes in liquid/liquid jet systems

NASA Astrophysics Data System (ADS)

Milosevic, Ilija N.

Many industries rely on liquid/liquid extraction systems, where jet pinch off occurs on a regular basis. Inherent short time and length scales make analytical and numerical simulation of the process very challenging. A main objective of this work was to document the details of various pinch-off modes at different length scales using Laser Induced Fluorescence and Particle Image Velocimetry. A water glycerine mixture was injected into ambient either silicone oil or 1-octanol. The resultant viscosity ratios, inner to outer fluid, were 1.6 and 2.8, respectively. Ohnesorge numbers were 0.013 for ambient silicone oil and 0.08 for ambient 1-octanol. Reynolds and Strouhal numbers ranged from 30 to 100 and 0.5 to 3.5, respectively. Decreasing the Strouhal number increased the number of drops formed per forcing. Increasing the Reynolds number suppressed satellite formation, and in some cases the number of drops decreased from two to one per cycle. Increasing the Ohnesorge number to 0.08 suppressed the pinch off yielding a longer jet with three-dimensional threads. At Ohnesorge number 0.013, increasing the forcing amplitude shortened the jet, and eventually led to a dripping mode. High-resolution measurements of pinch-off angles were compared to results from similarity theory. Two modes were investigated: drops breaking from the jet (jet/drop) and, one drop splitting into two (splitting drop). The jet/drop mode angle measurements agreed with similarity predictions. The splitting drop mode converged towards smaller angles. Scaling analysis showed that a Stokesian similarity regime applied for a neck radius of 6 microns or less. The smallest radius observed in experiments was 15 microns. Therefore, it is not known whether splitting drop mode might still converge to same behavior.

Fast ion stabilization of the ion temperature gradient driven modes in the Joint European Torus hybrid-scenario plasmas: a trigger mechanism for internal transport barrier formation

NASA Astrophysics Data System (ADS)

Romanelli, M.; Zocco, A.; Crisanti, F.; Contributors, JET-EFDA

2010-04-01

Understanding and modelling turbulent transport in thermonuclear fusion plasmas are crucial for designing and optimizing the operational scenarios of future fusion reactors. In this context, plasmas exhibiting state transitions, such as the formation of an internal transport barrier (ITB), are particularly interesting since they can shed light on transport physics and offer the opportunity to test different turbulence suppression models. In this paper, we focus on the modelling of ITB formation in the Joint European Torus (JET) [1] hybrid-scenario plasmas, where, due to the monotonic safety factor profile, magnetic shear stabilization cannot be invoked to explain the transition. The turbulence suppression mechanism investigated here relies on the increase in the plasma pressure gradient in the presence of a minority of energetic ions. Microstability analysis of the ion temperature gradient driven modes (ITG) in the presence of a fast-hydrogen minority shows that energetic ions accelerated by the ion cyclotron resonance heating (ICRH) system (hydrogen, nH,fast/nD,thermal up to 10%, TH,fast/TD,thermal up to 30) can increase the pressure gradient enough to stabilize the ITG modes driven by the gradient of the thermal ions (deuterium). Numerical analysis shows that, by increasing the temperature of the energetic ions, electrostatic ITG modes are gradually replaced by nearly electrostatic modes with tearing parity at progressively longer wavelengths. The growth rate of the microtearing modes is found to be lower than that of the ITG modes and comparable to the local E × B-velocity shearing rate. The above mechanism is proposed as a possible trigger for the formation of ITBs in this type of discharges.

All-optical logic gates and wavelength conversion via the injection locking of a Fabry-Perot semiconductor laser

NASA Astrophysics Data System (ADS)

Harvey, E.; Pochet, M.; Schmidt, J.; Locke, T.; Naderi, N.; Usechak, N. G.

2013-03-01

This work investigates the implementation of all-optical logic gates based on optical injection locking (OIL). All-optical inverting, NOR, and NAND gates are experimentally demonstrated using two distributed feedback (DFB) lasers, a multi-mode Fabry-Perot laser diode, and an optical band-pass filter. The DFB lasers are externally modulated to represent logic inputs into the cavity of the multi-mode Fabry-Perot slave laser. The input DFB (master) lasers' wavelengths are aligned with the longitudinal modes of the Fabry-Perot slave laser and their optical power is used to modulate the injection conditions in the Fabry-Perot slave laser. The optical band-pass filter is used to select a Fabry- Perot mode that is either suppressed or transmitted given the logic state of the injecting master laser signals. When the input signal(s) is (are) in the on state, injection locking, and thus the suppression of the non-injected Fabry-Perot modes, is induced, yielding a dynamic system that can be used to implement photonic logic functions. Additionally, all-optical photonic processing is achieved using the cavity-mode shift produced in the injected slave laser under external optical injection. The inverting logic case can also be used as a wavelength converter — a key component in advanced wavelength-division multiplexing networks. As a result of this experimental investigation, a more comprehensive understanding of the locking parameters involved in injecting multiple lasers into a multi-mode cavity and the logic transition time is achieved. The performance of optical logic computations and wavelength conversion has the potential for ultrafast operation, limited primarily by the photon decay rate in the slave laser.

Suppression of Rayleigh backscattering noise using cascaded-SOA and microwave photonic filter for 10 Gb/s loop-back WDM-PON.

PubMed

Feng, Hanlin; Ge, Jia; Xiao, Shilin; Fok, Mable P

2014-05-19

In this paper, we present a novel Rayleigh backscattering (RB) noise mitigation scheme based on central carrier suppression for 10 Gb/s loop-back wavelength division multiplexing passive optical network (WDM-PON). Microwave modulated multi-subcarrier optical signal is used as downstream seeding light, while cascaded semiconductor optical amplifier (SOA) are used in the optical network unit (ONU) for suppressing the central carrier of the multi-subcarrier upstream signal. With central carrier suppression, interference generated by carrier RB noise at low frequency region is eliminated successfully. Transmission performance over 45 km single mode fiber (SMF) is studied experimentally, and the optical-signal-to-Rayleigh-noise-ratio (OSRNR) can be reduced to 15 dB with central carrier suppression ratio (CCSR) of 21 dB. Receiver sensitivity is further improved by 6 dB with the use of microwave photonic filter (MPF) for suppressing residual upstream microwave signal and residual carrier RB at high frequency region.

Bending patterns of chlamydomonas flagella: III. A radial spoke head deficient mutant and a central pair deficient mutant.

PubMed

Brokaw, C J; Luck, D J

1985-01-01

Flash photomicrography at frequencies up to 300 Hz and computer-assisted image analysis have been used to obtain parameters describing the flagellar bending patterns of mutants of Chlamydomonas reinhardtii. All strains contained the uni1 mutation, to facilitate photography. The radial spoke head deficient mutant pf17, and the central pair deficient mutant, pf15, in combination with suppressor mutations that restore motility without restoring the ultrastructural or biochemical deficiencies, both generate forward mode bending patterns with increased shear amplitude and decreased asymmetry relative to the "wild-type" uni1 flagella described previously. In the reverse beating mode, the suppressed pf17 mutants generate reverse bending patterns with large shear amplitudes. Reverse beating of the suppressed pf15 mutants is rare. There is a reciprocal relationship between increased shear amplitude and decreased beat frequency, so that the velocity of sliding between flagellar microtubules is not increased by an increase in shear amplitude. The suppressor mutations alone cause decreased frequency and sliding velocity in both forward and reverse mode beating, with little change in shear amplitude or symmetry.

Suppressed Decays of Ds+ Mesons to Two Pseudoscalar Mesons

NASA Astrophysics Data System (ADS)

Adams, G. S.; Anderson, M.; Cummings, J. P.; Danko, I.; Hu, D.; Moziak, B.; Napolitano, J.; He, Q.; Insler, J.; Muramatsu, H.; Park, C. S.; Thorndike, E. H.; Yang, F.; Artuso, M.; Blusk, S.; Khalil, S.; Li, J.; Menaa, N.; Mountain, R.; Nisar, S.; Randrianarivony, K.; Sia, R.; Skwarnicki, T.; Stone, S.; Wang, J. C.; Bonvicini, G.; Cinabro, D.; Dubrovin, M.; Lincoln, A.; Asner, D. M.; Edwards, K. W.; Naik, P.; Briere, R. A.; Ferguson, T.; Tatishvili, G.; Vogel, H.; Watkins, M. E.; Rosner, J. L.; Adam, N. E.; Alexander, J. P.; Cassel, D. G.; Duboscq, J. E.; Ehrlich, R.; Fields, L.; Gibbons, L.; Gray, R.; Gray, S. W.; Hartill, D. L.; Heltsley, B. K.; Hertz, D.; Jones, C. D.; Kandaswamy, J.; Kreinick, D. L.; Kuznetsov, V. E.; Mahlke-Krüger, H.; Mohapatra, D.; Onyisi, P. U. E.; Patterson, J. R.; Peterson, D.; Riley, D.; Ryd, A.; Sadoff, A. J.; Shi, X.; Stroiney, S.; Sun, W. M.; Wilksen, T.; Athar, S. B.; Patel, R.; Yelton, J.; Rubin, P.; Eisenstein, B. I.; Karliner, I.; Lowrey, N.; Selen, M.; White, E. J.; Wiss, J.; Mitchell, R. E.; Shepherd, M. R.; Besson, D.; Pedlar, T. K.; Cronin-Hennessy, D.; Gao, K. Y.; Hietala, J.; Kubota, Y.; Klein, T.; Lang, B. W.; Poling, R.; Scott, A. W.; Zweber, P.; Dobbs, S.; Metreveli, Z.; Seth, K. K.; Tomaradze, A.; Ernst, J.; Ecklund, K. M.; Severini, H.; Love, W.; Savinov, V.; Lopez, A.; Mehrabyan, S.; Mendez, H.; Ramirez, J.; Ge, J. Y.; Miller, D. H.; Sanghi, B.; Shipsey, I. P. J.; Xin, B.

2007-11-01

Using data collected near the Ds*+Ds- peak production energy Ecm=4170MeV by the CLEO-c detector, we study the decays of Ds+ mesons to two pseudoscalar mesons. We report on searches for the singly Cabibbo-suppressed Ds+ decay modes K+η, K+η', π+KS0, K+π0, and the isospin-forbidden decay mode Ds+→π+π0. We normalize with respect to the Cabibbo-favored Ds+ modes π+η, π+η', and K+KS0, and obtain ratios of branching fractions: B(Ds+→K+η)/B(Ds+→π+η)=(8.9±1.5±0.4)%, B(Ds+→K+η')/B(Ds+→π+η')=(4.2±1.3±0.3)%, B(Ds+→π+KS0)/B(Ds+→K+KS0)=(8.2±0.9±0.2)%, B(Ds+→K+π0)/B(Ds+→K+KS0)=(5.5±1.3±0.7)%, and B(Ds+→π+π0)/B(Ds+→K+KS0)<4.1% at 90% C.L., where the uncertainties are statistical and systematic, respectively.

Switchable multi-wavelength erbium-doped fiber ring laser based on a tapered in-line Mach–Zehnder interferometer

NASA Astrophysics Data System (ADS)

Zhou, Yuxin; Wang, Xin; Tang, Zijuan; Lou, Shuqin

2018-05-01

In this paper, a switchable multi-wavelength erbium-doped fiber ring laser based on a tapered in-line Mach–Zehnder interferometer is proposed. The in-line Mach–Zehnder interferometer is fabricated by splicing a large-core fiber between two segments of single mode fibers, in which the first splicing point is tapered and the second splicing point is connected directly. By carefully rotating the polarization controller, switchable single-, dual-, triple- and quad-wavelength lasing outputs can be obtained with a side mode suppression ratio higher than 50 dB. The maximal peak power difference of multi-wavelength lasing is 3.67 dB, demonstrating a good power equalization performance. Furthermore, the proposed laser is proven to be very stable at room temperature. The wavelength shifts and peak power fluctuations are less than 0.02 nm and 1.3 dB over half an hour. In addition, stable quintuple-wavelength lasing with a side mode suppression ratio higher than 50 dB can also be realized when the filter length is changed.

Control system of neoclassical tearing modes in real time on HL-2A tokamak.

PubMed

Yan, Longwen; Ji, Xiaoquan; Song, Shaodong; Xia, Fan; Xu, Yuan; Ye, Jiruo; Jiang, Min; Chen, Wenjin; Sun, Tengfei; Liang, Shaoyong; Ling, Fei; Ma, Rui; Huang, Mei; Qu, Hongpeng; Song, Xianming; Yu, Deliang; Shi, Zhongbin; Liu, Yi; Yang, Qingwei; Xu, Min; Duan, Xuru; Liu, Yong

2017-11-01

The stability and performance of tokamak plasmas are routinely limited by various magneto-hydrodynamic instabilities, such as neoclassical tearing modes (NTMs). This paper presents a rather simple method to control the NTMs in real time (RT) on a tokamak, including the control principle of a feedback approach for RT suppression and stabilization for the NTMs. The control system combines Mirnov, electron cyclotron emission, and soft X-ray diagnostics used for determining the NTM positions. A methodology for fast detection of 2/1 or 3/2 NTM positions with 129 × 129 grid reconstruction is elucidated. The forty poloidal angles for steering the electron cyclotron resonance heating (ECRH)/electron cyclotron current drive launcher are used to establish the alignment of antenna mirrors with the center of the NTM and to ensure launcher emission intersecting with the rational surface of a magnetic island. Pilot experiments demonstrate the RT control capability to trace the conventional tearing modes (CTMs) in the HL-2A tokamak. The 2/1 CTMs have been suppressed or stabilized by the ECRH power deposition on site or with the steerable launcher.

Control system of neoclassical tearing modes in real time on HL-2A tokamak

NASA Astrophysics Data System (ADS)

Yan, Longwen; Ji, Xiaoquan; Song, Shaodong; Xia, Fan; Xu, Yuan; Ye, Jiruo; Jiang, Min; Chen, Wenjin; Sun, Tengfei; Liang, Shaoyong; Ling, Fei; Ma, Rui; Huang, Mei; Qu, Hongpeng; Song, Xianming; Yu, Deliang; Shi, Zhongbin; Liu, Yi; Yang, Qingwei; Xu, Min; Duan, Xuru; Liu, Yong

2017-11-01

The stability and performance of tokamak plasmas are routinely limited by various magneto-hydrodynamic instabilities, such as neoclassical tearing modes (NTMs). This paper presents a rather simple method to control the NTMs in real time (RT) on a tokamak, including the control principle of a feedback approach for RT suppression and stabilization for the NTMs. The control system combines Mirnov, electron cyclotron emission, and soft X-ray diagnostics used for determining the NTM positions. A methodology for fast detection of 2/1 or 3/2 NTM positions with 129 × 129 grid reconstruction is elucidated. The forty poloidal angles for steering the electron cyclotron resonance heating (ECRH)/electron cyclotron current drive launcher are used to establish the alignment of antenna mirrors with the center of the NTM and to ensure launcher emission intersecting with the rational surface of a magnetic island. Pilot experiments demonstrate the RT control capability to trace the conventional tearing modes (CTMs) in the HL-2A tokamak. The 2/1 CTMs have been suppressed or stabilized by the ECRH power deposition on site or with the steerable launcher.

First Light for Mimir, a Near-Infrared Wide-Field Imager, Spectrometer, and Polarimeter for the Perkins Telescope

NASA Astrophysics Data System (ADS)

Clemens, D. P.; Sarcia, D.; Tollestrup, E. V.; Grabau, A.; Bosh, A.; Buie, M.; Taylor, B.; Dunham, E.

2004-12-01

The Mimir instrument completed its 5-year development in our Boston University lab and was delivered this past July to Flagstaff, Arizona and the Perkins telescope for commissioning. Mimir is a "facility-class" multi-function near-infrared imager, spectrometer, and polarimeter developed under a joint program by Boston University and Lowell Observatory scientists, staff, and engineers. It fully covers the wavelength range 1-5 microns onto its 1024x1024 Aladdin III InSb array detector. In its wide-field imaging mode, a 10x10 arcmin field is sampled at 0.6 arcsec per pixel. In its narrow-field mode, the field is 3x3 arcmin, sampled at 0.2 arcsec per pixel. A full complement of JHKsL'M' broad-band filters are present in its four filter wheels. Spectroscopy is accomplished using a matched slit-plate and selector system, three grisms, and special spectroscopy filters (for order suppression). Polarimetry is accomplished using rotating half-wave plates and a fixed wire grid. All of these modes were certified in the lab; all have been certified at the Perkins telescope during the August/September commissioning run. Mode switches are accomplished in a matter of only seconds, making Mimir exceedingly versatile. The poster highlights the designs and components of Mimir as well as examples of images, spectra, and polarimetry from the commissioning telescope runs this past fall. Internal, shared-risk observations with Mimir begin this quarter. Mimir design and development has been funded by NASA, NSF, and the W.M. Keck Foundation.

Effect of Transport Coefficients on Excitation of Flare-induced Standing Slow-mode Waves in Coronal Loops

NASA Astrophysics Data System (ADS)

Wang, Tongjiang; Ofman, Leon; Sun, Xudong; Solanki, Sami K.; Davila, Joseph M.

2018-06-01

Standing slow-mode waves have been recently observed in flaring loops by the Atmospheric Imaging Assembly of the Solar Dynamics Observatory. By means of the coronal seismology technique, transport coefficients in hot (∼10 MK) plasma were determined by Wang et al., revealing that thermal conductivity is nearly suppressed and compressive viscosity is enhanced by more than an order of magnitude. In this study, we use 1D nonlinear MHD simulations to validate the predicted results from the linear theory and investigate the standing slow-mode wave excitation mechanism. We first explore the wave trigger based on the magnetic field extrapolation and flare emission features. Using a flow pulse driven at one footpoint, we simulate the wave excitation in two types of loop models: Model 1 with the classical transport coefficients and Model 2 with the seismology-determined transport coefficients. We find that Model 2 can form the standing wave pattern (within about one period) from initial propagating disturbances much faster than Model 1, in better agreement with the observations. Simulations of the harmonic waves and the Fourier decomposition analysis show that the scaling law between damping time (τ) and wave period (P) follows τ ∝ P 2 in Model 2, while τ ∝ P in Model 1. This indicates that the largely enhanced viscosity efficiently increases the dissipation of higher harmonic components, favoring the quick formation of the fundamental standing mode. Our study suggests that observational constraints on the transport coefficients are important in understanding both the wave excitation and damping mechanisms.

Papaloizou-Pringle instability suppression by the magnetorotational instability in relativistic accretion discs

NASA Astrophysics Data System (ADS)

Bugli, M.; Guilet, J.; Müller, E.; Del Zanna, L.; Bucciantini, N.; Montero, P. J.

2018-03-01

Geometrically thick tori with constant specific angular momentum have been widely used in the last decades to construct numerical models of accretion flows on to black holes. Such discs are prone to a global non-axisymmetric hydrodynamic instability, known as Papaloizou-Pringle instability (PPI), which can redistribute angular momentum and also lead to an emission of gravitational waves. It is, however, not clear yet how the development of the PPI is affected by the presence of a magnetic field and by the concurrent development of the magnetorotational instability (MRI). We present a numerical analysis using three-dimensional GRMHD simulations of the interplay between the PPI and the MRI considering, for the first time, an analytical magnetized equilibrium solution as initial condition. In the purely hydrodynamic case, the PPI selects as expected the large-scale m = 1 azimuthal mode as the fastest growing and non-linearly dominant mode. However, when the torus is threaded by a weak toroidal magnetic field, the development of the MRI leads to the suppression of large-scale modes and redistributes power across smaller scales. If the system starts with a significantly excited m = 1 mode, the PPI can be dominant in a transient phase, before being ultimately quenched by the MRI. Such dynamics may well be important in compact star mergers and tidal disruption events.

Effects of electron cyclotron current drive on the evolution of double tearing mode

NASA Astrophysics Data System (ADS)

Sun, Guanglan; Dong, Chunying; Duan, Longfang

2015-09-01

The effects of electron cyclotron current drive (ECCD) on the double tearing mode (DTM) in slab geometry are investigated by using two-dimensional compressible magnetohydrodynamics equations. It is found that, mainly, the double tearing mode is suppressed by the emergence of the secondary island, due to the deposition of driven current on the X-point of magnetic island at one rational surface, which forms a new non-complete symmetric magnetic topology structure (defined as a non-complete symmetric structure, NSS). The effects of driven current with different parameters (magnitude, initial time of deposition, duration time, and location of deposition) on the evolution of DTM are analyzed elaborately. The optimal magnitude or optimal deposition duration of driven current is the one which makes the duration of NSS the longest, which depends on the mutual effect between ECCD and the background plasma. Moreover, driven current introduced at the early Sweet-Parker phase has the best suppression effect; and the optimal moment also exists, depending on the duration of the NSS. Finally, the effects varied by the driven current disposition location are studied. It is verified that the favorable location of driven current is the X-point which is completely different from the result of single tearing mode.

Stabilizing effect of resistivity towards ELM-free H-mode discharge in lithium-conditioned NSTX

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

Banerjee, Debabrata; Zhu, Ping; Maingi, Rajesh

Linear stability analysis of the national spherical torus experiment (NSTX) Li-conditioned ELM-free H-mode equilibria is carried out in the context of the extended magneto-hydrodynamic (MHD) model in NIMROD. Our purpose is to investigate the physical cause behind edge localized mode (ELM) suppression in experiment after the Li-coating of the divertor and the first wall of the NSTX tokamak. Besides ideal MHD modeling, including finite-Larmor radius effect and two-fluid Hall and electron diamagnetic drift contributions, a non-ideal resistivity model is employed, taking into account the increase of Z eff after Li-conditioning in ELM-free H-mode. And unlike an earlier conclusion from anmore » eigenvalue code analysis of these equilibria, NIMROD results find that after reduced recycling from divertor plates, profile modification is necessary but insufficient to explain the mechanism behind complete ELMs suppression in ideal two-fluid MHD. After considering the higher plasma resistivity due to higher Z eff, the complete stabilization could be explained. Furthermore, a thorough analysis of both pre-lithium ELMy and with-lithium ELM-free cases using ideal and non-ideal MHD models is presented, after accurately including a vacuum-like cold halo region in NIMROD to investigate ELMs.« less

Stabilizing effect of resistivity towards ELM-free H-mode discharge in lithium-conditioned NSTX

DOE PAGES

Banerjee, Debabrata; Zhu, Ping; Maingi, Rajesh

2017-05-12

Linear stability analysis of the national spherical torus experiment (NSTX) Li-conditioned ELM-free H-mode equilibria is carried out in the context of the extended magneto-hydrodynamic (MHD) model in NIMROD. Our purpose is to investigate the physical cause behind edge localized mode (ELM) suppression in experiment after the Li-coating of the divertor and the first wall of the NSTX tokamak. Besides ideal MHD modeling, including finite-Larmor radius effect and two-fluid Hall and electron diamagnetic drift contributions, a non-ideal resistivity model is employed, taking into account the increase of Z eff after Li-conditioning in ELM-free H-mode. And unlike an earlier conclusion from anmore » eigenvalue code analysis of these equilibria, NIMROD results find that after reduced recycling from divertor plates, profile modification is necessary but insufficient to explain the mechanism behind complete ELMs suppression in ideal two-fluid MHD. After considering the higher plasma resistivity due to higher Z eff, the complete stabilization could be explained. Furthermore, a thorough analysis of both pre-lithium ELMy and with-lithium ELM-free cases using ideal and non-ideal MHD models is presented, after accurately including a vacuum-like cold halo region in NIMROD to investigate ELMs.« less

Ion wake field effects on the dust-ion-acoustic surface mode in a semi-bounded Lorentzian dusty plasma

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

Lee, Myoung-Jae; Jung, Young-Dae, E-mail: ydjung@hanyang.ac.kr; Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, 110 8th Street, Troy, New York 12180-3590

The dispersion relation for the dust ion-acoustic surface waves propagating at the interface of semi-bounded Lorentzian dusty plasma with supersonic ion flow has been kinetically derived to investigate the nonthermal property and the ion wake field effect. We found that the supersonic ion flow creates the upper and the lower modes. The increase in the nonthermal particles decreases the wave frequency for the upper mode whereas it increases the frequency for the lower mode. The increase in the supersonic ion flow velocity is found to enhance the wave frequency for both modes. We also found that the increase in nonthermalmore » plasmas is found to enhance the group velocity of the upper mode. However, the nonthermal particles suppress the lower mode group velocity. The nonthermal effects on the group velocity will be reduced in the limit of small or large wavelength limit.« less

Acoustic interference suppression of quartz crystal microbalance sensor arrays utilizing phononic crystals

NASA Astrophysics Data System (ADS)

Chen, Yung-Yu; Huang, Li-Chung; Wang, Wei-Shan; Lin, Yu-Ching; Wu, Tsung-Tsong; Sun, Jia-Hong; Esashi, Masayoshi

2013-04-01

Acoustic interference suppression of quartz crystal microbalance (QCM) sensor arrays utilizing phononic crystals is investigated in this paper. A square-lattice phononic crystal structure is designed to have a complete band gap covering the QCM's resonance frequency. The monolithic sensor array consisting of two QCMs separated by phononic crystals is fabricated by micromachining processes. As a result, 12 rows of phononic crystals with band gap boost insertion loss between the two QCMs by 20 dB and also reduce spurious modes. Accordingly, the phononic crystal is verified to be capable of suppressing the acoustic interference between adjacent QCMs in a sensor array.

Superhorizon fluctuations and acoustic oscillations in relativistic heavy-ion collisions

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

Mishra, Ananta P.; Mohapatra, Ranjita K.; Saumia, P. S.

2008-06-15

We focus on the initial-state spatial anisotropies, originating at the thermalization stage, for central collisions in relativistic heavy-ion collisions. We propose that a plot of the root-mean-square values of the flow coefficients {radical}(v{sub n}{sup 2}){identical_to}v{sub n}{sup rms}, calculated in a laboratory fixed coordinate system, for a large range of n from 1 to about 30, can give nontrivial information about the initial stages of the system and its evolution. We also argue that for all wavelengths {lambda} of the anisotropy (at the surface of the plasma region) much larger than the acoustic horizon size H{sub s}{sup fr} at the freeze-outmore » stage, the resulting values of v{sub n}{sup rms} should be suppressed by a factor of order 2H{sub s}{sup fr}/{lambda}. For noncentral collisions, these arguments naturally imply a certain amount of suppression of the elliptic flow. Further, by assuming that initial flow velocities are negligible at thermalization stage, we discuss the possibility that the resulting flow could show imprints of coherent oscillations in the plot of v{sub n}{sup rms} for subhorizon modes. For gold-gold collision at 200 GeV/nucleon center-of-mass energy, these features are expected to occur for n{>=}5, with n<4 modes showing suppression due to being superhorizon. This has strong similarities with the physics of the anisotropies of the cosmic microwave background radiation (CMBR) resulting from inflationary density fluctuations in the universe (despite important differences such as the absence of gravity effects for the heavy-ion case). It seems possible that the statistical fluctuations due to finite multiplicity may not be able to mask such features in the flow data or at least a nontrivial overall shape of the plot of v{sub n}{sup rms} may be inferred. In that case, the successes of analysis of CMBR anisotropy power spectrum to get cosmological parameters can be applied for relativistic heavy-ion collisions to learn about various relevant parameters at the early stages of the evolving system.« less

Inhibition of the de novo synthesis of PCDD/Fs on model fly ash by sludge drying gases.

PubMed

Chen, Tong; Zhan, Ming-Xiu; Lin, Xiao-Qing; Li, Xiao-Dong; Lu, Sheng-Yong; Yan, Jian-Hua; Buekens, Alfons; Cen, Ke-Fa

2014-11-01

Sludge drying gases (SDG), evolving from drying and mild thermal decomposition (<300°C) of raw sewage sludge contain NH3 and SO2 as well as other N- and S-compounds. All of these are potential PCDD/Fs suppressants. It is indeed observed that these SDG suppress 2,3,7,8-substitued PCDD/Fs formation on Model Fly Ash (MFA) with an efficiency up to 97.6% in wt. units and 96% in I-TEQ, respectively. This suppression is strong for (the bulk of) PCDD/Fs, adsorbed on the model fly ash; conversely, sludge drying gases enhance PCDD/Fs desorption from MFA. Moreover, TCDD/Fs are suppressed least, possibly following stepwise dechlorination of higher chlorinated PCDD/Fs. Characteristics, such as the type, origins and amount of sludge, its moisture-, nitrogen- and sulfur content and the nature of the thermal treatment applied are all expected to influence upon the suppression capabilities. In this study three types of dry sludge are tested and applied as suppressant in four different amounts or modes. The quality of the sludge drying gases is continuously monitored: the Gasmet results reveal that NH3 and SO2 are the most important components of SDG. The MFA reaction residue is scrutinized by Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS) analysis. A large number of particles attaching to the surface of model fly ash are observed by SEM. Moreover, EDS analysis reveals that part of the chlorine in MFA is carried away with the SDG and replaced by sulfur, so that eliminating chlorine may be part of the inhibition mechanism. However, further research is still needed to establish the optimum operating modes and to confirm the role of both inorganic and organic nitrogen and sulfur compounds in the suppression of PCDD/Fs formation on model fly ash. Copyright © 2014 Elsevier Ltd. All rights reserved.

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2010-02-09

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Filtering higher-order laser modes using leaky plasma channels

NASA Astrophysics Data System (ADS)

Djordjević, B. Z.; Benedetti, C.; Schroeder, C. B.; Esarey, E.; Leemans, W. P.

2018-01-01

Plasma structures based on leaky channels are proposed to filter higher-order laser mode content. The evolution and propagation of non-Gaussian laser pulses in leaky channels are studied, and it is shown that, for appropriate laser-plasma parameters, the higher-order laser mode content of the pulse may be removed while the fundamental mode remains well-guided. The behavior of multi-mode laser pulses is described analytically and numerically using envelope equations, including the derivation of the leakage coefficients, and compared to particle-in-cell simulations. Laser pulse propagation, with reduced higher-order mode content, improves guiding in parabolic plasma channels, enabling extended interaction lengths for laser-plasma accelerator applications.

Superconductivity and charge density wave in ZrTe 3–xSe x

DOE PAGES

Zhu, Xiangde; Ning, Wei; Li, Lijun; ...

2016-06-02

Charge density wave (CDW), the periodic modulation of the electronic charge density, will open a gap on the Fermi surface that commonly leads to decreased or vanishing conductivity. On the other hand superconductivity, a commonly believed competing order, features a Fermi surface gap that results in infinite conductivity. Here we report that superconductivity emerges upon Se doping in CDW conductor ZrTe 3 when the long range CDW order is gradually suppressed. Superconducting critical temperature T c(x) in ZrTe 3–xSe x (0 ≤ x ≤ 0.1) increases up to 4 K plateau for 0.04 ≤ x ≤ 0.07. Further increase inmore » Se content results in diminishing T c and filametary superconductivity. The CDW modes from Raman spectra are observed in x = 0.04 and 0.1 crystals, where signature of ZrTe 3 CDW order in resistivity vanishes. As a result, the electronic-scattering for high T c crystals is dominated by local CDW fluctuations at high temperatures, the resistivity is linear up to highest measured T = 300 K and contributes to substantial in-plane anisotropy.« less

Higher-order cladding mode excitation of femtosecond-laser-inscribed tilted FBGs.

PubMed

Ioannou, Andreas; Theodosiou, Antreas; Kalli, Kyriacos; Caucheteur, Christophe

2018-05-01

We study the modal behavior of plane-by-plane femtosecond laser fabricated tilted fiber Bragg gratings (FBGs). The focus is on the differential strain and temperature sensitivities between the cladding mode resonances of an nth grating order and those of the (n-i)th orders (with i=1-n), which are collocated in the same wavelength range. Whereas the Bragg mode exhibits an axial strain sensitivity of 1.2 pm/μϵ, we experimentally show that the strain sensitivity of ultrahigh-order cladding modes is negative and at -1.99  pm/μϵ in the same spectral window. Using a finite element mode solver, the modal refractive index value is computed to be well below 1, thus confirming that these modes, in reality, are leaky modes.

Tunable Er-doped fiber ring laser with single longitudinal mode operation based on Rayleigh backscattering in single mode fiber.

PubMed

Yin, Guolu; Saxena, Bhavaye; Bao, Xiaoyi

2011-12-19

A tunable and single longitudinal mode Er-doped fiber ring laser (SLM-EDFRL) is proposed and demonstrated based on Rayleigh backscattering (RBS) in single mode fiber-28e (SMF-28e). Theory and experimental study on formation of SLM from normal multi-mode ring laser is demonstrated. The RBS feedback in 660 m SMF-28e is the key to ensure SLM laser oscillation. This tunable SLM laser can be tuned over 1549.7-1550.18 nm with a linewidth of 2.5-3.0 kHz and a side mode suppression ratio (SMSR) of ~72 dB for electrical signal power. The tuning range is determined by the bandpass filter and gain medium used in the experiment. The laser is able to operate at S+C+L band.

m=1 diocotron mode damping in the Electron Diffusion Gauge (EDG) experiment

NASA Astrophysics Data System (ADS)

Paul, Stephen F.; Morrison, Kyle A.; Davidson, Ronald C.; Jenkins, Thomas G.

2002-01-01

The evolution of the amplitude of the m=1 diocotron mode is used to measure the background neutral pressure in the Electron Diffusion Gauge (EDG), a Malmberg-Penning trap. Below 5×10-8 Torr, the dependence on pressure scales as P1/4, and is sensitive to pressure changes as small as ΔP=5×10-11 Torr. Previous studies on the EDG showed that the diocotron mode is more strongly damped at higher neutral pressures. Both the diocotron mode damping rate and the plasma expansion rate depend similarly on experimental parameters, i.e., conditions which favor expansion also favor suppression of the diocotron mode. The sensitivity of the mode evolution is examined as a function of the resistive growth driving conditions, which are controlled by the amount of wall resistance connected to the trap.

In-Flight Suppression of an Unstable F/A-18 Structural Mode Using the Space Launch System Adaptive Augmenting Control System

NASA Technical Reports Server (NTRS)

VanZwieten, Tannen S.; Gilligan, Eric T.; Wall, John H.; Miller, Christopher J.; Hanson, Curtis E.; Orr, Jeb S.

2015-01-01

NASA's Space Launch System (SLS) Flight Control System (FCS) includes an Adaptive Augmenting Control (AAC) component which employs a multiplicative gain update law to enhance the performance and robustness of the baseline control system for extreme off-nominal scenarios. The SLS FCS algorithm including AAC has been flight tested utilizing a specially outfitted F/A-18 fighter jet in which the pitch axis control of the aircraft was performed by a Non-linear Dynamic Inversion (NDI) controller, SLS reference models, and the SLS flight software prototype. This paper describes test cases from the research flight campaign in which the fundamental F/A-18 airframe structural mode was identified using post-flight frequency-domain reconstruction, amplified to result in closed loop instability, and suppressed in-flight by the SLS adaptive control system.

Suppression of extraneous thermal noise in cavity optomechanics.

PubMed

Zhao, Yi; Wilson, Dalziel J; Ni, K-K; Kimble, H J

2012-02-13

Extraneous thermal motion can limit displacement sensitivity and radiation pressure effects, such as optical cooling, in a cavity-optomechanical system. Here we present an active noise suppression scheme and its experimental implementation. The main challenge is to selectively sense and suppress extraneous thermal noise without affecting motion of the oscillator. Our solution is to monitor two modes of the optical cavity, each with different sensitivity to the oscillator's motion but similar sensitivity to the extraneous thermal motion. This information is used to imprint "anti-noise" onto the frequency of the incident laser field. In our system, based on a nano-mechanical membrane coupled to a Fabry-Pérot cavity, simulation and experiment demonstrate that extraneous thermal noise can be selectively suppressed and that the associated limit on optical cooling can be reduced.

High-order orbital angular momentum mode generator based on twisted photonic crystal fiber.

PubMed

Fu, Cailing; Liu, Shen; Wang, Ying; Bai, Zhiyong; He, Jun; Liao, Changrui; Zhang, Yan; Zhang, Feng; Yu, Bin; Gao, Shecheng; Li, Zhaohui; Wang, Yiping

2018-04-15

High-order orbital angular momentum (OAM) modes, namely, OAM +5 and OAM +6 , were generated and demonstrated experimentally by twisting a solid-core hexagonal photonic crystal fiber (PCF) during hydrogen-oxygen flame heating. Leaky orbital resonances in the cladding depend strongly on the twist rate and length of the helical PCF. Moreover, the generated high-order OAM mode could be a polarized mode. The secret of the successful observation of high-order modes is that leaky orbital resonances in the twisted PCF cladding have a high coupling efficiency of more than -20  dB.

Lattice and magnetic dynamics in perovskite Y1 -xLaxTiO3

NASA Astrophysics Data System (ADS)

Li, Bing; Louca, Despina; Niedziela, Jennifer; Li, Zongyao; Zhang, Libin; Zhou, Jianshi; Goodenough, John B.

2016-12-01

Inelastic neutron scattering combined with the dynamic pair density function (DPDF) analysis were used to investigate the magnetic and lattice dynamics in the orbitally active Y1 -xLaxTiO3 as it crosses the antiferromagnetic (AFM) to ferromagnetic (FM) phase boundary. Upon doping, the FM state present in YTiO3 is suppressed on approaching a critical concentration of xc˜0.3 in which TC≃0 , and is replaced by the AFM phase of LaTiO3. Below xc, magnetic scattering from spin waves is dominant at low energies. At xc with a TC≃0 , magnetic scattering is also observed and is most likely due to AFM fluctuations. At the same time, local atomic fluctuations extending to 50 meV are observed above and below the magnetic transitions from 0 ≤x ≤1 that show distinct characteristics with x . From Y to La, a clear difference is observed in the phonon density of states as a function of doping as well. At x =0.15 and 0.3, low-energy modes involving predominantly the rare-earth ion become suppressed with increasing temperature, while in x =1 , strong suppression of phonon modes across a wide range in energy is observed above TN. It is likely that in the Y heavy samples, phonon modes below 20 meV have a stronger influence on the orbital excitations, while in LaTiO3, a strong phonon dependence is observed upon cooling up to TN.

Normal modes in an overmoded circular waveguide coated with lossy material

NASA Technical Reports Server (NTRS)

Lee, C. S.; Lee, S. W.; Chuang, S. L.

1985-01-01

The normal modes in an overmoded waveguide coated with a lossy material are analyzed, particularly for their attenuation properties as a function of coating material, layer thickness, and frequency. When the coating material is not too lossy, the low-order modes are highly attenuated even with a thin layer of coating. This coated guide serves as a mode suppressor of the low-order modes, which can be particularly useful for reducing the radar cross section (RCS) of a cavity structure such as a jet inlet. When the coating material is very lossy, low-order modes fall into two distinct groups: highly and lowly attenuated modes. However, as a/lambda (a = radius of the cylinder; lambda = the free-space wavelength) increases, the separation between these two groups becomes less distinctive. The attenuation constants of most of the low-order modes become small, and decrease as a function of lambda sup 2/a sup 3.

Ultra-low crosstalk, CMOS compatible waveguide crossings for densely integrated photonic interconnection networks.

PubMed

Jones, Adam M; DeRose, Christopher T; Lentine, Anthony L; Trotter, Douglas C; Starbuck, Andrew L; Norwood, Robert A

2013-05-20

We explore the design space for optimizing CMOS compatible waveguide crossings on a silicon photonics platform. This paper presents simulated and experimental excess loss and crosstalk suppression data for vertically integrated silicon nitride over silicon-on-insulator waveguide crossings. Experimental results show crosstalk suppression exceeding -49/-44 dB with simulation results as low as -65/-60 dB for the TE/TM mode in a waveguide crossing with a 410 nm vertical gap.

System and Method for Suppression of Unwanted Noise in Ground Test Facilities

NASA Technical Reports Server (NTRS)

Zaman, Khairul B. M. Q. (Inventor); Clem, Michelle M. (Inventor); Fagan, Amy F. (Inventor)

2015-01-01

Systems and methods for the suppression of unwanted noise from a jet discharging into a duct are disclosed herein. The unwanted noise may be in the form of excited duct modes or howl due to super resonance. A damper member is used to reduce acoustic velocity perturbations at the velocity anti-node, associated with the half-wave resonance of the duct, weakening the resonance condition and reducing the amplitudes of the spectral peaks.

Chaos Suppression in Fractional order Permanent Magnet Synchronous Generator in Wind Turbine Systems

NASA Astrophysics Data System (ADS)

Rajagopal, Karthikeyan; Karthikeyan, Anitha; Duraisamy, Prakash

2017-06-01

In this paper we investigate the control of three-dimensional non-autonomous fractional-order uncertain model of a permanent magnet synchronous generator (PMSG) via a adaptive control technique. We derive a dimensionless fractional order model of the PMSM from the integer order presented in the literatures. Various dynamic properties of the fractional order model like eigen values, Lyapunov exponents, bifurcation and bicoherence are investigated. The system chaotic behavior for various orders of fractional calculus are presented. An adaptive controller is derived to suppress the chaotic oscillations of the fractional order model. As the direct Lyapunov stability analysis of the robust controller is difficult for a fractional order first derivative, we have derived a new lemma to analyze the stability of the system. Numerical simulations of the proposed chaos suppression methodology are given to prove the analytical results derived through which we show that for the derived adaptive controller and the parameter update law, the origin of the system for any bounded initial conditions is asymptotically stable.

240 GHz pedestal-free colliding-pulse mode-locked laser with a wide operation range

NASA Astrophysics Data System (ADS)

Hou, L.; Haji, M.; Marsh, J. H.

2014-11-01

A 240 GHz, sixth-harmonic monolithic ~1.55 μm colliding-pulse mode-locked laser is reported using a three-quantum-well active layer design and a passive far-field reduction layer. The device emits 0.88 ps pulses with a peak power of 65 mW and intermediate longitudinal modes suppressed by >30 dB. The device demonstrates a wide operation range compared to the conventional five-quantum-well design as well as having a low divergence angle (12.7° × 26.3°), granting a twofold improvement in butt-coupling efficiency into a flat cleaved single-mode fibre.

Stabilized and tunable single-longitudinal-mode erbium fiber laser employing ytterbium-doped fiber based interference filter

NASA Astrophysics Data System (ADS)

Yeh, Chien-Hung; Tsai, Ning; Zhuang, Yuan-Hong; Chow, Chi-Wai; Chen, Jing-Heng

2017-02-01

In this demonstration, to achieve stabilized and wavelength-selectable single-longitudinal-mode (SLM) erbium-doped fiber (EDF) laser, a short length of ytterbium-doped fiber (YDF) is utilized to serve as a spatial multi-mode interference (MMI) inside a fiber cavity for suppressing multi-longitudinal-mode (MLM) significantly. In the measurement, the output powers and optical signal to noise ratios (OSNRs) of proposed EDF ring laser are measured between -9.85 and -5.71 dBm; and 38.03 and 47.95 dB, respectively, in the tuning range of 1530.0-1560.0 nm. In addition, the output SLM and stability performance are also analyzed and discussed experimentally.

Ultra-low noise dual-frequency VECSEL at telecom wavelength using fully correlated pumping.

PubMed

Liu, Hui; Gredat, Gregory; De, Syamsundar; Fsaifes, Ihsan; Ly, Aliou; Vatré, Rémy; Baili, Ghaya; Bouchoule, Sophie; Goldfarb, Fabienne; Bretenaker, Fabien

2018-04-15

An ultra-low intensity and beatnote phase noise dual-frequency vertical-external-cavity surface-emitting laser is built at telecom wavelength. The pump laser is realized by polarization combining two single-mode fibered laser diodes in a single-mode fiber, leading to a 100% in-phase correlation of the pump noises for the two modes. The relative intensity noise is lower than -140  dB/Hz, and the beatnote phase noise is suppressed by 30 dB, getting close to the spontaneous emission limit. The role of the imperfect cancellation of the thermal effect resulting from unbalanced pumping of the two modes in the residual phase noise is evidenced.

When is an INP not an INP?

NASA Astrophysics Data System (ADS)

Simpson, Emma; Connolly, Paul; McFiggans, Gordon

2016-04-01

Processes such as precipitation and radiation depend on the concentration and size of different hydrometeors within clouds therefore it is important to accurately predict them in weather and climate models. A large fraction of clouds present in our atmosphere are mixed phase; contain both liquid and ice particles. The number of drops and ice crystals present in mixed phase clouds strongly depends on the size distribution of aerosols. Cloud condensation nuclei (CCN), a subset of atmospheric aerosol particles, are required for liquid drops to form in the atmosphere. These particles are ubiquitous in the atmosphere. To nucleate ice particles in mixed phase clouds ice nucleating particles (INP) are required. These particles are rarer than CCN. Here we investigate the case where CCN and INPs are in direct competition with each other for water vapour within a cloud. Focusing on the immersion and condensation modes of freezing (where an INP must be immersed within a liquid drop before it can freeze) we show that the presence of CCN can suppress the formation of ice. CCN are more hydrophilic than IN and as such are better able to compete for water vapour than, typically insoluble, INPs. Therefore water is more likely to condense onto a CCN than INP, leaving the INP without enough condensed water on it to be able to freeze in the immersion or condensation mode. The magnitude of this suppression effect strongly depends on a currently unconstrained quantity. Here we refer to this quantity as the critical mass of condensed water required for freezing, Mwc. Mwc is the threshold amount of water that must be condensed onto a INP before it can freeze in the immersion or condensation mode. Using the detailed cloud parcel model, Aerosol-Cloud-Precipiation-Interaction Model (ACPIM), developed at the University of Manchester we show that if only a small amount of water is required for freezing there is little suppression effect and if a large amount of water is required there is a large suppression effect. In this poster possible ways to constrain Mwc are discussed as well as conditions where the suppression effect is likely to be greatest. Key Words: Clouds, aerosol, CCN, IN, modelling

Magnetic control of magnetohydrodynamic instabilities in tokamaks

DOE PAGES

Strait, Edward J.

2014-11-24

Externally applied, non-axisymmetric magnetic fields form the basis of several relatively simple and direct methods to control magnetohydrodynamic (MHD) instabilities in a tokamak, and most present and planned tokamaks now include a set of non-axisymmetric control coils for application of fields with low toroidal mode numbers. Non-axisymmetric applied fields are routinely used to compensate small asymmetries ( δB/B ~ 10 -3 to 10 -4) of the nominally axisymmetric field, which otherwise can lead to instabilities through braking of plasma rotation and through direct stimulus of tearing modes or kink modes. This compensation may be feedback-controlled, based on the magnetic responsemore » of the plasma to the external fields. Non-axisymmetric fields are used for direct magnetic stabilization of the resistive wall mode — a kink instability with a growth rate slow enough that feedback control is practical. Saturated magnetic islands are also manipulated directly with non-axisymmetric fields, in order to unlock them from the wall and spin them to aid stabilization, or position them for suppression by localized current drive. Several recent scientific advances form the foundation of these developments in the control of instabilities. Most fundamental is the understanding that stable kink modes play a crucial role in the coupling of non-axisymmetric fields to the plasma, determining which field configurations couple most strongly, how the coupling depends on plasma conditions, and whether external asymmetries are amplified by the plasma. A major advance for the physics of high-beta plasmas ( β = plasma pressure/magnetic field pressure) has been the understanding that drift-kinetic resonances can stabilize the resistive wall mode at pressures well above the ideal-MHD stability limit, but also that such discharges can be very sensitive to external asymmetries. The common physics of stable kink modes has brought significant unification to the topics of static error fields at low beta and resistive wall modes at high beta. Furthermore, these and other scientific advances, and their application to control of MHD instabilities, will be reviewed with emphasis on the most recent results and their applicability to ITER.« less

Suppression in high-order above-threshold ionization: destructive interference from quantum orbits

NASA Astrophysics Data System (ADS)

Lai, Xuan Yang; Quan, Wei; Yu, Shao Gang; Huang, Yi Yi; Liu, Xiao Jun

2018-05-01

We experimentally study the above-threshold ionization (ATI) spectra of noble gas argon in an intense laser field and focus on a novel suppression structure in the high-order ATI (HATI) spectra. It is found that, when a well-documented resonancelike enhancement feature appears in the HATI spectra, a significant suppression structure is followed in a higher energy region of the spectra. The observation is well reproduced by a numerical solution of the time-dependent Schrödinger equation. In terms of quantum-orbit theory, the observed suppression structure can be ascribed to the destructive interference from longer quantum orbits. Furthermore, an intrinsic relation between the ionization suppression and the ionization enhancement in the HATI spectra is well established.

Culture, emotion regulation, and adjustment.

PubMed

Matsumoto, David; Yoo, Seung Hee; Nakagawa, Sanae

2008-06-01

This article reports differences across 23 countries on 2 processes of emotion regulation--reappraisal and suppression. Cultural dimensions were correlated with country means on both and the relationship between them. Cultures that emphasized the maintenance of social order--that is, those that were long-term oriented and valued embeddedness and hierarchy--tended to have higher scores on suppression, and reappraisal and suppression tended to be positively correlated. In contrast, cultures that minimized the maintenance of social order and valued individual Affective Autonomy and Egalitarianism tended to have lower scores on Suppression, and Reappraisal and Suppression tended to be negatively correlated. Moreover, country-level emotion regulation was significantly correlated with country-level indices of both positive and negative adjustment. (PsycINFO Database Record (c) 2008 APA, all rights reserved).

Analysis on the mechanism of pulse-shortening in an X-band triaxial klystron amplifier due to the asymmetric mode competition

NASA Astrophysics Data System (ADS)

Qi, Zumin; Zhang, Jun; Xie, Yongjie; Zhang, Yi; Wang, Zehua; Zhou, Xiaofeng; Zhu, Jianhui; Zi, Yanyong; Zhong, Huihuang

2016-12-01

Asymmetric mode competitions are observed in the design of an X-band triaxial klystron amplifier with an asymmetric input cavity, and the generation mechanism of the asymmetric mode competition is analyzed in the paper. The results indicate that the asymmetric modes are excited in the buncher cavity. The asymmetric mode (coaxial TM612 mode) in the buncher cavity with the highest shunt impedance can start up first among the asymmetric modes with negative beam loading conductance. The coupling of the corresponding coaxial TE mode between the buncher and input cavity exacerbates the start oscillation of the asymmetric mode competition. The rationality of the analysis is demonstrated by cutting off the propagation of the corresponding coaxial TE modes between the buncher cavity and the input cavity, and the asymmetric mode competitions are thoroughly suppressed by specially designed reflectors and lossy material. In simulation, a microwave with a power of 1.28 GW and a frequency of 9.375 GHz is generated, and the extraction efficiency and the gain are 34.5% and 41.5 dB, respectively.

Modal sensing and control of paraboloidal shell structronic system

NASA Astrophysics Data System (ADS)

Yue, Honghao; Lu, Yifan; Deng, Zongquan; Tzou, Hornsen

2018-02-01

Paraboloidal shells of revolution are commonly used as important components in the field of advanced aerospace structures and aviation mechanical systems. This study is to investigate the modal sensing behavior and the modal vibration control effect of distributed PVDF patches laminated on the paraboloidal shell. A paraboloidal shell sensing and control testing platform is set up first. Frequencies of lower order modes of the shell are obtained with the PVDF sensor and compared with the previous testing results to prove its accuracy. Then sensor patches are laminated on different positions (or different sides) of the shell and tested to reveal the relation between the sensing behaviors and their locations. Finally, a mathematical model of the structronic system is built by parameter identifications and the transfer function is derived. Independent and coupled modal controllers are designed based on the pole placement method and modal vibration control experiments are performed. The amplitude suppression ratio of each mode controlled by the pole placement controller is calculated and compared with the results obtained by using a PPF controller. Advantages of both methods are concluded and suggestions are given on how to choose control algorithm for different purpose.

Probing the effects of Lorentz-symmetry violating Chern-Simons and Ricci-Cotton terms in higher derivative gravity

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

Pereira-Dias, B.; Hernaski, C. A.; Helayeel-Neto, J. A.

The combined effects of the Lorentz-symmetry violating Chern-Simons and Ricci-Cotton actions are investigated for the Einstein-Hilbert gravity in the second-order formalism modified by higher derivative terms, and their consequences on the spectrum of excitations are analyzed. We follow the lines of previous works and build up an orthonormal basis of projector-like operators for the degrees of freedom, rather than for the spin modes of the fields. With this new basis, the attainment of the propagators is remarkably simplified and the identification of the physical and unphysical modes becomes more immediate. Our conclusion is that the only tachyon- and ghost-free modelmore » is the Einstein-Hilbert action added up by the Chern-Simons term with a timelike vector of the type v{sup {mu}=}({mu},0-vector). Spectral consistency imposes that the Ricci-Cotton term must be switched off. We then infer that gravity with Lorentz-symmetry violation imposes a drastically different constraint on the background if compared to ordinary gauge theories whenever conditions for the suppression of tachyons and ghosts are imposed.« less

[Expression analysis of a transformer gene in Daphnia pulex after RNAi].

PubMed

Guo, C Y; Chen, P; Zhang, M M; Ning, J J; Wang, С L; Wang, D L; Zhao, Y L

2016-01-01

In order to explore the importance of the transformer (tra) gene in reproductive mode switching in Daphnia pulex, we studied the effect of silencing of this gene using RNA interference (RNAi). We obtained Dptra dsRNA by constructing and using a dsRNA expression vector and transcription method in vitro. D. pulex individuals in different reproductive modes were treated by soaking in a solution of Dptra dsRNA. We then assayed the expression of the endogenous Dptra mRNA after RNAi treatment using RT-PCR and obtained the suppression ratio. Expression of the tra gene in the RNAi groups was down-regulated compared with the controls after 16 h (p < 0.05). We also analyzed the effect of RNAi on the expression of the TRA protein using Western blot, which showed that the expression level of the TRA protein was reduced after RNAi treatment. Our experimental results showed that soaking of D. pulex adults in tra-specific dsRNA transcribed in vitro can specifically reduce the level of tra mRNA and also reduce the expression of the TRA protein, demonstrating effective in vivo silencing of the tra gene.

Second order hydrodynamics for a special class of gravity duals

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

Springer, T.

2009-04-15

The sound mode hydrodynamic dispersion relation is computed up to order q{sup 3} for a class of gravitational duals which includes both Schwarzschild AdS and Dp-brane metrics. The implications for second order transport coefficients are examined within the context of Israel-Stewart theory. These sound mode results are compared with previously known results for the shear mode. This comparison allows one to determine the third order hydrodynamic contributions to the shear mode for the class of metrics considered here.

Second-Order Consensus in Multiagent Systems via Distributed Sliding Mode Control.

PubMed

Yu, Wenwu; Wang, He; Cheng, Fei; Yu, Xinghuo; Wen, Guanghui

2016-11-22

In this paper, the new decoupled distributed sliding-mode control (DSMC) is first proposed for second-order consensus in multiagent systems, which finally solves the fundamental unknown problem for sliding-mode control (SMC) design of coupled networked systems. A distributed full-order sliding-mode surface is designed based on the homogeneity with dilation for reaching second-order consensus in multiagent systems, under which the sliding-mode states are decoupled. Then, the SMC is applied to the decoupled sliding-mode states to reach their origin in finite time, which is the sliding-mode surface. The states of agents can first reach the designed sliding-mode surface in finite time and then move to the second-order consensus state along the surface in finite time as well. The DSMC designed in this paper can eliminate the influence of singularity problems and weaken the influence of chattering, which is still very difficult in the SMC systems. In addition, DSMC proposes a general decoupling framework for designing SMC in networked multiagent systems. Simulations are presented to verify the theoretical results in this paper.

A component modes projection and assembly model reduction methodology for articulated, multi-flexible body structures

NASA Technical Reports Server (NTRS)

Lee, Allan Y.; Tsuha, Walter S.

1993-01-01

A two-stage model reduction methodology, combining the classical Component Mode Synthesis (CMS) method and the newly developed Enhanced Projection and Assembly (EP&A) method, is proposed in this research. The first stage of this methodology, called the COmponent Modes Projection and Assembly model REduction (COMPARE) method, involves the generation of CMS mode sets, such as the MacNeal-Rubin mode sets. These mode sets are then used to reduce the order of each component model in the Rayleigh-Ritz sense. The resultant component models are then combined to generate reduced-order system models at various system configurations. A composite mode set which retains important system modes at all system configurations is then selected from these reduced-order system models. In the second stage, the EP&A model reduction method is employed to reduce further the order of the system model generated in the first stage. The effectiveness of the COMPARE methodology has been successfully demonstrated on a high-order, finite-element model of the cruise-configured Galileo spacecraft.

Experimental determination of the particle motions associated with the low order acoustic modes in enclosures

NASA Technical Reports Server (NTRS)

Byrne, K. P.; Marshall, S. E.

1983-01-01

A procedure for experimentally determining, in terms of the particle motions, the shapes of the low order acoustic modes in enclosures is described. The procedure is based on finding differentiable functions which approximate the shape functions of the low order acoustic modes when these modes are defined in terms of the acoustic pressure. The differentiable approximating functions are formed from polynomials which are fitted by a least squares procedure to experimentally determined values which define the shapes of the low order acoustic modes in terms of the acoustic pressure. These experimentally determined values are found by a conventional technique in which the transfer functions, which relate the acoustic pressures at an array of points in the enclosure to the volume velocity of a fixed point source, are measured. The gradient of the function which approximates the shape of a particular mode in terms of the acoustic pressure is evaluated to give the mode shape in terms of the particle motion. The procedure was tested by using it to experimentally determine the shapes of the low order acoustic modes in a small rectangular enclosure.

Higher-harmonic collective modes in a trapped gas from second-order hydrodynamics

DOE PAGES

Lewis, William E.; Romatschke, P.

2017-02-21

Utilizing a second-order hydrodynamics formalism, the dispersion relations for the frequencies and damping rates of collective oscillations as well as spatial structure of these modes up to the decapole oscillation in both two- and three- dimensional gas geometries are calculated. In addition to higher-order modes, the formalism also gives rise to purely damped "non-hydrodynamic" modes. We calculate the amplitude of the various modes for both symmetric and asymmetric trap quenches, finding excellent agreement with an exact quantum mechanical calculation. Furthermore, we find that higher-order hydrodynamic modes are more sensitive to the value of shear viscosity, which may be of interestmore » for the precision extraction of transport coefficients in Fermi gas systems.« less

Higher-harmonic collective modes in a trapped gas from second-order hydrodynamics

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

Lewis, William E.; Romatschke, P.

Utilizing a second-order hydrodynamics formalism, the dispersion relations for the frequencies and damping rates of collective oscillations as well as spatial structure of these modes up to the decapole oscillation in both two- and three- dimensional gas geometries are calculated. In addition to higher-order modes, the formalism also gives rise to purely damped "non-hydrodynamic" modes. We calculate the amplitude of the various modes for both symmetric and asymmetric trap quenches, finding excellent agreement with an exact quantum mechanical calculation. Furthermore, we find that higher-order hydrodynamic modes are more sensitive to the value of shear viscosity, which may be of interestmore » for the precision extraction of transport coefficients in Fermi gas systems.« less

Optimal second order sliding mode control for nonlinear uncertain systems.

PubMed

Das, Madhulika; Mahanta, Chitralekha

2014-07-01

In this paper, a chattering free optimal second order sliding mode control (OSOSMC) method is proposed to stabilize nonlinear systems affected by uncertainties. The nonlinear optimal control strategy is based on the control Lyapunov function (CLF). For ensuring robustness of the optimal controller in the presence of parametric uncertainty and external disturbances, a sliding mode control scheme is realized by combining an integral and a terminal sliding surface. The resulting second order sliding mode can effectively reduce chattering in the control input. Simulation results confirm the supremacy of the proposed optimal second order sliding mode control over some existing sliding mode controllers in controlling nonlinear systems affected by uncertainty. Copyright © 2014 ISA. Published by Elsevier Ltd. All rights reserved.

Lateral mode control in edge-emitting lasers with modified mirrors

NASA Astrophysics Data System (ADS)

Payusov, A.; Serin, A.; Mukhin, I.; Shernyakov, Y.; Zadiranov, Y.; Maximov, M.; Gordeev, N.

2017-11-01

We present a study on lateral mode control in edge-emitting lasers with profiled mirror reflectivity. The object was to eliminate high-order lateral modes in conventional ridge-waveguide InAs/InGaAs QD (quantum dot) lasers with the stripe width of 10 μm. We have used a FIB (focused ion beam) technique to selectively etch windows in the AR (anti-reflection) facet coatings in order to introduce extra mirror losses for the high order modes. This approach allowed us to eliminate the first-order mode lasing without deterioration of the laser parameters. We suppose that further optimisation of the laser heterostructure and window designs may lead to a pure lateral single-mode lasing in the broadened ridge waveguides.