NASA Astrophysics Data System (ADS)
Mizukami, S.; Iihama, S.; Sasaki, Y.; Sugihara, A.; Ranjbar, R.; Suzuki, K. Z.
2016-10-01
Mn-based hard magnets are potentially suitable for advanced ultra-high frequency spintronics applications because they exhibit the Larmor precession of magnetization at THz wave-range frequencies with low magnetic relaxation. However, the low magnetic relaxation properties are not well understood; thus, a more detailed study is necessary. In this study, magnetization precessions in L10 Mn1.54Ga, D022 Mn2.12Ga, and C38 MnAlGe epitaxial films grown on MgO substrates were investigated using an all-optical pump-probe method under a magnetic field of ˜20 kOe. The coherent magnetization precessions at frequencies of more than 0.1, 0.2, and 0.3 THz for the C38 MnAlGe, L10 Mn1.54Ga, and D022 Mn2.12Ga films, respectively, were clearly measured. The effective damping constant for the C38 MnAlGe film was smaller than the previously reported value measured at 10 kOe by a factor of 2, whereas those showed a large angular dependence. The effective damping constants for the L10 Mn1.54Ga and D022 Mn2.12Ga films were independent of the field angle and approximately identical to the values measured at 10 kOe. Thus, it was concluded that the values for the Gilbert damping constant, α, were 0.008 and 0.012 for the L10 Mn1.54Ga and D022 Mn2.12Ga films, respectively. The possible origin of the discrepancy between the experimental and theoretical α values for these films is discussed.
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.
NASA Astrophysics Data System (ADS)
Eto, Yujiro; Sekine, Sawako; Hasegawa, Sho; Sadgrove, Mark; Saito, Hiroki; Hirano, Takuya
2013-05-01
Radio-frequency pulses are applied to probe and control the Larmor precession of a spin-2 Bose-Einstein condensate subject to a magnetic field gradient. Using the techniques of Ramsey interferometry and Stern-Gerlach absorption imaging, a helical spin pattern was clearly observed as spatial variations in the atomic density distribution. We experimentally show that the spin echo technique reduces the effects of spatially inhomogeneous and temporally fluctuating spin evolution, and improves the repeatability of the interferometry.
A Precessing Ferromagnetic Needle Magnetometer
NASA Astrophysics Data System (ADS)
Jackson Kimball, Derek; Sushkov, Alexander; Budker, Dmitry
2016-05-01
A ferromagnetic needle is predicted to precess about the magnetic field axis at a Larmor frequency Ω when IΩ << Nℏ , where 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, the sensitivity of a precessing needle magnetometer can far surpass that of magnetometers based on spin precession of atoms in the gas phase. The phenomenon of ferromagnetic needle precession may be of particular interest for precision measurements testing fundamental physics. Supported by the Heising-Simons Foundation, Simons Foundation, and the National Science Foundation.
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.
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.
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.
Larmor frequency dressing by a nonharmonic transverse magnetic field
NASA Astrophysics Data System (ADS)
Bevilacqua, G.; Biancalana, V.; Dancheva, Y.; Moi, L.
2012-04-01
We present a theoretical and experimental study of spin precession in the presence of both a static and an orthogonal oscillating magnetic field, which is nonresonant, not harmonically related to the Larmor precession, and of arbitrary strength. Due to the intrinsic nonlinearity of the system, previous models that account only for the simple sinusoidal case cannot be applied. We suggest an alternative approach and develop a model that closely agrees with experimental data produced by an optical-pumping atomic magnetometer. We demonstrate that an appropriately designed nonharmonic field makes it possible to extract a linear response to a weak dc transverse field, despite the scalar nature of the magnetometer, which normally causes a much weaker, second-order response.
A sensitive and accurate atomic magnetometer based on free spin precession
NASA Astrophysics Data System (ADS)
Grujić, Zoran D.; Koss, Peter A.; Bison, Georg; Weis, Antoine
2015-05-01
We present a laser-based atomic magnetometer that allows inferring the modulus of a magnetic field from the free Larmor precession of spin-oriented Cs vapour atoms. The detection of free spin precession (FSP) is not subject to systematic readout errors that occur in phase feedback-controlled magnetometers in which the spin precession is actively driven by an oscillating field or a modulation of light parameters, such as frequency, amplitude, or polarization. We demonstrate that an FSP-magnetometer can achieve a ˜200 fT/√Hz sensitivity (<100 fT/√Hz in the shotnoise limit) and an absolute accuracy at the same level.
Quantum Larmor radiation in de Sitter spacetime
NASA Astrophysics Data System (ADS)
Blaga, Robert; Busuioc, Sergiu
2016-09-01
We study the radiation emitted by inertial charge evolving on the expanding de Sitter spacetime. Performing a perturbative calculation, within scalar quantum electrodynamics (sQED), we obtain the transition amplitude for the process and using this we define the energy radiated by the source. In the non-relativistic limit we find that the leading term is compatible with the classical result (Larmor formula). The first quantum correction is found to be negative, a result which is in line with a number of similar quantum field theory results. For the ultra-relativistic case we find a logarithmic divergence of the emitted energy for large frequencies, which we link to the nature of the spacetime. We compare our results with that of Nomura et al. (JCAP 11:013, 2006), where the authors make a similar calculation for a general conformally flat spacetime.
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.
Finite Larmor radius modification of the Mercier criterion
Connor, J.W.; Tang, W.M.; Allen, L.
1984-04-01
The finite Larmor radius modification of the Suydam criterion involves a competition between stabilizing finite Larmor radius effects and destabilizing curvature. In the case of the toroidal calculation, corresponding to the Mercier criterion, ballooning effects from regions of unfavorable curvature must be taken into account. In the case of a model equilibrium, valid near the magnetic axis, a complete solution is obtained. Results indicate that the amount of finite Larmor radius stabilization needed to overcome the effects of unfavorable average curvature increases as a function of the toroidal ballooning parameter.
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.
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.
NASA Astrophysics Data System (ADS)
Fukushima, Toshio
2005-01-01
First we modified J.G. Williams' formulation of precession/nutation by using the 3-1-3-1 rotation matrix as NP = R1( -ɛ -Δɛ) R1( -ψ -Δψ) R1(ϕ) R1(γ). Next we determined the polynomial formulas of the modified planetary precession angles numerically from the non-linear harmonic analysis of DE405. Then we estimated those of the modified luni-solar precession angles from their corrections converted from the VLBI pole offset observations during 1979-2000 by adopting the above planetary precession formulas and a recent theory of nutation SF2001. The results in the rotational sense are γR = +0.04126 +10.55378 t +0.49318 t2 ϕR = 84381.41461 -46.81325 t +0.04843 t2 ψR = -0.04305 +5038.47776 t +1.55835 t2 ɛR = 84381.40955 -46.83607 t -0.00017 t2 +0.00200 t3 and the differences between the rotational and inertial senses are γR - γI = +0.09366 +0.00060 t ϕR - ϕI = +0.00334 -0.00060 t ψR - ψI = -0.00001 -0.00035 t ɛR - ɛI = +0.00334 -0.00148 t. These consitute a new set of precession formulas referred to ICRF.
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.
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.
Control and imaging of O(1D2) precession
NASA Astrophysics Data System (ADS)
Wu, Shiou-Min; Radenovic, Dragana Č.; van der Zande, Wim J.; Groenenboom, Gerrit C.; Parker, David H.; Vallance, Claire; Zare, Richard N.
2011-01-01
Larmor precession of a quantum mechanical angular momentum vector about an applied magnetic field forms the basis for a range of magnetic resonance techniques, including nuclear magnetic resonance spectroscopy and magnetic resonance imaging. We have used a polarized laser pump-probe scheme with velocity-map imaging detection to visualize, for the first time, the precessional motion of a quantum mechanical angular momentum vector. Photodissociation of O2 at 157 nm provides a clean source of fast-moving O(1D2) atoms, with their electronic angular momentum vector strongly aligned perpendicular to the recoil direction. In the presence of an external magnetic field, the distribution of atomic angular momenta precesses about the field direction, and polarization-sensitive images of the atomic scattering distribution recorded as a function of field strength yield ‘time-lapse-photography’ style movies of the precessional motion. We present movies recorded in various experimental geometries, and discuss potential consequences and applications in atmospheric chemistry and reaction dynamics.
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.
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.
New Determination of Precession Formulas
NASA Astrophysics Data System (ADS)
Fukushima, Toshio
First we modified J.G. Williams' formulation of precession/nutation by using the 3-1-3-1 rotation matrix as NP = R1( -ɛ -Δɛ) R1( -ψ -Δψ) R1(ϕ) R1(γ). Next we determined the polynomial formulas of the modified planetary precession angles numerically from the non-linear harmonic analysis of DE405. Then we estimated those of the modified luni-solar precession angles from their corrections converted from the VLBI pole offset observations during 1979-2000 by adopting the above planetary precession formulas and a recent theory of nutation SF2001. The results in the rotational sense are γR = +0.04126 +10.55378 t +0.49318 t2 ϕR = 84381.41461 -46.81325 t +0.04843 t2 ψR = -0.04305 +5038.47776 t +1.55835 t2 ɛR = 84381.40955 -46.83607 t -0.00017 t2 +0.00200 t3 and the differences between the rotational and inertial senses are γR - γI = +0.09366 +0.00060 t ϕR - ϕI = +0.00334 -0.00060 t ψR - ψI = -0.00001 -0.00035 t ɛR - ɛI = +0.00334 -0.00148 t. These consitute a new set of precession formulas referred to ICRF
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.
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
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.
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.
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.
Direct CW - NMR observation of forbidden transitions at double larmor frequency in hydrogen
NASA Astrophysics Data System (ADS)
Skrbek, L.; Sebek, J.; Safrata, R. S.
1990-08-01
By means of the classical transverse continuous wave nuclear magnetic resonance (NMR) the forbidden transitions at double Larmor frequency for hydrogen have been observed. The NMR spectra have been measured directly by scanning the external magnetic field up to 10 mT at temperatures about 30 mK. The intensity of the forbidden transition at double Larmor frequency I 2 is of the same order of magnitude as the intensity I 1 of the main Larmor line under these conditions. The intensity ratio I 1/I 2 depends on the external magnetic field in accordance with Cheng theory and NMR-SQUID measurements of Kohl and coworkers.
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.
NASA Astrophysics Data System (ADS)
Holmqvist, C.; Belzig, W.; Fogelström, M.
2012-08-01
The supercurrent through a quantum point contact coupled to a nanomagnet strongly depends on the dynamics of the nanomagnet's spin. We employ a fully microscopic model to calculate the transport properties of a junction coupled to a spin whose dynamics is modeled as Larmor precession brought about by an external magnetic field and find that the dynamics affects the charge and spin currents by inducing transitions between the continuum states outside the superconducting gap region and the Andreev levels. This redistribution of the quasiparticles leads to a nonequilibrium population of the Andreev levels and an enhancement of the supercurrent which is visible as a modified current-phase relation as well as a nonmonotonous critical current as function of temperature. The nonmonotonous behavior is accompanied by a corresponding change in spin-transfer torques acting on the precessing spin and leads to the possibility of using temperature as a means to tune the back-action on the spin.
Effects of a Guide Field on the Larmor Electric Field in Collisionless Asymmetric Reconnection
NASA Astrophysics Data System (ADS)
Ruffolo, D. J.; Malakit, K.; Ek-In, S.; Shay, M. A.; Cassak, P.
2014-12-01
Recently it has been pointed out that when the inflow conditions of magnetic reconnection are asymmetric, a new in-plane electric field can arise from the physics of finite ion Larmor radius, called the Larmor electric field. It is located next to the Hall electric field structure, making it a potential indicator of proximity to the diffusion region. However, the properties of the Larmor electric field have not previously been explored for the case of a nonzero guide field, which could occur for many reconnection sites, including the day-side magnetopause. In this study, we therefore further explore the properties of the Larmor electric field by adding guide fields with different strengths into our simulations. The results show that the width of the Larmor electric field structure will be smaller, but the strength of the field will be stronger as the guide field increases, consistent with what we expect from the existing theory. Moreover, we show that in the region where the Larmor electric field occurs, there also appears an electron anisotropy. The widths of the electron anisotropy and Larmor electric field structures are found to be similar, suggesting that observing the combination of these two signatures provides a useful indicator of proximity to a reconnection site. Partially supported by a Mahidol University Postdoctoral Fellowship and the Thailand Research Fund. This research was supported by the postdoctoral research sponsorship of Mahidol University (K. M.), the Thailand Research Fund (D. R.), NSF Grants No. ATM-0645271 (M. A. S.) and No. AGS-0953463 (P.A. C.), NASA Grants No. NNX08A083G—MMS IDS, No. NNX11AD69G, and No. NNX13AD72G(M. A. S.).
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…
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.
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.
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
NASA Astrophysics Data System (ADS)
Shimogonya, Yuji; Sawano, Yoichiro; Wakebe, Hiromichi; Inoue, Yuichi; Ishijima, Akihiko; Ishikawa, Takuji
2015-12-01
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.
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
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
Precession and Nutation of the Earth
NASA Astrophysics Data System (ADS)
Souchay, Jean; Capitaine, Nicole
Precession and nutation of the Earth originate in the tidal forces exerted by the Moon, the Sun, and the planets on the equatorial bulge of the Earth. Discovered respectively in the 2nd century B.C. by Hipparcus and in the 18th century by Bradley, their existence and characteristics were deduced theoretically by Newton for the precession and by d'Alembert for the nutation. After a historical review we explain, both in an intuitive manner and by simple calculations, the gravitational origin and the main characteristics of the precession-nutation. Then we describe in detail two fundamental theories, one using the Lagrangian formalism, the other the Hamiltonian one. A large final part is devoted to successive improvements of the precession-nutation theory in the last decades, both when considering the Earth as a rigid body and when taking into account the small effects of non-rigidity.
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.
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.
Quantum Larmor Radiation from a Moving Charge in AN Electromagnetic Plane Wave Background
NASA Astrophysics Data System (ADS)
Nakamura, Gen; Yamamoto, Kazuhiro
2012-09-01
We extend our previous work [Phys. Rev. D83, 045030 (2011)], which investigated the first-order quantum effect in the Larmor radiation from a moving charge in a spatially homogeneous time-dependent electric field. Specifically, we investigate the quantum Larmor radiation from a moving charge in a monochromatic electromagnetic plane wave background based on the scalar quantum electrodynamics at the lowest order of the perturbation theory. Using the in-in formalism, we derive the theoretical formula of the total radiation energy from a charged particle in the initial states being at rest and being in a relativistic motion. Expanding the theoretical formula in terms of the Planck constant ℏ, we obtain the first-order quantum effect on the Larmor radiation. The quantum effect generally suppresses the total radiation energy compared with the prediction of the classical Larmor formula, which is a contrast to the previous work. The reason is explained by the fact that the radiation from a moving charge in a monochromatic electromagnetic plane wave is expressed in terms of the inelastic collisions between an electron and photons of the background electromagnetic waves.
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.
The free precession and libration of Mercury
NASA Astrophysics Data System (ADS)
Peale, S. J.
2005-11-01
An analysis based on the direct torque equations including tidal dissipation and a viscous core-mantle coupling is used to determine the damping time scales of O(10) years for free precession of the spin about the Cassini state and free libration in longitude for Mercury. The core-mantle coupling dominates the damping over the tides by one to two orders of magnitude for the plausible parameters chosen. The short damping times compared with the age of the Solar System means we must find recent or on-going excitation mechanisms if such free motions are found by the current radar experiments or the future measurement by the MESSENGER and BepiColombo spacecraft that will orbit Mercury. We also show that the average precession rate is increased by about 30% over that obtained from the traditional precession constant because of a spin-orbit resonance induced contribution by the C term in the expansion of the gravitational field. The C contribution also causes the path of the spin during the precession to be slightly elliptical with a variation in the precession rate that is a maximum when the obliquity is a minimum. An observable free precession will compromise the determination of obliquity of the Cassini state and hence of C/MR for Mercury, but a detected free libration will not compromise the determination of the forced libration amplitude and thus the verification of a liquid core.
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
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.
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.
Is 1220 Crocus a precessing, binary asteroid?
NASA Technical Reports Server (NTRS)
Binzel, R. P.
1985-01-01
Photoelectric data of the asteroid 1220 Crocus over a 13 night period in 1984 revealed the presence of two separate periods. The light curves were indicative of a precessing body, but not one in free precession due to motions induced by a collision. Closer examinations revealed periods of 30.7 and 7.9 hr with amplitudes of 0.87 and 0.15 mag, respectively. An analysis of the source of an external torque which could be causing a forced precession led to the hypothesis that 1220 Crocus has a satellite. Verification of the binary asteroid configuration will depend on more detailed light curves, the possible modulation of the shorter period by the longer, and possible use of the Space Telescope.
Is 1220 Crocus a precessing, binary asteroid?
NASA Astrophysics Data System (ADS)
Binzel, R. P.
1985-07-01
Photoelectric data of the asteroid 1220 Crocus over a 13 night period in 1984 revealed the presence of two separate periods. The light curves were indicative of a precessing body, but not one in free precession due to motions induced by a collision. Closer examinations revealed periods of 30.7 and 7.9 hr with amplitudes of 0.87 and 0.15 mag, respectively. An analysis of the source of an external torque which could be causing a forced precession led to the hypothesis that 1220 Crocus has a satellite. Verification of the binary asteroid configuration will depend on more detailed light curves, the possible modulation of the shorter period by the longer, and possible use of the Space Telescope.
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.
Electron precession: A guide for implementation
NASA Astrophysics Data System (ADS)
Own, C. S.; Marks, L. D.; Sinkler, Wharton
2005-03-01
The design approach for electron precession systems designed at Northwestern University is described, and examples of systems retrofitted onto two different transmission electron microscopes using this method are demonstrated. The precession diffraction patterns from these instruments are of good quality while simultaneously being very easy to acquire. A 15-minute procedure for aligning these instruments is described in the appendix. Partnering this user-friendly and inexpensive hardware implementation with fast and user-friendly crystallography software offers potentially speedy and routine solution of crystal structures.
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)
Thomas precession and squeezed states of light
NASA Astrophysics Data System (ADS)
Han, D.; Hardekopf, E. E.; Kim, Y. S.
1989-02-01
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.
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.
spin pumping occurred under nonlinear spin precession
NASA Astrophysics Data System (ADS)
Zhou, Hengan; Fan, Xiaolong; Ma, Li; Zhou, Shiming; Xue, Desheng
Spin pumping occurs when a pure-spin current is injected into a normal metal thin layer by an adjacent ferromagnetic metal layer undergoing ferromagnetic resonance, which can be understood as the inverse effect of spin torque, and gives access to the physics of magnetization dynamics and damping. An interesting question is that whether spin pumping occurring under nonlinear spin dynamics would differ from linear case. It is known that nonlinear spin dynamics differ distinctly from linear response, a variety of amplitude dependent nonlinear effect would present. It has been found that for spin precession angle above a few degrees, nonlinear damping term would present and dominated the dynamic energy/spin-moment dissipation. Since spin pumping are closely related to the damping process, it is interesting to ask whether the nonlinear damping term could be involved in spin pumping process. We studied the spin pumping effect occurring under nonlinear spin precession. A device which is a Pt/YIG microstrip coupled with coplanar waveguide was used. High power excitation resulted in spin precession entering in a nonlinear regime. Foldover resonance lineshape and nonlinear damping have been observed. Based on those nonlinear effects, we determined the values of the precession cone angles, and the maximum cone angle can reach a values as high as 21.5 degrees. We found that even in nonlinear regime, spin pumping is still linear, which means the nonlinear damping and foldover would not affect spin pumping process.
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.
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.``
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.
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.
Geodetic precession or dragging of inertial frames
Ashby, N. ); Shahid-Saless, B. )
1990-08-15
In metric theories of gravity the principle of general covariance allows one to describe phenomena by means of any convenient choice of coordinate system. In this paper it is shown that in an appropriately chosen coordinate system, geodetic precession of a gyroscope orbiting a spherically symmetric, spinning mass can be recast as a Lense-Thirring frame-dragging effect without invoking spatial curvature. The origin of this reference frame moves around the source but the frame axes point in fixed directions. The drag can be interpreted to arise from the orbital angular momentum of the source around the origin of the reference frame. In this reference frame the effects of geodetic precession and Lense-Thirring drag due to intrinsic angular momentum of the source have the same origin, namely, gravitomagnetism.
Spin precession modulation in a magnetic bilayer
Stupakiewicz, A.; Maziewski, A.; Pashkevich, M.; Stognij, A.; Novitskii, N.
2012-12-24
We report on modulation of the spin precession in a Co/garnet bilayer by femtosecond laser excitation using time-resolved magneto-optical tools. Damped oscillations in the Faraday rotation transients representing precessional motion of the magnetization vector are observed in both the 2 nm Co layer and 1.8 {mu}m garnet of the bilayer with distinct frequencies differing by about a factor of two. The excitation efficiency of these precessions strongly depends on the out-of-plane magnetic field. The modulation effect with the coupling in a magnetic bilayer can be useful for non-thermally controlling the magnetization of nanomagnets and ultrafast switching in magnetic nanodevices.
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%.
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
Thomas precession, Wigner rotations and gauge transformations
NASA Technical Reports Server (NTRS)
Han, D.; Kim, Y. S.; Son, D.
1987-01-01
The exact Lorentz kinematics of the Thomas precession is discussed in terms of Wigner's O(3)-like little group which describes rotations in the Lorentz frame in which the particle is at rest. A Lorentz-covariant form for the Thomas factor is derived. It is shown that this factor is a Lorentz-boosted rotation matrix, which becomes a gauge transformation in the infinite-momentum or zero-mass limit.
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.
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.
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".
Concise CIO based precession-nutation formulations
NASA Astrophysics Data System (ADS)
Capitaine, N.; Wallace, P. T.
2008-01-01
Context: The IAU 2000/2006 precession-nutation models have precision goals measured in microarcseconds. To reach this level of performance has required series containing terms at over 1300 frequencies and involving several thousand amplitude coefficients. There are many astronomical applications for which such precision is not required and the associated heavy computations are wasteful. This justifies developing smaller models that achieve adequate precision with greatly reduced computing costs. Aims: We discuss strategies for developing simplified IAU 2000/2006 precession-nutation procedures that offer a range of compromises between accuracy and computing costs. Methods: The chain of transformations linking celestial and terrestrial coordinates comprises frame bias, precession-nutation, Earth rotation and polar motion. We address the bias and precession-nutation (NPB) portion of the chain, linking the Geocentric Celestial Reference System (GCRS) with the Celestial Intermediate Reference System (CIRS), the latter based on the Celestial Intermediate Pole (CIP) and Celestial Intermediate Origin (CIO). Starting from direct series that deliver the CIP coordinates X,Y and (via the quantity s + XY/2) the CIO locator s, we look at the opportunities for simplification. Results: The biggest reductions come from truncating the series, but some additional gains can be made in the areas of the matrix formulation, the expressions for the nutation arguments and by subsuming long period effects into the bias quantities. Three example models are demonstrated that approximate the IAU 2000/2006 CIP to accuracies of 1 mas, 16 mas and 0.4 arcsec throughout 1995-2050 but with computation costs reduced by 1, 2 and 3 orders of magnitude compared with the full model. Appendices A to G are only available in electronic form at http://www.aanda.org
Kiyani, K. H.; Fauvarque, O.; Chapman, S. C.; Hnat, B.; Sahraoui, F.; Khotyaintsev, Yu. V.
2013-01-20
The anisotropic nature of solar wind magnetic turbulence fluctuations is investigated scale by scale using high cadence in situ magnetic field measurements from the Cluster and ACE spacecraft missions. The data span five decades in scales from the inertial range to the electron Larmor radius. In contrast to the inertial range, there is a successive increase toward isotropy between parallel and transverse power at scales below the ion Larmor radius, with isotropy being achieved at the electron Larmor radius. In the context of wave-mediated theories of turbulence, we show that this enhancement in magnetic fluctuations parallel to the local mean background field is qualitatively consistent with the magnetic compressibility signature of kinetic Alfven wave solutions of the linearized Vlasov equation. More generally, we discuss how these results may arise naturally due to the prominent role of the Hall term at sub-ion Larmor scales. Furthermore, computing higher-order statistics, we show that the full statistical signature of the fluctuations at scales below the ion Larmor radius is that of a single isotropic globally scale-invariant process distinct from the anisotropic statistics of the inertial range.
Simulations of Slowly Precessing Molecular Jets
NASA Astrophysics Data System (ADS)
Rosen, A.; Smith, M. D.
2003-12-01
Molecular jets are frequently associated with the star formation process, and so examining simulated jets for molecular emission can help to answer questions related to the energy budget for the jets, the nature of the ambient medium and the evolution of the underlying source. Previously, we have simulated 3D molecular jets and examined them for the effects of the jet-to-ambient density, rapid mass flux changes, and the angle of a fast precessing jet. Here, we extend the work on precessing jets by slowing the rate of the precession to one turn in a jet axis crossing time (for our small grid, this is about 400 years). In one of the two simulations presented here, we removed the pulsation that had been present in all of our previous molecular jet simulations. We will show simulated images in some molelcular hydrogen and CO emission lines, some sample position velocity and velocity channel maps from both simulations. We also analyse the simulations for the mass-velocity and intensity-velocity relationships. This work has been done with the support of PPARC and the Cosmogrid project, funded under PRTLI through the Irish Higher Education Authority.
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.
Finite Larmor radii effects in fast ion measurements with neutron emission spectrometry
NASA Astrophysics Data System (ADS)
Eriksson, J.; Hellesen, C.; Andersson Sundén, E.; Cecconello, M.; Conroy, S.; Ericsson, G.; Gatu Johnson, M.; Pinches, S. D.; Sharapov, S. E.; Weiszflog, M.; EFDA contributors, JET
2013-01-01
When analysing data from fast ion measurements it is normally assumed that the gyro-phase distribution of the ions is isotropic within the field of view of the measuring instrument. This assumption is not valid if the Larmor radii of the fast ions are comparable to—or larger than—the gradient scale length in the spatial distribution of the ions, and if this scale length is comparable to—or smaller than—the width of the field of view of the measuring instrument. In this paper the effect of such an anisotropy is demonstrated by analysing neutron emission spectrometry data from a JET experiment with deuterium neutral beams together with radiofrequency heating at the third harmonic of the deuterium cyclotron frequency. In the experiment, the neutron time-of-flight spectrometer TOFOR was used to measure the neutrons from the d(d,n)3He-reaction. Comparison of the experimental data with Monte Carlo calculations shows that the finite Larmor radii of the fast ions need to be included in the modelling to get a good description of the data. Similar effects are likely to be important for other fast ion diagnostics, such as γ-ray spectroscopy and neutral particle analysis, as well.
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.
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
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.
NASA Astrophysics Data System (ADS)
Marengo, Edwin A.; Khodja, Mohamed R.
2006-09-01
The nonrelativistic Larmor radiation formula, giving the power radiated by an accelerated charged point particle, is generalized for a spatially extended particle in the context of the classical charged harmonic oscillator. The particle is modeled as a spherically symmetric rigid charge distribution that possesses both translational and spinning degrees of freedom. The power spectrum obtained exhibits a structure that depends on the form factor of the particle, but reduces, in the limit of an infinitesimally small particle and for the charge distributions considered, to Larmor’s familiar result. It is found that for finite-duration small-enough accelerations as well as perpetual uniform accelerations the power spectrum of the spatially extended particle reduces to that of a point particle. It is also found that when the acceleration is violent or the size parameter of the particle is very large compared to the wavelength of the emitted radiation the power spectrum is highly suppressed. Possible applications are discussed.
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.
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
Two spinning ways for precession dynamo.
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 1/2π, 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. PMID:27176396
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°.
TILT, WARP, AND SIMULTANEOUS PRECESSIONS IN DISKS
Montgomery, M. M.
2012-07-10
Warps are suspected in disks around massive compact objects. However, the proposed warping source-non-axisymmetric radiation pressure-does not apply to white dwarfs. In this Letter, we report the first smoothed particle hydrodynamic simulations of accretion disks in SU UMa-type systems that naturally tilt, warp, and simultaneously precess in the prograde and retrograde directions using white dwarf V344 Lyrae in the Kepler field as our model. After {approx}79 days in V344 Lyrae, the disk angular momentum L{sub d} becomes misaligned to the orbital angular momentum L{sub o} . As the gas stream remains normal to L{sub o} , hydrodynamics (e.g., the lift force) is a likely source to disk tilt. In addition to tilt, the outer disk annuli cyclically change shape from circular to highly eccentric due to tidal torques by the secondary star. The effect of simultaneous prograde and retrograde precession is a warp of the colder, denser midplane as seen along the disk rim. The simulated rate of apsidal advance to nodal regression per orbit nearly matches the observed ratio in V344 Lyrae.
Two spinning ways for precession dynamo.
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 1/2π, 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.
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.
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.
Thomas precession: Where is the torque
Muller, R.A. )
1992-04-01
Special relativity appears to violate the conservation of angular momentum {bold L} since it predicts that an accelerated gyroscope will precess, i.e., {bold L} will change in the absence of any applied torque. The paradox is resolved in a simple example by demonstrating that there is a torque present. The mass distribution in the gyroscope undergoes a relativistic distortion, and the center of mass is displaced away from the position of the accelerating force. The resulting torque {tau}={ital d}{bold L}/{ital dt}. The model also shows the physical origins of spin-orbit coupling and of the oscillating term.'' A related calculation shows why a moving magnetic dipole has an {ital electric} dipole moment.
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.
Radiation from plasmas with sub-Larmor scale magnetic fields -- generalized jitter radiation
NASA Astrophysics Data System (ADS)
Medvedev, Mikhail
2009-11-01
Radiation produced by relativistic electrons in random magnetic fields of a sub-Larmor scale is referred to as the jitter radiation. It has been predicted to be produced from high- energy density environments which naturally generate such fields via Weibel-type (e.g., streaming) instabilities. Thus, it was argued to be a new diagnostic of Weibel turbulence in relativistic collisionless shocks, in reconnection in electron- positron plasmas and in laser-produced plasmas, the latter is of interest to both laser-plasma applications (e.g., Fast Ignition) and to Laboratory Astrophysics. The spectral characteristics of jitter radiation are markedly different from those of synchrotron and carry information about the magnetic fields structure (e.g., its spatial spectrum). Conventional treatment of jitter radiation assumes negligibly small deflections of particles in the magnetic fields, which is not always the case. Here we relax this assumption and discuss the transition between jitter and synchrotron regimes. Although the full treatment is model-dependent, certain important conclusions can be drawn. We will also address applications to both laboratory studies of the Weibel turbulence and astrophysical phenomena.
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.
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.
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.
Freeman Dyson and Gravitational Spin Precession
NASA Astrophysics Data System (ADS)
Hari Dass, N. D.
2014-04-01
In 1974 Hulse and Taylor1 discovered the binary pulsar. At that time Prof. Dyson was visiting the Max Planck Institute for Physics at Munich, where I was also working. He initiated a number of discussions on this object. During them it occurred to me that this system could be used to test Geodetic Precession in Einsteins theory, which, even after years of work by the Stanford gyroscope expt,2 had remained a challenge. I showed some preliminary calculations to Prof Dyson and he encouraged me to do a more refined job. To be applicable to the binary pulsar, one needed to generalise the general relativistic calculations to beyond the so called test particle assumption. Barker and O'Connell3 had obtained such a result from analysing the gravitational interactions of spin-1/2 Dirac fermions in linearized spin-2 theories of gravitation. With C. F. Cho I produced a purely classical calculation, using Schwingers Source theory.4 Börner, Ehlers and Rudolf confirmed this result with their general relativistic calculations shortly after.5 With V. Radhakrishnan, I gave a detailed model for the pulse width and polarization sweep as a means of observing this effect.6-9 All throughout Prof. Dyson was supportive with reading the manuscripts and his critical comments. In 2005, coincidentally the centennial of the Annus Mirabilis (1905), Hotan, Bailes and Ord observed this in the binary pulsar J1141-6545.10
Concise algorithms for precession-nutation
NASA Astrophysics Data System (ADS)
Wallace, P. T.; Capitaine, N.
2008-04-01
The precession-nutation models based on the IAU 2000A nutation series involve several thousand amplitude coefficients, many under 1 µas in size, and the sines and cosines of about 1350 angles. For the many applications that do not require the utmost accuracy this represents an unnecessary or even excessive computational overhead. The IAU 2000B model offers one alternative, an order of magnitude smaller than IAU 2000A and delivering classical nutation components of 1 mas accuracy in the current era. In a recent paper (Capitaine & Wallace 2007), the main results of which are provided here, we looked at other options, based on series for the CIP coordinates and the CIO locator and with the GCRS to CIRS rotation matrix as the end product. Truncation of the series provides most of the savings, but certain other measures can be taken also. Three example formulations are presented that achieve 1 mas, 16 mas and 0.4 arcsec accuracy throughout 1995-2050 with computational costs 1, 2 and 3 orders of magnitude less than the full models. A few examples of possible applications are presented.
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.
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
NASA Astrophysics Data System (ADS)
Schmidt, Patricia; Ohme, Frank; Hannam, Mark
2015-01-01
Gravitational waves (GWs) emitted by generic black-hole binaries show a rich structure that directly reflects the complex dynamics introduced by the precession of the orbital plane, which poses a real challenge to the development of generic waveform models. Recent progress in modelling these signals relies on an approximate decoupling between the nonprecessing secular inspiral and a precession-induced rotation. However, the latter depends in general on all physical parameters of the binary which makes modelling efforts as well as understanding parameter-estimation prospects prohibitively complex. Here we show that the dominant precession effects can be captured by a reduced set of spin parameters. Specifically, we introduce a single effective precession spin parameter, χp, which is defined from the spin components that lie in the orbital plane at some (arbitrary) instant during the inspiral. We test the efficacy of this parameter by considering binary inspiral configurations specified by the physical parameters of a corresponding nonprecessing-binary configuration (total mass, mass ratio, and spin components (anti)parallel to the orbital angular momentum), plus the effective precession spin applied to the larger black hole. We show that for an overwhelming majority of random precessing configurations, the precession dynamics during the inspiral are well approximated by our equivalent configurations. Our results suggest that in the comparable-mass regime waveform models with only three spin parameters faithfully represent generic waveforms, which has practical implications for the prospects of GW searches, parameter estimation and the numerical exploration of the precessing-binary parameter space.
A Relativistic Long-term Precession of the Earth
NASA Astrophysics Data System (ADS)
Tang, K.
2016-05-01
A long-term precession represents a secular motion of the ecliptic and th equator in a long time interval. With Vondrák et al. (2011), we assume that precession covers all periods longer than 100 centuries, while the shorter ones are included in the nutation. This thesis deals with the long-term precession in a relativistic framework. Compared with the P03 precession theory which is only valid for several centuries around the epoch J2000.0, the new theory better reflects the realistic long-term behavior of precession. All previous works are not fully consistent with General Relativity. They only consider the dominant relativistic corrections: the first-order post-Newtonian corrections due to the Sun and the geodetic precession. Their standard way to account for the geodetic precession is to solve the purely Newtonian equations of rotational motion and add the geodetic precession as a correction to the solution. In this thesis, we aim to determine the acceleration of the SSB from astrometric and geodetic observations obtained by Very Long Baseline Interferometry (VLBI), which is a technique using the telescopes globally distributed on the Earth to observe a radio source simultaneously, and with the capacity of angular positioning for compact radio sources at 10-milliarcsecond level. The method of the global solution, which allows the acceleration vector to be estimated as a global parameter in the data analysis, is developed. Through the formal error given by the solution, this method shows directly the VLBI observations' capability to constrain the acceleration of the SSB, and demonstrates the significance level of the result. In the next step, the impact of the acceleration on the ICRS is studied in order to obtain the correction of the celestial reference frame (CRF) orientation. Recently, Klioner, Gerlach, and Soffel (2010) have constructed a relativistic theory of Earth's rotation. According to the post-Newtonian equations of rotational motion given by Klioner
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.
Finite Larmor radius effects on the (m = 2, n = 1) cylindrical tearing mode
Chen, Y.; Chowdhury, J.; Parker, S. E.; Wan, W.
2015-04-15
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 ∼ η{sup 1∕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.
Bistable flows forced by precession in planetary cores
NASA Astrophysics Data System (ADS)
Cebron, D.
2015-12-01
The presence of the Moon leads the Earth to precess, which forces a flow in its outer core via the spheroidal Core-Mantle Boundary (CMB). Reciprocally, this is also true for the liquid core core of the Moon, but the CMB is rather a triaxial ellipsoid in this case. In this work, we investigate if the precession can force two different stable flows for the same control parameters, allowing then the core to switch from one state to the other in presence of noise (convection, turbulence, etc.). To do so, we systematically study the parameter ranges where the well-known equations obtained by Busse (1968 J. Fluid Mech. 33 739-51) lead to multiple solutions. Then, using the models recently proposed by Noir and Cébron (2013 J. Fluid Mech. 737 412-39), which are more generic in the inviscid limit than the equations of Busse, we analytically describe these multiple solutions, their conditions of existence, and their stability. We also report for the first time the theoretical possibility that time-dependent multiple flows can coexist in precessing triaxial ellipsoids (such as the liquid core of the Moon). Finally, using the formula we have derived from pre-existent models of the literature, we conclude that the Earth and the Moon do not undergo such a bistable flow forced by precession. However, according to the models of the literature, such a bistable precession forced state exists for geophysically relevant ranges of parameters, and is thus always possible a priori in precessing liquid cores of terrestrial bodies.
Nutation control during precession of a spin-stabilized spacecraft
NASA Technical Reports Server (NTRS)
1974-01-01
Precession maneuver control laws for single-spin spacecraft are investigated so that nutation is concurrently controlled. Analysis has led to the development of two types of control laws employing precession modulation for concurrent nutation control. Results were verified through digital simulation of a Synchronous Meteorological Satellite (SMS) configuration. An addition research effort was undertaken to investigate the cause and elimination of nutation anomalies in dual-spin spacecraft. A literature search was conducted and a dual-spin configuration was simulated to verify that nutational anomalies are not predicted by the existing nonlinear model. No conclusions were drawn as to the cause of the observed nutational anomalies in dual-spin spacecraft.
Vorticity, gyroscopic precession, and spin-curvature force
NASA Astrophysics Data System (ADS)
Liang, Wei Chieh; Lee, Si Chen
2013-02-01
In investigating the relationship between vorticity and gyroscopic precession, we calculate the vorticity vector in Godel, Kerr, Lewis, Schwarzschild, and Minkowski metrics and find that the vorticity vector of the specific observers is the angular velocity of the gyroscopic precession. Furthermore, when space-time torsion is included, the vorticity and spin-curvature force change sign. This result is very similar to the behavior of the positive and negative helicities of quantum spin in the Stern-Gerlach force. It implies that the inclusion of torsion will lead to an analogous property of quantum spin even in classical treatment.
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.
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).
Lense-Thirring Precession in the Astrophysical Context
NASA Astrophysics Data System (ADS)
Stella, Luigi; Possenti, Andrea
2009-12-01
This paper surveys some of the astrophysical environments in which the effects of Lense-Thirring precession and, more generally, frame dragging are expected to be important. We concentrate on phenomena that can probe in situ the very strong gravitational field and single out Lense-Thirring precession in the close vicinity of accreting neutron stars and black holes: these are the fast quasi periodic oscillations in the X-ray flux of accreting compact objects. We emphasise that the expected magnitude of Lense-Thirring/frame dragging effects in the regions where these signals originate are large and thus their detection does not pose a challenge; rather it is the interpretation of these phenomena that needs to be corroborated through deeper studies. Relativistic precession in the spin axis of radio pulsars hosted in binary systems hosting another neutron star has also been measured. The remarkable properties of the double pulsar PSR J0737-3039 has opened a new perspective for testing the predictions of general relativity also in relation to the precession of spinning bodies.
Remark on orbital precession due to central-force perturbations
Chashchina, O. I.; Silagadze, Z. K.
2008-05-15
We show that the main result of the recent paper by G. S. Adkins and J. McDonnell, Phys. Rev. D 75, 082001 (2007), the formula for the precession of Keplerian orbits induced by central-force perturbations, can be obtained very simply by the use of Hamilton's vector.
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.
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
General Relativistic Precession in Small Solar System Bodies
NASA Astrophysics Data System (ADS)
Sekhar, Aswin; Werner, Stephanie; Hoffmann, Volker; Asher, David; Vaubaillon, Jeremie; Hajdukova, Maria; Li, Gongjie
2016-10-01
Introduction: One of the greatest successes of the Einstein's General Theory of Relativity (GR) was the correct prediction of the precession of perihelion of Mercury. The closed form expression to compute this precession tells us that substantial GR precession would occur only if the bodies have a combination of both moderately small perihelion distance and semi-major axis. Minimum Orbit Intersection Distance (MOID) is a quantity which helps us to understand the closest proximity of two orbits in space. Hence evaluating MOID is crucial to understand close encounters and collision scenarios better. In this work, we look at the possible scenarios where a small GR precession in argument of pericentre (ω) can create substantial changes in MOID for small bodies ranging from meteoroids to comets and asteroids.Analytical Approach and Numerical Integrations: Previous works have looked into neat analytical techniques to understand different collision scenarios and we use those standard expressions to compute MOID analytically. We find the nature of this mathematical function is such that a relatively small GR precession can lead to drastic changes in MOID values depending on the initial value of ω. Numerical integrations were done with package MERCURY incorporating the GR code to test the same effects. Numerical approach showed the same interesting relationship (as shown by analytical theory) between values of ω and the peaks/dips in MOID values. Previous works have shown that GR precession suppresses Kozai oscillations and this aspect was verified using our integrations. There is an overall agreement between both analytical and numerical methods.Summary and Discussion: We find that GR precession could play an important role in the calculations pertaining to MOID and close encounter scenarios in the case of certain small solar system bodies (depending on their initial orbital elements). Previous works have looked into impact probabilities and collision scenarios on
Alfvén Eigenmode Induced Fast Ion Transport in DIII-D Resulting From Finite Larmor Radius Effects
NASA Astrophysics Data System (ADS)
Kramer, G. J.; Fu, G. Y.; Nazikian, R.; van Zeeland, M. A.; Fisher, R. K.; Pace, D. C.; Chen, L.; Chen, X.; Heidbrink, W. W.
2013-10-01
Alfvén Eigenmode (AE) induced fast-ion redistribution and loss are commonly observed in DIII-D. In those experiments the perpendicular wave vector times the fast-ion Larmor radius is of order unity (k⊥ρi ~ 1), which allows fast ion orbits to traverse the AE mode structures asymmetrically causing a significant change in magnetic moment. Full-orbit simulations of the expected transport in DIII-D plasmas show that this effect can lead to fast-ion radial diffusion constants of 5 m2/s at the measured mode amplitudes. This level of diffusion is not captured with a guiding center approximation and is in agreement with that deduced in DIII-D experiments when AE activity was present. Work supported by the US Department of Energy under DE-AC02-09CH11466, DE-FC02-04ER54698, and SC-G903402.
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.
NASA Astrophysics Data System (ADS)
de Guillebon, L.; Vittot, M.
2013-10-01
Guiding-center reduction is studied using gyro-gauge-independent coordinates. The Lagrangian 1-form of charged particle dynamics is Lie transformed without introducing a gyro-gauge, but using directly the unit vector of the component of the velocity perpendicular to the magnetic field as the coordinate corresponding to Larmor gyration. The reduction is shown to provide a maximal reduction for the Lagrangian and to work for all orders in the Larmor radius, following exactly the same procedure as when working with the standard gauge-dependent coordinate. The gauge-dependence is removed from the coordinate system by using a constrained variable for the gyro-angle. The closed 1-form dθ is replaced by a more general non-closed 1-form, which is equal to dθ in the gauge-dependent case. The gauge vector is replaced by a more general connection in the definition of the gradient, which behaves as a covariant derivative, in perfect agreement with the circle-bundle picture. This explains some results of previous works, whose gauge-independent expressions did not correspond to gauge fixing but did indeed correspond to connection fixing. In addition, some general results are obtained for the guiding-center reduction. The expansion is polynomial in the cotangent of the pitch-angle as an effect of the structure of the Lagrangian, preserved by Lie derivatives. The induction for the reduction is shown to rely on the inversion of a matrix, which is the same for all orders higher than three. It is inverted and explicit induction relations are obtained to go to an arbitrary order in the perturbation expansion. The Hamiltonian and symplectic representations of the guiding-center reduction are recovered, but conditions for the symplectic representation at each order are emphasized.
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
Proposal for a Cosmic Axion Spin Precession Experiment (CASPEr)
NASA Astrophysics Data System (ADS)
Budker, Dmitry; Graham, Peter W.; Ledbetter, Micah; Rajendran, Surjeet; Sushkov, Alexander O.
2014-04-01
We propose an experiment to search for QCD axion and axionlike-particle dark matter. Nuclei that are interacting with the background axion dark matter acquire time-varying CP-odd nuclear moments such as an electric dipole moment. In analogy with nuclear magnetic resonance, these moments cause precession of nuclear spins in a material sample in the presence of an electric field. Precision magnetometry can be used to search for such precession. An initial phase of this experiment could cover many orders of magnitude in axionlike-particle parameter space beyond the current astrophysical and laboratory limits. And with established techniques, the proposed experimental scheme has sensitivity to QCD axion masses ma≲10-9 eV, corresponding to theoretically well-motivated axion decay constants fa≳1016 GeV. With further improvements, this experiment could ultimately cover the entire range of masses ma≲μ eV, complementary to cavity searches.
Nonlinear dynamo action in a cylindrical container driven by precession
NASA Astrophysics Data System (ADS)
Nore, C.; Léorat, J.; Guermond, J.-L.; Luddens, F.
2011-12-01
Precession, which results simply from the composition of two rotations with distinct axes, is an efficient way to drive a 3D flow in a closed rigid container. Are such flows relevant to dynamo action in some astrophysical bodies? Positive answers are available for a spherical and a spheroidal containers, using parameters which are, however, not realistic. An experimental approach could be relevant to natural dynamos and seems within reach using a cylindrical container (cf. the experiment now planned at the DREsden Sodium facility for DYNamo and thermohydraulic studies in Germany (DRESDYN), F. Stefani, personal communication, 2011). Using a nonlinear magnetohydrodynamics (MHD) code (SFEMaNS), we numerically demonstrate that precession is able to drive a cylindrical dynamo.
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.
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.
NASA Astrophysics Data System (ADS)
Kiyani, K.; Sahraoui, F.; Hnat, B.; Chapman, S. C.; Fauvarque, O.; Khotyaintsev, Y. V.
2012-12-01
The anisotropic nature of solar wind magnetic turbulence fluctuations is investigated scale-by-scale using high cadence in-situ magnetic field measurements from the Cluster and ACE spacecraft missions. The data span five decades in scales from the inertial range to the electron Larmor radius. In contrast to the inertial range, there is a successive increase towards isotropy between parallel and transverse power at scales below the ion Larmor radius, with isotropy being achieved at the electron Larmor radius. In the context of wave-mediated theories of turbulence, we show that this enhancement in magnetic fluctuations parallel to the local mean background field is qualitatively consistent with the magnetic compressibility signature of kinetic Alfvén wave solutions of the linearized Vlasov equation. More generally, we discuss how these results may arise naturally due to the prominent role of the Hall term at sub-ion Larmor scales. Furthermore, computing higher-order statistics, we show that the full statistical signature of the fluctuations at scales below the ion Larmor radius is that of a single isotropic globally scale-invariant process distinct from the anisotropic statistics of the inertial range.(Upper panel) PSD (from Cluster) of the transverse and parallel components spanning the inertial and dissipation ranges. (Lower panel) Ratio of parallel over transverse PSD. Horizontal dot-dashed line indicates a ratio of 1/3 where isotropy in power occurs. Vertical dashed and dashed-dotted lines indicate the ion and electron gyro-radii respectively, Doppler-shifted to spacecraft frequency using the Taylor hypothesis.
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.
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.
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.
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.
Evolution of Supermassive Black Hole Binaries and Acceleration of Jet Precession in Galactic Nuclei
NASA Astrophysics Data System (ADS)
Liu, F. K.; Chen, X.
2007-12-01
Supermassive black hole binaries (SMBHBs) are expected with the hierarchical galaxy formation model. Currently, physics processes dominating the evolution of a SMBHB are unclear. An interesting question is whether we could observationally determine the evolution of SMBHBs and give constraints on the physical processes. Jet precession has been observed in many active galactic nuclei (AGNs) and is generally attributed to disk precession. In this paper we calculate the time variation of jet precession and conclude that jet precession is accelerated in SMBHB systems but decelerated in others. The acceleration of jet precession, dPpr/dt, is related to the jet precession timescale, Ppr, and the SMBHB evolution timescale, τa, as dPpr/dt~=-Λ(Ppr/τa). Our calculations based on the models for jet precession and SMBHB evolution show that dPpr/dt can be as high as about -1.0, with a typical value of -0.2, and can be easily detected. We discuss the differential jet precession for NGC 1275 that has been observed in the literature. If its observed rapid acceleration of jet precession is true, the jet precession is due to the orbital motion of an unbound SMBHB with a mass ratio of q~0.76. When jets precess from ancient bubbles to the currently active jets, the separation of the SMBHB decreases from about 1.46 kpc to 0.80 kpc, with an averaged decreasing velocity of da/dt~=-1.54×106 cm s-1 and an evolution timescale of τa~7.5×107 yr. However, if we assume steady jet precession for many cycles, the observations imply a hard SMBHB with a mass ratio of a q~0.21 and a separation of a~0.29 pc.
Gyroscope precession along bound equatorial plane orbits around a Kerr black hole
NASA Astrophysics Data System (ADS)
Bini, Donato; Geralico, Andrea; Jantzen, Robert T.
2016-09-01
The precession of a test gyroscope along stable bound equatorial plane orbits around a Kerr black hole is analyzed, and the precession angular velocity of the gyro's parallel transported spin vector and the increment in the precession angle after one orbital period is evaluated. The parallel transported Marck frame which enters this discussion is shown to have an elegant geometrical explanation in terms of the electric and magnetic parts of the Killing-Yano 2-form and a Wigner rotation effect.
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.
Nonlinear Amplification of Small Spin Precession Using Long-Range Dipolar Interactions
NASA Astrophysics Data System (ADS)
Ledbetter, M. P.; Savukov, I. M.; Romalis, M. V.
2005-02-01
In measurements of small signals using spin precession the precession angle usually grows linearly in time. We show that a dynamic instability caused by spin interactions can lead to an exponentially growing spin-precession angle, amplifying small signals and raising them above the noise level of a detection system. We demonstrate amplification by a factor of greater than 8 of a spin-precession signal due to a small magnetic field gradient in a spherical cell filled with hyperpolarized liquid 129Xe. This technique can improve the sensitivity in many measurements that are limited by the noise of the detection system, rather than the fundamental spin-projection noise.
NASA Astrophysics Data System (ADS)
Kaothekar, Sachin
2016-08-01
I have studied the effects of finite electron inertia, finite ion Larmor radius (FLR) corrections, and radiative heat-loss function on the thermal instability of an infinite homogeneous, viscous plasma incorporating the effect of thermal conductivity for star formation in interstellar medium (ISM). A general dispersion relation is derived using the normal mode analysis method with the help of relevant linearized perturbation equations of the problem. The wave propagation is discussed for longitudinal and transverse directions to the external magnetic field and the conditions of modified thermal instabilities and stabilities are discussed in different cases. We find that the thermal instability criterion is get modified into radiative instability criterion by inclusion of radiative heat-loss functions with thermal conductivity. The viscosity of medium removes the effect of FLR corrections from the condition of radiative instability. Numerical calculation shows stabilizing effect of heat-loss function, viscosity and FLR corrections, and destabilizing effect of finite electron inertia on the thermal instability. Results carried out in this paper shows that stars are formed in interstellar medium mainly due to thermal instability.
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.
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.
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.
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.
Gravitomagnetic gyroscope precession in Palatini f(R) gravity
Ruggiero, Matteo Luca
2009-04-15
We study gravitomagnetic effects in the Palatini formalism of f(R) gravity. On using the Kerr-de Sitter metric, which is a solution of f(R) field equations, we calculate the impact of f(R) gravity on the gravitomagnetic precession of an orbiting gyroscope. We show that, even though an f(R) contribution is present in principle, its magnitude is negligibly small and far to be detectable in the present (like GP-B) and foreseeable space missions or observational tests around the Earth.
A semiclassical kinetic theory of Dirac particles and Thomas precession
NASA Astrophysics Data System (ADS)
Dayi, Ömer F.; Kilinçarslan, Eda
2015-10-01
Kinetic theory of Dirac fermions is studied within the matrix valued differential forms method. It is based on the symplectic form derived by employing the semiclassical wave packet build of the positive energy solutions of the Dirac equation. A satisfactory definition of the distribution matrix elements imposes to work in the basis where the helicity is diagonal which is also needed to attain the massless limit. We show that the kinematic Thomas precession correction can be studied straightforwardly within this approach. It contributes on an equal footing with the Berry gauge fields. In fact in equations of motion it eliminates the terms arising from the Berry gauge fields.
Observation of self-induced optical vortex precession.
Ketara, Mohamed El; Brasselet, Etienne
2013-06-01
We report on the observation of self-induced precession of an optical vortex as a result of the nonlinear interaction between light and liquid crystals. The phenomenon corresponds to an instability for the spin-orbit interaction of light that manifests as a spontaneous axial symmetry breaking, which leads to the orbital motion of the optical vortex around the beam propagation. A nonlinear spin Hall effect of light is experimentally identified, thereby unveiling an original demonstration of spin to extrinsic orbital light angular momentum self-conversion.
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
Parameter estimation for inspiraling eccentric compact binaries including pericenter precession
NASA Astrophysics Data System (ADS)
Mikóczi, Balázs; Kocsis, Bence; Forgács, Péter; Vasúth, Mátyás
2012-11-01
Inspiraling supermassive black hole binary systems with high orbital eccentricity are important sources for space-based gravitational wave observatories like the Laser Interferometer Space Antenna. Eccentricity adds orbital harmonics to the Fourier transform of the gravitational wave signal, and relativistic pericenter precession leads to a three-way splitting of each harmonic peak. We study the parameter estimation accuracy for such waveforms with different initial eccentricity, using the Fisher matrix method and a Monte Carlo sampling of the initial binary orientation. The eccentricity improves the parameter estimation by breaking degeneracies between different parameters. In particular, we find that the source localization precision improves significantly for higher-mass binaries due to eccentricity. The typical sky position errors are ˜1deg for a nonspinning, 107M⊙, equal-mass binary at redshift z=1, if the initial eccentricity 1 yr before merger is e0˜0.6. Pericenter precession does not affect the source localization accuracy significantly, but it does further improve the mass and eccentricity estimation accuracy systematically by a factor of 3-10 for masses between 106M⊙ and 107M⊙ for e0˜0.3.
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.
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.
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.
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
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.
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.
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.
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
Noninvasive cineangiography by magnetic resonance global coherent free precession.
Rehwald, Wolfgang G; Chen, Enn-Ling; Kim, Raymond J; Judd, Robert M
2004-05-01
Cardiovascular disease is primarily diagnosed using invasive X-ray cineangiography. Here we introduce a new concept in magnetic resonance imaging (MRI) that, for the first time, produces similar images noninvasively and without a contrast agent. Protons in moving blood are 'tagged' every few milliseconds as they travel through an arbitrary region in space. Simultaneous with ongoing tagging of new blood, previously tagged blood is maintained in a state of global coherent free precession (GCFP), which allows acquisition of consecutive movie frames as the heart pushes blood through the vascular bed. Body tissue surrounding the moving blood is never excited and therefore remains invisible. In 18 subjects, pulsating blood could be seen flowing through three-dimensional (3D) space for distances of up to 16 cm outside the stationary excitation region. These data underscore that our approach noninvasively characterizes both anatomy and blood flow in a manner directly analogous to invasive procedures.
Progress toward the Cosmic Axion Spin Precession Experiments (CASPEr)
NASA Astrophysics Data System (ADS)
Budker, D.; Afach, S.; Antypas, D.; Blanchard, J.; Blümler, P.; Bougas, L.; Leefer, N.; Wickenbrock, A.; Ledbetter, M. P.; Patton, B.; Rajendran, S.; Graham, P. W.; Sushkov, A. O.; Jackson Kimball, D. F.
2015-05-01
We discuss progress on the design and construction of a new set of experiments to search for the QCD axion and axionlike-particle dark matter. Nuclei that interact with an oscillating background axion field acquire time-varying nuclear moments (for example, electric and magnetic dipole moments). Magnetic resonance techniques can be applied to search for precession of nuclear spins induced by the oscillating axion field. An initial phase of these experiments will cover many orders of magnitude in axionlike-particle parameter space beyond the current astrophysical and laboratory limits. It is anticipated that future versions of the experiments will offer sensitivity to QCD axions with masses ma <10-9 eV. Supported by the Heising-Simons Foundation and the National Science Foundation.
Precession of parent bodies from historical meteor outbursts
NASA Astrophysics Data System (ADS)
Ahn, S.-H.
2015-01-01
We collect records of meteor outbursts from world-wide historical archives, and analyzed them to see which meteor outbursts have existed during the last two millennia. We calculate the dates of occurrence within the sidereal year for each record, and find four prominent major meteor streams having existed continuously. The prominent and continuous meteor streams are the Lyrids, the Perseids, the Leonids, and the eta- Aquariids/Orionids pair. We also check the regression of nodal points of these streams, and find that both the Leonids and the eta-Aquariids/Orionids pair have relatively large precession rates, while the other streams have small rates. We discuss that the near-type outbursts have occurred more frequently than the far-type outbursts.
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.
On precession of entangled spins in a strong laser field
NASA Astrophysics Data System (ADS)
Eliashvili, M.; Gerdt, V.; Khvedelidze, A.
2009-05-01
A dynamics of the entanglement under an environmental influence is modelled by a bound state composed of two heavy particles interacting with a strong laser. Adopting the semiclassical attitude, a trajectory of the bound state’s center-of-mass is found from the Newton equations solved beyond the dipole approximation and taking into account the magnetic field effect. At the same time the dynamics of constituent spins under the laser coupling is studied quantum mechanically solving the nonrelativistic von Neumann equation with the effective Hamiltonian determined by the bound state’s classical trajectory. Based on the solution, the effects of an intense linearly polarized monochromatic plane wave on the precession of entangled spins are discussed for a specific kind of mixed initial states including a family of maximally entangled Werner states.
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.
Effective-one-body modeling of precessing black hole binaries
NASA Astrophysics Data System (ADS)
Taracchini, Andrea; Babak, Stanislav; Buonanno, Alessandra
2016-03-01
Merging black hole binaries with generic spins that undergo precessional motion emit complicated gravitational-wave signals. We discuss how such waveforms can be accurately modeled within an effective-one-body approach by (i) exploiting the simplicity of the signals in a frame that corotates with the orbital plane of the binary and (ii) relying on an accurate model of nonprecessing black hole binaries. The model is validated by extensive comparisons to 70 numerical relativity simulations of precessing black hole binaries and can generate inspiral-merger-ringdown waveforms for mass ratios up to 100 and any spin configuration. This work is an essential tool for studying and characterizing candidate gravitational-wave events in science runs of advanced LIGO.
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.
Measuring the polarization of a rapidly precessing deuteron beam
NASA Astrophysics Data System (ADS)
Bagdasarian, Z.; Bertelli, S.; Chiladze, D.; Ciullo, G.; Dietrich, J.; Dymov, S.; Eversmann, D.; Fanourakis, G.; Gaisser, M.; Gebel, R.; Gou, B.; Guidoboni, G.; Hejny, V.; Kacharava, A.; Kamerdzhiev, V.; Lehrach, A.; Lenisa, P.; Lorentz, B.; Magallanes, L.; Maier, R.; Mchedlishvili, D.; Morse, W. M.; Nass, A.; Oellers, D.; Pesce, A.; Prasuhn, D.; Pretz, J.; Rathmann, F.; Shmakova, V.; Semertzidis, Y. K.; Stephenson, E. J.; Stockhorst, H.; Ströher, H.; Talman, R.; Thörngren Engblom, P.; Valdau, Yu.; Weidemann, C.; Wüstner, P.
2014-05-01
This paper describes a time-marking system that enables a measurement of the in-plane (horizontal) polarization of a 0.97-GeV/c deuteron beam circulating in the Cooler Synchrotron (COSY) at the Forschungszentrum Jülich. The clock time of each polarimeter event is used to unfold the 120-kHz spin precession and assign events to bins according to the direction of the horizontal polarization. After accumulation for one or more seconds, the down-up scattering asymmetry can be calculated for each direction and matched to a sinusoidal function whose magnitude is proportional to the horizontal polarization. This requires prior knowledge of the spin tune or polarization precession rate. An initial estimate is refined by resorting the events as the spin tune is adjusted across a narrow range and searching for the maximum polarization magnitude. The result is biased toward polarization values that are too large, in part because of statistical fluctuations but also because sinusoidal fits to even random data will produce sizable magnitudes when the phase is left free to vary. An analysis procedure is described that matches the time dependence of the horizontal polarization to templates based on emittance-driven polarization loss while correcting for the positive bias. This information will be used to study ways to extend the horizontal polarization lifetime by correcting spin tune spread using ring sextupole fields and thereby to support the feasibility of searching for an intrinsic electric dipole moment using polarized beams in a storage ring. This paper is a combined effort of the Storage Ring EDM collaboration and the JEDI collaboration.
Effective potentials and morphological transitions for binary black-hole spin precession
NASA Astrophysics Data System (ADS)
Kesden, Michael; Gerosa, Davide; O'Shaughnessy, Richard; Berti, Emanuele; Sperhake, Ulrich
2015-04-01
We derive an effective potential ξ+/-(S) for binary black-hole (BBH) spin precession as a function of the magnitude of the total spin S. This allows us to solve the 2PN orbit-averaged spin-precession equations analytically for arbitrary BBH mass ratios and spins. These solutions are quasiperiodic functions of time: after a period τ the spins return to their initial relative orientations and precess about the total angular momentum by an angle α. We classify BBH spin precession into three distinct morphologies between which BBHs can transition during their inspiral. Our new solutions constitute fundamental progress in our understanding of BBH spin precession and also have important applications to astrophysical BBHs. We derive a precession-averaged evolution equation for the total angular momentum that can be integrated on the radiation-reaction time, allowing us to statistically track BBH spins from formation to merger far more efficiently than was possible with previous orbit-averaged precession equations. This will greatly help us predict the signatures of BBH formation in the GWs emitted near merger and the distributions of final spins and gravitational recoils. The solutions may also help efforts to model and interpret GWs from generic BBH mergers.
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.
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.
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.
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.
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.
Giant enhancement of spin pumping in the out-of-phase precession mode
Takahashi, S.
2014-02-03
We theoretically study the spin pumping from the two ferromagnetic layers embedded in a normal metal and investigate the spin current and spin accumulation generated by the precessing magnetizations, focusing on their dependence on the relative precessional motion and the layer separation. We demonstrate a giant enhancement of spin pumping induced in the out-of-phase precession mode of the magnetizations in which the pumped spin current and spin accumulation are greatly enhanced compared to those in the in-phase precession mode. The giant enhancement of spin pumping is discussed in relation to an enhanced Gilbert damping.
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.
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.
NASA Astrophysics Data System (ADS)
Wid, O.; Wahler, M.; Homonnay, N.; Richter, T.; Schmidt, G.
2015-11-01
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.
Coherent collective precession of molecular rotors with chiral propellers.
Tabe, Yuka; Yokoyama, Hiroshi
2003-12-01
Successful attempts to manufacture synthetic molecular motors have recently been reported. However, compared with natural systems such as motor proteins, synthetic motors are smaller molecules and are therefore subject to thermal fluctuations that prevent them from performing any useful function. A mechanism is needed to amplify the single molecular motion to such a level that it becomes distinguishable from the thermal background. Condensation of molecular motors into soft ordered phases (such as liquid crystals) will be a feasible approach, because there is evidence that they support molecularly driven non-equilibrium motions. Here we show that a chiral liquid-crystalline monolayer spread on a glycerol surface acts as a condensed layer of molecular rotors, which undergo a coherent molecular precession driven by the transmembrane transfer of water molecules. Composed of simple rod-like molecules with chiral propellers, the monolayer exhibits a spatiotemporal pattern in molecular orientations that closely resembles 'target patterns' in Belousov-Zhabotinsky reactions. Inversion of either the molecular chirality or the transfer direction of water molecules reverses the rotation direction associated with switching from expanding to converging target patterns. Endowed only with the soft directional order, the liquid crystal is an optimal medium that helps molecular motors to manifest their individual motions collectively.
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.
Spinning gas clouds with precession: a new formulation
NASA Astrophysics Data System (ADS)
Gaffet, B.
2010-04-01
We consider Dyson's model (Dyson F J 1968 J. Math. Mech. 18 91) of an ellipsoidally stratified ideal gas cloud expanding adiabatically into a vacuum, in the Liouville integrable case where the gas is monatomic (γ = 5/3) and there is no vorticity (Gaffet B 2001a J. Phys. A: Math. Gen. 34 2097; Paper I). In the cases of rotation about a fixed axis the separation of variables can be achieved, and the separable variables are linearly related to a set of three variables denoted by ρ, R, W (Gaffet B 2001b J. Phys. A: Math. Gen. 34 9195; Paper II). We show in the present work that these variables admit a natural generalization to cases of rotation about a movable axis (precessing motion). The present study is restricted to the consideration of the so-called degenerate cases (see Gaffet B 2006 J. Phys. A: Math. Gen. 39 99; Paper III), but we hope to generalize our results in the future to the non-degenerate ones as well. We also present a new, compact and generally valid formulation of one of the integrals of motion, of the sixth degree in the momenta, denoted by I6.
Phase precession and phase-locking of hippocampal pyramidal cells.
Bose, A; Recce, M
2001-01-01
We propose that the activity patterns of CA3 hippocampal pyramidal cells in freely running rats can be described as a temporal phenomenon, where the timing of bursts is modulated by the animal's running speed. With this hypothesis, we explain why pyramidal cells fire in specific spatial locations, and how place cells phase-precess with respect to the EEG theta rhythm for rats running on linear tracks. We are also able to explain why wheel cells phase-lock with respect to the theta rhythm for rats running in a wheel. Using biophysically minimal models of neurons, we show how the same network of neurons displays these activity patterns. The different rhythms are the result of inhibition being used in different ways by the system. The inhibition is produced by anatomically and physiologically diverse types of interneurons, whose role in controlling the firing patterns of hippocampal cells we analyze. Each firing pattern is characterized by a different set of functional relationships between network elements. Our analysis suggests a way to understand these functional relationships and transitions between them.
Flows driven by libration, precession, and tides, in planetary cores
NASA Astrophysics Data System (ADS)
Le Bars, Michael
2015-11-01
Because of gravitational interactions with their companions, the rotational dynamics of planets involve periodic perturbations of their shape, the direction of their rotational vector, and their rotation rate. These perturbations correspond in planetary terms to tides, precession, and longitudinal libration. I will review the flows driven by those mechanical forcings in the liquid iron core of planets, as well as their possible consequences on the planetary dynamics. Special focus will be placed on the associated instabilities and on the various routes toward turbulence recently studied, combining laboratory experiments and numerical simulations. The key point is that mechanical forcings do not provide the energy to the excited flows: They convey part of the available rotational energy and generate intense fluid motions through the excitation of localized jets, shear layers, and resonant inertial modes. Hence, even very small forcings - as it is the case in planets - may have large scale consequences. Mechanically driven flows thus play a fundamental role in planets, providing for instance alternative mechanisms to the standard convective models in explaining the puzzling past magnetic fields recorded on Moon and Mars, and in rationalizing the variety of shapes and rotational states observed in exoplanets.
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
Book Review: Precession, Nutation, and Wobble of the Earth
NASA Astrophysics Data System (ADS)
Sterken, Christiaan; Dehant, V.; Mathews, P. M.
2016-10-01
This great book describes and explains observational and computational aspects of three apparently tiny changes in the Earth's motion and orientation, viz., precession, nutation, and wobble. The three introductory chapters of this book present fundamental definitions, elementary geodetic theory, and celestial/terrestrial reference systems - including transformations between reference frames. The next chapter on observational techniques describes the principle of accurate measurements of the orientation of the Earth's axis, as obtained from measurements of extra-galactic radio sources using Very Long Baseline Interferometry and GPS observations. Chapter 5 handles precession and nutation of the rigid Earth (i.e., a celestial body that cannot, by definition, deform) and the subsequent chapter takes deformation into consideration, viz., the effect of a centrifugal force caused by a constant-rate rotation that causes the Earth's shape and structure to become ellipsoidal. Deformations caused by external solar-system bodies are discussed in terms of deformability parameters. The next three chapters handle additional complex deviations: non-rigid Earth and more general Earth models, anelastic Earth parameters, and the effects of the fluid layers (i.e., ocean and atmosphere) on Earth rotation. Chapter 10 complements Chapter 7 with refinements that take into account diverse small effects such as the effect of a thermal conductive layer at the top of the core, Core Mantle and Inner Boundary coupling effects on nutation, electromagnetic coupling, and so-called topographic coupling. Chapter 11 covers comparison of observation and theory, and tells us that the present-date precision of the nutation theory is at the level of milliarcseconds in the time domain, and of a tenth of a microsecond in the frequency domain (with some exceptions). This chapter is followed by a 25-page chapter of definitions of equator, equinox, celestial intermediate pole and origin, stellar angle
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
NASA Astrophysics Data System (ADS)
Jain, Shweta; Sharma, Prerana; Kaothekar, Sachin; Chhajlani, R. K.
2016-10-01
The thermal instability of an infinite homogeneous, thermally conducting, and rotating plasma, incorporating finite electrical resistivity, finite electron inertia, and an arbitrary radiative heat-loss function in the presence of finite Larmor radius corrections and Hall current, has been studied. Analysis has been made with the help of linearized magnetohydrodynamics (MHD) equations. A general dispersion relation is obtained using the normal mode analysis method, and the dispersion relation is discussed for longitudinal propagation and transverse propagation separately. The dispersion relation has been solved numerically to obtain the dependence of the growth rate on the various parameters involved. The conditions of modified thermal instability and stability are discussed in the different cases of interest.
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.
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
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.
TIDALLY INDUCED APSIDAL PRECESSION IN DOUBLE WHITE DWARFS: A NEW MASS MEASUREMENT TOOL WITH LISA
Valsecchi, F.; Farr, W. M.; Willems, B.; Deloye, C. J.; Kalogera, V.
2012-02-01
Galactic interacting double white dwarfs (DWDs) are guaranteed gravitational wave (GW) sources for the Laser Interferometer Space Antenna GW detector, with more than 10{sup 4} binaries expected to be detected over the mission's lifetime. Part of this population is expected to be eccentric, and here we investigate the potential for constraining the white dwarf (WD) properties through apsidal precession in these binaries. We analyze the tidal, rotational, and general relativistic contributions to apsidal precession by using detailed He WD models, where the evolution of the star's interior is followed throughout the cooling phase. In agreement with previous studies of zero-temperature WDs, we find that apsidal precession in eccentric DWDs can lead to a detectable shift in the emitted GW signal when binaries with cool (old) components are considered. This shift increases significantly for hot (young) WDs. We find that apsidal motion in hot (cool) DWDs is dominated by tides at orbital frequencies above {approx}> 10{sup -4} Hz (10{sup -3} Hz). The analysis of apsidal precession in these sources while ignoring the tidal component would lead to an extreme bias in the mass determination, and could lead us to misidentify WDs as neutron stars or black holes. We use the detailed WD models to show that for older, cold WDs, there is a unique relationship that ties the radius and apsidal precession constant to the WD masses, therefore allowing tides to be used as a tool to constrain the source masses.
Gauge-invariant disturbing function in precessing frames of reference.
NASA Astrophysics Data System (ADS)
Efroimsky, M.; Goldreich, P.
2003-08-01
reference-system choice. We apply our results to description of a satellite motion about a precessing planet.
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.
Comments on the effect of adopting new precession and equinox corrections
NASA Technical Reports Server (NTRS)
Williams, J. G.; Melbourne, W. G.
1982-01-01
It is shown that the derived terrestrial longitude zero point and UT1 rate will be different when determined by classical optical and space techniques so long as the precession constant and equinox offset and drift are imperfectly known. For the uncertainty of the new IAU precession constant, this inconsistency is expected to be nearly 0.04 arcsec in longitude and 0.1 ms/yr in UT1 rate. The consistency of constants does not guarantee consistent results. The classical practice of defining Greenwich Mean Sidereal Time (GMST) as invariant with respect to a fixed equinox if the longitude and UT1 results from the inertial techniques are to be stable against changes in the precession constant. One form for GMST is given.
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.
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
Rouviere, Jean-Luc Martin, Yannick; Denneulin, Thibaud; Cooper, David
2013-12-09
NanoBeam Electron Diffraction is a simple and efficient technique to measure strain in nanostructures. Here, we show that improved results can be obtained by precessing the electron beam while maintaining a few nanometer probe size, i.e., by doing Nanobeam Precession Electron Diffraction (N-PED). The precession of the beam makes the diffraction spots more uniform and numerous, making N-PED more robust and precise. In N-PED, smaller probe size and better precision are achieved by having diffraction disks instead of diffraction dots. Precision in the strain measurement better than 2 × 10{sup −4} is obtained with a probe size approaching 1 nm in diameter.
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).
How to Determine The Precession of the Inner Accretion Disk in Cygnus X-1
Torres, D F; Romero, G E; Barcons, X; Lu, Y
2005-01-05
We show that changes in the orientation of the inner accretion disk of Cygnus X-1 affect the shape of the broad Fe K{alpha} emission line emitted from this object, in such a way that eV-level spectral resolution observations (such as those that will be carried out by the ASTRO-E2 satellite) can be used to analyze the dynamics of the disk. We here present a new diagnosis tool, supported by numerical simulations, by which short observations of Cygnus X-1, separated in time, can determine whether its accretion disk actually processes, and if so, determine its period and precession angle. Knowing the precession parameters of Cygnus X-1 would result in a clarification of the origin of such precession, distinguishing between tidal and spin-spin coupling. This approach could also be used for similar studies in other microquasar systems.
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.
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.
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.
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.
NASA Astrophysics Data System (ADS)
Apostolatos, Theocharis A.; Cutler, Curt; Sussman, Gerald J.; Thorne, Kip S.
1994-06-01
Merging compact binaries are currently regarded as the most promising source of gravitational waves for the planned Earth-based LIGO/VIRGO laser-interferometer detector system, and will be an important source also for similar, lower-frequency detectors that might be flown in space (e.g., the proposed LISA mission). During the orbital inspiral, if one or both bodies are rapidly rotating, the general relativistic spin-orbit and spin-spin coupling (i.e., the ``dragging of inertial frames'' by the bodies' spins) cause the binary's orbital plane to process. In this paper we analyze the resulting modulation of the inspiral gravitational waveform, using post2-Newtonian equations to describe the precession of the orbital plane, but only the leading-order (Newtonian, quadrupole-moment approximation) equations to describe the orbit, the radiation reaction, the inspiral, and the wave generation. We derive all the formulas one needs to readily compute the spin-modulated gravitational waveform (within the post-Newtonian approximation and the approximation that the precession frequency is much smaller than the orbital frequency). We also develop intuition into what the modulated signals ``look like,'' by a variety of means. We provide approximate, analytical solutions for the precessional motion and the modulated waveforms for two important special cases: the case where the bodies have nearly equal masses and the case where one of the bodies has negligible spin. For these cases, for almost all choices of binary parameters, the motion is a simple precession of the orbital angular momentum around the nearly fixed direction of the total angular momentum, with a few tens of precession periods as the waves sweep through the LIGO/VIRGO observational band. However, when the spin and orbital angular momenta are approximately antialigned, there is a transitional-precession epoch during which their near cancellation causes the binary to ``lose its gyroscopic bearings'' and tumble in space
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
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.
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.
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.
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.
NASA Astrophysics Data System (ADS)
Okano, Genki; Nozaki, Yukio
2016-06-01
Microwave-assisted magnetization reversal utilizing a transient precession of magnetization was demonstrated in a permalloy hexagon by applying a 25-ns-wide microwave field and a 500-ps-wide pulsed field with a tunable delay to the microwave field. The switching field in a combination of these two fields becomes smaller than that in only the microwave field, and this additional reduction in switching field oscillates relative to the delay time. From the comparison with the results of micromagnetic simulations, we found that the oscillatory behavior is attributed to the beats in transient precession that occurs in the early stage of microwave-field-induced magnetization excitation.
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.
NASA Astrophysics Data System (ADS)
Moeck, Peter; Rouvimov, Sergei; Nicolopoulos, Stavros
2009-09-01
Precession electron diffraction (PED) in a transmission electron microscope (TEM) is discussed in order to illustrate its utility for structural fingerprinting of nanocrystals. While individual nanocrystals may be fingerprinted structurally from PED spot patterns, ensembles of nanocrystals may be fingerprinted from powder PED ring patterns.
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,…
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.
Short Foucault Pendulum: A Way to Eliminate the Precession Due to Ellipticity.
ERIC Educational Resources Information Center
Crane, H. Richard
1981-01-01
Discusses the problem of ellipticity in the motion of the ordinary Foucault pendulum and the error caused by it. Presents a simple method of slightly modifying the force-displacement relation in such a way that precession does not result from ellipticity. (Author/SK)
NASA Astrophysics Data System (ADS)
Walker, D. D.; Beaucamp, A. T. H.; Doubrovski, V.; Dunn, C.; Freeman, R.; McCavana, G.; Morton, R.; Riley, D.; Simms, J.; Wei, X.
2005-09-01
Zeeko's Precession polishing process uses a bulged, rotating membrane tool, creating a contact-area of variable size. In separate modes of operation, the bonnet rotation-axis is orientated pole-down on the surface, or inclined at an angle and then precessed about the local normal. The bonnet, covered with standard polishing cloth and working with standard slurry, has been found to give superb surface textures in the regime of nanometre to sub-nanometre Ra values, starting with parts directly off precision CNC aspheric grinding machines. This paper reports an important extension of the process to the precision-controlled smoothing (or 'fining') operation required between more conventional diamond milling and subsequent Precession polishing. The method utilises an aggressive surface on the bonnet, again with slurry. This is compared with an alternative approach using diamond abrasives bound onto flexible carriers attached to the bonnets. The results demonstrate the viability of smoothing aspheric surfaces, which extends Precessions processing to parts with inferior input-quality. This may prove of particular importance to large optics where significant volumes of material may need to be removed, and to the creation of more substantial aspheric departures from a parent sphere. The paper continues with a recent update on results obtained, and lessons learnt, processing free-form surfaces, and concludes with an assessment of the relevance of the smoothing and free-form operations to the fabrication of off-axis parts including segments for extremely large telescopes.
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
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.
NASA Astrophysics Data System (ADS)
Kaothekar, Sachin
2016-09-01
The effects of finite ion Larmor radius (FLR) corrections, Hall current and radiative heat-loss function on the thermal instability of an infinite homogeneous, viscous plasma incorporating the effects of finite electrical resistivity, thermal conductivity and permeability for star formation in interstellar medium have been investigated. A general dispersion relation is derived using the normal mode analysis method with the help of relevant linearized perturbation equations of the problem. The wave propagation is discussed for longitudinal and transverse directions to the external magnetic field and the conditions of modified thermal instabilities and stabilities are discussed in different cases. We find that the thermal instability criterion gets modified into radiative instability criterion. The finite electrical resistivity removes the effect of magnetic field and the viscosity of the medium removes the effect of FLR from the condition of radiative instability. The Hall parameter affects only the longitudinal mode of propagation and it has no effect on the transverse mode of propagation. Numerical calculation shows stabilizing effect of viscosity, heat-loss function and FLR corrections, and destabilizing effect of finite resistivity and permeability on the thermal instability. The outcome of the problem discussed the formation of star in the interstellar medium.
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
Palatinus, Lukáš; Corrêa, Cinthia Antunes; Steciuk, Gwladys; Jacob, Damien; Roussel, Pascal; Boullay, Philippe; Klementová, Mariana; Gemmi, Mauro; Kopeček, Jaromír; Domeneghetti, M Chiara; Cámara, Fernando; Petříček, Václav
2015-12-01
The recently published method for the structure refinement from three-dimensional precession electron diffraction data using dynamical diffraction theory [Palatinus et al. (2015). Acta Cryst. A71, 235-244] has been applied to a set of experimental data sets from five different samples - Ni2Si, PrVO3, kaolinite, orthopyroxene and mayenite. The data were measured on different instruments and with variable precession angles. For each sample a reliable reference structure was available. A large series of tests revealed that the method provides structure models with an average error in atomic positions typically between 0.01 and 0.02 Å. The obtained structure models are significantly more accurate than models obtained by refinement using kinematical approximation for the calculation of model intensities. The method also allows a reliable determination of site occupancies and determination of absolute structure. Based on the extensive tests, an optimal set of the parameters for the method is proposed.
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.
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
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.
A systematic approach to interpreting Hanle spin precession data in non-local spin valves
NASA Astrophysics Data System (ADS)
Swartz, Adrian G.; McCreary, Kathleen M.; Han, Wei; Wen, Hua; Kawakami, Roland K.
2013-09-01
Graphene's two dimensional nature and high surface sensitivity have led to fascinating predictions regarding induced spin-based phenomena through careful control of adsorbates on the graphene surface, including the extrinsic spin Hall effect, band gap opening, and induced magnetism. By taking advantage of atomic scale control provided by MBE, we have investigated submonolayer deposition of adsorbates and their interactions with graphene. Spin transport measurements performed in-situ during systematic introduction of atomic hydrogen demonstrated that hydrogen adsorbed on graphene forms magnetic moments that couple via exchange to the injected spin current. The effects of induced magnetic moments are evident in the non-local magnetoresistance and Hanle spin precession. Exchange coupling between the injected spin current and the induced moments impact the Hanle curves through an effective exchange field leading to new interpretations of Hanle spin precession data and analysis. Here we present a simple procedure in which Hanle curves can be reliably interpreted.
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
Magnetohydrodynamic instabilities in rotating and precessing sheared flows: an asymptotic analysis.
Salhi, A; Lehner, T; Cambon, C
2010-07-01
Linear magnetohydrodynamic instabilities are studied analytically in the case of unbounded inviscid and electrically conducting flows that are submitted to both rotation and precession with shear in an external magnetic field. For given rotation and precession the possible configurations of the shear and of the magnetic field and their interplay are imposed by the "admissibility" condition (i.e., the base flow must be a solution of the magnetohydrodynamic Euler equations): we show that an "admissible" basic magnetic field must align with the basic absolute vorticity. For these flows with elliptical streamlines due to precession we undertake an analytical stability analysis for the corresponding Floquet system, by using an asymptotic expansion into the small parameter ε (ratio of precession to rotation frequencies) by a method first developed in the magnetoelliptical instabilities study by Lebovitz and Zweibel [Astrophys. J. 609, 301 (2004)]10.1086/420972. The present stability analysis is performed into a suitable frame that is obtained by a systematic change of variables guided by symmetry and the existence of invariants of motion. The obtained Floquet system depends on three parameters: ε , η (ratio of the cyclotron frequency to the rotation frequency) and χ=cos α, with α being a characteristic angle which, for circular streamlines, ε=0, identifies with the angle between the wave vector and the axis of the solid body rotation. We look at the various (centrifugal or precessional) resonant couplings between the three present modes: hydrodynamical (inertial), magnetic (Alfvén), and mixed (magnetoinertial) modes by computing analytically to leading order in ε the instabilities by estimating their threshold, growth rate, and maximum growth rate and their bandwidths as functions of ε, η, and χ. We show that the subharmonic "magnetic" mode appears only for η>square root of 5/2 and at large η (>1) the maximal growth rate of both the "hydrodynamic" and
Precession of orbits around the stellar-mass black hole in H 1743-322
NASA Astrophysics Data System (ADS)
Ingram, Adam
2016-07-01
Accreting stellar-mass black holes often show a quasi-periodic oscillation (QPO) in their X-ray flux with a period that slowly drifts from ~10s to ~0.05s, and an iron emission line in their X-ray spectrum. The iron line is generated by fluorescent re-emission, by the accretion disk, of X-ray photons originating in the innermost hot flow. The line shape is distorted by relativistic motion of the orbiting plasma and the gravitational pull of the black hole. The QPO arises from the immediate vicinity of the black hole, but its physical origin has long been debated. It has been suggested that the QPO originates via Lense-Thirring precession, a General Relativistic effect causing the inner flow to precess as the spinning black hole twists up the surrounding space-time. This predicts a characteristic rocking of the iron line between red and blue shift as the receding and approaching sides of the disk are respectively illuminated. I will talk about our observations of the black hole binary H 1743-322 in which the line energy varies in step with the ~4.5s QPO cycle, providing strong evidence that such QPOs originate via Lense-Thirring precession. This effect has previously been measured in our Solar System but our detection is in the strong field regime of General Relativity, at a precession rate 14 orders of magnitude faster than possible in the Earth's gravitational field. Our result enables the application of tomographic techniques to map the motion of matter in the strong gravity near black hole event horizons.
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.
Spin-Wave Eigenmodes of a Saturated Magnetic Square at Different Precession Angles
NASA Astrophysics Data System (ADS)
Demidov, Vladislav E.; Hansen, Ulf-Hendrik; Demokritov, Sergej O.
2007-04-01
Using low-loss dielectric magnetic films in combination with space-resolved Brillouin light scattering spectroscopy we have studied nonlinear modification of eigenmode spatial distributions in saturated magnetic squares. We have found that, as the angle of magnetization precession increases, the eigenmode spatial distributions experience significant qualitative changes due to a nonlinear coupling between forming them standing spin waves. We show that the found nonlinear eigenmodes cannot be described by means of the linear theoretical approach even qualitatively.
Weisberg, J. M.; Everett, J. E.; Morgan, J. J.; Brisbin, D. G.; Cordes, J. M.
2010-10-01
In order to study precession and interstellar magnetic field variations, we measured the polarized position angle of 81 pulsars at several-month intervals for four years. We show that the uncertainties in a single-epoch measurement of position angle are usually dominated by random pulse-to-pulse jitter of the polarized subpulses. Even with these uncertainties, we find that the position angle variations in 19 pulsars are significantly better fitted (at the 3{sigma} level) by a sinusoid than by a constant. Such variations could be caused by precession, which would then indicate periods of {approx}(200-1300) days and amplitudes of {approx}(1-12) degrees. We narrow this collection to four pulsars that show the most convincing evidence of sinusoidal variation in position angle. Also, in a handful of pulsars, single discrepant position angle measurements are observed which may result from the line of sight passing across a discrete ionized, magnetized structure. We calculate the standard deviation of position angle measurements from the mean for each pulsar and relate these to limits on precession and interstellar magnetic field variations.
Kim, Sang-Koog; Yoo, Myoung-Woo; Lee, Jehyun; Lee, Ha-Youn; Lee, Jae-Hyeok; Gaididei, Yuri; Kravchuk, Volodymyr P; Sheka, Denis D
2015-01-01
We found resonantly excited precession motions of a three-dimensional vortex core in soft magnetic nanospheres and controllable precession frequency with the sphere diameter 2R, as studied by micromagnetic numerical and analytical calculations. The precession angular frequency for an applied static field HDC is given as ωMV = γeffHDC, where γeff = γ〈mΓ〉 is the effective gyromagnetic ratio in collective vortex dynamics, with the gyromagnetic ratio γ and the average magnetization component 〈mΓ〉 of the ground-state vortex in the core direction. Fitting to the micromagnetic simulation data for 〈mΓ〉 yields a simple explicit form of 〈mΓ〉 ≈ (73.6 ± 3.4)(lex/2R)(2.20±0.14), where lex is the exchange length of a given material. This dynamic behavior might serve as a foundation for potential bio-applications of size-specific resonant excitation of magnetic vortex-state nanoparticles, for example, magnetic particle resonance imaging. PMID:26079895
Resonantly exited precession motion of three-dimensional vortex core in magnetic nanospheres
Kim, Sang-Koog; Yoo, Myoung-Woo; Lee, Jehyun; Lee, Ha-Youn; Lee, Jae-Hyeok; Gaididei, Yuri; Kravchuk, Volodymyr P.; Sheka, Denis D.
2015-01-01
We found resonantly excited precession motions of a three-dimensional vortex core in soft magnetic nanospheres and controllable precession frequency with the sphere diameter 2R, as studied by micromagnetic numerical and analytical calculations. The precession angular frequency for an applied static field HDC is given as ωMV = γeffHDC, where γeff = γ〈mΓ〉 is the effective gyromagnetic ratio in collective vortex dynamics, with the gyromagnetic ratio γ and the average magnetization component 〈mΓ〉 of the ground-state vortex in the core direction. Fitting to the micromagnetic simulation data for 〈mΓ〉 yields a simple explicit form of 〈mΓ〉 ≈ (73.6 ± 3.4)(lex/2R)2.20±0.14, where lex is the exchange length of a given material. This dynamic behavior might serve as a foundation for potential bio-applications of size-specific resonant excitation of magnetic vortex-state nanoparticles, for example, magnetic particle resonance imaging. PMID:26079895
Equatorial Precession Drove Mid-Latitude Changes in ENSO-Scale Variation in the Earliest Miocene
NASA Astrophysics Data System (ADS)
Fox, B.; D'Andrea, W. J.; Lee, D. E.; Wilson, G. S.
2014-12-01
Foulden Maar is an annually laminated lacustrine diatomite deposit from the South Island of New Zealand. The deposit was laid down over ~100 kyr of the latest Oligocene and earliest Miocene, during the peak and deglaciation phase of the Mi-1 Antarctic glaciation event. At this time, New Zealand was located at approximately the same latitude as today (~45°S). Evidence from organic geochemical proxies (δD, δ13C) and physical properties (density, colour) indicates the presence of an 11-kyr cycle at the site. Although it is known that 11-kyr insolation (half-precession) cycles occur between the Tropics, this cycle is rarely seen in sedimentary archives deposited outside the immediate vicinity of the Equator. Records from Foulden Maar correlate well with the amplitude and phase of the modelled equatorial half-precession cycle for the earliest Miocene. High-resolution (50 µm) colour intensity measurements and lamina thickness measurements both indicate the presence of significant ENSO-like (2-8 year) variation in the Foulden Maar sediments. Early results from targeted lamina thickness measurements suggest that ENSO-band variation is modulated by the 11-kyr cycle, with power in the ENSO band increasing during periods of increased insolation at the Equator. This implies that equatorial half-precession had a significant effect on ENSO-like variation in the early Miocene, and that this effect was felt as far afield as the mid-latitudes of the Southern Hemisphere.
POLARIZATION MODULATION FROM LENSE–THIRRING PRECESSION IN X-RAY BINARIES
Ingram, Adam; Maccarone, Thomas J.; Poutanen, Juri; Krawczynski, Henric
2015-07-01
It has long been recognized that quasi-periodic oscillations (QPOs) in the X-ray light curves of accreting black hole and neutron star binaries have the potential to be powerful diagnostics of strong field gravity. However, this potential cannot be fulfilled without a working theoretical model, which has remained elusive. Perhaps, the most promising model associates the QPO with Lense–Thirring precession of the inner accretion flow, with the changes in viewing angle and Doppler boosting modulating the flux over the course of a precession cycle. Here, we consider the polarization signature of a precessing inner accretion flow. We use simple assumptions about the Comptonization process generating the emitted spectrum and take all relativistic effects into account, parallel transporting polarization vectors toward the observer along null geodesics in the Kerr metric. We find that both the degree of linear polarization and the polarization angle should be modulated on the QPO frequency. We calculate the predicted absolute rms variability amplitude of the polarization degree and angle for a specific model geometry. We find that it should be possible to detect these modulations for a reasonable fraction of parameter space with a future X-ray polarimeter such as NASA’s Polarization Spectroscopic Telescope Array (the satellite incarnation of the balloon experiment X-Calibur)
Montgomery, M. M.
2012-02-15
Accretion disks around black hole, neutron star, and white dwarf systems are thought to sometimes tilt, retrogradely precess, and produce hump-shaped modulations in light curves that have a period shorter than the orbital period. Although artificially rotating numerically simulated accretion disks out of the orbital plane and around the line of nodes generate these short-period superhumps and retrograde precession of the disk, no numerical code to date has been shown to produce a disk tilt naturally. In this work, we report the first naturally tilted disk in non-magnetic cataclysmic variables using three-dimensional smoothed particle hydrodynamics. Our simulations show that after many hundreds of orbital periods, the disk has tilted on its own and this disk tilt is without the aid of radiation sources or magnetic fields. As the system orbits, the accretion stream strikes the bright spot (which is on the rim of the tilted disk) and flows over and under the disk on different flow paths. These different flow paths suggest the lift force as a source to disk tilt. Our results confirm the disk shape, disk structure, and negative superhump period and support the source to disk tilt, source to retrograde precession, and location associated with X-ray and He II emission from the disk as suggested in previous works. Our results identify the fundamental negative superhump frequency as the indicator of disk tilt around the line of nodes.
Lense-Thirring precession around supermassive black holes during tidal disruption events
NASA Astrophysics Data System (ADS)
Franchini, Alessia; Lodato, Giuseppe; Facchini, Stefano
2016-01-01
A tidal disruption event occurs when a star wanders close enough to a black hole to be disrupted by its tidal force. The debris of a tidally disrupted star are expected to form an accretion disc around the supermassive black hole. The light curves of these events sometimes show a quasi-periodic modulation of the flux that can be associated with the precession of the accretion disc due to the Lense-Thirring (`frame-dragging') effect. Since the initial star orbit is in general inclined with respect to the black hole spin, this misalignment combined with the Lense-Thirring effect leads to a warp in the disc. In this paper, we provide a simple model of the system composed by a thick and narrow accretion disc surrounding a spinning supermassive black hole, with the aim to: (a) compute the expected precession period as a function of the system parameters, (b) discuss the conditions that have to be satisfied in order to have rigid precession, (c) investigate the alignment process, highlighting how different mechanisms play a role leading the disc and the black hole angular momenta into alignment.
Kim, Sang-Koog; Yoo, Myoung-Woo; Lee, Jehyun; Lee, Ha-Youn; Lee, Jae-Hyeok; Gaididei, Yuri; Kravchuk, Volodymyr P; Sheka, Denis D
2015-06-16
We found resonantly excited precession motions of a three-dimensional vortex core in soft magnetic nanospheres and controllable precession frequency with the sphere diameter 2R, as studied by micromagnetic numerical and analytical calculations. The precession angular frequency for an applied static field HDC is given as ωMV = γeffHDC, where γeff = γ〈mΓ〉 is the effective gyromagnetic ratio in collective vortex dynamics, with the gyromagnetic ratio γ and the average magnetization component 〈mΓ〉 of the ground-state vortex in the core direction. Fitting to the micromagnetic simulation data for 〈mΓ〉 yields a simple explicit form of 〈mΓ〉 ≈ (73.6 ± 3.4)(lex/2R)(2.20±0.14), where lex is the exchange length of a given material. This dynamic behavior might serve as a foundation for potential bio-applications of size-specific resonant excitation of magnetic vortex-state nanoparticles, for example, magnetic particle resonance imaging.
Anomalous Lense-Thirring precession in Kerr-Taub-NUT spacetimes
NASA Astrophysics Data System (ADS)
Chakraborty, Chandrachur
2015-12-01
Exact Lense-Thirring (LT) precession in Kerr-Taub-NUT spacetime is reviewed. It is shown that the LT precession does not obey the general inverse cube law of distance at strong gravity regime in Kerr-Taub-NUT spacetime. Rather, it becomes maximum just near the horizon, falls sharply and becomes zero near the horizon. The precession rate increases again and after that it falls obeying the general inverse cube law of distance. This anomaly is maximum at the polar region of this spacetime and it vanishes after crossing a certain `critical' angle towards the equator from the pole. We highlight that this particular `anomaly' also arises in the LT effect at the interior spacetime of the pulsars and such a signature could be used to identify a role of Taub-NUT solutions in the astrophysical observations or equivalently, a signature of the existence of a NUT charge in the pulsars. In addition, we show that if the Kerr-Taub-NUT spacetime rotates with the angular momentum J=Mn (mass × dual mass), the inner horizon goes to r=0 and only the event horizon exists at the distance r=2M.
Ma, T. P.; Zhang, S. F.; Yang, Y.; Chen, Z. H.; Zhao, H. B.; Wu, Y. Z.
2015-01-07
Rotational field dependence of laser-induced magnetization precession in a single-crystal Fe/MgO(001) sample was studied by the time resolved magneto-optical Kerr effect. Polar and longitudinal magnetization components were separated by measuring precession dynamics under opposite fields. When the applied field is weaker than the anisotropy field of an Fe film, the precession amplitude is small for the field direction near the easy axis and becomes larger as the field rotates towards the hard axis, showing a four-fold symmetry in agreement with the in-plane magnetic anisotropy; whereas at higher fields, the amplitude displays a drop near the hard axis. Such precession behavior can be well reproduced using an excitation model with rapidly modified but slowly recovered magnetic anisotropy and considering the elliptical precession trajectory. Our results indicate that the dominant mechanism for triggering Fe spin precession is the anisotropy modulation correlating with the lattice thermalization, rather than the transient anisotropy modulation due to the high electron temperature within 1 ps.
Near-IR imaging toward a puzzling young stellar object precessing jet
NASA Astrophysics Data System (ADS)
Paron, S.; Fariña, C.; Ortega, M. E.
2016-10-01
Aims: The study of jets that are related to stellar objects in formation is important because it enables us to understand the history of how the stars have built up their mass. Many studies currently examine jets towards low-mass young stellar objects, while equivalent studies toward massive or intermediate-mass young stellar objects are rare. In a previous study, based on 12CO J = 3-2 and public near-IR data, we found highly misaligned molecular outflows toward the infrared point source UGPS J185808.46+010041.8 (IRS) and some infrared features suggesting the existence of a precessing jet. Methods: Using near-IR data acquired with Gemini-NIRI at the JHKs broad- and narrowbands centered on the emission lines of [FeII], H2 1-0 S(1), H2 2-1 S(1), Brγ, and CO 2-0 (bh), we studied the circumstellar environment of IRS with an angular resolution between 0.̋35 and 0.̋45. Results: The emission in the JHKs broadbands shows in great detail a cone-shaped nebula extending to the north-northeast of the point source, which appears to be attached to it by a jet-like structure. In the three bands the nebula is resolved in a twisted-shaped feature composed of two arc-like features and a bow-shock-like structure seen mainly in the Ks band, which strongly suggests the presence of a precessing jet. An analysis of proper motions based on our Gemini observations and UKIDSS data additionally supports the precession scenario. We present one of the best-resolved cone-like nebula that is most likely related to a precessing jet up to date. The analysis of the observed near-IR lines shows that the H2 is collisionally excited, and the spatially coincidence of the [FeII] and H2 emissions in the closer arc-like feature suggests that this region is affected by a J shock. The second arc-like feature presents H2 emission without [FeII], which suggests a nondissociated C shock or a less energetic J shock. The H2 1-0 S(1) continuum-subtracted image reveals several knots and filaments at a larger
Modeling North American Ice Sheet Response to Changes in Precession and Obliquity
NASA Astrophysics Data System (ADS)
Tabor, C.; Poulsen, C. J.; Pollard, D.
2012-12-01
precession on the Laurentide and Cordillera ice sheets of North America. Preliminary model results show that the ice sheet response to changes in obliquity are larger than for precession despite providing a smaller direct insolation variation in the Northern Hemisphere high latitudes. A combination of enhanced Northern Hemisphere mid-latitude temperature gradient and longer cycle duration allow for a larger ice sheet response to obliquity than would be expected from insolation forcing alone. Conversely, a shorter duration dampens the ice sheet response to precession. Nevertheless, the precession cycle does cause significant changes in ice volume, a feature not observed in the Early Pleistocene δ18O records (Raymo and Nisancioglu, 2003). Future work will examine the climate response to an idealized transient orbit that includes concurrent variations in obliquity, precession, and eccentricity.
NASA Astrophysics Data System (ADS)
Murdin, P.
2000-11-01
Physicist, born in Magheragall, County Antrim, Ireland, became Lucasian professor in Cambridge, working on electricity, dynamics and thermodynamics, and especially the ether, the postulated material which pervades space and in which electromagnetic radiation travels. Finding no evidence that the ether existed, he was led to some of the results inherent in EINSTEIN's theory of relativity, giving a...
NASA Astrophysics Data System (ADS)
Escapa, Alberto; Ferrándiz, José M.; Baenas, Tomás; Getino, Juan; Navarro, Juan F.; Belda-Palazón, Santiago
2016-03-01
The complexity of the modeling of the rotational motion of the Earth in space has produced that no single theory has been adopted to describe it in full. Hence, it is customary using at least a theory for precession and another one for nutation. The classic approach proceeds by deriving some of the fundamental parameters from the precession theory, like, e.g., the dynamical ellipticity Hd, and then using those values in the nutation theory. The former IAU 1976 precession and IAU 1980 nutation theories followed that scheme. Along with the improvement of the accuracy of the determination of Earth orientation parameters, IAU 1980 was superseded by IAU2000, based on the application of the MHB2000 transfer function to the previous rigid Earth analytical theory REN2000. The latter was derived while the precession model IAU 1976 was still in force, therefore it used the corresponding values for some of the fundamental parameters, as the precession rate, associated to the dynamical ellipticity. The new precession model P03 was adopted as IAU 2006. That change introduced some inconsistency since P03 used different values for some of the fundamental parameters that MHB2000 inherited from REN2000. Besides, the derivation of the basic Earth parameters of MHB2000 itself comprised a fitted variation of the dynamical ellipticity adopted in the background rigid theory. Due to the strict requirements of accuracy of the present and coming times, the magnitude of the inconsistencies originated by this twofold approach is no longer negligible as earlier, hence the need of discussing the effects of considering slightly different values for H_d in precession and nutation theories.
NASA Astrophysics Data System (ADS)
Zhang, Shi-Chang
2013-01-01
It is revealed that at anti-resonance in a free-electron laser with a reversed guide magnetic field, the beam self-fields can act to focus the beam transport and prevent the electrons from striking on the waveguide wall before the wiggler exit. It is found that the focusing function results from the modulation of the periodically-varying self-field tangential and normal components on the electron's Larmor rotation. As a potential application, substantial improvement of the wave gain and output power at anti-resonance could be expected, since the beam current loss can be obviated by using this modulation mechanism.
Theta phase precession and phase selectivity: a cognitive device description of neural coding
NASA Astrophysics Data System (ADS)
Zalay, Osbert C.; Bardakjian, Berj L.
2009-06-01
Information in neural systems is carried by way of phase and rate codes. Neuronal signals are processed through transformative biophysical mechanisms at the cellular and network levels. Neural coding transformations can be represented mathematically in a device called the cognitive rhythm generator (CRG). Incoming signals to the CRG are parsed through a bank of neuronal modes that orchestrate proportional, integrative and derivative transformations associated with neural coding. Mode outputs are then mixed through static nonlinearities to encode (spatio) temporal phase relationships. The static nonlinear outputs feed and modulate a ring device (limit cycle) encoding output dynamics. Small coupled CRG networks were created to investigate coding functionality associated with neuronal phase preference and theta precession in the hippocampus. Phase selectivity was found to be dependent on mode shape and polarity, while phase precession was a product of modal mixing (i.e. changes in the relative contribution or amplitude of mode outputs resulted in shifting phase preference). Nonlinear system identification was implemented to help validate the model and explain response characteristics associated with modal mixing; in particular, principal dynamic modes experimentally derived from a hippocampal neuron were inserted into a CRG and the neuron's dynamic response was successfully cloned. From our results, small CRG networks possessing disynaptic feedforward inhibition in combination with feedforward excitation exhibited frequency-dependent inhibitory-to-excitatory and excitatory-to-inhibitory transitions that were similar to transitions seen in a single CRG with quadratic modal mixing. This suggests nonlinear modal mixing to be a coding manifestation of the effect of network connectivity in shaping system dynamic behavior. We hypothesize that circuits containing disynaptic feedforward inhibition in the nervous system may be candidates for interpreting upstream rate codes to
Hysteresis and precession of a swirling jet normal to a wall.
Shtern, V; Mi, J
2004-01-01
Interaction of a swirling jet with a no-slip surface has striking features of fundamental and practical interest. Different flow states and transitions among them occur at the same conditions in combustors, vortex tubes, and tornadoes. The jet axis can undergo precession and bending in combustors; this precession enhances large-scale mixing and reduces emissions of NOx. To explore the mechanisms of these phenomena, we address conically similar swirling jets normal to a wall. In addition to the Serrin model of tornadolike flows, a new model is developed where the flow is singularity free on the axis. New analytical and numerical solutions of the Navier-Stokes equations explain occurrence of multiple states and show that hysteresis is a common feature of wall-normal vortices or swirling jets no matter where sources of motion are located. Then we study the jet stability with the aid of a new approach accounting for deceleration and nonparallelism of the base flow. An appropriate transformation of variables reduces the stability problem for this strongly nonparallel flow to a set of ordinary differential equations. A particular flow whose stability is studied in detail is a half-line vortex normal to a rigid plane-a model of a tornado and of a swirling jet issuing from a nozzle in a combustor. Helical counter-rotating disturbances appear to be first growing as Reynolds number increases. Disturbance frequency changes its sign along the neutral curve while the wave number remains positive. Short disturbance waves propagate downstream and long waves propagate upstream. This helical instability causes bending of the vortex axis and its precession-the effects observed in technological flows and in tornadoes. PMID:14995717
A Statistical Approach to Determine the Values of the Correction for the Precession
NASA Astrophysics Data System (ADS)
Marco, F. J.; Martinez, M. J.; Lopez, J. A.
2010-10-01
The Hipparcos catalogue [1] provides a reference frame at optical wavelengths for the new ICRS. The adoption of this new reference system was decided following a resolution that was agreed at the 23rd IAU assembly held in Kyoto in 1997. Differences in the Hipparcos system of proper motions and the previous materialization of the reference frame, the FK5, are expected to be caused only by the combined effects of the motion of the equinox of the FK5 and the Luni-solar and planetary precession. Several authors have, however, pointed out an inconsistency in the differences in proper motion of the FK5-Hipparcos with the Δp of the Luni-solar precession as determined from VLBI and LLR, and most of them have claimed that these discrepancies are due to slightly biased proper motions in the FK5 catalogue [3], [5]. The different mathematical models employed to explain these errors have not completely accounted for the previous discrepancies in the precessional parameters. Our goal is to offer an explanation for this fact. To this end and according to [2] we propose the use of independent parametric and non-parametric methods. Thus, the introduction of a non-parametric method, combined with the inner product in L2 over S2, would give us values which do not depend on the possible interdependencies existing in the data-set. In addition, the evidence shows that zonal studies are needed. This would lead us to introduce a local non-parametric model [4]. All these models will provide independent precessional values which could be compared in order to study their reliability. Finally, we obtain values for the precession corrections that are very consistent with those that are currently adopted.
Magnetohydrodynamic instabilities in rotating and precessing sheared flows: An asymptotic analysis
NASA Astrophysics Data System (ADS)
Salhi, A.; Lehner, T.; Cambon, C.
2010-07-01
Linear magnetohydrodynamic instabilities are studied analytically in the case of unbounded inviscid and electrically conducting flows that are submitted to both rotation and precession with shear in an external magnetic field. For given rotation and precession the possible configurations of the shear and of the magnetic field and their interplay are imposed by the “admissibility” condition (i.e., the base flow must be a solution of the magnetohydrodynamic Euler equations): we show that an “admissible” basic magnetic field must align with the basic absolute vorticity. For these flows with elliptical streamlines due to precession we undertake an analytical stability analysis for the corresponding Floquet system, by using an asymptotic expansion into the small parameter ɛ (ratio of precession to rotation frequencies) by a method first developed in the magnetoelliptical instabilities study by Lebovitz and Zweibel [Astrophys. J. 609, 301 (2004)]10.1086/420972. The present stability analysis is performed into a suitable frame that is obtained by a systematic change of variables guided by symmetry and the existence of invariants of motion. The obtained Floquet system depends on three parameters: ɛ , η (ratio of the cyclotron frequency to the rotation frequency) and χ=cosα , with α being a characteristic angle which, for circular streamlines, ɛ=0 , identifies with the angle between the wave vector and the axis of the solid body rotation. We look at the various (centrifugal or precessional) resonant couplings between the three present modes: hydrodynamical (inertial), magnetic (Alfvén), and mixed (magnetoinertial) modes by computing analytically to leading order in ɛ the instabilities by estimating their threshold, growth rate, and maximum growth rate and their bandwidths as functions of ɛ , η , and χ . We show that the subharmonic “magnetic” mode appears only for η>5/2 and at large η (≫1) the maximal growth rate of both the
The jet of the Low Luminosity AGN of M81. Evidence of Precession
NASA Astrophysics Data System (ADS)
Alberdi, A.; Martí-Vidal, I.; Marcaide, J. M.; Guirado, J. C.; Pérez-Torres, M. A.; Ros, E.; Brunthaler, A.
2013-12-01
In this contribution, we summarize our main results of a big campaign of global VLBI observations of the AGN in M81 (M81*) phase-referenced to the radio supernova SN 1993J. Thanks to the precise multi-epoch and multi-frequency astrometry, we have determined the normalized core-shift of the relativistic jet of M81* and estimated both the magnetic field and the particle density at the jet base. We have also found evidence of jet precession in M81* coming from the systematic time evolution of the jet orientation correlated with changes in the overall flux density.
NASA Astrophysics Data System (ADS)
Marzocchi, Alice; Flecker, Rachel; Lunt, Dan; Gladstone, Rupert; Hilgen, Frits; Krijgsman, Wout; Sierro, Francisco; Ivanovic, Ruza
2014-05-01
The Messinian Salinity Crisis (MSC) drastically modified the environment of the Mediterranean Sea. The large signal-noise ratio preserved in the geological record for this extreme event makes it a perfect target for exploring the biogeochemical processes involved through palaeoclimate modelling. In addition, Late Miocene sequences in the Mediterranean have been astronomically tuned, providing a very high-resolution age model that resolves sediment data on a millennial timescale or shorter. Consequently it is possible to carry out robust model-data comparison where the precise orbital phasing is equivalent. Sequences of laminated sapropelitic beds interbedded within homogeneous marls are frequently found in Late Miocene sections in the Mediterranean and have been associated with orbitally-driven climate responses. In fact, the deposition of these sediments has been linked to freshwater input causing both stratification of the water column and increased surface productivity, at times of high summer insolation. Most of the hypotheses relating the phasing of the sedimentary record to the orbital forcing are, however, still untested. Insight can therefore be gained by investigating the impact of varying orbital parameters on the Mediterranean's hydrologic budget using global climate models. A series of 22 fully coupled atmosphere-ocean-vegetation snap-shot simulations have been run at evenly spaced intervals (1kyr) through an entire precession cycle during the pre-evaporite stage of the MSC (~6.5 Ma). In our simulations, the Mediterranean Sea's hydrologic budget exhibits high seasonal variability. Model results can be directly compared with high-resolution geological data that is available for our selected time slice; for instance, cyclic changes in microfaunal assemblages that have a strong seasonal bias can be compared with our model output. This allows us to test the biogeochemical phasing of Mediterranean successions in relation to orbital forcing. Our simulations
Negative muon spin precession measurement of the hyperfine states of muonic sodium
Brewer, J.H.; Ghandi, K.; Froese, A.M.; Fryer, B.A.
2005-05-01
Both hyperfine states of muonic {sup 23}Na and the rate R of conversion between them have been observed directly in a high field negative muon spin precession experiment using a backward muon beam with transverse spin polarization. The result in metallic sodium, R=13.7{+-}2.2 {mu}s{sup -1}, is consistent with Winston's prediction in 1963 based on Auger emission of core electrons, and with the measurements of Gorringe et al. in Na metal, but not with their smaller result in NaF. In NaOH we find R=23.5{+-}8 {mu}s{sup -1}, leaving medium-dependent effects ambiguous.
Mizukami, S; Wu, F; Sakuma, A; Walowski, J; Watanabe, D; Kubota, T; Zhang, X; Naganuma, H; Oogane, M; Ando, Y; Miyazaki, T
2011-03-18
Spin precession with frequencies up to 280 GHz is observed in Mn(3-δ)Ga alloy films with a perpendicular magnetic anisotropy constant K(u)∼15 M erg/cm(3). The damping constant α, characterizing macroscopic spin relaxation and being a key factor in spin-transfer-torque systems, is not larger than 0.008 (0.015) for the δ=1.46 (0.88) film. Those are about one-tenth of α values for known materials with large K(u). First-principles calculations well describe both low α and large K(u) for these alloys.
Balanced steady state-free precession (b-SSFP) imaging for MRCP: techniques and applications.
Glockner, James F; Lee, Christine U
2014-12-01
Balanced steady state-free precession (b-SSFP) pulse sequences have a number of properties which can be useful in magnetic resonance cholangiopancreatography (MRCP), including short acquisition times, high signal-to-noise ratios, and T2/T1 contrast weighting. The utility and versatility of b-SSFP sequences for MRCP imaging are probably underappreciated, and this pictorial essay briefly discusses benefits and limitations of 2D and 3D b-SSFP techniques used in place of or in addition to conventional single-shot fast spin echo or 3D fast spin echo acquisitions and illustrates their appearance in several clinical cases.
An interacting binary system powers precessing outflows of an evolved star.
Boffin, Henri M J; Miszalski, Brent; Rauch, Thomas; Jones, David; Corradi, Romano L M; Napiwotzki, Ralf; Day-Jones, Avril C; Köppen, Joachim
2012-11-01
Stars are generally spherical, yet their gaseous envelopes often appear nonspherical when ejected near the end of their lives. This quirk is most notable during the planetary nebula phase, when these envelopes become ionized. Interactions among stars in a binary system are suspected to cause the asymmetry. In particular, a precessing accretion disk around a companion is believed to launch point-symmetric jets, as seen in the prototype Fleming 1. Our finding of a post-common-envelope binary nucleus in Fleming 1 confirms that this scenario is highly favorable. Similar binary interactions are therefore likely to explain these kinds of outflows in a large variety of systems. PMID:23139326
Spin transport and precession in graphene measured by nonlocal and three-terminal methods
Dankert, André Kamalakar, Mutta Venkata; Bergsten, Johan; Dash, Saroj P.
2014-05-12
We investigate the spin transport and precession in graphene by using the Hanle effect in nonlocal and three-terminal measurement geometries. Identical spin lifetimes, spin diffusion lengths, and spin polarizations are observed in graphene devices for both techniques over a wide range of temperatures. The magnitude of the spin signals is well explained by spin transport models. These observations rules out any signal enhancements or additional scattering mechanisms at the interfaces for both geometries. This validates the applicability of both the measurement methods for graphene based spintronics devices and their reliable extractions of spin parameters.
Computing precession and spin-curvature coupling for small bodies orbiting Kerr black holes
NASA Astrophysics Data System (ADS)
Hughes, Scott; Ruangsri, Uchupol; Vigeland, Sarah
2016-03-01
A non-spinning small body that orbits a Kerr black hole follows a trajectory that looks like a geodesic corrected by ``self force'' effects that drive inspiral and shift the small body's orbital frequencies. If the small body is spinning, then additional forces arise from the coupling of its spin to the curvature of the larger black hole. In this talk, I will describe recent work to compute the precession of this small body in the frequency domain for generic orbit geometries and generic small body orientations, and show how this result can be used to compute the spin-curvature force in a computationally effective way.
An interacting binary system powers precessing outflows of an evolved star.
Boffin, Henri M J; Miszalski, Brent; Rauch, Thomas; Jones, David; Corradi, Romano L M; Napiwotzki, Ralf; Day-Jones, Avril C; Köppen, Joachim
2012-11-01
Stars are generally spherical, yet their gaseous envelopes often appear nonspherical when ejected near the end of their lives. This quirk is most notable during the planetary nebula phase, when these envelopes become ionized. Interactions among stars in a binary system are suspected to cause the asymmetry. In particular, a precessing accretion disk around a companion is believed to launch point-symmetric jets, as seen in the prototype Fleming 1. Our finding of a post-common-envelope binary nucleus in Fleming 1 confirms that this scenario is highly favorable. Similar binary interactions are therefore likely to explain these kinds of outflows in a large variety of systems.
Goto, R.; Hatori, T.; Miura, H. Ito, A.; Sato, M.
2015-03-15
Two-fluid and the finite Larmor effects on linear and nonlinear growth of the Rayleigh-Taylor instability in a two-dimensional slab are studied numerically with special attention to high-wave-number dynamics and nonlinear structure formation at a low β-value. The two effects stabilize the unstable high wave number modes for a certain range of the β-value. In nonlinear simulations, the absence of the high wave number modes in the linear stage leads to the formation of the density field structure much larger than that in the single-fluid magnetohydrodynamic simulation, together with a sharp density gradient as well as a large velocity difference. The formation of the sharp velocity difference leads to a subsequent Kelvin-Helmholtz-type instability only when both the two-fluid and finite Larmor radius terms are incorporated, whereas it is not observed otherwise. It is shown that the emergence of the secondary instability can modify the outline of the turbulent structures associated with the primary Rayleigh-Taylor instability.
Capua, Amir; Rettner, Charles; Parkin, Stuart S P
2016-01-29
We study the parametric excitation of high orders of magnetization precession in ultrathin films having perpendicular magnetic anisotropy. We observe that for a given driving field amplitude the harmonic generation can be increased by lowering the barrier with the application of an in-plane magnetic field in the manner of the Smit-Beljers effect. In this effect, the magnetic stiffness is reduced not by lowering the magnitude of the magnetic field upon which the spins precess, but rather by effectively releasing the field's "anchoring" point. This results in a shallow energy barrier where the electrons' spin is locally unconstrained. While the observation is unveiled in the form of nonlinear high harmonic generation, we believe that the physics whereby the barrier is suppressed by an external magnetic field may apply to other phenomena associated with ultrathin films. In these cases, such unconstrained motion may serve as a sensitive probe of the torques associated with proximate spin currents. Moreover, our approach may be used as a model system for the study of phase transitions in the field of nonlinear dynamics.
Constraints on Galileon-induced precessions from solar system orbital motions
Iorio, L.
2012-07-01
We use latest data from solar system planetary orbital motions to put constraints on some Galileon-induced precessional effects. Due to the Vainshtein mechanism, the Galileon-type spherically symmetric field of a monopole induces a small, screened correction ∝(r){sup 1/2} to the r{sup −1} Newtonian potential which causes a secular precession of the pericenter of a test particle. In the case of our solar system, latest data from Mars allow to constrain the magnitude of such an interaction down to α ≤ 0.3 level, where α corresponds to the non minimal coupling of the Galileon to matter. Another Galileon-type effect which might impact solar system dynamics is due to an unscreened constant gradient induced by the peculiar motion of the Galaxy. The magnitude of such an effect, depending on the different gravitational binding energies of the Sun and the planets, taken into account by ξ, is ξ ≤ 0.004 from the latest bounds on the supplementary perihelion precession of Saturn.
THE EVOLUTION OF PSR J0737-3039B AND A MODEL FOR RELATIVISTIC SPIN PRECESSION
Perera, B. B. P.; McLaughlin, M. A.; Kramer, M.; Lyne, A. G.; Stairs, I. H.; Ferdman, R. D.; Freire, P. C. C.; Possenti, A.; Burgay, M.; Breton, R. P.; Manchester, R. N.; Camilo, F.
2010-10-01
We present the evolution of the radio emission from the 2.8 s pulsar of the double pulsar system PSR J0737- 3039A/B. We provide an update on the Burgay et al. analysis by describing the changes in the pulse profile and flux density over five years of observations, culminating in the B pulsar's radio disappearance in 2008 March. Over this time, the flux density decreases by 0.177 mJy yr{sup -1} at the brightest orbital phases and the pulse profile evolves from a single to a double peak, with a separation rate of 2.{sup 0}6 yr{sup -1}. The pulse profile changes are most likely caused by relativistic spin precession but cannot be easily explained with a circular hollow-cone beam as in the model of Clifton and Weisberg. Relativistic spin precession, coupled with an elliptical beam, can model the pulse profile evolution well and the reappearance is expected to happen in {approx}2035 with the same part of the beam or in {approx}2014 if we assume a symmetric beam shape. This particular beam shape predicts geometrical parameters for the two bright orbital phases which are consistent with and similar to those derived by Breton et al. However, the observed decrease in flux over time and B's eventual disappearance cannot be easily explained by the model and may be due to the changing influence of A on B.
Fischetti, Sebastian; Cadonati, Laura; Mohapatra, Satyanarayan R. P.; Healy, James; London, Lionel; Shoemaker, Deirdre
2011-02-15
Recent years have witnessed tremendous progress in numerical relativity and an ever improving performance of ground-based interferometric gravitational wave detectors. In preparation for the Advanced Laser Interferometer Gravitational Wave Observatory (Advanced LIGO) and a new era in gravitational wave astronomy, the numerical relativity and gravitational wave data analysis communities are collaborating to ascertain the most useful role for numerical relativity waveforms in the detection and characterization of binary black hole coalescences. In this paper, we explore the detectability of equal mass, merging black hole binaries with precessing spins and total mass M{sub T}(set-membership sign)[80,350]M{sub {center_dot}}, using numerical relativity waveforms and templateless search algorithms designed for gravitational wave bursts. In particular, we present a systematic study using waveforms produced by the MayaKranc code that are added to colored, Gaussian noise and analyzed with the Omega burst search algorithm. Detection efficiency is weighed against the orientation of one of the black-hole's spin axes. We find a strong correlation between the detection efficiency and the radiated energy and angular momentum, and that the inclusion of the l=2, m={+-}1, 0 modes, at a minimum, is necessary to account for the full dynamics of precessing systems.
Intrinsic fat suppression in TIDE balanced steady-state free precession imaging.
Paul, Dominik; Hennig, Jürgen; Zaitsev, Maxim
2006-12-01
A novel fat-suppressed balanced steady-state free precession (b-SSFP) imaging method based on the transition into driven equilibrium (TIDE) sequence with variable flip angles is presented. The new method, called fat-saturated (FS)-TIDE, exploits the special behavior of TIDE signals from off-resonance spins during the flip angle ramp. As shown by simulations and experimental data, the TIDE signal evolution for off-resonant isochromats during the transition from turbo spin-echo (TSE)-like behavior to the true fast imaging with steady precession (TrueFISP) mode undergoes a zero crossing. The resulting signal notch for off-resonant spins is then used for fat suppression. The efficiency of FS-TIDE is demonstrated in phantoms and healthy volunteers on a 1.5T system. The resulting images are compared with standard TrueFISP data with and without fat suppression. It is demonstrated that FS-TIDE provides a fast and stable means for homogenous fat suppression in abdominal imaging while maintaining balanced SSFP-like image contrast and signal-to-noise ratio (SNR). The scan time of FS-TIDE is not increased compared to normal TrueFISP imaging without fat suppression and identical k-space trajectories. Because of the intrinsic fat suppression, no additional preparation is needed. Possible repetition times (TRs) are not firmly limited to special values and are nearly arbitrary.
Capua, Amir; Rettner, Charles; Parkin, Stuart S P
2016-01-29
We study the parametric excitation of high orders of magnetization precession in ultrathin films having perpendicular magnetic anisotropy. We observe that for a given driving field amplitude the harmonic generation can be increased by lowering the barrier with the application of an in-plane magnetic field in the manner of the Smit-Beljers effect. In this effect, the magnetic stiffness is reduced not by lowering the magnitude of the magnetic field upon which the spins precess, but rather by effectively releasing the field's "anchoring" point. This results in a shallow energy barrier where the electrons' spin is locally unconstrained. While the observation is unveiled in the form of nonlinear high harmonic generation, we believe that the physics whereby the barrier is suppressed by an external magnetic field may apply to other phenomena associated with ultrathin films. In these cases, such unconstrained motion may serve as a sensitive probe of the torques associated with proximate spin currents. Moreover, our approach may be used as a model system for the study of phase transitions in the field of nonlinear dynamics. PMID:26871356
Electrical detection of coherent spin precession using the ballistic intrinsic spin Hall effect.
Choi, Won Young; Kim, Hyung-jun; Chang, Joonyeon; Han, Suk Hee; Koo, Hyun Cheol; Johnson, Mark
2015-08-01
The spin-orbit interaction in two-dimensional electron systems provides an exceptionally rich area of research. Coherent spin precession in a Rashba effective magnetic field in the channel of a spin field-effect transistor and the spin Hall effect are the two most compelling topics in this area. Here, we combine these effects to provide a direct demonstration of the ballistic intrinsic spin Hall effect and to demonstrate a technique for an all-electric measurement of the Datta-Das conductance oscillation, that is, the oscillation in the source-drain conductance due to spin precession. Our hybrid device has a ferromagnet electrode as a spin injector and a spin Hall detector. Results from multiple devices with different channel lengths map out two full wavelengths of the Datta-Das oscillation. We also use the original Datta-Das technique with a single device of fixed length and measure the channel conductance as the gate voltage is varied. Our experiments show that the ballistic spin Hall effect can be used for efficient injection or detection of spin polarized electrons, thereby enabling the development of an integrated spin transistor. PMID:26005997
High-frequency and type-C QPOs from oscillating, precessing hot, thick flow
NASA Astrophysics Data System (ADS)
Fragile, P. Chris; Straub, Odele; Blaes, Omer
2016-09-01
Motivated by recent studies showing an apparent correlation between the high-frequency quasi-periodic oscillations (QPOs) and the low-frequency, type-C QPO in black hole low-mass X-ray binaries (LMXBs), we explore a model that explains all three QPOs in terms of an oscillating, precessing hot flow in the truncated-disc geometry. Our model favours attributing the two high-frequency QPOs, often occurring in a near 3:2 frequency ratio, to the breathing and vertical epicyclic frequency modes of the hot, thick flow, although we cannot rule out the Keplerian and m = -1 radial epicyclic modes. In either case, the type-C QPO is attributed to precession. The correlation of the QPOs comes from the fact that all three frequencies are associated with the same geometrical structure. While the exact QPO frequencies are sensitive to the black hole mass and spin, their evolution over the course of an outburst is mainly tied to the truncation radius between the geometrically thin, optically thick disc and the inner, hot flow. We show that, in the case of the LMXB GRO J1655-40, this model can explain the one simultaneous observation of all three QPOs and that an extrapolation of the model appears to match lower frequency observations where only two of the three components are seen. Thus, this model may be able to unify multiple QPO observations using the properties of a single, simple, geometrical model.
Comet Encke - Precession of the spin axis, nongravitational motion, and sublimation
NASA Technical Reports Server (NTRS)
Whipple, F. L.; Sekanina, Z.
1979-01-01
From the observed light curve of P/Encke the jet force from sublimation is calculated both as a (precessing) torque and as a (perturbing) force transverse to the radius vector. An integral iteration is carried out over 59 perihelion passages, 1786-1977, to fit the previously determined nongravitational transverse force and to derive the precession of the spin axis. It is shown that the spin axis turned more than 100 degrees in longitude and almost 30 degrees in latitude from 1786 to 1977, but appears to have been almost fixed in direction for hundreds of revolutions before 1700. It is suggested that ejected meteoroidal debris accumulated on the currently less active hemisphere, insulating it to maintain a low activity level. A tentative rotation period of 6 h 33 min is derived, using Whipple's halo method. The suggested spinup rate is 21 min/century, while the current rate of relative mass loss by sublimation is 0.09% of the comet's mass per revolution. Moreover, the mass of the nucleus is estimated at less than 10 to the 16th grams, and its oblateness at less than 4%.
Precessing jets in Sagittarius A: Gas dynamics in the central parsec of the Galaxy
Brown, R.L.
1982-11-01
We suggest that the asymmetric velocity field and the point-reflection symmetry of the radio continuum brightness distribution of the inner parsec of the galaxy can be understood as complementary manifestations of collimated gaseous outflow along twin opposing beams that emanate from a central object. That object appears to be the compact nonthermal radio source Sgr A*. The data are best reproduced by a model in which material is expelled along the rotation axis of Sgr A* and Sgr A* precesses with a period approx.2300 yr such that the precession axis is inclined approx.49/sup 0/ with respect to the line of sight. On the plane of the sky the jets appear to rotate anticlockwise about an axis having a position angle approx.80/sup 0/ (or an inclination of approx.41/sup 0/ with respect to the rotation axis of the Galaxy). The western jet lies between the Sun and Sgr A* and appears blueshifted; the eastern jet appears redshifted and is on the far side of Sgr A*. The ejection velocity is approx.300 km s/sup -1/ and the mass loss rate is one the order of 10/sup -3/ M/sub sun/ yr/sup -1/.
Determination of the spin-lifetime anisotropy in graphene using oblique spin precession
Raes, Bart; Scheerder, Jeroen E.; Costache, Marius V.; Bonell, Frédéric; Sierra, Juan F.; Cuppens, Jo; Van de Vondel, Joris; Valenzuela, Sergio O.
2016-01-01
We determine the spin-lifetime anisotropy of spin-polarized carriers in graphene. In contrast to prior approaches, our method does not require large out-of-plane magnetic fields and thus it is reliable for both low- and high-carrier densities. We first determine the in-plane spin lifetime by conventional spin precession measurements with magnetic fields perpendicular to the graphene plane. Then, to evaluate the out-of-plane spin lifetime, we implement spin precession measurements under oblique magnetic fields that generate an out-of-plane spin population. We find that the spin-lifetime anisotropy of graphene on silicon oxide is independent of carrier density and temperature down to 150 K, and much weaker than previously reported. Indeed, within the experimental uncertainty, the spin relaxation is isotropic. Altogether with the gate dependence of the spin lifetime, this indicates that the spin relaxation is driven by magnetic impurities or random spin-orbit or gauge fields. PMID:27157318
TIME EVOLUTION OF FLARES IN GRB 130925A: JET PRECESSION IN A BLACK HOLE ACCRETION SYSTEM
Hou, Shu-Jin; Liu, Tong; Gu, Wei-Min; Sun, Mou-Yuan; Lu, Ju-Fu; Lin, Da-Bin; Wu, Xue-Feng
2014-01-20
GRB 130925A, composed of three gamma-ray emission episodes and a series of orderly flares, has been detected by Swift, Fermi, Konus-Wind, and INTEGRAL. If the third weakest gamma-ray episode can be considered a giant flare, we find that after the second gamma-ray episode observed by INTEGRAL located at about 2000 s, a positive relation exists between the time intervals of the adjacent flares and the time since the episode. We suggest that the second gamma-ray episode and its flares originate from the resumption of the accretion process due to the fragments from the collapsar falling back; such a relation may be related to a hyperaccretion disk around a precessed black hole (BH). We propose that the origin and time evolution of the flares, and the approximately symmetrical temporal structure and spectral evolution of the single flare can be explained well by a jet precession model. In addition, the mass and spin of the BH can be constrained, which indicates a stellar-mass, fast-rotating BH located in the center of GRB 130925A.
ALTERED PHASE PRECESSION AND COMPRESSION OF TEMPORAL SEQUENCES BY PLACE CELLS IN EPILEPTIC RATS
Lenck-Santini, Pierre-Pascal; Holmes, Gregory L.
2009-01-01
In the hippocampus, pyramidal cells encode information in two major ways: rate coding and temporal coding. Rate coding, where information is coded through firing frequency, is exemplarily illustrated by place cells, characterized by their location specific firing. In addition, the precise temporal organization of firing of multiple place cells provides information, in a compressed time window, about the temporal sequence of the locations visited by the animal. This encoding is accomplished through phase precession, a phenomenon whereby unit firing is linked to theta rhythm, one of the major hippocampal EEG oscillations. Although it is likely that this type of processing is critical for normal brain function, its involvement in pathologies associated with cognitive disorders is unknown. In this experiment, we determined if the temporal organization of place cell firing is affected in an animal model of mesial temporal lobe epilepsy (MTLE), a disease accompanied with cognitive impairment. We investigated hippocampal coding and its relationship to theta rhythm in rats following status epilepticus (SE), a condition that leads to MTLE. We found a great proportion of SE place cells had aberrant phase/precession pattern and temporal organization of firing among pairs of neurons, which constitutes the compression of temporal sequences, was altered in SE rats. The same animals were also markedly impaired in the water maze task, a measure of spatial memory. We propose that the synaptic and cellular alterations observed in MTLE induce aberrant temporal coding in the hippocampus, contributing in turn to cognitive dysfunction. PMID:18463258
Precession, nutation, and variation of UT1 due to the Sun's post-Newtonian torque
NASA Astrophysics Data System (ADS)
Fukushima, Toshio
We derived the post-Newtonian transformation laws of the coordinate velocity and the coordinate acceleration between a global and a body-centric coordinate system, which is related to each other by a kinematically non-rotating coordinate transformation. Next, by using the latter transformation, we obtained an explicit expression of the post-Newtonian tidal acceleration. Then, by conducting a special volume integral of torque element on an equal body-centric coordinate time hypersurface, we computed the post-Newtonian form of the gravitational torque. Finally, by integrating the Poisson approximation of the post-Newtonian extension of the Eulerian equation of rotational motion of the Earth moving along an elliptic orbit around the Sun and suffering the Sun's torque only, we evaluated post-Newtonian corrections to the precession, the nutation, and the variation of UT1. Except the geodesic precession and the geodesic nutation (Fukushima 1991), the largest effects are those related to the rotation angle of the Earth, UT1, as much as ΔUT1 = 10.50 sin l' + 0.09 sin 2l' where the unit is millisecond and l' denotes the mean anomaly of the Sun. The associated variation of the angular velocity of the Earth rotation becomes ΔΩ = 2.4 cos l' in the unit of 10-14rad/s. These are comparable with the tidal effects due to the nonrigidity of the Earth.
Binary system and jet precession and expansion in G35.20-0.74N
NASA Astrophysics Data System (ADS)
Beltrán, M. T.; Cesaroni, R.; Moscadelli, L.; Sánchez-Monge, Á.; Hirota, T.; Kumar, M. S. N.
2016-09-01
Context. Atacama Large Millimeter/submillimeter Array (ALMA) observations of the high-mass star-forming region G35.20-0.74N have revealed the presence of a Keplerian disk in core B rotating about a massive object of 18 M⊙, as computed from the velocity field. The luminosity of such a massive star would be comparable to (or higher than) the luminosity of the whole star-forming region. To solve this problem it has been proposed that core B could harbor a binary system. This could also explain the possible precession of the radio jet associated with this core, which has been suggested by its S-shaped morphology. Aims: We establish the origin of the free-free emission from core B and investigate the existence of a binary system at the center of this massive core and the possible precession of the radio jet. Methods: We carried out VLA continuum observations of G35.20-0.74N at 2 cm in the B configuration and at 1.3 cm and 7 mm in the A and B configurations. The bandwidth at 7 mm covers the CH3OH maser line at 44.069 GHz. Continuum images at 6 and 3.6 cm in the A configuration were obtained from the VLA archive. We also carried out VERA observations of the H2O maser line at 22.235 GHz. Results: The observations have revealed the presence of a binary system of UC/HC Hii regions at the geometrical center of the radio jet in G35.20-0.74N. This binary system, which is associated with a Keplerian rotating disk, consists of two B-type stars of 11 and 6 M⊙. The S-shaped morphology of the radio jet has been successfully explained as being due to precession produced by the binary system. The analysis of the precession of the radio jet has allowed us to better interpret the IR emission in the region, which would be not tracing a wide-angle cavity open by a single outflow with a position angle of ~55°, but two different flows: a precessing one in the NE-SW direction associated with the radio jet, and a second one in an almost E-W direction. Comparison of the radio jet images
NASA Astrophysics Data System (ADS)
Gurfil, Pini; Lainey, Valéry; Efroimsky, Michael
2007-12-01
Construction of an accurate theory of orbits about a precessing and nutating oblate planet, in terms of osculating elements defined in a frame associated with the equator of date, was started in Efroimsky and Goldreich (2004) and Efroimsky (2004, 2005, 2006a, b). Here we continue this line of research by combining that analytical machinery with numerical tools. Our model includes three factors: the J 2 of the planet, its nonuniform equinoctial precession described by the Colombo formalism, and the gravitational pull of the Sun. This semianalytical and seminumerical theory, based on the Lagrange planetary equations for the Keplerian elements, is then applied to Deimos on very long time scales (up to 1 billion years). In parallel with the said semianalytical theory for the Keplerian elements defined in the co-precessing equatorial frame, we have also carried out a completely independent, purely numerical, integration in a quasi-inertial Cartesian frame. The results agree to within fractions of a percent, thus demonstrating the applicability of our semianalytical model over long timescales. Another goal of this work was to make an independent check of whether the equinoctial-precession variations predicted for a rigid Mars by the Colombo model could have been sufficient to repel its moons away from the equator. An answer to this question, in combination with our knowledge of the current position of Phobos and Deimos, will help us to understand whether the Martian obliquity could have undergone the large changes ensuing from the said model (Ward 1973; Touma and Wisdom 1993, 1994; Laskar and Robutel 1993), or whether the changes ought to have been less intensive (Bills 2006; Paige et al. 2007). It has turned out that, for low initial inclinations, the orbit inclination reckoned from the precessing equator of date is subject only to small variations. This is an extension, to non-uniform equinoctial precession given by the Colombo model, of an old result obtained by
NASA Astrophysics Data System (ADS)
Dobson, G. J.
1998-07-01
Newton's treatment of the precession of the equinoxes in his Philosophiae Naturalis Principia Mathematica was recognised by d'Alembert in 1749 as being faulty, despite the very close agreement between Newton's calculated value for the rate of precesion and the observed value. Here, the author presents an analysis of Newton's geometrical methods applied in his treatment of precession and claims that it was basically flawed because Newton lacked knowledge of the principles of rigid body dynamics and, in particular, was unaware of the idea of angular momentum.
Dong, Hattie Z; Worters, Pauline W; Wu, Holden H; Ingle, R Reeve; Vasanawala, Shreyas S; Nishimura, Dwight G
2013-08-01
Noncontrast-enhanced renal angiography techniques based on balanced steady-state free precession avoid external contrast agents, take advantage of high inherent blood signal from the T 2 / T 1 contrast mechanism, and have short steady-state free precession acquisition times. However, background suppression is limited; inflow times are inflexible; labeling region is difficult to define when tagging arterial flow; and scan times are long. To overcome these limitations, we propose the use of multiple inversion recovery preparatory pulses combined with alternating pulse repetition time balanced steady-state free precession to produce renal angiograms. Multiple inversion recovery uses selective spatial saturation followed by four nonselective inversion recovery pulses to concurrently null a wide range of background T 1 species while allowing for adjustable inflow times; alternating pulse repetition time steady-state free precession maintains vessel contrast and provides added fat suppression. The high level of suppression enables imaging in three-dimensional as well as projective two-dimensional formats, the latter of which has a scan time as short as one heartbeat. In vivo studies at 1.5 T demonstrate the superior vessel contrast of this technique.
NASA Astrophysics Data System (ADS)
Alfonso, W. D.; Sánchez, L. A.; Mosquera, H. J.
2015-11-01
The electromagnetic radiation emitted from some astrophysical objects such as active galactic nuclei (AGN), micro-quasars (M-QSRs), and central engines of gamma-ray burst (GRBs), seems to have a similar physical origin: a powerful jet of plasma ejected from a localized system, presumably composed of an accretion disk encircling a compact object. This radiation is generally beamed in the polar directions and in some cases, it appears to have a spiral-like structure that could be explained if the central system itself precesses. In this work, we use the slim disk accretion model, presented by Popham et al. (1999), to studying the gravitational waves (GWs) emitted by the precession of the accretion disk around a solar-mass Kerr black hole (KBH). For practical purposes, this model describes the central engine of a class of GRBs when some astrophysical constrains are fulfilled. The induced precession considered here is driven by the Bardeen-Petterson effect, which results from the combination of viscous effects in such disks and the relativistic frame-dragging effect. We evaluate the feasibility of direct detection of the GWs computed for such a model and show that the precession of this kind of systems could be detected by gravitational wave observatories like DECIGO, ultimate-DECIGO, and BBO, with higher probability if such a class of sources are placed at distances less than 1 Mpc.
NASA Astrophysics Data System (ADS)
Efroimsky, M.; Lainey, V.; Gurfil, P.
2005-12-01
Construction of an accurate theory of orbits about a precessing and nutating oblate planet, in terms of osculating elements defined in a frame associated with the equator of date, was started in Efroimsky & Goldreich (2004) and Efroimsky (2005a,b). Here we continue this line of research by combining those analytics with numerical tools. This semianalytical and seminumerical theory, based on the Lagrange-type planetary equations for the Keplerian elements, is then applied to Deimos at very large time scales. In parallel with the said semianalytical-seminumerical theory for the Keplerian elements, we have also carried out a completely independent, purely numerical, integration in a fixed inertial Cartesian frame. These parallel efforts were taken to make sure that the results are reliable and robust. One goal of this work was to make an independent check of whether the equinoctial precession predicted for a rigid Mars could have been sufficient to repel the orbits away from the equator, on a billion-year time scale. The answer to this question, in combination with our knowledge of the current position of Phobos and Deimos, will help us to understand whether this precession could indeed be as large as predicted or whether it ought to have been less. Another goal was to trace the history of a hypothetical satellite captured at a high inclination and to see if its inclination could decrease through aeons. The latter numerical experiment was motivated by the ongoing discussion on the possible scenarios of the Martian satellites capture. It has turned out that, both for high and low initial inclinations, the orbit inclination, reckoned from the precessing equator of date, is subject only to extremely small variations. This is an extension, to non-uniform equinoctial precession given by the Colombo model, of an old result obtained by Goldreich (1965) for the case of uniform precession. Such ``inclination locking" confirms that an oblate planet can, indeed, afford a large
NASA Astrophysics Data System (ADS)
Fontana, A.; Marzari, F.
2016-05-01
Context. Planetesimals and planets embedded in a circumstellar disk are dynamically perturbed by the disk gravity. It causes an apsidal line precession at a rate that depends on the disk density profile and on the distance of the massive body from the star. Aims: Different analytical models are exploited to compute the precession rate of the perihelion ϖ˙. We compare them to verify their equivalence, in particular after analytical manipulations performed to derive handy formulas, and test their predictions against numerical models in some selected cases. Methods: The theoretical precession rates were computed with analytical algorithms found in the literature using the Mathematica symbolic code, while the numerical simulations were performed with the hydrodynamical code FARGO. Results: For low-mass bodies (planetesimals) the analytical approaches described in Binney & Tremaine (2008, Galactic Dynamics, p. 96), Ward (1981, Icarus, 47, 234), and Silsbee & Rafikov (2015a, ApJ, 798, 71) are equivalent under the same initial conditions for the disk in terms of mass, density profile, and inner and outer borders. They also match the numerical values computed with FARGO away from the outer border of the disk reasonably well. On the other hand, the predictions of the classical Mestel disk (Mestel 1963, MNRAS, 126, 553) for disks with p = 1 significantly depart from the numerical solution for radial distances beyond one-third of the disk extension because of the underlying assumption of the Mestel disk is that the outer disk border is equal to infinity. For massive bodies such as terrestrial and giant planets, the agreement of the analytical approaches is progressively poorer because of the changes in the disk structure that are induced by the planet gravity. For giant planets the precession rate changes sign and is higher than the modulus of the theoretical value by a factor ranging from 1.5 to 1.8. In this case, the correction of the formula proposed by Ward (1981) to
NASA Astrophysics Data System (ADS)
Feng, Z. Q.; Chen, Y. X.; Wu, G. L.; Yang, Y. Q.
2015-08-01
Surface mechanical grinding of a Ni-based superalloy can introduce a gradient microstructure in the surface layer with a grain size from nanoscale to microscale. In-depth investigation of the crystal orientation distribution of the surface nanostructured layer is more often, however, not an easy work by using the scanning electron microscope (SEM) based electron backscatter diffraction (EBSD) method due to its sensitivity to lattice distortions and spatial resolution limitation. Here we use a newly developed precession electron diffraction (PED) technique coupled with transmission electron microscopy (TEM) to investigate the microstructural and crystallographic characteristics of the surface gradient nanostructure, with particular emphasis on the topmost nanocrystalline layer. A strong shear texture and a minor Copper texture were identified according to orientation analyses of the 1.6 pm thick near-surface nanocrystalline layer. The PED technique is proved to be practical for two dimensional orientation mapping of severely deformed microstructures at the nanoscale.
Physiological and Functional Magnetic Resonance Imaging Using Balanced Steady-state Free Precession
Han, Paul Kyu; Choi, Seung Hong
2015-01-01
Balanced steady-state free precession (bSSFP) is a highly efficient pulse sequence that is known to provide the highest signal-to-noise ratio per unit time. Recently, bSSFP is getting increasingly popular in both the research and clinical communities. This review will be focusing on the application of the bSSFP technique in the context of probing the physiological and functional information. In the first part of this review, the basic principles of bSSFP are briefly covered. Afterwards, recent developments related to the application of bSSFP, in terms of physiological and functional imaging, are introduced and reviewed. Despite its long development history, bSSFP is still a promising technique that has many potential benefits for obtaining high-resolution physiological and functional images. PMID:25995684
Topological currents in neutron stars: kicks, precession, toroidal fields, and magnetic helicity
Charbonneau, James; Zhitnitsky, Ariel E-mail: arz@phas.ubc.ca
2010-08-01
The effects of anomalies in high density QCD are striking. We consider a direct application of one of these effects, namely topological currents, on the physics of neutron stars. All the elements required for topological currents are present in neutron stars: degenerate matter, large magnetic fields, and parity violating processes. These conditions lead to the creation of vector currents capable of carrying momentum and inducing magnetic fields. We estimate the size of these currents for many representative states of dense matter in the neutron star and argue that they could be responsible for the large proper motion of neutron stars (kicks), the toroidal magnetic field and finite magnetic helicity needed for stability of the poloidal field, and the resolution of the conflict between type-II superconductivity and precession. Though these observational effects appear unrelated, they likely originate from the same physics — they are all P-odd phenomena that stem from a topological current generated by parity violation.
SPIN-PRECESSION: BREAKING THE BLACK HOLE-NEUTRON STAR DEGENERACY
Chatziioannou, Katerina; Cornish, Neil; Klein, Antoine; Yunes, Nicolás
2015-01-01
Mergers of compact stellar remnants are prime targets for the LIGO/Virgo gravitational wave detectors. The gravitational wave signals from these merger events can be used to study the mass and spin distribution of stellar remnants, and provide information about black hole horizons and the material properties of neutron stars. However, it has been suggested that degeneracies in the way that the star's mass and spin are imprinted in the waveforms may make it impossible to distinguish between black holes and neutron stars. Here we show that the precession of the orbital plane due to spin-orbit coupling breaks the mass-spin degeneracy, and allows us to distinguish between standard neutron stars and alternative possibilities, such as black holes or exotic neutron stars with large masses and spins.
Confinement and precession of vortex pairs in coherently coupled Bose-Einstein condensates
NASA Astrophysics Data System (ADS)
Tylutki, Marek; Pitaevskii, Lev P.; Recati, Alessio; Stringari, Sandro
2016-04-01
The dynamic behavior of vortex pairs in two-component coherently (Rabi) coupled Bose-Einstein condensates is investigated in the presence of harmonic trapping. We discuss the role of the surface tension associated with the domain wall connecting two vortices in condensates of atoms occupying different spin states and its effect on the precession of the vortex pair. The results, based on the numerical solution of the Gross-Pitaevskii equations, are compared with the predictions of an analytical macroscopic model and are discussed as a function of the size of the pair, the Rabi coupling, and the intercomponent interaction. We show that the increase of the Rabi coupling results in the disintegration of the domain wall into smaller pieces, connecting vortices of newly created vortex pairs. The resulting scenario is the analog of quark confinement and string breaking in quantum chromodynamics.
Conductance dips and spin precession in a nonuniform waveguide with spin–orbit coupling
Malyshev, A. I. Kozulin, A. S.
2015-07-15
An infinite waveguide with a nonuniformity, a segment of finite length with spin–orbit coupling, is considered in the case when the Rashba and Dresselhaus parameters are identical. Analytical expressions have been derived in the single-mode approximation for the conductance of the system for an arbitrary initial spin state. Based on numerical calculations with several size quantization modes, we have detected and described the conductance dips arising when the waves are localized in the nonuniformity due to the formation of an effective potential well in it. We show that allowance for the evanescent modes under carrier spin precession in an effective magnetic field does not lead to a change in the direction of the average spin vector at the output of the system.
Light-induced collective pseudospin precession resonating with Higgs mode in a superconductor.
Matsunaga, Ryusuke; Tsuji, Naoto; Fujita, Hiroyuki; Sugioka, Arata; Makise, Kazumasa; Uzawa, Yoshinori; Terai, Hirotaka; Wang, Zhen; Aoki, Hideo; Shimano, Ryo
2014-09-01
Superconductors host collective modes that can be manipulated with light. We show that a strong terahertz light field can induce oscillations of the superconducting order parameter in NbN with twice the frequency of the terahertz field. The result can be captured as a collective precession of Anderson's pseudospins in ac driving fields. A resonance between the field and the Higgs amplitude mode of the superconductor then results in large terahertz third-harmonic generation. The method we present here paves a way toward nonlinear quantum optics in superconductors with driving the pseudospins collectively and can be potentially extended to exotic superconductors for shedding light on the character of order parameters and their coupling to other degrees of freedom.
Physiological and Functional Magnetic Resonance Imaging Using Balanced Steady-state Free Precession.
Park, Sung-Hong; Han, Paul Kyu; Choi, Seung Hong
2015-01-01
Balanced steady-state free precession (bSSFP) is a highly efficient pulse sequence that is known to provide the highest signal-to-noise ratio per unit time. Recently, bSSFP is getting increasingly popular in both the research and clinical communities. This review will be focusing on the application of the bSSFP technique in the context of probing the physiological and functional information. In the first part of this review, the basic principles of bSSFP are briefly covered. Afterwards, recent developments related to the application of bSSFP, in terms of physiological and functional imaging, are introduced and reviewed. Despite its long development history, bSSFP is still a promising technique that has many potential benefits for obtaining high-resolution physiological and functional images.
NASA Astrophysics Data System (ADS)
Shchigolev, V. K.
2015-12-01
We propose a new approach in studying the planetary orbits and the perihelion precession in General Relativity by means of the Homotopy Perturbation Method (HPM).For this purpose, we give a brief review of the nonlinear geodesic equations in the spherical symmetry spacetime which are to be studied in our work. On the basis of the main idea of HPM, we construct the appropriate homotopy what leads to the problem of solving the set of linear equations. First of all, we consider the simple example of the Schwarzschild metric for which the approximate geodesics solutions are known, in order to compare the HPM solution for orbits with those obtained earlier. Moreover, we obtain an approximate HPM solution for the Reissner-Nordstorm spacetime of a charged star.
NASA Astrophysics Data System (ADS)
Mizukami, S.; Sugihara, A.; Iihama, S.; Sasaki, Y.; Suzuki, K. Z.; Miyazaki, T.
2016-01-01
Laser-induced magnetization precessional dynamics was investigated in epitaxial films of Mn3Ge, which is a tetragonal Heusler-like nearly compensated ferrimagnet. The ferromagnetic resonance (FMR) mode was observed, the precession frequency for which exceeded 0.5 THz and originated from the large magnetic anisotropy field of approximately 200 kOe for this ferrimagnet. The effective damping constant was approximately 0.03. The corresponding effective Landau-Lifshitz constant is approximately 60 Mrad/s and is comparable with those of the similar Mn-Ga materials. The physical mechanisms for the Gilbert damping and for the laser-induced excitation of the FMR mode were also discussed in terms of the spin-orbit-induced damping and the laser-induced ultrafast modulation of the magnetic anisotropy, respectively.
Nutation and precession control of the High Energy Solar Physics (HESP) satellite
NASA Technical Reports Server (NTRS)
Jayaraman, C. P.; Robertson, B. P.
1993-01-01
The High Energy Solar Physics (HESP) spacecraft is an intermediate class satellite proposed by NASA to study solar high-energy phenomena during the next cycle of high solar activity in the 1998 to 2005 time frame. The HESP spacecraft is a spinning satellite which points to the sun with stringent pointing requirements. The natural dynamics of a spinning satellite includes an undesirable effect: nutation, which is due to the presence of disturbances and offsets of the spin axis from the angular momentum vector. The proposed Attitude Control System (ACS) attenuates nutation with reaction wheels. Precessing the spacecraft to track the sun in the north-south and east-west directions is accomplished with the use of torques from magnetic torquer bars. In this paper, the basic dynamics of a spinning spacecraft are derived, control algorithms to meet HESP science requirements are discussed and simulation results to demonstrate feasibility of the ACS concept are presented.
Emergence of electromotive force in precession-less rigid motion of deformed domain wall
NASA Astrophysics Data System (ADS)
Farajollahpour, Tohid; Darmiani, Narges; Phirouznia, Arash
2016-08-01
Recently it has been recognized that the electromotive force (emf) can be induced just by the spin precession where the generation of the electromotive force has been considered as a real-space topological pumping effect. It has been shown that the amount of the electromotive force is independent of the functionality of the localized moments. It was also demonstrated that the rigid domain wall (DW) motion cannot generate electromotive force in the system. Based on real-space topological pumping approach in the current study we show that the electromotive force can be induced by rigid motion of a deformed DW. We also demonstrate that the generated electromotive force strongly depends on the DW bulging. Meanwhile results show that the DW bulging leads to generation of the electromotive force both along the axis of the DW motion and normal to the direction of motion.
NASA Astrophysics Data System (ADS)
Borzdov, G. N.
2016-06-01
The fundamental solution of the Dirac equation for an electron in an electromagnetic field with harmonic dependence on space-time coordinates is obtained. The field is composed of three standing plane harmonic waves with mutually orthogonal phase planes and the same frequency. Each standing wave consists of two eigenwaves with different complex amplitudes and opposite directions of propagation. The fundamental solution is obtained in the form of the projection operator defining the subspace of solutions to the Dirac equation. It is illustrated by the analysis of the ground state and the spin precession of the Dirac electron in the field of two counterpropagating plane waves with left and right circular polarizations. Interrelations between the fundamental solution and approximate partial solutions is discussed and a criterion for evaluating the accuracy of approximate solutions is suggested.
NASA Technical Reports Server (NTRS)
Zhu, S. Y.; Mueller, I. I.
1982-01-01
The effect of adopting definitive precession and equinox corrections on the terrestrial reference frame was investigated. It is noted that the effect on polar motion is a diurnal periodic term with an amplitude increasing linearly in time whole on UT1 it is a linear term: general principles are given to determine the effects of small rotations of the frame of a conventional inertial reference system (CIS) on the frame of the conventional terrestrial reference system (CTS); seven CTS options are presented, one of which is necessary to accommodate such rotation. Accommodating possible future changes in the astronomical nutation is discussed. The effects of differences which may exist between the various CTS's and CIS's on Earth rotation parameters (ERP) and how these differences can be determined are examined. It is shown that the CTS differences can be determined from observations made at the same site. The CIS differences by comparing the ERP's are determined by the different techniques during the same time period.
Kim, Steve M; Ganguli, Surya; Frank, Loren M
2012-08-22
Hippocampal place cells convey spatial information through a combination of spatially selective firing and theta phase precession. The way in which this information influences regions like the subiculum that receive input from the hippocampus remains unclear. The subiculum receives direct inputs from area CA1 of the hippocampus and sends divergent output projections to many other parts of the brain, so we examined the firing patterns of rat subicular neurons. We found a substantial transformation in the subicular code for space from sparse to dense firing rate representations along a proximal-distal anatomical gradient: neurons in the proximal subiculum are more similar to canonical, sparsely firing hippocampal place cells, whereas neurons in the distal subiculum have higher firing rates and more distributed spatial firing patterns. Using information theory, we found that the more distributed spatial representation in the subiculum carries, on average, more information about spatial location and context than the sparse spatial representation in CA1. Remarkably, despite the disparate firing rate properties of subicular neurons, we found that neurons at all proximal-distal locations exhibit robust theta phase precession, with similar spiking oscillation frequencies as neurons in area CA1. Our findings suggest that the subiculum is specialized to compress sparse hippocampal spatial codes into highly informative distributed codes suitable for efficient communication to other brain regions. Moreover, despite this substantial compression, the subiculum maintains finer scale temporal properties that may allow it to participate in oscillatory phase coding and spike timing-dependent plasticity in coordination with other regions of the hippocampal circuit.
Kim, Steve M.; Ganguli, Surya; Frank, Loren M.
2012-01-01
Hippocampal place cells convey spatial information through a combination of spatially-selective firing and theta phase precession. The way in which this information influences regions like the subiculum that receive input from the hippocampus remains unclear. The subiculum receives direct inputs from area CA1 of the hippocampus and sends divergent output projections to many other parts of the brain, so we examined the firing patterns of rat subicular neurons. We found a substantial transformation in the subicular code for space from sparse to dense firing rate representations along a proximal-distal anatomical gradient: neurons in the proximal subiculum are more similar to canonical, sparsely firing hippocampal place cells, whereas neurons in the distal subiculum have higher firing rates and more distributed spatial firing patterns. Using information theory, we found that the more distributed spatial representation in the subiculum carries, on average, more information about spatial location and context than the sparse spatial representation in CA1. Remarkably, despite the disparate firing rate properties of subicular neurons, we found that neurons at all proximal-distal locations exhibit robust theta phase precession, with similar spiking oscillation frequencies as neurons in area CA1. Our findings suggest that the subiculum is specialized to compress sparse hippocampal spatial codes into highly informative distributed codes suitable for efficient communication to other brain regions. Moreover, despite this substantial compression, the subiculum maintains finer scale temporal properties that may allow it to participate in oscillatory phase coding and spike timing-dependent plasticity in coordination with other regions of the hippocampal circuit. PMID:22915100
Constraining the String Gauge Field by Galaxy Rotation Curves and Perihelion Precession of Planets
NASA Astrophysics Data System (ADS)
Cheung, Yeuk-Kwan E.; Xu, Feng
2013-09-01
We discuss a cosmological model in which the string gauge field coupled universally to matter gives rise to an extra centripetal force and will have observable signatures on cosmological and astronomical observations. Several tests are performed using data including galaxy rotation curves of 22 spiral galaxies of varied luminosities and sizes and perihelion precessions of planets in the solar system. The rotation curves of the same group of galaxies are independently fit using a dark matter model with the generalized Navarro-Frenk-White (NFW) profile and the string model. A remarkable fit of galaxy rotation curves is achieved using the one-parameter string model as compared to the three-parameter dark matter model with the NFW profile. The average χ2 value of the NFW fit is 9% better than that of the string model at a price of two more free parameters. Furthermore, from the string model, we can give a dynamical explanation for the phenomenological Tully-Fisher relation. We are able to derive a relation between field strength, galaxy size, and luminosity, which can be verified with data from the 22 galaxies. To further test the hypothesis of the universal existence of the string gauge field, we apply our string model to the solar system. Constraint on the magnitude of the string field in the solar system is deduced from the current ranges for any anomalous perihelion precession of planets allowed by the latest observations. The field distribution resembles a dipole field originating from the Sun. The string field strength deduced from the solar system observations is of a similar magnitude as the field strength needed to sustain the rotational speed of the Sun inside the Milky Way. This hypothesis can be tested further by future observations with higher precision.
Precession of a two-layer Earth: contributions of the core and elasticity
NASA Astrophysics Data System (ADS)
Baenas, Tomás; Ferrándiz, José M.; Escapa, Alberto; Getino, Juan; Navarro, Juan F.
2016-04-01
The Earth's internal structure contributes to the precession rate in a small but non-negligible amount, given the current accuracy goals demanded by IAG/GGOS to the reference frames, namely 30 μas and 3 μas/yr. These contributions come from a variety of sources. One of those not yet accounted for in current IAU models is associated to the crossed effects of certain nutation-rising terms of a two-layer Earth model; intuitively, it gathers an 'indirect' effect of the core via the NDFW, or FCN, resonance as well as a 'direct' effect arising from terms that account for energy variations depending on the elasticity of the core. Similar order of magnitude reaches the direct effect of the departure of the Earth's rheology from linear elasticity. To compute those effects we work out the problem in a unified way within the Hamiltonian framework developed by Getino and Ferrándiz (2001). It allows a consistent treatment of the problem since all the perturbations are derived from the same tide generating expansion and the crossing effects are rigorously obtained through Hori's canonical perturbation method. The problem admits an asymptotic analytical solution. The Hamiltonian is constructed by considering a two-layer Earth model made up of an anelastic mantle and a fluid core, perturbed by the gravitational action of the Moon and the Sun. The former effects reach some tens of μas/yr in the longitude rate, hence above the target accuracy level. We outline their influence in the estimation of the Earth's dynamical ellipticity, a main parameter factorizing both precession and nutation.
CONSTRAINING THE STRING GAUGE FIELD BY GALAXY ROTATION CURVES AND PERIHELION PRECESSION OF PLANETS
Cheung, Yeuk-Kwan E.; Xu Feng
2013-09-01
We discuss a cosmological model in which the string gauge field coupled universally to matter gives rise to an extra centripetal force and will have observable signatures on cosmological and astronomical observations. Several tests are performed using data including galaxy rotation curves of 22 spiral galaxies of varied luminosities and sizes and perihelion precessions of planets in the solar system. The rotation curves of the same group of galaxies are independently fit using a dark matter model with the generalized Navarro-Frenk-White (NFW) profile and the string model. A remarkable fit of galaxy rotation curves is achieved using the one-parameter string model as compared to the three-parameter dark matter model with the NFW profile. The average {chi}{sup 2} value of the NFW fit is 9% better than that of the string model at a price of two more free parameters. Furthermore, from the string model, we can give a dynamical explanation for the phenomenological Tully-Fisher relation. We are able to derive a relation between field strength, galaxy size, and luminosity, which can be verified with data from the 22 galaxies. To further test the hypothesis of the universal existence of the string gauge field, we apply our string model to the solar system. Constraint on the magnitude of the string field in the solar system is deduced from the current ranges for any anomalous perihelion precession of planets allowed by the latest observations. The field distribution resembles a dipole field originating from the Sun. The string field strength deduced from the solar system observations is of a similar magnitude as the field strength needed to sustain the rotational speed of the Sun inside the Milky Way. This hypothesis can be tested further by future observations with higher precision.
Precessão do jato de 3C120: simulações hidrodinâmicas 3D
NASA Astrophysics Data System (ADS)
Caproni, A.; de Gouveia dal Pino, E. M.; Abraham, Z.; Raga, A. C.
2003-08-01
Observações com técnicas de interferometria com longa linha de base têm mostrado a existência de um jato relativístico com componentes superluminais na região central de 3C 120. Estas componentes são ejetadas em distintas direções no plano do céu e com diferentes velocidades aparentes. Estas características foram interpretadas em trabalhos anteriores como efeitos da precessão do jato relativístico. Neste trabalho, realizamos simulações tri-dimensionais do jato de 3C 120 utilizando os parâmetros de precessão determinados em trabalhos anteriores e variando as características iniciais do jato e meio ambiente, tais como densidade numérica e temperatura. Todas as simulações foram feitas com o código hidrodinâmico YGUAZÚ-A, assumindo-se um jato adiabático descrito por uma equação de estado relativística. Pelo fato de estarmos utilizando um código hidrodinâmico, nós assumimos que a intensidade do campo magnético e a distribuição de partículas, necessários para se calcular a emissão sincrotron, são proporcionais à pressão hidrodinâmica. Comparação entre dois cenários distintos, nos quais o material do jato é ejetado com velocidade constante (jato contínuo) e com velocidade modulada por um padrão sinusoidal no tempo (jato intermitente), é apresentada e discutida. Para jatos que apresentam fenômenos de precessão e intermitência, com amplitude de variação na velocidade de injeção maior que dez por cento da velocidade média de injeção, a hipótese balística, controlada pela intermitencia, é mais provável. Por outro lado, para jatos com precessão mas sem intermitência (ou com amplitude de variabilidade em velocidade mais baixa que no caso anterior), o efeito da precessão na morfologia do jato não é desprezível. Portanto, de um modo geral, ambos efeitos (precessão e movimentos balísticos) devem estar concorrendo para afetar a morfologia dos jatos superluminais.
Lense-Thirring precession in neutron-star low-mass X-ray binaries
NASA Astrophysics Data System (ADS)
Homan, Jeroen
Quasi-periodic oscillations (QPOs) with low frequencies (0.01-70 Hz) have been observed in the X-ray light curves of most neutron-star and black-hole low-mass X-ray binaries. Despite having been discovered more than 25 years ago, their origin is still not well understood. Similarities between the low-frequency QPOs in the two types of systems suggest that they have a common origin in the accretion flows around black holes and neutron stars. Some of the proposed models that attempt to explain low- frequency QPOs invoke a General Relativistic effect known as Lense-Thirring precession (or "frame dragging"). However, for Lense-Thirring precession to produce substantial modulations of the X-ray flux through relativistic beaming and gravitational lensing, the rotation axis of the inner part of the accretion disk needs to have a substantial tilt (10-20 degrees) with respect to the spin axis of the compact object. We argue that observational evidence for such titled inner accretion disks can be found in the variability of neutron- star low-mass X-ray binaries that are viewed at inclination angles of 60-80 degrees. In these systems low-frequency QPOs at ~0.1-15 Hz are observed that modulate the emission from the neutron star by quasi-periodic obscuration, presumably by a titled inner disc. The goal of our proposed program is to test whether the frequency evolution and spectral state dependence of these QPOs is similar to what is observed for the low-frequency QPOs that are observed in lower-inclination neutron-star X-ray binaries. To make such a comparison, we need to better characterize the properties and behavior of these QPOs. Our study will make use of almost 1300 RXTE observations of 11 sources, totaling 5.7 Ms of data. Signatures of strong gravity have long been sought after in accreting compact objects. While strong evidence from spectral features has emerged in the last decade (e.g. gravitationally broadened iron emission lines), there have only been hints of such
Detection of jet precession in the active nucleus of M 81
NASA Astrophysics Data System (ADS)
Martí-Vidal, I.; Marcaide, J. M.; Alberdi, A.; Pérez-Torres, M. A.; Ros, E.; Guirado, J. C.
2011-09-01
We report on very-long-baseline-interferometry (VLBI) monitoring observations of the low-luminosity active galactic nucleus (LLAGN) in the galaxy M 81 at the frequencies of 1.7, 2.3, 5.0, and 8.4 GHz. The observations reported here are phase-referenced to the supernova SN 1993J (located in the same galaxy) and cover from late 1993 to late 2005. The large amount of available observations allows us to study the stability of the AGN position in the frame of its host galaxy at different frequencies and chromatic effects in the jet morphology, together with their time evolution. The source consists at all frequencies of a slightly resolved core and a small jet extension towards the northeast direction (position angle of ~65 degrees) in agreement with previous publications. We find that the position of the intensity peak in the images at 8.4 GHz is very stable in the galactic frame of M 81 (proper motion upper limit about 10 μas per year). We confirm previous reports that the peaks at all frequencies are systematically shifted among them, possibly due to opacity effects in the jet as predicted by the standard relativistic jet model. We use this model, under plausible assumptions, to estimate the magnetic field in the jet close to the jet base and the mass of the central black hole. We obtain a black-hole mass of ~2 × 107 M⊙, comparable to estimates previously reported using different approaches, but the magnetic fields obtained are 103-104 times lower than previous estimates. We find that the positions of the cores at 1.7, 2.3, and 5.0 GHz are less stable than that at 8.4 GHz and evolve systematically, shifting southward at a rate of several tens of μas per year. The evolution in the jet orientation seems to be related to changes in the inclination of the cores at all frequencies. These results can be interpreted as due to a precessing jet. The evolving jet orientation also seems to be related to a flare in the peak flux densities at 5.0 and 8.4 GHz, which lasts ~4
NASA Astrophysics Data System (ADS)
Khodri, Myriam; Cane, Mark A.; Kukla, George; Gavin, Joyce; Braconnot, Pascale
2005-07-01
Three sensitivity experiments using an Ocean Atmosphere General Circulation Model (OAGCM) are conducted to simulate the climate impact of precession. The relative contributions of components of the hydrological cycle including the albedo of Arctic sea ice, advection of atmospheric water vapor and sea surface temperature to the summer Arctic melt process are evaluated. Timing of the perihelion is varied in each experiment with meteorological spring (SP), winter (WP) and autumn (AP) perihelion corresponding to conditions at 110, 115 and 120 ky BP, respectively. Obliquity is unchanged at the 115 ky level which is lower than today. The experiments are assessed relative to the present day control, which has been shown to simulate current conditions based on observations. In the SP experiment, top of the atmosphere (TOA) insolation is weaker than today between the summer solstice and autumnal equinox. In the AP case representing the interglacial, it is less intense between vernal equinox and summer solstice but stronger during the remainder of the year. Although the incident solar radiation is reduced in summer in the SP experiment, increased melting of snow is found primarily as a result of feedbacks from the delayed seasonal cycle of hydrologic components. This is in contrast to both the WP and AP cases in which the perennial snow cover is simulated. At the time of the last glacial inception, 115 ky BP, the WP experiment shows lower insolation to the high northern latitudes in late spring and summer mainly as a result of lower obliquity than today. Dynamical ocean-atmosphere interactions in response to precession maintain the reduced sea ice melting in late spring, strengthen the annual equator-to-pole sea surface temperature (SST) gradient and increase atmospheric moisture convergence in glaciation-sensitive regions. In both the WP and AP experiments seasonal sea ice melting is weakened resulting in pronounced outgoing radiative flux at the locations of expanded sea
Possible interpretation of the precession of comet 67P/Churyumov-Gerasimenko
NASA Astrophysics Data System (ADS)
Gutiérrez, P. J.; Jorda, L.; Gaskell, R. W.; Davidsson, B. J. R.; Capanna, C.; Hviid, S. F.; Keller, H. U.; Maquet, L.; Mottola, S.; Preusker, F.; Scholten, F.; Lara, L. M.; Moreno, F.; Rodrigo, R.; Sierks, H.; Barbieri, C.; Lamy, P.; Koschny, D.; Rickman, H.; Agarwal, J.; A'Hearn, M. F.; Auger, A. T.; Barucci, M. A.; Bertaux, J. L.; Bertini, I.; Cremonese, G.; Da Deppo, V.; Debei, S.; De Cecco, M.; El-Maarry, M. R.; Fornasier, S.; Fulle, M.; Groussin, O.; Gutiérrez-Marques, P.; Güttler, C.; Ip, W. H.; Knollenberg, J.; Kramm, J. R.; Kührt, E.; Küppers, M.; La Forgia, F.; Lazzarin, M.; López-Moreno, J. J.; Magrin, S.; Marchi, S.; Marzari, F.; Naletto, G.; Oklay, N.; Pajola, M.; Pommerol, A.; Sabau, D.; Thomas, N.; Toth, I.; Tubiana, C.; Vincent, J. B.
2016-05-01
Context. Data derived from the reconstruction of the nucleus shape of comet 67P/Churyumov-Gerasimenko (67P) from images of the OSIRIS camera onboard ROSETTA show evidence that the nucleus rotates in complex mode. First, the orientation of the spin axis is not fixed in an inertial reference frame, which suggests a precessing motion around the angular momentum vector with a periodicity of approximately 257 h ± 12 h.Second, periodograms of the right ascension and declination (RA/Dec) coordinates of the body-frame Z axis show a very significant (higher than 99.99%) periodicity at 276 h ± 12 h, different from the rotational period of 12.40 h as previously determined from light-curve analysis. Aims: The main goal is to interpret the data and associated periodicities of the spin axis orientation in space. Methods: We analyzed the spin axis orientation in space and associated periodicities and compared them with solutions of Euler equations under the assumption that the body rotates in torque-free conditions. Statistical tests comparing the observationally derived spin axis orientation with the outcome from simulations were applied to determine the most likely inertia moments, excitation level, and periods. Results: Under the assumption that the body is solid-rigid and rotates in torque-free conditions, the most likely interpretation is that 67P is spinning around the principal axis with the highest inertia moment with a period of about 13 h. At the same time, the comet precesses around the angular momentum vector with a period of about 6.35 h. While the rotating period of such a body would be about 12.4 h, RA/Dec coordinates of the spin axis would have a periodicity of about 270 h as a result of the combination of the two aforementioned motions. Conclusions: The most direct and simple interpretation of the complex rotation of 67P requires a ratio of inertia moments significantly higher than that of a homogeneous body.
NASA Astrophysics Data System (ADS)
Howarth, Ian D.
2016-04-01
Published photometry of fading events in the PTFO8-8695 system is modelled using improved treatments of stellar geometry, surface intensities, and, particularly, gravity darkening, with a view to testing the planetary-transit hypothesis. Variability in the morphology of fading events can be reproduced by adopting convective-envelope gravity darkening, but near-critical stellar rotation is required. This leads to inconsistencies with spectroscopic observations; the model also predicts substantial photometric variability associated with stellar precession, contrary to observations. Furthermore, the empirical ratio of orbital to rotational angular momenta is at odds with physically plausible values. An exoplanet transiting a precessing, gravity-darkened star may not be the correct explanation of periodic fading events in this system.
NASA Astrophysics Data System (ADS)
Li, Hang; Zhang, Xinhui; Liu, Xinyu; Furdyna, Jacek K.
2015-11-01
Ultrafast laser-triggered coherent magnetization dynamics in ferromagnetic (Ga,Mn)As films have been investigated by time-resolved magneto-optical spectroscopy. Dynamic phase reversal in the magnetic precession process is observed when the ambient temperature or the external magnetic field is varied. This phenomenon is found to be sensitive to the spontaneous magnetization orientation, and is attributed to the giant magnetic linear dichroism (MLD) effect in (Ga,Mn)As. Our findings suggest that this effect will enable the sensitive measurement of the dynamic phase of in-plane magnetization precession on picosecond time scale in the collective spin excitation in (Ga,Mn)As, thus enabling efficient and ultrafast magneto-optical detection for magnetization dynamics in ferromagnetic semiconductor-based spintronic devices.
NASA Astrophysics Data System (ADS)
Husar, Ladislav
2013-01-01
The article analyzes the precession-nutation variations in right ascension of stars after the introduction Celestial Intermediate Origin (CIO) as a new origin of the right ascensions. It points out that changes in right ascension depend not only on the motion of the origin, but also on the changes of the pole and hour circles, depending on the position of stars. This explains the apparent paradox that, for certain groups of stars, despite the almost complete elimination of the precession and nutation motion of the CIO on the equator, the magnitude of the variations in right ascension related to the CIO can exceed the magnitude of the classic variations referred to the equinox.
Nakajima, M; Namai, A; Ohkoshi, S; Suemoto, T
2010-08-16
We report the first observation of sub-terahertz bulk-magnetization precession, using terahertz time-domain spectroscopy. The magnetization precession in gallium-substituted epsilon-iron oxide nano-ferromagnets under zero magnetic field is induced by the impulsive magnetic field of the THz wave through the gyromagnetic effect. Just at the resonance frequency, the linear to circular polarized wave conversion is realized. This is understood as the free induction decay signal radiated from a rotating magnetic dipole corresponding to the natural resonance. Furthermore, this demonstration reveals that the series of gallium-substituted epsilon-iron oxide nano-ferromagnets is very prospective for magneto-optic devices, which work at room temperature without external magnetic field, in next-generation wireless communication.
NASA Astrophysics Data System (ADS)
Schempp, Walter J.
2013-09-01
Based on projective geometry, a quantum holographic approach to the orbiton / spinon dynamics of quantum blackholography and clinical magnetic resonance tomography is mathematically described. Crucial applications of the conformal steady-state free-precession modality and automorphic scattering theory are the evidence for a supermassive central black hole in the Milky Way galaxy and the modalities of clinical cardiovascular magnetic resonance tomography and diffusion weighted magnetic resonance tomography of non-invasive radiological diagnostics.
Use of the 'Precessions' process for prepolishing and correcting 2D & 2(1/2)D form.
Walker, David D; Freeman, Richard; Morton, Roger; McCavana, Gerry; Beaucamp, Anthony
2006-11-27
The Precessions process polishes complex surfaces from the ground state preserving the ground-in form, and subsequently rectifies measured form errors. Our first paper introduced the technology and focused on the novel tooling. In this paper we describe the unique CNC machine tools and how they operate in polishing and correcting form. Experimental results demonstrate both the '2D' and '2(1/2)D' form-correction modes, as applied to aspheres with rotationally-symmetric target-form.
Yung, Bosco H. K.; Nakashima, Jun-ichi; Kwok, Sun; Imai, Hiroshi; Deguchi, Shuji; Diamond, Philip J.
2011-11-10
We report the results of multi-epoch Very Long Baseline Array observations of the 22.2 GHz H{sub 2}O maser emission associated with the 'water fountain' IRAS 18286-0959. We suggest that this object is the second example of a highly collimated bipolar precessing outflow traced by H{sub 2}O maser emission, the other is W 43A. The detected H{sub 2}O emission peaks are distributed over a velocity range from -50 km s{sup -1} to 150 km s{sup -1}. The spatial distribution of over 70% of the identified maser features is found to be highly collimated along a spiral jet (jet 1) extended southeast to northwest; the remaining features appear to trace another spiral jet (jet 2) with a different orientation. The two jets form a 'double-helix' pattern which lies across {approx}200 mas. The maser distribution is reasonably fit by a model consisting of two bipolar precessing jets. The three-dimensional velocities of jet 1 and jet 2 are derived to be 138 km s{sup -1} and 99 km s{sup -1}, respectively. The precession period of jet 1 is about 56 years. For jet 2, three possible models are tested and they give different values for the kinematic parameters. We propose that the appearance of two jets is the result of a single driving source with significant proper motion.
Goulon, Jośe; Rogalev, Andrei; Goujon, Gérard; Wilhelm, Fabrice; Ben Youssef, Jamal; Gros, Claude; Barbe, Jean-Michel; Guilard, Roger
2011-01-01
X-ray Detected Magnetic Resonance (XDMR) is a novel spectroscopy in which X-ray Magnetic Circular Dichroism (XMCD) is used to probe the resonant precession of local magnetization components in a strong microwave pump field. We review the conceptual bases of XDMR and recast them in the general framework of the linear and nonlinear theories of ferromagnetic resonance (FMR). Emphasis is laid on the information content of XDMR spectra which offer a unique opportunity to disentangle the precession dynamics of spin and orbital magnetization components at given absorbing sites. For the sake of illustration, we focus on selected examples in which marked differences were found between FMR and XDMR spectra simultaneously recorded on ferrimagnetically ordered iron garnets. With pumping capabilities extended up to sub-THz frequencies, high-field XDMR should allow us to probe the precession of orbital magnetization components in paramagnetic organometallic complexes with large zero-field splitting. Even more challenging, we suggest that XDMR spectra might be recorded on selected antiferromagnetic crystals for which orbital magnetism is most often ignored in the absence of any supporting experimental evidence. PMID:22272105
2012-01-01
Hydrophobic helical peptides interact with lipid bilayers in various modes, determined by the match between the length of the helix’s hydrophobic core and the thickness of the hydrocarbon region of the bilayer. For example, long helices may tilt with respect to the membrane normal to bury their hydrophobic cores in the membrane, and the lipid bilayer may stretch to match the helix length. Recent molecular dynamics simulations and potential of mean force calculations have shown that some TM helices whose lengths are equal to, or even shorter than, the bilayer thickness may also tilt. The tilt is driven by a gain in the helix precession entropy, which compensates for the free energy penalty resulting from membrane deformation. Using this free energy balance, we derived theoretically an equation of state, describing the dependence of the tilt on the helix length and membrane thickness. To this end, we conducted coarse-grained Monte Carlo simulations of the interaction of helices of various lengths with lipid bilayers of various thicknesses, reproducing and expanding the previous molecular dynamics simulations. Insight from the simulations facilitated the derivation of the theoretical model. The tilt angles calculated using the theoretical model agree well with our simulations and with previous calculations and measurements. PMID:24932138
Laboratory Simulation of the Effect of Rocket Thrust on a Precessing Space Vehicle
NASA Technical Reports Server (NTRS)
Alvarez, Oscar; Bausley, Henry; Cohen, Sam; Falcon-Martin, Miguel; Furumoto, Gary (Editor); Horio, Asikin; Levitt, David; Walsh, Amy
1990-01-01
Ground tests of solid propellant rocket motors have shown that metal-containing propellants produce various amounts of slag (primarily aluminum oxide) which is trapped in the motor case, causing a loss of specific impulse. Although not yet definitely established, the presence of a liquid pool of slag also may contribute to nutational instabilities that have been observed with certain spin-stabilized, upper-stage vehicles. Because of the rocket's axial acceleration, absent in the ground tests, estimates of in-flight slag mass have been very uncertain. Yet such estimates are needed to determine the magnitude of the control authority of the systems required for eliminating the instability. A test rig with an eccentrically mounted hemispherical bowl was designed and built which incorporates a follower force that properly aligns the thrust vector along the axis of spin. A program that computes the motion of a point mass in the spinning and precessing bowl was written. Using various RPMs, friction factors, and initial starting conditions, plots were generated showing the trace of the point mass around the inside of the fuel tank. The apparatus will incorporate future design features such as a variable nutation angle and a film height measuring instrument. Data obtained on the nutational instability characteristics will be used to determine order of magnitude estimates of control authority needed to minimize the sloshing effect.
Bär, Sébastien; Weigel, Matthias; von Elverfeldt, Dominik; Hennig, Jürgen; Leupold, Jochen
2015-11-01
The purpose of this work was to analyze the intrinsic diffusion sensitivity of the balanced steady-state free precession (bSSFP) imaging sequence, meaning the observation of diffusion-induced attenuation of the bSSFP steady-state signal due to the imaging gradients. Although these diffusion effects are usually neglected for most clinical gradient systems, such strong gradient systems are employed for high resolution imaging of small animals or MR Microscopy. The impact on the bSSFP signal of the imaging gradients characterized by their b-values was analyzed with simulations and experiments at a 7T animal scanner using a gradient system with maximum gradient amplitude of approx. 700 mT/m. It was found that the readout gradients have a stronger impact on the attenuation than the phase encoding gradients. Also, as the PE gradients are varying with each repetition interval, the diffusion effects induce strong modulations of the bSSFP signal over the sequence repetition cycles depending on the phase encoding gradient table. It is shown that a signal gain can be obtained through a change of flip angle as a new optimal flip angle maximizing the signal can be defined. The dependency of the diffusion effects on relaxation times and b-values were explored with simulations. The attenuation increases with T2. In conclusion, diffusion attenuation of the bSSFP signal becomes significant for high resolution imaging voxel size (roughly < 100 μm) of long T2 substances.
Fast and accurate inference on gravitational waves from precessing compact binaries
NASA Astrophysics Data System (ADS)
Smith, Rory; Field, Scott E.; Blackburn, Kent; Haster, Carl-Johan; Pürrer, Michael; Raymond, Vivien; Schmidt, Patricia
2016-08-01
Inferring astrophysical information from gravitational waves emitted by compact binaries is one of the key science goals of gravitational-wave astronomy. In order to reach the full scientific potential of gravitational-wave experiments, we require techniques to mitigate the cost of Bayesian inference, especially as gravitational-wave signal models and analyses become increasingly sophisticated and detailed. Reduced-order models (ROMs) of gravitational waveforms can significantly reduce the computational cost of inference by removing redundant computations. In this paper, we construct the first reduced-order models of gravitational-wave signals that include the effects of spin precession, inspiral, merger, and ringdown in compact object binaries and that are valid for component masses describing binary neutron star, binary black hole, and mixed binary systems. This work utilizes the waveform model known as "IMRPhenomPv2." Our ROM enables the use of a fast reduced-order quadrature (ROQ) integration rule which allows us to approximate Bayesian probability density functions at a greatly reduced computational cost. We find that the ROQ rule can be used to speed-up inference by factors as high as 300 without introducing systematic bias. This corresponds to a reduction in computational time from around half a year to half a day for the longest duration and lowest mass signals. The ROM and ROQ rules are available with the main inference library of the LIGO Scientific Collaboration, LALInference.
Precessing jets in Sagittarius A - Gas dynamics in the central parsec of the galaxy
NASA Astrophysics Data System (ADS)
Brown, R. L.
1982-11-01
The maps of 12.8 micrometer Ne II fine-structure line emission from the galactic center presented by Lacy et al. (1979, 1980) demonstrate that the ionized gas within the central parsec of the galaxy is moving in a highly supersonic manner. Lacy et al. (1980) concluded that the ionized gas was dynamically in circular rotation about the galactic center in a disklike configuration. The high resolution Very Large Array (VLA) map of the galactic center obtained by Brown et al. (1981) provides also information concerning the low surface brightness emission. This emission suggests a different interpretation for the dynamics of the ionized gas at the galactic center. Specifically, the radio contours exhibit an S-shaped symmetry about the galactic center that is one important signature of a precessing twin-nozzle jet such as has been proposed to explain the radio structure of NGC 315 and NGC 326. The present investigation is concerned with an interpretation of the radio structure of the galactic center on the basis of such a twin-jet model.
Investigating relativity using lunar laser ranging - Geodetic precession and the Nordtvedt effect
NASA Technical Reports Server (NTRS)
Dickey, J. O.; Newhall, X. X.; Williams, J. G.
1989-01-01
The emplacement of retroreflectors on the moon by Apollo astronauts and the Russian Lunakhod spacecraft marked the inception of lunar laser ranging (LLR) and provided a natural laboratory for the study of general relativity. Continuing acquisition of increasingly accurate LLR data has provided enhanced sensitivity to general relativity parameters. Two relativistic effects are investigated in this paper: (1) the Nordtvedt effect, yielding a test of the strong equivalence principle, would appear as a distortion of the geocentric lunar orbit in the direction of the sun. The inclusion of recent LLR data limits the size of any such effect to 3 + or - 4 cm. The sensitivities to the various PPN quantities are also highlighted. (2) the geodetic precession of the lunar perigee is predicted by general relativity as a consequence of the motion of the earth-moon system about the sun; its theoretical magnitude is 19.2 mas/yr. Analysis presented here confirms this value and determines this quality to a 2 percent level.
Corrective finishing of extreme ultraviolet photomask blanks by precessed bonnet polisher.
Beaucamp, Anthony; Namba, Yoshiharu; Charlton, Phillip
2014-05-10
The progressive transition from Excimer to extreme ultraviolet (EUV) lithography is driving a need for flatter and smoother photomask blanks. It is, however, proving difficult to meet the next-generation specification with the conventional chemical mechanical polishing technology commonly used for finishing photomask blanks. This paper reports on the application of subaperture computer numerical control precessed bonnet polishing technology to the corrective finishing of photomask substrates for EUV lithography. Full-factorial analysis was used to identify process parameters capable of delivering microroughness below 0.5 nm rms while retaining relatively high removal rates. Experimental results show that masks prepolished to 300-600 nm peak-to-valley (P-V) flatness by chemical/mechanical polishing can then be improved down to 50-100 nm P-V flatness using the automated technology described in this paper. A series of edge polishing experiments also hints at the possibility of increasing the quality area beyond the 142 mm square defined in the official EUV photomask specification. PMID:24922029
NASA Astrophysics Data System (ADS)
Belyanin, S.; Gurfil, P.
2009-03-01
Previous studies of geosynchronous orbits indicated that the equinoctial precession (EP) of the Earth affects the long-term behavior of geosynchronous satellites for missions exceeding ten years. However, these studies did not include the lunisolar gravitation and tesseral resonance. In the present study, a model that includes the latter effects is developed. In particular, it is shown that the EP affects motion in the vicinity of the stable and unstable geostationary points. This effect is pronounced in the vicinity of the unstable points, shifting the satellite away from the geosynchronous altitude. Moreover, it is shown that secular inclination growth on time scales of 10-20 years is induced by the EP. This requires additional stationkeeping maneuvers that may increase the overall fuel usage by about 1%. An additional contribution of the present study is an analysis of EP-perturbed orbits with free inclination drift. An optimal initial node location, minimizing the inclination drift, is calculated while taking into account the effect of the EP. It is shown that the classical optimal initial node locations are changed due to the effect of the EP. A maneuvering program in the presence of EP is developed. It is shown that the timing and number of stationkeeping maneuvers is affected by the EP. The models developed herein utilize non-singular orbital elements.
Driben, R.; Konotop, V. V.; Meier, T.
2016-01-01
Nonlinearity is the driving force for numerous important effects in nature typically showing transitions between different regimes, regular, chaotic or catastrophic behavior. Localized nonlinear modes have been the focus of intense research in areas such as fluid and gas dynamics, photonics, atomic and solid state physics etc. Due to the richness of the behavior of nonlinear systems and due to the severe numerical demands of accurate three-dimensional (3D) numerical simulations presently only little knowledge is available on the dynamics of complex nonlinear modes in 3D. Here, we investigate the dynamics of 3D non-coaxial matter wave vortices that are trapped in a parabolic potential and interact via a repulsive nonlinearity. Our numerical simulations demonstrate the existence of an unexpected and fascinating nonlinear regime that starts immediately when the nonlinearity is switched-on and is characterized by a smooth dynamics representing torque-free precession with nutations. The reported motion is proven to be robust regarding various effects such as the number of particles, dissipation and trap deformations and thus should be observable in suitably designed experiments. Since our theoretical approach, i.e., coupled nonlinear Schrödinger equations, is quite generic, we expect that the obtained novel dynamical behavior should also exist in other nonlinear systems. PMID:26964759
NASA Astrophysics Data System (ADS)
Pachón, Leonardo A.; Rueda, Jorge A.; Valenzuela-Toledo, César A.
2012-09-01
Whether or not analytic exact vacuum (electrovacuum) solutions of the Einstein (Einstein-Maxwell) field equations can accurately describe the exterior space-time of compact stars still remains an interesting open question in relativistic astrophysics. As an attempt to establish their level of accuracy, the radii of the innermost stable circular orbits (ISCOs) of test particles given by analytic exterior space-time geometries have been compared with those given by numerical solutions for neutron stars (NSs) obeying a realistic equation of state (EOS). It has been so shown that the six-parametric solution of Pachón et al. (PRS) more accurately describes the NS ISCO radii than other analytic models do. We propose here an additional test of accuracy for analytic exterior geometries based on the comparison of orbital frequencies of neutral test particles. We compute the Keplerian, frame-dragging, and precession and oscillation frequencies of the radial and vertical motions of neutral test particles for the Kerr and PRS geometries and then compare them with the numerical values obtained by Morsink & Stella for realistic NSs. We identify the role of high-order multipole moments such as the mass quadrupole and current octupole in the determination of the orbital frequencies, especially in the rapid rotation regime. The results of this work are relevant to cast a separatrix between black hole and NS signatures and to probe the nuclear-matter EOS and NS parameters from the quasi-periodic oscillations observed in low-mass X-ray binaries.
Pachon, Leonardo A.; Rueda, Jorge A.; Valenzuela-Toledo, Cesar A. E-mail: jorge.rueda@icra.it
2012-09-01
Whether or not analytic exact vacuum (electrovacuum) solutions of the Einstein (Einstein-Maxwell) field equations can accurately describe the exterior space-time of compact stars still remains an interesting open question in relativistic astrophysics. As an attempt to establish their level of accuracy, the radii of the innermost stable circular orbits (ISCOs) of test particles given by analytic exterior space-time geometries have been compared with those given by numerical solutions for neutron stars (NSs) obeying a realistic equation of state (EOS). It has been so shown that the six-parametric solution of Pachon et al. (PRS) more accurately describes the NS ISCO radii than other analytic models do. We propose here an additional test of accuracy for analytic exterior geometries based on the comparison of orbital frequencies of neutral test particles. We compute the Keplerian, frame-dragging, and precession and oscillation frequencies of the radial and vertical motions of neutral test particles for the Kerr and PRS geometries and then compare them with the numerical values obtained by Morsink and Stella for realistic NSs. We identify the role of high-order multipole moments such as the mass quadrupole and current octupole in the determination of the orbital frequencies, especially in the rapid rotation regime. The results of this work are relevant to cast a separatrix between black hole and NS signatures and to probe the nuclear-matter EOS and NS parameters from the quasi-periodic oscillations observed in low-mass X-ray binaries.
Feasibility study of Lense-Thirring precession in LS I +61°303
NASA Astrophysics Data System (ADS)
Massi, M.; Zimmermann, L.
2010-06-01
Context. Very recent analysis of the radio spectral index and high energy observations have shown that the two-peak accretion/ejection microquasar model applies for LS I +61°303. Aims: The fast variations of the position angle observed with MERLIN and confirmed by consecutive VLBA images must therefore be explained in the context of the microquasar scenario. Methods: We calculate what could be the precessional period for the accretion disk in LS I +61°303 under tidal forces of the Be star (Ptidal-forces) or under the effect of frame dragging produced by the rotation of the compact object (PLense-Thirring). Results: Ptidal-forces is more than one year. PLense-Thirring depends on the truncated radius of the accretion disk, Rtr. We determined Rtr = 300 rg for observed QPO at 2 Hz. This value is much above the few rg, where the Bardeen-Petterson effect should align the midplane of the disk. For this truncated radius of the accretion disk PLense-Thirring for a slow rotator results in a few days. Conclusions: Lense-Thirring precession induced by a slowly rotating compact object could be compatible with the daily variations of the ejecta angle observed in LS I +61°303.
NASA Astrophysics Data System (ADS)
Frederick, Sara; Privitera, Stephen; Weinstein, Alan J.; LIGO Scientific Collaboration
2015-01-01
The Advanced LIGO and Virgo gravitational wave detectors will come online within the year and are expected to outperform the strain sensitivity of initial LIGO/Virgo detectors by an order of magnitude and operate with greater bandwidth, possibly to frequencies as low as 10 Hz. Coalescing binary black holes (BBH) are anticipated to be among the most likely sources of gravitational radiation observable by the detectors. Searches for such systems benefit greatly from the use of accurate predictions for the gravitational wave signal to filter the data. The component black holes of these systems are predicted to have substantial spin, which greatly influences the gravitational waveforms from these sources; however, recent LIGO/Virgo searches have made use of banks of waveform models which neglect the effects of the component spins. The inclusion of spinning components is relatively simplified when the spins are taken to be aligned with the orbital angular momentum, though the difficult task of including precession (allowing for mis-aligned component spins) remains a goal of this work. We aim to assess the ability of the GSTLAL gravitational wave search pipeline using IMR aligned-spin template waveforms to recover signals from generically spinning black hole binaries injected into simulated Advanced LIGO and Virgo detector noise. If black holes are highly spinning as predicted, use of aligned-spin template banks in upcoming searches could increase the detection rate of these systems in Advanced LIGO and Virgo data, providing the opportunity for a deeper understanding of the sources.
Simple model of complete precessing black-hole-binary gravitational waveforms.
Hannam, Mark; Schmidt, Patricia; Bohé, Alejandro; Haegel, Leïla; Husa, Sascha; Ohme, Frank; Pratten, Geraint; Pürrer, Michael
2014-10-10
The construction of a model of the gravitational-wave (GW) signal from generic configurations of spinning-black-hole binaries, through inspiral, merger, and ringdown, is one of the most pressing theoretical problems in the buildup to the era of GW astronomy. We present the first such model in the frequency domain, PhenomP, which captures the basic phenomenology of the seven-dimensional parameter space of binary configurations with only three key physical parameters. Two of these (the binary's mass ratio and an effective total spin parallel to the orbital angular momentum, which determines the inspiral rate) define an underlying nonprecessing-binary model. The nonprecessing-binary waveforms are then twisted up with approximate expressions for the precessional motion, which require only one additional physical parameter, an effective precession spin, χ(p). All other parameters (total mass, sky location, orientation and polarization, and initial phase) can be specified trivially. The model is constructed in the frequency domain, which will be essential for efficient GW searches and source measurements. We have tested the model's fidelity for GW applications by comparison against hybrid post-Newtonian-numerical-relativity waveforms at a variety of configurations--although we did not use these numerical simulations in the construction of the model. Our model can be used to develop GW searches, to study the implications for astrophysical measurements, and as a simple conceptual framework to form the basis of generic-binary waveform modeling in the advanced-detector era.
The BANANA project. V. Misaligned and precessing stellar rotation axes in CV Velorum
Albrecht, Simon; Winn, Joshua N.; Triaud, Amaury; Torres, Guillermo; Fabrycky, Daniel C.; Setiawan, Johny; Gillon, Michaël; Jehin, Emmanuel; Queloz, Didier; Snellen, Ignas; Eggleton, Peter
2014-04-20
As part of the Binaries Are Not Always Neatly Aligned project (BANANA), we have found that the eclipsing binary CV Velorum has misaligned rotation axes. Based on our analysis of the Rossiter-McLaughlin effect, we find sky-projected spin-orbit angles of β{sub p} = –52° ± 6° and β{sub s} = 3° ± 7° for the primary and secondary stars (B2.5V + B2.5V, P = 6.9 days). We combine this information with several measurements of changing projected stellar rotation speeds (vsin i {sub *}) over the last 30 yr, leading to a model in which the primary star's obliquity is ≈65°, and its spin axis precesses around the total angular momentum vector with a period of about 140 yr. The geometry of the secondary star is less clear, although a significant obliquity is also implicated by the observed time variations in the vsin i {sub *}. By integrating the secular tidal evolution equations backward in time, we find that the system could have evolved from a state of even stronger misalignment similar to DI Herculis, a younger but otherwise comparable binary.
Black hole - neutron star merger simulations: Precessing binaries with neutrino treatment
NASA Astrophysics Data System (ADS)
Desai, Dhruv; Foucart, Francois; Kasen, Daniel
2016-06-01
Black hole-neutron star (BH-NS) mergers are exciting events to model, as they are a source of gravitational waves, like those discovered for the first time by Advanced LIGO earlier this year. These mergers are also the source of gamma-ray bursts and radioactively powered transients. We present here an outline of our entire research process. We first display results of general relativistic-hydrodynamic simulations using the Spectral Einstein Code (SpEC). We ran a set of BH-NS merger simulations varying three of the initial parameters of the black hole: mass, spin magnitude, and spin inclination (relative to the orbital angular momentum of the binary system). The code factors in neutrino cooling and use a temperature dependent, nuclear theory based equation of state, as opposed to simpler equations of state previously used. Though systems which treat precession and neutrino cooling have been simulated individually, the systems we analyzed are the first to take both into account. Once a disk has formed and settled down, we take data from the GR simulations and input it into the particle evolution code, which reads in the positions/velocities and further evolves the system in a Newtonian potential. We then present the fallback rate of bound particles throughout this period of evolution, the approximate density evolution, and the spatial distribution of ejecta.
A Precessing Ring Model for Low-Frequency Quasi-periodic Oscillations
NASA Astrophysics Data System (ADS)
Schnittman, Jeremy D.; Homan, Jeroen; Miller, Jon M.
2006-05-01
We develop a simple physical model to describe the most common type of low-frequency quasi-periodic oscillations (QPOs) seen in a number of accreting black hole systems, as well as the shape of the relativistically broadened iron emission lines that often appear simultaneously in such sources. The model is based on an inclined ring of hot gas that orbits the black hole along geodesic trajectories. For spinning black holes, this ring will precess around the spin axis of the black hole at the Lense-Thirring (``frame-dragging'') frequency. Using a relativistic ray-tracing code, we calculate X-ray light curves and observed energy spectra as a function of the radius and tilt angle of the ring, the spin magnitude, and the inclination of the black hole. The model predicts higher amplitude QPOs for systems with high inclinations, as seen in a growing number of black hole binary systems. We find that the Rossi X-Ray Timing Explorer observations of low-frequency QPOs in GRS 1915+105 are consistent with a ring of radius R~10M orbiting a black hole with spin a/M~0.5 and inclination angle of iBH~70deg. Finally, we describe how future X-ray missions may be able to use simultaneous timing and spectroscopic observations to measure the black hole spin and probe the innermost regions of the accretion disk.
Robust energy transfer mechanism via precession resonance in nonlinear turbulent wave systems
NASA Astrophysics Data System (ADS)
Lucas, Dan; Bustamante, Miguel; Quinn, Brenda
2014-11-01
The precise mechanisms by which energy is most efficiently transferred in a turbulent system remain an important open question for the fluid mechanics community. In this talk we present a newly discovered resonance which is found to drive transfers across the spectrum of Fourier modes in a nonlinear wave system. Quadratic nonlinearity results in modes interacting in triads and, by considering the ``truly dynamical degrees of freedom'' (amplitudes and triad phases) and the precessional frequencies of the triads, we show transfers are maximal when the precession resonates with the nonlinear temporal frequencies. This can lead to a collective state of synchronised triads with intense cascades at intermediate nonlinearity; we find greatest transfer between the traditional weak and strong turbulence regimes and discover that this new mechanism is dominant here. We present the effect in a hierarchy of models including a full DNS of the Charney-Hasegawa-Mima equation and confirm analytical predictions. Supported by Science Foundation Ireland (SFI) under Grant Number 12/IP/1491.
NASA Astrophysics Data System (ADS)
Blackman, Jonathan; Field, Scott; Galley, Chad; Hemberger, Daniel; Scheel, Mark; Schmidt, Patricia; Smith, Rory; SXS Collaboration Collaboration
2016-03-01
We are now in the advanced detector era of gravitational wave astronomy, and the merger of two black holes (BHs) is one of the most promising sources of gravitational waves that could be detected on earth. To infer the BH masses and spins, the observed signal must be compared to waveforms predicted by general relativity for millions of binary configurations. Numerical relativity (NR) simulations can produce accurate waveforms, but are prohibitively expensive to use for parameter estimation. Other waveform models are fast enough but may lack accuracy in portions of the parameter space. Numerical relativity surrogate models attempt to rapidly predict the results of a NR code with a small or negligible modeling error, after being trained on a set of input waveforms. Such surrogate models are ideal for parameter estimation, as they are both fast and accurate, and have already been built for the case of non-spinning BHs. Using 250 input waveforms, we build a surrogate model for waveforms from the Spectral Einstein Code (SpEC) for a subspace of precessing systems.
NASA Astrophysics Data System (ADS)
Driben, R.; Konotop, V. V.; Meier, T.
2016-03-01
Nonlinearity is the driving force for numerous important effects in nature typically showing transitions between different regimes, regular, chaotic or catastrophic behavior. Localized nonlinear modes have been the focus of intense research in areas such as fluid and gas dynamics, photonics, atomic and solid state physics etc. Due to the richness of the behavior of nonlinear systems and due to the severe numerical demands of accurate three-dimensional (3D) numerical simulations presently only little knowledge is available on the dynamics of complex nonlinear modes in 3D. Here, we investigate the dynamics of 3D non-coaxial matter wave vortices that are trapped in a parabolic potential and interact via a repulsive nonlinearity. Our numerical simulations demonstrate the existence of an unexpected and fascinating nonlinear regime that starts immediately when the nonlinearity is switched-on and is characterized by a smooth dynamics representing torque-free precession with nutations. The reported motion is proven to be robust regarding various effects such as the number of particles, dissipation and trap deformations and thus should be observable in suitably designed experiments. Since our theoretical approach, i.e., coupled nonlinear Schrödinger equations, is quite generic, we expect that the obtained novel dynamical behavior should also exist in other nonlinear systems.
Impaired spatial selectivity and intact phase precession in two-dimensional virtual reality.
Aghajan, Zahra M; Acharya, Lavanya; Moore, Jason J; Cushman, Jesse D; Vuong, Cliff; Mehta, Mayank R
2015-01-01
During real-world (RW) exploration, rodent hippocampal activity shows robust spatial selectivity, which is hypothesized to be governed largely by distal visual cues, although other sensory-motor cues also contribute. Indeed, hippocampal spatial selectivity is weak in primate and human studies that use only visual cues. To determine the contribution of distal visual cues only, we measured hippocampal activity from body-fixed rodents exploring a two-dimensional virtual reality (VR). Compared to that in RW, spatial selectivity was markedly reduced during random foraging and goal-directed tasks in VR. Instead we found small but significant selectivity to distance traveled. Despite impaired spatial selectivity in VR, most spikes occurred within ∼2-s-long hippocampal motifs in both RW and VR that had similar structure, including phase precession within motif fields. Selectivity to space and distance traveled were greatly enhanced in VR tasks with stereotypical trajectories. Thus, distal visual cues alone are insufficient to generate a robust hippocampal rate code for space but are sufficient for a temporal code.
NASA Technical Reports Server (NTRS)
Zhu, S. Y.; Mueller, I. I.
1982-01-01
The effects of adopting new definitive precession and equinox corrections on the terrestrial reference frame was investigated. It is noted that: (1) the effect on polar motion is a diurnal periodic term with an amplitude increasing linearly in time whole on UT1 it is a linear term; (2) general principles are given to determine the effects of small rotations of the frame of a conventional inertial reference system (CIS) on the frame of the conventional terrestrial reference system (CTS); (3) seven CTS options are presented, one of which is necessary to accommodate such rotation. Accommodating possible future changes in the astronomical nutation is discussed. The effects of differences which may exist between the various CTS's and CIS's on Earth rotation parameters (ERP) and how these differences can be determined are examined. It is shown that the CTS differences can be determined from observations made at the same site, while the CIS differences by comparing the ERP's determined by the different techniques during the same time period.
Influence of Titan's climate-driven surface mass redistribution on spin pole precession
NASA Astrophysics Data System (ADS)
Bills, B. G.; Nimmo, F.; Aharonson, O.
2010-12-01
The spin pole of Titan is very close to a classic Cassini state, or tidally damped configuration. However, the observed obliquity is larger than would be expected for a body with the moments of inertia inferred from the observed gravity field. This suggests that some agent is acting to excite the motion of the spin pole, and frustrate its approach to a steady state, in which the spin pole and orbit pole of Titan would be co-planar with Saturn’s spin pole. A possible excitation mechanism is climate driven mass transport Titan’s orbit plane lies very nearly in the equator plane of Saturn, and the main influence on the seasonal distribution of insolation comes from slow changes in the orbit of Saturn. Saturn’s current obliquity is 26.7 degrees and its orbital eccentricity is 0.054. The distribution of liquid methane lakes on Titan is notably asymmetric, with many more in the north than in the south. It is also true that the current insolation pattern is rather asymmetric, with higher peak values in the south than in the north. If the changing orbit of Saturn drives the liquid hydrocarbons from south to north and back again on the 45 kyr apsidal precession period, this will also influence the moments of inertia of Titan and thereby excite modes of spin pole precessional motion. The hypothesis we seek to test is that this climate-driven mass transport is adequate to excite the observed departure of Titan’s spin pole orientation from a Cassini state. The proposed mechanism for additional driving of Titan’s spin pole precession differs from the mode of excitation of obliquity variations on Earth and Mars, where the dominant effect is variation in the orientation of the orbit plane. What we envision here is instead a parametric excitation of the spin pole motion. In a damped, forced spin pole state, the changes in polar moment will mainly change the obliquity (angular separation of spin and orbit poles), while dissipation will rotate the spin pole out of the
A precessing molecular jet signaling an obscured, growing supermassive black hole in NGC 1377?
NASA Astrophysics Data System (ADS)
Aalto, S.; Costagliola, F.; Muller, S.; Sakamoto, K.; Gallagher, J. S.; Dasyra, K.; Wada, K.; Combes, F.; García-Burillo, S.; Kristensen, L. E.; Martín, S.; van der Werf, P.; Evans, A. S.; Kotilainen, J.
2016-05-01
With high resolution (0.̋25 × 0.̋18) ALMA CO 3-2 (345 GHz) observations of the nearby (D = 21 Mpc, 1'' = 102 pc), extremely radio-quiet galaxy NGC 1377, we have discovered a high-velocity, very collimated nuclear outflow which we interpret as a molecular jet with a projected length of ±150 pc. The launch region is unresolved and lies inside a radius r< 10 pc. Along the jet axis we find strong velocity reversals where the projected velocity swings from -150km s-1 to +150 km s-1. A simple model of a molecular jet precessing around an axis close to the plane of the sky can reproduce the observations. The velocity of the outflowing gas is difficult to constrain due to the velocity reversals but we estimate it to be between 240 and 850 km s-1 and the jet to precess with a period P = 0.3-1.1 Myr. The CO emission is clumpy along the jet and the total molecular mass in the high-velocity (±(60 to 150 km s-1)) gas lies between 2 × 106M⊙ (light jet) and 2 × 107M⊙ (massive jet). There is also CO emission extending along the minor axis of NGC 1377. It holds > 40% of the flux in NGC 1377 and may be a slower, wide-angle molecular outflow which is partially entrained by the molecular jet. We discuss the driving mechanism of the molecular jet and suggest that it is either powered by a (faint) radio jet or by an accretion disk-wind similar to those found towards protostars. It seems unlikely that a massive jet could have been driven out by the current level of nuclear activity which should then have undergone rapid quenching. The light jet would only have expelled 10% of the inner gas and may facilitate nuclear activity instead of suppressing it. The nucleus of NGC 1377 harbours intense embedded activity and we detect emission from vibrationally excited HCN J = 4-3ν2 = 1f which is consistent with hot gas and dust. We find large columns of H2 in the centre of NGC 1377 which may be a sign of a high rate of recent gas infall. The dynamical age ofthe molecular jet is short
3C 273 variability at 7 mm: evidence of shocks and precession in the jet
NASA Astrophysics Data System (ADS)
Beaklini, Pedro Paulo B.; Abraham, Zulema
2014-01-01
We report on four years of observations of 3C 273 at 7 mm obtained with the Itapetinga radio telescope, in Brazil, between 2009 and 2013. We detected a flare in 2010 March, when the flux density increased by 50 per cent and reached 35 Jy. After the flare, the flux density started to decrease and reached values lower than 10 Jy. We suggest that the 7-mm flare is the radio counterpart of the γ-ray flare observed by the Fermi Large Area Telescope in 2009 September, in which the flux density at high energies reached a factor of 50 of its average value. A delay of 170 d between the radio and γ-ray flares was revealed using the discrete correlation function (DCF) that can be interpreted in the context of a shock model, in which each flare corresponds to the formation of a compact superluminal component that expands and becomes optically thin at radio frequencies at latter epochs. The differences in flare intensity between frequencies and at different times are explained as a consequence of an increase in the Doppler factor δ, as predicted by the 16-yr precession model proposed by Abraham & Romero. This increase has a large effect on boosting at high frequencies while it does not affect the observed optically thick radio emission too much. We discuss other observable effects of the variation in δ, such as the increase in the formation rate of superluminal components, the variations in the time delay between flares and the periodic behaviour of the radio light curve that we have found to be compatible with changes in the Doppler factor.
Whole-brain perfusion imaging with balanced steady-state free precession arterial spin labeling.
Han, Paul Kyu; Ye, Jong Chul; Kim, Eung Yeop; Choi, Seung Hong; Park, Sung-Hong
2016-03-01
Recently, balanced steady-state free precession (bSSFP) readout has been proposed for arterial spin labeling (ASL) perfusion imaging to reduce susceptibility artifacts at a relatively high spatial resolution and signal-to-noise ratio (SNR). However, the main limitation of bSSFP-ASL is the low spatial coverage. In this work, methods to increase the spatial coverage of bSSFP-ASL are proposed for distortion-free, high-resolution, whole-brain perfusion imaging. Three strategies of (i) segmentation, (ii) compressed sensing (CS) and (iii) a hybrid approach combining the two methods were tested to increase the spatial coverage of pseudo-continuous ASL (pCASL) with three-dimensional bSSFP readout. The spatial coverage was increased by factors of two, four and six using each of the three approaches, whilst maintaining the same total scan time (5.3 min). The number of segments and/or CS acceleration rate (R) correspondingly increased to maintain the same bSSFP readout time (1.2 s). The segmentation approach allowed whole-brain perfusion imaging for pCASL-bSSFP with no penalty in SNR and/or total scan time. The CS approach increased the spatial coverage of pCASL-bSSFP whilst maintaining the temporal resolution, with minimal impact on the image quality. The hybrid approach provided compromised effects between the two methods. Balanced SSFP-based ASL allows the acquisition of perfusion images with wide spatial coverage, high spatial resolution and SNR, and reduced susceptibility artifacts, and thus may become a good choice for clinical and neurological studies. Copyright © 2015 John Wiley & Sons, Ltd. PMID:26676386
Individual and combined effects of ice sheets and precession on MIS-13 climate
NASA Astrophysics Data System (ADS)
Yin, Q. Z.; Berger, A.; Crucifix, M.
2009-02-01
Simulations with an Earth System Model of Intermediate Complexity are made to investigate the role of insolation and the size of ice sheets on the regional and global climate for marine isotope stage (MIS) 13. The astronomical forcing is selected at two dates with opposite precession, one when Northern Hemisphere summer (NHS) occurs at perihelion (at 506 ka BP) and the other when it occurs at aphelion (at 495 ka BP). Experiments with five different volumes of the Eurasian and North American ice sheets (ranging from 0 to the Last Glacial Maximum one) are done under these two astronomical conditions. When NHS is at perihelion, the Earth is warmer, the seasonal contrast in Northern (Southern) Hemisphere is larger (smaller) and summer precipitation in Northern Hemisphere monsoon regions is more abundant than when it is at aphelion. The global cooling due to the ice sheets is mainly related to the ice sheet area, little to their height. The regional cooling and warming anomalies caused by the ice sheets get intensified with increasing ice sheet size. The cooling is different whether the NHS occurs at aphelion or at perihelion. Precipitation over different monsoon regions responds differently to the size of the ice sheets. Over North Africa, the ice sheets always reduce precipitation, larger the size less the precipitation. Over East China, when NHS is at perihelion, the ice sheets reinforce the summer precipitation whatever their sizes. But when NHS is at aphelion, there is a threshold in the ice volume beyond which the ice sheets start to reduce the precipitation over East China. This underlies the importance of insolation in shaping the ice sheet impact on the precipitation over the East Asian Summer Monsoon (EASM) region.
MAGNETOHYDRODYNAMIC SIMULATION OF A DISK SUBJECTED TO LENSE-THIRRING PRECESSION
Sorathia, Kareem A.; Krolik, Julian H.; Hawley, John F.
2013-11-01
When matter orbits around a central mass obliquely with respect to the mass's spin axis, the Lense-Thirring effect causes it to precess at a rate declining sharply with radius. Ever since the work of Bardeen and Petterson, it has been expected that when a fluid fills an orbiting disk, the orbital angular momentum at small radii should then align with the mass's spin. Nearly all previous work has studied this alignment under the assumption that a phenomenological 'viscosity' isotropically degrades fluid shears in accretion disks, even though it is now understood that internal stress in flat disks is due to anisotropic MHD turbulence. In this paper we report a pair of matched simulations, one in MHD and one in pure (non-viscous) HD in order to clarify the specific mechanisms of alignment. As in the previous work, we find that disk warps induce radial flows that mix angular momentum of different orientation; however, we also show that the speeds of these flows are generically transonic and are only very weakly influenced by internal stresses other than pressure. In particular, MHD turbulence does not act in a manner consistent with an isotropic viscosity. When MHD effects are present, the disk aligns, first at small radii and then at large; alignment is only partial in the HD case. We identify the specific angular momentum transport mechanisms causing alignment and show how MHD effects permit them to operate more efficiently. Last, we relate the speed at which an alignment front propagates outward (in the MHD case) to the rate at which Lense-Thirring torques deliver angular momentum at smaller radii.
NASA Astrophysics Data System (ADS)
Ivanov, A. N.; Wellenzohn, M.
2016-02-01
We analyze a spin precession of slow neutrons in the Einstein-Cartan gravity with torsion, chameleon and magnetic field. For the derivation of the Heisenberg equation of motion of the neutron spin we use the effective low-energy potential, derived by Ivanov and Wellenzohn [Phys. Rev. D 92, 125004 (2015)] for slow neutrons, coupled to gravitational, chameleon, and torsion fields to order 1 /m , where m is the neutron mass. In addition to these low-energy interactions we switch on the interaction of slow neutrons with a magnetic field. We show that to linear order approximation with respect to gravitational, chameleon, and torsion fields the Dirac Hamilton operator for fermions (neutrons), moving in spacetimes created by rotating coordinate systems, contains the anti-Hermitian operators of torsion-fermion (neutron) interactions, caused by torsion scalar and tensor space-space-time and time-space-space degrees of freedom. Such anti-Hermitian operators violate C P and T invariance. In the low-energy approximation the C P and T violating torsion-fermion (neutron) interactions appear only to order O (1 /m ). One may assume that in the rotating Universe and galaxies the obtained anti-Hermitian torsion-fermion interactions might be an origin of (i) violation of C P and T invariance in the Universe and (ii) of baryon asymmetry. We show that anti-Hermitian torsion-fermion interactions of relativistic fermions, violating C P and T invariance, (i) cannot be removed by nonunitary transformations of the Dirac fermion wave functions and (ii) are conformal invariant. According to general requirements of conformal invariance of massive particle theories in gravitational fields [see R. H. Dicke, Phys. Rev. 125, 2163 (1962) and A. J. Silenko, Phys. Rev. D 91, 065012 (2015)], conformal invariance of anti-Hermitian torsion-fermion interactions is valid only if the fermion mass is changed by a conformal factor.
Quantitative in vivo diffusion imaging of cartilage using double echo steady-state free precession.
Bieri, Oliver; Ganter, Carl; Scheffler, Klaus
2012-09-01
Single-shot echo-planar imaging techniques are commonly used for diffusion-weighted imaging (DWI) but offer rather poor spatial resolution and field-of-view coverage for species with short T(2) . In contrast, steady-state free precession (SSFP) has shown promising results for DWI of the musculoskeletal system, but quantification is generally hampered by its prominent sensitivity on relaxation times. In this work, a new and truly diffusion-weighted (that is relaxation time independent) SSFP DWI technique is introduced using a double-echo steady-state approach. Within this framework (and this is in contrast to common SSFP DWI techniques using SSFP-Echo) both primary echo paths of nonbalanced SSFP are acquired, namely the FID and the Echo. Simulations and in vitro measurements reveal that the ratio of the Echo/FID signal ratios of two double-echo steady-state scans acquired with and without diffusion sensitizing dephasing moments provides a highly relaxation independent quantity for diffusion quantification. As a result, relaxation-independent high-resolution (0.4 × 0.4 - 0.6 × 0.6 mm(2) in-plane resolution) quantitative in vivo SSFP DWI is demonstrated for human articular cartilage using diffusion-weighted double-echo steady-state scans in the knee and ankle joint at 3.0 T. The derived diffusion coefficients for cartilage (D ∼ 1.0-1.5 μm(2) /ms) and synovial fluid (D ∼ 2.6 μm(2) /ms) are in agreement with previous work.
Whole-brain perfusion imaging with balanced steady-state free precession arterial spin labeling.
Han, Paul Kyu; Ye, Jong Chul; Kim, Eung Yeop; Choi, Seung Hong; Park, Sung-Hong
2016-03-01
Recently, balanced steady-state free precession (bSSFP) readout has been proposed for arterial spin labeling (ASL) perfusion imaging to reduce susceptibility artifacts at a relatively high spatial resolution and signal-to-noise ratio (SNR). However, the main limitation of bSSFP-ASL is the low spatial coverage. In this work, methods to increase the spatial coverage of bSSFP-ASL are proposed for distortion-free, high-resolution, whole-brain perfusion imaging. Three strategies of (i) segmentation, (ii) compressed sensing (CS) and (iii) a hybrid approach combining the two methods were tested to increase the spatial coverage of pseudo-continuous ASL (pCASL) with three-dimensional bSSFP readout. The spatial coverage was increased by factors of two, four and six using each of the three approaches, whilst maintaining the same total scan time (5.3 min). The number of segments and/or CS acceleration rate (R) correspondingly increased to maintain the same bSSFP readout time (1.2 s). The segmentation approach allowed whole-brain perfusion imaging for pCASL-bSSFP with no penalty in SNR and/or total scan time. The CS approach increased the spatial coverage of pCASL-bSSFP whilst maintaining the temporal resolution, with minimal impact on the image quality. The hybrid approach provided compromised effects between the two methods. Balanced SSFP-based ASL allows the acquisition of perfusion images with wide spatial coverage, high spatial resolution and SNR, and reduced susceptibility artifacts, and thus may become a good choice for clinical and neurological studies. Copyright © 2015 John Wiley & Sons, Ltd.
NASA Astrophysics Data System (ADS)
Lhotka, C.; Reimond, S.; Souchay, J.; Baur, O.
2016-02-01
The aim of this study is first to determine the gravity field of the comet 67P/Churyumov-Gerasimenko and second to derive the solar component of the precession rate and nutation coefficients of the spin-axis of the comet nucleus, i.e. without the direct, usually larger, effect of outgassing. The gravity field and related moments of inertia are obtained from two polyhedra, which are provided by the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) and NAVigation CAMera (NAVCAM) experiments on Rosetta, and are based on the assumption of uniform density for the comet nucleus. We also calculate the forced precession rate as well as the nutation coefficients on the basis of Kinoshita's theory of rotation of the rigid Earth and adapted it to be able to indirectly include the effect of outgassing on the rotational parameters. The second degree denormalized Stokes coefficients of comet 67P/C-G turn out to be (bracketed numbers refer to second shape model) C20 ≃ -6.74 [-7.93] × 10-2, C22 ≃ 2.60 [2.71] × 10-2, consistent with normalized principal moments of inertia A/MR2 ≃ 0.13 [0.11], B/MR2 ≃ 0.23 [0.22], with polar moment c = C/MR2 ≃ 0.25, depending on the choice of the polyhedron model. The obliquity between the rotation axis and the mean orbit normal is ε ≃ 52°, and the precession rate only due to solar torques becomes dot{ψ }in [20,30] arcsec yr^{-1}. Oscillations in longitude caused by the gravitational pull of the Sun turn out to be of the order of Δψ ≃ 1 arcmin, and oscillations in obliquity can be estimated to be of the order of Δε ≃ 0.5 arcmin.
Castro, Luísa; Aguiar, Paulo
2012-08-01
Phase precession is one of the most well known examples within the temporal coding hypothesis. Here we present a biophysical spiking model for phase precession in hippocampal CA1 which focuses on the interaction between place cells and local inhibitory interneurons. The model's functional block is composed of a place cell (PC) connected with a local inhibitory cell (IC) which is modulated by the population theta rhythm. Both cells receive excitatory inputs from the entorhinal cortex (EC). These inputs are both theta modulated and space modulated. The dynamics of the two neuron types are described by integrate-and-fire models with conductance synapses, and the EC inputs are described using non-homogeneous Poisson processes. Phase precession in our model is caused by increased drive to specific PC/IC pairs when the animal is in their place field. The excitation increases the IC's firing rate, and this modulates the PC's firing rate such that both cells precess relative to theta. Our model implies that phase coding in place cells may not be independent from rate coding. The absence of restrictive connectivity constraints in this model predicts the generation of phase precession in any network with similar architecture and subject to a clocking rhythm, independently of the involvement in spatial tasks.
NASA Astrophysics Data System (ADS)
Opat, Geoffrey I.
1991-09-01
A conical pendulum has slightly different frequencies of vibration when it rotates clockwise or anticlockwise in a laboratory on a rotating Earth. This splitting of the frequency is due to the presence of the Lorentzlike Coriolis force which presses either radially inward or outward on the pendulum bob depending on the sense with which it traverses its circular orbit. The precession of the plane of a Foucault pendulum may be viewed as a beat phenomenon in the planar superposition of the clockwise and anticlockwise circular motions of the conical pendulum.
GRBs by thin persistent precessing lepton Jets: the long life GRB110328 and the Neutrino signal
NASA Astrophysics Data System (ADS)
Fargion, D.
Gamma Ray Burst sources are apparently evolving around us in a harder and brighter samples at far and far redshift. The average output may range from a near Supernova (nearest events) output to a billion time that power for most distant events. Such a tuned evolution around us is not an anti-copernican signature. It is a clear imprint of a off-axis (nearest sources) beaming versus a rarest in-axis blazing (far redshift sources) by a thin relativistic beam (Lorentz factor up 104 or above, micro-nano steradian solid angle). The main consequence is the rarer and rarer presences of hardest gamma events (hundreds MeV, GeVs, tens GeVs), nearly one over a twenty, observed with difficulty at largest redshift inside their thinner beamed jets. For this reason these rarest tens GeV beamed events, even observed by EGRET and Fermi, are hardly seen at hundred GeV by Cherenkov telescope (Magic,Hess,Veritas) on Earth. For the same reason and because tens GeV neutrino energy is below Icecube thresholds (threshold to hundreds GeV) we have not been observed yet a neutrino GRB. However if the GRBs primaries contains tens GeV neutrino traces (at comparable GRB gamma rate) their presence may rise in few years at Deep Core (a more dense array inside ICECUBE) detector whose lower threshold, ranges just one or few tens GeV energy. Moreover the very recent X ray persistent GRB110328 or( J164449.3 transient event), whose understanding was first associated to a cannibal star AGN eating \\cite{Shao}, but now \\cite{Bloom},\\cite{Zauderer} , to a cannibal AGN feeding beamed jet, it is, more naturally consistent to our GRB (by few solar mass compact source, not an AGN) spinning, precessing and blazing model jet, whose geometry is more aligned and stable (than other GRBs) to us: its decay law and its average output is fully consistent with our earliest proposals.
SS 433: Total Coverage of 162-Day Precession Phase in Four Years
NASA Technical Reports Server (NTRS)
Band, David L.
1997-01-01
The observations prior to AO-4 covered a number of precession phases, leaving a gap at phase 0.8. In addition, ASCA and previous observations of SS 433 did not observe the spectrum above approx. 10 keV, and consequently the continuum underlying the spectral lines was poorly constrained. Therefore RXTE observations were scheduled for April 1997 to extend the observed spectrum to higher energies; these observations were planned to sample the X-ray lightcurve during the 13.08 day binary period, concentrating on the eclipse of the compact object which emits the jets. We proposed and were awarded ASCA observations simultaneous with the RXTE observations; the purpose of the ASCA observations was to provide greater spectral resolution at the low end of the spectrum observed by RXTE, and to complete the phase coverage of SS 433. As a result of scheduling difficulties early in the mission the RXTE observations were confined to a much shorter time range than originally planned, April 18-91 1997. Optical observations of SS 433 were performed at a number of observatories. The ASCA observations occurred from April 18 13:10 (UT) to April 21 13:20 (UT) for a total effective exposure of 120 ks. The continuum X-ray light curve shows that the ASCA observations started shortly before the ingress into the X-ray partial eclipse, and ended approximately at the time of the egress. Light curves were also obtained for the prominent Fe emission lines in the blue-shifted frame (approaching jet), red-shifted frame (receding jet), and the stationary frame (fluorescent line from the ambient matter). Through the eclipse mapping technique using the light curves, the parameters of the jet emission model were constrained, showing that the kinetic power in the jet exceeds 104? erg s-l. If the energy source is gravitational accretion, as is commonly believed, the derived l;inetic power implies extremely supercritical accretion even for a black; hole with 10M. These results will be described more
Wu, Pei-Hsin; Chung, Hsiao-Wen; Tsai, Ping-Huei; Wu, Ming-Long; Chuang, Tzu-Chao; Shih, Yi-Yu; Huang, Teng-Yi
2013-12-15
Purpose: One of the technical advantages of functional magnetic resonance imaging (fMRI) is its precise localization of changes from neuronal activities. While current practice of fMRI acquisition at voxel size around 3 × 3 × 3 mm{sup 3} achieves satisfactory results in studies of basic brain functions, higher spatial resolution is required in order to resolve finer cortical structures. This study investigated spatial resolution effects on brain fMRI experiments using balanced steady-state free precession (bSSFP) imaging with 0.37 mm{sup 3} voxel volume at 3.0 T. Methods: In fMRI experiments, full and unilateral visual field 5 Hz flashing checkerboard stimulations were given to healthy subjects. The bSSFP imaging experiments were performed at three different frequency offsets to widen the coverage, with functional activations in the primary visual cortex analyzed using the general linear model. Variations of the spatial resolution were achieved by removing outerk-space data components. Results: Results show that a reduction in voxel volume from 3.44 × 3.44 × 2 mm{sup 3} to 0.43 × 0.43 × 2 mm{sup 3} has resulted in an increase of the functional activation signals from (7.7 ± 1.7)% to (20.9 ± 2.0)% at 3.0 T, despite of the threefold SNR decreases in the original images, leading to nearly invariant functional contrast-to-noise ratios (fCNR) even at high spatial resolution. Activation signals aligning nicely with gray matter sulci at high spatial resolution would, on the other hand, have possibly been mistaken as noise at low spatial resolution. Conclusions: It is concluded that the bSSFP sequence is a plausible technique for fMRI investigations at submillimeter voxel widths without compromising fCNR. The reduction of partial volume averaging with nonactivated brain tissues to retain fCNR is uniquely suitable for high spatial resolution applications such as the resolving of columnar organization in the brain.
NASA Technical Reports Server (NTRS)
Borsody, J.
1976-01-01
Equations are derived by using branched trajectory optimization techniques and the maximum principle to maximize the payload capability of a reusable tug/expendable kickstage vehicle configuration for planetary missions. The two stages and the payload are launched into a low earth orbit by a single space shuttle. The analysis includes correction for precession of the orbit. This correction is done by the tug. The tug propels the payload and the kickstage to an energy beyond earth escape and returns within a specified time to the precessed orbit. After separating from the tug, the kickstage accelerates the payload to the required injection conditions. Planetary injection conditions are specified by the mission energy and a fixed declination and right ascension of the outgoing asymptote. The multipoint boundary value problem resulting from the analysis is solved by a Newton-Raphson iteration technique. Partial derivatives of the boundary conditions are obtained by perturbing the initial conditions one at a time, integrating the trajectory and adjoint equations, and observing the changes in boundary conditions. Maximum payload capability is derived for two typical mission energies. In addition, the variations of several mission and stage parameters are also examined.
NASA Astrophysics Data System (ADS)
Mahfouzi, Farzad; Nagaosa, Naoto; Nikolić, Branislav K.
2014-09-01
Using the charge-conserving Floquet-Green function approach to open quantum systems driven by an external time-periodic potential, we analyze how spin current pumped by the precessing magnetization of a ferromagnetic (F) layer is injected laterally into the interface with strong spin-orbit coupling (SOC) and converted into charge current flowing in the same direction. In the case of a metallic interface with the Rashba SOC used in recent experiments [J. C. R. Sánchez, L. Vila, G. Desfonds, S. Gambarelli, J. P. Attané, J. M. De Teresa, C. Magén, and A. Fert, Nat. Commun. 4, 2944 (2013), 10.1038/ncomms3944], both spin ISα and charge I current flow within the interface where I /ISα≃ 2-8% (depending on the precession cone angle), while for a F/topological-insulator (F/TI) interface employed in related experiments [Y. Shiomi, K. Nomura, Y. Kajiwara, K. Eto, M. Novak, K. Segawa, Y. Ando, and E. Saitoh, arXiv:1312.7091] the conversion efficiency is greatly enhanced (I /ISα≃ 40-60%) due to perfect spin-momentum locking on the surface of a TI. The spin-to-charge conversion occurs also when spin current is pumped vertically through the F/TI interface with smaller efficiency (I /ISα˜0.001%), but with the charge current signal being sensitive to whether the Dirac fermions at the interface are massive or massless.
Vigouroux, M. P.; Delaye, V.; Bernier, N.; Lafond, D.; Audoit, G.; Bertin, F.; Cipro, R.; Baron, T.; Martin, M.; Rouvière, J. L.; Chenevier, B.
2014-11-10
Precession electron diffraction is an efficient technique to measure strain in nanostructures by precessing the electron beam, while maintaining a few nanometre probe size. Here, we show that an advanced diffraction pattern treatment allows reproducible and precise strain measurements to be obtained using a default 512 × 512 DigiSTAR off-axis camera both in advanced or non-corrected transmission electron microscopes. This treatment consists in both projective geometry correction of diffraction pattern distortions and strain Delaunay triangulation based analysis. Precision in the strain measurement is improved and reached 2.7 × 10{sup −4} with a probe size approaching 4.2 nm in diameter. This method is applied to the study of the strain state in InGaAs quantum-well (QW) devices elaborated on Si substrate. Results show that the GaAs/Si mismatch does not induce in-plane strain fluctuations in the InGaAs QW region.
NASA Astrophysics Data System (ADS)
Walker, D. D.; Beaucamp, A. T. H.; Doubrovski, V.; Dunn, C.; Freeman, R.; Hobbs, G.; McCavana, G.; Morton, R.; Riley, D.; Simms, J.; Wei, X.
2006-02-01
The recent upsurge in the demand for off-axis and complex "freeform" optical surfaces is driving the development of novel processes for their fabrication. This paper focuses on recent developments of the Precessions CNC polishing process for freeform surfaces, including off-axis as a special case. First, the surface-prescription and metrology-data, and their relation to the data-input for the polishing machines, are considered. The relevance of consistent coordinate frames is emphasised. An outline of how the process can 'polish' a ground freeform part (improve the texture), and then 'figure' the part (reduce the form errors) is given. Specific experimental case-studies are then presented, illustrating the versatility of the process on different materials and forms. Recent work is included in which the process-speed has been moderated in order to remove tens of nanometres of stock material, rather then the more usual hundreds of nanometres to tens of microns as in the standard Precessions process. The relevance of this to improving the ultimate surface-precision that should be achievable by this method is described. As a final illustration, the potential of the process to the rapid fabrication of the hundreds to thousands of 1-2 metre class mirror segments required for extremely large telescopes is considered.
NASA Astrophysics Data System (ADS)
Postnov, K.; Shakura, N.; Staubert, R.; Kochetkova, A.; Klochkov, D.; Wilms, J.
2013-10-01
Accretion of matter on to the surface of a freely precessing neutron star (NS) with a complex non-dipole magnetic field can explain the change of X-ray pulse profiles of Her X-1 observed by RXTE with the phase of the 35-d cycle. We demonstrate this using all available measurements of X-ray pulse profiles in the 9-13 keV energy range obtained with the RXTE/Proportional Counter Array (PCA). The measured profiles guided the elaboration of a geometrical model and the definition of locations of emitting poles, arcs and spots on the NS surface which satisfactorily reproduce the observed pulse profiles and their dependence on free precession phase. We have found that the observed trend of the times of the 35-d turn-ons on the O-C diagram, which can be approximated by a collection of consecutive linear segments around the mean value, can be described by our model by assuming a variable free precession period, with a fractional period change of about a few per cent. Under this assumption and using our model, we have found that the times of phase zero of the NS free precession (which we identify with the maximum separation of the brightest spot on the NS surface with the NS spin axis) occur about 1.6 d after the mean turn-on times inside each `stable' epoch, producing a linear trend on the O-C diagram with the same slope as the observed times of turn-ons. We propose that the 2.5 per cent changes in the free precession period that occur on time scales of several to tens of 35-d cycles can be related to wandering of the principal inertia axis of the NS body due to variations in the patterns of accretion on to the NS surface. The closeness of periods of the disc precession and the NS free precession can be explained by the presence of a synchronization mechanism in the system, which modulates the dynamical interaction of the gas streams and the accretion disc with the NS free precession period.
Malkus, W V
1968-04-19
I have proposed that the precessional torques acting on the earth can sustain a turbulent hydromagnetic flow in the molten core. A gross balance of the Coriolis force, the Lorentz force, and the precessional force in the core fluid provided estimates of the fluid velocity and the interior magnetic field characteristic of such flow. Then these numbers and a balance of the processes responsible for the decay and regeneration of the magnetic field provided an estimate of the magnetic field external to the core. This external field is in keeping with the observations, but its value is dependent upon the speculative value for the electrical conductivity of core material. The proposal that turbulent flow due to precession can occur in the core was tested in a study of nonmagnetic laboratory flows induced by the steady precession of fluid-filled rotating spheroids. It was found that these flows exhibit both small wavelike instabilities and violent finite-amplitude instability to turbulent motion above critical values of the precession rate. The observed critical parameters indicate that a laminar flow in the core, due to the earth's precession, would have weak hydrodynamic instabilities at most, but that finite-amplitude hydromagnetic instability could lead to fully turbulent flow. PMID:17788230
Homan, Jeroen
2012-12-01
Relativistic Lense-Thirring precession of a tilted inner accretion disk around a compact object has been proposed as a mechanism for low-frequency ({approx}0.01-70 Hz) quasi-periodic oscillations (QPOs) in the light curves of X-ray binaries. A substantial misalignment angle ({approx}15 Degree-Sign -20 Degree-Sign ) between the inner-disk rotation axis and the compact-object spin axis is required for the effects of this precession to produce observable modulations in the X-ray light curve. A consequence of this misalignment is that in high-inclination X-ray binaries the precessing inner disk will quasi-periodically intercept our line of sight to the compact object. In the case of neutron-star systems, this should have a significant observational effect, since a large fraction of the accretion energy is released on or near the neutron-star surface. In this Letter, I suggest that this specific effect of Lense-Thirring precession may already have been observed as {approx}1 Hz QPOs in several dipping/eclipsing neutron-star X-ray binaries.
Makishima, K; Enoto, T; Hiraga, J S; Nakano, T; Nakazawa, K; Sakurai, S; Sasano, M; Murakami, H
2014-05-01
Magnetars are a special type of neutron stars, considered to have extreme dipole magnetic fields reaching ∼ 10(11) T. The magnetar 4 U 0142+61, one of the prototypes of this class, was studied in broadband x rays (0.5-70 keV) with the Suzaku observatory. In hard x rays (15-40 keV), its 8.69 sec pulsations suffered slow phase modulations by ± 0.7 sec, with a period of ∼ 15 h. When this effect is interpreted as free precession of the neutron star, the object is inferred to deviate from spherical symmetry by ∼ 1.6 × 10(-4) in its moments of inertia. This deformation, when ascribed to magnetic pressure, suggests a strong toroidal magnetic field, ∼ 10(12) T, residing inside the object. This provides one of the first observational approaches towards toroidal magnetic fields of magnetars. PMID:24836230
Makishima, K; Enoto, T; Hiraga, J S; Nakano, T; Nakazawa, K; Sakurai, S; Sasano, M; Murakami, H
2014-05-01
Magnetars are a special type of neutron stars, considered to have extreme dipole magnetic fields reaching ∼ 10(11) T. The magnetar 4 U 0142+61, one of the prototypes of this class, was studied in broadband x rays (0.5-70 keV) with the Suzaku observatory. In hard x rays (15-40 keV), its 8.69 sec pulsations suffered slow phase modulations by ± 0.7 sec, with a period of ∼ 15 h. When this effect is interpreted as free precession of the neutron star, the object is inferred to deviate from spherical symmetry by ∼ 1.6 × 10(-4) in its moments of inertia. This deformation, when ascribed to magnetic pressure, suggests a strong toroidal magnetic field, ∼ 10(12) T, residing inside the object. This provides one of the first observational approaches towards toroidal magnetic fields of magnetars.
Structure solution of the new titanate Li4Ti8Ni3O21 using precession electron diffraction.
Gemmi, Mauro; Klein, Holger; Rageau, Amelie; Strobel, Pierre; Le Cras, Federic
2010-02-01
A sample having stoichiometry Li[Ti(1.5)Ni(0.5)]O(4) has been synthesized to obtain a spinel structure. The resulting crystalline powder revealed a multiphase nature with spinel as the minor phase. The main phase is a new trigonal phase having a = 5.05910 (1), c = 32.5371 (1) A. The structure has been solved by direct methods working on a three-dimensional set of intensities obtained from a precession electron-diffraction experiment, and refined on synchrotron powder diffraction data in the space group P3c1. The model consists of hexagonal layers of edge-sharing octahedra occupied either by the heavy cations Ti and Ni, or preferentially by Li. On the basis of cation-site occupancies the stoichiometry becomes Li(4)Ti(8)Ni(3)O(21), which is compatible with the microanalysis results.
FRAME DRAGGING, DISK WARPING, JET PRECESSING, AND DIPPED X-RAY LIGHT CURVE OF Sw J1644+57
Lei, Wei-Hua; Zhang, Bing; Gao, He E-mail: zhang@physics.unlv.edu
2013-01-10
The X-ray transient source Sw J1644+57 recently discovered by Swift is believed to be triggered by tidal disruption of a star by a rapidly spinning supermassive black hole (SMBH). For such events, the outer disk is very likely misaligned with respect to the equatorial plane of the spinning SMBH, since the incoming star before disruption most likely has an inclined orbital plane. The tilted disk is subject to the Lense-Thirring torque, which tends to twist and warp due to the Bardeen-Petterson effect. The inner disk tends to align with the SMBH spin, while the outer region tends to remain in the stellar orbital plane, with a transition zone around the Bardeen-Petterson radius. The relativistic jet launched from the spinning SMBH would undergo precession. The 5-30 day X-ray light curve of Sw J1644+57 shows a quasi-periodic (2.7 day) variation with noticeable narrow dips. We numerically solve a warped disk and propose a jet-precessing model by invoking a Blandford-Znajek jet collimated by a wind launched near the Bardeen-Petterson radius. Through simulations, we show that the narrow dips in the X-ray light curve can be reproduced for a range of geometric configurations. From the data we infer that the inclination angle of the initial stellar orbit is in the range of 10 Degree-Sign -20 Degree-Sign from the SMBH equatorial plane, that the jet should have a moderately high Lorentz factor, and that the inclination angle, jet opening angle, and observer's viewing angle are such that the duty cycle of the line of sight sweeping the jet cone is somewhat less than 0.5.
Frame Dragging, Disk Warping, Jet Precessing, and Dipped X-Ray Light Curve of Sw J1644+57
NASA Astrophysics Data System (ADS)
Lei, Wei-Hua; Zhang, Bing; Gao, He
2013-01-01
The X-ray transient source Sw J1644+57 recently discovered by Swift is believed to be triggered by tidal disruption of a star by a rapidly spinning supermassive black hole (SMBH). For such events, the outer disk is very likely misaligned with respect to the equatorial plane of the spinning SMBH, since the incoming star before disruption most likely has an inclined orbital plane. The tilted disk is subject to the Lense-Thirring torque, which tends to twist and warp due to the Bardeen-Petterson effect. The inner disk tends to align with the SMBH spin, while the outer region tends to remain in the stellar orbital plane, with a transition zone around the Bardeen-Petterson radius. The relativistic jet launched from the spinning SMBH would undergo precession. The 5-30 day X-ray light curve of Sw J1644+57 shows a quasi-periodic (2.7 day) variation with noticeable narrow dips. We numerically solve a warped disk and propose a jet-precessing model by invoking a Blandford-Znajek jet collimated by a wind launched near the Bardeen-Petterson radius. Through simulations, we show that the narrow dips in the X-ray light curve can be reproduced for a range of geometric configurations. From the data we infer that the inclination angle of the initial stellar orbit is in the range of 10°-20° from the SMBH equatorial plane, that the jet should have a moderately high Lorentz factor, and that the inclination angle, jet opening angle, and observer's viewing angle are such that the duty cycle of the line of sight sweeping the jet cone is somewhat less than 0.5.
NASA Astrophysics Data System (ADS)
Maslin, M. A.; Brierley, C. M.
2015-12-01
The Early-Middle Pleistocene Transition (EMPT) is the term used to describe the prolongation and intensification of glacial-interglacial climate cycles that initiated after 900,000 years ago. During the transition glacial-interglacial cycles shift from lasting 41,000 years to an average of 100,000 years. The structure of these glacial-interglacial cycles shifts from smooth to more abrupt 'saw-toothed' like transitions. In fact we argue there is shift from a bimodal climate to a tripartite climate system (see Figure). Despite eccentricity having by far the weakest influence on insolation received at the Earth's surface of any of the orbital parameters; it is often assumed to be the primary driver of the post-EMPT 100,000 years climate cycles because of the similarity in duration. The traditional solution to this is to call for a highly nonlinear response by the global climate system to eccentricity. This 'eccentricity myth' is due to an artefact of spectral analysis which means that the last 8 glacial-interglacial average out at about 100,000 years in length despite ranging from 80,000 to 120,000 years. With the realisation that eccentricity is not the major driving force a debate has emerged as to whether precession or obliquity controlled the timing of the most recent glacial-interglacial cycles. Some argue that post-EMPT deglaciations occurred every four or five precessional cycle while others argue it is every second or third obliquity cycle. We review these current theories and suggest that though phase-locking between orbital forcing and global ice volume may occur and seem to primarily driven by the timing of precession; the chaotic nature of the climate system response means the relationship is not consistent through the last 900,000 years.
NASA Astrophysics Data System (ADS)
Favrel, A.; Landry, C.; Müller, A.; Yamamoto, K.; Avellan, F.
2014-03-01
Francis turbines operating at part load condition experience the development of a cavitating helical vortex rope in the draft tube cone at the runner outlet. The precession movement of this vortex rope induces local convective pressure fluctuations and a synchronous pressure pulsation acting as a forced excitation for the hydraulic system, propagating in the entire system. In the draft tube, synchronous pressure fluctuations with a frequency different to the precession frequency may also be observed in presence of cavitation. In the case of a matching between the precession frequency and the synchronous surge frequency, hydro-acoustic resonance occurs in the draft tube inducing high pressure fluctuations throughout the entire hydraulic system, causing torque and power pulsations. The risk of such resonances limits the possible extension of the Francis turbine operating range. A more precise knowledge of the phenomenon occurring at such resonance conditions and prediction capabilities of the induced pressure pulsations needs therefore to be developed. This paper proposes a detailed study of the occurrence of hydro-acoustic resonance for one particular part load operating point featuring a well-developed precessing vortex rope and corresponding to 64% of the BEP. It focuses particularly on the evolution of the local interaction between the pressure fluctuations at the precession frequency and the synchronous surge mode passing through the resonance condition. For this purpose, an experimental investigation is performed on a reduced scale model of a Francis turbine, including pressure fluctuation measurements in the draft tube and in the upstream piping system. Changing the pressure level in the draft tube, resonance occurrences are highlighted for different Froude numbers. The evolution of the hydro-acoustic response of the system suggests that a lock-in effect between the excitation frequency and the natural frequency may occur at low Froude number, inducing a hydro
Liu, Xianyin; Zhu, Qiyuan; Zhang, Senfu; Liu, Qingfang E-mail: wangjb@lzu.edu.cn; Wang, Jianbo E-mail: wangjb@lzu.edu.cn
2015-08-15
An interesting type of skyrmion-like spin texture, 2π-vortex, is obtained in a thin nano-disk with Dzyaloshinskii-Moriya interaction. We have simulated the existence of 2π-vortex by micromagnetic method. Furthermore, the spin polarized current is introduced in order to drive the motion of 2π-vortex in a nano-disk with diameter 2 R = 140 nm. When the current density matches with the current injection area, 2π-vortex soon reaches a stable precession (3∼4 ns). The relationship between the precession frequency of 2π-vortex and the current density is almost linear. It may have potential use in spin torque nano-oscillators.
NASA Astrophysics Data System (ADS)
Kupryaev, N. V.
2016-07-01
The precession of the perihelion of Mercury's orbit for 100 years in the gravitational field of the Sun and the planets has been numerically modeled within the framework of a generalized law of universal gravitation with refined data on the parameters of the orbits of the planets (including the asteroid belt and Pluto), and also the gravitational constant and with a smaller iteration step (0.0002 s). The calculations were performed with enhanced computational accuracy. It has been shown that the average precession of Mercury's orbit in 100 years within the framework of the generalized law of universal gravitation comprises ~565.3''. This is less than the observed shift of the perihelion by about 8.8''. The observed shift of the perihelion, as is well known, comprises ~574.1''. It is not ruled out that inside Mercury's orbit some unknown undetected object (or several such objects) of small size remains to be found.
NASA Technical Reports Server (NTRS)
Stumpff, P.; Lieske, J. H.
1984-01-01
Properties of astronomical time scales (ET and UT) are considered, with particular emphasis on correctly determining of-date longitude as the sum of inertial mean longitude of the sun relative to the mean equinox of a fixed epoch (1950.0), and the general precession in longitude accumulated since the epoch. The inertial mean longitude and motion (relative to the mean equinox) are derived from tabular ephemerides such as the Jet Propulsion Laboratories' DE 102 and DE 96, by comparisons with subroutines based on Newcomb's perturbation theory. An unresolved inconsistency of approximately 1 second per century among the mean inertial motion of DE 102, IAU precession speed (1976), and the classical Newcomb of-date mean motion is found. Interpretation difficulties arising from the use of different systems of Ephemeris Time are also discussed.
Wang, Y. Y.; Cooper, D.; Bernier, N.; Rouviere, J.; Murray, C. E.; Bruley, J.
2015-01-26
The detailed strain distributions produced by embedded SiGe stressor structures are measured at high spatial resolution with high precision, with dual lens dark field electron holography and precession electron diffraction. Shear strain and lattice rotation within the crystalline lattice are observed at the boundaries between the SiGe and Si regions. The experimental results are compared to micromechanical modeling simulations to understand the mechanisms of elastic relaxation on all the modes of deformation at a sub-micron length scale.
O’Halloran, R; Aksoy, M; Aboussouan, E; Peterson, E; Van, A; Bammer, R
2014-01-01
Purpose Diffusion contrast in diffusion-weighted steady state free precession MRI is generated through the constructive addition of signal from many coherence pathways. Motion-induced phase causes destructive interference which results in loss of signal magnitude and diffusion contrast. In this work, a 3D navigator-based real-time correction of the rigid-body-motion-induced phase errors is developed for diffusion-weighted steady state free precession MRI. Methods The efficacy of the real-time prospective correction method in preserving phase coherence of the steady-state is tested in 3D phantom experiments and 3D scans of healthy human subjects. Results In nearly all experiments, the signal magnitude in images obtained with proposed prospective correction was higher than the signal magnitude in images obtained with no correction. In the human subjects the mean magnitude signal in the data was up to 30 percent higher with prospective motion correction than without. Prospective correction never resulted in a decrease in mean signal magnitude in either the data or in the images. Conclusions The proposed prospective motion correction method is shown to preserve the phase coherence of the steady state in diffusion-weighted steady state free precession MRI, thus mitigating signal magnitude losses that would confound the desired diffusion contrast. PMID:24715414
Cooper, Mitchell A; Nguyen, Thanh D; Spincemaille, Pascal; Prince, Martin R; Weinsaft, Jonathan W; Wang, Yi
2012-11-01
Fast methods using balanced steady-state free precession have been developed to reduce the scan time of T₁ and T₂ mapping. However, flip angle (FA) profiles created by the short radiofrequency pulses used in steady-state free precession deviate substantially from the ideal rectangular profile, causing T₁ and T₂ mapping errors. The purpose of this study was to develop a FA profile correction for T₁ and T₂ mapping with Look-Locker 2D inversion recovery steady-state free precession and to validate this method using 2D spin echo as a reference standard. Phantom studies showed consistent improvement in T₁ and T₂ accuracy using profile correction at multiple FAs. Over six human calves, profile correction provided muscle T₁ estimates with mean error ranging from excellent (-0.6%) at repetition time/FA = 18 ms/60° to acceptable (6.8%) at repetition time/FA = 4.9 ms/30°, while muscle T₂ estimates were less accurate with mean errors of 31.2% and 47.9%, respectively.
NASA Astrophysics Data System (ADS)
Ruangsri, Uchupol; Vigeland, Sarah J.; Hughes, Scott A.
2016-08-01
A small body orbiting a black hole follows a trajectory that, at leading order, is a geodesic of the black hole spacetime. Much effort has gone into computing "self-force" corrections to this motion, arising from the small body's own contributions to the system's spacetime. Another correction to the motion arises from coupling of the small body's spin to the black hole's spacetime curvature. Spin-curvature coupling drives a precession of the small body, and introduces a "force" (relative to the geodesic) which shifts the small body's worldline. These effects scale with the small body's spin at leading order. In this paper, we show that the equations which govern spin-curvature coupling can be analyzed with a frequency-domain decomposition, at least to leading order in the small body's spin. We show how to compute the frequency of precession along generic orbits, and how to describe the small body's precession and motion in the frequency domain. We illustrate this approach with a number of examples. This approach is likely to be useful for understanding spin coupling effects in the extreme mass ratio limit, and may provide insight into modeling spin effects in the strong field for nonextreme mass ratios.
NASA Technical Reports Server (NTRS)
Uemaatsu, Hirohiko; Parkinson, Bradford W.; Lockhart, James M.; Muhlfelder, Barry
1993-01-01
Gravity Probe B (GP-B) is a relatively gyroscope experiment begun at Stanford University in 1960 and supported by NASA since 1963. This experiment will check, for the first time, the relativistic precession of an Earth-orbiting gyroscope that was predicted by Einstein's General Theory of Relativity, to an accuracy of 1 milliarcsecond per year or better. A drag-free satellite will carry four gyroscopes in a polar orbit to observe their relativistic precession. The primary sensor for measuring the direction of gyroscope spin axis is the SQUID (superconducting quantum interference device) magnetometer. The data reduction scheme designed for the GP-B program processes the signal from the SQUID magnetometer and estimates the relativistic precession rates. We formulated the data reduction scheme and designed the Niobium bird experiment to verify the performance of the data reduction scheme experimentally with an actual SQUID magnetometer within the test loop. This paper reports the results from the first phase of the Niobium bird experiment, which used a commercially available SQUID magnetometer as its primary sensor, and adresses the issues they raised. The first phase resulted in a large, temperature-dependent bias drift in the insensitive design and a temperature regulation scheme.
Herment, Alain; Lefort, Muriel; Kachenoura, Nadjia; De Cesare, Alain; Taviani, Valentina; Graves, Martin J; Pellot-Barakat, Claire; Frouin, Frédérique; Mousseaux, Elie
2011-04-01
The strain values extracted from steady-state free-precession (SSFP) and phase contrast (PC) images acquired with a 1.5T scanner on a compliant flow phantom and within the thoracic aorta of 52 healthy subjects were compared. Aortic data were acquired perpendicular to the aorta at the level of the pulmonary artery bifurcation. Cross sectional areas were obtained by using an automatic and robust segmentation method. While a good correlation (r = 0.99) was found between the aortic areas extracted from SSFP and PC sequences, a lower correlation (r = 0.71) was found between the corresponding aortic strain values. Strain values estimated using SSFP and PC sequences were equally correlated with age. Interobserver reproducibility was better for SSFP than for PC. Strain values in the ascending and descending aorta were better correlated for SSFP (r = 0.8) than for PC (r = 0.65) and fitted with the expectation of a larger strain in the ascending aorta when using SSFP. The spatial and temporal resolutions of the acquisitions had a minor influence upon the estimated strain values. Thus, if PC acquisitions can be used to estimate both pulse wave velocity and aortic strain, an additional SSFP sequence may be useful to improve the accuracy in estimating the aortic strain.
NASA Astrophysics Data System (ADS)
Alomar, M. I.; Serra, Llorenç; Sánchez, David
2016-08-01
We investigate the transmission properties of a spin transistor coupled to two quantum point contacts acting as a spin injector and detector. In the Fabry-Pérot regime, transport is mediated by quasibound states formed between tunnel barriers. Interestingly, the spin-orbit interaction of the Rashba type can be tuned in such a way that nonuniform spin-orbit fields can point along distinct directions at different points of the sample. We discuss both spin-conserving and spin-flipping transitions as the spin-orbit angle of orientation increases from parallel to antiparallel configurations. Spin precession oscillations are clearly seen as a function of the length of the central channel. Remarkably, we find that these oscillations combine with the Fabry-Pérot motion, giving rise to quasiperiodic transmissions in the purely one-dimensional case. Furthermore, we consider the more realistic case of a finite width in the transverse direction and find that the coherent oscillations become deteriorated for moderate values of the spin-orbit strength. Our results then determine the precise role of the spin-orbit intersubband coupling potential in the Fabry-Pérot-Datta-Das intermixed oscillations.
Li, A E; Wilkinson, M D; McGrillen, K M; Stoodley, M A; Magnussen, J S
2015-12-01
The purpose of this article is to review the physiology of normal brain and spinal cord motion in the subarachnoid space, principles of cine balanced steady-state free precession (bSSFP) magnetic resonance imaging (MRI), clinical applications, and the pitfalls encountered with this technique. The brain and spinal cord are dynamic structures that move with each heartbeat due to transmitted arterial pulse waves. Conventional MRI sequences do not allow anatomic evaluation of the pulsatile movement of the neural structures in the subarachnoid space due to limitations in temporal resolution. Cine bSSFP MRI uses cardiac gating to evaluate dynamically the brain and spinal cord with high contrast and temporal resolution.Cine bSSFP can be used in the evaluation of idiopathic syringomyelia to assess an underlying treatable cause, including arachnoid bands, which are usually not well visualized with conventional MR sequences due to motion artifact. This MRI technique is also useful in the evaluation of intraspinal and intracranial arachnoid cysts and the degree of mass effect on the cord. Other applications include preoperative and postoperative evaluation of Chiari I malformation and the evaluation of lateral ventricular asymmetry. The major limitation of cine bSSFP is the presence of banding artifacts, which can be reduced by shimming and modifying other scan parameters.
NASA Astrophysics Data System (ADS)
Moraes, Tiago Bueno; Monaretto, Tatiana; Colnago, Luiz Alberto
2016-09-01
Longitudinal (T1) and transverse (T2) relaxation times have been widely used in time-domain NMR (TD-NMR) to determine several physicochemical properties of petroleum, polymers, and food products. The measurement of T2 through the CPMG pulse sequence has been used in most of these applications because it denotes a rapid, robust method. On the other hand, T1 has been occasionally used in TD-NMR due to the long measurement time required to collect multiple points along the T1 relaxation curve. Recently, several rapid methods to measure T1 have been proposed. Those methods based upon single shot, known as Continuous Wave Free Precession (CWFP) pulse sequences, have been employed in the simultaneous measurement of T1 and T2 in a rapid fashion. However, these sequences can be used exclusively in instrument featuring short dead time because the magnitude of the signal at thermal equilibrium is required. In this paper, we demonstrate that a special CWFP sequence with a low flip angle can be a simple and rapid method to measure T1 regardless of instruments dead time. Experimental results confirmed that the method called CWFP-T1 may be used to measure both single T1 value and T1 distribution in heterogeneous samples. Therefore, CWFP-T1 sequence can be a feasible alternative to CPMG in the determination of physicochemical properties, particularly in processes where fast protocols are requested such as industrial applications.
NASA Astrophysics Data System (ADS)
Li, Lin-Jia; Qian, Sheng-Bang
2013-12-01
We determined forty-two new times of light maximum from our photometry observations and WASP project, and collected all times of light maximum observed between 1961 and 2013 in order to calculate the orbital elements of the SZ Lyncis system and the secular change of the pulsation period with the classical O - C method. We confirmed the decrease of the longitude of the periastron passage with a rate of (-1.˚15 ±0.˚25) yr-1 , and discussed the causative mechanism. The results show that the precession of the star's orbit might be due to a close binary system, which means that the companion of SZ Lyncis is actually a binary system. We used the Hipparcos Intermediate Astrometric Data to obtain the complete orbital elements of the SZ Lyncis system, and found that the inclination, i, and parallax, πt , are 39.˚5 ± 17.˚7 and 2.61 ± 0.98 mas (corresponds to 380 ± 140 pc), respectively. We reanalyzed the mean radial velocities of SZ Lyncis given by Bardin and Imbert (1984), and noticed a weak variation existing in the residuals from a single-Keplerian fit. We suggest that more detailed high-precision spectroscopic observations are definitely needed in the future to check this short periodic change.
NASA Astrophysics Data System (ADS)
Cygorek, M.; Axt, V. M.
2015-08-01
Starting from a quantum kinetic theory for the spin dynamics in diluted magnetic semiconductors, we derive simplified equations that effectively describe the spin transfer between carriers and magnetic impurities for an arbitrary initial impurity magnetization. Taking the Markov limit of these effective equations, we obtain good quantitative agreement with the full quantum kinetic theory for the spin dynamics in bulk systems at high magnetic doping. In contrast, the standard rate description where the carrier-dopant interaction is treated according to Fermi’s golden rule, which involves the assumption of a short memory as well as a perturbative argument, has been shown previously to fail if the impurity magnetization is non-zero. The Markov limit of the effective equations is derived, assuming only a short memory, while higher order terms are still accounted for. These higher order terms represent the precession of the carrier-dopant correlations in the effective magnetic field due to the impurity spins. Numerical calculations show that the Markov limit of our effective equations reproduces the results of the full quantum kinetic theory very well. Furthermore, this limit allows for analytical solutions and for a physically transparent interpretation.
Martay, Hugo E. L.; England, Duncan G.; McCabe, David J.; Walmsley, Ian A.
2011-04-15
The complexity of ultrafast molecular photoionization presents an obstacle to the modeling of pump-probe experiments. Here, a simple optimized model of atomic rubidium is combined with a molecular dynamics model to predict quantitatively the results of a pump-probe experiment in which long-range rubidium dimers are first excited, then ionized after a variable delay. The method is illustrated by the outline of two proposed feasible experiments and the calculation of their outcomes. Both of these proposals use Feshbach {sup 87}Rb{sub 2} molecules. We show that long-range molecular pump-probe experiments should observe spin-orbit precession given a suitable pump pulse, and that the associated high-frequency beat signal in the ionization probability decays after a few tens of picoseconds. If the molecule was to be excited to only a single fine-structure state, then a low-frequency oscillation in the internuclear separation would be detectable through the time-dependent ionization cross section, giving a mechanism that would enable observation of coherent vibrational motion in this molecule.
FIESTA-ET: high-resolution cardiac imaging using echo-planar steady-state free precession.
Slavin, Glenn S; Saranathan, Manojkumar
2002-12-01
This work describes a technique that combines multishot echo-planar imaging (EPI) with steady-state free precession (SSFP, also known as TrueFISP, FIESTA, and balanced FFE) for multislice, cine MR imaging of the heart. Unlike recently reported methods, the technique presented here (FIESTA-ET) is high-resolution and does not require offline reconstruction or postprocessing. It is therefore suitable for use on standard clinical scanners. FIESTA-ET was compared with conventional FIESTA imaging in 10 volunteers and quantitative analyses of myocardial signal-to-noise ratios (SNR) and ventricular volumes were performed. While providing comparable image quality, FIESTA-ET required half the acquisition time per slice of conventional FIESTA. Because multiple slices could be imaged in a single breathhold, the entire heart could be scanned in less than 2 min. Although the FIESTA-ET images exhibited an unexpected increase (P < 0.0005) in myocardial SNR of 16% over FIESTA, the volumetric measurements showed excellent correlation.
Moraes, Tiago Bueno; Monaretto, Tatiana; Colnago, Luiz Alberto
2016-09-01
Longitudinal (T1) and transverse (T2) relaxation times have been widely used in time-domain NMR (TD-NMR) to determine several physicochemical properties of petroleum, polymers, and food products. The measurement of T2 through the CPMG pulse sequence has been used in most of these applications because it denotes a rapid, robust method. On the other hand, T1 has been occasionally used in TD-NMR due to the long measurement time required to collect multiple points along the T1 relaxation curve. Recently, several rapid methods to measure T1 have been proposed. Those methods based upon single shot, known as Continuous Wave Free Precession (CWFP) pulse sequences, have been employed in the simultaneous measurement of T1 and T2 in a rapid fashion. However, these sequences can be used exclusively in instrument featuring short dead time because the magnitude of the signal at thermal equilibrium is required. In this paper, we demonstrate that a special CWFP sequence with a low flip angle can be a simple and rapid method to measure T1 regardless of instruments dead time. Experimental results confirmed that the method called CWFP-T1 may be used to measure both single T1 value and T1 distribution in heterogeneous samples. Therefore, CWFP-T1 sequence can be a feasible alternative to CPMG in the determination of physicochemical properties, particularly in processes where fast protocols are requested such as industrial applications. PMID:27376553
Precession of Fast S0 Stars in the Vicinity of Supermassive Black Hole in the Galactic Center
NASA Astrophysics Data System (ADS)
Dokuchaev, V. I.; Eroshenko, Yu. N.; Klimkov, K. S.
2015-09-01
We elaborate the model of the influence of the diffuse dark matter, invisible stars or stellar mass black holes on the motion of the observed fast moving S0 stars [1-4] around the supermassive black hole SgrA* in the Galactic center with a mass MBH = 4×10^6 Full-size image (<1 K). We will call all this invisible mass as a dark matter. The additional mass perturbs the elliptical orbits of the S0 mass resulting in the so called Newtonian precession of the elliptical orbits. The major aim of our research is the fitting of the published dates on the observed orbital positions of the S0 stars by the theoretically modeling orbit with a power-law profile of the additional (dark matter) mass. Nowadays the observational data provide only the upper limit on the additional mass. In the nearest years the observations of the S0 stars may provide the real weighing of the dark matter inside the orbits of these S0 stars in the Galactic center. This method is a very perspective for the elucidation of the formation and evolution of the dark matter in the Galactic nucleus.
NASA Astrophysics Data System (ADS)
Pan, Yi
This thesis deals with the detection of gravitational-wave signals from the inspiral of precessing, compact binaries using interferometric gravitational- wave detectors (e.g., LIGO), and the design of the signal-recycling cavity for Advanced LIGO (the second generation LIGO). The detection of complicated signals from the inspiral of precessing binaries using the standard matched filter technique requires a computational cost far exceeding what is available with current technology. Alessandra Buonanno, Yanbei Chen, and Michele Vallisneri (BCV) proposed the use of detection template families (DTFs)---phenomenological templates capable of mimicking inspiral waveforms while having simpler functional forms. In Chapter 2 (in collaboration with BCV, and Hideyuki Tagoshi), a BCV2 DTF suggested by BCV is studied. We show a good signal-matching performance of this DTF, propose a template-placement strategy, and estimate that the computational cost required by this DTF is feasible. We also propose a BCV2P DTF to estimate binary parameters. In Chapters 3 and 4 (in collaboration with BCV), I investigate a physical template family (PTF) suggested by BCV. This PTF uses the most accurate known waveforms for inspiraling, precessing binaries with one spinning component, formulated using a new precessing convention to reduce computational cost. PTF has the obvious advantages of a perfect signal snatching, a lower false-alarm rate, and direct estimates of binary parameters. We show how this PTF can be used to detect inspiral waveforms from general precessing binaries. The second part of this thesis concerns a potential problem in the current design of the signal-recycling cavity (SRC) for Advanced LIGO: The SRC is nearly degenerate. In Chapter 5, I show with a numerical simulation that if the current design is used, there will be a serious constraint on the magnitude of mirror deformations, in order to keep the reduction of the signal-to-noise ratio below a few percent. This
Quist, Brady; Hargreaves, Brian A; Cukur, Tolga; Morrell, Glen R; Gold, Garry E; Bangerter, Neal K
2012-04-01
Balanced steady-state free precession (bSSFP) MRI is a rapid and signal-to-noise ratio-efficient imaging method, but suffers from characteristic bands of signal loss in regions of large field inhomogeneity. Several methods have been developed to reduce the severity of these banding artifacts, typically involving the acquisition of multiple bSSFP datasets (and the accompanying increase in scan time). Fat suppression with bSSFP is also challenging; most existing methods require an additional increase in scan time, and some are incompatible with bSSFP band-reduction techniques. This work was motivated by the need for both robust fat suppression and band reduction in the presence of field inhomogeneity when using bSSFP for flow-independent peripheral angiography. The large flip angles used in this application to improve vessel conspicuity and contrast lead to specific absorption rate considerations, longer repetition times, and increased severity of banding artifacts. In this work, a novel method that simultaneously suppresses fat and reduces bSSFP banding artifact with the acquisition of only two phase-cycled bSSFP datasets is presented. A weighted sum of the two bSSFP acquisitions is taken on a voxel-by-voxel basis, effectively synthesizing an off-resonance profile at each voxel that puts fat in the stop band while keeping water in the pass band. The technique exploits the near-sinusoidal shape of the bSSFP off-resonance spectrum for many tissues at large (>50°) flip angles.
NASA Astrophysics Data System (ADS)
Wang, Gang; Ni, Wei-Tou
2015-05-01
ASTROD-GW (ASTROD [astrodynamical space test of relativity using optical devices] optimized for gravitational wave detection) is a gravitational-wave mission with the aim of detecting gravitational waves from massive black holes, extreme mass ratio inspirals (EMRIs) and galactic compact binaries together with testing relativistic gravity and probing dark energy and cosmology. Mission orbits of the 3 spacecrafts forming a nearly equilateral triangular array are chosen to be near the Sun-Earth Lagrange points L3, L4, and L5. The 3 spacecrafts range interferometrically with one another with arm length about 260 million kilometers. For 260 times longer arm length, the detection sensitivity of ASTROD-GW is 260 fold better than that of eLISA/NGO in the lower frequency region by assuming the same acceleration noise. Therefore, ASTROD-GW will be a better cosmological probe. In previous papers, we have worked out the time delay interferometry (TDI) for the ecliptic formation. To resolve the reflection ambiguity about the ecliptic plane in source position determination, we have changed the basic formation into slightly inclined formation with half-year precession-period. In this paper, we optimize a set of 10-year inclined ASTROD-GW mission orbits numerically using ephemeris framework starting at June 21, 2035, including cases of inclination angle with 0° (no inclination), 0.5°, 1.0°, 1.5°, 2.0°, 2.5°, and 3.0°. We simulate the time delays of the first and second generation TDI configurations for the different inclinations, and compare/analyse the numerical results to attain the requisite sensitivity of ASTROD-GW by suppressing laser frequency noise below the secondary noises. To explicate our calculation process for different inclination cases, we take the 1.0° as an example to show the orbit optimization and TDI simulation.
NASA Astrophysics Data System (ADS)
Matsuda, T.; Munekata, H.
2016-02-01
In order to investigate the mechanism of photoexcited precession of magnetization in ferromagnetic G a1 -xM nxAs , magneto-optical (MO) and differential reflectivity (Δ R /R ; DR) temporal profiles are studied at relatively long (picosecond to nanosecond) and ultrashort (1 ps or less) time scales for samples with different Mn content (x =0.01 -0.11 ) . As to the oscillatory MO profiles observed in the long time scale, simulation based on the Landau-Lifshitz-Gilbert equation combined with two different MO effects confirms photoinducement of the perpendicular anisotropy component Δ Heff ,⊥ . As for the profiles observed in the ultrashort time scale, they are consistently explained in terms of the dynamics of photogenerated carriers, but not by the sudden reduction in magnetization (the ultrafast demagnetization). In light of these experimental results and analyses, a mechanism that accounts for the photoinduced Δ Heff ,⊥ is addressed: namely, photoionizationlike excitation of M n2 + , M n2 ++h ν →M n2 +,*=M n3++e- . That such excitation tips magnetic anisotropy toward the out-of-plane direction through the inducement of orbital angular momentum and the gradient ∂ (M n2 +,* )/∂ z is discussed. The validity of the proposed mechanism is examined by estimating the efficiency of excitation on the basis of the Lambert-Beer law and the experimental Δ Heff ,⊥ values, through which an efficiency of 1-10 ppm with a nominal optical cross section of around 5 ×10-12m2 is obtained.
Lucic, Milos A; Koprivsek, Katarina; Kozic, Dusko; Spero, Martina; Spirovski, Milena; Lucic, Silvija
2014-08-16
The aim of the study was to determine the possibilities of two differently acquired two-dimensional fast imaging with steady-state precession (FISP 2D) magnetic resonance sequences in estimation of the third ventricle floor fenestration patency after endoscopic third ventriculostomy (ETV) in the subjects with aqueductal stenosis/obstruction.Fifty eight subjects (37 males, 21 females, mean age 27 years) with previously successfully performed ETV underwent brain MRI on 1.5T MR imager 3-6 months after the procedure. Two different FISP 2D sequences (one included in the standard vendor provided software package, and the other, experimentally developed by our team) were performed respectively at two fixed slice positions: midsagittal and perpendicular to the ETV fenestration, and displayed in a closed-loop cinematographic format in order to estimate the patency. The ventricular volume reduction has been observed as well.Cerebrospinal fluid (CSF) flow through the ETV fenestration was observed in midsagittal plane with both FISP 2D sequences in 93.11% subjects, while in 6.89% subjects the dynamic CSF flow MRI was inconclusive. In the perpendicular plane CSF flow through the ETV fenestration was visible only by use of experimentally developed FISP 2D (TR30/FA70) sequence. Postoperative volume reduction of lateral and third ventricle was detected in 67.24% subjects.Though both FISP 2D sequences acquired in midsagittal plane may be used to estimate the effects of performed ETV, due to achieved higher CSF pulsatile flow sensitivity, only the use of FISP 2D (TR30/FA70) sequence enables the estimation of the treatment effect in perpendicular plane in the absence of phase-contrast sequences.
Minhas, Atul S; Woo, Eung Je; Lee, Soo Yeol
2009-01-01
Magnetic Resonance Electrical Impedance Tomography (MREIT) utilizes the magnetic flux density B(z), generated due to current injection, to find conductivity distribution inside an object. This B(z) can be measured from MR phase images using spin echo pulse sequence. The SNR of B(z) and the sensitivity of phase produced by B(z) in MR phase image are critical in deciding the resolution of MREIT conductivity images. The conventional spin echo based data acquisition has poor phase sensitivity to current injection. Longer scan time is needed to acquire data with higher SNR. We propose a balanced steady state free precession (b-SSFP) based pulse sequence which is highly sensitive to small off-resonance phase changes. A procedure to reconstruct B(z) from MR signal obtained with b-SSFP sequence is described. Phases for b-SSFP signals for two conductivity phantoms of TX 151 and Gelatin are simulated from the mathematical models of b-SSFP signal. It was observed that the phase changes obtained from b-SSFP pulse sequence are highly sensitive to current injection and hence would produce higher magnetic flux density. However, the b-SSFP signal is dependent on magnetic field inhomogeneity and the signal deteriorated highly for small offset from resonance frequency. The simulation results show that the b-SSFP sequence can be utilized for conductivity imaging of a local region where magnetic field inhomogeneity is small. A proper shimming of magnet is recommended before using the b-SSFP sequence.
NASA Astrophysics Data System (ADS)
Dorman, L. I.
2001-08-01
On the bases of available Homestake experimental data (Cleveland et al., 1998) for more than two solar cycles (1970-1994) we determine for each solar neutrino run "n" effective helio-latitude Lef(n). Then we separate all Homestake runs on three equal helio -latitudinal zones: SOUTHERLY, EQUATORIAL, and NORTHERLY with average helio-latitudes -5.3, -0.3 and +5.3 degrees, correspondingly. For each zone and each run we found effective Zurich sunspot number Zef(n), total effective surface of sunspots STef(n), as well as effective surfaces of sunspots in different non-symmetrical helio-latitudinal belts. We separated also all runs on 3 equal groups of LOW, MEDIUM and HIGH solar activity with average sunspot numbers 25.0, 80.1 and 149.9. We found that the biggest decrease of solar neutrino flux with increasing of solar activity was observed in EQUATORIAL zone: from 3.6 SNU at LOW solar activity to 2.1 SNU at HIGH solar activity. The biggest SOUTH -NORTH asymmetry in solar neutrino fluxes was observed in group of runs at LOW solar activity: 2.9 SNU in SOUTHERLY zone and 2.1 SNU in NORTHERLY zone. The SOUTHNORTH asymmetry is found also in correlation coefficients between solar neutrino fluxes in the helio-latitudinal zones SOUTHERLY, EQUATORIAL, and NORTHERLY with solar activity in different non-symmetrical helio-latitudinal belts. Obtained results support the model of magnetic neutrino resonant spin-flavor precession.
NASA Astrophysics Data System (ADS)
Winguth, Arne; Winguth, Cornelia
2013-06-01
By the end of the Late Permian, most continents had collided to form the supercontinent of Pangea. The associated climatic changes at the Permian-Triassic boundary coincided with the most severe mass extinction in the Phanerozoic. One extinction hypothesis favors a climatic response to an increase in large-scale volcanism resulting in ocean stagnation and widespread anoxia with fatal consequences for marine and land organisms. Recent interpretations of geochemical data suggest that orbitally-driven periodic upwelling of toxic hydrogen-sulfide rich water masses contributed to the extinction of species. In this paper, we use the Community Climate System Model (CCSM3) in order to explore the effect of eccentricity-modulated changes of the precession on the strength of Pangean megamonsoons and their impact on productivity and oxygen distribution. The climate model simulates high variability in monsoonal precipitation, trade winds and equatorial upwelling in response to precessional extremes, leading to remarkable fluctuations in the export of carbon from the euphotic zone and hence reduction in dissolved oxygen concentrations in subsurface layers. These findings are in general agreement with increased primary productivity, intensified euxinia within the oxygen-minimum zone, and decimation of the radiolarian zooplankton community as inferred from Japanese marine sections. Strong changes in river run-off linked to precipitation oscillations possibly led to a high variability in the nutrient supply to the Tethys Ocean, thus affecting regional productivity and oxygen distribution. The model results suggest that orbital variability in the sedimentary record and the associated extinction of species are related rather to periodic anoxia in near surface-to-intermediate depth than to widespread anoxic events in the Panthalassic deep-sea.
NASA Astrophysics Data System (ADS)
Barker, Adrian J.
2016-08-01
The spin axis of a rotationally deformed planet is forced to precess about its orbital angular momentum vector, due to the tidal gravity of its host star, if these directions are misaligned. This induces internal fluid motions inside the planet that are subject to a hydrodynamic instability. We study the turbulent damping of precessional fluid motions, as a result of this instability, in the simplest local computational model of a giant planet (or star), with and without a weak internal magnetic field. Our aim is to determine the outcome of this instability, and its importance in driving tidal evolution of the spin-orbit angle in precessing planets (and stars). We find that this instability produces turbulent dissipation that is sufficiently strong that it could drive significant tidal evolution of the spin-orbit angle for hot Jupiters with orbital periods shorter than about 10-18 d. If this mechanism acts in isolation, this evolution would be towards alignment or anti-alignment, depending on the initial angle, but the ultimate evolution (if other tidal mechanisms also contribute) is expected to be towards alignment. The turbulent dissipation is proportional to the cube of the precession frequency, so it leads to much slower damping of stellar spin-orbit angles, implying that this instability is unlikely to drive evolution of the spin-orbit angle in stars (either in planetary or close binary systems). We also find that the instability-driven flow can act as a system-scale dynamo, which may play a role in producing magnetic fields in short-period planets.
Variabilidade óptica de longo período e precessão de jato: o caso de BL Lacertae
NASA Astrophysics Data System (ADS)
Caproni, A.; Abraham, Z.
2003-08-01
Variabilidade é tipicamente uma característica de AGNs, sendo observada em toda a faixa eletromagnética. Em relação às escalas de tempo, variações desde horas até de algumas décadas foram encontradas por vários autores. Em alguns casos, análises temporais de curvas de luz mostram a existência de periodicidade nas variações observadas. Um exemplo de objeto que preenche as características mencionadas acima é BL Lacertae, o protótipo da classe BL Lac dos AGNs. Neste trabalho, nós interpretamos a variabilidade periódica de longo período detectada na curva de luz na banda B (~7,5 anos) como o resultado da periodicidade na amplificação da radiação oriunda do jato relativístico. Neste cenário, a amplificação periódica seria induzida pela precessão, que muda o ângulo entre o jato e a linha de visada. Com esta abordagem e vínculos adicionais fornecidos por observações em altas energias, nós podemos impor limites para os parâmetros do modelo de precessão, tais como o fator de Lorentz associado ao movimento global do jato, o ângulo de abertura do cone de precessão e o ângulo entre o eixo do cone e a linha de visada.
Surovtsev, E. V. Fomin, I. A.
2010-08-15
The magnetic-field dependences of the threshold temperature of the low-temperature instability of uniform spin precession in pure {sup 3}He-B and {sup 3}He-B in an aerogel have been determined for the bulk mechanism. These dependences appear to be different. The theoretical dependence of the threshold temperature for the pure case has been compared with the experimental dependence. The threshold temperature of the instability for {sup 3}He in the aerogel has been estimated for typical experimental conditions.
Bratkovsky, A M; Osipov, V V
2004-03-01
A new mechanism of magnetoresistance, based on tunneling emission of spin-polarized electrons from ferromagnets (FM) into semiconductors (S) and precession of electron spin in the semiconductor layer under external magnetic field, is described. The FM-S-FM structure is considered, which includes very thin heavily doped (delta-doped) layers at FM-S interfaces. At certain parameters the structure is highly sensitive at room temperature to variations of the field with frequencies up to 100 GHz. The current oscillates with the field, and its relative amplitude is determined only by the spin polarizations of FM-S junctions. PMID:15089518
NASA Astrophysics Data System (ADS)
Erb, M. P.; Jackson, C. S.; Broccoli, A. J.; Lea, D. W.
2015-12-01
We present a detection and attribution approach to interpret the forcings and feedbacks that shaped Quaternary climate stemming from known variations in Earth's obliquity, precession, greenhouse gases, and ice sheet extent. Because future climate changes will be driven largely by only one forcing, CO2, it is important to better separate and understand the individual contributions of different forcings in producing past recorded changes. We use idealized equilibrium GCM simulations to fingerprint the annual mean and seasonal responses to individual changes in obliquity, precession, CO2, and ice sheets. These idealized "fingerprint" simulations are scaled by time series of past forcings and summed together to create a time-varying linear reconstruction of past climate that can be compared against proxy records. A multiple linear regression is conducted using Bayesian inference between the components of the linear reconstruction and long proxy time series, such as temperature from deuterium in Antarctic ice cores, to determine whether the modeled response to each forcing needs to be stronger or weaker to better match the data. This methodology offers a simple framework for exploring uncertainties affecting the interpretation of long time series of Quaternary climate variability and a way to use proxy data to test climate response processes relevant to future climate change.
NASA Astrophysics Data System (ADS)
Tanasa, Constantin; Susan-Resiga, Romeo; Muntean, Sebastian; Stuparu, Adrian; Bosioc, Alin; Ciocan, Tiberiu
2015-12-01
Decelerated swirling flows in conical diffusers can develop self-induced instabilities for some configurations of incoming flow. As a result, an upstream steady and axis-symmetrical flow becomes unsteady and three-dimensional with associated pressure fluctuations that hinder the operation of tubomachines. This paper introduces a new approach for mitigating the swirling flow instabilities using a diaphragm into the cone. As a result, the severe flow deceleration is diminished, taming the precessing helical vortex and its associated pressure fluctuations. A full three-dimensional unsteady numerical study is performed for swirling flow apparatus developed at the Politehnica University of Timisoara. Fourier spectra corresponding to unsteady numerical data acquired without and with diaphragm are compared in several locations displaced along to the element of the cone in order to assess the novel concept. It is clearly revealed that the diaphragm mitigates the unsteadiness effects associated to the swirling flow with precessing helical vortex in the conical diffuser. The novel concept paves the way towards a new passive control technique.
NASA Astrophysics Data System (ADS)
Boulila, Slah; Charbonnier, Guillaume; Galbrun, Bruno; Gardin, Silvia
2015-07-01
The Valanginian sediments outcropping in the Vocontian Basin (SE France) exhibit striking marl-limestone alternations, which were formed under the influence of orbital forcing and which have served for geochronological and paleoenvironmental studies. Previous studies have suggested an obliquity forcing during the Late Valanginian interval, reflecting specific environmental conditions such as polar ice. Using a cyclostratigraphic correlation of previously studied sections and performing time-series analysis on the most complete Late Valanginian interval we argue that the climatic precession cycle is the primary driver of these marl-limestone alternations. In addition, we highlight the modulation of the precession by the ~ 100 and 405 kyr eccentricity cycles. We suggest that the cyclostratigraphic misinterpretation (i.e., obliquity-forcing hypothesis) results mainly from poorly preserved 405 kyr eccentricity cycles, due to local hiatuses and/or "missed beats". This study shows the potential of cyclostratigraphic correlations for the detection and quantification of differential hiatuses and/or "missed beats" within intrabasinal sequences, hence providing constraints on cyclostratigraphic interpretations. The recorded 405 kyr eccentricity cycle is of prominent amplitude, and controlled the fourth-order sea-level sequences. These latter are faithfully detected through cyclostratigraphically inferred sedimentation rate. Finally, we show that the well-known, pronounced lithostratigraphic markers/intervals in the basin were orbitally paced by the 405 kyr eccentricity extrema. This is a good argument for the strong impact of this cyclicity on the sedimentary processes, especially during greenhouse periods.
NASA Astrophysics Data System (ADS)
Baland, Rose-Marie; Yseboodt, Marie; Van Hoolst, Tim; Rivoldini, Attilio
2016-10-01
Mercury's spin axis occupies the Cassini state 1, in which the orbit normal and spin axis precess together with a long period of about 300 000 years. An accurate model of the Cassini state is needed to get a reliable estimate of its polar moment of inertia from the measured orientation of its spin axis. The polar moment of inertia provides a strong constraint on the interior structure. For long, it has been assumed that Mercury precesses as a solid body, meaning that the estimate of the polar moment of inertia may be inaccurate. Recently, there has been renewed interest for the topic, because of the recent determination of Mercury's rotation state (Earth-based radar observations, MESSENGER data), as well as the possibility of future more accurate measurements with the BepiColombo mission.Here, we revisit the influence of the liquid outer core, solid inner core, and precession of the pericenter (period of about 127 000 years). Previous studies have concluded that those effects may have an influence above or up to about an order of magnitude below the present uncertainty on the obliquity. We consider three-layer interior models with a mantle (including the crust), a liquid outer core and a solid inner core. Those models are constrained by the mass, radius, second-degree gravity field coefficients and libration amplitude. We adapt to Mercury a Cassini state model previously developed for synchronous satellites, in which we express the spin axis motion in a frame based on the Laplace plane. We take into account the solar gravitational torque exerted on each layer, the internal gravitational torques between the internal layers and the pressure torques as well as the dissipative viscous torques exerted at the interfaces. We reassess the effect of tidal periodic deformations on the torques, currently thought to be two orders of magnitude below the present uncertainty on the spin orientation determination. Finally, we use the current rotation data to constrain Mercury
Cooper, David; Bernier, Nicolas; Rouvière, Jean-Luc
2015-08-12
Precession electron diffraction has been used to provide accurate deformation maps of a device structure showing that this technique can provide a spatial resolution of better than 2 nm and a precision of better than 0.02%. The deformation maps have been fitted to simulations that account for thin specimen relaxation. By combining the experimental deformation maps and simulations, we have been able to separate the effects of the stressor and recessed sources and drains and show that the Si3N4 stressor increases the in-plane deformation in the silicon channel from 0.92 to 1.52 ± 0.02%. In addition, the stress in the deposited Si3N4 film has been calculated from the simulations, which is an important parameter for device design.
Glockner, James F; Saranathan, Manojkumar; Bayram, Ersin; Lee, Christine U
2013-10-01
A novel 3D breath-held Dixon fat-water separated balanced steady state free precession (b-SSFP) sequence for MR cholangiopancreatography (MRCP) is described and its potential clinical utility assessed in a series of patients. The main motivation is to develop a robust breath-held alternative to the respiratory gated 3D Fast Spin Echo (FSE) sequence, the current clinical sequence of choice for MRCP. Respiratory gated acquisitions are susceptible to motion artifacts and blurring in patients with significant diaphragmatic drift, erratic respiratory rhythms or sleep apnea. A two point Dixon fat-water separation scheme was developed which eliminates signal loss arising from B0 inhomogeneity effects and minimizes artifacts from perturbation of the b-SSFP steady state. Preliminary results from qualitative analysis of 49 patients demonstrate robust performance of the 3D Dixon b-SSFP sequence with diagnostic image quality acquired in a 20-24s breath-hold.
Roussel, Pascal; Palatinus, Lukas; Belva, Frédéric; Daviero-Minaud, Sylvie; Mentre, Olivier; Huve, Marielle
2014-04-01
The crystal structure of Sr{sub 4}Ru{sub 6}ClO{sub 18}, a new Ru{sup 4+/5+} oxo-chloride, has been determined from Precession Electron Diffraction (PED) data acquired on a nanocrystal in a transmission electron microscope using the technique of electron diffraction tomography. This approach is described in details following a pedagogic route and a systematic comparison is made of this rather new method with other experimental methods of electron diffraction, and with the standard single crystal X-ray diffraction technique. Both transport and magnetic measurements, showed a transition at low temperature that may be correlated to Ru{sup 4+}/Ru{sup 5+} charge ordering. - Graphical abstract: Structure of Sr{sub 4}Ru{sub 6}ClO{sub 18}, determined using Precession Electron Diffraction data. - Highlights: • Structure of Sr{sub 4}Ru{sub 6}ClO{sub 18} was solved ab initio using precession electron diffraction. • This was done both on a nanometric sample and on a micrometric one. • Different type of experimental methods of electron diffraction are compared. • Single crystal X-ray diffraction was used to confirm the results. • Transport properties were characterized and show “exotic” behavior.
NASA Astrophysics Data System (ADS)
Schunck, Thérèse; Darée, Karl; Krüger, Denis; Himmelsbach, Ralf; Merlat, Lionel
2012-06-01
Nuclear quadrupole resonance is a promising technique for the detection of illicit substances. It relies on the magnetic properties of some specific nuclei, such as nitrogen and chlorine, widely spread among explosives, narcotics or counterfeit medicines. In the basic NQR experiment, the signal (Free Induction Decay (FID)) is generated by a single radio frequency pulse. Because of its small amplitude, the signal is enhanced by averaging several measurements. However, the excitation cannot be repeated until the spin system relaxes back towards equilibrium and this recovery depends on the spin-lattice relaxation time (T1). This can be sorted out by using multi-pulse sequences. One type of multi-pulse sequence, Steady State Free Precession (SSFP), could be used when the spin-spin relaxation time (T2) of the compound is of the same order as T1. It has been claimed that SSFP is a more efficient acquisition sequence than the accumulation of ordinary FIDs. The present study will show, by using simulations and experimental data, that SSFP is a useful sequence for RDX measurements at 5.192 MHz, but is not more effective than a series of well-separated FIDs with a repetition rate lower than 1/T1.
Mulkern, Robert V; Balasubramanian, Mukund; Orbach, Darren B; Mitsouras, Dimitrios; Haker, Steven J
2013-04-01
Among the multiple sequences available for functional magnetic resonance imaging (fMRI), the Steady State Free Precession (SSFP) sequence offers the highest signal-to-noise ratio (SNR) per unit time as well as distortion free images not feasible with the more commonly employed single-shot echo planar imaging (EPI) approaches. Signal changes occurring with activation in SSFP sequences reflect underlying changes in both irreversible and reversible transverse relaxation processes. The latter are characterized by changes in the central frequencies and widths of the inherent frequency distribution present within a voxel. In this work, the well-known frequency response of the SSFP signal intensity is generalized to include the widths and central frequencies of some common frequency distributions on SSFP signal intensities. The approach, using a previously unnoted series expansion, allows for a separation of reversible from irreversible transverse relaxation effects on SSFP signal intensity changes. The formalism described here should prove useful for identifying and modeling mechanisms associated with SSFP signal changes accompanying neural activation.
CAN THE 62 DAY X-RAY PERIOD OF ULX M82 X-1 BE DUE TO A PRECESSING ACCRETION DISK?
Pasham, Dheeraj R.; Strohmayer, Tod E. E-mail: tod.strohmayer@nasa.gov
2013-09-10
We have analyzed all archival Rossi X-Ray Timing Explorer/Proportional Counter Array monitoring observations of the ultraluminous X-ray source M82 X-1 in order to study the properties of its 62 day X-ray period, which was found by Kaaret and Feng in 2007. Based on its high coherence, it has been argued that the observed period is the orbital period of the binary. Utilizing a much longer data set than in previous studies, we find the following. (1) The phase-resolved X-ray (3-15 keV) spectra-modeled with a thermal accretion disk and a power law-suggest that the accretion disk's contribution to the total flux is strongly modulated with phase. (2) Suggestive evidence for a sudden phase shift of approximately 0.4 in phase (25 days) between the first and the second halves of the light curve separated by roughly 1000 days. If confirmed, the implied timescale to change the period is {approx}10 yr, which is exceptionally fast for an orbital phenomenon. These two independent pieces of evidence are consistent with the periodicity being due to a precessing accretion disk, similar to the super-orbital periods observed in systems like Her X-1, LMC X-4, and SS433. However, the timing evidence for a change in the period needs to be confirmed with additional observations. This should be possible with further monitoring of M82 with instruments such as the Swift X-Ray Telescope.
Ruiz-Zepeda, Francisco; Casallas-Moreno, Yenny L; Cantu-Valle, Jesus; Alducin, Diego; Santiago, Ulises; José-Yacaman, Miguel; López-López, Máximo; Ponce, Arturo
2014-12-01
The control growth of the cubic meta-stable nitride phase is a challenge because of the crystalline nature of the nitrides to grow in the hexagonal phase, and accurately identifying the phases and crystal orientations in local areas of the nitride semiconductor films is important for device applications. In this study, we obtained phase and orientation maps of a metastable cubic GaN thin film using precession electron diffraction (PED) under scanning mode with a point-to-point 1 nm probe size beam. The phase maps revealed a cubic GaN thin film with hexagonal GaN inclusions of columnar shape. The orientation maps showed that the inclusions have nucleation sites at the cubic GaN {111} facets. Different growth orientations of the inclusions were observed due to the possibility of the hexagonal {0001} plane to grow on any different {111} cubic facet. However, the generation of the hexagonal GaN inclusions is not always due to a 60° rotation of a {111} plane. These findings show the advantage of using PED along with phase and orientation mapping, and the analysis can be extended to differently composed semiconductor thin films.
Mulkern, Robert V; Balasubramanian, Mukund; Orbach, Darren B; Mitsouras, Dimitrios; Haker, Steven J
2013-04-01
Among the multiple sequences available for functional magnetic resonance imaging (fMRI), the Steady State Free Precession (SSFP) sequence offers the highest signal-to-noise ratio (SNR) per unit time as well as distortion free images not feasible with the more commonly employed single-shot echo planar imaging (EPI) approaches. Signal changes occurring with activation in SSFP sequences reflect underlying changes in both irreversible and reversible transverse relaxation processes. The latter are characterized by changes in the central frequencies and widths of the inherent frequency distribution present within a voxel. In this work, the well-known frequency response of the SSFP signal intensity is generalized to include the widths and central frequencies of some common frequency distributions on SSFP signal intensities. The approach, using a previously unnoted series expansion, allows for a separation of reversible from irreversible transverse relaxation effects on SSFP signal intensity changes. The formalism described here should prove useful for identifying and modeling mechanisms associated with SSFP signal changes accompanying neural activation. PMID:23337079
Sinko, K; Czerny, C; Jagsch, R; Baumann, A
2015-01-01
Objectives: To compare the image quality of MRI scans produced with 1.5- and 3.0-T devices during functional test condition. Methods: 65 MRI scans obtained with 1.5- (n = 43) or 3.0-T (n = 22) true fast imaging with steady-state precession (trueFISP) sequences from patients with a history of a cleft palate were evaluated. Two experts assessed the MRI scans, independently of each other, and blinded to the MRI technique used. Subjective ratings were entered on a five-point Likert scale. The median planes of three anatomical structures (velum, tongue and pharyngeal wall) were assessed in three functional states (at rest, during phonation of sustained “e” and during articulation of “kkk”). In addition, MRI scans taken during velopharyngeal closure were evaluated. Results: Under blinded conditions, both observers (radiologist and orthodontist) independently rated the quality of 1.5-T scans higher than that of 3.0 T. Statistical analysis of pooled data showed that the differences were highly significant (p < 0.009) in 4 out of 10 test conditions. The greatest differences in favour of 1.5 T were observed for MRI scans of the velum. Conclusions: 1.5 T used with trueFISP may be preferable over 3.0-T trueFISP for the evaluation of the velopharyngeal structures in the clinical routine. PMID:26090932
NASA Astrophysics Data System (ADS)
Török, Gabriel; Bakala, Pavel; Šrámková, Eva; Stuchlík, Zdeněk; Urbanec, Martin
2010-05-01
Boutloukos et al. discovered twin-peak quasi-periodic oscillations (QPOs) in 11 observations of the peculiar Z-source Circinus X-1. Among several other conjunctions the authors briefly discussed the related estimate of the compact object mass following from the geodesic relativistic precession model for kHz QPOs. Neglecting the neutron star rotation they reported the inferred mass M 0 = 2.2 ± 0.3 M sun. We present a more detailed analysis of the estimate which involves the frame-dragging effects associated with rotating spacetimes. For a free mass we find acceptable fits of the model to data for (any) small dimensionless compact object angular momentum j = cJ/GM 2. Moreover, quality of the fit tends to increase very gently with rising j. Good fits are reached when M ~ M 0[1 + 0.55(j + j 2)]. It is therefore impossible to estimate the mass without independent knowledge of the angular momentum and vice versa. Considering j up to 0.3 the range of the feasible values of mass extends up to 3 M sun. We suggest that similar increase of estimated mass due to rotational effects can be relevant for several other sources.
Toeroek, Gabriel; Bakala, Pavel; Sramkova, Eva; StuchlIk, Zdenek; Urbanec, Martin E-mail: pavel.bakala@fpf.slu.c E-mail: zdenek.stuchlik@fpf.slu.c
2010-05-01
Boutloukos et al. discovered twin-peak quasi-periodic oscillations (QPOs) in 11 observations of the peculiar Z-source Circinus X-1. Among several other conjunctions the authors briefly discussed the related estimate of the compact object mass following from the geodesic relativistic precession model for kHz QPOs. Neglecting the neutron star rotation they reported the inferred mass M{sub 0} = 2.2 {+-} 0.3 M{sub sun}. We present a more detailed analysis of the estimate which involves the frame-dragging effects associated with rotating spacetimes. For a free mass we find acceptable fits of the model to data for (any) small dimensionless compact object angular momentum j = cJ/GM {sup 2}. Moreover, quality of the fit tends to increase very gently with rising j. Good fits are reached when M {approx} M{sub 0}[1 + 0.55(j + j {sup 2})]. It is therefore impossible to estimate the mass without independent knowledge of the angular momentum and vice versa. Considering j up to 0.3 the range of the feasible values of mass extends up to 3 M{sub sun}. We suggest that similar increase of estimated mass due to rotational effects can be relevant for several other sources.
Park, Sung-Hong; Wang, Danny J.J.; Duong, Timothy Q.
2013-01-01
We implemented pseudo-continuous ASL (pCASL) with 2D and 3D balanced steady state free precession (bSSFP) readout for mapping blood flow in the human brain, retina, and kidney, free of distortion and signal dropout, which are typically observed in the most commonly used echo-planar imaging acquisition. High resolution functional brain imaging in the human visual cortex was feasible with 3D bSSFP pCASL. Blood flow of the human retina could be imaged with pCASL and bSSFP in conjunction with a phase cycling approach to suppress the banding artifacts associated with bSSFP. Furthermore, bSSFP based pCASL enabled us to map renal blood flow within a single breath hold. Control and test-retest experiments suggested that the measured blood flow values in retina and kidney were reliable. Because there is no specific imaging tool for mapping human retina blood flow and the standard contrast agent technique for mapping renal blood flow can cause problems for patients with kidney dysfunction, bSSFP based pCASL may provide a useful tool for the diagnosis of retinal and renal diseases and can complement existing imaging techniques. PMID:23664680
Gao, Ying; Goodnough, Candida L; Erokwu, Bernadette O; Farr, George W; Darrah, Rebecca; Lu, Lan; Dell, Katherine M; Yu, Xin; Flask, Chris A
2014-08-01
Arterial spin labeling (ASL) is a valuable non-contrast perfusion MRI technique with numerous clinical applications. Many previous ASL MRI studies have utilized either echo-planar imaging (EPI) or true fast imaging with steady-state free precession (true FISP) readouts, which are prone to off-resonance artifacts on high-field MRI scanners. We have developed a rapid ASL-FISP MRI acquisition for high-field preclinical MRI scanners providing perfusion-weighted images with little or no artifacts in less than 2 s. In this initial implementation, a flow-sensitive alternating inversion recovery (FAIR) ASL preparation was combined with a rapid, centrically encoded FISP readout. Validation studies on healthy C57/BL6 mice provided consistent estimation of in vivo mouse brain perfusion at 7 and 9.4 T (249 ± 38 and 241 ± 17 mL/min/100 g, respectively). The utility of this method was further demonstrated in the detection of significant perfusion deficits in a C57/BL6 mouse model of ischemic stroke. Reasonable kidney perfusion estimates were also obtained for a healthy C57/BL6 mouse exhibiting differential perfusion in the renal cortex and medulla. Overall, the ASL-FISP technique provides a rapid and quantitative in vivo assessment of tissue perfusion for high-field MRI scanners with minimal image artifacts.
Larmor and the Prehistory of the Lorentz Transformations
ERIC Educational Resources Information Center
Kittel, C.
1974-01-01
A historical analysis is given of the development in 1900 of the Lorentz transformation of coordinates and time, and of electric and magnetic field components. The earlier work of Voight is discussed. (RH)
Lin, Kai; Bi, Xiaoming; Taimen, Kirsi; Zuehlsdorff, Sven; Lu, Biao; Carr, James; Li, Debiao
2012-03-01
We assessed the hypothesis that black-blood steady-state free precession (SSFP) would provide coronary wall images comparable to images from TSE and have better performance than TSE under conditions of fast heart rate. With IRB approval, thirty participants without a history of coronary artery disease (19 men, 11 women, 26-83 y/o) were scanned with a 1.5 T MR scanner. Cross-sectional black-blood images of the proximal portions of coronary arteries were acquired with a two-dimensional (2D), double inversion recovery (DIR) prepared TSE sequence and a 2D DIR SSFP sequence on the same planes. Image quality (ranked with a 4-point system, scored from 0 to 3), vessel wall area and thickness, signal-to-noise ratio (SNR) of the wall and contrast-to-noise ratio (CNR, wall to lumen) were compared between SSFP and TSE with SPSS software (v 13.0). Totally 28 scans were completed. For SSFP and TSE, there was no difference in image quality. SSFP had a higher SNR (23.7 ± 10.1 vs. 14.4 ± 5.2, P < 0.001) and wall-lumen CNR (8.8 ± 4.5 vs. 6.7 ± 3.2, P = 0.001). Good agreements between measured wall area (r = 0.701, P < 0.001) and thickness (r = 0.560, P < 0.001) were found. For 10 participants with heart rate more than 80 beats/min, the image quality of SSFP was higher than TSE (P = 0.016). SSFP provided image quality and measurement accuracy that was comparable to TSE. With its higher performance under fast heart rate conditions, SSFP may break through the existing thresholds for heart rate and extend clinical applicability of coronary wall MR imaging to a larger population.
2010-01-01
Background Left ventricular mass (LVM) is used when expressing infarct or fibrosis as a percentage of the left ventricle (LV). Quantification of LVM is interchangeably carried out in cine steady state free precession (SSFP) and delayed enhancement (DE) magnetic resonance imaging (MRI). However, these techniques may yield different LVM. Therefore, the aim of the study was to compare LVM determined by SSFP and DE MRI in patients and determine the agreement with these sequences with ex vivo data in an experimental animal model. Methods Ethics committees approved human and animal studies. Informed written consent was obtained from all patients. SSFP and DE images were acquired in 60 patients (20 with infarction, 20 without infarction and 20 pediatric patients). Ex vivo MRI was used as reference method for LVM in 19 pigs and compared to in vivo SSFP and DE. Results LVM was greater in SSFP than in DE (p < 0.001) with a bias of 5.0 ± 6.7% in humans (r2 = 0.98), and a bias of 7.3 ± 6.7% (p < 0.001) in pigs (r2 = 0.83). Bias for SSFP and DE images compared to ex vivo LVM was -0.2 ± 9.0% and -7.7 ± 8.5% respectively. Conclusions LVM was higher when measured with SSFP compared to DE. Thus, the percentage infarction of the LV will differ if SSFP or DE is used to determine LVM. There was no significant difference between SSFP and ex vivo LVM suggesting that SSFP is more accurate for LVM quantification. To avoid intrinsic error due to the differences between the sequences, we suggest using DE when expressing infarct as a percentage of LVM. PMID:20096134
Can the 62 Day X-ray Period of ULX M82 X-1 Be Due to a Precessing Accretion Disk?
NASA Technical Reports Server (NTRS)
Pasham, Dheeraj R.; Strohmayer, Tod E.
2013-01-01
We have analyzed all the archival RXTE/PCA monitoring observations of the ultraluminous X-ray source (ULX) M82 X-1 in order to study the properties of its previously discovered 62 day X-ray period (Kaaret & Feng 2007). Based on the high coherence of the modulation it has been argued that the observed period is the orbital period of the binary. Utilizing a much longer data set than in previous studies we find: (1) The phase-resolved X-ray (3-15 keV) energy spectra - modeled with a thermal accretion disk and a power-law corona - suggest that the accretion disk's contribution to the total flux is responsible for the overall periodic modulation while the power-law flux remains approximately constant with phase. (2) Suggestive evidence for a sudden phase shift-of approximately 0.3 in phase (20 days)-between the first and the second halves of the light curve separated by roughly 1000 days. If confirmed, the implied timescale to change the period is approx. = 10 yrs, which is exceptionally fast for an orbital phenomenon. These independent pieces of evidence are consistent with the 62 day period being due to a precessing accretion disk, similar to the so-called super-orbital periods observed in systems like Her X-1, LMC X-4, and SS433. However, the timing evidence for a change in the period needs to be confirmed with additional observations. This should be possible with further monitoring of M82 with instruments such as the X-ray telescope (XRT) on board Swift.
Schmitt, Peter; Bi, Xiaoming; Chappell, Michael A.; Tijssen, Rob H. N.; Sheerin, Fintan; Miller, Karla L.; Jezzard, Peter
2016-01-01
Vessel‐selective dynamic angiograms provide a wealth of useful information about the anatomical and functional status of arteries, including information about collateral flow and blood supply to lesions. Conventional x‐ray techniques are invasive and carry some risks to the patient, so non‐invasive alternatives are desirable. Previously, non‐contrast dynamic MRI angiograms based on arterial spin labeling (ASL) have been demonstrated using both spoiled gradient echo (SPGR) and balanced steady‐state free precession (bSSFP) readout modules, but no direct comparison has been made, and bSSFP optimization over a long readout period has not been fully explored. In this study bSSFP and SPGR are theoretically and experimentally compared for dynamic ASL angiography. Unlike SPGR, bSSFP was found to have a very low ASL signal attenuation rate, even when a relatively large flip angle and short repetition time were used, leading to a threefold improvement in the measured signal‐to‐noise ratio (SNR) efficiency compared with SPGR. For vessel‐selective applications, SNR efficiency can be further improved over single‐artery labeling methods by using a vessel‐encoded pseudo‐continuous ASL (VEPCASL) approach. The combination of a VEPCASL preparation with a time‐resolved bSSFP readout allowed the generation of four‐dimensional (4D; time‐resolved three‐dimensional, 3D) vessel‐selective cerebral angiograms in healthy volunteers with 59 ms temporal resolution. Good quality 4D angiograms were obtained in all subjects, providing comparable structural information to 3D time‐of‐flight images, as well as dynamic information and vessel selectivity, which was shown to be high. A rapid 1.5 min dynamic two‐dimensional version of the sequence yielded similar image features and would be suitable for a busy clinical protocol. Preliminary experiments with bSSFP that included the extracranial vessels showed signal loss in regions of poor magnetic field
Zeineh, Michael; Parekh, Mansi; Zaharchuk, Greg; Su, Jason; Rosenberg, Jarrett; Fischbein, Nancy; Rutt, Brian
2015-01-01
Objective To acquire ultra-high resolution images of the brain using balanced steady-state free precession (bSSFP) at 7.0T and to identify the potential utility of this sequence. Materials and Methods 8 subjects participated in this study after providing informed consent. Each subject was scanned with 8 phase-cycles of bSSFP at 0.4mm isotropic resolution using 0.5 NEX and two-dimensional parallel acceleration of 1.75 × 1.75. Each phase cycle required 5 minutes of scanning, with pauses between the phase cycles allowing short periods of rest. The individual phase cycles were aligned and then averaged. The same subjects underwent scanning using 3D multi-echo GRE at 0.8mm isotropic resolution, 3D CUBE T2 at 0.7mm isotropic resolution, and thin-section coronal oblique T2-weighted FSE at 0.22 × 0.22 × 2.0 mm resolution for comparison. Two neuroradiologists assessed image quality and potential research and clinical utility. Results Subjects generally tolerated the scan sessions well, and composite high-resolution bSSFP images were produced for each subject. Rater analysis demonstrated that bSSFP had superior 3D visualization of the microarchitecture of the hippocampus, very good contrast to delineate the borders of the subthalamic nucleus, and relatively good B1 homogeneity throughout. In addition to excellent visualization of the cerebellum, subtle details of brain and skull base anatomy were also easier to identify on the bSSFP images, including the line of Gennari, membrane of Lillequist, and cranial nerves. bSSFP had a strong iron contrast similar to or better than the comparison sequences. However, cortical gray-white contrast was significantly better with CUBE T2 and T2-weighted FSE. Conclusions bSSFP can facilitate ultra-high resolution imaging of the brain. While total imaging times are long, the individually short phase-cycles can be acquired separately, improving exam tolerability. These images may be beneficial for studies of the hippocampus, iron
Electron Spin Precession at CEBAF
Douglas Higinbotham
2009-08-01
The nuclear physics experiments at the Thomas Jefferson National Accelerator Facility often require longitudinally polarized electrons to be simultaneously delivered to three experimental halls. The degree of longitudinal polarization to each hall varies as function of the accelerator settings, making it challenging in certain situations to deliver a high degree of longitudinal polarization to all the halls simultaneously. Normally, the degree of longitudinal polarization the halls receive is optimized by changing the initial spin direction at the beginning of the machine with a Wien filter. Herein, it is shown that it is possible to further improve the degree of longitudinal polarization for multiple experimental halls by redistributing the energy gain of the CEBAF linacs while keeping the total energy gain fixed.
A self-sustaining atomic magnetometer with τ(-1) averaging property.
Xu, C; Wang, S G; Feng, Y Y; Zhao, L; Wang, L J
2016-06-30
Quantum measurement using coherent superposition of intrinsic atomic states has the advantage of being absolute measurement and can form metrological standards. One example is the absolute measurement of magnetic field by monitoring the Larmor precession of atomic spins whilst another being the Ramsey type atomic clock. Yet, in almost all coherent quantum measurement, the precision is limited by the coherence time beyond which, the uncertainty decreases only as τ(-1/2). Here we show that by non-destructively measuring the phase of the Larmor precession and regenerating the coherence via optical pumping, the self-sustaining Larmor precession signal can persist indefinitely. Consequently, the precision of the magnetometer increases with time following a much faster τ(-1) rule. A mean sensitivity of 240 from 1 Hz to 10 Hz is realized, being close to the shot noise level. This method of coherence regeneration may also find important applications in improving the performance of atomic clocks.
Teleportation and spin squeezing utilizing multimode entanglement of light with atoms
Hammerer, K.; Cirac, J. I.; Polzik, E. S.
2005-11-15
We present a protocol for the teleportation of the quantum state of a pulse of light onto the collective spin state of an atomic ensemble. The entangled state of light and atoms employed as a resource in this protocol is created by probing the collective atomic spin, Larmor precessing in an external magnetic field, off resonantly with a coherent pulse of light. We take here full account of the effects of Larmor precession and show that it gives rise to a qualitatively different type of multimode entangled state of light and atoms. The protocol is shown to be robust against the dominating sources of noise and can be implemented with an atomic ensemble at room temperature interacting with free-space light. We also provide a scheme to perform the readout of the Larmor precessing spin state enabling the verification of successful teleportation as well as the creation of spin squeezing.
Vomir, Mircea; Turnbull, Robin; Birced, Ipek; Parreira, Pedro; MacLaren, Donald A; Lee, Stephen L; André, Pascal; Bigot, Jean-Yves
2016-08-10
For spintronic devices excited by a sudden magnetic or optical perturbation, the torque acting on the magnetization plays a key role in its precession and damping. However, the torque itself can be a dynamical quantity via the time-dependent anisotropies of the system. A challenging problem for applications is then to disentangle the relative importance of various sources of anisotropies in the dynamical torque, such as the dipolar field, the crystal structure or the shape of the particular interacting magnetic nanostructures. Here, we take advantage of a range of colloidal cobalt ferrite nanocubes assembled in 2D thin films under controlled magnetic fields to demonstrate that the phase, ϕPrec, of the precession carries a strong signature of the dynamical anisotropies. Performing femtosecond magneto-optics, we show that ϕPrec displays a π-shift for a particular angle θH of an external static magnetic field, H. θH is controlled with the cobalt concentration, the laser intensity, as well as the interparticle interactions. Importantly, it is shown that the shape anisotropy, which strongly departs from those of equivalent bulk thin films or individual noninteracting nanoparticles, reveals the essential role played by the interparticle collective effects. This work shows the reliability of a noninvasive optical approach to characterize the dynamical torque in high density magnetic recording media made of organized and interacting nanoparticles.
Vomir, Mircea; Turnbull, Robin; Birced, Ipek; Parreira, Pedro; MacLaren, Donald A; Lee, Stephen L; André, Pascal; Bigot, Jean-Yves
2016-08-10
For spintronic devices excited by a sudden magnetic or optical perturbation, the torque acting on the magnetization plays a key role in its precession and damping. However, the torque itself can be a dynamical quantity via the time-dependent anisotropies of the system. A challenging problem for applications is then to disentangle the relative importance of various sources of anisotropies in the dynamical torque, such as the dipolar field, the crystal structure or the shape of the particular interacting magnetic nanostructures. Here, we take advantage of a range of colloidal cobalt ferrite nanocubes assembled in 2D thin films under controlled magnetic fields to demonstrate that the phase, ϕPrec, of the precession carries a strong signature of the dynamical anisotropies. Performing femtosecond magneto-optics, we show that ϕPrec displays a π-shift for a particular angle θH of an external static magnetic field, H. θH is controlled with the cobalt concentration, the laser intensity, as well as the interparticle interactions. Importantly, it is shown that the shape anisotropy, which strongly departs from those of equivalent bulk thin films or individual noninteracting nanoparticles, reveals the essential role played by the interparticle collective effects. This work shows the reliability of a noninvasive optical approach to characterize the dynamical torque in high density magnetic recording media made of organized and interacting nanoparticles. PMID:27398653
2016-01-01
For spintronic devices excited by a sudden magnetic or optical perturbation, the torque acting on the magnetization plays a key role in its precession and damping. However, the torque itself can be a dynamical quantity via the time-dependent anisotropies of the system. A challenging problem for applications is then to disentangle the relative importance of various sources of anisotropies in the dynamical torque, such as the dipolar field, the crystal structure or the shape of the particular interacting magnetic nanostructures. Here, we take advantage of a range of colloidal cobalt ferrite nanocubes assembled in 2D thin films under controlled magnetic fields to demonstrate that the phase, ϕPrec, of the precession carries a strong signature of the dynamical anisotropies. Performing femtosecond magneto-optics, we show that ϕPrec displays a π-shift for a particular angle θH of an external static magnetic field, H. θH is controlled with the cobalt concentration, the laser intensity, as well as the interparticle interactions. Importantly, it is shown that the shape anisotropy, which strongly departs from those of equivalent bulk thin films or individual noninteracting nanoparticles, reveals the essential role played by the interparticle collective effects. This work shows the reliability of a noninvasive optical approach to characterize the dynamical torque in high density magnetic recording media made of organized and interacting nanoparticles. PMID:27398653
NASA Astrophysics Data System (ADS)
van den Berg, Bas; Sierro, Francisco Javier; Abel Flores, Jose; Civis, Jorge; González-Delgado, Jose Angel; Mata, Pilar; Cruz Larrasoaña, Juan
2014-05-01
The volume of evaporite deposits in the Mediterranean during the Messinian Salinity Crisis (MSC) requires an on-going supply of sea water from the Atlantic. The location of the connecting corridor(s) at this time however remains elusive. One possibility is that the Guadalquivir Basin at the western end of the Betic Strait linked the Atlantic and Mediterranean during the MSC. The Messinian sediments deposited here are largely preserved in the sub-surface. Recent results based on paleobathymetric and magnetostratigraphic data from two boreholes indicate that this region accumulated marine sediments continuously, right up until the Miocene-Pliocene boundary (Larrasoaña et al., 2008; Pérez-Asensio et al., 2012a). These boreholes, located at the north-western margin of the Guadalquivir Basin, have been dated in a low resolution chronostratigraphic framework using magneto- and biostratigraphy (Larrasoaña et al., 2008) and by extrapolation using global, obliquity-driven, glacial records (Pérez-Asensio et al., 2012b). We hereby present a high-resolution chronostratigraphic framework for these two boreholes (Montemayor and Huelva) using cyclostratigraphy and additional bio-events. Cyclostratigraphic results were obtained using high resolution XRF data. We correlate patterns in the elemental composition of the sediments between the two boreholes and subsequently tune them to the astronomical solution. From these results we have interpreted that the cyclic sedimentary features are the result of oscillations in carbonate input and dilution, forced by precession and obliquity. Remarkably, we see the phase relation between various proxies change throughout the core, which we try to explain by a gradual change in the sedimentary setting. Besides, we can accurately locate the position of the Miocene-Pliocene boundary within these boreholes, and relate changes in sedimentation rate and phase relation to major events within the Mediterranean Basin (e.g. onset of the MSC and
Suppression of Spin-Exchange Relaxation Using Pulsed Parametric Resonance
NASA Astrophysics Data System (ADS)
Korver, A.; Wyllie, R.; Lancor, B.; Walker, T. G.
2013-07-01
We demonstrate that spin-exchange dephasing of Larmor precession at near-Earth-scale fields is effectively eliminated by dressing the alkali-metal atom spins in a sequence of ac-coupled 2π pulses, repeated at the Larmor precession frequency. The contribution of spin-exchange collisions to the spectroscopic linewidth is reduced by a factor of the duty cycle of the pulses. We experimentally demonstrate resonant transverse pumping in magnetic fields as high as 0.1 G, present experimental measurements of the suppressed spin-exchange relaxation, and show enhanced magnetometer response relative to a light-narrowed scalar magnetometer.
Ribot, Emeline J.; Martinez-Santiesteban, Francisco M.; Simedrea, Carmen; Steeg, Patricia S.; Chambers, Ann F.; Rutt, Brian K.; Foster, Paula J.
2012-01-01
Purpose To simultaneously detect iron-labeled cancer cells and brain tumors in vivo in one scan, the balanced steady-state free precession (b-SSFP) imaging sequence was optimized at 1.5 T on mice developing brain metastases subsequent to the injection of micron-sized iron oxide particle-labeled human breast cancer cells. Materials and Methods b-SSFP sequence parameters (repetition time, flip angle, and receiver bandwidth) were varied and the signal-to-noise ratio, contrast between the brain and tumors, and the number of detected iron-labeled cells were evaluated. Results Optimal b-SSFP images were acquired with a 26 msec repetition time, 35° flip angle, and bandwidth of ±21 kHz. b-SSFP images were compared with T2-weighted 2D fast spin echo (FSE) and 3D spoiled gradient recalled echo (SPGR) images. The mean tumor-brain contrast-to-noise ratio and the ability to detect iron-labeled cells were the highest in the b-SSFP images. Conclusion A single b-SSFP scan can be used to visualize both iron-labeled cells and brain metastases. PMID:21698713
Tenjin, Hiroshi; Tanigawa, Seisuke; Takadou, Michiko; Ogawa, Takahiro; Mandai, Ayako; Nanto, Masataka; Osaka, Yasuhiko; Nakahara, Yoshikazu; Umeda, Masahiro; Higuchi, Toshihiro
2013-01-01
This study evaluated the aneurysm wall thickness by high-resolution T1-weighted imaging and the contact between the aneurysm and surrounding tissue by steady-state free precession (SSFP) imaging. The surgical findings were prospectively compared with these preoperative magnetic resonance (MR) imaging findings in 35 consecutive patients with 37 unruptured cerebral aneurysms (UCAs). The aneurysm wall was not visible in 13 UCAs, but was visible in 23. Subarachnoid space between the aneurysm and surrounding tissue was visible in 16 UCAs, a visible layer of cerebrospinal fluid (CSF) between the aneurysm and surrounding tissue in 12, and no visible layer in 7. MR imaging predicted the surgical findings in 29 UCAs (78%), showed different findings in six UCAs (16%), and two (5%) could not be evaluated due to insufficient quality of preoperative MR images. Among the UCAs with different findings, five UCAs had a partially thin wall even though high-resolution T1-weighted imaging had shown a visible wall, and one UCA showed less contact with the surrounding tissue even though the SSFP imaging had shown no visible CSF layer. In conclusion, high-resolution T1-weighted imaging and SSFP imaging provided significant additional preoperative information regarding UCAs and the surrounding tissue.
Kawahara, Seiya; Ohno, Tsuyoshi; Furuta, Akihiro; Togashi, Kaori
2015-01-01
Background A 3 Tesla (3 T) magnetic resonance (MR) scanner is a promising tool for upper abdominal angiography. However, no report has focused on the contrast behavior of non-contrast-enhanced hepatic MR arteriography at 3 T. Purpose To establish the optimal inversion time (TI) for favorable selective visualization of the hepatic arteries on non-contrast-enhanced MR arteriography with time spatial labeling inversion pulse (Time-SLIP) at 3 T. Material and Methods Twenty-five healthy volunteers were examined using respiratory-triggered three-dimensional balanced steady-state free-precession combined with Time-SLIP. According to the difference in the TI, five image groups (A, B, C, D, and E, from 1200 to 2000 ms, increasing at 200-ms intervals) were performed and compared to detect the optimal TI for hepatic artery visualization. The relative Cv-l (vessel-to-liver contrast) was quantified. For qualitative evaluation, the vessel visualization quality and order of the depicted hepatic artery branches were evaluated. Results In group C (TI of 1600 ms), the Cv-l showed the highest probably due to a favorable balance between the hepatic vessel signal and signal recovery of the surrounding tissue. Regarding qualitative assessment, in group C, the mean image quality score of all hepatic arteries and mean maximal visible order of the hepatic artery branches were the highest. However, there was no significant difference between these results. Conclusion Non-contrast-enhanced hepatic MR arteriography with Time-SLIP at 3 T enabled the selective visualization of hepatic arteries at a TI of 1600 ms with an optimal balance between Cv-l and peripheral hepatic artery visualization. PMID:26668756
Jang, Jihye; Bellm, Steven; Roujol, Sébastien; Basha, Tamer A; Nezafat, Maryam; Kato, Shingo; Weingärtner, Sebastian; Nezafat, Reza
2016-10-01
Cardiac T1 mapping allows non-invasive imaging of interstitial diffuse fibrosis. Myocardial T1 is commonly calculated by voxel-wise fitting of the images acquired using balanced steady-state free precession (SSFP) after an inversion pulse. However, SSFP imaging is sensitive to B1 and B0 imperfection, which may result in additional artifacts. A gradient echo (GRE) imaging sequence has been used for myocardial T1 mapping; however, its use has been limited to higher magnetic field to compensate for the lower signal-to-noise ratio (SNR) of GRE versus SSFP imaging. A slice-interleaved T1 mapping (STONE) sequence with SSFP readout (STONE-SSFP) has been recently proposed for native myocardial T1 mapping, which allows longer recovery of magnetization (>8 R-R) after each inversion pulse. In this study, we hypothesize that a longer recovery allows higher SNR and enables native myocardial T1 mapping using STONE with GRE imaging readout (STONE-GRE) at 1.5T. Numerical simulations and phantom and in vivo imaging were performed to compare the performance of STONE-GRE and STONE-SSFP for native myocardial T1 mapping at 1.5T. In numerical simulations, STONE-SSFP shows sensitivity to both T2 and off resonance. Despite the insensitivity of GRE imaging to T2 , STONE-GRE remains sensitive to T2 due to the dependence of the inversion pulse performance on T2 . In the phantom study, STONE-GRE had inferior accuracy and precision and similar repeatability as compared with STONE-SSFP. In in vivo studies, STONE-GRE and STONE-SSFP had similar myocardial native T1 times, precisions, repeatabilities and subjective T1 map qualities. Despite the lower SNR of the GRE imaging readout compared with SSFP, STONE-GRE provides similar native myocardial T1 measurements, precision, repeatability, and subjective image quality when compared with STONE-SSFP at 1.5T. PMID:27658506
The seasons, global temperature, and precession
Thompson, D.J.
1995-12-31
Analysis of instrumental temperature records beginning in 1659 shows that in much of the world the dominant frequency of the seasons is one cycle per anomalistic year (the time from perihelion to perihelion, 265.25964 days), not one cycle per tropical year (the time from equinox to equinox, 265.24220 days), and that the timing of the annual temperature cycle is controlled by perihelion. The assumption that the seasons were timed by the equinoxes has caused many statistical analyses of climate data to be badly biased. Coherence between changes in the amplitude of the annual cycle and those in the average temperature show that between 1854 and 1922 there were small temperature variations, probable of solar origin. Since 1922, the phase of the Northern Hemisphere coherence between these quantities switched from 0{degrees} to 180{degrees} and implies that solar variability cannot be the sole cause of the increasing temperature over the last century. About 1940, the phase patterns of the previous 300 years began to change and now appear to be changing at an unprecendented rate. The average change in phase is not coherent with the logarithm of atmospheric CO{sub 2} concentration.
The seasons, global temperature, and precession
Thomson, D.J.
1995-04-07
Analysis of instrumental temperature records beginning in 1659 shows that in much of the world the dominant frequency of the seasons is one cycle per anomalistic year (the time from perihelion to perihelion, 365.25964 days), not one cycle per tropical year (the time from equinox to equinox, 365.24220 days), and that the timing of the annual temperature cycle is controlled by perihelion. The assumption that the seasons were timed by the equinoxes has caused many statistical analyses of climate data to be badly biased. Coherence between changes in the amplitude of the annual cycle and those in the average temperature show that between 1854 and 1922 there were small temperature variations, probably of solar origin. Since 1922, the phase of the Northern Hemisphere coherence between these quantities switched from 0{degrees} to 180{degrees} and implies that solar variability cannot be the sole cause of the increasing temperature over the last century. About 1940, the phase patterns of the previous 300 years began to change and now appear to be changing at an unprecedented rate. The average change in phase is now coherent with the logarithm of atmospheric CO{sub 2} concentration. 80 refs., 13 figs.
Dumbbell galaxies and precessing radio jets
NASA Astrophysics Data System (ADS)
Wirth, A.; Smarr, L.; Gallagher, J. S.
1982-04-01
It is suggested that a subclass of inversion-symmetric distorted extended radio sources (Z-shapes) have shapes produced by effects on large scales compared with the central engine. The subclass is defined by those sources whose underlying galaxies have a dumbbell or multiple nuclei optical morphology. New optical observations are presented which indicate that in one well-studied Z-shape source, NGC 326, there are two galaxies passing at a projected distance of about 10 kpc and that the gravitational coupling of the nonradio galaxy on the radio galaxy's atmosphere may be the mechanism which has realigned the jet direction. If the proposed interpretation is correct, some large-scale jet properties of double radio sources reveal more about properties of the gas distribution in galaxies and less about the central engine than heretofore supposed.
Conformal Weyl Gravity and Perihelion Precession
NASA Technical Reports Server (NTRS)
Sultana, Joseph; Kazanas, Demosthenes; Said, Jakson, Levi
2012-01-01
We investigate the perihelion shift of planetary motion in conformal Weyl gravity using the metric of the static, spherically symmetric solution discovered by Mannheim and Kazanas. To this end we employ a procedure similar to that used by Weinberg for the Schwarzschild solution, which has also been used recently to study the solar system effects of the cosmological constant Lambda. We show that besides the general relativistic terms obtained earlier from the Schwarzschild-de Sitter solution, the expression for the perihelion shift includes a negative contribution which arises from the linear term gamma ray in the metric. Using data for perihelion shift observations, we obtain constraints on the value of the constant gammma similar to that obtained earlier using galactic rotational curves.
Formulas for precession. [motion of mean equator
NASA Technical Reports Server (NTRS)
Kinoshita, H.
1975-01-01
Literal expressions for the precessional motion of the mean equator referred to an arbitrary epoch are constructed. Their numerical representations, based on numerical values recommended at the working meeting of the International Astronomical Union Commission held in Washington in September 1974, are obtained. In constructing the equations of motion, the second-order secular perturbation and the secular perturbation due to the long-periodic terms in the motions of the moon and the sun are taken into account. These perturbations contribute more to the motion of the mean equator than does the term due to the secular perturbation of the orbital eccentricity of the sun.
Absence of Complete Finite-Larmor-Radius Stabilization in Extended MHD
Zhu, P.; Schnack, D. D.; Ebrahimi, F.; Zweibel, E. G.; Suzuki, M.; Hegna, C. C.; Sovinec, C. R.
2008-08-22
The dominant finite-Larmour-radius (FLR) stabilization effects on interchange instability can be retained by taking into account the ion gyroviscosity or the generalized Ohm's law in an extended MHD model. However, recent simulations and theoretical calculations indicate that complete FLR stabilization of the interchange mode may not be attainable by ion gyroviscosity or the two-fluid effect alone in the framework of extended MHD. For a class of plasma equilibria in certain finite-{beta} or nonisentropic regimes, the critical wave number for complete FLR stabilization tends toward infinity.
Search For The Electric Dipole Moment Of The Neutron
Grinten, Maurits van der
2006-07-11
We report on the nEDM experiment at the Institut Laue Langevin (ILL), based on a precision measurement of the Larmor precession frequency of polarised ultra-cold neutrons stored in a cell in a magnetic field. An EDM would reveal itself by a response of the Larmor precession frequency of the neutron to an electric field applied over the storage volume. The experiment has been taking data over a period of six years and has subsequently been running for one year devoted to systematic studies related to the experiment. These systematic studies have now been completed. This experiment will result in an EDM measurement with a sensitivity of the order of 10-26 e cm. The experimental techniques used in the experiment are presented as well as the systematic studies and results of the data analysis of the experiment.
Vector magnetic field sensing by a single nitrogen vacancy center in diamond
NASA Astrophysics Data System (ADS)
Chen, X.-D.; Sun, F.-W.; Zou, C.-L.; Cui, J.-M.; Zhou, L.-M.; Guo, G.-C.
2013-03-01
In this letter, we proposed and experimentally demonstrated a method to detect the vector magnetic field with a single nitrogen vacancy (NV) center in diamond. The magnetic field in parallel with the axis of the NV center can be obtained by detecting the electron Zeeman shift, while the Larmor precession of an ancillary nuclear spin close to the NV center can be used to measure the field perpendicular to the axis. Experimentally, both the Zeeman shift and Larmor precession can be measured through the fluorescence from the NV center. By applying additional calibrated magnetic fields, complete information on the vector magnetic field can be achieved with such a method. This vector magnetic-field detection method is insensitive to temperature fluctuation and it can be applied to nanoscale magnetic measurements.
A self-sustaining atomic magnetometer with τ‑1 averaging property
NASA Astrophysics Data System (ADS)
Xu, C.; Wang, S. G.; Feng, Y. Y.; Zhao, L.; Wang, L. J.
2016-06-01
Quantum measurement using coherent superposition of intrinsic atomic states has the advantage of being absolute measurement and can form metrological standards. One example is the absolute measurement of magnetic field by monitoring the Larmor precession of atomic spins whilst another being the Ramsey type atomic clock. Yet, in almost all coherent quantum measurement, the precision is limited by the coherence time beyond which, the uncertainty decreases only as τ‑1/2. Here we show that by non-destructively measuring the phase of the Larmor precession and regenerating the coherence via optical pumping, the self-sustaining Larmor precession signal can persist indefinitely. Consequently, the precision of the magnetometer increases with time following a much faster τ‑1 rule. A mean sensitivity of 240 from 1 Hz to 10 Hz is realized, being close to the shot noise level. This method of coherence regeneration may also find important applications in improving the performance of atomic clocks.
A self-sustaining atomic magnetometer with τ−1 averaging property
Xu, C.; Wang, S. G.; Feng, Y. Y.; Zhao, L.; Wang, L. J.
2016-01-01
Quantum measurement using coherent superposition of intrinsic atomic states has the advantage of being absolute measurement and can form metrological standards. One example is the absolute measurement of magnetic field by monitoring the Larmor precession of atomic spins whilst another being the Ramsey type atomic clock. Yet, in almost all coherent quantum measurement, the precision is limited by the coherence time beyond which, the uncertainty decreases only as τ−1/2. Here we show that by non-destructively measuring the phase of the Larmor precession and regenerating the coherence via optical pumping, the self-sustaining Larmor precession signal can persist indefinitely. Consequently, the precision of the magnetometer increases with time following a much faster τ−1 rule. A mean sensitivity of 240 from 1 Hz to 10 Hz is realized, being close to the shot noise level. This method of coherence regeneration may also find important applications in improving the performance of atomic clocks. PMID:27357490
A self-sustaining atomic magnetometer with τ(-1) averaging property.
Xu, C; Wang, S G; Feng, Y Y; Zhao, L; Wang, L J
2016-01-01
Quantum measurement using coherent superposition of intrinsic atomic states has the advantage of being absolute measurement and can form metrological standards. One example is the absolute measurement of magnetic field by monitoring the Larmor precession of atomic spins whilst another being the Ramsey type atomic clock. Yet, in almost all coherent quantum measurement, the precision is limited by the coherence time beyond which, the uncertainty decreases only as τ(-1/2). Here we show that by non-destructively measuring the phase of the Larmor precession and regenerating the coherence via optical pumping, the self-sustaining Larmor precession signal can persist indefinitely. Consequently, the precision of the magnetometer increases with time following a much faster τ(-1) rule. A mean sensitivity of 240 from 1 Hz to 10 Hz is realized, being close to the shot noise level. This method of coherence regeneration may also find important applications in improving the performance of atomic clocks. PMID:27357490
Liu, Changjiang; Patel, Sahil J.; Peterson, Timothy A.; Geppert, Chad C.; Christie, Kevin D.; Stecklein, Gordon; Palmstrøm, Chris J.; Crowell, Paul A.
2016-01-01
A distinguishing feature of spin accumulation in ferromagnet–semiconductor devices is its precession in a magnetic field. This is the basis for detection techniques such as the Hanle effect, but these approaches become ineffective as the spin lifetime in the semiconductor decreases. For this reason, no electrical Hanle measurement has been demonstrated in GaAs at room temperature. We show here that by forcing the magnetization in the ferromagnet to precess at resonance instead of relying only on the Larmor precession of the spin accumulation in the semiconductor, an electrically generated spin accumulation can be detected up to 300 K. The injection bias and temperature dependence of the measured spin signal agree with those obtained using traditional methods. We further show that this approach enables a measurement of short spin lifetimes (<100 ps), a regime that is not accessible in semiconductors using traditional Hanle techniques. PMID:26777243
NASA Astrophysics Data System (ADS)
Phan, T. D.; Shay, M. A.; Haggerty, C. C.; Gosling, J. T.; Eastwood, J. P.; Fujimoto, M.; Malakit, K.; Mozer, F. S.; Cassak, P. A.; Oieroset, M.; Angelopoulos, V.
2016-09-01
We report a Time History of Events and Macroscale Interactions during Substorms (THEMIS-D) spacecraft crossing of a magnetopause reconnection exhaust ~9 ion skin depths (di) downstream of an X line. The crossing was characterized by ion jetting at speeds substantially below the predicted reconnection outflow speed. In the magnetospheric inflow region THEMIS detected (a) penetration of magnetosheath ions and the resulting flows perpendicular to the reconnection plane, (b) ion outflow extending into the magnetosphere, and (c) enhanced electron parallel temperature. Comparison with a simulation suggests that these signatures are associated with the gyration of magnetosheath ions onto magnetospheric field lines due to the shift of the flow stagnation point toward the low-density magnetosphere. Our observations indicate that these effects, ~2-3 di in width, extend at least 9 di downstream of the X line. The detection of these signatures could indicate large-scale proximity of the X line but do not imply that the spacecraft was upstream of the electron diffusion region.
Spin precession by pulsed inductive magnetometry in thin amorphous plates
NASA Astrophysics Data System (ADS)
Magni, Alessandro; Bottauscio, Oriano; Caprile, Ambra; Celegato, Federica; Ferrara, Enzo; Fiorillo, Fausto
2014-05-01
Broadband magnetic loss and damping behavior of Co-based amorphous ribbons and thin films have been investigated. The permeability and loss response of the transverse anisotropy ribbon samples in the frequency range DC to 1 GHz is interpreted in terms of combined and distinguishable contributions to the magnetization process by domain wall displacements and magnetization rotations. The latter alone are shown to survive at the highest frequencies, where the losses are calculated via coupled Maxwell and Landau-Lifshitz-Gilbert (LLG) equations. Remarkably high values of the LLG damping coefficient α = 0.1-0.2 are invoked in this theoretical prediction. Direct measurements of α by pulsed inductive microwave magnetometry are thus performed, both in these laminae and in amorphous films of identical composition, obtaining about one order of magnitude increase of the α value upon the 100 nm÷10 μm thickness range. This confirms that dissipation by eddy currents enters the LLG equation via large increase of the damping coefficient.
Experimental Demonstration of Scanned Spin-Precession Microscopy
NASA Astrophysics Data System (ADS)
Bhallamudi, V. P.; Wolfe, C. S.; Amin, V. P.; Labanowski, D. E.; Berger, A. J.; Stroud, D.; Sinova, J.; Hammel, P. C.
2013-09-01
We present a new tool for imaging spin properties. We show that a spatially averaged spin signal, measured as a function of a scanned magnetic probe’s position, contains information about the local spin properties. In this first demonstration we map the injected spin density in GaAs by measuring spin photoluminescence with a resolution of 1.2μm. The ultimate limit of the technique is set by the gradient of the probe’s field, allowing for a resolution beyond the optical diffraction limit. Such probes can also be integrated with other detection methods. This generality allows the technique to be extended to buried interfaces and optically inactive materials.
Spin precession by pulsed inductive magnetometry in thin amorphous plates
Magni, Alessandro; Bottauscio, Oriano; Caprile, Ambra Celegato, Federica; Ferrara, Enzo; Fiorillo, Fausto
2014-05-07
Broadband magnetic loss and damping behavior of Co-based amorphous ribbons and thin films have been investigated. The permeability and loss response of the transverse anisotropy ribbon samples in the frequency range DC to 1 GHz is interpreted in terms of combined and distinguishable contributions to the magnetization process by domain wall displacements and magnetization rotations. The latter alone are shown to survive at the highest frequencies, where the losses are calculated via coupled Maxwell and Landau–Lifshitz–Gilbert (LLG) equations. Remarkably high values of the LLG damping coefficient α = 0.1–0.2 are invoked in this theoretical prediction. Direct measurements of α by pulsed inductive microwave magnetometry are thus performed, both in these laminae and in amorphous films of identical composition, obtaining about one order of magnitude increase of the α value upon the 100 nm÷10 μm thickness range. This confirms that dissipation by eddy currents enters the LLG equation via large increase of the damping coefficient.
Precession of a rapidly rotating cylinder flow: traverse through resonance
NASA Astrophysics Data System (ADS)
Lopez, Juan; Marques, Francisco
2014-11-01
The flow in a rapidly rotating cylinder that is titled and also rotating around another axis can undergo sudden transitions to turbulence. Experimental observations of this have been associated with triadic resonances. The experimental and theoretical results are well-established in the literature, but there remains a lack of understanding of the physical mechanisms at play in the sudden transition from laminar to turbulent flow with very small variations in the governing parameters. Here, we present direct numerical simulations of a traverse in parameter space through an isolated resonance, and describe in detail the bifurcations involved in the sudden transition. U.S. National Science Foundation Grant CBET-1336410 and Spanish Ministry of Education and Science Grant (with FEDER funds) FIS2013-40880.
Precession of a Spinning Ball Rolling down an Inclined Plane
ERIC Educational Resources Information Center
Cross, Rod
2015-01-01
A routine problem in an introductory physics course considers a rectangular block at rest on a plane inclined at angle a to the horizontal. In order for the block not to slide down the incline, the coefficient of sliding friction, µ, must be at least tan a. The situation is similar for the case of a ball rolling down an inclined plane. In order…
Paramagnetic colloidal ribbons in a precessing magnetic field
NASA Astrophysics Data System (ADS)
Alvarez-Nodarse, R.; Quintero, N. R.; Mertens, F. G.; Casic, N.; Fischer, Th. M.
2015-03-01
We investigate the dynamics of a kink in a damped parametrically driven nonlinear Klein-Gordon equation. We show by using a method of averaging that, in the high-frequency limit, the kink moves in an effective potential and is driven by an effective constant force. We demonstrate that the shape of the solitary wave can be controlled via the frequency and the eccentricity of the modulation. This is in accordance with the experimental results reported in a recent paper [Casic et al., Phys. Rev. Lett. 110, 168302 (2013), 10.1103/PhysRevLett.110.168302], where the dynamic self-assembly and propulsion of a ribbon formed from paramagnetic colloids in a time-dependent magnetic field has been studied.
Paramagnetic colloidal ribbons in a precessing magnetic field.
Alvarez-Nodarse, R; Quintero, N R; Mertens, F G; Casic, N; Fischer, Th M
2015-03-01
We investigate the dynamics of a kink in a damped parametrically driven nonlinear Klein-Gordon equation. We show by using a method of averaging that, in the high-frequency limit, the kink moves in an effective potential and is driven by an effective constant force. We demonstrate that the shape of the solitary wave can be controlled via the frequency and the eccentricity of the modulation. This is in accordance with the experimental results reported in a recent paper [Casic et al., Phys. Rev. Lett. 110, 168302 (2013)], where the dynamic self-assembly and propulsion of a ribbon formed from paramagnetic colloids in a time-dependent magnetic field has been studied.
The Equivalence of Precession Phenomena in Metric Theories of Gravity
NASA Technical Reports Server (NTRS)
Krisher, Timothy P.
1996-01-01
The requirement of general covariance imparts to metric theories of gravity, such as general relativity, important structural features. A precise mathematical form results, ensuring that computation of observable physical effects in the theory gives the same answers independently of the chosen system of coordinates. This coordinate independence property, in turn, can lead to an equivalence of apparently different physical effects.
Asteroid mission departure strategies from a precessing Space Station orbit
NASA Technical Reports Server (NTRS)
Sharma, Jayant
1990-01-01
In using the Space Station as a point of departure for interplanetary missions, the precission of its orbit complicates the process of determining the available departure period. The constantly changing ascending node of the Space Station orbit defines the departure geometry. Severe Delta V penalties occur if favorable departure opportunities are missed and a plane change is required at departure. This paper compares two strategies to reduce the cost of the plane change maneuver, and increase the available departure opportunities. A 3-impulse injection strategy is compared to a deep space plane change for two asteroid rendezvous missions. Results indicate that the deep space plane change strategy has lower propellant mass requirements for the two missions studied. The difference in propellant requirements for the two strategies is a function of the departure geometry.
Precession of Uranus and Neptune and their magnetic field
NASA Technical Reports Server (NTRS)
Dolginov, Sh. SH.
1993-01-01
The strength of the dipole magnetic field of a planet, H(sub p), can be estimated relative to that of the Earth at the epoch of the observation. The generation of magnetic fields in Uranus and Neptune occurs at very different depths for different values of sigma. This assertion is confirmed by the estimation of the Reynolds number (R(sub m)) and agrees with the difference of the contributions of the Joule heat losses into the observed heat fluxes of Uranus and Neptune.
Magneto-optical studies of Gd-implanted GaN: No spin alignment of conduction band electrons
NASA Astrophysics Data System (ADS)
Buß, J. H.; Rudolph, J.; Shvarkov, S.; Semond, F.; Reuter, D.; Wieck, A. D.; Hägele, D.
2013-08-01
Gd-implanted wurtzite GaN as a candidate for a ferromagnetic dilute magnetic semiconductor is investigated by time-resolved magneto-optical spectroscopy. We observe a strong increase of the electron spin lifetimes for increasing Gd doses, while the electron spin Larmor precession frequency is independent of the Gd concentration. These findings are well explained by carrier localization at defects and a negligible interaction with Gd ions. The data show that Gd-implanted GaN cannot be used for an electron spin aligner.
Langer, L; Poltavtsev, S V; Yugova, I A; Yakovlev, D R; Karczewski, G; Wojtowicz, T; Kossut, J; Akimov, I A; Bayer, M
2012-10-12
We report on magnetic field-induced oscillations of the photon echo signal from negatively charged excitons in a CdTe/(Cd,Mg)Te semiconductor quantum well. The oscillatory signal is due to Larmor precession of the electron spin about a transverse magnetic field and depends sensitively on the polarization configuration of the exciting and refocusing pulses. The echo amplitude can be fully tuned from the maximum down to zero depending on the time delay between the two pulses and the magnetic-field strength. The results are explained in terms of the optical Bloch equations accounting for the spin level structure of electrons and trions.
Low Temperature and Neutron Physics Studies: Final Progress Report, March 1, 1986--May 31, 1987
DOE R&D Accomplishments Database
Shull, C.G.
1989-07-27
A search for a novel coupling interaction between the Pendelloesung periodicity which is formed in a diffracting crystal and the Larmor precession of neutrons in a magnetic field has been carried out. This interaction is expected to exhibit a resonant behavior when the two spatial periodicities become matched upon scanning the magnetic field being applied to the crystal. Observations on a diffracting, perfect crystal of silicon with neutrons of wavelength 1 Angstrom show the expected resonant action but some discrepancy between the observed magnitude of the resonance effects remains for interpretation.
New Measurement of the Anomalous Magnetic Moment of the Positive Muon
NASA Astrophysics Data System (ADS)
Carey, R. M.; Earle, W.; Efstathiadis, E.; Hare, M. F.; Hazen, E. S.; Hughes, B. J.; Krienen, F.; Miller, J. P.; Monich, V.; Ouyang, J.; Rind, O.; Roberts, B. L.; Sulak, L. R.; Trofimov, A.; Varner, G.; Worstell, W. A.; Benedict, E.; Logashenko, I.; Benante, J.; Brown, H. N.; Bunce, G.; Cullen, J.; Danby, G. T.; Geller, J.; Hseuh, H.; Jackson, J. W.; Jia, L.; Kochis, S.; Larsen, R.; Lee, Y. Y.; Mapes, M.; Meng, W.; Morse, W. M.; Pai, C.; Pearson, C.; Polk, I.; Prigl, R.; Rankowitz, S.; Sandberg, J.; Semertzidis, Y. K.; Shutt, R.; Snydstrup, L.; Soukas, A.; Stillman, A.; Tallerico, T.; Tanaka, M.; Toldo, F.; von Lintig, D.; Warburton, D.; Woodle, K.; Chertovskikh, A.; Druzhinin, V. P.; Fedotovich, G. V.; Grigorev, D. N.; Golubev, V. B.; Khazin, B. I.; Maksimov, A.; Merzliakov, Yu.; Ryskulov, N.; Serednyakov, S.; Shatunov, Yu. M.; Solodov, E.; Orlov, Y.; Winn, D.; Grossmann, A.; Gerhaeuser, J.; Jungmann, K.; von Walter, P.; Zu Putlitz, G.; Bunker, B.; Deninger, W.; Debevec, P. T.; Hertzog, D. W.; Jones, T. D.; Polly, C.; Sedykh, S.; Urner, D.; Haeberlen, U.; Endo, K.; Hirabayashi, H.; Kurokawa, S.; Yamamoto, A.; Green, M. A.; Cushman, P.; Kindem, J.; Duong, L.; Giron, S.; McNabb, R.; Miller, D.; Timmermans, C.; Zimmerman, D.; Mizumachi, Y.; Iwasaki, M.; Ahn, H. E.; Deng, H.; Dhawan, S. K.; Disco, A.; Farley, F. J.; Fei, X.; Grosse-Perdekamp, M.; Hughes, V. W.; Kawall, D.; Redin, S. I.; Steinmetz, A.
1999-02-01
The muon anomalous magnetic moment has been measured in a new experiment at Brookhaven. Polarized muons were stored in a superferric ring, and the angular frequency difference, ωa, between the spin precession and orbital frequencies was determined by measuring the time distribution of high-energy decay positrons. The ratio R of ωa to the Larmor precession frequency of free protons, ωp, in the storage-ring magnetic field was measured. We find R = 3.707 220\\(48\\)×10-3. With μμ/μp = 3.183 345 47\\(47\\) this gives aμ+ = 1 165 925\\(15\\)×10-9 ( +/-13 ppm), in good agreement with the previous CERN measurements for μ+ and μ- and of approximately the same precision.
One- and Two-Dimensional Nuclear Magnetic Resonance Spectroscopy with a Diamond Quantum Sensor.
Boss, J M; Chang, K; Armijo, J; Cujia, K; Rosskopf, T; Maze, J R; Degen, C L
2016-05-13
We report on Fourier spectroscopy experiments performed with near-surface nitrogen-vacancy centers in a diamond chip. By detecting the free precession of nuclear spins rather than applying a multipulse quantum sensing protocol, we are able to unambiguously identify the NMR species devoid of harmonics. We further show that, by engineering different Hamiltonians during free precession, the hyperfine coupling parameters as well as the nuclear Larmor frequency can be selectively measured with up to five digits of precision. The protocols can be combined to demonstrate two-dimensional Fourier spectroscopy. Presented techniques will be useful for mapping nuclear coordinates in molecules deposited on diamond sensor chips, en route to imaging their atomic structure.
One- and Two-Dimensional Nuclear Magnetic Resonance Spectroscopy with a Diamond Quantum Sensor
NASA Astrophysics Data System (ADS)
Boss, J. M.; Chang, K.; Armijo, J.; Cujia, K.; Rosskopf, T.; Maze, J. R.; Degen, C. L.
2016-05-01
We report on Fourier spectroscopy experiments performed with near-surface nitrogen-vacancy centers in a diamond chip. By detecting the free precession of nuclear spins rather than applying a multipulse quantum sensing protocol, we are able to unambiguously identify the NMR species devoid of harmonics. We further show that, by engineering different Hamiltonians during free precession, the hyperfine coupling parameters as well as the nuclear Larmor frequency can be selectively measured with up to five digits of precision. The protocols can be combined to demonstrate two-dimensional Fourier spectroscopy. Presented techniques will be useful for mapping nuclear coordinates in molecules deposited on diamond sensor chips, en route to imaging their atomic structure.
Liquid-State Nuclear Spin Comagnetometers
NASA Astrophysics Data System (ADS)
Ledbetter, M. P.; Pustelny, S.; Budker, D.; Romalis, M. V.; Blanchard, J. W.; Pines, A.
2012-06-01
We discuss nuclear spin comagnetometers based on ultralow-field nuclear magnetic resonance in mixtures of miscible solvents, each rich in a different nuclear spin. In one version thereof, Larmor precession of protons and F19 nuclei in a mixture of thermally polarized pentane and hexafluorobenzene is monitored via a sensitive alkali-vapor magnetometer. We realize transverse relaxation times in excess of 20 s and suppression of magnetic field fluctuations by a factor of 3400. We estimate it should be possible to achieve single-shot sensitivity of about 5×10-9Hz, or about 5×10-11Hz in ≈1 day of integration. In a second version, spin precession of protons and Xe129 nuclei in a mixture of pentane and hyperpolarized liquid xenon is monitored using superconducting quantum interference devices. Application to spin-gravity experiments, electric dipole moment experiments, and sensitive gyroscopes is discussed.
Synchronously pumped nuclear magnetic oscillator
NASA Astrophysics Data System (ADS)
Korver, Anna; Thrasher, Daniel; Bulatowicz, Michael; Walker, Thad
2015-05-01
We present progress towards a synchronously pumped nuclear magnetic oscillator. Alkali frequency shifts and quadrupole shifts are the dominant systematic effects in dual Xe isotope co-magnetometers. By synchronously pumping the Xe nuclei using spin-exchange with an oscillating Rb polarization, the Rb and Xe spins precess transverse to the longitudinal bias field. This configuration is predicted to be insensitive to first order quadrupole interactions and alkali spin-exchange frequency shifts. A key feature that allows co-precession of the Rb and Xe spins, despite a ~ 1000 fold ratio of their gyromagnetic ratios, is to apply the bias field in the form of a sequence of Rb 2 π pulses whose repetition frequency is equal to the Rb Larmor frequency. The 2 π pulses result in an effective Rb magnetic moment of zero, while the Xe precession depends only on the time average of the pulsed field amplitude. Polarization modulation of the pumping light at the Xe NMR frequency allows co-precession of the Rb and Xe spins. We will present our preliminary experimental studies of this new approach to NMR of spin-exchange pumped Xe. Support by the NSF and Northrop Grumman Co.
Search for a Permanent Electric Dipole Moment of 225Ra
NASA Astrophysics Data System (ADS)
Kalita, Mukut Ranjan
The observation of a permanent electric dipole moment (EDM) in a non-degenerate system would indicate the violation of discrete symmetries of Time reversal (T) or combined application of Charge (C) and Parity (P) symmetry violation through the CPT theorem. The diamagnetic 225Ra atom with nuclear spin I=1/2 is a favorable candidate for an EDM search. Experimental sensitivity to its EDM is enhanced due to its high atomic mass and the increased Schiff moment of its octupole deformed nucleus. An experimental setup is developed where laser cooled neutral radium atoms are collected in a magneto-optical trap (MOT). The collected atoms are transported 1 meter with a far off-resonant optical dipole trap (ODT) and then the atoms are transferred to a second standing-wave ODT in an experimental chamber. The atoms are then optically polarized and allowed to Larmor precess in parallel and antiparallel electric and magnetic fields. The difference between the Larmor precession frequency for parallel and antiparallel fields is experimentally determined to measure the EDM. This thesis is about the first measurement of the EDM of the 225Ra atom where an upper limit of |d(225Ra)| < 5.0 x 10-22 e·cm (95% confidence) is reached. Keywords: Permanent EDM, CP violation, laser cooling and trapping, rare isotopes, radium.
Constraining interactions mediated by axion-like particles with ultracold neutrons
NASA Astrophysics Data System (ADS)
Afach, S.; Ban, G.; Bison, G.; Bodek, K.; Burghoff, M.; Daum, M.; Fertl, M.; Franke, B.; Grujić, Z. D.; Hélaine, V.; Kasprzak, M.; Kermaïdic, Y.; 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.; Pignol, G.; Prashanth, P. N.; Quéméner, G.; Rebreyend, D.; Ries, D.; Roccia, S.; Schmidt-Wellenburg, P.; Schnabel, A.; Severijns, N.; Voigt, J.; Weis, A.; Wyszynski, G.; Zejma, J.; Zenner, J.; Zsigmond, G.
2015-05-01
We report a new limit on a possible short range spin-dependent interaction from the precise measurement of the ratio of Larmor precession frequencies of stored ultracold neutrons and 199Hg atoms confined in the same volume. The measurement was performed in a ∼ 1μT vertical magnetic holding field with the apparatus searching for a permanent electric dipole moment of the neutron at the Paul Scherrer Institute. A possible coupling between freely precessing polarized neutron spins and unpolarized nucleons of the wall material can be investigated by searching for a tiny change of the precession frequencies of neutron and mercury spins. Such a frequency change can be interpreted as a consequence of a short range spin-dependent interaction that could possibly be mediated by axions or axion-like particles. The interaction strength is proportional to the CP violating product of scalar and pseudoscalar coupling constants gSgP. Our result confirms limits from complementary experiments with spin-polarized nuclei in a model-independent way. Limits from other neutron experiments are improved by up to two orders of magnitude in the interaction range of 10-6 < λ <10-4m.
Quadrupolar and anisotropy effects on dephasing in two-electron spin qubits in GaAs
Botzem, Tim; McNeil, Robert P. G.; Mol, Jan-Michael; Schuh, Dieter; Bougeard, Dominique; Bluhm, Hendrik
2016-01-01
Understanding the decoherence of electron spins in semiconductors due to their interaction with nuclear spins is of fundamental interest as they realize the central spin model and of practical importance for using them as qubits. Interesting effects arise from the quadrupolar interaction of nuclear spins with electric field gradients, which have been shown to suppress diffusive nuclear spin dynamics and might thus enhance electron spin coherence. Here we show experimentally that for gate-defined GaAs quantum dots, quadrupolar broadening of the nuclear Larmor precession reduces electron spin coherence by causing faster decorrelation of transverse nuclear fields. However, this effect disappears for appropriate field directions. Furthermore, we observe an additional modulation of coherence attributed to an anisotropic electronic g-tensor. These results complete our understanding of dephasing in gated quantum dots and point to mitigation strategies. They may also help to unravel unexplained behaviour in self-assembled quantum dots and III–V nanowires. PMID:27079269
NASA Astrophysics Data System (ADS)
Ishmuratov, I. K.; Baibekov, E. I.
2015-12-01
We investigate the possibility to restore transient nutations of electron spin centers embedded in the solid using specific composite pulse sequences developed previously for the application in nuclear magnetic resonance spectroscopy. We treat two types of systematic errors simultaneously: (i) rotation angle errors related to the spatial distribution of microwave field amplitude in the sample volume, and (ii) off-resonance errors related to the spectral distribution of Larmor precession frequencies of the electron spin centers. Our direct simulations of the transient signal in erbium- and chromium-doped CaWO4 crystal samples with and without error corrections show that the application of the selected composite pulse sequences can substantially increase the lifetime of Rabi oscillations. Finally, we discuss the applicability limitations of the studied pulse sequences for the use in solid-state electron paramagnetic resonance spectroscopy.
Observation on the Visibility Decrease in a VCN Spin Resonator Interferometry.
Utsuro, M; Hino, M; Geltenbort, P; Butterworth, J
2005-01-01
The present paper reports on the detailed studies concerning the neutron spin interference visibility observed after transmitting through multilayer magnetic resonators in a spin echo condition with very cold neutrons from a high flux reactor. The observed visibility of the interference between upward and downward spin components perpendicular to the Larmor precession plane of the neutron spin are compared with the numerical simulations in the plane wave theory and also in the Schrödinger wave-packet model. The comparison revealed the instructive characteristic features of obvious additional visibility decrease observed in the interference between the tunnelling and refractive transmissions of each spin components in a single as well as a couple of multilayer magnetic resonators.
Li Dachuang; Yuan Chunhua; Zhang Weiping; Cao Zhuoliang
2011-08-15
We present a proposal for storing and retrieving a continuous-variable quadripartite polarization-entangled cluster state, using macroscopic atomic ensembles in a magnetic field. The Larmor precession of the atomic spins leads to a symmetry between the atomic canonical operators. In this scheme, each of the four spatially separated pulses passes twice through the respective ensemble in order to map the polarization-entangled cluster state onto the long-lived atomic ensembles. The stored state can then be retrieved by another four read-out pulses, each crossing the respective ensemble twice. By calculating the variances, we analyzed the fidelities of the storage and retrieval, and our scheme is feasible under realistic experimental conditions.
Magnetic-like field inducing negative Dirac mass in graphene on hexagonal boron nitride
NASA Astrophysics Data System (ADS)
Soodchomshom, Bumned; Tang, I.-Ming; Hoonsawat, Rassmidara
2013-08-01
The tight-binding electrons in graphene grown on top of hexagonal boron nitride (h-BN) substrate are studied. The two types of surfaces on the h-BN substrate give rise to Dirac fermions having positive and negative masses. The positive and negative masses of the Dirac fermions lead to the gapped graphene to behave as a “pseudo” ferromagnet. A very large (pseudo) tunneling magnetoresistance is predicted when the Fermi level approaches the gap region. The energy gap due to the breaking of sublattice symmetry in graphene on h-BN substrate is analogous to magnetic-induced energy gap on surface of topological insulators. We point out that positive and negative masses may correspond to signs of magnetic-like field perpendicular to graphene sheet acting on pseudo magnetic dipole moment of electrons, leading to pseudo-Larmor precession and Stern-Gerlach magnetic force.
Improving sodium laser guide star brightness by polarization switching
Fan, Tingwei; Zhou, Tianhua; Feng, Yan
2016-01-01
Optical pumping with circularly polarized light has been used to enhance the brightness of sodium laser guide star. But the benefit is reduced substantially due to the precession of sodium atoms in geomagnetic field. Switching the laser between left and right circular polarization at the Larmor frequency is proposed to improve the return. With ESO’s laser guide star system at Paranal as example, numerical simulation shows that the return flux is increased when the angle between geomagnetic field and laser beam is larger than 60°, as much as 50% at 90°. The proposal is significant since most astronomical observation is at angle between 60° and 90° and it only requires a minor addition to the delivery optics of present laser system. PMID:26797503
NASA Astrophysics Data System (ADS)
Gill, Michael; Miller, M.; Richardson, D.; Trenti, M.
2010-01-01
Extreme Mass Ratio Inspirals (EMRIs), during which a stellar-mass compact object in close orbit around a supermassive black hole gradually loses energy and angular momentum through the emission of gravitational radiation, are likely to be key sources of long-wavelength gravitational waves. Because the expected wavelengths fall in the band to which the Laser Interferometer Space Antenna will be most sensitive, these events should be detectable and thus provide a probe of the strong-field limit of gravity. Despite many years of study of EMRIs, there exist key uncertainties in relevant processes such as resonant relaxation. We present preliminary simulations of the center of a typical galaxy using a tree N-body code, and discuss the implications of our results for resonant relaxation in relativistic gravity. This work was funded in part by NASA grant NNX08AH29G.
NASA Technical Reports Server (NTRS)
Jakeman, Hali L.
2013-01-01
The Ka-Band Object Observation and Monitoring, or KaBOOM, project is designed mainly to track and characterize near Earth objects. However, a smaller goal of the project would be to monitor pulsars and study their radio frequency signals for use as a clock in interstellar travel. The use of pulsars and their timing accuracy has been studied for decades, but never in the Ka-band of the radio frequency spectrum. In order to begin the use of KaBOOM for this research, the control systems need to be analyzed to ensure its capability. Flaws in the control documentation leave it unclear as to whether the control software processes coordinates from the J200 epoch. This experiment will examine the control software of the Intertronic 12m antennas used for the KaBOOM project and detail its capabilities in its "equatorial mode." The antennas will be pointed at 4 chosen points in the sky on several days while probing the virtual azimuth and elevation (horizon coordinate) registers. The input right ascension and declination coordinates will then be converted separately from the control software to horizontal coordinates and compared, thus determining the ability of the control software to process equatorial coordinates.
NASA Astrophysics Data System (ADS)
Kim, Tae Heon; Hamh, Sun Young; Han, Jeong Woo; Kang, Chul; Kee, Chul-Sik; Jung, Seonghoon; Park, Jaehun; Tokunaga, Yusuke; Tokura, Yoshinori; Lee, Jong Seok
2014-09-01
We investigate the details of the precessional motion of the magnetic moment in canted antiferromagnetic YFeO3, which is excited by a linearly polarized terahertz (THz) pulse at room temperature. By tuning the spectral component of the input THz pulse around the quasi-ferromagnetic mode located near 0.3 THz, we have experimentally clarified the resonance effect in the THz control of the spin state. We were able to confirm this result from the simulation based on the Landau-Lifshitz-Gilbert equation with the two sub-lattice model for the canted antiferromagnet. Finally, we discuss a crossover from a linear to a nonlinear magnetic response to the input THz pulse during the THz-induced precessional switching of the magnetization.
Azimuthally symmetric theory of gravitation - I. On the perihelion precession of planetary orbits
NASA Astrophysics Data System (ADS)
Nyambuya, G. G.
2010-04-01
From a purely non-general relativistic standpoint, we solve the empty space Poisson equation (∇2Φ = 0) for an azimuthally symmetric setting (i.e. for a spinning gravitational system like the Sun). We seek the general solution of the form Φ = Φ(r, θ). This general solution is constrained such that in the zeroth-order approximation it reduces to Newton's well-known inverse square law of gravitation. For this general solution, it is seen that it has implications on the orbits of test bodies in the gravitational field of this spinning body. We show that to second-order approximation, this azimuthally symmetric gravitational field is capable of explaining at least two things: (i) the observed perihelion shift of solar planets; (ii) the fact that the mean Earth-Sun distance must be increasing (this resonates with the observations of two independent groups of astronomers, who have measured that the mean Earth-Sun distance must be increasing at a rate between about 7.0 +/- 0.2 m century-1 and 15.0 +/- 0.3 m cy-1). In principle, we are able to explain this result as a consequence of the loss of orbital angular momentum; this loss of orbital angular momentum is a direct prediction of the theory. Further, we show that the theory is able to explain at a satisfactory level the observed secular increase in the Earth year (1.70 +/- 0.05 ms yr-1). Furthermore, we show that the theory makes a significant and testable prediction to the effect that the period of the solar spin must be decreasing at a rate of at least 8.00 +/- 2.00 s cy-1.
Realizations of magnetic-monopole gauge fields - Diatoms and spin precession
NASA Technical Reports Server (NTRS)
Moody, J.; Shapere, A.; Wilczek, F.
1986-01-01
It is found that the effective Hamiltonian for nuclear rotation in a diatom is equivalent to that of a charged particle in a background magnetic-monopole field. In certain cases, half-integer orbital angular momentum or non-Abelian fields occur. Furthermore, the effects of magnetic-monopole-like gauge fields can be experimentally observed in spin-resonance experiments with variable magnetic fields.
Velocity and pressure fluctuations induced by the precessing helical vortex in a conical diffuser
NASA Astrophysics Data System (ADS)
Javadi, A.; Bosioc, A.; Nilsson, H.; Muntean, S.; Susan-Resiga, R.
2014-03-01
The flow unsteadiness generated in the draft tube cone of hydraulic turbines affects the turbine operation. Therefore, several swirling flow configurations are investigated using a swirling apparatus in order to explore the unsteady phenomena. The swirl apparatus has two parts: the swirl generator and the test section. The swirl generator includes two blade rows being designed such that the exit velocity profile resembles that of a turbine with fixed pitch. The test section includes a divergent part similar to the draft tube cone of a Francis turbine. A new control method based on a magneto rheological brake is used in order to produce several swirling flow configurations. As a result, the investigations are performed for six operating regimes in order to quantify the flow from part load operation, corresponding to runaway speed, to overload operation, corresponding to minimum speed, at constant guide vane opening. The part load operation corresponds to 0.7 times the best efficiency discharge, while the overload operation corresponds to 1.54 times the best efficiency discharge. LDV measurements are performed along three survey axes in the test section. The first survey axis is located just downstream the runner in order to check the velocity field at the swirl generator exit, while the next two survey axes are located at the inlet and at the outlet of the draft tube cone. Two velocity components are simultaneously measured on each survey axis. The measured unsteady velocity components are used to validate the results of unsteady numerical simulations, conducted using the OpenFOAM CFD code. The computational domain covers the entire swirling apparatus, including strouts, guide vanes, runner, and the conical diffuser. A dynamic mesh is used together with sliding GGI interfaces to include the effect of the rotating runner. The Reynolds averaged Navier-Stokes equations coupled with the RNG k-ε turbulence model are utilized to simulate the unsteady turbulent flow throughout the swirl generator.
Slow-light propagation using mode locking of spin precession in quantum dots
Shabaev, A.; Dutton, Z.; Kennedy, T. A.; Efros, Al. L.
2010-11-15
We propose using mode locking to enable coherent nonlinear optical effects in inhomogenously broadened spin ensembles. We carry out detailed calculations for quantum dot systems in which increased spin coherence via mode locking has been recently observed [A. Greilich et al., Science 313, 341 (2006); 317, 1896 (2007)]. We show how, in the presence of spin locking, a strong pulse-matching effect occurs, providing a powerful tool for high-bandwidth linear optical processing. We then go on to study 'slow light' in this system and show that high-bandwidth pulses can be controllably delayed by a time comparable to the pulse width.
Numerical investigation of the Earth's rotation during a complete precession cycle
NASA Technical Reports Server (NTRS)
Richardson, David L.
1992-01-01
A theory for the long-term rotational motion of the quasi-rigid Earth was constructed by numerical integration. The theory spans 72,000 years centered about 1968 A.D., and provides accurate rotational and positional data for the Earth in the recent past and the near future. The physical model is termed dynamically consistent because developments for the active forces and torques are truncated based solely on their magnitudes regardless of their origin. The model includes all appropriate forces and torques due to the geopotential and tidal effects as well as lunisolar and planetary contributions. The elastic and inelastic deformations due to tidal action were too small to affect the mass properties of the Earth at the truncation level of the model. However, long-term dissipative effects of the tidal forces and torques were not negligible. These considerations gave the model its quasi-rigid characterization. The numerical output provided both rotational and orbital-element data. The data were fitted throughout the 72,000-year range using Chebyshev polynomial series.
Digital data-acquisition system for use with a proton-precession base-station magnetometer
McPherron, R.L.
1982-08-26
At UCLA the base station magnetometer is a Scintrex MB -2 which uses a two inch wide chart record scaled to 100 nT. The magnetometer is also equipped with a digital readout. This is available in BCD format on a 37 pin connector at the back of the instrument. This reading may be recorded digitally if an appropriate data acquisition and storage system is available. The recent development of inexpensive microcomputers and audio cassette recorders provided motivation for our exploration group to develop a digital data acquisition system for the existing base station magnetometer. A block diagram of the data acquisition system is presented. The microcomputer utilizes a R6502 as the central processor. Data are entered into the computer via a 12 key keypad and are displayed on a 6 digit liquid crystal display. Data from the Scintrex base magnetometer is passed to the microcomputer via a 37 line connector. One line of this connector is used to signal the status of the internally controlled sampling circuit in the base station magnetometer. Digital data are stored temporarily in RAM memory until an output buffer is filled. When this occurs power is applied to the audio cassette tape transport mechanism and after a short delay a block of data is written onto tape. The tape interface implements the Kansas City standard which is nearly universally used for microcomputer recording on audio cassette recorders. The entire system is powered by the same 12V dc battery used by the base station magnetometer. (WHK)
THE PRECESSION OF THE HERBIG-HARO 111 FLOW IN THE INFRARED
Noriega-Crespo, A.; Carey, S. J.; Raga, A. C.; Lora, V.; Stapelfeldt, K. R.
2011-05-01
We present Spitzer Infrared Array Camera images of the Herbig-Haro (HH) 111 outflow that show a wealth of condensations/knots in both jet and counterjet. Studying the positional distribution of these knots, we find very suggestive evidence of a mirror symmetric pattern in the jet/counterjet flow. We model this pattern as the result of an orbital motion of the jet source around a binary companion. From a fit of an analytic, ballistic model to the observed path of the HH 111 system, we find that the motion in a binary with two {approx}1 M{sub sun} stars (one of them being the HH 111 source), in a circular orbit with a separation of {approx}186 AU, would produce the mirror symmetric pattern seen in the outflow.
NASA Astrophysics Data System (ADS)
O'Brien, L.; Spivak, D.; Krueger, N.; Peterson, T. A.; Erickson, M. J.; Bolon, B.; Geppert, C. C.; Leighton, C.; Crowell, P. A.
2016-09-01
In the nonlocal spin valve (NLSV) geometry, four-terminal electrical Hanle effect measurements have the potential to provide a particularly simple determination of the lifetime (τs) and diffusion length (λN) of spins injected into nonmagnetic (N) materials. Recent papers, however, have demonstrated that traditional models typically used to fit such data provide an inaccurate measurement of τs in ferromagnet (FM)/N metal devices with low interface resistance, particularly when the separation of the source and detector contacts is small. In the transparent limit, this shortcoming is due to the back diffusion and subsequent relaxation of spins within the FM contacts, which is not properly accounted for in standard models of the Hanle effect. Here we have used the separation dependence of the spin accumulation signal in NLSVs with multiple FM/N combinations, and interfaces in the diffusive limit, to determine λN in traditional spin valve measurements. We then compare these results to Hanle measurements as analyzed using models that either include or exclude spin sinking. We demonstrate that differences between the spin valve and Hanle measurements of λN can be quantitatively modelled provided that both the FM contact-induced isotropic spin sinking and the full three-dimensional geometry of the devices, which is particularly important at small contact separations, are accounted for. We find, however, that considerable difficulties persist, in particular due to the sensitivity of fitting to the contact interface resistance and the FM contact magnetization rotation, in precisely determining λN with the Hanle technique alone, particularly at small contact separations.
Light sterile neutrinos, spin flavor precession, and the solar neutrino experiments
NASA Astrophysics Data System (ADS)
Das, C. R.; Pulido, João; Picariello, Marco
2009-04-01
We generalize to three active flavors a previous two-flavor model for the resonant spin flavor conversion of solar neutrinos to sterile ones, a mechanism which is added to the well-known large mixing angle (LMA) one. The transition magnetic moments from the muon and tau neutrinos to the sterile play the dominant role in fixing the amount of active flavor suppression. We also show, through numerical integration of the evolution equations, that the data from all solar neutrino experiments except Borexino exhibit a clear preference for a sizable magnetic field either in the convection zone or in the core and radiation zone. This is possibly related to the fact that the data from the first set are average ones taken during a period of mostly intense solar activity, whereas in contrast Borexino data were taken during a period of quiet Sun. We argue that the solar neutrino experiments are capable of tracing the possible modulation of the solar magnetic field. Those monitoring the high-energy neutrinos, namely, the B8 flux, appear to be sensitive to a field modulation either in the convection zone or in the core and radiation zone. Those monitoring the low-energy fluxes will be sensitive to the second type of solar field profiles only. In this way Borexino alone may play an essential role, since it examines both energy sectors, although experimental redundancy from other experiments will be most important.
Commissioning of the first Precessions 1.2-m CNC polishing machines for large optics
NASA Astrophysics Data System (ADS)
Walker, D. D.; Beaucamp, A. T. H.; Doubrovski, V.; Dunn, C.; Evans, R.; Freeman, R.; McCavana, G.; Morton, R.; Riley, D.; Simms, J.; Yu, G.; Wei, X.
2006-08-01
This paper reports on the commissioning of the first of Zeeko's "IRP1200" 1.2m capacity 7-axis automated CNC polishing machines. These combo machines now support five different removal regimes, which are described. The machines differ substantially from Zeeko's more familiar 200mm machines on which we have focused before, in terms of overall architecture and detailed design. Large and small optics place different demands on part-fixturing, tooling, machine speeds and accelerations, metrology, slurry-handling, part-loading and access etc. These have had a profound effect on the development-path from 200 to 1.2m machines. Moreover, an advance in the kinematic design has extended the allowable range of surface slope-angles from typically 30° up to a hemisphere. The paper presents results from the pass-off trials, the first fluid-jet experiment, and the development of tooling to address a requirement to smooth a part with a local defect.
Passing particle toroidal precession induced by electric field in a tokamak
Andreev, V. V.; Ilgisonis, V. I.; Sorokina, E. A.
2013-12-15
Characteristics of a rotation of passing particles in a tokamak with radial electric field are calculated. The expression for time-averaged toroidal velocity of the passing particle induced by the electric field is derived. The electric-field-induced additive to the toroidal velocity of the passing particle appears to be much smaller than the velocity of the electric drift calculated for the poloidal magnetic field typical for the trapped particle. This quantity can even have the different sign depending on the azimuthal position of the particle starting point. The unified approach for the calculation of the bounce period and of the time-averaged toroidal velocity of both trapped and passing particles in the whole volume of plasma column is presented. The results are obtained analytically and are confirmed by 3D numerical calculations of the trajectories of charged particles.
NASA Astrophysics Data System (ADS)
Hell, M.; Wegewijs, M. R.; DiVincenzo, D. P.
2016-01-01
We theoretically investigate the backaction of a sensor quantum dot with strong local Coulomb repulsion on the transient dynamics of a qubit that is probed capacitively. We show that the measurement backaction induced by the noise of electron cotunneling through the sensor is surprisingly mitigated by the recently identified coherent backaction [M. Hell, M. R. Wegewijs, and D. P. DiVincenzo, Phys. Rev. B 89, 195405 (2014), 10.1103/PhysRevB.89.195405] arising from quantum fluctuations. This indicates that a sensor with quantized states may be switched off better than naively expected. This renormalization effect is missing in semiclassical stochastic fluctuator models and typically also in Born-Markov approaches, which try to avoid the calculation of the nonstationary, nonequilibrium state of the qubit plus sensor. Technically, we integrate out the current-carrying electrodes to obtain kinetic equations for the joint, nonequilibrium detector-qubit dynamics. We show that the sensor current response, level renormalization, cotunneling broadening, and leading non-Markovian corrections always appear together and cannot be turned off individually in an experiment or ignored theoretically. We analyze the backaction on the reduced qubit state—capturing the full non-Markovian effects imposed by the sensor quantum dot on the qubit—by applying a Liouville-space decomposition into quasistationary and rapidly decaying modes. Importantly, the sensor cannot be eliminated completely even in the simplest high-temperature, weak-measurement limit since the qubit state experiences an initial slip depending on the initial preparation of qubit plus sensor quantum dot. The slip persists over many qubit cycles, i.e., also on the time scale of the qubit decoherence induced by the backaction. A quantum-dot sensor can thus not be modeled as usual as a "black box" without accounting for its dynamical variables; it is part of the quantum circuit. We furthermore find that the Bloch vector relaxes (rate 1 /T1 ) along an axis that is not orthogonal to the plane in which the Bloch vector dephases (rate 1 /T2 ), blurring the notions of relaxation and dephasing times. Moreover, the precessional motion of the Bloch vector is distorted into an ellipse in the tilted dephasing plane.
Past dynamics of the Australian monsoon: precession, phase and links to the global monsoon concept
NASA Astrophysics Data System (ADS)
Beaufort, L.; van der Kaars, S.; Bassinot, F. C.; Moron, V.
2010-10-01
Past variations in the dynamics of the Australian monsoon have been estimated from multi-proxy analysis of a core retrieved in the Eastern Banda Sea. Records of coccolith and pollen assemblages, spanning the last 150 000 years, allow reconstruction of past primary production in the Banda Sea, summer moisture availability, and the length of the dry season in northern Australia and southeastern Indonesia. The amount of moisture available during the summer monsoon follows typical glacial/interglacial dynamics with a broad asymmetrical 100-kyr cycle. Primary production and length of the dry season appear to be closely related, given that they follow the precessional cycle with the same phase. This indicates their independence from ice-volume variations. The present inter-annual variability of both parameters is related to El Niño Southern Oscillation (ENSO), which modulates the Australian Winter Monsoon (AWM). The precessional pattern observed in the past dynamics of the AWM is found in ENSO and monsoon records of other regions. A marked shift in the monsoon intensity occurring during the mid Holocene during a period of constant ice volume, suggests that low latitude climatic variation precedes increases in global ice volume. This precessional pattern suggests that a common forcing mechanism underlies low latitude climate dynamics, acting specifically and synchronously on the different monsoon systems.
Past dynamics of the Australian monsoon: precession, phase and links to the global monsoon
NASA Astrophysics Data System (ADS)
Beaufort, L.; van der Kaars, S.; Bassinot, F. C.; Moron, V.
2010-06-01
Past variations in the dynamics of the Australian monsoon have been estimated from multi-proxy analysis of a core retrieved in the Eastern Banda Sea. Records of coccolith and pollen assemblages, spanning the last 150,000 years, allow reconstruction of past primary production in the Banda Sea, summer moisture availability, and the length of the dry season in Northern Australia and Southeastern Indonesia. The amount of moisture available during the summer monsoon follows typical glacial/interglacial dynamics with a broad asymmetrical 100-kyr cycle. Primary production and length of the dry season appear to be closely related, given that they follow the precessional cycle with the same phase (August insolation). This indicates their independence from ice-volume variations. The present inter-annual variability of both parameters is related to El Niño Southern Oscillation (ENSO), which modulates the Australian Winter Monsoon (AWM). The precessional pattern observed in the past dynamics of the AWM is found in ENSO and monsoon records of other regions. A marked shift in the monsoon intensity occurring during the mid Holocene during a period of constant ice volume, suggest that low latitude climatic variation precedes global ice volume. This precessional pattern suggests that a common forcing mechanism underlies low latitude climate dynamics, acting specifically and synchronically on the different monsoon systems.
Magnetic field optimization and design of a superconducting neutron Wollaston prism
NASA Astrophysics Data System (ADS)
Li, F.; Parnell, S. R.; Wang, T.; Baxter, D. V.; Pynn, R.
2016-04-01
We present finite element simulations of a superconducting magnetic Wollaston prism (WP) for neutron scattering with high encoding efficiency and low Larmor phase aberrations. To achieve this, we develop and quantify the design criteria. The validation of simulation tools used for this work are investigated by using two software packages: RADIA and MagNet©. Based on the optimization criteria, various possible configurations of WP are explored with MagNet, from which the best configuration is chosen for further optimization. To optimize the best configuration, the influence of various physical parameters is investigated, including the dimensions, shapes and arrangements of components of the device. The optimum WP was built and measured at both pulsed and constant wavelength neutron sources. In flipping mode, a neutron spin flipping efficiency of ∼98.5% was measured independent of neutron wavelength and applied current. In a precession mode, measurements showed a highly linear Larmor phase variation along the horizontal direction with low depolarization. Simulations of the device agree well with the experimental measurements. Possible applications of the device are also discussed.
Investigating hard sphere interactions through spin echo scattering angle measurement
NASA Astrophysics Data System (ADS)
Washington, Adam
Spin Echo Scattering Angle Measurement (SESAME) allows neutron scattering instruments to perform real space measurements on large micron scale samples by encoding the scattering angle into the neutron's spin state via Larmor precession. I have built a SESAME instrument at the Low Energy Neutron Source. I have also assisted in the construction of a modular SESAME instrument on the ASTERIX beamline at Los Alamos National lab. The ability to tune these instruments has been proved mathematically and optimized and automated experimentally. Practical limits of the SESAME technique with respect to polarization analyzers, neutron spectra, Larmor elements, and data analysis were investigated. The SESAME technique was used to examine the interaction of hard spheres under depletion. Poly(methyl methacrylate) spheres suspended in decalin had previously been studied as a hard sphere solution. The interparticle correlations between the spheres were found to match the Percus-Yevick closure, as had been previously seen in dynamical light scattering experiments. To expand beyond pure hard spheres, 900kDa polystyrene was added to the solution in concentrations of less than 1% by mass. The steric effects of the polystyrene were expected to produce a short-range, attractive, "sticky" potential. Experiment showed, however, that the "sticky" potential was not a stable state and that the spheres would eventually form long range aggregates.
Magnetic field nonuniformities and NMR of protons diffusing in a porous medium.
Bergman, D J; Dunn, K J; LaTorraca, G A
1996-01-01
Magnetic field inhomogeneity can arise either because of an externally applied field gradient or because of spatial variations in magnetic susceptibility. The latter are most important when the solid matrix includes paramagnetic substances and when the uniform applied field, and, consequently, also the Larmor precession frequency are very large. Both types of field inhomogeneity add extra phase shifts to the precessing spins. These phase shifts vary with time and position in a complex and random fashion as a result of the diffusive motion of the spins. We have studied these effects by performing detailed calculations for the case of a fluid filled porous medium with a periodic microstructure. Special attention was devoted to the question of whether the statistical distribution of the phase shifts encountered in a Hahn spin echo experiment or in a Carr-Purcell-Meiboom-Gill (CPMG) spin-echo train can be approximated as a Gaussian. The mean square phase shift is measured in such experiments as an enhanced relaxation rate of the precessing transverse magnetization. We determine this mean square phase shift for periodic composites from the diffusion eigenstates, which were calculated using a previously developed Fourier expansion method. The enhanced relaxation rate depends on the echo spacing time tau in a way that can be correlated with important length scales of the porous microstructure. Those correlations can be extended also to disordered microstructures, like the ones that are found in natural rocks. We compare these theoretically predicted correlations with CPMG measurements performed on protons in laboratory samples of brine saturated sandstone. PMID:8970094
Shelton, S.D.; Anderson, E.J. . Dept. of Geology)
1993-03-01
The Williamsport Sandstone Member, located at the base of the Wills Creek Formation, contains a complete 5th order sequence, traceable for more than 100 kilometers. This 5th order sequence is initiated with a massive iron-rich sandstone unit. The upper iron-rich sand of the Williamsport Member marks the beginning of the next 5th order sequence. The first 5th order rock cycle, interpreted as the product of the 100 k.y. Milankovitch eccentricity cycle, is divisible into five meter-scale 6th order precessional cycles (PACs). At Cedar Cliff, Maryland, the lithology of each of the five 6th order cycles is distinct. The first cycle (.8m thick) is a massive iron-rich sandstone. The second cycle (.75m thick) is an argillaceous nodular micrite. The third cycle (.75m thick) consists totally of thin-bedded quartz sandstone. The fourth cycle (2m thick) is represented by bedded limestones that thicken upward. The fifth cycle (.6m thick) is very thin-bedded to nodular limestone. This 5th order sequence and most of its internal cyclic elements can be traced over 100 kilometers to Mount Union, Pennsylvania where its facies are largely non-marine. Detailed correlation of these 6th order cycles reveals that the uppermost PAC is missing at Cumberland and Mount Union. At these localities, the prominent iron bed of the next 5th order sequence rests unconformably on the fourth PAC in the sequence. The fifth 6th order cycle was either not deposited or removed by erosion at these proximal localities. The laterally traceable hierarchic cyclic structure in the Williamsport Sandstone is consistent with the Milankovitch forcing model and provides a detailed stratigraphic basis for analysis of lateral patterns of cyclic accumulation in the late Silurian of the central Appalachians.
NASA Technical Reports Server (NTRS)
Coyle, D. B.
1991-01-01
In the design of space-qualifiable laser systems for ranging and altimetry, such as NASA's Geodynamic Laser Ranging System (GLRS), the transmitter must be kept small, powerful yet efficient, and must consist of as few components as possible. A novel preamplifier design is examined which requires no external beam steering optics, yielding a compact component with simple alignment procedures. The gains achieved are comparable to multipass zigzag amplifiers using two or more sets of external optics for extra passes through the amplifying medium.
Large spin pumping effect in antisymmetric precession of Ni79Fe21/Ru/Ni79Fe21
NASA Astrophysics Data System (ADS)
Yang, H.; Li, Y.; Bailey, W. E.
2016-06-01
In magnetic trilayer structures, a contribution to the Gilbert damping of ferromagnetic resonance arises from spin currents pumped from one layer to another. This contribution has been demonstrated for layers with weakly coupled, separated resonances, where magnetization dynamics are excited predominantly in one layer and the other layer acts as a spin sink. Here, we show that trilayer structures in which magnetizations are excited simultaneously, antisymmetrically, show a spin-pumping effect roughly twice as large. The antisymmetric (optical) mode of antiferromagnetically coupled Ni79Fe21(8 nm)/Ru/Ni79Fe21(8 nm) trilayers shows a Gilbert damping constant greater than that of the symmetric (acoustic) mode by an amount as large as the intrinsic damping of Py ( Δα≃0.006 ). The effect is shown equally in field-normal and field-parallel to film plane geometries over 3-25 GHz. The results confirm a prediction of the spin pumping model and have implications for the use of synthetic antiferromagnets (SAF)-structures in GHz devices.