Babb, James; Kunstatter, Gabor; Daghigh, Ramin
2011-10-15
Quasinormal modes provide valuable information about the structure of spacetime outside a black hole. There is also a conjectured relationship between the highly damped quasinormal modes and the semiclassical spectrum of the horizon area/entropy. In this paper, we show that for spacetimes characterized by more than one scale, the 'infinitely damped' modes in principle probe the structure of spacetime outside the horizon at the shortest length scales. We demonstrate this with the calculation of the highly damped quasinormal modes of the nonsingular, single-horizon, quantum corrected black hole derived in [A. Peltola and G. Kunstatter, Phys. Rev. D 79, 061501 (2009); ].
Highly damped quasinormal modes of generic single-horizon black holes
NASA Astrophysics Data System (ADS)
Daghigh, Ramin G.; Kunstatter, Gabor
2005-10-01
We calculate analytically the highly damped quasinormal mode spectra of generic single-horizon black holes using the rigorous WKB techniques of Andersson and Howls (2004 Class. Quantum Grav. 21 1623). We thereby provide a firm foundation for previous analysis, and point out some of their possible limitations. The numerical coefficient in the real part of the highly damped frequency is generically determined by the behaviour of coupling of the perturbation to the gravitational field near the origin, as expressed in tortoise coordinates. This fact makes it difficult to understand how the famous ln(3) could be related to the quantum gravitational microstates near the horizon.
Damped and zero-damped quasinormal modes of charged, nearly extremal black holes
NASA Astrophysics Data System (ADS)
Zimmerman, Aaron; Mark, Zachary
2016-02-01
Despite recent progress, the complete understanding of the perturbations of charged, rotating black holes as described by the Kerr-Newman metric remains an open and fundamental problem in relativity. In this study, we explore the existence of families of quasinormal modes of Kerr-Newman black holes whose decay rates limit to zero at extremality, called zero-damped modes in past studies. We review the nearly extremal and WKB approximation methods for spin-weighted scalar fields (governed by the Dudley-Finley equation) and give an accounting of the regimes where scalar zero-damped and damped modes exist. Using Leaver's continued fraction method, we verify that these approximations give accurate predictions for the frequencies in their regimes of validity. In the nonrotating limit, we argue that gravito-electromagnetic perturbations of nearly extremal Reissner-Nordström black holes have zero-damped modes in addition to the well-known spectrum of damped modes. We provide an analytic formula for the frequencies of these modes, verify their existence using a numerical search, and demonstrate the accuracy of our formula. These results, along with recent numerical studies, point to the existence of a simple universal equation for the frequencies of zero-damped gravito-electromagnetic modes of Kerr-Newman black holes, whose precise form remains an open question.
Mesonic quasinormal modes of the Sakai-Sugimoto model at high temperature
Evans, Nick; Threlfall, Ed
2008-06-15
We examine the mesonic thermal spectrum of the Sakai-Sugimoto model of holographic QCD by finding the quasinormal frequencies of the supergravity dual. If flavor is added using D8-D8 branes there exist embeddings where the D-brane world volume contains a black hole. For these embeddings (the high-temperature phase of the Sakai-Sugimoto model) we determine the quasinormal spectra of scalar and vector mesons arising from the world volume Dirac-Born-Infeld (DBI) action of the D-brane. We stress the importance of a coordinate change that makes the infalling quasinormal modes regular at the horizon allowing a simple numerical shooting technique. Finally we examine the effect of finite spatial momentum on quasinormal spectra.
Stability and quasinormal modes of the massive scalar field around Kerr black holes
NASA Astrophysics Data System (ADS)
Konoplya, R. A.; Zhidenko, A. V.
2006-06-01
In this paper, we find quasinormal spectrum of the massive scalar field in the background of the Kerr black holes. We show that all found modes are damped under the quasinormal modes boundary conditions when μM≲1, thereby implying stability of the massive scalar field. This complements the region of stability determined by the Beyer inequality for large masses of the field. We show that, similar to the case of a nonrotating black hole, the massive term of the scalar field does not contribute in the regime of high damping. Therefore, the high damping asymptotic should be the same as for the massless scalar field.
Behavior of quasinormal modes and high dimension RN-AdS black hole phase transition
NASA Astrophysics Data System (ADS)
Chabab, M.; Moumni, H. El; Iraoui, S.; Masmar, K.
2016-12-01
In this work we use the quasinormal frequencies of a massless scalar perturbation to probe the phase transition of the high dimension charged AdS black hole. The signature of the critical behavior of this black hole solution is detected in the isobaric as well as in isothermal process. This paper is a natural generalization of Liu et al. (JHEP 1409:179, 2014) to higher dimensional spacetime. More precisely our study shows a clear signal for any dimension d in the isobaric process. As to the isothermal case, we find that this signature can be affected by other parameters like the pressure and the horizon radius. We conclude that the quasinormal modes can be an efficient tool to investigate the first-order phase transition, but fail to disclose the signature of the second-order phase transition.
Exact quasinormal modes for a special class of black holes
Oliva, Julio; Troncoso, Ricardo
2010-07-15
Analytic exact expressions for the quasinormal modes of scalar and electromagnetic perturbations around a special class of black holes are found in d{>=}3 dimensions. It is shown that the size of the black hole provides a lower bound for the angular momentum of the perturbation. Quasinormal modes appear when this bound is fulfilled; otherwise the excitations become purely damped.
Konoplya, R. A.
2006-01-15
We consider the perturbations of the massive vector field around Schwarzschild, Schwarzschild-de Sitter, and Schwarzschild-anti-de Sitter black holes. Equations for a spherically symmetric massive vector perturbation can be reduced to a single wavelike equation. We have proved the stability against these perturbations and investigated the quasinormal spectrum. The quasinormal behavior for Schwarzschild black hole is quite unexpected: the fundamental mode and higher overtones show totally different dependence on the mass of the field m: as m is increasing, the damping rate of the fundamental mode is decreasing, what results in appearing of the infinitely long living modes, while, on the contrary, damping rate of all higher overtones are increasing, and their real oscillation frequencies gradually go to tiny values. Thereby, for all higher overtones, almost nonoscillatory, damping modes can exist. In the limit of asymptotically high damping, Re{omega} goes to ln3/(8{pi}M), while imaginary part shows equidistant behavior with spacing Im{omega}{sub n+1}-Im{omega}{sub n}=1/4M. In addition, we have found quasinormal spectrum of massive vector field for Schwarzschild-anti-de Sitter black hole.
Quasinormal modes in a time-dependent black hole background
Shao Chenggang; Wang Bin; Abdalla, Elcio; Su Rukeng
2005-02-15
We have studied the evolution of the massless scalar field propagating in a time-dependent charged Vaidya black hole background. A generalized tortoise coordinate transformation was used to study the evolution of the massless scalar field. It is shown that, for the slowest damped quasinormal modes, the approximate formulas in the stationary Reissner-Nordstroem black hole turn out to be a reasonable prescription, showing that results from quasinormal mode analysis are rather robust.
Quasinormal modes of superfluid neutron stars
NASA Astrophysics Data System (ADS)
Gualtieri, L.; Kantor, E. M.; Gusakov, M. E.; Chugunov, A. I.
2014-07-01
We study nonradial oscillations of neutron stars with superfluid baryons, in a general relativistic framework, including finite temperature effects. Using a perturbative approach, we derive the equations describing stellar oscillations, which we solve by numerical integration, employing different models of nucleon superfluidity, and determining frequencies and gravitational damping times of the quasinormal modes. As expected by previous results, we find two classes of modes, associated to superfluid and non-superfluid degrees of freedom, respectively. We study the temperature dependence of the modes, finding that at specific values of the temperature, the frequencies of the two classes of quasinormal modes show avoided crossings, and their damping times become comparable. We also show that, when the temperature is not close to the avoided crossings, the frequencies of the modes can be accurately computed by neglecting the coupling between normal and superfluid degrees of freedom. Our results have potential implications on the gravitational wave emission from neutron stars.
Highly damped kinematic coupling for precision instruments
Hale, Layton C.; Jensen, Steven A.
2001-01-01
A highly damped kinematic coupling for precision instruments. The kinematic coupling provides support while causing essentially no influence to its nature shape, with such influences coming, for example, from manufacturing tolerances, temperature changes, or ground motion. The coupling uses three ball-cone constraints, each combined with a released flexural degree of freedom. This arrangement enables a gain of higher load capacity and stiffness, but can also significantly reduce the friction level in proportion to the ball radius divided by the distance between the ball and the hinge axis. The blade flexures reduces somewhat the stiffness of the coupling and provides an ideal location to apply constrained-layer damping which is accomplished by attaching a viscoelastic layer and a constraining layer on opposite sides of each of the blade flexures. The three identical ball-cone flexures provide a damped coupling mechanism to kinematically support the projection optics system of the extreme ultraviolet lithography (EUVL) system, or other load-sensitive apparatus.
Model for Quasinormal Mode Excitation by a Particle Plunging into a Black Hole
NASA Astrophysics Data System (ADS)
Mark, Zachary; Zimmerman, Aaron; Yang, Huan; Chen, Yanbei
2016-03-01
It is known that the late time gravitational waveform produced by a particle plunging into a Kerr black hole is well described by a sum of quasinormal modes. However it is not yet understood how the early part of the waveform gives way to the quasinormal mode description, which diverges at early times, nor how the inhomogenous part of the waveform contributes. Motivated by, we offer a model for quasinormal mode excitation by a particle plunging into a Schwarzschild black hole. To develop our model we study approximations to the Regge-Wheeler equation that allow for a closed-form expression for the frequency-domain Green's function, which we use to isolate the component of the waveform that should be identified with quasinormal ringing. Our description of quasinormal ringing does not diverge at early times and reveals that quasinormal ringing should be understood in analogy with a damped harmonic oscillator experiencing a transient driving source.
Damping of hard excitations in strongly coupled N = 4 plasma
NASA Astrophysics Data System (ADS)
Fuini, John F.; Uhlemann, Christoph F.; Yaffe, Laurence G.
2016-12-01
The damping of high momentum excitations in strongly coupled maximally supersymmetric Yang-Mills plasma is studied. Previous calculations of the asymptotic behavior of the quasinormal mode spectrum are extended and clarified. We confirm that subleading corrections to the lightlike dispersion relation ω( q) = | q| have a universal | q|-1/3 form. Sufficiently narrow, weak planar shocks may be viewed as coherent superpositions of short wavelength quasinormal modes. The attenuation and evolution in profile of narrow planar shocks are examined as an application of our results.
Fast damping in mismatched high intensity beam transportation
NASA Astrophysics Data System (ADS)
Variale, V.
2001-08-01
A very fast damping of beam envelope oscillation amplitudes was recently observed in simulations of high intensity beam transport, through periodic FODO cells, in mismatched conditions [V. Variale, Nuovo Cimento Soc. Ital. Fis. 112A, 1571-1582 (1999) and T. Clauser et al., in Proceedings of the Particle Accelerator Conference, New York, 1999 (IEEE, Piscataway, NJ, 1999), p. 1779]. A Landau damping mechanism was proposed at the origin of observed effect. In this paper, to further investigate the source of this fast damping, extensive simulations have been carried out. The results presented here support the interpretation of the mechanism at the origin of the fast damping as a Landau damping effect.
Damping in high-temperature superconducting levitation systems
Hull, John R.
2009-12-15
Methods and apparatuses for improved damping in high-temperature superconducting levitation systems are disclosed. A superconducting element (e.g., a stator) generating a magnetic field and a magnet (e.g. a rotor) supported by the magnetic field are provided such that the superconducting element is supported relative to a ground state with damped motion substantially perpendicular to the support of the magnetic field on the magnet. Applying this, a cryostat housing the superconducting bearing may be coupled to the ground state with high damping but low radial stiffness, such that its resonant frequency is less than that of the superconducting bearing. The damping of the cryostat may be substantially transferred to the levitated magnetic rotor, thus, providing damping without affecting the rotational loss, as can be derived applying coupled harmonic oscillator theory in rotor dynamics. Thus, damping can be provided to a levitated object, without substantially affecting the rotational loss.
Quasi-normal frequencies: key analytic results
NASA Astrophysics Data System (ADS)
Boonserm, Petarpa; Visser, Matt
2011-03-01
The study of exact quasi-normal modes [QNMs], and their associated quasi-normal frequencies [QNFs], has had a long and convoluted history — replete with many rediscoveries of previously known results. In this article we shall collect and survey a number of known analytic results, and develop several new analytic results — specifically we shall provide several new QNF results and estimates, in a form amenable for comparison with the extant literature. Apart from their intrinsic interest, these exact and approximate results serve as a backdrop and a consistency check on ongoing efforts to find general model-independent estimates for QNFs, and general model-independent bounds on transmission probabilities. Our calculations also provide yet another physics application of the Lambert W function. These ideas have relevance to fields as diverse as black hole physics, (where they are related to the damped oscillations of astrophysical black holes, to greybody factors for the Hawking radiation, and to more speculative state-counting models for the Bekenstein entropy), to quantum field theory (where they are related to Casimir energies in unbounded systems), through to condensed matter physics, (where one may literally be interested in an electron tunnelling through a physical barrier).
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.
Quasinormal ringing of acoustic black holes in Laval nozzles: Numerical simulations
Okuzumi, Satoshi; Sakagami, Masa-aki
2007-10-15
Quasinormal ringing of acoustic black holes in Laval nozzles is discussed. The equation for sounds in a transonic flow is written into a Schroedinger-type equation with a potential barrier, and the quasinormal frequencies are calculated semianalytically. From the results of numerical simulations, it is shown that the quasinormal modes are actually excited when the transonic flow is formed or slightly perturbed, as well as in the real black hole case. In an actual experiment, however, the purely-outgoing boundary condition will not be satisfied at late times due to the wave reflection at the end of the apparatus, and a late-time ringing will be expressed as a superposition of boxed quasinormal modes. It is shown that the late-time ringing damps more slowly than the ordinary quasinormal ringing, while its central frequency is not greatly different from that of the ordinary one. Using this fact, an efficient way for experimentally detecting the quasinormal ringing of an acoustic black hole is discussed.
Quasinormal ringing of acoustic black holes in Laval nozzles: Numerical simulations
NASA Astrophysics Data System (ADS)
Okuzumi, Satoshi; Sakagami, Masa-Aki
2007-10-01
Quasinormal ringing of acoustic black holes in Laval nozzles is discussed. The equation for sounds in a transonic flow is written into a Schrödinger-type equation with a potential barrier, and the quasinormal frequencies are calculated semianalytically. From the results of numerical simulations, it is shown that the quasinormal modes are actually excited when the transonic flow is formed or slightly perturbed, as well as in the real black hole case. In an actual experiment, however, the purely-outgoing boundary condition will not be satisfied at late times due to the wave reflection at the end of the apparatus, and a late-time ringing will be expressed as a superposition of boxed quasinormal modes. It is shown that the late-time ringing damps more slowly than the ordinary quasinormal ringing, while its central frequency is not greatly different from that of the ordinary one. Using this fact, an efficient way for experimentally detecting the quasinormal ringing of an acoustic black hole is discussed.
Monitoring of soft high damping elastomeric bearings for earthquake isolation
Coveney, V.A.; Kuroda, T.; Kobatake, M.; Nita, Y.; Kulak, R.F.; Chang, Y.W.; Seidensticker, R.W.
1993-07-01
Over the last 20 years several practical systems for the protection of buildings and their contents against the effects of earthquakes were developed. These systems rely on effectively decoupling the building from the strong horizontal ground accelerations that are some of the most damaging features of an earthquake. The isolation of small buildings against earthquakes poses particular problems for high damping elastomer. systems. It was recognized that one way to overcome these problems was to use elastomers with particularly low moduli, high damping and other necessary characteristics. This paper describes some key features of the development of soft high damping natural bearings. Their use for the earthquake isolation of a small highly instrumented building at Tohoku University in Sendai, Japan is discussed. The paper focuses on the monitoring of the bearings during production and their performance in situ under static and earthquake (dynamic) conditions.
Damping of High-temperature Shape Memory Alloys
NASA Technical Reports Server (NTRS)
Duffy, Kirsten P.; Padula, Santo A., II; Scheiman, Daniel A.
2008-01-01
Researchers at NASA Glenn Research Center have been investigating high temperature shape memory alloys as potential damping materials for turbomachinery rotor blades. Analysis shows that a thin layer of SMA with a loss factor of 0.04 or more would be effective at reducing the resonant response of a titanium alloy beam. Two NiTiHf shape memory alloy compositions were tested to determine their loss factors at frequencies from 0.1 to 100 Hz, at temperatures from room temperature to 300 C, and at alternating strain levels of 34-35x10(exp -6). Elevated damping was demonstrated between the M(sub s) and M(sub f) phase transformation temperatures and between the A(sub s) and A(sub f) temperatures. The highest damping occurred at the lowest frequencies, with a loss factor of 0.2-0.26 at 0.1 Hz. However, the peak damping decreased with increasing frequency, and showed significant temperature hysteresis in heating and cooling. Keywords: High-temperature, shape memory alloy, damping, aircraft engine blades, NiTiHf
Enthalpy damping for high Mach number Euler solutions
NASA Technical Reports Server (NTRS)
Moitra, Anutosh
1990-01-01
An improvement on the enthalpy damping procedure currently in use in solving supersonic flow fields is described. A correction based on entropy values is shown to produce a very efficient scheme for simulation of high Mach number three-dimensional flows. Substantial improvements in convergence rates have been achieved by incorporating this enthalpy damping scheme in a finite-volume Runge-Kutta method for solving the Euler equations. Results obtained for blended wing-body geometries at very high Mach numbers are presented.
High-Speed Video Analysis of Damped Harmonic Motion
ERIC Educational Resources Information Center
Poonyawatpornkul, J.; Wattanakasiwich, P.
2013-01-01
In this paper, we acquire and analyse high-speed videos of a spring-mass system oscillating in glycerin at different temperatures. Three cases of damped harmonic oscillation are investigated and analysed by using high-speed video at a rate of 120 frames s[superscript -1] and Tracker Video Analysis (Tracker) software. We present empirical data for…
Looking at the Gregory-Laflamme instability through quasinormal modes
Konoplya, R. A.; Murata, Keiju; Soda, Jiro; Zhidenko, A.
2008-10-15
We study evolution of gravitational perturbations of black strings. It is well known that for all wave numbers less than some threshold value, the black string is unstable against the scalar type of gravitational perturbations, which is named the Gregory-Laflamme instability. Using numerical methods, we find the quasinormal modes and time-domain profiles of the black string perturbations in the stable sector and also show the appearance of the Gregory-Laflamme instability in the time domain. The dependence of the black string quasinormal spectrum and late-time tails on such parameters as the wave vector and the number of extra dimensions is discussed. There is numerical evidence that at the threshold point of instability, the static solution of the wave equation is dominant. For wave numbers slightly larger than the threshold value, in the region of stability, we see tiny oscillations with very small damping rate. While, for wave numbers slightly smaller than the threshold value, in the region of the Gregory-Laflamme instability, we observe tiny oscillations with very small growth rate. We also find the level crossing of imaginary part of quasinormal modes between the fundamental mode and the first overtone mode, which accounts for the peculiar time domain profiles.
NASA Astrophysics Data System (ADS)
Saleh, Mahamat; Bouetou, Bouetou Thomas; Kofane, Timoleon Crepin
2016-04-01
In this work, quasinormal modes (QNMs) of the Schwarzschild black hole are investigated by taking into account the quantum fluctuations. Gravitational and Dirac perturbations were considered for this case. The Regge-Wheeler gauge and the Dirac equation were used to derive the perturbation equations of the gravitational and Dirac fields respectively and the third order Wentzel-Kramers-Brillouin (WKB) approximation method is used for the computing of the quasinormal frequencies. The results show that due to the quantum fluctuations in the background of the Schwarzschild black hole, the QNMs of the black hole damp more slowly when increasing the quantum correction factor (a), and oscillate more slowly.
Ultrasoft Quark Damping in High-T QCD
Abada, Abdessamad; Daira-Aifa, Nacera; Bouakaz, Karima
2007-02-27
We determine the ultrasoft quark damping rates in the context of next-to-leading order hard-thermal-loop summed perturbation of high-temperature QCD. Three types of divergences are encountered: infrared, light-cone and at specific points determined by the gluon energies. The infrared divergence persists and is logarithmic whereas the two others are circumvented.
Simultaneously high stiffness and damping in nanoengineered microtruss composites.
Meaud, Julien; Sain, Trisha; Yeom, Bongjun; Park, Sei Jin; Shoultz, Anna Brieland; Hulbert, Gregory; Ma, Zheng-Dong; Kotov, Nicholas A; Hart, A John; Arruda, Ellen M; Waas, Anthony M
2014-04-22
Materials combining high stiffness and mechanical energy dissipation are needed in automotive, aviation, construction, and other technologies where structural elements are exposed to dynamic loads. In this paper we demonstrate that a judicious combination of carbon nanotube engineered trusses held in a dissipative polymer can lead to a composite material that simultaneously exhibits both high stiffness and damping. Indeed, the combination of stiffness and damping that is reported is quite high in any single monolithic material. Carbon nanotube (CNT) microstructures grown in a novel 3D truss topology form the backbone of these nanocomposites. The CNT trusses are coated by ceramics and by a nanostructured polymer film assembled using the layer-by-layer technique. The crevices of the trusses are then filled with soft polyurethane. Each constituent of the composite is accurately modeled, and these models are used to guide the manufacturing process, in particular the choice of the backbone topology and the optimization of the mechanical properties of the constituent materials. The resulting composite exhibits much higher stiffness (80 times) and similar damping (specific damping capacity of 0.8) compared to the polymer. Our work is a step forward in implementing the concept of materials by design across multiple length scales.
Frequency and temperature dependence of high damping elastomers
Kulak, R.F.; Hughes, T.H.
1993-08-01
High damping steel-laminated elastomeric seismic isolation bearings are one of the preferred devices for isolating large buildings and structures. In the US, the current reference design for the Advanced Liquid Metal Reactor (ALMR) uses laminated bearings for seismic isolation. These bearings are constructed from alternating layers of high damping rubber and steel plates. They are typically designed for shear strains between 50 and 100% and are expected to sustain two to three times these levels for beyond design basis loading conditions. Elastomeric bearings are currently designed to provide a system frequency between 0.4 and 0.8 Hz and expected to operate between {minus}20 and 40 degrees Centigrade. To assure proper performance of isolation bearings, it is necessary to characterize the elastomer`s response under expected variations of frequency and temperature. The dynamic response of the elastomer must be characterized within the frequency range that spans the bearing acceptance test frequency, which may be as low as 0.005 Hz, and the design frequency. Similarly, the variation in mechanical characteristics of the elastomer must be determined over the design temperature range, which is between {minus}20 and 40 degrees Centigrade. This paper reports on (1) the capabilities of a testing facility at ANL for testing candidate elastomers, (2) the variation with frequency and temperature of the stiffness and damping of one candidate elastomer, and (3) the effect of these variations on bearing acceptance testing criteria and on the choice of bearing design values for stiffness and damping.
Landau damping with high frequency impedance
Blaskiewicz,M.
2009-05-04
Coupled bunch longitudinal stability in the presence of high frequency impedances is considered. A frequency domain technique is developed and compared with simulations. The frequency domain technique allows for absolute stability tests and is applied to the problem of longitudinal stability in RHIC with the new 56 MHz RF system.
High-Efficiency Absorber for Damping the Transverse Wake Fields
Novokhatski, A.; Seeman, J.; Weathersby, S.; /SLAC
2007-02-28
Transverse wake fields generated by intense beams may propagate long distances in the vacuum chamber and dissipate power in different shielded elements such as bellows, vacuum valves or vacuum pumps. Induced heating in these elements may be high enough to deteriorate vacuum conditions. We have developed a broadband water-cooled bellows-absorber to capture and damp these harmful transverse fields without impacting the longitudinal beam impedance. Experimental results at the PEP-II SLAC B-factory demonstrate high efficiency of this device. This absorber may be useful in other machines like synchrotron light sources or International Linear Collider.
High resolution upgrade of the ATF damping ring BPM system
Terunuma, N.; Urakawa, J.; Frisch, J.; May, J.; McCormick, D.; Nelson, J.; Seryi, A.; Smith, T.; Woodley, M.; Briegel, C.; Dysert, R.; /Fermilab
2008-05-01
A beam position monitor (BPM) upgrade at the KEK Accelerator Test Facility (ATF) damping ring has been accomplished in its first stage, carried out by a KEK/FNAL/SLAC collaboration under the umbrella of the global ILC R&D effort. The upgrade consists of a high resolution, high reproducibility read-out system, based on analog and digital downconversion techniques, digital signal processing, and also tests a new automatic gain error correction schema. The technical concept and realization, as well as preliminary results of beam studies are presented.
High frequency atmospheric gravity wave damping in the mesosphere
NASA Astrophysics Data System (ADS)
Swenson, G. R.; Liu, A. Z.; Li, F.; Tang, J.
2003-09-01
Correlative measurements of temperature and winds by Na lidar and brightness in OH and O 2 Atmospheric band airglow have been made at Albuquerque, NM and Maui, HI for a study of high frequency (period less than 30 minutes) Atmospheric Gravity Waves. Wave studies from four nights have been made and the correlative information describes the intrinsic wave properties with altitude, their damping characteristics, and resulting accelerations to the large scale circulation in the 85-100 km altitude region. Generally, saturated to super-saturated conditions were observed below 95 km. Above this altitude, they were less saturated to freely propagating.
Quasi-exactly solvable quasinormal modes
Ho, C.-L.; Cho, H.-T.
2007-11-20
We consider quasinormal modes with complex energies from the point of view of the theory of quasi-exactly solvable (QES) models. We demonstrate that it is possible to find new potentials which admit exactly solvable or QES quasinormal modes by suitable complexification of parameters defining the QES potentials. Particularly, we obtain one QES and four exactly solvable potentials out of the five one-dimensional QES systems based on the sl(2) algebra.
Quasinormal modes of a Schwarzschild white hole
Bishop, Nigel T.; Kubeka, Amos S.
2009-09-15
We investigate perturbations of the Schwarzschild geometry using a linearization of the Einstein vacuum equations within a Bondi-Sachs, or null cone, formalism. We develop a numerical method to calculate the quasinormal modes, and present results for the case l=2. The values obtained are different than those of a Schwarzschild black hole, and we interpret them as quasinormal modes of a Schwarzschild white hole.
Coatings for High-Temperature Vibration Damping of Turbines
2009-10-01
damping is provided by both the thin bond- coat and thermal barrier coating (TBC) in TBC coated superalloy system, (ii) the damping from each component...bond- coat and the TBC itself, and (iii) damping from EB-PVD deposited TBCs and platinum-modified nickel aluminide bond- coats occur at the same...closer to chemical equilibrium with existing superalloys than those currently used as bond- coats . Also, depending on the platinum content, the nickel
Development of Composite Materials with High Passive Damping Properties
2006-05-15
SPONSOR/MONITOR’S REPORT NUMBER(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT 13. SUPPLEMENTARY NOTES 14 . ABSTRACT The structures studied in this ONR...2.1.2 Measures of damping 8 2.1.3 Measurement methods 9 2.2 Damping in Sandwich Structures. 9 2.2.1 Analytical models 10 2.2.2 Damping and damage 14 ...2.2.3 Finite element models 14 2.2.4 Statistical energy analysis method 15 CHAPTER 3 ANALYSIS OF DAMPING IN SANDWICH MATERIALS. 24 3.1 Equation of
Suppression of radiation damping for high precision quantitative NMR.
Bayle, Kevin; Julien, Maxime; Remaud, Gérald S; Akoka, Serge
2015-10-01
True quantitative analysis of concentrated samples by (1)H NMR is made very difficult by Radiation Damping. A novel NMR sequence (inspired by the WET NMR sequence and by Outer Volume Saturation methods) is therefore proposed to suppress this phenomenon by reducing the spatial area and consequently the number of spins contributing to the signal detected. The size of the detected volume can be easily chosen in a large range and line shape distortions are avoided thanks to a uniform signal suppression of the outer volume. Composition of a mixture can as a result be determined with very high accuracy (precision and trueness) at the per mille level whatever the concentrations and without hardware modification.
Translational damping on high-frequency flapping wings
NASA Astrophysics Data System (ADS)
Parks, Perry A.
Flapping fliers such as insects and birds depend on passive translational and rotational damping to terminate quick maneuvers and to provide a source of partial stability in an otherwise unstable dynamic system. Additionally, passive translational and rotational damping reduce the amount of active kinematic changes that must be made to terminate maneuvers and maintain stability. The study of flapping-induced damping phenomena also improves the understanding of micro air vehicle (MAV) dynamics needed for the synthesis of effective flight control strategies. Aerodynamic processes which create passive translational and rotational damping as a direct result of symmetric flapping with no active changes in wing kinematics have been previously studied and were termed flapping counter-force (FCF) and flapping counter-torque (FCT), respectively. In this first study of FCF measurement in air, FCF generation is measured using a pendulum system designed to isolate and measure the relationship of translational flapping-induced damping with wingbeat frequency for a 2.86 gram mechanical flapper equipped with real cicada wings. Analysis reveals that FCF generation and wingbeat frequency are directly proportional, as expected from previous work. The quasi-steady FCF model using Blade-Element-Theory is used as an estimate for translational flapping-induced damping. In most cases, the model proves to be accurate in predicting the relationship between flapping-induced damping and wingbeat frequency. "Forward-backward" motion proves to have the strongest flapping-induced damping while "up-down" motion has the weakest.
Damping Effect Studies for X-band Normal Conducting High Gradient Standing Wave Structures
Pei, S.; Li, Z.; Tantawi, S.G.; Dolgashev, V.A.; Wang, J.; /SLAC
2009-08-03
The Multi-TeV colliders should have the capability to accelerate low emittance beam with high rf efficiency, X-band normal conducting high gradient accelerating structure is one of the promising candidate. However, the long range transverse wake field which can cause beam emittance dilution is one of the critical issues. We examined effectiveness of dipole mode damping in three kinds of X-band, {pi}-mode standing wave structures at 11.424GHz with no detuning considered. They represent three damping schemes: damping with cylindrical iris slot, damping with choke cavity and damping with waveguide coupler. We try to reduce external Q factor below 20 in the first two dipole bands, which usually have very high (R{sub T}/Q){sub T}. The effect of damping on the acceleration mode is also discussed.
Damping and support in high-temperature superconducting levitation systems
Hull, John R.; McIver, Carl R.; Mittleider, John A.
2009-12-15
Methods and apparatuses to provide improved auxiliary damping for superconducting bearings in superconducting levitation systems are disclosed. In a superconducting bearing, a cryostat housing the superconductors is connected to a ground state with a combination of a damping strip of material, a set of linkage arms to provide vertical support, and spring washers to provide stiffness. Alternately, the superconducting bearing may be supported by a cryostat connected to a ground state by posts constructed from a mesh of fibers, with the damping and stiffness controlled by the fiber composition, size, and mesh geometry.
Quasinormal ringing on the brane
NASA Astrophysics Data System (ADS)
Chung, Hyeyoun; Randall, Lisa; Rodriguez, Maria J.; Varela, Oscar
2016-12-01
While the linear behavior of gravity in braneworld models is well understood, much less is known about full nonlinear gravitational effects. Even when they agree at the linear level, these could be expected to distinguish braneworlds from a lower-dimensional theory with no brane. Black holes are a good testing ground for such studies, as they are nonlinear solutions that would be expected to reflect the background geometry. In particular, we assess the role of black hole quasinormal modes (QNMs) in gravitational experiments devised to be sensitive to the existence of the brane, in a lower-dimensional setting where we have analytical control. We compute QNMs of brane-localized black holes and find that they follow the entropy of the corresponding black hole. This observation allows us to conclude that, surprisingly, the scattering problem we consider, at least in some regimes, does not distinguish between nonlinear gravitational effects of black holes in AdS space with a brane and black holes in a spacetime of one lower dimension.
NASA Astrophysics Data System (ADS)
Enpuku, Keiji; Doi, Hideki; Tokita, Go; Maruo, Taku
1994-05-01
The effect of damping resistance on the voltage versus flux (V -Φ) relation of the high T c dc superconducting quantum interference device (SQUID) is studied experimentally. Dc SQUID using YBaCuO step-edge junction and damping resistance in parallel with SQUID inductance is fabricated. Measured values of modulation voltage in the V -Φ relation are compared with those of the conventional SQUID without damping resistance. It is shown that modulation voltage is much improved by using damping resistance. The obtained experimental results agree reasonably with theoretical predictions reported previously.
Quasinormal Modes of Charged Dilaton Black Holes and Their Entropy Spectra
NASA Astrophysics Data System (ADS)
Sakalli, I.
2013-08-01
In this study, we employ the scalar perturbations of the charged dilaton black hole (CDBH) found by Chan, Horne and Mann (CHM), and described with an action which emerges in the low-energy limit of the string theory. A CDBH is neither asymptotically flat (AF) nor non-asymptotically flat (NAF) spacetime. Depending on the value of its dilaton parameter a, it has both Schwarzschild and linear dilaton black hole (LDBH) limits. We compute the complex frequencies of the quasinormal modes (QNMs) of the CDBH by considering small perturbations around its horizon. By using the highly damped QNM in the process prescribed by Maggiore, we obtain the quantum entropy and area spectra of these black holes (BHs). Although the QNM frequencies are tuned by a, we show that the quantum spectra do not depend on a, and they are equally spaced. On the other hand, the obtained value of undetermined dimensionless constant ɛ is the double of Bekenstein's result. The possible reason of this discrepancy is also discussed.
High Resolution Spectra of Low Redshift Damped Lyalpha Absorption Systems
NASA Astrophysics Data System (ADS)
Cohen, R. D.; Beaver, E. A.; Junkkarinen, V. T.; Lyons, R. W.; Smith, H. E.
1998-05-01
We have been able to form a fairly complete picture of the galaxy responsible for the z_a=0.395 absorption line system in PKS 1229--021 by combining Keck HIRES and LRIS spectroscopy with observations taken with the Hubble Space Telescope. The image of the absorber is consistent with the inclined disk of a moderately luminous spiral galaxy. We have not been able to detect the continuum from this galaxy spectroscopically, but our LRIS spectra show emission from [O II] lambda3727 which can be interpreted to be indicative of star formation at the rate of a few M_⊙ per year. The HIRES spectra clearly show an ``edge--leading'' absorption profile. Prochaska and Wolfe have predicted that the velocity of the center of mass of the absorbing galaxy should fall near one edge of the absorption profile if the damped Lyalpha systems are due to the rotating disks of spiral galaxies. The [O II] emission velocity is consistent with this, but there is some ambiguity due to the doublet nature of the [O II] emission. Although the absorption lines of the abundant elements are saturated in the components which correspond to the H I absorption, we have been able to measure accurate column densities for Ca II, Ti II, and Mn II for comparison with the H I column density determined from low resolution HST/FOS spectra. The abundances are compatible with approximately 0.1 of solar, with little or no dust, but they are also consistent with lines of sight toward zeta Oph through warm interstellar clouds. HIRES observations of the z_a=0.692 absorption line system in 3CR 286 will also be discussed, after the data are fully analyzed. This work is part of the Goddard High Resolution Spectrograph Guaranteed Time Observations and is supported by NASA grant NAG5--1858 and the NSF.
Quasinormal modes of near extremal black branes
NASA Astrophysics Data System (ADS)
Starinets, Andrei O.
2002-12-01
We find quasinormal modes of near extremal black branes by solving a singular boundary value problem for the Heun equation. The corresponding eigenvalues determine the dispersion law for the collective excitations in the dual strongly coupled N=4 supersymmetric Yang-Mills theory at finite temperature.
Dynamic Stiffness and Damping Characteristics of a High-Temperature Air Foil Journal Bearing
NASA Technical Reports Server (NTRS)
Howard, Samuel A.; DellaCorte, Christopher; Valco, Mark J.; Prahl, Joseph M.; Heshmat, Hooshang
2001-01-01
Using a high-temperature optically based displacement measurement system, a foil air bearing's stiffness and damping characteristics were experimentally determined. Results were obtained over a range of modified Sommerfeld Number from 1.5E6 to 1.5E7, and at temperatures from 25 to 538 C. An Experimental procedure was developed comparing the error in two curve fitting functions to reveal different modes of physical behavior throughout the operating domain. The maximum change in dimensionless stiffness was 3.0E-2 to 6.5E-2 over the Sommerfeld Number range tested. Stiffness decreased with temperature by as much as a factor of two from 25 to 538 C. Dimensionless damping was a stronger function of Sommerfeld Number ranging from 20 to 300. The temperature effect on damping being more qualitative, showed the damping mechanism shifted from viscous type damping to frictional type as temperature increased.
Numerical study of the quasinormal mode excitation of Kerr black holes
Dorband, Ernst Nils; Diener, Peter; Tiglio, Manuel; Berti, Emanuele; Schnetter, Erik
2006-10-15
We present numerical results from three-dimensional evolutions of scalar perturbations of Kerr black holes. Our simulations make use of a high-order accurate multiblock code which naturally allows for adapted grids and smooth inner (excision) and outer boundaries. We focus on the quasinormal ringing phase, presenting a systematic method for extraction of the quasinormal mode frequencies and amplitudes and comparing our results against perturbation theory. The detection of a single mode in a ringdown waveform allows for a measurement of the mass and spin of a black hole; a multimode detection would allow a test of the Kerr nature of the source. Since the possibility of a multimode detection depends on the relative mode amplitude, we study this topic in some detail. The amplitude of each mode depends exponentially on the starting time of the quasinormal regime, which is not defined unambiguously. We show that this time-shift problem can be circumvented by looking at appropriately chosen relative mode amplitudes. From our simulations we extract the quasinormal frequencies and the relative and absolute amplitudes of corotating and counterrotating modes (including overtones in the corotating case). We study the dependence of these amplitudes on the shape of the initial perturbation, the angular dependence of the mode, and the black hole spin, comparing against results from perturbation theory in the so-called asymptotic approximation. We also compare the quasinormal frequencies from our numerical simulations with predictions from perturbation theory, finding excellent agreement. For rapidly rotating black holes (of spin j=0.98) we can extract the quasinormal frequencies of not only the fundamental mode, but also of the first two overtones. Finally we study under what conditions the relative amplitude between given pairs of modes gets maximally excited and present a quantitative analysis of rotational mode-mode coupling. The main conclusions and techniques of our
High Temperature Damping Behavior of Plasma-Sprayed Thermal Barrier and Protective Coatings
NASA Technical Reports Server (NTRS)
Zhu, Dongming; Miller, Robert A.; Duffy, Kirsten P.; Ghosn, Louis J.
2010-01-01
A high temperature damping test apparatus has been developed using a high heat flux CO 2 laser rig in conjunction with a TIRA S540 25 kHz Shaker and Polytec OFV 5000 Vibrometer system. The test rig has been successfully used to determine the damping performance of metallic and ceramic protective coating systems at high temperature for turbine engine applications. The initial work has been primarily focused on the microstructure and processing effects on the coating temperature-dependence damping behavior. Advanced ceramic coatings, including multicomponent tetragonal and cubic phase thermal barrier coatings, along with composite bond coats, have also been investigated. The coating high temperature damping mechanisms will also be discussed.
Sub-synchronous resonance damping using high penetration PV plant
NASA Astrophysics Data System (ADS)
Khayyatzadeh, M.; Kazemzadeh, R.
2017-02-01
The growing need to the clean and renewable energy has led to the fast development of transmission voltage-level photovoltaic (PV) plants all over the world. These large scale PV plants are going to be connected to power systems and one of the important subjects that should be investigated is the impact of these plants on the power system stability. Can large scale PV plants help to damp sub-synchronous resonance (SSR) and how? In this paper, this capability of a large scale PV plant is investigated. The IEEE Second Benchmark Model aggregated with a PV plant is utilized as the case study. A Wide Area Measurement System (WAMS) based conventional damping controller is designed and added to the main control loop of PV plant in order to damp the SSR and also investigation of the destructive effect of time delay in remote feedback signal. A new optimization algorithm called teaching-learning-based-optimization (TLBO) algorithm has been used for managing the optimization problems. Fast Furrier Transformer (FFT) analysis and also transient simulations of detailed nonlinear system are considered to investigate the performance of the controller. Robustness of the proposed system has been analyzed by facing the system with disturbances leading to significant changes in generator and power system operating point, fault duration time and PV plant generated power. All the simulations are carried out in MATLAB/SIMULINK environment.
MANIFOLD DAMPING OF WAKEFIELDS IN HIGH PHASE ADVANCE LINACS FOR THE NLC
Jones, Roger M
2002-06-20
Earlier RDDS (Rounded Damped Detuned Structures) [1,2], designed, fabricated and tested at SLAC, in collaboration with KEK, have been shown to damp wakefields successfully. However, electrical breakdown has been found to occur in these structures and this makes them inoperable at the desired gradient. Recent results [3] indicate that lowering the group velocity of the accelerating mode reduces electrical breakdown events. In order to preserve the filling time of each structure a high synchronous phase advance (150 degrees as opposed to 120 used in previous NLC designs) has been chosen. Here, damping of the wakefield is analyzed. Manifold damping and interleaving of structure cell frequencies is discussed. These wakefields impose alignment tolerances on the cells and on the structure as a whole. Tolerance calculations are performed and these are compared with analytic estimations.
Dynamic characteristics of Bridgestone low shear modulus-high damping seismic isolation bearings
Chang, Y.W.; Seidensticker, R.W.
1993-06-01
Bridgestone Company of Japan is one of the leading seismic bearing manufacturers in the world. Their bearings have very good performance records. It appears that Bridgestone`s high damping bearings are made of a blend of filled natural and synthetic rubbers with fillers and plastizers whereas in the United States, the high damping compound is a carbon filled natural rubber. To compare the properties of the two different kinds of high damping compounds, Argonne National Laboratory (ANL) purchased eight bearings from Bridgestone: four of which were made of high shear modulus-high damping rubber compound KL401; the other four were made of low shear modulus-high damping rubber compounds: two with KL301 elastomer and two with KL302 elastomer. Tests of the Bridgestone bearings were performed at the Earthquake Engineering Research Center. The dynamic characteristics of the high shear modulus Bridgestone bearings, KL401, are described in ANL/Shimizu Report ANL-003. This report describes the dynamic and failure characteristics of the low shear modulus Bridgestone bearings, KL301 and KL302.
Design of high gradient, high repetition rate damped C -band rf structures
NASA Astrophysics Data System (ADS)
Alesini, David; Bellaveglia, Marco; Bini, Simone; Gallo, Alessandro; Lollo, Valerio; Pellegrino, Luigi; Piersanti, Luca; Cardelli, Fabio; Migliorati, Mauro; Mostacci, Andrea; Palumbo, Luigi; Tocci, Simone; Ficcadenti, Luca; Pettinacci, Valerio
2017-03-01
The gamma beam system of the European Extreme Light Infrastructure-Nuclear Physics project foresees the use of a multibunch train colliding with a high intensity recirculated laser pulse. The linac energy booster is composed of 12 traveling wave C -band structures, 1.8 m long with a field phase advance per cell of 2 π /3 and a repetition rate of 100 Hz. Because of the multibunch operation, the structures have been designed with a dipole higher order mode (HOM) damping system to avoid beam breakup (BBU). They are quasiconstant gradient structures with symmetric input couplers and a very effective damping of the HOMs in each cell based on silicon carbide (SiC) rf absorbers coupled to each cell through waveguides. An optimization of the electromagnetic and mechanical design has been done to simplify the fabrication and to reduce the cost of the structures. In the paper, after a review of the beam dynamics issues related to the BBU effects, we discuss the electromagnetic and thermomechanic design criteria of the structures. We also illustrate the criteria to compensate the beam loading and the rf measurements that show the effectiveness of the HOM damping.
Quasinormal frequencies of self-dual black holes
NASA Astrophysics Data System (ADS)
Santos, Victor; Maluf, R. V.; Almeida, C. A. S.
2016-04-01
One simplified black hole model constructed from a semiclassical analysis of loop quantum gravity (LQG) is called the self-dual black hole. This black hole solution depends on a free dimensionless parameter P known as the polymeric parameter and also on the a0 area related to the minimum area gap of LQG. In the limit of P and a0 going to zero, the usual Schwarzschild solution is recovered. Here we investigate the quasinormal modes (QNMs) of massless scalar perturbations in the self-dual black hole background. We compute the QN frequencies using the sixth-order WKB approximation method and compare them with numerical solutions of the Regge-Wheeler equation. Our results show that, as the parameter P grows, the real part of the QN frequencies suffers an initial increase and then starts to decrease while the magnitude of the imaginary one decreases for fixed area gap a0. This particular feature means that the damping of scalar perturbations in the self-dual black hole spacetimes is slower, and the oscillations are faster or slower according to the value of P .
Seismic response analyses of base isolated structures with high damping elastomeric bearings
Wang, C.Y.; Tang, Y.; Chang, Y.W.; Seidensticker, R.W. ); Marchertas, A.H. )
1991-01-01
Seismic response analysis of base-isolated structures with high damping elastomeric bearings is described. Emphasis is placed on the adaptation of a nonlinear constitutive model for the isolation bearing together with the treatment of foundation embedment for the soil-structure-interaction analysis. The constitutive model requires six input parameters derived from bearing experimental data under sinusoidal loading. The characteristic behavior of bearing, such as the variation of shear modulus and material damping with the change of maximum shear deformation, can be captured closely by the formulation. In the treatment of soil embedment a spring method is utilized to evaluate the foundation input motion as well as soil stiffness and damping. The above features have been incorporated into a three-dimensional system response program, SISEC, developed at Argonne National Laboratory. Sample problems are presented to illustrate the relative response of isolated and unisolated structures. 11 refs., 12 figs.
The effect of vulcanization on dynamic properties of high damping rubber bearing
Murota, Nobuo; Yoshizawa, Toshikazu
1995-12-01
The effect of vulcanization on the dynamic properties of the High Damping Rubber Bearing (HDR) was estimated by shear testing with the ASTM D4014 Tuning Fork (TF) specimens and scale model testing with 225mm diameter HDR isolators. TF specimens, which were vulcanized under various temperature and time conditions, apparently show cure state effect on shear modulus and equivalent damping properties. The same effect was observed with scale models whose cure state were made to correspond to the TF specimens by prediction of heat transfer with F.E.M analysis.
High-damping-performance magnetorheological material for passive or active vibration control
NASA Astrophysics Data System (ADS)
Liu, Taixiang; Yang, Ke; Yan, Hongwei; Yuan, Xiaodong; Xu, Yangguang
2016-10-01
Optical assembly and alignment system plays a crucial role for the construction of high-power or high-energy laser facility, which attempts to ignite fusion reaction and go further to make fusion energy usable. In the optical assembly and alignment system, the vibration control is a key problem needs to be well handled and a material with higher damping performance is much desirable. Recently, a new kind of smart magneto-sensitive polymeric composite material, named magnetorheological plastomer (MRP), was synthesized and reported as a high-performance magnetorheological material and this material has a magneto-enhanced high-damping performance. The MRP behaves usually in an intermediate state between fluid-like magnetorheological fluid and solid-like magnetorheological elastomer. The state of MRP, as well as the damping performance of MRP, can be tuned by adjusting the ratio of hard segments and soft segments, which are ingredients to synthesize the polymeric matrix. In this work, a series of MRP are prepared by dispersing micron-sized, magneto-sensitive carbonyl iron powders with related additives into polyurethane-based, magnetically insensitive matrix. It is found that the damping performance of MRP depends much on magnetic strength, shear rate, carbonyl iron content and shear strain amplitude. Especially, the damping capacity of MRP can be tuned in a large range by adjusting external magnetic field. It is promising that the MRP will have much application in passive and active vibration control, such as vibration reduction in optical assembly and alignment system, vibration isolation or absorption in vehicle suspension system, etc.
TOPICAL REVIEW: Quasinormal modes of black holes and black branes
NASA Astrophysics Data System (ADS)
Berti, Emanuele; Cardoso, Vitor; Starinets, Andrei O.
2009-08-01
Quasinormal modes are eigenmodes of dissipative systems. Perturbations of classical gravitational backgrounds involving black holes or branes naturally lead to quasinormal modes. The analysis and classification of the quasinormal spectra require solving non-Hermitian eigenvalue problems for the associated linear differential equations. Within the recently developed gauge-gravity duality, these modes serve as an important tool for determining the near-equilibrium properties of strongly coupled quantum field theories, in particular their transport coefficients, such as viscosity, conductivity and diffusion constants. In astrophysics, the detection of quasinormal modes in gravitational wave experiments would allow precise measurements of the mass and spin of black holes as well as new tests of general relativity. This review is meant as an introduction to the subject, with a focus on the recent developments in the field.
Collisional damping of helicon waves in a high density hydrogen linear plasma device
Caneses, Juan F.; Blackwell, Boyd D.
2016-09-28
In this paper, we investigate the propagation and damping of helicon waves along the length (~50 cm) of a helicon-produced 20 kW hydrogen plasma ( ~1-2 1019 m-3, ~1-6 eV, H2 8 mTorr) operated in a magnetic mirror configuration (antenna region: 50-200 G and mirror region: 800 G). Experimental results show the presence of traveling helicon waves (~10 G and ~ 10-15 cm) propagating away from the antenna region which become collisionally absorbed within 40 to 50 cm. We describe the use of the WKB method to calculate wave damping and provide an expression to assess its validity based on experimental measurements. By comparing theory and experiment, we show that for the conditions associated with this paper classical collisions are sufficient to explain the observed wave damping along the length of the plasma column. Based on these results, we provide an expression for the scaling of helicon wave damping relevant to high density discharges and discuss the location of surfaces for plasma-material interaction studies in our device (MAGPIE).
Collisional damping of helicon waves in a high density hydrogen linear plasma device
NASA Astrophysics Data System (ADS)
Caneses, Juan F.; Blackwell, Boyd D.
2016-10-01
In this paper, we investigate the propagation and damping of helicon waves along the length (50 cm) of a helicon-produced 20 kW hydrogen plasma ({{n}\\text{e}}˜ 1-2 × 1019 m-3, {{T}\\text{e}}˜ 1-6 eV, H2 8 mTorr) operated in a magnetic mirror configuration (antenna region: 50-200 G and mirror region: 800 G). Experimental results show the presence of traveling helicon waves (4-8 G and {λz}˜ 10-15 cm) propagating away from the antenna region which become collisionally absorbed within 40-50 cm. We describe the use of the WKB method to calculate wave damping and provide an expression to assess its validity based on experimental measurements. Theoretical calculations are consistent with experiment and indicate that for conditions where Coulomb collisions are dominant classical collisionality is sufficient to explain the observed wave damping along the length of the plasma column. Based on these results, we provide an expression for the scaling of helicon wave damping relevant to high density discharges and discuss the location of surfaces for plasma-material interaction studies in helicon based linear plasma devices.
High Harmonic Fast Wave Damping on an Ion Beam: NSTX and DIII-D Regimes Compared
NASA Astrophysics Data System (ADS)
Pinsker, R. I.; Choi, C. C.; Petty, C. C.; Porkolab, M.; Wilson, J. R.; Murakami, M.; Harvey, R. W.
2004-11-01
Both NSTX and DIII-D use the combination of fast Alfven waves (FW) and neutral beam injection (NBI) for central electron heating and current drive. Damping of the fast wave on the beam ions at moderate to high harmonics (4th--20th) of the beam ion cyclotron frequency represents a loss process. In DIII-D current drive experiments at low density in which 4th and 8th harmonics were compared, damping at the 8th harmonic damping was much weaker than at the 4th [1]. However, recent simulations have predicted that in higher density and higher beam power regimes (of interest to the Advanced Tokamak program) the beam ion absorption will transition to the unmagnetized ion regime, where the damping is significant and essentially independent of harmonic number. In the present work, the transition from magnetized to unmagnetized ion regimes for the NSTX and DIII-D HHFW experiments is studied theoretically, with a combination of simple semi-analytic models and numerical models. \\vspace0.25 em [1] C.C. Petty, et al., Plasma Phys. and Contr. Fusion 43, 1747 (2001).
Resonant ultrasound spectroscopy for materials with high damping and samples of arbitrary geometry
Remillieux, Marcel C.; Ulrich, T. J.; Payan, Cédric; Rivière, Jacques; Lake, Colton R.; Le Bas, Pierre -Yves
2015-07-23
This paper describes resonant ultrasound spectroscopy (RUS) as a powerful and established technique for measuring elastic constants of a material with general anisotropy. The first step of this technique consists of extracting resonance frequencies and damping from the vibrational frequency spectrum measured on a sample with free boundary conditions. An inversion technique is then used to retrieve the elastic tensor from the measured resonance frequencies. As originally developed, RUS has been mostly applicable to (i) materials with small damping such that the resonances of the sample are well separated and (ii) samples with simple geometries for which analytical solutions exist. In this paper, these limitations are addressed with a new RUS approach adapted to materials with high damping and samples of arbitrary geometry. Resonances are extracted by fitting a sum of exponentially damped sinusoids to the measured frequency spectrum. The inversion of the elastic tensor is achieved with a genetic algorithm, which allows searching for a global minimum within a discrete and relatively wide solution space. First, the accuracy of the proposed approach is evaluated against numerical data simulated for samples with isotropic symmetry and transversely isotropic symmetry. Subsequently, the applicability of the approach is demonstrated using experimental data collected on a composite structure consisting of a cylindrical sample of Berea sandstone glued to a large piezoelectric disk. In the proposed experiments, RUS is further enhanced by the use of a 3-D laser vibrometer allowing the visualization of most of the modes in the frequency band studied.
Resonant ultrasound spectroscopy for materials with high damping and samples of arbitrary geometry
Remillieux, Marcel C.; Ulrich, T. J.; Payan, Cédric; ...
2015-07-23
This paper describes resonant ultrasound spectroscopy (RUS) as a powerful and established technique for measuring elastic constants of a material with general anisotropy. The first step of this technique consists of extracting resonance frequencies and damping from the vibrational frequency spectrum measured on a sample with free boundary conditions. An inversion technique is then used to retrieve the elastic tensor from the measured resonance frequencies. As originally developed, RUS has been mostly applicable to (i) materials with small damping such that the resonances of the sample are well separated and (ii) samples with simple geometries for which analytical solutions exist.more » In this paper, these limitations are addressed with a new RUS approach adapted to materials with high damping and samples of arbitrary geometry. Resonances are extracted by fitting a sum of exponentially damped sinusoids to the measured frequency spectrum. The inversion of the elastic tensor is achieved with a genetic algorithm, which allows searching for a global minimum within a discrete and relatively wide solution space. First, the accuracy of the proposed approach is evaluated against numerical data simulated for samples with isotropic symmetry and transversely isotropic symmetry. Subsequently, the applicability of the approach is demonstrated using experimental data collected on a composite structure consisting of a cylindrical sample of Berea sandstone glued to a large piezoelectric disk. In the proposed experiments, RUS is further enhanced by the use of a 3-D laser vibrometer allowing the visualization of most of the modes in the frequency band studied.« less
Collisional damping of helicon waves in a high density hydrogen linear plasma device
Caneses, Juan F.; Blackwell, Boyd D.
2016-09-28
In this paper, we investigate the propagation and damping of helicon waves along the length (~50 cm) of a helicon-produced 20 kW hydrogen plasma ( ~1-2 1019 m-3, ~1-6 eV, H2 8 mTorr) operated in a magnetic mirror configuration (antenna region: 50-200 G and mirror region: 800 G). Experimental results show the presence of traveling helicon waves (~10 G and ~ 10-15 cm) propagating away from the antenna region which become collisionally absorbed within 40 to 50 cm. We describe the use of the WKB method to calculate wave damping and provide an expression to assess its validity based onmore » experimental measurements. By comparing theory and experiment, we show that for the conditions associated with this paper classical collisions are sufficient to explain the observed wave damping along the length of the plasma column. Based on these results, we provide an expression for the scaling of helicon wave damping relevant to high density discharges and discuss the location of surfaces for plasma-material interaction studies in our device (MAGPIE).« less
Recovery characteristics of high damping elastomers used in seismic isolation bearings.
Kulak, R. F.
1998-06-02
The protection of nuclear and civil structures from the destructive effects of earthquakes has been the focus of intense research and development throughout the world. Seismic isolation is an effective means for reducing and even eliminating the devastating consequences of earthquakes on people, equipment and structures. Engineers have developed many devices for implementing the seismic isolation strategy and the most effective and economical ones have been identified through the test of time. One of these devices is the laminated elastomeric isolation bearing. The behavior of high damping elastomer bearings during several recent earthquakes has shown that they are a viable device for mitigating the effects of earthquakes. In this paper, results are presented from recent tests on two different elastomers. The first is a highly filled, high modulus, high damping elastomer and the second is a highly-filled, low modulus, high damping elastomer. The stiffness recovery characteristics of the high modulus elastomer subjected to beyond design basis strains and the results of seven years of aging on the low modulus elastomer are presented.
Novel Slide-Ring Material/Natural Rubber Composites with High Damping Property
Wang, Wencai; Zhao, Detao; Yang, Jingna; Nishi, Toshio; Ito, Kohzo; Zhao, Xiuying; Zhang, Liqun
2016-01-01
A novel class of polymers called “slide-ring” (SR) materials with slideable junctions were used for high damping composites for the first time. The SR acts as the high damping phase dispersed in the natural rubber (NR) matrix, and epoxidized natural rubber (ENR) acts as the compatibilizer. The morphological, structural, and mechanical properties of the composites were investigated by atomic force microscope (AFM), transmission electron microscope (TEM), dynamic mechanical thermal analyzer (DMTA), rubber processing analyzer (RPA), and tensile tester. AFM and TEM results showed that the SR phase was uniformly dispersed in the composites, in a small size that is a function of ENR. DMTA and RPA results showed that the damping factor of the composites is much higher than that of NR, especially at room temperatures. Stretch hysteresis was used to study the energy dissipation of the composites at large strains. The results showed that SR and ENR can significantly improve the dissipation efficiency at strains lower than 200% strain. Wide-angle X-ray diffraction was used to study the strain-induced crystallization of the composites. The results indicated that the impact of the SR on the crystallization of NR is mitigated by the insulating effect of ENR. PMID:26949077
Highly compliant shape memory polymer gels for tunable damping and reversible adhesion
NASA Astrophysics Data System (ADS)
Mrozek, Randy A.; Berg, Michael C.; Gold, Christopher S.; Leighliter, Brad; Morton, Jeffrey T.; Lenhart, Joseph L.
2016-02-01
Materials that can dynamically change their properties to better adapt to the local environment have potential utility in robotics, aerospace, and coatings. For some of these applications, most notably robotics, it is advantageous for these responsive materials to be highly compliant in an effort to provide dynamic changes in adhesion and mechanical damping within a broad temperature operational environment. In this report, non-aqueous, highly compliant shape-memory polymer gels are developed by incorporating a low density of chemical cross-links into a physically cross-linked thermoplastic elastomer gel. Chemical cross-linkers were evaluated by varying there size and degree of functionality to determine the impact on the mechanical and adhesive properties. As a result of the chemical cross-linking, the gels exhibit modulus plateaus around room temperature and at elevated temperatures above 100 °C, where the thermoplastic elastomer gel typically melts. The materials were designed so that moduli in the plateaued regions were above and below the Dahlquist criteria of 4 × 104 Pa, respectively, where materials with a modulus below this value typically exhibit an increase in adhesion. The shape memory polymer gels were also integrated into fiber-reinforced composites to determine the temperature-dependent changes in mechanical damping. It is anticipated that this work will provide insight into materials design to provide dynamic changes in adhesion and damping to improve robotic appendage manipulation and platform mobility.
Magneto-induced large deformation and high-damping performance of a magnetorheological plastomer
NASA Astrophysics Data System (ADS)
Liu, Taixiang; Gong, Xinglong; Xu, Yangguang; Pang, Haoming; Xuan, Shouhu
2014-10-01
A magnetorheological plastomer (MRP) is a new kind of soft magneto-sensitive polymeric composite. This work reports on the large magneto-deforming effect and high magneto-damping performance of MRPs under a quasi-statical shearing condition. We demonstrate that an MRP possesses a magnetically sensitive malleability, and its magneto-mechanical behavior can be analytically described by the magneto-enhanced Bingham fluid-like model. The magneto-induced axial stress, which drives the deformation of the MRP with 70 wt % carbonyl iron powder, can be tuned in a large range from nearly 0.0 kPa to 55.4 kPa by an external 662.6 kA m-1 magnetic field. The damping performance of an MRP has a significant correlation with the magnetic strength, shear rate, carbonyl iron content and shear strain amplitude. For an MRP with 60 wt % carbonyl iron powder, the relative magneto-enhanced damping effect can reach as high as 716.2% under a quasi-statically shearing condition. Furthermore, the related physical mechanism is proposed, and we reveal that the magneto-induced, particle-assembled microstructure directs the magneto-mechanical behavior of the MRP.
Novel Slide-Ring Material/Natural Rubber Composites with High Damping Property
NASA Astrophysics Data System (ADS)
Wang, Wencai; Zhao, Detao; Yang, Jingna; Nishi, Toshio; Ito, Kohzo; Zhao, Xiuying; Zhang, Liqun
2016-03-01
A novel class of polymers called “slide-ring” (SR) materials with slideable junctions were used for high damping composites for the first time. The SR acts as the high damping phase dispersed in the natural rubber (NR) matrix, and epoxidized natural rubber (ENR) acts as the compatibilizer. The morphological, structural, and mechanical properties of the composites were investigated by atomic force microscope (AFM), transmission electron microscope (TEM), dynamic mechanical thermal analyzer (DMTA), rubber processing analyzer (RPA), and tensile tester. AFM and TEM results showed that the SR phase was uniformly dispersed in the composites, in a small size that is a function of ENR. DMTA and RPA results showed that the damping factor of the composites is much higher than that of NR, especially at room temperatures. Stretch hysteresis was used to study the energy dissipation of the composites at large strains. The results showed that SR and ENR can significantly improve the dissipation efficiency at strains lower than 200% strain. Wide-angle X-ray diffraction was used to study the strain-induced crystallization of the composites. The results indicated that the impact of the SR on the crystallization of NR is mitigated by the insulating effect of ENR.
NASA Astrophysics Data System (ADS)
Bach, Kiehunn
2017-01-01
Incorporating the time-dependent second-order perturbation theory for the Lyman scattering cross-section, we investigate the intergalactic absorption profiles of extremely high column density systems near the end of cosmic reionization. Assuming a representative set of the redshift distribution of neutral hydrogen, we quantitatively examined the impact of inhomogeneous density on the intrinsic absorption profiles. The cumulative absorption by neutral patches in the line of sight mainly affects the far off-centre region of the red damping wing, but the effect is not significant. The shape of the line centre can be modified by the near-zone distribution due to high opacities of the near-resonance scattering. On the other hand, the HWHM (half width at half-maximum) as an effective line width is relatively less sensitive to the local inhomogeneity. Specifically, when the two local damping wings of Lyα and Lyβ are close in spectra of the strongly damped systems, accurate profiles of both lines are required. In the case of N_{H I}≲ 10^{21} { cm^{-2}}, the two-level approximation is marginally applicable for the damping wing fit within 5 - 7 per cent errors. However, as the local column density reaches N_{H I}˜ 10^{22.3} { cm^{-2}}, this classical approximation yields a relative error of a 10 per cent overestimation in the red wing and a 20 per cent underestimation in the blue wing of Lyα. If severe extinction by the Lyα forests is carefully subtracted, the intrinsic absorption profile will provide a better constraint on the local ionized states. For practical applications, an analytic fitting function for the Lyβ scattering is derived.
Lateral Damping in a Magnet-High T_c SC System
NASA Astrophysics Data System (ADS)
Brunet, Y.; Biarrotte, J. L.; Tixador, P.
1997-03-01
The properties shown by a magnet levitating above a high T_c superconductor pellet can lead to use them in magnetic bearings or other applications such as coupling devices or dampers. The levitation properties and the static stability are well demonstrated but it is not clear if their damping properties are sufficient for applications to avoid any active damping device. The work presented here studies the damping of the oscillations of a magnet above a superconducting pellet, in a pendulum device where displacements and forces are simultaneously measured. Magnet and superconducting pellet dimensions are of the same order. The pulsation of the harmonic motion is governed by the static lateral forces but the damping seems to be dependent on the initial amplitudes. In our configuration, even for the first oscillations, the damping is less efficient than with copper at 77 K, and the small oscillations are quite undamped. Les propriétés de lévitation entre un aimant permanent et un supraconducteur massif à haute température critique permettent d'envisager leur utilisation dans des paliers magnétiques ou dans d'autres applications (coupleurs, amortisseurs). Si leurs propriétés de lévitation et de stabilité statique sont démontrées, une des clés de leur application est leur stabilité dynamique, qui doit permettre de réaliser des dispositifs entièrement passifs performants. Ce travail présente une étude de l'amortissement à l'aide d'un dispositif permettant de mesurer en même temps les oscillations et les forces entre un aimant vibrant librement au-dessus d'une pastille supraconductrice, les deux éléments ayant des tailles analogues. La pulsation du mouvement harmonique amorti vérifie bien un comportement dans lequel les forces latérales modifient la pulsation propre, les propriétés d'amortissement paraissent non linéaires et dépendent de l'amplitude des oscillations. Dans notre configuration, même en prenant les premières oscillations, l
The Eikonal Quasinormal Modes of Kerr-Newman Black Holes
NASA Astrophysics Data System (ADS)
Mark, Zachary; Yang, Huan; Zimmerman, Aaron; Chen, Yanbei
2015-04-01
Due to the complicated coupling between gravity and electromagnetism near a Kerr-Newman black hole, a master, separable equation governing gravitational or electromagnetic perturbations has yet to be discovered, impeding efforts to calculate the quasinormal modes of perturbed black holes with arbitrary spin and charge. Instead, gravitational and electromagnetic perturbations are found to obey a pair of coupled, partial differential equations. To study the quasinormal modes, we examine these equations in the eikonal limit (where the waves are rapidly changing in space and time) via a newly developed WKB technique capable of handling coupled wave equations. Surprisingly, it turns out that an approximate master equation introduced by Dudley and Finley provides an accurate description of perturbations in the eikonal regime. These techniques allow the ``geometric correspondence'' between quasinormal modes and photon geodesics that is known to be true for Kerr black holes to be extended to Kerr-Newman black holes.
Quasi-Normal Modes of Stars and Black Holes.
Kokkotas, Kostas D; Schmidt, Bernd G
1999-01-01
Perturbations of stars and black holes have been one of the main topics of relativistic astrophysics for the last few decades. They are of particular importance today, because of their relevance to gravitational wave astronomy. In this review we present the theory of quasi-normal modes of compact objects from both the mathematical and astrophysical points of view. The discussion includes perturbations of black holes (Schwarzschild, Reissner-Nordström, Kerr and Kerr-Newman) and relativistic stars (non-rotating and slowly-rotating). The properties of the various families of quasi-normal modes are described, and numerical techniques for calculating quasi-normal modes reviewed. The successes, as well as the limits, of perturbation theory are presented, and its role in the emerging era of numerical relativity and supercomputers is discussed.
On the Possibility of Using Nonlinear Elements for Landau Damping in High-Intensity Beams
Alexahin, Y.; Gianfelice-Wendt, E.; Lebedev, V.; Valishev, A.
2016-09-30
Direct space-charge force shifts incoherent tunes downwards from the coherent ones breaking the Landau mechanism of coherent oscillations damping at high beam intensity. To restore it nonlinear elements can be employed which move back tunes of large amplitude particles. In the present report we consider the possibility of creating a “nonlinear integrable optics” insertion in the Fermilab Recycler to host either octupoles or hollow electron lens for this purpose. For comparison we also consider the classic scheme with distributed octupole families. It is shown that for the Proton Improvement Plan II (PIP II) parameters the required nonlinear tune shift can be created without destroying the dynamic aperture.
Second-order quasinormal mode of the Schwarzschild black hole
NASA Astrophysics Data System (ADS)
Nakano, Hiroyuki; Ioka, Kunihito
2007-10-01
We formulate and calculate the second-order quasinormal modes (QNMs) of a Schwarzschild black hole (BH). Gravitational waves (GW) from a distorted BH, the so-called ringdowns, are well understood as QNMs in general relativity. Since QNMs from binary BH mergers will be detected with a high signal-to-noise ratio by GW detectors, it is also possible to detect the second perturbative order of QNMs, generated by nonlinear gravitational interaction near the BH. In the BH perturbation approach, we derive the master Zerilli equation for the metric perturbation to second order and explicitly regularize it at the horizon and spatial infinity. We numerically solve the second-order Zerilli equation by implementing the modified Leaver continued fraction method. The second-order QNM frequencies are found to be twice the first-order ones, and the GW amplitude is up to ˜10% that of the first order for the binary BH mergers. Since the second-order QNMs always exist, we can use their detections (i) to test the nonlinearity of general relativity, in particular, the no-hair theorem, (ii) to remove fake events in the data analysis of QNM GWs, and (iii) to measure the distance to the BH.
Morphology-controlled ZnO nanowire arrays for tailored hybrid composites with high damping.
Malakooti, Mohammad H; Hwang, Hyun-Sik; Sodano, Henry A
2015-01-14
Hybrid fiber reinforced composites using a nanoscale reinforcement of the interface have not reached their optimal performance in practical applications due to their complex design and the challenging assembly of their multiscale components. One promising approach to the fabrication of hybrid composites is the growth of zinc oxide (ZnO) nanowire arrays on the surface of carbon fibers to provide improved interfacial strength and out of plane reinforcement. However, this approach has been demonstrated mainly on fibers and thus still requires complex processing conditions. Here we demonstrate a simple approach to the fabrication of such composites through the growth of the nanowires on the fabric. The fabricated composites with nanostructured graded interphase not only exhibit remarkable damping enhancement but also stiffness improvement. It is demonstrated that these two extremely important properties of the composite can be controlled by tuning the morphology of the ZnO nanowires at the interface. Higher damping and flexural rigidity of these composites over traditional ones offer practical high-performance composites.
Characterization of high damping bearings and their responses to earthquake motions
Wu, Ting-shu; Seidensticker, R.W.
1990-01-01
An isolation system consisting of six (6) laminated high-damping rubber bearings has been installed in a test facility on the Tohoku University site in Sendai, Japan. The isolation system is designed to have a frequency of 0.75 Hz. This frequency, however, is obtained only when there is a strong earthquake, resulting in significant horizontal displacements. After the installation of this system, in April 1989, static and dynamic tests were performed to obtained fundamental dynamic response properties of the system. The day after these tests were completed, an earthquake of magnitude M = 4.9 occurred in the area. The maximum acceleration experienced by the building was only about 0.03 g. Several other earthquakes have occurred since then, all of which resulted in low input acceleration at the Tohoku facility. Analytical investigations for the building have been carried out using a model with stiffness and damping of the isolation system obtained from the in-situ tests. Response of the simulated model to this earthquake show good agreement with the recorded data at each floor of the isolated building. Both the recorded data and the analytical results indicate that the bearings installed in this building are stiff enough to prevent drift of the superstructure under minor tremors or wind loads. Results of all in-situ tests are presented. 5 refs., 10 figs., 1 tab.
Excitation, propagation and damping of helicon waves in a high density, low temperature plasma
NASA Astrophysics Data System (ADS)
Caneses, J. F.; Blackwell, B. D.
2015-11-01
The MAGnetized Plasma Interaction Experiment (MAGPIE) is a helicon linear plasma device built to study fusion relevant plasma-surface interactions. In this work, we investigate helicon wave propagation in high density (1018-1019 m-3) low temperature (2-4 eV) magnetized (50-200 G) hydrogen plasma produced by a half-helical antenna operated at 7 MHz and 20 kW. Using the cold dielectric tensor with collisional terms (electron-neutral and Coulomb), helicon wave damping is calculated along the length of MAGPIE using a WKB approximation. Comparison with experiment indicates that wave damping, under these conditions, is entirely collisional. Numerical results from a fully electromagnetic wave code and 2D wavefield measurements indicate that helicon waves are excited at the plasma edge by the antenna's transverse current straps while the helical straps play a secondary role. These waves propagate towards the center of the discharge along the whistler wave ray direction (19 degrees to the background magnetic field), interfere on-axis and form the axial interference pattern commonly observed in helicon devices.
Quasinormal modes of Reissner-Nordstrom black holes
NASA Technical Reports Server (NTRS)
Leaver, Edward W.
1990-01-01
A matrix-eigenvalue algorithm is presented for accurately computing the quasi-normal frequencies and modes of charged static blackholes. The method is then refined through the introduction of a continued-fraction step. The approach should generalize to a variety of nonseparable wave equations, including the Kerr-Newman case of charged rotating blackholes.
Damped Ly alpha absorbers at high redshift: Large disks or galactic building blocks?
NASA Technical Reports Server (NTRS)
Haehnelt, Martin G.; Steinmetz, Matthias; Rauch, Michael
1997-01-01
The nature of the physical structures giving rise to damped Lyman alpha absorption systems (DLAS) at high redshifts is investigated. The proposal that rapidly rotating large disks are the only viable explanation for the observed asymmetric profiles of low ionization absorption lines is examined. Using hydrodynamic simulations of galaxy formation, it is demonstated that irregular protogalactic clumps can reproduce the observed velocity width distribution and asymmetries of the absorption profiles equally well. The velocity broadening in the simulated clumps is due to a mixture of rotation, random motions, infall and merging. The observed velocity width correlates with the virial velocity for the dark matter halo of the forming protogalactic clump. The typical virial velocity of the halos required to lead to the DLAS population is approximately 100 km/s. It is concluded that the evidence that DLAS at high redshift are related to large, rapidly rotating disks, is not compelling.
ERIC Educational Resources Information Center
Fay, Temple H.
2012-01-01
Quadratic friction involves a discontinuous damping term in equations of motion in order that the frictional force always opposes the direction of the motion. Perhaps for this reason this topic is usually omitted from beginning texts in differential equations and physics. However, quadratic damping is more realistic than viscous damping in many…
Validation of High-Resolution CFD Method for Slosh Damping Extraction of Baffled Tanks
NASA Technical Reports Server (NTRS)
Yang, H. Q.; West, Jeff
2016-01-01
The predicted slosh damping values from Loci-Stream-VOF agree with experimental data very well for all fill levels in the vicinity of the baffle. Grid refinement study is conducted and shows that the current predictions are grid independent. The increase of slosh damping due to the baffle is shown to arise from: a) surface breakup; b) cascade of energy from the low order slosh mode to higher modes; and c) recirculation inside liquid phase around baffle. The damping is a function of slosh amplitude, consistent with previous observation. Miles equation under predicts damping in the upper dome section.
NASA Astrophysics Data System (ADS)
Oh, J.; Ray, Manas C.; Baz, Amr M.
2001-07-01
Engineered Damping Treatments (EDT) that have high damping characteristics per unit volume are presented. The EDT's under consideration, consist of cellular viscoelastic damping matrices with optimally selected cell configuration, size and distribution. The cellular topology of the EDT's is designed using Computer-Aided-Design (CAD) strategies and the obtained optimal configurations will be manufactured using the state-of-the-art technology of Rapid Prototyping (RP). The EDT's are modeled using the finite element method in an attempt to determine the optimal topologies that maximize the strain energy, maximize the damping characteristics and minimize the total weight. The CAD files of the prototypes of the EDT's. The damping characteristics of the manufactured EDT's are evaluated and compared with the corresponding characteristics obtained by conventional solid damping treatments in order to emphasize the importance of using optimally configured damping treatment to achieve high damping characteristics. The presented procedures are invaluable for designing efficient damping treatments for many military and civilian structures whose vibrations and noise must be effectively controlled.
Validation of High-Resolution CFD Method for Slosh Damping Extraction of Baffled Tanks
NASA Technical Reports Server (NTRS)
Yang, H. Q.; West, Jeff
2016-01-01
Determination of slosh damping is a very challenging task as there is no analytical solution. The damping physics involve the vorticity dissipation which requires the full solution of the nonlinear Navier-Stokes equations. As a result, previous investigations and knowledge were mainly carried out by extensive experimental studies. A Volume-Of-Fluid (VOF) based CFD program developed at NASA MSFC was applied to extract slosh damping in a baffled tank from the first principle. First, experimental data using water with subscale smooth wall tank were used as the baseline validation. CFD simulation was demonstrated to be capable of accurately predicting natural frequency and very low damping value from the smooth wall tank at different fill levels. The damping due to a ring baffle at different liquid fill levels from barrel section and into the upper dome was then investigated to understand the slosh damping physics due to the presence of a ring baffle. Based on this study, the Root-Mean-Square error of our CFD simulation in estimating slosh damping was less than 4.8%, and the maximum error was less than 8.5%. Scalability of subscale baffled tank test using water was investigated using the validated CFD tool, and it was found that unlike the smooth wall case, slosh damping with baffle is almost independent of the working fluid and it is reasonable to apply water test data to the full scale LOX tank when the damping from baffle is dominant. On the other hand, for the smooth wall, the damping value must be scaled according to the Reynolds number. Comparison of experimental data, CFD, with the classical and modified Miles equations for upper dome was made, and the limitations of these semi-empirical equations were identified.
NASA Technical Reports Server (NTRS)
Ku, C.-P. Roger; Walton, James F., Jr.; Lund, Jorgen W.
1994-01-01
This paper provided an opportunity to quantify the angular stiffness and equivalent viscous damping coefficients of an axial spline coupling used in high-speed turbomachinery. A unique test methodology and data reduction procedures were developed. The bending moments and angular deflections transmitted across an axial spline coupling were measured while a nonrotating shaft was excited by an external shaker. A rotor dynamics computer program was used to simulate the test conditions and to correlate the angular stiffness and damping coefficients. In addition, sensitivity analyses were performed to show that the accuracy of the dynamic coefficients do not rely on the accuracy of the data reduction procedures.
Aseeva, N. V. Gromov, E. M.; Tyutin, V. V.
2015-12-15
The dynamics of high-frequency field solitons is considered using the extended nonhomogeneous nonlinear Schrödinger equation with induced scattering from damped low-frequency waves (pseudoinduced scattering). This scattering is a 3D analog of the stimulated Raman scattering from temporal spatially homogeneous damped low-frequency modes, which is well known in optics. Spatial inhomogeneities of secondorder linear dispersion and cubic nonlinearity are also taken into account. It is shown that the shift in the 3D spectrum of soliton wavenumbers toward the short-wavelength region is due to nonlinearity increasing in coordinate and to decreasing dispersion. Analytic results are confirmed by numerical calculations.
Harnessing the damping properties of materials for high-speed atomic force microscopy
NASA Astrophysics Data System (ADS)
Adams, Jonathan D.; Erickson, Blake W.; Grossenbacher, Jonas; Brugger, Juergen; Nievergelt, Adrian; Fantner, Georg E.
2016-02-01
The success of high-speed atomic force microscopy in imaging molecular motors, enzymes and microbes in liquid environments suggests that the technique could be of significant value in a variety of areas of nanotechnology. However, the majority of atomic force microscopy experiments are performed in air, and the tapping-mode detection speed of current high-speed cantilevers is an order of magnitude lower in air than in liquids. Traditional approaches to increasing the imaging rate of atomic force microscopy have involved reducing the size of the cantilever, but further reductions in size will require a fundamental change in the detection method of the microscope. Here, we show that high-speed imaging in air can instead be achieved by changing the cantilever material. We use cantilevers fabricated from polymers, which can mimic the high damping environment of liquids. With this approach, SU-8 polymer cantilevers are developed that have an imaging-in-air detection bandwidth that is 19 times faster than those of conventional cantilevers of similar size, resonance frequency and spring constant.
High damping properties of magnetic particles doped rubber composites at wide frequency
Tian, Ye; Liu, Yaqing; He, Minhong; Zhao, Guizhe; Sun, Youyi
2013-05-15
Highlights: ► A new kind of permanent magnetic rubber was prepared. ► The microstructure and magnetic properties were investigated. ► The mechanical and damping properties were discussed. ► The new material is expected to be an isolator material to a changed frequency. - Abstract: A new kind of rubber composite was prepared by doping SrFe{sub 12}O{sub 19} nanoparticles coated with silane coupling agents (Si-69) into nitrile butadiene rubber (NBR) matrix, which was characterized by the scanning electron microscopy and X-ray spectroscopy. The results showed that the SrFe{sub 12}O{sub 19} nanoparticles were well dispersed in rubber matrix. Furthermore, the mechanical and magnetic properties of the rubber composites were investigated, in which the high tensile strength (15.8 MPa) and high saturation magnetization (22.9 emu/g) were observed. What is more, the high loss factor of the rubber composites was also obtained in a wide frequency range (0–100 Hz) at high loading (80 phr). The result is attributed to that the permanent magnetic field in rubber nanocomposites can absorb shock energy. These results indicate that the new kind of permanent magnetic rubber is expected to be a smart isolator material, in which the isolator will be able to adapt to a changed frequency.
Quasinormal modes and classical wave propagation in analogue black holes
Berti, Emanuele; Cardoso, Vitor; Lemos, Jose P.S.
2004-12-15
Many properties of black holes can be studied using acoustic analogues in the laboratory through the propagation of sound waves. We investigate in detail sound wave propagation in a rotating acoustic (2+1)-dimensional black hole, which corresponds to the 'draining bathtub' fluid flow. We compute the quasinormal mode frequencies of this system and discuss late-time power-law tails. Because of the presence of an ergoregion, waves in a rotating acoustic black hole can be superradiantly amplified. We also compute superradiant reflection coefficients and instability time scales for the acoustic black hole bomb, the equivalent of the Press-Teukolsky black hole bomb. Finally we discuss quasinormal modes and late-time tails in a nonrotating canonical acoustic black hole, corresponding to an incompressible, spherically symmetric (3+1)-dimensional fluid flow.
NASA Astrophysics Data System (ADS)
Nguyen, Q. H.; Choi, S. B.; Lee, Y. S.; Han, M. S.
2013-11-01
This paper focuses on the optimal design of a compact and high damping force engine mount featuring magnetorheological fluid (MRF). In the mount, a MR valve structure with both annular and radial flows is employed to generate a high damping force. First, the configuration and working principle of the proposed MR mount is introduced. The MRF flows in the mount are then analyzed and the governing equations of the MR mount are derived based on the Bingham plastic behavior of the MRF. An optimal design of the MR mount is then performed to find the optimal structure of the MR valve to generate a maximum damping force with certain design constraints. In addition, the gap size of MRF ducts is empirically chosen considering the ‘lockup’ problem of the mount at high frequency. Performance of the optimized MR mount is then evaluated based on finite element analysis and discussions on performance results of the optimized MR mount are given. The effectiveness of the proposed MR engine mount is demonstrated via computer simulation by presenting damping force and power consumption.
Piezoelectric Shunt Vibration Damping of F-15 Panel under High Acoustic Excitation
NASA Technical Reports Server (NTRS)
Wu, Shu-Yau; Turner, Travis L.; Rizzi, Stephen A.
2000-01-01
At last year's SPIE symposium, we reported results of an experiment on structural vibration damping of an F-15 underbelly panel using piezoelectric shunting with five bonded PZT transducers. The panel vibration was induced with an acoustic speaker at an overall sound pressure level (OASPL) of about 90 dB. Amplitude reductions of 13.45 and 10.72 dB were achieved for the first and second modes, respectively, using single- and multiple-mode shunting. It is the purpose of this investigation to extend the passive piezoelectric shunt-damping technique to control structural vibration induced at higher acoustic excitation levels, and to examine the controllability and survivability of the bonded PZT transducers at these high levels. The shunting experiment was performed with the Thermal Acoustic Fatigue Apparatus (TAFA) at the NASA Langley Research Center using the same F-15 underbelly panel. The TAFA is a progressive wave tube facility. The panel was mounted in one wall of the TAFA test section using a specially designed mounting fixture such that the panel was subjected to grazing-incidence acoustic excitation. Five PZT transducers were used with two shunt circuits designed to control the first and second modes of the structure between 200 and 400 Hz. We first determined the values of the shunt inductance and resistance at an OASPL of 130 dB. These values were maintained while we gradually increased the OASPL from 130 to 154 dB in 6-dB steps. During each increment, the frequency response function between accelerometers on the panel and the acoustic excitation measured by microphones, before and after shunting, were recorded. Good response reduction was observed up to the 148dB level. The experiment was stopped at 154 dB due to wire breakage from vibration at a transducer wire joint. The PZT transducers, however, were still bonded well on the panel and survived at this high dB level. We also observed shifting of the frequency peaks toward lower frequency when the OASPL
ERIC Educational Resources Information Center
Fay, Temple H.
2012-01-01
Viscous damping is commonly discussed in beginning differential equations and physics texts but dry friction or Coulomb friction is not despite dry friction being encountered in many physical applications. One reason for avoiding this topic is that the equations involve a jump discontinuity in the damping term. In this article, we adopt an energy…
High damping NiTi/Ti_{3}Sn in situ composite with transformation-mediated plasticity
Zhang, Junsong; Liu, Yinong; Huan, Yong; Hao, Shijie; Jiang, Daqiang; Ren, Yang; Shao, Yang; Ru, Yadong; Wang, Zhongqiang; Cui, Lishan
2014-11-01
The concept of transformation-induced plasticity effect is introduced in this work to improve the plasticity of brittle intermetallic compound Ti3Sn, which is a potent high damping material. This concept is achieved in an in situ NiTi/Ti3Sn composite. The composite is composed of primary Ti3Sn phase and (NiTi + Ti3Sn) eutectic structure formed via hypereutectic solidification. The composite exhibits a high damping capacity of 0.075 (indexed by tan δ), a high ultimate compressive strength of 1350 MPa, and a large plasticity of 27.5%. In situ synchrotron high-energy X-ray diffraction measurements revealed clear evidence of the stress-induced martensitic transformation (B2 → B19) of the NiTi component during deformation. The strength of the composite mainly stems from the Ti3Sn, whereas the NiTi component is responsible for the excellent plasticity of the composite.
The Lyα emission from high- z galaxies hosting strong damped Lyα systems
NASA Astrophysics Data System (ADS)
Joshi, Ravi; Srianand, Raghunathan; Noterdaeme, Pasquier; Petitjean, Patrick
2017-02-01
We study the average Lyα emission associated with high-z strong (log N(H I) ≥ 21) damped Lyα systems (DLAs). We report Lyα luminosities (LLyα) for the full as well as various sub-samples based on N(H I), z, (r - i) colours of QSOs and rest equivalent width of Si IIλ1526 line (i.e. W1526). For the full sample, we find LLyα < 1041(3σ) erg s- 1 with a 2.8σ level detection of Lyα emission in the red part of the DLA trough. The LLyα is found to be higher for systems with higher W1526 with its peak, detected at ≥3σ, redshifted by about 300-400 km s-1 with respect to the systemic absorption redshift, as seen in Lyman break galaxies (LBGs) and Lyα emitters. A clear signature of a double-hump Lyα profile is seen when we consider W1526 ≥0.4 Å and (r - i) < 0.05. Based on the known correlation between metallicity and W1526, we interpret our results in terms of star formation rate (SFR) being higher in high-metallicity (mass) galaxies with high velocity fields that facilitates easy Lyα escape. The measured Lyα surface brightness requires local ionizing radiation that is 4-10 times stronger than the metagalactic UV background at these redshifts. The relationship between the SFR and surface mass density of atomic gas seen in DLAs is similar to that of local dwarf and metal-poor galaxies. We show that the low-luminosity galaxies will contribute appreciably to the stacked spectrum if the size-luminosity relation seen for H I at low z is also present at high-z. Alternatively, large Lyα haloes seen around LBGs could also explain our measurements.
High temperature dynamic modulus and damping of aluminum and titanium matrix composites
NASA Technical Reports Server (NTRS)
Dicarlo, J. A.; Maisel, J. E.
1979-01-01
Dynamic modulus and damping capacity property data were measured from 20 to over 500 C for unidirectional B/Al (1100), B/Al (6061), B/SiC/Al (6061), Al2O3/Al, SiC/Ti-6Al-4V, and SiC/Ti composites. The measurements were made under vacuum by the forced vibration of composite bars at free-free flexural resonance near 2000 Hz and at amplitudes below 0.000001. Whereas little variation was observed in the dynamic moduli of specimens with approximately the same fiber content (50 percent), the damping of B/Al composites was found at all temperatures to be significantly greater than the damping of the Al2O3/Al and SiC/Ti composites. For those few situations where slight deviations from theory were observed, the dynamic data were examined for information concerning microstructural changes induced by composite fabrication and thermal treatment. The 270 C damping peak observed in B/Al (6061) composites after heat treatment above 460 C appears to be the result of a change in the 6061 aluminum alloy microstructure induced by interaction with the boron fibers. The growth characteristics of the damping peak suggest its possible value for monitoring fiber strength degration caused by excess thermal treatment during B/Al (6061) fabrication and use.
Quasinormal modes of asymptotically (A)dS black hole in Lovelock background
NASA Astrophysics Data System (ADS)
Abbasvandi, N.; Soleimani, M. J.; Abdullah, W. A. T. Wan; Radiman, Shahidan
2017-03-01
We study the quasinormal modes of the massless scalar field in asymptotically (A)dS black holes in Lovelock spacetime by using the sixth order of the WKB approximation. We consider the effects of the second and third order of Lovelock coupling constants on quasinormal frequencies spectrum as well as cosmological constant.
The first detection of [OIII] emission from high-redshift damped Lyman-α galaxies
NASA Astrophysics Data System (ADS)
Weatherley, S. J.; Warren, S. J.; Møller, P.; Fall, S. M.; Fynbo, J. U.; Croom, S. M.
2005-04-01
We present the detection of [OIII] emission lines from the galaxies responsible for two high-redshift z > 1.75 damped Lyman-α (DLA) absorption lines. We find two sources of [OIII] emission corresponding to the z= 1.92 DLA absorber towards the quasar Q2206-1958, and we also detect [OIII] emission from the galaxy responsible for the z= 3.10 DLA absorber towards the quasar 2233.9+1381. These are the first detections of rest-frame optical emission lines from high-redshift DLA galaxies. Unlike the Lyα line, the [OIII] line provides a measure of the systemic velocity of the galaxy. We compare the [OIII] redshifts with the velocity profile of the low-ionization metal lines in these two absorbers, with the goal of distinguishing between the model of Prochaska and Wolfe of DLA absorbers as large rapidly rotating cold thick discs, and the standard hierarchical cold dark matter model of structure formation, in which DLAs arise in protogalactic fragments. We find some discrepancies with the predictions of the former model. Furthermore, the image of the DLA galaxy towards Q2206-1958 shows a complex disturbed morphology, which is more in accord with the hierarchical picture. We use the properties of the rest-frame optical emission lines to further explore the question posed by Møller et al.: are high-redshift DLA galaxies Lyman-break galaxies (LBGs) selected by gas cross-section? The measured velocity dispersions of the DLA galaxies are in agreement with this picture, while the data on the [OIII] luminosities and the velocity differences between the Lyα and [OIII] lines are inconclusive, as there are insufficient LBG measurements overlapping in luminosity. Finally, we estimate the star formation rates in these two DLA galaxies, using a variety of diagnostics, and include a discussion of the extent to which the [OIII] line is useful for this purpose.
NASA Technical Reports Server (NTRS)
Yang, H. Q.; West, Jeff
2016-01-01
Propellant slosh is a potential source of disturbance critical to the stability of space vehicles. The slosh dynamics are typically represented by a mechanical model of a spring-mass-damper. This mechanical model is then included in the equation of motion of the entire vehicle for Guidance, Navigation and Control analysis. A Volume-Of-Fluid (VOF) based Computational Fluid Dynamics (CFD) program developed at MSFC was applied to extract slosh damping in the baffled tank from the first principle. First the experimental data using water with sub-scale smooth wall tank were used as the baseline validation. It is demonstrated that CFD can indeed accurately predict low damping values from the smooth wall at different fill levels. The damping due to a ring baffles at different depths from the free surface was then simulated, and fairly good agreement with experimental measurement was observed. Comparison with an empirical correlation of Miles equation is also made.
Controllable damping of high-Q violin modes in fused silica suspension fibers
NASA Astrophysics Data System (ADS)
Dmitriev, A. V.; Mescheriakov, S. D.; Tokmakov, K. V.; Mitrofanov, V. P.
2010-01-01
Fused silica fiber suspension of the test masses will be used in the interferometric gravitational wave detectors of the next generation. This allows a significant reduction of losses in the suspension and thermal noise associated with the suspension. Unfortunately, unwanted violin modes may be accidentally excited in the suspension fibers. The Q-factor of the violin modes also exceeds 108. They have a ring-down time that is too long and may complicate the stable control of the interferometer. Results of the investigation of a violin mode active damping system are described. An original sensor and actuator were especially developed to realize the effective coupling of a thin, optically transparent, non-conducting fused silica fiber with an electric circuit. The damping system allowed the changing of the violin mode's damping rate over a wide range.
NASA Astrophysics Data System (ADS)
Wang, Xian-Ping; Zhang, Yi; Xia, Yu; Jiang, Wei-Bing; Liu, Hui; Liu, Wang; Gao, Yun-Xia; Zhang, Tao; Fang, Qian-Feng
2016-12-01
A novel micro-vibration sensitive-type high-damping Al matrix composites reinforced with Li7-xLa3Zr2-xNbxO12 (LLZNO, x = 0.25) was designed and prepared using an advanced spark plasma sintering (SPS) technique. The damping capacity and mechanical properties of LLZNO/Al composites (LLZNO content: 0-40 wt.%) were found to be greatly improved by the LLZNO addition. The maximum damping capacity and the ultimate tensile strength (UTS) of LLZNO/Al composite can be respectively up to 0.033 and 101.2 MPa in the case of 20 wt.% LLZNO addition. The enhancement of damping and mechanical properties of the composites was ascribed to the intrinsic high-damping capacity and strengthening effects of hard LLZNO particulate. This investigation provides a new insight to sensitively suppress micro-vibration of payloads in the aerospace environment.
NASA Astrophysics Data System (ADS)
Wang, Xian-Ping; Zhang, Yi; Xia, Yu; Jiang, Wei-Bing; Liu, Hui; Liu, Wang; Gao, Yun-Xia; Zhang, Tao; Fang, Qian-Feng
2017-03-01
A novel micro-vibration sensitive-type high-damping Al matrix composites reinforced with Li7- x La3Zr2- x Nb x O12 (LLZNO, x = 0.25) was designed and prepared using an advanced spark plasma sintering (SPS) technique. The damping capacity and mechanical properties of LLZNO/Al composites (LLZNO content: 0-40 wt.%) were found to be greatly improved by the LLZNO addition. The maximum damping capacity and the ultimate tensile strength (UTS) of LLZNO/Al composite can be respectively up to 0.033 and 101.2 MPa in the case of 20 wt.% LLZNO addition. The enhancement of damping and mechanical properties of the composites was ascribed to the intrinsic high-damping capacity and strengthening effects of hard LLZNO particulate. This investigation provides a new insight to sensitively suppress micro-vibration of payloads in the aerospace environment.
Prediction of Liquid Slosh Damping Using a High Resolution CFD Tool
NASA Technical Reports Server (NTRS)
Yang, H. Q.; Purandare, Ravi; Peugeot, John; West, Jeff
2012-01-01
Propellant slosh is a potential source of disturbance critical to the stability of space vehicles. The slosh dynamics are typically represented by a mechanical model of a spring mass damper. This mechanical model is then included in the equation of motion of the entire vehicle for Guidance, Navigation and Control analysis. Our previous effort has demonstrated the soundness of a CFD approach in modeling the detailed fluid dynamics of tank slosh and the excellent accuracy in extracting mechanical properties (slosh natural frequency, slosh mass, and slosh mass center coordinates). For a practical partially-filled smooth wall propellant tank with a diameter of 1 meter, the damping ratio is as low as 0.0005 (or 0.05%). To accurately predict this very low damping value is a challenge for any CFD tool, as one must resolve a thin boundary layer near the wall and must minimize numerical damping. This work extends our previous effort to extract this challenging parameter from first principles: slosh damping for smooth wall and for ring baffle. First the experimental data correlated into the industry standard for smooth wall were used as the baseline validation. It is demonstrated that with proper grid resolution, CFD can indeed accurately predict low damping values from smooth walls for different tank sizes. The damping due to ring baffles at different depths from the free surface and for different sizes of tank was then simulated, and fairly good agreement with experimental correlation was observed. The study demonstrates that CFD technology can be applied to the design of future propellant tanks with complex configurations and with smooth walls or multiple baffles, where previous experimental data is not available.
NASA Astrophysics Data System (ADS)
Yu, Miao; Qi, Song; Fu, Jie; Zhu, Mi
2015-09-01
A high-damping magnetorheological elastomer (MRE) with bi-directional magnetic-control modulus is developed. This MRE was synthesized by filling NdFeB particles into polyurethane (PU)/ epoxy (EP) interpenetrating network (IPN) structure. The anisotropic samples were prepared in a permanent magnetic field and magnetized in an electromagnetic field of 1 T. Dynamic mechanical responses of the MRE to applied magnetic fields are investigated through magneto-rheometer, and morphology of MREs is observed via scanning electron microscope (SEM). Test result indicates that when the test field orientation is parallel to that of the sample's magnetization, the shear modulus of sample increases. On the other hand, when the orientation is opposite to that of the sample's magnetization, shear modulus decreases. In addition, this PU/EP IPN matrix based MRE has a high-damping property, with high loss factor and can be controlled by applying magnetic field. It is expected that the high damping property and the ability of bi-directional magnetic-control modulus of this MRE offer promising advantages in seismologic application.
Itacolumite like High Damping Ceramics in the System Al2O3-TiO2-MgO
Shimazu, T.; Miura, M.; Isu, N.; Ogawa, T.; Ichikawa, A.; Ishida, E. H.
2006-05-15
Ceramics is rigid and brittle originally. If the weakness could be overcome, the application will be widely expanded. Itacolumite known as high flexibility rock is the group of sand stone which consist of quartz and slight amount of muscovite. The microstructure of itacolumite has a lot of narrow gaps between the grains, the gap was thought to be formed by the dissolution of minerals in between quartz grains into the groundwater. This narrow space enables a little displacement of the particles, and the rock can bend with stress like plastic deformation. These characters of itacolumite showed the new ceramic functions such as stress relaxation properties and high damping capacity (internal friction Q-1=0.03). The authors tried to develop high damping ceramics by the mimic of itacolumite, and found the Al2O3-TiO2-MgO ceramics. The ceramics had stress relaxation properties and high damping capacity (Q-1=0.01) since microcracks were formed during sintering by the discontinuous grain growth and the anisotropic thermal expansion in the cooling process.
Yu, Miao Qi, Song; Fu, Jie; Zhu, Mi
2015-09-14
A high-damping magnetorheological elastomer (MRE) with bi-directional magnetic-control modulus is developed. This MRE was synthesized by filling NdFeB particles into polyurethane (PU)/ epoxy (EP) interpenetrating network (IPN) structure. The anisotropic samples were prepared in a permanent magnetic field and magnetized in an electromagnetic field of 1 T. Dynamic mechanical responses of the MRE to applied magnetic fields are investigated through magneto-rheometer, and morphology of MREs is observed via scanning electron microscope (SEM). Test result indicates that when the test field orientation is parallel to that of the sample's magnetization, the shear modulus of sample increases. On the other hand, when the orientation is opposite to that of the sample's magnetization, shear modulus decreases. In addition, this PU/EP IPN matrix based MRE has a high-damping property, with high loss factor and can be controlled by applying magnetic field. It is expected that the high damping property and the ability of bi-directional magnetic-control modulus of this MRE offer promising advantages in seismologic application.
Rax, J.M.
1992-04-01
The dynamics of electrons in two-dimensional, linearly or circularly polarized, ultra-high intensity (above 10{sup 18}W/cm{sup 2}) laser waves, is investigated. The Compton harmonic resonances are identified as the source of various stochastic instabilities. Both Arnold diffusion and resonance overlap are considered. The quasilinear kinetic equation, describing the evolution of the electron distribution function, is derived, and the associated collisionless damping coefficient is calculated. The implications of these new processes are considered and discussed.
Design of the magnetorheological mount with high damping force for medium speed diesel generators
NASA Astrophysics Data System (ADS)
Kang, O.-H.; Kim, W.-H.; Joo, W. H.; Park, J.-H.
2013-04-01
This paper investigates the controllable magnetorheological (MR) mount for the marine diesel-generator (D/G) sets. Sometimes, significant vibrations over the allowable limit are observed on the D/G sets due to their huge excitation forces. Because the severe vibration can lead to structural damages to the D/G sets, it should be reduced to below the limit. Although passive mounts with rubber isolators are usually used, the vibration reduction performance is not always sufficient. In addition, expecting that the vibration levels required by customers will get more severe, semi-active vibration isolation system needs to be developed. To the aim, the valve (flow) mode type of MR mount has been designed. Especially, the annular-radial configuration was adopted to enhance the damping force within the restricted space. The geometry of the mount has been optimized to obtain the required damping force and the magnetic field analysis has been carried out using ANSYS APDL. To verify the performance of the developed MR mount, excitation test was conducted and the dynamic characteristics were identified. Since damping property of the MR fluid is changed by the applied magnetic field strength and excitation frequency, responses to changing applied currents and frequencies were obtained. From the results, damping performance of the MR mount was evaluated.
NASA Astrophysics Data System (ADS)
Pioldi, Fabio; Ferrari, Rosalba; Rizzi, Egidio
2016-02-01
The present paper deals with the seismic modal dynamic identification of frame structures by a refined Frequency Domain Decomposition (rFDD) algorithm, autonomously formulated and implemented within MATLAB. First, the output-only identification technique is outlined analytically and then employed to characterize all modal properties. Synthetic response signals generated prior to the dynamic identification are adopted as input channels, in view of assessing a necessary condition for the procedure's efficiency. Initially, the algorithm is verified on canonical input from random excitation. Then, modal identification has been attempted successfully at given seismic input, taken as base excitation, including both strong motion data and single and multiple input ground motions. Rather than different attempts investigating the role of seismic response signals in the Time Domain, this paper considers the identification analysis in the Frequency Domain. Results turn-out very much consistent with the target values, with quite limited errors in the modal estimates, including for the damping ratios, ranging from values in the order of 1% to 10%. Either seismic excitation and high values of damping, resulting critical also in case of well-spaced modes, shall not fulfill traditional FFD assumptions: this shows the consistency of the developed algorithm. Through original strategies and arrangements, the paper shows that a comprehensive rFDD modal dynamic identification of frames at seismic input is feasible, also at concomitant high damping.
First detection of CO in a high-redshift damped Lyman-α system
NASA Astrophysics Data System (ADS)
Srianand, R.; Noterdaeme, P.; Ledoux, C.; Petitjean, P.
2008-05-01
We present the first detection of carbon monoxide (CO) in a damped Lyman-α system (DLA) at z_abs = 2.41837 toward SDSS J143912.04+111740.5. We also detected H2 and HD molecules. The measured total column densities (in log units) of H i, H2, and CO are 20.10±0.10, 19.38±0.10, and 13.89±0.02, respectively. The molecular fraction, f = 2N(H2)/(N(H i)+2N(H2)) = 0.27^+0.10-0.08, is the highest among all known DLAs. The abundances relative to solar of S, Zn, Si, and Fe are -0.03±0.12, +0.16±0.11, -0.86±0.11, and -1.32±0.11, respectively, indicating a high metal enrichment and a depletion pattern onto dust-grains similar to the cold ISM of our Galaxy. The measured N(CO)/N(H2) = 3×10-6 is much less than the conventional CO/H2 ratio used to convert the CO emission into gaseous mass but is consistent with what is measured along translucent sightlines in the Galaxy. The CO rotational excitation temperatures are higher than those measured in our Galactic ISM for similar kinetic temperature and density. Using the C i fine structure absorption lines, we show that this is a consequence of the excitation being dominated by radiative pumping by the cosmic microwave background radiation (CMBR). From the CO excitation temperatures, we derive T_CMBR = 9.15±0.72 K, while 9.315±0.007 K is expected from the hot big-bang theory. This is the most precise high-redshift measurement of T_CMBR and the first confirmation of the theory using molecular transitions at high redshift. Based on observations carried out at the European Southern Observatory (ESO), under programme 278.A-5062 with the UVES echelle spectrograph installed at the ESO Very Large Telescope (VLT), unit Kueyen, on Mount Paranal in Chile.
Matching High-z Observations of Damped Ly-α Absorption Systems
NASA Astrophysics Data System (ADS)
Hamer, Jacob; Maller, Ariyeh; Somerville, Rachel S.
2016-01-01
Damped Lyman Alpha Absorption systems, the highest column density quasar absorption systems, can place tight constraints on models of galaxy formation. While many current models can match the properties of these objects at z ~ 2-3, all current models severely underestimate their abundances at z~5. We study the ability of a semi-analytic model to match the line density of damped systems and find that serious changes to the model must be made. If gas disks give rise to these systems, then more baryons must be in HI than is currently assumed in the model, either because fewer stars are formed or less gas is ejected by supernova. In addition, the disks must be much larger than assumed in the model. Alternatively, gas outflows could account for much of the cross section, placing constraints on the physics of supernova feedback.
Computing black hole partition functions from quasinormal modes
Arnold, Peter; Szepietowski, Phillip; Vaman, Diana
2016-07-07
We propose a method of computing one-loop determinants in black hole space-times (with emphasis on asymptotically anti-de Sitter black holes) that may be used for numerics when completely-analytic results are unattainable. The method utilizes the expression for one-loop determinants in terms of quasinormal frequencies determined by Denef, Hartnoll and Sachdev in [1]. A numerical evaluation must face the fact that the sum over the quasinormal modes, indexed by momentum and overtone numbers, is divergent. A necessary ingredient is then a regularization scheme to handle the divergent contributions of individual fixed-momentum sectors to the partition function. To this end, we formulate an effective two-dimensional problem in which a natural refinement of standard heat kernel techniques can be used to account for contributions to the partition function at fixed momentum. We test our method in a concrete case by reproducing the scalar one-loop determinant in the BTZ black hole background. Furthermore, we then discuss the application of such techniques to more complicated spacetimes.
Resolving nanophotonic spectra with quasi-normal modes (Conference Presentation)
NASA Astrophysics Data System (ADS)
Powell, David A.
2016-09-01
Many nanophotonic systems are strongly coupled to radiating waves, or suffer significant dissipative losses. Furthermore, they may have complex shapes which are not amenable to closed form calculations. This makes it challenging to determine their modes without resorting to quasi-static or point dipole approximations. To solve this problem, the quasi-normal modes (QNMs) are found from an integral equation model of the particle. These give complex frequencies where excitation can be supported without any incident field. The corresponding eigenvectors yield the modal distributions, which are non-orthogonal due to the non-Hermitian nature of the system. The model based on quasi-normal modes is applied to plasmonic and dielectric particles, and compared with a spherical multipole decomposition. Only with the QNMs is it possible to resolve all features of the extinction spectrum, as each peak in the spectrum can be attributed to a particular mode. In contrast, many of the multipole coefficient have multiple peaks and dips. Furthermore, by performing a multipolar decomposition of each QNM, the spectrum of multipole coefficients is explained in terms of destructive interference between modes of the same multipole order.
Computing black hole partition functions from quasinormal modes
Arnold, Peter; Szepietowski, Phillip; Vaman, Diana
2016-07-07
We propose a method of computing one-loop determinants in black hole space-times (with emphasis on asymptotically anti-de Sitter black holes) that may be used for numerics when completely-analytic results are unattainable. The method utilizes the expression for one-loop determinants in terms of quasinormal frequencies determined by Denef, Hartnoll and Sachdev in [1]. A numerical evaluation must face the fact that the sum over the quasinormal modes, indexed by momentum and overtone numbers, is divergent. A necessary ingredient is then a regularization scheme to handle the divergent contributions of individual fixed-momentum sectors to the partition function. To this end, we formulatemore » an effective two-dimensional problem in which a natural refinement of standard heat kernel techniques can be used to account for contributions to the partition function at fixed momentum. We test our method in a concrete case by reproducing the scalar one-loop determinant in the BTZ black hole background. Furthermore, we then discuss the application of such techniques to more complicated spacetimes.« less
Computing black hole partition functions from quasinormal modes
NASA Astrophysics Data System (ADS)
Arnold, Peter; Szepietowski, Phillip; Vaman, Diana
2016-07-01
We propose a method of computing one-loop determinants in black hole space-times (with emphasis on asymptotically anti-de Sitter black holes) that may be used for numerics when completely-analytic results are unattainable. The method utilizes the expression for one-loop determinants in terms of quasinormal frequencies determined by Denef, Hartnoll and Sachdev in [1]. A numerical evaluation must face the fact that the sum over the quasinormal modes, indexed by momentum and overtone numbers, is divergent. A necessary ingredient is then a regularization scheme to handle the divergent contributions of individual fixed-momentum sectors to the partition function. To this end, we formulate an effective two-dimensional problem in which a natural refinement of standard heat kernel techniques can be used to account for contributions to the partition function at fixed momentum. We test our method in a concrete case by reproducing the scalar one-loop determinant in the BTZ black hole background. We then discuss the application of such techniques to more complicated spacetimes.
Operating experience with high beam currents and transient beam loading in the SLC damping rings
Minty, M.G.; Akre, R.; Krejcik, P.; Siemann, R.H.
1995-06-01
During the 1994 SLC run the nominal operating intensity in the damping rings was raised from 3.5 {times} 10{sup 10} to greater than 4 {times} 10{sup 10} particles per bunch (ppb). Stricter regulation of rf system parameters was required to maintain stability of the rf system and particle beam. Improvements were made in the feedback loops which control the cavity amplitude and loading angles. Compensation for beam loading was also required to prevent klystron saturation during repetition rate changes. To minimize the effects of transient loading on the rf system, the gain of the direct rf feedback loop and the loading angles were optimized.
Quasinormal modes of non-Abelian hyperscaling violating Lifshitz black holes
NASA Astrophysics Data System (ADS)
Bécar, Ramón; González, P. A.; Vásquez, Yerko
2017-02-01
We study the quasinormal modes of scalar field perturbations in the background of non-Abelian hyperscaling violating Lifshitz black holes. We find that the quasinormal frequencies have no real part so there is no oscillatory behavior in the perturbations, only exponential decay, that is, the system is always overdamped, which guarantees the mode stability of non-Abelian hyperscaling violating Lifshitz black holes. We determine analytically the quasinormal modes for massless scalar fields for a dynamical exponent z=2 and hyperscaling violating exponent tilde{θ }>-2. Also, we obtain numerically the quasinormal frequencies for different values of the dynamical exponent and the hyperscaling violating exponent by using the improved asymptotic iteration method.
Damping in Space Constructions
NASA Astrophysics Data System (ADS)
de Vreugd, Jan; de Lange, Dorus; Winters, Jasper; Human, Jet; Kamphues, Fred; Tabak, Erik
2014-06-01
Monolithic structures are often used in optomechanical designs for space applications to achieve high dimensional stability and to prevent possible backlash and friction phenomena. The capacity of monolithic structures to dissipate mechanical energy is however limited due to the high Q-factor, which might result in high stresses during dynamic launch loads like random vibration, sine sweeps and shock. To reduce the Q-factor in space applications, the effect of constrained layer damping (CLD) is investigated in this work. To predict the damping increase, the CLD effect is implemented locally at the supporting struts in an existing FE model of an optical instrument. Numerical simulations show that the effect of local damping treatment in this instrument could reduce the vibrational stresses with 30-50%. Validation experiments on a simple structure showed good agreement between measured and predicted damping properties. This paper presents material characterization, material modeling, numerical implementation of damping models in finite element code, numerical results on space hardware and the results of validation experiments.
NASA Astrophysics Data System (ADS)
Samanta, T.; Singh, J.; Sindhuja, G.; Banerjee, D.
2016-01-01
During the total solar eclipse of 11 July 2010, multi-slit spectroscopic observations of the solar corona were performed from Easter Island, Chile. To search for high-frequency waves, observations were taken at a high cadence in the green line at 5303 Å that is due to [Fe xiv] and the red line at 6374 Å that is due to [Fe x]. The data were analyzed to study the periodic variations in intensity, Doppler velocity, and line width using wavelet analysis. The data with high spectral and temporal resolution enabled us to study the rapid dynamical changes within coronal structures. We find that at certain locations, each parameter shows significant oscillation with periods ranging from 6 - 25 s. For the first time, we were able to detect damping of high-frequency oscillations with periods of about 10 s. If the observed damped oscillations are due to magnetohydrodynamic waves, then they can contribute significantly to the heating of the corona. From a statistical study we try to characterize the nature of the observed oscillations while considering the distribution of power in different line parameters.
Quasinormal Modes for Schwarzschild-AdS Black Holes: Exponential Convergence to the Real Axis
NASA Astrophysics Data System (ADS)
Gannot, Oran
2014-09-01
We study quasinormal modes for massive scalar fields in Schwarzschild-anti-de Sitter black holes. When the mass-squared is above the Breitenlohner-Freedman bound, we show that for large angular momenta, ℓ, there exist quasinormal modes with imaginary parts of size exp(- ℓ/ C). We provide an asymptotic expansion for the real parts of the modes closest to the real axis and identify the vanishing of certain coefficients depending on the dimension.
Quasinormal modes and the phase structure of strongly coupled matter
NASA Astrophysics Data System (ADS)
Janik, Romuald A.; Jankowski, Jakub; Soltanpanahi, Hesam
2016-06-01
We investigate the poles of the retarded Green's functions of strongly coupled field theories exhibiting a variety of phase structures from a crossover up to different first order phase transitions. These theories are modeled by a dual gravitational description. The poles of the holographic Green's functions appear at the frequencies of the quasinormal modes of the dual black hole background. We focus on quantifying linearized level dynamical response of the system in the critical region of phase diagram. Generically non-hydrodynamic degrees of freedom are important for the low energy physics in the vicinity of a phase transition. For a model with linear confinement in the meson spectrum we find degeneracy of hydrodynamic and non-hydrodynamic modes close to the minimal black hole temperature, and we establish a region of temperatures with unstable non-hydrodynamic modes in a branch of black hole solutions.
The Joint Damping Experiment (JDX)
NASA Technical Reports Server (NTRS)
Folkman, Steven L.; Bingham, Jeff G.; Crookston, Jess R.; Dutson, Joseph D.; Ferney, Brook D.; Ferney, Greg D.; Rowsell, Edwin A.
1997-01-01
The Joint Damping Experiment (JDX), flown on the Shuttle STS-69 Mission, is designed to measure the influence of gravity on the structural damping of a high precision three bay truss. Principal objectives are: (1) Measure vibration damping of a small-scale, pinjointed truss to determine how pin gaps give rise to gravity-dependent damping rates; (2) Evaluate the applicability of ground and low-g aircraft tests for predicting on-orbit behavior; and (3) Evaluate the ability of current nonlinear finite element codes to model the dynamic behavior of the truss. Damping of the truss was inferred from 'Twang' tests that involve plucking the truss structure and recording the decay of the oscillations. Results are summarized as follows. (1) Damping, rates can change by a factor of 3 to 8 through changing the truss orientation; (2) The addition of a few pinned joints to a truss structure can increase the damping by a factor as high as 30; (3) Damping is amplitude dependent; (4) As gravity induced preloads become large (truss long axis perpendicular to gravity vector) the damping is similar to non-pinjointed truss; (5) Impacting in joints drives higher modes in structure; (6) The torsion mode disappears if gravity induced preloads are low.
Bearing-Cartridge Damping Seal
NASA Technical Reports Server (NTRS)
Goggins, David G.; Scharrer, Joseph K.; Chen, Wei C.
1991-01-01
In proposed design for improved ball-bearing cartridge, damping seal in form of thin-layer fluid journal bearing incorporated into cartridge. Damping seal acts as auxiliary bearing, relieving bearing balls of significant portions of both static and dynamic bearing loads. Damping from seal reduces dynamic loads even further by reducing amplitude of vibrations in second vibrational mode of rotor, which mode occurs when rotor turning at nearly full operating speed. Intended for use in high-pressure-oxygen turbopump of Space Shuttle main engine, also applicable to other turbomachinery bearings.
NASA Astrophysics Data System (ADS)
Maller, Ariyeh H.; Prochaska, Jason X.; Somerville, Rachel S.; Primack, Joel R.
2001-10-01
We investigate the properties of damped Lyman α systems (DLAS) in semi-analytic models, focusing on whether the models can reproduce the kinematic properties of low-ionization metal lines described by Prochaska & Wolfe. We explore a variety of approaches for modelling the radial distribution of the cold neutral gas associated with the galaxies in our models, and find that our results are very sensitive to this ingredient. If we use an approach based on work by Fall & Efstathiou, in which the sizes of the discs are determined by conservation of angular momentum, we find that the majority of the DLAS correspond to a single galactic disc. These models generically fail to reproduce the observed distribution of velocity widths. In alternative models in which the gas discs are considerably more extended, a significant fraction of DLAS arise from lines of sight intersecting multiple gas discs in a common halo. These models produce kinematics that fit the observational data, and also seem to agree well with the results of recent hydrodynamical simulations. Thus we conclude that cold dark matter based models of galaxy formation can be reconciled with the kinematic data, but only at the expense of the standard assumption that DLAS are produced by rotationally supported gas discs whose sizes are determined by conservation of angular momentum. We suggest that the distribution of cold gas at high redshift may be dominated by another process, such as tidal streaming caused by mergers.
McEwan, Thomas E.
1998-01-01
A radar range finder and hidden object locator is based on ultra-wide band radar with a high resolution swept range gate. The device generates an equivalent time amplitude scan with atypical range of 4 inches to 20 feet, and an analog range resolution as limited by a jitter of on the order of 0.01 inches. A differential sampling receiver is employed to effectively eliminate ringing and other aberrations induced in the receiver by the near proximity of the transmit antenna, so a background subtraction is not needed, simplifying the circuitry while improving performance. Uses of the invention include a replacement of ultrasound devices for fluid level sensing, automotive radar, such as cruise control and parking assistance, hidden object location, such as stud and rebar finding. Also, this technology can be used when positioned over a highway lane to collect vehicle count and speed data for traffic control. Techniques are used to reduce clutter in the receive signal, such as decoupling the receive and transmit cavities by placing a space between them, using conductive or radiative damping elements on the cavities, and using terminating plates on the sides of the openings.
McEwan, T.E.
1998-06-30
A radar range finder and hidden object locator is based on ultra-wide band radar with a high resolution swept range gate. The device generates an equivalent time amplitude scan with atypical range of 4 inches to 20 feet, and an analog range resolution as limited by a jitter of on the order of 0.01 inches. A differential sampling receiver is employed to effectively eliminate ringing and other aberrations induced in the receiver by the near proximity of the transmit antenna, so a background subtraction is not needed, simplifying the circuitry while improving performance. Uses of the invention include a replacement of ultrasound devices for fluid level sensing, automotive radar, such as cruise control and parking assistance, hidden object location, such as stud and rebar finding. Also, this technology can be used when positioned over a highway lane to collect vehicle count and speed data for traffic control. Techniques are used to reduce clutter in the receive signal, such as decoupling the receive and transmit cavities by placing a space between them, using conductive or radiative damping elements on the cavities, and using terminating plates on the sides of the openings. 20 figs.
Landau damping in space plasmas
NASA Technical Reports Server (NTRS)
Thorne, Richard M.; Summers, Danny
1991-01-01
The Landau damping of electrostatic Langmuir waves and ion-acoustic waves in a hot, isotropic, nonmagnetized, generalized Lorentzian plasma is analyzed using the modified plasma dispersion function. Numerical solutions for the real and imaginary parts of the wave frequency omega sub 0 - (i)(gamma) have been obtained as a function of the normalized wave number (k)(lambda sub D), where lambda sub D is the electron Debye length. For both particle distributions the electrostatic modes are found to be strongly damped at short wavelengths. At long wavelengths, this damping becomes less severe, but the attenuation of Langmuir waves is much stronger for a generalized Lorentzian plasma than for a Maxwellian plasma. It is concluded that Landau damping of ion-acoustic waves is only slightly affected by the presence of a high energy tail, but is strongly dependent on the ion temperature.
Quasi-normal modes of extremal BTZ black holes in TMG
NASA Astrophysics Data System (ADS)
Afshar, Hamid R.; Alishahiha, Mohsen; Mosaffa, Amir E.
2010-08-01
We study the spectrum of tensor perturbations on extremal BTZ black holes in topologically massive gravity for arbitrary values of the coefficient of the Chern-Simons term, μ. Imposing proper boundary conditions at the boundary of the space and at the horizon, we find that the spectrum contains quasi-normal modes.
Damping model of traveling waves by corona effect along extra high voltage three phase lines
Guillier, J.F.; Poloujadoff, M.; Rioual, M.
1995-10-01
The paper describes a corona effect model which takes the variation in the coupling coefficients of a three-phase lines into account during the propagation of a lightning wave. As the corona is often modeled by capacitances between phase to earth, the aim was to take also into account the corona effect between conductors, to evaluate precisely all the losses due to this phenomenon. The propagation of a lightning wave is simulated with E.M.T.P., taking the skin effect and the corona effect into account. Simulation results are compared with tests performed on a real 220 kV line. It can be noticed that the incident lightning wave and induced waves are highly influenced by the skin effect and the corona effect. The results from the proposed model are very close to the values recorded during the tests.
NASA Technical Reports Server (NTRS)
Horwath, T. G.
1992-01-01
The propagation of vibrational energy in bulk, torsional, and flexural modes, in electrically conducting media can undergo strong attenuation if subjected to high magnetic fields in certain spatial arrangements. The reasons for this are induced Eddy currents which are generated by the volume elements in the media moving transversally to the magnetic field at acoustic velocities. In magnetic fields achievable with superconductors, the non-conservative (dissipative) forces are compared to the elastic and inertial forces for most metals. Strong dissipation of vibrational energy in the form of heat takes place as a result. A simplified theory is presented based on engineering representations of electrodynamics, attenuation values for representative metals are calculated, and problems encountered in formulating a generalized theory based on electrodynamics of moving media are discussed. General applications as well as applications specific to maglev are discussed.
NASA Technical Reports Server (NTRS)
Merchant, D. H.; Gates, R. M.; Straayer, J. W.
1975-01-01
The effect of localized structural damping on the excitability of higher-order large space telescope spacecraft modes is investigated. A preprocessor computer program is developed to incorporate Voigt structural joint damping models in a finite-element dynamic model. A postprocessor computer program is developed to select critical modes for low-frequency attitude control problems and for higher-frequency fine-stabilization problems. The selection is accomplished by ranking the flexible modes based on coefficients for rate gyro, position gyro, and optical sensor, and on image-plane motions due to sinusoidal or random PSD force and torque inputs.
36 new, high-probability, damped Lyα absorbers at redshift 0.42 < z < 0.70
NASA Astrophysics Data System (ADS)
Turnshek, David A.; Monier, Eric M.; Rao, Sandhya M.; Hamilton, Timothy S.; Sardane, Gendith M.; Held, Ryan
2015-05-01
Quasar damped Lyα (DLA) absorption-line systems with redshifts z < 1.65 are used to trace neutral gas over approximately 70 per cent of the most recent history of the Universe. However, such systems fall in the UV and are rarely found in blind UV spectroscopic surveys. Therefore, it has been difficult to compile a moderate-sized sample of UV DLAs in any narrow cosmic time interval. However, DLAs are easy to identify in low-resolution spectra because they have large absorption rest equivalent widths. We have performed an efficient strong-Mg II-selected survey for UV DLAs at redshifts z = [0.42, 0.70] using Hubble Space Telescope's low-resolution ACS-HRC-PR200L prism. This redshift interval covers ˜1.8 Gyr in cosmic time, i.e. t ≈ [7.2, 9.0] Gyr after the big bang. A total of 96 strong Mg II absorption-line systems identified in Sloan Digital Sky Survey spectra were successfully observed with the prism at the predicted UV wavelengths of Lyα absorption. We found that 35 of the 96 systems had a significant probability of being DLAs. One additional observed system could be a very high N_{H I} DLA (N_{H I} ˜ 2× 10^{22} atoms cm-2 or possibly higher), but since very high N_{H I} systems are extremely rare, it would be unusual for this system to be a DLA given the size of our sample. Here we present information on our prism sample, including our best estimates of N_{H I} and errors for the 36 systems fitted with DLA profiles. This list is valuable for future follow-up studies of low-redshift DLAs in a small redshift interval, although such work would clearly benefit from improved UV spectroscopy to more accurately determine their neutral hydrogen column densities.
Turbomachinery rotor support with damping
NASA Technical Reports Server (NTRS)
Vonpragenau, George L. (Inventor)
1990-01-01
Damping seals, damping bearings, and a support sleeve are presented for the ball bearings of a high speed rotor. The ball bearings consist of a duplex set having the outer races packaged tightly within the sleeve while the sleeve provides a gap with a support member so that the bearings may float with the sleeve. The sleeve has a web extending radially between the pair of outer races and acts in conjunction with one or more springs to apply an axial preload to the outer races. The sleeves have a series of slits which provide the sleeve with a spring-like quality so that the spring acts to center the rotor upon which the bearings are mounted during start up and shut down. A damping seal or a damping bearing may be used in conjunction with the ball bearings and supporting sleeve, the damping seal and damping bearing having rotor portions including rigid outer surfaces mounted within the bore of a stator portion having triangular shaped pockets on the surface facing the rotor. Axial gates are provided between adjacent pockets in sections of the stator permitting fluid to flow with less resistance axially relative to the flow of fluids circumferentially between the rotor and the stator.
THE MOST METAL-POOR DAMPED Lyα SYSTEMS: AN INSIGHT INTO DWARF GALAXIES AT HIGH-REDSHIFT
Cooke, Ryan J.; Pettini, Max; Jorgenson, Regina A.
2015-02-10
In this paper we analyze the kinematics, chemistry, and physical properties of a sample of the most metal-poor damped Lyα systems (DLAs), to uncover their links to modern-day galaxies. We present evidence that the DLA population as a whole exhibits a ''knee'' in the relative abundances of the α-capture and Fe-peak elements when the metallicity is [Fe/H] ≅ –2.0, assuming that Zn traces the buildup of Fe-peak elements. In this respect, the chemical evolution of DLAs is clearly different from that experienced by Milky Way halo stars, but resembles that of dwarf spheroidal galaxies in the Local Group. We also find a close correspondence between the kinematics of Local Group dwarf galaxies and of high-redshift metal-poor DLAs, which further strengthens this connection. On the basis of such similarities, we propose that the most metal-poor DLAs provide us with a unique opportunity to directly study the dwarf galaxy population more than ten billion years in the past, at a time when many dwarf galaxies were forming the bulk of their stars. To this end, we have measured some of the key physical properties of the DLA gas, including their neutral gas mass, size, kinetic temperature, density, and turbulence. We find that metal-poor DLAs contain a warm neutral medium with T {sub gas} ≅ 9600 K predominantly held up by thermal pressure. Furthermore, all of the DLAs in our sample exhibit a subsonic turbulent Mach number, implying that the gas distribution is largely smooth. These results are among the first empirical descriptions of the environments where the first few generations of stars may have formed in the universe.
Zhu, S.; Cai, Y.; Rote, D. M.; ...
1998-01-01
Magnetic damping is one of the important parameters that control the response and stability of maglev systems. An experimental study to measure magnetic damping directly is presented. A plate attached to a permanent magnet levitated on a rotating drum was tested to investigate the effect of various parameters, such as conductivity, gap, excitation frequency, and oscillation amplitude, on magnetic damping. The experimental technique is capable of measuring all of the magnetic damping coefficients, some of which cannot be measured indirectly.
Wang, Ding-Shuo; Lai, Shu-Yu; Lin, Tzu-Ying; Wang, Liang-Wei; Liao, Jung-Wei; Lai, Chih-Huang; Chien, Cheng-Wei; Wang, Yung-Hung; Ellsworth, David; Lu, Lei; Wu, Mingzhong
2014-04-07
We demonstrate that the magnetic anisotropy of the CoFeB/MgO bilayer can be manipulated by adding an aluminum capping layer. After rapid thermal annealing, we can achieve large perpendicular magnetic anisotropy of CoFeB with a high thermal stability factor (Δ = 72) while the Gilbert damping constant can be reduced down to only 0.011 simultaneously. The boron and residual oxygen in the bulk CoFeB layer are properly absorbed by the Al capping layer during annealing, leading to the enhanced exchange stiffness and reduced damping. The interfacial Fe-O bonding can be optimized by tuning annealing temperature and thickness of Al, resulting in enhanced perpendicular anisotropy.
NASA Astrophysics Data System (ADS)
Wang, Ding-Shuo; Lai, Shu-Yu; Lin, Tzu-Ying; Chien, Cheng-Wei; Ellsworth, David; Wang, Liang-Wei; Liao, Jung-Wei; Lu, Lei; Wang, Yung-Hung; Wu, Mingzhong; Lai, Chih-Huang
2014-04-01
We demonstrate that the magnetic anisotropy of the CoFeB/MgO bilayer can be manipulated by adding an aluminum capping layer. After rapid thermal annealing, we can achieve large perpendicular magnetic anisotropy of CoFeB with a high thermal stability factor (Δ = 72) while the Gilbert damping constant can be reduced down to only 0.011 simultaneously. The boron and residual oxygen in the bulk CoFeB layer are properly absorbed by the Al capping layer during annealing, leading to the enhanced exchange stiffness and reduced damping. The interfacial Fe-O bonding can be optimized by tuning annealing temperature and thickness of Al, resulting in enhanced perpendicular anisotropy.
NASA Astrophysics Data System (ADS)
Chen, Zhong; Chen, Guisheng; Zhang, Xianmin
2015-05-01
Flexure-based mechanism like compliant actuation system embeds complex dynamics that will reduce the control bandwidth and limits their dynamic positioning precision. This paper presents a theoretical model of a leaf flexure hinge with damping layers using strain energy method and Kelvin damping model. The modified loss factor of the damped leaf flexure hinge is derived, and the equivalent viscous damping coefficient of the damped leaf hinge is obtained, which could be used to improve the pseudo-rigid-model. The free vibration signals of the hinge in three different damping configurations are measured. The experimental modal analysis also is performed on the three kinds of damped leaf flexure hinges in order to evaluate their 1st order bending natural frequency and vibration-suppressing effects. The evaluation of modified loss factor model also is performed. The experimental results indicate that the constrained layer damping can enhance the structure damping of the hinge even if only single damping layer each side, the modified loss factor model can get good predicts of a damped leaf flexure hinge in the frequency range below 1st order natural frequency, and it is necessary that the dimensional parameters of the damping layers and basic layer of the hinge should be optimized for simplification at the mechanism's design stage.
Viscous damped space structure for reduced jitter
NASA Technical Reports Server (NTRS)
Wilson, James F.; Davis, L. Porter
1987-01-01
A technique to provide modal vibration damping in high performance space structures was developed which uses less than one once of incompressible fluid. Up to 50 percent damping can be achieved which can reduce the settling times of the lowest structural mode by as much as 50 to 1. This concept allows the designers to reduce the weight of the structure while improving its dynamic performance. Damping by this technique is purely viscous and has been shown by test to be linear over 5 orders of input magnitude. Amplitudes as low as 0.2 microinch were demonstrated. Damping in the system is independent of stiffness and relatively insensitive to temperature.
NASA Astrophysics Data System (ADS)
Preziosi-Ribero, Antonio; Peñaloza-Giraldo, Jorge; Escobar-Vargas, Jorge; Donado-Garzón, Leonardo
2016-04-01
Groundwater - Surface water interaction is a topic that has gained relevance among the scientific community over the past decades. However, several questions remain unsolved inside this topic, and almost all the research that has been done in the past regards the transport phenomena and has little to do with understanding the dynamics of the flow patterns of the above mentioned interactions. The aim of this research is to verify the attenuation of the water velocity that comes from the free surface and enters the porous media under the bed of a high mountain river. The understanding of this process is a key feature in order to characterize and quantify the interactions between groundwater and surface water. However, the lack of information and the difficulties that arise when measuring groundwater flows under streams make the physical quantification non reliable for scientific purposes. These issues suggest that numerical simulations and in-stream velocity measurements can be used in order to characterize these flows. Previous studies have simulated the attenuation of a sinusoidal pulse of vertical velocity that comes from a stream and goes into a porous medium. These studies used the Burgers equation and the 1-D Navier-Stokes equations as governing equations. However, the boundary conditions of the problem, and the results when varying the different parameters of the equations show that the understanding of the process is not complete yet. To begin with, a Spectral Multi Domain Penalty Method (SMPM) was proposed for quantifying the velocity damping solving the Navier - Stokes equations in 1D. The main assumptions are incompressibility and a hydrostatic approximation for the pressure distributions. This method was tested with theoretical signals that are mainly trigonometric pulses or functions. Afterwards, in order to test the results with real signals, velocity profiles were captured near the Gualí River bed (Honda, Colombia), with an Acoustic Doppler
1988-03-01
Atoms (e,g., stress induced movement of carbon or nitrogen in iron). * Point Defects. * Dislocations. * Grain Boundaries. * Twin boundaries . * Magnetic...domain boundaries. * Interphase boundaries. While all of these features provide some damping, some are better than others. Twin boundaries , magnetic...Stress-induced movement of the FCT:FCT twin boundaries . c. Some sort of subtle fine-scale response within a tweed microstructure. Question: Which
NASA Astrophysics Data System (ADS)
Wang, Yun-Che
The manufacture of negative Poisson's ratio polymeric foams was based on a thermal transformation technique to convert the convex cell shape of conventional foams to a concave or re-entrant shape through triaxial compression and heating. Poisson's ratio measurements were performed with a laser-based setup for non-transparent materials with high accuracy. Contrary to the predictions of the theory of elasticity, we observed cell size influences on Poisson's ratio of conventional and transformed foams. The theoretical study of the contact problem involving materials with negative Poisson's ratios revealed a further reduction on contact pressure between the contacting two bodies in comparison with materials with positive Poisson's ratio. The classical Hertz contact theory and 3D elasticity solution in an asymptotic form for finite-thickness, layered media indented by an elastic spherical were used. As for advanced composite materials, theoretically, significant amplification was found in composites' mechanical, thermal, electrical or coupled field properties due to negative stiffness inclusions. Experimentally, we fabricated high damping and high stiffness composite materials, SiC-InSn, to obtain a realization of the prediction from composite theory. With the idea of using negative stiffness components, we manufactured Sn, Zn or Al composites with 1% VO2 particles by volume, where the transforming particles, VO 2, were used as a negative stiffness source, and observed anomalies both in overall stiffness and tan delta. Broadband viscoelastic spectroscopy (BVS) was used to measure mechanical properties. The transformation of the eutectoid ZnAl was studied with resonant ultrasound spectroscopy (RUS), and about a 30% increase in shear modulus and tan delta, respectively, were observed. To investigate the stability of systems with negative stiffness elements, several discrete viscoelastic models were analyzed. With the Lyapunov indirect stability theorem, we found that
NASA Astrophysics Data System (ADS)
Fredette, Luke; Singh, Rajendra
2017-02-01
A spectral element approach is proposed to determine the multi-axis dynamic stiffness terms of elastomeric isolators with fractional damping over a broad range of frequencies. The dynamic properties of a class of cylindrical isolators are modeled by using the continuous system theory in terms of homogeneous rods or Timoshenko beams. The transfer matrix type dynamic stiffness expressions are developed from exact harmonic solutions given translational or rotational displacement excitations. Broadband dynamic stiffness magnitudes (say up to 5 kHz) are computationally verified for axial, torsional, shear, flexural, and coupled stiffness terms using a finite element model. Some discrepancies are found between finite element and spectral element models for the axial and flexural motions, illustrating certain limitations of each method. Experimental validation is provided for an isolator with two cylindrical elements (that work primarily in the shear mode) using dynamic measurements, as reported in the prior literature, up to 600 Hz. Superiority of the fractional damping formulation over structural or viscous damping models is illustrated via experimental validation. Finally, the strengths and limitations of the spectral element approach are briefly discussed.
Quasinormal modes, scattering, and Hawking radiation of Kerr-Newman black holes in a magnetic field
Kokkotas, K. D.; Konoplya, R. A.; Zhidenko, A.
2011-01-15
We perform a comprehensive analysis of the spectrum of proper oscillations (quasinormal modes), transmission/reflection coefficients, and Hawking radiation for a massive charged scalar field in the background of the Kerr-Newman black hole immersed in an asymptotically homogeneous magnetic field. There are two main effects: the Zeeman shift of the particle energy in the magnetic field and the difference of values of an electromagnetic potential between the horizon and infinity, i.e. the Faraday induction. We have shown that 'turning on' the magnetic field induces a stronger energy-emission rate and leads to 'recharging' of the black hole. Thus, a black hole immersed in a magnetic field evaporates much quicker, achieving thereby an extremal state in a shorter period of time. Quasinormal modes are moderately affected by the presence of a magnetic field which is assumed to be relatively small compared to the gravitational field of the black hole.
Connection between black-hole quasinormal modes and lensing in the strong deflection limit.
Stefanov, Ivan Zh; Yazadjiev, Stoytcho S; Gyulchev, Galin G
2010-06-25
The purpose of the current Letter is to give some relations between gravitational lensing in the strong-deflection limit and the frequencies of the quasinormal modes of spherically symmetric, asymptotically flat black holes. On the one side, the relations obtained can give a physical interpretation of the strong-deflection limit parameters. On the other side, they also give an alternative method for the measurement of the frequencies of the quasinormal modes of spherically symmetric, asymptotically flat black holes. They could be applied to the localization of the sources of gravitational waves and could tell us what frequencies of the gravitational waves we could expect from a black hole acting simultaneously as a gravitational lens and a source of gravitational waves.
On Quasi-Normal Modes, Area Quantization and Bohr Correspondence Principle
NASA Astrophysics Data System (ADS)
Corda, Christian
2015-10-01
In (Int. Journ. Mod. Phys. D 14, 181 2005), the author Khriplovich verbatim claims that "the correspondence principle does not dictate any relation between the asymptotics of quasinormal modes and the spectrum of quantized black holes" and that "this belief is in conflict with simple physical arguments". In this paper we analyze Khriplovich's criticisms and realize that they work only for the original proposal by Hod, while they do not work for the improvements suggested by Maggiore and recently finalized by the author and collaborators through a connection between Hawking radiation and black hole (BH) quasi-normal modes (QNMs). This is a model of quantum BH somewhat similar to the historical semi-classical model of the structure of a hydrogen atom introduced by Bohr in 1913. Thus, QNMs can be really interpreted as BH quantum levels (the "electrons" of the "Bohr-like BH model").Our results have also important implications on the BH information puzzle.
Damping constant estimation in magnetoresistive readers
Stankiewicz, Andrzej Hernandez, Stephanie
2015-05-07
The damping constant is a key design parameter in magnetic reader design. Its value can be derived from bulk or sheet film ferromagnetic resonance (FMR) line width. However, dynamics of nanodevices is usually defined by presence of non-uniform modes. It triggers new damping mechanisms and produces stronger damping than expected from traditional FMR. This work proposes a device-level technique for damping evaluation, based on time-domain analysis of thermally excited stochastic oscillations. The signal is collected using a high bandwidth oscilloscope, by direct probing of a biased reader. Recorded waveforms may contain different noise signals, but free layer FMR is usually a dominating one. The autocorrelation function is a reflection of the damped oscillation curve, averaging out stochastic contributions. The damped oscillator formula is fitted to autocorrelation data, producing resonance frequency and damping constant values. Restricting lag range allows for mitigation of the impact of other phenomena (e.g., reader instability) on the damping constant. For a micromagnetically modeled reader, the technique proves to be much more accurate than the stochastic FMR line width approach. Application to actual reader waveforms yields a damping constant of ∼0.03.
NASA Astrophysics Data System (ADS)
Zhang, Zhongyang; Berti, Emanuele; Cardoso, Vitor
2013-08-01
The analytical understanding of quasinormal mode ringing requires an accurate knowledge of the Green’s function describing the response of the black hole to external perturbations. We carry out a comprehensive study of quasinormal mode excitation for Kerr black holes. Relying on the formalism developed by Mano, Suzuki, and Takasugi, we improve and extend previous calculations of the quasinormal mode residues in the complex frequency plane (“excitation factors Bq”). Using these results we compute the “excitation coefficients” Cq (essentially the mode amplitudes) in the special case where the source of the perturbations is a particle falling into the black hole along the symmetry axis. We compare this calculation with numerical integrations of the perturbation equations, and we show quantitatively how the addition of higher overtones improves the agreement with the numerical waveforms. Our results should find applications in models of the ringdown stage and in the construction of semianalytical template banks for gravitational-wave detectors, especially for binaries with large mass ratios and/or fast-spinning black holes.
1999-08-01
1953 3. Vigo T.L., "High-Tech Fibrous Materials", American Chemical Society, 1991 4. Warner S.B., ’’Fiber Science", Prentice Hall, 1995 5. Brown W.E...used in the actuator, orthodontics and eyeglass market. They have supplied us with wire and thread for our samples. They have the ability to produce...and orthodontic designs. Memrv Corp. - Zaffir Chaudhry Memry produces a large number of high volume Nitinol and shape memory alloy parts for the
Critically damped quantum search.
Mizel, Ari
2009-04-17
Although measurement and unitary processes can accomplish any quantum evolution in principle, thinking in terms of dissipation and damping can be powerful. We propose a modification of Grover's algorithm in which the idea of damping plays a natural role. Remarkably, we find that there is a critical damping value that divides between the quantum O(sqrt[N]) and classical O(N) search regimes. In addition, by allowing the damping to vary in a fashion we describe, one obtains a fixed-point quantum search algorithm in which ignorance of the number of targets increases the number of oracle queries only by a factor of 1.5.
Low Gilbert damping and in-plane magnetic anisotropy in Ni-Mn-Sn thin film with high L21 order
NASA Astrophysics Data System (ADS)
Modak, Rajkumar; Samantaray, B.; Mandal, P.; Srinivasan, A.
2016-03-01
Mn-rich off-stoichiometric Ni-Mn-Sn Heusler alloy thin film of thickness of 1000 nm was deposited on Si (100) substrate at ambient temperature by dc magnetron sputtering and then annealed ex situ at 550 °C for 1 h under high vacuum. X-ray diffraction and atomic force microscopy analyses show that the annealed film has high L21 crystalline ordering with a lattice constant 5.96 Å and average surface roughness of 1.8 nm. Annealed film exhibited ferromagnetism at room temperature with high saturation magnetization of 162 emu/cm3, low retentivity of 22 emu/cm3 and easy axis of magnetization along the plane of the film. Magneto-dynamic analysis using micro-strip ferromagnetic resonance spectra shows the presence of small in-plane anisotropy K u = 1.4 × 104 erg/cm3 with 4πM s = 2075 ± 10 Oe and g-factor of 2.1. Line width analysis yields a low intrinsic damping constant ( α = 0.008). A significant contribution from extrinsic two-magnon scattering to the line width of the order of Γ = 50 Oe was observed which may be due to surface roughness or/and presence of inhomogeneity and atomic site disorder in the film. The film exhibits the unique combination of low damping constant, low K u, high magnetic saturation and low retentivity.
Quasienergy formulation of damped response theory.
Kristensen, Kasper; Kauczor, Joanna; Kjaergaard, Thomas; Jørgensen, Poul
2009-07-28
We present a quasienergy-based formulation of damped response theory where a common effective lifetime parameter has been introduced for all excited states in terms of complex excitation energies. The introduction of finite excited state lifetimes leads to a set of (complex) damped response equations, which have the same form to all orders in the perturbation. An algorithm is presented for solving the damped response equations in Hartree-Fock theory and Kohn-Sham density functional theory. The use of the quasienergy formulation allows us to obtain directly the computationally simplest expressions for damped response functions by applying a set of response parameter elimination rules, which minimize the total number of damped response equations to be solved. In standard response theory broadened absorption spectra are obtained by ad hoc superimposing lineshape functions onto the absorption stick spectra, whereas an empirical lineshape function common to all excitations is an integrated part of damped response theory. By superimposing the lineshape functions inherent in damped response theory onto the stick spectra of standard response theory, we show that the absorption spectra obtained in standard and damped response theory calculations are identical. We demonstrate that damped response theory may be applied to obtain absorption spectra in all frequency ranges, also those that are not readily addressed using standard response theory. This makes damped response theory an effective tool, e.g., for determining absorption spectra for large molecules, where the density of the excited states may be very high, and where standard response theory therefore is not applicable in practice. A thorough comparison is given between our formulation of damped response theory and the formulation by Norman et al. [J. Chem. Phys. 123, 194103 (2005)].
Decoherence and Landau-Damping
Ng, K.Y.; /Fermilab
2005-12-01
The terminologies, decoherence and Landau damping, are often used concerning the damping of a collective instability. This article revisits the difference and relation between decoherence and Landau damping. A model is given to demonstrate how Landau damping affects the rate of damping coming from decoherence.
NASA Technical Reports Server (NTRS)
Dominic, R. J.
1984-01-01
Research results and progress on the performance of bladed systems is reported the different topics discussed include: the study of turbine blade damping; forced vibrations of friction damped beam moistures in two dimensions; and a users manual for a computer program for dynamic analysis of bladed systems.
NASA Technical Reports Server (NTRS)
Srinivasan, A. V.; Cutts, D. G.; Sridhar, S.
1981-01-01
The potentials of various sources of nonaerodynamic damping in engine blading are evaluated through a combination of advanced analysis and testing. The sources studied include material hysteresis, dry friction at shroud and root disk interfaces as well as at platform type external dampers. A limited seris of tests was conducted to evaluate damping capacities of composite materials (B/AL, B/AL/Ti) and thermal barrier coatings. Further, basic experiments were performed on titanium specimens to establish the characteristics of sliding friction and to determine material damping constants J and n. All the tests were conducted on single blades. Mathematical models were develthe several mechanisms of damping. Procedures to apply this data to predict damping levels in an assembly of blades are developed and discussed.
NASA Astrophysics Data System (ADS)
Lam, Margaretha J.; Inman, Daniel J.; Saunders, William R.
1998-06-01
Damping is important to structures and can be achieved through the addition of viscoelastic materials (VEM). The damping of the VEM is enhanced if a constraining layer is attached to the VEM. If this constraining layer is active, the treatment is called active constrained layer damping (ACLD). In the last few years, ACLD has proven to be superior in vibration control to active or passive damping. The active element makes ACLD more effective than passive constrained layer damping. It also provides a fail-safe in case of breakdown of the active element that is not present for purely active control. It is shown that the control effort needed to damp vibration using ACLD can be significantly higher than purely active control. In order to combine the inherent damping of passive control with the effectiveness of the active element, this paper will explore different variations of active, passive and hybrid damping. Some of the variations include: passive constrained layer damping (PCLD) separate from active element but on the same side of beam, PCLD separate from active on the opposite side of the beam, and active element underneath PCLD. The discretized system equations will be obtained using assumed modes method and Lagrange's equation. The damping will be modeled using the Golla-Hughes-McTavish (GHM) method. The optimal placement and size of the active, passive, ACLD and hybrid treatments will be found using different schemes. The issue of overshoot and settling time of the output and control force using LQR will be addressed, as well as the control effort, passive and active vibration suppression, and LQR cost function. It will be shown that the hybrid treatments are capable of greater vibration control for lower control effort for different optimization schemes. 31
Quasinormal modes of self-dual warped AdS{sub 3} black hole in topological massive gravity
Li Ran; Ren Jirong
2011-03-15
We consider the scalar, vector and spinor field perturbations in the background of self-dual warped AdS{sub 3} black hole of topological massive gravity. The corresponding exact expressions for quasinormal modes are obtained by analytically solving the perturbation equations and imposing the vanishing Dirichlet boundary condition at asymptotic infinity. It is expected that the quasinormal modes agree with the poles of retarded Green's functions of the CFT dual to self-dual warped AdS{sub 3} black hole. Our results provide a quantitative test of the warped AdS/CFT correspondence.
Introduction to the scientific application system of DAMPE (On behalf of DAMPE collaboration)
NASA Astrophysics Data System (ADS)
Zang, Jingjing
2016-07-01
The Dark Matter Particle Explorer (DAMPE) is a high energy particle physics experiment satellite, launched on 17 Dec 2015. The science data processing and payload operation maintenance for DAMPE will be provided by the DAMPE Scientific Application System (SAS) at the Purple Mountain Observatory (PMO) of Chinese Academy of Sciences. SAS is consisted of three subsystems - scientific operation subsystem, science data and user management subsystem and science data processing subsystem. In cooperation with the Ground Support System (Beijing), the scientific operation subsystem is responsible for proposing observation plans, monitoring the health of satellite, generating payload control commands and participating in all activities related to payload operation. Several databases developed by the science data and user management subsystem of DAMPE methodically manage all collected and reconstructed science data, down linked housekeeping data, payload configuration and calibration data. Under the leadership of DAMPE Scientific Committee, this subsystem is also responsible for publication of high level science data and supporting all science activities of the DAMPE collaboration. The science data processing subsystem of DAMPE has already developed a series of physics analysis software to reconstruct basic information about detected cosmic ray particle. This subsystem also maintains the high performance computing system of SAS to processing all down linked science data and automatically monitors the qualities of all produced data. In this talk, we will describe all functionalities of whole DAMPE SAS system and show you main performances of data processing ability.
A Resonant Damping Study Using Piezoelectric Materials
NASA Technical Reports Server (NTRS)
Min, J. B.; Duffy, K. P.; Choi, B. B.; Morrison, C. R.; Jansen, R. H.; Provenza, A. J.
2008-01-01
Excessive vibration of turbomachinery blades causes high cycle fatigue (HCF) problems requiring damping treatments to mitigate vibration levels. Based on the technical challenges and requirements learned from previous turbomachinery blade research, a feasibility study of resonant damping control using shunted piezoelectric patches with passive and active control techniques has been conducted on cantilever beam specimens. Test results for the passive damping circuit show that the optimum resistive shunt circuit reduces the third bending resonant vibration by almost 50%, and the optimum inductive circuit reduces the vibration by 90%. In a separate test, active control reduced vibration by approximately 98%.
Quasinormal modes, bifurcations, and nonuniqueness of charged scalar-tensor black holes
Doneva, Daniela D.; Yazadjiev, Stoytcho S.; Kokkotas, Kostas D.; Stefanov, Ivan Zh.
2010-09-15
In the present paper, we study the scalar sector of the quasinormal modes of charged general relativistic, static, and spherically symmetric black holes coupled to nonlinear electrodynamics and embedded in a class of scalar-tensor theories. We find that for a certain domain of the parametric space, there exists unstable quasinormal modes. The presence of instabilities implies the existence of scalar-tensor black holes with primary hair that bifurcate from the embedded general relativistic black-hole solutions at critical values of the parameters corresponding to the static zero modes. We prove that such scalar-tensor black holes really exist by solving the full system of scalar-tensor field equations for the static, spherically symmetric case. The obtained solutions for the hairy black holes are nonunique, and they are in one-to-one correspondence with the bounded states of the potential governing the linear perturbations of the scalar field. The stability of the nonunique hairy black holes is also examined, and we find that the solutions for which the scalar field has zeros are unstable against radial perturbations. The paper ends with a discussion of possible formulations of a new classification conjecture.
NASA Astrophysics Data System (ADS)
Fiziev, Plamen; Staicova, Denitsa
2011-12-01
Although finding numerically the quasinormal modes of a nonrotating black hole is a well-studied question, the physics of the problem is often hidden behind complicated numerical procedures aimed at avoiding the direct solution of the spectral system in this case. In this article, we use the exact analytical solutions of the Regge-Wheeler equation and the Teukolsky radial equation, written in terms of confluent Heun functions. In both cases, we obtain the quasinormal modes numerically from spectral condition written in terms of the Heun functions. The frequencies are compared with ones already published by Andersson and other authors. A new method of studying the branch cuts in the solutions is presented—the epsilon method. In particular, we prove that the mode n=8 is not algebraically special and find its value with more than 6 firm figures of precision for the first time. The stability of that mode is explored using the ɛ method, and the results show that this new method provides a natural way of studying the behavior of the modes around the branch cut points.
Partition functions in even dimensional AdS via quasinormal mode methods
NASA Astrophysics Data System (ADS)
Keeler, Cynthia; Ng, Gim Seng
2014-06-01
In this note, we calculate the one-loop determinant for a massive scalar (with conformal dimension Δ) in even-dimensional AdS d+1 space, using the quasinormal mode method developed in [1] by Denef, Hartnoll, and Sachdev. Working first in two dimensions on the related Euclidean hyperbolic plane H 2, we find a series of zero modes for negative real values of Δ whose presence indicates a series of poles in the one-loop partition function Z(Δ) in the Δ complex plane; these poles contribute temperature-independent terms to the thermal AdS partition function computed in [1]. Our results match those in a series of papers by Camporesi and Higuchi, as well as Gopakumar et al. [2] and Banerjee et al. [3]. We additionally examine the meaning of these zero modes, finding that they Wick-rotate to quasinormal modes of the AdS2 black hole. They are also interpretable as matrix elements of the discrete series representations of SO(2, 1) in the space of smooth functions on S 1. We generalize our results to general even dimensional AdS2 n , again finding a series of zero modes which are related to discrete series representations of SO(2 n, 1), the motion group of H 2 n .
Quasinormal modes and holographic correlators in a crunching AdS geometry
NASA Astrophysics Data System (ADS)
Kumar, S. Prem; Vaganov, Vladislav
2016-02-01
We calculate frequency space holographic correlators in an asymptotically AdS crunching background, dual to a relevant deformation of the M2-brane CFT placed in de Sitter spacetime. For massless bulk scalars, exploiting the connection to a solvable supersymmetric quantum mechanical problem, we obtain the exact frequency space correlator for the dual operator in the deformed CFT. Controlling the shape of the crunching surface in the Penrose diagram by smoothly dialling the deformation from zero to infinity, we observe that in the large deformation limit the Penrose diagram becomes a `square', and the exact holographic correlators display striking similarities to their counterparts in the BTZ black hole and its higher dimensional generalisations. We numerically determine quasinormal poles for relevant and irrelevant operators, and find an intricate pattern of these in the complex frequency plane. In the case of relevant operators, the deformation parameter has an infinite sequence of critical values, each one characterised by a pair of poles colliding and moving away from the imaginary frequency axis with increasing deformation. In the limit of infinite deformation all scalar operators have identical quasinormal spectra. We compare and contrast our strongly coupled de Sitter QFT results with strongly coupled thermal correlators from AdS black holes.
Asymptotic quasinormal frequencies of different spin fields in spherically symmetric black holes
Cho, H. T.
2006-01-15
We consider the asymptotic quasinormal frequencies of various spin fields in Schwarzschild and Reissner-Nordstroem black holes. In the Schwarzschild case, the real part of the asymptotic frequency is ln3 for the spin 0 and the spin 2 fields, while for the spin 1/2, the spin 1, and the spin 3/2 fields it is zero. For the nonextreme charged black holes, the spin 3/2 Rarita-Schwinger field has the same asymptotic frequency as that of the integral spin fields. However, the asymptotic frequency of the Dirac field is different, and its real part is zero. For the extremal case, which is relevant to the supersymmetric consideration, all the spin fields have the same asymptotic frequency, the real part of which is zero. For the imaginary parts of the asymptotic frequencies, it is interesting to see that it has a universal spacing of 1/4M for all the spin fields in the single-horizon cases of the Schwarzschild and the extreme Reissner-Nordstroem black holes. The implications of these results to the universality of the asymptotic quasinormal frequencies are discussed.
NASA Astrophysics Data System (ADS)
Wang, Mengjie; Herdeiro, Carlos; Sampaio, Marco O. P.
2015-12-01
Perturbations of asymptotically anti-de-Sitter (AdS) spacetimes are often considered by imposing field vanishing boundary conditions (BCs) at the AdS boundary. Such BCs, of Dirichlet-type, imply a vanishing energy flux at the boundary, but the converse is, generically, not true. Regarding AdS as a gravitational box, we consider vanishing energy flux (VEF) BCs as a more fundamental physical requirement and we show that these BCs can lead to a new branch of modes. As a concrete example, we consider Maxwell perturbations on Kerr-AdS black holes in the Teukolsky formalism, but our formulation applies also for other spin fields. Imposing VEF BCs, we find a set of two Robin BCs, even for Schwarzschild-AdS black holes. The Robin BCs on the Teukolsky variables can be used to study quasinormal modes, superradiant instabilities and vector clouds. As a first application, we consider here the quasinormal modes of Schwarzschild-AdS black holes. We find that one of the Robin BCs yields the quasinormal spectrum reported in the literature, while the other one unveils a new branch for the quasinormal spectrum.
The impact damped harmonic oscillator in free decay
NASA Technical Reports Server (NTRS)
Brown, G. V.; North, C. M.
1987-01-01
The impact-damped oscillator in free decay is studied by using time history solutions. A large range of oscillator amplitude is covered. The amount of damping is correlated with the behavior of the impacting mass. There are three behavior regimes: (1) a low amplitude range with less than one impact per cycle and very low damping, (2) a useful middle amplitude range with a finite number of impacts per cycle, and (3) a high amplitude range with an infinite number of impacts per cycle and progressively decreasing damping. For light damping the impact damping in the middle range is: (1) proportional to impactor mass, (2) additive to proportional damping, (3) a unique function of vibration amplitude, (4) proportional to 1-epsilon, where epsilon is the coefficient of restitution, and (5) very roughly inversely proportional to amplitude. The system exhibits jump phenomena and period doublings. An impactor with 2 percent of the oscillator's mass can produce a loss factor near 0.1.
Xu Feng; Zhang Xiaoyu; Nguyen Nguyen Phuoc; Ma Yungui; Ong, C. K.
2009-02-15
In this work, we investigate the high-frequency permeability spectra of as-sputtered FeCoSiN/Al{sub 2}O{sub 3} laminated films, and discuss their dependence on the thickness of each FeCoSiN layer, based on the phenomenological Landau-Lifshitz-Gilbert equation. The damping factor and coercivity show their minima with lamination, deviating from the expectation based on the grain size confinement effect. Such dependences on the layer thickness indicate the influence of magnetic coupling. The decreases in the damping factor and the coercivities with lamination can be partially attributed to the decrease in the magnetostatic coupling induced by ripple structures. The enhanced damping and enlarged coercivity values obtained with further lamination are ascribed to the enhanced Neel couplings. The dependences show that the lamination can be effective in tuning the magnetization dynamics by changing the magnetic couplings.
DuBois, Neil J.; Amaral, Antonio M.
1992-10-27
A damped flexible seal assembly for a torpedo isolates the tailcone thereof rom vibrational energy present in the drive shaft assembly. A pair of outside flanges, each of which include an inwardly facing groove and an O-ring constrained therein, provide a watertight seal against the outer non-rotating surface of the drive shaft assembly. An inside flange includes an outwardly-facing groove and an O-ring constrained therein, and provides a watertight seal against the inner surface of the tail cone. Two cast-in-place elastomeric seals provide a watertight seal between the flanges and further provide a damping barrier between the outside flanges and the inside flanges for damping vibrational energy present in the drive shaft assembly before the energy can reach the tailcone through the seal assembly.
The Derivation and Quasinormal Mode Spectrum of Acoustic Anti-de Sitter Black Hole Analogues
NASA Astrophysics Data System (ADS)
Babb, James Patrick
Dumb holes (also known as acoustic black holes) are fluid flows which include an "acoustic horizon": a surface, analogous to a gravitational horizon, beyond which sound may pass but never classically return. Soundwaves in these flows will therefore experience "effective geometries" which are identical to black hole spacetimes up to a conformal factor. By adjusting the parameters of the fluid flow, it is possible to create an effective geometry which is conformal to the Anti-de Sitter black hole spacetime---a geometry which has received a great deal of attention in recent years due to its conjectured holographic duality to Conformal Field Theories. While we would not expect an acoustic analogue of the AdS-CFT correspondence to exist, this dumb hole provides a means, at least in principle, of experimentally testing the theoretical properties of the AdS spacetime. In particular, I have calculated the quasinormal mode spectrum of this acoustic geometry.
Partition functions with spin in AdS2 via quasinormal mode methods
NASA Astrophysics Data System (ADS)
Keeler, Cynthia; Lisbão, Pedro; Ng, Gim Seng
2016-10-01
We extend the results of [1], computing one loop partition functions for massive fields with spin half in AdS2 using the quasinormal mode method proposed by Denef, Hartnoll, and Sachdev [2]. We find the finite representations of SO(2, 1) for spin zero and spin half, consisting of a highest weight state | h> and descendants with non-unitary values of h. These finite representations capture the poles and zeroes of the one loop determinants. Together with the asymptotic behavior of the partition functions (which can be easily computed using a large mass heat kernel expansion), these are sufficient to determine the full answer for the one loop determinants. We also discuss extensions to higher dimensional AdS2 n and higher spins.
NASA Astrophysics Data System (ADS)
Kamandar Dezfouli, Mohsen; Axelrod, Simon; Wang, Herman M. K.; Helmy, Amr; Gordon, Reuven; Hughes, Stephen
2016-09-01
We describe a powerful quasinormal mode (QNM) approach to characterizing the decay properties of quantum emitters in metal-dielectric resonator systems, including hybrid plasmonic-photonic coupled cavities as well as hyperbolic metamaterial resonators. We quantify both the radiative and non-radiative decay rates in these complex structures using these QNMs and a Green function expansion, which yields an excellent agreement with full-dipole calculations of Maxwell's equations. Using this analytical QNM theory, we can map the Purcell factor for the system over a wide range of frequencies and dipole positions. We further show that how individual QNMs of these systems contribute to the underlying physics, whether it is strong interference effects between the sub-systems, in the case of a hybrid structure, or it is a physically meaningful explanation of very low beta factor for single photon emission in the case of hyperbolic metamaterials.
NASA Astrophysics Data System (ADS)
Yan, Zhang; Tao, Ma; Yongyi, Huang
2016-07-01
The first Chinese space observatory DAMPE (DArk Matter Particle Explorer) was successfully launched on Dec. 17th, 2015. One major scientific object of DAMPE is to measure electrons between 5GeV to 10TeV with excellent energy resolution (1.5% at 800GeV) to search for possible dark matter signatures. The detector consists of four subsystems: a plastic scintillator detector (PSD), a silicon-tungsten tracker (STK), a BGO calorimeter (BGO), and a neutron detector (NUD). The NUD on board DAMPE is designed to detect moderated neutrons via the boron capture of thermal neutrons in boron-doped plastics. Given the fact that hadron showers initiated in the BGO calorimeter by incident nuclei tend to be followed by significantly more neutron activities comparing to electromagnetic cascades triggered by electrons, the NUD provides an additional order of magnitude hadron rejection capability to improve the overall e/p discrimination of DAMPE up to 10 ^{5}. Preliminary analysis of the in-orbit data is given, together with comparisons to the results obtained by a detailed GEANT4 simulation of the NUD instrument.
Palmer, R.B.
1987-05-01
This paper looks at, and compares three types of damping ring lattices: conventional, wiggler lattice with finite ..cap alpha.., wiggler lattice with ..cap alpha.. = 0, and observes the attainable equilibrium emittances for the three cases assuming a constraint on the attainable longitudinal impedance of 0.2 ohms. The emittance obtained are roughly in the ratio 4:2:1 for these cases.
Radiation damping on cryoprobes.
Shishmarev, Dmitry; Otting, Gottfried
2011-12-01
Radiation damping on 600 and 800 MHz cryoprobes was investigated. The phase angle β between a vector 90° phase shifted to the precessing magnetization and the rf field induced in the coil was found to depend markedly on whether an FID was being acquired or not. The magnitude of the radiation damping field was sufficiently strong to restore 95% of the equilibrium water magnetization of a 90% H2O sample in a 5 mm sample tube within about 5 ms following a 165° pulse. This can be exploited in water flip-back versions of NOESY and TOCSY experiments of proteins, but care must be taken to limit the effect of the radiation damping field from the water on the Ha protons. Long water-selective pulses can be applied only following corrections. We developed a program for correcting pulse shapes if β is non-zero. The WATERGATE scheme is shown to be insensitive to imperfections introduced by radiation damping.
NASA Astrophysics Data System (ADS)
Burns, J. A.; Sharma, I.
2000-10-01
Motivated by the recent detection of complex rotational states for several asteroids and comets, as well as by the ongoing and planned spacecraft missions to such bodies, which should allow their rotational states to be accurately determined, we revisit the problem of the nutational damping of small solar system bodies. The nutational damping of asteroids has been approximately analyzed by Prendergast (1958), Burns and Safronov (1973), and Efroimsky and Lazarian (2000). Many other similar dynamical studies concern planetary wobble decay (e.g., Peale 1973; Yoder and Ward 1979), interstellar dust grain alignment (e.g., Purcell 1979; Lazarian and Efroimsky 1999) and damping of Earth's Chandler wobble (Lambeck 1980). Recall that rotational energy loss for an isolated body aligns the body's angular momentum vector with its axis of maximum inertia. Assuming anelastic dissipation, simple dimensional analysis determines a functional form of the damping timescale, on which all the above authors agree. However, the numerical coefficients of published results are claimed to differ by orders of magnitude. Differences have been ascribed to absent physics, to solutions that fail to satisfy boundary conditions perfectly, and to unphysical choices for the Q parameter. The true reasons for the discrepancy are unclear since, despite contrary claims, the full 3D problem (nutational damping of an anelastic ellipsoid) is analytically intractable so far. To move the debate forward, we compare the solution of a related 2D problem to the expressions found previously, and we present results from a finite element model. On this basis, we feel that previous rates for the decay of asteroidal tumbling (Harris 1994), derived from Burns and Safronov (1973), are likely to be accurate, at least to a factor of a few. Funded by NASA.
Higher order mode damping in an ALS test cavity
Jacob, A.F.; Lamberston, G.R. ); Barry, W. )
1990-06-01
The higher order mode attenuation scheme proposed for the Advanced Light Source accelerating cavities consists of two broad-band dampers placed 90{degrees} apart on the outer edge. In order to assess the damping efficiency a test assembly was built. The HOM damping was obtained by comparing the peak values of the transmission through the cavity for both the damped and the undamped case. Because of the high number of modes and frequency shifts due to the damping gear, the damping was assessed statistically, by averaging over several modes. In the frequency range from 1.5 to 5.5 GHz, average damping greater than 100 was obtained. 1 ref., 6 figs.
Interdigitated interdigital transducer for surface elastometry of soft damping tissue.
Danicki, Eugene; Nowicki, Andrzej; Tasinkevych, Yuriy
2013-06-01
Measurement of the shear elastic constant of soft and highly damping tissue of high Poisson ratio is quite a challenging task. It is proposed to evaluate shear wave velocity and damping of tissue by measuring the shear skimming bulk waves using one interdigitated interdigital transducer on a piezoelectric layer, such as polyvinylidene fluoride, applied to the surface of the small tissue sample.
NASA Astrophysics Data System (ADS)
Thomas, A. G. R.; Ridgers, C. P.; Bulanov, S. S.; Griffin, B. J.; Mangles, S. P. D.
2012-10-01
A number of theoretical calculations have studied the effect of radiation-reaction forces on radiation distributions in strong-field counterpropagating electron-beam-laser interactions, but could these effects—including quantum corrections—be observed in interactions with realistic bunches and focusing fields, as is hoped in a number of soon-to-be-proposed experiments? We present numerical calculations of the angularly resolved radiation spectrum from an electron bunch with parameters similar to those produced in laser-wakefield-acceleration experiments, interacting with an intense, ultrashort laser pulse. For our parameters, the effect of radiation damping on the angular distribution and energy distribution of photons is not easily discernible for a realistic moderate-emittance electron beam. However, experiments using such a counterpropagating beam-laser geometry should be able to measure these effects using current laser systems through measurement of the electron-beam properties. In addition, the brilliance of this source is very high, with peak spectral brilliance exceeding 1029photonss-1mm-2mrad-2(0.1%bandwidth)-1 with an approximately 2% conversion efficiency and with a peak energy of 10 MeV.
Excitation of magnetization using a modulated radiation damping field.
Walls, Jamie D; Huang, Susie Y; Lin, Yung-Ya
2006-10-12
In this work, pulsed-field gradients are used to modulate the radiation damping field generated by the detection coil in an NMR experiment in order that spins with significantly different chemical shifts can affect one another via the radiation damping field. Experiments performed on solutions of acetone/water and acetone/DMSO/water demonstrate that spins with chemical shift differences much greater than the effective radiation damping field strength can still be coupled by modulating the radiation damping field. Implications for applications in high-field NMR and for developing sensitive magnetization detectors are discussed.
Introduction to DAMPE event reconstruction (On behalf of DAMPE collaboration)
NASA Astrophysics Data System (ADS)
Zang, Jingjing
2016-07-01
The Dark Matter Particle Explorer (DAMPE) is a high energy particle physics experiment satellite, launched on 17 Dec 2015. To measure basic attributes of cosmic ray particles, DAMPE is equipped with four sub-detectors, BGO calorimeter (BGO), plastic scintillator detector (PSD), silicon tungsten tracker (STK) and neutron detector (NUD). On orbit, the high energy particle data are acquired and recorded by well-designed Data Acquisition system. After that, a series of elaborate event reconstruction algorithms are implemented to determine the energy, direction and particle ID of each event. The energy reconstruction algorithm firstly treats the sum of the BGO crystal energy as the overall energy estimator and various corrections are performed to calculate energy leakage from side and back of the calorimeter. The track reconstruction starts with cluster finding in STK, then shower axis of BGO and barycentre of clusters are used to extract seed of tracks. These seeds will be projected on the next layer by Kalman Filter method which will finally give location and direction of particle tracks. Based on shower development in BGO and tracks reconstructed by STK, we also combine data from PSD and NUD and developed a series of algorithms to evaluate particle's charge and identification. In this talk, we will describe technical strategies of event reconstruction and provide their basic performance.
DAMPING THE HIGH ORDER MODES IN THE PUMPING CHAMBER OF THE PEP-II LOW ENERGY RING
Novokhatski, A
2004-06-30
The Low Energy Ring of the PEP-II B-factory operates with extremely high currents of short positron bunches. Any discontinuity in the vacuum chamber can excite a broad-band spectrum of high order modes (HOM). A temperature rise has been found in the vacuum chamber elements in one junction of straight and arc chambers. The power in the wake fields was high enough to char beyond use the feed-through for the titanium sublimation pump (TSP). This pumping section is 5.5 m long and consists of the beam chamber and an ante-chamber. Electromagnetic fields, excited in the beam chamber penetrate to the ante-chamber and then through the heater feed-through come out. To be sure that these electromagnetic fields are present a small ceramic tile with a high loss tangent was placed near the TSP feed-through outside of the pumping chamber. A thermocouple that was attached to this tile showed a strong temperature rise. A short wire antenna was also placed there. The antenna was connected directly to a spectrum analyzer. Measurements show a wide frequency HOM spectrum with a maximum in the 2-3 GHz region. Based on these measurements a special water cooled HOM absorber was designed and installed in the vacuum chamber. As a result, the HOM power in the section decreased and the temperature rise went down. The power loss in the absorber reaches 1200 W for a positron beam current of 2.4 A. The absorber helped to find the source of HOM. Steering the beam on the vertical collimators upstream of the absorber resulted in the significant HOM power change in the absorber.
Damping Goes the Distance in Golf
NASA Technical Reports Server (NTRS)
2004-01-01
In the late 1980s, Dr. Benjamin Dolgin of NASA s Jet Propulsion Laboratory developed a concept for a high-damping graphite/viscoelastic material for the Strategic Defense Initiative (popularly referred to as "Star Wars"), as part of a space-based laser anti-missile program called "Asterix." Dolgin drummed up this concept with the intention of stabilizing weapons launch platforms in space, where there is no solid ground to firmly support these structures. Without the inclusion of high-damping material, the orbital platforms were said to vibrate for 20 minutes after force was applied - a rate deemed "unacceptable" by leaders of the Strategic Defense Initiative.
Comparison of damping treatments for gas turbine blades
NASA Astrophysics Data System (ADS)
Gordon, Robert W.; Hollkamp, Joseph J.
1996-05-01
High frequency vibration of gas turbine fan blades is a high cycle fatigue concern. Friction damping devices are ineffective in suppressing high frequency vibration modes and external damping treatments are plagued by creep concerns. An alternative approach is to apply viscoelastic material internally in the blades. In this paper, an analytical comparison of internal damping treatments for fan blades is presented. The fan blade is modeled as a solid, flat, cantilevered titanium plate. Internal portions are removed producing cavities that are filled with viscoelastic material. Configurations with one, two, and three cavities are modeled using the modal strain energy method in conjunction with finite element analysis to estimate damping. Results show that appreciable damping levels for high frequency modes are possible with stiff viscoelastic material. Other design criteria are also considered. Results indicate that the hydrostatic load from the viscoelastic material on the cavity walls may be a concern.
Experimental Investigation of Temperature-Dependent Gilbert Damping in Permalloy Thin Films
Zhao, Yuelei; Song, Qi; Yang, See-Hun; Su, Tang; Yuan, Wei; Parkin, Stuart S. P.; Shi, Jing; Han, Wei
2016-01-01
The Gilbert damping of ferromagnetic materials is arguably the most important but least understood phenomenological parameter that dictates real-time magnetization dynamics. Understanding the physical origin of the Gilbert damping is highly relevant to developing future fast switching spintronics devices such as magnetic sensors and magnetic random access memory. Here, we report an experimental study of temperature-dependent Gilbert damping in permalloy (Py) thin films of varying thicknesses by ferromagnetic resonance. From the thickness dependence, two independent contributions to the Gilbert damping are identified, namely bulk damping and surface damping. Of particular interest, bulk damping decreases monotonically as the temperature decreases, while surface damping shows an enhancement peak at the temperature of ~50 K. These results provide an important insight to the physical origin of the Gilbert damping in ultrathin magnetic films. PMID:26961411
Radiation damping in microcoil NMR probes
NASA Astrophysics Data System (ADS)
Krishnan, V. V.
2006-04-01
Radiation damping arises from the field induced in the receiver coil by large bulk magnetization and tends to selectively drive this magnetization back to equilibrium much faster than relaxation processes. The demand for increased sensitivity in mass-limited samples has led to the development of microcoil NMR probes that are capable of obtaining high quality NMR spectra with small sample volumes (nL-μL). Microcoil probes are optimized to increase sensitivity by increasing either the sample-to-coil ratio (filling factor) of the probe or quality factor of the detection coil. Though radiation damping effects have been studied in standard NMR probes, these effects have not been measured in the microcoil probes. Here a systematic evaluation of radiation damping effects in a microcoil NMR probe is presented and the results are compared with similar measurements in conventional large volume samples. These results show that radiation-damping effects in microcoil probe is much more pronounced than in 5 mm probes, and that it is critically important to optimize NMR experiments to minimize these effects. As microcoil probes provide better control of the bulk magnetization, with good RF and B0 inhomogeneity, in addition to negligible dipolar field effects due to nearly spherical sample volumes, these probes can be used exclusively to study the complex behavior of radiation damping.
Radiation damping in microcoil NMR probes.
Krishnan, V V
2006-04-01
Radiation damping arises from the field induced in the receiver coil by large bulk magnetization and tends to selectively drive this magnetization back to equilibrium much faster than relaxation processes. The demand for increased sensitivity in mass-limited samples has led to the development of microcoil NMR probes that are capable of obtaining high quality NMR spectra with small sample volumes (nL-microL). Microcoil probes are optimized to increase sensitivity by increasing either the sample-to-coil ratio (filling factor) of the probe or quality factor of the detection coil. Though radiation damping effects have been studied in standard NMR probes, these effects have not been measured in the microcoil probes. Here a systematic evaluation of radiation damping effects in a microcoil NMR probe is presented and the results are compared with similar measurements in conventional large volume samples. These results show that radiation-damping effects in microcoil probe is much more pronounced than in 5 mm probes, and that it is critically important to optimize NMR experiments to minimize these effects. As microcoil probes provide better control of the bulk magnetization, with good RF and B0 inhomogeneity, in addition to negligible dipolar field effects due to nearly spherical sample volumes, these probes can be used exclusively to study the complex behavior of radiation damping.
Damping by branching: a bioinspiration from trees.
Theckes, B; Langre, E de; Boutillon, X
2011-12-01
Man-made slender structures are known to be sensitive to high levels of vibration due to their flexibility which often cause irreversible damage. In nature, trees repeatedly endure large amplitudes of motion, mostly caused by strong climatic events, yet with minor or no damage in most cases. A new damping mechanism inspired by the architecture of trees is identified here and characterized in the simplest tree-like structure, a Y-shaped branched structure. Through analytical and numerical analyses of a simple two-degree-of-freedom model, branching is shown to be the key ingredient in this protective mechanism that we call damping-by-branching. It originates in the geometrical nonlinearities so that it is specifically efficient to damp out large amplitudes of motion. A more realistic model, using flexible beam approximation, shows that the mechanism is robust. Finally, two bioinspired architectures are analyzed, showing significant levels of damping achieved via branching with typically 30% of the energy being dissipated in one oscillation. This concept of damping-by-branching is of simple practical use in the design of very slender and flexible structures subjected to extreme dynamical loadings.
Resolving photons from cosmic ray in DAMPE
NASA Astrophysics Data System (ADS)
Xu, Zunlei; Chang, Jin; Li, Xiang; Dong, TieKuang; Zang, Jingjing
2016-07-01
The Dark Matter Particle Explorer(DAMPE), which took to the skies on 17 December, is designed for high energy cosmic ray ion detection. The proportion of photons in the cosmic ray is very small, so it's difficult to distinguish between photons and 'background', but necessary for any DAMPE gamma-ray science goals.The paper present a algorithm to identify photons from 'background' mainly by the tracker/converter, which promote pair conversion and measure the directions of incident particles, and an anticoincidence detector,featuring an array of plastic scintillator to detect the charged particles.The method has been studied by simulating using the GEANT4 Monte Carlo simulation code and adjusted by the BeamTest at CERN in December,2014.In addition,DAMPE photon detection capabilities can be checked using the flight data.
Biomimetic Gradient Polymers with Enhanced Damping Capacities.
Wang, Dong; Zhang, Huan; Guo, Jing; Cheng, Beichen; Cao, Yuan; Lu, Shengjun; Zhao, Ning; Xu, Jian
2016-04-01
Designing gradient structures, mimicking biological materials, such as pummelo peels and tendon, is a promising strategy for developing advanced materials with superior energy damping capacities. Here a facile and effective approach for fabricating polymers with composition gradients at millimeter length scale is presented. The gradient thiol-ene polymers (TEPs) are created by the use of density difference of ternary thiol-ene-ene precursors and the subsequent photo-crosslinking via thiol-ene reaction. The compositional gradients are analyzed via differential scanning calorimeter (DSC), compressive modulus testing, atomic force microscopy (AFM) indentation, and swelling measurements. In contrast to homogeneous TEPs networks, the resultant gradient polymer shows a broader effective damping temperature range combining with good mechanical properties. The present result provides an effective route toward high damping materials by the fabrication of gradient structures.
NASA Astrophysics Data System (ADS)
Petitjean, P.; Ledoux, C.
Recently, Prochaska & Wolfe (1997) have used Keck spectra of 17 DLA absorbers to investigate the kinematics of the neutral gas using unsaturated low excitation transitions such as Si iiλ 1808. They show that the absorption profiles are inconsistent with models of galactic haloes with random motions, spherically infalling gas and slowly rotating hot disks. The CDM model (Kauffmann 1996) is rejected as it produces disks with rotation velocities too small to account for the large observed velocity broadening of the absorption lines. Models of thick disks (h ~0.3 R, where h is the vertical scale and R the radius) with large rotational velocity (v 225kms-1) can reproduce the data. By combining new data on five damped systems with information gathered in the literature, we study the kinematics of the low and high-ionization phases in a sample of 26 damped Lyman-α systems in the redshift range 1.17 - 4.38. We show that the broader the line the more asymmetric, as expected in case rotation dominates the line broadening. However this correlation does not hold for velocities larger than 150 km/s indicating that evidence for rotational motions if any is restricted to velocity broadenings Δ V < 150kms-1. The systems with Δ V > 200kms-1 are peculiar with kinematics consistent with random motions. They show sub-systems as those expected if the objects are in the process of merging.
Relaxation damping in oscillating contacts
Popov, M.; Popov, V.L.; Pohrt, R.
2015-01-01
If a contact of two purely elastic bodies with no sliding (infinite coefficient of friction) is subjected to superimposed oscillations in the normal and tangential directions, then a specific damping appears, that is not dependent on friction or dissipation in the material. We call this effect “relaxation damping”. The rate of energy dissipation due to relaxation damping is calculated in a closed analytic form for arbitrary axially-symmetric contacts. In the case of equal frequency of normal and tangential oscillations, the dissipated energy per cycle is proportional to the square of the amplitude of tangential oscillation and to the absolute value of the amplitude of normal oscillation, and is dependent on the phase shift between both oscillations. In the case of low frequency tangential oscillations with superimposed high frequency normal oscillations, the dissipation is proportional to the ratio of the frequencies. Generalization of the results for macroscopically planar, randomly rough surfaces as well as for the case of finite friction is discussed. PMID:26549011
Acoustic transducer with damping means
Smith, Richard W.; Adamson, Gerald E.
1976-11-02
An ultrasonic transducer specifically suited to high temperature sodium applications is described. A piezoelectric active element is joined to the transducer faceplate by coating the faceplate and juxtaposed active element face with wetting agents specifically compatible with the bonding procedure employed to achieve the joint. The opposite face of the active element is fitted with a backing member designed to assure continued electrical continuity during adverse operating conditions which can result in the fracturing of the active element. The fit is achieved employing a spring-loaded electrode operably arranged to electrically couple the internal transducer components, enclosed in a hermetically sealed housing, to accessory components normally employed in transducer applications. Two alternative backing members are taught for assuring electrical continuity. The first employs a resilient, discrete multipoint contact electrode in electrical communication with the active element face. The second employs a resilient, elastomeric, electrically conductive, damped member in electrical communication with the active element face in a manner to effect ring-down of the transducer. Each embodiment provides continued electrical continuity within the transducer in the event the active element fractures, while the second provides the added benefit of damping.
NASA Astrophysics Data System (ADS)
Alhan, Cenk; Gazi, Hatice; Kurtuluş, Hakan
2016-10-01
High Damping Rubber Bearings (HDRBs) are among various types of laterally flexible isolation system elements that effectively protect structures from detrimental effects of earthquakes by lengthening their fundamental periods. However, large isolator displacements resulting in strains larger than 100% may come into scene in case of near-fault ground motions containing long-period and large-amplitude velocity and/or displacement pulses. This is particularly important when HDRBs are used since the post-yield stiffness of an HDRB increases due to inherent strain hardening characteristics when a threshold isolator displacement limit is exceeded. Therefore, it may be critical to consider the stiffening of HDRBs in modeling of these elements for accurate seismic response evaluation of the buildings equipped with HDRBs that are located in near-fault regions. In this study, the significance of stiffening of HDRBs on the response of base-isolated buildings is investigated by conducting nonlinear time history analyses of benchmark six-story base-isolated buildings which employ HDRBs that are represented by non-stiffening or stiffening models under both historical and synthetic near-fault ground motions of various magnitudes and fault distances. The structural response parameters included in the comparisons are base displacements, story drifts, and floor accelerations. It is found that, the significance of stiffening of HDRBs on the response of base-isolated buildings under near-fault earthquakes becomes more prominent as the earthquake magnitude increases and the fault distance decreases and thus suggestions for modifications to seismic code regulations are made accordingly.
On damping mechanisms in beams
NASA Technical Reports Server (NTRS)
Banks, H. T.; Inman, D. J.
1989-01-01
A partial differential equation model of a cantilevered beam with a tip mass at its free end is used to study damping in a composite. Four separate damping mechanisms consisting of air damping, strain rate damping, spatial hysteresis and time hysteresis are considered experimentally. Dynamic tests were performed to produce time histories. The time history data is then used along with an approximate model to form a sequence of least squares problems. The solution of the least squares problem yields the estimated damping coefficients. The resulting experimentally determined analytical model is compared with the time histories via numerical simulation of the dynamic response. The procedure suggested here is compared with a standard modal damping ratio model commonly used in experimental modal analysis.
On damping mechanisms in beams
NASA Technical Reports Server (NTRS)
Banks, H. T.; Inman, D. J.
1991-01-01
A partial differential equation model of a cantilevered beam with a tip mass at its free end is used to study damping in a composite. Four separate damping mechanisms consisting of air damping, strain rate damping, spatial hysteresis and time hysteresis are considered experimentally. Dynamic tests were performed to produce time histories. The time history data is then used along with an approximate model to form a sequence of least squares problems. The solution of the least squares problem yields the estimated damping coefficients. The resulting experimentally determined analytical model is compared with the time histories via numerical simulation of the dynamic response. The procedure suggested here is compared with a standard modal damping ratio model commonly used in experimental modal analysis.
The DAMPE experiment: first data from space
NASA Astrophysics Data System (ADS)
De Mitri, Ivan
2017-03-01
The DAMPE satellite has been successfully launched in orbit on December 2015. The science goals of the mission include the study of high energy cosmic ray electrons, photons, protons and nuclei in a wide energy range: 109 - 1014 eV. A report on the mission status will be presented, together with on-orbit detector performance and first data coming from space.
Magnetically Damped Furnace (MDF)
NASA Technical Reports Server (NTRS)
1998-01-01
The Magnetically Damped Furnace (MDF) breadboard is being developed in response to NASA's mission and goals to advance the scientific knowledge of microgravity research, materials science, and related technologies. The objective of the MDF is to dampen the fluid flows due to density gradients and surface tension gradients in conductive melts by introducing a magnetic field during the sample processing. The MDF breadboard will serve as a proof of concept that the MDF performance requirements can be attained within the International Space Station resource constraints.
Embedding viscoelastic damping materials in low-cost VARTM composite structures
NASA Astrophysics Data System (ADS)
Robinson, M. J.; Kosmatka, J. B.
2005-05-01
It has been well established that using viscoelastic damping materials in structural applications can greatly reduce the dynamic response and thus improve structural fatigue life. Previously these materials have been used to solve vibration problems in metallic structures, where the damping material is attached to the structure and then a stiff outer layer is attached to promote shear deformation in the damping material. More recently, these materials have been used successfully in expensive aerospace composite structures, where the damping material is embedded between plies of prepreg graphite/epoxy prior to being cured in a high-temperature, high-pressure autoclave. The current research involves embedding these damping layers into low-cost composite structures fabricated using the Vacuum Assisted Resin Transfer Molding (VARTM) process. The damping layers are perforated with a series of small holes to allow the resin to flow through the damping layer and completely wet-out the structure. Experimental fabrication, vibration testing, and stiffness testing investigate the effect of hole diameter versus hole spacing. Results show that the damping and stiffness can be very sensitive to perforation spacing and size. It is shown that for closely spaced perforations (95% damping area) that damping increases by only a factor of 2.2 over the undamped plate. However, for greater perforation spacing (99.7% damping area) the damping is increased by a factor of 14.3. Experimental results as well as practical design considerations for fabricating damped composite structures using the VARTM process are presented.
Linear mode stability of the Kerr-Newman black hole and its quasinormal modes.
Dias, Óscar J C; Godazgar, Mahdi; Santos, Jorge E
2015-04-17
We provide strong evidence that, up to 99.999% of extremality, Kerr-Newman black holes (KNBHs) are linear mode stable within Einstein-Maxwell theory. We derive and solve, numerically, a coupled system of two partial differential equations for two gauge invariant fields that describe the most general linear perturbations of a KNBH. We determine the quasinormal mode (QNM) spectrum of the KNBH as a function of its three parameters and find no unstable modes. In addition, we find that the lowest radial overtone QNMs that are connected continuously to the gravitational ℓ=m=2 Schwarzschild QNM dominate the spectrum for all values of the parameter space (m is the azimuthal number of the wave function and ℓ measures the number of nodes along the polar direction). Furthermore, the (lowest radial overtone) QNMs with ℓ=m approach Reω=mΩH(ext) and Imω=0 at extremality; this is a universal property for any field of arbitrary spin |s|≤2 propagating on a KNBH background (ω is the wave frequency and ΩH(ext) the black hole angular velocity at extremality). We compare our results with available perturbative results in the small charge or small rotation regimes and find good agreement.
NASA Astrophysics Data System (ADS)
Ge, Rong-Chun; Hughes, Stephen
2016-05-01
Understanding light-matter interactions using localized surface plasmons (LSPs) is of fundamental interest in classical and quantum plasmonics and has a wide range of applications. In order to understand the spatial properties of LSPs, electron energy loss spectroscopy (EELS) is a common and powerful method of spatially resolving the extreme localized fields that can be obtained with metal resonators. However, modelling EELS for general shaped resonators presents a major challenge in computational electrodynamics, requiring the full photon Green function as a function of two space points and frequency. Here we present an intuitive and computationally simple method for computing EELS maps of plasmonic resonators using a quasinormal mode (QNM) expansion technique. By separating the contribution of the QNM and the bulk material, we give closed-form analytical formulas for the plasmonic QNM contribution to the EELS maps. We exemplify our technique for a split ring resonator, a gold nanorod, and a nanorod dimer structure. The method is accurate, intuitive, and gives orders of magnitude improvements over direct dipole simulations that numerically solve the full 3D Maxwell equations. We also show how the same QNM Green function can be used to obtain the Purcell factor (and projected local density of optical states) from quantum dipole emitters or two level atoms, and we demonstrate how the spectral features differ in general to the EELS spectrum.
Analytical description of quasi-normal mode in resonant plasmonic nano cavities
NASA Astrophysics Data System (ADS)
Yang, Fan; Liu, Haitao; Jia, Hongwei; Zhong, Ying
2016-03-01
We propose an analytical model of quasi-normal mode (QNM) for resonant plasmonic nano cavities formed by sub wavelength grooves in metallic substrate. The QNM has shown great advantages in understanding and calculating the frequency response of resonant nano-structures. With our model we show that the QNM originates from a resonance of the fundamental mode in every individual groove and its interaction via surface waves. Analytical expression for the complex eigenfrequency as well as the field distribution of the QNM can be derived from the model. With the analytical model and a few assumptions on the scattered field, the legitimacy of the expansion of scattered field with QNMs under external illuminations is justified with the Mittag-Leffler's theorem of meromorphic function. The expansion coefficients of QNMs are analytically expressed with a finite set of elementary scattering coefficients, which avoids the calculation of the mode volume of QNMs that have a spatial divergence at infinity. The model clarifies the physical origin of QNMs and drastically reduces the computational load of QNMs, especially for a large ensemble of grooves for which brute-force numerical tools are not available. The validity of the proposed model is tested against fully vectorial numerical results.
Active Damping Using Distributed Anisotropic Actuators
NASA Technical Reports Server (NTRS)
Schiller, Noah H.; Cabell, Randolph H.; Quinones, Juan D.; Wier, Nathan C.
2010-01-01
A helicopter structure experiences substantial high-frequency mechanical excitation from powertrain components such as gearboxes and drive shafts. The resulting structure-borne vibration excites the windows which then radiate sound into the passenger cabin. In many cases the radiated sound power can be reduced by adding damping. This can be accomplished using passive or active approaches. Passive treatments such as constrained layer damping tend to reduce window transparency. Therefore this paper focuses on an active approach utilizing compact decentralized control units distributed around the perimeter of the window. Each control unit consists of a triangularly shaped piezoelectric actuator, a miniature accelerometer, and analog electronics. Earlier work has shown that this type of system can increase damping up to approximately 1 kHz. However at higher frequencies the mismatch between the distributed actuator and the point sensor caused control spillover. This paper describes new anisotropic actuators that can be used to improve the bandwidth of the control system. The anisotropic actuators are composed of piezoelectric material sandwiched between interdigitated electrodes, which enables the application of the electric field in a preferred in-plane direction. When shaped correctly the anisotropic actuators outperform traditional isotropic actuators by reducing the mismatch between the distributed actuator and point sensor at high frequencies. Testing performed on a Plexiglas panel, representative of a helicopter window, shows that the control units can increase damping at low frequencies. However high frequency performance was still limited due to the flexible boundary conditions present on the test structure.
Effects of ion motion on linear Landau damping
NASA Astrophysics Data System (ADS)
Xu, Hui; Sheng, Zheng-Ming; Kong, Xiang-Mu; Su, Fu-Fang
2017-02-01
The effects of ion motion on Landau damping has been studied by the use of one-dimensional Vlasov-Poisson simulation. It is shown that the ion motion may significantly change the development of the linear Landau damping. When the ion mass is multiple of proton mass, its motion will halt the linear Landau damping at some time due to the excitation of ion acoustic waves. The latter will dominate the system evolution at the later stage and hold a considerable fraction of the total energy in the system. With very small ion mass, such as in electron-positron plasma, the ion motion can suppress the linear Landau damping very quickly. When the initial field amplitude is relatively high such as with the density perturbation amplitude δn/n0 > 0.1, the effect of ion motion on Landau damping is found to be weak or even ignorable.
Impact of Damping Uncertainty on SEA Model Response Variance
NASA Technical Reports Server (NTRS)
Schiller, Noah; Cabell, Randolph; Grosveld, Ferdinand
2010-01-01
Statistical Energy Analysis (SEA) is commonly used to predict high-frequency vibroacoustic levels. This statistical approach provides the mean response over an ensemble of random subsystems that share the same gross system properties such as density, size, and damping. Recently, techniques have been developed to predict the ensemble variance as well as the mean response. However these techniques do not account for uncertainties in the system properties. In the present paper uncertainty in the damping loss factor is propagated through SEA to obtain more realistic prediction bounds that account for both ensemble and damping variance. The analysis is performed on a floor-equipped cylindrical test article that resembles an aircraft fuselage. Realistic bounds on the damping loss factor are determined from measurements acquired on the sidewall of the test article. The analysis demonstrates that uncertainties in damping have the potential to significantly impact the mean and variance of the predicted response.
Bullock, Jack C.; Kelly, Benjamin E.
1980-01-01
A valve having a mechanism for damping out flow surges in a vacuum system which utilizes a slotted spring-loaded disk positioned adjacent the valve's vacuum port. Under flow surge conditions, the differential pressure forces the disk into sealing engagement with the vacuum port, thereby restricting the flow path to the slots in the disk damping out the flow surge.
Damping measurements using operational data
James, G.H.; Carne, T.G.; Veers, P.S.
1996-08-01
The authors have measured modal damping using strain-gauge data from an operating wind turbine. This new technique for measuring modal damping is easier and less expensive than previously used methods. Auto-correlation and cross-correlation functions of the strain-gauge data have been shown to consist of decaying sinusoids which correspond to the modal frequencies and damping ratios of the wind turbine. The authors have verified the method by extracting damping values from an analytically generated data set. Actual operating response data from the DOE/Sandia 34-m Test Bed has been used to calculate modal damping ratios as a function of rotor rotation rate. This capability will allow more accurate fatigue life prediction and control.
Radiation damping in pulsed Gaussian beams
NASA Astrophysics Data System (ADS)
Harvey, Chris; Marklund, Mattias
2012-01-01
We consider the effects of radiation damping on the electron dynamics in a Gaussian-beam model of a laser field. For high intensities, i.e., with dimensionless intensity a0≫1, it is found that the dynamics divides into three regimes. For low-energy electrons (low initial γ factor, γ0) the radiation damping effects are negligible. At higher energies, but still at 2γ0
Scattering Theory of Mesoscopic Gilbert Damping
NASA Astrophysics Data System (ADS)
Brataas, Arne
2010-03-01
Magnetic damping determines the performance of magnetic devices including high-frequency oscillators, hard drives, magnetic random access memories, magnetic logic devices, and magnetic field sensors. The drive to improve these devices, to reduce the response time of sensors and the physical dimensions has led to a greater focus on studying the friction force a changing magnetization experiences. We study the magnetization dynamics of single domain ferromagnets and domain walls in contact with a thermal bath by scattering theory. We recover the Landau-Lifshitz-Gilbert equation and express the Gilbert damping tensor in terms of the scattering matrix [1,2]. Dissipation of magnetic energy equals energy current pumped out of the system by the time-dependent magnetization, with separable spin-relaxation induced bulk and spin-pumping generated interface contributions [3]. The scattering theory of Gilbert damping is suitable for first-principles calculations that include disorder and spin-orbit coupling on an equal footing [4]. In linear response, our scattering theory for the Gilbert damping tensor is equivalent with the Kubo formalism. [4pt] [1] A. Brataas, Y. Tserkovnyak, and G. E. W. Bauer, Phys. Rev. Lett. 101, 037207 (2008). [0pt] [2] K. M. D. Hals, A. K. Nguyen, and A. Brataas, Phys. Rev. Lett. 102, 256601 (2009). [0pt] [3] Y. Tserkovnyak, A. Brataas, G. E. W. Bauer, and B. I. Halperin, Rev. Mod. Phys. 77, 1375 (2005). [0pt] [4] A. A. Starikov, P. J. Kelly, A. Brataas, Y. Tserkovnyak, and G. E. W. Bauer, unpublished.
The DAMPE silicon-tungsten tracker
NASA Astrophysics Data System (ADS)
Azzarello, P.; Ambrosi, G.; Asfandiyarov, R.; Bernardini, P.; Bertucci, B.; Bolognini, A.; Cadoux, F.; Caprai, M.; De Mitri, I.; Domenjoz, M.; Dong, Y.; Duranti, M.; Fan, R.; Fusco, P.; Gallo, V.; Gargano, F.; Gong, K.; Guo, D.; Husi, C.; Ionica, M.; La Marra, D.; Loparco, F.; Marsella, G.; Mazziotta, M. N.; Mesa, J.; Nardinocchi, A.; Nicola, L.; Pelleriti, G.; Peng, W.; Pohl, M.; Postolache, V.; Qiao, R.; Surdo, A.; Tykhonov, A.; Vitillo, S.; Wang, H.; Weber, M.; Wu, D.; Wu, X.; Zhang, F.
2016-09-01
The DArk Matter Particle Explorer (DAMPE) is a spaceborne astroparticle physics experiment, launched on 17 December 2015. DAMPE will identify possible dark matter signatures by detecting electrons and photons in the 5 GeV-10 TeV energy range. It will also measure the flux of nuclei up to 100 TeV, for the study of the high energy cosmic ray origin and propagation mechanisms. DAMPE is composed of four sub-detectors: a plastic strip scintillator, a silicon-tungsten tracker-converter (STK), a BGO imaging calorimeter and a neutron detector. The STK is composed of six tracking planes of 2 orthogonal layers of single-sided micro-strip detectors, for a total detector surface of ca. 7 m2. The STK has been extensively tested for space qualification. Also, numerous beam tests at CERN have been done to study particle detection at silicon module level, and at full detector level. After description of the DAMPE payload and its scientific mission, we will describe the STK characteristics and assembly. We will then focus on some results of single ladder performance tests done with particle beams at CERN.
Atomistic Mechanisms for Viscoelastic Damping in Inorganic Solids
NASA Astrophysics Data System (ADS)
Ranganathan, Raghavan
Viscoelasticity, a ubiquitous material property, can be tuned to engineer a wide range of fascinating applications such as mechanical dampers, artificial tissues, functional foams and optoelectronics, among others. Traditionally, soft matter such as polymers and polymer composites have been used extensively for viscoelastic damping applications, owing to the inherent viscous nature of interactions between polymer chains. Although this leads to good damping characteristics, the stiffness in these materials is low, which in turn leads to limitations. In this context, hard inorganic materials and composites are promising candidates for enhanced damping, owing to their large stiffness and, in some cases large loss modulus. Viscoelasticity in these materials has been relatively unexplored and atomistic mechanisms responsible for damping are not apparent. Therefore, the overarching goal of this work is to understand mechanisms for viscoelastic damping in various classes of inorganic composites and alloys at an atomistic level from molecular dynamics simulations. We show that oscillatory shear deformation serves as a powerful probe to explain mechanisms for exceptional damping in hitherto unexplored systems. The first class of inorganic materials consists of crystalline phases of a stiff inclusion in a soft matrix. The two crystals within the composite, namely the soft and a stiff phase, individually show a highly elastic behavior and a very small loss modulus. On the other hand, a composite with the two phases is seen to exhibit damping that is about 20 times larger than predicted theoretical bounds. The primary reason for the damping is due to large anharmonicity in phonon-phonon coupling, resulting from the composite microstructure. A concomitant effect is the distribution of shear strain, which is observed to be highly inhomogeneous and mostly concentrated in the soft phase. Interestingly, the shear frequency at which the damping is greatest is observed to scale with
Synchrotron and collisional damping effects on runaway electron distributions
NASA Astrophysics Data System (ADS)
Paz-Soldan, C.; Eidietis, N.; Pace, D.; Cooper, C.; Shiraki, D.; Commaux, N.; Hollmann, E.; Moyer, R.; Granetz, R.; Embreus, O.; Fulop, T.; Stahl, A.; Wilkie, G.; Aleynikov, P.; Brennan, D. P.; Liu, C.
2016-10-01
Validated models of runaway electron (RE) dissipation are required to confidently approve safe ITER Q = 10 operation. DIII-D experiments using quiescent REs are exploring the importance of synchrotron and collisional damping terms to RE dissipation. New time and energy-resolved measurements of RE bremsstrahlung hard X-ray (HXR) emission reveal stark differences between high and low energy REs as damping terms are varied. Previously reported anomalously high RE dissipation only applies to low energy REs. At high energy (where synchrotron effects are strongest) low synchrotron damping cases reach higher peak RE energy despite weaker particle confinement. Low-energy RE decay is observed concurrently with high-energy RE growth. RE dissipation models predict bump-on-tail distributions whose properties depend on the damping terms. Measured HXR spectra are very broad, as expected for bump-on-tail distributions. Work supported by the U.S. DOE under DE-FC02-04ER54698.
Resummation and the gluon damping rate in hot QCD
Pisarski, R.D.
1990-08-01
At high temperature a consistent perturbative expansion requires the resummation of an infinite subset of loop corrections into an effective expansion. This effective exansion is used to compute the gluon damping rate at leading order. 25 refs.
Wakefield Damping for the CLIC Crab Cavity
Ambattu, P.K.; Burt, G.; Dexter, A.C.; Carter, R.G.; Khan, V.; Jones, R.M.; Dolgashev, V.; /SLAC
2011-12-01
A crab cavity is required in the CLIC to allow effective head-on collision of bunches at the IP. A high operating frequency is preferred as the deflection voltage required for a given rotation angle and the RF phase tolerance for a crab cavity are inversely proportional to the operating frequency. The short bunch spacing of the CLIC scheme and the high sensitivity of the crab cavity to dipole kicks demand very high damping of the inter-bunch wakes, the major contributor to the luminosity loss of colliding bunches. This paper investigates the nature of the wakefields in the CLIC crab cavity and the possibility of using various damping schemes to suppress them effectively.
Damping and energy dissipation in soft tissue vibrations during running.
Khassetarash, Arash; Hassannejad, Reza; Enders, Hendrik; Ettefagh, Mir Mohammad
2015-01-21
It has been well accepted that the vibrations of soft tissue cannot be simulated by a single sinusoidal function. In fact, these vibrations are a combination of several vibration modes. In this study, these modes are extracted applying a recently developed method namely, partly ensemble empirical mode decomposition (PEEMD). Then, a methodology for estimating the damping properties and energy dissipation caused by damping for each mode is used. Applying this methodology on simulated signals demonstrates high accuracy. This methodology is applied to the acceleration signals of the gastrocnemius muscle during sprinting and the differences between the damping properties of different vibration modes were identified. The results were 1) the damping property of high-frequency mode was higher than that for low-frequency modes. 2) All identified modes were in under damped condition, therefore, the vibrations had an oscillatory nature. 3) The damping ratios of lower modes are about 100% increased compared to higher modes. 4) The energy dissipation occurred in lower modes were much more than that for higher mode; According to the power spectrum of the ground reaction force (GRF), which is the input force into the body, the recent finding supports the muscle tuning paradigm. It is suggested that the damping properties and energy dissipation can be used to distinguish between different running conditions (surface, fatigue, etc.).
NASA Technical Reports Server (NTRS)
Weddendorf, Bruce
1993-01-01
Self-damping sprung wheel provides shock-absorbing suspension for wheelchair, reducing user's discomfort when traversing rough terrain or obstacles. Pair of self-damping sprung wheels installed in place of conventional large rear wheels of standard wheelchair, which user operates in conventional manner. Rim deflects in vicinity of contact with ground or floor. Includes inner and outer hoops bending when obstacle encountered. Shear deformation of elastomeric hoop between them absorbs energy. Thus, three hoops act together as damping spring. Alternative version of wheel designed for bicycle.
Damping MEMS Devices in Harsh Environments Using Active Thin Films
2008-06-17
properties of the layers was developed. Damping properties in Nitinol thin film due only to residual stresses was measured to be as high as tan delta...0.17 for large strain (0.9%). At lower strain levels a Nitinol /Silicon laminate was tested in a cantilever load frame. The damping value of the...film was measured to be 0.28 (at 0.27% strain). A Nitinol /Terfenol-D/Nickel laminate was fabricated and tested in a cantilever loading. The damping
Electrorheologically damped impact system
NASA Astrophysics Data System (ADS)
Hardt, Lee R.
1991-05-01
An impact switch is described having a housing containing a rigid coaxial conductor entering one end. An inner cylindrical contact extends axially inward from and beyond the in housing end of an outer tubular contact which has a spiral spring extending axially from within a recess therein. The free end of the spring supports a mass spaced from the end of the inner contact. The contacts, spring and mass are enclosed within a flexible shroud spaced from the inner wall of the housing. The space between the shroud and housing contains an electrorheological fluid, the viscosity of which is a function of the voltage supplied by two electrodes extending through the housing and into the fluid. The voltage controlled viscosity permits control of damping of the shroud, mass, and spring movements in response to impact caused switch deceleration and control of time for switch closure and fuze delay by means of mass contact with the inner cylindrical contact, or spring contact with the outer tubular contact.
Turbine blade friction damping study
NASA Technical Reports Server (NTRS)
Dominic, R. J.
1985-01-01
A lumped parameter method, implemented on a VAX 11/780 computer shows that the primary parameters affecting the performance of the friction damper of the first stage turbine of the SSME high pressure fuel pump are: the damper-blade coefficient of friction; the normal force applied to the friction interface; the amplitude of the periodic forcing function; the relative phase angle of the forcing functions for adjacent blades bridged by a damper (effectively, the engine order of the forcing function); and the amount of hysteretic damping that acts to limit the vibration amplitude of the blade in its resonance modes. The low order flexural resonance vibration modes of HPFTP blades without dampers, with production dampers, and with two types of lightweight experimental dampers were evaluated in high speed spin pit tests. Results agree with those of the analytical study in that blades fitted with production friction dampers experienced the airfoil-alone flexural resonance mode, while those without dampers or with lighter weight dampers did not. No blades fitted with dampers experienced the whole blade flexural resonance mode during high speed tests, while those without dampers did.
Cellular Magnesium Matrix Foam Composites for Mechanical Damping Applications
NASA Astrophysics Data System (ADS)
Shunmugasamy, Vasanth Chakravarthy; Mansoor, Bilal; Gupta, Nikhil
2016-01-01
The damping characteristics of metal alloys and metal matrix composites are relevant to the automotive, aerospace, and marine structures. Use of lightweight materials can help in increasing payload capacity and in decreasing fuel consumption. Lightweight composite materials possessing high damping capabilities that can be designed as structural members can greatly benefit in addressing these needs. In this context, the damping properties of lightweight metals such as aluminum and magnesium and their respective composites have been studied in the existing literature. This review focuses on analyzing the damping properties of aluminum and magnesium alloys and their cellular composites. The damping properties of various lightweight alloys and composites are compared on the basis of their density to understand the potential for weight saving in structural applications. Magnesium alloys are observed to possess better damping properties in comparison to aluminum. However, aluminum matrix syntactic foams reinforced with silicon carbide hollow particles possess a damping capacity and density comparable to magnesium alloy. By using the data presented in the study, composites with specific compositions and properties can be selected for a given application. In addition, the comparison of the results helps in identifying the areas where attention needs to be focused to address the future needs.
Damping measurements using operational data
James, G.H.; Carne, T.G.; Veers, P.S.
1991-01-01
We have measured modal damping using strain-gauge data from an operating wind turbine. Previously, such measurements were difficult and expensive. Auto-correlation and cross-correlation functions of the strain-gauge data have been shown to consist of decaying sinusoids which correspond to the modal frequencies and damping ratios of the wind turbine. We have verified the method by extracting damping values from an analytically generated data set. Actual operating response data from the DOE/Sandia 34-meter Test Bed has been used to calculate modal damping ratios as a function of rotor rotation rate. This capability will allow more accurate fatigue life prediction and control. 16 refs., 3 figs., 2 tabs.
Damping in Ferrous Shape Memory Alloys
1993-08-01
time it has been proposed that the solution lies in the approach of energy dissipation by using metallic structural materials which have inherent...and automotive manufacturing plants, has never achieved commercial producton . 1-b. Ferromagnetic alloys, such as Fe-Cr alloys High damping Fe-Cr alloys...Pre-exsiring mar~en-si,ýe worms orwie treenred orieL a ion ! A Lr cow s SL AL 14- L AL Figure 26. Schematic illustration of various processes involved
Vibration damping method and apparatus
Redmond, James M.; Barney, Patrick S.; Parker, Gordon G.; Smith, David A.
1999-01-01
The present invention provides vibration damping method and apparatus that can damp vibration in more than one direction without requiring disassembly, that can accommodate varying tool dimensions without requiring re-tuning, and that does not interfere with tool tip operations and cooling. The present invention provides active dampening by generating bending moments internal to a structure such as a boring bar to dampen vibration thereof.
Vibration damping method and apparatus
Redmond, J.M.; Barney, P.S.; Parker, G.G.; Smith, D.A.
1999-06-22
The present invention provides vibration damping method and apparatus that can damp vibration in more than one direction without requiring disassembly, that can accommodate varying tool dimensions without requiring re-tuning, and that does not interfere with tool tip operations and cooling. The present invention provides active dampening by generating bending moments internal to a structure such as a boring bar to dampen vibration thereof. 38 figs.
Simple suppression of radiation damping.
Khitrin, A K; Jerschow, Alexej
2012-12-01
Radiation damping is known to cause line-broadening and frequency shifts of strong resonances in NMR spectra. While several techniques exist for the suppression of these effects, many require specialized hardware, or are only compatible with the presence of few strong resonances. We describe a simple pulse sequence for radiation damping suppression in spectra with many strong resonances. The sequence can be used as-is to generate simple spectra or as a signal excitation part in more advanced experiments.
Damping characterization in large structures
NASA Technical Reports Server (NTRS)
Eke, Fidelis O.; Eke, Estelle M.
1991-01-01
This research project has as its main goal the development of methods for selecting the damping characteristics of components of a large structure or multibody system, in such a way as to produce some desired system damping characteristics. The main need for such an analytical device is in the simulation of the dynamics of multibody systems consisting, at least partially, of flexible components. The reason for this need is that all existing simulation codes for multibody systems require component-by-component characterization of complex systems, whereas requirements (including damping) often appear at the overall system level. The main goal was met in large part by the development of a method that will in fact synthesize component damping matrices from a given system damping matrix. The restrictions to the method are that the desired system damping matrix must be diagonal (which is almost always the case) and that interbody connections must be by simple hinges. In addition to the technical outcome, this project contributed positively to the educational and research infrastructure of Tuskegee University - a Historically Black Institution.
Influence of damping on quantum interference - An exactly soluble model
NASA Technical Reports Server (NTRS)
Caldeira, A. O.; Leggett, A. J.
1985-01-01
This paper reports the result of a calculation which shows the effect of damping on the quantum interference of two Gaussian wave packets in a harmonic potential. The influence-functional method, which seems to be the most appropriate one for this kind of calculation, is used. It is shown that quantum-interference effects are severely diminished by the presence of damping even when its influence on the system is only light. The corrections to the undamped formulas are always expressible in terms of the phenomenological damping constant, the temperature (in the high-temperature limit), the cutoff frequency of the reservoir oscillators, and the mean number of quanta of energy intially present in the system. Both weakly and strongly damped systems are analyzed in the regime of low and high temperatures.
Composite slip table of dissimilar materials for damping longitudinal modes
Gregory, Danny L.; Priddy, Tommy G.; Smallwood, David O.; Woodall, Tommy D.
1991-01-01
A vibration slip table for use in a vibration testing apparatus. The table s comprised of at least three composite layers of material; a first metal layer, a second damping layer, and a third layer having a high acoustic velocity relative to the first layer. The different acoustic velocities between the first and third layers cause relative shear displacements between the layers with the second layer damping the displacements between the first and third layers to reduce the table longitudinal vibration modes.
Harmonic cavities for the NLC damping rings
de Santis, S.; Wolski, A.
2003-05-29
To achieve high luminosity, a linear collider needs damping rings to produce beams with very small transverse emittances. In the NLC, design constraints place the Main Damping Rings in a parameter regime where intrabeam scattering (IBS) is likely to be a limitation on the emittance, and hence on the final luminosity. It is possible to mitigate the effects of IBS by lengthening the bunch: this may be achieved by redesigning the lattice with higher momentum compaction, or by use of higher harmonic cavities. Here, we consider the latter approach. We estimate the required bunch lengthening that might be needed, outline some appropriate parameters for the harmonic cavities, and discuss some of the effects that might be introduced or exacerbated by the cavities, such as synchronous phase variation along the bunch train.
Movers and shakers: granular damping in microgravity.
Bannerman, M N; Kollmer, J E; Sack, A; Heckel, M; Mueller, P; Pöschel, T
2011-07-01
The response of an oscillating granular damper to an initial perturbation is studied using experiments performed in microgravity and granular dynamics simulations. High-speed video and image processing techniques are used to extract experimental data. An inelastic hard sphere model is developed to perform simulations and the results are in excellent agreement with the experiments. In line with previous work, a linear decay of the amplitude is observed. Although this behavior is typical for a friction-damped oscillator, through simulation it is shown that this effect is still present even when friction forces are absent. A simple expression is developed which predicts the optimal damping conditions for a given amplitude and is independent of the oscillation frequency and particle inelasticities.
On the damping capacity of cast irons
NASA Astrophysics Data System (ADS)
Golovin, S. A.
2012-07-01
The treatment of experimental data on the amplitude-dependent internal friction (ADIF) in terms of various theoretical models has revealed a staged character and the main mechanisms of the processes of energy dissipation in graphite with increasing amplitude of vibrations upon cyclic loading. It is shown that the level of the damping capacity of lamellar cast iron depends on the relationship between the elastic and strength characteristics of graphite and the matrix phase. In cast irons with a rigid matrix structure (pearlite, martensite), the energy dissipation is determined by the volume fraction and morphology of the initial graphite phase. In cast irons with a softer metallic phase (ferrite), the contact interaction of graphite inclusions with the matrix and the properties of the matrix introduce additional sources of high damping.
Development of Transverse Modes Damped DLA Structure
Jing, C.; Kanareykin, A.; Schoessow, P.; Gai, W.; Konecny, R.; Power, J. G.; Conde, M.
2009-01-22
As the dimensions of accelerating structures become smaller and beam intensities higher, the transverse wakefields driven by the beam become quite large with even a slight misalignment of the beam from the geometric axis. These deflection modes can cause inter-bunch beam breakup and intra-bunch head-tail instabilities along the beam path, and thus BBU control becomes a critical issue. All new metal based accelerating structures, like the accelerating structures developed at SLAC or power extractors at CLIC, have designs in which the transverse modes are heavily damped. Similarly, minimizing the transverse wakefield modes (here the HEMmn hybrid modes in Dielectric-Loaded Accelerating (DLA) structures) is also very critical for developing dielectric based high energy accelerators. In this paper, we present the design of a 7.8 GHz transverse mode damped DLA structure currently under construction, along with plans for the experimental program.
Plasmon damping in graphene out of equilibrium
NASA Astrophysics Data System (ADS)
Sun, Zhiyuan; Basov, Dimitri; Fogler, Michael
Motivated by recent experiments with graphene under high photoexcitation, we study theoretically plasmons of graphene in the two-temperature regime, i.e., the regime where electrons are much hotter than the lattice. We calculate the plasmon damping due to scattering of electrons by acoustic phonons, which is the dominant intrinsic contribution in clean graphene. As the system relaxes to equilibrium, the plasmon frequency adiabatically changes with time. We show that this causes a partial compensation of the plasmon damping. A similar mechanism may apply to another collective mode (the energy wave) predicted to exist in graphene in the low-frequency hydrodynamic regime. Implications for infrared and THz pump-probe experiments are discussed.
A comparison of viscoelastic damping models
NASA Technical Reports Server (NTRS)
Slater, Joseph C.; Belvin, W. Keith; Inman, Daniel J.
1993-01-01
Modern finite element methods (FEM's) enable the precise modeling of mass and stiffness properties in what were in the past overwhelmingly large and complex structures. These models allow the accurate determination of natural frequencies and mode shapes. However, adequate methods for modeling highly damped and high frequency dependent structures did not exist until recently. The most commonly used method, Modal Strain Energy, does not correctly predict complex mode shapes since it is based on the assumption that the mode shapes of a structure are real. Recently, many techniques have been developed which allow the modeling of frequency dependent damping properties of materials in a finite element compatible form. Two of these methods, the Golla-Hughes-McTavish method and the Lesieutre-Mingori method, model the frequency dependent effects by adding coordinates to the existing system thus maintaining the linearity of the model. The third model, proposed by Bagley and Torvik, is based on the Fractional Calculus method and requires fewer empirical parameters to model the frequency dependence at the expense of linearity of the governing equations. This work examines the Modal Strain Energy, Golla-Hughes-McTavish and Bagley and Torvik models and compares them to determine the plausibility of using them for modeling viscoelastic damping in large structures.
Metallic materials for mechanical damping capacity applications
NASA Astrophysics Data System (ADS)
Crăciun, R. C.; Stanciu, S.; Cimpoeșu, R.; (Dragoș Ursanu, A. I.; Manole, V.; Paraschiv, P.; Chicet, D. L.
2016-08-01
Some metallic materials exhibit good damping capacity of mechanical energy into thermal energy. This property along with the others metallic characteristics make this materials interesting for a big number of applications. These materials can be used as bumpers in different applications including automotive field. Beside grey cast iron and shape memory alloys few new metallic materials are presented for the supposition of high damping capacity. We analyze the causes that increase the internal friction of some metallic materials and possibilities to enhance this property through different mechanical, physical or chemical methods. Shape memory alloys, especially those based on copper, present a different damping capacity on martensite, austenite or transition state. In the transformation range M ↔A, which in case of copper base shape memory alloys is quite large, the metallic intelligent materials present a high internal friction, almost comparable with natural rubber behavior that can transform mechanical energy into thermal energy till a certain value of the external solicitation. These materials can be used as noise or small vibrations bumpers or even as shock absorbers in automotive industry.
The effect of mechanical damping loads on disabling action tremor.
Aisen, M L; Arnold, A; Baiges, I; Maxwell, S; Rosen, M
1993-07-01
Patients with severe action tremor have uncontrollable, relatively rapid oscillatory motion super-imposed on otherwise useable slower voluntary motor activity. Because a mechanical damper produces an opposing force proportional to velocity, applying damping loads to tremorous limbs should attenuate the (high-velocity) tremor component of movement while permitting the slower purposeful portion to proceed relatively unopposed. In this study, the effect of upper extremity damping in three degrees of freedom was examined in 10 patients with cerebellar action tremor due to multiple sclerosis or traumatic brain injury. Variable amounts of damping were applied by prototype energy-dissipating orthoses which generated resistive viscous loads by means of computer-controlled magnetic particle brakes. All patients experienced statistically and functionally significant tremor reduction with the application of damping.
An Active Damping at Blade Resonances Using Piezoelectric Transducers
NASA Technical Reports Server (NTRS)
Choi, Benjamin; Morrison, Carlos; Duffy, Kirsten
2008-01-01
The NASA Glenn Research Center (GRC) is developing an active damping at blade resonances using piezoelectric structure to reduce excessive vibratory stresses that lead to high cycle fatigue (HCF) failures in aircraft engine turbomachinery. Conventional passive damping work was shown first on a nonrotating beam made by Ti-6A1-4V with a pair of identical piezoelectric patches, and then active feedback control law was derived in terms of inductor, resister, and capacitor to control resonant frequency only. Passive electronic circuit components and adaptive feature could be easily programmable into control algorithm. Experimental active damping was demonstrated on two test specimens achieving significant damping on tip displacement and patch location. Also a multimode control technique was shown to control several modes.
Damping mechanisms of a pendulum
NASA Astrophysics Data System (ADS)
Dolfo, Gilles; Castex, Daniel; Vigué, Jacques
2016-11-01
In this paper, we study the damping mechanisms of a pendulum. The originality of our setup is the use of a metal strip suspension and the development of extremely sensitive electric measurements of the pendulum velocity and position. Their sensitivity is absolutely necessary for a reliable measurement of the pendulum damping time constant because this measurement is possible only for very low oscillation amplitudes, when air friction forces quadratic in velocity have a negligible contribution to the observed damping. We have thus carefully studied damping by air friction forces, which is the dominant mechanism for large values of the Reynolds number Re but which is negligible in the Stokes regime, {Re} ∼ 1. In this last case, we have found that the dominant damping is due to internal friction in the metal strip, a universal effect called anelasticity, and, for certain frequencies, to resonant coupling to the support of the pendulum. All our measurements are well explained by theory. We believe this paper would be of interest to students in an undergraduate classical mechanics course.
Reducing extrinsic damping of surface acoustic waves at gigahertz frequencies
NASA Astrophysics Data System (ADS)
Gelda, Dhruv; Sadhu, Jyothi; Ghossoub, Marc G.; Ertekin, Elif; Sinha, Sanjiv
2016-04-01
High-frequency surface acoustic waves (SAWs) in the gigahertz range can be generated using absorption from an ultrafast laser in a patterned metallic grating on a substrate. Reducing the attenuation at these frequencies can yield better sensors as well as enable them to better probe phonon and electron-phonon interactions near surfaces. It is not clear from existing experiments which mechanisms dominate damping at high frequencies. We calculate damping times of SAWs due to various mechanisms in the 1-100 GHz range to find that mechanical loading of the grating on the substrate dominates dissipation by radiating energy from the surface into the bulk. To overcome this and enable future measurements to probe intrinsic damping, we propose incorporating distributed acoustic Bragg reflectors in the experimental structure. Layers of alternating materials with contrasting acoustic impedances embedded a wavelength away from the surface serve to reflect energy back to the surface. Using numerical simulations, we show that a single Bragg reflector is sufficient to increase the energy density at the surface by more than five times. We quantify the resulting damping time to find that it is longer than the intrinsic damping time. The proposed structure can enable future measurements of intrinsic damping in SAWs at ˜100 GHz.
Increased damping in irregular resonators
NASA Astrophysics Data System (ADS)
Sapoval, Bernard; Asch, Mark; Felix, Simon; Filoche, Marcel
2005-04-01
The relation between shape and damping of shallow acoustical cavities has been studied numerically in the case where the dissipation occurs only on the cavity walls. It is first found that whatever the type of geometrical irregularity, many, but not all the modes are localized. It is shown that the localization mechanism is what is called weak localization. The more irregular, the smaller the quality factors are found. However this effect is very different for the non-localized and the localized modes. For non-localized modes the damping increases roughly proportionally to the cavity surface. The localized modes are even more damped. These results generalize the results already obtained both numerically and experimentally on prefractal acoustical cavities. [B. Sapoval, O. Haeberle, and S. Russ, J. Acoust. Soc. Am. 102, 2014-2019 (1997); B. Hebert, B. Sapoval, and S. Russ, ibid. 105, 1567-1576 (1999)].
Increased damping of irregular resonators.
Russ, S; Sapoval, B
2002-03-01
It is shown that fractal drums and jagged geometry resonators may be more damped than ordinary Euclidean systems. Several damping mechanisms are examined and studied by numerical calculations. The results depend on the dissipation mechanisms but globally they increase with localization, frequency, and the irregularity of the resonator. The increased dissipation is due to the uneven spatial distribution of the vibrational amplitude in two different ways. First, it is related to the partial confinement of the vibrational modes. Secondly, increased dissipation may be due to singularities in the amplitude distribution. This is the case when a few points exist where the vibration is pinned to zero inducing local logarithmic singularities. This last effect can be spectacular: a single defect can dominate the surface damping by viscous forces of a square drum.
de Lasson, Jakob Rosenkrantz; Kristensen, Philip Trøst; Mørk, Jesper; Gregersen, Niels
2015-12-15
We present and validate a semianalytical quasi-normal mode (QNM) theory for the local density of states (LDOS) in coupled photonic crystal (PhC) cavity-waveguide structures. By means of an expansion of the Green's function on one or a few QNMs, a closed-form expression for the LDOS is obtained, and for two types of two-dimensional PhCs, with one and two cavities side-coupled to an extended waveguide, the theory is validated against numerically exact computations. For the single cavity, a slightly asymmetric spectrum is found, which the QNM theory reproduces, and for two cavities, a nontrivial spectrum with a peak and a dip is found, which is reproduced only when including both the two relevant QNMs in the theory. In both cases, we find relative errors below 1% in the bandwidth of interest.
NASA Astrophysics Data System (ADS)
Prasia, P.; Kuriakose, V. C.
2017-01-01
In this work we study the Quasi-Normal Modes (QNMs) under massless scalar perturbations and the thermodynamics of linearly charged BTZ black holes in massive gravity in the (Anti)de Sitter ((A)dS) space-time. It is found that the behavior of QNMs changes with the massive parameter of the graviton and also with the charge of the black hole. The thermodynamics of such black holes in the (A)dS space-time is also analyzed in detail. The behavior of specific heat with temperature for such black holes gives an indication of a phase transition that depends on the massive parameter of the graviton and also on the charge of the black hole.
Landau damping of auroral hiss
NASA Technical Reports Server (NTRS)
Morgan, D. D.; Gurnett, D. A.; Menietti, J. D.; Winningham, J. D.; Burch, J. L.
1994-01-01
Auroral hiss is observed to propagate over distances comparable to an Earth radius from its source in the auroral oval. The role of Landau damping is investigated for upward propagating auroral hiss. By using a ray tracing code and a simplified model of the distribution function, the effect of Landau damping is calculated for auroral hiss propagation through the environment around the auroral oval. Landau damping is found to be the likely mechanism for explaining some of the one-sided auroral hiss funnels observed by Dynamics Explorer 1. It is also found that Landau damping puts a lower limit on the wavelength of auroral hiss. Poleward of the auroral oval, Landau damping is found in a typical case to limit omega/k(sub parallel) to values of 3.4 x 10(exp 4) km/s or greater, corresponding to resonance energies of 3.2 keV or greater and wavelengths of 2 km or greater. For equatorward propagation, omega/k(sub parallel) is limited to values greater than 6.8 x 10(exp 4) km/s, corresponding to resonance energies greater than 13 keV and wavelengths greater than 3 km. Independent estimates based on measured ratios of the magnetic to electric field intensity also show that omega/k(sub parallel) corresponds to resonance energies greater than 1 keV and wavelengths greater than 1 km. These results lead to the difficulty that upgoing electron beams sufficiently energetic to directly generate auroral hiss of the inferred wavelength are not usually observed. A partial transmission mechanism utilizing density discontinuities oblique to the magnetic field is proposed for converting auroral hiss to wavelengths long enough to avoid damping of the wave over long distances. Numerous reflections of the wave in an upwardly flared density cavity could convert waves to significantly increased wavelengths and resonance velocities.
Rubin, David L.
2015-01-23
Accelerators that collide high energy beams of matter and anti-matter are essential tools for the investigation of the fundamental constituents of matter, and the search for new forms of matter and energy. A “Linear Collider” is a machine that would bring high energy and very compact bunches of electrons and positrons (anti-electrons) into head-on collision. Such a machine would produce (among many other things) the newly discovered Higgs particle, enabling a detailed study of its properties. Among the most critical and challenging components of a linear collider are the damping rings that produce the very compact and intense beams of electrons and positrons that are to be accelerated into collision. Hot dilute particle beams are injected into the damping rings, where they are compressed and cooled. The size of the positron beam must be reduced more than a thousand fold in the damping ring, and this compression must be accomplished in a fraction of a second. The cold compact beams are then extracted from the damping ring and accelerated into collision at high energy. The proposed International Linear Collider (ILC), would require damping rings that routinely produce such cold, compact and intense beams. The goal of the Cornell study was a credible design for the damping rings for the ILC. Among the technical challenges of the damping rings; the development of instrumentation that can measure the properties of the very small beams in a very narrow window of time, and mitigation of the forces that can destabilize the beams and prevent adequate cooling, or worse lead to beam loss. One of the most pernicious destabilizing forces is due to the formation of clouds of electrons in the beam pipe. The electron cloud effect is a phenomenon in particle accelerators in which a high density of low energy electrons, build up inside the vacuum chamber. At the outset of the study, it was anticipated that electron cloud effects would limit the intensity of the positron ring
Inverse design of nonlinearity in energy harvesters for optimum damping
NASA Astrophysics Data System (ADS)
Ghandchi Tehrani, Maryam; Elliott, S. J.
2016-09-01
This paper presents the inverse design method for the nonlinearity in an energy harvester in order to achieve an optimum damping. A single degree-of-freedom electromechanical oscillator is considered as an energy harvester, which is subjected to a harmonic base excitation. The harvester has a limited throw due to the physical constraint of the device, which means that the amplitude of the relative displacement between the mass of the harvester and the base cannot exceed a threshold when the device is driven at resonance and beyond a particular amplitude. This physical constraint requires the damping of the harvester to be adjusted for different excitation amplitudes, such that the relative displacement is controlled and maintained below the limit. For example, the damping can be increased to reduce the amplitude of the relative displacement. For high excitation amplitudes, the optimum damping is, therefore, dependent on the amplitude of the base excitation, and can be synthesised by a nonlinear function. In this paper, a nonlinear function in the form of a bilinear is considered to represent the damping model of the device. A numerical optimisation using Matlab is carried out to fit a curve to the amplitude-dependent damping in order to determine the optimum bilinear model. The nonlinear damping is then used in the time-domain simulations and the relative displacement and the average harvested power are obtained. It is demonstrated that the proposed nonlinear damping can maintain the relative displacement of the harvester at its maximum level for a wide range of excitation, therefore providing the optimum condition for power harvesting.
Thielen, M; Schmitt, C N Z; Eckert, S; Speck, T; Seidel, R
2013-06-01
The mechanical properties of artificial foams are mainly determined by the choice of bulk materials and relative density. In natural foams, in contrast, variation to optimize properties is achieved by structural optimization rather than by conscious substitution of bulk materials. Pomelos (Citrus maxima) have a thick foam-like peel which is capable of dissipating considerable amounts of kinetic energy and thus this fruit represents an ideal role model for the development of biomimetic impact damping structures. This paper focuses on the analysis of the biomechanics of the pomelo peel and on its structure-function relationship. It deals with the determination of the onset strain of densification of this foam-like tissue and on how this property is influenced by the arrangement of vascular bundles. It was found here that the vascular bundles branch in a very regular manner-every 16.5% of the radial peel thickness-and that the surrounding peel tissue (pericarp) attains its exceptional thickness mainly by the expansion of existing interconnected cells causing an increasing volume of the intercellular space, rather than by cell division. These findings lead to the discussion of the pomelo peel as an inspiration for fibre-reinforced cast metallic foams with the capacity for excellent energy dissipation.
Damping capacity of TiNi-based shape memory alloys
NASA Astrophysics Data System (ADS)
Rong, L. J.; Jiang, H. C.; Liu, S. W.; Zhao, X. Q.
2007-07-01
Damping capacity is another primary characteristic of shape memory alloys (SMA) besides shape memory effect and superelasticity. Damping behavior of Ti-riched TiNi SMA, porous TiNi SMA and a novel TiNi/AlSi composite have been investigated using dynamic mechanical analyzer (DMA) in this investigation. All these alloys are in martensitic state at room temperature and thus possess the high potential application value. Ti 50.2Ni 49.8 SMA has better damping capacity in pure martensitic state and phase transformation region due to the motion of martensite twin interface. As a kind of promising material for effective dampers and shock absorbing devices, porous TiNi SMA can exhibit higher damping capacity than the dense one due to the existence of the three-dimensioned connecting pore structure. It is found that the internal friction of porous TiNi SMA mainly originates from microplastic deformation and mobility of martensite interface and increases with the increase of the porosity. A novel TiNi/AlSi composite has been developed successfully by infiltrating AlSi alloy into the open pores of porous TiNi alloy with 60% porosity through compression casting. It shows the same phase transformation characteristics as the porous TiNi alloy. The damping capacity of the composite has been increased and the compressive strength has been also promoted remarkably. Suggestions for developing higher damping alloys based on TiNi shape memory alloy are proposed in this paper.
Researches on Track Reconstruction for DAMPE
NASA Astrophysics Data System (ADS)
Lu, T. S.; Lei, S. J.; Zang, J. J.; Chang, J.; Wu, J.
2016-05-01
The Dark Matter Particle Explorer (DAMPE) is aimed to study the existence and distribution of dark matter via observation of high energy particles in space with unprecedented large energy bandwidth, high energy resolution, and high space resolution. The track reconstruction is to restore the positions and angles of the incident particles using the multiple observations of different channels at different positions, and its accuracy determines the angular resolution of the detector. The track reconstruction is mainly based on the observations of two sub-detectors, namely, the Silicon Tracker (STK) detector and the BGO (Bi_4Ge_3O12) calorimeter. In accordance with the design and structure of the two sub-detectors and using the data collected during the beam tests and ground tests, we provide a detailed introduction of the track reconstruction of DAMPE data, including three basic steps, the selection of track hits, the fitting of track hits, and the judgement of the best track among (most probably) many of them. Since a high energy particle most probably leaves more than one hit in each level of the STK and BGO, we first provide a method to constrain the STK clusters for the track reconstruction using the rough result of the BGO reconstruction. We apply two different algorithms, the Kalman filter and the least square linear fitting, to fit the track hits. The consistency of the results obtained independently via the two algorithms confirms the validity of our track reconstruction results, and we discuss the advantages/disadvantages of each method. Several criteria combining the BGO and STK detection are discussed for picking out the most possible track among all the tracks found in the track reconstruction. Using the track reconstruction methods mentioned in this article and the beam test data, we confirm that the angular resolution of DAMPE satisfies the requirement in design.
Vibration Damping Circuit Card Assembly
NASA Technical Reports Server (NTRS)
Hunt, Ronald Allen (Inventor)
2016-01-01
A vibration damping circuit card assembly includes a populated circuit card having a mass M. A closed metal container is coupled to a surface of the populated circuit card at approximately a geometric center of the populated circuit card. Tungsten balls fill approximately 90% of the metal container with a collective mass of the tungsten balls being approximately (0.07) M.
Red cell DAMPs and inflammation.
Mendonça, Rafaela; Silveira, Angélica A A; Conran, Nicola
2016-09-01
Intravascular hemolysis, or the destruction of red blood cells in the circulation, can occur in numerous diseases, including the acquired hemolytic anemias, sickle cell disease and β-thalassemia, as well as during some transfusion reactions, preeclampsia and infections, such as those caused by malaria or Clostridium perfringens. Hemolysis results in the release of large quantities of red cell damage-associated molecular patterns (DAMPs) into the circulation, which, if not neutralized by innate protective mechanisms, have the potential to activate multiple inflammatory pathways. One of the major red cell DAMPs, heme, is able to activate converging inflammatory pathways, such as toll-like receptor signaling, neutrophil extracellular trap formation and inflammasome formation, suggesting that this DAMP both activates and amplifies inflammation. Other potent DAMPs that may be released by the erythrocytes upon their rupture include heat shock proteins (Hsp), such as Hsp70, interleukin-33 and Adenosine 5' triphosphate. As such, hemolysis represents a major inflammatory mechanism that potentially contributes to the clinical manifestations that have been associated with the hemolytic diseases, such as pulmonary hypertension and leg ulcers, and likely plays a role in specific complications of sickle cell disease such as endothelial activation, vaso-occlusive processes and tissue injury.
Surfactant damping of water waves
NASA Astrophysics Data System (ADS)
Lapham, Gary S.; Dowling, David R.; Schultz, William W.
1997-11-01
The most well known and perhaps most important distinguishing characteristic of a water surface laden with surfactant is the profound increase in small-wave damping with the addition of even small amounts of surfactant material. It would seem to follow that damping increases with increasing surfactant concentration. This is undoubtedly true for some surfactants, however our experiments with a soluble surfactant show that it is possible to increase surfactant concentration and measure a decrease in damping. While the increased concentration is accompanied by a dramatic decrease in measured static surface tension, some of the capillary-wave frequency regime is less damped. Experimental measurements of the real and imaginary parts of the wave speed are compared with existing theory where at least one other physical quantity besides surface tension is needed to properly model the interface. Our on-going work with insoluble surfactants may also provide an example of this type of behavior for materials that do not readily transfer to and from the bulk water. [Supported by the Office of Naval Research
Technology Transfer Automated Retrieval System (TEKTRAN)
Damping-off is a common disease that rots and kills both seeds and recently germinated seedlings. The disease is caused by number of different soilborne pathogens, including true fungi (Botrytis, Fusarium, and Rhizoctonia species) and oomycetes (Phytophthora and Pythium species). The seedlings of mo...
Damped Oscillator with Delta-Kicked Frequency
NASA Technical Reports Server (NTRS)
Manko, O. V.
1996-01-01
Exact solutions of the Schrodinger equation for quantum damped oscillator subject to frequency delta-kick describing squeezed states are obtained. The cases of strong, intermediate, and weak damping are investigated.
Squeezed states of damped oscillator chain
NASA Technical Reports Server (NTRS)
Manko, O. V.
1993-01-01
The Caldirola-Kanai model of one-dimensional damped oscillator is extended to the chain of coupled parametric oscillators with damping. The correlated and squeezed states for the chain of coupled parametric oscillators with damping are constructed. Based on the concept of the integrals of motion, it is demonstrated how squeezing phenomenon arises due to parametric excitation.
Characterization of damping in microfibrous material
NASA Astrophysics Data System (ADS)
Soobramaney, Pregassen; Flowers, George T.; Dean, Robert N.
2012-04-01
MEMS gyroscopes are used in many applications including harsh environments such as high-power, high-frequency acoustic noise. If the latter is at the natural frequency of the gyroscope, the proof mass will be overexcited giving rise to a corrupted gyroscope output. To mitigate the effect of the high-power, high-frequency acoustic noise, it is proposed to use nickel microfibrous sheets as an acoustic damper. For this purpose, the characterization of vibration damping in Nickel microfibrous sheets was examined in the present research effort. The sheets were made from nickel fibers with cellulose as a binding agent using a wet-lay papermaking technique. Sintering was done at 1000 °C to remove all the cellulose giving rise to a porous material. Square sheets of 20 cm were made from three diameters of nickel fibers namely 4, 8, and 12 microns. The sheets were cut into smaller pieces to fit the requirements of a fixture specially designed for this study. The fixture was attached to a LDS V408 shaker with a mass resting on a stack of the microfibrous sheets to simulate transmitted vibration by base motion with the sheet stack acting as a damper. A series of experiments was conducted using these 3 fiber diameters, different number of layers of microfibrous sheets and varying the vibration amplitude. From the collected vibration data, the stiffness and damping ratio of the microfibrous material was characterized.
Dynamic Modulus and Damping of Boron, Silicon Carbide, and Alumina Fibers
NASA Technical Reports Server (NTRS)
Dicarlo, J. A.; Williams, W.
1980-01-01
The dynamic modulus and damping capacity for boron, silicon carbide, and silicon carbide coated boron fibers were measured from-190 to 800 C. The single fiber vibration test also allowed measurement of transverse thermal conductivity for the silicon carbide fibers. Temperature dependent damping capacity data for alumina fibers were calculated from axial damping results for alumina-aluminum composites. The dynamics fiber data indicate essentially elastic behavior for both the silicon carbide and alumina fibers. In contrast, the boron based fibers are strongly anelastic, displaying frequency dependent moduli and very high microstructural damping. Ths single fiber damping results were compared with composite damping data in order to investigate the practical and basic effects of employing the four fiber types as reinforcement for aluminum and titanium matrices.
Imaging of Damped Ly-alpha Absorbers
NASA Astrophysics Data System (ADS)
Jim, K. T. C.; Roth, K. C.
1998-05-01
Intervening H I gas clouds toward QSOs give rise to damped Ly-alpha absorption. Because of the high column density (N(H I)>= 2*E(20) cm(-2) ) these systems have been thought to be galactic disks in some stage of formation. However, because potential optical counterparts have not been identified for most damped Ly-alpha systems, it is possible that some of the absorbing systems could be dwarf irregular galaxies or low surface brightness galaxies, and are thus difficult to image. In any case, the absorbers are expected to have small angular separation from the QSOs, and so high resolution imaging is required to differentiate the absorbers from the QSOs. Because previous studies have not shown any dominant morphological form for the few candidate objects known, our images are obtained with the Hawaii tip-tilt system in order to achieve the best possible morphological classification. By imaging in the NIR and optical bands that bracket the 4000 Angstroms break of these Ly-alpha absorbers, we can more readily select candidate objects by photometrically constraining their redshifts. In our sample of 14 QSOs with abosorbers from 1
The effect of simulated space thermal environment on damping capacity of metal matrix composites
NASA Astrophysics Data System (ADS)
Jiang, X.; Ouellet, L.; Nikanpour, Darius; Lo, J.
2003-09-01
Damping capacity is one of important parameters that engineers need to consider when they select materials for space structure applications. The materials studied in this paper are high performance SiC particulate reinforced aluminum and Al2O3 woven fabric reinforced aluminum composites. Changes in damping capacity of the materials in simulated space thermal environment were studied using Dynamic Mechanical Analyzer (DMA). Comparing to the conventional aluminum alloy, the composites have significantly higher damping capacity. The experiment demonstrated that thermal cycling to sub-ambient temperature can significantly affects the damping capacity of metal matrix composites. The long-term effects of space thermal cycling on the composites were also discussed.
Cocured damped layers in composite structure
Rotz, C.A. ); Barrett, D.J. )
1992-01-01
A study was made on the feasibility of laminating and cocuring graphite fiber-epoxy prepreg with plies of commercially available damping materials for form beams and hat-stiffened panels. Experiments showed that cocuring did not adversely affect the damping materials and that excellent structural damping properties could be obtained. The construction of the hat-stiffened panels proved that complex parts containing damping materials could be fabricated. Dynamic testing of these components showed that internal architectural features could be designed to promote damping in primary structure.
Evaluation of Drogue Parachute Damping Effects Utilizing the Apollo Legacy Parachute Model
NASA Technical Reports Server (NTRS)
Currin, Kelly M.; Gamble, Joe D.; Matz, Daniel A.; Bretz, David R.
2011-01-01
Drogue parachute damping is required to dampen the Orion Multi Purpose Crew Vehicle (MPCV) crew module (CM) oscillations prior to deployment of the main parachutes. During the Apollo program, drogue parachute damping was modeled on the premise that the drogue parachute force vector aligns with the resultant velocity of the parachute attach point on the CM. Equivalent Cm(sub q) and Cm(sub alpha) equations for drogue parachute damping resulting from the Apollo legacy parachute damping model premise have recently been developed. The MPCV computer simulations ANTARES and Osiris have implemented high fidelity two-body parachute damping models. However, high-fidelity model-based damping motion predictions do not match the damping observed during wind tunnel and full-scale free-flight oscillatory motion. This paper will present the methodology for comparing and contrasting the Apollo legacy parachute damping model with full-scale free-flight oscillatory motion. The analysis shows an agreement between the Apollo legacy parachute damping model and full-scale free-flight oscillatory motion.
Dynamic aperture study for the NLC main damping rings
Wolski, Andrzej; Venturini, Marco; Marks, Steve
2004-07-05
A sufficiently large acceptance is critical for the NLC Main Damping Rings (MDR) as the high power carried by the beams demands very high injection efficiency. Chromatic sextupoles and wiggler insertions (needed for rapid damping) are substantial sources of nonlinearities limiting the dynamic aperture. We report on the techniques we are using for analysis of single-particle beam dynamics in the presence of wiggler fields with significant nonlinear components. We demonstrate that our approach gives results in good agreement with experimental data when applied to the BL11 wiggler in SPEAR2, and discuss the present status of studies for the NLC MDR.
Radiation damping in real time.
Mendes, A C; Takakura, F I
2001-11-01
We study the nonequilibrium dynamics of a charge interacting with its own radiation, which originates the radiation damping. The real-time equation of motion for the charge and the associated Langevin equation is found in classical limit. The equation of motion for the charge allows one to obtain the frequency-dependent coefficient of friction. In the lowest order we find that although the coefficient of static friction vanishes, there is dynamical dissipation represented by a non-Markovian dissipative kernel.
Hydro-dynamic damping theory in flowing water
NASA Astrophysics Data System (ADS)
Monette, C.; Nennemann, B.; Seeley, C.; Coutu, A.; Marmont, H.
2014-03-01
Fluid-structure interaction (FSI) has a major impact on the dynamic response of the structural components of hydroelectric turbines. On mid-head to high-head Francis runners, the rotor-stator interaction (RSI) phenomenon always has to be considered carefully during the design phase to avoid operational issues later on. The RSI dynamic response amplitudes are driven by three main factors: (1) pressure forcing amplitudes, (2) excitation frequencies in relation to natural frequencies and (3) damping. The prediction of the two first factors has been largely documented in the literature. However, the prediction of fluid damping has received less attention in spite of being critical when the runner is close to resonance. Experimental damping measurements in flowing water on hydrofoils were presented previously. Those results showed that the hydro-dynamic damping increased linearly with the flow. This paper presents development and validation of a mathematical model, based on momentum exchange, to predict damping due to fluid structure interaction in flowing water. The model is implemented as an analytical procedure for simple structures, such as cantilever beams, but is also implemented in more general ways using three different approaches for more complex structures such as runner blades: a finite element procedure, a CFD modal work based approach and a CFD 1DOF approach. The mathematical model and all three implementation approaches are shown to agree well with experimental results.
Eddy damping effect of additional conductors in superconducting levitation systems
NASA Astrophysics Data System (ADS)
Jiang, Zhao-Fei; Gou, Xiao-Fan
2015-12-01
Passive superconducting levitation systems consisting of a high temperature superconductor (HTSC) and a permanent magnet (PM) have demonstrated several fascinating applications such as the maglev system, flywheel energy storage. Generally, for the HTSC-PM levitation system, the HTSC with higher critical current density Jc can obtain larger magnetic force to make the PM levitate over the HTSC (or suspended below the HTSC), however, the process of the vibration of the levitated PM, provides very limited inherent damping (essentially hysteresis). To improve the dynamic stability of the levitated PM, eddy damping of additional conductors can be considered as the most simple and effective approach. In this article, for the HTSC-PM levitation system with an additional copper damper attached to the HTSC, we numerically and comprehensively investigated the damping coefficient c, damping ratio, Joule heating of the copper damper, and the vibration frequency of the PM as well. Furthermore, we comparatively studied four different arrangements of the copper damper, on the comprehensive analyzed the damping effect, efficiency (defined by c/VCu, in which VCu is the volume of the damper) and Joule heating, and finally presented the most advisable arrangement.
Design of passive piezoelectric damping for space structures. Final Report Ph.D. Thesis
NASA Technical Reports Server (NTRS)
Hagood, Nesbitt W., IV; Aldrich, Jack B.; Vonflotow, Andreas H.
1994-01-01
Passive damping of structural dynamics using piezoceramic electromechanical energy conversion and passive electrical networks is a relatively recent concept with little implementation experience base. This report describes an implementation case study, starting from conceptual design and technique selection, through detailed component design and testing to simulation on the structure to be damped. About 0.5kg. of piezoelectric material was employed to damp the ASTREX testbed, a 500kg structure. Emphasis was placed upon designing the damping to enable high bandwidth robust feedback control. Resistive piezoelectric shunting provided the necessary broadband damping. The piezoelectric element was incorporated into a mechanically-tuned vibration absorber in order to concentrate damping into the 30 to 40 Hz frequency modes at the rolloff region of the proposed compensator. A prototype of a steel flex-tensional motion amplification device was built and tested. The effective stiffness and damping of the flex-tensional device was experimentally verified. When six of these effective springs are placed in an orthogonal configuration, strain energy is absorbed from all six degrees of freedom of a 90kg. mass. A NASTRAN finite element model of the testbed was modified to include the six-spring damping system. An analytical model was developed for the spring in order to see how the flex-tensional device and piezoelectric dimensions effect the critical stress and strain energy distribution throughout the component. Simulation of the testbed demonstrated the damping levels achievable in the completed system.
NASA Astrophysics Data System (ADS)
Han, Y. H.; Park, B. J.; Jung, S. Y.; Han, S. C.; Lee, W. R.; Bae, Y. C.
2013-02-01
A 35 kWh Superconductor Flywheel Energy Storage system (SFES) using hybrid bearing sets, which is composed of a high temperature superconductor (HTS) bearing and an active magnet damper (AMD), has been developed at KEPCO Research Institute (KEPRI). Damping is a source of energy loss but necessary for the stability of the flywheel system. We found that the damping of HTS bearings can be improved by thermal insulating bolts, which play a role of passive type external damper. To investigate the source of the increased damping, damping coefficients were measured with HTS bearings using insulating bolts made of three kinds of polymer materials. The damping coefficient was raised over 3000 N s/m in the case of PEEK bolts. The value was almost a quarter of the AMD. In this study, thermoelastic and Coulomb friction damping mechanisms are discussed. The main damping mechanism was the thermoelastic damping of the bolts themselves. And interfacial gap between the insulating bolt and metal chamber, which increased during the cooling process, was considered to be the cause of the anisotropic damping coefficients. Finally, the effects of the HTS bearings on the first critical speed are shown.
A novel approach to the analysis of squeezed-film air damping in microelectromechanical systems
NASA Astrophysics Data System (ADS)
Yang, Weilin; Li, Hongxia; Chatterjee, Aveek N.; Elfadel, Ibrahim (Abe M.; Ender Ocak, Ilker; Zhang, TieJun
2017-01-01
Squeezed-film damping (SFD) is a phenomenon that significantly affects the performance of micro-electro-mechanical systems (MEMS). The total damping force in MEMS mainly include the viscous damping force and elastic damping force. Quality factor (Q factor) is usually used to evaluate the damping in MEMS. In this work, we measure the Q factor of a resonator through experiments in a wide range of pressure levels. In fact, experimental characterizations of MEMS have some limitations because it is difficult to conduct experiments at very high vacuum and also hard to differentiate the damping mechanisms from the overall Q factor measurements. On the other hand, classical theoretical analysis of SFD is restricted to strong assumptions and simple geometries. In this paper, a novel numerical approach, which is based on lattice Boltzmann simulations, is proposed to investigate SFD in MEMS. Our method considers the dynamics of squeezed air flow as well as fluid-solid interactions in MEMS. It is demonstrated that Q factor can be directly predicted by numerical simulation, and our simulation results agree well with experimental data. Factors that influence SFD, such as pressure, oscillating amplitude, and driving frequency, are investigated separately. Furthermore, viscous damping and elastic damping forces are quantitatively compared based on comprehensive simulation. The proposed numerical approach as well as experimental characterization enables us to reveal the insightful physics of squeezed-film air damping in MEMS.
NASA Astrophysics Data System (ADS)
Capua, Amir; Yang, See-hun; Phung, Timothy; Parkin, Stuart S. P.
2015-12-01
Magnetization dynamics are strongly influenced by damping, namely, the loss of spin angular momentum from the magnetic system to the lattice. An "effective" damping constant αeff is often determined experimentally from the spectral linewidth of the free induction decay of the magnetization after the system is excited to its nonequilibrium state. Such an αeff, however, reflects both intrinsic damping as well as inhomogeneous broadening that arises, for example, from spatial variations of the anisotropy field. In this paper, we compare measurements of the magnetization dynamics in ultrathin nonepitaxial films having perpendicular magnetic anisotropy using two different techniques, time-resolved magneto-optical Kerr effect (TRMOKE) and hybrid optical-electrical ferromagnetic resonance (OFMR). By using an external magnetic field that is applied at very small angles to the film plane in the TRMOKE studies, we develop an explicit closed-form analytical expression for the TRMOKE spectral linewidth and show how this can be used to reliably extract the intrinsic Gilbert damping constant. The damping constant determined in this way is in excellent agreement with that determined from the OFMR method on the same samples. Our studies indicate that the asymptotic high-field approach that is often used in the TRMOKE method to distinguish the intrinsic damping from the effective damping may result in significant error, because such high external magnetic fields are required to make this approach valid that they are out of reach. The error becomes larger at lower intrinsic damping constants and thus may account for the anomalously high damping constants that are often reported in TRMOKE studies. In conventional ferromagnetic resonance (FMR) studies, inhomogeneous contributions can be readily distinguished from intrinsic damping contributions by studying the magnetic field dependence of the FMR linewidth. Using an analogous approach, we show how reliable values of the intrinsic
Damping mechanisms of single-clamped and prestressed double-clamped resonant polymer microbeams
NASA Astrophysics Data System (ADS)
Schmid, S.; Hierold, C.
2008-11-01
In this article, an investigation of the damping mechanisms of resonant single- and double-clamped polymer microbeams for a frequency range from 10 kHz to 5 MHz is presented. The suspended structures are made of SU-8, an epoxy-type photoresist, by means of a sacrificial layer technique. The vibration was measured with a laser-Doppler vibrometer in high vacuum at different temperatures and at atmospheric pressure. The influence of air damping in rarefied air was investigated and the intrinsic damping mechanisms were determined in high vacuum (p <0.05 Pa). After excluding a variety of possible damping factors, the dominant intrinsic dissipation mechanism of the single-clamped microbeams was understood to be the material damping with maximum quality factors (Q) of around 70 at 20 °C. Quality factors of up to 720 at 20 °C were measured for stringlike double-clamped microbeams, which suggest a different intrinsic damping mechanism than material loss. It is shown that internal damping mechanisms due to flexure and elongation have a small impact on the damping of stretched strings. Modeling the clamping loss based on the wave transmission into the suspended anchor plates indicates that it is the dominant intrinsic dissipation in the prestressed double-clamped microresonators. At atmospheric pressure it was shown that at low frequencies the quality factors of single-clamped and stringlike double-clamped microbeams are limited by the squeeze-film air damping. At high frequencies the quality factors are limited by the specific intrinsic damping. In between the two particular regions with a specific dominant damping mechanism the quality factors show a maximum.
Dynamic buckling of containments: The influence of damping
Farrar, C.R.; Duffey, T.A.; Goldman, P.A.; Bennett, J.G.
1993-02-01
The seismic buckling capacities of representative thin, unstiffened elastic containment shells are investigated to evaluate the sensitivity of buckling to the damping level. The finite element method with transient time integration is utilized with both actual earthquake acceleration-time signals and artificial time histories generated from regulatory spectra. The dynamic response and subsequent buckling of the selected containment shells are found to be highly dependent on both damping level and the degree to which the input signal excites the fundamental shear-bending mode of the shell. Transient stresses and buckling levels for the two containment shells induced by the seismic inputs were reduced in the range of 12% to 111% by increasing the damping level from 1% to 4% of critical.
Modulation of effective damping constant using spin Hall effect
Kasai, Shinya Kondou, Kouta; Sukegawa, Hiroaki; Mitani, Seiji; Tsukagoshi, Kazuhito; Otani, Yoshichika
2014-03-03
We have investigated modulation of the effective damping constant α{sub eff} via spin currents through the spin Hall effect for Permalloy/Pt bilayer films with various thicknesses. The observed linear and sinusoidal dependences of current density and field direction on α{sub eff} are in agreement with the analytical model. By comparing the thickness dependence of spin Hall angle obtained from the damping modulation with that previously obtained by spin-torque-induced ferromagnetic resonance, we show that there is no clear extrinsic contribution in the present method. We also show the large modulation of the effective damping constant (down to ∼20%) in the high-current-density region.
Nonlinear damping identification from transient data
NASA Astrophysics Data System (ADS)
Smith, Clifford B.; Wereley, Norman M.
1999-06-01
To study new damping augmentation methods for helicopter rotor systems, accurate and reliable nonlinear damping identification techniques are needed. For example, current studies on applications of magnetorheological (MR) dampers for rotor stability augmentation suggest that a strong Coulomb damping characteristic will be manifested as the field applied to the MR fluid is maximized. Therefore, in this work, a single degree of freedom (SDOF) system having either nonlinear Coulomb or quadratic damping is considered. This paper evaluates three analyses for identifying damping from transient test data; an FFT-based moving block analysis, an analysis based on a periodic Fourier series decomposition, and a Hilbert transform based technique. Analytical studies are used to determine the effects of block length, noise, and error in identified modal frequency on the accuracy of the identified damping level. The FFT-based moving block has unacceptable performance for systems with nonlinear damping. These problems were remedied in the Fourier series based analysis and acceptable performance is obtained for nonlinear damping identification from both this technique and the Hilbert transform based method. To more closely simulate a helicopter rotor system test, these techniques were then applied to a signal composed of two closely spaced modes. This data was developed to simulate a response containing the first lag and 1/rev modes. The primary mode of interest (simulated lag mode) had either Coulomb or quadratic damping, and the close mode (1/rev) was either undamped or had a specified viscous damping level. A comprehensive evaluation of the effects of close mode amplitude, frequency, and damping level was performed. A classifier was also developed to identify the dominant damping mechanism in a signal of 'unknown' composition. This classifier is based on the LMS error of a fit of the analytical envelope expression to the experimentally identified envelope signal. In most
Composite slip table of dissimilar materials for damping longitudinal modes
Gregory, D.L.; Priddy, T.G.; Smallwood, D.O.; Woodall, T.D.
1991-06-18
A vibration slip table for use in a vibration testing apparatus is disclosed. The tables comprised of at least three composite layers of material; a first metal layer, a second damping layer, and a third layer having a high acoustic velocity relative to the first layer. The different acoustic velocities between the first and third layers cause relative shear displacements between the layers with the second layer damping the displacements between the first and third layers to reduce the table longitudinal vibration modes. 6 figures.
Landau damping in a multi-component dusty plasma
Zhang, Heng; Yang, Yang; Zhang, Jie; Hong, Xue-Ren; Lin, Mai-Mai; Qi, Xin E-mail: duanws@nwnu.edu.cn; Duan, Wen-Shan E-mail: duanws@nwnu.edu.cn; Yang, Lei
2014-11-15
Effect of the dust size distribution on the landau damping and the wave frequency is studied in the present paper. It is found that wave frequency increases as either the difference between the largest and the smallest dust size increases or the wave number increases. It seems that wave frequency is smaller for dusty plasma whose density of the smaller grains is larger than that of the larger ones, while it is larger in the opposite case. The effect of the dust size distribution can increase the Landau damping in the cases where the temperature of the dust grains is small enough or high enough.
Quantifying acoustic damping using flame chemiluminescence
NASA Astrophysics Data System (ADS)
Boujo, E.; Denisov, A.; Schuermans, B.; Noiray, N.
2016-12-01
Thermoacoustic instabilities in gas turbines and aeroengine combustors falls within the category of complex systems. They can be described phenomenologically using nonlinear stochastic differential equations, which constitute the grounds for output-only model-based system identification. It has been shown recently that one can extract the governing parameters of the instabilities, namely the linear growth rate and the nonlinear component of the thermoacoustic feedback, using dynamic pressure time series only. This is highly relevant for practical systems, which cannot be actively controlled due to a lack of cost-effective actuators. The thermoacoustic stability is given by the linear growth rate, which results from the combination of the acoustic damping and the coherent feedback from the flame. In this paper, it is shown that it is possible to quantify the acoustic damping of the system, and thus to separate its contribution to the linear growth rate from the one of the flame. This is achieved by post-processing in a simple way simultaneously acquired chemiluminescence and acoustic pressure data. It provides an additional approach to further unravel from observed time series the key mechanisms governing the system dynamics. This straightforward method is illustrated here using experimental data from a combustion chamber operated at several linearly stable and unstable operating conditions.
NASA Astrophysics Data System (ADS)
Kinugawa, Tomoya; Nakano, Hiroyuki; Nakamura, Takashi
2016-10-01
Focusing on the remnant black holes after merging binary black holes, we show that ringdown gravitational waves of Population III binary black hole mergers can be detected at the rate of 5.9-500 events yr(SFR/(10M yr Mpc))ṡ([f/(1+f)]/0.33) for various parameters and functions. This rate is estimated for events with SNR>8 for second-generation gravitational wave detectors such as KAGRA. Here, SFR and f are the peak value of the Population III star formation rate and the fraction of binaries, respectively. When we consider only events with SNR>35, the event rate becomes 0.046-4.21 events yr(SFR/(10M yr Mpc))ṡ([f/(1+f)]/0.33). This suggest that for a remnant black hole spin of q>0.95 we have an event rate of quasinormal modes with SNR>35 of less than 0.037 events yr(SFR/(10M yr Mpc))ṡ([f/(1+f)]/0.33), while it is 3-30 events yr(SFR/(10M yr Mpc))ṡ([f/(1+f)]/0.33) for third-generation detectors such as the Einstein Telescope. If we detect many Population III binary black hole mergers, it may be possible to constrain the Population III binary evolution paths not only by the mass distribution but also by the spin distribution.
NASA Astrophysics Data System (ADS)
Décanini, Yves; Folacci, Antoine; Ould El Hadj, Mohamed
2015-07-01
With the possibility of testing massive gravity in the context of black hole physics in mind, we consider the radiation produced by a particle plunging from slightly below the innermost stable circular orbit into a Schwarzschild black hole. In order to circumvent the difficulties associated with black hole perturbation theory in massive gravity, we use a toy model in which we replace the graviton field with a massive scalar field and consider a linear coupling between the particle and this field. We compute the waveform generated by the plunging particle and study its spectral content. This permits us to highlight and interpret some important effects occurring in the plunge regime which are not present for massless fields, such as (i) the decreasing and vanishing, as the mass parameter increases, of the signal amplitude generated when the particle moves on quasicircular orbits near the innermost stable circular orbit; and (ii) in addition to the excitation of the quasinormal modes, the excitation of the quasibound states of the black hole.
ICAN/DAMP-integrated composite analyzer with damping analysis capabilities: User's manual
NASA Technical Reports Server (NTRS)
Saravanos, Dimitrious A.; Sanfeliz, Jose G.
1992-01-01
This manual describes the use of the computer code ICAN/DAMP (Integrated Composite Analyzer with Damping Analysis Capabilities) for the prediction of damping in polymer-matrix composites. The code is written in FORTRAN 77 and is a version of the ICAN (Integrated Composite ANalyzer) computer program. The code incorporates a new module for synthesizing the material damping from micromechanics to laminate level. Explicit micromechanics equations based on hysteretic damping are programmed relating the on-axis damping capacities to the fiber and matrix properties and fiber volume ratio. The damping capacities of unidirectional composites subjected to off-axis loading are synthesized from on-axis damping values. The hygrothermal effect on the damping performance of unidirectional composites caused by temperature and moisture variation is modeled along with the damping contributions from interfacial friction between broken fibers and matrix. The temperature rise is continuously vibrating composite plies and composite laminates is also estimated. The ICAN/DAMP user's manual provides descriptions of the damping analysis module's functions, structure, input requirements, output interpretation, and execution requirements. It only addresses the changes required to conduct the damping analysis and is used in conjunction with the 'Second Generation Integrated Composite Analyzer (ICAN) Computer Code' user's manual (NASA TP-3290).
Damped transverse oscillations of interacting coronal loops
NASA Astrophysics Data System (ADS)
Soler, Roberto; Luna, Manuel
2015-10-01
Damped transverse oscillations of magnetic loops are routinely observed in the solar corona. This phenomenon is interpreted as standing kink magnetohydrodynamic waves, which are damped by resonant absorption owing to plasma inhomogeneity across the magnetic field. The periods and damping times of these oscillations can be used to probe the physical conditions of the coronal medium. Some observations suggest that interaction between neighboring oscillating loops in an active region may be important and can modify the properties of the oscillations. Here we theoretically investigate resonantly damped transverse oscillations of interacting nonuniform coronal loops. We provide a semi-analytic method, based on the T-matrix theory of scattering, to compute the frequencies and damping rates of collective oscillations of an arbitrary configuration of parallel cylindrical loops. The effect of resonant damping is included in the T-matrix scheme in the thin boundary approximation. Analytic and numerical results in the specific case of two interacting loops are given as an application.
Rhizoctonia seedling damping-off in sugar beet in Michigan
Technology Transfer Automated Retrieval System (TEKTRAN)
Rhizoctonia solani is an important seedling pathogen of sugar beet, causing damping-off following seedling emergence. Anastomosis group (AG)-4 has been the primary seedling pathogen reported on sugar beet, however, recent screening has found high incidence of infection by AG-2-2. Isolations of R. so...
Damped Mechanical Oscillator: Experiment and Detailed Energy Analysis
ERIC Educational Resources Information Center
Corridoni, Tommaso; D'Anna, Michele; Fuchs, Hans
2014-01-01
The damped oscillator is discussed in every high school textbook or introductory physics course, and a large number of papers are devoted to it in physics didactics journals. Papers typically focus on kinematic and dynamic aspects and less often on energy. Among the latter, some are devoted to the peculiar decreasing behavior of energy…
Vitreous Enamel Damping Material Development.
1982-11-01
PROCEDURES 3 2.1. EXPERIMENTAL 3 2.1.1. GLASS PREPARATION 3 2.1.2. METHOD OF COATING APPLICATION 3 2.1.3. VIBRATION DAMPING MEASUREMENTS 3 2.2. CALCULATION OF...discussion in this report. fL 2 SECTION II TECHNICAL PROCEDURES 2.1 EXPERIMENTAL 2.1.1 Glass Preparation All of the compositions, except the standard...After heat treatments of composition "B", a- cristobalite and devitrite (Na20.3CaO-6SiO 2) appear as crystalline phases; a- cristobalite being the major
CHARACTERIZATION OF DAMPING IN BOLTED LAP JOINTS
C. MALONEY; D. PEAIRS; ET AL
2000-08-01
The dynamic response of a jointed beam was measured in laboratory experiments. The data were analyzed and the system was mathematically modeled to establish plausible representations of joint damping behavior. Damping is examined in an approximate, local linear framework using log decrement and half power bandwidth approaches. in addition, damping is modeled in a nonlinear framework using a hybrid surface irregularities model that employs a bristles-construct. Experimental and analytical results are presented.
Radiation damping in metal nanoparticle pairs.
Dahmen, Christian; Schmidt, Benjamin; von Plessen, Gero
2007-02-01
The radiation damping rate of plasmon resonances in pairs of spherical gold nanoparticles is calculated. The radiative line width of the plasmon resonance indicates significant far-field coupling between the nanoparticles over distances many times the particle diameter. The radiation damping of the coupled particle-plasmon mode alternates between superradiant and subradiant behavior when the particle spacing is varied. At small particle spacings where near-field coupling occurs, the radiation damping rate lies far below that of an isolated particle.
Damping of Resonantly Forced Density Waves in Dense Planetary Rings
NASA Astrophysics Data System (ADS)
Lehmann, Marius; Schmidt, Jürgen; Salo, Heikki
2016-10-01
We address the stability of resonantly forced density waves in dense planetary rings.Already by Goldreich and Tremaine (1978) it has been argued that density waves might be unstable, depending on the relationship between the ring's viscosity and the surface mass density. In the recent paper (Schmidt et al. 2016) we have pointed out that when - within a fluid description of the ring dynamics - the criterion for viscous overstability is satisfied, forced spiral density waves become unstable as well. In this case, linear theory fails to describe the damping.We apply the multiple scale formalism to derive a weakly nonlinear damping relation from a hydrodynamical model.This relation describes the resonant excitation and nonlinear viscous damping of spiral density waves in a vertically integrated fluid disk with density dependent transport coefficients. The model consistently predicts linear instability of density waves in a ring region where the conditions for viscous overstability are met. In this case, sufficiently far away from the Lindblad resonance, the surface mass density perturbation is predicted to saturate to a constant value due to nonlinear viscous damping. In general the model wave damping lengths depend on a set of input parameters, such as the distance to the threshold for viscous overstability and the ground state surface mass density.Our new model compares reasonably well with the streamline model for nonlinear density waves of Borderies et al. 1986.Deviations become substantial in the highly nonlinear regime, corresponding to strong satellite forcing.Nevertheless, we generally observe good or at least qualitative agreement between the wave amplitude profiles of both models. The streamline approach is superior at matching the total wave profile of waves observed in Saturn's rings, while our new damping relation is a comparably handy tool to gain insight in the evolution of the wave amplitude with distance from resonance, and the different regimes of
Hysteretic damping in rotordynamics: An equivalent formulation
NASA Astrophysics Data System (ADS)
Genta, Giancarlo; Amati, Nicola
2010-10-01
The hysteretic damping model cannot be applied to time domain dynamic simulations: this is a well-known feature that has been discussed in the literature since the time when analog computers were widespread. The constant equivalent damping often introduced to overcome this problem is also discussed, and its limitations are stated, in particular those linked with its application in rotordynamics to simulate rotating damping. An alternative model based on the nonviscous damping (NVD) model, but with a limited number of additional degrees of freedom, is proposed, and the relevant equations are derived. Some examples show applications to the rotordynamics field.
Material Damping Experiments at Cryogenic Temperatures
NASA Technical Reports Server (NTRS)
Levine, Marie; White, Christopher
2003-01-01
A unique experimental facility has been designed to measure damping of materials at cryogenic temperatures. The test facility pays special attention to removing other sources of damping in the measurement by avoiding frictional interfaces, decoupling the test specimen from the support system, and by using a non-contacting measurement device; Damping data is obtained for materials (AI, GrEp, Be, Fused Quartz), strain amplitudes (less than 10-6 ppm), frequencies (20Hz-330Hz) and temperatures (20K-293K) relevant to future precision optical space missions. The test data shows a significant decrease in viscous damping at cryogenic temperatures and can be as low as 10-4%, but the amount of the damping decrease is a function of frequency and material. Contrary to the other materials whose damping monotonically decreased with temperature, damping of Fused Quartz increased substantially at cryo, after reaching a minimum at around l50 K. The damping is also shown to be insensitive to strain for low strain levels. At room temperatures, the test data correlates well to the analytical predictions of the Zener damping model. Discrepancies at cryogenic temperatures between the model predictions and the test data are observed.
Climate Variability and Vadose Zone Controls on Damping of Transient Recharge Fluxes
NASA Astrophysics Data System (ADS)
Corona, C.; Gurdak, J. J.; Dickinson, J.; Ferré, T. P. A.
2015-12-01
We investigate the effects of interannual to multidecadal climate variability on groundwater resources by exploring the physical processes in the vadose zone that partially control transient infiltration and recharge fluxes. The vadose zone connects climate variability modes to groundwater systems by influencing infiltration events. Infiltration events become time-varying water flux through the vadose zone and are controlled by highly nonlinear, complex interactions between mean infiltration flux, infiltration period, soil textures, and depth to water table. We focus on the behavior and damping depth of water flux in the vadose zone. The damping depth is defined as the depth that the flux variation damps to 5% of the land surface variation. When the damping depth is above the water table, recharge may be considered steady; when the damping depth is below the water table, recharge may be considered transient. Previous work shows that the damping depth is sensitive to the frequency of the infiltration pattern and the unsaturated hydraulic properties of the media. We examine controls on the damping depth by modeling transient water fluxes at the land surface using the Gardner-Kozeny soil model for diffuse unsaturated flow in HYDRUS 1-D. Results for homogeneous profiles show that shorter-period oscillations, smaller mean fluxes, and finer-grained soil textures generally produce damping depths closer to land surface. Modeling layered soil textures indicates similar, but more complicated responses in the damping depth. Model results indicate that finer-textured layers in a coarser soil profile generally result in damping depths closer to land surface, while coarser-textured layers in a coarser soil profile result in damping depths deeper in the vadose zone. Findings from this study will enhance understanding of the vadose zone's influence on transient water flux and improve the simulation of recharge processes and climate variability effects in groundwater models.
NASA Astrophysics Data System (ADS)
Unruh, Oliver
2016-09-01
In order to reduce noise emitted by vibrating structures additional damping treatments such as constraint layer damping or embedded elastomer layers can be used. To save weight and cost, the additional damping is often placed at some critical locations of the structure, what leads to spatially inhomogeneous distribution of damping. This inhomogeneous distribution of structural damping leads to an occurrence of complex vibration modes, which are no longer dominated by pure standing waves, but by a superposition of travelling and standing waves. The existence of complex vibration modes raises the question about their influence on sound radiation. Previous studies on the sound radiation of complex modes of rectangular plates reveal, that, depending on the direction of travelling waves, the radiation efficiency of structural modes can slightly decrease or significantly increase. These observations have been made using a rectangular plate with a simple inhomogeneous damping configuration which includes a single plate boundary with a higher structural damping ratio. In order to answer the question about the influence of other possible damping configurations on the sound radiation properties, this paper addresses the self- and mutual-radiation efficiencies of the resulting complex vibration modes. Numerical simulations are used for the calculation of complex structural modes of different inhomogeneous damping configurations with varying geometrical form and symmetry. The evaluation of self- and mutual-radiation efficiencies reveals that primarily the symmetry properties of the inhomogeneous damping distribution affect the sound radiation characteristics. Especially the asymmetric distributions of inhomogeneous damping show a high influence on the investigated acoustic metrics. The presented study also reveals that the acoustic cross-coupling between structural modes, which is described by the mutual-radiation efficiencies, generally increases with the presence of
Damping of Magnetohydrodynamic Waves in Solar Prominence Fine Structures
NASA Astrophysics Data System (ADS)
Soler, Roberto
2010-05-01
High-resolution observations of solar filaments and prominences reveal that these large-scale coronal structures are formed by a myriad of long and thin ribbons, here called threads, which are piled up to form the prominence body. Evidences suggest that these fine structures are magnetic flux tubes anchored in the solar photosphere, which are partially filled with the cool and dense prominence material. Individual and collective oscillations of prominence and filament fine structures are frequently reported by means of oscillatory variations in Doppler signals and spectral line intensity. Common features of these observations are that the reported oscillatory periods are usually in a narrow range between 2 and 10 minutes, that the velocity amplitudes are smaller than ˜3 km/s, and that the oscillations seem to be strongly damped after a few periods. Typically, the ratio of the damping time, tD, to the period, P, is tD/P < 10. While the oscillations have been interpreted in the context of the magnetohydrodynamic (MHD) theory, i.e., in terms of the MHD normal modes supported by the filament thread body and/or propagating MHD waves, the mechanism or mechanisms responsible for the damping are not well-known and a comparative study between different damping mechanisms is needed. In this Thesis, we study the efficiency of several physical mechanisms for the damping of MHD oscillations in prominence fine structures. Both individual and collective oscillations of threads are analyzed. We model a filament thread as a straight cylindrical magnetic flux tube with prominence conditions, embedded in a magnetized environment representing the solar coronal medium. The basic MHD equations are applied to the model and contain non-ideal terms accounting for effects as, e.g., non-adiabatic mechanisms, magnetic diffusion, ion-neutral collisions, etc., that may be of relevance in prominence plasmas and whose role on the damping of the oscillations is assessed. Our method combines
NASA Technical Reports Server (NTRS)
Dolgin, Benjamin P. (Inventor)
1994-01-01
A superconductive load bearing support without a mechanical contact and vibration damping for cryogenic instruments in space is presented. The levitation support and vibration damping is accomplished by the use of superconducting magnets and the 'Meissner' effect. The assembly allows for transfer of vibration energy away from the cryogenic instrument which then can be damped by the use of either an electronic circuit or conventional vibration damping mean.
Foust, F. R.; Bell, T. F.; Spasojevic, M.; Inan, U. S.
2011-06-15
We present results showing the measured Landau damping rate using a high-order discontinuous Galerkin particle-in-cell (DG-PIC) [G. B. Jacobs and J. S. Hesthaven, J. Comput. Phys. 214, 96 (2006)] method. We show that typical damping rates measured in particle-in-cell (PIC) simulations can differ significantly from the linearized Landau damping coefficient and propose a simple numerical method to solve the plasma dispersion function exactly for moderate to high damping rates. Simulation results show a high degree of agreement between the high-order PIC results and this calculated theoretical damping rate.
Tuned vibration absorbers with nonlinear viscous damping for damped structures under random load
NASA Astrophysics Data System (ADS)
Shum, K. M.
2015-06-01
The classical problem for the application of a tuned vibration absorber is to minimize the response of a structural system, such as displacement, velocity, acceleration or to maximize the energy dissipated by tuned vibration absorber. The development of explicit optimal absorber parameters is challenging for a damped structural system since the fixed points no longer exist in the frequency response curve. This paper aims at deriving a set of simple design formula of tuned vibration absorber with nonlinear viscous damping based on the frequency tuning for harmonic load for a damped structural system under white noise excitation. The vibration absorbers being considered include tuned mass damper (TMD) and liquid column vibration absorber (LCVA). Simple approximate expression for the standard deviation velocity response of tuned vibration absorber for damped primary structure is also derived in this study to facilitate the estimation of the damping coefficient of TMD with nonlinear viscous damping and the head loss coefficient of LCVA. The derived results indicate that the higher the structural inherent damping the smaller the supplementary damping provided by a tuned vibration absorber. Furthermore, the optimal damping of tuned vibration absorber is shown to be independent of structural damping when it is tuned using the frequency tuning for harmonic load. Finally, the derived closed-form expressions are demonstrated to be capable of predicting the optimal parameters of tuned vibration absorbers with sufficient accuracy for preliminary design of tuned vibration absorbers with nonlinear viscous damping for a damped primary structure.
NASA Technical Reports Server (NTRS)
Taylor, Larry; Leary, Terry; Stewart, Eric
1987-01-01
The damping for structural dynamic models of flexible spacecraft is usually ignored and then added after modal frequencies and mode shapes are calculated. It is common practice to assume the same damping ratio for all modes, although it is known that damping due to bending and that due to torsion are sometimes ignored. Two methods of including damping in the modeling process from its onset are examined. First, the partial derivative equations of motion are analyzed for a pinned-pinned beam with damping. The end conditions are altered to handle bodies with mass and inertia for the Spacecraft Control Laboratory Experiment (SCOLE) configuration. Second, a massless beam approximation is used for the modes with low frequencies, and a clamped-clamped system is used to approximate the modes for arbitrarily high frequency. The model is then modified to include gravity effects and is compared with experimental results.
Research on the damping properties of Fe12O19Sr/the polyurethane elastomer composite
NASA Astrophysics Data System (ADS)
Li, Y.; Qin, Yan; Sun, P. C.; Huang, Z. X.
2016-07-01
Magnetic elastomer composite is a promising damping material. In this paper, both strontium ferrite (Fe12O19Sr) powders and polyurethane elastomer which were mixed by mechanical blending method were used as the magnetic filler and as the matrix respectively, the properties of the magnetic damping composite materials were studied. The results show that the magnetic properties of the magnetic elastomers composite are enhanced with the ferrite loading. The mechanical properties and Shore hardness are highly influenced by mass fraction of ferrite particles. The damping properties of magnetic elastomer composite reach best when the strontium ferrite loading is 15phr, and the damping properties deteriorate when the loading continue increasing. The damping properties of the composites with the X direction of magnetization are better than that with Y direction of magnetization.
Choke-mode damped structure design for the Compact Linear Collider main linac
NASA Astrophysics Data System (ADS)
Zha, Hao; Shi, Jiaru; Chen, Huaibi; Grudiev, Alexej; Wuensch, Walter; Tang, Chuanxiang; Huang, Wenhui
2012-12-01
Choke-mode damped structures are being studied as an alternative design to waveguide damped structures for the main linac of the Compact Linear Collider (CLIC). Choke-mode structures have the potential for lower pulsed temperature rise and simpler and less expensive fabrication. An equivalent circuit model based on transmission line theory for higher-order-mode damping is presented. Using this model, a new choke geometry is proposed and the wakefield performance is verified using Gdfidl. This structure has a comparable wakefield damping effect to the baseline design which uses waveguide damping. A prototype structure with the same iris dimensions and accelerating gradient as the nominal CLIC design, but with the new choke geometry, has been designed for high-power tests.
Zheng, Yelong; Song, Le; Hu, Gang; Zhao, Meirong; Tian, Yanling; Zhang, Zihui; Fang, Fengzhou
2014-05-01
A micro/nano force can be traced to the International System of Units by means of an electrostatic force balance weight system. However, the micro/nano force measurement system is susceptible to environmental disturbances. Various methods have been proposed to reduce the effect of environmental disturbances and obtain high resolution and fast response. In this paper, we introduce a combination of air damping and inherent damping from the internal molecular friction of spring suspension. This will optimize system stability and improve environmental noise suppression. Results from the air damping model show that the damping ratio increases from 0.0005 to 0.1, which improves the vibration resistance. We found that the system with air damping has the advantages of fast response and low scatter.
Thermoelastic damping in torsion microresonators with coupling effect between torsion and bending
NASA Astrophysics Data System (ADS)
Tai, Yongpeng; Li, Pu; Fang, Yuming
2014-02-01
Predicting thermoelastic damping (TED) is crucial in the design of high Q MEMS resonators. In the past, there have been few works on analytical modeling of thermoelastic damping in torsion microresonators. This could be related to the assumption of pure torsional mode for the supporting beams in the torsion devices. The pure torsional modes of rectangular supporting beams involve no local volume change, and therefore, they do not suffer any thermoelastic loss. However, the coupled motion of torsion and bending usually exists in the torsion microresonator when it is not excited by pure torque. The bending component of the coupled motion causes flexural vibrations of supporting beams which may result in significant thermoelastic damping for the microresonator. This paper presents an analytical model for thermoelastic damping in torsion microresonators with the coupling effect between torsion and bending. The theory derives a dynamic model for torsion microresonators considering the coupling effect, and approximates the thermoelastic damping by assuming the energy loss to occur only in supporting beams of flexural vibrations. The thermoelastic damping obtained by the present model is compared to the measured internal friction of single paddle oscillators. It is found that thermoelastic damping contributes significantly to internal friction for the case of the higher modes at room temperature. The present model is validated by comparing its results with the finite-element method (FEM) solutions. The effects of structural dimensions and other parameters on thermoelastic damping are investigated for the representative case of torsion microresonators.
Magnetic Damping of Solid Solution Semiconductor Alloys
NASA Technical Reports Server (NTRS)
Szofran, Frank R.; Benz, K. W.; Corell, Arne; Dold, Peter; Cobb, Sharon D.; Volz, Martin P.; Motakef, Shariar
1998-01-01
The objective of this study is to conduct the Earth-based research sufficient to successfully propose a flight experiment (1) to experimentally test the validity of the modeling predictions applicable to the magnetic damping of convective flows in conductive melts as this applies to the bulk growth of solid solution semiconducting materials in the reduced gravitational levels available in low Earth orbit and (2) to assess the effectiveness of steady magnetic fields in reducing the fluid flows occurring in these materials during space processing. To achieve the objectives of this investigation, we are carrying out a comprehensive program in the Bridgman and floating-zone configurations using the solid solution alloy system Ge-Si. This alloy system was chosen because it has been studied extensively in environments that have not simultaneously included both low gravity and an applied magnetic field. Also, all compositions have a high electrical conductivity, and the materials parameters permit high growth rates compared to many other commonly studied alloy semiconductors. An important supporting investigation is determining the role, if any, that thermoelectromagnetic convection (TEMC) plays during growth of these materials in a magnetic field. Some compositional anomalies observed by us in magnetic grown crystals can only be explained by TEMC; this has significant implications for the deployment of a Magnetic Damping Furnace in space. This effect will be especially important in solid solutions where the growth interface is, in general, neither isothermal nor isoconcentrational. It could be important in single melting point materials, also, if faceting takes place producing a non-isothermal interface.
Study for ILC Damping Ring at KEKB
Flanagan, J.W.; Fukuma, H.; Kanazawa, K.I.; Koiso, H.; Masuzawa, M.; Ohmi, Kazuhito; Ohnishi, Y.; Oide, Katsunobu; Suetsugu, Y.; Tobiyama, M.; Pivi, M.; /SLAC
2011-11-04
ILC damping ring consists of very low emittance electron and positron storage rings. It is necessary for ILC damping ring to study electron cloud effects in such low emittance positron ring. We propose a low emittance operation of KEKB to study the effects.
Understanding the Damped SHM without ODEs
ERIC Educational Resources Information Center
Ng, Chiu-king
2016-01-01
Instead of solving ordinary differential equations (ODEs), the damped simple harmonic motion (SHM) is surveyed qualitatively from basic mechanics and quantitatively by the instrumentality of a graph of velocity against displacement. In this way, the condition b ? [square root]4mk for the occurrence of the non-oscillating critical damping and…
Bending rate damping in elastic systems
NASA Technical Reports Server (NTRS)
Banks, H. T.; Wang, Y.; Fabiano, R. H.
1989-01-01
Preliminary results of an investigation of the bending rate damping model for elastic structures are presented. A model for which the internal damping term is physically plausible and which can accomodate cantilevered boundary conditions is discussed. The model formulation and mathematical foundations are given, and numerical results are discussed.
Damping device for a stationary labyrinth seal
NASA Technical Reports Server (NTRS)
El-Aini, Yehia M. (Inventor); Mitchell, William S. (Inventor); Roberts, Lawrence P. (Inventor); Montgomery, Stuart K. (Inventor); Davis, Gary A. (Inventor)
2010-01-01
A stationary labyrinth seal system includes a seal housing having an annular cavity, a plurality of damping devices, and a retaining ring. The damping devices are positioned within the annular cavity and are maintained within the annular cavity by the retaining ring.
Magnetic dipole oscillations and radiation damping
NASA Astrophysics Data System (ADS)
Stump, Daniel R.; Pollack, Gerald L.
1997-01-01
We consider the problem of radiation damping for a magnetic dipole oscillating in a magnetic field. An equation for the radiation reaction torque is derived, and the damping of the oscillations is described. Also discussed are runaway solutions for a rotating magnetic dipole moving under the influence of the reaction torque, with no external torque.
DAMPs from Cell Death to New Life
Vénéreau, Emilie; Ceriotti, Chiara; Bianchi, Marco Emilio
2015-01-01
Our body handles tissue damage by activating the immune system in response to intracellular molecules released by injured tissues [damage-associated molecular patterns (DAMPs)], in a similar way as it detects molecular motifs conserved in pathogens (pathogen-associated molecular patterns). DAMPs are molecules that have a physiological role inside the cell, but acquire additional functions when they are exposed to the extracellular environment: they alert the body about danger, stimulate an inflammatory response, and finally promote the regeneration process. Beside their passive release by dead cells, some DAMPs can be secreted or exposed by living cells undergoing a life-threatening stress. DAMPs have been linked to inflammation and related disorders: hence, inhibition of DAMP-mediated inflammatory responses is a promising strategy to improve the clinical management of infection- and injury-elicited inflammatory diseases. However, it is important to consider that DAMPs are not only danger signals but also central players in tissue repair. Indeed, some DAMPs have been studied for their role in tissue healing after sterile or infection-associated inflammation. This review is focused on two exemplary DAMPs, HMGB1 and adenosine triphosphate, and their contribution to both inflammation and tissue repair. PMID:26347745
NASA Astrophysics Data System (ADS)
Thomas, Alexander; Ridgers, Christopher; Bulanov, Stepan; Griffin, Blake; Mangles, Stuart
2012-10-01
We present numerical calculations of the angularly resolved radiation spectrum from a relativistic electron beam interacting with an ultrashort laser pulse. These calculations include the effect of semi-classical radiation reaction forces including a Gaunt factor for synchrotron radiation. For a laser of 5x10^21 Wcm-2 intensity interacting with a 200 MeV electron beam with an emittance similar to that in laser wakefield acceleration experiments, radiation reaction does not produce a significant change in the angular and energy distribution of photons. However the effects of radiation reaction are clear when observing the electron beam properties. The result is that near-term experiments using such a counter-propagating beam-laser geometry should be able to measure the effects of quantum effects in radiation reaction. The calculations also show that the brilliance of this source is very high, with a peak spectral brilliance exceeding 10^29 photons,s-1mm-2mrad-2(0.1% bandwidth)-1 with approximately 2% efficiency and with a peak energy of 10 MeV.
Landau damping in a turbulent setting
Plunk, G. G.
2013-03-15
To address the problem of Landau damping in kinetic turbulence, we consider the forcing of the linearized Vlasov equation by a stationary random source. It is found that the time-asymptotic density response is dominated by resonant particle interactions that are synchronized with the source. The energy consumption of this response is calculated, implying an effective damping rate, which is the main result of this paper. Evaluating several cases, it is found that the effective damping rate can differ from the Landau damping rate in magnitude and also, remarkably, in sign. A limit is demonstrated in which the density and current become phase-locked, which causes the effective damping to be negligible; this result offers a fresh perspective from which to reconsider recent observations of kinetic turbulence satisfying critical balance.
Damping characteristics of damaged fiber composite components
NASA Technical Reports Server (NTRS)
Eberle, K.
1986-01-01
Defects in fiber composite components produce changes with respect to the vibrational characteristics of the material. These changes can be recognized in the form of a frequency shift or an alteration of the damping process. The present investigation is concerned with questions regarding the possibility of a utilization of the changes in suitable defect-detecting inspection procedures. A description is given of a method for measuring the damping characteristics of a specimen. This method provides a spectrum of the damping coefficients of the sample as a basis for a comprehensive evaluation of the damping behavior. The correlation between defects and change in the damping characteristics is demonstrated with the aid of results obtained in measurements involving specimens of carbon-fiber composites and a component consisting of glass-fiber-reinforced plastics.
Magnetic damping of rotation. [in satellites
NASA Technical Reports Server (NTRS)
Opik, E. J.
1977-01-01
Based on Wilson's (1977) article on the magnetic effects on space vehicles and other celestial bodies, the magnetic damping of rotation is considered. The inadequacy of the interstellar magnetic field in overcoming solar wind shielding and thus influencing the rotation of bodies is described. The ionospheric shielding of the interstellar field is discussed along with the permeability and magnetic damping by the solar or stellar wind. Star formation and angular momentum is discussed and attention is given to the magnetic damping of unshielded small bodies. Calculations of the rate for damping through random particle impact are made. Theories concerning the rotation of asteroids and the origin of meteorites are reviewed. The shielding process of ionospheric plasmas is outlined and the damping effect of the geomagnetic field on the rotation of artificial satellites is evaluated.
VIBRATION DAMPING AND SHOCK MOUNT
Stevens, D.J.; Forman, G.W.
1963-12-10
A shock absorbing mount in which vibrations are damped by an interference fit between relatively movable parts of the mount is described. A pair of generally cup-shaped parts or members have skirt portions disposed in an oppositely facing nesting relationship with the skirt of one member frictionally engaging the skirt of the other. The outermost skirt may be slotted to provide spring-like segments which embrace the inner skirt for effecting the interference fit. Belleville washers between the members provide yieldable support for a load carried by the mount. When a resonant frequency of vibration forces acting upon the moumt attains a certain level the kinetic energy of these forces is absorbed by sliding friction between the parts. (AEC)
Large space structure damping design
NASA Technical Reports Server (NTRS)
Pilkey, W. D.; Haviland, J. K.
1983-01-01
Several FORTRAN subroutines and programs were developed which compute complex eigenvalues of a damped system using different approaches, and which rescale mode shapes to unit generalized mass and make rigid bodies orthogonal to each other. An analytical proof of a Minimum Constrained Frequency Criterion (MCFC) for a single damper is presented. A method to minimize the effect of control spill-over for large space structures is proposed. The characteristic equation of an undamped system with a generalized control law is derived using reanalysis theory. This equation can be implemented in computer programs for efficient eigenvalue analysis or control quasi synthesis. Methods to control vibrations in large space structure are reviewed and analyzed. The resulting prototype, using electromagnetic actuator, is described.
Vibration damping using a spiral acoustic black hole.
Lee, Jae Yeon; Jeon, Wonju
2017-03-01
This study starts with a simple question: can the vibration of plates or beams be efficiently reduced using a lightweight structure that occupies a small space? As an efficient technique to damp vibration, the concept of an acoustic black hole (ABH) is adopted with a simple modification of the geometry. The original shape of an ABH is a straight wedge-type profile with power-law thickness, with the reduction of vibration in beams or plates increasing as the length of the ABH increases. However, in real-world applications, there exists an upper bound of the length of an ABH due to space limitations. Therefore, in this study, the authors propose a curvilinear shaped ABH using the simple mathematical geometry of an Archimedean spiral, which allows a uniform gap distance between adjacent baselines of the spiral. In numerical simulations, the damping performance increases as the arc length of the Archimedean spiral increases, regardless of the curvature of the spiral in the mid- and high-frequency ranges. Adding damping material to an ABH can also strongly enhance the damping performance while not significantly increasing the weight. In addition, the radiated sound power of a spiral ABH is similar to that of a standard ABH.
Recommendation for the Feasibility of more Compact LC Damping Rings
Pivi, M.T.F.; Wang, L.; Demma, T.; Guiducci, S.; Suetsugu, Y.; Shibata, K.; Ohmi, K.; Dugan, G.; Palmer, M.; Crittenden, J.A.; Harkay, K.; Boon, L.; Furman, M.A.; Venturini, M.; Celata, C.; Malyshev, O.B.; Papaphilippou, I.; /CERN
2010-06-15
As part of the international Linear Collider (ILC) collaboration, we have compared the electron cloud (EC) effect for different Damping Ring (DR) designs respectively with 6.4 km and 3.2 km circumference and investigated the feasibility of the shorter damping ring with respect to the electron cloud build-up and related beam instabilities. The studies for a 3.2 km ring were carried out with beam parameters of the ILC Low Power option. A reduced damping ring circumference has been proposed for the new ILC baseline design SB2009 [1] and would allow considerable reduction of the number of components, wiggler magnets and costs. We discuss the impact of the proposed operation of the ILC at high repetition rate 10 Hz and address the necessary modifications for the DRs. We also briefly discuss the plans for future studies including the luminosity upgrade option with shorter bunch spacing, the evaluation of mitigation techniques and the integration of the CesrTA results into the Damping Ring design.
Recommendation for the Feasibility of more Compact LC Damping Rings
Pivi, M. T. F.; Wang, L.; Demma, T.; Guiducci, S.; Suetsugu, Y.; Fukuma, H.; Shibata, K.; Dugan, K.,G.; Palmer, M.; Crittenden, J.; Harkay, K.; Boon, L.; Furman, M. A.; Venturini, M.; Celata, C.; Malyshev, O.; Papaphilippou, I.
2010-05-23
As part of the international Linear Collider (ILC) collaboration, we have compared the electron cloud (EC) effect for different Damping Ring (DR) designs respectively with 6.4 km and 3.2 km circumference and investigated the feasibility of a shorter damping ring with respect to the electron cloud build-up and related beam instability. The studies for a 3.2 km ring were carried out with beam parameters of the ILC Low Power option. A reduced damping ring circumference has been proposed for the new ILC baseline design SB2009 [1] and would allow to considerably reduce the number of components, wiggler magnets and costs. We discuss the impact of the proposed operation of the ILC at high repetition rate 10 Hz and address the necessary modifications for the DRs. We also briefly discuss the plans for future studies including the luminosity upgrade option with shorter bunch spacing, the evaluation of mitigations and the integration of the CesrTA results into the Damping Ring design.
NASA Technical Reports Server (NTRS)
Min, James B.; Harris, Donald L.; Ting, J. M.
2011-01-01
For advanced aerospace propulsion systems, development of ceramic matrix composite integrally-bladed turbine disk technology is attractive for a number of reasons. The high strength-to-weight ratio of ceramic composites helps to reduce engine weight and the one-piece construction of a blisk will result in fewer parts count, which should translate into reduced operational costs. One shortcoming with blisk construction, however, is that blisks may be prone to high cycle fatigue due to their structural response to high vibration environments. Use of ceramic composites is expected to provide some internal damping to reduce the vibratory stresses encountered due to unsteady flow loads through the bladed turbine regions. A goal of our research was to characterize the vibration viscous damping behavior of C/SiC composites. The vibration damping properties were measured and calculated. Damping appeared to decrease with an increase in the natural frequency. While the critical damping amount of approximately 2% is required for typical aerospace turbomachinery engines, the C/SiC damping at high frequencies was less than 0.2% from our study. The advanced high-performance aerospace propulsion systems almost certainly will require even more damping than what current vehicles require. A purpose of this paper is to review some work on C/SiC vibration damping by the authors for the NASA CMC turbine blisk development program and address an importance of the further investigation of the blade vibration damping characteristics on candidate CMC materials for the NASA s advanced aerospace turbomachinery engine systems.
Magnetic Damping of Solid Solution Semiconductor Alloys
NASA Technical Reports Server (NTRS)
Szofran, Frank R.; Benz, K. W.; Croell, Arne; Dold, Peter; Cobb, Sharon D.; Volz, Martin P.; Motakef, Shariar
1999-01-01
The objective of this study is to: (1) experimentally test the validity of the modeling predictions applicable to the magnetic damping of convective flows in electrically conductive melts as this applies to the bulk growth of solid solution semiconducting materials; and (2) assess the effectiveness of steady magnetic fields in reducing the fluid flows occurring in these materials during processing. To achieve the objectives of this investigation, we are carrying out a comprehensive program in the Bridgman and floating-zone configurations using the solid solution alloy system Ge-Si. This alloy system has been studied extensively in environments that have not simultaneously included both low gravity and an applied magnetic field. Also, all compositions have a high electrical conductivity, and the materials parameters permit reasonable growth rates. An important supporting investigation is determining the role, if any, that thermoelectromagnetic convection (TEMC) plays during growth of these materials in a magnetic field. TEMC has significant implications for the deployment of a Magnetic Damping Furnace in space. This effect will be especially important in solid solutions where the growth interface is, in general, neither isothermal nor isoconcentrational. It could be important in single melting point materials, also, if faceting takes place producing a non-isothermal interface. In conclusion, magnetic fields up to 5 Tesla are sufficient to eliminate time-dependent convection in silicon floating zones and possibly Bridgman growth of Ge-Si alloys. In both cases, steady convection appears to be more significant for mass transport than diffusion, even at 5 Tesla in the geometries used here. These results are corroborated in both growth configurations by calculations.
Measurement of damping of graphite epoxy composite materials and structural joints
NASA Technical Reports Server (NTRS)
Crocker, Malcolm J.; Rao, Mohan D.; Raju, P. K.; Yan, Xinche
1989-01-01
The damping capacity of graphite epoxy materials and structural joints was evaluated. The damping ratio of different composite specimens and bonded joints were systematically evaluated under normal atmospheric conditions and in a vacuum environment. Free and forced vibration test methods were employed for measuring the damping ratios. The effect of edge support conditions on the damping value of a composite tube specimen was studied by using a series of experiments performed on the specimen with different edge supports. It was found that simulating a free-free boundary conditions by having no constraints at the ends gives the lowest value of the material damping of the composite. The accuracy of the estimation of the damping ratio value was improved by using a curve-fitting technique on the response data obtained through measurement. The effect of outgassing (moisture desorption) on the damping capacity was determined by measuring the damping ratio of the tube specimen in a vacuum environment before and after outgassing had occurred. The effects of high and low temperatures on the damping was also investigated by using a series of experiments on tube and beam specimens. An analytical model to study the vibrations of a bonded lap joint system was formulated. Numerical results were generated for different overlap ratios of the system. These were compared with experimental results. In order to determine the influence of bonded joints on the material damping capacity, experiments were conducted on bonded lap-jointed and double-butt-jointed specimens. These experimental results were compared with simple beam specimens with no joints.
The ROSETTA PHILAE Lander damping mechanism as probe for the Comet soil strength.
NASA Astrophysics Data System (ADS)
Roll, R.
2015-10-01
The ROSETTA Lander is equipped with an one axis damping mechanism to dissipate kinetic energy during the touch down. This damping is necessary to avoid damages to the Lander by a hard landing shock and more important to avoid re-bouncing from ground with high velocity. The damping mechanism works best for perpendicular impact, which means the velocity vector is parallel to the damper axis and all three feet touch the ground at the same time. That is usually not the case. Part of the impact energy can be transferred into rotational energy at ground contact if the impact is not perpendicular. This energy will lift up the Lander from the ground if the harpoons and the hold down thruster fail, as happen in mission. The damping mechanism itself is an electrical generator, driven by a spindle inside a telescopic tube. This tube was extended in mission for landing by 200mm. A maximum damping length of 140mm would be usually required to compensate a landing velocity of 1m/s, if the impact happens perpendicular on hard ground. After landing the potentiometer of the telescopic tube reading shows a total damping length of only 42,5mm. The damping mechanism and the overall mechanical behavior of the Lander at touch down are well tested and characterized and transferred to a multi-body computer model. The incoming and outgoing flightpath of PHILAE allow via computer-simulation the reconstruction of the touch down. It turns out, that the outgoing flight direction is dominated by the local ground slope and that the damping length is strongly dependent on the soil strength. Damping of soft comet ground must be included to fit the damping length measured. Scenario variations of the various feet contact with different local surface features (stone or regolith) and of different soil models finally lead to a restricted range for the soil strength at the touch down area.
Some frequency and damping measuements of laminated beryllium beams
Andriulli, J.; Rogers, L.C.
1993-01-01
A quantum leap in vibration performance of beryllium structure has been experimentally investigated. Laminations, segmentation, and sandwich syntactic foam core have been demonstrated to have both high specific flexural structural stiffness and high damping for reduced vibratory response. Acquisition cost, weight, machinability and environmental benefits are also expected. Applications to structure of optical and inertial navigation equipment would lead to reductions in jitter levels and other vibratory response measures.
Some frequency and damping measuements of laminated beryllium beams
Andriulli, J.; Rogers, L.C.
1993-06-01
A quantum leap in vibration performance of beryllium structure has been experimentally investigated. Laminations, segmentation, and sandwich syntactic foam core have been demonstrated to have both high specific flexural structural stiffness and high damping for reduced vibratory response. Acquisition cost, weight, machinability and environmental benefits are also expected. Applications to structure of optical and inertial navigation equipment would lead to reductions in jitter levels and other vibratory response measures.
Damped Topological Magnons in the Kagome-Lattice Ferromagnets
NASA Astrophysics Data System (ADS)
Chernyshev, A. L.; Maksimov, P. A.
2016-10-01
We demonstrate that interactions can substantially undermine the free-particle description of magnons in ferromagnets on geometrically frustrated lattices. The anharmonic coupling, facilitated by the Dzyaloshinskii-Moriya interaction, and a highly degenerate two-magnon continuum yield a strong, nonperturbative damping of the high-energy magnon modes. We provide a detailed account of the effect for the S =1 /2 ferromagnet on the kagome lattice and propose further experiments.
Damped Topological Magnons in the Kagome-Lattice Ferromagnets.
Chernyshev, A L; Maksimov, P A
2016-10-28
We demonstrate that interactions can substantially undermine the free-particle description of magnons in ferromagnets on geometrically frustrated lattices. The anharmonic coupling, facilitated by the Dzyaloshinskii-Moriya interaction, and a highly degenerate two-magnon continuum yield a strong, nonperturbative damping of the high-energy magnon modes. We provide a detailed account of the effect for the S=1/2 ferromagnet on the kagome lattice and propose further experiments.
NASA Astrophysics Data System (ADS)
Totani, Tomonori; Aoki, Kentaro; Hattori, Takashi; Kawai, Nobuyuki
2016-02-01
The unprecedentedly bright afterglow of Swift GRB 130606A at z = 5.91 gave us a unique opportunity to probe the reionization era through high-precision analyses of the redward damping wing of Lyα absorption, but the reported constraints on the neutral hydrogen fraction (f_{H I}) in intergalactic medium (IGM) derived from spectra taken by different telescopes are in contradiction to each other. Here we examine the origin of this discrepancy by analyzing the spectrum taken by the Very Large Telescope (VLT) with our own analysis code previously used to fit the Subaru spectrum. Though the VLT team reported no evidence for IGM H I using the VLT spectrum, we confirm our previous result of preferring non-zero IGM H I (the best fit f_{H I} ˜ 0.06, when IGM H I extends to the GRB redshift). The fit residuals of the VLT spectrum using the model without IGM H I show the same systematic trend as the Subaru spectrum. We consider that the likely origin of the discrepancy between the two teams is the difference of the wavelength ranges adopted in the fittings; our wavelength range is wider than that of the VLT team, and also we avoided the shortest wavelength range of deep Lyα absorption (λobs < 8426 Å), because this region is dominated by H I in the host galaxy and the systematic uncertainty about host H I velocity distribution is large. We also study the sensitivity of these results to the adopted Lyα cross-section formulae, ranging from the classical Lorentzian function to the most recent one taking into account fully quantum mechanical scattering. It is found that the preference for non-zero IGM H I is robust against the choice of the cross-section formulae, but it is quantitatively not negligible and hence one should be careful in future analyses.
Validation Of Equivalent Viscous Damping Methodologies
NASA Astrophysics Data System (ADS)
Vaquer Araujo, Xavier; Fransen, S. H. J. A.; Germes, S.; Thiry, N.
2012-07-01
An important step in the design and verification process of spacecraft structures is the coupled dynamic analysis with the launch vehicle in the low-frequency domain. To obtain accurate predictions of the satellite’s dynamic environment it is essential that the damping of the system is correctly defined and taken into account within the resolution methodologies for the Coupled Loads Analysis (CLA). When working with finite element models, the materials’ damping is characterized by structural damping ratios. In addition, most of the load cases present in the CLA are transient excitations so the resolution of the equations of motion must be done in the time domain. Unfortunately, transient analyses cannot be carried out using structural damping models. Thus, a transformation from a structural to a viscous damping characterization is necessary. Nevertheless, this transformation is not trivial. There exist many methodologies aiming at computing an equivalent viscous damping matrix of the system so it can be used in transient analyses. This paper describes the results obtained in the validation of equivalent viscous damping methodologies used in the European Space Agency. This work permitted to identify the limitations of these methodologies and to come up with an enhanced methodology that predicts more reliable results.
SLC positron damping ring optics design
Delahaye, J.P.; Rivkin, L.
1984-12-01
The basic SLAC Linear Collider operation scheme assumes the use of two damping rings, one for the e/sup -/, one for the e/sup +/, in order to reduce the colliding beam normalized emittances to 30..pi.. ..mu..radm hence raising the corresponding luminosity by a factor 170. The e/sup -/ damping ring which optics was designed by H. Wiedemann, has been extensively studied and modelled since it's completion at the end of 1982. The e/sup +/ damping ring to be built soon will be based on the same design except for some modifications resulting from the studies on the e/sup -/ damping ring which clearly pointed out two major optics weak points: the extracted normalized emittances are 30 to 60% bigger than the design values, which already left no margin for unavoidable blow-up between the damping rings and the SLC interaction point, and the chromaticity correction based on distributed sextupole components provided by shaping the ends of the bending magnet poles was insufficient. Moreover the QDI quadrupoles introduce a strong coupling between transverse planes due to an undesirable skew component. The present note describes the basic modifications of the ring lattice and main equipment positions in order to improve the first two points in the Positron Damping Ring. The QDI quadrupole design has already been modified and magnets of a new type will be implemented in both damping rings.
Material damping experiments at cryogenic temperatures
NASA Astrophysics Data System (ADS)
Levine, Marie B.; White, Christopher
2003-12-01
NASA's James Webb Space Telescope (JWST) will be operating at temperatures below 40K to image in the infrared. The 7-m class telescope will require nanometric jitter stability of the optical elements such as the primary and secondary mirrors. Of particular concern is the vibration response of these cryogenic systems when subjected to on-board disturbance sources such as the reaction wheels, the amplitude of which is governed by damping. Unfortunately there is relatively little data available for flight grade materials at these temperatures and within the frequency bands of interest. The paper will describe the experimental setup designed to measure viscous damping to values as low 10^-4%. The tests measure damping from room temperature all the way down to 20K in a controlled thermal and disturbance free environment. Data is obtained for strain levels of about 0.1 micro-strain down to nano-strains to verify vibration level effects on material damping. Damping is also measured for several frequencies in the range of 20Hz to 300Hz to assess the trend of damping as a function of vibrational frequency. Data for several materials, such as Aluminum, Beryllium, Quartz, and various composites are presented. The data is compared to analytical predictions using the Zener damping theory and is shown to match well at room temperature but to disagree at colder temperatures.
Damping performance of bean bag dampers in zero gravity environments
NASA Astrophysics Data System (ADS)
Zhang, Chao; Chen, Tianning; Wang, Xiaopeng
2016-06-01
Bean bag dampers (BBDs), developed from impact damping technology, have been widely applied in engineering field to attenuate the vibration of a structural system. The damping effect of a BBD on vibration control in ground gravity environments is good, but its performance in zero gravity environments is not clear, and there are few studies on it. Therefore, the damping effect of BBDs in zero gravity environments was investigated based on the discrete element method (DEM) in this paper. Firstly, a three-dimensional DEM model of a BBD was established, and the damping effects of the single degree of freedom (SDOF) systems with BBDs and non-obstructive particle dampers (NOPDs) in zero gravity environments were compared. Moreover, the influences of the diameter of the inner ball, the tightness of BBD, the vibration frequency of SDOF system and the gap between BBD and cavity on the vibration reduction effect of BBD in zero gravity environments were also studied, and the results were compared with the system with BBD in ground gravity environments. There are optimum ranges of the diameter of the inner ball, tightness and gap for BBD, and the effects of these parameters on the damping performances of BBD in gravity and zero gravity environments are similar in evolving trends, and the values are without big differences in the optimum ranges. Thereby the parameter selection in BBD design in zero gravity environments is similar to that in gravity environments. However, the diameter of BBD should be a slightly larger than the size of the cavity when the structures with BBD work in zero gravity environments. The BBD is supposed to be picked tightly when the vibration frequency is high, and the BBD has better to be picked more tightly in zero gravity environments. These results can be used as a guide in the design of BBDs in zero gravity environments.
Optimization of SMA layers in composite structures to enhance damping
NASA Astrophysics Data System (ADS)
Haghdoust, P.; Cinquemani, S.; Lecis, N.; Bassani, P.
2016-04-01
The performance of lightweight structures can be severely affected by vibration. New design concepts leading to lightweight, slender structural components can increase the vulnerability of the components to failure due to excessive vibration. The intelligent approach to address the problem would be the use of materials which are more capable in dissipating the energy due to their high value of loss factor. Among the different materials available to achieve damping, much attention has been attached to the use of shape memory alloys (SMAs) because of their unique microstructure, leading to good damping capacity. This work describes the design and optimization of a hybrid layered composite structure for the passive suppression of flexural vibrations in slender and light structures. Embedding the SMA layers in composite structure allows to combine different properties: the lightness of the base composite (e.g. fiber glass), the mechanical strength of the insert of metallic material and the relevant damping properties of SMA, in the martensitic phase. In particular, we put our attention on embedding the CuZnAl in the form of thin sheet in a layered composite made by glass fiber reinforced epoxy. By appropriately positioning of the SMA sheets so that they are subjected to the maximum curvature, the damping of the hybrid system can be considerably enhanced. Accordingly analytical method for evaluating the energy dissipation of the thin sheets with different shapes and patterns is developed and is followed by a shape optimization based on genetic algorithm. Eventually different configurations of the hybrid beam structure with different patterns of SMA layer are proposed and compared in the term of damping capacity.
Damping Effects of Drogue Parachutes on Orion Crew Module Dynamics
NASA Technical Reports Server (NTRS)
Aubuchon, Vanessa V.; Owens, D. Bruce
2016-01-01
Because simulations of the Orion Crew Module (CM) dynamics with drogue parachutes deployed were under-predicting the amount of damping seen in free-flight tests, an attach-point damping model was applied to the Orion system. A key hypothesis in this model is that the drogue parachutes' net load vector aligns with the CM drogue attachment point velocity vector. This assumption seems reasonable and has historically produced good results, but has never been experimentally verified. The wake of the CM influences the drogue parachutes, which makes performance predictions of the parachutes difficult. Many of these effects are not currently modeled in the simulations. A forced oscillation test of the CM with parachutes was conducted in the NASA LaRC 20-Ft Vertical Spin Tunnel (VST) to gather additional data to validate and refine the attach-point damping model. A second loads balance was added to the original Orion VST model to measure the drogue parachute loads independently of the CM. The objective of the test was to identify the contribution of the drogues to CM damping and provide additional information to quantify wake effects and the interactions between the CM and parachutes. The drogue parachute force vector was shown to be highly dependent on the CM wake characteristics. Based on these wind tunnel test data, the attach-point damping model was determined to be a sufficient approximation of the parachute dynamics in relationship to the CM dynamics for preliminary entry vehicle system design. More wake effects should be included to better model the system.
Analytical Solution and Physics of a Propellant Damping Device
NASA Technical Reports Server (NTRS)
Yang, H. Q.; Peugeot, John
2011-01-01
NASA design teams have been investigating options for "detuning" Ares I to prevent oscillations originating in the vehicle solid-rocket main stage from synching up with the natural resonance of the rest of the vehicle. An experimental work started at NASA MSFC center in 2008 using a damping device showed great promise in damping the vibration level of an 8 resonant tank. However, the mechanisms of the vibration damping were not well understood and there were many unknowns such as the physics, scalability, technology readiness level (TRL), and applicability for the Ares I vehicle. The objectives of this study are to understand the physics of intriguing slosh damping observed in the experiments, to further validate a Computational Fluid Dynamics (CFD) software in propellant sloshing against experiments with water, and to study the applicability and efficiency of the slosh damper to a full scale propellant tank and to cryogenic fluids. First a 2D fluid-structure interaction model is built to model the system resonance of liquid sloshing and structure vibration. A damper is then added into the above model to simulate experimentally observed system damping phenomena. Qualitative agreement is found. An analytical solution is then derived from the Newtonian dynamics for the thrust oscillation damper frequency, and a slave mass concept is introduced in deriving the damper and tank interaction dynamics. The paper will elucidate the fundamental physics behind the LOX damper success from the derivation of the above analytical equation of the lumped Newtonian dynamics. Discussion of simulation results using high fidelity multi-phase, multi-physics, fully coupled CFD structure interaction model will show why the LOX damper is unique and superior compared to other proposed mitigation techniques.
Shunted Piezoelectric Vibration Damping Analysis Including Centrifugal Loading Effects
NASA Technical Reports Server (NTRS)
Min, James B.; Duffy, Kirsten P.; Provenza, Andrew J.
2011-01-01
Excessive vibration of turbomachinery blades causes high cycle fatigue problems which require damping treatments to mitigate vibration levels. One method is the use of piezoelectric materials as passive or active dampers. Based on the technical challenges and requirements learned from previous turbomachinery rotor blades research, an effort has been made to investigate the effectiveness of a shunted piezoelectric for the turbomachinery rotor blades vibration control, specifically for a condition with centrifugal rotation. While ample research has been performed on the use of a piezoelectric material with electric circuits to attempt to control the structural vibration damping, very little study has been done regarding rotational effects. The present study attempts to fill this void. Specifically, the objectives of this study are: (a) to create and analyze finite element models for harmonic forced response vibration analysis coupled with shunted piezoelectric circuits for engine blade operational conditions, (b) to validate the experimental test approaches with numerical results and vice versa, and (c) to establish a numerical modeling capability for vibration control using shunted piezoelectric circuits under rotation. Study has focused on a resonant damping control using shunted piezoelectric patches on plate specimens. Tests and analyses were performed for both non-spinning and spinning conditions. The finite element (FE) shunted piezoelectric circuit damping simulations were performed using the ANSYS Multiphysics code for the resistive and inductive circuit piezoelectric simulations of both conditions. The FE results showed a good correlation with experimental test results. Tests and analyses of shunted piezoelectric damping control, demonstrating with plate specimens, show a great potential to reduce blade vibrations under centrifugal loading.
Damping Behavior of Alumina Epoxy Nano-Composites
NASA Astrophysics Data System (ADS)
Katiyar, Priyanka; Kumar, Anand
2016-10-01
Polymer nano composites, consisting of a polymer matrix with nanoparticle filler, have been predicted to be one of the most beneficial applications of nanotechnology. Addition of nano particulates to a polymer matrix enhances its performance by capitalizing on the nature and properties of the nano-scale fillers. The damping behavior of composites with nano structured phases is significantly different from that of micro structured materials. Viscoelastic homopolymer exhibit a high material damping response over a relatively narrow range of temperature and frequencies. In many practical situations, a polymeric structure is required to possess better strength and stiffness properties together with a reasonable damping behavior. Viscoelastic polymers show higher loss factor beyond the glassy region which comes with a significant drop in the specific modulus. Addition of nano alumina particles to epoxy leads to improved strength and stiffness properties with an increase in glass transition temperature while retaining its damping capability. Experimental investigations are carried out on composite beam specimen fabricated with different compositions of alumina nano particles in epoxy to evaluate loss factor, tan δ. Impact damping method is used for time response analysis. A single point Laser is used to record the transverse displacement of a point on the composite beam specimen. The experimental results are compared with theoretical estimation of loss factor using Voigt estimation. The effect of inter phase is included in theoretical estimation of loss factor. The result reveals that the study of interface properties is very important in deriving the overall loss factor of the composite since interface occupies a significant volume fraction in the composite.
Experimental verification of damping mechanisms in a composite beam
NASA Technical Reports Server (NTRS)
Cudney, Harley H.; Inman, Daniel J.
1989-01-01
A method of estimating the distributed damping parameters based on the measured modal parameters (frequency and damping ratios) was derived. Three different mathematical models were used to model the damping mechanism of a quasi-isotropic pultruded cantilevered beam. These three models were (1) viscous (air) damping, (2) strain rate damping, and (3) both viscous and strain rate damping. The eigenvalues of the partial differential equation model were found to be uninfluenced by any of the three assumed damping models. Values were obtained for each of the damping models as well as the modulus of elasticity of the beam. It was found that the two-parameter damping model provided the best fit to measured modal data. However, the two-parameter damping model could only reproduce the measured damping ratios to within 85 percent.
Investigation on the mechanism of damping behavior of magnetorheological elastomers
NASA Astrophysics Data System (ADS)
Yang, Jie; Gong, Xinglong; Deng, Huaxia; Qin, Lijun; Xuan, Shouhu
2012-12-01
Magnetorheological elastomers (MREs) are a group of smart materials which have many applications such as dynamic vibration absorbers, engine mounts, and so on. The damping behavior is important for applications of MREs. However, the mechanism of the damping of MREs has not been investigated thoroughly. In this study, MREs are modeled as special particle reinforced composites with magneto-induced properties and the mechanism of the damping behavior of MREs is investigated theoretically and experimentally. It has been found that there are three types of damping property in MREs: the intrinsic damping, the interface damping and the magneto-mechanical damping. The presented damping model is successfully validated by damping tests on a series of MRE samples. Furthermore, the relationships between the damping properties and formulas of MREs are discussed; this provides guidance for the manufacture of MREs with various damping properties.
Nonlinear Landau damping of Alfven waves.
NASA Technical Reports Server (NTRS)
Hollweg, J. V.
1971-01-01
Demonstration that large-amplitude linearly or elliptically polarized Alfven waves propagating parallel to the average magnetic field can be dissipated by nonlinear Landau damping. The damping is due to the longitudinal electric field associated with the ion sound wave which is driven (in second order) by the Alfven wave. The damping rate can be large even in a cold plasma (beta much less than 1, but not zero), and the mechanism proposed may be the dominant one in many plasmas of astrophysical interest.
Oscillation damped movement of suspended objects
Jones, J.F.; Petterson, B.J.
1988-01-01
Transportation of objects using overhead cranes or manipulators can induce pendulum motion of the object. Residual oscillation from transportation typically must be damped or allowed to decay before the next process can take place. By properly programming the acceleration of the transporting device (e.g., crane) an oscillation damped transport and swing free stop is obtainable. This paper reviews the theory associated with oscillation damped trajectories for simply suspended objects and describes a particular implementation using a CIMCORP XR 6100 gantry robot. 8 refs., 7 figs., 1 tab.
NASA Technical Reports Server (NTRS)
Rugina, I.; Paven, H. T. O.
1974-01-01
One of the most important methods of reducing the noise and vibration level is the damping of the secondary sources, such as metal plates, often used in vehicle structures, by means of covering materials with high internal viscosity. Damping layers are chosen at an optimum thickness corresponding to the frequency and temperature range in which a certain structure works. The structure's response corresponding to various real situations is analyzed by means of a measuring chain including electroacoustical or electromechanical transducers. The experimental results provide the dependence of the loss factor and damping transmission coefficient as a function of the damping layer thickness or of the frequency for various viscoelastic covering materials.
Experimentally determined stiffness and damping of an inherently compensated air squeeze-film damper
NASA Technical Reports Server (NTRS)
Cunningham, R. E.
1975-01-01
Values of damping and stiffness were determined experimentally for an externally pressurized, inherently compensated, compressible squeeze-film damper up to excitation frequencies of 36,000 cycles per minute. Experimental damping values were higher than theory predicted at low squeeze numbers and less than predicted at high squeeze numbers. Experimental values of air film stiffness were less than theory predicted at low squeeze numbers and much greater at higher squeeze numbers. Results also indicate sufficient damping to attenuate amplitudes and forces at the critical speed when using three dampers in the flexible support system of a small, lightweight turborotor.
Nonlinear damping for vibration isolation of microsystems using shear thickening fluid
NASA Astrophysics Data System (ADS)
Iyer, S. S.; Vedad-Ghavami, R.; Lee, H.; Liger, M.; Kavehpour, H. P.; Candler, R. N.
2013-06-01
This work reports the measurement and analysis of nonlinear damping of micro-scale actuators immersed in shear thickening fluids (STFs). A power-law damping term is added to the linear second-order model to account for the shear-dependent viscosity of the fluid. This nonlinear model is substantiated by measurements of oscillatory motion of a torsional microactuator. At high actuation forces, the vibration velocity amplitude saturates. The model accurately predicts the nonlinear damping characteristics of the STF using a power-law index extracted from independent rheology experiments. This result reveals the potential to use STFs as adaptive, passive dampers for vibration isolation of microelectromechanical systems.
Asymptotic spectrum of Kerr black holes in the small angular momentum limit
NASA Astrophysics Data System (ADS)
Daghigh, Ramin G.; Green, Michael D.; Mulligan, Brian W.
2011-02-01
We study analytically the highly damped quasinormal modes of Kerr black holes in the small angular momentum limit. To check the previous analytic calculations in the literature, which use a combination of radial and tortoise coordinates, we reproduce all the results using the radial coordinate only. According to the earlier calculations, the real part of the highly damped quasinormal mode frequency of Kerr black holes approaches zero in the limit where the angular momentum goes to zero. This result is not consistent with the Schwarzschild limit where the real part of the highly damped quasinormal mode frequency is equal to c3ln(3)/(8πGM). In this paper, our calculations suggest that the highly damped quasinormal modes of Kerr black holes in the zero angular momentum limit make a continuous transition from the Kerr value to the Schwarzschild value. We explore the nature of this transition using a combination of analytical and numerical techniques. Finally, we calculate the highly damped quasinormal modes of the extremal case in which the topology of Stokes/anti-Stokes lines takes a different form.
Asymptotic spectrum of Kerr black holes in the small angular momentum limit
Daghigh, Ramin G.; Green, Michael D.; Mulligan, Brian W.
2011-02-15
We study analytically the highly damped quasinormal modes of Kerr black holes in the small angular momentum limit. To check the previous analytic calculations in the literature, which use a combination of radial and tortoise coordinates, we reproduce all the results using the radial coordinate only. According to the earlier calculations, the real part of the highly damped quasinormal mode frequency of Kerr black holes approaches zero in the limit where the angular momentum goes to zero. This result is not consistent with the Schwarzschild limit where the real part of the highly damped quasinormal mode frequency is equal to c{sup 3}ln(3)/(8{pi}GM). In this paper, our calculations suggest that the highly damped quasinormal modes of Kerr black holes in the zero angular momentum limit make a continuous transition from the Kerr value to the Schwarzschild value. We explore the nature of this transition using a combination of analytical and numerical techniques. Finally, we calculate the highly damped quasinormal modes of the extremal case in which the topology of Stokes/anti-Stokes lines takes a different form.
Eigensolutions of non-proportionally damped systems based on continuous damping sensitivity
NASA Astrophysics Data System (ADS)
Lázaro, Mario
2016-02-01
The viscous damping model has been widely used to represent dissipative forces in structures under mechanical vibrations. In multiple degree of freedom systems, such behavior is mathematically modeled by a damping matrix, which in general presents non-proportionality, that is, it does not become diagonal in the modal space of the undamped problem. Eigensolutions of non-proportional systems are usually estimated assuming that the modal damping matrix is diagonally dominant (neglecting the off-diagonal terms) or, in the general case, using the state-space approach. In this paper, a new closed-form expression for the complex eigenvalues of non-proportionally damped system is proposed. The approach is derived assuming small damping and involves not only the diagonal terms of the modal damping matrix, but also the off-diagonal terms, which appear under higher order. The validity of the proposed approach is illustrated through a numerical example.
Calibration of BGO Calorimeter of the DAMPE in Space
NASA Astrophysics Data System (ADS)
Wang, Chi
2016-07-01
The Dark Matter Particle Explore (DAMPE) is a satellite based experiment which launched on December 2015 and aims at indirect searching for dark matter by measuring the spectra of high energy e±, γ from 5GeV up to 10TeV originating from deep space. The 3D imaging BGO calorimeter of DAMPE was designed to precisely measurement the primary energy of the electromagnetic particle and provides a highly efficient rejection of the hadronic background by reconstruct the longitudinal and lateral profiles of showers. To achieve the expected accuracy on the energy measurement, each signal channel has to be calibrated. The energy equalization is performed using the signal that Minimum Ionizing Particles (MIP) leave in each BGO bar, the MIPs measurement method with orbit data and, data quality, time stability using MIPs data will be presented, too.
NASA Technical Reports Server (NTRS)
Sireteanu, T.
1974-01-01
An oscillating system with quadratic damping subjected to white noise excitation is replaced by a nonlinear, statistically equivalent system for which the associated Fokker-Planck equation can be exactly solved. The mean square responses are calculated and the optimum damping coefficient is determined with respect to the minimum mean square acceleration criteria. An application of these results to the optimization of automobile suspension damping is given.
Simplified Model of Nonlinear Landau Damping
N. A. Yampolsky and N. J. Fisch
2009-07-16
The nonlinear interaction of a plasma wave with resonant electrons results in a plateau in the electron distribution function close to the phase velocity of the plasma wave. As a result, Landau damping of the plasma wave vanishes and the resonant frequency of the plasma wave downshifts. However, this simple picture is invalid when the external driving force changes the plasma wave fast enough so that the plateau cannot be fully developed. A new model to describe amplification of the plasma wave including the saturation of Landau damping and the nonlinear frequency shift is proposed. The proposed model takes into account the change of the plasma wave amplitude and describes saturation of the Landau damping rate in terms of a single fluid equation, which simplifies the description of the inherently kinetic nature of Landau damping. A proposed fluid model, incorporating these simplifications, is verified numerically using a kinetic Vlasov code.
Roll Damping Characterisation Program: User Guide
2014-06-01
sallying test. The Defence Science and Technology Organisation (DSTO) have developed a software-based tool called the Roll Damping Characterisation...Murray Riding Maritime Division Murray obtained a Bachelor of Science (Honours) Degree from the
Electron beam depolarization in a damping ring
Minty, M.
1993-04-01
Depolarization of a polarized electron beam injected into a damping ring is analyzed by extending calculations conventionally applied to proton synchrotrons. Synchrotron radiation in an electron ring gives rise to both polarizing and depolarizing effects. In a damping ring, the beam is stored for a time much less than the time for self polarization. Spin flip radiation may therefore be neglected. Synchrotron radiation without spin flips, however, must be considered as the resonance strength depends on the vertical betatron oscillation amplitude which changes as the electron beam is radiation damped. An expression for the beam polarization at extraction is derived which takes into account radiation damping. The results are applied to the electron ring at the Stanford Linear Collider and are compared with numerical matrix formalisms.
Oscillation damping means for magnetically levitated systems
Post, Richard F.
2009-01-20
The present invention presents a novel system and method of damping rolling, pitching, or yawing motions, or longitudinal oscillations superposed on their normal forward or backward velocity of a moving levitated system.
Modification of spastic gait through mechanical damping.
Maki, B E; Rosen, M J; Simon, S R
1985-01-01
The effect of dissipative mechanical loads on spastic gait has been studied, to evaluate the feasibility of using mechanically damped orthoses to effect functional improvements in the gait of spastic patients. This concept is based on a hypothesis citing uninhibited, velocity-dependent stretch reflexes as a possible causal factor in spastic gait abnormalities, such as equinus and back-kneeing. In order to screen potential experimental subjects and to quantify velocity-dependent reflex behaviour, ankle rotation experiments and filmed gait analysis were performed. The results supported the existence of a velocity threshold. Orthosis simulation experiments were performed with one spastic subject, using a wearable, computer-controlled, electromechanical, below-knee orthosis simulator to apply a variety of damping loads to the ankle as the subject walked. Results indicated that appropriate damping can improve local joint kinematics. The damping causes a reduction in muscle stretch velocity which apparently results in reduced spastic reflex activity.
Collisional damping of the geodesic acoustic mode
Gao Zhe
2013-03-15
The frequency and damping rate of the geodesic acoustic mode (GAM) is revisited by using a gyrokinetic model with a number-conserving Krook collision operator. It is found that the damping rate of the GAM is non-monotonic as the collision rate increases. At low ion collision rate, the damping rate increases linearly with the collision rate; while as the ion collision rate is higher than v{sub ti}/R, where v{sub ti} and R are the ion thermal velocity and major radius, the damping rate decays with an increasing collision rate. At the same time, as the collision rate increases, the GAM frequency decreases from the (7/4+{tau})v{sub ti}/R to (1+{tau})v{sub ti}/R, where {tau} is the ratio of electron temperature to ion temperature.
Methods for elimination of dampness in Building walls
NASA Astrophysics Data System (ADS)
Campian, Cristina; Pop, Maria
2016-06-01
Dampness elimination in building walls is a very sensitive problem, with high costs. Many methods are used, as: chemical method, electro osmotic method or physical method. The RECON method is a representative and a sustainable method in Romania. Italy has the most radical method from all methods. The technology consists in cutting the brick walls, insertion of a special plastic sheeting and injection of a pre-mixed anti-shrinking mortar.
Spatial versus time hysteresis in damping mechanisms
NASA Technical Reports Server (NTRS)
Banks, H. T.; Fabiano, R. H.; Wang, Y.; Inman, D. J.; Cudney, H., Jr.
1988-01-01
A description is given of continuing investigations on the task of estimating internal damping mechanisms in flexible structures. Specifically, two models for internal damping in Euler-Bernoulli beams are considered: spatial hysteresis and time hysteresis. A theoretically sound computational algorithm for estimation is described, and experimental results are discussed. It is concluded that both models perform well in the sense that they accurately predict response for the experiments conducted.
Microscale damping using thin film active materials
NASA Astrophysics Data System (ADS)
Kerrigan, Catherine A.; Ho, Ken K.; Mohanchandra, K. P.; Carman, Gregory P.
2007-04-01
This paper focuses on understanding and developing a new approach to dampen MEMS structures using both experiments and analytical techniques. Thin film Nitinol and thin film Terfenol-D are evaluated as a damping solution to the micro scale damping problem. Stress induced twin boundary motion in Nitinol is used to passively dampen potentially damaging vibrations. Magnetic domain wall motion is used to passively dampen vibration in Terfenol-D. The thin films of Nitinol, Nitinol/Silicon laminates and Nitinol/Terfenol-D/Nickel laminates have been produced using a sputter deposition process and damping properties have been evaluated. Dynamic testing shows substantial damping (tan δ) measurable in each case. Nitinol film samples were tested in the Differential Scanning Calorimetry (DSC) to determine phase transformation temperatures. The twin boundary mechanism by which energy absorption occurs is present at all points below the Austenite start temperature (approximately 69°C in our film) and therefore allows damping at cold temperatures where traditional materials fail. Thin film in the NiTi/Si laminate was found to produce substantially higher damping (tan δ = 0.28) due to the change in loading condition. The NiTi/Si laminate sample was tested in bending allowing the twin boundaries to be reset by cyclic tensile and compressive loads. The thin film Terfenol-D in the Nitinol/Terfenol-D/Nickel laminate was shown to produce large damping (tan δ = 0.2). In addition to fabricating and testing, an analytical model of a heterogeneous layered thin film damping material was developed and compared to experimental work.
Turbine blade with tuned damping structure
Campbell, Christian X.; Messmann, Stephen J.
2015-09-01
A turbine blade is provided comprising: a root; an airfoil comprising an external wall extending radially from the root and having a radially outermost portion; and a damping structure. The external wall may comprise first and second side walls joined together to define an inner cavity of the airfoil. The damping structure may be positioned within the airfoil inner cavity and coupled to the airfoil so as to define a tuned mass damper.
Analysis of nonlinear damping properties of carbon
NASA Astrophysics Data System (ADS)
Kazakova, Olga I.; Smolin, Igor Yu.; Bezmozgiy, Iosif M.
2016-11-01
This paper describes research results of nonlinear damping properties of carbon fiber reinforced plastics. The experimental and computational research is performed on flat composite specimens with the gradual structure complication (from 1 to 12 layers). Specimens are subjected to three types of testing which are modal, harmonic and transient analyses. Relationships between the amplitude response and damping ratio are obtained by means of the analysis of variance as the result of this research.
Quantum damped oscillator I: Dissipation and resonances
Chruscinski, Dariusz
2006-04-15
Quantization of a damped harmonic oscillator leads to so called Bateman's dual system. The corresponding Bateman's Hamiltonian, being a self-adjoint operator, displays the discrete family of complex eigenvalues. We show that they correspond to the poles of energy eigenvectors and the corresponding resolvent operator when continued to the complex energy plane. Therefore, the corresponding generalized eigenvectors may be interpreted as resonant states which are responsible for the irreversible quantum dynamics of a damped harmonic oscillator.
Aerospace Structures Technology Damping Design Guide. Volume 3. Damping Material Data
1985-12-01
1.1 DAMPING MATERIAL PROPERTIES 1 3 1.2 THE STANDARIZED MATERIAL DATA I 1.2.1 Nomogram Cover Sheet 3 ’ 1.2.2 The Reduced Nomogram 4 1.2.3 Reading...MATERIALS 6 2 DAMPING MATERIAL PROPERTY DATA 14 3 STRUCTURAL EPOXIES AND OTHER MATERIALS 469 3.1 STRUCTURAL EPOXIES 469 3.2 STRUCTURAL PLASTICS 477 3.3...Data Listing II 6 Temperature Shift Function and Its Properties 12 7 Typical TCA Plot 13 8 Quick Reference Chart for Damping Materials 15 9 Damping vs
NASA Astrophysics Data System (ADS)
Smith, Clifford B.; Wereley, Norman M.
1996-10-01
The first objective of this paper is to evaluate the performance of damping identification algorithms. The second objective is to determine the feasibility of damping augmentation in rotating composite beams via passive constrained layer damping (PCLD). Damping identification schemes were applied to four rectangular cross-section laminated composite beams with cocured integral damping layers over the span of the beam. The cocured beam consisted of a twenty-ply balanced and symmetric cross-ply Gr/Ep composite host structure, a top and bottom damping layer of viscoelastic material (VEM), and a 2-ply Gr/Ep constraining layer sandwiching the viscoelastic material to the host structure. Four VEM thicknesses were considered: 0, 5, 10, and 15 mils. The cantilevered beams were tested at rotational speeds ranging from 0 to 900 RPM in a vacuum chamber. Excitation in bending was provided using piezo actuators, and the bending response was measured using full strain gauge bridges. Transient data were analysed using logarithmic decrement, a Hilbert transform technique, and an FFT- based moving block analysis. When compared to the beam with no VEM, a 19.2% volume fraction (15 mil layer) of viscoelastic in the beam produced a 400% increase in damping ratio in the non-rotating case, while at 900 RPM, the damping ratio increased only 360%. Overall structural damping was reduced as a function of RPM, due to centrifugal stiffening.
Validation of equivalent viscous damping methodologies
NASA Astrophysics Data System (ADS)
Vaquer Araujo, Xavier; Fransen, Sebastiaan H. J. A.; Germès, Sylvain; Thiry, Nicolas
2013-06-01
An important step in the design and verification process of spacecraft structures is the coupled dynamic analysis with the launch vehicle in the low-frequency domain. To obtain accurate predictions of the satellite's dynamic environment, it is essential that the damping of the system is correctly defined and taken into account within the resolution methodologies for the coupled loads analysis (CLA). When working with finite element models, the materials' damping is characterized by structural damping ratios. In addition, most of the load cases present in the CLA are transient excitations, and so the resolution of the equations of motion must be done in the time domain. Unfortunately, in the CLA, transient analyses cannot be carried out using structural damping models. Thus, a transformation from a structural to a viscous damping characterization is necessary in this case. Nevertheless, this transformation is not trivial. There exist many methodologies for computing an equivalent viscous damping (EqVD) matrix of the system which can be used in transient analyses. This paper describes the results obtained from the validation of EqVD methodologies used in the European Space Agency. This work identifies the limitations of these methodologies and comes up with an enhanced methodology that predicts more reliable results.
Hybrid Damping System for an Electronic Equipment Mounting Shelf
NASA Technical Reports Server (NTRS)
Voracek, David; Kolkailah, Faysal A.; Cavalli, J. R.; Elghandour, Eltahry
1997-01-01
The objective of this study was to design and construct a vibration control system for an electronic equipment shelf to be evaluated in the NASA Dryden FTF-11. The vibration control system was a hybrid system which included passive and active damping techniques. Passive damping was fabricated into the equipment shelf using ScothDamp(trademark) damping film and aluminum constraining layers. Active damping was achieved using a two channel active control circuit employing QuickPack(trademark) sensors and actuators. Preliminary Chirp test results indicated passive damping smoothed the frequency response while active damping reduced amplitudes of the frequency response for most frequencies below 500Hz.
Hybrid Damping System for an Electronic Equipment Mounting Shelf
NASA Technical Reports Server (NTRS)
Voracek, David; Kolkailah, Faysal A.; Cavalli, J. R.; Elghandour, Eltahry
1997-01-01
The objective of this study was to design and construct a vibration control system for an electronic equipment shelf to be evaluated in the NASA Dryden FTF-II. The vibration control system was a hybrid system which included passive and active damping techniques. Passive damping was fabricated into the equipment shelf using ScothDamp(trademark) damping film and aluminum constraining layers. Active damping was achieved using a two channel active control circuit employing QuickPack(trademark) sensors and actuators. Preliminary Chirp test results indicated passive damping smoothed the frequency response while active damping reduced amplitudes of the frequency response for most frequencies below 500Hz.
Bubble-induced damping in displacement-driven microfluidic flows.
Lee, Jongho; Rahman, Faizur; Laoui, Tahar; Karnik, Rohit
2012-08-01
Bubble damping in displacement-driven microfluidic flows was theoretically and experimentally investigated for a Y-channel microfluidic network. The system was found to exhibit linear behavior for typical microfluidic flow conditions. The bubbles induced a low-pass filter behavior with a characteristic cutoff frequency that scaled proportionally with flow rate and inversely with bubble volume and exhibited a minimum with respect to the relative resistances of the connecting channels. A theoretical model based on the electrical circuit analogy was able to predict experimentally observed damping of fluctuations with excellent agreement. Finally, a flowmeter with high resolution (0.01 μL/min) was demonstrated as an application of the bubble-aided stabilization. This study may aid in the design of many other bubble-stabilized microfluidic systems.
DAMPE silicon tracker on-board data compression algorithm
NASA Astrophysics Data System (ADS)
Dong, Yi-Fan; Zhang, Fei; Qiao, Rui; Peng, Wen-Xi; Fan, Rui-Rui; Gong, Ke; Wu, Di; Wang, Huan-Yu
2015-11-01
The Dark Matter Particle Explorer (DAMPE) is an upcoming scientific satellite mission for high energy gamma-ray, electron and cosmic ray detection. The silicon tracker (STK) is a subdetector of the DAMPE payload. It has excellent position resolution (readout pitch of 242 μm), and measures the incident direction of particles as well as charge. The STK consists of 12 layers of Silicon Micro-strip Detector (SMD), equivalent to a total silicon area of 6.5 m2. The total number of readout channels of the STK is 73728, which leads to a huge amount of raw data to be processed. In this paper, we focus on the on-board data compression algorithm and procedure in the STK, and show the results of initial verification by cosmic-ray measurements. Supported by Strategic Priority Research Program on Space Science of Chinese Academy of Sciences (XDA040402) and National Natural Science Foundation of China (1111403027)
Damping Effects of Drogue Parachutes on Orion Crew Module Dynamics
NASA Technical Reports Server (NTRS)
Aubuchon, Vanessa V.
2013-01-01
Currently, simulation predictions of the Orion Crew Module (CM) dynamics with drogue parachutes deployed are under-predicting the amount of damping as seen in free-flight tests. The Apollo Legacy Chute Damping model has been resurrected and applied to the Orion system. The legacy model has been applied to predict CM damping under drogue parachutes for both Vertical Spin Tunnel free flights and the Pad Abort-1 flight test. Comparisons between the legacy Apollo prediction method and test data are favorable. A key hypothesis in the Apollo legacy drogue damping analysis is that the drogue parachutes' net load vector aligns with the CM drogue attachment point velocity vector. This assumption seems reasonable and produces good results, but has never been quantitatively proven. The wake of the CM influences the drogue parachutes, which makes performance predictions of the parachutes difficult. Many of these effects are not currently modeled in the simulations. A forced oscillation test of the CM with parachutes was conducted in the NASA LaRC 20-Ft Vertical Spin Tunnel (VST) to gather additional data to validate and refine the Apollo legacy drogue model. A second loads balance was added to the original Orion VST model to measure the drogue parachute loads independently of the CM. The objective of the test was to identify the contribution of the drogues to CM damping and provide additional information to quantify wake effects and the interactions between the CM and parachutes. The drogue parachute force vector was shown to be highly dependent on the CM wake characteristics. Based on these wind tunnel test data, the Apollo Legacy Chute Damping model was determined to be a sufficient approximation of the parachute dynamics in relationship to the CM dynamics for preliminary entry vehicle system design. More wake effects should be included to better model the system. These results are being used to improve simulation model fidelity of CM flight with drogues deployed, which has
Effects of radiation and creep on viscoelastic damping materials
NASA Astrophysics Data System (ADS)
Henderson, John P.; Lewis, Tom M.; Murrell, Fred H.; Mangra, Danny
1995-05-01
The Advanced Photon Source (APS), under construction at Argonne National Laboratory (ANL), requires precise alignment of several large magnets. Submicron vibratory displacements of the magnets can degrade the performance of this important facility. Viscoelastic materials (VEM) have been shown to be effective in the control of the vibration of these magnets. Damping pads, placed under the magnet support structures in the APS storage ring, use thin layers of VEM. These soft VEM layers are subject to both high-energy radiation environment and continuous through-the-thickness compressive loads. Material experiments were conducted to answer concerns over the long term effects of the radiation environment and creep in the viscoelastic damping layers. The effects of exposure to radiation as high as 108 rad on the complex modulus were measured. Through-the-thickness creep displacements of VEM thin layers subjected to static loads of 50 psi were measured. Creep tests were conducted at elevated temperatures. Time-temperature equivalence principles were used to project creep displacements at room temperatures over several years. These damping material measurements should be of interest to vibration control engineers working with a variety of applications of fields ranging from aerospace to industrial machinery.
Xia, Hong; Liang, Yaojun; Wang, Xiao; Bao, Wenduona; Yun, Shifeng; Ye, Yuting; Zheng, Chunxia; Liu, Zhihong; Shi, Shaolin
2015-01-01
Mitochondria in eukaryotic cells are derived from bacteria in evolution. Like bacteria, mitochondria contain DNA with unmethylated CpG motifs and formyl peptides, both of which have recently been shown to be damage associated molecular patterns (DAMPs) and induce immune response and cell injury. Based on the facts that circulating mitochondrial DAMPs (mtDAMPs) are increased in the patients of trauma or burn injury who also have proteinuria, that mtDAMPs can activate immune cells which in turn secrete glomerular permeability factors, that renal intrinsic cells express a variety of DAMP receptors, and that mtDAMPs can directly increase endothelial cell permeability in vitro, we hypothesized that mtDAMPs may be novel circulating factors inducing proteinuria and kidney injury. We tested this hypothesis by directly injecting mtDAMPs into rodents and examining urinary protein and kidney histology. We prepared mtDAMP samples, including mitochondrial DNA (mtDNA) and mitochondrial debris (MTD), from rodent liver. In mice, injection of mtDNA for 20 μg/ml initial concentration in circulation (much higher than the clinical range), did not cause any renal manifestations. However, an increased dose leading to 45 μg/ml initial concentration in circulation resulted in a transient, slight increase in urinary albumin. In rats, MTD injection resulting in 450 μg/ml initial concentration of MTD protein in circulation, which was much higher than the clinical range, caused mild, transient proteinuria and lung lesions. Multiple injections of such large amount of either mtDNA or MTD into rodents on 3 consecutive days also failed in inducing proteinuria and kidney injury. In summary, clinical levels of circulating mtDAMPs do not induce proteinuria and clinically irrelevant high levels of mtDAMPs cause only a transient and slight increase in urinary protein in rodents, suggesting that circulating mtDAMPs may not be responsible for the proteinuria and kidney injury in patients with trauma
On the modal damping ratios of shear-type structures equipped with Rayleigh damping systems
NASA Astrophysics Data System (ADS)
Trombetti, T.; Silvestri, S.
2006-04-01
The effects of added manufactured viscous dampers upon shear-type structures are analytically investigated here for the class of Rayleigh damping systems. The definitions of mass proportional damping (MPD) and stiffness proportional damping (SPD) systems are briefly recalled and their physical counterpart is derived. From basic physics, a detailed mathematical demonstration that the first modal damping ratio of a structure equipped with the MPD system is always larger than the first modal damping ratio of a structure equipped with the SPD system is provided here. All results are derived for the class of structures characterised by constant values of lateral stiffness and storey mass, under the equal "total size" constraint. The paper also provides closed form demonstrations of other properties of modal damping ratios which further indicate that the MPD and the SPD systems are respectively characterised by the largest and the smallest damping efficiency among Rayleigh damping systems subjected to base excitation. A numerical application with realistic data corresponding to an actual seven-storey building structure is presented to illustrate and verify the theoretical findings.
Nonlinear Landau damping in the ionosphere
NASA Technical Reports Server (NTRS)
Kiwamoto, Y.; Benson, R. F.
1979-01-01
A model which explains the nonresonant waves which produce the diffuse resonance observed near 3/2 f(H) by the Alouette and Isis topside sounders, where f(H) is the ambient electron cyclotron frequency, is presented. These waves are the result of plasma wave instabilities driven by anisotropic electron velocity distributions initiated by the high-power short-duration sounder pulse. Calculations of the nonlinear wave-particle coupling coefficients show that the diffuse resonance wave can be maintained by nonlinear Landau damping of the sounder-stimulated 2f(H) wave which is observed with a time duration longer than that of the diffuse resonance wave. The time duration of the diffuse resonance is determined by the transit time of the instability-generated and nonlinearly maintained diffuse resonance wave from the remote short-lived hot region back to the antenna. The model is consistent with the Alouette/Isis observations and it demonstrates the existence of nonlinear wave-particle interactions in the ionosphere.
Influence of quasiparticle damping on magnetic stability
NASA Astrophysics Data System (ADS)
Herrmann, T.; Nolting, W.
1996-04-01
We propose a modified alloy analogy for the single-band Hubbard model, by which we investigate the possibility of spontaneous ferromagnetism in narrow energy bands. It is shown that a proper definition of the fictitious alloy enables self-consistent magnetic solutions to be found. The existence of spontaneous magnetism is mainly influenced by the lattice structure, the effective Coulomb coupling, and the band occupation. In accordance with the simple Stoner criterion, ferromagnetism appears in strongly correlated electron systems for band occupations, which locate the chemical potential μ in regions of high quasiparticle density of states. Rather realistic Curie temperatures are found. The macroscopic magnetic properties explain themselves via temperature-dependent quasiparticle densities of states, quasiparticle band structures, and respective spectral densities. It is shown how quasiparticle damping may depress quite substantially the stability of magnetic states by broadening corresponding spectral density peaks. Correlation effects lead to the expected splitting into two quasiparticle subbands (``Hubbard bands''), and under certain conditions to an additional exchange splitting of each of these quasiparticle subbands, as well as to a spin-dependent band narrowing, the combination of which gives rise to an unconventional ``inverse'' exchange shift at certain positions of the Brillouin zone.
Robust time-domain identification of mass stiffness, and damping matrices
NASA Technical Reports Server (NTRS)
Roemer, Michael J.; Mook, D. Joseph
1990-01-01
Accurate estimates of the mass, stiffness, and damping characteristics of a structure is necessary for determining the control laws best suited for active control methodologies. There are several modal identification techniques available for determining the frequencies, damping ratios, and mode shapes of a structure. However, modal identification methods in both the frequency and time domains have difficulties for certain circumstances. Frequency domain techniques which utilize the steady-state response from various harmonic inputs often encounter difficulties when the frequencies are closely distributed, the structure exhibits a high degree of damping, or the steady-state condition is hard to establish. Time domain techniques have produced successful results, but lack robustness with respect to measurement noise. In this paper, two identification techniques and an estimation method are combined to form a time-domain technique to accurately identify the mass, stiffness, and damping matrices from noisy measurements.
Modeling and measurement of geometrically nonlinear damping in a microcantilever-nanotube system.
Jeong, Bongwon; Cho, Hanna; Yu, Min-Feng; Vakakis, Alexander F; McFarland, Donald Michael; Bergman, Lawrence A
2013-10-22
Nonlinear mechanical systems promise broadband resonance and instantaneous hysteretic switching that can be used for high sensitivity sensing. However, to introduce nonlinear resonances in widely used microcantilever systems, such as AFM probes, requires driving the cantilever to an amplitude that is too large for any practical applications. We introduce a novel design for a microcantilever with a strong nonlinearity at small cantilever oscillation amplitude arising from the geometrical integration of a single BN nanotube. The dynamics of the system was modeled theoretically and confirmed experimentally. The system, besides providing a practical design of a nonlinear microcantilever-based probe, demonstrates also an effective method of studying the nonlinear damping properties of the attached nanotube. Beyond the typical linear mechanical damping, the nonlinear damping contribution from the attached nanotube was found to be essential for understanding the dynamical behavior of the designed system. Experimental results obtained through laser microvibrometry validated the developed model incorporating the nonlinear damping contribution.
Effect of substitutional defects on Kambersky damping in L1{sub 0} magnetic materials
Qu, T.; Victora, R. H.
2015-02-16
Kambersky damping, representing the loss of magnetic energy from the electrons to the lattice through the spin orbit interaction, is calculated for L1{sub 0} FePt, FePd, CoPt, and CoPd alloys versus chemical degree of order. When more substitutional defects exist in the alloys, damping is predicted to increase due to the increase of the spin-flip channels allowed by the broken symmetry. It is demonstrated that this corresponds to an enhanced density of states (DOS) at the Fermi level, owing to the rounding of the DOS with loss of long-range order. Both the damping and the DOS of the Co-based alloy are found to be less affected by the disorder. Pd-based alloys are predicted to have lower damping than Pt-based alloys, making them more suitable for high density spintronic applications.
NASA Astrophysics Data System (ADS)
Strain, K. A.; Shapiro, B. N.
2012-04-01
The mirrors of laser interferometric gravitational wave detectors hang from multi-stage suspensions. These support the optics against gravity while isolating them from external vibration. Thermal noise must be kept small so mechanical loss must be minimized and the resulting structure has high-Q resonances rigid-body modes, typically in the frequency range between about 0.3 Hz and 20 Hz. Operation of the interferometer requires these resonances to be damped. Active damping provides the design flexibility required to achieve rapid settling with low noise. In practice there is a compromise between sensor performance, and hence cost and complexity, and sophistication of the control algorithm. We introduce a novel approach which combines the new technique of modal damping with methods developed from those applied in GEO 600. This approach is predicted to meet the goals for damping and for noise performance set by the Advanced LIGO project.
Effect of substitutional defects on Kambersky damping in L10 magnetic materials
NASA Astrophysics Data System (ADS)
Qu, T.; Victora, R. H.
2015-02-01
Kambersky damping, representing the loss of magnetic energy from the electrons to the lattice through the spin orbit interaction, is calculated for L10 FePt, FePd, CoPt, and CoPd alloys versus chemical degree of order. When more substitutional defects exist in the alloys, damping is predicted to increase due to the increase of the spin-flip channels allowed by the broken symmetry. It is demonstrated that this corresponds to an enhanced density of states (DOS) at the Fermi level, owing to the rounding of the DOS with loss of long-range order. Both the damping and the DOS of the Co-based alloy are found to be less affected by the disorder. Pd-based alloys are predicted to have lower damping than Pt-based alloys, making them more suitable for high density spintronic applications.
Effects of damping wigglers on beam dynamics in the NLC damping rings
Wolski, Andrzej; Wu, Ying
2001-06-16
To achieve the required damping time in the main damping rings for the Next Linear Collider (NLC), a wiggler will be required in each ring with integrated squared field strength up to 110 T{sup 2}m. There are concerns that nonlinear components of the wiggler field will damage the dynamic aperture of the ring, leading to poor injection efficiency. Severe effects from an insertion device have been observed and corrected in SPEAR 2. In this paper, we describe a model that we have developed to study the effects of the damping wiggler, compare the predictions of the model with actual experience in the case of the SPEAR 2 wiggler, and consider the predicted effects of current damping wiggler design on the NLC main damping rings.
Gilbert damping in magnetic layered systems
NASA Astrophysics Data System (ADS)
Barati, E.; Cinal, M.; Edwards, D. M.; Umerski, A.
2014-07-01
The Gilbert damping constant present in the phenomenological Landau-Lifshitz-Gilbert equation describing the dynamics of magnetization is calculated for ferromagnetic metallic films as well as Co/nonmagnet (NM) bilayers. The calculations are done within a realistic nine-orbital tight-binding model including spin-orbit coupling. The convergence of the damping constant expressed as a sum over the Brillouin zone is remarkably improved by introducing finite temperature into the electronic occupation factors and subsequent summation over the Matsubara frequencies. We investigate how the Gilbert damping constant depends on the ferromagnetic film thickness as well as on the thickness of the nonmagnetic cap in Co/NM bilayers (NM=Cu, Pd, Ag, Pt, and Au). The obtained theoretical dependence of the damping constant on the electron-scattering rate, describing the average lifetime of electronic states, varies substantially with the ferromagnetic film thickness and it differs significantly from the dependence for bulk ferromagnetic metals. The presence of nonmagnetic caps is found to largely enhance the magnetic damping in Co/NM bilayers in accordance with experimental data. Unlike Cu, Ag, and Au a particularly strong enhancement is obtained for Pd and Pt caps. This is attributed to the combined effect of the large spin-orbit couplings of Pd and Pt and the simultaneous presence of d states at the Fermi level in these two metals. The calculated Gilbert damping constant also shows an oscillatory dependence on the thicknesses of both ferromagnetic and nonmagnetic parts of the investigated systems which is attributed to quantum-well states. Finally, the expression for contributions to the damping constant from individual atomic layers is derived. The obtained distribution of layer contributions in Co/Pt and Co/Pd bilayers proves that the enhanced damping which affects the dynamics of the magnetization in the Co film originates mainly from a region within the nonmagnetic part of the
Damping and spectral formation of upstream whistlers
Orlowski, D.S.; Russell, C.T.; Krauss-Varban, D.
1995-09-01
Previous studies have indicated that damping rates of upstream whistlers strongly depend on the details of the electron distribution function. Moreover, detailed analysis of Doppler shift and the whistler dispersion relation indicate that upstream whistlers propagate obliquely in a finite band of frequencies. In this paper we present results of a kinetic calculation of damping lengths of wideband whistlers using the sum of seven drifting bi-Maxwellian electron distributions as a best fit to the ISEE 1 electron data. For two cases, when upstream whistlers are observed, convective damping lengths derived from ISEE magnetic field and ephemeris data are compared with theoretical results. We find that the calculated convective damping lengths are consistent with the data and that upstream whistlers remain marginally stable. We also show that the slope of plasma frame spectra of upstream whistlers, obtained by direct fitting of the observed spectra, is between 5 and 7. The overall spectral, wave, and particle characteristics, proximity to the shock, as well as propagation and damping properties indicated that these waves cannot be generated locally. Instead, the observed upstream whistlers arise in the shock ramp, most likely by a variety of cross-field drift and/or anisotropy driven instabilities. 57 refs., 11 figs.
Anti-damping effect of radiation reaction
NASA Astrophysics Data System (ADS)
Wang, G.; Li, H.; Shen, Y. F.; Yuan, X. Z.; Zi, J.
2010-01-01
The anti-damping effect of radiation reaction, which means the radiation reaction does non-negative work on a radiating charge, is investigated at length by using the Lorentz-Dirac equation (LDE) for the motion of a point charge respectively acted on by (a) a pure electric field, (b) a pure magnetic field and (c) the fields of an electromagnetic wave. We found that the curvature of the charge's trajectory plays an important role in the radiation reaction force, and the anti-damping effect cannot take place for the real macroscopic motions of a point charge. The condition for this anti-damping effect to take place is that the gradient of the external force field must exceed a certain value over the region of magnitude of the classical radius of massive charges (~10-15 m). Our results are potentially helpful to lessen the controversy on LDE and justify it as the correct classical equation describing the radiating charge's motion. If this anti-damping effect of LDE were a real existing physical process, it could serve as a mechanism within the context of classical electrodynamics for the stability of hydrogen atoms. Using the picture of an electron in quantum electrodynamics, namely the negative bare charge surrounded by the polarized positive charges of vacuum, we can obtain a reasonable explanation for the energy transferred to the electron during the occurrence of the anti-damping effect, on which the venerable work of Wheeler and Feynman has thrown some light.
Thin-layer magnetostrictive composite films for turbomachinery fan blade damping
NASA Astrophysics Data System (ADS)
Pulliam, Wade J.; Lee, Donggun; Carman, Gregory P.; McKnight, Geoffrey P.
2003-08-01
Recently, there have been significant advances in using magnetostrictive particles in a polymer matrix; finding uses in many applications, both as an active transducer and a passive dumper. Termed magnetostrictive particulate composites (MPC), the material provides capabilities identical or superior to the monolithic material. Fortis Technologies has been pursuing improvements in the applications and fabrication of this innovative material. Specifically, this MPC technology provides a passive, broadband, large temperature range, high stiffness, damping material to be used where current technologies fall short. A novel manufacturing technique based on magnetic fields has been developed to distribute magnetostrictive particulates in a polymer resin and apply it in thin-layer on surfaces for vibration damping in environments typical of turbomachinery fan blades. These magnetostrictive particulates provide damping through domain wall switching, a non-conservative action which provides a high loss factor, and, in turn, significant vibration mitigation. The magnetostrictive damping composites can be easily fabricated into thin films, provide stiffness and strength while also incorporating damping capabilities which exceed in performance and temperature range viscoelastic materials, the current state of the art for applied blade damping. Analytical studies, a finite element analysis and experimental study of the new material in a typical turbomachinery blade loading condition has been conducted and has demonstrated the benefits of this technology.
Modeling Techniques for Evaluation the Effectiveness of Particle Damping in Turbomachinery
NASA Technical Reports Server (NTRS)
Ehrgott, R.; Panossian, H.; Davis, G.
2009-01-01
High power turbopumps are frequently used to supply propellants to the combustion chambers of rocket engines. Due to the high pressures and flow-rates required, turbopump components are subjected to harsh environments which include dynamic excitation due to random, sine, and acoustic vibration. Additionally, fluid-induced forces can couple with the dynamics of the structure resulting in flow induced instabilities (flutter). Structural response to these forms of excitation results in reduced fatigue life and increases the likelihood of an operational failure. Particle damping has been used successfully on vibration problems in the past by increasing the damping and therefore reducing the response to acceptable levels. Empirical methods have typically been employed to evaluate the performance of the particles in reducing the structural response. This report explores the use of finite element methods to estimate the effectiveness of particle damping in a typical non-rotating turbopump component. Axisymmetric harmonic models are used to estimate the increase in modal damping produced by the addition of particles in the cavity of an axisymmetric seal. Target modes of vibration are evaluated to quantify how the effective particle damping is altered by geometry changes in the seal design. A new method to predict the performance of particle dampers is developed and shown to provide more reasonable estimates of damping.
A numerical and experimental study on viscoelastic damping of a 3D structure
NASA Astrophysics Data System (ADS)
Rijnen, M. W. L. M.; Pasteuning, F.; Fey, R. H. B.; Schothorst, G. van; Nijmeijer, H.
2015-08-01
Structural vibrations often cause problems in high precision instruments, which may be solved by introducing passive damping. In this paper, different ways of introducing passive damping via viscoelastic materials (VEM) are discussed. Discrete damping elements and constrained layer (CL) configurations are selected and used to efficiently damp an open aluminum box. For the constrained layer configurations, a distinction is made between full and partial coverage of the structure. The steady-state dynamics of the box are simulated using a finite element (FE) model, which includes frequency dependent VEM properties. This model is used to find a design that possesses high damping while taking into account design constraints. The simulation results are experimentally validated using both modal parameters and frequency response functions (FRFs). For the computation of model based FRFs, a new method based on Interpolated Modal Parameter Superposition (IMPS) is proposed. Model based results and experimental results show good resemblance, even without updating the model with deviations in the realized structure. The local dampers add most damping to a limited number of modes. Partially covering the box with CL dampers is found to be more effective than full coverage of the structure with the same mass addition.
Magnetic Susceptibility Effects and Lorentz Damping in Diamagnetic Fluids
NASA Technical Reports Server (NTRS)
Ramachandran, Narayanan; Leslie, Fred W.
2000-01-01
A great number of crystals (semi-conductor and protein) grown in space are plagued by convective motions which contribute to structural flaws. The character of these instabilities is not well understood but is associated with density variations in the presence of residual gravity and g-jitter. Both static and dynamic (rotating or travelling wave) magnetic fields can be used to reduce the effects of convection in materials processing. In semi-conductor melts, due to their relatively high electrical conductivity, the induced Lorentz force can be effectively used to curtail convective effects. In melts/solutions with reduced electrical conductivity, such as aqueous solutions used in solution crystal growth, protein crystal growth and/or model fluid experiments for simulating melt growth, however, the variation of the magnetic susceptibility with temperature and/or concentration can be utilized to better damp fluid convection than the Lorentz force method. This paper presents a comprehensive, comparative numerical study of the relative damping effects using static magnetic fields and gradients in a simple geometry subjected to a thermal gradient. The governing equations are formulated in general terms and then simplified for the numerical calculations. Operational regimes, based on the best damping technique for different melts/solutions are identified based on fluid properties. Comparisons are provided between the numerical results and available results from experiments in surveyed literature.
Damping of Electron Density Structures and Implications for Interstellar Scintillation
NASA Astrophysics Data System (ADS)
Smith, K. W.; Terry, P. W.
2011-04-01
The forms of electron density structures in kinetic Alfvén wave (KAW) turbulence are studied in connection with scintillation. The focus is on small scales L ~ 108-1010 cm where the KAW regime is active in the interstellar medium, principally within turbulent H II regions. Scales at 10 times the ion gyroradius and smaller are inferred to dominate scintillation in the theory of Boldyrev et al. From numerical solutions of a decaying KAW turbulence model, structure morphology reveals two types of localized structures, filaments and sheets, and shows that they arise in different regimes of resistive and diffusive damping. Minimal resistive damping yields localized current filaments that form out of Gaussian-distributed initial conditions. When resistive damping is large relative to diffusive damping, sheet-like structures form. In the filamentary regime, each filament is associated with a non-localized magnetic and density structure, circularly symmetric in cross section. Density and magnetic fields have Gaussian statistics (as inferred from Gaussian-valued kurtosis) while density gradients are strongly non-Gaussian, more so than current. This enhancement of non-Gaussian statistics in a derivative field is expected since gradient operations enhance small-scale fluctuations. The enhancement of density gradient kurtosis over current kurtosis is not obvious, yet it suggests that modest density fluctuations may yield large scintillation events during pulsar signal propagation. In the sheet regime the same statistical observations hold, despite the absence of localized filamentary structures. Probability density functions are constructed from statistical ensembles in both regimes, showing clear formation of long, highly non-Gaussian tails.
Backscattering and Nonparaxiality Arrest Collapse of Damped Nonlinear Waves
NASA Technical Reports Server (NTRS)
Fibich, G.; Ilan, B.; Tsynkov, S.
2002-01-01
The critical nonlinear Schrodinger equation (NLS) models the propagation of intense laser light in Kerr media. This equation is derived from the more comprehensive nonlinear Helmholtz equation (NLH) by employing the paraxial approximation and neglecting the backscattered waves. It is known that if the input power of the laser beam (i.e., L(sub 2) norm of the initial solution) is sufficiently high, then the NLS model predicts that the beam will self-focus to a point (i.e.. collapse) at a finite propagation distance. Mathematically, this behavior corresponds to the formation of a singularity in the solution of the NLS. A key question which has been open for many years is whether the solution to the NLH, i.e., the 'parent' equation, may nonetheless exist and remain regular everywhere, in particular for those initial conditions (input powers) that lead to blowup in the NLS. In the current study, we address this question by introducing linear damping into both models and subsequently comparing the numerical solutions of the damped NLH (boundary-value problem) with the corresponding solutions of the damped NLS (initial-value problem). Linear damping is introduced in much the same way as done when analyzing the classical constant-coefficient Helmholtz equation using the limiting absorption principle. Numerically, we have found that it provides a very efficient tool for controlling the solutions of both the NLH and NHS. In particular, we have been able to identify initial conditions for which the NLS solution does become singular. whereas the NLH solution still remains regular everywhere. We believe that our finding of a larger domain of existence for the NLH than that for the NLS is accounted for by precisely those mechanisms, that have been neglected when deriving the NLS from the NLH, i.e., nonparaxiality and backscattering.
Passive damping concepts for slender columns in space structures
NASA Technical Reports Server (NTRS)
Razzaq, Z.; Ekhelikar, R. K.
1985-01-01
An experimental and theoretical study of three different passive damping concepts is conducted for a slender member with partial rotational end restraints. Over a hundred full-scale natural vibration experiments were conducted to evaluate the effectiveness of mass-string, polyethylene tubing, and chain damping concepts. The damping properties obtained from the experiments were used in the approximate analyses based on the partial differential equation of motion for the problem. The comparison of the experimental and the theoretical deflection-time relations shows that the velocity-dependent damping model used in the theory is adequate. From the experimental results, the effect of end connection friction and induced axial forces on damping is identified. The definition of an efficiency index is proposed based on the damping ratio and the mass of a given passive damping device. Using this definition, the efficiencies of the three damping devices are compared. The polyethylene tubing concept resulted into a low damping efficiency.
Measurement of damping of graphite epoxy materials
NASA Technical Reports Server (NTRS)
Crocker, M. J.
1985-01-01
The design of an experiment to measure the damping of a cylindrical graphite-epoxy specimen with a three point support and a knife edge support is described as well as equipment used in tests conducted to determine the influence of the support at the two ends of the specimen and to simulate an idealized free-free boundary condition at the two edges. A curve fitting technique is being used to process the frequency response data obtained. Experiments conducted on the thin plate specimen also reveal the influence of the end support condition on the damping ratio of the specimen. The damping ratio values measured for both specimens appear to be strongly influenced by the shape of the specimen and appear to depend on length and fiber orientation as well as the presence of discontinuities such as sharp bends, corners, and notches.
Turbine blade damping device with controlled loading
Marra, John J
2013-09-24
A damping structure for a turbomachine rotor. The damping structure including an elongated snubber element including a first snubber end rigidly attached to a first blade and extending toward an adjacent second blade, and an opposite second snubber end positioned adjacent to a cooperating surface associated with the second blade. The snubber element has a centerline extending radially inwardly in a direction from the first blade toward the second blade along at least a portion of the snubber element between the first and second snubber ends. Rotational movement of the rotor effects relative movement between the second snubber end and the cooperating surface to position the second snubber end in frictional engagement with the cooperating surface with a predetermined damping force determined by a centrifugal force on the snubber element.
Radiation damping in focusing-dominated systems
Huang, Zhirong; Chen, Pisin; Ruth, R.D.
1995-06-01
A quasi-classical method is developed to calculate the radiation damping of a relativistic particle in a straight, continuous focusing system. In one limiting case where the pitch angle of the particle {theta}{sub p} is much larger than the radiation opening angle 1/{gamma}, the radiation power spectrum is similar to synchrotron radiation and the relative damping rate of the transverse action is proportional to the relative energy loss rate. In the other limiting case where {theta}{sub p} {much_lt} 1/{gamma}, the radiation is dipole in nature and the relative damping rate of the transverse action is energy-independent and is much faster than the relative energy rate. Quantum excitation to the transverse action is absent in this focusing channel. These results can be extended to bent systems provided that the focusing field dominates over the bending field.
Turbine blade damping device with controlled loading
Marra, John J.
2015-09-29
A damping structure for a turbomachine rotor. The damping structure including an elongated snubber element including a first snubber end rigidly attached to a first blade and extending toward an adjacent second blade, and an opposite second snubber end positioned adjacent to a cooperating surface associated with the second blade. The snubber element has a centerline extending radially inwardly in a direction from the first blade toward the second blade along at least a portion of the snubber element between the first and second snubber ends. Rotational movement of the rotor effects relative movement between the second snubber end and the cooperating surface to position the second snubber end in frictional engagement with the cooperating surface with a predetermined damping force determined by a centrifugal force on the snubber element.
Viscous damping of perforated planar micromechanical structures
Homentcovschi, D.; Miles, R.N.
2008-01-01
The paper gives an analytical approximation to the viscous damping coefficient due to the motion of a gas between a pair of closely spaced fluctuating plates in which one of the plates contains a regular system of circular holes. These types of structures are important parts of many microelectromechanical devices realized in MEMS technology as microphones, microaccelerometers, resonators, etc. The pressure satisfies a Reynolds’ type equation with coefficients accounting for all the important effects: compressibility of the gas, inertia and possibly slip of the gas on the plates. An analytical expression for the optimum number of circular holes which assure a minimum value of the total damping coefficient is given. This value realizes an equilibrium between the squeeze-film damping and the viscous resistance of the holes. The paper also provides analytical design formulas to be used in the case of regular circular perforated plates. PMID:19365579
Passively damped vibration welding system and method
Tan, Chin-An; Kang, Bongsu; Cai, Wayne W.; Wu, Tao
2013-04-02
A vibration welding system includes a controller, welding horn, an anvil, and a passive damping mechanism (PDM). The controller generates an input signal having a calibrated frequency. The horn vibrates in a desirable first direction at the calibrated frequency in response to the input signal to form a weld in a work piece. The PDM is positioned with respect to the system, and substantially damps or attenuates vibration in an undesirable second direction. A method includes connecting the PDM having calibrated properties and a natural frequency to an anvil of an ultrasonic welding system. Then, an input signal is generated using a weld controller. The method includes vibrating a welding horn in a desirable direction in response to the input signal, and passively damping vibration in an undesirable direction using the PDM.
Fluid damping of cylindrical liquid storage tanks.
Habenberger, Joerg
2015-01-01
A method is proposed in order to calculate the damping effects of viscous fluids in liquid storage tanks subjected to earthquakes. The potential equation of an ideal fluid can satisfy only the boundary conditions normal to the surface of the liquid. To satisfy also the tangential interaction conditions between liquid and tank wall and tank bottom, the potential flow is superimposed by a one-dimensional shear flow. The shear flow in this boundary layer yields to a decrease of the mechanical energy of the shell-liquid-system. A damping factor is derived from the mean value of the energy dissipation in time. Depending on shell geometry and fluid viscosity, modal damping ratios are calculated for the convective component.
Radiation Damping in a Focusing Channel
NASA Astrophysics Data System (ADS)
Ruth, Ronald D.
1996-05-01
In electron storage rings synchrotron radiation leads to the damping of the three degrees of freedom of the particle trajectory towards a stable closed orbit transversely and a fixed stable phase longitudinally. At the same time, the emission of discrete quanta leads to diffusion in all three degrees of freedom. These two competing effects result in an equilibrium beam emittance that depends upon the parameters of the storage ring. In the case above, the radiation in the bending fields dominates, and the radiation due to the focusing fields is either neglected or taken into account perturbatively. In this talk we study the opposite case, a continuous focusing channel in which the radiation and its reaction are dominated by the strong focusing field. If there is a bending field, it is much weaker than the focusing field. In such focusing systems, we find that the radiation is synchrotron-like for larger betatron oscillation amplitudes and undulator-like for smaller amplitudes. However, quantum excitation is absent for any oscillation amplitude, and the damping exhibits asymmetry in favor of the transverse degree of freedom as the amplitude becomes smaller. In the undulator regime, the damping turns into exponential in the transverse direction, much faster than the total energy damping in this system. In principle, the particle could damp to the transverse ground state of the harmonic oscillator, reaching a minimum normalized emittance, γ ɛ_min = hbar/2mc, limited only by the uncertainty principle. In the case of a bent focusing system, we find that the lack of quantum excitation and asymmetric damping still hold provided that the bending field is sufficiently weak.
Lag-stabilized force feedback damping
Petterson, B.J.; Robinett, R.D.; Werner, J.C.
1991-05-01
A lag-stabilized, force feedback controller for damping initial and residual oscillations of a planar, cantilevered flexible arm has been analytically developed and experimentally implemented on a commercial robot. The controller feeds back force sensor measurements that are delayed in time and proportional to the displacement (angular orientation) of the arm in order to damp the oscillation. As a result of the lag (contrary to popular belief), the controlled robot system is stable and provides tunable performance on a Cincinnati Milacron T3-786 robot. 3 refs., 9 figs., 2 tabs.
Particle systems and nonlinear Landau damping
Villani, Cédric
2014-03-15
Some works dealing with the long-time behavior of interacting particle systems are reviewed and put into perspective, with focus on the classical Kolmogorov–Arnold–Moser theory and recent results of Landau damping in the nonlinear perturbative regime, obtained in collaboration with Clément Mouhot. Analogies are discussed, as well as new qualitative insights in the theory. Finally, the connection with a more recent work on the inviscid Landau damping near the Couette shear flow, by Bedrossian and Masmoudi, is briefly discussed.
Optimal piezoelectric switching technique for vibration damping
NASA Astrophysics Data System (ADS)
Neubauer, Marcus; Oleskiewicz, Robert
2007-04-01
This paper describes piezoelectric switching techniques for vibration damping. The dynamical behaviour of a piezoceramics connected to a switching LR shunt and the dissipated energy are obtained using a fundamental piezoelectric model. All calculations are performed in a normalized way and highlight the influence of the electromechanical coupling coefficient of the piezoceramics and the shunt parameters. For the first time, a precise result for the dynamics of a shunted piezoceramics is derived. The analytic results are used to determine the optimal switching sequence and external branch parameters in order to maximize the damping performance. The results are validated by measurements of a clamped beam.
Wind turbine blade with viscoelastic damping
Sievers, Ryan A.; Mullings, Justin L.
2017-01-10
A wind turbine blade (60) damped by viscoelastic material (54, 54A-F) sandwiched between stiffer load-bearing sublayers (52A, 52B, 56A, 56B) in portions of the blade effective to damp oscillations (38) of the blade. The viscoelastic material may be located in one or more of: a forward portion (54A) of the shell, an aft portion (54D) of the shell, pressure and suction side end caps (54B) of an internal spar, internal webbing walls (54C, 54E), and a trailing edge core (54F).
Inertia-Wheel Vibration-Damping System
NASA Technical Reports Server (NTRS)
Fedor, Joseph V.
1990-01-01
Proposed electromechanical system would damp vibrations in large, flexible structure. In active vibration-damping system motors and reaction wheels at tips of appendages apply reaction torques in response to signals from accelerometers. Velocity signal for vibrations about one axis processes into control signal to oppose each of n vibrational modes. Various modes suppressed one at a time. Intended primarily for use in spacecraft that has large, flexible solar panels and science-instrument truss assembly, embodies principle of control interesting in its own right and adaptable to terrestrial structures, vehicles, and instrument platforms.
Mechanical Design of the DAMPE BGO Calorimeter
NASA Astrophysics Data System (ADS)
Hu, Yiming; Wu, Jian; Feng, Changqing; Zhang, Yunlong; Chen, Dengyi; Chang, Jin
The Dark Matter Particle Explorer, DAMPE, is a new designed satellite developed for the CASs new Innovation 2020 program. As the main component of DAMPE, the new designed BGO calorimeter consists of 308 BGO Crystals coupled with photomultiplier tube.The reliability and safety of the BGO Calorimeter structure play a very important role in the operation of whole detector. During the rocket launch, the calorimeter structure should be stable against vibration and environmental factors to ensure detector works in good conditions. In this article, we make the BGO calorimeter structure design, and then prove that it will work in the environments of rocket launch and flight.
Delay of Transition Using Forced Damping
NASA Technical Reports Server (NTRS)
Exton, Reginald J.
2014-01-01
Several experiments which have reported a delay of transition are analyzed in terms of the frequencies of the induced disturbances generated by different flow control elements. Two of the experiments employed passive stabilizers in the boundary layer, one leading-edge bluntness, and one employed an active spark discharge in the boundary layer. It is found that the frequencies generated by the various elements lie in the damping region of the associated stability curve. It is concluded that the creation of strong disturbances in the damping region stabilizes the boundary-layer and delays the transition from laminar to turbulent flow.
Diocotron Damping in Ion Plasmas in the Presence of a Few Electrons
NASA Astrophysics Data System (ADS)
Anderegg, F. A.
2005-10-01
Here, we present diocotron damping measurements of quiescent Mg^+ ion plasma columns including the effects of a small number of electrons. The ion plasma is contained in a 3 Tesla Penning-Malmberg trap with total number of particles N ˜10^8 - 10^9. For the mθ= 1, kz= 0 diocotron mode, γ/ φ vs T was measured as the temperature was varied over the range 0.1 < T < 10 eV with an ion column length Lp= 12cm. We find 4 x10-6 < γ/ φ< 10-4 decreasing with temperature for 0.1 < T < 1 eV, increasing to 10-2 at T ˜10 eV in the range of 1 eV < T < 10 eV. The low temperature damping may represent ``rotational pumping,'' or trapped-particle-mediated asymmetry-induced damping; but the high temperature result is not understood. These new measurements of ion diocotron mode damping will be compared to previous work on diocotron mode damping in pure electron plasmas. Rapid loss of Mg^+ plasmas has been observed from overlapping nested electrons, but no instability is observed with a weak transiting electron beam, possibly due to concurrent damping. Ion plasma results will be compared to the analogous case of an electron column with transiting ions.
Homentcovschi, Dorel; Miles, Ronald N.
2008-01-01
The paper presents a model for the squeezed film damping, the resistance of the holes, and the corresponding spring forces for a periodic perforated microstructure including the effects of compressibility, inertia, and rarefied gas. The viscous damping and spring forces are obtained by using the continuity equation. The analytical formula for the squeezed film damping is applied to analyze the response of an ultrasonic transducer. The inclusion of these effects in a model significantly improves the agreement with measured results. Finally, it is shown that the frequency dependence of the total damping and total spring force for a cell are very similar to those corresponding to a rectangular open microstructure without holes. A separate analysis reveals the importance of each particular correction. The most important is the compressibility correction; the inertia has to be considered only for determining the spring force and the damping force for sufficiently high frequencies. PMID:18646964
Damping of the wrist joint during voluntary movement.
Milner, T E; Cloutier, C
1998-10-01
Damping characteristics of the musculoskeletal system were investigated during rapid voluntary wrist flexion movements. Oscillations about the final position were induced by introducing a load with the characteristics of negative damping, which artificially reduced the damping of the wrist. Subjects responded to increases in the negatively damped load by stronger cocontraction of wrist flexor and extensor muscles during the stabilization phase of the movement. However, their ability to counteract the effects of the negatively damped load diminished as the negative damping increased. Consequently, the number and frequency of oscillations increased. The oscillations were accompanied by phase-locked muscle activity superimposed on underlying tonic muscle activation. The wrist stiffness and damping coefficient increased with the increased cocontraction that accompanied more negatively damped loads, although changes in the damping coefficient were less systematic than the stiffness. Analysis of successive half-cycles of the oscillation revealed that the wrist stiffness and damping coefficient increased, despite decreasing muscle activation, as oscillation amplitude and velocity declined. This indicates that the inverse dependence of the damping coefficient on oscillation velocity contributes significantly to damping of joint motion. It is suggested that this property helps to offset a negative contribution to damping from the stretch reflex.
NASA Astrophysics Data System (ADS)
Ginés, R.; Bergamini, A.; Motavalli, M.; Ermanni, P.
2015-09-01
The damping capacity of a novel composite film, designed to exhibit high dielectric strength and a high friction coefficient for an electrostatic tuneable friction damper, is tested on a cantilever beam. Such a system consists of a carbon fibre reinforced polymer stiffening element which is reversibly laminated onto a host structure with a dielectric material by means of electrostatic fields. Damping is achieved when the maximum shear at the interface between the stiffening element and structure exceeds the shear strength of the electrostatically laminated interface. The thin films tested consist of barium titanate particles and alumina platelets in an epoxy matrix. Their high dielectric constant and high coefficient of friction compared to a commercial available polymer film, polyvinylidene fluoride, lead to a reduction of the required electric field to stiffen and damp the cantilever beam. Reducing the operating voltage affects different aspects of the studied damper. The cost of possible applications of the frictional damper can be reduced, as the special components necessary at high voltages become redundant. Furthermore, the enhanced security positively affects the damping system’s appeal as an alternative damping method.
Nonlinear Landau damping and Alfven wave dissipation
NASA Technical Reports Server (NTRS)
Vinas, Adolfo F.; Miller, James A.
1995-01-01
Nonlinear Landau damping has been often suggested to be the cause of the dissipation of Alfven waves in the solar wind as well as the mechanism for ion heating and selective preacceleration in solar flares. We discuss the viability of these processes in light of our theoretical and numerical results. We present one-dimensional hybrid plasma simulations of the nonlinear Landau damping of parallel Alfven waves. In this scenario, two Alfven waves nonresonantly combine to create second-order magnetic field pressure gradients, which then drive density fluctuations, which in turn drive a second-order longitudinal electric field. Under certain conditions, this electric field strongly interacts with the ambient ions via the Landau resonance which leads to a rapid dissipation of the Alfven wave energy. While there is a net flux of energy from the waves to the ions, one of the Alfven waves will grow if both have the same polarization. We compare damping and growth rates from plasma simulations with those predicted by Lee and Volk (1973), and also discuss the evolution of the ambient ion distribution. We then consider this nonlinear interaction in the presence of a spectrum of Alfven waves, and discuss the spectrum's influence on the growth or damping of a single wave. We also discuss the implications for wave dissipation and ion heating in the solar wind.
The Stochastic Nonlinear Damped Wave Equation
Barbu, V. Da Prato, G.
2002-12-19
We prove the existence of an invariant measure for the transition semigroup associated with a nonlinear damped stochastic wave equation in R{sup n} of the Klein-Gordon type. The uniqueness of the invariant measure and the structure of the corresponding Kolmogorov operator are also studied.
Active damping of spacecraft structural appendage vibrations
NASA Technical Reports Server (NTRS)
Fedor, Joseph V. (Inventor)
1990-01-01
An active vibration damper system, for bending in two orthogonal directions and torsion, in each of three mutually perpendicular axes is located at the extremities of the flexible appendages of a space platform. The system components for each axis includes: an accelerometer, filtering and signal processing apparatus, and a DC motor-inertia wheel torquer. The motor torquer, when driven by a voltage proportional to the relative vibration tip velocity, produces a reaction torque for opposing and therefore damping a specific modal velocity of vibration. The relative tip velocity is obtained by integrating the difference between the signal output from the accelerometer located at the end of the appendage with the output of a usually carried accelerometer located on a relatively rigid body portion of the space platform. A selector switch, with sequential stepping logic or highest modal vibration energy logic, steps to another modal tip velocity channel and receives a signal voltage to damp another vibration mode. In this manner, several vibration modes can be damped with a single sensor/actuator pair. When a three axis damper is located on each of the major appendages of the platform, then all of the system vibration modes can be effectively damped.
Vibration damping for the Segmented Mirror Telescope
NASA Astrophysics Data System (ADS)
Maly, Joseph R.; Yingling, Adam J.; Griffin, Steven F.; Agrawal, Brij N.; Cobb, Richard G.; Chambers, Trevor S.
2012-09-01
The Segmented Mirror Telescope (SMT) at the Naval Postgraduate School (NPS) in Monterey is a next-generation deployable telescope, featuring a 3-meter 6-segment primary mirror and advanced wavefront sensing and correction capabilities. In its stowed configuration, the SMT primary mirror segments collapse into a small volume; once on location, these segments open to the full 3-meter diameter. The segments must be very accurately aligned after deployment and the segment surfaces are actively controlled using numerous small, embedded actuators. The SMT employs a passive damping system to complement the actuators and mitigate the effects of low-frequency (<40 Hz) vibration modes of the primary mirror segments. Each of the six segments has three or more modes in this bandwidth, and resonant vibration excited by acoustics or small disturbances on the structure can result in phase mismatches between adjacent segments thereby degrading image quality. The damping system consists of two tuned mass dampers (TMDs) for each of the mirror segments. An adjustable TMD with passive magnetic damping was selected to minimize sensitivity to changes in temperature; both frequency and damping characteristics can be tuned for optimal vibration mitigation. Modal testing was performed with a laser vibrometry system to characterize the SMT segments with and without the TMDs. Objectives of this test were to determine operating deflection shapes of the mirror and to quantify segment edge displacements; relative alignment of λ/4 or better was desired. The TMDs attenuated the vibration amplitudes by 80% and reduced adjacent segment phase mismatches to acceptable levels.
Chiral damping of magnetic domain walls.
Jué, Emilie; Safeer, C K; Drouard, Marc; Lopez, Alexandre; Balint, Paul; Buda-Prejbeanu, Liliana; Boulle, Olivier; Auffret, Stephane; Schuhl, Alain; Manchon, Aurelien; Miron, Ioan Mihai; Gaudin, Gilles
2016-03-01
Structural symmetry breaking in magnetic materials is responsible for the existence of multiferroics, current-induced spin-orbit torques and some topological magnetic structures. In this Letter we report that the structural inversion asymmetry (SIA) gives rise to a chiral damping mechanism, which is evidenced by measuring the field-driven domain-wall (DW) motion in perpendicularly magnetized asymmetric Pt/Co/Pt trilayers. The DW dynamics associated with the chiral damping and those with Dzyaloshinskii-Moriya interaction (DMI) exhibit identical spatial symmetry. However, both scenarios are differentiated by their time reversal properties: whereas DMI is a conservative effect that can be modelled by an effective field, the chiral damping is purely dissipative and has no influence on the equilibrium magnetic texture. When the DW motion is modulated by an in-plane magnetic field, it reveals the structure of the internal fields experienced by the DWs, allowing one to distinguish the physical mechanism. The chiral damping enriches the spectrum of physical phenomena engendered by the SIA, and is essential for conceiving DW and skyrmion devices owing to its coexistence with DMI (ref. ).
Apparatus and method of preloading vibration-damping bellows
Cutburth, Ronald W.
1988-01-01
An improved vibration damping bellows mount or interconnection is disclosed. In one aspect, the bellows is compressively prestressed along its length to offset vacuum-generated tensile loads and thereby improve vibration damping characteristics.
Experimental determination of material damping using vibration analyzer
NASA Technical Reports Server (NTRS)
Chowdhury, Mostafiz R.; Chowdhury, Farida
1990-01-01
Structural damping is an important dynamic characteristic of engineering materials that helps to damp vibrations by reducing their amplitudes. In this investigation, an experimental method is illustrated to determine the damping characteristics of engineering materials using a dual channel Fast Fourier Transform (FFT) analyzer. A portable Compaq III computer which houses the analyzer, is used to collect the dynamic responses of three metal rods. Time-domain information is analyzed to obtain the logarithmic decrement of their damping. The damping coefficients are then compared to determine the variation of damping from material to material. The variations of damping from one point to another of the same material, due to a fixed point excitation, and the variable damping at a fixed point due to excitation at different points, are also demonstrated.
Lateral acoustic wave resonator comprising a suspended membrane of low damping resonator material
Olsson, Roy H.; El-Kady; , Ihab F.; Ziaei-Moayyed, Maryam; Branch; , Darren W.; Su; Mehmet F.,; Reinke; Charles M.,
2013-09-03
A very high-Q, low insertion loss resonator can be achieved by storing many overtone cycles of a lateral acoustic wave (i.e., Lamb wave) in a lithographically defined suspended membrane comprising a low damping resonator material, such as silicon carbide. The high-Q resonator can sets up a Fabry-Perot cavity in a low-damping resonator material using high-reflectivity acoustic end mirrors, which can comprise phononic crystals. The lateral overtone acoustic wave resonator can be electrically transduced by piezoelectric couplers. The resonator Q can be increased without increasing the impedance or insertion loss by storing many cycles or wavelengths in the high-Q resonator material, with much lower damping than the piezoelectric transducer material.
Resistor-damped electromechanical lever blocks
NASA Astrophysics Data System (ADS)
Zago, Lorenzo; Genequand, Pierre M.; Kjelberg, Ivar
1998-06-01
The paper presents an innovative technical solution which provides a combined damping and isolation interface with the appropriate transmissibility characteristics between a vibrating base and a sensitive payload, typically an optical terminal/telescope. The novelty of the solution is primarily found in the implementation of uncoupling and magnification of the incurred vibrations by means of flexures combined with the implementation of energy dissipation by means of a linear electro-magnetic actuator to constitute a passive integrated resistor-damped electromechanic lever block. By means of frictionless flexible lever systems, the amplitude of the payload vibrations is adapted to the optimal range of the actuator with a magnification by a factor ranging typically between 10 and 30. Passive viscous damping is obtained by simply short-circuiting the electro-magnetic motor and can be adapted by setting the impedance of the shorting connection. The desired stiffness is provided by the passive springs of the elastic motor suspension and by the stiffness of the lever flexure blades. The mobile mass of the motors also provide a reaction mass which, like damping and stiffness, is amplified by the square of the lever factor. A theoretical model of resistor-damped electromechanical lever blocks has been established. A particular property is it the good attenuation of excited vibrations only over a set frequency range. Above this range the interface properties rejoin the ones of a rigid connection. This performance makes this type of isolators particularly suitable for integration into multi-layer vibration control systems where sensitive equipment is protected by a mix of passive and active damping/isolation devices acting optimally at different frequency ranges. Experiments performed with a dummy load (80 Kg) representative of a satellite based optical terminal demonstrated the efficiency of the system in protecting the payload by passive damping for vibration excitations
Nonlinear damping and quasi-linear modelling.
Elliott, S J; Ghandchi Tehrani, M; Langley, R S
2015-09-28
The mechanism of energy dissipation in mechanical systems is often nonlinear. Even though there may be other forms of nonlinearity in the dynamics, nonlinear damping is the dominant source of nonlinearity in a number of practical systems. The analysis of such systems is simplified by the fact that they show no jump or bifurcation behaviour, and indeed can often be well represented by an equivalent linear system, whose damping parameters depend on the form and amplitude of the excitation, in a 'quasi-linear' model. The diverse sources of nonlinear damping are first reviewed in this paper, before some example systems are analysed, initially for sinusoidal and then for random excitation. For simplicity, it is assumed that the system is stable and that the nonlinear damping force depends on the nth power of the velocity. For sinusoidal excitation, it is shown that the response is often also almost sinusoidal, and methods for calculating the amplitude are described based on the harmonic balance method, which is closely related to the describing function method used in control engineering. For random excitation, several methods of analysis are shown to be equivalent. In general, iterative methods need to be used to calculate the equivalent linear damper, since its value depends on the system's response, which itself depends on the value of the equivalent linear damper. The power dissipation of the equivalent linear damper, for both sinusoidal and random cases, matches that dissipated by the nonlinear damper, providing both a firm theoretical basis for this modelling approach and clear physical insight. Finally, practical examples of nonlinear damping are discussed: in microspeakers, vibration isolation, energy harvesting and the mechanical response of the cochlea.
Landau damping of surface plasmons in metal nanostructures
NASA Astrophysics Data System (ADS)
Shahbazyan, Tigran V.
2016-12-01
We develop a quantum-mechanical theory for Landau damping of surface plasmons in metal nanostructures of arbitrary shape. We show that the electron surface scattering, which facilitates plasmon decay in small nanostructures, can be incorporated into the metal dielectric function on par with phonon and impurity scattering. The derived surface scattering rate is determined by the local field polarization relative to the metal-dielectric interface and is highly sensitive to the system geometry. We illustrate our model by providing analytical results for surface scattering rate in some common shape nanostructures. Our results can be used for calculations of hot carrier generation rates in photovoltaics and photochemistry applications.
Nautiyal, Pranjal; Boesl, Benjamin; Agarwal, Arvind
2017-03-01
Graphene foam-based hierarchical polyimide composites with nanoengineered interface are fabricated in this study. Damping behavior of graphene foam is probed for the first time. Multiscale mechanisms contribute to highly impressive damping in graphene foam. Rippling, spring-like interlayer van der Waals interactions and flexing of graphene foam branches are believed to be responsible for damping at the intrinsic, interlayer and anatomical scales, respectively. Merely 1.5 wt% graphene foam addition to the polyimide matrix leads to as high as ≈300% improvement in loss tangent. Graphene nanoplatelets are employed to improve polymer-foam interfacial adhesion by arresting polymer shrinkage during imidization and π-π interactions between nanoplatelets and foam walls. As a result, damping behavior is further improved due to effective stress transfer from the polymer matrix to the foam. Thermo-oxidative stability of these nanocomposites is investigated by exposing the specimens to glass transition temperature of the polyimide (≈400 °C). The composites are found to retain their damping characteristics even after being subjected to such extreme temperature, attesting their suitability in high temperature structural applications. Their unique hierarchical nanostructure provides colossal opportunity to engineer and program material properties.
GEANT4 Simulation of Neutron Detector for DAMPE
NASA Astrophysics Data System (ADS)
He, M.; Ma, T.; Chang, J.; Zhang, Y.; Huang, Y. Y.; Zang, J. J.; Wu, J.; Dong, T. K.
2016-01-01
During recent tens of years dark matter has gradually become a hot topic in astronomical research field, and related theory researches and experiment projects change with each passing day. The Dark Matter Particle Explorer (DAMPE) of our country is proposed under this background. As the probing object involves high energy electrons, appropriate methods must be taken to distinguish them from protons in order to reduce the event probability of other charged particles (e.g. a proton) being mistaken as electrons. The experiments show that, the hadronic shower of high energy proton in BGO electromagnetic calorimeter, which is usually accompanied by the emitting of large number of secondary neutrons, is significantly different from the electromagnetic shower of high energy electron. Through the detection of secondary neutron signal emitting from the bottom of BGO electromagnetic calorimeter and the shower shape of incident particles in BGO electromagnetic calorimeter, we can effectively distinguish whether the incident particles are high energy protons or electrons. This paper introduces the structure and detecting principle of DAMPE neutron detector. We use Monte-Carlo method with GEANT4 software to simulate the signal emitting from protons and electrons at characteristic energy in the neutron detector, and finally summarize the neutron detector's ability to distinguish protons and electrons under different electron acception efficiencies.
GEANT4 Simulation of Neutron Detector for DAMPE
NASA Astrophysics Data System (ADS)
Ming, He; Tao, Ma; Jin, Chang; Yan, Zhang; Yong-yi, Huang; Jing-jing, Zang; Jian, Wu; Tie-kuang, Dong
2016-10-01
In recent decades, dark matter has gradually become a hot topic in astronomical research, and the related theoretical research and experimental project are updated with each passing day. The Dark Matter Particle Explorer (DAMPE) of our country was proposed under this background. As the detected object involves high-energy electrons, appropriate methods must be taken to distinguish them from protons, in order to reduce the event probability of other charged particles (for example protons) being mistaken as electrons. The experiments show that the hadron shower of high-energy proton in BGO (Bismuth Germanium Oxide) calorimeter, which is usually accompanied with the emitting of a large number of secondary neutrons, is significantly different from the electromagnetic shower of high-energy electron. Through the detection of secondary neutron signals emerging from the bottom of BGO calorimeter, and the shower shape of incident particles in the BGO calorimeter, we can effectively distinguish whether the incident particles are high-energy protons or electrons. This paper introduces the structure and detection principle of the DAMPE neutron detector. We use the Monte-Carlo method and the GEANT4 software to simulate the signals produced by protons and electrons at the characteristic energy in the neutron detector, and finally summarize the neutron detector's ability to distinguish protons and electrons under different electron acceptabilities.
Determining material damping type by comparing modal frequency estimators.
Anthony, D K; Simón, F; Juan, Jesús
2009-09-01
The accuracy of modal frequency and damping estimators for non-lightly damped single degree of freedom systems depend on the response parameter used as well as the damping mechanism. Therefore, in order to make accurate modal parameter measurements, the damping mechanism at play must be known to be either viscous or hysteretic a priori. Here, comparisons between the evaluated frequency values are used to glean this information. The damping mechanism of an experimental system (consisting of resilient layer and mass plate) is then determined using two simple modal parameter estimators and applying statistical methods.
Effects of Landau-Lifshitz-Gilbert damping on domain growth.
Kudo, Kazue
2016-12-01
Domain patterns are simulated by the Landau-Lifshitz-Gilbert (LLG) equation with an easy-axis anisotropy. If the Gilbert damping is removed from the LLG equation, it merely describes the precession of magnetization with a ferromagnetic interaction. However, even without the damping, domains that look similar to those of scalar fields are formed, and they grow with time. It is demonstrated that the damping has no significant effects on domain growth laws and large-scale domain structure. In contrast, small-scale domain structure is affected by the damping. The difference in small-scale structure arises from energy dissipation due to the damping.
Effects of damping on mode shapes, volume 1
NASA Technical Reports Server (NTRS)
Gates, R. M.
1977-01-01
Displacement, velocity, and acceleration admittances were calculated for a realistic NASTRAN structural model of space shuttle for three conditions: liftoff, maximum dynamic pressure and end of solid rocket booster burn. The realistic model of the orbiter, external tank, and solid rocket motors included the representation of structural joint transmissibilities by finite stiffness and damping elements. Methods developed to incorporate structural joints and their damping characteristics into a finite element model of the space shuttle, to determine the point damping parameters required to produce realistic damping in the primary modes, and to calculate the effect of distributed damping on structural resonances through the calculation of admittances.
Modified thiol-ene networks: Tuning the glass transition temperature and energy damping capabilities
NASA Astrophysics Data System (ADS)
Sun, Ning; Rafailovich, Miriam; Gersappe, Dilip
2013-03-01
Utilizing thiol-ene `click' reactions, it is possible to produce thermoset networks that are highly homogeneous and thus exhibit enhanced energy damping capabilities. This talk will present recent results in the characterization and impact testing of modified thiol-ene networks with tunable physical properties. In particular, we synthesize ternary networks containing (1) bulky side-chain substituents, (2) isocyanate functionality, or (3) dual thiol components to improve control over the glass transition temperature and strain at break. In addition, we present results in the high-impact compression testing to demonstrate the energy damping capabilities of these materials.
A soft damping function for dispersion corrections with less overfitting.
Ucak, Umit V; Ji, Hyunjun; Singh, Yashpal; Jung, Yousung
2016-11-07
The use of damping functions in empirical dispersion correction schemes is common and widespread. These damping functions contain scaling and damping parameters, and they are usually optimized for the best performance in practical systems. In this study, it is shown that the overfitting problem can be present in current damping functions, which can sometimes yield erroneous results for real applications beyond the nature of training sets. To this end, we present a damping function called linear soft damping (lsd) that suffers less from this overfitting. This linear damping function damps the asymptotic curve more softly than existing damping functions, attempting to minimize the usual overcorrection. The performance of the proposed damping function was tested with benchmark sets for thermochemistry, reaction energies, and intramolecular interactions, as well as intermolecular interactions including nonequilibrium geometries. For noncovalent interactions, all three damping schemes considered in this study (lsd, lg, and BJ) roughly perform comparably (approximately within 1 kcal/mol), but for atomization energies, lsd clearly exhibits a better performance (up to 2-6 kcal/mol) compared to other schemes due to an overfitting in lg and BJ. The number of unphysical parameters resulting from global optimization also supports the overfitting symptoms shown in the latter numerical tests.
A soft damping function for dispersion corrections with less overfitting
NASA Astrophysics Data System (ADS)
Ucak, Umit V.; Ji, Hyunjun; Singh, Yashpal; Jung, Yousung
2016-11-01
The use of damping functions in empirical dispersion correction schemes is common and widespread. These damping functions contain scaling and damping parameters, and they are usually optimized for the best performance in practical systems. In this study, it is shown that the overfitting problem can be present in current damping functions, which can sometimes yield erroneous results for real applications beyond the nature of training sets. To this end, we present a damping function called linear soft damping (lsd) that suffers less from this overfitting. This linear damping function damps the asymptotic curve more softly than existing damping functions, attempting to minimize the usual overcorrection. The performance of the proposed damping function was tested with benchmark sets for thermochemistry, reaction energies, and intramolecular interactions, as well as intermolecular interactions including nonequilibrium geometries. For noncovalent interactions, all three damping schemes considered in this study (lsd, lg, and BJ) roughly perform comparably (approximately within 1 kcal/mol), but for atomization energies, lsd clearly exhibits a better performance (up to 2-6 kcal/mol) compared to other schemes due to an overfitting in lg and BJ. The number of unphysical parameters resulting from global optimization also supports the overfitting symptoms shown in the latter numerical tests.
The Development of a 3D Imaging Calorimeter of DAMPE for Cosmic Ray Physics
NASA Astrophysics Data System (ADS)
Zhang, Yunlong; Hu, Yiming; Feng, Changqing; Liu, Shubin; Wang, Chi; Zhang, Zhiyong; Wei, Yifeng; Huang, Guangshun
2016-07-01
The DArk Matter Particle Explorer (DAMPE) experiment began its on-orbit operations on December 17, 2015. The BGO Electromagnetic Calorimeter (BGO ECAL) of the DAMPE is a total absorption calorimeter that allows for a precise three-dimensional imaging of the shower shape. It provides a good energy resolution (<1%@200GeV) and high electron/hadron discrimination (>10^5). The calorimeter also provides a trigger capability to DAMPE. The BGO ECAL light collection system and electronics are designed to measure electromagnetic particles over a wide energy range, from 5 GeV to 10 TeV. An Engineering qualified model was built and tested using high energy electron and proton beams with energy ranging from 1 GeV to 250GeV. Some pre results will be introduced in this talk.
Relativity Damps OPEP in Nuclear Matter
NASA Astrophysics Data System (ADS)
Banerjee, Manoj K.
1998-09-01
Using a relativistic Dirac--Brueckner analysis the OPEP contribution to the ground state energy of nuclear matter is studied. In the study the pion is derivative-coupled. We find that the role of the tensor force in the saturation mechanism is substantially reduced compared to its dominant role in a usual nonrelativistic treatment. We show that the damping of derivative-coupled OPEP is actually due to the decrease of M*/M with increasing density. We point out that if derivative-coupled OPEP is the preferred form of nuclear effective Lagrangian nonrelativistic treatment of nuclear matter is in trouble. Lacking the notion of M* it cannot replicate the damping. We suggest an examination of the feasibility of using pseudoscalar coupled πN interaction before reaching a final conclusion about nonrelativistic treatment of nuclear matter.
Nonlinear Landau damping in the ionosphere
NASA Technical Reports Server (NTRS)
Kiwamoto, Y.; Benson, R. F.
1978-01-01
A model is presented to explain the non-resonant waves which give rise to the diffuse resonance observed near 3/2 f sub H by the Alouette and ISIS topside sounders, where f sub H is the ambient electron cyclotron frequency. In a strictly linear analysis, these instability driven waves will decay due to Landau damping on a time scale much shorter than the observed time duration of the diffuse resonance. Calculations of the nonlinear wave particle coupling coefficients, however, indicate that the diffuse resonance wave can be maintained by the nonlinear Landau damping of the sounder stimulated 2f sub H wave. The time duration of the diffuse resonance is determined by the transit time of the instability generated and nonlinearly maintained diffuse resonance wave from the remote short lived hot region back to the antenna. The model is consistent with the Alouette/ISIS observations, and clearly demonstrates the existence of nonlinear wave-particle interactions in the ionosphere.
Relativity damps OPEP in nuclear matter
Banerjee, M.K.
1998-06-01
Using a relativistic Dirac-Brueckner analysis the OPEP contribution to the ground state energy of nuclear matter is studied. In the study the pion is derivative-coupled. The author finds that the role of the tensor force in the saturation mechanism is substantially reduced compared to its dominant role in a usual nonrelativistic treatment. He shows that the damping of derivative-coupled OPEP is actually due to the decrease of M{sup *}/M with increasing density. He points out that if derivative-coupled OPEP is the preferred form of nuclear effective lagrangian nonrelativistic treatment of nuclear matter is in trouble. Lacking the notion of M{sup *} it cannot replicate the damping. He suggests an examination of the feasibility of using pseudoscalar coupled {pi}N interaction before reaching a final conclusion about nonrelativistic treatment of nuclear matter.
Enthalpy damping for the steady Euler equations
NASA Technical Reports Server (NTRS)
Jespersen, D. C.
1984-01-01
For inviscid steady flow problems where the enthalpy is constant at steady state, it was previously proposed to use the difference between the local enthalpy and the steady state enthalpy as a driving term to accelerate convergence of iterative schemes. This idea is analyzed, both on the level of the partial differential equation and on the level of a particular finite difference scheme. It is shown that for the two-dimensional unsteady Euler equations, a hyperbolic system with eigenvalues on the imaginary axis, there is no enthalpy damping strategy which moves all the eigenvalues into the open left half plane. For the numerical scheme, however, the analysis shows and examples verify that enthalpy damping is potentially effective in accelerating convergence to steady state.
Enthalpy damping for the steady Euler equations
NASA Technical Reports Server (NTRS)
Jespersen, D. C.
1985-01-01
For inviscid steady flow problems where the enthalpy is constant at steady state, it was previously proposed to use the difference between the local enthalpy and the steady state enthalpy as a driving term to accelerate convergence of iterative schemes. This idea is analyzed, both on the level of the partial differential equation and on the level of a particular finite difference scheme. It is shown that for the two-dimensional unsteady Euler equations, a hyperbolic system with eigenvalues on the imaginary axis, there is no enthalpy damping strategy which moves all the eigenvalues into the open left half plane. For the numerical scheme, however, the analysis shows and examples verify that enthalpy damping is potentially effective in accelerating convergence to steady state.
Utilising HVDC to damp power oscillations
Smed, T.; Andersson, G. . Dept. of Electric Power Systems)
1993-04-01
In this paper, damping of slow oscillations with active and reactive power modulation of HVDC-links is analyzed with the aim of gaining a physical insight into the problem. The analysis shows that active power modulation is efficient when applied to a short mass-scaled electrical distance from one of the swinging machines, and reactive power modulation is most efficient when there exists a well-defined power flow direction and the modulation is made at a point close to the electrical midpoint between the swinging machines. It is shown that the intuitively appealing feedback signals frequency and derivative of the voltage are appropriate for active and reactive power modulation, respectively. The impact of the constraints imposed by the HVDC equations are analyzed, and it is determined when the implicit reactive power modulation resulting from constant [gamma] control may be detrimental for the damping.
Pressurized fluid damping of nanoelectromechanical systems.
Svitelskiy, Oleksiy; Sauer, Vince; Liu, Ning; Cheng, Kar-Mun; Finley, Eric; Freeman, Mark R; Hiebert, Wayne K
2009-12-11
Interactions of nanoscale structures with fluids are of current interest both in the elucidation of fluid dynamics at these small scales, and in determining the ultimate performance of nanoelectromechanical systems outside of vacuum. We present a comprehensive study of nanomechanical damping in three gases (He, N2, CO2), and liquid CO2. Resonant dynamics in multiple devices of varying size and frequency is measured over 10 decades of pressure (1 mPa-20 MPa) using time-domain stroboscopic optical interferometry. The wide pressure range allows full exploration of the regions of validity of Newtonian and non-Newtonian flow damping models. Observing free molecular flow behavior extending above 1 atm, we find a fluid relaxation time model to be valid throughout, but not beyond, the non-Newtonian regime, and a Newtonian flow vibrating spheres model to be valid in the viscous limit.
Active Vibration Damping of Solar Arrays
NASA Astrophysics Data System (ADS)
Reinicke, Gunar; Baier, Horst; Grillebeck, Anton; Scharfeld, Frank; Hunger, Joseph; Abou-El-Ela, A.; Lohberg, Andreas
2012-07-01
Current generations of large solar array panels are lightweight and flexible constructions to reduce net masses. They undergo strong vibrations during launch. The active vibration damping is one convenient option to reduce vibration responses and limit stresses in facesheets. In this study, two actuator concepts are used for vibration damping. A stack interface actuator replaces a panel hold down and is decoupled from bending moments and shear forces. Piezoelectric patch actuators are used as an alternative, where the number, position and size of actuators are mainly driven by controllability analyses. Linear Quadratic Gaussian control is used to attenuate vibrations of selected mode shapes with both actuators. Simulations as well as modal and acoustic tests show the feasibility of selected actuator concepts.
Fluidic Technology Investigation - Suspension Damping Simulations
1977-01-01
IF (w (I LT’ CVM)~4$1 IF ( Wrf 1 0 i CmpY MX2)V?1112wW~ CALL ORPArIP:(Pcx) pP,i.,IERR) .......-or pi i v~,R4p CAlLA (QAI)Rr7,4,?,T.ERR) T F Z (I ~LT C V...Damper Damping Devices Suspension Systems Shock Absorbers Adaptive Suspension Systems Hydro -Fluidics 20. ABSTRACT (Continue on reverse side if necessary
Robot vibration control using inertial damping forces
NASA Technical Reports Server (NTRS)
Lee, Soo Han; Book, Wayne J.
1991-01-01
This paper concerns the suppression of the vibration of a large flexible robot by inertial forces of a small robot which is located at the tip of the large robot. A controller for generating damping forces to a large robot is designed based on the two time scale model. The controller does not need to calculate the quasi-steady variables and is efficient in computation. Simulation results show the effectiveness of the inertial forces and the controller designed.
Robot vibration control using inertial damping forces
NASA Technical Reports Server (NTRS)
Lee, Soo Han; Book, Wayne J.
1989-01-01
The suppression is examined of the vibration of a large flexible robot by inertial forces of a small robot which is located at the tip of the large robot. A controller for generating damping forces to a large robot is designed based on the two time scale mode. The controller does not need to calculate the quasi-steady state variables and is efficient in computation. Simulation results show the effectiveness of the inertial forces and the controller designed.
Damping Materials, Finite Elements and Special Projects.
1982-12-01
made of either Haynes Alloy Number 188, Hastalloy C, Hastalloy X, or 17 - 4PH stainless steel Hastalloy X. Figure 1.26 is a schematic of the test...Motors Corporation (DDA), conducted a cooperative effort to characterize a DDA proprietary temperature damping material. The UDRI supplied two 17 - 4PH ...range at which the 17 - 4PH stainless steel beams could be tested. Serious discrepancy was noted between the structural loss factors derived from the room
Vibration Damping Response of Composite Materials
1991-04-01
to predict the vibration damping of these coposites. L lein Irauu, .. rii. se i-s foi tesi specimel gC-miLtrics oSl0y, so that - material...manner that the strain in the x direction was determined. This development results in the transverse strain given as av (x,y,z) avO (x,y)ei~ t a 2wO(xy) ei
Collisional damping rates for plasma waves
NASA Astrophysics Data System (ADS)
Tigik, S. F.; Ziebell, L. F.; Yoon, P. H.
2016-06-01
The distinction between the plasma dynamics dominated by collisional transport versus collective processes has never been rigorously addressed until recently. A recent paper [P. H. Yoon et al., Phys. Rev. E 93, 033203 (2016)] formulates for the first time, a unified kinetic theory in which collective processes and collisional dynamics are systematically incorporated from first principles. One of the outcomes of such a formalism is the rigorous derivation of collisional damping rates for Langmuir and ion-acoustic waves, which can be contrasted to the heuristic customary approach. However, the results are given only in formal mathematical expressions. The present brief communication numerically evaluates the rigorous collisional damping rates by considering the case of plasma particles with Maxwellian velocity distribution function so as to assess the consequence of the rigorous formalism in a quantitative manner. Comparison with the heuristic ("Spitzer") formula shows that the accurate damping rates are much lower in magnitude than the conventional expression, which implies that the traditional approach over-estimates the importance of attenuation of plasma waves by collisional relaxation process. Such a finding may have a wide applicability ranging from laboratory to space and astrophysical plasmas.
Synchrosqueezed wavelet transform for damping identification
NASA Astrophysics Data System (ADS)
Mihalec, Marko; Slavič, Janko; Boltežar, Miha
2016-12-01
Synchrosqueezing is a procedure for improving the frequency localization of a continuous wavelet transform. This research focuses on using a synchrosqueezed wavelet transform (SWT) to determine the damping ratios of a vibrating system using a free-response signal. While synchrosqueezing is advantageous due to its localisation in the frequency, damping identification with the original SWT is not sufficiently accurate. Here, the synchrosqueezing was researched in detail, and it was found that an error in the frequency occurs as a result of the numerical calculation of the preliminary frequencies. If this error were to be compensated, a better damping identification would be expected. To minimize the frequency-shift error, three different strategies are investigated: the scale-dependent coefficient method, the shifted-coefficient method and the autocorrelated-frequency method. Furthermore, to improve the SWT, two synchrosqueezing criteria are introduced: the average SWT and the proportional SWT. Finally, the proposed modifications are tested against close modes and the noise in the signals. It was numerically and experimentally confirmed that the SWT with the proportional criterion offers better frequency localization and performs better than the continuous wavelet transform when tested against noisy signals.
Active damping of the SOFIA Telescope assembly
NASA Astrophysics Data System (ADS)
Keas, Paul J.; Dunham, Edward; Lampater, Ulrich; Pfüller, Enrico; Teufel, Stefan; Roeser, Hans-Peter; Wiedemann, Manuel; Wolf, Jürgen
2012-09-01
The NASA/DLR Stratospheric Observatory for Infrared Astronomy (SOFIA) employs a 2.5-meter reflector telescope in a Boeing 747SP. The telescope is housed in an open cavity and is subjected to aeroacoustic and inertial disturbances in flight. To meet pointing requirements, SOFIA must achieve a pointing stability of approximately 0.5 arcseconds RMS. An active damping control system is being developed for SOFIA to reduce image jitter and image degradation due to resonance of the telescope assembly. Our paper discusses the history of the active damping design for SOFIA, from early concepts to the current implementation which has recently completed a ground and flight testing for proof-of-concept. We describe some milestones in the analysis and testing of the telescope assembly which guided the development of the vibration control system. The control synthesis approach and current implementation of the active damping control system is presented. Finally, we summarize the performance observed in early flight tests and the steps that are currently foreseen to completing the development of this system.
Random Response of Linear Hysteretic Damping
Floris, Claudio
2008-07-08
The probabilistic characterization of the response of a single-degree-of-freedom (SDOF) oscillator with linear hysteretic damping excited by ground motion described by zero mean stationary Gaussian processes is achieved by profiting from a steady-state solution of the motion equation, valid when the excitation is given by the superposition of harmonics. The model of linear hysteretic damping has been introduced to fit damping mechanisms in which the dissipation rate is independent of frequency, and mathematically it is described by the Hilbert transform of the response. Though this model is debated since it violates the principle of causality, its intrinsic simplicity makes it preferable to other models. The steady-state solution of the motion equation proposed in this paper allows a closed form evaluation of the respone mean square value. However, the numerical examples show that this quantity is affected by the mechanism of energy dissipation only when this is large. On the contrary, for a low capacity of dissipation the response mean square value is rather insensitive to the dissipation mechanism.
Nembach, Hans T; Shaw, Justin M; Boone, Carl T; Silva, T J
2013-03-15
We demonstrate a strong dependence of the effective damping on the nanomagnet size and the particular spin-wave mode that can be explained by the theory of intralayer transverse-spin pumping. The effective Landau-Lifshitz damping is measured optically in individual, isolated nanomagnets as small as 100 nm. The measurements are accomplished by use of a novel heterodyne magneto-optical microwave microscope with unprecedented sensitivity. Experimental data reveal multiple standing spin-wave modes that we identify by use of micromagnetic modeling as having either localized or delocalized character, described generically as end and center modes. The damping parameter of the two modes depends on both the size of the nanomagnet as well as the particular spin-wave mode that is excited, with values that are enhanced by as much as 40% relative to that measured for an extended film. Contrary to expectations based on the ad hoc consideration of lithography-induced edge damage, the damping for the end mode decreases as the size of the nanomagnet decreases. The data agree with the theory for damping caused by the flow of intralayer transverse spin currents driven by the magnetization curvature. These results have serious implications for the performance of nanoscale spintronic devices such as spin-torque-transfer magnetic random access memory.
Turner, Neil A
2016-05-01
Cardiac fibroblasts (CF) are well-established as key regulators of extracellular matrix (ECM) turnover in the context of myocardial remodelling and fibrosis. Recently, this cell type has also been shown to act as a sensor of myocardial damage by detecting and responding to damage-associated molecular patterns (DAMPs) upregulated with cardiac injury. CF express a range of innate immunity pattern recognition receptors (TLRs, NLRs, IL-1R1, RAGE) that are stimulated by a host of different DAMPs that are evident in the injured or remodelling myocardium. These include intracellular molecules released by necrotic cells (heat shock proteins, high mobility group box 1 protein, S100 proteins), proinflammatory cytokines (interleukin-1α), specific ECM molecules up-regulated in response to tissue injury (fibronectin-EDA, tenascin-C) or molecules modified by a pathological environment (advanced glycation end product-modified proteins observed with diabetes). DAMP receptor activation on fibroblasts is coupled to altered cellular function including changes in proliferation, migration, myofibroblast transdifferentiation, ECM turnover and production of fibrotic and inflammatory paracrine factors, which directly impact on the heart's ability to respond to injury. This review gives an overview of the important role played by CF in responding to myocardial DAMPs and how the DAMP/CF axis could be exploited experimentally and therapeutically.
The role of DAMPS in ALA-PDT for skin squamous cell carcinoma (Conference Presentation)
NASA Astrophysics Data System (ADS)
Wang, Xiuli; Wang, Xiaojie; Ji, Jie; Zhang, Haiyan; Shi, Lei
2016-03-01
5-Aminolevulinic acid mediated photodynamic therapy (ALA-PDT) is an established local approach for skin squamous cell carcinoma. It is believed that dangerous signals damage-associated molecular patterns (DAMPs) play an important role in ALA-PDT. In this study, we evaluated in vitro and in vivo expressions of major DAMPs, calreticulin (CRT), heat shock proteins 70 (HSP70), and high mobility group box 1 (HMGB1), induced by ALA-PDT using immunohistochemistry, western blot, and ELISA in a squamous cell carcinoma (SCC) mouse model. The role of DAMPs in the maturation of DCs potentiated by ALA-PDT-treated tumor cells was detected by FACS and ELISA. Our results showed that ALA-PDT enhanced the expression of CRT, HSP70, and HMGB1. These induced DAMPs played an important role in activating DCs by PDT-treated tumor cells, including phenotypic maturation (upregulation of surface expression of MHC-II, CD80, and CD86) and functional maturation (enhanced capability to secrete IFN-γ and IL-12). Furthermore, injecting ALA-PDT-treated tumor cells into naïve mice resulted in complete protection against cancer cells of the same origin. Our findings indicate that ALA-PDT can upregulate DAMPs and enhance tumor immunogenicity, providing a promising strategy for inducing a systemic anticancer immune response.
The in-plane anisotropic magnetic damping of ultrathin epitaxial Co{sub 2}FeAl film
Qiao, Shuang; Yan, Wei; Nie, Shuaihua; Zhao, Jianhua; Zhang, Xinhui
2015-08-15
The in-plane orientation-dependent effective damping of ultrathin Co{sub 2}FeAl film epitaxially grown on GaAs(001) substrate by molecular beam epitaxy (MBE) has been investigated by employing the time-resolved magneto-optical Kerr effect (TR-MOKE) measurements. It is found that the interface-induced uniaxial anisotropy is favorable for precession response and the anisotropy of precession frequency is mainly determined by this uniaxial anisotropy, while the magnetic relaxation time and damping factor exhibit the fourfold anisotropy at high-field regime. The field-independent anisotropic damping factor obtained at high fields indicates that the effective damping shows an intrinsic fourfold anisotropy for the epitaxial Co{sub 2}FeAl thin films.
Discrete-layered damping model of multilayer plate with account of internal damping
NASA Astrophysics Data System (ADS)
Paimushin, V. N.; Gazizullin, R. K.
2016-11-01
Construction of discrete-layered damping model of multilayer plate in small displacement and deformations with account of internal damping of layers of Thompson- Kelvin-Voight model is presented. Based on derived equations, analytical solution is given to the static damping problem of simply supported single-layer rectangular plate subjected to uniformly distributed pressure, which is applied to one of its boundary planes. Convergence to the three-dimensional case is analysed for the obtained solution with respect to the dependence on dimension of mesh in the thickness direction of plate. For thin plates, dimension reduction of the formulated problem is set on the basis of simplifying hypothesis applied for each layer.
Delay-Independent L2 Stability of Four-Channel Bilateral Teleoperators with Damping Injection
NASA Astrophysics Data System (ADS)
Tumerdem, Ugur; Ohnishi, Kouhei
This paper presents an augmented four channel teleoperation architecture with local damping injection, which renders the teleoperation system L2 stable independent of time delay. It is well known that four channel teleoperation architecture, which is based on the transmission of force and position measurements of both the master and the slave robots, provides perfect transparency, when there is no time delay between the robots. In the presence of delay, four channel systems are not stable and they can not provide transparency. With damping injection, stability is guaranteed independent of the size of the delay, as long as it is constant, and furthermore better transparency with high frequency force feedback can be realized. This is an improvement over conventional methods. As transparency and stability are two conflicting goals, there is a tradeoff that a constant damping is felt in free motion. In this paper stability and transparency analyses are presented and the validity of the method is also confirmed with experiments.
Damped and thermal motion of large, laser-aligned molecules in droplet beams
Starodub, D; Doak, B; Schmidt, K; Weierstall, U; Wu, J; Spence, J; Howells, M; Marcus, M; Shapiro, D; Barty, A; Chapman, H
2005-09-29
We consider a monodispersed Rayleigh droplet beam of water droplets doped with proteins. An intense infrared laser is used to align these droplets. The arrangement has been proposed for electron and X-ray diffraction studies of proteins which are difficult to crystallize. This paper considers the effect of thermal fluctuations on the angular spread of alignment in thermal equilibrium, and relaxation phenomena, particularly the damping of oscillations excited as the molecules enter the field. The possibility of adiabatic alignment is also considered. We find that damping times in high pressure gas cell as used in X-ray diffraction experiments are short compared to the time taken for molecules to traverse the beam, and that a suitably shaped field might be used for electron diffraction experiments in vacuum to provide adiabatic alignment, thus obviating the need for a damping gas cell.
Inhomogeneous and intrinsic damping of giant dipole resonance in hot rotating nuclei with A ~ 150
NASA Astrophysics Data System (ADS)
Chakrabarty, D. R.; Datar, V. M.; Kumar, Suresh; Mirgule, E. T.; Mitra, A.; Nanal, V.; Pillay, R. G.; Rout, P. C.
2010-05-01
High-energy gamma rays in the range of ~4-28 MeV were measured in the reaction 28Si+124Sn at E(28Si) ~ 185 MeV in coincidence with low-energy gamma ray multiplicities and evaporation residues. The centroid energy and width of the giant dipole resonance were extracted for various multiplicity windows from the statistical model analysis. These extracted widths, along with those from an earlier measurement at E(28Si) ~ 149 MeV, show a discrepancy with the results of a calculation under the thermal shape fluctuation model which describes the inhomogeneous damping of the resonance. An empirical form of the temperature and angular momentum dependence of the width, describing the data at both the beam energies, has been derived. The present results suggest that the contributions from both the inhomogeneous damping and the intrinsic collisional damping processes should be included.
The Frequency and Damping of Soil-Structure Systems with Embedded Foundation
Ghannad, M. Ali; Rahmani, Mohammad T.; Jahankhah, Hossein
2008-07-08
The effect of foundation embedment on fundamental period and damping of buildings has been the title of several researches in three past decades. A review of the literature reveals some discrepancies between proposed formulations for dynamic characteristics of soil-embedded foundation-structure systems that raise the necessity of more investigation on this issue. Here, first a set of approximate polynomial equations for soil impedances, based on numerical data calculated from well known cone models, are presented. Then a simplified approach is suggested to calculate period and damping of the whole system considering soil medium as a viscoelastic half space. The procedure includes both material and radiation damping while frequency dependency of soil impedance functions is not ignored. Results show that soil-structure interaction can highly affect dynamic properties of system. Finally the results are compared with one of the commonly referred researches.
Air damping of atomically thin MoS{sub 2} nanomechanical resonators
Lee, Jaesung; Wang, Zenghui; Feng, Philip X.-L.; He, Keliang; Shan, Jie
2014-07-14
We report on experimental measurement of air damping effects in high frequency nanomembrane resonators made of atomically thin molybdenum disulfide (MoS{sub 2}) drumhead structures. Circular MoS{sub 2} nanomembranes with thickness of monolayer, few-layer, and multi-layer up to ∼70 nm (∼100 layers) exhibit intriguing pressure dependence of resonance characteristics. In completely covered drumheads, where there is no immediate equilibrium between the drum cavity and environment, resonance frequencies and quality (Q) factors strongly depend on environmental pressure due to bulging of the nanomembranes. In incompletely covered drumheads, strong frequency shifts due to compressing-cavity stiffening occur above ∼200 Torr. The pressure-dependent Q factors are limited by free molecule flow (FMF) damping, and all the mono-, bi-, and tri-layer devices exhibit lower FMF damping than thicker, conventional devices do.
NASA Technical Reports Server (NTRS)
Sutton, M. A.; Davis, P. K.
1976-01-01
Numerical solutions of the governing equations of motion of a liquid squeeze film damped forced vibration system were carried out to examine the feasibility of using a liquid squeeze film to cushion and protect large structures, such as buildings, located in areas of high seismic activity. The mathematical model used was that for a single degree of freedom squeeze film damped spring mass system. The input disturbance was simulated by curve fitting actual seismic data with an eleventh order Lagranging polynomial technique. Only the normal component of the seismic input was considered. The nonlinear, nonhomogeneous governing differential equation of motion was solved numerically to determine the transmissibility over a wide range of physical parameters using a fourth-order Runge-Kutta technique. It is determined that a liquid squeeze film used as a damping agent in a spring-mass system can significantly reduce the response amplitude for a seismic input disturbance.
Non-Linear Slosh Damping Model Development and Validation
NASA Technical Reports Server (NTRS)
Yang, H. Q.; West, Jeff
2015-01-01
Propellant tank slosh dynamics are typically represented by a mechanical model of spring mass damper. This mechanical model is then included in the equation of motion of the entire vehicle for Guidance, Navigation and Control (GN&C) analysis. For a partially-filled smooth wall propellant tank, the critical damping based on classical empirical correlation is as low as 0.05%. Due to this low value of damping, propellant slosh is potential sources of disturbance critical to the stability of launch and space vehicles. It is postulated that the commonly quoted slosh damping is valid only under the linear regime where the slosh amplitude is small. With the increase of slosh amplitude, the critical damping value should also increase. If this nonlinearity can be verified and validated, the slosh stability margin can be significantly improved, and the level of conservatism maintained in the GN&C analysis can be lessened. The purpose of this study is to explore and to quantify the dependence of slosh damping with slosh amplitude. Accurately predicting the extremely low damping value of a smooth wall tank is very challenging for any Computational Fluid Dynamics (CFD) tool. One must resolve thin boundary layers near the wall and limit numerical damping to minimum. This computational study demonstrates that with proper grid resolution, CFD can indeed accurately predict the low damping physics from smooth walls under the linear regime. Comparisons of extracted damping values with experimental data for different tank sizes show very good agreements. Numerical simulations confirm that slosh damping is indeed a function of slosh amplitude. When slosh amplitude is low, the damping ratio is essentially constant, which is consistent with the empirical correlation. Once the amplitude reaches a critical value, the damping ratio becomes a linearly increasing function of the slosh amplitude. A follow-on experiment validated the developed nonlinear damping relationship. This discovery can
Molecular Dynamics Simulation of Squeeze-Film Damping in the Free-Molecule Regime
NASA Astrophysics Data System (ADS)
Hong, Gang; Ye, Wenjing
2008-12-01
A molecular dynamics (MD) simulation tool was developed for the prediction of squeeze-film damping on a micro beam/plate resonator oscillating in a highly rarefied gas environment. This tool was then employed to identify important parameters that characterize the damping and to study the dependence of the quality factor of the resonator on these parameters. Particular focus is on air flows that are in the free-molecule regime. An excellent agreement between the predicted quality factor and the measurement data in the low pressure range has been achieved and favorable comparisons with other models have also been demonstrated.
Experimental and Numerical Assessment of Vibro-Acoustic Behavior of Rubber-Damped Railway Wheels
NASA Astrophysics Data System (ADS)
Pešek, Luděk; Půst, Ladislav
The reduction of noise and vibrations is very important task in many industrial and transport applications. The sources of intensive noise and vibrations are also tram and railway wheels at high speeds. Therefore the modern types of steel railway wheels contain the visco-elastic paddings. The first problem treated in this contribution is concerned with the theoretical and experimental investigation of the thermo-mechanical properties of rubber-like damping elements loaded with prestress by harmonic force. The dynamic modal and spectral properties of the whole railway wheel with damping elements will be investigated by the 3-D FEM model as the second problem.
Interface electronic complexes and Landau damping of magnons in ultrathin magnets.
Buczek, Paweł; Ernst, Arthur; Sandratskii, Leonid M
2011-04-15
The damping of magnons in ultrathin metallic magnets is studied from first-principles. We contrast Fe/Cu(100) and Fe/W(110) systems for which the influence of the substrate on the magnon life time differs strongly. We introduce the concept of Landau map in momentum space to assess the role of different electronic states in the attenuation. The formation of electronic complexes localized at the film-substrate interface leads to hot spots in the Landau maps and enhances the damping. This finding allows tuning the attenuation of high-frequency magnetization dynamics in nanostructures.
NASA Astrophysics Data System (ADS)
Schoerling, Daniel; Antoniou, Fanouria; Bernhard, Axel; Bragin, Alexey; Karppinen, Mikko; Maccaferri, Remo; Mezentsev, Nikolay; Papaphilippou, Yannis; Peiffer, Peter; Rossmanith, Robert; Rumolo, Giovanni; Russenschuck, Stephan; Vobly, Pavel; Zolotarev, Konstantin
2012-04-01
To achieve high luminosity at the collision point of the Compact Linear Collider (CLIC), the normalized horizontal and vertical emittances of the electron and positron beams must be reduced to 500 and 4 nm before the beams enter the 1.5 TeV linear accelerators. An effective way to accomplish ultralow emittances with only small effects on the electron polarization is using damping rings operating at 2.86 GeV equipped with superconducting wiggler magnets. This paper describes a technical design concept for the CLIC damping wigglers.
A large-scale magnetic shield with 10{sup 6} damping at millihertz frequencies
Altarev, I.; Bales, M.; Fierlinger, K.; Fierlinger, P.; Kuchler, F.; Marino, M. G.; Niessen, B.; Petzoldt, G.; Singh, J. T.; Stoepler, R.; Stuiber, S.; Sturm, M.; Taubenheim, B.; Beck, D. H.; Chupp, T.; Lins, T.; Schläpfer, U.; Schnabel, A.; Voigt, J.
2015-05-14
We present a magnetically shielded environment with a damping factor larger than 1 × 10{sup 6} at the mHz frequency regime and an extremely low field and gradient over an extended volume. This extraordinary shielding performance represents an improvement of the state-of-the-art in the difficult regime of damping very low-frequency distortions by more than an order of magnitude. This technology enables a new generation of high-precision measurements in fundamental physics and metrology, including searches for new physics far beyond the reach of accelerator-based experiments. We discuss the technical realization of the shield with its improvements in design.
Computational Issues in Damping Identification for Large Scale Problems
NASA Technical Reports Server (NTRS)
Pilkey, Deborah L.; Roe, Kevin P.; Inman, Daniel J.
1997-01-01
Two damping identification methods are tested for efficiency in large-scale applications. One is an iterative routine, and the other a least squares method. Numerical simulations have been performed on multiple degree-of-freedom models to test the effectiveness of the algorithm and the usefulness of parallel computation for the problems. High Performance Fortran is used to parallelize the algorithm. Tests were performed using the IBM-SP2 at NASA Ames Research Center. The least squares method tested incurs high communication costs, which reduces the benefit of high performance computing. This method's memory requirement grows at a very rapid rate meaning that larger problems can quickly exceed available computer memory. The iterative method's memory requirement grows at a much slower pace and is able to handle problems with 500+ degrees of freedom on a single processor. This method benefits from parallelization, and significant speedup can he seen for problems of 100+ degrees-of-freedom.
Chiral damping in magnetic domain-walls (Conference Presentation)
NASA Astrophysics Data System (ADS)
Jue, Emilie; Safeer, C. K.; Drouard, Marc; Lopez, Alexandre; Balint, Paul; Buda-Prejbeanu, Liliana; Boulle, Olivier; Auffret, Stéphane; Schuhl, Alain; Manchon, Aurélien; Miron, Ioan Mihai; Gaudin, Gilles
2016-10-01
The Dzyaloshinskii-Moriya interaction is responsible for chiral magnetic textures (skyrmions, spin spiral structures, …) in systems with structural inversion asymmetry and high spin-orbit coupling. It has been shown that the domain wall (DW) dynamics in such materials can be explained by chiral DWs with (partly or fully) Néel structure, whose stability derives from an interfacial DMI [1]. In this work, we show that DMI is not the only effect inducing chiral dynamics and demonstrate the existence of a chiral damping [2]. This result is supported by the study of the asymmetry induced by an in-plane magnetic field on field induced domain wall motion in perpendicularly magnetized asymmetric Pt/Co/Pt trilayers. Whereas the asymmetry of the DW motion is consistent with the spatial symmetries expected with the DMI, we show that this asymmetry cannot be attributed to an effective field but originates from a purely dissipative mechanism. The observation of chiral damping, not only enriches the spectrum of physical phenomena engendered by the SIA, but since it can coexist with DMI it is essential for conceiving DW and skyrmion devices. [1] A. Thiaville, et al., EPL 100, 57002 (2012) [2] E. Jué, et al., Nat. Mater., in press (doi: 10.1038/nmat4518)
RESONANTLY DAMPED PROPAGATING KINK WAVES IN LONGITUDINALLY STRATIFIED SOLAR WAVEGUIDES
Soler, R.; Verth, G.; Goossens, M.; Terradas, J.
2011-07-20
It has been shown that resonant absorption is a robust physical mechanism for explaining the observed damping of magnetohydrodynamic kink waves in the solar atmosphere due to naturally occurring plasma inhomogeneity in the direction transverse to the direction of the magnetic field. Theoretical studies of this damping mechanism were greatly inspired by the first observations of post-flare standing kink modes in coronal loops using the Transition Region and Coronal Explorer. More recently, these studies have been extended to explain the attenuation of propagating coronal kink waves observed by the Coronal Multi-Channel Polarimeter. In the present study, for the first time we investigate the properties of propagating kink waves in solar waveguides including the effects of both longitudinal and transverse plasma inhomogeneity. Importantly, it is found that the wavelength is only dependent on the longitudinal stratification and the amplitude is simply a product of the two effects. In light of these results the advancement of solar atmospheric magnetoseismology by exploiting high spatial/temporal resolution observations of propagating kink waves in magnetic waveguides to determine the length scales of the plasma inhomogeneity along and transverse to the direction of the magnetic field is discussed.
Dynamic Stall in Pitching Airfoils: Aerodynamic Damping and Compressibility Effects
NASA Astrophysics Data System (ADS)
Corke, Thomas C.; Thomas, Flint O.
2015-01-01
Dynamic stall is an incredibly rich fluid dynamics problem that manifests itself on an airfoil during rapid, transient motion in which the angle of incidence surpasses the static stall limit. It is an important element of many manmade and natural flyers, including helicopters and supermaneuverable aircraft, and low-Reynolds number flapping-wing birds and insects. The fluid dynamic attributes that accompany dynamic stall include an eruption of vorticity that organizes into a well-defined dynamic stall vortex and massive excursions in aerodynamic loads that can couple with the airfoil structural dynamics. The dynamic stall process is highly sensitive to surface roughness that can influence turbulent transition and to local compressibility effects that occur at free-stream Mach numbers that are otherwise incompressible. Under some conditions, dynamic stall can result in negative aerodynamic damping that leads to limit-cycle growth of structural vibrations and rapid mechanical failure. The mechanisms leading to negative damping have been a principal interest of recent experiments and analysis. Computational fluid dynamic simulations and low-order models have not been good predictors so far. Large-eddy simulation could be a viable approach although it remains computationally intensive. The topic is technologically important owing to the desire to develop next-generation rotorcraft that employ adaptive rotor dynamic stall control.
Damping identification in frequency domain using integral method
NASA Astrophysics Data System (ADS)
Guo, Zhiwei; Sheng, Meiping; Ma, Jiangang; Zhang, Wulin
2015-03-01
A new method for damping identification of linear system in frequency domain is presented, by using frequency response function (FRF) with integral method. The FRF curve is firstly transformed to other type of frequency-related curve by changing the representations of horizontal and vertical axes. For the newly constructed frequency-related curve, integral is conducted and the area forming from the new curve is used to determine the damping. Three different methods based on integral are proposed in this paper, which are called FDI-1, FDI-2 and FDI-3 method, respectively. For a single degree of freedom (Sdof) system, the formulated relation of each method between integrated area and loss factor is derived theoretically. The numeral simulation and experiment results show that, the proposed integral methods have high precision, strong noise resistance and are very stable in repeated measurements. Among the three integral methods, FDI-3 method is the most recommended because of its higher accuracy and simpler algorithm. The new methods are limited to linear system in which modes are well separated, and for closely spaced mode system, mode decomposition process should be conducted firstly.
Active member bridge feedback control for damping augmentation
NASA Technical Reports Server (NTRS)
Chen, Gun-Shing; Lurie, Boris J.
1992-01-01
An active damping augmentation approach using active members in a structural system is described. The problem of maximizing the vibration damping in a lightly damped structural system is considered using the analogy of impedance matching between the load and source impedances in an electrical network. The proposed active damping augmentation approach therefore consists of finding the desired active member impedances that maximize the vibration damping, and designing a feedback control in order to achieve desired active member impedances. This study uses a bridge feedback concept that feeds back a combination of signals from sensors of the axial force and relative velocity across the active member to realize the desired active member impedance. The proposed active damping augmentation approach and bridge feedback concept were demonstrated on a three-longeron softly suspended truss structure.
Vibration control through passive constrained layer damping and active control
NASA Astrophysics Data System (ADS)
Lam, Margaretha J.; Inman, Daniel J.; Saunders, William R.
1997-05-01
To add damping to systems, viscoelastic materials (VEM) are added to structures. In order to enhance the damping effects of the VEM, a constraining layer is attached. When this constraining layer is an active element, the treatment is called active constrained layer damping (ACLD). Recently, the investigation of ACLD treatments has shown it to be an effective method of vibration suppression. In this paper, the treatment of a beam with a separate active element and passive constrained layer (PCLD) element is investigated. A Ritz- Galerkin approach is used to obtain discretized equations of motion. The damping is modeled using the GHM method and the system is analyzed in the time domain. By optimizing on the performance and control effort for both the active and passive case, it is shown that this treatment is capable of lower control effort with more inherent damping, and is therefore a better approach to damp vibration.
Research on damping properties optimization of variable-stiffness plate
NASA Astrophysics Data System (ADS)
Wen-kai, QI; Xian-tao, YIN; Cheng, SHEN
2016-09-01
This paper investigates damping optimization design of variable-stiffness composite laminated plate, which means fibre paths can be continuously curved and fibre angles are distinct for different regions. First, damping prediction model is developed based on modal dissipative energy principle and verified by comparing with modal testing results. Then, instead of fibre angles, the element stiffness and damping matrixes are translated to be design variables on the basis of novel Discrete Material Optimization (DMO) formulation, thus reducing the computation time greatly. Finally, the modal damping capacity of arbitrary order is optimized using MMA (Method of Moving Asymptotes) method. Meanwhile, mode tracking technique is employed to investigate the variation of modal shape. The convergent performance of interpolation function, first order specific damping capacity (SDC) optimization results and variation of modal shape in different penalty factor are discussed. The results show that the damping properties of the variable-stiffness plate can be increased by 50%-70% after optimization.
Dynamic analyses of viscoelastic dielectric elastomers incorporating viscous damping effect
NASA Astrophysics Data System (ADS)
Zhang, Junshi; Zhao, Jianwen; Chen, Hualing; Li, Dichen
2017-01-01
In this paper, based on the standard linear solid rheological model, a dynamics model of viscoelastic dielectric elastomers (DEs) is developed with incorporation of viscous damping effect. Numerical calculations are employed to predict the damping effect on the dynamic performance of DEs. With increase of damping force, the DEs show weak nonlinearity and vibration strength. Phase diagrams and Poincaré maps are utilized to detect the dynamic stability of DEs, and the results indicate that a transition from aperiodic vibration to quasi-periodic vibration occurs with enlargement of damping force. The resonance properties of DEs including damping effect are subsequently analyzed, demonstrating a reduction of resonant frequency and resonance peak with increase of damping force.
Landau damping in a dipolar Bose-Fermi mixture in the Bose-Einstein condensation (BEC) limit
NASA Astrophysics Data System (ADS)
Moniri, S. M.; Yavari, H.; Darsheshdar, E.
2016-12-01
By using a mean-field approximation which describes the coupled oscillations of condensate and noncondensate atoms in the collisionless regime, Landau damping in a dilute dipolar Bose-Fermi mixture in the BEC limit where Fermi superfluid is treated as tightly bounded molecules, is investigated. In the case of a uniform quasi-two-dimensional (2D) case, the results for the Landau damping due to the Bose-Fermi interaction are obtained at low and high temperatures. It is shown that at low temperatures, the Landau damping rate is exponentially suppressed. By increasing the strength of dipolar interaction, and the energy of boson quasiparticles, Landau damping is suppressed over a broader temperature range.
Nutation damping in viscoelastic tumbling rotators
NASA Astrophysics Data System (ADS)
Frouard, Julien; Efroimsky, Michael
2015-11-01
Presently, 138 asteroids show signs of being in non-principal spin states (Warner et al. 2009, updated September 2015). Such spin is often called `tumble' or `wobble'. The instantaneous rotation axis of a wobbling body performs nutation about the direction of the (conserved) angular-momentum vector. Incited by collisions and YORP, wobble is mitigated by internal dissipation due to the nutation-caused alternating stresses inside the asteroid.The knowledge of the timescale related to the damping of the nutation angle is complementary to the knowledge of the timescales associated with collisions and YORP. Previous evaluations of the nutation relaxation rate were based on an inherently inconsistent approach that may be called "Q-model". First, the elastic energy in a periodically deforming rotator was calculated in assumption of the deformation being elastic. Therefrom, the energy dissipation rate was determined by introducing an ad hoc quality factor Q. This ignored the fact that friction (and the ensuing existence of Q) is due to deviation from elasticity.We use the viscoelastic Maxwell model which naturally implies dissipation (as any other viscoelastic model would). In this approach, we compute the power and damping time for an oblate ellipsoid and a prism. Now, the viscosity assumes the role of the product μQ in the empirical Q-model, with μ being the rigidity. Contrarily to the Q-model, our model naturally gives a null dissipation for a shape tending to a sphere. We also explore when the constant part of the stress can be ignored in the derivation of the damping time. The neglect of prestressing turns out to be legitimate for the mean viscosity exceeding a certain threshold value.
Proceedings of Damping , Held in San Diego, California on 13 - 15 February 1991. Volume 1
1991-08-01
an Optima /3 digital controller capable of handling up to 32 inputs and 32 outputs. In the PACOSS experiment, the processor rpn the LOG/LTR control law...and as damping materials at high temperatures. Those materials could include the various vinyls, styrenes, PMMA, PEEK , PVC, polypropylenes
Survey for z>3 damped Ly alpha absorption systems: the evolution of neutral gas
NASA Technical Reports Server (NTRS)
Storrie-Lombardi, L. J.; Wolfe, A. M.
2000-01-01
We have completed spectroscopic observations using LRIS on the Keck 1 telescope of 30 very high redshift quasars, 11 selected for the presence of damped Ly alpha absorption systems and 19 with redshifts z>3.5 not previously surveyed for absorption systems.
DESIGN AND ANALYSIS OF AN FPGA-BASED ACTIVE FEEDBACK DAMPING SYSTEM
Xie, Zaipeng; Schulte, Mike; Deibele, Craig Edmond
2010-01-01
The Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory is a high-intensity proton-based accelerator that produces neutron beams for neutronscattering research. As the most powerful pulsed neutron source in the world, the SNS accelerator has experienced an unprecedented beam instability that has a wide bandwidth (0 to 300MHz) and fast growth time (10 to100 s). In this paper, we propose and analyze several FPGA-based designs for an active feedback damping system. This signal processing system is the first FPGA-based design for active feedback damping of wideband instabilities in high intensity accelerators. It can effectively mitigate instabilities in highintensity protons beams, reduce radiation, and boost the accelerator s luminosity performance. Unlike existing systems, which are designed using analog components, our FPGA-based active feedback damping system offers programmability while maintaining high performance. To meet the system throughput and latency requirements, our proposed designs are guided by detailed analysis of resource and performance tradeoffs. These designs are mapped onto a reconfigurable platform that includes Xilinx Virtex-II Pro FPGAs and high-speed analog-to-digital and digital-toanalog converters. Our results show that our FPGA-based active feedback damping system can provide increased flexibility and improved signal processing performance that are not feasible with existing analog systems.
Chickpea damping-off due to metalaxyl-resistant Pythium: An emerging disease in the Palouse
Technology Transfer Automated Retrieval System (TEKTRAN)
Legumes and large-seeded (Kabuli-type) chickpeas are highly vulnerable to Pythium damping-off when planted in cold, wet soil in the spring, due to their thin seed coat and copious seed exudates during germination. For decades, the preferred and only available seed treatment for reliable control of d...
Status of the SLC damping rings
Hutton, A.M.; Davies-White, W.A.; Delahaye, J.P.; Fieguth, T.H.; Hofmann, A.; Jager, J.; Kloeppel, P.K.; Lee, M.J.; Linebarger, W.A.; Rivkin, L.
1985-06-01
Electron beams of full design energy 1.21 GeV and nearly full design intensity 4 x 10/sup 10/ particles/pulse (design 5 x 10/sup 10/) have been extracted from the Stanford Linac and successfully stored in the electron damping ring. Beams of less intensity have been extracted from the ring and reinjected into the Linac. The present intensity limits are not thought to be fundamental. The operating experience with the electron ring and the status of the construction of the positron ring will be discussed. 11 refs., 1 fig., 2 tabs.
Bridge feedback for active damping augmentation
NASA Technical Reports Server (NTRS)
Chen, G.-S.; Lurie, B. J.
1990-01-01
A method is described for broadband damping augmentation of a structural system in which the active members (with feedback control) were developed such that their mechanical input impedance can be electrically adjusted to maximize the energy dissipation rate in the structural system. The active member consists of sensors, an actuator, and a control scheme. A mechanical/electrical analogy is described to model the passive structures and the active members in terms of their impedance representation. As a result, the problem of maximizing dissipative power is analogous to the problem of impedance matching in the electrical network. Closed-loop performance was demonstrated for single- and multiple-active-member controlled truss structure.
HVDC system control for damping subsynchronous oscillations
Piwko, R.J.; Larsen, E.V.
1982-07-01
A method for designing a supplemental subsynchronous damping control (SSDC) for an HVDC transmission system is described. The SSDC eliminates torsional instabilities caused by interaction between conventional HVDC controls and turbine-generator rotor torsional modes of vibration. Results of digital simulation used in the design process are compared with measurements made on an HVDC simulator. Results of both digital simulations and HVDC simulator tests which demonstrate SSDC performance are shown. This research and development effort was sponsored by EPRI under RP1425-1.
Radiation damping in closed expanding universes
NASA Astrophysics Data System (ADS)
Bernui, Armando
The dynamics of a coupled model (harmonic oscillator-relativistic scalar field) in Conformal Robertson-Walker (k = +1) spacetimes is investigated. The exact radiation-reaction equation of the source-including the retarded radiation terms due to the closed space geometry - is obtained and analyzed. A suitable family of Lyapunov functions is constructed to show that, if the spacetime expands monotonely, then the source's energy damps. A numerical simulation of this equation for expanding Universes, with and without Future Event Horizon, is performed.
System for damping vibrations in a turbine
Roberts, III, Herbert Chidsey; Johnson, Curtis Alan; Taxacher, Glenn Curtis
2015-11-24
A system for damping vibrations in a turbine includes a first rotating blade having a first ceramic airfoil, a first ceramic platform connected to the first ceramic airfoil, and a first root connected to the first ceramic platform. A second rotating blade adjacent to the first rotating blade includes a second ceramic airfoil, a second ceramic platform connected to the second ceramic airfoil, and a second root connected to the second ceramic platform. A non-metallic platform damper has a first position in simultaneous contact with the first and second ceramic platforms.
Test particle study of Landau damping of steepening magnetosonic waves
NASA Technical Reports Server (NTRS)
Matsumoto, H.; Barnes, A.
1982-01-01
A test particle study of Landau damping of steepening large-amplitude magnetosonic waves is made. Motions of test particles in a model of a steepening large-amplitude magnetosonic wave are traced. The kinetic energy change of the ensemble of test particles is computed to estimate the effective Landau damping rate of the magnetosonic wave. The numerical results are compared with the linear kinetic theory of Landau damping and interpreted in terms of a simple physical picture for particle trapping.
Critical damping constant of microwave-assisted magnetization switching
NASA Astrophysics Data System (ADS)
Yamaji, Toshiki; Arai, Hiroko; Matsumoto, Rie; Imamura, Hiroshi
2016-02-01
Microwave-assisted switching of magnetization in a perpendicularly magnetized disk was theoretically studied and special attention was paid to the effect of a damping constant on the switching field. We found that there exists a critical damping constant above which the switching field suddenly increases. We derived an analytical expression of the critical damping constant and showed that it decreases with increasing frequency of the microwave field, while it increases with increasing amplitude of the microwave field and the effective anisotropy field.
Existence and damping of toroidicity-induced Alfven eigenmodes
Mahajan, S.M.; Mett, R.R.
1991-12-01
A new method of analyzing the toroidicity-induced Alfven eigenmode (TAE) from kinetic theory is presented. The analysis includes electron parallel dynamics non-perturbatively, an effect which is found to strongly influence the character and damping of the TAE -- contrary to previous theoretical predictions. The normal electron Landau damping of the TAE is found to be higher than previously expected, and may explain recent experimental measurements of the TAE damping coefficient. 11 refs., 1 fig., 1 tab.
Confinement-dependent damping in a layered liquid.
de Beer, Sissi; van den Ende, Dirk; Mugele, Frieder
2011-03-23
We present atomic force microscopy (AFM) measurements of the conservative oscillatory solvation forces and the damping in confined films of octamethylcyclotetrasiloxane using small amplitude modulation with magnetic driving. We find distinct maxima in the interaction damping upon probing the discrete molecular layers, supporting earlier observations of the same phenomenon using AFM with an acoustic driving scheme. The maxima in the damping are located at the same tip-surface separation as the maxima in the conservative oscillatory interaction stiffness.
Elliptical Cavity Shape Optimization for Acceleration and HOM Damping
Haipeng Wang; Robert Rimmer; Genfa Wu
2005-05-01
We report a survey of center cell shapes developed for Superconducting Radio Frequency (SRF) multi-cell cavities for different projects. Using a set of normalized parameters, we compare the designs for different frequencies and particle velocities for the fundamental mode. Using dispersion curves of High Order Modes (HOM) (frequency verse phase advance) calculated by MAFIA for a single cell, we further optimize the cavity shape to avoid a light cone line crossing at the dangerous resonance frequencies determined by the beam bunch structure and eliminate the trapped (or high R/Q) modes with a low group velocity. We developed this formulation to optimize a 5-cell, 750MHz cavity shape, with good real-estate accelerating gradient and a strong HOM damping waveguide structure for the JLab 1MW ERL-FEL project.
Higher Order Mode Damping Simulation and Multipacting Analysis
NASA Astrophysics Data System (ADS)
Xiao, Liling
2015-10-01
When the beam is passing through an accelerator, it will generate higher order modes (HOM), which will affect to the beam quality especially in high energy accelerators such as International Linear accelerator Collider (ILC). In order to preserve the beam quality, HOM couplers are required to be installed to extract HOM power. Most of HOM couplers are 3D complex structures including small features. In addition, many physics process are involved in HOM coupler design such as RF heating and multipacting. Numerical modeling and simulation are essential for HOM coupler design and optimization for successful operation of high energy accelerators. SLAC developed 3D finite element parallel electromagnetics code suite ACE3P can be used to accelerator modeling with higher accuracy in fast turnaround time. In this paper, ACE3P application for HOM damping simulation and multipating analysis is presented for ILC 3.9 GHz crab cavity.
Damping element for reducing the vibration of an airfoil
Campbell, Christian X; Marra, John J
2013-11-12
An airfoil (10) is provided with a tip (12) having an opening (14) to a center channel (24). A damping element (16) is inserted within the opening of the center channel, to reduce an induced vibration of the airfoil. The mass of the damping element, a spring constant of the damping element within the center channel, and/or a mounting location (58) of the damping element within the center channel may be adjustably varied, to shift a resonance frequency of the airfoil outside a natural operating frequency of the airfoil.
Design and fabrication of integrally damped composite fan blades
NASA Astrophysics Data System (ADS)
Kosmatka, John B.; Appuhn, Geoffrey
1999-06-01
The design, analysis, and fabrication methods of embedding small viscoelastic damping patches into scaled composite fan blades is presented, where the goal is to improve the blade fatigue characteristics by increasing the damping in the chord-wise modes. This discussion concentrates on improving the damping levels in a research composite shell/titanium spar fan blade, developed by NASA-Lewis and Pratt and Whitney. First, the geometry and material definition of the existing composite fan blade are presented. Second, methods for sizing and locating the damping patch are presented based upon the modal strain energy method. The layered damping patch is composed of outer layers of a TEDLAR (or KAPTON) barrier film, which encompasses a viscoelastic damping material and loose- weave scrim cloth (creep protection). Two different patch sizes and locations are discussed to provide maximum damping as well as optimal damping. Finally, procedures are outlined for fabricating the integrally damped composite fan blades. Fabricated blades will be tested at the NASA-Lewis vacuum facility.
Dependence of Kambersky damping on Fermi level and spin orientation
Qu, T.; Victora, R. H.
2014-05-07
Kambersky damping represents the loss of magnetic energy from the electrons to the lattice through the spin orbit interaction. It is demonstrated that, for bcc Fe-based transition metal alloys, the logarithm of the energy loss is proportional to the density of states at the Fermi level. Both inter and intraband damping are calculated for spins at arbitrary angle to the previously examined [001] direction. Although the easy axis 〈100〉 shows isotropic relaxation and achieves the minimum damping value of 0.002, other directions, such as 〈110〉, show substantial anisotropic damping.
Significance of modeling internal damping in the control of structures
NASA Technical Reports Server (NTRS)
Banks, H. T.; Inman, D. J.
1992-01-01
Several simple systems are examined to illustrate the importance of the estimation of damping parameters in closed-loop system performance and stability. The negative effects of unmodeled damping are particularly pronounced in systems that do not use collocated sensors and actuators. An example is considered for which even the actuators (a tip jet nozzle and flexible hose) for a simple beam produce significant damping which, if ignored, results in a model that cannot yield a reasonable time response using physically meaningful parameter values. It is concluded that correct damping modeling is essential in structure control.
Damping of superfluid flow by a thermal cloud.
Meppelink, R; Koller, S B; Vogels, J M; Stoof, H T C; van der Straten, P
2009-12-31
One of the principal signatures of superfluidity is the frictionless flow of a superfluid through another substance. Here, we study the flow of a Bose-Einstein condensate through a thermal cloud and study its damping for different harmonic confinements and temperatures. The damping rates close to the collisionless regime are found to be in good agreement with Landau damping and become smaller for more homogeneous systems. In the hydrodynamic regime, we observe additional damping due to collisions, and we discuss the implications of these findings for superfluidity in this system.
Ishima, Rieko
2016-01-01
Abundant solvent nuclear spins, such as water protons in aqueous solution, cause radiation damping in NMR experiments. It is important to know how the effect of radiation damping appears in high-resolution protein NMR because macromolecular studies always require very high magnetic field strengths with a highly sensitive NMR probe that can easily cause radiation damping. Here, we show the behavior of water magnetization after a pulsed-field gradient (PFG) using nutation experiments at 900 MHz with a cryogenic probe: when water magnetization is located in the upper hemisphere (having +Z component, parallel to the external magnetic field), dephasing of the magnetization by a PFG effectively suppresses residual water magnetization in the transverse plane. In contrast, when magnetization is located in the lower hemisphere (having −Z component), the small residual transverse component remaining after a PFG is still sufficient to induce radiation damping. Based on this observation, we designed 1H-15N HSQC experiments in which water magnetization is maintained in the upper hemisphere, but not necessarily along Z, and compared them with the conventional experiments, in which water magnetization is inverted during the t1 period. The result demonstrates moderate gain of signal-to-noise ratio, 0–28%. Designing the experiments such that water magnetization is maintained in the upper hemisphere allows shorter pulses to be used compared to the complete water flip-back and, thereby, is useful as a building block of protein NMR pulse programs in solution. PMID:27524944
Hamiltonian and Lagrangian dynamics of charged particles including the effects of radiation damping
NASA Astrophysics Data System (ADS)
Qin, Hong; Burby, Joshua; Davidson, Ronald; Fisch, Nathaniel; Chung, Moses
2015-11-01
The effects of radiation damping (radiation reaction) on accelerating charged particles in modern high-intensity accelerators and high-intensity laser beams have becoming increasingly important. Especially for electron accelerators and storage rings, radiation damping is an effective mechanism and technique to achieve high beam luminosity. We develop Hamiltonian and Lagrangian descriptions of the classical dynamics of a charged particle including the effects of radiation damping in the general electromagnetic focusing channels encountered in accelerators. The direct connection between the classical Hamiltonian and Lagrangian theories and the more fundamental QED description of the synchrotron radiation process is also addressed. In addition to their theoretical importance, the classical Hamiltonian and Lagrangian theories of the radiation damping also enable us to numerically integrate the dynamics using advanced structure-preserving geometric algorithms. These theoretical developments can also be applied to runaway electrons and positrons generated during the disruption or startup of tokamak discharges. This research was supported by the U.S. Department of Energy (DE-AC02-09CH11466).
Ishima, Rieko
2015-09-01
Abundant solvent nuclear spins, such as water protons in aqueous solution, cause radiation damping in NMR experiments. It is important to know how the effect of radiation damping appears in high-resolution protein NMR because macromolecular studies always require very high magnetic field strengths with a highly sensitive NMR probe that can easily cause radiation damping. Here, we show the behavior of water magnetization after a pulsed-field gradient (PFG) using nutation experiments at 900 MHz with a cryogenic probe: when water magnetization is located in the upper hemisphere (having +Z component, parallel to the external magnetic field), dephasing of the magnetization by a PFG effectively suppresses residual water magnetization in the transverse plane. In contrast, when magnetization is located in the lower hemisphere (having -Z component), the small residual transverse component remaining after a PFG is still sufficient to induce radiation damping. Based on this observation, we designed (1)H-(15)N HSQC experiments in which water magnetization is maintained in the upper hemisphere, but not necessarily along Z, and compared them with the conventional experiments, in which water magnetization is inverted during the t1 period. The result demonstrates moderate gain of signal-to-noise ratio, 0-28%. Designing the experiments such that water magnetization is maintained in the upper hemisphere allows shorter pulses to be used compared to the complete water flip-back and, thereby, is useful as a building block of protein NMR pulse programs in solution.
Damping of Crank-Nicolson error oscillations.
Britz, D; Østerby, O; Strutwolf, J
2003-07-01
The Crank-Nicolson (CN) simulation method has an oscillatory response to sharp initial transients. The technique is convenient but the oscillations make it less popular. Several ways of damping the oscillations in two types of electrochemical computations are investigated. For a simple one-dimensional system with an initial singularity, subdivision of the first time interval into a number of equal subintervals (the Pearson method) works rather well, and so does division with exponentially increasing subintervals, where however an optimum expansion parameter must be found. This method can be computationally more expensive with some systems. The simple device of starting with one backward implicit (BI, or Laasonen) step does damp the oscillations, but not always sufficiently. For electrochemical microdisk simulations which are two-dimensional in space and using CN, the use of a first BI step is much more effective and is recommended. Division into subintervals is also effective, and again, both the Pearson method and exponentially increasing subintervals methods are effective here. Exponentially increasing subintervals are often considerably more expensive computationally. Expanding intervals over the whole simulation period, although capable of satisfactory results, for most systems will require more cpu time compared with subdivision of the first interval only.
Quasi-static magnetohydrodynamic turbulence at high Reynolds number
NASA Astrophysics Data System (ADS)
Delache, A.; Favier, B.; Godeferd, F. S.; Cambon, C.; Bos, W. J. T.
2011-12-01
We analyse the anisotropy of turbulence in an electrically conducting fluid submitted to a uniform magnetic field, for low magnetic Reynolds number, using the quasi-static approximation. In the linear limit, the kinetic energy of velocity components normal to the magnetic field decays faster than the kinetic energy of the component along the magnetic field (Moffatt, 1967). However, numerous numerical studies predict a different behaviour, wherein the final state is characterised by dominant horizontal energy. We investigate the corresponding nonlinear phenomenon using Direct Numerical Simulations (DNS) and spectral closures based on Eddy Damping Quasi-Normal Markovian (EDQNM) models. The initial temporal evolution of the decaying flow indicates that the turbulence is very similar to the so-called "two-and-a-half-dimensional" flow (Montgomery & Turner, 1982) which explains the observations in numerical studies. EDQNM models confirm this statement at higher Reynolds number.
Vibrational resonance in Duffing systems with fractional-order damping.
Yang, J H; Zhu, H
2012-03-01
The phenomenon of vibrational resonance (VR) is investigated in over- and under-damped Duffing systems with fractional-order damping. It is found that the factional-order damping can induce change in the number of the steady stable states and then lead to single- or double-resonance behavior. Compared with vibrational resonance in the ordinary systems, the following new results are found in the fractional-order systems. (1) In the overdamped system with double-well potential and ordinary damping, there is only one kind of single-resonance, whereas there are double-resonance and two kinds of single-resonance for the case of fractional-order damping. The necessary condition for these new resonance behaviors is the value of the fractional-order satisfies α > 1. (2) In the overdamped system with single-well potential and ordinary damping, there is no resonance, whereas there is a single-resonance for the case of fractional-order damping. The necessary condition for the new result is α > 1. (3) In the underdamped system with double-well potential and ordinary damping, there are double-resonance and one kind of single-resonance, whereas there are double-resonance and two kinds of single-resonance for the case of fractional-order damping. The necessary condition for the new single-resonance is α < 1. (4) In the underdamped system with single-well potential, there is at most a single-resonance existing for both the cases of ordinary and fractional-order damping. In the underdamped systems, varying the value of the fractional-order is equivalent to change the damping parameter for some cases.
NASA Astrophysics Data System (ADS)
Perfetto, S.; Rohlfing, J.; Infante, F.; Mayer, D.; Herold, S.
2016-09-01
Piezoelectric transducers can be used to harvest electrical energy from structural vibrations in order to power continuously operating condition monitoring systems local to where they operate. However, excessive vibrations can compromise the safe operation of mechanical systems. Therefore, absorbers are commonly used to control vibrations. With an integrated device, the mechanical energy that otherwise would be dissipated can be converted via piezoelectric transducers. Vibration absorbers are designed to have high damping factors. Hence, the integration of transducers would lead to a low energy conversion. Efficient energy harvesters usually have low damping capabilities; therefore, they are not effective for vibration suppression. Thus, the design of an integrated device needs to consider the two conflicting requirements on the damping. This study focuses on the development of a laboratory test rig with a host structure and a vibration absorber with tunable damping via an active relative velocity feedback. A voice coil actuator is used for this purpose. To overcome the passive damping effects of the back electromagnetic force a novel voltage feedback control is proposed, which has been validated both in simulation and experimentally. The aim of this study is to have a test rig ready for the introduction of piezo-transducers and available for future experimental evaluations of the damping effect on the effectiveness of vibration reduction and energy harvesting efficiency.
NASA Astrophysics Data System (ADS)
Audenino, A. L.; Calderale, P. M.
1996-12-01
The specific damping capacity of metallic materials is not linear and depends upon temperature, strain and strain rate. To evaluate the strain influence on material damping, homogeneous strain fields are recommended; these homogenous fields generally are not realized in damping measurement. In this paper the development of an automated experimental procedure is presented; the procedure is based on an improved method able to evaluate the material damping by sinusoidally exciting the specimen in uniaxal traction or compression with a frequency from 60 to 300 Hz. The test machine is a high frequency Amsler vibrofore and the experimental method is based on the acquisition of the decay signal when the machine excitation force has been removed. Signals are acquired by means of an A/D board installed in a personal computer; dedicated software has been created which performs complete analysis and directly provides graphic results. The method can discriminate between material damping and damping of the machine and fixtures. The resulting curves of the loss factor as a function of strain amplitude for three steels and two cast irons are presented.
An identification method for damping ratio in rotor systems
NASA Astrophysics Data System (ADS)
Wang, Weimin; Li, Qihang; Gao, Jinji; Yao, Jianfei; Allaire, Paul
2016-02-01
Centrifugal compressor testing with magnetic bearing excitations is the last step to assure the compressor rotordynamic stability in the designed operating conditions. To meet the challenges of stability evaluation, a new method combining the rational polynomials method (RPM) with the weighted instrumental variables (WIV) estimator to fit the directional frequency response function (dFRF) is presented. Numerical simulation results show that the method suggested in this paper can identify the damping ratio of the first forward and backward modes with high accuracy, even in a severe noise environment. Experimental tests were conducted to study the effect of different bearing configurations on the stability of rotor. Furthermore, two example centrifugal compressors (a nine-stage straight-through and a six-stage back-to-back) were employed to verify the feasibility of identification method in industrial configurations as well.
Local structural modeling for implementation of optimal active damping
NASA Astrophysics Data System (ADS)
Blaurock, Carl A.; Miller, David W.
1993-09-01
Local controllers are good candidates for active control of flexible structures. Local control generally consists of low order, frequency benign compensators using collocated hardware. Positive real compensators and plant transfer functions ensure that stability margins and performance robustness are high. The typical design consists of an experimentally chosen gain on a fixed form controller such as rate feedback. The resulting compensator performs some combination of damping (dissipating energy) and structural modification (changing the energy flow paths). Recent research into structural impedance matching has shown how to optimize dissipation based on the local behavior of the structure. This paper investigates the possibility of improving performance by influencing global energy flow, using local controllers designed using a global performance metric.
Decentralized H ∞ control for damping power system oscillations
NASA Astrophysics Data System (ADS)
Li, Guo-Jie; Lie, Tek Tjing
2012-03-01
Inter-area oscillations are serious problems to large-scale power systems. A decentralized H ∞ generator excitation controller of a power system is proposed to damp the inter-area oscillations and to enhance power system stability. The design procedure for a linear composite system is presented in terms of positive semi-definite solutions to modified algebraic inequalities. The resulting controller guarantees closed-loop stability, robustness and an H ∞-norm bound on disturbance attenuation even under uncertainties such as high frequency noise. The control is decentralized in the sense that the control of each generator depends on local information only. The effectiveness of the H ∞ controller is demonstrated through digital simulation studies on a two-machine power system.
Laser induced inverse Landau damping in metallic nanoparticles
NASA Astrophysics Data System (ADS)
Garcia, Martin E.; Castro, Alberto; Alonso, J. A.; Rubio, Angel
2002-03-01
We perform real space time-dependent density functional calculations to study the response of small metallic nanoparticles to femtosecond laser pulses. In particular, we analyze the role of screening effects for different laser pulse intensities and frequencies. Calculations are performed on sodium clusters using both the Jellium model and pseudopitentials Based on our results we predict that, if a pulse of sufficiently high intensity ( > 10^14 W/cm^2) excites a single-particle state of the nanoparticle, the response of the system involves both the single-particle- and the surface-plasmon states. We argue that this creation of plasmons from the decay of single-particle excitations, which can be viewed as the inverse of the well known Landau-damping effect, is related to the time-evolution of the screening of charge fluctuations.