NASA Astrophysics Data System (ADS)
Huang, Biqin; Appelbaum, Ian
2010-12-01
Drift-diffusion theory—which fully describes charge transport in semiconductors—is also universally used to model transport of spin-polarized electrons in the presence of longitudinal electric fields. By transforming spin transit time into spin orientation with precession (a technique called the “Larmor clock”) in current-sensing vertical-transport intrinsic Si devices, we show that spin diffusion (and concomitant spin dephasing) can be greatly enhanced with respect to charge diffusion, in direct contrast to predictions of spin Coulomb-drag diffusion suppression.
NASA Technical Reports Server (NTRS)
Souder, P. A.; Casperson, D. E.; Crane, T. W.; Hughes, V. W.; Lu, D. C.; Yam, M. H.; Orth, H.; Reist, H. W.; Zu Putlitz, G.
1975-01-01
Experiments are described in which it proved possible to form the muonic helium atom by stopping polarized negative muons in a helium gas with a 2% xenon admixture at a pressure of 14 atm. The observed Larmor precession amplitudes are plotted against the gyromagnetic ratio for both muons and antimuons stopped in He + 2% Xe. In addition, a non-zero residual polarization of 0.06 plus or minus 0.01 was measured for muons stopped in pure helium gas, which corresponds to a depolarization factor of 18 plus or minus 3.
Precessing Ferromagnetic Needle Magnetometer.
Jackson Kimball, Derek F; Sushkov, Alexander O; Budker, Dmitry
2016-05-13
A ferromagnetic needle is predicted to precess about the magnetic field axis at a Larmor frequency Ω under conditions where its intrinsic spin dominates over its rotational angular momentum, Nℏ≫IΩ (I is the moment of inertia of the needle about the precession axis and N is the number of polarized spins in the needle). In this regime the needle behaves as a gyroscope with spin Nℏ maintained along the easy axis of the needle by the crystalline and shape anisotropy. A precessing ferromagnetic needle is a correlated system of N spins which can be used to measure magnetic fields for long times. In principle, by taking advantage of rapid averaging of quantum uncertainty, the sensitivity of a precessing needle magnetometer can far surpass that of magnetometers based on spin precession of atoms in the gas phase. Under conditions where noise from coupling to the environment is subdominant, the scaling with measurement time t of the quantum- and detection-limited magnetometric sensitivity is t^{-3/2}. The phenomenon of ferromagnetic needle precession may be of particular interest for precision measurements testing fundamental physics. PMID:27232012
Precessing Ferromagnetic Needle Magnetometer
NASA Astrophysics Data System (ADS)
Jackson Kimball, Derek F.; Sushkov, Alexander O.; Budker, Dmitry
2016-05-01
A ferromagnetic needle is predicted to precess about the magnetic field axis at a Larmor frequency Ω under conditions where its intrinsic spin dominates over its rotational angular momentum, N ℏ≫I Ω (I is the moment of inertia of the needle about the precession axis and N is the number of polarized spins in the needle). In this regime the needle behaves as a gyroscope with spin N ℏ maintained along the easy axis of the needle by the crystalline and shape anisotropy. A precessing ferromagnetic needle is a correlated system of N spins which can be used to measure magnetic fields for long times. In principle, by taking advantage of rapid averaging of quantum uncertainty, the sensitivity of a precessing needle magnetometer can far surpass that of magnetometers based on spin precession of atoms in the gas phase. Under conditions where noise from coupling to the environment is subdominant, the scaling with measurement time t of the quantum- and detection-limited magnetometric sensitivity is t-3 /2. The phenomenon of ferromagnetic needle precession may be of particular interest for precision measurements testing fundamental physics.
Calibration of a Larmor clock for tunneling time experiments
NASA Astrophysics Data System (ADS)
Ramos, Jesus; Potnis, Shreyas; Spierings, David; Ebadi, Sapehr; Steinberg, Aephraim
2016-05-01
How much time does it take for a particle to tunnel? This has been a controversial question since the early times of quantum mechanics. The debate stems mainly from the inability to measure time directly. One proposal to measure the tunnelling time is the Larmor clock, in which the spin degree of freedom of the tunneling particle is used as a clock. This clock only ``ticks'' inside the forbidden region due to the precession of the spin about a magnetic field localized within the barrier. Here, we report the calibration of a Larmor clock to measure tunneling times of a 87 Rb Bose Einstein condensate. We use the Zeeman sublevels of the ground-state F = 2 manifold and Raman beams for the implementation of a Larmor clock. Experimental progress towards measuring the tunneling time and the challenges involved in this measurement will also be discussed.
Large-Larmor-radius interchange instability
Ripin, B.H.; McLean, E.A.; Manka, C.K.; Pawley, C.; Stamper, J.A.; Peyser, T.A.; Mostovych, A.N.; Grun, J.; Hassam, A.B.; Huba, J.
1987-11-16
We observe linear and nonlinear features of a strong plasma/magnetic field interchange Rayleigh-Taylor instability in the limit of large ion Larmor radius. The instability undergoes rapid linear growth culminating in free-streaming flute tips.
Binder, Bernd
2008-01-21
An advanced and exact geometric description of nonlinear precession dynamics modeling very accurately natural and artificial couplings showing Lorentz symmetry is derived. In the linear description it is usually ignored that the geometric phase of relativistic motion couples back to the orbital motion providing for a non-linear recursive precession dynamics. The high coupling strength in the nonlinear case is found to be a gravitomagnetic charge proportional to the precession angle and angular velocity generated by geometric phases, which are induced by high-speed relativistic rotations and are relevant to propulsion technologies but also to basic interactions. In the quantum range some magic precession angles indicating strong coupling in a phase-locked chaotic system are identified, emerging from a discrete time dynamical system known as the cosine map showing bifurcations at special precession angles relevant to heavy nuclei stability. The 'Magic Angle Precession' (MAP) dynamics can be simulated and visualized by cones rolling in or on each other, where the apex and precession angles are indexed by spin, charge or precession quantum numbers, and corresponding magic angles. The most extreme relativistic warping and twisting effect is given by the Dirac spinor half spin constellation with 'Hyperdiamond' MAP, which resembles quark confinement.
Zhao, Jinkui Hamilton, William A.; Robertson, J. L.; Crow, Lowell; Lee, Sung-Woo; Kang, Yoon W.
2015-09-14
The analysis of neutron diffraction experiments often assumes that neutrons are elastically scattered from the sample. However, there is growing evidence that a significant fraction of the detected neutrons is in fact inelastically scattered, especially from soft materials and aqueous samples. Ignoring these inelastic contributions gives rise to inaccurate experimental results. To date, there has been no simple method with broad applicability for inelastic signal separation in neutron diffraction experiments. Here, we present a simple and robust method that we believe could be suited for this purpose. We use two radio frequency resonant spin flippers integrated with a Larmor precession field to modulate the neutron intensity and to encode the inelastic scattering information into the neutron data. All three components contribute to the spin encoding. The Larmor field serves several additional purposes. Its usage facilitates neutron time-focusing, eliminates the need for stringent magnetic shielding, and allows for compact setups. The scheme is robust, simple, and flexible. We believe that, with further improvements, it has the potential of adding inelastic signal discrimination capabilities to many existing diffraction instruments in the future.
NASA Astrophysics Data System (ADS)
Zhao, Jinkui; Hamilton, William A.; Lee, Sung-Woo; Robertson, J. L.; Crow, Lowell; Kang, Yoon W.
2015-09-01
The analysis of neutron diffraction experiments often assumes that neutrons are elastically scattered from the sample. However, there is growing evidence that a significant fraction of the detected neutrons is in fact inelastically scattered, especially from soft materials and aqueous samples. Ignoring these inelastic contributions gives rise to inaccurate experimental results. To date, there has been no simple method with broad applicability for inelastic signal separation in neutron diffraction experiments. Here, we present a simple and robust method that we believe could be suited for this purpose. We use two radio frequency resonant spin flippers integrated with a Larmor precession field to modulate the neutron intensity and to encode the inelastic scattering information into the neutron data. All three components contribute to the spin encoding. The Larmor field serves several additional purposes. Its usage facilitates neutron time-focusing, eliminates the need for stringent magnetic shielding, and allows for compact setups. The scheme is robust, simple, and flexible. We believe that, with further improvements, it has the potential of adding inelastic signal discrimination capabilities to many existing diffraction instruments in the future.
Photon-assisted electronic and spin transport in a junction containing precessing molecular spin
NASA Astrophysics Data System (ADS)
Filipović, Milena; Belzig, Wolfgang
2016-02-01
We study the ac charge and -spin transport through an orbital of a magnetic molecule with spin precessing in a constant magnetic field. We assume that the source and drain contacts have time-dependent chemical potentials. We employ the Keldysh nonequilibrium Green's functions method to calculate the spin and charge currents to linear order in the time-dependent potentials. The molecular and electronic spins are coupled via exchange interaction. The time-dependent molecular spin drives inelastic transitions between the molecular quasienergy levels, resulting in a rich structure in the transport characteristics. The time-dependent voltages allow us to reveal the internal precession time scale (the Larmor frequency) by a dc conductance measurement if the ac frequency matches the Larmor frequency. In the low-ac-frequency limit the junction resembles a classical electric circuit. Furthermore, we show that the setup can be used to generate dc-spin currents, which are controlled by the molecular magnetization direction and the relative phases between the Larmor precession and the ac voltage.
Experimental study of finite Larmor radius effects
Struve, K.W.
1980-08-01
Linear Z-pinches in Ar, Kr, Xe, N/sub 2/, and He are experimentally studied in regimes where strong finite Larmor radius effects could provide a significant stabilizing effect. Scaling arguments show that for deuterium such a pinch has an electron line density of order 2 x 10/sup 15//cm. For higher Z plasmas a higher line density is allowed, the exact value of which depends on the average ion charge. The pinch is formed by puffing gas axially through the cathode towards the anode of an evacuated pinch chamber. When the gas reaches the anode, the pinch bank is fired. The pinch current rises in 2 to 3 ..mu..sec to a maximum of 100 to 200 kA. The pinch bank capacitance is 900 ..mu..F, and the external inductance is 100 nH. Additionally, the bank is fused to increase dI/dt. The primary diagnostics are a framing camera, a spatially resolved Mach-Zehnder interferometer, and X-ray absorption.
NASA Astrophysics Data System (ADS)
Hirata, R.
2007-03-01
From the polarimetric observation of Pleione, we found that the intrinsic polarization angle varied from 60° to 130° in 1974-2003. The Hα profile also changed dramatically from the edge-on type (shell-line profile) to the surface-on type (wine-bottle profile). These facts clearly indicate the spatial motion of the disk axis. We interpret these variations in terms of the disk precession, caused by the secondary of this spectroscopic binary with a period of 218d. We performed the χ^2 minimization for the polarization angle, assuming uniform precession with an imposed condition that the shell maximum occurred at edge-on view. The resulting precession angle is 59° with a period of 81 years. Then, we can describe chronologically the spatial motion of disk axis. We also derived the Hα disk radius from the peak separation, assuming the Keplerian disk. The precession of the disk gives natural explanation of the mysterious long-term spectroscopic behaviors of this star.
NASA Astrophysics Data System (ADS)
Hester, R. E., Jr.
2015-12-01
The study considers a north-south pair of mid-latitude rings of atmospheric mass, symmetric with respect to the equator, and rotating with respect to the distant stars. The mass and angular velocity are assigned similar to the annual and zonal mean upper level westerlies. Their relatively rapid rotation is assumed to allow a rigid body approximation on long time and space scales. The rings are constrained to move as if rigidly connected to a common axis of rotation. The pair thus constitutes a symmetric top with a fixed pivot point at the center of mass. Analysis of the dynamics follows the classical mechanics approach used for precession of the equinoxes. The theoretical rate of precession for this highly idealized system yields a period on the order of decades. The predicted dynamics appears consistent with three prior studies of observational data: latitudinal movements of atmospheric circulation above far Southern Australia, latitudinal movements of ocean circulation in the Kuroshio Extension, and changes in global Atmospheric Angular Momentum before and after 1976. Each of these observational records indicates correlation with the Pacific Decadal Oscillation. The theoretical dynamics in combination with the observations suggests the axis of rotation of the atmospheric westerlies is offset from the Earth axis by a few degrees, and further, that this axis precesses around a mean axis on a time scale of a few decades.
Finite Larmor radius flute mode theory with end loss
Kotelnikov, I.A.; Berk, H.L.
1993-08-01
The theory of flute mode stability is developed for a two-energy- component plasma partially terminated by a conducting limiter. The formalism is developed as a preliminary study of the effect of end-loss in open-ended mirror machines where large Larmor radius effects are important.
Effect of limiter end loss in finite Larmor radius theory
Berk, H.L.; Kotelnikov, I.A.
1993-08-01
We have examined the effect of incomplete line tying on the MHD flute mode with FLR (finite Larmor radius) effects. We show that the combination of line tying and FLR effects can slow down MHD instability, but cannot produce complete stabilization.
Spin precession in anisotropic cosmologies
NASA Astrophysics Data System (ADS)
Kamenshchik, A. Yu.; Teryaev, O. V.
2016-05-01
We consider the precession of a Dirac particle spin in some anisotropic Bianchi universes. This effect is present already in the Bianchi-I universe. We discuss in some detail the geodesics and the spin precession for both the Kasner and the Heckmann-Schucking solutions. In the Bianchi-IX universe the spin precession acquires the chaotic character due to the stochasticity of the oscillatory approach to the cosmological singularity. The related helicity flip of fermions in the very early universe may produce the sterile particles contributing to dark matter.
Flute waves at the ion Larmor radius scales
Onishchenko, O. G.
2010-12-14
The theory of the magnetic Rayleigh-Taylor instability (RTI) is discussed. Modified linear kinetic theory allows us to investigate RTI and flute waves with arbitrary perpendicular spatial scales compared to the ion Larmor radius. It is shown that in the linear limit a Fourier transform of these equations yields the dispersion relation which in the so-called Pade approximation corresponds to results of the kinetic theory. This analysis represents an extension of the previous study of the magnetic RTI obtained in the large wave scale approximation. It is shown that incorporation of the effects associated with wave scales of the order of the ion Larmor radius leads to a broader wave number range of the magnetic RTI.
Larmor labeling of neutron spin using superconducting Wollaston prisms
NASA Astrophysics Data System (ADS)
Li, Fankang
Neutron spin Larmor labeling using magnetic Wollaston prisms (WP) provides a way to overcome some of the limitations arising from the nature of neutron beams: low flux and divergence. Using superconducting films and tapes, a series of strong, well-defined shaped magnetic fields can be produced due to both the zero-resistance and Meissner effect in superconductors. Using finite element simulations, the criterion to build a superconducting magnetic Wollaston prism with high encoding efficiency and low Larmor phase aberrations are presented. To achieve a high magnetic field and simplify the maintenance, we optimize the design using careful thermal analysis. The measured neutron spin flipping efficiency is measured to be independent of both the neutron wavelength and energizing current, which is a significant improvement over other devices with similar functions. A highly linear variation of the Larmor phase is measured across the device, which ensures a highly uniform encoding of scattering angles into the neutron spin Larmor phase. Using two WPs, the correlation function for a colloidal silica sample was measured by spin echo modulated small angle neutron scattering (SEMSANS) and agrees well with other techniques. Using Monte Carlo code (McStas), we further investigated the SEMSANS setup and showed the requirements to improve its performance. We have proposed a new technique to implement neutron spin echo on a triple axis neutron spectrometer to achieve high resolution measurements of the lifetime of dispersive phonon excitations. The spin echo is tuned by appropriate choice of magnetic fields instead of physically tilting the coils used in traditional methods. This new approach allows a higher energy resolution and a larger effective tilting angle and hence larger group velocity to be measured.
Quantum Larmor radiation in a conformally flat universe
Kimura, Rampei; Nakamura, Gen; Yamamoto, Kazuhiro
2011-02-15
We investigate the quantum effect on the Larmor radiation from a moving charge in an expanding universe based on the framework of the scalar quantum electrodynamics. A theoretical formula for the radiation energy is derived at the lowest order of the perturbation theory with respect to the coupling constant of the scalar quantum electrodynamics. We evaluate the radiation energy on the background universe so that the Minkowski spacetime transits to the Milne universe, in which the equation of motion for the mode function of the free complex scalar field can be exactly solved in an analytic way. Then, the result is compared with the WKB approach, in which the equation of motion of the mode function is constructed with the WKB approximation which is valid as long as the Compton wavelength is shorter than the Hubble horizon length. This demonstrates that the quantum effect on the Larmor radiation of the order e{sup 2}({h_bar}/2{pi}) is determined by a nonlocal integration in time depending on the background expansion. We also compare our result with a recent work by Higuchi and Walker [Phys. Rev. D 80, 105019 (2009)], which investigated the quantum correction to the Larmor radiation from a charged particle in a nonrelativistic motion in a homogeneous electric field.
Quantum Larmor radiation in a conformally flat universe
NASA Astrophysics Data System (ADS)
Kimura, Rampei; Nakamura, Gen; Yamamoto, Kazuhiro
2011-02-01
We investigate the quantum effect on the Larmor radiation from a moving charge in an expanding universe based on the framework of the scalar quantum electrodynamics. A theoretical formula for the radiation energy is derived at the lowest order of the perturbation theory with respect to the coupling constant of the scalar quantum electrodynamics. We evaluate the radiation energy on the background universe so that the Minkowski spacetime transits to the Milne universe, in which the equation of motion for the mode function of the free complex scalar field can be exactly solved in an analytic way. Then, the result is compared with the WKB approach, in which the equation of motion of the mode function is constructed with the WKB approximation which is valid as long as the Compton wavelength is shorter than the Hubble horizon length. This demonstrates that the quantum effect on the Larmor radiation of the order e2ℏ is determined by a nonlocal integration in time depending on the background expansion. We also compare our result with a recent work by Higuchi and Walker [Phys. Rev. DPRVDAQ1550-7998 80, 105019 (2009)10.1103/PhysRevD.80.105019], which investigated the quantum correction to the Larmor radiation from a charged particle in a nonrelativistic motion in a homogeneous electric field.
Gravitomagnetism: a novel explanation of the precession of planets and binary pulsars
NASA Astrophysics Data System (ADS)
Arbab, Arbab I.
2010-11-01
We have studied the consequences of applying gravitomagnetism to gravitating objects. Gravitomagnetism was the missing part of the Newton’s law of gravitation. This phenomenon is manifest in the generalized Newton’s law of gravitation that is published in A.I. Arbab, Astrophys. Space Sci. 325:37, 2010a. Owing to gravitomagnetism, we have shown, the precession of planetary and pulsars orbits is due to the interaction of these objects with the gravitomagnetic field. We have calculated the gravitomagnetic fields arising from the orbital motion of the planets and binary pulsars and we have shown that they are double the Larmor-like frequency. This effect coincides with the prediction of general relativity and places the general theory of relativity on new affirmative grounds. Consequently, a modified Newton law of gravitation of Lorentz-type is proposed, which explains this precession.
Harnessing spin precession with dissipation
NASA Astrophysics Data System (ADS)
Crisan, A. D.; Datta, S.; Viennot, J. J.; Delbecq, M. R.; Cottet, A.; Kontos, T.
2016-01-01
Non-collinear spin transport is at the heart of spin or magnetization control in spintronics devices. The use of nanoscale conductors exhibiting quantum effects in transport could provide new paths for that purpose. Here we study non-collinear spin transport in a quantum dot. We use a device made out of a single-wall carbon nanotube connected to orthogonal ferromagnetic electrodes. In the spin transport signals, we observe signatures of out of equilibrium spin precession that are electrically tunable through dissipation. This could provide a new path to harness spin precession in nanoscale conductors.
Harnessing spin precession with dissipation
Crisan, A. D.; Datta, S.; Viennot, J. J.; Delbecq, M. R.; Cottet, A.; Kontos, T.
2016-01-01
Non-collinear spin transport is at the heart of spin or magnetization control in spintronics devices. The use of nanoscale conductors exhibiting quantum effects in transport could provide new paths for that purpose. Here we study non-collinear spin transport in a quantum dot. We use a device made out of a single-wall carbon nanotube connected to orthogonal ferromagnetic electrodes. In the spin transport signals, we observe signatures of out of equilibrium spin precession that are electrically tunable through dissipation. This could provide a new path to harness spin precession in nanoscale conductors. PMID:26816050
Toroidal Precession as a Geometric Phase
J.W. Burby and H. Qin
2012-09-26
Toroidal precession is commonly understood as the orbit-averaged toroidal drift of guiding centers in axisymmetric and quasisymmetric configurations. We give a new, more natural description of precession as a geometric phase effect. In particular, we show that the precession angle arises as the holonomy of a guiding center's poloidal trajectory relative to a principal connection. The fact that this description is physically appropriate is borne out with new, manifestly coordinate-independent expressions for the precession angle that apply to all types of orbits in tokamaks and quasisymmetric stellarators alike. We then describe how these expressions may be fruitfully employed in numerical calculations of precession.
The Precession of Asteroid 1620 Geographos
NASA Astrophysics Data System (ADS)
Prokof'eva, V. V.; Tarashchuk, V. P.; Karachkina, L. G.
The frequency analysis of the fine photometric effects in the photometric observation obtained during asteroid 1620 Geographos approaching to Earth in 1994 allowed to derive the precession of asteroid spin axis. The periods of 0({rm) d!.8 and 2({rm) d!.8 or multiple to them were revealed. The magnitude of precession angle was estimated to be near 3({circ) . The nature of the precession discussed. The emergence of the free precession may be supported at time of the formation of the asteroid or by the collision with another body. The forced precession does not contradict to the Geographos connection with meteor streams and the assumption that Geographos may have small satellites.
Finite Larmor radius effect on ion pickup at Venus
NASA Technical Reports Server (NTRS)
Phillips, J. L.; Luhmann, J. G.; Russell, C. T.; Moore, K. R.
1987-01-01
The interaction of the solar wind with Venus is influenced by the pickup of newly born exospheric oxygen ions by the convecting magnetosheath plasma. The flow and field configuration of the magnetosheath plasma, together with the large gyroradius of the pickup ions, cause mass loading to occur preferentially on one side of the magnetosheath. The observed hemispherical asymmetry in the magnetic field in the near-planet magnetosheath, attributed to this pickup process, is confirmed by direct observation of the picked-up planetary particles. Test particle calculations show that a current system created by ion pickup has the appropriate location and magnitude to account for the magnetic field asymmetry. The results indicate that a fluid treatment of the Venus mass-loading problem is not entirely appropriate; a hybrid or kinetic model is necessary to incorporate the finite Larmor radius of the pickup particles which produces the observed asymmetry.
RF Field Visualization of RF Ablation at the Larmor Frequency
Stang, Pascal; Kerr, Adam; Pauly, John; Scott, Greig
2012-01-01
Radiofrequency ablation is an effective minimally invasive treatment for tumors. One primary source of difficulty is monitoring and controlling the ablation region. Currently, RF ablation is performed at 460 kHz, for which MRI could play a role given its capability for temperature monitoring and tumor visualization. If instead the ablation were to be performed at the MRI Larmor frequency, then the MR capability for B1 field mapping could be used to directly visualize the RF fields created by the ablation currents. Visualizing the RF fields may enable better control of the ablation currents, enabling better control of lesion shape and size and improving repeatability. We demonstrate the feasibility of performing RF ablations at 64 MHz and show preliminary results from imaging the RF fields from the ablation. The post-ablation RF fields show an increase in current density in the ablated region, consistent with an increase in conductivity of the ablated tissue. PMID:21775256
Noninvasive measurement of conductivity anisotropy at larmor frequency using MRI.
Lee, Joonsung; Song, Yizhuang; Choi, Narae; Cho, Sungmin; Seo, Jin Keun; Kim, Dong-Hyun
2013-01-01
Anisotropic electrical properties can be found in biological tissues such as muscles and nerves. Conductivity tensor is a simplified model to express the effective electrical anisotropic information and depends on the imaging resolution. The determination of the conductivity tensor should be based on Ohm's law. In other words, the measurement of partial information of current density and the electric fields should be made. Since the direct measurements of the electric field and the current density are difficult, we use MRI to measure their partial information such as B1 map; it measures circulating current density and circulating electric field. In this work, the ratio of the two circulating fields, termed circulating admittivity, is proposed as measures of the conductivity anisotropy at Larmor frequency. Given eigenvectors of the conductivity tensor, quantitative measurement of the eigenvalues can be achieved from circulating admittivity for special tissue models. Without eigenvectors, qualitative information of anisotropy still can be acquired from circulating admittivity. The limitation of the circulating admittivity is that at least two components of the magnetic fields should be measured to capture anisotropic information. PMID:23554838
Free nuclear precession gradiometer system
Hinton, G. F.
1985-10-08
A free nuclear precession gradiometer uses a fluid sample surrounded by a coil the fluid sample containing one or more nuclear species which display a magnetic moment. Current in the coil polarizes the nucleii, which when the current is abruptly terminated precess coherently about the earth's magnetic field. The exact frequency generated is a precise measure of the absolute value of the earth's magnetic field. The signal is in the form of a damped sinusoid with the rate of decay being a function of gradients in the ambient magnetic field. Two vector magnetometers are mounted rigidly on the sensor at the right angles to each other and to the earth's magnetic field. A servo system continuously orients the sensor in a two-axis gimbal system to reduce the output of the vector magnetometers to zero. The instrument is polarized, a counter is triggered to make the frequency measurement, and the signal is analyzed by determining the average amplitude of the signal over a precise interval of time. The result is simultaneous measurement of total intensity and total gradient.
Non-Mathematical Explanation of Precession
ERIC Educational Resources Information Center
Cordell, John
2011-01-01
The phenomenon of precession is necessary to explain the motion of footballs, gyroscopes, tops, the Earth, and many other interesting physical systems, but it was very hard for me to understand as a student and is very difficult to teach to students now. Many explanations of precession in physics textbooks are highly mathematical and hard to…
Insolation and the Precession Index
NASA Technical Reports Server (NTRS)
Rubincam, David Parry
2000-01-01
Simple nonlinear climate models yield a precession index-like term in the temperature. Despite its importance in the geologic record, the precession index e sin omega, where e is the Earth's orbital eccentricity and omega is the Sun's perigee in the geocentric frame, is not present in the insolation at the top of the atmosphere. Hence there is no one-for-one mapping of 23,000 and 19,000 year periodicities from the insolation to the paleoclimate record; a nonlinear climate model is needed to produce these periods. Two such models, a grey body and an energy balance climate model with an added quadratic term, produce e sin omega terms in temperature. These terms, which without feedback mechanisms achieve extreme values of about plus or minus 0.48 K for the grey body and plus or minus 0.64 K for the energy balance model, simultaneously cool one hemisphere while they warm the other. Moreover, they produce long-term cooling in the northern hemisphere when the Sun's perigee is near northern solstice and long-term warming in the northern hemisphere when the perigee is near southern solstice. Thus this seemingly paradoxical mechanism works against the standard model which requires cool northern summers (Sun far from Earth in northern summer) to build up northern ice sheets, so that if the standard model is correct it may be more efficient than previously thought. Alternatively, the new mechanism could possibly be dominant and indicate southern hemisphere control of the northern ice sheets, wherein the southern oceans undergo a long-term cooling when the Sun is close to the Earth during southern summer. The cold water eventually flows north, cooling the northern hemisphere. This might explain why the northern oceans lag the southern ones when it comes to orbital forcing.
Torque-induced precession of bacterial flagella.
Shimogonya, Yuji; Sawano, Yoichiro; Wakebe, Hiromichi; Inoue, Yuichi; Ishijima, Akihiko; Ishikawa, Takuji
2015-01-01
The bacterial flagellar motor is an ion-driven rotary machine in the cell envelope of bacteria. Using a gold nanoparticle as a probe, we observed the precession of flagella during rotation. Since the mechanism of flagella precession was unknown, we investigated it using a combination of full simulations, theory, and experiments. The results show that the mechanism can be well explained by fluid mechanics. The validity of our theory was confirmed by our full simulation, which was utilized to predict both the filament tilt angle and motor torque from experimental flagellar precession data. The knowledge obtained is important in understanding mechanical properties of the bacterial motor and hook. PMID:26691402
Trapped Electron Precession Shear Induced Fluctuation Decorrelation
T.S. Hahm; P.H. Diamond; E.-J. Kim
2002-07-29
We consider the effects of trapped electron precession shear on the microturbulence. In a similar way the strong E x B shear reduces the radial correlation length of ambient fluctuations, the radial variation of the trapped electron precession frequency can reduce the radial correlation length of fluctuations associated with trapped electrons. In reversed shear plasmas, with the explicit dependence of the trapped electron precession shearing rate on B(subscript)theta, the sharp radial gradient of T(subscript)e due to local electron heating inside qmin can make the precession shearing mechanism more effective, and reduce the electron thermal transport constructing a positive feedback loop for the T(subscript)e barrier formation.
About detection of precessing circumpulsar discs
NASA Astrophysics Data System (ADS)
Grimani, Catia
2016-08-01
Detections of circumpulsar discs and planetary systems through electromagnetic observations appear quite rare. In the case of PSR 1931+24 and B0656+14, the hypothesis of a precessing disc penetrating the pulsar light cylinder is found consistent with radio and gamma observations from these stars. Disc self-occultation and precession may affect electromagnetic measurements. We investigate here under which conditions gravitational waves generated by circumpulsar disc precession may be detected by the proposed second-generation space interferometers DECI-hertz Interferometer Gravitational Wave Observatory and Big Bang Observer. The characteristics of circumpulsar detectable precessing discs are estimated as a function of distance from the Solar system. Speculations on detection rates are presented.
Consistent Numerical Expressions for Precession Formulae.
NASA Astrophysics Data System (ADS)
Soma, M.
The precession formulae by Lieske et al. (1977) have been used since 1984 for calculating apparent positions and reducing astrometric observations of celestial objects. These formulae are based on the IAU (1976) Astronomical Constants, some of which deviate from their recently determined values. They are also derived using the secular variations of the ecliptic pole from Newcomb's theory, which is not consistent with the recent planetary theories. Accordingly Simon et al. (1994) developed new precession formulae using the recently determined astronomical constants and also being based on the new planetary theory VSOP87. There are two differing definitions of the ecliptic: ecliptic in the inertial sense and ecliptic in the rotating sense (Standish 1981). The ecliptic given by the VSOP87 theory is that in the inertial sense, but the value for obliquity Simon et al. used is the obliquity in the rotating sense. Therefore their precession formulae has inconsistency. This paper gives corrections for consistent precession formulae.
About detection of precessing circumpulsar disks
NASA Astrophysics Data System (ADS)
Grimani, Catia
2016-05-01
Detections of circumpulsar disks and planetary systems through electromagnetic observations appear quite rare. In the case of PSR 1931+24 and B0656+14, the hypothesis of a precessing disk penetrating the pulsar light cylinder is found consistent with radio and gamma observations from these stars. Disk self-occultation and precession may affect electromagnetic measurements. We investigate here under which conditions gravitational waves generated by circumpulsar disk precession may be detected by the proposed second generation space interferometers DECIGO (DECI-hertz Interferometer Gravitational Wave Observatory) and BBO (Big Bang Observer). The characteristics of circumpulsar detectable precessing disks are estimated as a function of distance from the Solar System. Speculations on detection rates are presented.
Larmor electric field observed at the Earth's magnetopause by Polar satellite
Koga, D. Gonzalez, W. D.; Silveira, M. V. D.; Mozer, F. S.; Cardoso, F. R.
2014-10-15
We present, for the first time, observational evidence of a kinetic electric field near the X-line associated with asymmetric reconnection at the Earth's dayside magnetopause using Polar observations. On March 29, 2003, Polar satellite detected an asymmetric collisionless reconnection event. This event shows a unipolar Hall electric field signature and a simple deviation from the guide field during the magnetopause crossing, with the absence of an ion plasma jet outflow indicating that the magnetopause crossing was near the X-line. As expected from particle-in-cell simulations by Malakit et al. (Phys. Rev. Lett. 111, 135001 (2013)), an earthward pointing normal electric field appears in the magnetospheric side of the ion diffusion region. The electric field satisfies two necessary conditions for the existence of the finite ion Larmor radius effect: (1) the ion Larmor radius (r{sub g2}) is larger than the distance between the stagnation point and the edge of the ion diffusion region in the strong magnetic field side (δ{sub S2}) and (2) the spatial extent of the kinetic electric field (δ{sub EL}) is of the order of the ion Larmor radius. Furthermore, it is shown that the peak value of the Larmor electric field is comparable to the predicted value. The observation of the Larmor electric field can be valuable in other analyses to show that the crossing occurred near the X-line.
Collisional damping of zonal flows due to finite Larmor radius effects
NASA Astrophysics Data System (ADS)
Ricci, Paolo; Rogers, B. N.; Dorland, W.
2010-07-01
The collisional damping of seeded E ×B zonal flows on the ion Larmor radius scale is studied using a gyrokinetic model. The focus is on flow damping due to finite Larmor radius effects, which cause a v∥/v anisotropy of the ion distribution function that is damped by ion-ion collisions. The gyrokinetic equations are solved in a slab geometry with no gradients or curvature, and a gyroaveraged Lorentz collision operator that conserves particle number, momentum, and energy is used. The solution of the gyrokinetic equations explores the dependence of the damping rate on the wavelength of the flows and the impact of the collisions on the ion distribution function. These numerical results can be used as a benchmark test during the implementation of finite Larmor radius effects in the collision operator of gyrokinetic codes.
The modulational instability in the extended Hasegawa-Mima equation with a finite Larmor radius
Gallagher, S.; Hnat, B.; Rowlands, G.; Connaughton, C.; Nazarenko, S.
2012-12-15
The effects of the finite Larmor radius on the generation of zonal flows by the four-wave modulational instability are investigated using an extended form of the Hasegawa-Mima equation. Growth rates of the zonal mode are quantified using analytical predictions from a four-mode truncated model, as well as from direct numerical simulation of the nonlinear extended Hasegawa-Mima equation. We not only consider purely zonal flows but also examine the generic oblique case and show that, for small Larmor radii, off-axis modes may become dominant. We find a key parameter M{sub {rho}} which characterises the behaviour of the system due to changes in the Larmor radius. We find that, similarly to previous results obtained by changing the driving wave amplitude, two separate dynamical regimes can be accessed. These correspond to oscillatory energy transfer between zonal flows and a driving wave and the fully saturated zonal flow.
The modulational instability in the extended Hasegawa-Mima equation with a finite Larmor radius
NASA Astrophysics Data System (ADS)
Gallagher, S.; Hnat, B.; Connaughton, C.; Nazarenko, S.; Rowlands, G.
2012-12-01
The effects of the finite Larmor radius on the generation of zonal flows by the four-wave modulational instability are investigated using an extended form of the Hasegawa-Mima equation. Growth rates of the zonal mode are quantified using analytical predictions from a four-mode truncated model, as well as from direct numerical simulation of the nonlinear extended Hasegawa-Mima equation. We not only consider purely zonal flows but also examine the generic oblique case and show that, for small Larmor radii, off-axis modes may become dominant. We find a key parameter Mρ which characterises the behaviour of the system due to changes in the Larmor radius. We find that, similarly to previous results obtained by changing the driving wave amplitude, two separate dynamical regimes can be accessed. These correspond to oscillatory energy transfer between zonal flows and a driving wave and the fully saturated zonal flow.
Improvement of the IAU 2000 precession model
NASA Astrophysics Data System (ADS)
Capitaine, N.; Wallace, P. T.; Chapront, J.
2005-03-01
The IAU 2000 precession consists of the IAU 1976 ecliptic precession (Lieske et al. [CITE], A&A, 58, 1) and the precession part of the IAU 2000A equator adopted by IAU 2000 Resolution B1.6 (Mathews et al. [CITE], J. Geophys. Res., 107, B4, 10.1029/2001JB000390). In this paper we provide a range of new expressions as possible replacements for the IAU 2000 precession. The new expressions are based upon the so-called P03 solution of Capitaine et al. ([CITE], A&A, 412, 567) for the equator and the ecliptic. In addition an improved model for the precession of the equator is discussed. This improved solution was obtained in exactly the same way as P03 but using a refined model for the contributions of the non-rigid Earth (Mathews [CITE], private communication) and revised integration constants for the precession rates resulting from fits to the most recent VLBI data. The paper reports on the procedure that was used for improving the P03 solution and on the comparisons of this solution with the MHB 2000, IAU 2000 and P03 solutions. It also discusses the choices for the solution to be put forward as a replacement for IAU 2000. We concluded that the existing VLBI data were insufficient to provide convincing evidence that the improved solutions would deliver better accuracy than the existing P03 solution, and we recommend retaining P03 as the replacement for IAU 2000. P03, which unlike the IAU 2000 precession is dynamically consistent, has the advantage of already having been used experimentally by a number of groups; the model is recalled in Tables [see full text]- [see full text]. Due to the strong dependence of the precession expressions on the precession rates and of the precession in longitude (or equivalently the celestial CIP X coordinate) on the J2 rate model, we also provide a parameterized P04 solution for these quantities as functions of those parameters. The expressions include the quantities to be used in both the equinox-based and CIO-based (i.e. referred to
Ng Sheungwah; Hassam, A.B.
2005-06-15
Finite Larmor radius (FLR) effects, originally shown to stabilize magnetized plasma interchange modes at short wavelength, are shown to assist velocity shear stabilization of long wavelength interchanges. It is shown that the FLR effects result in stabilization with roughly the same efficacy as the stabilization from dissipative (resistive and viscous) effects found earlier.
The magnetic Rayleigh-Taylor instability and flute waves at the ion Larmor radius scales
Onishchenko, O. G.; Pokhotelov, O. A.; Stenflo, L.; Shukla, P. K.
2011-02-15
The theory of flute waves (with arbitrary spatial scales compared to the ion Larmor radius) driven by the Rayleigh-Taylor instability (RTI) is developed. Both the kinetic and hydrodynamic models are considered. In this way we have extended the previous analysis of RTI carried out in the long wavelength limit. It is found that complete finite ion Larmor radius stabilization is absent when the ion diamagnetic velocity attains the ion gravitation drift velocity. The hydrodynamic approach allowed us to deduce a new set of nonlinear equations for flute waves with arbitrary spatial scales. It is shown that the previously deduced equations are inadequate when the wavelength becomes of the order of the ion Larmor radius. In the linear limit a Fourier transform of these equations yields the dispersion relation which in the so-called Pade approximation corresponds to the results of the fully kinetic treatment. The development of such a theory gives us enough grounds for an adequate description of the RTI stabilization by the finite ion Larmor radius effect.
Spin Precession in Oblique Magnetic Fields
NASA Astrophysics Data System (ADS)
Li, Jing; Huang, Biqin; Appelbaum, Ian
2009-03-01
Spin precession and dephasing (``Hanle effect'') provide an unambiguous means to establish the presence of spin transport in semiconductors. We compare theoretical modeling with experimental data from drift-dominated silicon spin-transport devices, illustrating the non-trivial consequences of employing oblique magnetic fields (due to misalignment or intentional, fixed in-plane field components) to measure the effects of spin precession. Model results are also calculated for Hanle measurements under conditions of diffusion-dominated transport, revealing an expected Hanle peak-widening effect induced by the presence of fixed in-plane magnetic bias fields.
NASA Astrophysics Data System (ADS)
Xia, Hong; Chen, Jie; Zeng, Xiaoyan; Yan, Ming
2016-04-01
The Doppler effect is a fundamental physical phenomenon observed for waves propagating in vacuum or various media, commonly gaseous or liquid. Here, we report on the occurrence of a Doppler effect in a solid medium. Instead of a real object, a topological soliton, i.e., a magnetic domain wall (DW) traveling in a current-carrying ferromagnetic nanowire, plays the role of the moving wave source. The Larmor precession of the DW in an external field stimulates emission of monochromatic spin waves (SWs) during its motion, which show a significant Doppler effect, comparable to the acoustic one of a train whistle. This process involves two prominent spin-transfer-torque effects simultaneously, the current-driven DW motion and the current-induced SW Doppler shift. The latter gives rise to an interesting feature, i.e., the observed SW Doppler effect appears resulting from a stationary source and a moving observer, contrary to the laboratory frame.
Precession of the Earth-Moon System
ERIC Educational Resources Information Center
Urbassek, Herbert M.
2009-01-01
The precession rate of the Earth-Moon system by the gravitational influence of the Sun is derived. Attention is focussed on a physically transparent but complete presentation accessible to first- or second-year physics students. Both a shortcut and a full analysis are given, which allows the inclusion of this material as an example of the physics…
Thomas precession and squeezed states of light
NASA Technical Reports Server (NTRS)
Han, D.; Hardekopf, E. E.; Kim, Y. S.
1989-01-01
The Lorentz group, which is the language of special relativity, is a useful theoretical toll in modern optics. Optics experiments can therefore serve as analog computers for special relativity. Possible optics experiments involving squeezed states are discussed in connection with the Thomas precession and the Wigner rotation.
Spinor approach to gravitational motion and precession
Hestenes, D.
1986-06-01
The translational and rotational equations of motion for a small rigid body in a gravitational field are combined in a single spinor equation. Besides its computational advantages, this unifies the description of gravitational interaction in classical and quantum theory. Explicit expressions for gravitational precession rates are derived.
Nonrelativistic Contribution to Mercury's Perihelion Precession.
ERIC Educational Resources Information Center
Price, Michael P.; Rush, William F.
1979-01-01
Presents a calculation of the precession of the perihelion of Mercury due to the perturbations from the outer planets. The time-average effect of each planet is calculated by replacing that planet with a ring of linear mass density equal to the mass of the planet divided by the circumference of its orbit. (Author/GA)
The precession dynamo experiment at HZDR
NASA Astrophysics Data System (ADS)
Giesecke, A.; Gundrum, T.; Herault, J.; Stefani, F.; Gerbeth, G.
2015-12-01
In a next generation dynamo experiment currently under development atthe Helmholtz-Zentrum Dresden-Rossendorf (HZDR) a fluid flow of liquidsodium, solely driven by precession, will be considered as a possiblesource for magnetic field generation. The experiment is mainlymotivated by alternative concepts for astrophysical dynamos that arebased on mechanical flow driving. For example, it has long beendiscussed whether precession may be a complementary power source forthe geodynamo (Malkus, Science 1968) or for the ancient lunar dynamodue to the Earth-driven precession of the lunar spin axis (Dwyer, Nature 2011).We will present the current state of development of the dynamoexperiment together with results from non-linear hydrodynamicsimulations with moderate precessional forcing. Our simulations reveala non-axisymmetric forced mode with an amplitude of up to one fourthof the rotation velocity of the cylindrical container confirming thatprecession provides a rather efficient flow driving mechanism even atmoderate precession rates.More relevant for dynamo action might be free Kelvin modes (thenatural flow eigenmodes in a rotating cylinder) with higher azimuthalwave number. These modes may become relevant when constituting atriadic resonance with the fundamental forced mode, i.e., when theheight of the container matches their axial wave lengths. We findtriadic resonances at aspect ratios close to those predicted by thelinear theory except around the primary resonance of the forcedmode. In that regime we still identify free Kelvin modes propagatingin retrograde direction but none of them can be assigned to a triade.Our results will enter into the development of flow models that willbe used in kinematic simulations of the electromagnetic inductionequation in order to determine whether a precession driven flow willbe capable to drive a dynamo at all and to limit the parameter spacewithin which the occurrence of dynamo action is most promising.
Interchange and Flow Velocity Shear Instabilities in the Presence of Finite Larmor Radius Effects
NASA Astrophysics Data System (ADS)
Sotnikov, V.; Kim, T.; Mishin, E.; Genoni, T.; Rose, D.; Mehlhorn, T.
2014-09-01
Ionospheric irregularities cause scintillations of electromagnetic signals that can severely affect navigation and transionospheric communication, in particular during Equatorial Plasma Bubbles (EPBs) events. However, the existing ionospheric models do not describe density irregularities with typical scales of several ion Larmor radii that affect UHF and L bands. These irregularities can be produced in the process of nonlinear evolution of interchange or flow velocity shear instabilities. The model of nonlinear development of these instabilities based on two-fluid hydrodynamic description with inclusion of finite Larmor radius effects will be presented. The derived nonlinear equations will be numerically solved by using the code Flute, which was originally developed for High Energy Density applications and modified to describe interchange and flow velocity shear instabilities in the ionosphere. The high-resolution simulations will be driven by the ambient conditions corresponding to the AFRL C/NOFS satellite low-resolution data during EPBs.
NASA Astrophysics Data System (ADS)
Medvedev, Mikhail
2010-02-01
An extensive body of studies indicate that small-scale (sub-Larmor-scale) magnetic turbulence are produced at relativistic shocks, in reconnection events and other high-energy density environments. Here we present a general description of radiation produced by relativistic electrons moving in such fields and stress its non-synchrotron spectral characteristics. We illustrate the results with spectral data from gamma-ray burst observations. )
Finite ion Larmor radius effects and wall effects on m = 1 instabilities
Cayton, T.E.
1980-12-01
A set of fluid-like equations that simultaneously includes effects due to geometry and finite ion gyroradii is used to examine the stability of a straight, radially diffuse screw pinch in the regime where the poloidal magnetic field is very small compared with the axial magnetic field. It is shown that this pinch may be rendered completely stable through a combination of finite Larmor radius effects and wall effects. Many of the m = 1 modes of the diffuse pinch can be stabilized by finite ion Larmor radius effects, just as all flute modes can be stabilized. Because of the special nature of the m = 1 eigenfunctions, finite ion gyroradius effects are negligible for the kink modes of very large wavelength. This special nature of the eigenfunctions, however, makes these modes good candidates for wall stabilization. The finite Larmor radius stabilization of m = 1 modes of a diffuse pinch is contrary to the conventional wisdom that has evolved from studies of sharp-boundary, skin-current models of the pinch.
Prospects for aberration corrected electron precession.
Own, C S; Sinkler, W; Marks, L D
2007-01-01
Recent developments in aberration control in the TEM have yielded a tremendous enhancement of direct imaging capabilities for studying atomic structures. However, aberration correction also has substantial benefits for achieving ultra-resolution in the TEM through reciprocal space techniques. Several tools are available that allow very accurate detection of the electron distribution in surfaces allowing precise atomic-scale characterization through statistical inversion techniques from diffraction data. The precession technique now appears to extend this capability to the bulk. This article covers some of the progress in this area and details requirements for a next-generation analytical diffraction instrument. An analysis of the contributions offered by aberration correction for precision electron precession is included. PMID:17207934
Relativistic spin precession in the double pulsar.
Breton, Rene P; Kaspi, Victoria M; Kramer, Michael; McLaughlin, Maura A; Lyutikov, Maxim; Ransom, Scott M; Stairs, Ingrid H; Ferdman, Robert D; Camilo, Fernando; Possenti, Andrea
2008-07-01
The double pulsar PSR J0737-3039A/B consists of two neutron stars in a highly relativistic orbit that displays a roughly 30-second eclipse when pulsar A passes behind pulsar B. Describing this eclipse of pulsar A as due to absorption occurring in the magnetosphere of pulsar B, we successfully used a simple geometric model to characterize the observed changing eclipse morphology and to measure the relativistic precession of pulsar B's spin axis around the total orbital angular momentum. This provides a test of general relativity and alternative theories of gravity in the strong-field regime. Our measured relativistic spin precession rate of 4.77 degrees (-0 degrees .65)(+0 degrees .66) per year (68% confidence level) is consistent with that predicted by general relativity within an uncertainty of 13%. PMID:18599782
Geodetic precession or dragging of inertial frames
NASA Technical Reports Server (NTRS)
Ashby, Neil; Shahid-Saless, Bahman
1989-01-01
In General Relativity, the Principle of General Covariance allows one to describe phenomena by means of any convenient choice of coordinate system. Here, it is shown that the geodetic precession of a gyroscope orbiting a spherically symmetric, nonrotating mass can be recast as a Lense-Thirring frame-dragging effect, in an appropriately chosen coordinate frame whose origin falls freely along with the gyroscope and whose spatial coordinate axes point in fixed directions.
Uncertainty relations and precession of perihelion
NASA Astrophysics Data System (ADS)
Scardigli, Fabio; Casadio, Roberto
2016-03-01
We compute the corrections to the Schwarzschild metric necessary to reproduce the Hawking temperature derived from a Generalized Uncertainty Principle (GUP), so that the GUP deformation parameter is directly linked to the deformation of the metric. Using this modified Schwarzschild metric, we compute corrections to the standard General Relativistic predictions for the perihelion precession for planets in the solar system, and for binary pulsars. This analysis allows us to set bounds for the GUP deformation parameter from well-known astronomical measurements.
Using the P03 Precession Model
NASA Astrophysics Data System (ADS)
Wallace, P. T.; Capitaine, N.
2006-08-01
The precession model adopted by the IAU in 2000 comprised the existing Lieske et al. (1977) model plus rate corrections of about 300 mas/cy in longitude and 25 mas/cy in obliquity. Though accurate with respect to existing VLBI observations, the IAU 2000 model is not consistent with dynamical theory, and consequently the IAU Working Group on precession and the ecliptic has recommended (Hilton et al. 2006) that it be replaced by the "P03" model of Capitaine et al. (2003). P03 provides improved models for both the equator and the ecliptic, and also includes parameterized provision for future adjustment to match new determinations of properties of the non-rigid Earth such as the precession rates and J2 rate. Practical use of the new model involves choices of algorithm and computational procedure, and a number of ways have been studied (Capitaine & Wallace 2006) of generating the directions of the celestial intermediate pole and origin (CIP, CIO), from which the usual rotation matrices can be obtained. From a wide range of possible procedures we have selected two that target different classes of application, typified by the SOFA software and the IERS Conventions respectively. These procedures achieve a high standard of consistency, both internal and mutual, as well as being efficient and versatile. One is based on the Fukushima-Williams precession-nutation angles, the other on series for the CIP coordinates. Both use the CIO locator s, and both deliver the full range of products, supporting classical equinox/GST methods in addition to the CIO/ERA "new paradigm".
Turbulent mixing in a precessing sphere
Goto, Susumu Shimizu, Masaki; Kawahara, Genta
2014-11-15
By numerically simulating turbulent flows at high Reynolds numbers in a precessing sphere, we propose a method to enhance the mixing of a fluid confined within a smooth cavity by its rotational motion alone. To precisely evaluate the mixing efficiency, we extend the quantification method proposed by Danckwerts [“The definition and measurement of some characteristics of mixtures,” Appl. Sci. Res. A 3, 279–296 (1952)] to the case in which only a finite number of fluid particle trajectories can be known. Our accurate numerical tracking of fluid particles in the flow, which is controlled by the Reynolds number (an indicator of the spin rate) and the Poincaré number (the precession rate), shows the following results. First, the mixing process on the time scale normalized by the spin period is independent of the Reynolds number as long as it is high enough for the flow to be developed turbulence. Second, fastest mixing is achieved under weak precession (Poincaré number ≈0.1); in such cases, perfect mixing requires only 10–15 spins of the container. Third, the power to sustain turbulence is a weakly increasing function of the Poincaré number, and the energy efficiency of the mixing is also maximized when the Poincaré number is about 0.1. Fourth, efficient mixing driven by the weak precession arises from the effective cooperation of complex large-scale flow and small-scale turbulence, which itself is sustained by the large-scale flow.
Structure refinement from precession electron diffraction data.
Palatinus, Lukáš; Jacob, Damien; Cuvillier, Priscille; Klementová, Mariana; Sinkler, Wharton; Marks, Laurence D
2013-03-01
Electron diffraction is a unique tool for analysing the crystal structures of very small crystals. In particular, precession electron diffraction has been shown to be a useful method for ab initio structure solution. In this work it is demonstrated that precession electron diffraction data can also be successfully used for structure refinement, if the dynamical theory of diffraction is used for the calculation of diffracted intensities. The method is demonstrated on data from three materials - silicon, orthopyroxene (Mg,Fe)(2)Si(2)O(6) and gallium-indium tin oxide (Ga,In)(4)Sn(2)O(10). In particular, it is shown that atomic occupancies of mixed crystallographic sites can be refined to an accuracy approaching X-ray or neutron diffraction methods. In comparison with conventional electron diffraction data, the refinement against precession diffraction data yields significantly lower figures of merit, higher accuracy of refined parameters, much broader radii of convergence, especially for the thickness and orientation of the sample, and significantly reduced correlations between the structure parameters. The full dynamical refinement is compared with refinement using kinematical and two-beam approximations, and is shown to be superior to the latter two. PMID:23403968
Warp evidence in precessing galactic bar models
NASA Astrophysics Data System (ADS)
Sánchez-Martín, P.; Romero-Gómez, M.; Masdemont, J. J.
2016-04-01
Most galaxies have a warped shape when they are seen edge-on. The reason for this curious form is not completely known so far, so in this work we apply dynamical system tools to contribute to its explanation. Starting from a simple, but realistic model formed by a bar and a disc, we study the effect of a small misalignment between the angular momentum of the system and its angular velocity. To this end, a precession model was developed and considered, assuming that the bar behaves like a rigid body. After checking that the periodic orbits inside the bar continue to be the skeleton of the inner system even after inflicting a precession to the potential, we computed the invariant manifolds of the unstable periodic orbits departing from the equilibrium points at the ends of the bar to find evidence of their warped shapes. As is well known, the invariant manifolds associated with these periodic orbits drive the arms and rings of barred galaxies and constitute the skeleton of these building blocks. Looking at them from a side-on viewpoint, we find that these manifolds present warped shapes like those recognised in observations. Lastly, test particle simulations have been performed to determine how the stars are affected by the applied precession, this way confirming the theoretical results.
Quipus and System of Coordinated Precession
NASA Astrophysics Data System (ADS)
Campos, T. C.
2004-05-01
The Incas of ancient Peru possessed no writing. Instead, they developed a unique system expressed on spatial arrays of colored knotted cords called Quipus to record and transmit information throughout their vast empire. In their thorough description of quipus, Ascher & Ascher observed that in two cases the numbers registered in their strings have a very special relationship to each other. For this to occur the numbers must have been obtained through the multiplication of whole numbers by fractions or decimals, operations apparently beyond the arithmetic knowledge of the Incas. The quipus AS120 and AS143, coming from Ica (Peru) and conserved in the Museum of Berlin has the suitable characteristics previously. In the AS143 there is a the relationship with the systems of coordinated precession (tilt of Earth's spin axis (40036); eccentricity of Earth's orbit (97357); and precession of equinoxes (between 18504 and 23098)). For the history of the Earth are necessary an chronometer natural to coordinate and to classify the observations and this chronometer comes to be the vernal point, defining the vernal point as" a sensitive axis of maximum conductivity" as itdemonstrates it the stability of the geomagnetic equator (inclination of the field is zero grades), in the year 1939 calculated with the IGRF from the year 1900 up to the 2004 and that it is confirmed with tabulated data of the Geophysical Institute of Huancayo (Peru),from that date until this year (2004) and this fluctuating between the 12-14 South.,on the other hand in the area of Brazil it has advanced very quickly toward the north, and above to 108 km. approximately it is located the equatorial electrojet that is but intense in the equinoxes in South America. And this stability from the point of view of the precession of the equinoxes this coinciding with the entrance of the apparent sun for the constellation of Aquarius, being this mechanism the base to establish a system of coordinated precession where it is
Precession as a driving mechanism for the geodynamo
NASA Astrophysics Data System (ADS)
Tilgner, A.
Precession of the earth's rotation axis has long ago been proposed as a possible driving mechanism for the geodynamo. Past research has focused on convectively driven dynamos and relatively little is known about the hydrodynamics of precession, even in the absence of a magnetic field. Some properties of precession driven flows will be presented and the possiblity of these flows acting as dynamos will be discussed.
Compatibility of Larmor's Formula with Radiation Reaction for an Accelerated Charge
NASA Astrophysics Data System (ADS)
Singal, Ashok K.
2016-05-01
It is shown that the well-known disparity in classical electrodynamics between the power losses calculated from the radiation reaction and that from Larmor's formula, is succinctly understood when a proper distinction is made between quantities expressed in terms of a "real time" and those expressed in terms of a retarded time. It is explicitly shown that an accelerated charge, taken to be a sphere of vanishingly small radius r_o , experiences at any time a self-force proportional to the acceleration it had at a time r_o /c earlier, while the rate of work done on the charge is obtained by a scalar product of the self-force with the instantaneous (present) value of its velocity. Now if the retarded value of acceleration is expressed in terms of the present values of acceleration, then we get the rate of work done according to the radiation reaction equation, however if we instead express the present value of velocity in terms of its time-retarded value, then we get back the familiar Larmor's radiation formula. From this simple relation between the two we show that they differ because Larmor's formula, in contrast with the radiation reaction, is written not in terms of the real-time values of quantities specifying the charge motion but is instead expressed in terms of the time-retarded values. Moreover, it is explicitly shown that the difference in the two formulas for radiative power loss exactly matches the difference in the temporal rate of the change of energy in the self-fields between the retarded and real times. From this it becomes obvious that the ad hoc introduction of an acceleration-dependent energy term, usually referred to in the prevalent literature as Schott-term, in order to make the two formulas comply with each other, is redundant.
Finite Larmor radius effects on the (m = 2, n = 1) cylindrical tearing mode
NASA Astrophysics Data System (ADS)
Chen, Y.; Chowdhury, J.; Parker, S. E.; Wan, W.
2015-04-01
New field solvers are developed in the gyrokinetic code GEM [Chen and Parker, J. Comput. Phys. 220, 839 (2007)] to simulate low-n modes. A novel discretization is developed for the ion polarization term in the gyrokinetic vorticity equation. An eigenmode analysis with finite Larmor radius effects is developed to study the linear resistive tearing mode. The mode growth rate is shown to scale with resistivity as γ ˜ η1/3, the same as the semi-collisional regime in previous kinetic treatments [Drake and Lee, Phys. Fluids 20, 1341 (1977)]. Tearing mode simulations with gyrokinetic ions are verified with the eigenmode calculation.
Comments on finite Larmor radius models for ion cyclotron range of frequencies heating in tokamaks
Phillips, C.K.; Wilson, J.R.; Hosea, J.C.; Majeski, R.; Smithe, D.N.
1994-06-01
The accuracy of standard finite Larmor radius (FLR) models for wave propagation in the ion cyclotron range of frequencies (ICRF) is compared against full hot plasma models. For multiple ion species plasmas, the FLR model is shown to predict the presence of a spurious second harmonic ion-ion type resonance between the second harmonic cyclotron layers of two ion species. It is shown explicitly here that the spurious resonance is an artifact of the FLR models and that no absorption occurs in the plasma as a result of this ``resonance.``
Jain, Shweta Sharma, Prerana; Chhajlani, R. K.
2015-07-31
The Jeans instability of self-gravitating quantum plasma is examined considering the effects of viscosity, finite Larmor radius (FLR) corrections and rotation. The analysis is done by normal mode analysis theory with the help of relevant linearized perturbation equations of the problem. The general dispersion relation is obtained using the quantum magneto hydrodynamic model. The modified condition of Jeans instability is obtained and the numerical calculations have been performed to show the effects of various parameters on the growth rate of Jeans instability.
Finite Larmor radius effects on the coupled trapped electron and ion temperature gradient modes
Sandberg, I.; Isliker, H.; Pavlenko, V. P.
2007-09-15
The properties of the coupled trapped electron and toroidal ion temperature gradient modes are investigated using the standard reactive fluid model and taking rigorously into account the effects attributed to the ion polarization drift and to the drifts associated with the lowest-order finite ion Larmor radius effects. In the flat density regime, where the coupling between the modes is relatively weak, the properties of the unstable modes are slightly modified through these effects. For the peak density regions, where the coupling of the modes is rather strong, these second-order drifts determine the spectra of the unstable modes near the marginal conditions.
Comments on finite Larmor radius models for ion cyclotron range of frequencies heating in tokamaks
Phillips, C.K.; Wilson, J.R.; Hosea, J.C.; Majeski, R. ); Smithe, D.N. )
1994-12-01
The accuracy of standard finite Larmor radius (FLR) models for wave propagation in the ion cyclotron range of frequencies (ICRF) is compared against full hot plasma models. For multiple ion species plasmas, the FLR model is shown to predict the presence of a spurious second harmonic ion--ion type resonance between the second harmonic cyclotron layers of two ion species. It is shown explicitly here that the spurious resonance is an artifact of the FLR models and that no absorption occurs in the plasma as a result of this resonance.''
Review Of The Working Group On Precession And The Ecliptic
NASA Astrophysics Data System (ADS)
Hilton, J. L.
2006-08-01
The IAU Working Group on Precession and the Ecliptic was charged with providing a precession model that was both dynamically consistent and compatible with the IAU 2000A nutation model, along with an updated definition and model for the ecliptic. The report of the working group has been accepted for publication in Celestial Mechanics (Hilton et al. 2006, in press) and has resulted in a recommendation to be considered at this General Assembly of the IAU. Specifically, the working group recommends: 1. That the terms lunisolar precession and planetary precession be replaced by precession of the equator and precession of the ecliptic, respectively. 2. That, beginning on 1 January 2009, the precession component of the IAU 2000A precession-nutation model be replaced by the P03 precession theory, of Capitaine et al. (2003, A&A, 412, 567-586) for the precession of the equator (Eqs. 37) and the precession of the ecliptic (Eqs. 38); the same paper provides the polynomial developments for the P03 primary angles and a number of derived quantities for use in both the equinox based and Celestial Intermediate Origin based paradigms. 3. That the choice of precession parameters be left to the user. 4. That the ecliptic pole should be explicitly defined by the mean orbital angular momentum vector of the Earth-Moon barycenter in an inertial reference frame, and this definition should be explicitly stated to avoid confusion with other, older definitions. consistent and compatible with the IAU 2000A nutation model, along consistent and compatible with the IAU 2000A nutation model, along with an updated definition and model for the ecliptic. The report of the working group has been accepted for publication in Celestial Mechanics (Hilton et al. 2006, in press) and has resulted in a recommendation to be considered at this General Assembly of the IAU. Specifically, the working group recommends, * that the terms lunisolar precession and planetary precession be replaced by precession of the
A Precession-Driven Lunar Dynamo
NASA Astrophysics Data System (ADS)
Tian, B. Y.; Stanley, S.; Tikoo, S. M.; Weiss, B. P.
2014-12-01
Paleomagnetic studies of Apollo samples suggest that the Moon generated a magnetic field with surface field intensities of several tens of microteslas until at least 3.56 billion years ago (Ga). The field then declined by an order of magnitude from 3.56 - 3.19 Ga. Because of difficulties in reproducing such a long-lived and intense field with convection-driven dynamos, a dynamo driven by precession of the mantle relative to the core was proposed as an alternative. However, there have not been any detailed numerical models demonstrating the feasibility, lifetime, and intensity of such a lunar dynamo. Using fully 3D magnetohydrodynamic simulations, we determined the strength and duration of a mechanically-driven dynamo powered by mantle precession. We found that this mechanism was capable of not only generating the 10-100μT paleomagnetic intensities observed in Apollo samples aged between 4.25 and 3.56 Ga, but also reproducing the precipitous decline in paleointensity beyond 3.56 Ga as the obliquity of the Moon decreased below 15°.
Two spinning ways for precession dynamo
NASA Astrophysics Data System (ADS)
Cappanera, L.; Guermond, J.-L.; Léorat, J.; Nore, C.
2016-04-01
It is numerically demonstrated by means of a magnetohydrodynamic code that precession can trigger dynamo action in a cylindrical container. Fixing the angle between the spin and the precession axis to be 1/2 π , two limit configurations of the spinning axis are explored: either the symmetry axis of the cylinder is parallel to the spin axis (this configuration is henceforth referred to as the axial spin case), or it is perpendicular to the spin axis (this configuration is referred to as the equatorial spin case). In both cases, the centro-symmetry of the flow breaks when the kinetic Reynolds number increases. Equatorial spinning is found to be more efficient in breaking the centro-symmetry of the flow. In both cases, the average flow in the reference frame of the mantle converges to a counter-rotation with respect to the spin axis as the Reynolds number grows. We find a scaling law for the average kinetic energy in term of the Reynolds number in the axial spin case. In the equatorial spin case, the unsteady asymmetric flow is shown to be capable of sustaining dynamo action in the linear and nonlinear regimes. The magnetic field is mainly dipolar in the equatorial spin case, while it is is mainly quadrupolar in the axial spin case.
Ultra high resolution neutron scattering: Neutron Resonance Spin-Echo and Larmor Diffraction
NASA Astrophysics Data System (ADS)
Walters, Andrew; Keller, Thomas; Keimer, Bernhard
2012-02-01
The TRISP spectrometer at the FRM II neutron source near Munich, Germany, is a unique world-leading neutron scattering instrument which employs the Neutron Resonance Spin-Echo technique (NRSE). Linewidths of dispersive excitations with energy transfers up to 50 meV can be measured with an energy resolution in the μeV range without the restrictive flux limitations that normally apply to high resolution neutron triple-axis spectrometers. Pioneering studies on the electron-phonon interaction in elemental superconductorsootnotetextP. Aynajian et al., Science 319 1509 (2008) and the lifetimes of magnetic excitations in archetypal magnetic systems will be reviewed.ootnotetextS. Bayrakci et al., Science 312 1928 (2006) The instrument can also be used as a Larmor diffractometer, enabling d-spacings to be measured with a resolution of δdd ˜10-6, i.e. more than one order of magnitude more sensitive than conventional diffraction techniques.ootnotetextC. Pfleiderer et al., Science 316 1871 (2007) Ongoing and future NRSE and Larmor diffraction projects will be outlined, especially in regard to prospective studies which will take full advantage of the new low temperature and high pressure sample environment capabilities now available at TRISP.
A fluid finite ion Larmor radius model of the magnetopause layer
Stasiewicz, K. )
1989-07-01
A model of the magnetopause current layer is constructed on the basis of fluid equations for collision-free plasmas with finite ion Larmor radius (FLR). The model provides self-consistent solutions for the plasma flow vector, magnetic field, and electric currents inside the magnetopause layer. This is the first fluid model that offers explanations for some observations at the terrestrial magnetopause that are inexplicable by earlier models. In particular, it is shown that the erosion of the dayside magnetosphere can be explained by the normal component of the gyroviscous stress tensor that is related to the intensity of field-aligned currents inside the magnetopause layer. It is found that the sense of rotation of the magnetic field across the magnetopause is determined by the ratio of the normal component of the Alfven velocity to the normal flow velocity {xi}={ital B}{sub {ital n}}/({mu}{sub 0}{rho}){sup 1/2}{ital V}{sub {ital n}}. For {vert bar} {xi} {vert bar}{gt}1 the sense of rotation corresponds to electron polarization, and {vert bar} {xi} {vert bar}{lt}1 yields proton polarization. It is argued that the case {vert bar} {xi} {vert bar}=1 corresponds to the formation of transient flux transfer events. The observed departures from MHD jump conditions across the magnetopause are explained by additional, finite Larmor radius terms in the moment equations. An expression is also derived for the characteristic thickness of the magnetopause layer. {copyright} American Geophysical Union 1989
Ghosh, Sanjoy; Parashar, Tulasi N.
2015-04-15
The local k-space ratio of linear and nonlinear accelerations associated with a variety of initial conditions undergoing steady relaxation is investigated for the Hall–finite-Larmor-radius magnetohydrodynamics (MHD) system in the presence of a mean magnetic field. Building on a related study (Paper I) where it was shown that discrepancies exist between describing the global and local characterizations of the pure MHD system with mean magnetic field, we find regions of the Fourier space that are consistently dominated by linear acceleration and other regions that are consistently dominated by nonlinear acceleration, independent of the overall system's description as linear, weakly nonlinear, or turbulent. In general, dynamics within a certain angular range of the mean magnetic field direction are predominantly linear, while dynamics adjacent the Hall scales along the field-parallel direction and dynamics adjacent the finite Larmor radius scales in the field-perpendicular direction can become strongly nonlinear. The nonlinear influences are particularly significant as the plasma beta increases from unity to higher values.
The use of symmetry to correct Larmor phase aberrations in spin echo scattering angle measurement
NASA Astrophysics Data System (ADS)
Pynn, Roger; Lee, W. T.; Stonaha, P.; Shah, V. R.; Washington, A. L.; Kirby, B. J.; Majkrzak, C. F.; Maranville, B. B.
2008-06-01
Spin echo scattering angle measurement (SESAME) is a sensitive interference technique for measuring neutron diffraction. The method uses waveplates or birefringent prisms to produce a phase separation (the Larmor phase) between the "up" and "down" spin components of a neutron wavefunction that is initially prepared in a state that is a linear combination of in-phase up and down components. For neutrons, uniformly birefringent optical elements can be constructed from closed solenoids with appropriately shaped cross sections. Such elements are inconvenient in practice, however, both because of the precision they demand in the control of magnetic fields outside the elements and because of the amount of material required in the neutron beam. In this paper, we explore a different option in which triangular-cross-section solenoids used to create magnetic fields for SESAME have gaps in one face, allowing the lines of magnetic flux to "leak out" of the solenoid. Although the resulting field inhomogeneity produces aberrations in the Larmor phase, the symmetry of the solenoid gaps causes the aberrations produced by neighboring pairs of triangular solenoids to cancel to a significant extent. The overall symmetry of the SESAME apparatus leads to further cancellations of aberrations, providing an architecture that is easy to construct and robust in performance.
Keenan, Brett D; Ford, Alexander L; Medvedev, Mikhail V
2015-11-01
High-amplitude, chaotic or turbulent electromagnetic fluctuations are ubiquitous in high-energy-density laboratory and astrophysical plasmas, where they can be excited by various kinetic-streaming and/or anisotropy-driven instabilities, such as the Weibel instability. These fields typically exist on "sub-Larmor scales"-scales smaller than the electron Larmor radius. Electrons moving through such magnetic fields undergo small-angle stochastic deflections of their pitch angles, thus establishing diffusive transport on long time scales. We show that this behavior, under certain conditions, is equivalent to Coulomb collisions in collisional plasmas. The magnetic pitch-angle diffusion coefficient, which acts as an effective "collision" frequency, may be substantial in these, otherwise, collisionless environments. We show that this effect, colloquially referred to as the plasma "quasicollisionality," may radically alter the expected radiative transport properties of candidate plasmas. We argue that the modified magneto-optic effects in these plasmas provide an attractive, radiative diagnostic tool for the exploration and characterization of small-scale magnetic turbulence, as well as affect inertial confinement fusion and other laser-plasma experiments. PMID:26651797
NASA Astrophysics Data System (ADS)
Keenan, Brett D.; Ford, Alexander L.; Medvedev, Mikhail V.
2015-11-01
High-amplitude, chaotic or turbulent electromagnetic fluctuations are ubiquitous in high-energy-density laboratory and astrophysical plasmas, where they can be excited by various kinetic-streaming and/or anisotropy-driven instabilities, such as the Weibel instability. These fields typically exist on "sub-Larmor scales"—scales smaller than the electron Larmor radius. Electrons moving through such magnetic fields undergo small-angle stochastic deflections of their pitch angles, thus establishing diffusive transport on long time scales. We show that this behavior, under certain conditions, is equivalent to Coulomb collisions in collisional plasmas. The magnetic pitch-angle diffusion coefficient, which acts as an effective "collision" frequency, may be substantial in these, otherwise, collisionless environments. We show that this effect, colloquially referred to as the plasma "quasicollisionality," may radically alter the expected radiative transport properties of candidate plasmas. We argue that the modified magneto-optic effects in these plasmas provide an attractive, radiative diagnostic tool for the exploration and characterization of small-scale magnetic turbulence, as well as affect inertial confinement fusion and other laser-plasma experiments.
Geodetic precession in squashed Kaluza-Klein black hole spacetimes
Matsuno, Ken; Ishihara, Hideki
2009-11-15
We investigate the geodetic precession effect of a parallelly transported spin vector along a circular geodesic in five-dimensional squashed Kaluza-Klein black hole spacetime. Then we derive the higher-dimensional correction of the precession angle to general relativity. We find that the correction is proportional to the square of (size of extra dimension)/(gravitational radius of central object)
precession: Dynamics of spinning black-hole binaries with python
NASA Astrophysics Data System (ADS)
Gerosa, Davide; Kesden, Michael
2016-06-01
We present the numerical code precession, a new open-source python module to study the dynamics of precessing black-hole binaries in the post-Newtonian regime. The code provides a comprehensive toolbox to (i) study the evolution of the black-hole spins along their precession cycles, (ii) perform gravitational-wave-driven binary inspirals using both orbit-averaged and precession-averaged integrations, and (iii) predict the properties of the merger remnant through fitting formulas obtained from numerical-relativity simulations. precession is a ready-to-use tool to add the black-hole spin dynamics to larger-scale numerical studies such as gravitational-wave parameter estimation codes, population synthesis models to predict gravitational-wave event rates, galaxy merger trees and cosmological simulations of structure formation. precession provides fast and reliable integration methods to propagate statistical samples of black-hole binaries from/to large separations where they form to/from small separations where they become detectable, thus linking gravitational-wave observations of spinning black-hole binaries to their astrophysical formation history. The code is also a useful tool to compute initial parameters for numerical-relativity simulations targeting specific precessing systems. precession can be installed from the python Package Index, and it is freely distributed under version control on github, where further documentation is provided.
Keenan, Brett D; Ford, Alexander L; Medvedev, Mikhail V
2015-09-01
Plasmas with electromagnetic fields turbulent at sub-Larmor scales are a feature of a wide variety of high-energy-density environments and are essential to the description of many astrophysical and laboratory plasma phenomena. Radiation from particles, whether they are relativistic or nonrelativistic, moving through small-scale magnetic turbulence has spectral characteristics distinct from both synchrotron and cyclotron radiation. The radiation, carrying information on the statistical properties of the magnetic turbulence, is also intimately related to the particle diffusive transport. We have investigated, both theoretically and numerically, the transport of nonrelativistic and trans-relativistic particles in plasmas with high-amplitude isotropic sub-Larmor-scale magnetic turbulence, and its relation to the spectra of radiation simultaneously produced by these particles. Consequently, the diffusive and radiative properties of plasmas turbulent on sub-Larmor scales may serve as a powerful tool to diagnosis laboratory and astrophysical plasmas. PMID:26465572
Effect of equinoctial precession on geosynchronous earth satellites
NASA Astrophysics Data System (ADS)
Gurfil, P.
The long-periodic effects of the equinoctial precession on geosynchronous Earth orbit satellites are investigated. The equations of motion in a reference frame that coprecesses with the Earth are developed, and the resulting variational equations are derived using mean classical orbital elements. The Earth gravitational model includes the J_2 and J_3 zonal harmonics, which induce the equinoctial precession due to the lunisolar gravitational torque. It is shown that the ever-growing lifetime and mass of geosynchronous Earth orbit satellites render the equinoctial precession a significant factor, which should be taken into account during mission design, as it affects north-south stationkeeping maneuvers. The equilibria of the variational equations including the zonal harmonics and the equinoctial precession are investigated and a class of stable frozen orbits which are equinoctial precession invariant is derived.
Rectification and precession signals in the climate system
NASA Astrophysics Data System (ADS)
Huybers, P.; Wunsch, C.
2003-10-01
Precession of the equinoxes has no effect on the mean annual insolation, but does modulate the amplitude of the seasonal cycle. In a linear climate system, there would be no energy near the 21,000 year precession period. It is only when a non-linear mechanism rectifies the seasonal modulation that precession-period variability appears. Such rectification can arise from physical processes within the climate system, for example a dependence of ice cover only on summer maximum insolation. The possibility exists, however, that the seasonality inherent in many climate proxies will produce precession-period variability in the records independent of any precession-period variability in the climate. One must distinguish this instrumental effect from true climate responses. Careful examination of regions without seasonal cycles, for example the abyssal ocean, and the use of proxies with different seasonal responses, might permit separation of physical from instrumental effects.
Division I Working Group on `Precession and the Ecliptic'
NASA Astrophysics Data System (ADS)
Hilton, James L.; Capitaine, N.; Chapront, J.; Ferrandiz, J. M.; Fienga, A.; Fukushima, T.; Getino, J.; Mathews, P.; Simon, J.-L.; Soffel, M.; Vondrak, J.; Wallace, P.; Williams, J.
2007-03-01
The WG has conferred via email on the topics of providing a precession theory dynamically consistent with the IAU 2000A nutation theory and updating the expressions defining the ecliptic. The consensus of the WG is to recommend:(a) The terms lunisolar precession and planetary precession be replaced by precession of the equator and precession of the ecliptic, respectively.(b) The IAU adopt the P03 precession theory, of Capitaine et al (2003a, A& A 412, 567-586) for the precession of the equator (Eqs. 37) and the precession of the ecliptic (Eqs. 38); the same paper provides the polynomial developments for the P03 primary angles and a number of derived quantities for use in both the equinox based and celestial intermediate origin based paradigms.(c) The choice of precession parameters be left to the user.(d) The recommended polynomial coefficients for a number of precession angles are given in Table 1 of the WG report, including the P03 expressions set out in Tables 3-5 of Capitaine et al (2005, A& A 432, 355-367), and those of the alternative Fukushima (2003, AJ 126, 494-534) parameterization; the corresponding matrix representations are given in equations 1, 6, 11, and 22 of the WG report.(e) The ecliptic pole should be explicitly defined by the mean orbital angular momentum vector of the Earth-Moon barycenter in an inertial reference frame, and this definition should be explicitly stated to avoid confusion with older definitions. The formal WG report will be submitted, shortly to Celest. Mech. for publication and their recommendations will be submitted at the next General Assembly for adoption by the IAU.
Precession electron diffraction – a topical review
Midgley, Paul A.; Eggeman, Alexander S.
2015-01-01
In the 20 years since precession electron diffraction (PED) was introduced, it has grown from a little-known niche technique to one that is seen as a cornerstone of electron crystallography. It is now used primarily in two ways. The first is to determine crystal structures, to identify lattice parameters and symmetry, and ultimately to solve the atomic structure ab initio. The second is, through connection with the microscope scanning system, to map the local orientation of the specimen to investigate crystal texture, rotation and strain at the nanometre scale. This topical review brings the reader up to date, highlighting recent successes using PED and providing some pointers to the future in terms of method development and how the technique can meet some of the needs of the X-ray crystallography community. Complementary electron techniques are also discussed, together with how a synergy of methods may provide the best approach to electron-based structure analysis. PMID:25610633
Solutions to the relativistic precession model
NASA Astrophysics Data System (ADS)
Ingram, Adam; Motta, Sara
2014-11-01
The relativistic precession model (RPM) can be used to obtain a precise measurement of the mass and spin of a black hole when the appropriate set of quasi-periodic oscillations is detected in the power-density spectrum of an accreting black hole. However, in previous studies, the solution of the RPM equations could be obtained only through numerical methods at a price of an intensive computational effort. Here, we demonstrate that the RPM system of equations can be solved analytically, drastically reducing the computational load, now limited to the Monte Carlo simulation necessary to estimate the uncertainties. The analytical method not only provides an easy solution to the RPM system when three oscillations are detected, but in all the cases where the detection of two simultaneous oscillations is coupled with an independent mass measurement. We also present a computationally inexpensive method to place limits on the black hole mass and spin when only two oscillations are observed.
Precession, Nutation and Wobble of the Earth
NASA Astrophysics Data System (ADS)
Dehant, V.; Mathews, P. M.
2015-04-01
Covering both astronomical and geophysical perspectives, this book describes changes in the Earth's orientation, specifically precession and nutation, and how they are observed and computed in terms of tidal forcing and models of the Earth's interior. Following an introduction to key concepts and elementary geodetic theory, the book describes how precise measurements of the Earth's orientation are made using observations of extra-galactic radio-sources by Very Long Baseline Interferometry techniques. It demonstrates how models are used to accurately pinpoint the location and orientation of the Earth with reference to the stars and how to determine variations in its rotation speed. A theoretical framework is also presented that describes the role played by the structure and properties of the Earth's deep interior. Incorporating suggestions for future developments in nutation theory for the next generation models, this book is ideal for advanced-level students and researche! rs in solid Earth geophysics, planetary science and astronomy.
Precession electron diffraction - a topical review.
Midgley, Paul A; Eggeman, Alexander S
2015-01-01
In the 20 years since precession electron diffraction (PED) was introduced, it has grown from a little-known niche technique to one that is seen as a cornerstone of electron crystallography. It is now used primarily in two ways. The first is to determine crystal structures, to identify lattice parameters and symmetry, and ultimately to solve the atomic structure ab initio. The second is, through connection with the microscope scanning system, to map the local orientation of the specimen to investigate crystal texture, rotation and strain at the nanometre scale. This topical review brings the reader up to date, highlighting recent successes using PED and providing some pointers to the future in terms of method development and how the technique can meet some of the needs of the X-ray crystallography community. Complementary electron techniques are also discussed, together with how a synergy of methods may provide the best approach to electron-based structure analysis. PMID:25610633
P03-based precession-nutation matrices
NASA Astrophysics Data System (ADS)
Wallace, P.; Capitaine, N.
2006-10-01
The IAU WG on precession and the ecliptic has recommended the adoption of the P03 models of Capitaine et al. (2003). We discuss methods for generating the rotation matrices that transform celestial to terrestrial coordinates, taking into account frame bias (B), P03 precession (P), P03-adjusted IAU 2000A nutation (N) and Earth rotation. The NPB portion can refer either to the equinox or the celestial intermediate origin (CIO), requiring either the Greenwich sidereal time (GST) or the Earth rotation angle (ERA) as the measure of Earth rotation. The equinox based NPB transformation can be formed using various sequences of rotations, while the CIO based transformation can be formed using series for the X, Y coordinates of the celestial intermediate pole (CIP) and for the CIO locator s; also, either matrix can be computing using series for the x, y, z components of the "rotation vector". Common to both methods is the CIP, which forms the bottom row of the transformation matrix. In the case of the CIO based transformation, the CIO is the top row of the NPB matrix, whereas in the equinox based case it enters via the GST formulation in the form of the equation of the origins (EO). The EO is the difference between ERA and GST and equivalently the distance between the CIO and equinox. The choice of method is dictated by considerations of internal consistency, flexibility and ease of use; the different ways agree at the level of a few microarcseconds over several centuries, and consume similar computing resources.
Ion finite Larmor radius effects on the interchange instability in an open system
Katanuma, I.; Sato, S.; Okuyama, Y.; Kato, S.; Kubota, R.
2013-11-15
A particle simulation of an interchange instability was performed by taking into account the ion finite Larmor radius (FLR) effects. It is found that the interchange instability with large FLR grows in two phases, that is, linearly growing phase and the nonlinear phase subsequent to the linear phase, where the instability grows exponentially in both phases. The linear growth rates observed in the simulation agree well with the theoretical calculation. The effects of FLR are usually taken in the fluid simulation through the gyroviscosity, the effects of which are verified in the particle simulation with large FLR regime. The gyroviscous cancellation phenomenon observed in the particle simulation causes the drifts in the direction of ion diamagnetic drifts.
Forward and Backward Precession of a Vertical Anisotropically Supported Rotor
NASA Astrophysics Data System (ADS)
Muszynska, A.
1996-04-01
This paper presents the analytical and experimental study of a vertical, overhung imbalanced rotor supported by flexible, anisotropic bearings. The results show that existence of imbalance and shaft bow causes the synchronous forced precession of the rotor to be forward (below the first value of split balance resonance and above the second value of the split balance resonance) or backward (between the two values of the split resonance). This phenomenon is classical. The new result consists of exploring the existence of forward precession of the inboard and midspan rotor sections while the outboard disk is precessing backward. The sensitivity analysis shows which system parameters are mainly responsible for this apparently bizarre phenomenon.
Electronic spin transport and spin precession in single graphene layers at room temperature.
Tombros, Nikolaos; Jozsa, Csaba; Popinciuc, Mihaita; Jonkman, Harry T; van Wees, Bart J
2007-08-01
Electronic transport in single or a few layers of graphene is the subject of intense interest at present. The specific band structure of graphene, with its unique valley structure and Dirac neutrality point separating hole states from electron states, has led to the observation of new electronic transport phenomena such as anomalously quantized Hall effects, absence of weak localization and the existence of a minimum conductivity. In addition to dissipative transport, supercurrent transport has also been observed. Graphene might also be a promising material for spintronics and related applications, such as the realization of spin qubits, owing to the low intrinsic spin orbit interaction, as well as the low hyperfine interaction of the electron spins with the carbon nuclei. Here we report the observation of spin transport, as well as Larmor spin precession, over micrometre-scale distances in single graphene layers. The 'non-local' spin valve geometry was used in these experiments, employing four-terminal contact geometries with ferromagnetic cobalt electrodes making contact with the graphene sheet through a thin oxide layer. We observe clear bipolar (changing from positive to negative sign) spin signals that reflect the magnetization direction of all four electrodes, indicating that spin coherence extends underneath all of the contacts. No significant changes in the spin signals occur between 4.2 K, 77 K and room temperature. We extract a spin relaxation length between 1.5 and 2 mum at room temperature, only weakly dependent on charge density. The spin polarization of the ferromagnetic contacts is calculated from the measurements to be around ten per cent. PMID:17632544
Electronic spin transport and spin precession in single graphene layers at room temperature
NASA Astrophysics Data System (ADS)
Tombros, Nikolaos; Jozsa, Csaba; Popinciuc, Mihaita; Jonkman, Harry T.; van Wees, Bart J.
2007-08-01
Electronic transport in single or a few layers of graphene is the subject of intense interest at present. The specific band structure of graphene, with its unique valley structure and Dirac neutrality point separating hole states from electron states, has led to the observation of new electronic transport phenomena such as anomalously quantized Hall effects, absence of weak localization and the existence of a minimum conductivity. In addition to dissipative transport, supercurrent transport has also been observed. Graphene might also be a promising material for spintronics and related applications, such as the realization of spin qubits, owing to the low intrinsic spin orbit interaction, as well as the low hyperfine interaction of the electron spins with the carbon nuclei. Here we report the observation of spin transport, as well as Larmor spin precession, over micrometre-scale distances in single graphene layers. The `non-local' spin valve geometry was used in these experiments, employing four-terminal contact geometries with ferromagnetic cobalt electrodes making contact with the graphene sheet through a thin oxide layer. We observe clear bipolar (changing from positive to negative sign) spin signals that reflect the magnetization direction of all four electrodes, indicating that spin coherence extends underneath all of the contacts. No significant changes in the spin signals occur between 4.2K, 77K and room temperature. We extract a spin relaxation length between 1.5 and 2μm at room temperature, only weakly dependent on charge density. The spin polarization of the ferromagnetic contacts is calculated from the measurements to be around ten per cent.
The Equivalence of Precession Phenomena in Metric Theories of Gravity
NASA Technical Reports Server (NTRS)
Krisher, Timothy P.
1996-01-01
A simple argument is presented that demonstrates clearly, without the need for detailed calculation, how geodetic precession of a gyroscope and the effect of fram-draggin are fundamentally equivalent.
Suppression of vortex core precession in a swirling reacting flow
NASA Astrophysics Data System (ADS)
Litvinov, I. V.; Nazarov, A. V.; Shtork, S. I.
2016-03-01
The influence of combustion effect on unsteady vortex structure in the form of precessing vortex core was studied using the non-intrusive method of laser Doppler anemometry and special procedure of extracting the non-axisymmetric mode of flow fluctuations. The studies show that combustion has a significant effect on the parameters of such a core, reducing the amplitude (vortex deviation from the burner center) and increasing precession frequency. At the same time, the acoustic sensors detect almost an order reduction in the level of pressure pulsations generated by the precessing vortex core. Moreover, distributions of tangential velocity fluctuations and cross-correlation analysis show that vortex precession is quite pronounced even under the combustion conditions, bringing a significant coherent component to distributions of velocity fluctuations.
GRAVITATIONAL WAVES OF JET PRECESSION IN GAMMA-RAY BURSTS
Sun Mouyuan; Liu Tong; Gu Weimin; Lu Jufu
2012-06-10
The physical nature of gamma-ray bursts (GRBs) is believed to involve an ultra-relativistic jet. The observed complex structure of light curves motivates the idea of jet precession. In this work, we study the gravitational waves of jet precession based on neutrino-dominated accretion disks around black holes, which may account for the central engine of GRBs. In our model, the jet and the inner part of the disk may precess along with the black hole, which is driven by the outer part of the disk. Gravitational waves are therefore expected to be significant from this black-hole-inner-disk precession system. By comparing our numerical results with the sensitivity of some detectors, we find that it is possible for DECIGO and BBO to detect such gravitational waves, particularly for GRBs in the Local Group.
General spin precession and betatron oscillation in storage rings
NASA Astrophysics Data System (ADS)
Fukuyama, Takeshi
2016-07-01
Spin precession of particles having both anomalous magnetic and electric dipole moments (EDMs) is considered. We give the generalized expression of spin precession of these particles injected with transversal extent in magnetic storage rings. This is the generalization of the Farley’s pitch correction [F. J. N. Farley, Phys. Lett. B 42, 66 (1972)], including radial oscillation as well as vertical one. The transversal betatron oscillation formulae of these particles are also reproduced.
Experimental study of fluid flows in a precessing cylindrical annulus
NASA Astrophysics Data System (ADS)
Lin, Yufeng; Noir, Jerome; Jackson, Andrew
2014-04-01
The flow inside a precessing fluid cavity has been given particular attention since the end of the 19th century in geophysical and industrial contexts. The present study aims at shedding light on the underlying mechanism by which the flow inside a precessing cylindrical annulus transitions from laminar to multiple scale complex structures. We address this problem experimentally using ultrasonic Doppler velocimetry to diagnose the fluid velocity in a rotating and precessing cylindrical annulus. When precession is weak, the flow can be described as a superposition of forced inertial modes. Above a critical value of the precession rate, the forced flow couples with two free inertial modes satisfying triadic resonance conditions, leading to the classical growth and collapse. Using a Bayesian approach, we extract the wavenumber, frequency, growth rate, and amplitude of each mode involved in the instability. In some cases, we observe for the first time ever experimentally two pairs of free modes coexisting with the forced flow. At larger precession rates, we do not observe triadic resonance any more, instead we observe several harmonics whose frequencies are integer multiples of the rotation frequency.
Pulsar state switching, timing noise and free precession
NASA Astrophysics Data System (ADS)
Jones, D. I.
2012-03-01
Recent radio pulsar observations have shown that a number of pulsars display interesting long-term periodicities in their spin-down rates. At least some of these pulsars also undergo sharp changes in pulse profile. This has been convincingly attributed to the stars abruptly switching between two different magnetospheric states. The sharpness of these transitions has been taken as evidence against free precession as the mechanism behind the long-term variations. We argue that such a conclusion is premature. By performing a simple best-fitting analysis to the data, we show that the relationship between the observed spin and modulation periods is of approximately the correct form to be accounted for by the free precession of a population of neutron stars with strained crusts, the level of strain being similar in all of the stars, and consistent with the star retaining a memory of a former faster rotation rate. We also provide an argument as to why abrupt magnetospheric changes can occur in precessing stars, and how such changes would serve to magnify the effect of precession in the timing data, making the observation of the precession more likely in those stars where such switching occurs. We describe how future observations could further test the precession hypothesis advanced here.
Single-spin precessing gravitational waveform in closed form
NASA Astrophysics Data System (ADS)
Lundgren, Andrew; O'Shaughnessy, R.
2014-02-01
In coming years, gravitational-wave detectors should find black hole-neutron star (BH-NS) binaries, potentially coincident with astronomical phenomena like short gamma ray bursts. These binaries are expected to precess. Gravitational-wave science requires a tractable model for precessing binaries, to disentangle precession physics from other phenomena like modified strong field gravity, tidal deformability, or Hubble flow; and to measure compact object masses, spins, and alignments. Moreover, current searches for gravitational waves from compact binaries use templates where the binary does not precess and are ill-suited for detection of generic precessing sources. In this paper we provide a closed-form representation of the single-spin precessing waveform in the frequency domain by reorganizing the signal as a sum over harmonics, each of which resembles a nonprecessing waveform. This form enables simple analytic calculations of the Fisher matrix for use in template bank generation and coincidence metrics, and jump proposals to improve the efficiency of Markov chain Monte Carlo sampling. We have verified that for generic BH-NS binaries, our model agrees with the time-domain waveform to 2%. Straightforward extensions of the derivations outlined here (and provided in full online) allow higher accuracy and error estimates.
Perihelion precession, polar ice and global warming
NASA Astrophysics Data System (ADS)
Steel, Duncan
2013-03-01
The increase in mean global temperature over the past 150 years is generally ascribed to human activities, in particular the rises in the atmospheric mixing ratios of carbon dioxide and other greenhouse gases since the Industrial Revolution began. Whilst it is thought that ice ages and interglacial periods are mainly initiated by multi-millennial variations in Earth's heliocentric orbit and obliquity, shorter-term orbital variations and consequent observable climatic effects over decadal/centurial timescales have not been considered significant causes of contemporary climate change compared to anthropogenic influences. Here it is shown that the precession of perihelion occurring over a century substantially affects the intra-annual variation of solar radiation influx at different locations, especially higher latitudes, with northern and southern hemispheres being subject to contrasting insolation changes. This north/south asymmetry has grown since perihelion was aligned with the winter solstice seven to eight centuries ago, and must cause enhanced year-on-year springtime melting of Arctic (but not Antarctic) ice and therefore feedback warming because increasing amounts of land and open sea are denuded of high-albedo ice and snow across boreal summer and into autumn. The accelerating sequence of insolation change now occurring as perihelion moves further into boreal winter has not occurred previously during the Holocene and so would not have been observed before by past or present civilisations. Reasons are given for the significance of this process having been overlooked until now. This mechanism represents a supplementary - natural - contribution to climate change in the present epoch and may even be the dominant fundamental cause of global warming, although anthropogenic effects surely play a role too.
Finite Larmor Radius approximation for waves propagation in cylindrical plasma configurations
NASA Astrophysics Data System (ADS)
Galeotti, Laura; Ceccherini, Francesco; Brambilla, Marco; Barnes, Daniel C.; Pegoraro, Francesco
2011-10-01
We present an analytical derivation in cylindrical geometry of the Finite Larmor Radius approximation for the wave equations in the cyclotron frequency range and show a set of numerical results obtained with a new extended version of the code FELICE, which allows for arbitrary profiles of field, densities and temperatures. Obtaining a cylindrical FLR approximation is of great relevance for studying the wave propagation in plasma configurations like FRC's and theta-pinches in particular. The generic configuration we consider can be divided in the radial direction in two regions, i.e, a ``plasma region'' and a ``vacuum region''. In the former the wave propagation is computed numerically from the FRL approximation found, in the latter instead a general analytical solution has been calculated and implemented in the code. A detailed description on how to ensure both the overall causality of the propagation process and the correct matching conditions for the antenna surface and the vacuum/plasma surface is shown as well.
The effect of finite Larmor radius corrections on Jeans instability of quantum plasma
Sharma, Prerana; Chhajlani, R. K.
2013-09-15
The influence of finite Larmor radius (FLR) effects on the Jeans instability of infinitely conducting homogeneous quantum plasma is investigated. The quantum magnetohydrodynamic (QMHD) model is used to formulate the problem. The contribution of FLR is incorporated to the QMHD set of equations in the present analysis. The general dispersion relation is obtained analytically using the normal mode analysis technique which is modified due to the contribution of FLR corrections. From general dispersion relation, the condition of instability is obtained and it is found that Jeans condition is modified due to quantum effect. The general dispersion relation is reduced for both transverse and longitudinal mode of propagations. The condition of gravitational instability is modified due to the presence of both FLR and quantum corrections in the transverse mode of propagation. In longitudinal case, it is found to be unaffected by the FLR effects but modified due to the quantum corrections. The growth rate of Jeans instability is discussed numerically for various values of quantum and FLR corrections of the medium. It is found that the quantum parameter and FLR effects have stabilizing influence on the growth rate of instability of the system.
Kinetic-Scale Magnetic Turbulence and Finite Larmor Radius Effects at Mercury
NASA Technical Reports Server (NTRS)
Uritsky, V. M.; Slavin, J. A.; Khazanov, G. V.; Donovan, E. F.; Boardsen, S. A.; Anderson, B. J.; Korth, H.
2011-01-01
We use a nonstationary generalization of the higher-order structure function technique to investigate statistical properties of the magnetic field fluctuations recorded by MESSENGER spacecraft during its first flyby (01/14/2008) through the near-Mercury space environment, with the emphasis on key boundary regions participating in the solar wind - magnetosphere interaction. Our analysis shows, for the first time, that kinetic-scale fluctuations play a significant role in the Mercury's magnetosphere up to the largest resolvable timescale (approx.20 s) imposed by the signal nonstationariry, suggesting that turbulence at this plane I is largely controlled by finite Larmor radius effects. In particular, we report the presence of a highly turbulent and extended foreshock system filled with packets of ULF oscillations, broad-band intermittent fluctuations in the magnetosheath, ion-kinetic turbulence in the central plasma sheet of Mercury's magnetotail, and kinetic-scale fluctuations in the inner current sheet encountered at the outbound (dawn-side) magnetopause. Overall, our measurements indicate that the Hermean magnetosphere, as well as the surrounding region, are strongly affected by non-MHD effects introduced by finite sizes of cyclotron orbits of the constituting ion species. Physical mechanisms of these effects and their potentially critical impact on the structure and dynamics of Mercury's magnetic field remain to be understood.
Two-fluid and finite Larmor radius effects on helicity evolution in a plasma pinch
NASA Astrophysics Data System (ADS)
Sauppe, J. P.; Sovinec, C. R.
2016-03-01
The evolution of magnetic energy, helicity, and hybrid helicity during nonlinear relaxation of a driven-damped plasma pinch is compared in visco-resistive magnetohydrodynamics and two-fluid models with and without the ion gyroviscous stress tensor. Magnetic energy and helicity are supplied via a boundary electric field which initially balances the resistive dissipation, and the plasma undergoes multiple relaxation events during the nonlinear evolution. The magnetic helicity is well conserved relative to the magnetic energy over each event, which is short compared with the global resistive diffusion time. The magnetic energy decreases by roughly 1.5% of its initial value over a relaxation event, while the magnetic helicity changes by at most 0.2% of the initial value. The hybrid helicity is dominated by magnetic helicity in low-β pinch conditions and is also well conserved. Differences of less than 1% between magnetic helicity and hybrid helicity are observed with two-fluid modeling and result from cross helicity evolution. The cross helicity is found to change appreciably due to the first-order finite Larmor radius effects which have not been included in contemporary relaxation theories. The plasma current evolves towards the flat parallel current state predicted by Taylor relaxation theory but does not achieve it. Plasma flow develops significant structure for two-fluid models, and the flow perpendicular to the magnetic field is much more substantial than the flow along it.
Kohn's theorem, Larmor's equivalence principle and the Newton-Hooke group
Gibbons, G.W.; Pope, C.N.
2011-07-15
Highlights: > We show that non-relativistic electrons moving in a magnetic field with trapping potential admits as relativity group the Newton-Hooke group. > We use this fact to give a group theoretic interpretation of Kohn's theorem and to obtain the spectrum. > We obtain the lightlike lift of the system exhibiting showing it coincides with the Nappi-Witten spacetime. - Abstract: We consider non-relativistic electrons, each of the same charge to mass ratio, moving in an external magnetic field with an interaction potential depending only on the mutual separations, possibly confined by a harmonic trapping potential. We show that the system admits a 'relativity group' which is a one-parameter family of deformations of the standard Galilei group to the Newton-Hooke group which is a Wigner-Inoenue contraction of the de Sitter group. This allows a group-theoretic interpretation of Kohn's theorem and related results. Larmor's theorem is used to show that the one-parameter family of deformations are all isomorphic. We study the 'Eisenhart' or 'lightlike' lift of the system, exhibiting it as a pp-wave. In the planar case, the Eisenhart lift is the Brdicka-Eardley-Nappi-Witten pp-wave solution of Einstein-Maxwell theory, which may also be regarded as a bi-invariant metric on the Cangemi-Jackiw group.
An optical NMR spectrometer for Larmor-beat detection and high-resolution POWER NMR
NASA Astrophysics Data System (ADS)
Kempf, J. G.; Marohn, J. A.; Carson, P. J.; Shykind, D. A.; Hwang, J. Y.; Miller, M. A.; Weitekamp, D. P.
2008-06-01
Optical nuclear magnetic resonance (ONMR) is a powerful probe of electronic properties in III-V semiconductors. Larmor-beat detection (LBD) is a sensitivity optimized, time-domain NMR version of optical detection based on the Hanle effect. Combining LBD ONMR with the line-narrowing method of POWER (perturbations observed with enhanced resolution) NMR further enables atomically detailed views of local electronic features in III-Vs. POWER NMR spectra display the distribution of resonance shifts or line splittings introduced by a perturbation, such as optical excitation or application of an electric field, that is synchronized with a NMR multiple-pulse time-suspension sequence. Meanwhile, ONMR provides the requisite sensitivity and spatial selectivity to isolate local signals within macroscopic samples. Optical NMR, LBD, and the POWER method each introduce unique demands on instrumentation. Here, we detail the design and implementation of our system, including cryogenic, optical, and radio-frequency components. The result is a flexible, low-cost system with important applications in semiconductor electronics and spin physics. We also demonstrate the performance of our systems with high-resolution ONMR spectra of an epitaxial AlGaAs /GaAs heterojunction. NMR linewidths down to 4.1Hz full width at half maximum were obtained, a 103-fold resolution enhancement relative any previous optically detected NMR experiment.
NASA Astrophysics Data System (ADS)
Hilton, J. L.; Capitaine, N.; Chapront, J.; Ferrandiz, J. M.; Fienga, A.; Fukushima, T.; Getino, J.; Mathews, P.; Simon, J.-L.; Soffel, M.; Vondrak, J.; Wallace, P.; Williams, J.
2006-03-01
The IAU Working Group on Precession and the Equinox looked at several solutions for replacing the precession part of the IAU 2000A precession nutation model, which is not consistent with dynamical theory. These comparisons show that the (Capitaine et al., Astron. Astrophys., 412, 2003a) precession theory, P03, is both consistent with dynamical theory and the solution most compatible with the IAU 2000A nutation model. Thus, the working group recommends the adoption of the P03 precession theory for use with the IAU 2000A nutation. The two greatest sources of uncertainty in the precession theory are the rate of change of the Earth’s dynamical flattening, ΔJ 2, and the precession rates (i.e. the constants of integration used in deriving the precession). The combined uncertainties limit the accuracy in the precession theory to approximately 2 mas cent-2.
Electrical tissue property imaging using MRI at dc and Larmor frequency
NASA Astrophysics Data System (ADS)
Seo, Jin Keun; Kim, Dong-Hyun; Lee, Joonsung; In Kwon, Oh; Sajib, Saurav Z. K.; Woo, Eung Je
2012-08-01
Cross-sectional imaging of conductivity and permittivity distributions inside the human body has been actively investigated in impedance imaging areas such as electrical impedance tomography (EIT) and magnetic induction tomography (MIT). Since the conductivity and permittivity values exhibit frequency-dependent changes, it is worthwhile to perform spectroscopic imaging from almost dc to hundreds of MHz. To probe the human body, we may inject current using surface electrodes or induce current using external coils. In EIT and MIT, measured data are only available on the boundary or exterior of the body unless we invasively place sensors inside the body. Their image reconstruction problems are nonlinear and ill-posed to result in images with a relatively low spatial resolution. Noting that an MRI scanner can noninvasively measure magnetic fields inside the human body, electrical tissue property imaging methods using MRI have lately been proposed. Magnetic resonance EIT (MREIT) performs conductivity imaging at dc or below 1 kHz by externally injecting current into the human body and measuring induced internal magnetic flux density data using an MRI scanner. Magnetic resonance electrical property tomography (MREPT) produces both conductivity and permittivity images at the Larmor frequency of an MRI scanner based on B1-mapping techniques. Since internal data are only available in MREIT and MREPT, we may formulate well-posed inverse problems for image reconstructions. To develop related imaging techniques, we should clearly understand the basic principles of MREIT and MREPT, which are based on coupled physics of bioelectromagnetism and MRI as well as associated mathematical methods. In this paper, we describe the physical principles of MREIT and MREPT in a unified way and associate measurable quantities with the conductivity and permittivity. Clarifying the key relations among them, we examine existing image reconstruction algorithms to reveal their capabilities and
Rotation of rigid Venus: a complete precession-nutation model
NASA Astrophysics Data System (ADS)
Cottereau, L.; Souchay, J.
2009-12-01
Context: With the increasing knowledge of the terrestrial planets due to recent space probes it is possible to model their rotation with increasing accuracy. Despite that fact, an accurate determination of Venus precession and nutation is lacking Aims: Although Venus rotation has been studied in several aspects, a full and precise analytical model of its precession-nutation motion remains to be constructed. We propose to determine this motion with up-to-date physical parameters of the planet Methods: We adopt a theoritical framework already used for a precise precession-nutation model of the Earth, based on a Hamiltonian formulation, canonical equations and an accurate development of the perturbing function due to the Sun. Results: After integrating the disturbing function and applying the canonical equations, we can evaluate the precession constant dot{Psi} and the coefficients of nutation, both in longitude and in obliquity. We get dot{Psi} = 4474farcs35/Jcy ± 66.5 , corresponding to a precession period of 28 965.10±437 years. This result, based on recent estimations of the Venus moment of inertia is significantly different from previous estimations. The largest nutation coefficient in longitude with an argument 2 LS (where LS is the longitude of the Sun) has a 2''19 amplitude and a 112.35 d period. We show that the coefficients of nutation of Venus due to its triaxiality are of the same order of amplitude as these values due to its dynamical flattening, unlike of the Earth, for which they are negligible. Conclusions: We have constucted a complete theory of the rotation of a rigid body applied to Venus, with up-to-date determinations of its physical and rotational parameters. This allowed us to set up a new and better constrained value of the Venus precession constant and to calculate its nutation coefficients for the first time.
Precessive sand ripples in intense steady shear flows.
Restrepo, Juan M; Moulton, Derek E; Uys, Hermann
2011-03-01
We describe experimental observations of fully developed, large-amplitude bars under the action of a shearing fluid. The experiments were performed in an annular tank filled with water and sheared above by a steady motor source. The same steady shearing flow can produce a variety of different erodible bed manifestations: advective or precessive bars, which refer to bar structures with global regularity and a near-steady precession velocity; interactive bars, the structure of which depends on local rearrangements, which are in turn a response to complex background topography; and dispersive bars, which are created when an initially isolated mound of sand evolves into a train of sand ripples. Of these, the most amenable to analysis are the precessive bars. For precession bars, we find that the skin depth, which is the nondimensionalized mean-field transport rate, grows exponentially as a function of the shear velocity. From this, we arrive at an analytical expression that approximates the precession speed of the bars as a function of shear velocity. We use this to obtain a formula for sediment transport rate. However, in intense flows, the bars can get large engendering boundary layer separation, leading to a different dynamic for bar formation and evolution. Numerical flow calculations over an experimentally obtained set of precessive bars are presented and show that classical parametrizations of mass flux in terms of bottom gradients have shortcomings. Within the range of shear rates considered, a quantity that does not change appreciably in time is the aspect ratio, which is defined as the ratio of the average bar amplitude, with respect to a mean depth, to the average bar length. PMID:21517492
Precessive sand ripples in intense steady shear flows
NASA Astrophysics Data System (ADS)
Restrepo, Juan M.; Moulton, Derek E.; Uys, Hermann
2011-03-01
We describe experimental observations of fully developed, large-amplitude bars under the action of a shearing fluid. The experiments were performed in an annular tank filled with water and sheared above by a steady motor source. The same steady shearing flow can produce a variety of different erodible bed manifestations: advective or precessive bars, which refer to bar structures with global regularity and a near-steady precession velocity; interactive bars, the structure of which depends on local rearrangements, which are in turn a response to complex background topography; and dispersive bars, which are created when an initially isolated mound of sand evolves into a train of sand ripples. Of these, the most amenable to analysis are the precessive bars. For precession bars, we find that the skin depth, which is the nondimensionalized mean-field transport rate, grows exponentially as a function of the shear velocity. From this, we arrive at an analytical expression that approximates the precession speed of the bars as a function of shear velocity. We use this to obtain a formula for sediment transport rate. However, in intense flows, the bars can get large engendering boundary layer separation, leading to a different dynamic for bar formation and evolution. Numerical flow calculations over an experimentally obtained set of precessive bars are presented and show that classical parametrizations of mass flux in terms of bottom gradients have shortcomings. Within the range of shear rates considered, a quantity that does not change appreciably in time is the aspect ratio, which is defined as the ratio of the average bar amplitude, with respect to a mean depth, to the average bar length.
Bounce Precession Fishbones in the National Spherical Tokamak Experiment
Eric Fredrickson; Liu Chen; Roscoe White Eric Fredrickson; Roscoe White
2003-06-27
Bursting modes are observed on the National Spherical Torus Experiment [M. Ono et al., Nucl. Fusion 40 (2000) 557], which are identified as bounce-precession-frequency fishbone modes. They are predicted to be important in high-current, low-shear discharges with a significant population of trapped particles with a large mean-bounce angle, such as produced by near-tangential beam injection into a large aspect-ratio device. Such a distribution is often stable to the usual precession-resonance fishbone mode. These modes could be important in ignited plasmas, driven by the trapped-alpha-particle population.
A precessing relativistic jet model for 3C 449
NASA Technical Reports Server (NTRS)
Gower, A. C.; Hutchings, J. B.
1982-01-01
It is shown that the radio structure of 3C 449 can be matched with a model in which the jets are precessing and have relativistic (beta greater-than or equal to 0.4) velocities. The best-fit model implies a precession period of about 100,000 yr and a cone angle which increases with time. A similar model may be relevant for the radio structure of 3C 31. A brief discussion of the implications for 3C 449 is given.
Wigner-Thomas spin precession in polarized coincidence electronuclear scattering
Dmitrasinovic, V. )
1993-05-01
The role of the Wigner-Thomas precession in nucleon recoil polarization measurements in coincidence electron scattering processes is examined. The necessary formalism is developed within the framework of the Jacob-Wick method, and then applied to two processes: the pseudoscalar electroproduction off a nucleon and the deuteron two-body electrodisintegration.
Existence of Exotic Torus Isomer States and Their Precession Motions
NASA Astrophysics Data System (ADS)
Ichikawa, Takatoshi; Matsuyanagi, Kenichi; Maruhn, Joachim A.; Itagaki, Naoyuki
We systematically investigate the existence of exotic high-spin torus isomers and their precession motions for a series of N = Z even-even nuclei from 28Si to 56Ni. For this purpose, we use the cranked three-dimensional Hatree-Fock (HF) method in a systematic search for high-spin torus isomers and the three-dimensional time-dependent Hatree-Fock (TDHF) method for describing the precession motion of the torus isomer. We obtain high-spin torus isomers in 36Ar, 40Ca, 44Ti, 48Cr, and 52Fe. The emergence of the torus isomers is associated with the alignments of single-particle angular momenta, which is the same mechanism as found in 40Ca. We find that all the obtained torus isomers execute the precession motion at least two rotational periods. The moment of inertia about a perpendicular axis, which characterizes the precession motion, is found to be close to the classical rigid-body value.
Variations of a Constant -- On the History of Precession
NASA Astrophysics Data System (ADS)
Kokott, W.
The precession of the equinoxes, the phenomenon which defines one of the fundamental constants of astronomy, has been with us for more than two millennia. Discovered by Hipparchos who did notice a systematic difference of his star positions as compared with older observations, subsequently adopted by Ptolemaios, its correct value became the object of prolonged controversy. The apparent variability of the precession led to the superimposition of a so-called ''trepidation``, an oscillation of typically +/- 9 deg amplitude and 7000 years period, over a linear precession of only 26 arcsec per annum. This construction, finalized in the Alfonsine Tables (ca. 1280), did work for less than two centuries. The motion of the vernal equinox, at 39 arcsec p.a. too small from the outset, decreases according to this theory to 34 arcsec in the year 1475, the first year covered by the printed version of Johannes Regiomontanus' Ephemerides. Regiomontanus had to re-adjust his longitudes to the real situation, but the difficulties caused by the apparent nonlinearity did persist, leading to a prolonged debate which was finally put to rest by Tycho Brahe. Subsequent to Edmond Halley's successful derivation of a modern value of the precessional constant, again by comparing contemporary star positions with the Almagest catalogue, and Bradley's discovery of the nutation, the last long-term comparison of modern with Ptolemaic coordinates was published by Bode (1795). Shortly after, the analytical theory of precession was established by Bessel in his Fundamenta Astronomiae (1818).
Do Jets Precess... or Even Move at All?
NASA Astrophysics Data System (ADS)
Nixon, Chris; King, Andrew
2013-03-01
Observations of accreting black holes often provoke suggestions that their jets precess. The precession is usually supposed to result from a combination of the Lense-Thirring effect and accretion disk viscosity. We show that this is unlikely for any type of black hole system, as the disk generally has too little angular momentum compared with a spinning hole to cause any significant movement of the jet direction across the sky on short timescales. Uncorrelated accretion events, as in the chaotic accretion picture of active galactic nuclei (AGNs), change AGN jet directions only on timescales >~ 107 yr. In this picture AGN jet directions are stable on shorter timescales, but uncorrelated with any structure of the host galaxy, as observed. We argue that observations of black hole jets precessing on timescales short compared to the accretion time would be a strong indication that the accretion disk, and not the standard Blandford-Znajek mechanism, is responsible for driving the jet. This would be particularly convincing in a tidal disruption event. We suggest that additional disk physics is needed to explain any jet precession on timescales short compared with the accretion time. Possibilities include the radiation warping instability, or disk tearing.
Sparse representations of gravitational waves from precessing compact binaries.
Blackman, Jonathan; Szilagyi, Bela; Galley, Chad R; Tiglio, Manuel
2014-07-11
Many relevant applications in gravitational wave physics share a significant common problem: the seven-dimensional parameter space of gravitational waveforms from precessing compact binary inspirals and coalescences is large enough to prohibit covering the space of waveforms with sufficient density. We find that by using the reduced basis method together with a parametrization of waveforms based on their phase and precession, we can construct ultracompact yet high-accuracy representations of this large space. As a demonstration, we show that less than 100 judiciously chosen precessing inspiral waveforms are needed for 200 cycles, mass ratios from 1 to 10, and spin magnitudes ≤0.9. In fact, using only the first 10 reduced basis waveforms yields a maximum mismatch of 0.016 over the whole range of considered parameters. We test whether the parameters selected from the inspiral regime result in an accurate reduced basis when including merger and ringdown; we find that this is indeed the case in the context of a nonprecessing effective-one-body model. This evidence suggests that as few as ∼100 numerical simulations of binary black hole coalescences may accurately represent the seven-dimensional parameter space of precession waveforms for the considered ranges. PMID:25062160
Comparing post-Newtonian and numerical relativity precession dynamics
NASA Astrophysics Data System (ADS)
Ossokine, Serguei; Boyle, Michael; Kidder, Lawrence E.; Pfeiffer, Harald P.; Scheel, Mark A.; Szilágyi, Béla
2015-11-01
Binary black-hole systems are expected to be important sources of gravitational waves for upcoming gravitational-wave detectors. If the spins are not colinear with each other or with the orbital angular momentum, these systems exhibit complicated precession dynamics that are imprinted on the gravitational waveform. We develop a new procedure to match the precession dynamics computed by post-Newtonian (PN) theory to those of numerical binary black-hole simulations in full general relativity. For numerical relativity (NR) simulations lasting approximately two precession cycles, we find that the PN and NR predictions for the directions of the orbital angular momentum and the spins agree to better than ˜1 ° with NR during the inspiral, increasing to 5° near merger. Nutation of the orbital plane on the orbital time scale agrees well between NR and PN, whereas nutation of the spin direction shows qualitatively different behavior in PN and NR. We also examine how the PN equations for precession and orbital-phase evolution converge with PN order, and we quantify the impact of various choices for handling partially known PN terms.
Predicting Mercury's precession using simple relativistic Newtonian dynamics
NASA Astrophysics Data System (ADS)
Friedman, Y.; Steiner, J. M.
2016-03-01
We present a new simple relativistic model for planetary motion describing accurately the anomalous precession of the perihelion of Mercury and its origin. The model is based on transforming Newton's classical equation for planetary motion from absolute to real spacetime influenced by the gravitational potential and introducing the concept of influenced direction.
Comparing Post-Newtonian and Numerical-Relativity Precession Dynamics
NASA Astrophysics Data System (ADS)
Kidder, Lawrence; Ossokine, Sergei; Boyle, Michael; Pfeiffer, Harald; Scheel, Mark; Szilagyi, Bela
2015-04-01
Binary black-hole systems are expected to be important sources of gravitational waves for upcoming gravitational-wave detectors. If the spins are not colinear with each other or with the orbital angular momentum, these systems exhibit complicated precession dynamics that are imprinted on the gravitational waveform. We develop a new procedure to match the precession dynamics computed by post-Newtonian (PN) theory to those of numerical binary black-hole simulations in full general relativity. For numerical relativity (NR) simulations lasting approximately two precession cycles, we find that the PN and NR predictions for the directions of the orbital angular momentum and the spins agree to better than ~1° with NR during the inspiral, increasing to 5° near merger. Nutation of the orbital plane on the orbital time-scale agrees well between NR and PN, whereas nutation of the spin direction shows qualitatively different behavior in PN and NR. We also examine how the PN equations for precession and orbital-phase evolution converge with PN order, and we quantify the impact of various choices for handling partially known PN terms.
Lense-Thirring precession around neutron stars with known spin
NASA Astrophysics Data System (ADS)
Van Doesburgh, Marieke; van der Klis, Michiel
2016-07-01
Quasi periodic oscillations (QPOs) between 300 and 1200 Hz in the X-ray emission from low mass X-ray binaries have been linked to Keplerian orbital motion at the inner edge of accretion disks. Lense-Thirring precession is precession of the line of nodes of inclined orbits with respect to the equatorial plane of a rotating object due to the general relativistic effect of frame dragging. The Lense-Thirring model of Stella and Vietri (1998) explains QPOs observed in neutron star low mass X-ray binaries at frequencies of a few tens of Hz by the nodal precession of the orbits at the inner disk edge at a precession frequency, ν_{LT} , identical to the Lense-Thirring precession of a test particle orbit. A quadratic relation between ν_{LT} and the Keplerian orbital frequency, and a linear dependence on spin frequency are predicted. In early work (van Straaten et al., 2003) this quadratic relation was confirmed to remarkable precision in three objects of uncertain spin. Since the initial work, many neutron star spin frequencies have been measured in X-ray sources that show QPOs at both low and high frequency. Using archival data from the Rossi X-ray Timing Explorer, we compare the Lense-Thirring prediction to the properties of quasi periodic oscillations measured in a sample of 14 low mass X-ray binaries of which the neutron star spin frequencies can be inferred from their bursting behaviour. We find that in the range predicted for the precession frequency, we can distinguish two different oscillations that often occur simultaneously. In previous works, these two oscillations have often been confused. For both frequencies, we find correlations with inferred Keplerian frequency characterized by power laws with indices that differ significantly from the prediction of 2.0 and therefore inconsistent with the Lense-Thirring model. Also, the specific moment of inertia of the neutron star required by the observed frequencies exceeds values predicted for realistic equations of
Ballistic missile precession frequency extraction based on the Viterbi & Kalman algorithm
NASA Astrophysics Data System (ADS)
Wu, Longlong; Xie, Yongjie; Xu, Daping; Ren, Li
2015-12-01
Radar Micro-Doppler signatures are of great potential for target detection, classification and recognition. In the mid-course phase, warheads flying outside the atmosphere are usually accompanied by precession. Precession may induce additional frequency modulations on the returned radar signal, which can be regarded as a unique signature and provide additional information that is complementary to existing target recognition methods. The main purpose of this paper is to establish a more actual precession model of conical ballistic missile warhead and extract the precession parameters by utilizing Viterbi & Kalman algorithm, which improving the precession frequency estimation accuracy evidently , especially in low SNR.
Precessing rotating flows with additional shear: Stability analysis
NASA Astrophysics Data System (ADS)
Salhi, A.; Cambon, C.
2009-03-01
We consider unbounded precessing rotating flows in which vertical or horizontal shear is induced by the interaction between the solid-body rotation (with angular velocity Ω0 ) and the additional “precessing” Coriolis force (with angular velocity -ɛΩ0 ), normal to it. A “weak” shear flow, with rate 2ɛ of the same order of the Poincaré “small” ratio ɛ , is needed for balancing the gyroscopic torque, so that the whole flow satisfies Euler’s equations in the precessing frame (the so-called admissibility conditions). The base flow case with vertical shear (its cross-gradient direction is aligned with the main angular velocity) corresponds to Mahalov’s [Phys. Fluids A 5, 891 (1993)] precessing infinite cylinder base flow (ignoring boundary conditions), while the base flow case with horizontal shear (its cross-gradient direction is normal to both main and precessing angular velocities) corresponds to the unbounded precessing rotating shear flow considered by Kerswell [Geophys. Astrophys. Fluid Dyn. 72, 107 (1993)]. We show that both these base flows satisfy the admissibility conditions and can support disturbances in terms of advected Fourier modes. Because the admissibility conditions cannot select one case with respect to the other, a more physical derivation is sought: Both flows are deduced from Poincaré’s [Bull. Astron. 27, 321 (1910)] basic state of a precessing spheroidal container, in the limit of small ɛ . A Rapid distortion theory (RDT) type of stability analysis is then performed for the previously mentioned disturbances, for both base flows. The stability analysis of the Kerswell base flow, using Floquet’s theory, is recovered, and its counterpart for the Mahalov base flow is presented. Typical growth rates are found to be the same for both flows at very small ɛ , but significant differences are obtained regarding growth rates and widths of instability bands, if larger ɛ values, up to 0.2, are considered. Finally, both flow cases
High-spin torus isomers and their precession motions
NASA Astrophysics Data System (ADS)
Ichikawa, T.; Matsuyanagi, K.; Maruhn, J. A.; Itagaki, N.
2014-09-01
Background: In our previous study, we found that an exotic isomer with a torus shape may exist in the high-spin, highly excited states of Ca40. The z component of the total angular momentum, Jz=60ℏ, of this torus isomer is constructed by totally aligning 12 single-particle angular momenta in the direction of the symmetry axis of the density distribution. The torus isomer executes precession motion with the rigid-body moments of inertia about an axis perpendicular to the symmetry axis. The investigation, however, has been focused only on Ca40. Purpose: We systematically investigate the existence of exotic torus isomers and their precession motions for a series of N =Z even-even nuclei from Si28 to Ni56. We analyze the microscopic shell structure of the torus isomer and discuss why the torus shape is generated beyond the limit of large oblate deformation. Method: We use the cranked three-dimensional Hartree-Fock method with various Skyrme interactions in a systematic search for high-spin torus isomers. We use the three-dimensional time-dependent Hartree-Fock method for describing the precession motion of the torus isomer. Results: We obtain high-spin torus isomers in Ar36,Ca40,Ti44,Cr48, and Fe52. The emergence of the torus isomers is associated with the alignments of single-particle angular momenta, which is the same mechanism as found in Ca40. It is found that all the obtained torus isomers execute the precession motion at least two rotational periods. The moment of inertia about a perpendicular axis, which characterizes the precession motion, is found to be close to the classical rigid-body value. Conclusions: The high-spin torus isomer of Ca40 is not an exceptional case. Similar torus isomers exist widely in nuclei from Ar36 to Fe52 and they execute the precession motion. The torus shape is generated beyond the limit of large oblate deformation by eliminating the 0s components from all the deformed single-particle wave functions to maximize their mutual
Full-wave evaluation of RF absorption in NSTX, with accuracy to all orders in Larmor radius
Smithe, D.; Bettenhausen, M.; Phillips, C.; Wilson, R.; Majeski, R.; Hosea, J.
1999-09-20
RF heating scenarios for the magnetic geometry of NSTX are investigated using the most recent version of the METS RF analysis tool. This 1-D tool includes the full Bessel function expansion of the plasma dielectric tensor, and thus provides accuracy to all orders in Larmor radius, making it ideal for the full-wave analysis of heating at higher harmonics. A recent upgrade to the tool permits the study of the magnetic well geometry of NSTX. Other upgrades allow for realistic variation of local poloidal field and shear profile. Temperature anisotropy and nonzero rotation velocity are also treated properly. Ultimately, it is highly desirable that a 2-D full-wave solution, which is similarly complete in the Larmor expansion, be performed to better understand the 2-D power deposition profile for NSTX. Present thoughts on how to make this feasible are outlined, and new methods for treating the problem of passing-particle absorption and multi-pass correlation are also presented. (c) 1999 American Institute of Physics.
Spike phase precession persists after transient intrahippocampal perturbation
Zugaro, Michaël B; Monconduit, Lénaïc; Buzsáki, György
2007-01-01
Oscillatory spike timing in the hippocampus is regarded as a temporal coding mechanism for space, but the underlying mechanisms are poorly understood. To contrast the predictions of the different models of phase precession, we transiently turned off neuronal discharges for up to 250 ms and reset the phase of theta oscillations by stimulating the commissural pathway in rats. After recovery from silence, phase precession continued. The phase of spikes for the first theta cycle after the perturbation was more advanced than the phase of spikes for the last theta cycle just before the perturbation. These findings indicate that phase advancement that emerges within hippocampal circuitry may be updated at the beginning of each theta cycle by extrahippocampal inputs. PMID:15592464
Nonlinear dynamo action in a precessing cylindrical container.
Nore, C; Léorat, J; Guermond, J-L; Luddens, F
2011-07-01
It is numerically demonstrated by means of a magnetohydrodynamics code that precession can trigger the dynamo effect in a cylindrical container. When the Reynolds number, based on the radius of the cylinder and its angular velocity, increases, the flow, which is initially centrosymmetric, loses its stability and bifurcates to a quasiperiodic motion. This unsteady and asymmetric flow is shown to be capable of sustaining dynamo action in the linear and nonlinear regimes. The magnetic field thus generated is unsteady and quadrupolar. These numerical evidences of dynamo action in a precessing cylindrical container may be useful for an experiment now planned at the Dresden sodium facility for dynamo and thermohydraulic studies in Germany. PMID:21867314
Precession of cylindrical dust particles in the plasma sheath
Banu, N.; Ticoş, C. M.
2015-10-15
The vertical precession of cylindrical dust particles levitated in the sheath of an rf plasma is experimentally investigated. Typically, the dust particles have two equilibrium positions depending on the orientation of their longitudinal axis: horizontal and vertical. A transition between these two states is induced by rapidly increasing the neutral gas pressure in the plasma chamber. During this transition, the cylindrical dust particles make an angle with the horizontal and rotate about their center of mass. The rotation speed increases as the dust rods aligned with the vertical axis. All dust particles will eventually end up in the vertical state while spinning fast about their longitudinal axis. Dust-dust interaction and the attracting ion wakes are possible mechanisms for inducing the observed dust precession.
Triadic instability of a non-resonant precessing fluid cylinder
NASA Astrophysics Data System (ADS)
Lagrange, Romain; Meunier, Patrice; Eloy, Christophe
2016-06-01
Flows forced by a precessional motion can exhibit instabilities of crucial importance, whether they concern the fuel of a flying object or the liquid core of a telluric planet. So far, stability analyses of these flows have focused on the special case of a resonant forcing. Here, we address the instability of the flow inside a precessing cylinder in the general case. We first show that the base flow forced by the cylinder precession is a superposition of a vertical or horizontal shear flow and of an infinite sum of forced modes. We then perform a linear stability analysis of this base flow by considering its triadic resonance with two free Kelvin modes. Finally, we derive the amplitude equations of the free Kelvin modes and obtain an expression of the instability threshold and growth rate. xml:lang="fr"
Precession and circularization of elliptical space-tether motion
NASA Technical Reports Server (NTRS)
Chapel, Jim D.; Grosserode, Patrick
1993-01-01
In this paper, we present a simplified analytic model for predicting motion of long space tethers. The perturbation model developed here addresses skip rope motion, where each end of the tether is held in place and the middle of the tether swings with a motion similar to that of a child's skip rope. If the motion of the tether midpoint is elliptical rather than circular, precession of the ellipse complicates the procedures required to damp this motion. The simplified analytic model developed in this paper parametrically predicts the precession of elliptical skip rope motion. Furthermore, the model shows that elliptic skip rope motion will circularize when damping is present in the longitudinal direction. Compared with high-fidelity simulation results, this simplified model provides excellent predictions of these phenomena.
Chaotic spin precession in anisotropic universes and fermionic dark matter
NASA Astrophysics Data System (ADS)
Kamenshchik, A. Yu.; Teryaev, O. V.
2016-05-01
We consider the precession of a Dirac particle spin in some anisotropic Bianchi universes. This effect is present already in the Bianchi-I universe. In the Bianchi-IX universe it acquires the chaotic character due to the stochasticity of the oscillatory approach to the cosmological singularity. The related helicity flip of fermions in the veryearly Universe may produce the sterile particles contributing to dark matter.
Magnetic environment of hydrogen in Fe from muon precession measurements
NASA Technical Reports Server (NTRS)
Heiman, N.; Foy, M. L. G.; Kossler, W. J.; Stronach, C. E.
1974-01-01
Polarized positive muon radiation was stopped in an ellipsoidal iron target and its precession was observed in a transverse magnetic field. Results indicate that the conduction electron polarization in the 77 K-Fe Curie point region is less than expected, and that the relaxation time of the muon polarization is dominated by the static inhomogeneity to 900 K, at which point magnetization fluctuations become important.
Shear secondary instability in a precessing cylinder flow
NASA Astrophysics Data System (ADS)
Mouhali, Waleed; Lehner, Thierry; Ater Collaboration
2015-11-01
For a certain value of the forcing parameter, cyclones regime has been observed in our experiment involving water in a precessing cylinder. They result from an instability. We propose here to study the nature of this so-called instability. We consider first the mode coupling of two inertial waves with azimuthal wavenumber m =0 and m =1 (mode forced by the precession) in the inviscid regime (at high Re number limit) creates a differential rotation regime which has been observed in the same experiment at small enough Poincaré number ɛ (ratio of the precession to the rotation frequencies). Secondly, the radial profile of the corresponding axial mean flow vorticity shows an inflexion point leading to a localized inflectional secondary instability. We show that when ɛ is increased from low values the forced mode m =0 becomes the most instable in this induced differential rotation, which can be responsible for the observed eruptions of jets from the lateral walls of the cylinder leading to the cyclones formation within the volume from the development of an inviscid secondary shear instability.
Contribution of HIPPARCOS to the Determination of Precession
NASA Astrophysics Data System (ADS)
Vityazev, V. V.
2002-01-01
The IAU (1976) luni-solar precession constant was derived by Fricke from intensive study of the catalog of 512 FK4-FK4/Sup distant stars. At present, when the data from the catalog HIPPARCOS is available, it is helpful to reconsider Fricke's analysis. This paper presents a redetermination of precession based on the following new factors: (a) the accurate parallaxes of stars have been taken into account; (b) galactic rotation and other kinematics have been eliminated from the proper motions of 512 stars; (c) the systems of the FK5 and improved GC catalog were used in combination with the HIPPARCOS catalog; (d) a new method (the MOTOR) of studying stellar kinematics was used. This method is based on the decomposition of proper motions on a set of orthogonal functions. The MOTOR, in contrast to the commonly used Least Squares Procedure, provides a test for whether or not the model is compatible with the data. Derived corrections to the IAU (1976) luni-solar precession constant are consistent with the results from VLBI observations and kinematic study of modern catalogues of proper motions.
Wobbling and Precessing Jets from Warped Disks in Binary Systems
NASA Astrophysics Data System (ADS)
Sheikhnezami, Somayeh; Fendt, Christian
2015-12-01
We present results of the first ever three-dimensional (3D) magnetohydrodynamic (MHD) simulations of the accretion-ejection structure. We investigate the 3D evolution of jets launched symmetrically from single stars but also jets from warped disks in binary systems. We have applied various model setups and tested them by simulating a stable and bipolar symmetric 3D structure from a single star-disk-jet system. Our reference simulation maintains a good axial symmetry and also a bipolar symmetry for more than 500 rotations of the inner disk, confirming the quality of our model setup. We have then implemented a 3D gravitational potential (Roche potential) due by a companion star and run a variety of simulations with different binary separations and mass ratios. These simulations show typical 3D deviations from axial symmetry, such as jet bending outside the Roche lobe or spiral arms forming in the accretion disk. In order to find indications of precession effects, we have also run an exemplary parameter setup, essentially governed by a small binary separation of only ≃200 inner disk radii. This simulation shows a strong indication that we observe the onset of a jet precession caused by the wobbling of the jet-launching disk. We estimate the opening angle of the precession cone defined by the lateral motion of the jet axis to be about 4° after about 5000 dynamical time steps.
The precessing jets of 1E 1740.7-2942
NASA Astrophysics Data System (ADS)
Luque-Escamilla, Pedro L.; Martí, Josep; Martínez-Aroza, José
2015-12-01
Context. The source 1E 1740.7-2942 is believed to be one of the two prototypical microquasars towards the Galactic center region whose X-ray states strongly resemble those of Cygnus X-1. Yet, the bipolar radio jets of 1E 1740.7-2942 are very reminiscent of a radio galaxy. The true nature of the object has thus remained an open question for nearly a quarter of a century. Aims: Our main goal here is to confirm the Galactic membership of 1E 1740.7-2942 by searching for morphological changes of its extended radio jets in human timescales. This work was triggered as a result of recent positive detection of fast structural changes in the large-scale jets of the very similar source GRS 1758-258. Methods: We carried out an in-depth exploration of the Very Large Array public archives and fully recalibrated all 1E 1740.7-2942 extended data sets in the C configuration of the array. We obtained and analyzed matching beam radio maps for five epochs, covering years 1992, 1993, 1994, 1997 and 2000, with an angular resolution of a few arcseconds. Results: We clearly detected structural changes in the arc-minute jets of 1E 1740.7-2942 on timescales of roughly a year, which set a firm distance upper limit of 12 kpc. Moreover, a simple precessing twin-jet model was simultaneously fitted to the five observing epochs available. The observed changes in the jet flow are strongly suggestive of a precession period of ~1.3 yr. Conclusions: The fitting of the precession model to the data yields a distance of ~5 kpc. This value, and the observed changes, rule out any remaining doubts about the 1E 1740.7-2942 Galactic nature. To our knowledge, this microquasar is the second whose jet precession ephemeris become available after SS433. This kind of information is relevant to the physics of compact objects, since the genesis of the precession phenomenon occurs very close to the interplay region between the accretion disk and the compact object in the system. Appendix A and a movie associated to
Long-term evolution of orbits about a precessing oblate planet. 2. The case of variable precession
NASA Astrophysics Data System (ADS)
Efroimsky, Michael
2006-11-01
We continue the study undertaken in Efroimsky [Celest. Mech. Dyn. Astron. 91, 75 108 (2005a)] where we explored the influence of spin-axis variations of an oblate planet on satellite orbits. Near-equatorial satellites had long been believed to keep up with the oblate primary’s equator in the cause of its spin-axis variations. As demonstrated by Efroimsky and Goldreich [Astron. Astrophys. 415, 1187 1199 (2004)], this opinion had stemmed from an inexact interpretation of a correct result by Goldreich [Astron. J. 70, 5 9 (1965)]. Although Goldreich [Astron. J. 70, 5 9 (1965)] mentioned that his result (preservation of the initial inclination, up to small oscillations about the moving equatorial plane) was obtained for non-osculating inclination, his admonition had been persistently ignored for forty years. It was explained in Efroimsky and Goldreich [Astron. Astrophys. 415, 1187 1199 (2004)] that the equator precession influences the osculating inclination of a satellite orbit already in the first order over the perturbation caused by a transition from an inertial to an equatorial coordinate system. It was later shown in Efroimsky [Celest. Mech. Dyn. Astron. 91, 75 108 (2005a)] that the secular part of the inclination is affected only in the second order. This fact, anticipated by Goldreich [Astron. J. 70, 5 9 (1965)], remains valid for a constant rate of the precession. It turns out that non-uniform variations of the planetary spin state generate changes in the osculating elements, that are linear in | \\varvec{dot{μ}} |, where \\varvec{μ} is the planetary equator’s total precession rate that includes the equinoctial precession, nutation, the Chandler wobble, and the polar wander. We work out a formalism which will help us to determine if these factors cause a drift of a satellite orbit away from the evolving planetary equator.
Finite Larmor Radius and Three-Dimensional Effects on the Blobs in the Scrape-Off Layer
Jovanovic, D.; Shukla, P. K.; Pegoraro, F.
2008-10-15
The nonlinear processes in the tokamak core edge and in the scrape-off layer are studied within the electrostatic interchange paradigm, with the collisions among the plasma particles and with the neutras, including the effects of the finite ion Larmor radius and of fully three-dimensional electron dynamics. These new three-dimensional model equations are solved numerically, to study the propagation of plasma blobs in the scrape-off layer. It is shown that the coupling with the resistive drift mode causes the transverse contraction and the rotation of the blob. The parallel resistivity and the finite ion temperature give rise to the symmetry breaking and the poloidal propagation of the blobs, while their stability is only weakly affected.
Decoupling a spin qubit from high-frequency Larmor dynamics of a GaAs nuclear spin bath
NASA Astrophysics Data System (ADS)
Malinowski, Filip K.; Martins, Frederico; Nissen, Peter D.; Rudner, Mark S.; Marcus, Charles M.; Kuemmeth, Ferdinand; Barnes, Edwin; Fallahi, Saeed; Gardner, Geoffrey C.; Manfra, Michael J.
We present a technique of decoupling a spin qubit in a GaAs/AlGaAs heterostructure from low- and high-frequency noise arising from hyperfine interaction of electrons with nuclear spins. We use Carr-Purcell-Meiboom-Gill sequences in which we synchronize the repetition rate of π pulses to difference Larmor frequencies of 69Ga, 71Ga and 75As nuclei. This decouples the qubit both from low-frequency noise due to diffusion of nuclear spins and from noise at selected high frequencies, allowing us to apply more than a thousand π pulses in a sequence. We demonstrate a coherence time of a singlet-triplet qubit of 0.87 ms, i.e. five orders of magnitude longer than the inhomogeneous dephasing time intrinsic to GaAs. Support through IARPA-MQCO, Army Research Office, LPS-MPO-CMTC, the Villum Foundation and the Danish National Research Foundation is acknowledged.
The Combined Effect of Precession and Convection on the Dynamo Action
NASA Astrophysics Data System (ADS)
Wei, Xing
2016-08-01
To understand the generation of the Earth’s magnetic field and those of other planets, we numerically investigate the combined effect of precession and convection on dynamo action in a spherical shell. Convection alone, precession alone, and the combined effect of convection and precession are studied at the low Ekman number at which the precessing flow is already unstable. The key result is that although precession or convection alone are not strong enough to support the dynamo action, the combined effect of precession and convection can support the dynamo action because of the resonance of precessional and convective instabilities. This result may explain why the geodynamo has been maintained for such a long time compared to the Martian dynamo.
The forced precession of the Moon's inner core
NASA Astrophysics Data System (ADS)
Dumberry, Mathieu; Wieczorek, Mark A.
2016-07-01
The tilt angle of the 18.6 year precession of the Moon's solid inner core is unknown, but it is set by a balance between gravitational and pressure torques acting on its elliptical figure. We show here that to first order, the angle of precession of the inner core of a planetary body is determined by the frequency of the free inner core nutation, ωficn, relative to the precession frequency, Ωp. If |ωficn|≪|Ωp|, the inner core is blind to the gravitational influence of the mantle. If |ωficn|≫|Ωp|, the inner core is gravitationally locked to the mantle and is nearly aligned with it. If ωficn≈Ωp, large inner core tilt angles can result from resonant excitation. Viscous inner core relaxation and electromagnetic coupling can attenuate large tilt angles. For the specific case of the Moon, we show that ωficn is to within a factor of 2 of Ωp = 2π/18.6 yr-1. For a rigid inner core, this implies a tilt of 2 to 5° with respect to the mantle, and larger if ωficn is very close to Ωp. More modest tilt angles between 0 and 0.5° result if viscous relaxation within the inner core occurs on a timescale of one lunar day. Predictions from our model may be used in an attempt to detect the gravity signal resulting from a tilted inner core, to determine the past history of the inner core tilt angle, and to assess models of dynamo generation powered by differential rotation at the core-mantle and inner core boundaries.
Evolution and precession of accretion disk in tidal disruption events
NASA Astrophysics Data System (ADS)
Shen, R.-F.; Matzner, C. D.
2012-12-01
In a supermassive black hole (BH) tidal disruption event (TDE), the tidally disrupted star feeds the BH via an accretion disk. Most often it is assumed that the accretion rate history, hence the emission light curve, tracks the rate at which new debris mass falls back onto the disk, notably the t-5/3 power law. But this is not the case when the disk evolution due to viscous spreading - the driving force for accretion - is carefully considered. We construct a simple analytical model that comprehensively describes the accretion rate history across 4 different phases of the disk evolution, in the presence of mass fallback and disk wind loss. Accretion rate evolves differently in those phases which are governed by how the disk heat energy is carried away, early on by advection and later by radiation. The accretion rate can decline as steeply as t-5/3 only if copious disk wind loss is present during the early advection-cooled phase. Later, the accretion rate history is t-8/7 or shallower. These have great implications on the TDE flare light curve. A TDE accretion disk is most likely misaligned with the equatorial plane of the spinning BH. Moreover, in the TDE the accretion rate is super- or near-Eddington thus the disk is geometrically thick, for which case the BH's frame dragging effect may cause the disk precess as a solid body, which may manifest itself as quasi-periodic signal in the TDE light curve. Our disk evolution model predicts the disk precession period increases with time, typically as ∝ t. The results are applied to the recently jetted TDE flare Swift transient J1644 + 57 which shows numerous, quasi-periodic dips in its long-term X-ray light curve. As the current TDE sample increases, the identification of the disk precession signature provides a unique way of measuring BH spin and studying BH accretion physics.
Pluto and Charon: A Case of Precession-Orbit Resonance?
NASA Technical Reports Server (NTRS)
Rubincam, David Parry; Smith, David E. (Technical Monitor)
2000-01-01
Pluto may be the only known case of precession-orbit resonance in the solar system. The Pluto-Charon system orbits the Sun with a period of 1 Plutonian year, which is 250.8 Earth years. The observed parameters of the system are such that Charon may cause Pluto to precess with a period near 250.8 Earth years. This gives rise to two possible resonances, heretofore unrecognized. The first is due to Pluto's orbit being highly eccentric, giving solar torques on Charon with a period of 1 Plutonian year. Charon in turn drives Pluto near its precession period. Volatiles, which are expected to shuttle across Pluto's surface between equator and pole as Pluto's obliquity oscillates, might change the planet's dynamical flattening enough so that Pluto crosses the nearby resonance, forcing the planet's equatorial plane to depart from Charon's orbital plane. The mutual tilt can reach as much as 2 deg after integrating over 5.6 x 10(exp 6) years, depending upon how close Pluto is to the resonance and the supply of volatiles. The second resonance is due to the Sun's traveling above and below Charon's orbital plane; it has a period half that of the eccentricity resonance. Reaching this half-Plutonian year resonance requires a much larger but still theoretically possible amount of volatiles. In this case the departure of Charon from an equatorial orbit is about 1 deg after integrating for 5.6 x 10(exp 6) years. The calculations ignore libration and tidal friction. It is not presently known how large the mutual tilt can grow over the age of the solar system, but if it remains only a few degrees, then observing such small angles from a Pluto flyby mission would be difficult. It is not clear why the parameters of the Pluto-Charon system are so close to the eccentricity resonance.
NASA Technical Reports Server (NTRS)
Zimmerman, M.
1979-01-01
The classical mechanics results for free precession which are needed in order to calculate the weak field, slow-motion, quadrupole-moment gravitational waves are reviewed. Within that formalism, algorithms are given for computing the exact gravitational power radiated and waveforms produced by arbitrary rigid-body freely-precessing sources. The dominant terms are presented in series expansions of the waveforms for the case of an almost spherical object precessing with a small wobble angle. These series expansions, which retain the precise frequency dependence of the waves, may be useful for gravitational astronomers when freely-precessing sources begin to be observed.
Three-axis atomic magnetometer based on spin precession modulation
Huang, H. C.; Dong, H. F. Hu, X. Y.; Chen, L.; Gao, Y.
2015-11-02
We demonstrate a three-axis atomic magnetometer with one intensity-modulated pump beam and one orthogonal probe beam. The main field component is measured using the resonance of the pumping light, while the transverse field components are measured simultaneously using the optical rotation of the probe beam modulated by the spin precession. It is an all-optical magnetometer without using any modulation field or radio frequency field. Magnetic field sensitivity of 0.8 pT/Hz{sup 1∕2} is achieved under a bias field of 2 μT.
Precession-nutation procedures consistent with IAU 2006 resolutions
NASA Astrophysics Data System (ADS)
Wallace, P. T.; Capitaine, N.
2006-12-01
Context: .The 2006 IAU General Assembly has adopted the P03 model of Capitaine et al. (2003a) recommended by the WG on precession and the ecliptic (Hilton et al. 2006) to replace the IAU 2000 model, which comprised the Lieske et al. (1977) model with adjusted rates. Practical implementations of this new "IAU 2006" model are therefore required, involving choices of procedures and algorithms. Aims: .The purpose of this paper is to recommend IAU 2006 based precession-nutation computing procedures, suitable for different classes of application and achieving high standards of consistency. Methods: .We discuss IAU 2006 based procedures and algorithms for generating the rotation matrices that transform celestial to terrestrial coordinates, taking into account frame bias (B), P03 precession (P), P03-adjusted IAU 2000A nutation (N) and Earth rotation. The NPB portion can refer either to the equinox or to the celestial intermediate origin (CIO), requiring either the Greenwich sidereal time (GST) or the Earth rotation angle (ERA) as the measure of Earth rotation. Where GST is used, it is derived from ERA and the equation of the origins (EO) rather than through an explicit formula as in the past, and the EO itself is derived from the CIO locator. Results: .We provide precession-nutation procedures for two different classes of full-accuracy application, namely (i) the construction of algorithm collections such as the Standards Of Fundamental Astronomy (SOFA) library and (ii) IERS Conventions, and in addition some concise procedures for applications where the highest accuracy is not a requirement. The appendix contains a fully worked numerical example, to aid implementors and to illustrate the consistency of the two full-accuracy procedures which, for the test date, agree to better than 1 μas. Conclusions: .The paper recommends, for case (i), procedures based on angles to represent the PB and N components and, for case (ii), procedures based on series for the CIP X,Y. The two
Geometric phase and gravitational precession of D-branes
NASA Astrophysics Data System (ADS)
Pedder, Chris; Sonner, Julian; Tong, David
2007-12-01
We study Berry’s phase in the D0-D4-brane system. When a D0-brane moves in the background of D4-branes, the first excited states undergo a holonomy described by a non-Abelian Berry connection. At weak coupling this is an SU(2) connection over R5, known as the Yang monopole. At strong coupling, the holonomy is recast as the classical gravitational precession of a spinning particle. The Berry connection is the spin connection of the near-horizon limit of the D4-branes, which is a continuous deformation of the Yang and anti-Yang monopole.
Parametric pumping of precession modes in ferromagnetic nanodisks
NASA Astrophysics Data System (ADS)
Guo, Feng; Belova, L. M.; McMichael, R. D.
2014-03-01
We report on the parametric excitation of magnetic precession modes in nanodisks using a parallel pumping configuration. The excitations are detected using a ferromagnetic resonance force microscopy method, and the parallel-pumped spectra reveal nonlinear characteristics including instability thresholds and multiple, narrow, sawtooth-shaped resonances. These characteristics are in accord with analytical theory and micromagnetic modeling results. Modeled mode profiles of the excitations show that higher-order standing spin-wave modes with both even and odd symmetries are excited under parallel pumping.
Shear-induced molecular precession in a hexatic Langmuir monolayer.
Ignés-Mullol, J; Schwartz, D K
2001-03-15
Liquid crystalline behaviour is generally limited to a select group of specially designed bulk substances. By contrast, it is a common feature of simple molecular monolayers and other quasi-two-dimensional systems, which often possess a type of in-plane ordering that results from unbinding of dislocations-a 'hexatic' liquid crystalline phase. The flow of monolayers is closely related to molecular transport in biological membranes, affects foam and emulsion stability and is relevant to microfluidics research. For liquid crystalline phases, it is important to understand the coupling of the molecular orientation to the flow. Orientationally ordered (nematic) phases in bulk liquid crystals exhibit 'shear aligning' or 'tumbling' behaviour under shear, and are described quantitatively by Leslie-Ericksen theory. For hexatic monolayers, the effects of flow have been inferred from textures of Langmuir-Blodgett films and directly observed at the macroscopic level. However, there is no accepted model of hexatic flow at the molecular level. Here we report observations of a hexatic Langmuir monolayer that reveal continuous, shear-induced molecular precession, interrupted by occasional jump discontinuities. Although superficially similar to tumbling in a bulk nematic phase, the kinematic details are quite different and provide a possible mechanism for domain coarsening and eventual molecular alignment in monolayers. We explain the precession and jumps within a quantitative framework that involves coupling of molecular orientation to the local molecular hexatic 'lattice', which is continuously deformed by shear. PMID:11268206
Electromagnetic torques, precession and evolution of magnetic inclination of pulsars
NASA Astrophysics Data System (ADS)
Zanazzi, J. J.; Lai, Dong
2015-07-01
We present analytic calculations of the electromagnetic torques acting on a magnetic neutron star rotating in vacuum, including near-zone torques associated with the inertia of dipole and quadrupole magnetic fields. We incorporate these torques into the rotational dynamics of a rigid-body neutron star, and show that the effects of the inertial torque can be understood as a modification of the moment of inertia tensor of the star. We apply our rotational dynamics equation to the Crab pulsar, including intrinsic distortions of the star and various electromagnetic torques, to investigate the possibility that the counter-alignment of the magnetic inclination angle, as suggested by recent observations, could be explained by pulsar precession. We find that if the effective principal axis of the pulsar is nearly aligned with either the magnetic dipole axis or the rotation axis, then precession may account for the observed counter-alignment over decade time-scales. Over the spindown time-scale of the pulsar, the magnetic inclination angle always decreases.
Accretion-disc precession in UX Ursae Majoris
NASA Astrophysics Data System (ADS)
de Miguel, E.; Patterson, J.; Cejudo, D.; Ulowetz, J.; Jones, J. L.; Boardman, J.; Barret, D.; Koff, R.; Stein, W.; Campbell, T.; Vanmunster, T.; Menzies, K.; Slauson, D.; Goff, W.; Roberts, G.; Morelle, E.; Dvorak, S.; Hambsch, F.-J.; Starkey, D.; Collins, D.; Costello, M.; Cook, M. J.; Oksanen, A.; Lemay, D.; Cook, L. M.; Ogmen, Y.; Richmond, M.; Kemp, J.
2016-04-01
We report the results of a long campaign of time series photometry on the nova-like variable UX Ursae Majoris during 2015. It spanned 150 nights, with ˜ 1800 h of coverage on 121 separate nights. The star was in its normal `high state' near magnitude V = 13, with slow waves in the light curve and eclipses every 4.72 h. Remarkably, the star also showed a nearly sinusoidal signal with a full amplitude of 0.44 mag and a period of 3.680 ± 0.007 d. We interpret this as the signature of a retrograde precession (wobble) of the accretion disc. The same period is manifest as a ±33 s wobble in the timings of mid-eclipse, indicating that the disc's centre of light moves with this period. The star also showed strong `negative superhumps' at frequencies ωorb + N and 2ωorb + N, where ωorb and N are, respectively, the orbital and precession frequencies. It is possible that these powerful signals have been present, unsuspected, throughout the more than 60 yr of previous photometric studies.
Searching for gravitational waves from compact binaries with precessing spins
NASA Astrophysics Data System (ADS)
Harry, Ian; Privitera, Stephen; Bohé, Alejandro; Buonanno, Alessandra
2016-07-01
Current searches for gravitational waves from compact-object binaries with the LIGO and Virgo observatories employ waveform models with spins aligned (or antialigned) with the orbital angular momentum. Here, we derive a new statistic to search for compact objects carrying generic (precessing) spins. Applying this statistic, we construct banks of both aligned- and generic-spin templates for binary black holes and neutron star-black hole binaries, and compare the effectualness of these banks towards simulated populations of generic-spin systems. We then use these banks in a pipeline analysis of Gaussian noise to measure the increase in background incurred by using generic- instead of aligned-spin banks. Although the generic-spin banks have roughly a factor of ten more templates than the aligned-spin banks, we find an overall improvement in signal recovery at a fixed false-alarm rate for systems with high-mass ratio and highly precessing spins. This gain in sensitivity comes at a small loss of sensitivity (≲4 %) for systems that are already well covered by aligned-spin templates. Since the observation of even a single binary merger with misaligned spins could provide unique astrophysical insights into the formation of these sources, we recommend that the method described here be developed further to mount a viable search for generic-spin binary mergers in LIGO/Virgo data.
THE RECENTLY DETERMINED ANOMALOUS PERIHELION PRECESSION OF SATURN
Iorio, Lorenzo
2009-03-15
The astronomer E. V. Pitjeva, by analyzing with the EPM2008 ephemerides a large number of planetary observations including also two years (2004-2006) of normal points from the Cassini spacecraft, phenomenologically estimated a statistically significant nonzero correction to the usual Newtonian/Einsteinian secular precession of the longitude of the perihelion of Saturn, i.e., {delta}{omega}-bar-dot{sub Sat} = -0.006{+-}0''.002 cy{sup -1}; the formal, statistical error is 0.''0007. It can be explained neither by any of the standard classical and general relativistic dynamical effects mismodeled/unmodeled in the force models of the EPM2008 ephemerides nor by several exotic modifications of gravity recently put forth to accommodate certain cosmological/astrophysical observations without resorting to dark energy/dark matter. Both independent analyses by other teams of astronomers and further processing of larger data sets from Cassini will be helpful in clarifying the nature and the true existence of the anomalous precession of the perihelion of Saturn.
NASA Astrophysics Data System (ADS)
O'Shaughnessy, Richard; Farr, Benjamin; Ochsner, Evan; Cho, Hee-Suk; Raymond, V.; Kim, Chunglee; Lee, Chang-Hwan
2014-05-01
Precessing black hole-neutron star (BH-NS) binaries produce a rich gravitational wave signal, encoding the binary's nature and inspiral kinematics. Using the lalinference_mcmc Markov chain Monte Carlo parameter estimation code, we use two fiducial examples to illustrate how the geometry and kinematics are encoded into the modulated gravitational wave signal, using coordinates well adapted to precession. Extending previous work, we demonstrate that the performance of detailed parameter estimation studies can often be estimated by "effective" studies: comparisons of a prototype signal with its nearest neighbors, adopting a fixed sky location and idealized two-detector network. Using a concrete example, we show that higher harmonics provide nonzero but small local improvement when estimating the parameters of precessing BH-NS binaries. We also show that higher harmonics can improve parameter estimation accuracy for precessing binaries by breaking leading-order discrete symmetries and thus ruling out approximately degenerate source orientations. Our work illustrates quantities gravitational wave measurements can provide, such as the orientation of a precessing short gamma ray burst progenitor relative to the line of sight. More broadly, "effective" estimates may provide a simple way to estimate trends in the performance of parameter estimation for generic precessing BH-NS binaries in next-generation detectors. For example, our results suggest that the orbital chirp rate, precession rate, and precession geometry are roughly independent observables, defining natural variables to organize correlations in the high-dimensional BH-NS binary parameter space.
The precession constant of the Earth: Variations through the ice-age
Peltier, W.R.; Jiang, X.
1994-10-01
We directly calculate the history of variations in Earth`s precession constant H that are forced by variations in surface mass associated with late Pleistocene ice-age glaciation and deglaciation events. Our analyses show that the magnitude of Delta H/H(sub zero) is lower than that required to cause the recently hypothesized resonant reduction of the precession period.
NASA Astrophysics Data System (ADS)
Belyanin, S.; Gurfil, P.
2008-06-01
In this study, we investigate the effect of Earth's precession on the orbital dynamics of geostationary satellites. Our astrodynamical model includes second-order zonal and tesseral harmonics, and lunisolar gravitation. We show that the equinoctial precession induces secular inclination growth and thus bares a non-negligible effect on north-south stationkeeping for long mission lifetimes.
NASA Astrophysics Data System (ADS)
Belyanin, S.; Gurfil, P.
2008-02-01
In this study, we investigate the effect of Earth's precession on the orbital dynamics of geostationary satellites. Our astrodynamical model includes second-order zonal and tesseral harmonics, and lunisolar gravitation. We show that the equinoctial precession induces secular inclination growth and thus bares a non-negligible effect on north-south stationkeeping for long mission lifetimes.
NASA Astrophysics Data System (ADS)
Wolf, Carl
By considering a spin-one particle precession in a magnetic field, we demonstrate that if very refined measurements were made of both the precession frequency and the amplitude of spin polarization, these measurements could be used to probe for compositeness of gauge bosons, discrete time effects and possible Markov environmental effects.
The Pole Orientation, Pole Precession, and Moment of Inertia Factor of Saturn
NASA Technical Reports Server (NTRS)
Jacobson, R. A.; French, R. G.; Nicholson, P. D.; Hedman, M.; Colwell, J. E.; Marouf, E.; Rappaport, N.; McGhee, C.; Sepersky, T.; Lonergan, K.
2011-01-01
This paper discusses our determination of the Saturn's pole orientation and precession using a combination of Earthbased and spacecraft based observational data. From our model of the polar motion and the observed precession rate we obtain a value for Saturn's polar moment of inertia
Precession-driven dynamos in a full sphere and the role of large scale cyclonic vortices
NASA Astrophysics Data System (ADS)
Lin, Yufeng; Marti, Philippe; Noir, Jerome; Jackson, Andrew
2016-06-01
Precession has been proposed as an alternative power source for planetary dynamos. Previous hydrodynamic simulations suggested that precession can generate very complex flows in planetary liquid cores [Y. Lin, P. Marti, and J. Noir, "Shear-driven parametric instability in a precessing sphere," Phys. Fluids 27, 046601 (2015)]. In the present study, we numerically investigate the magnetohydrodynamics of a precessing sphere. We demonstrate precession driven dynamos in different flow regimes, from laminar to turbulent flows. In particular, we highlight the magnetic field generation by large scale cyclonic vortices, which has not been explored previously. In this regime, dynamos can be sustained at relatively low Ekman numbers and magnetic Prandtl numbers, which paves the way for planetary applications.
Dephasing in photoinduced large-angle spin precession of confined ferromagnetic structures
NASA Astrophysics Data System (ADS)
Lee, Kyeong-Dong; Ryu, Kwang-Su; Kim, Ji-Wan; Song, Hyon-Seok; Jeong, Jae-Woo; Shin, Sung-Chul
2010-10-01
Spin precessions in the stripes of α-MnAs films prepared on GaAs(001) are investigated using an all-optical pump-probe method. We find that a large-angle spin precession appears while the stripe width decreases. In addition, the large-angle precession considerably changes the resonance frequency, resulting in a significant decrease in the relaxation time. These changes in the precessional motion are mainly ascribed to the dephasing of the nonuniform spin waves existing at the large-angle precession, as experimentally confirmed by varying the precession angle via tuning pump fluence. Micromagnetic simulations using a single Gilbert damping constant well predict the experimental observations, which verifies the interpretation of the change in the precessional motion.
Jet-intracluster medium interaction in Hydra A - II. The effect of jet precession
NASA Astrophysics Data System (ADS)
Nawaz, M. A.; Bicknell, G. V.; Wagner, A. Y.; Sutherland, R. S.; McNamara, B. R.
2016-05-01
We present three-dimensional relativistic hydrodynamical simulations of a precessing jet interacting with the intracluster medium and compare the simulated jet structure with the observed structure of the Hydra A northern jet. For the simulations, we use jet parameters obtained in the parameter space study of the first paper in this series and probe different values for the precession period and precession angle. We find that for a precession period P ≈ 1 Myr and a precession angle ψ ≈ 20°, the model reproduces (i) the curvature of the jet, (ii) the correct number of bright knots within 20 kpc at approximately correct locations and (iii) the turbulent transition of the jet to a plume. The Mach number of the advancing bow shock ≈1.85 is indicative of gentle cluster atmosphere heating during the early stages of the AGN's activity.
The Precession Index, A Nonlinear Energy Balance Model, And Seversmith Psychroterms
NASA Technical Reports Server (NTRS)
Rubincam, David Parry
2004-01-01
An important component of Milankovitch's astronomical theory of climate change is the precession index. The precession index, along with the Earth's tilt and orbital eccentricity, are believed to be the major controlling factors of climate change in the last few million years. The precession index is e sin omega(sub s) where e is the Earth's orbital eccentricity and omega(sub s) measures how close the Sun is to the Earth at midsummer. When omega(sub s) = 90deg the Sun is close to the Earth during northern summer, and at 270deg it is far from the Earth during northern summer. The precession index varies with time, because both the eccentricity e and the parameter omega(sub s) are constantly changing due to disturbances in the Earth's orbit by other planets, and due to the precession of the Earth, The change is largely periodic, with a period of about 23,000 years.
Qiu, X. M.; Huang, L.; Jian, G. D.
2007-03-15
The Rayleigh-Taylor (RT) instability in Z pinches with sheared axial flow (SAF) is analyzed using finite Larmor radius (FLR) magnetohydrodynamic theory, in whose momentum equation the FLR effect (also referred to as the effect of gyroviscosity) is introduced through an anisotropic ion (FLR) stress tensor. A dispersion relation is derived for the linear RT instability. Both analytical and numerical solutions of the dispersion equation are given. The results indicate that the short-wavelength modes of the RT instability can be stabilized by a sufficient FLR, whereas the long-wavelength modes can be stabilized by a sufficient SAF. In the small-wavenumber region, for normalized wavenumber K<2.4, the hybrid RT/KH (Kelvin-Helmholtz) instability is shown to be the most difficult to stabilize. However the synergistic effect of the SAF and gyroviscosity can mitigate both the RT instability in the large-wavenumber region (K>2.4) and the hybrid RT/KH instability in the small-wavenumber region. In addition, this synergistic effect can compress the RT instability to a narrow wavenumber region. Even the thorough stabilization of the RT instability in the large-wavenumber region is possible with a sufficient SAF and a sufficient gyroviscosity.
System design and verification of the precession electron diffraction technique
NASA Astrophysics Data System (ADS)
Own, Christopher Su-Yan
2005-07-01
Bulk structural crystallography is generally a two-part process wherein a rough starting structure model is first derived, then later refined to give an accurate model of the structure. The critical step is the determination of the initial model. As materials problems decrease in length scale, the electron microscope has proven to be a versatile and effective tool for studying many problems. However, study of complex bulk structures by electron diffraction has been hindered by the problem of dynamical diffraction. This phenomenon makes bulk electron diffraction very sensitive to specimen thickness, and expensive equipment such as aberration-corrected scanning transmission microscopes or elaborate methodology such as high resolution imaging combined with diffraction and simulation are often required to generate good starting structures. The precession electron diffraction technique (PED), which has the ability to significantly reduce dynamical effects in diffraction patterns, has shown promise as being a "philosopher's stone" for bulk electron diffraction. However, a comprehensive understanding of its abilities and limitations is necessary before it can be put into widespread use as a standalone technique. This thesis aims to bridge the gaps in understanding and utilizing precession so that practical application might be realized. Two new PED systems have been built, and optimal operating parameters have been elucidated. The role of lens aberrations is described in detail, and an alignment procedure is given that shows how to circumvent aberration in order to obtain high-quality patterns. Multislice simulation is used for investigating the errors inherent in precession, and is also used as a reference for comparison to simple models and to experimental PED data. General trends over a large sampling of parameter space are determined. In particular, we show that the primary reflection intensity errors occur near the transmitted beam and decay with increasing angle and
Superhumps and Accretion Disk Precession in TT ARIETIS
NASA Astrophysics Data System (ADS)
Skillman, David R.; Harvey, David A.; Patterson, Joseph; Kemp, Jonathan; Jensen, Lasse; Fried, Robert E.; Garradd, Gordon; Gunn, Jerry; van Zyl, Liza; Kiyota, Seiichiro; Retter, Alon; Vanmunster, Tonny; Warhurst, Paul
1998-08-01
We have been conducting a long-term (1988-1998) photometric study of the nova-like variable TT Arietis. The main periodic signal in the star's light curve normally occurs at a period that varies but averages ~0.1329 days, which is about 3.5% shorter than the orbital period of the binary. In 1997, this signal disappeared and was replaced by a stronger signal 8.5% longer than the orbital period. This new wave strongly resembles the``superhumps'' commonly seen in SU UMa-type dwarf novae during superoutburst. In superhump parlance, we could say that a negative superhump was replaced by a positive superhump (P>Porb). This could signify the development of an eccentric instability in the accretion disk. The two superhumps probably signify two types of disk precession: apsidal advance and nodal regression. TT Ari is an excellent candidate for observational studies that probe the origin of superhumps.
Highly stable atomic vector magnetometer based on free spin precession.
Afach, S; Ban, G; Bison, G; Bodek, K; Chowdhuri, Z; Grujić, Z D; Hayen, L; Hélaine, V; Kasprzak, M; Kirch, K; Knowles, P; Koch, H-C; Komposch, S; Kozela, A; Krempel, J; Lauss, B; Lefort, T; Lemière, Y; Mtchedlishvili, A; Naviliat-Cuncic, O; Piegsa, F M; Prashanth, P N; Quéméner, G; Rawlik, M; Ries, D; Roccia, S; Rozpedzik, D; Schmidt-Wellenburg, P; Severjins, N; Weis, A; Wursten, E; Wyszynski, G; Zejma, J; Zsigmond, G
2015-08-24
We present a magnetometer based on optically pumped Cs atoms that measures the magnitude and direction of a 1 μT magnetic field. Multiple circularly polarized laser beams were used to probe the free spin precession of the Cs atoms. The design was optimized for long-time stability and achieves a scalar resolution better than 300 fT for integration times ranging from 80 ms to 1000 s. The best scalar resolution of less than 80 fT was reached with integration times of 1.6 to 6 s. We were able to measure the magnetic field direction with a resolution better than 10 μrad for integration times from 10 s up to 2000 s. PMID:26368184
Test of Lorentz Invariance with Spin Precession of Ultracold Neutrons
Altarev, I.; Gutsmiedl, E.; Baker, C. A.; Iaydjiev, P.; Ivanov, S. N.; Ban, G.; Lefort, T.; Naviliat-Cuncic, O.; Quemener, G.; Bodek, K.; Kistryn, S.; Zejma, J.; Daum, M.; Henneck, R.; Kirch, K.; Knecht, A.; Lauss, B.; Mtchedlishvili, A.; Petzoldt, G.
2009-08-21
A clock comparison experiment, analyzing the ratio of spin precession frequencies of stored ultracold neutrons and {sup 199}Hg atoms, is reported. No daily variation of this ratio could be found, from which is set an upper limit on the Lorentz invariance violating cosmic anisotropy field b{sub perpendicular}<2x10{sup -20} eV (95% C.L.). This is the first limit for the free neutron. This result is also interpreted as a direct limit on the gravitational dipole moment of the neutron |g{sub n}|<0.3 eV/c{sup 2} m from a spin-dependent interaction with the Sun. Analyzing the gravitational interaction with the Earth, based on previous data, yields a more stringent limit |g{sub n}|<3x10{sup -4} eV/c{sup 2} m.
A decadal precession of atmospheric pressures over the North Pacific
NASA Astrophysics Data System (ADS)
Anderson, Bruce T.; Gianotti, Daniel J. S.; Furtado, Jason C.; Di Lorenzo, Emanuele
2016-04-01
Sustained droughts over the Northwestern U.S. can alter water availability to the region's agricultural, hydroelectric, and ecosystem service sectors. Here we analyze decadal variations in precipitation across this region and reveal their relation to the slow (~10 year) progression of an atmospheric pressure pattern around the North Pacific, which we term the Pacific Decadal Precession (PDP). Observations corroborate that leading patterns of atmospheric pressure variability over the North Pacific evolve in a manner consistent with the PDP and manifest as different phases in its evolution. Further analysis of the data indicates that low-frequency fluctuations of the tropical Pacific Ocean state energize one phase of the PDP and possibly the other through coupling with the polar stratosphere. Evidence that many recent climate variations influencing the North Pacific/North American sector over the last few years are consistent with the current phase of the PDP confirms the need to enhance our predictive understanding of its behavior.
A PRECESSING JET IN THE CH Cyg SYMBIOTIC SYSTEM
Karovska, Margarita; Gaetz, Terrance J.; Raymond, John C.; Lee, Nicholas P.; Carilli, Christopher L.; Hack, Warren
2010-02-20
Jets have been detected in only a few symbiotic binaries to date, and CH Cyg is one of them. In 2001, a non-relativistic jet was detected in CH Cyg for the first time in X-rays. We carried out coordinated Chandra, Hubble Space Telescope (HST), and VLA observations in 2008 to study the propagation of this jet and its interaction with the circumbinary medium. We detected the jet with Chandra and HST and determined that the apex has expanded to the south from {approx}300 AU to {approx}1400 AU, with the shock front propagating with velocity <100 km s{sup -1}. The shock front has significantly slowed down since 2001. Unexpectedly, we also discovered a powerful jet in the NE-SW direction, in the X-ray, optical and radio. This jet has a multi-component structure, including an inner jet and a counterjet at {approx}170 AU, and a SW component ending in several clumps extending out to {approx}750 AU. The structure of the jet and the curvature of the outer portion of the SW jet suggest an episodically powered precessing jet or a continuous precessing jet with occasional mass ejections or pulses. We carried out detailed spatial mapping of the X-ray emission and correlation with the optical and radio emission. X-ray spectra were extracted from the central source, inner NE counterjet, and the brightest clump at a distance of {approx}500 AU from the central source. We discuss the initial results of our analyses, including the multi-component spectral fitting of the jet components and of the central source.
The Orientation and Precession of the Pole of Saturn - Revised
NASA Astrophysics Data System (ADS)
Jacobson, Robert A.; French, R. G.
2011-04-01
The effort to determine the orientation and precession of Saturn's pole is currently motivated by three needs: to orient the Saturn gravity field for ephemeris development and spacecraft navigation, to orient the Saturn ring plane for studies of ring structure and dynamics, and to determine Saturn's polar moment of inertia for studies of Saturn's interior. Boué, G. and Laskar, J. (2006 Icarus 185, 312) published an informative theoretical discussion of polar motion applicable to Saturn. However, their model cannot be easily used in practice. Jacobson (2007 BAAS 39, 317) presented a pole model in the standard IAU trigometric series representation based on the rigid body rotational equations of motion with couples exerted by the Sun, Titan, and Iapetus. He determined the orientation and precession by fitting Saturn ring occultation measurements, in particular: the radio occultation of Voyager 1, the occultation of the star δSco seen with the Voyager 2 Ultraviolet Spectrometer, the 1989 occultation of the star 28 Sgr seen from the Earth, the 1991 occultation of the star GSC 6323-01396 seen from HST, and ring plane crossing times (Nicholson and French, 1997 BAAS 29, 1097). We have since acquired measurements from the 1995 occultation of the star GSC 5249-01240 seen from HST and the re-reduced meansurements of the 1991 occultation (French et al. 2010 AJ 139, 1649). In this paper we present our current results using the occultation data together with satellite astrometry and tracking of the Voyager and Cassini spacecraft. We also discuss future plans for the incorporation of Cassini ring occultation observations.
Spin-orbit Larmor clock for ionization times in one-photon and strong-field regimes
NASA Astrophysics Data System (ADS)
Kaushal, Jivesh; Morales, Felipe; Torlina, Lisa; Ivanov, Misha; Smirnova, Olga
2015-12-01
Photoionization is a process where absorption of one or several photons liberates an electron and creates a hole in a quantum system, such as an atom or a molecule. Is it faster to remove an electron using one or many photons, and how to define this time? Here we introduce a clock that allows us to define ionization time for both one-photon and many-photon ionization regimes. The clock uses the interaction of the electron or hole spin with the magnetic field created by their orbital motion, known as the spin-orbit interaction. The angle of spin precession in the magnetic field records time. We use the combination of analytical theory and ab initio calculations to show how ionization delay depends on the number of absorbed photons, how it appears in the experiment and what electron dynamics it signifies. In particular, we apply our method to calculate the derived time delays in tunneling regime of strong-field ionization.
Spin-orbit Larmor clock for ionization times in one-photon and strong-field regimes
NASA Astrophysics Data System (ADS)
Kaushal, Jivesh; Morales, Felipe; Torlina, Lisa; Ivanov, Misha; Smirnova, Olga
2014-12-01
Photoionization is a process where absorption of one or several photons liberates an electron and creates a hole in a quantum system, such as an atom or a molecule. Is it faster to remove an electron using one or many photons, and how to define this time? Here we introduce a clock that allows us to define ionization time for both one-photon and many-photon ionization regimes. The clock uses the interaction of the electron or hole spin with the magnetic field created by their orbital motion, known as the spin-orbit interaction. The angle of spin precession in the magnetic field records time. We use the combination of analytical theory and ab initio calculations to show how ionization delay depends on the number of absorbed photons, how it appears in the experiment and what electron dynamics it signifies. In particular, we apply our method to calculate the derived time delays in tunneling regime of strong-field ionization.
Inspiral waveforms for spinning compact binaries in a new precessing convention
NASA Astrophysics Data System (ADS)
Gupta, Anuradha; Gopakumar, Achamveedu
2016-05-01
It is customary to use a precessing convention, based on Newtonian orbital angular momentum L N, to model inspiral gravitational waves from generic spinning compact binaries. A key feature of such a precessing convention is its ability to remove all spin precession induced modulations from the orbital phase evolution. However, this convention usually employs a postNewtonian (PN) accurate precessional equation, appropriate for the PN accurate orbital angular momentum L, to evolve the L N-based precessing source frame. This motivated us to develop inspiral waveforms for spinning compact binaries in a precessing convention that explicitly use L to describe the binary orbits. Our approach introduces certain additional 3PN order terms in the orbital phase and frequency evolution equations with respect to the usual L N-based implementation of the precessing convention. The implications of these additional terms are explored by computing the match between inspiral waveforms that employ L and L N-based precessing conventions. We found that the match estimates are smaller than the optimal value, namely 0.97, for a non-negligible fraction of unequal mass spinning compact binaries.
Determining phase relations of proxy data using the eccentricity-precession pattern
NASA Astrophysics Data System (ADS)
Zeeden, C.; Rivera, T. A.
2012-04-01
The phase relation between proxy data and orbital forcing is not always obvious; a link to both precession/insolation maxima or -minima can often be reasoned for. We present a novel approach to extract the phase relation using solely eccentricity-precession pattern from high quality proxy data. We determine the position of consecutive eccentricity maxima as precisely as possible from a stratigraphic record using both eccentricity filters and the amplitude modulation of precession. This way we obtain both the position of these eccentricity maxima as well as the sedimentation rate between successive maxima with error margins. Combining these results with the precession pattern in the geological record, we can determine whether precession-related patterns relate to precession (or insolation) minima or maxima. This approach relies on high quality geological data, the assumption of a direct eccentricity and precession response to orbital forcing, and a well defined orbital solution, but avoids the assumption of an instantaneous response to obliquity. For data with filtered components showing a good fit with the proxy data, this approach yields good results. Using high quality proxy data (color, magnetic susceptibility), we are able to determine the phase relation for equatorial Atlantic Miocene successions of ODP Leg 154. The research leading to these results has received funding from the [European Community's] Seventh Framework Programme ([FP7/2007-2013] under grant agreement n° [215458]. This research used data provided by IODP. Funding for this research was provided by NWO.
Importance of tides for periastron precession in eccentric neutron star-white dwarf binaries
Sravan, N.; Valsecchi, F.; Kalogera, V.; Althaus, L. G.
2014-09-10
Although not nearly as numerous as binaries with two white dwarfs, eccentric neutron star-white dwarf (NS-WD) binaries are important gravitational-wave (GW) sources for the next generation of space-based detectors sensitive to low frequency waves. Here we investigate periastron precession in these sources as a result of general relativistic, tidal, and rotational effects; such precession is expected to be detectable for at least some of the detected binaries of this type. Currently, two eccentric NS-WD binaries are known in the galactic field, PSR J1141–6545 and PSR B2303+46, both of which have orbits too wide to be relevant in their current state to GW observations. However, population synthesis studies predict the existence of a significant Galactic population of such systems. Though small in most of these systems, we find that tidally induced periastron precession becomes important when tides contribute to more than 3% of the total precession rate. For these systems, accounting for tides when analyzing periastron precession rate measurements can improve estimates of the inferred WD component mass and, in some cases, will prevent us from misclassifying the object. However, such systems are rare, due to rapid orbital decay. To aid the inclusion of tidal effects when using periastron precession as a mass measurement tool, we derive a function that relates the WD radius and periastron precession constant to the WD mass.
Regular and chaotic dynamics of magnetization precession in ferrite-garnet films
NASA Astrophysics Data System (ADS)
Shutyĭ, Anatoliy M.; Sementsov, Dmitriy I.
2009-03-01
By numerically solving equations of motion and constructing the spectrum of Lyapunov exponents, nonlinear dynamics of uniformly precessing magnetization in (110) thin film structures with perpendicular magnetic bias is investigated over a wide frequency range of the alternating field. Bifurcational changes in magnetization precession and the states of dynamical bistability are discovered. Conditions for the realization of high-amplitude regular and chaotic dynamic regimes are revealed. The possibility of controlling those precession regimes by using external magnetic fields is shown. The features of time analogs of the Poincaré section of trajectories in the chaotic regimes are studied.
Precessed electron beam electron energy loss spectroscopy of graphene: Beyond channelling effects
Yedra, Ll.; Estradé, S.; Torruella, P.; Eljarrat, A.; Peiró, F.; Darbal, A. D.; Weiss, J. K.
2014-08-04
The effects of beam precession on the Electron Energy Loss Spectroscopy (EELS) signal of the carbon K edge in a 2 monolayer graphene sheet are studied. In a previous work, we demonstrated the use of precession to compensate for the channeling-induced reduction of EELS signal when in zone axis. In the case of graphene, no enhancement of EELS signal is found in the usual experimental conditions, as graphene is not thick enough to present channeling effects. Interestingly, though it is found that precession makes it possible to increase the collection angle, and, thus, the overall signal, without a loss of signal-to-background ratio.
Modeling of magnetization precession in spin-torque nano-oscillators with a tilted polarizer
Lv, Gang; Zhang, Hong E-mail: yaowen@tongji.edu.cn; Cao, Xuecheng; Qin, Yufeng; Li, Guihua; Wang, Linhui; Liu, Yaowen E-mail: yaowen@tongji.edu.cn; Hou, Zhiwei
2015-07-15
The spin-torque induced magnetization precession dynamics are studied in a spin-valve with a tilted spin polarizer. Macrospin simulations demonstrate that the frequency of precession state depends both on the external DC current and the intrinsic parameters of devices such as the tilted angle of spin polarizer, the damping factor and saturation magnetization of the free layer. The dependence role of those parameters is characterized by phase diagrams. An analytical model is presented, which can successfully interpret the features of precession frequency.
Geodesic and Lense-Thirring precessions effects on the near earth artificial satellites
NASA Astrophysics Data System (ADS)
Radwan, M.; El-Salam, F. A. A.; El-Bar, S. E. A.
2013-02-01
The present work deals with the effect of the geodesic and Lense-Thirring precessions in a near Earth artificial satellite orbit. The effects of the geodesic and Lense-Thirring precessions on the orbit evolution are surveyed. The Picard method of successive approximation is described. The canonical equations of motion including forces non-derivable from a potential are presented. The acceleration components coming from the geodesic and Lense-Thirring precessions are first obtained, then, the images of these accelerations are evaluated. The integrations are effected using the method of Picard successive iteration.
First-order finite-Larmor-radius fluid modeling of tearing and relaxation in a plasma pincha)
NASA Astrophysics Data System (ADS)
King, J. R.; Sovinec, C. R.; Mirnov, V. V.
2012-05-01
Drift and Hall effects on magnetic tearing, island evolution, and relaxation in pinch configurations are investigated using a non-reduced first-order finite-Larmor-radius (FLR) fluid model with the nonideal magnetohydrodynamics (MHD) with rotation, open discussion (NIMROD) code [C.R. Sovinec and J. R. King, J. Comput. Phys. 229, 5803 (2010)]. An unexpected result with a uniform pressure profile is a drift effect that reduces the growth rate when the ion sound gyroradius (ρs) is smaller than the tearing-layer width. This drift is present only with warm-ion FLR modeling, and analytics show that it arises from ∇B and poloidal curvature represented in the Braginskii gyroviscous stress. Nonlinear single-helicity computations with experimentally relevant ρs values show that the warm-ion gyroviscous effects reduce saturated-island widths. Computations with multiple nonlinearly interacting tearing fluctuations find that m = 1 core-resonant-fluctuation amplitudes are reduced by a factor of two relative to single-fluid modeling by the warm-ion effects. These reduced core-resonant-fluctuation amplitudes compare favorably to edge coil measurements in the Madison Symmetric Torus (MST) reversed-field pinch [R. N. Dexter et al., Fusion Technol. 19, 131 (1991)]. The computations demonstrate that fluctuations induce both MHD- and Hall-dynamo emfs during relaxation events. The presence of a Hall-dynamo emf implies a fluctuation-induced Maxwell stress, and the simulation results show net transport of parallel momentum. The computed magnitude of force densities from the Maxwell and competing Reynolds stresses, and changes in the parallel flow profile, are qualitatively and semi-quantitatively similar to measurements during relaxation in MST.
The Precession Index and a Nonlinear Energy Balance Climate Model
NASA Technical Reports Server (NTRS)
Rubincam, David
2004-01-01
A simple nonlinear energy balance climate model yields a precession index-like term in the temperature. Despite its importance in the geologic record, the precession index e sin (Omega)S, where e is the Earth's orbital eccentricity and (Omega)S is the Sun's perigee in the geocentric frame, is not present in the insolation at the top of the atmosphere. Hence there is no one-for-one mapping of 23,000 and 19,000 year periodicities from the insolation to the paleoclimate record; a nonlinear climate model is needed to produce these long periods. A nonlinear energy balance climate model with radiative terms of form T n, where T is surface temperature and n less than 1, does produce e sin (omega)S terms in temperature; the e sin (omega)S terms are called Seversmith psychroterms. Without feedback mechanisms, the model achieves extreme values of 0.64 K at the maximum orbital eccentricity of 0.06, cooling one hemisphere while simultaneously warming the other; the hemisphere over which perihelion occurs is the cooler. In other words, the nonlinear energy balance model produces long-term cooling in the northern hemisphere when the Sun's perihelion is near northern summer solstice and long-term warming in the northern hemisphere when the aphelion is near northern summer solstice. (This behavior is similar to the inertialess gray body which radiates like T 4, but the amplitude is much lower for the energy balance model because of its thermal inertia.) This seemingly paradoxical behavior works against the standard Milankovitch model, which requires cool northern summers (Sun far from Earth in northern summer) to build up northern ice sheets, so that if the standard model is correct it must be more efficient than previously thought. Alternatively, the new mechanism could possibly be dominant and indicate southern hemisphere control of the northern ice sheets, wherein the southern oceans undergo a long-term cooling when the Sun is far from the Earth during northern summer. The cold
Wid, O.; Wahler, M.; Homonnay, N.; Richter, T.; Schmidt, G.
2015-11-15
We demonstrate coherent control of time domain ferromagnetic resonance by all electrical excitation and detection. Using two ultrashort magnetic field steps with variable time delay we control the induction decay in yttrium iron garnet (YIG). By setting suitable delay times between the two steps the precession of the magnetization can either be enhanced or completely stopped. The method allows for a determination of the precession frequency within a few precession periods and with an accuracy much higher than can be achieved using fast fourier transformation. Moreover it holds the promise to massively increase precession amplitudes in pulsed inductive microwave magnetometry (PIMM) using low amplitude finite pulse trains. Our experiments are supported by micromagnetic simulations which nicely confirm the experimental results.
SR calculation of the geodetic precession of gpb.
NASA Astrophysics Data System (ADS)
Collins, Russell
2003-03-01
The gpb satellite, see http://www.nas.edu/ssb/gpb.html, should enter a low circular polar orbit about earth July 2003. Its near-perfect gyroscopes will probe the metric of space near the earth. An in-plane precession is expected, termed the geodetic effect, because measured distance is not Euclidean in the presence of gravity. The circumference of a circle tangent to the outside of the gyroscope is, by SR, shortened slightly more than a circle tangent to the inside. The gyroscope axis is slowly tilted backward (counter to the orbital direction) by this geodetic effect, ΔΘ = -3π GM/r c^2 = -3π v^2/c^2 rad/rev = -6.55467 arcsec/year. This is identical to the GR result, arXiv:gr-qc/9909054 v2 21 Sep 1999, except for the sign. After including small perturbations due to the sun and the earth's oblateness, GR expects +6.58048 and SR expects - 6.56124 arcsec/yr. The predicted precision of the experiment is 0.00045 arcsec/yr. Let the experiment decide.
Tidal-Force-Induced Precessions of Accretion Disks
NASA Astrophysics Data System (ADS)
Inoue, Hajime
2012-04-01
The preccession of an accretion disk around a compact star in a close binary has been studied. When the accretion disk tilts, the tidal force from the companion star induces a torque on it, which causes a preccession of the disk. We firstly consider the properties of a preccessing motion of a ring, which is circularly rotating around a compact star, and is preccessing with a slightly tilting angle under the influence of a tidal force from a companion star. We next compare the predicted behaviors of the preccessing ring with observations, and find that several observational facts from Her X-1, SS 433, and some other X-ray binaries can be explained by a tidal-force-induced precession scheme quite reasonably. We further examine the energetics of the preccessing ring as a function of the tilting angle. It is shown that the kinetic and potential energies of the orbiting motions of the ring matter around the compact star increases as the tilting angle increases, while the thermal and effective potential energies for hydro-static balance in the meridian cross section of the ring decreases through adiabatic expansion. Quantitative estimations have shown that when the ring has sufficient thermal energy, the decrease of the energy for the hydro-static balance can be larger than the increase of the energy for circular motion around the compact star until the tilting angle reaches a certain value. It is strongly suggested that preccessions of accretion disks are often realized in close binaries.
Refinements on precession, nutation, and wobble of the Earth
NASA Astrophysics Data System (ADS)
Dehant, V. Folgueira M.; Puica, M.; Van Hoolst, T.
2015-08-01
Most of the essential elements of the theory of nutation of the nonrigid Earth have been presented in the IAU adopted model MHB2000 (Mathews et al., 2002) considering an ellipsoidal rotating Earth, with a solid inner core, a liquid outer core, and an ellipsoidal inelastic mantle, and with a magnetic field. However in the meantime, the observed nutation amplitudes have been redetermined with a better precision. A number of relatively small significant effects have to be taken into account before one can expect to have a theoretical framework that can yield numerical results matching the precession and nutation observations. The adopted model already accounts for the existence of a geomagnetic field passing through the mantle and the fluid core regions and beyond. The model MHB2000 considers an electromagnetic torque generated by this field when the core and the mantle are moving relative to each other, which can in turn affect some nutation amplitudes (both in phase and out-of-phase) to the extent of a few hundreds of microarcsecond (μas), playing thus a significant role. The paper revisits the last adopted model in order to incorporate potential additional coupling effects at the core-mantle boundary, that can be at an observable level, such as the existence of a non-hydrostatic core-mantle boundary topography, the viscosity of the liquid core, the existence of stratification in the core, the existence of boundary layers at both sides of the core-mantle boundary.
Reifenstein, Eric; Stemmler, Martin; Herz, Andreas V. M.; Kempter, Richard; Schreiber, Susanne
2014-01-01
As a rat moves, grid cells in its entorhinal cortex (EC) discharge at multiple locations of the external world, and the firing fields of each grid cell span a hexagonal lattice. For movements on linear tracks, spikes tend to occur at successively earlier phases of the theta-band filtered local field potential during the traversal of a firing field – a phenomenon termed phase precession. The complex movement patterns observed in two-dimensional (2D) open-field environments may fundamentally alter phase precession. To study this question at the behaviorally relevant single-run level, we analyzed EC spike patterns as a function of the distance traveled by the rat along each trajectory. This analysis revealed that cells across all EC layers fire spikes that phase-precess; indeed, the rate and extent of phase precession were the same, only the correlation between spike phase and path length was weaker in EC layer III. Both slope and correlation of phase precession were surprisingly similar on linear tracks and in 2D open-field environments despite strong differences in the movement statistics, including running speed. While the phase-precession slope did not correlate with the average running speed, it did depend on specific properties of the animal's path. The longer a curving path through a grid-field in a 2D environment, the shallower was the rate of phase precession, while runs that grazed a grid field tangentially led to a steeper phase-precession slope than runs through the field center. Oscillatory interference models for grid cells do not reproduce the observed phenomena. PMID:24959748
Exact solution for spin precession in the radiationless relativistic Kepler problem
NASA Astrophysics Data System (ADS)
Mane, S. R.
2014-11-01
There is interest in circulating beams of polarized particles in all-electric storage rings to search for nonzero permanent electric dipole moments of subatomic particles. To this end, it is helpful to derive exact analytical solutions of the spin precession in idealized models, both for pedagogical reasons and to serve as benchmark tests for analysis and design of experiments. This paper derives exact solutions for the spin precession in the relativistic Kepler problem. Some counterintuitive properties of the solutions are pointed out.
Reifenstein, Eric; Stemmler, Martin; Herz, Andreas V M; Kempter, Richard; Schreiber, Susanne
2014-01-01
As a rat moves, grid cells in its entorhinal cortex (EC) discharge at multiple locations of the external world, and the firing fields of each grid cell span a hexagonal lattice. For movements on linear tracks, spikes tend to occur at successively earlier phases of the theta-band filtered local field potential during the traversal of a firing field - a phenomenon termed phase precession. The complex movement patterns observed in two-dimensional (2D) open-field environments may fundamentally alter phase precession. To study this question at the behaviorally relevant single-run level, we analyzed EC spike patterns as a function of the distance traveled by the rat along each trajectory. This analysis revealed that cells across all EC layers fire spikes that phase-precess; indeed, the rate and extent of phase precession were the same, only the correlation between spike phase and path length was weaker in EC layer III. Both slope and correlation of phase precession were surprisingly similar on linear tracks and in 2D open-field environments despite strong differences in the movement statistics, including running speed. While the phase-precession slope did not correlate with the average running speed, it did depend on specific properties of the animal's path. The longer a curving path through a grid-field in a 2D environment, the shallower was the rate of phase precession, while runs that grazed a grid field tangentially led to a steeper phase-precession slope than runs through the field center. Oscillatory interference models for grid cells do not reproduce the observed phenomena. PMID:24959748
NASA Astrophysics Data System (ADS)
Pál, András; Kocsis, Bence
2008-09-01
Transiting exoplanetary systems are surpassingly important among the planetary systems since they provide the widest spectrum of information for both the planet and the host star. If a transiting planet is on an eccentric orbit, the duration of transits TD is sensitive to the orientation of the orbital ellipse relative to the line of sight. The precession of the orbit results in a systematic variation in both the duration of individual transit events and the observed period between successive transits, Pobs. The periastron of the ellipse slowly precesses due to general relativity and possibly the presence of other planets in the system. This secular precession can be detected through the long-term change in Pobs (transit timing variations, TTV) or in TD (transit duration variations, TDV). We estimate the corresponding precession measurement precision for repeated future observations of the known eccentric transiting exoplanetary systems (XO-3b, HD 147506b, GJ 436b and HD 17156b) using existing or planned space-borne instruments. The TDV measurement improves the precession detection sensitivity by orders of magnitude over the TTV measurement. We find that TDV measurements over a approximately 4yr period can typically detect the precession rate to a precision well exceeding the level predicted by general relativity.
NASA Technical Reports Server (NTRS)
DeHart, Russell; Smith, Eric; Lakin, John
2015-01-01
The spin period to precession period ratio of a non-axisymmetric spin-stabilized spacecraft, the Advanced Composition Explorer (ACE), was used to estimate the remaining mass and distribution of fuel within its propulsion system. This analysis was undertaken once telemetry suggested that two of the four fuel tanks had no propellant remaining, contrary to pre-launch expectations of the propulsion system performance. Numerical integration of possible fuel distributions was used to calculate moments of inertia for the spinning spacecraft. A Fast Fourier Transform (FFT) of output from a dynamics simulation was employed to relate calculated moments of inertia to spin and precession periods. The resulting modeled ratios were compared to the actual spin period to precession period ratio derived from the effect of post-maneuver nutation angle on sun sensor measurements. A Monte Carlo search was performed to tune free parameters using the observed spin period to precession period ratio over the life of the mission. This novel analysis of spin and precession periods indicates that at the time of launch, propellant was distributed unevenly between the two pairs of fuel tanks, with one pair having approximately 20% more propellant than the other pair. Furthermore, it indicates the pair of the tanks with less fuel expelled all of its propellant by 2014 and that approximately 46 kg of propellant remains in the other two tanks, an amount that closely matches the operational fuel accounting estimate. Keywords: Fuel Distribution, Moments of Inertia, Precession, Spin, Nutation
Gerhardt, S. P.; Belova, E. V.; Yamada, M.; Ji, H.; Jacobson, C. M.; McGeehan, B.; Ren, Y.; Inomoto, M.; Maqueda, R.
2008-02-15
Oblate field-reversed configurations (FRCs) have been sustained for >300 {mu}s, or >15 magnetic diffusion times, through the use of an inductive solenoid. These argon FRCs can have their poloidal flux sustained or increased, depending on the timing and strength of the induction. An inward pinch is observed during sustainment, leading to a peaking of the pressure profile and maintenance of the FRC equilibrium. The good stability observed in argon (and krypton) does not transfer to lighter gases, which develop terminal co-interchange instabilities. The stability in argon and krypton is attributed to a combination of external field shaping, magnetic diffusion, and finite-Larmor radius effects.
Yamamoto, Kazuhiro; Nakamura, Gen
2011-02-15
First-order quantum correction to the Larmor radiation is investigated on the basis of the scalar QED on a homogeneous background of a time-dependent electric field, which is a generalization of a recent work by Higuchi and Walker so as to be extended for an accelerated charged particle in a relativistic motion. We obtain a simple approximate formula for the quantum correction in the limit of the relativistic motion when the direction of the particle motion is parallel to that of the electric field.
Millennial scale climatic responses through a Late Miocene precession cycle
NASA Astrophysics Data System (ADS)
Marzocchi, Alice; Lunt, Dan; Flecker, Rachel; Bradshaw, Catherine
2014-05-01
Late Miocene (11.61-5.33 Ma) climate is thought to have been warmer and wetter than the present, with nearly ice-free conditions over the Northern Hemisphere, and significant differences in vegetation distribution. There still is considerable uncertainty in the reconstructed CO2 levels for this time period, fostered by the temporally and spatially biased distribution of the available proxy record. Previous model-data comparison studies (i.e. Bradshaw et al., 2012; Pound et al., 2011) highlighted the mismatch between model results and proxy data for this time period. Here, we investigate how taking into account the variability due to changes in orbital forcing can account for some of these differences. We also explore the orbital control on the monsoonal systems at millennial scale resolution, as well as the impact of background CO2 on orbital sensitivity. Long-term changes in seasonal and latitudinal solar insolation are generated by periodic oscillations in the Earth's orbit and tilt relative to the Sun. These cycles have a modulating effect on climate and ocean circulation patterns. A record of this signal can be found in a number of terrestrial and marine sedimentary sequences. A series of 22 fully coupled atmosphere-ocean-vegetation simulations has been run through an entire precession cycle during the Late Miocene (~6.5 Ma). These experiments were performed using HadCM3L (Hadley Centre Coupled Model, Version 3 - Low resolution ocean) with TRIFFID (Top-down Representation of Interactive Foliage and Flora Including Dynamics) to test the climatic response to changes in orbital forcing. The Mediterranean Sea provides a remarkable geological record for this time slice. Several sequences around the basin margins have been astronomically tuned so that high resolution geological data can be directly compared with our model results. However, this is not the case for the rest of the world, where the distribution of climate proxy data for the Late Miocene is sparse
Global temperatures, precession, and CO{sub 2}
Thomson, D.J.
1995-12-31
Despite much work, the effects of the increasing quantities of carbon dioxide and other so-called {open_quotes}greenhouse gases{close_quotes} on the earth`s climate remain controversial. I show that previous statistical analyses of the climate time series are flawed due to inappropriate assumptions about the timing of the seasons and that the seasonal cycle appears to be changing at an unprecedented rate as a result of greenhouse forcing. Writing the dominant component of the annual seasonal temperature cycle as A(t) cos(2{pi}t + {theta}(t)) where t time in years, and the phase, {theta}(t), describes the timing of the seasons, I show that: From the start of the instrumental series in 1659, up to about 1940, the phase of the Northern Hemisphere temperature {theta}(t) has a decreasing linear trend of about 50 arc-seconds per year. Since about 1940 the phase of the annual cycle has increased rapidly at an average rate of 300 arc-seconds per year with even more rapid changes at many individual stations. From these observations I conclude: (1) From 1669 to 1940 the temperature cycle usually follows perihelion rather the equinoxes. (2) The change after 1940 may be accounted for as a result in the increase in the direct radiation component of temperature by CO{sub 2} relative to transport. (3) The apparent seasonal dependence of the slope of the hemispheric temperature records over the last century noted by several researchers is an artifact of ignoring precession. (4) Changes in CO{sub 2} resulting from human activities are causing large, and readily observable, changes both in the average temperature and in the seasonal cycle.
Influence of orbital precession on the polar methane accumulation on Titan
NASA Astrophysics Data System (ADS)
Liu, J.; Schneider, T.
2014-12-01
Data collected by Cassini Spacecraft indicate that lakes on Titan are primarily found in the polar regions, preferentially in the north. It has been suggested that the hemispherical asymmetry in lake distribution is related to Saturn's orbital precession, which changes the seasonal distribution of solar radiation on Titan, but not the annual mean (Aharonson et al., 2009; Schneider et al., 2012). Saturn's current longitude of perihelion is near northern winter solstice. Hence, the northern summer on Titan is longer and less intense than the southern summer. The longer northern summer leads to greater net precipitation in the annual mean and the methane accumulation over the northern polar region (Schneider et al. 2012). Saturn's perihelion precesses over an approximately 45-kyr period, so the solar radiation at the top of Titan's atmosphere varies on this time scale. Here we investigate how the orbital precession influences the polar methane accumulation with a three-dimensional atmospheric model coupled to a dynamic surface reservoir of methane (Schneider et al. 2012). We find that methane accumulation is closely tied to Saturn's orbital precession. At the time when Saturn's longitude of perihelion is 180 degree away from the present day value, methane is mainly accumulated in the southern polar region due to the stronger annual-mean precipitation there induced by the longer southern summer. The annual-mean evaporation is largely unchanged with orbital precession, since it scales with the annual-mean insolation, which does not change under orbital precession. When Saturn's longitude of perihelion is close to equinox, methane is approximately evenly distributed in the northern and southern polar regions, and the lake dichotomy disappears. The timescale of methane redistribution from one pole to the other is short compared with the timescale of orbital precession, so the surface methane distribution can be viewed as being approximately in equilibrium with the solar
Precession and accretion in circumbinary discs: the case of HD 104237
NASA Astrophysics Data System (ADS)
Dunhill, A. C.; Cuadra, J.; Dougados, C.
2015-04-01
We present the results of smoothed particle hydrodynamics (SPH) simulations of the disc around the young, eccentric stellar binary HD 104237. We find that the binary clears out a large cavity in the disc, driving a significant eccentricity at the cavity edge. This then precesses around the binary at a rate of dot{\\varpi } = 0.48°Tb^{-1}, which for HD 104237 corresponds to a precession period of 40 years. We find that the accretion pattern into the cavity and on to the binary changes with this precession, resulting in a periodic accretion variability driven purely by the physical parameters of the binary and its orbit. For each star we find that this results in order of magnitude changes in the accretion rate. We also find that the accretion variability allows the primary to accrete gas at a higher rate than the secondary for approximately half of each precession period. Using a large number of three-body integrations of test particles orbiting different binaries, we find good agreement between the precession rate of a test particle and our SPH disc precession. These rates also agree very well with the precession rates predicted by the analytic theory of Leung & Lee, showing that their prescription can be accurately used to predict long-term accretion variability time-scales for eccentric binaries accreting from a disc. We discuss the implications of our result, and suggest that this process provides a viable way of preserving unequal-mass ratios in accreting eccentric binaries in both the stellar and supermassive black hole regimes.
Spectral element simulation of precession driven flows in the outer cores of spheroidal planets
NASA Astrophysics Data System (ADS)
Vormann, Jan; Hansen, Ulrich
2015-04-01
A common feature of the planets in the solar system is the precession of the rotation axes, driven by the gravitational influence of another body (e.g. the Earth's moon). In a precessing body, the rotation axis itself is rotating around another axis, describing a cone during one precession period. Similar to the coriolis and centrifugal force appearing from the transformation to a rotating system, the addition of precession adds another term to the Navier-Stokes equation, the so called Poincaré force. The main geophysical motivation in studying precession driven flows comes from their ability to act as magnetohydrodynamic dynamos in planets and moons. Precession may either act as the only driving force or operate together with other forces such as thermochemical convection. One of the challenges in direct numerical simulations of such flows lies in the spheroidal shape of the fluid volume, which should not be neglected since it contributes an additional forcing trough pressure torques. Codes developed for the simulation of flows in spheres mostly use efficient global spectral algorithms that converge fast, but lack geometric flexibility, while local methods are usable in more complex shapes, but often lack high accuracy. We therefore adapted the spectral element code Nek5000, developed at Argonne National Laboratory, to the problem. The spectral element method is capable of solving for the flow in arbitrary geometries while still offering spectral convergence. We present first results for the simulation of a purely hydrodynamic, precession-driven flow in a spheroid with no-slip boundaries and an inner core. The driving by the Poincaré force is in a range where theoretical work predicts multiple solutions for a laminar flow. Our simulations indicate a transition to turbulent flows for Ekman numbers of 10-6 and lower.
Understanding the Effect of Precession on South American Climate
NASA Astrophysics Data System (ADS)
Liu, X.; Battisti, D. S.
2014-12-01
The oxygen isotope concentration in calcite (δ18Oc) in speleothems over South America shows a distinct spatial pattern of change for the past 250,000 years orchestrated by precessional forcing. Using an isotope-enabled model (ECHAM4.6) coupled to a slab ocean model, we study how and why precession changes the climate of South America. Two experiments, called the "low insolation" experiment and "high insolation" experiment, were performed with the same modern boundary conditions, but forced with the extreme minimum and maximum of Southern Hemisphere (SH) summer insolation, respectively. Differences between these two experiments ("low" minus "high") display as a dipole pattern: less precipitation and heavier precipitation-weighted δ18O (δ18Op) along the Andes, and more precipitation and lighter δ18Op in northeastern Brazil. The differences in δ18Op are consistent with δ18Oc of speleothems, in terms of both sign and magnitude. Further analysis of the δ18O of precipitation, the δ18O of water vapor and the probability distribution function (pdf) of precipitation intensity reveals that changes in both the seasonality of precipitation and the "amount effect" contribute to the heavier δ18Op along the Andes, while the "amount effect" almost exclusively contributes to the lighter δ18Op in northeastern Brazil. To identify the causes of precipitation response, three additional experiments are performed with localized albedo increase over South America and/or Africa. These show that the decrease in precipitation along the Andes is caused by cooling of South American continent, whereas the increase in precipitation over northeastern Brazil is associated with cooling of northern Africa. Reduction of SH summer insolation cools both South America and northern Africa. Cooling of South America weakens the South American summer monsoon (SASM) and changes the pdf of precipitation intensity over tropical South America and along the Andes; contrary to previous suggestions
Theta Phase Precession in Rat Ventral Striatum Links Place and Reward Information
Redish, A. David
2011-01-01
A functional interaction between the hippocampal formation and the ventral striatum is thought to contribute to the learning and expression of associations between places and rewards. However, the mechanism of how such associations may be learned and used is currently unknown. We recorded neural ensembles and local field potentials from the ventral striatum and CA1 simultaneously as rats ran a modified T-maze. Theta-modulated cells in ventral striatum almost invariably showed firing phase precession relative to the hippocampal theta rhythm. Across the population of ventral striatal cells, phase precession was preferentially associated with an anticipatory ramping of activity up to the reward sites. In contrast, CA1 population activity and phase precession were distributed more uniformly. Ventral striatal phase precession was stronger to hippocampal than ventral striatal theta and was accompanied by increased theta coherence with hippocampus, suggesting that this effect is hippocampally derived. These results suggest that the firing phase of ventral striatal neurons contains motivationally relevant information and that phase precession serves to bind hippocampal place representations to ventral striatal representations of reward. PMID:21414906
Effective potentials and morphological transitions for binary black hole spin precession.
Kesden, Michael; Gerosa, Davide; O'Shaughnessy, Richard; Berti, Emanuele; Sperhake, Ulrich
2015-02-27
We derive an effective potential for binary black hole (BBH) spin precession at second post-Newtonian order. This effective potential allows us to solve the orbit-averaged spin-precession equations analytically for arbitrary mass ratios and spins. These solutions are quasiperiodic functions of time: after a fixed period, the BBH spins return to their initial relative orientations and jointly precess about the total angular momentum by a fixed angle. Using these solutions, we classify BBH spin precession into three distinct morphologies between which BBHs can transition during their inspiral. We also derive a precession-averaged evolution equation for the total angular momentum that can be integrated on the radiation-reaction time and identify a new class of spin-orbit resonances that can tilt the direction of the total angular momentum during the inspiral. Our new results will help efforts to model and interpret gravitational waves from generic BBH mergers and predict the distributions of final spins and gravitational recoils. PMID:25768748
Misaligned Spin and Orbital Axes Cause the Anomalous Precession of DI Herculis
NASA Technical Reports Server (NTRS)
Albrecht, Simon; Reffert, Sabine; Snellen, Ignas A. G.; Winn, Joshua N.
2009-01-01
In this case we applied our Rossiter-McLaughlin methodology to a binary star, rather than a star-planet system. The orbits of binary stars precess as a result of general relativistic effects, forces arising from the asphericity of the stars, and forces from any additional stars or planets in the system. For most binaries, the theoretical and observed precession rates are in agreement. However, one system known as DI Herculis has resisted explanation for 30 years. The observed precession rate is a factor of four slower than the theoretical rate, a disagreement that once was interpreted as evidence for a failure of general relativity. Among the contemporary explanations are the existence of a circumbinary planet and a large tilt of the stellar spin axes with respect to the orbit. In this paper we reported that both stars of DI Herculis rotate with their spin axes nearly perpendicular to the orbital axis (contrary to the usual assumption for close binary stars). The rotationally induced stellar oblateness causes precession in the direction opposite to that of relativistic precession, thereby reconciling the theoretical and observed rates.
The Origin of Warped, Precessing Accretion Disks in X-ray Binaries
NASA Technical Reports Server (NTRS)
Maloney, Philip R.; Begelman, Mitchell C.
1997-01-01
The radiation-driven warping instability discovered by Pringle holds considerable promise as the mechanism responsible for producing warped, precessing accretion disks in X-ray binaries. This instability is an inherently global mode of the disk, thereby avoiding the difficulties with earlier models for the precession. Here we follow up on earlier work to study the linear behavior of the instability in the specific context of a binary system. We treat the influence of the companion as an orbit-averaged quadrupole torque on the disk. The presence of this external torque allows the existence of solutions in which the direction of precession of the warp is retrograde with respect to disk rotation, in addition to the prograde solutions that exist in the absence of external torques.
Origin of light-induced precession of magnetization in ferromagnetic (Ga,Mn)As
NASA Astrophysics Data System (ADS)
Rozkotova, Eva; Nemec, Petr; Sprinzl, Daniel; Tesarova, Nada; Maly, Petr; Novak, Vit; Olejnik, Kamil; Zemen, Jan; Cukr, Miroslav; Jungwirth, Tomas; Wunderlich, Joerg
2009-03-01
The impact of femtosecond laser pulse leads to the precession of magnetization in (Ga,Mn)As, which can be detected by the time- resolved Kerr rotation (KR) technique. Even though this phenomenon is known for several years [1], the exact physical mechanism inducing the precession is still not clear [2,3]. We show, by a detailed comparison of the KR experimental results and the microscopic calculations of the magnetic anisotropy, that the precession is a consequence of the anisotropy field modification due to the laser pulse-induced change of hole concentration and lattice temperature. [1] A. Oiwa, H. Takechi, H. Munekata, J. Supercond. 18, 9 (2005).[2] Y. Hashimoto, S. Kobayashi, H. Munekata, PRL 100, 067202 (2008).[3] E. Rozkotova, P. Nemec, P. Horodyska, D. Sprinzl, F. Trojanek, P. Maly, V. Novak, K. Olejnik, M. Cukr, T. Jungwirth, Appl. Phys. Lett 92, 122507 (2008).
Park, Youn Ho; Kim, Hyung-Jun; Chang, Joonyeon; Choi, Heon-Jin; Koo, Hyun Cheol
2015-10-01
In a semiconductor channel, spin-orbit interaction is divided into two terms, Rashba and Dresselhaus effects, which are key phenomena for modulating spin precession angles. The direction of Rashba field is always perpendicular to the wavevector but that of Dresselhaus field depends on the crystal orientation. Based on the individual Rashba and Dresselhaus strengths, we calculate spin precession angles for various crystal orientations in an InAs quantum well structure. When the channel length is 1 μm, the precession angle is 550° for the [110] direction and 460° for the [1-10] direction, respectively. Using the two spin transistors with different crystal directions, which play roles of n- and p-type transistors in conventional charge transistors, we propose a complementary logic device. PMID:26726362
Precession-tracking coordinates for simulations of compact-object binaries
NASA Astrophysics Data System (ADS)
Ossokine, Serguei; Kidder, Lawrence E.; Pfeiffer, Harald P.
2013-10-01
Binary black hole simulations with black hole excision using spectral methods require a coordinate transformation into a corotating coordinate system where the black holes are essentially at rest. This paper presents and discusses two coordinate transformations that are applicable to precessing binary systems, one based on Euler angles, the other on quaternions. Both approaches are found to work well for binaries with moderate precession, i.e., for cases where the orientation of the orbital plane changes by ≪90°. For strong precession, performance of the Euler-angle parametrization deteriorates, eventually failing for a 90° change in orientation because of singularities in the parametrization (“gimbal lock”). In contrast, the quaternion representation is invariant under an overall rotation and handles any orientation of the orbital plane as well as the Euler-angle technique handles nonprecessing binaries.
Simulation of Statistical Fluctuations in the Spin Precession Measurements at RHIC
Poblaguev, A. A.
2014-02-25
Measurements of the driven spin coherent precession S_{x}(t)=S_{x}^{(0)} - S_{x}^{(1)} sin(ωt+φ_{0}) were initiated in RHIC Run13. The expected value of the precession amplitude S_{x}^{(1)} ~ 2 x 10^{-4} is about the statistical error in a single measurement and data fit gives a biased estimate of the S_{x}^{(1)}. For a proper statistical interpretation of the results of the several measurements, statistical fluctuations were studied using Monte-Carlo simulation. Preliminary results of the spin precession measurements in RHIC Run13 are presented.
Nonsingular modeling of the equinoctial precession of planets using the Euler parameters
NASA Astrophysics Data System (ADS)
Gurfil, Pini; Klein, Itzik
2007-01-01
This paper develops a nonsingular model for the effect of equinoctial precession on natural and artificial satellite orbits based on the Euler parameters instead of the Euler angles. The use of Euler parameters removes the zero-inclination singularity in the variational equations, thus facilitating numerical integration of low-inclination orbits. Euler-parameter-based planetary and variational equations are developed. These equations are subsequently used for modeling the long-periodic effect of a uniformly precessing reference frame on a given orbit. The Euler parameter-based model is used for simulating the orbit of Deimos, taking into account the Martian oblateness and precession of the spin axis. It is shown that the new model yields an order-of-magnitude faster simulation than the classical element-based model.
NASA Astrophysics Data System (ADS)
Newman, William I.
2012-05-01
Precession of the equinoxes and of satellite orbits for axisymmetric bodies is a celebrated part of the classical and orbital mechanics literature. The theory underlying the behavior of triaxial bodies, particularly when synchronous phase locking is present, has proven to be difficult to evaluate and controversial. We perform a first-principles derivation where we incorporate triaxial geometry into the analysis using a straightforward description of the configuration. We calculate the effect of triaxiality and phase locking upon precession rates by using multiple time scales techniques. This is required to make possible the direct numerical integration of the kinematic equations of motion over solar system time scales. In so doing, we provide a simple derivation of the time-averaged gravitational potential and the associated torque that drives precession, and resolve an outstanding controversy emerging from its calculation.
CYCLIC TRANSIT PROBABILITIES OF LONG-PERIOD ECCENTRIC PLANETS DUE TO PERIASTRON PRECESSION
Kane, Stephen R.; Von Braun, Kaspar; Horner, Jonathan
2012-09-20
The observed properties of transiting exoplanets are an exceptionally rich source of information that allows us to understand and characterize their physical properties. Unfortunately, only a relatively small fraction of the known exoplanets discovered using the radial velocity technique are known to transit their host due to the stringent orbital geometry requirements. For each target, the transit probability and predicted transit time can be calculated to great accuracy with refinement of the orbital parameters. However, the transit probability of short period and eccentric orbits can have a reasonable time dependence due to the effects of apsidal and nodal precession, thus altering their transit potential and predicted transit time. Here we investigate the magnitude of these precession effects on transit probabilities and apply this to the known radial velocity exoplanets. We assess the refinement of orbital parameters as a path to measuring these precessions and cyclic transit probabilities.
NASA Technical Reports Server (NTRS)
Zimmermann, M.; Szedenits, E., Jr.
1979-01-01
An axially symmetric, torque-free rigid body, rotating and precessing, emits gravitational quadrupole radiation at two frequencies, omega and 2 omega, corresponding to the l = 2, m = 1,2 spherical harmonics. The paper presents explicitly the waveforms of the two polarizations at both frequencies. From observations of gravitational waves, one can derive information about the body's orientation and its precession amplitude. Electromagnetic radiation emitted by a spot fixed on the surface of the body arrives in pulses at a mean frequency Omega which is typically different from omega. If the body is not axially symmetric but the amplitude of the precession is small, the gravitational radiation at the lower frequency omega is split into two frequencies on either side of the electromagnetic pulse frequency. Explicit waveforms for the two polarizations in this case are also presented.
Subcritical transition to turbulence of a precessing flow in a cylindrical vessel
NASA Astrophysics Data System (ADS)
Herault, Johann; Gundrum, Thomas; Giesecke, André; Stefani, Frank
2015-12-01
The transition to turbulence in a precessing cylindrical vessel is experimentally investigated. Our measurements are performed for a nearly resonant configuration with an initially laminar flow dominated by an inertial mode with azimuthal wave number m = 1 superimposed on a solid body rotation. By increasing the precession ratio, we observe a transition from the laminar to a non-linear regime, which then breakdowns to turbulence for larger precession ratio. Our measurements show that the transition to turbulence is subcritical, with a discontinuity of the wall-pressure and the power consumption at the threshold ɛLT. The turbulence is self-sustained below this threshold, describing a bifurcation diagram with a hysteresis. In this range of the control parameters, the turbulent flows can suddenly collapse after a finite duration, leading to a definitive relaminarization of the flow. The average lifetime <τ> of the turbulence increases rapidly when ɛ tends to ɛLT.
Predicting Precession Rates from Secular Dynamics for Extra-solar Multi-planet Systems
NASA Astrophysics Data System (ADS)
Van Laerhoven, Christa
2015-12-01
Considering the secular dynamics of multi-planet systems provides substantial insight into the interactions between planets in those systems. Secular interactions are those that don't involve knowing where a planet is along its orbit, and they dominate when planets are not involved in mean motion resonances. These interactions exchange angular momentum among the planets, evolving their eccentricities and inclinations. To second order in the planets' eccentricities and inclinations, the eccentricity and inclination perturbations are decoupled. Given the right variable choice, the relevant differential equations are linear and thus the eccentricity and inclination behaviors can be described as a sum of eigenmodes. Since the underlying structure of the secular eigenmodes can be calculated using only the planets' masses and semi-major axes, one can elucidate the eccentricity and inclination behavior of planets in exoplanet systems even without knowing the planets' current eccentricities and inclinations. I have calculated both the eccentricity and inclination secular eigenmodes for the population of known multi-planet systems whose planets have well determined masses and periods and have used this to predict what range of pericenter precession (and nodal regression) rates the planets may have. One might have assumed that in any given system the planets with shorter periods would have faster precession rates, but I show that this is not necessarily the case. Planets that are 'loners' have narrow ranges of possible precession rates, while planets that are 'groupies' can have a wider range of possible precession rates. Several planets are expected to undergo significant precession on few-year timescales and many planets (though not the majority of planets) will undergo significant precession on decade timescales.
On the three-dimensional precessing jet flow past a sudden expansion
NASA Astrophysics Data System (ADS)
Cafiero, Gioacchino; Ceglia, Giuseppe; Discetti, Stefano; Ianiro, Andrea; Astarita, Tommaso; Cardone, Gennaro
2014-02-01
A circular jet flow past an abrupt expansion under some conditions switches intermittently between two states: quasi-axisymmetric expansion and gyroscopic-like precessing motion. In this work, an experimental investigation into the self-excited precessing flow generated by a 5:1 expansion of a round jet in a coaxial cylindrical chamber is carried out by means of tomographic particle image velocimetry. The experiments are performed on a jet issued from a short pipe at a Reynolds number equal to 150,000. Proper orthogonal decomposition (POD) is applied to extract information on the organization of the large coherent structures of the precessing motion. The application of this technique highlights the dominance of three modes: the most energetic two are associated with the jet precession; the third one is representative of the axial motion. An estimate of the precession probability based on the modal energy obtained from the application of POD is proposed. The precession frequency is extracted using a low-order reconstruction (LOR) of a subset of the POD modes. The reconstructed flow field topology obtained by the LOR highlights an underlying mechanism of swirl generation in proximity of the inlet nozzle; the phenomenon is closely related to the interaction between the entrainment in the far field and the recirculation regions in the near field. The application of a stability criterion shows that the self-induced swirl flow results to be unstable. The instability is responsible for the generation of helical-shaped vortices in the near field, even though the dominant feature for the unconfined jet issued from the same nozzle is the axisymmetric ring-vortices generation.
Jupiter spin-pole precession rate and moment of inertia from Juno radio-science observations
NASA Astrophysics Data System (ADS)
Le Maistre, S.; Folkner, W. M.; Jacobson, R. A.; Serra, D.
2016-07-01
Through detailed and realistic numerical simulations, the present paper assesses the precision with which the Juno spacecraft can measure the normalized polar moment of inertia (MOI) of Jupiter. Based on Ka-band Earth-based Doppler data, created with realistic 10 μm/s of white noise at 60 s of integration, this analysis shows that the determination of the precession rate of Jupiter is by far more efficient than the Lense-Thirring effect previously proposed to determine the moment of inertia and therefore to constrain the internal structure of the giant planet with Juno. We show that the Juno mission will allow the estimation of the precession rate of Jupiter's pole with an accuracy better than 0.1%. We provide an equation relating the pole precession rate and the normalized polar moment of inertia of Jupiter. Accounting for the uncertainty in the parameters affecting precession, we show that the accuracy of the MOI inferred from the precession rate is also better than 0.1%, and at least 50 times better than inferred from the Lense-Thirring acceleration undergone by Juno. This accuracy of the MOI determination should provide tight constraints on the interior structure of Jupiter, especially the core size and mass, helping to distinguish among competing scenarios of formation and evolution of the giant planet. In addition, though the Juno mission operations are already defined, the exact duration of the tracking and its occurrence with respect to the spacecraft pericenter pass are not definitely scheduled. The simulations performed here quantify the impact of this aspect of the mission on the Juno sensitivity to (in particular) the spin-pole precession rate of Jupiter. Finally, additional simulations have been performed to test the usefulness of combining Doppler data with VLBI data, showing the latter measurements to be 104-105 times less sensitive than the former to our parameters of interest and therefore, obviously, totally needless.
Regular and chaotic precession of magnetization in magnetic films with a stripe domain structure
NASA Astrophysics Data System (ADS)
Shutyĭ, A. M.
2008-12-01
Based on a numerical solution of the equations of motion found over a wide range of frequencies of an alternating magnetic field, the nonlinear precession dynamics of magnetization are studied in thin-film structures of the (100) type with a stripe domain structure in a perpendicular bias field. The conditions are determined under which high-amplitude regular and chaotic dynamic regimes occur. Bifurcational variations in the precession of coupled magnetic moments and dynamic-bistability states are detected. The specific features of the spectrum of Lyapunov exponents and of time analogs of Poincaré cross sections of trajectories in chaotic regimes are considered.
Current-Controlled Spin Precession of Quasistationary Electrons in a Cubic Spin-Orbit Field.
Altmann, P; Hernandez, F G G; Ferreira, G J; Kohda, M; Reichl, C; Wegscheider, W; Salis, G
2016-05-13
Space- and time-resolved measurements of spin drift and diffusion are performed on a GaAs-hosted two-dimensional electron gas. For spins where forward drift is compensated by backward diffusion, we find a precession frequency in the absence of an external magnetic field. The frequency depends linearly on the drift velocity and is explained by the cubic Dresselhaus spin-orbit interaction, for which drift leads to a spin precession angle twice that of spins that diffuse the same distance. PMID:27232032
Current-Controlled Spin Precession of Quasistationary Electrons in a Cubic Spin-Orbit Field
NASA Astrophysics Data System (ADS)
Altmann, P.; Hernandez, F. G. G.; Ferreira, G. J.; Kohda, M.; Reichl, C.; Wegscheider, W.; Salis, G.
2016-05-01
Space- and time-resolved measurements of spin drift and diffusion are performed on a GaAs-hosted two-dimensional electron gas. For spins where forward drift is compensated by backward diffusion, we find a precession frequency in the absence of an external magnetic field. The frequency depends linearly on the drift velocity and is explained by the cubic Dresselhaus spin-orbit interaction, for which drift leads to a spin precession angle twice that of spins that diffuse the same distance.
Lyutyy, T V; Denisov, S I; Reva, V V; Bystrik, Yu S
2015-10-01
We study the deterministic and stochastic rotational dynamics of ferromagnetic nanoparticles in a precessing magnetic field. Our approach is based on the system of effective Langevin equations and on the corresponding Fokker-Planck equation. Two key characteristics of the rotational dynamics, namely the average angular frequency of precession of nanoparticles and their average magnetization, are of interest. Using the Langevin and Fokker-Planck equations, we calculate both analytically and numerically these characteristics in the deterministic and stochastic cases, determine their dependence on the model parameters, and analyze in detail the role of thermal fluctuations. PMID:26565245
Precession Constant Correction and Proper Motion Systems of FK5 and Hipparcos
NASA Astrophysics Data System (ADS)
Zhu, Zi
2007-07-01
Results of many researches have shown that the relation between the proper motion systems of FK5 and Hipparcos is not consistent with the precession constant corrections determined by VLBI and LLR. We analysed proper motion data of PPM and ACRS based on the FK5 system for many different sub-samples and found that consistent values of the precession correction and equinox motion correction can not be given by either PPM or ACRS proper motion data, thereby indicating that the internal systematic error of the FK5 proper motion is the main underlying factor of the inconsistency.
NASA Astrophysics Data System (ADS)
Lyutyy, T. V.; Denisov, S. I.; Reva, V. V.; Bystrik, Yu. S.
2015-10-01
We study the deterministic and stochastic rotational dynamics of ferromagnetic nanoparticles in a precessing magnetic field. Our approach is based on the system of effective Langevin equations and on the corresponding Fokker-Planck equation. Two key characteristics of the rotational dynamics, namely the average angular frequency of precession of nanoparticles and their average magnetization, are of interest. Using the Langevin and Fokker-Planck equations, we calculate both analytically and numerically these characteristics in the deterministic and stochastic cases, determine their dependence on the model parameters, and analyze in detail the role of thermal fluctuations.
New test of general relativity - Measurement of de Sitter geodetic precession rate for lunar perigee
NASA Technical Reports Server (NTRS)
Bertotti, Bruno; Ciufolini, Ignazio; Bender, Peter L.
1987-01-01
According to general relativity, the calculated rate of motion of lunar perigee should include a contribution of 19.2 msec/yr from geodetic precession. It is shown that existing analyses of lunar-laser-ranging data confirm the general-relativistic rate for geodetic precession with respect to the planetary dynamical frame. In addition, the comparison of earth-rotation results from lunar laser ranging and from VLBI shows that the relative drift of the planetary dynamical frame and the extragalactic VLBI reference frame is small. The estimated accuracy is about 10 percent.
NASA Technical Reports Server (NTRS)
Borsody, J.
1976-01-01
Equations are derived by using the maximum principle to maximize the payload of a reusable tug for planetary missions. The analysis includes a correction for precession of the space shuttle orbit. The tug returns to this precessed orbit (within a specified time) and makes the required nodal correction. A sample case is analyzed that represents an inner planet mission as specified by a fixed declination and right ascension of the outgoing asymptote and the mission energy. The reusable stage performance corresponds to that of a typical cryogenic tug. Effects of space shuttle orbital inclination, several trajectory parameters, and tug thrust on payload are also investigated.
Magnetization switching by microwaves initially rotating in opposite direction to precession
NASA Astrophysics Data System (ADS)
Taniguchi, Tomohiro
2015-12-01
A common understanding of magnetization switching in microwave-assisted magnetization reversal is that the rotation direction of the microwaves should be the same as the precession direction of the magnetization. In this letter, however, we show that microwaves initially rotating opposite to the magnetization precession destabilize the magnetization at an equilibrium and induce switching more efficiently when the microwave frequency depends on time. This argument is analytically deduced from an energy balance equation. We also establish a model satisfying this condition and confirm magnetization switching solely by microwaves by using numerical simulation.
Probing white dwarf interiors with LISA: periastron precession in eccentric double white dwarfs.
Willems, B; Vecchio, A; Kalogera, V
2008-02-01
In globular clusters, dynamical interactions give rise to a population of eccentric double white dwarfs detectable by the Laser Interferometer Space Antenna (LISA) up to the Large Magellanic Cloud. In this Letter, we explore the detectability of periastron precession in these systems with LISA. Unlike previous investigations, we consider contributions due to tidal and rotational distortions of the binary components in addition to general relativistic contributions to the periastron precession. At orbital frequencies above a few mHz, we find that tides and stellar rotation dominate, opening up a possibly unique window to the study of the interior and structure of white dwarfs. PMID:18352253
The evolution of adopted values for precession. [historical survey of reference systems
NASA Technical Reports Server (NTRS)
Lieske, J. H.
1985-01-01
The history of astronomical longitude precession determination is reviewed. Consideration is given to the work of Hipparchus and Ptolemy, the definition of rotation axes, the major 19th-century determinations, and 20th-century studies (using the data of Newcomb; based on PGC, GC, and McCormick/Cape catalogs; using FK3, FK4, and AGK3; involving galaxies; and using the dynamical method). Laser ranging and VLBI are seen as the most promising techniques for future precession measurements. Diagrams, graphs, and tables of numerical data are provided.
Niklowitz, P G; Pfleiderer, C; Keller, T; Vojta, M; Huang, Y-K; Mydosh, J A
2010-03-12
We report for the first time simultaneous microscopic measurements of the lattice constants, the distribution of the lattice constants, and the antiferromagnetic moment in high-purity URu(2)Si(2), combining Larmor and conventional neutron diffraction at low temperatures and pressures up to 18 kbar. Our data demonstrate quantitatively that the small moment in the hidden order (HO) of URu(2)Si(2) is purely parasitic. The excellent experimental conditions we achieve allow us to resolve that the transition line between HO and large-moment antiferromagnetism (LMAF), which stabilizes under pressure, is intrinsically first order and ends in a bicritical point. Therefore, the HO and LMAF must have different symmetry, which supports exotic scenarios of the HO such as orbital currents, helicity order, or multipolar order. PMID:20366444
Measurement of the Nodal Precession of WASP-33 b via Doppler Tomography
NASA Astrophysics Data System (ADS)
Johnson, Marshall C.; Cochran, William D.; Collier Cameron, Andrew; Bayliss, Daniel
2015-09-01
We have analyzed new and archival time series spectra taken six years apart during transits of the hot Jupiter WASP-33 b, and spectroscopically resolved the line profile perturbation caused by the Rossiter-McLaughlin effect. The motion of this line profile perturbation is determined by the path of the planet across the stellar disk, which we show to have changed between the two epochs due to nodal precession of the planetary orbit. We measured rates of change of the impact parameter and the sky-projected spin-orbit misalignment of {db}/{dt}={-0.0228}-0.0018+0.0050 {{yr}}-1 and dλ /{dt}={-0\\buildrel{\\circ}\\over{.} 487}-0.076+0.089 {{yr}}-1, respectively, corresponding to a rate of nodal precession of d{{Ω }}/{dt}=0\\buildrel{\\circ}\\over{.} {373}-0.083+0.031 {{yr}}-1. This is only the second measurement of nodal precession for a confirmed exoplanet transiting a single star. Finally, we used the rate of precession to set limits on the stellar gravitational quadrupole moment of 0.0054≤slant {J}2≤slant 0.035.
Numerical expressions for precession formulae and mean elements for the Moon and the planets
NASA Astrophysics Data System (ADS)
Simon, J. L.; Bretagnon, P.; Chapront, J.; Chapront-Touze, M.; Francou, G.; Laskar, J.
1994-02-01
We present, in this paper, a coherent set of formula giving numerical expressions for precession quantities and mean elements of the Moon and the planets. First, using the notations of Lieske et al. (1977), we construct expressions for the precession quantities based upon the use of the secular variations of the ecliptic pole from the planetary theories built at the Bureau des Longitudes and taking into account recent determinations of the precession constant and of the obliquity in J2000. Also we give the derivatives of these expressions with respect to the masses of the planets, to the precession constant and to the obliquity. So, this set of formulas is applicable whenever the values of the planetary masses and of the constants are improved. Afterwards, we give the mean elements of the Moon and the planets connected to the fixed J2000 ecliptic and connected to the ecliptic of date. At last, we give formula which enable one to compute approximate ephemerides of the Moon and the planets from mean elements.
Pure collective precession motion of a high-spin torus isomer
NASA Astrophysics Data System (ADS)
Ichikawa, T.; Matsuyanagi, K.; Maruhn, J. A.; Itagaki, N.
2014-01-01
We investigate the precession motion of the exotic torus configuration in high-spin excited states of 40Ca. For this aim, we use the three-dimensional time-dependent Hartree-Fock (TDHF) method. Although the high-spin torus isomer is a unique quantum object characterized by the alignment of angular momenta of independent single-particle motions, we find that the obtained moment of inertia for rotations about an axis perpendicular to the symmetry axis is close to the rigid-body value. We also analyze the microscopic structure of the precession motion using the random-phase approximation (RPA) method for high-spin states. In the RPA calculation, the precession motion of the torus isomer is generated by coherent superposition of many one-particle-one-hole excitations across the sloping Fermi surface that strongly violates the time-reversal symmetry. By comparing results of the TDHF and the RPA calculations, we find that the precession motion obtained by the TDHF calculation is a pure collective motion well decoupled from other collective modes.
THE DETECTABILITY OF TRANSIT DEPTH VARIATIONS DUE TO EXOPLANETARY OBLATENESS AND SPIN PRECESSION
Carter, Joshua A.; Winn, Joshua N.
2010-06-10
Knowledge of an exoplanet's oblateness and obliquity would give clues about its formation and internal structure. In principle, a light curve of a transiting planet bears information about the planet's shape, but previous work has shown that the oblateness-induced signal will be extremely difficult to detect. Here, we investigate the potentially larger signals due to planetary spin precession. The most readily detectable effects are transit depth variations (T{delta}V's) in a sequence of light curves. For a planet as oblate as Jupiter or Saturn, the transit depth will undergo fractional variations of order 1%. The most promising systems are those with orbital periods of approximately 15-30 days, which are short enough for the precession period to be less than about 40 yr and long enough to avoid spin-down due to tidal friction. The detectability of the T{delta}V signal would be enhanced by moons (which would decrease the precession period) or planetary rings (which would increase the amplitude). The Kepler mission should find several planets for which precession-induced T{delta}V signals will be detectable. Due to modeling degeneracies, Kepler photometry would yield only a lower bound on oblateness. The degeneracy could be lifted by observing the oblateness-induced asymmetry in at least one transit light curve or by making assumptions about the planetary interior.
ERIC Educational Resources Information Center
O'Donnell, Kane; Visser, Matt
2011-01-01
The purpose of this paper is to provide an elementary introduction to the qualitative and quantitative results of velocity combination in special relativity, including the Wigner rotation and Thomas precession. We utilize only the most familiar tools of special relativity, in arguments presented at three differing levels: (1) utterly elementary,…
Zhang, Shi-Chang
2013-10-15
Analytical formulas of the Larmor rotation are derived in detail for the equilibrium electrons motion in a free-electron laser with combination of a three-dimensional (3-D) helical wiggler and a positive or a reversed guide magnetic field. Generally, the Larmor radius in the configuration of a reversed guide field is much smaller than that in a positive guide field. At non-resonance, a helical orbit governed by the zero-order component of a 3-D wiggler field could hold; meanwhile, the higher-harmonic effect definitely influences those electrons with off-axis guiding centers and induces the electron-beam spreads. At resonance, the Larmor radius in the configuration of a positive guide field has a singularity with a limit tending to infinite, which causes all the electrons to hit the waveguide wall before the exit of the wiggler. Although Larmor-radius singularity does not exist in the configuration of a reversed guide field, at anti-resonance, the first-order harmonic of a 3-D wiggler field induces a transverse displacement which rapidly grows in proportion to a square of time, and leads part of the electron beam to hit the waveguide wall before reaching the wiggler exit, which depends on the specific parameters of the individual electrons. The analytical conclusions derived in the present paper are examined by the nonlinear simulations and the experimental observation. Disagreement with the previous literatures is discussed in detail.
The impact of precession and obliquity on the Late-Devonian greenhouse climate
NASA Astrophysics Data System (ADS)
De Vleeschouwer, D.; Crucifix, M.; Bounceur, N.; Claeys, P. F.
2012-12-01
To date, only few general circulation model (GCM) have been used to simulate the extremely warm greenhouse climate of the Late-Devonian (~370 Ma). As a consequence, the current knowledge on Devonian climate dynamics comes almost exclusively from geological proxy data. Given the fragmentary nature of these data sources, the understanding of the Devonian climate is rather limited. Nonetheless, the Late-Devonian is a key-period in the evolution of life on Earth: the continents were no longer bare but were invaded by land plants, the first forests appeared, soils were formed, fish evolved to amphibians and 70-80% of all animal species were wiped out during the Late Devonian extinction (~376 Ma). In order to better understand the functioning of the climate system during this highly important period in Earth's history, we applied the HadSM3 climate model to the Devonian period under different astronomical configurations. This approach provides insight into the response of Late-Devonian climate to astronomical forcing due to precession and obliquity. Moreover, the assessment of the sensitivity of the Late-Devonian climate to astronomical forcing, presented here, will allow cyclostratigraphers to make better and more detailed interpretations of recurring patterns often observed in Late-Devonian sections. We simulated Late-Devonian climates by prescribing palaeogeography, vegetation distribution and pCO2 concentration (2180 ppm). Different experiments were carried out under 31 different astronomical configurations: three levels for obliquity (ɛ = 22°; 23.5° and 24.5°) and eccentricity (e = 0; 0.03 and 0.07) were chosen. For precession, 8 levels were considered (longitude of the perihelion= 0°; 45°; 90°; 135°; 180°; 235°; 270°). First results suggest that the intensity of precipitation on the tropical Euramerican continent (also known as Laurussia) is highly dependent on changes in precession: During precession maxima (= maximal insolation in SH during winter
Relativistic 3D precessing jet simulations for the X-ray binary SS433
NASA Astrophysics Data System (ADS)
Monceau-Baroux, Rémi; Porth, Oliver; Meliani, Zakaria; Keppens, Rony
2014-01-01
Context. Modern high-resolution radio observations allow us a closer look into the objects that power relativistic jets. This is especially the case for SS433, an X-ray binary that emits a precessing jet that is observed down to the subparsec scale. Aims: We aim to study full 3D dynamics of relativistic jets associated with active galactic nuclei or X-ray binaries (XRB). In particular, we incorporate the precessing motion of a jet into a model for the jet associated with the XRB SS433. Our study of the jet dynamics in this system focuses on the subparsec scales. We investigate the impact of jet precession and the variation of the Lorentz factor of the injected matter on the general 3D jet dynamics and its energy transfer to the surrounding medium. After visualizing and quantifying jet dynamics, we aim to realize synthetic radio mapping of the data, to compare our results with observations. Methods: For our study we used a block-tree adaptive mesh refinement scheme and an inner time-dependent boundary prescription to inject precessing bipolar supersonic jets. Parameters extracted from observations were used. Different 3D jet realizations that match the kinetic flux of the SS433 jet were intercompared, which vary in density contrast and jet beam velocity. We tracked the energy content deposited in different regions of the domain affected by the jet. Our code allows us to follow the adiabatic cooling of a population of relativistic particles injected by the jet. This evolving energy spectrum of accelerated electrons, using a pressure-based proxy for the magnetic field, allowed us to obtain the radio emission from our simulation. Results: We find a higher energy transfer for a precessing jet than for standing jets with otherwise identical parameters as a result of the effectively increased interaction area. We obtain synthetic radio maps for all jets, from which one can see that dynamical flow features are clearly linked with enhanced emission sites. Conclusions: The
Analysis of spin precession in binary black hole systems including quadrupole-monopole interaction
NASA Astrophysics Data System (ADS)
Racine, Étienne
2008-08-01
We analyze in detail the spin precession equations in binary black hole systems, when the tidal torque on a Kerr black hole due to quadrupole-monopole coupling is taken into account. We show that completing the precession equations with this term reveals the existence of a conserved quantity at 2PN order when averaging over orbital motion. This quantity allows one to solve the (orbit-averaged) precession equations exactly in the case of equal masses and arbitrary spins, neglecting radiation reaction. For unequal masses, an exact solution does not exist in closed form, but we are still able to derive accurate approximate analytic solutions. We also show how to incorporate radiation-reaction effects into our analytic solutions adiabatically, and compare the results to solutions obtained numerically. For various configurations of the binary, the relative difference in the accumulated orbital phase computed using our analytic solutions versus a full numerical solution varies from ˜0.3% to ˜1.8% over ˜80 140 orbital cycles accumulated while sweeping over the orbital frequency range ˜20 300Hz. This typically corresponds to a discrepancy of order ˜5 6 radians. While this may not be accurate enough for implementation in LIGO template banks, we still believe that our new solutions are potentially quite useful for comparing numerical relativity simulations of spinning binary black hole systems with post-Newtonian theory. They can also be used to gain more understanding of precession effects, with potential application to the gravitational recoil problem, and to provide semianalytical templates for spinning, precessing binaries.
Effects of the observed J2 variations on the Earth's precession and nutation
NASA Astrophysics Data System (ADS)
Ferrándiz, José M.; Baenas, Tomás; Belda, Santiago
2016-04-01
The Earth's oblateness parameter J2 is closely related to the dynamical ellipticity H, which factorizes the main components of the precession and the different nutation terms. In most theoretical approaches to the Earth's rotation, with IAU2000 nutation theory among them, H is assumed to be constant. The precession model IAU2006 supposes H to have a conventional linear variation, based on the J2 time series derived mainly from satellite laser ranging (SLR) data for decades, which gives rise to an additional quadratic term of the precession in longitude and some corrections of the nutation terms. The time evolution of J2 is, however, too complex to be well approximated by a simple linear model. The effect of more general models including periodic terms and closer to the observed time series, although still unable to reproduce a significant part of the signal, has been seldom investigated. In this work we address the problem of deriving the effect of the observed J2 variations without resorting to such simplified models. The Hamiltonian approach to the Earth rotation is extended to allow the McCullagh's term of the potential to depend on a time-varying oblateness. An analytical solution is derived by means of a suitable perturbation method in the case of the time series provided by the Center for Space Research (CSR) of the University of Texas, which results in non-negligible contributions to the precession-nutation angles. The presentation focuses on the main effects on the longitude of the equator; a noticeable non-linear trend is superimposed to the linear main precession term, along with some periodic and decadal variations.
Magnetization precession of magnetic thin films studied by all optical pump-probe technique
NASA Astrophysics Data System (ADS)
Michalski, Steven A.
The study of magnetization dynamics such as magnetization precession and precessional damping provides insights into the behavior of complex magnetic systems, and indeed may lead to a better understanding of the fundamental limits of magnetic reversal process. In this work, a time-resolved magneto-optic Kerr effect system (TRMOKE) was developed to study magnetization dynamics: Precession and damping. The system uses a femtosecond laser in a pump-probe experiment with direct optical excitation, very similar to the method introduced by Ganping Ju and coworkers. Also, a model based on the Landau-Lifshitz-Gilbert equation (LLG) was developed and used to interpret and analyze the experimental magnetization precession data of a single magnetic layer. The model can be used to predict the precession frequencies with and without damping, the eigenvectors of the magnetization and allows the Gilbert damping parameter (alpha) to be determined. The model is extended to a system of two magnetic layers coupled through a nonmagnetic spacer layer. The capabilities of the TRMOKE system and the LLG models, were demonstrated by studying the magnetization dynamics of Ni/Pt bilayers. Static and dynamic magnetic properties of exchange-coupled magnetic layers have been investigated by magneto-optical measurements. The samples are [Pt/Co] multilayers with perpendicular magnetic anisotropy (PMA) exchange-coupled to a Co layer with in-plane magnetic anisotropy. The exchange is indirect, realized and tuned by an intervening Pt layer of varying thickness. Both the strength and the angle of an external applied magnetic field were varied and for many samples, two modes with two distinct precession frequencies were observed in the precession measurements. The frequencies of both modes depend on the strength and the angle of the applied magnetic field. The LLG model predicts two precessional modes ("acoustic" and "optic") whose behaviors depend on the strength and sign of the exchange coupling
Turbulence driven by precession in spherical and slightly elongated spheroidal cavities
Goto, Susumu; Matsunaga, Arihiro; Tsuda, Shinya; Fujiwara, Masahiro; Yamato, Masahiro; Nishioka, Michio; Kida, Shigeo
2014-05-15
Motivated by the fascinating fact that strong turbulence can be sustained in a weakly precessing container, we conducted a series of laboratory experiments on the flow in a precessing spherical cavity, and in a slightly elongated prolate spheroidal cavity with a minor-to-major axis ratio of 0.9. In order to determine the conditions required to sustain turbulence in these cavities, and to investigate the statistics of the sustained turbulence, we developed an experimental technique to conduct high-quality flow visualizations as well as measurements via particle image velocimetry on a turntable and by using an intense laser. In general, flows in a precessing cavity are controlled by two non-dimensional parameters: the Reynolds number Re (or its reciprocal, the Ekman number) which is defined by the cavity size, spin angular velocity, and the kinematic viscosity of the confined fluid, and the Poincaré number Po, which is defined by the ratio of the magnitude of the precession angular velocity to that of the spin angular velocity. However, our experiments show that the global flow statistics, such as the mean velocity field and the spatial distribution of the intensity of the turbulence, are almost independent of Re, and they are determined predominantly by Po, whereas the instability of these global flow structures is governed by Re. It is also shown that the turbulence statistics are most likely similar in the two cavities due to the slight difference between their shapes. However, the condition to sustain the unsteady flows, and therefore the turbulence, differs drastically depending on the cavity shape. Interestingly, the asymmetric cavity, i.e., the spheroid, requires a much stronger precession than a sphere to sustain such unsteady flows. The most developed turbulence for a given Re is generated in these cavities when 0.04 ≲ Po ≲ 0.1. In such cases, the sustained turbulence is always accompanied by vigorous large-scale vortical structures, and shearing
Eggeman, Alexander S; Krakow, Robert; Midgley, Paul A
2015-01-01
Three-dimensional (3D) reconstructions from electron tomography provide important morphological, compositional, optical and electro-magnetic information across a wide range of materials and devices. Precession electron diffraction, in combination with scanning transmission electron microscopy, can be used to elucidate the local orientation of crystalline materials. Here we show, using the example of a Ni-base superalloy, that combining these techniques and extending them to three dimensions, to produce scanning precession electron tomography, enables the 3D orientation of nanoscale sub-volumes to be determined and provides a one-to-one correspondence between 3D real space and 3D reciprocal space for almost any polycrystalline or multi-phase material. PMID:26028514
Eggeman, Alexander S.; Krakow, Robert; Midgley, Paul A.
2015-01-01
Three-dimensional (3D) reconstructions from electron tomography provide important morphological, compositional, optical and electro-magnetic information across a wide range of materials and devices. Precession electron diffraction, in combination with scanning transmission electron microscopy, can be used to elucidate the local orientation of crystalline materials. Here we show, using the example of a Ni-base superalloy, that combining these techniques and extending them to three dimensions, to produce scanning precession electron tomography, enables the 3D orientation of nanoscale sub-volumes to be determined and provides a one-to-one correspondence between 3D real space and 3D reciprocal space for almost any polycrystalline or multi-phase material. PMID:26028514
Laser induced spin precession in highly anisotropic granular L1{sub 0} FePt
Becker, J.; Mosendz, O.; Weller, D.; Kirilyuk, A.; Rasing, Th.; Kimel, A.; Maan, J. C.; Christianen, P. C. M.
2014-04-14
The dynamic magnetic properties of a highly anisotropic, granular L1{sub 0} FePt thin film in magnetic fields up to 7 T are investigated using time-resolved magneto-optical Kerr effect measurements. We find that ultrashort laser pulses induce coherent spin precession in the granular FePt sample. Frequencies of spin precession up to over 400 GHz are observed, which are strongly field and temperature dependent. The high frequencies can be ascribed to the high value of the magnetocrystalline anisotropy constant K{sub u} leading to large anisotropy fields H{sub a} of up to 10.7 T at 170 K. A Gilbert damping parameter of α ∼ 0.1 was derived from the lifetimes of the oscillations.
NASA Astrophysics Data System (ADS)
Mueller, R. S.
1991-02-01
The electromagnetic fields inside and outside a steadily rotating, magnetized, conducting sphere are determined for the cases of nonprecession and precession. In both cases the spin rotational axis is aligned with the magnetic axis of the sphere. The field expressions are those measured in the laboratory reference frame. For a nonprecessing sphere the magnetic fields are identical to the fields of a stationary sphere, but in addition there is an induced induction of order v-squared/c-squared whose lines of force radiate in loops above and below the equator. The electric and magnetic induction field expressions were derived into static and dynamic parts. The amplitudes of these parts were plotted as functions of the angle of inclination of the polar axis. The dynamic parts are circularly and elliptically polarized. The pivot point of the precessing sphere was chosen off center. The only two stable positions are at theta = 0 deg and 180 deg for a center pivot.
Measuring the Lense-Thirring precession using a second Lageos satellite
NASA Technical Reports Server (NTRS)
Tapley, B. D.; Ciufolini, I.
1989-01-01
A complete numerical simulation and error analysis was performed for the proposed experiment with the objective of establishing an accurate assessment of the feasibility and the potential accuracy of the measurement of the Lense-Thirring precession. Consideration was given to identifying the error sources which limit the accuracy of the experiment and proposing procedures for eliminating or reducing the effect of these errors. Analytic investigations were conducted to study the effects of major error sources with the objective of providing error bounds on the experiment. The analysis of realistic simulated data is used to demonstrate that satellite laser ranging of two Lageos satellites, orbiting with supplemental inclinations, collected for a period of 3 years or more, can be used to verify the Lense-Thirring precession. A comprehensive covariance analysis for the solution was also developed.
Self-precession and frequency shift for electromagnetic waves in homogeneous plasmas
NASA Technical Reports Server (NTRS)
Arons, J.; Max, C. E.
1974-01-01
The nonlinear propagation of an arbitrarily polarized electromagnetic wave in a uniform plasma is studied. It is shown that nonlinear effects cause precession of the polarization ellipse as the wave propagates. The ellipticity remains constant, but the orientation of the principal axes is rotated relative to its initial value. A relativistic Vlasov model is used to study nonlinear frequency shifts as well as self-precession, in a plasma of arbitrary temperature. Even when the electron temperature is much greater than the product of the electron mass times the square of the velocity of light, the qualitative nature of these two processes remains unchanged, although their dependence on the plasma density is altered in significant ways. Implications of these effects for plasma instabilities driven by strong electromagnetic waves are briefly discussed.
Non-ballistic motion and precessing helical trajectory in quasar NRAO 150
NASA Astrophysics Data System (ADS)
Qian, Shan-Jie
2016-01-01
NRAO 150 is a very special radio quasar in which prominent non-ballistic superluminal motion has been observed in its inner-jet region. We apply model-fittings to the kinematics of the superluminal knots (trajectory, distance from the core and apparent velocity) in terms of a helical precessing jet-nozzle model. Five cases are considered in which the angle between the jet axis and the line of sight is assumed to be 6°, 3°, 1°, 0.6° and 0.12°, respectively. It is shown that the superluminal components have intrinsic acceleration in the innermost regions (≲ 0.2 mas from the core). The phenomenon of precessing nozzle/trajectory can be understood on the basis of relativistic magnetohydrodynamic theories for relativistic jets.
Precession of the isolated neutron star PSR B1828-11
NASA Astrophysics Data System (ADS)
Akgün, Taner; Link, Bennett; Wasserman, Ira
2006-01-01
Stairs, Lyne & Shemar have found that the arrival-time residuals from PSR B1828-11 vary periodically with a period ~500 d. This behaviour can be accounted for by precession of the radio pulsar, an interpretation that is reinforced by the detection of variations in its pulse profile on the same time-scale. Here, we model the period residuals from PSR B1828-11 in terms of precession of a triaxial rigid body. We include two contributions to the residuals: (i) the geometric effect, which arises because the times at which the pulsar emission beam points towards the observer varies with precession phase; and (ii) the spin-down contribution, which arises from any dependence of the spin-down torque acting on the pulsar on the angle between its spin and magnetic axes. We use the data to probe numerous properties of the pulsar, most notably its shape, and the dependence of its spin-down torque on , for which we assume the sum of a spin-aligned component (with a weight 1 -a) and a dipolar component perpendicular to the magnetic beam axis (weight a), rather than the vacuum dipole torque (a= 1). We find that a variety of shapes are consistent with the residuals, with a slight statistical preference for a prolate star. Moreover, a range of torque possibilities fit the data equally well, with no strong preference for the vacuum model. In the case of a prolate star, we find evidence for an angle-dependent spin-down torque. Our results show that the combination of geometrical and spin-down effects associated with precession can account for the principal features of the timing behaviour of PSR B1828-11, without fine tuning of the parameters.
NASA Technical Reports Server (NTRS)
1974-01-01
The survey of negative pion absorption reactions on light and medium nuclei was continued. Muon spin precession was studied using an iron target. An impulse approximation model of the pion absorption process implied that the ion will absorb almost exclusively on nucleon pairs, single nucleon absorption being suppressed by energy and momentum conservation requirements. For measurements on both paramagnetic and ferromagnetic iron, the external magnetic field was supplied by a large C-type electromagnet carrying a current of about 100 amperes.