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Complex rotation with internal dissipation. Applications to cosmic-dust alignment and to wobbling comets and asteroids  [PDF]
Michael Efroimsky,A. Lazarian,Vladislav Sidorenko
Physics , 2002,
Abstract: Neutron stars, asteroids, comets, cosmic-dust granules, spacecraft, as well as whatever other freely spinning body dissipate energy when they rotate about any axis different from principal. We discuss the internal-dissipation-caused relaxation of a freely precessing rotator towards its minimal-energy mode (mode that corresponds to the spin about the maximal-inertia axis). While the body nutates at some rate, the internal stresses and strains within the body oscillate at frequencies both higher and lower than this rate. The internal dissipation takes place mostly the second and higher harmonics. We discuss the application of our findings to asteroids. Regarding the comets, estimates show that the currently available angular resolution of spacecraft-based instruments makes it possible to observe wobble damping within year- or maybe even month-long spans of time. We also discuss cosmic-dust astrophysics; in particular, the role played by precession damping in the dust alignment. We show that this damping provides coupling of the grain's rotational and vibrational degrees of freedom; this entails occasional flipping of dust grains due to thermal fluctuations. During such a flip, grain preserves its angular momentum, but the direction of torques arising from H2 formation reverses. As a result, flipping grain will not rotate fast in spite of the action of uncompensated H2 formation torques. The grains get ``thermally trapped,'' and their alignment is marginal.
Internal dissipation of a polymer  [PDF]
J. M. Deutsch
Physics , 2010, DOI: 10.1103/PhysRevE.81.061804
Abstract: The dynamics of flexible polymer molecules are often assumed to be governed by hydrodynamics of the solvent. However there is considerable evidence that internal dissipation of a polymer contributes as well. Here we investigate the dynamics of a single chain in the absence of solvent to characterize the nature of this internal friction. We model the chains as freely hinged but with localized bond angles and 3-fold symmetric dihedral angles. We show that the damping is close but not identical to Kelvin damping, which depends on the first temporal and second spatial derivative of monomer position. With no internal potential between monomers, the magnitude of the damping is small for long wavelengths and weakly damped oscillatory time dependent behavior is seen for a large range of spatial modes. When the size of the internal potential is increased, such oscillations persist, but the damping becomes larger. However underdamped motion is present even with quite strong dihedral barriers for long enough wavelengths.
Inelastic Dissipation in a Freely Rotating Body. Application to Cosmic-Dust Alignment  [PDF]
A. Lazarian,M. Efroimsky
Physics , 1998, DOI: 10.1046/j.1365-8711.1999.02235.x
Abstract: Motivated by a recent study by Lazarian and Draine, which showed that a high degree of grain alignment of the paramagnetic dust is achievable if the rates of internal relaxation are controlled by the Barnett relaxation process, we undertake a study of an alternative mechanism of internal dissipation, namely, the inelastic dissipation of energy in oblate dust grains. We find that deformations at double frequency that were disregarded in earlier studies dominate the inelastic relaxation. Our results indicate that for grains with 4:1 axis ratio, or/and grains formed via agglomeration inelastic relaxation dominates the Barnett relaxation within large (a>0.1 micron) grains even when they rotate at thermal rate. For grains with axis ratio less than 1:2 the inelastic relaxation is dominant when grains rotate suprathermally.
Propagation and dissipation of internal tides in the Oslofjord  [PDF]
A. Staalstr?m,E. Aas,B. Liljebladh
Ocean Science (OS) & Discussions (OSD) , 2012, DOI: 10.5194/os-8-525-2012
Abstract: Observations of velocity, pressure, temperature and salinity in the inner Oslofjord have been analysed to provide new information about the relationships between internal tides generated by tidal currents across the Dr bak Sill and dissipation and diffusivity in the fjord. The most energetic vertical displacement of density surfaces inside the sill is associated with the first internal mode that has maximum amplitude around sill depth. The amplitude of the vertical displacement around sill depth correlates with the amplitude of the surface elevation, and, at a distance of 1 km inside the sill, the ratio between the amplitudes is 38, decreasing to 11 at a distance of 10 km. The greatest vertical displacements inside the sill, however, are found at 40 m depth. These latter internal waves are not associated with a first-mode internal tide, but are rather associated with higher internal modes controlled by stratification. The energy flux of the internal wave propagating from the Dr bak Sill into the inner fjord on the east side of the H ya Island is estimated to vary in the range 155–430 kW. This is the same order of magnitude as the estimated barotropic energy loss over the Dr bak Sill (250 kW), but only 4–10% of the total barotropic flux. Approximately 40–70% of the internal energy flux is lost within a distance of 10 km from the sill. The mean diffusivity below 90 m depth in this area (~20 cm2 s 1) is more than four times higher than in the rest of the fjord (~5 cm2 s 1 or less).
Propagation and dissipation of internal tides in the Oslofjord  [PDF]
A. Staalstr?m,E. Aas,B. Liljebladh
Ocean Science Discussions (OSD) , 2012, DOI: 10.5194/osd-9-315-2012
Abstract: Observations of velocity, pressure, temperature and salinity in the inner Oslofjord have been analysed. The data is used to provide new information about energy dissipation and mixing efficiency of internal tides generated by tidal current across the Dr bak Sill. The ratio between the observed amplitude of the internal wave in the pycnocline and the amplitude of the surface elevation is in the range 38 ± 6 at a distance of 1 km inside the sill and 11 ± 2 at 10 km. The energy flux of the internal wave propagating from the Dr bak Sill into the inner fjord is estimated to vary in the range 155–480 kW. This is the same order of magnitude as the estimated baroclinic energy loss (250 kW). Approximately 40–70% of this energy flux is dissipated within a distance of 7 km from the sill. The mixing efficiency is estimated to 0.09–0.11 based on energy density and group velocity, and 0.22–0.26 based on perturbation pressure and baroclinic velocity. These numbers are larger than earlier estimates. Only a fraction in the range 0.01–0.03 is transferred to work against buoyancy in the first basin within a distance of 7 km from the sill.
Harmonic Oscillator Potential to describe Internal Dissipation  [PDF]
Randall D. Peters
Physics , 2003,
Abstract: Assuming that a constant potential energy function has meaning for a dissipated harmonic oscillator, then an important issue is the time dependence of the turning points. Turning point studies demonstrate that the common model of external (viscous) damping fails to properly describe those many systems where structural (internal friction) damping is the most important source of dissipation. For internal friction damping, the better model of potential energy is one in which the function is not stationary.
Dissipation due to tunneling two-level systems in gold nanomechanical resonators  [PDF]
A. Venkatesan,K. J. Lulla,M. J. Patton,A. D. Armour,C. J. Mellor,J. R. Owers-Bradley
Physics , 2009, DOI: 10.1103/PhysRevB.81.073410
Abstract: We present measurements of the dissipation and frequency shift in nanomechanical gold resonators at temperatures down to 10 mK. The resonators were fabricated as doubly-clamped beams above a GaAs substrate and actuated magnetomotively. Measurements on beams with frequencies 7.95 MHz and 3.87 MHz revealed that from 30 mK to 500 mK the dissipation increases with temperature as $T^{0.5}$, with saturation occurring at higher temperatures. The relative frequency shift of the resonators increases logarithmically with temperature up to at least 400 mK. Similarities with the behavior of bulk amorphous solids suggest that the dissipation in our resonators is dominated by two-level systems.
Internal dissipation and heat leaks in quantum thermodynamic cycles  [PDF]
Luis A. Correa,José P. Palao,Daniel Alonso
Physics , 2015, DOI: 10.1103/PhysRevE.92.032136
Abstract: The direction of the steady-state heat currents across a generic quantum system connected to multiple baths may be engineered so as to realize virtually any thermodynamic cycle. In spite of their versatility such continuous energy-conversion systems are generally unable to operate at maximum efficiency due to non-negligible sources of irreversible entropy production. In this paper we introduce a minimal model of irreversible absorption chiller. We identify and characterize the different mechanisms responsible for its irreversibility, namely heat leaks and internal dissipation, and gauge their relative impact in the overall cooling performance. We also propose reservoir engineering techniques to minimize these detrimental effects. Finally, by looking into a known three-qubit embodiment of the absorption cooling cycle, we illustrate how our simple model may help to pinpoint the different sources of irreversibility naturally arising in more complex practical heat devices.
Oscillator damping with more than one mechanism of internal friction dissipation  [PDF]
Randall D. Peters
Physics , 2003,
Abstract: The author's modified Coulomb damping model has been generalized to accommodate internal friction that derives from several dissipation mechanisms acting simultaneously. Because of its fundamental nonlinear nature, internal friction damping causes the quality factor Q of an oscillator in free-decay to change in time. Examples are given which demonstrate reasonable agreement between theory and experiment.
Intermittency of internal wave shear and turbulence dissipation  [PDF]
Carl H. Gibson
Physics , 1999,
Abstract: It is crucial to understand the extreme intermittency of ocean and lake turbulence and turbulent mixing in order to estimate vertical fluxes of momentum, heat and mass by Osborn-Cox flux-dissipation methods. Vast undersampling errors occur by this method when intermittency is not taken into account. Oceanic turbulence increases intermittency as the result of a self-similar nonlinear cascade covering a wide range of scales, mostly horizontal. Extremely large intermittency factors Ie and Ic measured for Galactic and oceanic turbulence are in the range 3-7. These values are consistent with the third universal similarity hypothesis for turbulence of Kolmogorov (1962) and a length scale range over 3-7 decades from viscous or diffusive to buoyancy or Coriolis force domination, where the measured universal intermittency constant m_u = 0.44, Gibson (1991a), is a result of singularities in multifractal turbulence dissipation networks and their degeneration, Bershadskii and Gibson (1994). Nonlinear cascades of gravitational structure formation produce intermittent lognormal number densities of cosmological objects for the same reasons.
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