ON THE ORBIT OF EXOPLANET WASP-12b

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

Campo, Christopher J.; Harrington, Joseph; Hardy, Ryan A.

We observed two secondary eclipses of the exoplanet WASP-12b using the Infrared Array Camera on the Spitzer Space Telescope. The close proximity of WASP-12b to its G-type star results in extreme tidal forces capable of inducing apsidal precession with a period as short as a few decades. This precession would be measurable if the orbit had a significant eccentricity, leading to an estimate of the tidal Love number and an assessment of the degree of central concentration in the planetary interior. An initial ground-based secondary-eclipse phase reported by Lopez-Morales et al. (0.510 {+-} 0.002) implied eccentricity at the 4.5{sigma} level.more » The spectroscopic orbit of Hebb et al. has eccentricity 0.049 {+-} 0.015, a 3{sigma} result, implying an eclipse phase of 0.509 {+-} 0.007. However, there is a well-documented tendency of spectroscopic data to overestimate small eccentricities. Our eclipse phases are 0.5010 {+-} 0.0006 (3.6 and 5.8 {mu}m) and 0.5006 {+-} 0.0007 (4.5 and 8.0 {mu}m). An unlikely orbital precession scenario invoking an alignment of the orbit during the Spitzer observations could have explained this apparent discrepancy, but the final eclipse phase of Lopez-Morales et al. (0.510 {+-}{sup +0.007}{sub -0.006}) is consistent with a circular orbit at better than 2{sigma}. An orbit fit to all the available transit, eclipse, and radial-velocity data indicates precession at <1{sigma}; a non-precessing solution fits better. We also comment on analysis and reporting for Spitzer exoplanet data in light of recent re-analyses.« less

Theta phase precession of grid and place cell firing in open environments

PubMed Central

Jeewajee, A.; Barry, C.; Douchamps, V.; Manson, D.; Lever, C.; Burgess, N.

2014-01-01

Place and grid cells in the rodent hippocampal formation tend to fire spikes at successively earlier phases relative to the local field potential theta rhythm as the animal runs through the cell's firing field on a linear track. However, this ‘phase precession’ effect is less well characterized during foraging in two-dimensional open field environments. Here, we mapped runs through the firing fields onto a unit circle to pool data from multiple runs. We asked which of seven behavioural and physiological variables show the best circular–linear correlation with the theta phase of spikes from place cells in hippocampal area CA1 and from grid cells from superficial layers of medial entorhinal cortex. The best correlate was the distance to the firing field peak projected onto the animal's current running direction. This was significantly stronger than other correlates, such as instantaneous firing rate and time-in-field, but similar in strength to correlates with other measures of distance travelled through the firing field. Phase precession was stronger in place cells than grid cells overall, and robust phase precession was seen in traversals through firing field peripheries (although somewhat less than in traversals through the centre), consistent with phase coding of displacement along the current direction. This type of phase coding, of place field distance ahead of or behind the animal, may be useful for allowing calculation of goal directions during navigation. PMID:24366140

[Multi-channel in vivo recording techniques: analysis of phase coupling between spikes and rhythmic oscillations of local field potentials].

PubMed

Wang, Ce-Qun; Chen, Qiang; Zhang, Lu; Xu, Jia-Min; Lin, Long-Nian

2014-12-25

The purpose of this article is to introduce the measurements of phase coupling between spikes and rhythmic oscillations of local field potentials (LFPs). Multi-channel in vivo recording techniques allow us to record ensemble neuronal activity and LFPs simultaneously from the same sites in the brain. Neuronal activity is generally characterized by temporal spike sequences, while LFPs contain oscillatory rhythms in different frequency ranges. Phase coupling analysis can reveal the temporal relationships between neuronal firing and LFP rhythms. As the first step, the instantaneous phase of LFP rhythms can be calculated using Hilbert transform, and then for each time-stamped spike occurred during an oscillatory epoch, we marked instantaneous phase of the LFP at that time stamp. Finally, the phase relationships between the neuronal firing and LFP rhythms were determined by examining the distribution of the firing phase. Phase-locked spikes are revealed by the non-random distribution of spike phase. Theta phase precession is a unique phase relationship between neuronal firing and LFPs, which is one of the basic features of hippocampal place cells. Place cells show rhythmic burst firing following theta oscillation within a place field. And phase precession refers to that rhythmic burst firing shifted in a systematic way during traversal of the field, moving progressively forward on each theta cycle. This relation between phase and position can be described by a linear model, and phase precession is commonly quantified with a circular-linear coefficient. Phase coupling analysis helps us to better understand the temporal information coding between neuronal firing and LFPs.

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

Wang, Bochong; Kubota, Hitoshi, E-mail: hit-kubota@aist.go.jp; Yakushiji, Kay

The dependence on diameter of the emission power in MgO-based nano-pillar spin torque oscillators (STOs) was systematically investigated. A maximum emission power of over 2.5 μW was obtained around 300 nm in diameter, which is the largest reported to date among the out-of-plane precession STOs. By analyzing physical quantities, precession cone angle of the free-layer magnetization was evaluated. In the diameter range below 300 nm, the increase in power was mainly due to the increase of the injected current. The power decrease above 300 nm is possibly attributed to the decrease in the averaged precession cone angle, suggesting spatial phase difference of magnetization precession.more » This study provides the method for estimating the optimum STO diameter, which is of great importance in practical use.« less

XTE Proposal #20102--"SS 433's High Energy Spectrum"

NASA Technical Reports Server (NTRS)

Band, David L.; Blanco, P.; Rothschild, R.; Kawai, N.; Kotani, T.; Oka, T.; Wagner, R. M.; Hjellming, R.; Rupen, M.; Brinkmann, W.

1999-01-01

We observed the jet-producing compact binary system SS 433 with RXTE during three multiwavelength campaigns, the first in conjunction with ASCA observations, the second simultaneous with a VLA-VLBA-MERLIN campaign, and the third associated with a Nobeyama millimeter-band campaign. All these campaigns included optical observations. Occurring at different jet precession and binary phases, the observations also monitored the system during a radio flare. The data provide SS 433's X-ray spectrum over more than an energy decade, and track the spectral variations as the X-ray source was partially eclipsed. The continuum can be modeled as a power law with an exponential cutoff, which can be detected to approximately 50 keV. Strong line emission is evident in the 5-10 keV range which can be modeled as a broad line whose energy is precession independent and a narrow line whose energy does vary with jet precession phase; this line model is clearly an over simplification since the PCA does not have sufficient energy resolution to detect the lines ASCA observed. The eclipses are deeper at high energy and at jet precession phases when the jets are more inclined towards and away from us. A large radio flare occurred between two sets of X-ray monitoring observations; an X-ray observation at the peak of the flare found a softer spectrum with a flux approximately 1/3 that of the quiescent level.

M-type potassium conductance controls the emergence of neural phase codes: a combined experimental and neuron modelling study

PubMed Central

Kwag, Jeehyun; Jang, Hyun Jae; Kim, Mincheol; Lee, Sujeong

2014-01-01

Rate and phase codes are believed to be important in neural information processing. Hippocampal place cells provide a good example where both coding schemes coexist during spatial information processing. Spike rate increases in the place field, whereas spike phase precesses relative to the ongoing theta oscillation. However, what intrinsic mechanism allows for a single neuron to generate spike output patterns that contain both neural codes is unknown. Using dynamic clamp, we simulate an in vivo-like subthreshold dynamics of place cells to in vitro CA1 pyramidal neurons to establish an in vitro model of spike phase precession. Using this in vitro model, we show that membrane potential oscillation (MPO) dynamics is important in the emergence of spike phase codes: blocking the slowly activating, non-inactivating K+ current (IM), which is known to control subthreshold MPO, disrupts MPO and abolishes spike phase precession. We verify the importance of adaptive IM in the generation of phase codes using both an adaptive integrate-and-fire and a Hodgkin–Huxley (HH) neuron model. Especially, using the HH model, we further show that it is the perisomatically located IM with slow activation kinetics that is crucial for the generation of phase codes. These results suggest an important functional role of IM in single neuron computation, where IM serves as an intrinsic mechanism allowing for dual rate and phase coding in single neurons. PMID:25100320

Spectroscopic monitoring of SS 433: A search for long-term variations of kinematic model parameters

NASA Astrophysics Data System (ADS)

Davydov, V. V.; Esipov, V. F.; Cherepashchuk, A. M.

2008-06-01

Between 1994 and 2006, we obtained uniform spectroscopic observations of SS 433 in the region of H α. We determined Doppler shifts of the moving emission lines, H α + and H α -, and studied various irregularities in the profiles for the moving emission lines. The total number of Doppler shifts measured in these 13 years is 488 for H α - and 389 for H α +. We have also used published data to study possible long-term variations of the SS 433 system, based on 755 Doppler shifts for H α - and 630 for H α + obtained over 28 years. We have derived improved kinematic model parameters for the precessing relativistic jets of S S 433 using five-and eight-parameter models. On average, the precession period was stable during the 28 years of observations (60 precession cycles), at 162.250d ± 0.003d. Phase jumps of the precession period and random variations of its length with amplitudes of ≈6% and ≈1%, respectively, were observed, but no secular changes in the precession period were detected. The nutation period, P nut = 6.2876d ± 0.00035d, and its phase were stable during 28 years (more than 1600 nutation cycles). We find no secular variations of the nutation cycle. The ejection speed of the relativistic jets, v, was, on average, constant during the 28 years, β = v/c = 0.2561 ± 0.0157. No secular variation of β is detected. In general, S S 433 demonstrates remarkably stable long-term characteristics of its precession and nutation, as well as of the central “engine” near the relativistic object that collimates the plasma in the jets and accelerates it to v = 0.2561 c. Our results support a model with a “slaved” accretion disk in S S 433, which follows the precession of the optical star’s rotation axis.

Spin–Orbit Misalignment and Precession in the Kepler-13Ab Planetary System

NASA Astrophysics Data System (ADS)

Herman, Miranda K.; de Mooij, Ernst J. W.; Huang, Chelsea X.; Jayawardhana, Ray

2018-01-01

Gravity darkening induced by rapid stellar rotation provides us with a unique opportunity to characterize the spin–orbit misalignment of a planetary system through analysis of its photometric transit. We use the gravity-darkened transit modeling code simuTrans to reproduce the transit light curve of Kepler-13Ab by separately analyzing phase-folded transits for 12 short-cadence Kepler quarters. We verify the temporal change in impact parameter indicative of spin–orbit precession identified by Szabó et al. and Masuda, reporting a rate of change {db}/{dt}=(-4.1+/- 0.2)× {10}-5 day‑1. We further investigate the effect of light dilution on the fitted impact parameter and find that less than 1% of additional light is sufficient to explain the seasonal variation seen in the Kepler quarter data. We then extend our precession analysis to the phase curve data from which we report a rate of change {db}/{dt}=(-3.2+/- 1.3)× {10}-5 day‑1. This value is consistent with that of the transit data at a lower significance and provides the first evidence of spin–orbit precession based solely on the temporal variation of the secondary eclipse.

Forced precession of the cometary nucleus with randomly placed active regions

NASA Technical Reports Server (NTRS)

Szutowicz, Slawomira

1992-01-01

The cometary nucleus is assumed to be triaxial or axisymmetric spheroid rotating about its axis of maximum moment of inertia and is forced to precess due to jets of ejected material. Randomly placed regions of exposed ice on the surface of the nucleus are assumed to produce gas and dust. The solution of the heat conduction equation for each active region is used to find the gas sublimation rate and the jet acceleration. Precession of the comet nucleus is followed numerically using a phase-averaged system of equations. The gas production curves and the variation of the spin axis during the orbital motion of the comet are presented.

Phobos' gravity field and its influence on its orbit and physical librations

NASA Technical Reports Server (NTRS)

Borderies, N.; Yoder, C. F.

1990-01-01

A model describing the physical libration in longitude and latitude for Phobos is derived. The major effect is the well-known longitude variation with the anomalistic orbital period and amplitude. Several additional meter-sized periodic librations in longitude exist. The latitude variation is dominated by the forced precession of Phobos' figure axis with the precession of Phobos' orbital plane. The contribution of Phobos' topography to its gravity field is estimated using the control network model of Duxbury and Callahan (1989).

Comparing post-Newtonian and numerical relativity precession dynamics

NASA Astrophysics Data System (ADS)

Ossokine, Serguei; Boyle, Michael; Kidder, Lawrence E.; Pfeiffer, Harald P.; Scheel, Mark A.; Szilágyi, Béla

2015-11-01

Binary black-hole systems are expected to be important sources of gravitational waves for upcoming gravitational-wave detectors. If the spins are not colinear with each other or with the orbital angular momentum, these systems exhibit complicated precession dynamics that are imprinted on the gravitational waveform. We develop a new procedure to match the precession dynamics computed by post-Newtonian (PN) theory to those of numerical binary black-hole simulations in full general relativity. For numerical relativity (NR) simulations lasting approximately two precession cycles, we find that the PN and NR predictions for the directions of the orbital angular momentum and the spins agree to better than ˜1 ° with NR during the inspiral, increasing to 5° near merger. Nutation of the orbital plane on the orbital time scale agrees well between NR and PN, whereas nutation of the spin direction shows qualitatively different behavior in PN and NR. We also examine how the PN equations for precession and orbital-phase evolution converge with PN order, and we quantify the impact of various choices for handling partially known PN terms.

Comparing Post-Newtonian and Numerical-Relativity Precession Dynamics

NASA Astrophysics Data System (ADS)

Kidder, Lawrence; Ossokine, Sergei; Boyle, Michael; Pfeiffer, Harald; Scheel, Mark; Szilagyi, Bela

2015-04-01

Binary black-hole systems are expected to be important sources of gravitational waves for upcoming gravitational-wave detectors. If the spins are not colinear with each other or with the orbital angular momentum, these systems exhibit complicated precession dynamics that are imprinted on the gravitational waveform. We develop a new procedure to match the precession dynamics computed by post-Newtonian (PN) theory to those of numerical binary black-hole simulations in full general relativity. For numerical relativity (NR) simulations lasting approximately two precession cycles, we find that the PN and NR predictions for the directions of the orbital angular momentum and the spins agree to better than ~1° with NR during the inspiral, increasing to 5° near merger. Nutation of the orbital plane on the orbital time-scale agrees well between NR and PN, whereas nutation of the spin direction shows qualitatively different behavior in PN and NR. We also examine how the PN equations for precession and orbital-phase evolution converge with PN order, and we quantify the impact of various choices for handling partially known PN terms.

The Gravity Probe B `Niobium bird' experiment: Verifying the data reduction scheme for estimating the relativistic precession of Earth-orbiting gyroscopes

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.

Tomographic reflection modelling of quasi-periodic oscillations in the black hole binary H 1743-322

NASA Astrophysics Data System (ADS)

Ingram, Adam; van der Klis, Michiel; Middleton, Matthew; Altamirano, Diego; Uttley, Phil

2017-01-01

Accreting stellar mass black holes (BHs) routinely exhibit Type-C quasi-periodic oscillations (QPOs). These are often interpreted as Lense-Thirring precession of the inner accretion flow, a relativistic effect whereby the spin of the BH distorts the surrounding space-time, inducing nodal precession. The best evidence for the precession model is the recent discovery, using a long joint XMM-Newton and NuSTAR observation of H 1743-322, that the centroid energy of the iron florescence line changes systematically with QPO phase. This was interpreted as the inner flow illuminating different azimuths of the accretion disc as it precesses, giving rise to a blueshifted/redshifted iron line when the approaching/receding disc material is illuminated. Here, we develop a physical model for this interpretation, including a self-consistent reflection continuum, and fit this to the same H 1743-322 data. We use an analytic function to parametrize the asymmetric illumination pattern on the disc surface that would result from inner flow precession, and find that the data are well described if two bright patches rotate about the disc surface. This model is preferred to alternatives considering an oscillating disc ionization parameter, disc inner radius and radial emissivity profile. We find that the reflection fraction varies with QPO phase (3.5σ), adding to the now formidable body of evidence that Type-C QPOs are a geometric effect. This is the first example of tomographic QPO modelling, initiating a powerful new technique that utilizes QPOs in order to map the dynamics of accreting material close to the BH.

Gas magnetometer

DOEpatents

Walker, Thad Gilbert; Lancor, Brian Robert; Wyllie, Robert

2016-05-03

Measurement of a precessional rate of a gas, such as an alkali gas, in a magnetic field is made by promoting a non-uniform precession of the gas in which substantially no net magnetic field affects the gas during a majority of the precession cycle. This allows sensitive gases that would be subject to spin-exchange collision de-phasing to be effectively used for extremely sensitive measurements in the presence of an environmental magnetic field such as the Earth's magnetic field.

Change in General Relativistic precession rates due to Lidov-Kozai oscillations in the Solar System

NASA Astrophysics Data System (ADS)

Sekhar, Aswin; Asher, David J.; Werner, Stephanie C.; Vaubaillon, Jeremie; Li, Gongjie

2017-04-01

Introduction: Two well known phenomena associated with low perihelion distance bodies in orbital dynamics are general relativistic (GR) precession and Lidov-Kozai (LK) oscillations. The accurate prediction of the perihelion shift of Mercury in accord with real observations is one of the significant triumphs of the general theory of relativity developed by Einstein. The Lidov-Kozai mechanism was first proposed and derived by Kozai and independently by Lidov explaining the periodic exchange between eccentricities e and inclinations i thereby increasing or decreasing the perihelion distance q secularly in the orbiting body. Co-existence of GR Precession and LK Oscillations: In this work, we were interested to identify bodies evolving in the near future (i.e. thousands of years in this case) into rapid sungrazing and sun colliding phases and undergoing inclination flips, due to LK oscillations and being GR active at the same time. Of all the bodies we checked from the IAU-Minor Planet Center, and Marsden plus Kracht families from the comet catalogue, 96P/Machholz 1 stands out because it shows all these trends in the near future. LK leads to secular lowering of q which in turn leads to a huge increase in GR precession of argument of pericentre. This in turn gives feedback to the LK mechanism as the e,i and argument of pericentre in Kozai cycles are closely correlated. In this work, we find real examples of solar system bodies which show the continuum nature between GR precession domi-nant and LK mechanism dominant regimes. Results and Discussion: We have shown that there are bodies in the solar system in which both GR precession and LK mechanism can co-exist at the same time and for which these effects can be measured and identified using analytical and numerical techniques. Thus there is a continuum of bodies encompassing, firstly GR precession dominant, secondly GR precession plus LK mechanism co-existing and finally LK mechanism dominant states which are all permissible in nature. A real solar system body in this intermediate state is identified using compiled observational records from IAU-Minor Planet Center, Cometary Catalogue, IAU-Meteor Data Center and performing analytical plus numerical tests on them. This intermediate state brings up the interesting possibility of drastic changes in GR precession rates (at some points peaking to about 60 times that of Mercury's GR precession) during orbital evolution due to sungrazing and sun colliding phases induced by the LK mechanism, thus combining both these important effects in a unique and dynamically interesting way. Comet 96P/Machholz 1 stands out as the only real body identified (from our simulations) to be exhibiting these interesting traits, as well as inclination flips, in the near future. Both these phenomena complimenting and co-existing at the same time has interesting implications in the long term impact studies of small bodies in general.

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.

Determination of the ferrimagnetic precession cone of in-plane magnetized garnet films using optical modulation technique

NASA Astrophysics Data System (ADS)

Bahlmann, N.; Gerhardt, R.; Wallenhorst, M.; Dötsch, H.

1996-10-01

Magnetic garnet films of composition (A, Bi)3(Fe, B)5 O12 are grown by liquid phase epitaxy on [111] oriented substrates of Gd3 Ga5 O12, where A=yttrium or lutetium and B=aluminum or gallium. The ferrimagnetic resonance (FMR) of in-plane magnetized films is studied by analyzing the modulation of light, which passes the film parallel to the film normal. Modulation efficiencies up to 1.8% at 2.9 GHz are observed at a wavelength of 0.633 μm. From the measured modulation intensities the precession angles of the FMR are derived. The dependence of the precession cone on the excitation frequency or on the external induction shows a foldover effect which, however, is smaller than for the FMR of perpendicularly magnetized films. Maximum precession angles up to 14° are achieved and the experiments indicate that saturation occurs. Light modulation is also observed at the first harmonic frequency, but the intensity is about 300 times weaker than at the fundamental frequency.

The Asian monsoon over the past 640,000 years and ice age terminations.

PubMed

Cheng, Hai; Edwards, R Lawrence; Sinha, Ashish; Spötl, Christoph; Yi, Liang; Chen, Shitao; Kelly, Megan; Kathayat, Gayatri; Wang, Xianfeng; Li, Xianglei; Kong, Xinggong; Wang, Yongjin; Ning, Youfeng; Zhang, Haiwei

2016-06-30

Oxygen isotope records from Chinese caves characterize changes in both the Asian monsoon and global climate. Here, using our new speleothem data, we extend the Chinese record to cover the full uranium/thorium dating range, that is, the past 640,000 years. The record's length and temporal precision allow us to test the idea that insolation changes caused by the Earth's precession drove the terminations of each of the last seven ice ages as well as the millennia-long intervals of reduced monsoon rainfall associated with each of the terminations. On the basis of our record's timing, the terminations are separated by four or five precession cycles, supporting the idea that the '100,000-year' ice age cycle is an average of discrete numbers of precession cycles. Furthermore, the suborbital component of monsoon rainfall variability exhibits power in both the precession and obliquity bands, and is nearly in anti-phase with summer boreal insolation. These observations indicate that insolation, in part, sets the pace of the occurrence of millennial-scale events, including those associated with terminations and 'unfinished terminations'.

Ultrahigh-resolution imaging of the human brain with phase-cycled balanced steady-state free precession at 7 T.

PubMed

Zeineh, Michael M; Parekh, Mansi B; Zaharchuk, Greg; Su, Jason H; Rosenberg, Jarrett; Fischbein, Nancy J; Rutt, Brian K

2014-05-01

The objectives of this study were to acquire ultra-high resolution images of the brain using balanced steady-state free precession (bSSFP) at 7 T and to identify the potential utility of this sequence. Eight volunteers participated in this study after providing informed consent. Each volunteer was scanned with 8 phase cycles of bSSFP at 0.4-mm isotropic resolution using 0.5 number of excitations and 2-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 volunteers underwent scanning using 3-dimensional (3D) multiecho gradient recalled echo at 0.8-mm isotropic resolution, 3D Cube T2 at 0.7-mm isotropic resolution, and thin-section coronal oblique T2-weighted fast spin echo at 0.22 × 0.22 × 2.0-mm resolution for comparison. Two neuroradiologists assessed image quality and potential research and clinical utility. The volunteers generally tolerated the scan sessions well, and composite high-resolution bSSFP images were produced for each volunteer. Rater analysis demonstrated that bSSFP had a 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 an excellent visualization of the cerebellum, subtle details of the brain and skull base anatomy were also easier to identify on the bSSFP images, including the line of Gennari, membrane of Liliequist, and cranial nerves. Balanced steady-state free precession 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 fast spin echo. Balanced steady-state free precession can facilitate ultrahigh-resolution imaging of the brain. Although total imaging times are long, the individually short phase cycles can be acquired separately, improving examination tolerability. These images may be beneficial for studies of the hippocampus, iron-containing structures such as the subthalamic nucleus and line of Gennari, and the basal cisterns and their contents.

LDV survey of cavitation and resonance effect on the precessing vortex rope dynamics in the draft tube of Francis turbines

NASA Astrophysics Data System (ADS)

Favrel, A.; Müller, A.; Landry, C.; Yamamoto, K.; Avellan, F.

2016-11-01

The large-scale penetration of the electrical grid by intermittent renewable energy sources requires a continuous operating range extension of hydropower plants. This causes the formation of unfavourable flow patterns in the draft tube of turbines and pump-turbines. At partial load operation, a precessing cavitation vortex rope is formed at the Francis turbine runner outlet, acting as an excitation source for the hydraulic system. In case of resonance, the resulting high-amplitude pressure pulsations can put at risk the stability of the machine and of the electrical grid to which it is connected. It is therefore crucial to understand and accurately simulate the underlying physical mechanisms in such conditions. However, the exact impact of cavitation and hydro-acoustic resonance on the flow velocity fluctuations in the draft tube remains to be established. The flow discharge pulsations expected to occur in the draft tube in resonance conditions have for instance never been verified experimentally. In this study, two-component Laser Doppler Velocimetry is used to investigate the axial and tangential velocity fluctuations at the runner outlet of a reduced scale physical model of a Francis turbine. The investigation is performed for a discharge equal to 64 % of the nominal value and three different pressure levels in the draft tube, including resonance and cavitation-free conditions. Based on the convective pressure fluctuations induced by the vortex precession, the periodical velocity fluctuations over one typical precession period are recovered by phase averaging. The impact of cavitation and hydro-acoustic resonance on both axial and tangential velocity fluctuations in terms of amplitude and phase shift is highlighted for the first time. It is shown that the occurrence of resonance does not have significant effects on the draft tube velocity fields, suggesting that the synchronous axial velocity fluctuations are surprisingly negligible compared to the velocity fluctuations induced by the vortex precession.

Validating the effective-one-body model of spinning, precessing binary black holes against numerical relativity

NASA Astrophysics Data System (ADS)

Babak, Stanislav; Taracchini, Andrea; Buonanno, Alessandra

2017-01-01

In Abbott et al. [Phys. Rev. X 6, 041014 (2016), 10.1103/PhysRevX.6.041014], the properties of the first gravitational wave detected by LIGO, GW150914, were measured by employing an effective-one-body (EOB) model of precessing binary black holes whose underlying dynamics and waveforms were calibrated to numerical-relativity (NR) simulations. Here, we perform the first extensive comparison of such an EOBNR model to 70 precessing NR waveforms that span mass ratios from 1 to 5, dimensionless spin magnitudes up to 0.5, generic spin orientations, and length of about 20 orbits. We work in the observer's inertial frame and include all ℓ=2 modes in the gravitational-wave polarizations. We introduce new prescriptions for the EOB ringdown signal concerning its spectrum and time of onset. For total masses between 10 M⊙ and 200 M⊙ , we find that precessing EOBNR waveforms have unfaithfulness within about 3% to NR waveforms when considering the Advanced-LIGO design noise curve. This result is obtained without recalibration of the inspiral-plunge signal of the underlying nonprecessing EOBNR model. The unfaithfulness is computed with maximization over time and phase of arrival, sky location, and polarization of the EOBNR waveform, and it is averaged over sky location and polarization of the NR signal. We also present comparisons between NR and EOBNR waveforms in a frame that tracks the orbital precession.

Spatial information outflow from the hippocampal circuit: distributed spatial coding and phase precession in the subiculum.

PubMed

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.

Fine-Tuning the Accretion Disk Clock in Hercules X-1

NASA Technical Reports Server (NTRS)

Still, M.; Boyd, P.

2004-01-01

RXTE ASM count rates from the X-ray pulsar Her X-1 began falling consistently during the late months of 2003. The source is undergoing another state transition similar to the anomalous low state of 1999. This new event has triggered observations from both space and ground-based observatories. In order to aid data interpretation and telescope scheduling, and to facilitate the phase-connection of cycles before and after the state transition, we have re-calculated the precession ephemeris using cycles over the last 3.5 years. We report that the source has displayed a different precession period since the last anomalous event. Additional archival data from CGRO suggests that each low state is accompanied by a change in precession period and that the subsequent period is correlated with accretion flux. Consequently our analysis reveals long-term accretion disk behaviour which is predicted by theoretical models of radiation-driven warping.

A self-sustaining atomic magnetometer with τ(-1) averaging property.

PubMed

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.

Technical Note: MR-visualization of interventional devices using transient field alterations and balanced steady-state free precession imaging.

PubMed

Eibofner, Frank; Martirosian, Petros; Würslin, Christian; Graf, Hansjörg; Syha, Roland; Clasen, Stephan

2015-11-01

In interventional magnetic resonance imaging, instruments can be equipped with conducting wires for visualization by current application. The potential of sequence triggered application of transient direct currents in balanced steady-state free precession (bSSFP) imaging is demonstrated. A conductor and a modified catheter were examined in water phantoms and in an ex vivo porcine liver. The current was switched by a trigger pulse in the bSSFP sequence in an interval between radiofrequency pulse and signal acquisition. Magnitude and phase images were recorded. Regions with transient field alterations were evaluated by a postprocessing algorithm. A phase mask was computed and overlaid with the magnitude image. Transient field alterations caused continuous phase shifts, which were separated by the postprocessing algorithm from phase jumps due to persistent field alterations. The overlaid images revealed the position of the conductor. The modified catheter generated visible phase offset in all orientations toward the static magnetic field and could be unambiguously localized in the ex vivo porcine liver. The application of a sequence triggered, direct current in combination with phase imaging allows conspicuous localization of interventional devices with a bSSFP sequence.

Relative influence of precession and obliquity in the early Holocene: Topographic modulation of subtropical seasonality during the Asian summer monsoon

NASA Astrophysics Data System (ADS)

Wu, Chi-Hua; Lee, Shih-Yu; Chiang, John C. H.

2018-07-01

On orbital timescales, higher summer insolation is thought to strengthen the continental monsoon while weakening the maritime monsoon in the Northern hemisphere. Through simulations using the Community Earth System Model, we evaluated the relative influence of perihelion precession and high obliquity in the early Holocene during the Asian summer monsoon. The major finding was that precession dominates the atmospheric heating change over the Tibetan Plateau-Himalayas and Maritime Continent, whereas obliquity is responsible for the heating change over the equatorial Indian Ocean. Thus, precession and obliquity can play contrasting roles in driving the monsoons on orbital timescales. In late spring-early summer, interior Asian continental heating drives the South and East Asian monsoons. The broad-scale monsoonal circulation further expands zonally in July-August, corresponding to the development of summer monsoons in West Africa and the subtropical Western North Pacific (WNP) as well as a sizable increase in convection over the equatorial Indian Ocean. Tropical and oceanic heating becomes crucial in late summer. Over South Asia-Indian Ocean (50°E-110°E), the precession maximum intensifies the monsoonal Hadley cell (heating with an inland/highland origin), which is opposite to the meridional circulation change induced by high obliquity (heating with a tropical origin). The existence of the Tibetan Plateau-Himalayas intensifies the precessional impact. During the late-summer phase of the monsoon season, the effect of obliquity on tropical heating can be substantial. In addition to competing with Asian continental heating, obliquity-enhanced heating over the equatorial Indian Ocean also has a Walker-type circulation impact, resulting in suppression of precession-enhanced heating over the Maritime Continent.

Automatic adjustment of astrochronologic correlations

NASA Astrophysics Data System (ADS)

Zeeden, Christian; Kaboth, Stefanie; Hilgen, Frederik; Laskar, Jacques

2017-04-01

Here we present an algorithm for the automated adjustment and optimisation of correlations between proxy data and an orbital tuning target (or similar datasets as e.g. ice models) for the R environment (R Development Core Team 2008), building on the 'astrochron' package (Meyers et al.2014). The basis of this approach is an initial tuning on orbital (precession, obliquity, eccentricity) scale. We use filters of orbital frequency ranges related to e.g. precession, obliquity or eccentricity of data and compare these filters to an ensemble of target data, which may consist of e.g. different combinations of obliquity and precession, different phases of precession and obliquity, a mix of orbital and other data (e.g. ice models), or different orbital solutions. This approach allows for the identification of an ideal mix of precession and obliquity to be used as tuning target. In addition, the uncertainty related to different tuning tie points (and also precession- and obliquity contributions of the tuning target) can easily be assessed. Our message is to suggest an initial tuning and then obtain a reproducible tuned time scale, avoiding arbitrary chosen tie points and replacing these by automatically chosen ones, representing filter maxima (or minima). We present and discuss the above outlined approach and apply it to artificial and geological data. Artificial data are assessed to find optimal filter settings; real datasets are used to demonstrate the possibilities of such an approach. References: Meyers, S.R. (2014). Astrochron: An R Package for Astrochronology. http://cran.r-project.org/package=astrochron R Development Core Team (2008). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www.R-project.org.

On the Timing and Forcing Mechanisms of Late Pleistocene Glacial Terminations: Insights from a New High-Resolution Benthic Stable Oxygen Isotope Record of the Eastern Mediterranean

NASA Astrophysics Data System (ADS)

Lourens, L. J.; Konijnendijk, T.; Ziegler, M.

2015-12-01

We present the first long (~1.2 Ma) benthic oxygen isotope record from the eastern Mediterranean, based on ODP Sites 967 and 968, which clearly reflects the behavior of global climate on a glacial-interglacial scale. The age model for our record is based on tuning the elemental ratio of titanium versus aluminum (Ti/Al) against insolation. The Ti/Al record is dominated by the precession-related changes in northern African climate, i.e. monsoonal forcing, and hence largely independent of glacial-interglacial variability. We found the largest offset between our chronology and that of the widely applied, open ocean stacked record LR04 (Lisiecki and Raymo, 2005) for TVII (~624 ka), which occurred ~9 kyr earlier according to our estimates, though in agreement with the AICC2012 δDice chronology of EPICA Dome C (Bazin et al., 2013). Spectral cross-correlation analysis between our benthic δ18O record and 65°N summer insolation reveals significant amounts of power in the obliquity and precession range, with an average lag of 5.5±0.8 kyr for obliquity, and 6.0±1.0 kyr for precession. In addition, our results show that the obliquity-related time lag was smaller (3.0±3.3 kyr) prior to ~900 ka than after (5.7±1.1 kyr), suggesting that on average the glacial response time to obliquity forcing increased during the mid-Pleistocene transition, much later than assumed by Lisiecki and Raymo (2005). Finally, we found that almost all glacial terminations have a consistent phase relationship of ~45±45 degrees with respect to the precession and obliquity-driven increases in 65°N summer insolation, consistent with the general consensus that both obliquity and precession are important for deglaciation during the Late Pleistocene. Exceptions are glacial terminations TIIIb, T36 and potentially T32 (and TVII T24 and T34), which show this consistent phase relationship only with precession (only with obliquity). Our findings point towards an early (>1200 ka) onset of the Mid Pleistocene Transition. Vice versa, the timing of TVII, which can only be explained as a response to obliquity forcing, indicates that the transition lasted until at least after MIS 15.

Explicit symplectic orbit and spin tracking method for electric storage ring

DOE PAGES

Hwang, Kilean; Lee, S. Y.

2016-08-18

We develop a symplectic charged particle tracking method for phase space coordinates and polarization in all electric storage rings. Near the magic energy, the spin precession tune is proportional to the fractional momentum deviation δ m from the magic energy, and the amplitude of the radial and longitudinal spin precession is proportional to η/δ m, where η is the electric dipole moment for an initially vertically polarized beam. As a result, the method can be used to extract the electron electric dipole moment of a charged particle by employing narrow band frequency analysis of polarization around the magic energy.

The Gravity-Probe-B relativity gyroscope experiment - An update on progress

NASA Technical Reports Server (NTRS)

Parkinson, Bradford W.; Everitt, C. W. Francis; Turneaure, John P.

1987-01-01

The Gravity-Probe-B (GP-B) relativity gyroscope experiment will test two effects of general relativity: (1) the geodetic precession of a gyroscope due to its Fermi-Walker transport around a massive central body; and (2) the motional or gravitomagnetic precession of the gyroscope due to rotation of the central body itself. The experiment will also provide a determination of the deflection of starlight by the sun and an improved determination of the distance to Rigel. In the Shuttle testing phase of the program, prototype hardware is being developed for a full-scale ground model of the GP-B instrument.

On the timing and forcing mechanisms of late Pleistocene glacial terminations: Insights from a new high-resolution benthic stable oxygen isotope record of the eastern Mediterranean

NASA Astrophysics Data System (ADS)

Konijnendijk, T. Y. M.; Ziegler, M.; Lourens, L. J.

2015-12-01

Benthic oxygen isotope records of deep marine sedimentary archives have yielded a wealth of information regarding ice sheet dynamics and climate change during the Pleistocene. However, since they often lack independent age control, these records are generally bound by a fixed phase relationship between orbital forcing and the climate response, e.g. ice volume changes. We present the first long (∼1.2 Ma) benthic oxygen isotope record from the eastern Mediterranean, based on ODP Sites 967 and 968, which clearly reflects the behavior of global climate on a glacial-interglacial scale throughout the late Pleistocene time period. The age model for our record is based on tuning the elemental ratio of titanium versus aluminum (Ti/Al) against insolation. The Ti/Al record is dominated by the precession-related changes in northern African climate, i.e. monsoonal forcing, and hence largely independent of glacial-interglacial variability. We found the largest offset between our chronology and that of the widely applied, open ocean stacked record LR04 (Lisiecki and Raymo, 2005) for TVII (∼624 ka), which occurred ∼9 kyr earlier according to our estimates, though in agreement with the AICC2012 δDice chronology of EPICA Dome C (Bazin et al., 2013). Spectral cross-correlation analysis between our benthic δ18O record and 65°N summer insolation reveals significant amounts of power in the obliquity and precession range, with an average lag of 5.5 ± 0.8 kyr for obliquity, and 6.0 ± 1.0 kyr for precession. In addition, our results show that the obliquity-related time lag was smaller (3.0 ± 3.3 kyr) prior to ∼900 ka than after (5.7 ± 1.1 kyr), suggesting that on average the glacial response time to obliquity forcing increased during the mid-Pleistocene transition, much later than assumed by Lisiecki and Raymo (2005). Finally, we found that almost all glacial terminations have a consistent phase relationship of ∼45 ± 45° with respect to the precession and obliquity-driven increases in 65°N summer insolation, consistent with the general consensus that both obliquity and precession are important for deglaciation during the Late Pleistocene. Exceptions are glacial terminations TIIIb, T36 and potentially T32 (and TVII T24 and T34), which show this consistent phase relationship only with precession (only with obliquity). Our findings point towards an early (>1200 ka) onset of the Mid Pleistocene Transition. Vice versa, the timing of TVII, which can only be explained as a response to obliquity forcing, indicates that the transition lasted until at least after MIS 15.

Dynamical current-induced ferromagnetic and antiferromagnetic resonances

NASA Astrophysics Data System (ADS)

Guimarães, F. S. M.; Lounis, S.; Costa, A. T.; Muniz, R. B.

2015-12-01

We demonstrate that ferromagnetic and antiferromagnetic excitations can be triggered by the dynamical spin accumulations induced by the bulk and surface contributions of the spin Hall effect. Due to the spin-orbit interaction, a time-dependent spin density is generated by an oscillatory electric field applied parallel to the atomic planes of Fe/W(110) multilayers. For symmetric trilayers of Fe/W/Fe in which the Fe layers are ferromagnetically coupled, we demonstrate that only the collective out-of-phase precession mode is excited, while the uniform (in-phase) mode remains silent. When they are antiferromagnetically coupled, the oscillatory electric field sets the Fe magnetizations into elliptical precession motions with opposite angular velocities. The manipulation of different collective spin-wave dynamical modes through the engineering of the multilayers and their thicknesses may be used to develop ultrafast spintronics devices. Our work provides a general framework that probes the realistic responses of materials in the time or frequency domain.

Astronomical dating in the 19th century

NASA Astrophysics Data System (ADS)

Hilgen, Frederik J.

2010-01-01

Today astronomical tuning is widely accepted as numerical dating method after having revolutionised the age calibration of the geological archive and time scale over the last decades. However, its origin is not well known and tracing its roots is important especially from a science historic perspective. Astronomical tuning developed in consequence of the astronomical theory of the ice ages and was repeatedly used in the second half of the 19th century before the invention of radio-isotopic dating. Building upon earlier ideas of Joseph Adhémar, James Croll started to formulate his astronomical theory of the ice ages in 1864 according to which precession controlled ice ages occur alternatingly on both hemispheres at times of maximum eccentricity of the Earth's orbit. The publication of these ideas compelled Charles Lyell to revise his Principles of Geology and add Croll's theory, thus providing an alternative to his own geographical cause of the ice ages. Both Croll and Lyell initially tuned the last glacial epoch to the prominent eccentricity maximum 850,000 yr ago. This age was used as starting point by Lyell to calculate an age of 240 million years for the beginning of the Cambrium. But Croll soon revised the tuning to a much younger less prominent eccentricity maximum between 240,000 and 80,000 yr ago. In addition he tuned older glacial deposits of late Miocene and Eocene ages to eccentricity maxima around 800,000 and 2,800,000 yr ago. Archibald and James Geikie were the first to recognize interglacials during the last glacial epoch, as predicted by Croll's theory, and attempted to tune them to precession. Soon after Frank Taylor linked a series of 15 end-moraines left behind by the retreating ice sheet to precession to arrive at a possible age of 300,000 yr for the maximum glaciation. In a classic paper, Axel Blytt (1876) explained the scattered distribution of plant groups in Norway to precession induced alternating rainy and dry periods as recorded by the layering in Holocene peat bogs. He specifically linked the exceptionally wet Atlantic period to the prolonged precession minimum at 33,300 yr ago and further related basic stratigraphic alternations to precession induced climate change in general. Such a linkage was also proposed by Grove Karl Gilbert for cyclic alternations in the marine Cretaceous of North America. Extrapolating sedimentation rates, he arrived at an astronomical duration for part of the Cretaceous that was roughly as long as the final estimate of William Thomson for the age of the Earth. Assuming that orbital parameters directly affect sea level, Karl Mayer-Eymar and Blytt correlated the well known succession of Tertiary stages to precession and eccentricity, respectively. Remarkably, Blytt, like Croll before him, used very long-period cycles in eccentricity to establish and validate his tuning. Understandably these studies in the second half of the 19th century were largely deductive in nature and proved partly incorrect later. Nevertheless, this fascinating period marks a crucial phase in the development of the astronomical theory of the ice ages and climate, and in astronomical dating. It preceded the final inductive phase, which started with the recovery of deep-sea cores in 1947 and led to a spectacular revival of the astronomical theory, by a century. The first half of the 20th century can best be regarded as an intermediate phase, despite the significant progress made in both theoretical aspects and tuning.

Long-timescale motions in glycerol-monopalmitate lipid bilayers investigated using molecular dynamics simulation.

PubMed

Laner, Monika; Horta, Bruno A C; Hünenberger, Philippe H

2015-02-01

The occurrence of long-timescale motions in glycerol-1-monopalmitate (GMP) lipid bilayers is investigated based on previously reported 600 ns molecular dynamics simulations of a 2×8×8 GMP bilayer patch in the temperature range 302-338 K, performed at three different hydration levels, or in the presence of the cosolutes methanol or trehalose at three different concentrations. The types of long-timescale motions considered are: (i) the possible phase transitions; (ii) the precession of the relative collective tilt-angle of the two leaflets in the gel phase; (iii) the trans-gauche isomerization of the dihedral angles within the lipid aliphatic tails; and (iv) the flipping of single lipids across the two leaflets. The results provide a picture of GMP bilayers involving a rich spectrum of events occurring on a wide range of timescales, from the 100-ps range isomerization of single dihedral angles, via the 100-ns range of tilt precession motions, to the multi-μs range of phase transitions and lipid-flipping events. Copyright © 2014 Elsevier Inc. All rights reserved.

Grid cell mechanisms and function: Contributions of entorhinal persistent spiking and phase resetting

PubMed Central

Hasselmo, Michael E.

2008-01-01

This article presents a model of grid cell firing based on the intrinsic persistent firing shown experimentally in neurons of entorhinal cortex. In this model, the mechanism of persistent firing allows individual neurons to hold a stable baseline firing frequency. Depolarizing input from speed modulated head direction cells transiently shifts the frequency of firing from baseline, resulting in a shift in spiking phase in proportion to the integral of velocity. The convergence of input from different persistent firing neurons causes spiking in a grid cell only when the persistent firing neurons are within similar phase ranges. This model effectively simulates the two-dimensional firing of grid cells in open field environments, as well as the properties of theta phase precession. This model provides an alternate implementation of oscillatory interference models. The persistent firing could also interact on a circuit level with rhythmic inhibition and neurons showing membrane potential oscillations to code position with spiking phase. These mechanisms could operate in parallel with computation of position from visual angle and distance of stimuli. In addition to simulating two-dimensional grid patterns, models of phase interference can account for context-dependent firing in other tasks. In network simulations of entorhinal cortex, hippocampus and postsubiculum, the reset of phase effectively replicates context-dependent firing by entorhinal and hippocampal neurons during performance of a continuous spatial alternation task, a delayed spatial alternation task with running in a wheel during the delay period, and a hairpin maze task. PMID:19021258

A History of Precession Dissipation Energy

NASA Astrophysics Data System (ADS)

Vanyo, J. P.

2006-05-01

I am not an historian, but here are a few of my remembrances of my 78 years. Precession theory and application had its formal beginning by Euler in 1758 to define rotation of rigid objects. A short burst of interest, theory, and application for precession and planetary motion and gyroscopes started around the1800s. Precession theory blossomed in the 1960s by the Soviet-American contest for space exploration and the contest for a geodynamo model. Precession interest then followed separate paths. Aerospace research introduced precession dissipation energy by America's 1958 satellite (Explorer I) where an instability was seen. Its antennae dissipated energy by material hysteresis. Liquid dissipation in precessing satellites became a major difficulty for designers, and physical experiments became the prime solution. Precession dissipation energy rates are difficult and expensive to measure, see Vanyo, "Rotating Fluids", 1993 Butterworth-Heinemann (2001 Dover), p.318. Geophysical research introduced nutation and precession by luni-solar forces. Luni-solar precession dissipation energy had become the criteria for adequacy for a geodynamo. Roberts and Busse both examined viscous models, but an attempt by Malkus (1968) for a viscous and magnetic model did not success. A precession model by Vanyo-Likins (1972) derived an aerospace application for dissipation energy. Rochester et al (1975) and Loper (1975) claimed that precession energy was inadequate for a geodynamo, but formal criteria were never published. The 1975 papers by Rochester et al and Loper were in error. Their estimate for precession energy rate is off by 4 magnitudes. New research now supports energetic precession geodynamo models, e.g., articles for precession experiments that have adequate geodynamo energy rates, articles for core-mantle motions that show geomagnetic CMB patterns, articles for viscous-electromagnetic analyses that show precession core-mantle coupling, and articles for computer simulations that have achieved laminar and turbulent precession geodynamo models. Please, by e-mail, ask for a survey of solutions and problems.

Predicting Precession Rates from Secular Dynamics for Extra-solar Multi-planet Systems

NASA Astrophysics Data System (ADS)

Van Laerhoven, Christa L.

2015-11-01

Considering the secular dynamics of multi-planet systems provides substantial insight into the interactions between planets in those systems. Secular interactions are those that don't involve knowing where a planet is along its orbit, and they dominate when planets are not involved in mean motion resonances. These interactions exchange angular momentum among the planets, evolving their eccentricities and inclinations. To second order in the planets' eccentricities and inclinations, the eccentricity and inclination perturbations are decoupled. Given the right variable choice, the relevant differential equations are linear and thus the eccentricity and inclination behaviors can be described as a sum of eigenmodes. Since the underlying structure of the secular eigenmodes can be calculated using only the planets' masses and semi-major axes, one can elucidate the eccentricity and inclination behavior of planets in exoplanet systems even without knowing the planets' current eccentricities and inclinations. I have calculated both the eccentricity and inclination secular eigenmodes for the population of known multi-planet systems whose planets have well determined masses and periods. Using this catalog, and assuming a Gausian distribution for the eigenmode amplitudes and a uniform distribution for the eigenmode phases, I have predicted what range of precession rates the planets may have. Generally, planets that have more than one eigenmode significantly contribute to their eccentricity ('groupies') can have a wide range of possible precession rates, while planets that are 'loners' have a narrow range of possible precession rates. One might have assumed that in any given system, the planets with shorter periods would have faster precession rates. However, I show that in systems where the planets suffer strong secular interactions this is not necessarily the case.

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 equator and precession of the ecliptic, respectively, * 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 basedand Celestial Intermediate Origin based paradigms, * that the choice of precession parameters be left to the user, and * 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.

Revisiting LS I +61°303 with VLBI astrometry

NASA Astrophysics Data System (ADS)

Wu, Y. W.; Torricelli-Ciamponi, G.; Massi, M.; Reid, M. J.; Zhang, B.; Shao, L.; Zheng, X. W.

2018-03-01

We conducted multi-epoch Very Long Baseline Array (VLBA) phase-referenced observations of LS I +61°303 in order to study its precessing radio jet. Compared to similar observations in 2006, we find that the observed elliptical trajectory of emission at 8.4 GHz repeats after the 9 yr gap. The accurate alignment of the emission patterns yields a precession period of 26.926 ± 0.005 d, which is consistent with that determined by Lomb-Scargle analysis of the radio light curve. We analytically model the projection on the sky plane of the peak position of a precessing, synchrotron-emitting jet, which traces an elliptical trajectory on the sky. Comparing the simulation with the VLBA astrometry we improve our knowledge of the geometry of the system. We measure the LS I +61°303 absolute proper motion to be -0.150 ± 0.006 mas yr-1 eastward and -0.264 ± 0.006 mas yr-1 northward. Removing Galactic rotation, this reveals a small, <20 km s-1, non-circular motion, which indicates a very low kick velocity when the black hole was formed.

Does the entorhinal cortex use the Fourier transform?

PubMed Central

Orchard, Jeff; Yang, Hao; Ji, Xiang

2013-01-01

Some neurons in the entorhinal cortex (EC) fire bursts when the animal occupies locations organized in a hexagonal grid pattern in their spatial environment. Place cells have also been observed, firing bursts only when the animal occupies a particular region of the environment. Both of these types of cells exhibit theta-cycle modulation, firing bursts in the 4–12 Hz range. Grid cells fire bursts of action potentials that precess with respect to the theta cycle, a phenomenon dubbed “theta precession.” Various models have been proposed to explain these phenomena, and how they relate to navigation. Among the most promising are the oscillator interference models. The bank-of-oscillators model proposed by Welday et al. (2011) exhibits all these features. However, their simulations are based on theoretical oscillators, and not implemented entirely with spiking neurons. We extend their work in a number of ways. First, we place the oscillators in a frequency domain and reformulate the model in terms of Fourier theory. Second, this perspective suggests a division of labor for implementing spatial maps: position vs. map layout. The animal's position is encoded in the phases of the oscillators, while the spatial map shape is encoded implicitly in the weights of the connections between the oscillators and the read-out nodes. Third, it reveals that the oscillator phases all need to conform to a linear relationship across the frequency domain. Fourth, we implement a partial model of the EC using spiking leaky integrate-and-fire (LIF) neurons. Fifth, we devise new coupling mechanisms, enlightened by the global phase constraint, and show they are capable of keeping spiking neural oscillators in consistent formation. Our model demonstrates place cells, grid cells, and phase precession. The Fourier model also gives direction for future investigations, such as integrating sensory feedback to combat drift, or explaining why grid cells exist at all. PMID:24376415

Reward Expectancy Strengthens CA1 Theta and Beta Band Synchronization and Hippocampal-Ventral Striatal Coupling.

PubMed

Lansink, Carien S; Meijer, Guido T; Lankelma, Jan V; Vinck, Martin A; Jackson, Jadin C; Pennartz, Cyriel M A

2016-10-12

The use of information from the hippocampal memory system in motivated behavior depends on its communication with the ventral striatum. When an animal encounters cues that signal subsequent reward, its reward expectancy is raised. It is unknown, however, how this process affects hippocampal dynamics and their influence on target structures, such as ventral striatum. We show that, in rats, reward-predictive cues result in enhanced hippocampal theta and beta band rhythmic activity during subsequent action, compared with uncued goal-directed navigation. The beta band component, also labeled theta's harmonic, involves selective hippocampal CA1 cell groups showing frequency doubling of firing periodicity relative to theta rhythmicity and it partitions the theta cycle into segments showing clear versus poor spike timing organization. We found that theta phase precession occurred over a wider range than previously reported. This was apparent from spikes emitted near the peak of the theta cycle exhibiting large "phase precessing jumps" relative to spikes in foregoing cycles. Neither this phenomenon nor the regular manifestation of theta phase precession was affected by reward expectancy. Ventral striatal neuronal firing phase-locked not only to hippocampal theta, but also to beta band activity. Both hippocampus and ventral striatum showed increased synchronization between neuronal firing and local field potential activity during cued compared with uncued goal approaches. These results suggest that cue-triggered reward expectancy intensifies hippocampal output to target structures, such as the ventral striatum, by which the hippocampus may gain prioritized access to systems modulating motivated behaviors. Here we show that temporally discrete cues raising reward expectancy enhance both theta and beta band activity in the hippocampus once goal-directed navigation has been initiated. These rhythmic activities are associated with increased synchronization of neuronal firing patterns in the hippocampus and the connected ventral striatum. When transmitted to downstream target structures, this expectancy-related state of intensified processing in the hippocampus may modulate goal-directed action. Copyright © 2016 the authors 0270-6474/16/3610598-13$15.00/0.

GABAergic contributions to gating, timing, and phase precession of hippocampal neuronal activity during theta oscillations.

PubMed

Cutsuridis, Vassilis; Hasselmo, Michael

2012-07-01

Successful spatial exploration requires gating, storage, and retrieval of spatial memories in the correct order. The hippocampus is known to play an important role in the temporal organization of spatial information. Temporally ordered spatial memories are encoded and retrieved by the firing rate and phase of hippocampal pyramidal cells and inhibitory interneurons with respect to ongoing network theta oscillations paced by intra- and extrahippocampal areas. Much is known about the anatomical, physiological, and molecular characteristics as well as the connectivity and synaptic properties of various cell types in the hippocampal microcircuits, but how these detailed properties of individual neurons give rise to temporal organization of spatial memories remains unclear. We present a model of the hippocampal CA1 microcircuit based on observed biophysical properties of pyramidal cells and six types of inhibitory interneurons: axo-axonic, basket, bistratistified, neurogliaform, ivy, and oriens lacunosum-moleculare cells. The model simulates a virtual rat running on a linear track. Excitatory transient inputs come from the entorhinal cortex (EC) and the CA3 Schaffer collaterals and impinge on both the pyramidal cells and inhibitory interneurons, whereas inhibitory inputs from the medial septum impinge only on the inhibitory interneurons. Dopamine operates as a gate-keeper modulating the spatial memory flow to the PC distal dendrites in a frequency-dependent manner. A mechanism for spike-timing-dependent plasticity in distal and proximal PC dendrites consisting of three calcium detectors, which responds to the instantaneous calcium level and its time course in the dendrite, is used to model the plasticity effects. The model simulates the timing of firing of different hippocampal cell types relative to theta oscillations, and proposes functional roles for the different classes of the hippocampal and septal inhibitory interneurons in the correct ordering of spatial memories as well as in the generation and maintenance of theta phase precession of pyramidal cells (place cells) in CA1. The model leads to a number of experimentally testable predictions that may lead to a better understanding of the biophysical computations in the hippocampus and medial septum. Copyright © 2011 Wiley Periodicals, Inc.

Spatial cell firing during virtual navigation of open arenas by head-restrained mice.

PubMed

Chen, Guifen; King, John Andrew; Lu, Yi; Cacucci, Francesca; Burgess, Neil

2018-06-18

We present a mouse virtual reality (VR) system which restrains head-movements to horizontal rotations, compatible with multi-photon imaging. This system allows expression of the spatial navigation and neuronal firing patterns characteristic of real open arenas (R). Comparing VR to R: place and grid, but not head-direction, cell firing had broader spatial tuning; place, but not grid, cell firing was more directional; theta frequency increased less with running speed; whereas increases in firing rates with running speed and place and grid cells' theta phase precession were similar. These results suggest that the omni-directional place cell firing in R may require local-cues unavailable in VR, and that the scale of grid and place cell firing patterns, and theta frequency, reflect translational motion inferred from both virtual (visual and proprioceptive) and real (vestibular translation and extra-maze) cues. By contrast, firing rates and theta phase precession appear to reflect visual and proprioceptive cues alone. © 2018, Chen et al.

Flexible theta sequence compression mediated via phase precessing interneurons

PubMed Central

Chadwick, Angus; van Rossum, Mark CW; Nolan, Matthew F

2016-01-01

Encoding of behavioral episodes as spike sequences during hippocampal theta oscillations provides a neural substrate for computations on events extended across time and space. However, the mechanisms underlying the numerous and diverse experimentally observed properties of theta sequences remain poorly understood. Here we account for theta sequences using a novel model constrained by the septo-hippocampal circuitry. We show that when spontaneously active interneurons integrate spatial signals and theta frequency pacemaker inputs, they generate phase precessing action potentials that can coordinate theta sequences in place cell populations. We reveal novel constraints on sequence generation, predict cellular properties and neural dynamics that characterize sequence compression, identify circuit organization principles for high capacity sequential representation, and show that theta sequences can be used as substrates for association of conditioned stimuli with recent and upcoming events. Our results suggest mechanisms for flexible sequence compression that are suited to associative learning across an animal’s lifespan. DOI: http://dx.doi.org/10.7554/eLife.20349.001 PMID:27929374

Magnetic flux density measurement with balanced steady state free precession pulse sequence for MREIT: a simulation study.

PubMed

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.

THE COMBINED EFFECT OF PRECESSION AND CONVECTION ON THE DYNAMO ACTION

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

Wei, Xing, E-mail: xing.wei@sjtu.edu.cn; Princeton University Observatory, Princeton, NJ 08544

2016-08-20

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 resultmore » may explain why the geodynamo has been maintained for such a long time compared to the Martian dynamo.« less

MR fingerprinting using fast imaging with steady state precession (FISP) with spiral readout.

PubMed

Jiang, Yun; Ma, Dan; Seiberlich, Nicole; Gulani, Vikas; Griswold, Mark A

2015-12-01

This study explores the possibility of using gradient echo-based sequences other than balanced steady-state free precession (bSSFP) in the magnetic resonance fingerprinting (MRF) framework to quantify the relaxation parameters . An MRF method based on a fast imaging with steady-state precession (FISP) sequence structure is presented. A dictionary containing possible signal evolutions with physiological range of T1 and T2 was created using the extended phase graph formalism according to the acquisition parameters. The proposed method was evaluated in a phantom and a human brain. T1 , T2 , and proton density were quantified directly from the undersampled data by the pattern recognition algorithm. T1 and T2 values from the phantom demonstrate that the results of MRF FISP are in good agreement with the traditional gold-standard methods. T1 and T2 values in brain are within the range of previously reported values. MRF-FISP enables a fast and accurate quantification of the relaxation parameters. It is immune to the banding artifact of bSSFP due to B0 inhomogeneities, which could improve the ability to use MRF for applications beyond brain imaging. © 2014 Wiley Periodicals, Inc.

Long-Term Evolution of Orbits About a Precessing Oblate Planet: 3. A Semianalytical and a Purely Numerical Approach

DTIC Science & Technology

2007-11-01

Keywords Orbital elements · Osculating elements · Mars · Natural satellites · Natural satellites’ orbits · Deimos · Equinoctial precession · The...theory of orbits about a precessing and nutating oblate planet, in terms of osculating elements defined in a frame associated with the equator of...solar-gravity-perturbed satellite orbiting an oblate planet subject to nonuniform equinoctial precession. This nonuniformity of precession is caused by

Hydrodynamic stability of jets produced by mass accreting systems

NASA Technical Reports Server (NTRS)

Hardee, P. E.

1982-01-01

The existing model for pulsed X-ray emission from the source Hercules X-1 is reviewed. A necessary part of this model is a processing accretion disk which turns the source on and off with 35 day cycle. It is usually assumed that precession of the primary star in this binary system, Hz Hercules, slaves the disk to its precession rate. This model can account for the system behavior in a qualitative manner. Precession of Hz Hercules with 35 day period requires precession of the binary orbit. Pulse arrival times from Herc X-1 have been analyzed for orbital precession. The inclusion of precession does not significantly improve the results obtained assuming a non-precessing orbit. The fluid dynamical stability of extra-galactic jets and the possible consequences of Kelvin-Helmholtz instability at the jet surface external medium interface are considered.

Hippocampal mechanisms for the context-dependent retrieval of episodes

PubMed Central

Hasselmo, Michael E.; Eichenbaum, Howard B.

2008-01-01

Behaviors ranging from delivering newspapers to waiting tables depend on remembering previous episodes to avoid incorrect repetition. Physiologically, this requires mechanisms for long-term storage and selective retrieval of episodes based on time of occurrence, despite variable intervals and similarity of events in a familiar environment. Here, this process has been modeled based on physiological properties of the hippocampal formation, including mechanisms for sustained activity in entorhinal cortex and theta rhythm oscillations in hippocampal subregions. The model simulates the context-sensitive firing properties of hippocampal neurons including trial specific firing during spatial alternation and trial by trial changes in theta phase precession on a linear track. This activity is used to guide behavior, and lesions of the hippocampal network impair memory-guided behavior. The model links data at the cellular level to behavior at the systems level, describing a physiologically plausible mechanism for the brain to recall a given episode which occurred at a specific place and time. PMID:16263240

Space and time reconstruction of the precessing vortex core in Francis turbine draft tube by 2D-PIV

NASA Astrophysics Data System (ADS)

Favrel, A.; Müller, A.; Landry, C.; Yamamoto, K.; Avellan, F.

2016-11-01

Francis turbines operating at part load conditions experience the development of a high swirling flow at the runner outlet, giving rise to the development of a cavitation precessing vortex rope in the draft tube. The latter acts as an excitation source for the hydro-mechanical system and may jeopardize the system stability if resonance conditions are met. Although many aspects of the part load issue have been widely studied in the past, the accurate stability analysis of hydro-power plants remains challenging. A better understanding of the vortex rope dynamics in a wide range of operating conditions is an important step towards the prediction and the transposition of the pressure fluctuations from reduced to prototype scale. For this purpose, an investigation of the flow velocity fields at the outlet of a Francis turbine reduced scale physical model operating at part load conditions is performed by means of 2D-PIV in three different horizontal cross-sections of the draft tube cone. The measurements are performed in cavitation-free conditions for three values of discharge factor, comprised between 60% and 81% of the value at the Best Efficiency Point. The present article describes a detailed methodology to properly recover the evolution of the velocity fields during one precession cycle by means of phase averaging. The vortex circulation is computed and the vortex trajectory over one typical precession period is finally recovered for each operating point. It is notably shown that below a given value of the discharge factor, the vortex dynamics abruptly change and loose its periodicity and coherence.

High-resolution scanning precession electron diffraction: Alignment and spatial resolution.

PubMed

Barnard, Jonathan S; Johnstone, Duncan N; Midgley, Paul A

2017-03-01

Methods are presented for aligning the pivot point of a precessing electron probe in the scanning transmission electron microscope (STEM) and for assessing the spatial resolution in scanning precession electron diffraction (SPED) experiments. The alignment procedure is performed entirely in diffraction mode, minimising probe wander within the bright-field (BF) convergent beam electron diffraction (CBED) disk and is used to obtain high spatial resolution SPED maps. Through analysis of the power spectra of virtual bright-field images extracted from the SPED data, the precession-induced blur was measured as a function of precession angle. At low precession angles, SPED spatial resolution was limited by electronic noise in the scan coils; whereas at high precession angles SPED spatial resolution was limited by tilt-induced two-fold astigmatism caused by the positive spherical aberration of the probe-forming lens. Copyright © 2016 Elsevier B.V. All rights reserved.

Expressions for IAU 2000 precession quantities

NASA Astrophysics Data System (ADS)

Capitaine, N.; Wallace, P. T.; Chapront, J.

2003-12-01

A new precession-nutation model for the Celestial Intermediate Pole (CIP) was adopted by the IAU in 2000 (Resolution B1.6). The model, designated IAU 2000A, includes a nutation series for a non-rigid Earth and corrections for the precession rates in longitude and obliquity. The model also specifies numerical values for the pole offsets at J2000.0 between the mean equatorial frame and the Geocentric Celestial Reference System (GCRS). In this paper, we discuss precession models consistent with IAU 2000A precession-nutation (i.e. MHB 2000, provided by Mathews et al. \\cite{Mathews02}) and we provide a range of expressions that implement them. The final precession model, designated P03, is a possible replacement for the precession component of IAU 2000A, offering improved dynamical consistency and a better basis for future improvement. As a preliminary step, we present our expressions for the currently used precession quantities zetaA, thetaA, zA, in agreement with the MHB corrections to the precession rates, that appear in the IERS Conventions 2000. We then discuss a more sophisticated method for improving the precession model of the equator in order that it be compliant with the IAU 2000A model. In contrast to the first method, which is based on corrections to the t terms of the developments for the precession quantities in longitude and obliquity, this method also uses corrections to their higher degree terms. It is essential that this be used in conjunction with an improved model for the ecliptic precession, which is expected, given the known discrepancies in the IAU 1976 expressions, to contribute in a significant way to these higher degree terms. With this aim in view, we have developed new expressions for the motion of the ecliptic with respect to the fixed ecliptic using the developments from Simon et al. (\\cite{Simon94}) and Williams (\\cite{Williams94}) and with improved constants fitted to the most recent numerical planetary ephemerides. We have then used these new expressions for the ecliptic together with the MHB corrections to precession rates to solve the precession equations for providing new solution for the precession of the equator that is dynamically consistent and compliant with IAU 2000. A number of perturbing effects have first been removed from the MHB estimates in order to get the physical quantities needed in the equations as integration constants. The equations have then been solved in a similar way to Lieske et al. (\\cite{Lieske77}) and Williams (\\cite{Williams94}), based on similar theoretical expressions for the contributions to precession rates, revised by using MHB values. Once improved expressions have been obtained for the precession of the ecliptic and the equator, we discuss the most suitable precession quantities to be considered in order to be based on the minimum number of variables and to be the best adapted to the most recent models and observations. Finally we provide developments for these quantities, denoted the P03 solution, including a revised Sidereal Time expression.

Wireless, Acoustically Linked, Undersea, Magnetometer Sensor Network

DTIC Science & Technology

2010-06-01

Hull Street, San Diego, CA 92152 mihajlo.tomic@navy.mil, sullivap@spawar.navy.mil, keyko.mcdonald.navy.mil Abstract—This paper presents a magnetometer...sensor node design that consists of a He3 nuclear precession total-field magne- tometer, data acquisition and recording electronics, and acoustic modem...detection range, thereby minimizing the overall number of required nodes to cover a given area. Given the aversion to continuously streaming data via the

The use of precession modulation for nutation control in spin-stabilized spacecraft

NASA Technical Reports Server (NTRS)

Taylor, J. M.; Donner, R. J.; Tasar, V.

1974-01-01

The relations which determine the nutation effects induced in a spinning spacecraft by periodic precession thrust pulses are derived analytically. By utilizing the idea that nutation need only be observed just before each precession thrust pulse, a difficult continuous-time derivation is replaced by a simple discrete-time derivation using z-transforms. The analytic results obtained are used to develop two types of modulated precession control laws which use the precession maneuver to concurrently control nutation. Results are illustrated by digital simulation of an actual spacecraft configuration.

Precipitate statistics in an Al-Mg-Si-Cu alloy from scanning precession electron diffraction data

NASA Astrophysics Data System (ADS)

Sunde, J. K.; Paulsen, Ø.; Wenner, S.; Holmestad, R.

2017-09-01

The key microstructural feature providing strength to age-hardenable Al alloys is nanoscale precipitates. Alloy development requires a reliable statistical assessment of these precipitates, in order to link the microstructure with material properties. Here, it is demonstrated that scanning precession electron diffraction combined with computational analysis enable the semi-automated extraction of precipitate statistics in an Al-Mg-Si-Cu alloy. Among the main findings is the precipitate number density, which agrees well with a conventional method based on manual counting and measurements. By virtue of its data analysis objectivity, our methodology is therefore seen as an advantageous alternative to existing routines, offering reproducibility and efficiency in alloy statistics. Additional results include improved qualitative information on phase distributions. The developed procedure is generic and applicable to any material containing nanoscale precipitates.

Electric-field assisted spin torque nano-oscillator and binary frequency shift keying modulation

NASA Astrophysics Data System (ADS)

Zhang, Xiangli; Chen, Hao-Hsuan; Zhang, Zongzhi; Liu, Yaowen

2018-04-01

Electric-controlled magnetization precession introduces technologically relevant possibility for developing spin torque nano-oscillators (STNO) with potential applications in microwave emission. Using the perpendicularly magnetized magnetic tunnel junction (MTJ), we show that the magnetization oscillation frequency can be tuned by the co-action of electric field and spin polarized current. The dynamical phase diagram of MTJ-based STNO is analytically predicted through coordinate transformation from the laboratory frame to the rotation frame, by which the nonstationary out-of-plane magnetization precession process is therefore transformed into the stationary process in the rotation frame. Furthermore, using this STNO as a microwave source, we numerically demonstrate that the bit signal can be transmitted by a binary frequency shift keying (BFSK) modulation technique. The BFSK scheme shows good modulation features with no transient state.

Numerical relativity simulations of precessing binary neutron star mergers

NASA Astrophysics Data System (ADS)

Dietrich, Tim; Bernuzzi, Sebastiano; Brügmann, Bernd; Ujevic, Maximiliano; Tichy, Wolfgang

2018-03-01

We present the first set of numerical relativity simulations of binary neutron mergers that include spin precession effects and are evolved with multiple resolutions. Our simulations employ consistent initial data in general relativity with different spin configurations and dimensionless spin magnitudes ˜0.1 . They start at a gravitational-wave frequency of ˜392 Hz and cover more than 1 precession period and about 15 orbits up to merger. We discuss the spin precession dynamics by analyzing coordinate trajectories, quasilocal spin measurements, and energetics, by comparing spin aligned, antialigned, and irrotational configurations. Gravitational waveforms from different spin configuration are compared by calculating the mismatch between pairs of waveforms in the late inspiral. We find that precession effects are not distinguishable from nonprecessing configurations with aligned spins for approximately face-on binaries, while the latter are distinguishable from nonspinning configurations. Spin precession effects are instead clearly visible for approximately edge-on binaries. For the parameters considered here, precession does not significantly affect the characteristic postmerger gravitational-wave frequencies nor the mass ejection. Our results pave the way for the modeling of spin precession effects in the gravitational waveform from binary neutron star events.

Three-Dimensional Numerical Hydrodynamical Simulation of Low/hard and High/soft States in Accretion Discs of Microquasars and Quasars on Base of Undefined Precession

NASA Astrophysics Data System (ADS)

Nazarenko, V. V.; Nazarenko, S. V.

In this study, the models of slaved precession of accretion disc and donors radiation-driven wind were performed using three-dimensional numerical astrophysical methods by the example of microquasar Cyg X-1. As is shown, in the course of precession of the accretion disc blown by the donor's wind the states with high and low temperature (low and high mass accretion rate, respectively) start being generated in the centre of disc. Our computations of disc precession performed on base of undefined precession that means each point of rotation axis of accretion disc makes unclosed difficult curve instead of a circle as it is in case of definite precession. In this case, the transition between states of high and low temperature takes place irregularly and not depend on precession period. The duration of transition between these both states is less than intervals of states on several orders of magnitudes.

Larmor precession and barrier tunneling time of a neutral spinning particle

NASA Astrophysics Data System (ADS)

Li, Zhi-Jian; Liang, J. Q.; Kobe, D. H.

2001-10-01

The Larmor precession of a neutral spinning particle in a magnetic field confined to the region of a one-dimensional rectangular barrier is investigated for both a nonrelativistic and a relativistic incoming particle. The spin precession serves as a clock to measure the time spent by a quantum particle traversing a potential barrier. With the help of a general spin coherent state it is explicitly shown that the precession time is equal to the dwell time in both the nonrelativistic and relativistic cases. We also present a numerical estimation of the precession time showing an apparent superluminal tunneling.

Non-thermal optical excitation of terahertz-spin precession in a magneto-optical insulator

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

Parchenko, Sergii; Maziewski, Andrzej; Stupakiewicz, Andrzej, E-mail: and@uwb.edu.pl

2016-01-18

We demonstrate non-thermal ultrafast laser excitation of spin precession with THz frequency in Gd-Bi-substituted iron garnet via the inverse Faraday effect. The modulation of THz precession by about 60 GHz below the compensation temperature of magnetic moment was observed. The THz frequency precession was caused by the exchange resonance between the Gd and Fe sublattices; we attributed the low-frequency modulation to dielectric resonance mode with a magnetic contribution. We demonstrate the possibility of polarization-sensitive control of spin precession under THz generation by laser pulses, helping to develop high-speed magneto-optical devices.

Investigation of a 129Xe magnetometer for the Neutron Electric Dipole Moment Experiment at TRIUMF

NASA Astrophysics Data System (ADS)

Lang, Michael; Nedm At Triumf Collaboration

2016-03-01

A non-zero neutron electric dipole moment (nEDM) would signify a previously unknown source of CP (or T) violation. New sources of CP violation are believed to be required to explain the baryon asymmetry of the universe. Employing a newly developed high-density UCN source, an experiment at TRIUMF aims to measure the nEDM to the level of 10-27 e . cm in its initial phase. Precession frequency differences for UCN stored in a bottle subject to parallel and anti-parallel E and B fields signify a permanent nEDM. Magnetic field instability and inhomogeneity, as well as field changes resulting from leakage currents (correlated with E fields) are the dominant systematic effects in nEDM measurements. To address this, passive and active magnetic shielding are in development along with a dual species (129Xe and 199Hg) atomic comagnetometer. Simultaneously introducing both atomic species into the UCN cell, the comagnetometer can mitigate false EDMs. 199Hg precession will be detected by Faraday rotation spectroscopy, and 129Xe precession will measured via two-photon excitation and emission. The present comagnetometer progress will be discussed, with focus on polarized 129Xe production and delivery. Work supported by the Natural Sciences and Engineering Research Council of Canada.

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

Lau, R. M.; Hankins, M. J.; Herter, T. L.

Massive, evolved stars play a crucial role in the metal enrichment, dust budget, and energetics of the interstellar medium; however, the details of their evolution are uncertain because of their rarity and short lifetimes before exploding as supernovae. Discrepancies between theoretical predictions from single-star evolutionary models and observations of massive stars have evoked a shifting paradigm that implicates the importance of binary interaction. We present mid- to far-infrared observations from the Stratospheric Observatory for Infrared Astronomy of a conical “helix” of warm dust (∼180 K) that appears to extend from the Wolf–Rayet star WR102c. Our interpretation of the helix ismore » a precessing, collimated outflow that emerged from WR102c during a previous evolutionary phase as a rapidly rotating luminous blue variable. We attribute the precession of WR102c to gravitational interactions with an unseen compact binary companion whose orbital period can be constrained to 800 days < P < 1400 days from the inferred precession period, τ{sub p} ∼ 1.4 × 10{sup 4} yr, and limits imposed on the stellar and orbital parameters of the system. Our results concur with the range of orbital periods (P ≲ 1500 days) where spin-up via mass exchange is expected to occur for massive binary systems.« less

Multishot EPI-SSFP in the Heart

PubMed Central

Herzka, Daniel A.; Kellman, Peter; Aletras, Anthony H.; Guttman, Michael A.; McVeigh, Elliot R.

2007-01-01

Refocused steady-state free precession (SSFP), or fast imaging with steady precession (FISP or TrueFISP), has recently proven valuable for cardiac imaging because of its high signal-to-noise ratio (SNR) and excellent blood-myocardium contrast. In this study, various implementations of multiecho SSFP or EPI-SSFP for imaging in the heart are presented. EPI-SSFP has higher scan-time efficiency than single-echo SSFP, as two or more phase-encode lines are acquired per repetition time (TR) at the cost of a modest increase in TR. To minimize TR, a noninterleaved phase-encode order in conjunction with a phased-array ghost elimination (PAGE) technique was employed, removing the need for echo time shifting (ETS). The multishot implementation of EPI-SSFP was used to decrease the breath-hold duration for cine acquisitions or to increase the temporal or spatial resolution for a fixed breath-hold duration. The greatest gain in efficiency was obtained with the use of a three-echo acquisition. Image quality for cardiac cine applications using multishot EPI-SSFP was comparable to that of single-echo SSFP in terms of blood-myocardium contrast and contrast-to-noise ratio (CNR). The PAGE method considerably reduced flow artifacts due to both the inherent ghost suppression and the concomitant reduction in phase-encode blip size. The increased TR of multishot EPI-SSFP led to a reduced specific absorption rate (SAR) for a fixed RF flip angle, and allowed the use of a larger flip angle without increasing the SAR above the FDA-approved limits. PMID:11948726

Mitigation of near-band balanced steady-state free precession through-plane flow artifacts using partial dephasing.

PubMed

Datta, Anjali; Cheng, Joseph Y; Hargreaves, Brian A; Baron, Corey A; Nishimura, Dwight G

2018-06-01

To mitigate artifacts from through-plane flow at the locations of steady-state stopbands in balanced steady-state free precession (SSFP) using partial dephasing. A 60° range in the phase accrual during a TR was created over the voxel by slightly unbalancing the slice-select dephaser. The spectral profiles of SSFP with partial dephasing for various constant flow rates and during pulsatile flow were simulated to determine if partial dephasing decreases through-plane flow artifacts originating near SSFP dark bands while maintaining on-resonant signal. Simulations were then validated in a flow phantom. Lastly, phase-cycled SSFP cardiac cine images were acquired with and without partial dephasing in six subjects. Partial dephasing decreased the strength and non-linearity of the dependence of the signal at the stopbands on the through-plane flow rate. It thus mitigated hyper-enhancement from out-of-slice signal contributions and transient-related artifacts caused by variable flow both in the phantom and in vivo. In six volunteers, partial dephasing noticeably decreased artifacts in all of the phase-cycled cardiac cine datasets. Partial dephasing can mitigate the flow artifacts seen at the stopbands in balanced SSFP while maintaining the sequence's desired signal. By mitigating hyper-enhancement and transient-related artifacts originating from the stopbands, partial dephasing facilitates robust multiple-acquisition phase-cycled SSFP in the heart. Magn Reson Med 79:2944-2953, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

Paleoproductivity and Nutrient Cycling on the Sumatra Margin during the Past Half Million Years

NASA Astrophysics Data System (ADS)

Gibson, K.; Mitt Schwamborn, T.; Thunell, R.; Tuten, E. C.; Swink, C.; Tappa, E.

2017-12-01

In the IndoPacific, changes in paleoproductivity on orbital timescales are often linked to changes in precession, particularly in areas of coastal upwelling. These changes are in turn related to variations in zonal wind patterns and thermocline tilt associated with the El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD), and commensurate changes in Asian, Indian, and Australian monsoon precipitation and wind-driven upwelling. Previous studies have revealed varying phase relationships amongst monsoon precipitation, upwelling variability and precession minima in the Indo-Pacific region. Regional records have additionally displayed power in the 41-kyr band, attributed to changes in deepwater ventilation and preservation, and the 100-kyr band, related to the influence of sea level on the Indonesian Throughflow (ITF). To provide further insight into the regional and distal forcing on paleoproductivity and nutrient cycling in this clearly complex region, we present %TOC, %CaCO3, and sedimentary δ15N data from core MD98-2152, off the Sumatra margin in a region influenced by both ITF variability and wind-driven upwelling. By comparing our paleoproductivity and paleonutrient data with planktonic δ18O (tuned to composite Chinese cave speleothem records) and benthic δ18O (tuned to the Lisiecki-Raymo Stack), we compare timing of local productivity changes to high latitude ice-volume changes and local hydrographic changes. A strong 23-kyr signal in the %TOC record supports the strong influence of precession on paleoproductivity in this region. In contrast, strong power in the 100 and 41-kyr bands is observed in %CaCO3 and δ15N with a relatively minor contribution from precession, indicating a complex relationship between nutrient cycling, upwelling, production, and preservation on the Sumatra coast.

Quasi-parallel precession diffraction: Alignment method for scanning transmission electron microscopes.

PubMed

Plana-Ruiz, S; Portillo, J; Estradé, S; Peiró, F; Kolb, Ute; Nicolopoulos, S

2018-06-06

A general method to set illuminating conditions for selectable beam convergence and probe size is presented in this work for Transmission Electron Microscopes (TEM) fitted with µs/pixel fast beam scanning control, (S)TEM, and an annular dark field detector. The case of interest of beam convergence and probe size, which enables diffraction pattern indexation, is then used as a starting point in this work to add 100 Hz precession to the beam while imaging the specimen at a fast rate and keeping the projector system in diffraction mode. The described systematic alignment method for the adjustment of beam precession on the specimen plane while scanning at fast rates is mainly based on the sharpness of the precessed STEM image. The complete alignment method for parallel condition and precession, Quasi-Parallel PED-STEM, is presented in block diagram scheme, as it has been tested on a variety of instruments. The immediate application of this methodology is that it renders the TEM column ready for the acquisition of Precessed Electron Diffraction Tomographies (EDT) as well as for the acquisition of slow Precessed Scanning Nanometer Electron Diffraction (SNED). Examples of the quality of the Precessed Electron Diffraction (PED) patterns and PED-STEM alignment images are presented with corresponding probe sizes and convergence angles. Copyright © 2018. Published by Elsevier B.V.

Gyroscope precession in special and general relativity from basic principles

NASA Astrophysics Data System (ADS)

Jonsson, Rickard M.

2007-05-01

In special relativity a gyroscope that is suspended in a torque-free manner will precess as it is moved along a curved path relative to an inertial frame S. We explain this effect, which is known as Thomas precession, by considering a real grid that moves along with the gyroscope, and that by definition is not rotating as observed from its own momentary inertial rest frame. From the basic properties of the Lorentz transformation we deduce how the form and rotation of the grid (and hence the gyroscope) will evolve relative to S. As an intermediate step we consider how the grid would appear if it were not length contracted along the direction of motion. We show that the uncontracted grid obeys a simple law of rotation. This law simplifies the analysis of spin precession compared to more traditional approaches based on Fermi transport. We also consider gyroscope precession relative to an accelerated reference frame and show that there are extra precession effects that can be explained in a way analogous to the Thomas precession. Although fully relativistically correct, the entire analysis is carried out using three-vectors. By using the equivalence principle the formalism can also be applied to static spacetimes in general relativity. As an example, we calculate the precession of a gyroscope orbiting a static black hole.

Ballistic missile precession frequency extraction by spectrogram's texture

NASA Astrophysics Data System (ADS)

Wu, Longlong; Xu, Shiyou; Li, Gang; Chen, Zengping

2013-10-01

In order to extract precession frequency, an crucial parameter in ballistic target recognition, which reflected the kinematical characteristics as well as structural and mass distribution features, we developed a dynamic RCS signal model for a conical ballistic missile warhead, with a log-norm multiplicative noise, substituting the familiar additive noise, derived formulas of micro-Doppler induced by precession motion, and analyzed time-varying micro-Doppler features utilizing time-frequency transforms, extracted precession frequency by measuring the spectrogram's texture, verified them by computer simulation studies. Simulation demonstrates the excellent performance of the method proposed in extracting the precession frequency, especially in the case of low SNR.

Gravitational waves from rotating and precessing rigid bodies. 2: General solutions and computationally useful formulae

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.

Effective-one-body model for black-hole binaries with generic mass ratios and spins

NASA Astrophysics Data System (ADS)

Taracchini, Andrea; Buonanno, Alessandra; Pan, Yi; Hinderer, Tanja; Boyle, Michael; Hemberger, Daniel A.; Kidder, Lawrence E.; Lovelace, Geoffrey; Mroué, Abdul H.; Pfeiffer, Harald P.; Scheel, Mark A.; Szilágyi, Béla; Taylor, Nicholas W.; Zenginoglu, Anil

2014-03-01

Gravitational waves emitted by black-hole binary systems have the highest signal-to-noise ratio in LIGO and Virgo detectors when black-hole spins are aligned with the orbital angular momentum and extremal. For such systems, we extend the effective-one-body inspiral-merger-ringdown waveforms to generic mass ratios and spins calibrating them to 38 numerical-relativity nonprecessing waveforms produced by the SXS Collaboration. The numerical-relativity simulations span mass ratios from 1 to 8, spin magnitudes up to 98% of extremality, and last for 40 to 60 gravitational-wave cycles. When the total mass of the binary is between 20 and 200M⊙, the effective-one-body nonprecessing (dominant mode) waveforms have overlap above 99% (using the advanced-LIGO design noise spectral density) with all of the 38 nonprecessing numerical waveforms, when maximizing only on initial phase and time. This implies a negligible loss in event rate due to modeling. We also show that—without further calibration— the precessing effective-one-body (dominant mode) waveforms have overlap above 97% with two very long, strongly precessing numerical-relativity waveforms, when maximizing only on the initial phase and time.

Near-Earth asteroids orbits using Gaia and ground-based observations

NASA Astrophysics Data System (ADS)

Bancelin, D.; Hestroffer, D.; Thuillot, W.

2011-05-01

Potentially Hazardous Asteroids (PHAs) are Near-Earth Asteroids caraterised by a Minimum Orbital Intersection Distance (MOID) with Earth less to 0.05 A.U and an absolute magnitude H<22. Those objects have sometimes a so significant close approach with Earth that they can be put on a chaotic orbit. This kind of orbit is very sensitive for exemple to the initial conditions, to the planetary theory used (for instance JPL's model versus IMCCE's model) or even to the numerical integrator used (Lie Series, Bulirsch-Stoer or Radau). New observations (optical, radar, flyby or satellite mission) can improve those orbits and reduce the uncertainties on the Keplerian elements.The Gaia mission is an astrometric mission that will be launched in 2012 and will observe a large number of Solar System Objects down to magnitude V≤20. During the 5-year mission, Gaia will continuously scan the sky with a specific strategy: objects will be observed from two lines of sight separated with a constant basic angle. Five constants already fixed determinate the nominal scanning law of Gaia: The inertial spin rate (1°/min) that describe the rotation of the spacecraft around an axis perpendicular to those of the two fields of view, the solar-aspect angle (45°) that is the angle between the Sun and the spacecraft rotation axis, the precession period (63.12 days) which is the precession of the spin axis around the Sun-Earth direction. Two other constants are still free parameters: the initial spin phase, and the initial precession angle that will be fixed at the start of the nominal science operations. These latter are constraint by scientific outcome (e.g. possibility of performing test of fundamental physics) together with operational requirements (downlink to Earth windows). Several sets of observations of specific NEOs will hence be provided according to the initial precession angle. The purpose here is to study the statistical impact of the initial precession angle on the error propagation and on the collision probability, especially for PHAs. We will also analyse the advantage of combining space-based to ground-based observation over long term, as well as in short term from observations in alert.

Near-Earth Asteroids Astrometry with Gaia

NASA Astrophysics Data System (ADS)

Bancelin, D.; Hestroffer, D.; Thuillot, W.

2011-05-01

Potentially Hazardous Asteroids (PHAs) are Near-Earth Asteroids caraterised by a Minimum Orbital Intersection Distance (MOID) with Earth less to 0.05 A.U and an absolute magnitude H<22. Those objects have sometimes a so significant close approach with Earth that they can be put on a chaotic orbit. This kind of orbit is very sensitive for exemple to the initial conditions, to the planetary theory used (for instance JPL's model versus IMCCE's model) or even to the numerical integrator used (Lie Series, Bulirsch-Stoer or Radau). New observations (optical, radar, flyby or satellite mission) can improve those orbits and reduce the uncertainties on the Keplerian elements.The Gaia mission is an astrometric mission that will be launched in 2012 and will observe a large number of Solar System Objects down to magnitude V≤20. During the 5-year mission, Gaia will continuously scan the sky with a specific strategy: objects will be observed from two lines of sight separated with a constant basic angle. Five constants already fixed determinate the nominal scanning law of Gaia: The inertial spin rate (1°/min) that describe the rotation of the spacecraft around an axis perpendicular to those of the two fields of view, the solar-aspect angle (45°) that is the angle between the Sun and the spacecraft rotation axis, the precession period (63.12 days) which is the precession of the spin axis around the Sun-Earth direction. Two other constants are still free parameters: the initial spin phase, and the initial precession angle that will be fixed at the start of the nominal science operations. These latter are constraint by scientific outcome (e.g. possibility of performing test of fundamental physics) together with operational requirements (downlink to Earth windows). Several sets of observations of specific NEOs will hence be provided according to the initial precession angle. The purpose here is to study the statistical impact of the initial precession angle on the error propagation and on the collision probability, especially for PHAs. We will also analyse the advantage of combining space-based to ground-based observation over long term, as well as in short term from observations in alert.

Progress Report of the IAU Working Group on Precession and the Ecliptic

DTIC Science & Technology

2006-12-01

may be used with either the traditional rotation matrix, or those rotation matrices described in Capitaine et al. (2003) and Fukushima (2003). We...precession of about 6.4 mas cent−2 in longitude. Thus, the precession theory was not dynamically consistent. 93 Furthermore, Fukushima (2003) showed that...2003, Capitaine et al. 2003, and Fukushima 2003) have been published recently to address the shortcomings of the precession portion, including the

Searching the Allais effect during the total sun eclipse of 11 July 2010

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

Salva, Horacio R.

2011-03-15

I have measured the precession change of the oscillation plane with an automated Foucault pendulum and found no evidence (within the measurement error) of the Allais effect. The precession speed was registered and, due the variations involved, if the precession speed would changed 0.3 degree per hour (increasing or decreasing the angle of the normal precession speed) during the all eclipse, it would be notice in this measurement.

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.

Precession missile feature extraction using sparse component analysis of radar measurements

NASA Astrophysics Data System (ADS)

Liu, Lihua; Du, Xiaoyong; Ghogho, Mounir; Hu, Weidong; McLernon, Des

2012-12-01

According to the working mode of the ballistic missile warning radar (BMWR), the radar return from the BMWR is usually sparse. To recognize and identify the warhead, it is necessary to extract the precession frequency and the locations of the scattering centers of the missile. This article first analyzes the radar signal model of the precessing conical missile during flight and develops the sparse dictionary which is parameterized by the unknown precession frequency. Based on the sparse dictionary, the sparse signal model is then established. A nonlinear least square estimation is first applied to roughly extract the precession frequency in the sparse dictionary. Based on the time segmented radar signal, a sparse component analysis method using the orthogonal matching pursuit algorithm is then proposed to jointly estimate the precession frequency and the scattering centers of the missile. Simulation results illustrate the validity of the proposed method.

Perihelion precession from power law central force and magnetic-like force

NASA Astrophysics Data System (ADS)

Xu, Feng

2011-04-01

By the Laplace-Runge-Lenz (LRL) vector, we analyzed perihelion precessions of orbit with arbitrary eccentricity from perturbations of 1) power law central force and 2) fThusmagnetic-like force. Exact and analytically closed expressions for the precession rate are derived in both cases. In the central force case, we give a further expansion expression of precession rate in orders of eccentricity, and a rule judging pro- or retrograde precession is also given. We applied the result of central force to precessions of a planet in 1) Schwarzschild space-time, for which the formula for the Mercury’s 43”/century is reproduced, and 2) spherically distributed dark matter, for which we find a formula that is a generalization of the result derived by others for circular orbit. In the magnetic case, the use of the LRL vector proves to be simple and efficient. An example of magnetic-like perturbation is also discussed.

Perihelion precession from power law central force and magnetic-like force

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

Xu Feng

2011-04-15

By the Laplace-Runge-Lenz (LRL) vector, we analyzed perihelion precessions of orbit with arbitrary eccentricity from perturbations of 1) power law central force and 2) fThusmagnetic-like force. Exact and analytically closed expressions for the precession rate are derived in both cases. In the central force case, we give a further expansion expression of precession rate in orders of eccentricity, and a rule judging pro- or retrograde precession is also given. We applied the result of central force to precessions of a planet in 1) Schwarzschild space-time, for which the formula for the Mercury's 43''/century is reproduced, and 2) spherically distributed darkmore » matter, for which we find a formula that is a generalization of the result derived by others for circular orbit. In the magnetic case, the use of the LRL vector proves to be simple and efficient. An example of magnetic-like perturbation is also discussed.« less

The influence of orbit selection on the accuracy of the Stanford Relativity gyroscope experiment

NASA Technical Reports Server (NTRS)

Vassar, R.; Everitt, C. W. F.; Vanpatten, R. A.; Breakwell, J. V.

1980-01-01

This paper discusses an error analysis for the Stanford Relativity experiment, designed to measure the precession of a gyroscope's spin-axis predicted by general relativity. Measurements will be made of the spin-axis orientations of 4 superconducting spherical gyroscopes carried by an earth-satellite. Two relativistic precessions are predicted: a 'geodetic' precession associated with the satellite's orbital motion and a 'motional' precession due to the earth's rotation. Using a Kalman filter covariance analysis with a realistic error model we have computed the error in determining the relativistic precession rates. Studies show that a slightly off-polar orbit is better than a polar orbit for determining the 'motional' drift.

Precession feature extraction of ballistic missile warhead with high velocity

NASA Astrophysics Data System (ADS)

Sun, Huixia

2018-04-01

This paper establishes the precession model of ballistic missile warhead, and derives the formulas of micro-Doppler frequency induced by the target with precession. In order to obtain micro-Doppler feature of ballistic missile warhead with precession, micro-Doppler bandwidth estimation algorithm, which avoids velocity compensation, is presented based on high-resolution time-frequency transform. The results of computer simulations confirm the effectiveness of the proposed method even with low signal-to-noise ratio.

New precession expressions, valid for long time intervals

NASA Astrophysics Data System (ADS)

Vondrák, J.; Capitaine, N.; Wallace, P.

2011-10-01

Context. The present IAU model of precession, like its predecessors, is given as a set of polynomial approximations of various precession parameters intended for high-accuracy applications over a limited time span. Earlier comparisons with numerical integrations have shown that this model is valid only for a few centuries around the basic epoch, J2000.0, while for more distant epochs it rapidly diverges from the numerical solution. In our preceding studies we also obtained preliminary developments for the precessional contribution to the motion of the equator: coordinates X,Y of the precessing pole and precession parameters ψA,ωA, suitable for use over long time intervals. Aims: The goal of the present paper is to obtain upgraded developments for various sets of precession angles that would fit modern observations near J2000.0 and at the same time fit numerical integration of the motions of solar system bodies on scales of several thousand centuries. Methods: We used the IAU 2006 solutions to represent the precession of the ecliptic and of the equator close to J2000.0 and, for more distant epochs, a numerical integration using the Mercury 6 package and solutions by Laskar et al. (1993, A&A, 270, 522) with upgraded initial conditions and constants to represent the ecliptic, and general precession and obliquity, respectively. From them, different precession parameters were calculated in the interval ± 200 millennia from J2000.0, and analytical expressions are found that provide a good fit for the whole interval. Results: Series for the various precessional parameters, comprising a cubic polynomial plus from 8 to 14 periodic terms, are derived that allow precession to be computed with an accuracy comparable to IAU 2006 around the central epoch J2000.0, a few arcseconds throughout the historical period, and a few tenths of a degree at the ends of the ± 200 millennia time span. Computer algorithms are provided that compute the ecliptic and mean equator poles and the precession matrix. The Appendix containing the computer code is available in electronic form at http://www.aanda.org

EARTH, MOON, SUN, AND CV ACCRETION DISKS

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

Montgomery, M. M.

2009-11-01

Net tidal torque by the secondary on a misaligned accretion disk, like the net tidal torque by the Moon and the Sun on the equatorial bulge of the spinning and tilted Earth, is suggested by others to be a source to retrograde precession in non-magnetic, accreting cataclysmic variable (CV) dwarf novae (DN) systems that show negative superhumps in their light curves. We investigate this idea in this work. We generate a generic theoretical expression for retrograde precession in spinning disks that are misaligned with the orbital plane. Our generic theoretical expression matches that which describes the retrograde precession of Earths'more » equinoxes. By making appropriate assumptions, we reduce our generic theoretical expression to those generated by others, or to those used by others, to describe retrograde precession in protostellar, protoplanetary, X-ray binary, non-magnetic CV DN, quasar, and black hole systems. We find that spinning, tilted CV DN systems cannot be described by a precessing ring or by a precessing rigid disk. We find that differential rotation and effects on the disk by the accretion stream must be addressed. Our analysis indicates that the best description of a retrogradely precessing spinning, tilted, CV DN accretion disk is a differentially rotating, tilted disk with an attached rotating, tilted ring located near the innermost disk annuli. In agreement with the observations and numerical simulations by others, we find that our numerically simulated CV DN accretion disks retrogradely precess as a unit. Our final, reduced expression for retrograde precession agrees well with our numerical simulation results and with selective observational systems that seem to have main-sequence secondaries. Our results suggest that a major source to retrograde precession is tidal torques like that by the Moon and the Sun on the Earth. In addition, these tidal torques should be common to a variety of systems where one member is spinning and tilted, regardless if accretion disks are present or not. Our results suggest that the accretion disk's geometric shape directly affects the disk's precession rate.« less

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.

Implications of the Occurrence of Glitches in Pulsar Free Precession Candidates.

PubMed

Jones, D I; Ashton, G; Prix, R

2017-06-30

The timing properties of radio pulsars provide a unique probe of neutron star interiors. Recent observations have uncovered quasiperiodicities in the timing and pulse properties of some pulsars, a phenomenon that has often been attributed to free precession of the neutron star, with profound implications for the distribution of superfluidity and superconductivity in the star. We advance this program by developing consistency relations between free precession and pulsars glitches, and we show that there are difficulties in reconciling the two phenomena in some precession candidates. This indicates that the precession model used here needs to be modified or some other phenomenon is at work in producing the quasiperiodicities, or even that there is something missing in terms of our understanding of glitches.

Investigation on the subsynchronous pseudo-vibration of rotating machinery

NASA Astrophysics Data System (ADS)

Qu, Lei; Liao, Yuhe; Lin, Jing; Zhao, Ming

2018-06-01

Subsynchronous pseudo-vibration (SPV) of rotating machinery is one of the primary reasons for fault misdiagnosis. SPV has similar signal signatures to those of a real fault, which usually leads to excessive maintenance or even unscheduled shutdown. For this reason, it is essential to investigate the root causes of SPV so as to reduce unnecessary downtime and maintenance cost. Aiming at this issue, a novel signal model for rotor non-contact vibration is built to describe the generating mechanism of one kind of SPV by considering the combined effects of rotor axial motion and detection surface runout on vibration signal. To obtain more discriminative fault features from the vibration signals, the two-dimension holospectrum (2DH) is employed to integrate the phase information from two perpendicularly installed sensors. The characteristics of precession orbit used to describe the lateral motion of a rotor could be fully extracted by 2DH. It is shown that the precession orbit at the fault feature frequency will degenerate into a straight line when SPV occurs, and thus the eccentricity of precession orbit could be considered as a key feature for discriminating SPV from real subsynchronous vibration (RSV). The effectiveness of proposed method was validated on a rotor test rig. By using this method, the SPV problem of a real gearbox in a blast furnace blower set in a steel mill was successfully diagnosed.

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.

Multishot EPI-SSFP in the heart.

PubMed

Herzka, Daniel A; Kellman, Peter; Aletras, Anthony H; Guttman, Michael A; McVeigh, Elliot R

2002-04-01

Refocused steady-state free precession (SSFP), or fast imaging with steady precession (FISP or TrueFISP), has recently proven valuable for cardiac imaging because of its high signal-to-noise ratio (SNR) and excellent blood-myocardium contrast. In this study, various implementations of multiecho SSFP or EPI-SSFP for imaging in the heart are presented. EPI-SSFP has higher scan-time efficiency than single-echo SSFP, as two or more phase-encode lines are acquired per repetition time (TR) at the cost of a modest increase in TR. To minimize TR, a noninterleaved phase-encode order in conjunction with a phased-array ghost elimination (PAGE) technique was employed, removing the need for echo time shifting (ETS). The multishot implementation of EPI-SSFP was used to decrease the breath-hold duration for cine acquisitions or to increase the temporal or spatial resolution for a fixed breath-hold duration. The greatest gain in efficiency was obtained with the use of a three-echo acquisition. Image quality for cardiac cine applications using multishot EPI-SSFP was comparable to that of single-echo SSFP in terms of blood-myocardium contrast and contrast-to-noise ratio (CNR). The PAGE method considerably reduced flow artifacts due to both the inherent ghost suppression and the concomitant reduction in phase-encode blip size. The increased TR of multishot EPI-SSFP led to a reduced specific absorption rate (SAR) for a fixed RF flip angle, and allowed the use of a larger flip angle without increasing the SAR above the FDA-approved limits. Copyright 2002 Wiley-Liss, Inc.

Gap junctions between interneurons are required for normal spatial coding in the hippocampus and short-term spatial memory

PubMed Central

Allen, Kevin; Fuchs, Elke C.; Jaschonek, Hannah; Bannerman, David M.; Monyer, Hannah

2011-01-01

Gap junctions containing connexin-36 (Cx36) electrically couple interneurons in many brain regions and synchronize their activity. We used Cx36 knockout mice (Cx36−/−) to study the importance of electrical coupling between interneurons for spatial coding in the hippocampus and for different forms of hippocampus-dependent spatial memory. Recordings in behaving mice revealed that the spatial selectivity of hippocampal pyramidal neurons was reduced and less stable in Cx36−/− mice. Altered network activity was reflected in slower theta oscillations in the mutants. Temporal coding, assessed by determining the presence and characteristics of theta phase precession, had different dynamics in Cx36−/− mice compared to controls. At the behavioral level, Cx36−/− mice displayed impaired short-term spatial memory but normal spatial reference memory. These results highlight the functional role of electrically coupled interneurons for spatial coding and cognition. Moreover, they suggest that the precise spatial selectivity of place cells is not essential for normal performance on spatial tasks assessing associative long-term memory. PMID:21525295

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

Are we close to putting the anomalous perihelion precessions from Verlinde's emergent gravity to the test?

NASA Astrophysics Data System (ADS)

Iorio, Lorenzo

2017-03-01

In the framework of the emergent gravity scenario by Verlinde, it was recently observed by Liu and Prokopec that, among other things, an anomalous pericenter precession would affect the orbital motion of a test particle orbiting an isolated central body. Here, it is shown that, if it were real, its expected magnitude for the inner planets of the Solar System would be at the same level of the present-day accuracy in constraining any possible deviations from their standard perihelion precessions as inferred from long data records spanning about the last century. The most favorable situation for testing the Verlinde-type precession seems to occur for Mars. Indeed, according to recent versions of the EPM and INPOP planetary ephemerides, non-standard perihelion precessions, of whatsoever physical origin, which are larger than some ≈ 0.02-0.11 milliarcseconds per century are not admissible, while the putative precession predicted by Liu and Prokopec amounts to 0.09 milliarcseconds per century. Other potentially interesting astronomical and astrophysical scenarios like, e.g., the Earth's LAGEOS II artificial satellite, the double pulsar system PSR J0737-3039A/B and the S-stars orbiting the Supermassive Black Hole in Sgr A^* are, instead, not viable because of the excessive smallness of the predicted precessions for them.

New Precession Formulas

NASA Astrophysics Data System (ADS)

Fukushima, T.

2003-08-01

We adapted J.G. Williams' expression of the precession and nutation by the 3-1-3-1 rotation (Williams 1994) to an arbitrary inertial frame of reference. The new expression of the precession matrix is P = R1(-ɛ ) R3(-ψ ) R1(ϕ) R3(γ ) while that of precession-nutation matrix is NP = R1(-ɛ -Δ ɛ ) R3(-ψ -Δ ψ ) R1(ϕ) R3(γ ). Here γ and ϕ are the new planetary precession angles, ψ and ɛ are the new luni-solar precession angles, and Δ ψ and Δ ɛ are the usual nutations. The modified formulation avoids a singularity caused by finite pole offsets near the epoch. By adopting the latest planetary precession formula determined from DE405 (Harada 2003) and by using a recent theory of the forced nutation of the non-rigid Earth, SF2001 (Shirai and Fukushima 2001), we analysed the celestial pole offsets observed by VLBI for 1979-2000 and compiled by USNO and determined the best-fit polynomials of the new luni-solar precession angles. Then we translated the results into the classic precessional quantities as sin π A sin Π A, sin π A \\cos Π A, π A, Π A, pA, ψ A, ω A, χA, ζ A, zA, and θ A. Also we evaluated the effect of the difference in the ecliptic definition between the inertial and rotational senses. The combination of these formulas and the periodic part of SF2001 serves as a good approximation of the precession-nutation matrix in the ICRF. As a by-product, we determined the mean celestial pole offset at J2000.0 as X0 = -(17.12 +/- 0.01) mas and Y0 = -(5.06 +/- 0.02) mas. Also we estimated the speed of general precession in longitude at J2000.0 as p = (5028.7955 +/- 0.0003)''/Julian century, the mean obliquity at J2000.0 in the rotational sense as ɛ 0 = (84381.40955 +/- 0.00001)'', and the dynamical flattening of the Earth as Hd = (0.0032737804 +/- 0.0000000003). Further, we established a fast way to compute the precession-nutation matrix and provided a best-fit polynomial of s, an angle to specify the mean CEO.

Precession effects on a liquid planetary core

NASA Astrophysics Data System (ADS)

Liu, Min; Li, Li-Gang

2018-02-01

Motivated by the desire to understand the rich dynamics of precessionally driven flow in a liquid planetary core, we investigate, through numerical simulations, the precessing fluid motion in a rotating cylindrical annulus, which simultaneously possesses slow precession. The same problemhas been studied extensively in cylinders, where the precessing flow is characterized by three key parameters: the Ekman number E, the Poincaré number Po and the radius-height aspect ratio Γ. While in an annulus, there is another parameter, the inner-radius-height aspect ratio ϒ, which also plays an important role in controlling the structure and evolution of the flow. By decomposing the nonlinear solution into a set of inertial modes, we demonstrate the properties of both weakly and moderately precessing flows. It is found that, when the precessional force is weak, the flow is stable with a constant amplitude of kinetic energy. As the precessional force increases, our simulation suggests that the nonlinear interaction between the boundary effects and the inertial modes can trigger more turbulence, introducing a transitional regime of rich dynamics to disordered flow. The inertial mode u 111, followed by u 113 or u 112, always dominates the precessing flow when 0.001 ≤ Po ≤ 0.05, ranging from weak to moderate precession. Moreover, the precessing flow in an annulus shows more stability than in a cylinder which is likely to be caused by the effect of the inner boundary that restricts the growth of resonant and non-resonant inertial modes. Furthermore, the mechanism of triadic resonance is not found in the transitional regime from a laminar to disordered flow.

A New Precession Formula

NASA Astrophysics Data System (ADS)

Fukushima, Toshio

2003-07-01

We adapt J. G. Williams' expression of the precession and nutation using the 3-1-3-1 rotation to an arbitrary inertial frame of reference. The modified formulation avoids a singularity caused by finite pole offsets near the epoch. By adopting the planetary precession formula numerically determined from DE405 and by using a recent theory of the forced nutation of the nonrigid Earth by Shirai & Fukishima, we analyze the celestial pole offsets observed by VLBI for 1979-2000 and determine the best-fit polynomials of the lunisolar precession angles. We then translate the results into classical precession quantities and evaluate the difference due to the difference in the ecliptic definition. The combination of these formulae and the periodic part of the Shirai-Fukishima nutation theory serves as a good approximation of the precession-nutation matrix in the International Celestial Reference Frame. As a by-product, we determine the mean celestial pole offset at J2000.0 as X0=-(17.12+/-0.01) mas and Y0=-(5.06+/-0.02) mas. Also, we estimate the speed of general precession in longitude at J2000.0 as p=5028.7955"+/-0.0003" per Julian century, the mean obliquity at J2000.0 in the inertial sense as (ɛ0)I=84381.40621"+/-0.00001" and in the rotational sense as (ɛ0)R=84381.40955"+/-0.00001", and the dynamical flattening of Earth as Hd=(3.2737804+/-0.0000003)×10-3. Furthermore, we establish a fast way to compute the precession-nutation matrix and provide a best-fit polynomial of an angle to specify the mean Celestial Ephemeris Origin.

Superfluid quenching of the moment of inertia in a strongly interacting Fermi gas

NASA Astrophysics Data System (ADS)

Riedl, S.; Sánchez Guajardo, E. R.; Kohstall, C.; Hecker Denschlag, J.; Grimm, R.

2011-03-01

We report on the observation of a quenched moment of inertia resulting from superfluidity in a strongly interacting Fermi gas. Our method is based on setting the hydrodynamic gas in slow rotation and determining its angular momentum by detecting the precession of a radial quadrupole excitation. The measurements distinguish between the superfluid and collisional origins of hydrodynamic behavior, and show the phase transition.

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

Zohar, S.; Sterbinsky, G. E.

Here, we propose an experimental technique for extending feedback compensation of dissipative radiation used in nuclear magnetic resonance (NMR) to encompass ferromagnetic resonance (FMR). This method uses a balanced microwave power detector whose output is phase shifted π/2, amplified, and fed back to drive precession. Using classical control theory, we predict an electronically controllable narrowing of field swept FMR line-widths. This technique is predicted to compensate other sources of spin dissipation in addition to radiative loss.

Comprehensive Fuel Spray Modeling and Impacts on Chamber Acoustics in Combustion Dynamics Simulations

DTIC Science & Technology

2013-05-01

multiple swirler configurations and fuel injector locations at atmospheric pressure con- ditions. Both single-element and multiple-element LDI...the swirl number, Reynolds’ number and injector location in the LDI element. Besides the multi-phase flow characteristics, several experimen- tal...region downstream of the fuel injector on account of a sta- ble and compact precessing vortex core. Recent ex- periments conducted by the Purdue group have

Radio crickets: chirping jets from black hole binaries entering their gravitational wave inspiral

NASA Astrophysics Data System (ADS)

Kulkarni, Girish; Loeb, Abraham

2016-03-01

We study a novel electromagnetic signature of supermassive black hole (BH) binaries whose inspiral starts being dominated by gravitational wave (GW) emission. Recent simulations suggest that the binary's member BHs can continue to accrete gas from the circumbinary accretion disc in this phase of the binary's evolution, all the way until coalescence. If one of the binary members produces a radio jet as a result of accretion, the jet precesses along a biconical surface due to the binary's orbital motion. When the binary enters the GW phase of its evolution, the opening angle widens, the jet exhibits milliarcsecond-scale wiggles, and the conical surface of jet precession is twisted due to apparent superluminal motion. The rapidly increasing orbital velocity of the binary gives the jet an appearance of a `chirp'. This helical chirping morphology of the jet can be used to infer the binary parameters. For binaries with mass 107-1010 M⊙ at redshifts z < 0.5, monitoring these features in current and archival data will place a lower limit on sources that could be detected by Evolved Laser Interferometer Space Antenna and Pulsar Timing Arrays. In the future, microarcsecond interferometry with the Square Kilometre Array will increase the potential usefulness of this technique.

Eastern South African hydroclimate over the past 270,000 years

NASA Astrophysics Data System (ADS)

Simon, Margit H.; Ziegler, Martin; Bosmans, Joyce; Barker, Stephen; Reason, Chris J. C.; Hall, Ian R.

2015-12-01

Processes that control the hydrological balance in eastern South Africa on orbital to millennial timescales remain poorly understood because proxy records documenting its variability at high resolution are scarce. In this work, we present a detailed 270,000 year-long record of terrestrial climate variability in the KwaZulu-Natal province based on elemental ratios of Fe/K from the southwest Indian Ocean, derived from X-ray fluorescence core scanning. Eastern South African climate variability on these time scales reflects both the long-term effect of regional insolation changes driven by orbital precession and the effects associated with high-latitude abrupt climate forcing over the past two glacial-interglacial cycles, including millennial-scale events not previously identified. Rapid changes towards more humid conditions in eastern South Africa as the Northern Hemisphere entered phases of extreme cooling were potentially driven by a combination of warming in the Agulhas Current and shifts of the subtropical anticyclones. These climate oscillations appear coherent with other Southern Hemisphere records but are anti-phased with respect to the East Asian Monsoon. Numerical modelling results reveal that higher precipitation in the KwaZulu-Natal province during precession maxima is driven by a combination of increased local evaporation and elevated moisture transport into eastern South Africa from the coast of Mozambique.

Eastern South African hydroclimate over the past 270,000 years.

PubMed

Simon, Margit H; Ziegler, Martin; Bosmans, Joyce; Barker, Stephen; Reason, Chris J C; Hall, Ian R

2015-12-21

Processes that control the hydrological balance in eastern South Africa on orbital to millennial timescales remain poorly understood because proxy records documenting its variability at high resolution are scarce. In this work, we present a detailed 270,000 year-long record of terrestrial climate variability in the KwaZulu-Natal province based on elemental ratios of Fe/K from the southwest Indian Ocean, derived from X-ray fluorescence core scanning. Eastern South African climate variability on these time scales reflects both the long-term effect of regional insolation changes driven by orbital precession and the effects associated with high-latitude abrupt climate forcing over the past two glacial-interglacial cycles, including millennial-scale events not previously identified. Rapid changes towards more humid conditions in eastern South Africa as the Northern Hemisphere entered phases of extreme cooling were potentially driven by a combination of warming in the Agulhas Current and shifts of the subtropical anticyclones. These climate oscillations appear coherent with other Southern Hemisphere records but are anti-phased with respect to the East Asian Monsoon. Numerical modelling results reveal that higher precipitation in the KwaZulu-Natal province during precession maxima is driven by a combination of increased local evaporation and elevated moisture transport into eastern South Africa from the coast of Mozambique.

Eastern South African hydroclimate over the past 270,000 years

PubMed Central

Simon, Margit H.; Ziegler, Martin; Bosmans, Joyce; Barker, Stephen; Reason, Chris J.C.; Hall, Ian R.

2015-01-01

Processes that control the hydrological balance in eastern South Africa on orbital to millennial timescales remain poorly understood because proxy records documenting its variability at high resolution are scarce. In this work, we present a detailed 270,000 year-long record of terrestrial climate variability in the KwaZulu-Natal province based on elemental ratios of Fe/K from the southwest Indian Ocean, derived from X-ray fluorescence core scanning. Eastern South African climate variability on these time scales reflects both the long-term effect of regional insolation changes driven by orbital precession and the effects associated with high-latitude abrupt climate forcing over the past two glacial-interglacial cycles, including millennial-scale events not previously identified. Rapid changes towards more humid conditions in eastern South Africa as the Northern Hemisphere entered phases of extreme cooling were potentially driven by a combination of warming in the Agulhas Current and shifts of the subtropical anticyclones. These climate oscillations appear coherent with other Southern Hemisphere records but are anti-phased with respect to the East Asian Monsoon. Numerical modelling results reveal that higher precipitation in the KwaZulu-Natal province during precession maxima is driven by a combination of increased local evaporation and elevated moisture transport into eastern South Africa from the coast of Mozambique. PMID:26686943

Some new thoughts about long-term precession formula

NASA Astrophysics Data System (ADS)

Vondrák, J.; Capitaine, N.; Wallace, P.

2011-10-01

In our preceding study (Vondrák et al. 2009) we formulated developments for the precessional contribution to the CIP X, Y coordinates suitable for use over long time intervals. They were fitted to IAU 2006 close to J2000.0 and to the numerical integration of the ecliptic (using the integrator package Mercury 6) and of the general precession and obliquity (using Laskar's solution LA93) for more distant epochs. Now we define the boundary between precession and nutation (both are periodic) to avoid their overlap. We use the IAU 2006 model (that is based on the Bretagnon's solution VSOP87 and the JPL planetary ephemerides DE406) to represent the precession of the ecliptic close to J2000.0, a new integration using Mercury 6 for more distant epochs, and Laskar's LA93 solution to represent general precession and obliquity. The goal is to obtain new developments for different sets of precession angles that would fit to modern observations near J2000.0, and at the same time to numerical integration of the translatory-rotatory motions of solar system bodies on scales of several thousand centuries.

Stochastic Template Bank for Gravitational Wave Searches for Precessing Neutron Star-Black Hole Coalescence Events

NASA Technical Reports Server (NTRS)

Indik, Nathaniel; Haris, K.; Dal Canton, Tito; Fehrmann, Henning; Krishnan, Badri; Lundgren, Andrew; Nielsen, Alex B.; Pai, Archana

2017-01-01

Gravitational wave searches to date have largely focused on non-precessing systems. Including precession effects greatly increases the number of templates to be searched over. This leads to a corresponding increase in the computational cost and can increase the false alarm rate of a realistic search. On the other hand, there might be astrophysical systems that are entirely missed by non-precessing searches. In this paper we consider the problem of constructing a template bank using stochastic methods for neutron star-black hole binaries allowing for precession, but with the restrictions that the total angular momentum of the binary is pointing toward the detector and that the neutron star spin is negligible relative to that of the black hole. We quantify the number of templates required for the search, and we explicitly construct the template bank. We show that despite the large number of templates, stochastic methods can be adapted to solve the problem. We quantify the parameter space region over which the non-precessing search might miss signals.

The Role Of Orbital Forcing On Polar Ice Volume And Global Sea-Level During The Late Pliocene (3.3-.2.6 Ma)

NASA Astrophysics Data System (ADS)

Naish, T.; Grant, G.; Dunbar, G. B.; Patterson, M. O.; Kominz, M. A.; Stocchi, P.

2017-12-01

Challenges remain concerning the potentially intractable problem of constraining the absolute magnitude of Pliocene eustatic sea-level change, and the role of orbital forcing on the frequency of ice volume/sea-level change is widely debated. Here, we present three new high-resolution geological archives for the MPWP: (i) ice-berg rafted debris (IBRD) mass accumulation rates from deep ocean sediment core (IODP U1361) off the Wilkes Margin of Antarctica recording fluctuations in the East Antarctic ice sheet; (ii) a continuous shallow-marine record of sea-level change from the Wanganui Basin, New Zealand; and (iii) a record sea-level-controlled terrigenous sedimentation (IODP 1124) to the deep ocean on Hikurangi margin of New Zealand. All three records are dominated by precession-paced cyclicity ( 20ka) in-phase with high-latitude southern hemisphere insolation between 3.3M-2.9Ma, and provide insights into orbital-forcing of ice volume and sea-level independent of the benthic oxygen isotope records. Moreover, we have back-stripped the Wanganui record to reveal glacial-interglacial sea-level changes of 20±10m amplitude. We conclude that during this interval, precession-paced Antarctic ice volume changes largely drove global glacial-interglacial sea-level fluctuations, in the absence of a significant northern hemisphere ice volume contribution. Prior to 3.3Ma, proxy data from IODP U1361 and ANDRILL 1-A records extending back to 5Ma, show that the Antarctic margin experienced warmer ocean temperatures, a lack of perennial sea-ice, and fluctuations in ice extent paced by obliquity. The emergence of precession at 3.3Ma coincident with the M2 glaciation in the benthic d18O record, also coincides with continent-wide cooling, ice expansion and the development of extensive seasonal sea-ice around Antarctica. We argue that a melt threshold response to orbital forcing was crossed, whereby Antarctic ice sheet melt was restricted to peak austral summer insolation (precession), rather than a longer summer melt-season controlled by mean annual insolation (obliquity). An obliquity-paced signal re-emerges in the New Zealand sea-level records after 2.9Ma, while the EAIS IBRD record continues to be paced by precession, implying an increasingly dominant influence of northern hemisphere ice sheets.

The Evaluation of the Earth's Dynamical Flattening Based on the IAU Precession-nutation and VLBI Observations

NASA Astrophysics Data System (ADS)

Capitaine, Nicole; Liu, Jia-Cheng

2014-12-01

The dynamical flattening H_{d} is a fundamental Earth's parameter and a crucial scale factor in constructing the precession-nutation models. Its value has generally been derived from astronomical observations of the luni-solar precession in longitude at epoch, or from geophysical determinations of the Earth's moment of inertia. It should be noted that the observed precession rates in longitude and obliquity result from several theoretical contributions, some of them, as well as the nutation amplitudes, being also dependent on H_{d}. This paper discusses the rigorous procedure to be used for deriving H_{d} from the best available astronomical observations. We use the IAU 2006/2000 precession-nutation and VLBI observations of the celestial pole offsets spanning about 32 years in order to calculate the observed position of the CIP (Celestial intermediate pole) in the GCRS (Geocentric celestial reference system). Then, the value of H_{d} is evaluated by a least squares method with a careful consideration of the various theoretical contributions to the precession rates and of the largest terms of nutation. We compare the results with an indirect fit of H_{d} to the estimated corrections to the linear term in precession and the 18.6-yr nutation. We discuss the limit of accuracy, given the characteristics of the available observations and the uncertainties in the models, as well as the parameters on which H_{d} is dependent.

Improved Analysis of GW150914 Using a Fully Spin-Precessing Waveform Model

NASA Astrophysics Data System (ADS)

Abbott, B. P.; Abbott, R.; Abbott, T. D.; Abernathy, M. R.; Acernese, F.; Ackley, K.; Adams, C.; Adams, T.; Addesso, P.; Adhikari, R. X.; Adya, V. B.; Affeldt, C.; Agathos, M.; Agatsuma, K.; Aggarwal, N.; Aguiar, O. D.; Aiello, L.; Ain, A.; Ajith, P.; Allen, B.; Allocca, A.; Altin, P. A.; Anderson, S. B.; Anderson, W. G.; Arai, K.; Araya, M. C.; Arceneaux, C. C.; Areeda, J. S.; Arnaud, N.; Arun, K. G.; Ascenzi, S.; Ashton, G.; Ast, M.; Aston, S. M.; Astone, P.; Aufmuth, P.; Aulbert, C.; Babak, S.; Bacon, P.; Bader, M. K. M.; Baker, P. T.; Baldaccini, F.; Ballardin, G.; Ballmer, S. W.; Barayoga, J. C.; Barclay, S. E.; Barish, B. C.; Barker, D.; Barone, F.; Barr, B.; Barsotti, L.; Barsuglia, M.; Barta, D.; Bartlett, J.; Bartos, I.; Bassiri, R.; Basti, A.; Batch, J. C.; Baune, C.; Bavigadda, V.; Bazzan, M.; Bejger, M.; Bell, A. S.; Berger, B. K.; Bergmann, G.; Berry, C. P. L.; Bersanetti, D.; Bertolini, A.; Betzwieser, J.; Bhagwat, S.; Bhandare, R.; Bilenko, I. A.; Billingsley, G.; Birch, J.; Birney, R.; Birnholtz, O.; Biscans, S.; Bisht, A.; Bitossi, M.; Biwer, C.; Bizouard, M. A.; Blackburn, J. K.; Blair, C. D.; Blair, D. G.; Blair, R. M.; Bloemen, S.; Bock, O.; Boer, M.; Bogaert, G.; Bogan, C.; Bohe, A.; Bond, C.; Bondu, F.; Bonnand, R.; Boom, B. A.; Bork, R.; Boschi, V.; Bose, S.; Bouffanais, Y.; Bozzi, A.; Bradaschia, C.; Brady, P. R.; Braginsky, V. B.; Branchesi, M.; Brau, J. E.; Briant, T.; Brillet, A.; Brinkmann, M.; Brisson, V.; Brockill, P.; Broida, J. E.; Brooks, A. F.; Brown, D. A.; Brown, D. D.; Brown, N. M.; Brunett, S.; Buchanan, C. C.; Buikema, A.; Bulik, T.; Bulten, H. J.; Buonanno, A.; Buskulic, D.; Buy, C.; Byer, R. L.; Cabero, M.; Cadonati, L.; Cagnoli, G.; Cahillane, C.; Calderón Bustillo, J.; Callister, T.; Calloni, E.; Camp, J. B.; Cannon, K. C.; Cao, J.; Capano, C. D.; Capocasa, E.; Carbognani, F.; Caride, S.; Casanueva Diaz, C.; Casentini, J.; Caudill, S.; Cavaglià, M.; Cavalier, F.; Cavalieri, R.; Cella, G.; Cepeda, C. B.; Cerboni Baiardi, L.; Cerretani, G.; Cesarini, E.; Chamberlin, S. J.; Chan, M.; Chao, S.; Charlton, P.; Chassande-Mottin, E.; Cheeseboro, B. D.; Chen, H. Y.; Chen, Y.; Cheng, C.; Chincarini, A.; Chiummo, A.; Cho, H. S.; Cho, M.; Chow, J. H.; Christensen, N.; Chu, Q.; Chua, S.; Chung, S.; Ciani, G.; Clara, F.; Clark, J. A.; Cleva, F.; Coccia, E.; Cohadon, P.-F.; Colla, A.; Collette, C. G.; Cominsky, L.; Constancio, M.; Conte, A.; Conti, L.; Cook, D.; Corbitt, T. R.; Cornish, N.; Corsi, A.; Cortese, S.; Costa, C. A.; Coughlin, M. W.; Coughlin, S. B.; Coulon, J.-P.; Countryman, S. T.; Couvares, P.; Cowan, E. E.; Coward, D. M.; Cowart, M. J.; Coyne, D. C.; Coyne, R.; Craig, K.; Creighton, J. D. E.; Cripe, J.; Crowder, S. G.; Cumming, A.; Cunningham, L.; Cuoco, E.; Dal Canton, T.; Danilishin, S. L.; D'Antonio, S.; Danzmann, K.; Darman, N. S.; Dasgupta, A.; Da Silva Costa, C. F.; Dattilo, V.; Dave, I.; Davier, M.; Davies, G. S.; Daw, E. J.; Day, R.; De, S.; DeBra, D.; Debreczeni, G.; Degallaix, J.; De Laurentis, M.; Deléglise, S.; Del Pozzo, W.; Denker, T.; Dent, T.; Dergachev, V.; De Rosa, R.; DeRosa, R. T.; DeSalvo, R.; Devine, R. C.; Dhurandhar, S.; Díaz, M. C.; Di Fiore, L.; Di Giovanni, M.; Di Girolamo, T.; Di Lieto, A.; Di Pace, S.; Di Palma, I.; Di Virgilio, A.; Dolique, V.; Donovan, F.; Dooley, K. L.; Doravari, S.; Douglas, R.; Downes, T. P.; Drago, M.; Drever, R. W. P.; Driggers, J. C.; Ducrot, M.; Dwyer, S. E.; Edo, T. B.; Edwards, M. C.; Effler, A.; Eggenstein, H.-B.; Ehrens, P.; Eichholz, J.; Eikenberry, S. S.; Engels, W.; Essick, R. C.; Etienne, Z.; Etzel, T.; Evans, M.; Evans, T. M.; Everett, R.; Factourovich, M.; Fafone, V.; Fair, H.; Fairhurst, S.; Fan, X.; Fang, Q.; Farinon, S.; Farr, B.; Farr, W. M.; Fauchon-Jones, E.; Favata, M.; Fays, M.; Fehrmann, H.; Fejer, M. M.; Fenyvesi, E.; Ferrante, I.; Ferreira, E. C.; Ferrini, F.; Fidecaro, F.; Fiori, I.; Fiorucci, D.; Fisher, R. P.; Flaminio, R.; Fletcher, M.; Fournier, J.-D.; Frasca, S.; Frasconi, F.; Frei, Z.; Freise, A.; Frey, R.; Frey, V.; Fritschel, P.; Frolov, V. V.; Fulda, P.; Fyffe, M.; Gabbard, H. A. G.; Gaebel, S.; Gair, J. R.; Gammaitoni, L.; Gaonkar, S. G.; Garufi, F.; Gaur, G.; Gehrels, N.; Gemme, G.; Geng, P.; Genin, E.; Gennai, A.; George, J.; Gergely, L.; Germain, V.; Ghosh, Abhirup; Ghosh, Archisman; Ghosh, S.; Giaime, J. A.; Giardina, K. D.; Giazotto, A.; Gill, K.; Glaefke, A.; Goetz, E.; Goetz, R.; Gondan, L.; González, G.; Gonzalez Castro, J. M.; Gopakumar, A.; Gordon, N. A.; Gorodetsky, M. L.; Gossan, S. E.; Gosselin, M.; Gouaty, R.; Grado, A.; Graef, C.; Graff, P. B.; Granata, M.; Grant, A.; Gras, S.; Gray, C.; Greco, G.; Green, A. C.; Groot, P.; Grote, H.; Grunewald, S.; Guidi, G. M.; Guo, X.; Gupta, A.; Gupta, M. K.; Gushwa, K. E.; Gustafson, E. K.; Gustafson, R.; Hacker, J. J.; Hall, B. R.; Hall, E. D.; Hammond, G.; Haney, M.; Hanke, M. M.; Hanks, J.; Hanna, C.; Hannam, M. D.; Hanson, J.; Hardwick, T.; Harms, J.; Harry, G. M.; Harry, I. W.; Hart, M. J.; Hartman, M. T.; Haster, C.-J.; Haughian, K.; Healy, J.; Heidmann, A.; Heintze, M. C.; Heitmann, H.; Hello, P.; Hemming, G.; Hendry, M.; Heng, I. S.; Hennig, J.; Henry, J.; Heptonstall, A. W.; Heurs, M.; Hild, S.; Hoak, D.; Hofman, D.; Holt, K.; Holz, D. E.; Hopkins, P.; Hough, J.; Houston, E. A.; Howell, E. J.; Hu, Y. M.; Huang, S.; Huerta, E. A.; Huet, D.; Hughey, B.; Husa, S.; Huttner, S. H.; Huynh-Dinh, T.; Indik, N.; Ingram, D. R.; Inta, R.; Isa, H. N.; Isac, J.-M.; Isi, M.; Isogai, T.; Iyer, B. R.; Izumi, K.; Jacqmin, T.; Jang, H.; Jani, K.; Jaranowski, P.; Jawahar, S.; Jian, L.; Jiménez-Forteza, F.; Johnson, W. W.; Johnson-McDaniel, N. K.; Jones, D. I.; Jones, R.; Jonker, R. J. G.; Ju, L.; K, Haris; Kalaghatgi, C. V.; Kalogera, V.; Kandhasamy, S.; Kang, G.; Kanner, J. B.; Kapadia, S. J.; Karki, S.; Karvinen, K. S.; Kasprzack, M.; Katsavounidis, E.; Katzman, W.; Kaufer, S.; Kaur, T.; Kawabe, K.; Kéfélian, F.; Kehl, M. S.; Keitel, D.; Kelley, D. B.; Kells, W.; Kennedy, R.; Key, J. S.; Khalili, F. Y.; Khan, I.; Khan, S.; Khan, Z.; Khazanov, E. A.; Kijbunchoo, N.; Kim, Chi-Woong; Kim, Chunglee; Kim, J.; Kim, K.; Kim, N.; Kim, W.; Kim, Y.-M.; Kimbrell, S. J.; King, E. J.; King, P. J.; Kissel, J. S.; Klein, B.; Kleybolte, L.; Klimenko, S.; Koehlenbeck, S. M.; Koley, S.; Kondrashov, V.; Kontos, A.; Korobko, M.; Korth, W. Z.; Kowalska, I.; Kozak, D. B.; Kringel, V.; Królak, A.; Krueger, C.; Kuehn, G.; Kumar, P.; Kumar, R.; Kuo, L.; Kutynia, A.; Lackey, B. D.; Landry, M.; Lange, J.; Lantz, B.; Lasky, P. D.; Laxen, M.; Lazzarini, A.; Lazzaro, C.; Leaci, P.; Leavey, S.; Lebigot, E. O.; Lee, C. H.; Lee, H. K.; Lee, H. M.; Lee, K.; Lenon, A.; Leonardi, M.; Leong, J. R.; Leroy, N.; Letendre, N.; Levin, Y.; Lewis, J. B.; Li, T. G. F.; Libson, A.; Littenberg, T. B.; Lockerbie, N. A.; Lombardi, A. L.; London, L. T.; Lord, J. E.; Lorenzini, M.; Loriette, V.; Lormand, M.; Losurdo, G.; Lough, J. D.; Lousto, C. O.; Lovelace, G.; Lück, H.; Lundgren, A. P.; Lynch, R.; Ma, Y.; Machenschalk, B.; MacInnis, M.; Macleod, D. M.; Magaña-Sandoval, F.; Magaña Zertuche, L.; Magee, R. M.; Majorana, E.; Maksimovic, I.; Malvezzi, V.; Man, N.; Mandic, V.; Mangano, V.; Mansell, G. L.; Manske, M.; Mantovani, M.; Marchesoni, F.; Marion, F.; Márka, S.; Márka, Z.; Markosyan, A. S.; Maros, E.; Martelli, F.; Martellini, L.; Martin, I. W.; Martynov, D. V.; Marx, J. N.; Mason, K.; Masserot, A.; Massinger, T. J.; Masso-Reid, M.; Mastrogiovanni, S.; Matichard, F.; Matone, L.; Mavalvala, N.; Mazumder, N.; McCarthy, R.; McClelland, D. E.; McCormick, S.; McGuire, S. C.; McIntyre, G.; McIver, J.; McManus, D. J.; McRae, T.; McWilliams, S. T.; Meacher, D.; Meadors, G. D.; Meidam, J.; Melatos, A.; Mendell, G.; Mercer, R. A.; Merilh, E. L.; Merzougui, M.; Meshkov, S.; Messenger, C.; Messick, C.; Metzdorff, R.; Meyers, P. M.; Mezzani, F.; Miao, H.; Michel, C.; Middleton, H.; Mikhailov, E. E.; Milano, L.; Miller, A. L.; Miller, A.; Miller, B. B.; Miller, J.; Millhouse, M.; Minenkov, Y.; Ming, J.; Mirshekari, S.; Mishra, C.; Mitra, S.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.; Moggi, A.; Mohan, M.; Mohapatra, S. R. P.; Montani, M.; Moore, B. C.; Moore, C. J.; Moraru, D.; Moreno, G.; Morriss, S. R.; Mossavi, K.; Mours, B.; Mow-Lowry, C. M.; Mueller, G.; Muir, A. W.; Mukherjee, Arunava; Mukherjee, D.; Mukherjee, S.; Mukund, N.; Mullavey, A.; Munch, J.; Murphy, D. J.; Murray, P. G.; Mytidis, A.; Nardecchia, I.; Naticchioni, L.; Nayak, R. K.; Nedkova, K.; Nelemans, G.; Nelson, T. J. N.; Neri, M.; Neunzert, A.; Newton, G.; Nguyen, T. T.; Nielsen, A. B.; Nissanke, S.; Nitz, A.; Nocera, F.; Nolting, D.; Normandin, M. E. N.; Nuttall, L. K.; Oberling, J.; Ochsner, E.; O'Dell, J.; Oelker, E.; Ogin, G. H.; Oh, J. J.; Oh, S. H.; Ohme, F.; Oliver, M.; Oppermann, P.; Oram, Richard J.; O'Reilly, B.; O'Shaughnessy, R.; Ottaway, D. J.; Overmier, H.; Owen, B. J.; Pai, A.; Pai, S. A.; Palamos, J. R.; Palashov, O.; Palomba, C.; Pal-Singh, A.; Pan, H.; Pankow, C.; Pannarale, F.; Pant, B. C.; Paoletti, F.; Paoli, A.; Papa, M. A.; Paris, H. R.; Parker, W.; Pascucci, D.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Patricelli, B.; Patrick, Z.; Pearlstone, B. L.; Pedraza, M.; Pedurand, R.; Pekowsky, L.; Pele, A.; Penn, S.; Perreca, A.; Perri, L. M.; Pfeiffer, H. P.; Phelps, M.; Piccinni, O. J.; Pichot, M.; Piergiovanni, F.; Pierro, V.; Pillant, G.; Pinard, L.; Pinto, I. M.; Pitkin, M.; Poe, M.; Poggiani, R.; Popolizio, P.; Post, A.; Powell, J.; Prasad, J.; Predoi, V.; Prestegard, T.; Price, L. R.; Prijatelj, M.; Principe, M.; Privitera, S.; Prix, R.; Prodi, G. A.; Prokhorov, L.; Puncken, O.; Punturo, M.; Puppo, P.; Pürrer, M.; Qi, H.; Qin, J.; Qiu, S.; Quetschke, V.; Quintero, E. A.; Quitzow-James, R.; Raab, F. J.; Rabeling, D. S.; Radkins, H.; Raffai, P.; Raja, S.; Rajan, C.; Rakhmanov, M.; Rapagnani, P.; Raymond, V.; Razzano, M.; Re, V.; Read, J.; Reed, C. M.; Regimbau, T.; Rei, L.; Reid, S.; Reitze, D. H.; Rew, H.; Reyes, S. D.; Ricci, F.; Riles, K.; Rizzo, M.; Robertson, N. A.; Robie, R.; Robinet, F.; Rocchi, A.; Rolland, L.; Rollins, J. G.; Roma, V. J.; Romano, R.; Romanov, G.; Romie, J. H.; Rosińska, D.; Rowan, S.; Rüdiger, A.; Ruggi, P.; Ryan, K.; Sachdev, S.; Sadecki, T.; Sadeghian, L.; Sakellariadou, M.; Salconi, L.; Saleem, M.; Salemi, F.; Samajdar, A.; Sammut, L.; Sanchez, E. J.; Sandberg, V.; Sandeen, B.; Sanders, J. R.; Sassolas, B.; Sathyaprakash, B. S.; Saulson, P. R.; Sauter, O. E. S.; Savage, R. L.; Sawadsky, A.; Schale, P.; Schilling, R.; Schmidt, J.; Schmidt, P.; Schnabel, R.; Schofield, R. M. S.; Schönbeck, A.; Schreiber, E.; Schuette, D.; Schutz, B. F.; Scott, J.; Scott, S. M.; Sellers, D.; Sengupta, A. S.; Sentenac, D.; Sequino, V.; Sergeev, A.; Setyawati, Y.; Shaddock, D. A.; Shaffer, T.; Shahriar, M. S.; Shaltev, M.; Shapiro, B.; Shawhan, P.; Sheperd, A.; Shoemaker, D. H.; Shoemaker, D. M.; Siellez, K.; Siemens, X.; Sieniawska, M.; Sigg, D.; Silva, A. D.; Singer, A.; Singer, L. P.; Singh, A.; Singh, R.; Singhal, A.; Sintes, A. M.; Slagmolen, B. J. J.; Smith, J. R.; Smith, N. D.; Smith, R. J. E.; Son, E. J.; Sorazu, B.; Sorrentino, F.; Souradeep, T.; Srivastava, A. K.; Staley, A.; Steinke, M.; Steinlechner, J.; Steinlechner, S.; Steinmeyer, D.; Stephens, B. C.; Stevenson, S. P.; Stone, R.; Strain, K. A.; Straniero, N.; Stratta, G.; Strauss, N. A.; Strigin, S.; Sturani, R.; Stuver, A. L.; Summerscales, T. Z.; Sun, L.; Sunil, S.; Sutton, P. J.; Swinkels, B. L.; Szczepańczyk, M. J.; Tacca, M.; Talukder, D.; Tanner, D. B.; Tápai, M.; Tarabrin, S. P.; Taracchini, A.; Taylor, R.; Theeg, T.; Thirugnanasambandam, M. P.; Thomas, E. G.; Thomas, M.; Thomas, P.; Thorne, K. A.; Thorne, K. S.; Thrane, E.; Tiwari, S.; Tiwari, V.; Tokmakov, K. V.; Toland, K.; Tomlinson, C.; Tonelli, M.; Tornasi, Z.; Torres, C. V.; Torrie, C. I.; Töyrä, D.; Travasso, F.; Traylor, G.; Trifirò, D.; Tringali, M. C.; Trozzo, L.; Tse, M.; Turconi, M.; Tuyenbayev, D.; Ugolini, D.; Unnikrishnan, C. S.; Urban, A. L.; Usman, S. A.; Vahlbruch, H.; Vajente, G.; Valdes, G.; Vallisneri, M.; van Bakel, N.; van Beuzekom, M.; van den Brand, J. F. J.; Van Den Broeck, C.; Vander-Hyde, D. C.; van der Schaaf, L.; van der Sluys, M. V.; van Heijningen, J. V.; Vano-Vinuales, A.; van Veggel, A. A.; Vardaro, M.; Vass, S.; Vasúth, M.; Vaulin, R.; Vecchio, A.; Vedovato, G.; Veitch, J.; Veitch, P. J.; Venkateswara, K.; Verkindt, D.; Vetrano, F.; Viceré, A.; Vinciguerra, S.; Vine, D. J.; Vinet, J.-Y.; Vitale, S.; Vo, T.; Vocca, H.; Vorvick, C.; Voss, D. V.; Vousden, W. D.; Vyatchanin, S. P.; Wade, A. R.; Wade, L. E.; Wade, M.; Walker, M.; Wallace, L.; Walsh, S.; Wang, G.; Wang, H.; Wang, M.; Wang, X.; Wang, Y.; Ward, R. L.; Warner, J.; Was, M.; Weaver, B.; Wei, L.-W.; Weinert, M.; Weinstein, A. J.; Weiss, R.; Wen, L.; Weßels, P.; Westphal, T.; Wette, K.; Whelan, J. T.; Whiting, B. F.; Williams, R. D.; Williamson, A. R.; Willis, J. L.; Willke, B.; Wimmer, M. H.; Winkler, W.; Wipf, C. C.; Wittel, H.; Woan, G.; Woehler, J.; Worden, J.; Wright, J. L.; Wu, D. S.; Wu, G.; Yablon, J.; Yam, W.; Yamamoto, H.; Yancey, C. C.; Yu, H.; Yvert, M.; ZadroŻny, A.; Zangrando, L.; Zanolin, M.; Zendri, J.-P.; Zevin, M.; Zhang, L.; Zhang, M.; Zhang, Y.; Zhao, C.; Zhou, M.; Zhou, Z.; Zhu, X. J.; Zucker, M. E.; Zuraw, S. E.; Zweizig, J.; Boyle, M.; Brügmann, B.; Campanelli, M.; Chu, T.; Clark, M.; Haas, R.; Hemberger, D.; Hinder, I.; Kidder, L. E.; Kinsey, M.; Laguna, P.; Ossokine, S.; Pan, Y.; Röver, C.; Scheel, M.; Szilagyi, B.; Teukolsky, S.; Zlochower, Y.; LIGO Scientific Collaboration; Virgo Collaboration

2016-10-01

This paper presents updated estimates of source parameters for GW150914, a binary black-hole coalescence event detected by the Laser Interferometer Gravitational-wave Observatory (LIGO) in 2015 [Abbott et al. Phys. Rev. Lett. 116, 061102 (2016).]. Abbott et al. [Phys. Rev. Lett. 116, 241102 (2016).] presented parameter estimation of the source using a 13-dimensional, phenomenological precessing-spin model (precessing IMRPhenom) and an 11-dimensional nonprecessing effective-one-body (EOB) model calibrated to numerical-relativity simulations, which forces spin alignment (nonprecessing EOBNR). Here, we present new results that include a 15-dimensional precessing-spin waveform model (precessing EOBNR) developed within the EOB formalism. We find good agreement with the parameters estimated previously [Abbott et al. Phys. Rev. Lett. 116, 241102 (2016).], and we quote updated component masses of 35-3+5 M⊙ and 3 0-4+3 M⊙ (where errors correspond to 90% symmetric credible intervals). We also present slightly tighter constraints on the dimensionless spin magnitudes of the two black holes, with a primary spin estimate <0.65 and a secondary spin estimate <0.75 at 90% probability. Abbott et al. [Phys. Rev. Lett. 116, 241102 (2016).] estimated the systematic parameter-extraction errors due to waveform-model uncertainty by combining the posterior probability densities of precessing IMRPhenom and nonprecessing EOBNR. Here, we find that the two precessing-spin models are in closer agreement, suggesting that these systematic errors are smaller than previously quoted.

Spectral element simulation of precession driven flows in the outer cores of spheroidal planets

NASA Astrophysics Data System (ADS)

Vormann, Jan; Hansen, Ulrich

2015-04-01

A common feature of the planets in the solar system is the precession of the rotation axes, driven by the gravitational influence of another body (e.g. the Earth's moon). In a precessing body, the rotation axis itself is rotating around another axis, describing a cone during one precession period. Similar to the coriolis and centrifugal force appearing from the transformation to a rotating system, the addition of precession adds another term to the Navier-Stokes equation, the so called Poincaré force. The main geophysical motivation in studying precession driven flows comes from their ability to act as magnetohydrodynamic dynamos in planets and moons. Precession may either act as the only driving force or operate together with other forces such as thermochemical convection. One of the challenges in direct numerical simulations of such flows lies in the spheroidal shape of the fluid volume, which should not be neglected since it contributes an additional forcing trough pressure torques. Codes developed for the simulation of flows in spheres mostly use efficient global spectral algorithms that converge fast, but lack geometric flexibility, while local methods are usable in more complex shapes, but often lack high accuracy. We therefore adapted the spectral element code Nek5000, developed at Argonne National Laboratory, to the problem. The spectral element method is capable of solving for the flow in arbitrary geometries while still offering spectral convergence. We present first results for the simulation of a purely hydrodynamic, precession-driven flow in a spheroid with no-slip boundaries and an inner core. The driving by the Poincaré force is in a range where theoretical work predicts multiple solutions for a laminar flow. Our simulations indicate a transition to turbulent flows for Ekman numbers of 10-6 and lower.

The Complex Dynamics of the Precessing Vortex Rope in a Straight Diffuser

NASA Astrophysics Data System (ADS)

Stuparu, Adrian; Susan-Resiga, Romeo

2016-11-01

The decelerated swirling flow in the discharge cone of Francis turbines operated at partial discharge develops a self-induced instability with a precessing helical vortex (vortex rope). In an axisymmetric geometry, this phenomenon is expected to generate asynchronous pressure fluctuations as a result of the precessing motion. However, numerical and experimental data indicate that synchronous (plunging) fluctuations, with a frequency lower than the precessing frequency, also develops as a result of helical vortex filament dynamics. This paper presents a quantitative approach to describe the precessing vortex rope by properly fitting a three-dimensional logarithmic spiral model with the vortex filament computed from the velocity gradient tensor. We show that the slope coefficient of either curvature or torsion radii of the helix is a good indicator for the vortex rope dynamics, and it supports the stretching - breaking up - bouncing back mechanism that may explain the plunging oscillations.

Expressions for the precession quantities based upon the IAU /1976/ system of astronomical constants

NASA Technical Reports Server (NTRS)

Lieske, J. H.; Lederle, T.; Fricke, W.; Morando, B.

1977-01-01

The structure of the expressions usually employed in calculating the effects of precession is examined, and a method is outlined for revising the expressions to account for changes in the fundamental astronomical constants. It is shown that the basic set of parameters, upon which depend the lengthy polynomials for computing the mean obliquity of data and the elements of the precession matrix, consists of the mean obliquity, the speed of general precession in longitude at a fixed epoch, and the system of planetary masses. Special attention is given to the motion of the ecliptic pole, formulations for a basic epoch as well as an arbitrary epoch, and ecliptic motion relative to the basic epoch. Numerical precession quantities at epoch J2000.0 (JED 2451545.0) are presented which result from the revision of astronomical constants adopted at the XVI General Assembly of the IAU.

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

Dai, Lixin; Escala, Andres; Coppi, Paolo, E-mail: lixin.dai@yale.edu

We have carried out general relativistic particle simulations of stars tidally disrupted by massive black holes. When a star is disrupted in a bound orbit with moderate eccentricity instead of a parabolic orbit, the temporal behavior of the resulting stellar debris changes qualitatively. The debris is initially all bound, returning to pericenter in a short time about the original stellar orbital timescale. The resulting fallback rate can thus be much higher than the Eddington rate. Furthermore, if the star is disrupted close to the hole, in a regime where general relativity is important, the stellar and debris orbits display generalmore » relativistic precession. Apsidal precession can make the debris stream cross itself after several orbits, likely leading to fast debris energy dissipation. If the star is disrupted in an inclined orbit around a spinning hole, nodal precession reduces the probability of self-intersection, and circularization may take many dynamical timescales, delaying the onset of flare activity. An examination of the particle dynamics suggests that quasi-periodic flares with short durations, produced when the center of the tidal stream passes pericenter, may occur in the early-time light curve. The late-time light curve may still show power-law behavior which is generic to disk accretion processes. The detection triggers for future surveys should be extended to capture such 'non-standard' short-term flaring activity before the event enters the asymptotic decay phase, as this activity is likely to be more sensitive to physical parameters such as the black hole spin.« less

Consistency problems associated to the improvement of precession-nutation theories

NASA Astrophysics Data System (ADS)

Ferrandiz, J. M.; Escapa, A.; Baenas, T.; Getino, J.; Navarro, J. F.; Belda, S.

2014-12-01

The complexity of the modelling 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 fundamentals parameters from the precession theory at hand, like, e.g. the dynamical ellipticity H, and then using that valuesin the nutation theory. The former IAU1976 precession and IAU1980 nutation theories followed that scheme. Along with the improvement of the accuracy of the determination of EOP (Earth orientation parameters), IAU1980 was superseded by IAU2000, based on the application of the MHB2000 (Mathews et al 2002) transfer function to the previous rigid earth analytical theory REN2000 (Souchay et al 1999). The latter was derived while the precession model IAU1976 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, and the obliquity of the ecliptic at the reference epoch. The new precession model P03 was adopted as IAU2006. 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 two-fold approach is no longer negligible as earlier. Some corrections have been proposed by Capitaine et al (2005) and Escapa et al (2014) in order to reach a better level of consistency between precession and nutation theories and parameters. In this presentation we revisit the problem taking into account some of the advances in precession theory not accounted for yet, stemming from the non-rigid nature of the Earth. Special attention is paid to the assessment of the level of consistency between the current IAU precession and nutation models and its impact on the adopted reference values. We suggest potential corrections and possibilities to incorporate theoretical advances and improve accuracy while being compliant with IAU resolutions.

Improved Analysis of GW150914 Using a Fully Spin-Precessing Waveform Model

NASA Technical Reports Server (NTRS)

Abbott, B. P.; Abbott, R.; Abbott, T. D.; Abernathy, M. R.; Acernese, F.; Ackley, K.; Adams, C.; Adams, T.; Addesso, P.; Camp, J. B.;

Fuel Distribution Estimate via Spin Period to Precession Period Ratio for the Advanced Composition Explorer

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

Precession Driven Instabilities and Dynamos in the Early Moon

NASA Astrophysics Data System (ADS)

Cebron, D.; Laguerre, R.; Noir, J.; Vidal, J.; Schaeffer, N.

2017-12-01

The Early Moon magnetic fields are probably due to a strong temporary dynamo, which may be due to lunar precession [1]. However, precession driven dynamos remain badly known, with only few studied cases [2,3,4]. Given the uncertainties of the early Moon precession, wider ranges of parameters need to be explored in order to assess if such lunar dynamos are possible. Using the efficient dynamo code XSHELLS, we have thus performed many simulations of precessing spherical shells, varying the parameters in a systematic way. This allows us to characterize the various excited instabilities, and to propose scaling laws. We also obtain that precession driven dynamos seem scarce and weak in our simulations, which makes difficult and uncertain the extrapolation of these dynamos to the Moon. However, our dynamo simulations, as every other in the literature, neglect the topographic torque effect on instabilities in order to use fast spectral codes [5]. By contrast, the topographic torque is dominant for the lunar core. Before exploring this effect numerically, which is a real challenge, we choose to study it theoretically. To do so, we have developed a novel global linear stability analysis of mechanically-driven flows in triaxial ellipsoids, with leading order viscous effects. Internal dissipation is obtained for the first time by extending the Greenspan's theory (1968) of geostrophic and inertial modes. By contrast with pioneering theories [6], we propose a new linear viscous model valid in arbitrary ellipsoid and for any precessing forcing. Then we perform the linear stability analysis by considering ellipsoidal perturbations of unprecedented spatial complexity with a self-consistent model of viscous damping. We show that forced precession-driven basic flows are bistable in triaxial ellipsoids. Then, we present the first stability analysis of precessing-flows in triaxial ellipsoids. [1] Dwyer et al. (2011), Nature, 479, 212-214.[2] Tilgner (2005), Phy. Fluids, 17, 034104.[3] Tilgner (2007), Geo. Astro. Fluid Dyn., 101 (1), 1-9.[4] Lin et al. (2016), Phys. Fluids, 28, 066601.[5] Tian et al., EPSL, in revision.[6] Busse (1968), J. Fluid. Mech, 33 (04), 739-751.

Pro/con a precessional geodynamo

NASA Astrophysics Data System (ADS)

Vanyo, J.

2003-04-01

The modest amount of research that exists on the ability, or lack of ability, of mantle precession to power a geodynamo developed mostly during the last half of the 1900s. Papers by Roberts and Stewartson (1965) and by Busse (1968) studied precession generally without a pro/con conclusion. Malkus in the late 1960s attempted to advance a positive role for precession through experiments and analysis. His experiments have survived criticism, but his analyses were discounted, especially by Rochester, Jacobs, Smylie, and Chong (1975) and by Loper (1975). Rochester, et al. critiqued existing analyses of precession, including those of Malkus, but did not reach a strong position either pro or con a precessional geodynamo. Loper argued emphatically that precession was not capable of powering the geodynamo. Explicit analyses that either critique or support Loper’s arguments have yet to appear in the literature. During the 1970s, Vanyo and associates studied energy dissipation during precession of satellite liquid fuels and its effect on satellite attitude stability. Engineers and scientists in every country that has launched satellites completed similar research. Some is published in the aerospace literature, more is available in company and government reports. Beginning in 1981, Vanyo and associates applied this knowledge to the very similar problem of energy dissipation and flow patterns in precessing mechanical models scaled geometrically and dynamically to the Earth’s liquid core. Energy experiments indicate massive amounts of mechanical energy are dissipated at the CMB, and flow experiments show complex motions within the boundary layer and axial flows with helicity throughout the interior. Analysis of Earth core precession also advanced, especially in several papers by Kerswell and by Tilgner in the late 1990s. Detail numerical models have yet to appear. Although progress in understanding the role of precession in Earth core motions has advanced, there remains a common belief, often expressed explicitly, that precession is incapable of energizing a geodynamo, a la Loper. We will present a critique of Loper’s 1975 paper and briefly discuss the common practice and belief that the geodynamo must be energized by thermal and/or compositional driven convection (motion). We note here that there is no observational evidence for existence of thermal or compositional convection within the liquid core or for growth of the solid core. Although there has been considerable success in adapting data in thermal/compositional models to yield near realistic solutions, that does not constitute a proof that those models apply to the Earth. There is absolute observational evidence for mantle precession, an Earth feature that is unique, along with the Earth’s magnetic field, among the terrestrial planets. We argue that great difficulty experienced in analysis and computation of precessional flow is a major explanation for its absence in current models of the geodynamo.

Catalog of 174 Binary Black Hole Simulations for Gravitational Wave Astronomy

NASA Astrophysics Data System (ADS)

Mroué, Abdul H.; Scheel, Mark A.; Szilágyi, Béla; Pfeiffer, Harald P.; Boyle, Michael; Hemberger, Daniel A.; Kidder, Lawrence E.; Lovelace, Geoffrey; Ossokine, Serguei; Taylor, Nicholas W.; Zenginoğlu, Anıl; Buchman, Luisa T.; Chu, Tony; Foley, Evan; Giesler, Matthew; Owen, Robert; Teukolsky, Saul A.

2013-12-01

This Letter presents a publicly available catalog of 174 numerical binary black hole simulations following up to 35 orbits. The catalog includes 91 precessing binaries, mass ratios up to 8∶1, orbital eccentricities from a few percent to 10-5, black hole spins up to 98% of the theoretical maximum, and radiated energies up to 11.1% of the initial mass. We establish remarkably good agreement with post-Newtonian precession of orbital and spin directions for two new precessing simulations, and we discuss other applications of this catalog. Formidable challenges remain: e.g., precession complicates the connection of numerical and approximate analytical waveforms, and vast regions of the parameter space remain unexplored.

Catalog of 174 binary black hole simulations for gravitational wave astronomy.

PubMed

Mroué, Abdul H; Scheel, Mark A; Szilágyi, Béla; Pfeiffer, Harald P; Boyle, Michael; Hemberger, Daniel A; Kidder, Lawrence E; Lovelace, Geoffrey; Ossokine, Serguei; Taylor, Nicholas W; Zenginoğlu, Anıl; Buchman, Luisa T; Chu, Tony; Foley, Evan; Giesler, Matthew; Owen, Robert; Teukolsky, Saul A

2013-12-13

This Letter presents a publicly available catalog of 174 numerical binary black hole simulations following up to 35 orbits. The catalog includes 91 precessing binaries, mass ratios up to 8∶1, orbital eccentricities from a few percent to 10(-5), black hole spins up to 98% of the theoretical maximum, and radiated energies up to 11.1% of the initial mass. We establish remarkably good agreement with post-Newtonian precession of orbital and spin directions for two new precessing simulations, and we discuss other applications of this catalog. Formidable challenges remain: e.g., precession complicates the connection of numerical and approximate analytical waveforms, and vast regions of the parameter space remain unexplored.

A long time span relativistic precession model of the Earth

NASA Astrophysics Data System (ADS)

Tang, Kai; Soffel, Michael H.; Tao, Jin-He; Han, Wen-Biao; Tang, Zheng-Hong

2015-04-01

A numerical solution to the Earth's precession in a relativistic framework for a long time span is presented here. We obtain the motion of the solar system in the Barycentric Celestial Reference System by numerical integration with a symplectic integrator. Special Newtonian corrections accounting for tidal dissipation are included in the force model. The part representing Earth's rotation is calculated in the Geocentric Celestial Reference System by integrating the post-Newtonian equations of motion published by Klioner et al. All the main relativistic effects are included following Klioner et al. In particular, we consider several relativistic reference systems with corresponding time scales, scaled constants and parameters. Approximate expressions for Earth's precession in the interval ±1 Myr around J2000.0 are provided. In the interval ±2000 years around J2000.0, the difference compared to the P03 precession theory is only several arcseconds and the results are consistent with other long-term precession theories. Supported by the National Natural Science Foundation of China.

The AAPM/RSNA physics tutorial for residents. Basic physics of MR imaging: an introduction.

PubMed

Hendrick, R E

1994-07-01

This article provides an introduction to the basic physical principles of magnetic resonance (MR) imaging. Essential basic concepts such as nuclear magnetism, tissue magnetization, precession, excitation, and tissue relaxation properties are presented. Hydrogen spin density and tissue relaxation times T1, T2, and T2* are explained. The basic elements of a planar MR pulse sequence are described: section selection during tissue excitation, phase encoding, and frequency encoding during signal measurement.

Pure-phase selective excitation in fast-relaxing systems.

PubMed

Zangger, K; Oberer, M; Sterk, H

2001-09-01

Selective pulses have been used frequently for small molecules. However, their application to proteins and other macromolecules has been limited. The long duration of shaped-selective pulses and the short T(2) relaxation times in proteins often prohibited the use of highly selective pulses especially on larger biomolecules. A very selective excitation can be obtained within a short time by using the selective excitation sequence presented in this paper. Instead of using a shaped low-intensity radiofrequency pulse, a cluster of hard 90 degrees pulses, delays of free precession, and pulsed field gradients can be used to selectively excite a narrow chemical shift range within a relatively short time. Thereby, off-resonance magnetization, which is allowed to evolve freely during the free precession intervals, is destroyed by the gradient pulses. Off-resonance excitation artifacts can be removed by random variation of the interpulse delays. This leads to an excitation profile with selectivity as well as phase and relaxation behavior superior to that of commonly used shaped-selective pulses. Since the evolution of scalar coupling is inherently suppressed during the double-selective excitation of two different scalar-coupled nuclei, the presented pulse cluster is especially suited for simultaneous highly selective excitation of N-H and C-H fragments. Experimental examples are demonstrated on hen egg white lysozyme (14 kD) and the bacterial antidote ParD (19 kD). Copyright 2001 Academic Press.

OJ287: Deciphering the "Rosetta stone of blazars★"

NASA Astrophysics Data System (ADS)

Britzen, S.; Fendt, C.; Witzel, G.; Qian, S.-J.; Pashchenko, I. N.; Kurtanidze, O.; Zajacek, M.; Martinez, G.; Karas, V.; Aller, M.; Aller, H.; Eckart, A.; Nilsson, K.; Arévalo, P.; Cuadra, J.; Subroweit, M.; Witzel, A.

2018-04-01

OJ287 is the best candidate Active Galactic Nucleus (AGN) for hosting a supermassive binary black hole (SMBBH) at very close separation. We present 120 Very Long Baseline Array (VLBA) observations (at 15 GHz) covering the time between Apr. 1995 and Apr. 2017. We find that the OJ287 radio jet is precessing on a timescale of ˜ 22 yr. In addition, our data are consistent with a jet-axis rotation on a yearly timescale. We model the precession (24±2 yr) and combined motion of jet precession and jet-axis rotation. The jet motion explains the variability of the total radio flux-density via viewing angle changes and Doppler beaming. Half of the jet-precession timescale is of the order of the dominant optical periodicity timescale. We suggest that the optical emission is synchrotron emission and related to the jet radiation. The jet dynamics and flux-density light curves can be understood in terms of geometrical effects. Disturbances of an accretion disc caused by a plunging black hole do not seem necessary to explain the observed variability. Although the SMBBH model does not seem necessary to explain the observed variability, a SMBBH or Lense-Thirring precession (disc aSround single black hole) seem to be required to explain the timescale of the precessing motion. Besides jet rotation also nutation of the jet axis could explain the observed motion of the jet axis. We find a strikingly similar scaling for the timescales for precession and nutation as indicated for SS433 with a factor of roughly 50 times longer in OJ287.

Precessing rotating flows with additional shear: stability analysis.

PubMed

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 Omega(0)) and the additional "precessing" Coriolis force (with angular velocity -epsilonOmega(0)), normal to it. A "weak" shear flow, with rate 2epsilon of the same order of the Poincaré "small" ratio epsilon , 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 epsilon . 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 epsilon , but significant differences are obtained regarding growth rates and widths of instability bands, if larger epsilon values, up to 0.2, are considered. Finally, both flow cases are briefly discussed in view of a subsequent nonlinear study using pseudospectral direct numerical simulations, which is a natural continuation of RDT.

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 forcing at any given historic time. These results indicate that the methane lake distribution on Titan likely varies over an approximately 45 Kyr time scale.

The statistical mechanics of relativistic orbits around a massive black hole

NASA Astrophysics Data System (ADS)

Bar-Or, Ben; Alexander, Tal

2014-12-01

Stars around a massive black hole (MBH) move on nearly fixed Keplerian orbits, in a centrally-dominated potential. The random fluctuations of the discrete stellar background cause small potential perturbations, which accelerate the evolution of orbital angular momentum by resonant relaxation. This drives many phenomena near MBHs, such as extreme mass-ratio gravitational wave inspirals, the warping of accretion disks, and the formation of exotic stellar populations. We present here a formal statistical mechanics framework to analyze such systems, where the background potential is described as a correlated Gaussian noise. We derive the leading order, phase-averaged 3D stochastic Hamiltonian equations of motion, for evolving the orbital elements of a test star, and obtain the effective Fokker-Planck equation for a general correlated Gaussian noise, for evolving the stellar distribution function. We show that the evolution of angular momentum depends critically on the temporal smoothness of the background potential fluctuations. Smooth noise has a maximal variability frequency {{ν }max }. We show that in the presence of such noise, the evolution of the normalized angular momentum j=\\sqrt{1-{{e}2}} of a relativistic test star, undergoing Schwarzschild (in-plane) general relativistic precession with frequency {{ν }GR}/{{j}2}, is exponentially suppressed for j\\lt {{j}b}, where {{ν }GR}/jb2˜ {{ν }max }, due to the adiabatic invariance of the precession against the slowly varying random background torques. This results in an effective Schwarzschild precession-induced barrier in angular momentum. When jb is large enough, this barrier can have significant dynamical implications for processes near the MBH.

Rapid 3D in vivo 1H human lung respiratory imaging at 1.5 T using ultra-fast balanced steady-state free precession.

PubMed

Pusterla, Orso; Bauman, Grzegorz; Wielpütz, Mark O; Nyilas, Sylvia; Latzin, Philipp; Heussel, Claus P; Bieri, Oliver

2017-09-01

To introduce a reproducible, nonenhanced 1H MRI method for rapid in vivo functional assessment of the whole lung at 1.5 Tesla (T). At different respiratory volumes, the pulmonary signal of ultra-fast steady-state free precession (ufSSFP) follows an adapted sponge model, characterized by a respiratory index α. From the model, α reflects local ventilation-related information, is virtually independent from the lung density and thus from the inspiratory phase and breathing amplitude. Respiratory α-mapping is evaluated for healthy volunteers and patients with obstructive lung disease from a set of five consecutive 3D ultra-fast steady-state free precession (ufSSFP) scans performed in breath-hold and at different inspiratory volumes. For the patients, α-maps were compared with CT, dynamic contrast-enhanced MRI (DCE-MRI), and Fourier decomposition (FD). In healthy volunteers, respiratory α-maps showed good reproducibility and were homogeneous on iso-gravitational planes, but showed a gravity-dependent respiratory gradient. In patients with obstructive pulmonary disease, the functional impairment observed in respiratory α-maps was associated with emphysematous regions present on CT images, perfusion defects observable on DCE-MRI, and impairments visualized on FD ventilation and perfusion maps. Respiratory α-mapping derived from multivolumetric ufSSFP provides insights into functional lung impairment and may serve as a reproducible and normative measure for clinical studies. Magn Reson Med 78:1059-1069, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

Lense-Thirring Precession and Quasi-periodic Oscillations in X-Ray Binaries

NASA Astrophysics Data System (ADS)

Marković , Dragoljub; Lamb, Frederick K.

1998-11-01

It has recently been suggested that gravitomagnetic precession of the inner part of the accretion disk, possibly driven by radiation torques, may be responsible for some of the quasi-periodic X-ray brightness oscillations (QPOs) and other spectral features with frequencies between 20 and 300 Hz observed in the power spectra of some low-mass binary systems containing accreting neutron stars and black hole candidates. We have explored the free and driven normal modes of geometrically thin disks in the presence of gravitomagnetic and radiation warping torques. We have found a family of low-frequency gravitomagnetic (LFGM) modes with precession frequencies that range from the lowest frequency allowed by the size of the disk up to a certain critical frequency ωcrit, which is ~1 Hz for a compact object of solar mass. The lowest frequency (lowest order) LFGM modes are similar to the previously known radiation warping modes, extend over much of the disk, and have damping rates >~10 times their precession frequencies. The highest frequency LFGM modes are tightly wound spiral corrugations of the disk that extend to ~10 times its inner radius and have damping rates >~103 times their precession frequencies. A radiation warping torque can cause a few of the lowest frequency LFGM modes to grow with time, but even a strong radiation warping torque has essentially no effect on the LFGM modes with frequencies >~10-4 Hz. We have also discovered a second family of high-frequency gravitomagnetic (HFGM) modes with precession frequencies that range from ωcrit up to slightly less than the gravitomagnetic precession frequency ωgm,i of a particle at the inner edge of the disk, which is 30 Hz if the disk extends inward to the innermost stable circular orbit around a 2 M⊙ compact object with dimensionless angular momentum cJ/GM2 = 0.2. The lowest frequency HFGM modes are very strongly damped and have warp functions and precession frequencies very similar to those of the highest frequency LFGM modes. In contrast, the highest frequency (lowest order) HFGM modes are very localized spiral corrugations of the inner disk and are weakly damped, with Q-values of ~2-50. We discuss the implications of our results for the observability of Lense-Thirring precession in X-ray binaries.

Predicting Precession Rates from Secular Dynamics for Extra-solar Multi-planet Systems

NASA Astrophysics Data System (ADS)

Van Laerhoven, Christa

2015-12-01

Considering the secular dynamics of multi-planet systems provides substantial insight into the interactions between planets in those systems. Secular interactions are those that don't involve knowing where a planet is along its orbit, and they dominate when planets are not involved in mean motion resonances. These interactions exchange angular momentum among the planets, evolving their eccentricities and inclinations. To second order in the planets' eccentricities and inclinations, the eccentricity and inclination perturbations are decoupled. Given the right variable choice, the relevant differential equations are linear and thus the eccentricity and inclination behaviors can be described as a sum of eigenmodes. Since the underlying structure of the secular eigenmodes can be calculated using only the planets' masses and semi-major axes, one can elucidate the eccentricity and inclination behavior of planets in exoplanet systems even without knowing the planets' current eccentricities and inclinations. I have calculated both the eccentricity and inclination secular eigenmodes for the population of known multi-planet systems whose planets have well determined masses and periods and have used this to predict what range of pericenter precession (and nodal regression) rates the planets may have. One might have assumed that in any given system the planets with shorter periods would have faster precession rates, but I show that this is not necessarily the case. Planets that are 'loners' have narrow ranges of possible precession rates, while planets that are 'groupies' can have a wider range of possible precession rates. Several planets are expected to undergo significant precession on few-year timescales and many planets (though not the majority of planets) will undergo significant precession on decade timescales.

Measuring coalescing massive binary black holes with gravitational waves: The impact of spin-induced precession

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

Lang, Ryan N.; Hughes, Scott A.

The coalescence of massive black holes generates gravitational waves (GWs) that will be measurable by space-based detectors such as LISA to large redshifts. The spins of a binary's black holes have an important impact on its waveform. Specifically, geodetic and gravitomagnetic effects cause the spins to precess; this precession then modulates the waveform, adding periodic structure which encodes useful information about the binary's members. Following pioneering work by Vecchio, we examine the impact upon GW measurements of including these precession-induced modulations in the waveform model. We find that the additional periodicity due to spin precession breaks degeneracies among certain parameters,more » greatly improving the accuracy with which they may be measured. In particular, mass measurements are improved tremendously, by one to several orders of magnitude. Localization of the source on the sky is also improved, though not as much--low redshift systems can be localized to an ellipse which is roughly 10-a fewx10 arcminutes in the long direction and a factor of 2 smaller in the short direction. Though not a drastic improvement relative to analyses which neglect spin precession, even modest gains in source localization will greatly facilitate searches for electromagnetic counterparts to GW events. Determination of distance to the source is likewise improved: We find that relative error in measured luminosity distance is commonly {approx}0.1%-0.4% at z{approx}1. Finally, with the inclusion of precession, we find that the magnitude of the spins themselves can typically be determined for low redshift systems with an accuracy of about 0.1%-10%, depending on the spin value, allowing accurate surveys of mass and spin evolution over cosmic time.« less

Orbits: Computer simulation

NASA Technical Reports Server (NTRS)

Muszynska, A.

1985-01-01

In rotating machinery dynamics an orbit (Lissajous curve) represents the dynamic path of the shaft centerline motion during shaft rotation and resulting precession. The orbit can be observed with an oscilloscope connected to XY promixity probes. The orbits can also be simulated by a computer. The software for HP computer simulates orbits for two cases: (1) Symmetric orbit with four frequency components with different radial amplitudes and relative phase angles; and (2) Nonsymmetric orbit with two frequency components with two different vertical/horizontal amplitudes and two different relative phase angles. Each orbit carries a Keyphasor mark (one-per-turn reference). The frequencies, amplitudes, and phase angles, as well as number of time steps for orbit computation, have to be chosen and introduced to the computer by the user. The orbit graphs can be observed on the computer screen.

Application of the Nonballistic Model to the Black Hole Candidate XTE J1752-223 and the Quasar NRAO 150

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

Zheng, T. Y.; Gong, B. P., E-mail: bpgong@mail.hust.edu.cn

2017-02-01

Optical and radio observations of the black hole candidate XTE J1752-223 have exhibited a slightly curved motion of the jet components, which is associated with its radio light curve. In addition, observations of the quasar NRAO 150 have revealed a core–jet structure wobbling with a high angular speed. In this paper, the phenomena displayed in these two different sources are interpreted as the precession of a bent jet. In such a scenario, hot spots reproduced at different separations from the core precess on the same precession cone, in which different components correspond to different propagation times to the observer. Bymore » fitting the kinematics of the components of XTE J1752-223 and its light curve with a curved pattern of precession period 314 days, we find that the propagation time can make an earlier event appear later, and the jet axis can oscillate during its precession. Simulating the quasar NRAO 150 with the same scenario reveals that the knots at larger separation from the core precess at a slower speed than those closer in. A possible mechanism relating to the cooling time of a component is proposed. These three new results are of importance in understanding the physics underlying the curved jet as well as the activity of the central engine of different black hole systems.« less

A record of astronomically forced climate change in a late Ordovician (Sandbian) deep marine sequence, Ordos Basin, North China

NASA Astrophysics Data System (ADS)

Fang, Qiang; Wu, Huaichun; Hinnov, Linda A.; Wang, Xunlian; Yang, Tianshui; Li, Haiyan; Zhang, Shihong

2016-07-01

The late Ordovician Pingliang Formation on the southwestern margin of the Ordos Basin, North China, consists of rhythmic alternations of shale, limestone, and siliceous beds. To explore the possible astronomical forcing preserved in this lithological record, continuous lithological rank and magnetic susceptibility (MS) stratigraphic series were obtained from a 34 m thick section of the Pingliang Formation at Guanzhuang. Power spectral analysis of the MS and rank series reveal 85.5 cm to 124 cm, 23 cm to 38 cm, and 15 cm to 27 cm thick sedimentary cycles that in ratio match that of late Ordovician short eccentricity, obliquity and precession astronomical cycles. The power spectrum of the MS time series, calibrated to interpreted short orbital eccentricity cycles, aligns with spectral peaks to astronomical parameters, including 95 kyr short orbital eccentricity, 35.3 kyr and 30.6 kyr obliquity, and 19.6 kyr and 16.3 kyr precession cycles. The 15 cm to 27 cm thick limestone-shale couplets mainly represent precession cycles, and siliceous bed deposition may be related to both precession and obliquity forcing. We propose that precession-forced sea-level fluctuations mainly controlled production of lime mud in a shallow marine environment, and transport to the basin. Precession and obliquity controlled biogenic silica productivity, and temperature-dependent preservation of silica may have been influenced by obliquity forcing.

Direct extraction of electron parameters from magnetoconductance analysis in mesoscopic ring array structures

NASA Astrophysics Data System (ADS)

Sawada, A.; Faniel, S.; Mineshige, S.; Kawabata, S.; Saito, K.; Kobayashi, K.; Sekine, Y.; Sugiyama, H.; Koga, T.

2018-05-01

We report an approach for examining electron properties using information about the shape and size of a nanostructure as a measurement reference. This approach quantifies the spin precession angles per unit length directly by considering the time-reversal interferences on chaotic return trajectories within mesoscopic ring arrays (MRAs). Experimentally, we fabricated MRAs using nanolithography in InGaAs quantum wells which had a gate-controllable spin-orbit interaction (SOI). As a result, we observed an Onsager symmetry related to relativistic magnetic fields, which provided us with indispensable information for the semiclassical billiard ball simulation. Our simulations, developed based on the real-space formalism of the weak localization/antilocalization effect including the degree of freedom for electronic spin, reproduced the experimental magnetoconductivity (MC) curves with high fidelity. The values of five distinct electron parameters (Fermi wavelength, spin precession angles per unit length for two different SOIs, impurity scattering length, and phase coherence length) were thereby extracted from a single MC curve. The methodology developed here is applicable to wide ranges of nanomaterials and devices, providing a diagnostic tool for exotic properties of two-dimensional electron systems.

Why does a spinning egg rise?

NASA Astrophysics Data System (ADS)

Cross, Rod

2018-03-01

Experimental and theoretical results are presented concerning the rise of a spinning egg. It was found that an egg rises quickly while it is sliding and then more slowly when it starts rolling. The angular momentum of the egg projected in the XZ plane changed in the same direction as the friction torque, as expected, by rotating away from the vertical Z axis. The latter result does not explain the rise. However, an even larger effect arises from the Y component of the angular momentum vector. As the egg rises, the egg rotates about the Y axis, an effect that is closely analogous to rotation of the egg about the Z axis. Both effects can be described in terms of precession about the respective axes. Steady precession about the Z axis arises from the normal reaction force in the Z direction, while precession about the Y axis arises from the friction force in the Y direction. Precession about the Z axis ceases if the normal reaction force decreases to zero, and precession about the Y axis ceases if the friction force decreases to zero.

A POSSIBLE SIGNATURE OF LENSE-THIRRING PRECESSION IN DIPPING AND ECLIPSING NEUTRON-STAR LOW-MASS X-RAY BINARIES

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

Homan, Jeroen, E-mail: jeroen@space.mit.edu

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-starmore » 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.« less

Perihelion precession caused by solar oblateness variation in equatorial and ecliptic coordinate systems

NASA Astrophysics Data System (ADS)

Xu, Yan; Shen, Yunzhong; Xu, Guochang; Shan, Xinjian; Rozelot, Jean-Pierre

2017-12-01

Analytic solutions of planetary orbits disturbed by solar gravitational oblateness have been derived and given in the solar equatorial coordinate system, although the results usually have to be represented in the ecliptic coordinate system. The perihelion precession of interest in the solar equatorial and ecliptic coordinate systems is partly periodical and not negligible. The result shows that the difference in Mercury's perihelion precession between the solar equatorial plane and the ecliptic plane can reach a magnitude of 126708J2, which is even bigger than the perihelion precession itself (101516J2). Due to the temporal variability of the oblateness, the periodic variation of the J2 term, instead of simply a constant, is taken into account and solutions are derived. In the case of Mercury, the periodic J2 has an effect of nearly 0.8 per cent of the secular perihelion precession of Mercury. This indicates that a better understanding of the solar oblateness is required, which could be done through observation in the solar orbits instead of on Earth.

A proposed method for electronic feedback compensation of damping in ferromagnetic resonance

DOE PAGES

Zohar, S.; Sterbinsky, G. E.

2017-07-10

Here, we propose an experimental technique for extending feedback compensation of dissipative radiation used in nuclear magnetic resonance (NMR) to encompass ferromagnetic resonance (FMR). This method uses a balanced microwave power detector whose output is phase shifted π/2, amplified, and fed back to drive precession. Using classical control theory, we predict an electronically controllable narrowing of field swept FMR line-widths. This technique is predicted to compensate other sources of spin dissipation in addition to radiative loss.

A proposed method for electronic feedback compensation of damping in ferromagnetic resonance

NASA Astrophysics Data System (ADS)

Zohar, S.; Sterbinsky, G. E.

2017-12-01

We propose an experimental technique for extending feedback compensation of dissipative radiation used in nuclear magnetic resonance (NMR) to encompass ferromagnetic resonance (FMR). This method uses a balanced microwave power detector whose output is phase shifted π / 2 , amplified, and fed back to drive precession. Using classical control theory, we predict an electronically controllable narrowing of field swept FMR line-widths. This technique is predicted to compensate other sources of spin dissipation in addition to radiative loss.

Rotation Detection Using the Precession of Molecular Electric Dipole Moment

NASA Astrophysics Data System (ADS)

Ke, Yi; Deng, Xiao-Bing; Hu, Zhong-Kun

2017-11-01

We present a method to detect the rotation by using the precession of molecular electric dipole moment in a static electric field. The molecular electric dipole moments are polarized under the static electric field and a nonzero electric polarization vector emerges in the molecular gas. A resonant radio-frequency pulse electric field is applied to realize a 90° flip of the electric polarization vector of a particular rotational state. After the pulse electric field, the electric polarization vector precesses under the static electric field. The rotation induces a shift in the precession frequency which is measured to deduce the angular velocity of the rotation. The fundamental sensitivity limit of this method is estimated. This work is only a proposal and does not involve experimental results.

A complete solution for GP-B's gyroscopic precession by retarded gravitational theory

NASA Astrophysics Data System (ADS)

Tang, Keyun

Mainstream physicists generally believe that Mercury’s Perihelion precession and GP-B’ gyroscopic precession are two of the strongest evidences supporting Einstein’ curved spacetime and general relativity. However, most classical literatures and textbooks (e.g. Ohanain: Gravitation and Spacetime) paint an incorrect picture of Mercury’s orbit anomaly, namely Mercury’s perihelion precessed 43 arc-seconds per century; a correct picture should be that Mercury rotated 43 arc-seconds per century more than along Newtonian theoretical orbit. The essence of Le Verrier’s and Newcomb’s observation and analysis is that the angular speed of Mercury is slightly faster than the Newtonian theoretical value. The complete explanation to Mercury’s orbit anomaly should include two factors, perihelion precession is one of two factors, in addition, the change of orbital radius will also cause a change of angular speed, which is another component of Mercury's orbital anomaly. If Schwarzschild metric is correct, then the solution of the Schwarzschild orbit equation must contain three non-ignorable items. The first corresponds to Newtonian ellipse; the second is a nonlinear perturbation with increasing amplitude, which causes the precession of orbit perihelion; this is just one part of the angular speed anomaly of Mercury; the third part is a linear perturbation, corresponding to a similar figure of the Newton's ellipse, but with a minimal radius; this makes no contribution to the perihelion precession of the Schwarzschild orbit, but makes the Schwarzschild orbital radius slightly smaller, leading to a slight increase in Mercury’s angular speed. All classical literatures of general relativity ignored this last factor, which is a gross oversight. If you correctly take all three factors into consideration, the final result is that the difference between the angles rotated along Schwarzschild’s orbit and the angle rotated along Newton’s orbit for one hundred years should be more than 130.5 arc-seconds; this means that Le Verrier’s observation on Mercury’s orbital anomaly can not be explained correctly by the Schwarzschild metric. In contrast, Mercury’s angular speed anomaly can be explained satisfactorily by the radial induction component and angular component of retarded gravitation. From the perspective of energy, the additional radial component of retarded gravitation makes the radius of Mercury’s orbit slightly smaller, i.e. some potential energy is lost. And the angular component of retarded gravitation changes the Mercury's angular momentum; this proves that the changes of Mercury’s orbit and angular speed are the results of gravitational radiation. I have found that there are similar errors in the explanation on the gyroscopic precession of GP-B, i.e. physicists only consider the contribution of the nonlinear perturbation terms and never consider the contribution of linear perturbation terms. For the precession of GP-B, the complete Schwarzschild’s solution should be about 19.8 arc-seconds per year; it is far more than the experimental results of 6.602 arc-seconds per year. I have calculated the gyroscopic precession of GP-B due to retarded gravitation, the result is 6.607 arc-seconds per year; this matches well with the experimental results. These successful explanations for both anomalies of Mercury’s orbit and the gyroscopic precession of GP -B shows that Retarded Gravitation is indeed a sound gravitational theory, and that spacetime is in fact flat, and gravity travels at the speed of light. Both Mercury’s angular speed anomaly and GP - B gyro precession were the result of the gravitational radiation!

A New Model of Orbital Pacing for Pliocene Glaciations

NASA Astrophysics Data System (ADS)

Herbert, T.; Dowsett, H. J.; Caballero-Gill, R. P.

2015-12-01

The earth's climate system has gone through major changes over time that serve as natural experiments to test our understanding of linkages and feedbacks that may come into play if the Earth continues to warm, as expected from greenhouse gas forcing. Our project investigates patterns of climate change between the northern and southern hemispheres during the mid-Pliocene epoch (~3-4 Myr ago) when the overall climate state was warmer than today. Critically, evidence suggests that the amount of ice on Antarctica was similar to today, but that there was little or no permanent ice on land in the northern hemisphere. Most climate scientists have therefore supposed that orbitally-paced climate change would initiate in the region around the Antarctic, and be driven primarily by the 41,000 year obliquity cycle. Using distributed data sets on both sea surface temperature and the combination of deep sea temperature and global ice volume recorded by ð18O, we find a pervasive influence of eccentricity/precession on Pliocene paleoclimate that has been under-appreciated. We tentatively constrain the phase of the climate response by calibrating temperature patterns to the precessional "clock" of the Mediterranean sapropel sequence. Large Pliocene glacial events were paced by precession, and coincide with minimum northern hemisphere summer insolation. This mode is in many ways the opposite of the late Pleistocene, where climate positively follows the envelope of northern hemisphere precession. In the Pliocene case, glacial periods instead followed the lower envelope of precession and nodes of low precessional variance supported peak interglacial conditions. The observations can be explained by positing that during the warmer Pliocene, the high latitudes of the northern hemisphere could only support cryosphere expansion during times of minimal summer insolation. While the presence of ice-rafted debris in the North Atlantic and North Pacific unambiguously confirm a northern hemisphere component to peak Pliocene glaciations, the amplitude of the ð18O excursions in features such as isotope stage M2 almost certainly requires a significant coupling to Antarctic ice volume as well.

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

Ma, Q. L., E-mail: maqinli@gmail.com, E-mail: mizukami@wpi-aimr.tohoku.ac.jp; Miyazaki, T.; Mizukami, S., E-mail: maqinli@gmail.com, E-mail: mizukami@wpi-aimr.tohoku.ac.jp

The laser-induced spin dynamics of FeCo in perpendicularly magnetized L1{sub 0}-MnGa/FeCo bilayers with ferromagnetic and antiferromagnetic interfacial exchange coupling (IEC) are examined using the time-resolved magneto-optical Kerr effect. We found a precessional phase reversal of the FeCo layer as the IEC changes from ferromagnetic to antiferromagnetic. Moreover, a precession-suspension window was observed when the magnetic field was applied in a certain direction for the bilayer with ferromagnetic IEC. Our observations reveal that the spin dynamics modulation is strongly dependent on the IEC type within the Landau-Lifshitz-Gilbert depiction. The IEC dependence of the precessional phase and amplitude suggests the interesting methodmore » for magnetization dynamics modulation.« less

Exact solution for spin precession in the radiationless relativistic Kepler problem

NASA Astrophysics Data System (ADS)

Mane, S. R.

2014-11-01

There is interest in circulating beams of polarized particles in all-electric storage rings to search for nonzero permanent electric dipole moments of subatomic particles. To this end, it is helpful to derive exact analytical solutions of the spin precession in idealized models, both for pedagogical reasons and to serve as benchmark tests for analysis and design of experiments. This paper derives exact solutions for the spin precession in the relativistic Kepler problem. Some counterintuitive properties of the solutions are pointed out.

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 planets from different small body populations. This work aims to find certain sub-sets of orbits where GR could play an interesting role. Certain parallels are drawn between the cases of asteroids, comets and small perihelion distance meteoroid streams.

Observation of a Time Quasicrystal and Its Transition to a Superfluid Time Crystal.

PubMed

Autti, S; Eltsov, V B; Volovik, G E

2018-05-25

We report experimental realization of a quantum time quasicrystal and its transformation to a quantum time crystal. We study Bose-Einstein condensation of magnons, associated with coherent spin precession, created in a flexible trap in superfluid ^{3}He-B. Under a periodic drive with an oscillating magnetic field, the coherent spin precession is stabilized at a frequency smaller than that of the drive, demonstrating spontaneous breaking of discrete time translation symmetry. The induced precession frequency is incommensurate with the drive, and hence, the obtained state is a time quasicrystal. When the drive is turned off, the self-sustained coherent precession lives a macroscopically long time, now representing a time crystal with broken symmetry with respect to continuous time translations. Additionally, the magnon condensate manifests spin superfluidity, justifying calling the obtained state a time supersolid or a time supercrystal.

Numerical simulations of bistable flows in precessing spheroidal shells

NASA Astrophysics Data System (ADS)

Vormann, J.; Hansen, U.

2018-05-01

Precession of the rotation axis is an often neglected mechanical driving mechanism for flows in planetary interiors, through viscous coupling at the boundaries and topographic forcing in non-spherical geometries. We investigate precession-driven flows in spheroidal shells over a wide range of parameters and test the results against theoretical predictions. For Ekman numbers down to 8.0 × 10-7, we see a good accordance with the work of Busse, who assumed the precession-driven flow to be dominated by a rigid rotation component that is tilted to the main rotation axis. The velocity fields show localized small-scale structures for lower Ekman numbers and clear signals of inertial waves for some parameters. For the case of moderate viscosity and strong deformation, we report the realization of multiple solutions at the same parameter combination, depending on the initial condition.

Observation of a Time Quasicrystal and Its Transition to a Superfluid Time Crystal

NASA Astrophysics Data System (ADS)

Autti, S.; Eltsov, V. B.; Volovik, G. E.

2018-05-01

We report experimental realization of a quantum time quasicrystal and its transformation to a quantum time crystal. We study Bose-Einstein condensation of magnons, associated with coherent spin precession, created in a flexible trap in superfluid 3He-B . Under a periodic drive with an oscillating magnetic field, the coherent spin precession is stabilized at a frequency smaller than that of the drive, demonstrating spontaneous breaking of discrete time translation symmetry. The induced precession frequency is incommensurate with the drive, and hence, the obtained state is a time quasicrystal. When the drive is turned off, the self-sustained coherent precession lives a macroscopically long time, now representing a time crystal with broken symmetry with respect to continuous time translations. Additionally, the magnon condensate manifests spin superfluidity, justifying calling the obtained state a time supersolid or a time supercrystal.

Possible quasi-periodic ejections in quasar B1308+326

NASA Astrophysics Data System (ADS)

Qian, S. J.; Britzen, S.; Witzel, A.; Krichbaum, T. P.; Gan, H. Q.

2017-08-01

Context. The search for periodic features in flux variability and kinematics of superluminal components in blazars is capable of providing significant clues for the understanding of the physical processes in their central engines (black-hole/accretion-disk systems), especially concerning the formation and structure of their relativistic jets and radiation mechanisms. Aims: The jet swing on parsec-scales and the change of the ejection position angle of the superluminal components with time in the quasar B1308+326 (z = 0.997) are investigated as quasi-periodic behaviors. Methods: A previously published precessing jet nozzle model is applied to model the source kinematics and a possible jet precession period is found. Results: Based on the model fitting of the kinematics for a subset of components, it is shown that their kinematics, including the shape of the inner trajectories and the motion of the components, could be well fitted in terms of the precessing jet nozzle model and a precession period of 16.9 ± 0.3 yr is derived. Different precession mechanisms are discussed and compared. Conclusions: It is shown that the swing of the ejection position angle of the superluminal knots observed in B1308+326 may be due to the orbital motion of a putative supermassive black hole binary in its nucleus. Some relevant parameters of the binary model are estimated. We also discuss the spin-induced precession mechanism in the single black hole scenario and an estimate for the spin of the Kerr black hole is obtained.

Impact of a small ellipticity on the sustainability condition of developed turbulence in a precessing spheroid

NASA Astrophysics Data System (ADS)

Horimoto, Yasufumi; Simonet-Davin, Gabriel; Katayama, Atsushi; Goto, Susumu

2018-04-01

We experimentally investigate the flow transition to developed turbulence in a precessing spheroid with a small ellipticity. Fully developed turbulence appears through a subcritical transition when we fix the Reynolds number (the spin rate) and gradually increase the Poincaré number (the precession rate). In the transitional range of the Poincaré number, two qualitatively different turbulent states (i.e., fully developed turbulence and quiescent turbulence with a spin-driven global circulation) are stable and they are connected by a hysteresis loop. This discontinuous transition is in contrast to the continuous transition in a precessing sphere, for which neither bistable turbulent states nor hysteresis loops are observed. The small ellipticity of the container makes the global circulation of the confined fluid more stable, and it requires much stronger precession of the spheroid, than a sphere, for fully developed turbulence to be sustained. Nevertheless, once fully developed turbulence is sustained, its flow structures are almost identical in the spheroid and sphere. The argument [Lorenzani and Tilgner, J. Fluid Mech. 492, 363 (2003), 10.1017/S002211200300572X; Noir et al., Geophys. J. Int. 154, 407 (2003), 10.1046/j.1365-246X.2003.01934.x] on the basis of the analytical solution [Busse, J. Fluid Mech. 33, 739 (1968), 10.1017/S0022112068001655] of the steady global circulation in a weak precession range well describes the onset of the fully developed turbulence in the spheroid.

The theta/gamma discrete phase code occuring during the hippocampal phase precession may be a more general brain coding scheme.

PubMed

Lisman, John

2005-01-01

In the hippocampus, oscillations in the theta and gamma frequency range occur together and interact in several ways, indicating that they are part of a common functional system. It is argued that these oscillations form a coding scheme that is used in the hippocampus to organize the readout from long-term memory of the discrete sequence of upcoming places, as cued by current position. This readout of place cells has been analyzed in several ways. First, plots of the theta phase of spikes vs. position on a track show a systematic progression of phase as rats run through a place field. This is termed the phase precession. Second, two cells with nearby place fields have a systematic difference in phase, as indicated by a cross-correlation having a peak with a temporal offset that is a significant fraction of a theta cycle. Third, several different decoding algorithms demonstrate the information content of theta phase in predicting the animal's position. It appears that small phase differences corresponding to jitter within a gamma cycle do not carry information. This evidence, together with the finding that principle cells fire preferentially at a given gamma phase, supports the concept of theta/gamma coding: a given place is encoded by the spatial pattern of neurons that fire in a given gamma cycle (the exact timing within a gamma cycle being unimportant); sequential places are encoded in sequential gamma subcycles of the theta cycle (i.e., with different discrete theta phase). It appears that this general form of coding is not restricted to readout of information from long-term memory in the hippocampus because similar patterns of theta/gamma oscillations have been observed in multiple brain regions, including regions involved in working memory and sensory integration. It is suggested that dual oscillations serve a general function: the encoding of multiple units of information (items) in a way that preserves their serial order. The relationship of such coding to that proposed by Singer and von der Malsburg is discussed; in their scheme, theta is not considered. It is argued that what theta provides is the absolute phase reference needed for encoding order. Theta/gamma coding therefore bears some relationship to the concept of "word" in digital computers, with word length corresponding to the number of gamma cycles within a theta cycle, and discrete phase corresponding to the ordered "place" within a word. Copyright 2005 Wiley-Liss, Inc.

A new reference frame for astronomically-tuned Plio-Pleistocene climate variability derived from a benthic oxygen isotope splice of the Mediterranean

NASA Astrophysics Data System (ADS)

Lourens, L. J.; Ziegler, M.; Konijnendijk, T. Y. M.; Hilgen, F. J.; Bos, R.; Beekvelt, B.; van Loevezijn, A.; Collin, S.

2017-12-01

The astronomical theory of climate has revolutionized our understanding of past climate change and the development of highly accurate geologic time scales for the entire Cenozoic. Most of this understanding has come from the construction of astronomically tuned global ocean benthic foraminiferal oxygen isotope (δ18O) stacked record, derived by the international drilling operations of DSDP, ODP and IODP. The tuning includes fixed phase relationships between the obliquity and precession cycles and the inferred high-latitude climate, i.e. glacial-interglacial, response, which hark back to SPECMAP, using simple ice sheet models and a limited number of radiometric dates. This approach was largely implemented in the widely applied LR04 stack, though LR04 assumed shorter response times for the smaller ice caps during the Pliocene. In the past decades, an astronomically calibrated time scale for the Pliocene and Pleistocene of the Mediterranean has been developed, which has become the reference for the standard Geologic Time Scale. Typical of the Mediterranean marine sediments are the cyclic lithological alternations, reflecting the interference between obliquity and precession-paced low latitude climate variability, such as the African monsoon. Here we present the first benthic foraminiferal based oxygen isotope record of the Mediterranean reference scale, which strikingly mirrors the LR04. We will use this record to discuss the assumed open ocean glacial-interglacial related phase relations over the past 5.3 million years.

Intrinsic diffusion sensitivity of the balanced steady-state free precession (bSSFP) imaging sequence.

PubMed

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. Copyright © 2015 John Wiley & Sons, Ltd.

Noncontrast-enhanced renal angiography using multiple inversion recovery and alternating TR balanced steady-state free precession.

PubMed

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. © 2012 Wiley Periodicals, Inc.

Vector solitons with locked and precessing states of polarization.

PubMed

Sergeyev, Sergey V; Mou, Chengbo; Rozhin, Aleksey; Turitsyn, Sergei K

2012-11-19

We demonstrate experimentally new families of vector solitons with locked and precessing states of polarization for fundamental and multipulse soliton operations in a carbon nanotube mode-locked fiber laser with anomalous dispersion laser cavity.

Polynomial approximation of the Lense-Thirring rigid precession frequency

NASA Astrophysics Data System (ADS)

De Falco, Vittorio; Motta, Sara

2018-05-01

We propose a polynomial approximation of the global Lense-Thirring rigid precession frequency to study low-frequency quasi-periodic oscillations around spinning black holes. This high-performing approximation allows to determine the expected frequencies of a precessing thick accretion disc with fixed inner radius and variable outer radius around a black hole with given mass and spin. We discuss the accuracy and the applicability regions of our polynomial approximation, showing that the computational times are reduced by a factor of ≈70 in the range of minutes.

Carbon Cycle Dynamics through the Early Eocene Climatic Optimum: Orbital Couplings to Lacustrine Cycling

NASA Astrophysics Data System (ADS)

Rosengard, S. Z.; Grogan, D. S.; Whiteside, J. H.; van Keuren, M.; Musher, D.

2010-12-01

The early Eocene represents the most recent hothouse climate state of Earth history, a period during which Earth’s surface temperatures warmed and reached a steady peak at the Early Eocene Climatic Optimum (EECO), 53.5-50 Ma. Interspersed through the primary warming interval were several hyperthermals, or rapid peaks in surface temperature and pulses of carbon dioxide into the atmosphere, followed by rapid declines, lasting 10^4 to 10^5 years. Various hypotheses have been offered to explain the climatic triggers during the hothouse interval, including changes in ocean circulation, methane release from hydrates, volcanism, and turnover of terrestrial organic matter, implicating various couplings and feedbacks in the global carbon cycle. The present study investigates the prevailing changes in carbon cycle dynamics that occurred during a specific subinterval of the Early Eocene Climatic Optimum. We sampled a carbon-rich 300-ft ( 1100 kyr) section of lacustrine Green River Formation sediments from the TOSCO core in the Uinta Basin at a one-foot resolution for organic carbon content and δ^{13}C. The compiled data comprise a high-resolution profile of total organic carbon and isotopic organic carbon composition through the section, showing cyclic patterns that we hypothesize reflect orbital signals. Bulk isotopic carbon and shale oil measurements from an earlier Fischer Assay across TOSCO’s entire 1030-ft core were then filtered using the expected frequency of a 23-kyr precession cycle. The overlaid cycles reveal δ^{13}C and oil content to be anti-phase through the 300-ft section, except for an interval of 50 feet (180 kyr) from the Mahogany Zone to the B-groove of the core, where the two measurements are in-phase. Given that shale oil, a proxy for lake primary productivity and carbon burial, and δ^{13}C typically correlate inversely, this short, 180-kyr interval of in-phase variation suggests a significant alteration in the local carbon cycle. These preliminary findings reveal a dynamic, inconstant coupling between precessional variations in solar insolation and the carbon cycle during the EECO. As the organic carbon profile fundamentally records ecosystem processes, this precession-carbon cycle coupling is likely modulated by ecological dynamics within the paleolake, such as changing trophic and community structure. Because precession-driven changes in solar insolation dominantly control hydrology and lake water balance, the lacustrine ecosystem response to such perturbations may have precipitated key shifts in the dynamics of carbon cycling through the most stable interval of Earth’s latest hothouse.

The Role of Orbital Forcing in the Early-Middle Pleistocene Transition: Continuing the Precession Verses Obliquity Debate

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.

Rapid Jet Precession During the 2015 Outburst of the Black Hole X-ray Binary V404 Cygni

NASA Astrophysics Data System (ADS)

Sivakoff, Gregory R.; Miller-Jones, James; Tetarenko, Alex J.

2017-08-01

In stellar-mass black holes that are orbited by lower-mass companions (black hole low-mass X-ray binaries), the accretion process can undergo dramatic outbursts that can be accompanied by the launching of powerful relativistic jets. We still do not know the exact mechanism responsible for launching these jets, despite decades of research and the importance of determining this mechanism given the clear analogue of accreting super-massive black holes and their jets. The two main models for launching jets involve the extraction of the rotational energy of a spinning black hole (Blandford-Znajek) and the centrifugal acceleration of particles by open magnetic field lines rotating with the accretion flow (Blandford-Payne). Since some relativistic jets are not fully aligned with the angular momentum of the binary's orbit, the inner accretion flow of some black hole X-ray binaries may precess due to frame-dragging by a spinning black hole (Lense-Thirring precession). This precession has been previously observed close to the black hole as second-timescale quasi-periodic (X-ray) variability. In this talk we will present radio-through-sub-mm timing and high-angular resolution radio imaging (including a high-timing resolution movie) of the black hole X-ray binary V404 Cygni during its 2015 outburst. These data show that at the peak of the outburst the relativistic jets in this system were precessing on timescales of hours. We will discuss how rapid precession can be explained by Lense-Thirring precession of a vertically-extended slim disc that is maintained out to a radius of 6 X 1010 cm by a highly super-Eddington accretion rate. This would imply that the jet axis of V404 Cyg is not aligned with the black hole spin. More importantly, this places a key requirement on any model for launching jets, and may favour launching the jet from the rotating magnetic fields threading the disc.

Change in Minimum Orbit Intersection Distance due to General Relativistic Precession in Small Solar System Bodies

NASA Astrophysics Data System (ADS)

Sekhar, Aswin; Valsecchi, Giovanni B.; Asher, David; Werner, Stephanie; Vaubaillon, Jeremie; Li, Gongjie

2017-06-01

One of the greatest successes of Einstein's General Theory of Relativity (GR) was the correct prediction of the perihelion precession 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 can create substantial changes in MOID for small bodies ranging from meteoroids to comets and asteroids.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 argument of pericentre. Numerical integrations were done with the MERCURY package incorporating GR code to test the same effects. A numerical approach showed the same interesting relationship (as shown by analytical theory) between values of argument of pericentre and the peaks or dips in MOID values. There is an overall agreement between both analytical and numerical methods.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) when long term impact risk possibilities are considered. Previous works have looked into impact probabilities and collision scenarios on planets from different small body populations. This work aims to find certain sub-sets of small bodies where GR could play an interesting role. Certain parallels are drawn between the cases of asteroids, comets and small perihelion distance meteoroid streams.

Testing the relativistic precession model using low-frequency and kHz quasi-periodic oscillations in neutron star low-mass X-ray binaries with known spin

NASA Astrophysics Data System (ADS)

van Doesburgh, Marieke; van der Klis, Michiel

2017-03-01

We analyse all available RXTE data on a sample of 13 low-mass X-ray binaries with known neutron star spin that are not persistent pulsars. We carefully measure the correlations between the centroid frequencies of the quasi-periodic oscillations (QPOs). We compare these correlations to the prediction of the relativistic precession model that, due to frame dragging, a QPO will occur at the Lense-Thirring precession frequency νLT of a test-particle orbit whose orbital frequency is the upper kHz QPO frequency νu. Contrary to the most prominent previous studies, we find two different oscillations in the range predicted for νLT that are simultaneously present over a wide range of νu. Additionally, one of the low-frequency noise components evolves into a (third) QPO in the νLT range when νu exceeds 600 Hz. The frequencies of these QPOs all correlate to νu following power laws with indices between 0.4 and 3.3, significantly exceeding the predicted value of 2.0 in 80 per cent of the cases (at 3 to >20σ). Also, there is no evidence that the neutron star spin frequency affects any of these three QPO frequencies, as would be expected for frame dragging. Finally, the observed QPO frequencies tend to be higher than the νLT predicted for reasonable neutron star specific moment of inertia. In the light of recent successes of precession models in black holes, we briefly discuss ways in which such precession can occur in neutron stars at frequencies different from test-particle values and consistent with those observed. A precessing torus geometry and other torques than frame dragging may allow precession to produce the observed frequency correlations, but can only explain one of the three QPOs in the νLT range.

The gravitomagnetic interaction and its relationship to other relativistic gravitational effects

NASA Technical Reports Server (NTRS)

Nordtvedt, Kenneth

1991-01-01

To better understand the relationship between the expected precession rates of an orbiting gyroscope (GP-B) and other observable consequences in the solar system of relativistic, post-Newtonian gravity, a phenomenological model was developed of post-Newtonian gravity which presupposes the very minimum possible concerning the nature and foundations of the gravitational interaction. Solar system observations, chiefly interplanetary ranging, fix all the parameters in the phenomenological model to various levels of precision. This permits prediction of gyroscope precession rates to better than 10 pct. accuracy. A number of new precession terms are calculated which would exist if gravity were not a metric field phenomenon, but this would clash with other empirical observations of post-Newtonian effects in gravity. It is shown that gravitomagnetism, the post-Newtonian gravitational corrections to the interactions between moving matter, plays a ubiquitous role in determining a wide variety of gravitational effects, including the precession of orbiting gyroscopes.

Measuring Parameters of Massive Black Hole Binaries with Partially-Aligned Spins

NASA Technical Reports Server (NTRS)

Lang, Ryan N.; Hughes, Scott A.; Cornish, Neil J.

2010-01-01

It is important to understand how well the gravitational-wave observatory LISA can measure parameters of massive black hole binaries. It has been shown that including spin precession in the waveform breaks degeneracies and produces smaller expected parameter errors than a simpler, precession-free analysis. However, recent work has shown that gas in binaries can partially align the spins with the orbital angular momentum, thus reducing the precession effect. We show how this degrades the earlier results, producing more pessimistic errors in gaseous mergers. However, we then add higher harmonics to the signal model; these also break degeneracies, but they are not affected by the presence of gas. The harmonics often restore the errors in partially-aligned binaries to the same as, or better than/ those that are obtained for fully precessing binaries with no harmonics. Finally, we investigate what LISA measurements of spin alignment can tell us about the nature of gas around a binary,

4963 Kanroku: Asteroid with a possible precession of rotation axis

NASA Astrophysics Data System (ADS)

Sokova, Iraida A.; Marchini, Alessandro; Franco, Lorenzo; Papini, Riccardo; Salvaggio, Fabio; Palmas, Teodora; Sokov, Eugene N.; Garlitz, Joe; Knight, Carl R.; Bretton, Marc

2018-04-01

Based on photometric observations of 4963 Kanroku as part of a campaign to measure its light-curve, changes of the light-curve profile have been detected. These changes are of a periodic nature, i.e. the profiles change with a detected period P = 16.4032 h. Based on simulations of the shape of the asteroid and using observational data, we make the assumption that such changes of the light-curve of the asteroid could be caused by the existence of a precession force acting on the axis of rotation of the asteroid. Simulations of the 4963 Kanroku light-curve, taking into account the detected precession, and the parameters for the shape of the asteroid, the modeled light-curves are in good agreement with the light-curves obtained from the observation campaign. Thus, the detected precession force may indicate a possible satellite of the asteroid 4963 Kanroku.

The hippocampal physiology of approaching middle-age: early indicators of change.

PubMed

Huxter, John R; Miranda, Jason A; Dias, Rebecca

2012-09-01

Age-related cognitive decline presents serious lifestyle challenges, and anatomical changes to the hippocampus are often implicated in clinical conditions later in life. However, relatively little is known about how hippocampal physiology is altered in the transition to middle-age, when early detection may offer the best opportunity for successful treatment. High-yield extracellular recording is a powerful tool for understanding brain function in freely moving animals at single-cell resolution and with millisecond precision. We used this technique to characterize changes to hippocampal physiology associated with maturation in 35-week-old rats. Combining a series of behavioral tasks with recordings of large numbers of neurons, local field potentials (LFP), and network patterns of activation, we were able to generate a comprehensive picture based on more than 25 different assays for each subject. Notable changes associated with aging included increased firing rates in interneurons, reduced LFP power but increased frequency in the 4-12 Hz theta band, and impairment in hippocampal pattern-separation for different environments. General properties of pyramidal cell firing and spatial map integrity were preserved. There was no impairment in theta phase-precession, experience-dependent place field expansion, or sleep reactivation of waking network patterns. There were however changes in foraging strategy and behavioral responses to the introduction of a novel environment. Taken together the results reveal a diverse pattern of changes which are of increasing relevance in an aging population. They also highlight areas where high-yield electrophysiological assays can be used to provide the sensitivity and throughput required for pre-clinical drug-discovery programs. Copyright © 2012 Wiley Periodicals, Inc.

Lense-Thirring Precession of Accretion Disks and Quasi-Periodic Oscillations in X-Ray Binaries

NASA Astrophysics Data System (ADS)

Markovic, D.; Lamb, F. K.

2003-05-01

It has recently been suggested that gravitomagnetic precession of the inner part of the accretion disk, possibly driven by radiation torques, may be responsible for some of the 20-300 Hz quasi-periodic X-ray brightness oscillations (QPOs) observed in some low-mass binary systems containing accreting neutron stars and black hole candidates. We have explored warping modes of geometrically thin disks in the presence of gravitomagnetic and radiation torques. We have found a family of overdamped, low-frequency gravitomagnetic (LFGM) modes all of which have precession frequencies lower than a certain critical frequency ωcrit, which is 1 Hz for a compact object of solar mass. A radiation warping torque can cause a few of the lowest-frequency LFGM modes to grow with time, but even a strong radiation warping torque has essentially no effect on the LFGM modes with frequencies ≳10-4 Hz. We have also discovered a second family of high-frequency gravitomagnetic (HFGM) modes with precession frequencies that range from ωcrit up to slightly less than the gravitomagnetic precession frequency of a particle at the inner edge of the disk, which is 30 Hz if the disk extends inward to the innermost stable circular orbit around a 2M⊙ compact object with dimensionless angular momentum cJ/GM2 = 0.2. The highest-frequency HFGM modes are very localized spiral corrugations of the inner disk and are weakly damped, with Q values as large as 50. We discuss the implications of our results for the observability of Lense-Thirring precession in X-ray binaries.

Non-Rigid Earth Contributions to the Precession in Longitude and Indirect Effects on Nutations

NASA Astrophysics Data System (ADS)

Ferrandiz, J. M.; Escapa, A.; Baenas, T.; Getino, J.

2016-12-01

Precession in longitude is affected by the internal structure of the Earth. Although this effect is small, typically described as of second-order, it must be considered in current precession theories due to the stringent accuracy and consistency requirements. The current IAU2006 precession theory is based on Capitaine at al. (2003, 2005). The influence of the Earth's geophysical model is taken into account in IAU2006 only through a sole contribution, the so-called "non-linear effect" computed by Mathews (2004). In elastic Earth models the contributions are twofold. A main part comes from 2nd order terms of the mathematical solution stemming from crossed influences of certain nutation-rising terms. Only the Hamiltonian theory of the non-rigid Earth has succeeded in deriving a solution for those terms so far, and they were not considered in IAU2006 precession theory. Another contributions are caused by geopotential variations resulting from the tidal deformations of the Earth, or redistribution tidal potential. IAU2006 non-linear effect belongs to this category, although it just represents a partial, simplified approach to the total effect (Lambert & Mathews 2006, 2008). The mass redistribution is induced by the gravitational action of Moon and Sun, but also by the tidal variations of the Earth's angular velocity and the resultant changes of the centrifugal potential. We present a comprehensive study of the contributions to the precession in longitude due to the non-rigidity of the Earth, based on the Hamiltonian formalism developed by Getino and Ferrándiz for a two-layer Earth elastic model. To this end, we recall the achievements made by our group recently (Ferrándiz et al 2016, Baenas et al 2016) and complete them by incorporating the contributions due to the tidal variations of the Earth's angular velocity, as well as anelasticity effects consistent with the IERS Conventions. After that, we compute the total final correction to the precession in longitude due to non-rigid Earth contributions, and the associated change of its dynamical ellipticity. This change entails further corrections of the nutation series, known as indirect (Escapa et al. 2016). Both modifications should be taken into account to improve the accuracy and mutual consistency of the IAU2000 and IAU2006 nutation/precession theories.

Ultrafast optical excitation of magnetic skyrmions

NASA Astrophysics Data System (ADS)

Ogawa, N.; Seki, S.; Tokura, Y.

2015-04-01

Magnetic skyrmions in an insulating chiral magnet Cu2OSeO3 were studied by all-optical spin wave spectroscopy. The spins in the conical and skyrmion phases were excited by the impulsive magnetic field from the inverse-Faraday effect, and resultant spin dynamics were detected by using time-resolved magneto-optics. Clear dispersions of the helimagnon were observed, which is accompanied by a distinct transition into the skyrmion phase, by sweeping temperature and magnetic field. In addition to the collective excitations of skyrmions, i.e., rotation and breathing modes, several spin precession modes were identified, which would be specific to optical excitation. The ultrafast, nonthermal, and local excitation of the spin systems by photons would lead to the efficient manipulation of nano-magnetic structures.

Mode locking of electron spin coherences in singly charged quantum dots.

PubMed

Greilich, A; Yakovlev, D R; Shabaev, A; Efros, Al L; Yugova, I A; Oulton, R; Stavarache, V; Reuter, D; Wieck, A; Bayer, M

2006-07-21

The fast dephasing of electron spins in an ensemble of quantum dots is detrimental for applications in quantum information processing. We show here that dephasing can be overcome by using a periodic train of light pulses to synchronize the phases of the precessing spins, and we demonstrate this effect in an ensemble of singly charged (In,Ga)As/GaAs quantum dots. This mode locking leads to constructive interference of contributions to Faraday rotation and presents potential applications based on robust quantum coherence within an ensemble of dots.

Background Information on the He(3) Nuclear Gyroscope.

DTIC Science & Technology

1983-02-01

however, that sincew0 is not fixed by any constant of nature , its phase and frequency must be initially established by measurement when the gyro case is...sequence of longitudinal relaxation time (T1) measurements were made on a standard He3 -He4 liquid mixture (He3 concentration of 7 x 10 4) as a function of...Analysis of Experimental FPD Data on a Liquid Mixture Free precession data of a standard He 3-He4 liquid mixture (He3 concentration of 7 x 10- 4) were

Consequences of a new experimental determination of the quadrupole moment of the sun for gravitation theory

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

Moffat, J.W.

1983-03-07

A preliminary experimental determination by Hill, Bos and Goode of the interior rotation of the sun leads to a nonzero value for the quadrupole-moment coefficient J/sub 2/. This produces a deviation of 1.6% from Einstein's prediction of the precession of the perihelion of Mercury. A nonsymmetric gravitational theory can fit the measured precession with this J/sub 2/ and all other solar-system relativity experiments for one value of a post-Newtonian parameter in the theory. A prediction is made for the perihelion precession of Icarus.

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.

Precessional quantities for the Earth over 10 Myr

NASA Technical Reports Server (NTRS)

Laskar, Jacques

1992-01-01

The insolation parameters of the Earth depend on its orbital parameters and on the precession and obliquity. Until 1988, the usually adopted solution for paleoclimate computation consisted in (Bretagnon, 1974) for the orbital elements of the Earth, which was completed by (Berger, 1976) for the computation of the precession and obliquity of the Earth. In 1988, I issued a solution for the orbital elements of the Earth, which was obtained in a new manner, gathering huge analytical computations and numerical integration (Laskar, 1988). In this solution, which will be denoted La88, the precession and obliquity quantities necessary for paleoclimate computations were integrated at the same time, which insure good consistency of the solutions. Unfortunately, due to various factors, this latter solution for the precession and obliquity was not widely distributed (Berger, Loutre, Laskar, 1988). On the other side, the orbital part of the solution La88 for the Earth, was used in (Berger and Loutre, 1991) to derive another solution for precession and obliquity, aimed to climate computations. I also issued a new solution (La90) which presents some slight improvements with respect to the previous one (Laskar, 1990). As previously, this solution contains orbital, precessional, and obliquity variables. The main features of this new solution are discussed.

Precession of the Earth as the Cause of Geomagnetism: Experiments lend support to the proposal that precessional torques drive the earth's dynamo.

PubMed

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.

Detectability of gravitational waves from binary black holes: Impact of precession and higher modes

NASA Astrophysics Data System (ADS)

Calderón Bustillo, Juan; Laguna, Pablo; Shoemaker, Deirdre

2017-05-01

Gravitational wave templates used in current searches for binary black holes omit the effects of precession of the orbital plane and higher-order modes. While this omission seems not to impact the detection of sources having mass ratios and spins similar to those of GW150914, even for total masses M >200 M⊙ , we show that it can cause large fractional losses of sensitive volume for binaries with mass ratio q ≥4 and M >100 M⊙, measured in the detector frame. For the highest precessing cases, this is true even when the source is face-on to the detector. Quantitatively, we show that the aforementioned omission can lead to fractional losses of sensitive volume of ˜15 %, reaching >25 % for the worst cases studied. Loss estimates are obtained by evaluating the effectualness of the SEOBNRv2-ROM double spin model, currently used in binary black hole searches, towards gravitational wave signals from precessing binaries computed by means of numerical relativity. We conclude that, for sources with q ≥4 , a reliable search for binary black holes heavier than M >100 M⊙ needs to consider the effects of higher-order modes and precession. The latter seems especially necessary when Advanced LIGO reaches its design sensitivity.

Empirical Corrections to Nutation Amplitudes and Precession Computed from a Global VLBI Solution

NASA Astrophysics Data System (ADS)

Schuh, H.; Ferrandiz, J. M.; Belda-Palazón, S.; Heinkelmann, R.; Karbon, M.; Nilsson, T.

2017-12-01

The IAU2000A nutation and IAU2006 precession models were adopted to provide accurate estimations and predictions of the Celestial Intermediate Pole (CIP). However, they are not fully accurate and VLBI (Very Long Baseline Interferometry) observations show that the CIP deviates from the position resulting from the application of the IAU2006/2000A model. Currently, those deviations or offsets of the CIP (Celestial Pole Offsets - CPO), can only be obtained by the VLBI technique. The accuracy of the order of 0.1 milliseconds of arc (mas) allows to compare the observed nutation with theoretical prediction model for a rigid Earth and constrain geophysical parameters describing the Earth's interior. In this study, we empirically evaluate the consistency, systematics and deviations of the IAU 2006/2000A precession-nutation model using several CPO time series derived from the global analysis of VLBI sessions. The final objective is the reassessment of the precession offset and rate, and the amplitudes of the principal terms of nutation, trying to empirically improve the conventional values derived from the precession/nutation theories. The statistical analysis of the residuals after re-fitting the main nutation terms demonstrates that our empirical corrections attain an error reduction by almost 15 micro arc seconds.

On the free-precession candidate PSR B1828-11: Evidence for increasing deformation

NASA Astrophysics Data System (ADS)

Ashton, G.; Jones, D. I.; Prix, R.

2017-05-01

We observe that the periodic variations in spin-down rate and beamwidth of the radio pulsar PSR B1828-11 are getting faster. In the context of a free precession model, this corresponds to a decrease in the precession period Pfp. We investigate how a precession model can account for such a decrease in Pfp, in terms of an increase over time in the absolute biaxial deformation (|ɛp| ˜ 10-8) of this pulsar. We perform a Bayesian model comparison against the 'base' precession model (with constant ɛp) developed in Ashton et al., and we obtain decisive odds in favour of a time-varying deformation. We study two types of time variation: (I) a linear drift with a posterior estimate of \\dot{ɛ }_p{˜ }10^{-18} s^{-1} and odds of 1075 compared to the base model, and (II) N discrete positive jumps in ɛp with very similar odds to the linear ɛp drift model. The physical mechanism explaining this behaviour is unclear, but the observation could provide a crucial probe of the interior physics of neutron stars. We also place an upper bound on the rate at which the precessional motion is damped, and translate this into a bound on a dissipative mutual friction-type coupling between the star's crust and core.

Spin precession in a black hole and naked singularity spacetimes

NASA Astrophysics Data System (ADS)

Chakraborty, Chandrachur; Kocherlakota, Prashant; Joshi, Pankaj S.

2017-02-01

We propose here a specific criterion to address the existence or otherwise of Kerr naked singularities, in terms of the precession of the spin of a test gyroscope due to the frame dragging by the central spinning body. We show that there is indeed an important characteristic difference in the behavior of gyro spin precession frequency in the limit of approach to these compact objects, and this can be used, in principle, to differentiate the naked singularity from a black hole. Specifically, if gyroscopes are fixed all along the polar axis up to the horizon of a Kerr black hole, the precession frequency becomes arbitrarily high, blowing up as the event horizon is approached. On the other hand, in the case of naked singularity, this frequency remains always finite and well behaved. Interestingly, this behavior is intimately related to and is governed by the geometry of the ergoregion in each of these cases, which we analyze here. One intriguing behavior that emerges is, in the Kerr naked singularity case, the Lense-Thirring precession frequency (ΩLT ) of the gyroscope due to frame-dragging effect decreases as (ΩLT∝r ) after reaching a maximum, in the limit of r =0 , as opposed to r-3 dependence in all other known astrophysical cases.

The Apparently Decaying Orbit of WASP-12b

NASA Astrophysics Data System (ADS)

Patra, Kishore C.; Winn, Joshua N.; Holman, Matthew J.; Yu, Liang; Deming, Drake; Dai, Fei

2017-07-01

We present new transit and occultation times for the hot Jupiter WASP-12b. The data are compatible with a constant period derivative: \\dot{P}=-29+/- 3 ms yr-1 and P/\\dot{P}=3.2 {Myr}. However, it is difficult to tell whether we have observed orbital decay or a portion of a 14-year apsidal precession cycle. If interpreted as decay, the star’s tidal quality parameter {Q}\\star is about 2× {10}5. If interpreted as precession, the planet’s Love number is 0.44 ± 0.10. Orbital decay appears to be the more parsimonious model: it is favored by {{Δ }}{χ }2=5.5 despite having two fewer free parameters than the precession model. The decay model implies that WASP-12 was discovered within the final ˜0.2% of its existence, which is an unlikely coincidence but harmonizes with independent evidence that the planet is nearing disruption. Precession does not invoke any temporal coincidence, but it does require some mechanism to maintain an eccentricity of ≈ 0.002 in the face of rapid tidal circularization. To distinguish unequivocally between decay and precession will probably require a few more years of monitoring. Particularly helpful will be occultation timing in 2019 and thereafter.

Long-term evolution of orbits about a precessing oblate planet: 3. A semianalytical and a purely numerical approach

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 Goldreich (1965) for the case of uniform precession and a low initial inclination. However, near-polar initial inclinations may exhibit considerable variations for up to ±10 deg in magnitude. This result is accentuated when the obliquity is large. Nevertheless, the analysis confirms that an oblate planet can, indeed, afford large variations of the equinoctial precession over hundreds of millions of years, without repelling its near-equatorial satellites away from the equator of date: the satellite inclination oscillates but does not show a secular increase. Nor does it show secular decrease, a fact that is relevant to the discussion of the possibility of high-inclination capture of Phobos and Deimos.

Observation of the Leggett-Rice Effect in a Unitary Fermi Gas

NASA Astrophysics Data System (ADS)

Trotzky, S.; Beattie, S.; Luciuk, C.; Smale, S.; Bardon, A. B.; Enss, T.; Taylor, E.; Zhang, S.; Thywissen, J. H.

2015-01-01

We observe that the diffusive spin current in a strongly interacting degenerate Fermi gas of 40K precesses about the local magnetization. As predicted by Leggett and Rice, precession is observed both in the Ramsey phase of a spin-echo sequence, and in the nonlinearity of the magnetization decay. At unitarity, we measure a Leggett-Rice parameter γ =1.08 (9 ) and a bare transverse spin diffusivity D0⊥=2.3 (4 )ℏ/m for a normal-state gas initialized with full polarization and at one-fifth of the Fermi temperature, where m is the atomic mass. One might expect γ =0 at unitarity, where two-body scattering is purely dissipative. We observe γ →0 as temperature is increased towards the Fermi temperature, consistent with calculations that show the degenerate Fermi sea restores a nonzero γ . Tuning the scattering length a , we find that a sign change in γ occurs in the range 0 <(kFa )-1≲1.3 , where kF is the Fermi momentum. We discuss how γ reveals the effective interaction strength of the gas, such that the sign change in γ indicates a switching of branch between a repulsive and an attractive Fermi gas.

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

Ghamarian, I.; Samani, P.; Rohrer, G. S.

Grain boundary engineering and other fundamental materials science problems (e.g., phase transformations and physical properties) require an improvement in the understanding of the type and population of grain boundaries in a given system – yet, databases are limited in number and spare in detail, including for hcp crystals such as zirconium. One way to rapidly obtain databases to analyze is to use small-grained materials and high spatial resolution orientation microscopy techniques, such as ASTAR™/precession electron diffraction. To demonstrate this, a study of grain boundary character distributions was conducted for α-zirconium deposited at room temperature on fused silica substrates using physicalmore » vapor deposition. The orientation maps of the nanocrystalline thin films were acquired by the ASTARα/precession electron diffraction technique, a new transmission electron microscope based orientation microscopy method. The reconstructed grain boundaries were classified as pure tilt, pure twist, 180°-twist and 180°-tilt grain boundaries based on the distribution of grain boundary planes with respect to the angle/axis of misorientation associated with grain boundaries. The results of the current study were compared to the results of a similar study on α-titanium and the molecular dynamics results of grain boundary energy for α-titanium.« less

MR Fingerprinting Using Fast Imaging with Steady State Precession (FISP) with Spiral Readout

PubMed Central

Jiang, Yun; Ma, Dan; Seiberlich, Nicole; Gulani, Vikas; Griswold, Mark A.

2015-01-01

Purpose This study explores the possibility of using gradient echo based sequences other than bSSFP in the magnetic resonance fingerprinting (MRF) framework to quantify the relaxation parameters. Methods An MRF method based on a fast imaging with steady state precession (FISP) sequence structure is presented. A dictionary containing possible signal evolutions with physiological range of T1 and T2 was created using the extended phase graph (EPG) formalism according to the acquisition parameters. The proposed method was evaluated in a phantom and a human brain. T1, T2 and proton density were quantified directly from the undersampled data by the pattern recognition algorithm. Results T1 and T2 values from the phantom demonstrate that the results of MRF FISP are in good agreement with the traditional gold-standard methods. T1 and T2 values in brain are within the range of previously reported values. Conclusion MRF FISP enables a fast and accurate quantification of the relaxation parameters, while is immune to the banding artifact of bSSFP due to B0 inhomogeneities, which could improve the ability to use MRF for applications beyond brain imaging. PMID:25491018

Accuracy of Estimating Highly Eccentric Binary Black Hole Parameters with Gravitational-wave Detections

NASA Astrophysics Data System (ADS)

Gondán, László; Kocsis, Bence; Raffai, Péter; Frei, Zsolt

2018-03-01

Mergers of stellar-mass black holes on highly eccentric orbits are among the targets for ground-based gravitational-wave detectors, including LIGO, VIRGO, and KAGRA. These sources may commonly form through gravitational-wave emission in high-velocity dispersion systems or through the secular Kozai–Lidov mechanism in triple systems. Gravitational waves carry information about the binaries’ orbital parameters and source location. Using the Fisher matrix technique, we determine the measurement accuracy with which the LIGO–VIRGO–KAGRA network could measure the source parameters of eccentric binaries using a matched filtering search of the repeated burst and eccentric inspiral phases of the waveform. We account for general relativistic precession and the evolution of the orbital eccentricity and frequency during the inspiral. We find that the signal-to-noise ratio and the parameter measurement accuracy may be significantly higher for eccentric sources than for circular sources. This increase is sensitive to the initial pericenter distance, the initial eccentricity, and the component masses. For instance, compared to a 30 {M}ȯ –30 {M}ȯ non-spinning circular binary, the chirp mass and sky-localization accuracy can improve by a factor of ∼129 (38) and ∼2 (11) for an initially highly eccentric binary assuming an initial pericenter distance of 20 M tot (10 M tot).

Elastic continuum theory: towards understanding of the twist-bend nematic phases.

PubMed

Barbero, G; Evangelista, L R; Rosseto, M P; Zola, R S; Lelidis, I

2015-09-01

The twist-bend nematic phase, N_{TB}, may be viewed as a heliconical molecular arrangement in which the director n precesses uniformly about an extra director field, t. It corresponds to a nematic ground state exhibiting nanoscale periodic modulation. To demonstrate the stability of this phase from the elastic point of view, a natural extension of the Frank elastic energy density is proposed. The elastic energy density is built in terms of the elements of symmetry of the new phase in which intervene the components of these director fields together with the usual Cartesian tensors. It is shown that the ground state corresponds to a deformed state for which K_{22}>K_{33}. In the framework of the model, the phase transition between the usual and the twist-bend nematic phase is of second order with a finite wave vector. The model does not require a negative K_{33} in agreement with recent experimental data that yield K_{33}>0. A threshold is predicted for the molecular twist power below which no transition to a twist-bend nematic may occur.

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.

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.

Behavior of a test gyroscope moving towards a rotating traversable wormhole

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

Chakraborty, Chandrachur; Pradhan, Parthapratim, E-mail: chandrachur.chakraborty@tifr.res.in, E-mail: pppradhan77@gmail.com

2017-03-01

The geodesic structure of the Teo wormhole is briefly discussed and some observables are derived that promise to be of use in detecting a rotating traversable wormhole indirectly, if it does exist. We also deduce the exact Lense-Thirring (LT) precession frequency of a test gyroscope moving toward a rotating traversable Teo wormhole. The precession frequency diverges on the ergoregion, a behavior intimately related to and governed by the geometry of the ergoregion, analogous to the situation in a Kerr spacetime. Interestingly, it turns out that here the LT precession is inversely proportional to the angular momentum ( a ) ofmore » the wormhole along the pole and around it in the strong gravity regime, a behavior contrasting with its direct variation with a in the case of other compact objects. In fact, divergence of LT precession inside the ergoregion can also be avoided if the gyro moves with a non-zero angular velocity in a certain range. As a result, the spin precession frequency of the gyro can be made finite throughout its whole path, even very close to the throat, during its travel to the wormhole. Furthermore, it is evident from our formulation that this spin precession not only arises due to curvature or rotation of the spacetime but also due to the non-zero angular velocity of the spin when it does not move along a geodesic in the strong gravity regime. If in the future, interstellar travel indeed becomes possible through a wormhole or at least in its vicinity, our results would prove useful in determining the behavior of a test gyroscope which is known to serve as a fundamental navigation device.« less

Temporal and Rate Coding for Discrete Event Sequences in the Hippocampus.

PubMed

Terada, Satoshi; Sakurai, Yoshio; Nakahara, Hiroyuki; Fujisawa, Shigeyoshi

2017-06-21

Although the hippocampus is critical to episodic memory, neuronal representations supporting this role, especially relating to nonspatial information, remain elusive. Here, we investigated rate and temporal coding of hippocampal CA1 neurons in rats performing a cue-combination task that requires the integration of sequentially provided sound and odor cues. The majority of CA1 neurons displayed sensory cue-, combination-, or choice-specific (simply, "event"-specific) elevated discharge activities, which were sustained throughout the event period. These event cells underwent transient theta phase precession at event onset, followed by sustained phase locking to the early theta phases. As a result of this unique single neuron behavior, the theta sequences of CA1 cell assemblies of the event sequences had discrete representations. These results help to update the conceptual framework for space encoding toward a more general model of episodic event representations in the hippocampus. Copyright © 2017 Elsevier Inc. All rights reserved.

Simulation of kinematics of SS 433 radio jets that interact with the ambient medium

NASA Astrophysics Data System (ADS)

Panferov, A.

2014-02-01

Context. The mildly relativistic jets of SS 433 are believed to inflate the surrounding supernova remnant W 50, possibly depositing more than 99% of their kinetic energy in the remnant expansion. Where and how this transformation of the energy occurs is as yet unknown. We can learn from this that the jets decelerate and that this deceleration is non-dissipative. Aims: We uncover the deviation of the arcsecond-scale precessing radio jets of SS 433 from the ballistic locus described by the kinematic model as a signature of the dynamics issuing from the interaction of the jets with the ambient medium. Methods: To do this, we simulated the kinematics of these jets, taking into account the ram pressure on the jets, which we estimated from the profile of brightness of synchrotron radiation along the radio jets, assuming pressure balance in the jets. Results: We found that to fit an observable locus in all scales the radio jets need to be decelerated and twisted in addition to the precession torsion, mostly within the first one-fifth of the precession period, and subsequently they extend in a way that imitates ballistic jets. This jet kinematics implies a smaller distance to SS 433 than the currently accepted 5.5 kpc. The physical parameters of the jet model, which links jets dynamics with radiation, are physically reliable and characteristic for the SS 433 jets. The model proposes that beyond the radio-brightening zone, the jet clouds expand because they are in pressure balance with the intercloud medium, and heat up with distance according to the law T = 2 × 104(r/1015 cm)1.5 K. Conclusions: This model naturally explains and agrees with, the observed properties of the radio jets: a) the shock-pressed morphology; b) the brightness profile; c) the ~10% deflections of the jet kinematics from the standard kinematic model - a magnitude of the jet speed decrement in our simulation; d) the precession-phase deviations from the standard kinematic model predictions; e) the dichotomy of the distances to the object, 4.8 kpc vs. 5.5 kpc, which are determined on the basis of the jet kinematics on scales of sub-arcsecond and several arcseconds, respectively; and f) the reheating on arcsecond scales.

Black Hole with Wobbling Disk Artist Concept

NASA Image and Video Library

2016-07-12

This artist's impression depicts the accretion disc surrounding a black hole, in which the inner region of the disc precesses. "Precession" means that the orbit of material surrounding the black hole changes orientation around the central object. In these three views, the precessing inner disc shines high-energy radiation that strikes the matter in the surrounding accretion disc. This causes the iron atoms in that disc to emit X-rays, depicted as the glow on the accretion disc to the right (in view a), to the front (in view b) and to the left (in view c) (see Figure 1). In a study published in July 2016, astronomers used data from ESA's XMM-Newton X-ray Observatory and NASA's NuSTAR telescope to measure this "wobble" in X-ray emission from excited iron atoms. Scientists interpreted this as evidence for the Lense-Thirring effect -- a name for the precession phenomenon -- in the strong gravitational field of a black hole. http://photojournal.jpl.nasa.gov/catalog/PIA20697

On HPM approximation for the perihelion precession angle in general relativity

NASA Astrophysics Data System (ADS)

Shchigolev, Victor; Bezbatko, Dmitrii

2017-03-01

In this paper, the homotopy perturbation method (HPM) is applied for calculating the perihelion precession angle of planetary orbits in General Relativity. The HPM is quite efficient and is practically well suited for use in many astrophysical and cosmological problems. For our purpose, we applied HPM to the approximate solutions for the orbits in order to calculate the perihelion shift. On the basis of the main idea of HPM, we construct the appropriate homotopy that leads to the problem of solving the set of linear algebraic equations. As a result, we obtain a simple formula for the angle of precession avoiding any restrictions on the smallness of physical parameters. First of all, we consider the simple examples of the Schwarzschild metric and the Reissner - Nordström spacetime of a charged star for which the approximate geodesics solutions are known. Furthermore, the implementation of HPM has allowed us to readily obtain the precession angle for the orbits in the gravitational field of Kiselev black hole.

Obliquity, precession rate, and nutation coefficients for a set of 100 asteroids

NASA Astrophysics Data System (ADS)

Lhotka, C.; Souchay, J.; Shahsavari, A.

2013-08-01

Context. Thanks to various space missions and the progress of ground-based observational techniques, the knowledge of asteroids has considerably increased in the recent years. Aims: Due to this increasing database that accompanies this evolution, we compute for a set of 100 asteroids their rotational parameters: the moments of inertia along the principal axes of the object, the obliquity of the axis of rotation with respect to the orbital plane, the precession rates, and the nutation coefficients. Methods: We select 100 asteroids for which the parameters for the study are well-known from observations or space missions. For each asteroid, we determine the moments of inertia, assuming an ellipsoidal shape. We calculate their obliquity from their orbit (instead of the ecliptic) and the orientation of the spin-pole. Finally, we calculate the precession rates and the largest nutation components. The number of asteroids concerned leads to some statistical studies of the output. Results: We provide a table of rotational parameters for our set of asteroids. The table includes the obliquity, their axes ratio, their dynamical ellipticity Hd, and the scaling factor K. We compute the precession rate ψ˙ and the leading nutation coefficients Δψ and Δɛ. We observe similar characteristics, as observed by previous authors that is, a significantly larger number of asteroids rotates in the prograde mode (≈ 60%) than in the retrograde one with a bimodal distribution. In particular, there is a deficiency of objects with a polar axis close to the orbit. The precession rates have a mean absolute value of 18″/y, and the leading nutation coefficients have an average absolute amplitude of 5.7″ for Δψ and 5.2″ for Δɛ. At last, we identify and characterize some cases with large precession rates, as seen in 25143 Itokawa, with has a precession rate of about - 475''/y. Tables 1 and 2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/556/A8

Phase measurement for driven spin oscillations in a storage ring

NASA Astrophysics Data System (ADS)

Hempelmann, N.; Hejny, V.; Pretz, J.; Soltner, H.; Augustyniak, W.; Bagdasarian, Z.; Bai, M.; Barion, L.; Berz, M.; Chekmenev, S.; Ciullo, G.; Dymov, S.; Eversmann, D.; Gaisser, M.; Gebel, R.; Grigoryev, K.; Grzonka, D.; Guidoboni, G.; Heberling, D.; Hetzel, J.; Hinder, F.; Kacharava, A.; Kamerdzhiev, V.; Keshelashvili, I.; Koop, I.; Kulikov, A.; Lehrach, A.; Lenisa, P.; Lomidze, N.; Lorentz, B.; Maanen, P.; Macharashvili, G.; Magiera, A.; Mchedlishvili, D.; Mey, S.; Müller, F.; Nass, A.; Nikolaev, N. N.; Nioradze, M.; Pesce, A.; Prasuhn, D.; Rathmann, F.; Rosenthal, M.; Saleev, A.; Schmidt, V.; Semertzidis, Y.; Senichev, Y.; Shmakova, V.; Silenko, A.; Slim, J.; Stahl, A.; Stassen, R.; Stephenson, E.; Stockhorst, H.; Ströher, H.; Tabidze, M.; Tagliente, G.; Talman, R.; Thörngren Engblom, P.; Trinkel, F.; Uzikov, Yu.; Valdau, Yu.; Valetov, E.; Vassiliev, A.; Weidemann, C.; Wrońska, A.; Wüstner, P.; Zuprański, P.; Żurek, M.; JEDI Collaboration

2018-04-01

This paper reports the first simultaneous measurement of the horizontal and vertical components of the polarization vector in a storage ring under the influence of a radio frequency (rf) solenoid. The experiments were performed at the Cooler Synchrotron COSY in Jülich using a vector polarized, bunched 0.97 GeV /c deuteron beam. Using the new spin feedback system, we set the initial phase difference between the solenoid field and the precession of the polarization vector to a predefined value. The feedback system was then switched off, allowing the phase difference to change over time, and the solenoid was switched on to rotate the polarization vector. We observed an oscillation of the vertical polarization component and the phase difference. The oscillations can be described using an analytical model. The results of this experiment also apply to other rf devices with horizontal magnetic fields, such as Wien filters. The precise manipulation of particle spins in storage rings is a prerequisite for measuring the electric dipole moment (EDM) of charged particles.

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.

Optimal three-dimensional reusable tug trajectories for planetary missions including correction for nodal precession

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.

Resonant obliquity of Mars?. [climate driven by spin axis and orbit plane precession caused oscillations

NASA Technical Reports Server (NTRS)

Ward, William R.; Rudy, Donald J.

1991-01-01

The large-scale oscillations generated by the obliquity of Mars through spin-axis and orbit-plane precessions constitute basic climate system drivers with periodicities of 100,000 yrs in differential spin axis-orbit precession rates and of over 1 million yrs in amplitude modulations due to orbital-inclination changes. Attention is presently given to a third time-scale for climate change, which involves a possible spin-spin resonance and whose mechanism operates on a 10-million-yr time-scale: this effect implies an average obliquity increase for Mars of 15 deg only 5 million yrs ago, with important climatic consequences.

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.

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 solstice), precipitation is up to 300 mm/month higher compared to precession minima during the wet season (September - May). During the dry season (June-July-August), the climate is up to 7°C colder during a precession maxima compared to a precession minima. Obliquity doesn't show a significant influence on the climate of the tropical Euramerican continent. However, the imprint of obliquity on the polar climates is extensive with up to 6°C temperature-differences between obliquity maxima and minima at both poles.

Pseudo Steady-State Free Precession for MR-Fingerprinting.

PubMed

Assländer, Jakob; Glaser, Steffen J; Hennig, Jürgen

2017-03-01

This article discusses the signal behavior in the case the flip angle in steady-state free precession sequences is continuously varied as suggested for MR-fingerprinting sequences. Flip angle variations prevent the establishment of a steady state and introduce instabilities regarding to magnetic field inhomogeneities and intravoxel dephasing. We show how a pseudo steady state can be achieved, which restores the spin echo nature of steady-state free precession. Based on geometrical considerations, relationships between the flip angle, repetition and echo time are derived that suffice to the establishment of a pseudo steady state. The theory is tested with Bloch simulations as well as phantom and in vivo experiments. A typical steady-state free precession passband can be restored with the proposed conditions. The stability of the pseudo steady state is demonstrated by comparing the evolution of the signal of a single isochromat to one resulting from a spin ensemble. As confirmed by experiments, magnetization in a pseudo steady state can be described with fewer degrees of freedom compared to the original fingerprinting and the pseudo steady state results in more reliable parameter maps. The proposed conditions restore the spin-echo-like signal behavior typical for steady-state free precession in fingerprinting sequences, making this approach more robust to B 0 variations. Magn Reson Med 77:1151-1161, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

How do accretion discs break?

NASA Astrophysics Data System (ADS)

Dogan, Suzan

2016-07-01

Accretion discs are common in binary systems, and they are often found to be misaligned with respect to the binary orbit. The gravitational torque from a companion induces nodal precession in misaligned disc orbits. In this study, we first calculate whether this precession is strong enough to overcome the internal disc torques communicating angular momentum. We compare the disc precession torque with the disc viscous torque to determine whether the disc should warp or break. For typical parameters precession wins: the disc breaks into distinct planes that precess effectively independently. To check our analytical findings, we perform 3D hydrodynamical numerical simulations using the PHANTOM smoothed particle hydrodynamics code, and confirm that disc breaking is widespread and enhances accretion on to the central object. For some inclinations, the disc goes through strong Kozai cycles. Disc breaking promotes markedly enhanced and variable accretion and potentially produces high-energy particles or radiation through shocks. This would have significant implications for all binary systems: e.g. accretion outbursts in X-ray binaries and fuelling supermassive black hole (SMBH) binaries. The behaviour we have discussed in this work is relevant to a variety of astrophysical systems, for example X-ray binaries, where the disc plane may be tilted by radiation warping, SMBH binaries, where accretion of misaligned gas can create effectively random inclinations and protostellar binaries, where a disc may be misaligned by a variety of effects such as binary capture/exchange, accretion after binary formation.

Spin-orbit torque-driven magnetization switching in 2D-topological insulator heterostructure

NASA Astrophysics Data System (ADS)

Soleimani, Maryam; Jalili, Seifollah; Mahfouzi, Farzad; Kioussis, Nicholas

2017-02-01

Charge pumping and spin-orbit torque (SOT) are two reciprocal phenomena widely studied in ferromagnet (FM)/topological insulator (TI) heterostructures. However, the SOT and its corresponding switching phase diagram for a FM island in proximity to a two-dimensional topological insulator (2DTI) has not been explored yet. We have addressed these features, using the recently developed adiabatic expansion of time-dependent nonequilibrium Green's function (NEGF) in the presence of both precessing magnetization and bias voltage. We have calculated the angular and spatial dependence of different components of the SOT on the FM island. We determined the switching phase diagram of the FM for different orientations of the easy axis. The results can be used as a guideline for the future experiments on such systems.

Phased array ghost elimination (PAGE) for segmented SSFP imaging with interrupted steady-state.

PubMed

Kellman, Peter; Guttman, Michael A; Herzka, Daniel A; McVeigh, Elliot R

2002-12-01

Steady-state free precession (SSFP) has recently proven to be valuable for cardiac imaging due to its high signal-to-noise ratio and blood-myocardium contrast. Data acquired using ECG-triggered, segmented sequences during the approach to steady-state, or return to steady-state after interruption, may have ghost artifacts due to periodic k-space distortion. Schemes involving several preparatory RF pulses have been proposed to restore steady-state, but these consume imaging time during early systole. Alternatively, the phased-array ghost elimination (PAGE) method may be used to remove ghost artifacts from the first several frames. PAGE was demonstrated for cardiac cine SSFP imaging with interrupted steady-state using a simple alpha/2 magnetization preparation and storage scheme and a spatial tagging preparation.

Horizontal Axis Levitron--A Physics Demonstration

ERIC Educational Resources Information Center

Michaelis, Max M.

2014-01-01

After a brief history of the Levitron, the first horizontal axis Levitron is reported. Because it is easy to operate, it lends itself to educational physics experiments and analogies. Precession and nutation are visualized by reflecting the beam from a laser pointer off the "spignet". Precession is fundamental to nuclear magnetic…

MR fingerprinting Deep RecOnstruction NEtwork (DRONE).

PubMed

Cohen, Ouri; Zhu, Bo; Rosen, Matthew S

2018-09-01

Demonstrate a novel fast method for reconstruction of multi-dimensional MR fingerprinting (MRF) data using deep learning methods. A neural network (NN) is defined using the TensorFlow framework and trained on simulated MRF data computed with the extended phase graph formalism. The NN reconstruction accuracy for noiseless and noisy data is compared to conventional MRF template matching as a function of training data size and is quantified in simulated numerical brain phantom data and International Society for Magnetic Resonance in Medicine/National Institute of Standards and Technology phantom data measured on 1.5T and 3T scanners with an optimized MRF EPI and MRF fast imaging with steady state precession (FISP) sequences with spiral readout. The utility of the method is demonstrated in a healthy subject in vivo at 1.5T. Network training required 10 to 74 minutes; once trained, data reconstruction required approximately 10 ms for the MRF EPI and 76 ms for the MRF FISP sequence. Reconstruction of simulated, noiseless brain data using the NN resulted in a RMS error (RMSE) of 2.6 ms for T 1 and 1.9 ms for T 2 . The reconstruction error in the presence of noise was less than 10% for both T 1 and T 2 for SNR greater than 25 dB. Phantom measurements yielded good agreement (R 2  = 0.99/0.99 for MRF EPI T 1 /T 2 and 0.94/0.98 for MRF FISP T 1 /T 2 ) between the T 1 and T 2 estimated by the NN and reference values from the International Society for Magnetic Resonance in Medicine/National Institute of Standards and Technology phantom. Reconstruction of MRF data with a NN is accurate, 300- to 5000-fold faster, and more robust to noise and dictionary undersampling than conventional MRF dictionary-matching. © 2018 International Society for Magnetic Resonance in Medicine.

Atomic structure solution of the complex quasicrystal approximant Al77Rh15Ru8 from electron diffraction data.

PubMed

Samuha, Shmuel; Mugnaioli, Enrico; Grushko, Benjamin; Kolb, Ute; Meshi, Louisa

2014-12-01

The crystal structure of the novel Al77Rh15Ru8 phase (which is an approximant of decagonal quasicrystals) was determined using modern direct methods (MDM) applied to automated electron diffraction tomography (ADT) data. The Al77Rh15Ru8 E-phase is orthorhombic [Pbma, a = 23.40 (5), b = 16.20 (4) and c = 20.00 (5) Å] and has one of the most complicated intermetallic structures solved solely by electron diffraction methods. Its structural model consists of 78 unique atomic positions in the unit cell (19 Rh/Ru and 59 Al). Precession electron diffraction (PED) patterns and high-resolution electron microscopy (HRTEM) images were used for the validation of the proposed atomic model. The structure of the E-phase is described using hierarchical packing of polyhedra and a single type of tiling in the form of a parallelogram. Based on this description, the structure of the E-phase is compared with that of the ε6-phase formed in Al-Rh-Ru at close compositions.

Manifestations of geometric phases in a proton electric-dipole-moment experiment in an all-electric storage ring

NASA Astrophysics Data System (ADS)

Silenko, Alexander J.

2017-12-01

We consider a proton electric-dipole-moment experiment in an all-electric storage ring when the spin is frozen and local longitudinal and vertical electric fields alternate. In this experiment, the geometric (Berry) phases are very important. Due to the these phases, the spin rotates about the radial axis. The corresponding systematic error is rather important while it can be canceled with clockwise and counterclockwise beams. The geometric phases also lead to the spin rotation about the radial axis. This effect can be canceled with clockwise and counterclockwise beams as well. The sign of the azimuthal component of the angular velocity of the spin precession depends on the starting point where the spin orientation is perfect. The radial component of this quantity keeps its value and sign for each starting point. When the longitudinal and vertical electric fields are joined in the same sections without any alternation, the systematic error due to the geometric phases does not appear but another systematic effect of the spin rotation about the azimuthal axis takes place. It has opposite signs for clockwise and counterclockwise beams.

Observation of spin superfluidity: YIG magnetic films and beyond

NASA Astrophysics Data System (ADS)

Sonin, Edouard

2018-03-01

From topology of the order parameter of the magnon condensate observed in yttrium-iron-garnet (YIG) magnetic films one must not expect energetic barriers making spin supercurrents metastable. But we show that some barriers of dynamical origin are possible nevertheless until the gradient of the phase (angle of spin precession) does not exceed the critical value (analog of the Landau critical velocity in superfluids). On the other hand, recently published claims of experimental detection of spin superfluidity in YIG films and antiferromagnets are not justified, and spin superfluidity in magnetically ordered solids has not yet been experimentally confirmed.

Quantum Spin Stabilized Magnetic Levitation

NASA Astrophysics Data System (ADS)

Rusconi, C. C.; Pöchhacker, V.; Kustura, K.; Cirac, J. I.; Romero-Isart, O.

2017-10-01

We theoretically show that, despite Earnshaw's theorem, a nonrotating single magnetic domain nanoparticle can be stably levitated in an external static magnetic field. The stabilization relies on the quantum spin origin of magnetization, namely, the gyromagnetic effect. We predict the existence of two stable phases related to the Einstein-de Haas effect and the Larmor precession. At a stable point, we derive a quadratic Hamiltonian that describes the quantum fluctuations of the degrees of freedom of the system. We show that, in the absence of thermal fluctuations, the quantum state of the nanomagnet at the equilibrium point contains entanglement and squeezing.

Quantum Spin Stabilized Magnetic Levitation.

PubMed

Rusconi, C C; Pöchhacker, V; Kustura, K; Cirac, J I; Romero-Isart, O

2017-10-20

We theoretically show that, despite Earnshaw's theorem, a nonrotating single magnetic domain nanoparticle can be stably levitated in an external static magnetic field. The stabilization relies on the quantum spin origin of magnetization, namely, the gyromagnetic effect. We predict the existence of two stable phases related to the Einstein-de Haas effect and the Larmor precession. At a stable point, we derive a quadratic Hamiltonian that describes the quantum fluctuations of the degrees of freedom of the system. We show that, in the absence of thermal fluctuations, the quantum state of the nanomagnet at the equilibrium point contains entanglement and squeezing.

Dynamics of a spherical tippe top

NASA Astrophysics Data System (ADS)

Cross, Rod

2018-05-01

Experimental and theoretical results are presented concerning the inversion of a spherical tippe top. It was found that the top rises quickly while it is sliding and then more slowly when it starts rolling, in a manner similar to that observed previously with a spinning egg. As the top rises it rotates about the horizontal Y axis, an effect that is closely analogous to rotation of the top about the vertical Z axis. Both effects can be described in terms of precession about the respective axes. Steady precession about the Z axis arises from the normal reaction force in the Z direction, while precession about the Y axis arises from the friction force in the Y direction.

Linear frictional forces cause orbits to neither circularize nor precess

NASA Astrophysics Data System (ADS)

Hamilton, B.; Crescimanno, M.

2008-06-01

For the undamped Kepler potential the lack of precession has historically been understood in terms of the Runge-Lenz symmetry. For the damped Kepler problem this result may be understood in terms of the generalization of Poisson structure to damped systems suggested recently by Tarasov (2005 J. Phys. A: Math. Gen. 38 2145). In this generalized algebraic structure the orbit-averaged Runge-Lenz vector remains a constant in the linearly damped Kepler problem to leading order in the damping coefficient. Beyond Kepler, we prove that, for any potential proportional to a power of the radius, the orbit shape and precession angle remain constant to leading order in the linear friction coefficient.

A Mechanical Principle for Acquisition of useful Power on a Celestial Body Through Utilisation of its Planetary Precession

NASA Astrophysics Data System (ADS)

Vulkov, K.

In consequence of the phenomenon of planetary precession there emerges a possibility for acquisition of power through utilisation of the rotary motions in the universe. The idea is to acquire useful power on the working shaft of a properly designed machine installed on a celestial body (planet), at the expense of the motional energy of the latter. Strange as it may appear, this is possible if only the regulation of the machine be brought in line with the parameters of the precession. The principle of action of such a planetary engine, including an energy balance, is put forward in the present paper.

Nonlinear dynamo action in a precessing cylindrical container.

PubMed

Nore, C; Léorat, J; Guermond, J-L; Luddens, F

2011-07-01

It is numerically demonstrated by means of a magnetohydrodynamics code that precession can trigger the dynamo effect in a cylindrical container. When the Reynolds number, based on the radius of the cylinder and its angular velocity, increases, the flow, which is initially centrosymmetric, loses its stability and bifurcates to a quasiperiodic motion. This unsteady and asymmetric flow is shown to be capable of sustaining dynamo action in the linear and nonlinear regimes. The magnetic field thus generated is unsteady and quadrupolar. These numerical evidences of dynamo action in a precessing cylindrical container may be useful for an experiment now planned at the Dresden sodium facility for dynamo and thermohydraulic studies in Germany.

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…

METHODOLOGICAL NOTES: Rotation of the swing plane of Foucault's pendulum and Thomas spin precession: two sides of one coin

NASA Astrophysics Data System (ADS)

Krivoruchenko, Mikhail I.

2009-08-01

Using elementary geometric tools, we apply essentially the same methods to derive expressions for the rotation angle of the swing plane of Foucault's pendulum and the rotation angle of the spin of a relativistic particle moving in a circular orbit (the Thomas precession effect).

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.

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)

Estimate of procession and polar motion errors from planetary encounter station location solutions

NASA Technical Reports Server (NTRS)

Pease, G. E.

1978-01-01

Jet Propulsion Laboratory Deep Space Station (DSS) location solutions based on two JPL planetary ephemerides, DE 84 and DE 96, at eight planetary encounters were used to obtain weighted least squares estimates of precession and polar motion errors. The solution for precession error in right ascension yields a value of 0.3 X 10 to the minus 5 power plus or minus 0.8 X 10 to the minus 6 power deg/year. This maps to a right ascension error of 1.3 X 10 to the minus 5 power plus or minus 0.4 X 10 to the minus 5 power deg at the first Voyager 1979 Jupiter encounter if the current JPL DSS location set is used. Solutions for precession and polar motion using station locations based on DE 84 agree well with the solution using station locations referenced to DE 96. The precession solution removes the apparent drift in station longitude and spin axis distance estimates, while the encounter polar motion solutions consistently decrease the scatter in station spin axis distance estimates.

Correcting Concomitant Gradient Distortion in Microtesla Magnetic Resonance Imaging

NASA Astrophysics Data System (ADS)

Myers, Whittier

2005-03-01

Progress in ultra-low field magnetic resonance imaging (MRI) using an untuned gradiometer coupled to a Superconducting Quantum Interference Device (SQUID) has resulted in three-dimensional images with an in-plane resolution of 2 mm. Protons in samples up to 80 mm in size were prepolarized in a 100 mT field, manipulated by ˜100 μT/m gradients for image encoding, and detected by the SQUID in the ˜65 μT precession field. Maxwell's equations prohibit a unidirectional magnetic field gradient. While the additional concomitant gradients can be neglected in high-field MRI, they distort high-resolution images of large samples taken in microtesla precession fields. We propose two methods to mitigate such distortion: raising the precession field during image encoding, and software post-processing. Both approaches are demonstrated using computer simulations and MRI images. Simulations show that the combination of these techniques can correct the concomitant gradient distortion present in a 4-mm resolution image of an object the size of a human brain with a precession field of 50 μT. Supported by USDOE.

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 fully in a major presentation of all the ASCA observations of SS 433.

Understanding the d18O Response to Precession in the South Asian Monsoon Region

NASA Astrophysics Data System (ADS)

Tabor, C. R.; Otto-Bliesner, B. L.; Brady, E. C.; Nusbaumer, J. M.; Zhu, J.; Erb, M. P.

2017-12-01

Speleothem records from the South Asian Monsoon (SAM) region display d18O variability at orbital frequencies. The dominant mode of variability in many of these records reflects cycles of precession. There are several potential explanations for why speleothem records from the SAM region show a strong precession signal, including the amount effect, temperature differences, and circulation changes. Here, we use a version of the Community Earth System Model with water isotope tracking capability to explore the mechanisms responsible for precession driven d18O variability in the SAM region. By using a fully coupled model with idealized orbits and regional isotope tracking techniques, we are able to tease apart the various contributions to the precession driven d18O signal found in the SAM speleothem records. Our preliminary results suggest that neither the amount effect nor temperature differences cause the majority of SAM d18O response to changes in precession. Instead, changes in the relative moisture contributions from different source regions drive much of the d18O variability. During Northern Hemisphere summer at aphelion, much of the SAM precipitation sources from the nearby ocean. The nearby location of these sources limits the amount of rainout that occurs before reaching the SAM region, which results in a relatively enriched precipitation d18O signal. Conversely, during Northern Hemisphere summer at perihelion, a greater portion of the SAM precipitation sources from far away regions such as the Southern Hemisphere and Northern Africa. Water vapor from these sources is more depleted by the time it reaches the SAM region, leading to precipitation relatively depleted in d18O as well. Further, we find that the modeled d18O signals of soil water better match the d18O signals in the SAM speleothems, suggesting that local evaporation also plays an important role.

Modeling of micro thrusters for gravity probe B

NASA Technical Reports Server (NTRS)

Jones, Kenneth M.

1996-01-01

The concept of testing Einstein's general theory of relativity by means of orbiting gyroscopes was first proposed in 1959, which lead to the development of the Gravity Probe B experiment. Einstein's theory concerns the predictions of the relativistic precession of a gyroscope in orbit around earth. According to his theory, there will be two precessions due to the warping of space-time by the earth's gravitational field: the geodetic precession in the plane of the orbit, and the frame-dragging effect, in the direction of earth rotation. For a polar orbit, these components are orthogonal. In order to simplify the measurement of the precessions, Gravity Probe B (GP-B) will be placed in a circular polar orbit at 650 km, for which the predicted precessions will be 6.6 arcsec/year (geodetic) and 42 milli-arcsec/year (frame-dragging). As the gyroscope precesses, the orientation of its spin-axis will be measured with respect to the line-of-sight to Rigel, a star whose proper motion is known to be within the required accuracy. The line-of-sight to Rigel will be established using a telescope, and the orientation of the gyroscope spin axis will be measured using very sensitive SQUID (Superconducting Quantum Interference Device) magnetometers. The four gyroscopes will be coated with niobium. Below 2K, the niobium becomes superconducting and a dipole field will be generated which is precisely aligned with the gyroscope spin-axis. The change in orientation of these fields, as well as the spin-axis, is sensed by the SQUID magnetometers. In order to attain the superconducting temperatures for the gyroscopes and the SQUID's, the experiment package will be housed in a dewar filled with liquid helium. The helium flow through a GP-B micro thruster and into a vacuum is investigated using the Direct Simulation Monte Carlo method.

Tilting Uranus without a Collision

NASA Astrophysics Data System (ADS)

Rogoszinski, Zeeve; Hamilton, Douglas P.

2016-10-01

The most accepted hypothesis for the origin of Uranus' 98° obliquity is a giant collision during the late stages of planetary accretion. This model requires a single Earth mass object striking Uranus at high latitudes; such events occur with a probability of about 10%. Alternatively, Uranus' obliquity may have arisen from a sequence of smaller impactors which lead to a uniform distribution of obliquities. Here we explore a third model for tilting Uranus using secular spin-orbit resonance theory. We investigate early Solar System configurations in which a secular resonance between Uranus' axial precession frequency and another planet's orbital node precession frequency might occur.Thommes et al. (1999) hypothesized that Uranus and Neptune initially formed between Jupiter and Saturn, and were then kicked outward. In our scenario, Neptune leaves first while Uranus remains behind. As an exterior Neptune slowly migrates outward, it picks up both Uranus and Saturn in spin-orbit resonances (Ward and Hamilton 2004; Hamilton and Ward 2004). Only a distant Neptune has a nodal frequency slow enough to resonate with Uranus' axial precession.This scenario, with diverging orbits, results in resonance capture. As Neptune migrates outward its nodal precession slows. While in resonance, Uranus and Saturn each tilt a bit further, slowing their axial precession rates to continually match Neptune's nodal precession rate. Tilting Uranus to high obliquities takes a few 100 Myrs. This timescale may be too long to hold Uranus captive between Jupiter and Saturn, and we are investigating how to reduce it. We also find that resonance capture is rare if Uranus' initial obliquity is greater than about 10°, as the probability of capture decreases as the planet's initial obliquity increases. We will refine this estimate by quantifying capture statistics, and running accretion simulations to test the likelihood of a low early obliquity. Our preliminary findings show that most assumptions about planetary accretion lead to nearly isotropic obliquity distributions for early Uranus. Thus, the odds of Uranus having an initial low obliquity is also about 10%.

Response of the Asian summer monsoons to idealized precession and obliquity forcing in a set of GCMs

NASA Astrophysics Data System (ADS)

Bosmans, J. H. C.; Erb, M. P.; Dolan, A. M.; Drijfhout, S. S.; Tuenter, E.; Hilgen, F. J.; Edge, D.; Pope, J. O.; Lourens, L. J.

2018-05-01

We examine the response of the Indian and East Asian summer monsoons to separate precession and obliquity forcing, using a set of fully coupled high-resolution models for the first time: EC-Earth, GFDL CM2.1, CESM and HadCM3. We focus on the effect of insolation changes on monsoon precipitation and underlying circulation changes, and find strong model agreement despite a range of model physics, parameterization, and resolution. Our results show increased summer monsoon precipitation at times of increased summer insolation, i.e. minimum precession and maximum obliquity, accompanied by a redistribution of precipitation and convection from ocean to land. Southerly monsoon winds over East Asia are strengthened as a consequence of an intensified land-sea pressure gradient. The response of the Indian summer monsoon is less straightforward. Over south-east Asia low surface pressure is less pronounced and winds over the northern Indian Ocean are directed more westward. An Indian Ocean Dipole pattern emerges, with increased precipitation and convection over the western Indian Ocean. Increased temperatures occur during minimum precession over the Indian Ocean, but not during maximum obliquity when insolation is reduced over the tropics and southern hemisphere during northern hemisphere summer. Evaporation is reduced over the northern Indian Ocean, which together with increased precipitation over the western Indian Ocean dampens the increase of monsoonal precipitation over the continent. The southern tropical Indian Ocean as well as the western tropical Pacific (for precession) act as a moisture source for enhanced monsoonal precipitation. The models are in closest agreement for precession-induced changes, with more model spread for obliquity-induced changes, possibly related to a smaller insolation forcing. Our results indicate that a direct response of the Indian and East Asian summer monsoons to insolation forcing is possible, in line with speleothem records but in contrast to what most marine proxy climate records suggest.

The Obliquities of the Giant Planets

NASA Astrophysics Data System (ADS)

Hamilton, D. P.; Ward, Wm. R.

2002-09-01

Jupiter has by far the smallest obliquity ( ~ 3o) of the planets (not counting tidally de-spun Mercury and Venus) which may be reflective of its formation by hydrodynamic gas flow rather than stochastic impacts. Saturn's obliquity ( ~ 26o), however, seems to belie this simple formation picture. But since the spin angular momentum of any planet is much smaller than its orbital angular momentum, post-formation obliquity can be strongly modified by passing through secular spin-orbit resonances, i.e., when the spin axis precession rate of the planet matches one of the frequencies describing the precession of the orbit plane. Spin axis precession is due to the solar torque on both the oblate figure of the planet and any orbiting satellites. In the case of Jupiter, the torque on the Galilean satellites is the principal cause of its 4.5*105 year precession; Saturn's precession of 1.8*106 years is dominated by Titan. In the past, the planetary spin axis precession rates should have been much faster due to the massive circumplanetary disks from which the current satellites condensed. The regression of the orbital node of a planet is due to the gravitational perturbations of the other planets. Nodal regression is not uniform, but is instead a composite of the planetary system's normal modes. For Jupiter and Saturn, the principal frequency is the nu16, with a period of ~ 49,000 years; the amplitude of this term is I ~ 0o.36 for Jupiter and I ~ 0o.90 for Saturn. In spite of the small amplitudes, slow adiabatic passages through this resonance (due to circumplanetary disk dispersal) could increase planetary obliquities from near zero to ~ [tan1/3 I] ~ 10o. We will discuss scenarios in which giant planet obliquities are affected by this and other resonances, and will use Jupiter's low obliquity to constrain the mass and duration of a satellite precursor disk. DPH acknowledges support from NSF Career Grant AST 9733789 and WRW is grateful to the NASA OSS and PGG programs.

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.

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

Barnes, Jason W.; Van Eyken, Julian C.; Jackson, Brian K.

PTFO 8-8695b represents the first transiting exoplanet candidate orbiting a pre-main-sequence star (van Eyken et al. 2012, ApJ, 755, 42). We find that the unusual lightcurve shapes of PTFO 8-8695 can be explained by transits of a planet across an oblate, gravity-darkened stellar disk. We develop a theoretical framework for understanding precession of a planetary orbit's ascending node for the case when the stellar rotational angular momentum and the planetary orbital angular momentum are comparable in magnitude. We then implement those ideas to simultaneously and self-consistently fit two separate lightcurves observed in 2009 December and 2010 December. Our two self-consistentmore » fits yield M{sub p} = 3.0 M{sub Jup} and M{sub p} = 3.6 M{sub Jup} for assumed stellar masses of M{sub *} = 0.34 M{sub Sun} and M{sub *} = 0.44 M{sub Sun} respectively. The two fits have precession periods of 293 days and 581 days. These mass determinations (consistent with previous upper limits) along with the strength of the gravity-darkened precessing model together validate PTFO 8-8695b as just the second hot Jupiter known to orbit an M-dwarf. Our fits show a high degree of spin-orbit misalignment in the PTFO 8-8695 system: 69 Degree-Sign {+-} 2 Degree-Sign or 73. Degree-Sign 1 {+-} 0. Degree-Sign 5, in the two cases. The large misalignment is consistent with the hypothesis that planets become hot Jupiters with random orbital plane alignments early in a system's lifetime. We predict that as a result of the highly misaligned, precessing system, the transits should disappear for months at a time over the course of the system's precession period. The precessing, gravity-darkened model also predicts other observable effects: changing orbit inclination that could be detected by radial velocity observations, changing stellar inclination that would manifest as varying vsin i, changing projected spin-orbit alignment that could be seen by the Rossiter-McLaughlin effect, changing transit shapes over the course of the precession, and differing lightcurves as a function of wavelength. Our measured planet radii of 1.64 R{sub Jup} and 1.68 R{sub Jup} in each case are consistent with a young, hydrogen-dominated planet that results from a ''hot-start'' formation mechanism.« less

Probable Rotation States of Rocket Bodies in Low Earth Orbit

NASA Astrophysics Data System (ADS)

Ojakangas, G.; Anz-Meador, P.; Cowardin, H.

2012-09-01

In order for Active Debris Removal to be accomplished, it is critically important to understand the probable rotation states of orbiting, spent rocket bodies (RBs). However, rotational dynamics is non-intuitive and misconceptions are common. Determinations of rotation and precession rates from light curves have been published that are inconsistent with the theory presented here. In a state of free precession, the total angular momentum of the object is constant, while kinetic energy decreases due to internal friction, approaching rotation about the axis of maximum inertia. For solid internal friction the timescale is hundreds to thousands of years for quality factors of ~100 and assuming metallic rigidities, but for friction in partially-filled liquid fuel tanks we predict that the preferred rotational state is approached rapidly, within days to months. However, history has shown that theoretical predictions of the timescale have been notoriously inaccurate. In free precession, the 3-1-3 Euler angle rates dphi/dt (precession rate of long axis about fixed angular momentum with cone angle theta) and dpsi/dt (roll rate around long axis) have comparable magnitudes until very close to theta=pi/2, so that otherwise the true rotation period is not simply twice the primary light curve period. Furthermore dtheta/dt, nonzero due to friction, becomes asymptotically smaller as theta=pi/2 is approached, so that theta can linger within several degrees of flat spin for a relatively long time. Such a condition is likely common, and cannot be distinguished from the wobble of a cylinder with a skewed inertia tensor unless the RB has non-axisymmetric reflectivity characteristics. For an RB of known dimensions, a given value of theta fixes the relative values of dpsi/dt and dphi/dt. In forced precession, the angular momentum precesses about a symmetry axis defined by the relevant torque. However, in LEO, only gravity gradient and magnetic eddy current torques are dominant, and these cannot cause precession periods shorter than a week, or more likely, months. Thus forced precession is probably not observable over observation campaigns spanning a few days or less. Spin-orbit resonances are likely for low rotation rates approaching the mean motion, possibly causing large deviations between the symmetry axis and the geocentric direction. An expression for the eddy current torque on an arbitrarily rotating cylinder, hitherto not available in the literature, is presented here. Numerical integrations of the equations of motion for a cylindrical RB in LEO with arbitrary initial conditions and subject to eddy current and gravity gradient torques as well as prescribed internal dissipation are in progress. Acknowledgements: This work was produced under NASA contract NNJ05HI05.

Determination of the five parameter grain boundary character distribution of nanocrystalline alpha-zirconium thin films using transmission electron microscopy

DOE PAGES

Ghamarian, I.; Samani, P.; Rohrer, G. S.; ...

2017-03-24

Grain boundary engineering and other fundamental materials science problems (e.g., phase transformations and physical properties) require an improvement in the understanding of the type and population of grain boundaries in a given system – yet, databases are limited in number and spare in detail, including for hcp crystals such as zirconium. One way to rapidly obtain databases to analyze is to use small-grained materials and high spatial resolution orientation microscopy techniques, such as ASTAR™/precession electron diffraction. To demonstrate this, a study of grain boundary character distributions was conducted for α-zirconium deposited at room temperature on fused silica substrates using physicalmore » vapor deposition. The orientation maps of the nanocrystalline thin films were acquired by the ASTARα/precession electron diffraction technique, a new transmission electron microscope based orientation microscopy method. The reconstructed grain boundaries were classified as pure tilt, pure twist, 180°-twist and 180°-tilt grain boundaries based on the distribution of grain boundary planes with respect to the angle/axis of misorientation associated with grain boundaries. The results of the current study were compared to the results of a similar study on α-titanium and the molecular dynamics results of grain boundary energy for α-titanium.« less

A unified lense-thirring precession model for optical and X-ray quasi-periodic oscillations in black hole binaries

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

Veledina, Alexandra; Poutanen, Juri; Ingram, Adam, E-mail: alexandra.veledina@oulu.fi, E-mail: juri.poutanen@oulu.fi

2013-12-01

Recent observations of accreting black holes reveal the presence of quasi-periodic oscillations (QPO) in the optical power density spectra. The corresponding oscillation periods match those found in X-rays, implying a common origin. Among the numerous suggested X-ray QPO mechanisms, some may also work in the optical. However, their relevance to the broadband—optical through X-ray—spectral properties have not been investigated. For the first time, we discuss the QPO mechanism in the context of the self-consistent spectral model. We propose that the QPOs are produced by Lense-Thirring precession of the hot accretion flow, whose outer parts radiate in optical wavelengths. At themore » same time, its innermost parts are emitting X-rays, which explains the observed connection of QPO periods. We predict that the X-ray and optical QPOs should be either in phase or shifted by half a period, depending on the observer position. We investigate the QPO harmonic content and find that the variability amplitudes at the fundamental frequency are larger in the optical, while the X-rays are expected to have strong harmonics. We then discuss the QPO spectral dependence and compare the expectations to the existing data.« less

Alternating steady state free precession for estimation of current-induced magnetic flux density: A feasibility study.

PubMed

Lee, Hyunyeol; Jeong, Woo Chul; Kim, Hyung Joong; Woo, Eung Je; Park, Jaeseok

2016-05-01

To develop a novel, current-controlled alternating steady-state free precession (SSFP)-based conductivity imaging method and corresponding MR signal models to estimate current-induced magnetic flux density (Bz ) and conductivity distribution. In the proposed method, an SSFP pulse sequence, which is in sync with alternating current pulses, produces dual oscillating steady states while yielding nonlinear relation between signal phase and Bz . A ratiometric signal model between the states was analytically derived using the Bloch equation, wherein Bz was estimated by solving a nonlinear inverse problem for conductivity estimation. A theoretical analysis on the signal-to-noise ratio of Bz was given. Numerical and experimental studies were performed using SSFP-FID and SSFP-ECHO with current pulses positioned either before or after signal encoding to investigate the feasibility of the proposed method in conductivity estimation. Given all SSFP variants herein, SSFP-FID with alternating current pulses applied before signal encoding exhibits the highest Bz signal-to-noise ratio and conductivity contrast. Additionally, compared with conventional conductivity imaging, the proposed method benefits from rapid SSFP acquisition without apparent loss of conductivity contrast. We successfully demonstrated the feasibility of the proposed method in estimating current-induced Bz and conductivity distribution. It can be a promising, rapid imaging strategy for quantitative conductivity imaging. © 2015 Wiley Periodicals, Inc.

Utilization of a balanced steady state free precession signal model for improved fat/water decomposition.

PubMed

Henze Bancroft, Leah C; Strigel, Roberta M; Hernando, Diego; Johnson, Kevin M; Kelcz, Frederick; Kijowski, Richard; Block, Walter F

2016-03-01

Chemical shift based fat/water decomposition methods such as IDEAL are frequently used in challenging imaging environments with large B0 inhomogeneity. However, they do not account for the signal modulations introduced by a balanced steady state free precession (bSSFP) acquisition. Here we demonstrate improved performance when the bSSFP frequency response is properly incorporated into the multipeak spectral fat model used in the decomposition process. Balanced SSFP allows for rapid imaging but also introduces a characteristic frequency response featuring periodic nulls and pass bands. Fat spectral components in adjacent pass bands will experience bulk phase offsets and magnitude modulations that change the expected constructive and destructive interference between the fat spectral components. A bSSFP signal model was incorporated into the fat/water decomposition process and used to generate images of a fat phantom, and bilateral breast and knee images in four normal volunteers at 1.5 Tesla. Incorporation of the bSSFP signal model into the decomposition process improved the performance of the fat/water decomposition. Incorporation of this model allows rapid bSSFP imaging sequences to use robust fat/water decomposition methods such as IDEAL. While only one set of imaging parameters were presented, the method is compatible with any field strength or repetition time. © 2015 Wiley Periodicals, Inc.

Imaging of dynamic magnetic fields with spin-polarized neutron beams

DOE PAGES

Tremsin, A. S.; Kardjilov, N.; Strobl, M.; ...

2015-04-22

Precession of neutron spin in a magnetic field can be used for mapping of a magnetic field distribution, as demonstrated previously for static magnetic fields at neutron beamline facilities. The fringing in the observed neutron images depends on both the magnetic field strength and the neutron energy. In this paper we demonstrate the feasibility of imaging periodic dynamic magnetic fields using a spin-polarized cold neutron beam. Our position-sensitive neutron counting detector, providing with high precision both the arrival time and position for each detected neutron, enables simultaneous imaging of multiple phases of a periodic dynamic process with microsecond timing resolution.more » The magnetic fields produced by 5- and 15-loop solenoid coils of 1 cm diameter, are imaged in our experiments with ~100 μm resolution for both dc and 3 kHz ac currents. Our measurements agree well with theoretical predictions of fringe patterns formed by neutron spin precession. We also discuss the wavelength dependence and magnetic field quantification options using a pulsed neutron beamline. Furthermore, the ability to remotely map dynamic magnetic fields combined with the unique capability of neutrons to penetrate various materials (e.g., metals), enables studies of fast periodically changing magnetic processes, such as formation of magnetic domains within metals due to the presence of ac magnetic fields.« less

Imaging of dynamic magnetic fields with spin-polarized neutron beams

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

Tremsin, A. S.; Kardjilov, N.; Strobl, M.

Precession of neutron spin in a magnetic field can be used for mapping of a magnetic field distribution, as demonstrated previously for static magnetic fields at neutron beamline facilities. The fringing in the observed neutron images depends on both the magnetic field strength and the neutron energy. In this paper we demonstrate the feasibility of imaging periodic dynamic magnetic fields using a spin-polarized cold neutron beam. Our position-sensitive neutron counting detector, providing with high precision both the arrival time and position for each detected neutron, enables simultaneous imaging of multiple phases of a periodic dynamic process with microsecond timing resolution.more » The magnetic fields produced by 5- and 15-loop solenoid coils of 1 cm diameter, are imaged in our experiments with ~100 μm resolution for both dc and 3 kHz ac currents. Our measurements agree well with theoretical predictions of fringe patterns formed by neutron spin precession. We also discuss the wavelength dependence and magnetic field quantification options using a pulsed neutron beamline. Furthermore, the ability to remotely map dynamic magnetic fields combined with the unique capability of neutrons to penetrate various materials (e.g., metals), enables studies of fast periodically changing magnetic processes, such as formation of magnetic domains within metals due to the presence of ac magnetic fields.« less

Balanced steady state free precession for arterial spin labeling MRI: Initial experience for blood flow mapping in human brain, retina, and kidney.

PubMed

Park, Sung-Hong; Wang, Danny J J; Duong, Timothy Q

2013-09-01

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. Copyright © 2013 Elsevier Inc. All rights reserved.

Annual, orbital, and enigmatic variations in tropical oceanography recorded by the Equatorial Atlantic amplifier

NASA Technical Reports Server (NTRS)

Mcintyre, Andrew

1992-01-01

Equatorial Atlantic surface waters respond directly to changes in zonal and meridional lower tropospheric winds forced by annual insolation. This mechanism has its maximum effect along the equatorial wave guide centered on 10 deg W. The result is to amplify even subtle tropical climate changes such that they are recorded by marked amplitude changes in the proxy signals. Model realizations, NCAR AGCM and OGCM for 0 Ka and 126 Ka (January and July), and paleoceanographic proxy data show that these winds are also forced by insolation changes at the orbital periods of precession and obliquity. Perhelion in boreal summer produces a strengthened monsoon, e.g., increase meridional and decrease zonal wind stress. This reduces oceanic Ekman divergence and thermocline/nutricline shallowing. The result, in the equatorial Atlantic, is reduced primary productivity and higher euphotic zone temperatures; vice versa for perihelion in boreal winter. Perihelion is controlled by precession. Thus, the dominant period in spectra from a stacked SST record (0-252 Ka BP) at the site of the equatorial Atlantic amplifier is 23 Ky (53 percent of the total variance). This precessional period is coherent (k = 0.920) and in phase with boreal summer insolation. Oscillations of shorter period are present in records from cores sited beneath the amplifier region. These occur between 12.5 and 74.5 Ka BP, when eccentricity modulation of precession is at a minimum. Within this time interval there are 21 cycles with mean periods of 3.0 plus or minus 0.5 Ky. Similar periods have been documented from high latitude regions, e.g., Greenland ice cores from Camp Century. The Camp Century signal in this same time interval contains 21 cycles. A subjective correlation was made between the Camp Century and the equatorial records; the signals were statistically similar, r = 0.722 and k = 0.960.

Quantifying the Mediterranean freshwater budget throughout the late Miocene: New implications for sapropel formation and the Messinian Salinity Crisis

NASA Astrophysics Data System (ADS)

Simon, Dirk; Marzocchi, Alice; Flecker, Rachel; Lunt, Daniel J.; Hilgen, Frits J.; Meijer, Paul Th.

2017-08-01

The cyclic sedimentary record of the late Miocene Mediterranean shows a clear transition from open marine to restricted conditions and finally to evaporitic environments associated with the Messinian Salinity Crisis. This evolution has been attributed to changes in Mediterranean-Atlantic connectivity and regional climate, which has a strong precessional pulse. 31 Coupled climate simulations with different orbital configurations have been combined in a regression model that estimates the evolution of the freshwater budget of the Mediterranean throughout the late Miocene. The study suggests that wetter conditions occur at precession minima and are enhanced at eccentricity maxima. We use the wetter peaks to predict synthetic sapropel records. Using these to retune two Mediterranean sediment successions indicates that the overall net freshwater budget is the most likely mechanism driving sapropel formation in the late Miocene. Our sapropel timing is offset from precession minima and boreal summer insolation maxima during low eccentricity if the present-day drainage configuration across North Africa is used. This phase offset is removed if at least 50% more water drained into the Mediterranean during the late Miocene, capturing additional North African monsoon precipitation, for example via the Chad-Eosahabi catchment in Libya. In contrast with the clear expression of precession and eccentricity in the model results, obliquity, which is visible in the sapropel record during minimum eccentricity, does not have a strong signal in our model. By exploring the freshwater evolution curve in a box model that also includes Mediterranean-Atlantic exchange, we are able, for the first time, to estimate the Mediterranean's salinity evolution, which is quantitatively consistent with precessional control. Additionally, we separate and quantify the distinct contributions regional climate and tectonic restriction make to the lithological changes associated with the Messinian Salinity Crisis. The novel methodology and results of this study have numerous potential applications to other regions and geological scenarios, as well as to astronomical tuning.

Elementary Analysis of the Special Relativistic Combination of Velocities, Wigner Rotation and Thomas Precession

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,…

Steady flow in a rotating sphere with strong precession

NASA Astrophysics Data System (ADS)

Kida, Shigeo

2018-04-01

The steady flow in a rotating sphere is investigated by asymptotic analysis in the limit of strong precession. The whole spherical body is divided into three regions in terms of the flow characteristics: the critical band, which is the close vicinity surrounding the great circle perpendicular to the precession axis, the boundary layer, which is attached to the whole sphere surface and the inviscid region that occupies the majority of the sphere. The analytic expressions, in the leading order of the asymptotic expansion, of the velocity field are obtained in the former two, whereas partial differential equations for the velocity field are derived in the latter, which are solved numerically. This steady flow structure is confirmed by the corresponding direct numerical simulation.

Coherent spin transport through a 350 micron thick silicon wafer.

PubMed

Huang, Biqin; Monsma, Douwe J; Appelbaum, Ian

2007-10-26

We use all-electrical methods to inject, transport, and detect spin-polarized electrons vertically through a 350-micron-thick undoped single-crystal silicon wafer. Spin precession measurements in a perpendicular magnetic field at different accelerating electric fields reveal high spin coherence with at least 13pi precession angles. The magnetic-field spacing of precession extrema are used to determine the injector-to-detector electron transit time. These transit time values are associated with output magnetocurrent changes (from in-plane spin-valve measurements), which are proportional to final spin polarization. Fitting the results to a simple exponential spin-decay model yields a conduction electron spin lifetime (T1) lower bound in silicon of over 500 ns at 60 K.

Spin-orbit precession along eccentric orbits: Improving the knowledge of self-force corrections and of their effective-one-body counterparts

NASA Astrophysics Data System (ADS)

Bini, Donato; Damour, Thibault; Geralico, Andrea

2018-05-01

The (first-order) gravitational self-force correction to the spin-orbit precession of a spinning compact body along a slightly eccentric orbit around a Schwarzschild black hole is computed through the ninth post-Newtonian order and to second order in the eccentricity, improving recent results by Kavanagh et al. [Phys. Rev. D 96, 064012 (2017), 10.1103/PhysRevD.96.064012]. We show that our higher-accurate theoretical estimates of the spin precession exhibits an improved agreement with corresponding numerical self-force data. We convert our new theoretical results into its corresponding effective-one-body counterpart, thereby determining several new post-Newtonian terms in the gyrogravitomagnetic ratio gS * .

Parametrically disciplined operation of a vibratory gyroscope

NASA Technical Reports Server (NTRS)

Shcheglov, Kirill V. (Inventor); Challoner, A. Dorian (Inventor); Hayworth, Ken J. (Inventor); Peay, Chris S. (Inventor)

2008-01-01

Parametrically disciplined operation of a symmetric nearly degenerate mode vibratory gyroscope is disclosed. A parametrically-disciplined inertial wave gyroscope having a natural oscillation frequency in the neighborhood of a sub-harmonic of an external stable clock reference is produced by driving an electrostatic bias electrode at approximately twice this sub-harmonic frequency to achieve disciplined frequency and phase operation of the resonator. A nearly symmetric parametrically-disciplined inertial wave gyroscope that can oscillate in any transverse direction and has more than one bias electrostatic electrode that can be independently driven at twice its oscillation frequency at an amplitude and phase that disciplines its damping to zero in any vibration direction. In addition, operation of a parametrically-disciplined inertial wave gyroscope is taught in which the precession rate of the driven vibration pattern is digitally disciplined to a prescribed non-zero reference value.

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".

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.

The precession dynamo experiment at HZDR

NASA Astrophysics Data System (ADS)

Giesecke, A.; Albrecht, T.; Gerbeth, G.; Gundrum, T.; Nore, C.; Stefani, F.; Steglich, C.

2013-12-01

Most planets of the solar system are accompanied by a magnetic field with a large scale structure. These fields are generated by the dynamo effect, the process that provides for the transfer of kinetic energy from a flow of a conducting fluid into magnetic energy. In case of planetary dynamos it is generally assumed that these flows are driven by thermal and/or chemical convection but other driving sources like libration, tidal forcing or precession are possible as well. Precessional forcing, in particular, has been discussed since long as an at least additional power source for the geodynamo. A fluid flow of liquid sodium, solely driven by precession, will be the source for magnetic field generation in the next generation dynamo experiment currently under development at the Helmholz-Zentrum Dresden-Rossendorf (HZDR). In contrast to previous dynamo experiments no internal blades, propellers or complex systems of guiding tubes will be used for the optimization of the flow properties. However, in order to reach sufficiently high magnetic Reynolds numbers required for the onset of dynamo action rather large dimensions of the container are necessary making the construction of the experiment a challenge. At present state a small scale water experiment is running in order to estimate the hydrodynamic flow properties in dependence of precession angle and precession rate. The measurements are utilized in combination with numerical simulations of the hydrodynamic case as input data for kinematic simulations of the induction equation. The resulting growth rates and the corresponding critical magnetic Reynolds numbers will provide a restriction of the useful parameter regime and will allow an optimization of the experimental configuration.

Precessionally driven dynamos in ellipsoidal geometry

NASA Astrophysics Data System (ADS)

Ernst-Hullermann, J.; Harder, H.; Hansen, U.

2013-12-01

Precession was suggested as an alternative driving mechanism for Earth's and planetary magnetic fields by Bullard in 1949. Recent estimates of the thermal and electrical conductivity of Earth's core even show that the energy budget for buoyancy driven dynamos might be very tight. Therefore it seems worth to consider precession at least as an additional if not the only source of energy for the geodynamo. We are going to investigate precessionally driven dynamos by the use of a Finite Volume code. As precession drives a flow only due to the movement of the boundaries the shape of the container is essential for the character of the flow. In planets, it is much more effective to drive a precessional flow by the pressure differences induced by the topography of the precessing body rather than by viscous coupling to the walls. Numerical simulations are the only method offering the possibility to investigate the influence of the topography since laboratory experiments normally are constrained by the predetermined geometry of the vessel. We discuss how ellipticity of the planets can be included in our simulations by the use of a non-orthogonal grid. We will show that even laminar precession-driven flows are capable to generate a magnetic field. Most of the magnetic energy of this dynamos resides in the outer viscous boundary layer. While at lower Ekman number the kinematic dynamos also have magnetic fields located in the bulk, these diminish in the full magneto-hydrodynamic case. The laminar dynamos may not scale to Earth-like parameters. Nevertheless, with our new method we have the possibility to explore the parameter space much more systematically.

Long-Term Changes in the Appearance of the Sky

NASA Astrophysics Data System (ADS)

Ruggles, Clive L. N.

Precession - the precession of the equinoxes - causes the rising and setting positions of the stars to change significantly over the centuries, but does not affect the rising and setting positions of the sun, moon, and planets. These change by a much smaller amount, significant over timescales of millennia, owing to a gradual change in the obliquity of the ecliptic.

Orbital-plane precessional resonances for binary black-hole systems

NASA Astrophysics Data System (ADS)

Kesden, Michael; Zhao, Xinyu; Gerosa, Davide

2016-03-01

We derive a new class of post-Newtonian precessional resonances for binary black holes (BBHs) with misaligned spins. According to the orbit-averaged spin-precession equations, the angle between the orbital angular momentum L and the total angular momentum J oscillates with a period τ during which time L precesses about J by an angle α. If α is a rational multiple of 2 π, the precession of L will be closed indicating a resonance between the polar and azimuthal evolution of L . If α is an integer multiple of 2 π, the misalignment between the angular momentum ΔL radiated over the period τ and J will be minimized, as will the opening angle of the cone about which J precesses in an inertial frame. However, the direction of ΔL will remain nearly fixed in an inertial frame over many precessional periods, causing the direction of J to tilt as inspiraling BBHs pass through such a resonance. Generic BBHs encounter many such resonances during an inspiral from large separations. We derive the evolution of J near a resonance and assess their detectability by gravitational-wave detectors and astrophysical implications.

A sparse representation of gravitational waves from precessing compact binaries

NASA Astrophysics Data System (ADS)

Blackman, Jonathan; Szilagyi, Bela; Galley, Chad; Tiglio, Manuel

2014-03-01

With the advanced generation of gravitational wave detectors coming online in the near future, there is a need for accurate models of gravitational waveforms emitted by binary neutron stars and/or black holes. Post-Newtonian approximations work well for the early inspiral and there are models covering the late inspiral as well as merger and ringdown for the non-precessing case. While numerical relativity simulations have no difficulty with precession and can now provide accurate waveforms for a broad range of parameters, covering the 7 dimensional precessing parameter space with ~107 simulations is not feasible. There is still hope, as reduced order modelling techniques have been highly successful in reducing the impact of the curse of dimensionality for lower dimensional cases. We construct a reduced basis of Post-Newtonian waveforms for the full parameter space with mass ratios up to 10 and spins up to 0 . 9 , and find that for the last 100 orbits only ~ 50 waveforms are needed. The huge compression relies heavily on a reparametrization which seeks to reduce the non-linearity of the waveforms. We also show that the addition of merger and ringdown only mildly increases the size of the basis.

Simple picture for neutrino flavor transformation in supernovae

NASA Astrophysics Data System (ADS)

Duan, Huaiyu; Fuller, George M.; Qian, Yong-Zhong

2007-10-01

We can understand many recently discovered features of flavor evolution in dense, self-coupled supernova neutrino and antineutrino systems with a simple, physical scheme consisting of two quasistatic solutions. One solution closely resembles the conventional, adiabatic single-neutrino Mikheyev-Smirnov-Wolfenstein (MSW) mechanism, in that neutrinos and antineutrinos remain in mass eigenstates as they evolve in flavor space. The other solution is analogous to the regular precession of a gyroscopic pendulum in flavor space, and has been discussed extensively in recent works. Results of recent numerical studies are best explained with combinations of these solutions in the following general scenario: (1) Near the neutrino sphere, the MSW-like many-body solution obtains. (2) Depending on neutrino vacuum mixing parameters, luminosities, energy spectra, and the matter density profile, collective flavor transformation in the nutation mode develops and drives neutrinos away from the MSW-like evolution and toward regular precession. (3) Neutrino and antineutrino flavors roughly evolve according to the regular precession solution until neutrino densities are low. In the late stage of the precession solution, a stepwise swapping develops in the energy spectra of νe and νμ/ντ. We also discuss some subtle points regarding adiabaticity in flavor transformation in dense-neutrino systems.

Momentum Biased Performance of LAPAN-A3 Satellite for Multispectral Pushbroom Imager Operation

NASA Astrophysics Data System (ADS)

Utama, S.; Saifudin, M. A.; Mukhayadi, M.

2018-05-01

One of LAPAN-A3 satellite’s missions is for earth observation using multispectral pushbroom imager. This mission needs a stable and accurate attitude to capture any area of interest. To accomplish the mission LAPAN-A3 satellite use momentum biased attitude control. The satellite use magnetic torquers to control the angular momentum vector and a reaction wheel to spin the satellite to remain nadir pointing. When the satellite spinning there are nutation and precession occurred. This paper observes attitude accuracy and stability due to nutation and precession of the satellite’s momentum and the effect to pushbroom imager operation. Nutation observed with 0.28° amplitude and 73 seconds period, and precession observed with 1° amplitude and 92 minutes period. This nutation and precession profile will lead to 2.6° attitude accuracy and maximum movement on ground track 0.055 km/s in along track direction and 0.259 km/s (0.026°/s) in cross track direction. Both of attitude accuracy and movement are outperformed the limitation. However due to satellite movement in orbit there is still blurring effect on the imager.

Negative-Mass Instability of the Spin and Motion of an Atomic Gas Driven by Optical Cavity Backaction

NASA Astrophysics Data System (ADS)

Kohler, Jonathan; Gerber, Justin A.; Dowd, Emma; Stamper-Kurn, Dan M.

2018-01-01

We realize a spin-orbit interaction between the collective spin precession and center-of-mass motion of a trapped ultracold atomic gas, mediated by spin- and position-dependent dispersive coupling to a driven optical cavity. The collective spin, precessing near its highest-energy state in an applied magnetic field, can be approximated as a negative-mass harmonic oscillator. When the Larmor precession and mechanical motion are nearly resonant, cavity mediated coupling leads to a negative-mass instability, driving exponential growth of a correlated mode of the hybrid system. We observe this growth imprinted on modulations of the cavity field and estimate the full covariance of the resulting two-mode state by observing its transient decay during subsequent free evolution.

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.

Transit Duration Variations due to Secular Interactions in Systems with Tightly-packed Inner Planets

NASA Astrophysics Data System (ADS)

Boley, Aaron; Van Laerhoven, Christa; Granados Contreras, A. Paula

2018-04-01

Secular interactions among planets in multi-planet systems will lead to variations in orbital inclinations and to the precession of orbital nodes. Taking known system architectures at face value, we calculate orbital precession rates for planets in tightly-packed systems using classical second-order secular theory, in which the orientation of the orbits can be described as a vector sum of eigenmodes and the eigenstructure is determined only by the masses and semi-major axes of the planets. Using this framework, we identify systems that have fast precession frequencies, and use those systems to explore the range of transit duration variation that could occur using amplitudes that are consistent with tightly-packed planetary systems. We then further assess how transit duration variations could be used in practice.

Relativistic spin precession in the double pulsar.

PubMed

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

2008-07-04

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%.

Modulation of ultrafast laser-induced magnetization precession in BiFeO3-coated La0.67Sr0.33MnO3 thin films

NASA Astrophysics Data System (ADS)

Wan, Qian; Jin, KuiJuan; Wang, JieSu; Yao, HongBao; Gu, JunXing; Guo, HaiZhong; Xu, XiuLai; Yang, GuoZhen

2017-04-01

The ultrafast laser-excited magnetization dynamics of ferromagnetic (FM) La0.67Sr0.33MnO3 (LSMO) thin films with BiFeO3 (BFO) coating layers grown by laser molecular beam epitaxy are investigated using the optical pump-probe technique. Uniform magnetization precessions are observed in the films under an applied external magnetic field by measuring the time-resolved magneto-optical Kerr effect. The magnetization precession frequencies of the LSMO thin films with the BFO coating layers are lower than those of uncoated LSMO films, which is attributed to the suppression of the anisotropy field induced by the exchange interaction at the interface between the antiferromagnetic order of BFO and the FM order of LSMO.

System design and verification of the precession electron diffraction technique

NASA Astrophysics Data System (ADS)

Own, Christopher Su-Yan

2005-07-01

Bulk structural crystallography is generally a two-part process wherein a rough starting structure model is first derived, then later refined to give an accurate model of the structure. The critical step is the determination of the initial model. As materials problems decrease in length scale, the electron microscope has proven to be a versatile and effective tool for studying many problems. However, study of complex bulk structures by electron diffraction has been hindered by the problem of dynamical diffraction. This phenomenon makes bulk electron diffraction very sensitive to specimen thickness, and expensive equipment such as aberration-corrected scanning transmission microscopes or elaborate methodology such as high resolution imaging combined with diffraction and simulation are often required to generate good starting structures. The precession electron diffraction technique (PED), which has the ability to significantly reduce dynamical effects in diffraction patterns, has shown promise as being a "philosopher's stone" for bulk electron diffraction. However, a comprehensive understanding of its abilities and limitations is necessary before it can be put into widespread use as a standalone technique. This thesis aims to bridge the gaps in understanding and utilizing precession so that practical application might be realized. Two new PED systems have been built, and optimal operating parameters have been elucidated. The role of lens aberrations is described in detail, and an alignment procedure is given that shows how to circumvent aberration in order to obtain high-quality patterns. Multislice simulation is used for investigating the errors inherent in precession, and is also used as a reference for comparison to simple models and to experimental PED data. General trends over a large sampling of parameter space are determined. In particular, we show that the primary reflection intensity errors occur near the transmitted beam and decay with increasing angle and decreasing specimen thickness. These errors, occurring at the lowest spatial frequencies, fortuitously coincide with reflections for which phases are easiest to determine via imaging methods. A general two-beam dynamical model based upon an existing approximate model is found to be fairly accurate across most experimental conditions, particularly where it is needed for providing a correction to distorted data. Finally, the practical structure solution procedure using PED is demonstrated for several model material systems. Of the experiment parameters investigated, the cone semi-angle is found to be the most important (it should be as large as possible), followed closely by specimen thickness (thinner is better). Assuming good structure projection characteristics in the specimen, the thickness tractable by PED is extended to 40-50 nm without correction, demonstrated for complex oxides. With a forward calculation based upon the two-beam dynamical model (using known structure factors), usable specimen thickness can be extended past 150 nm. For a priori correction, using the squared amplitudes approximates the two-beam model for most thicknesses if the scattering from the structure adheres to psuedo-kinematical behavior. Practically, crystals up to 60 nm in thickness can now be processed by the precession methods developed in this thesis.

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.

A Theoretical Approach to Selection of a Biologically Active Substance in Ultra-Low Doses for Effective Action on a Biological System.

PubMed

Boldyreva, Liudmila Borisovna

2018-05-01

 An approach is offered to selecting a biologically active substance (BAS) in ultra-low dose for effective action on a biological system (BS). The technique is based on the assumption that BAS in ultra-low doses exerts action on BS by means of spin supercurrent emerging between the spin structure created by BAS, on the one hand, and the spin structure created by BS, on the other hand. According to modern quantum-mechanical concepts, these spin structures may be virtual particles pairs having precessing spin (that is, be essentially spin vortices in the physical vacuum) and created by the quantum entities that BAS and BS consist of. The action is effective provided there is equality of precession frequencies of spins in these spin structures.  In this work, some methods are considered for determining the precession frequencies of spins in virtual particles pairs: (1) determination of energy levels of quantum entities that BS and BAS consist of; (2) the use of spin-flip effect of the virtual particles pair spin, the effect being initiated by action of magnetic vector potential (the spin-flip effect takes place when the varied frequency of the magnetic vector potential equals the precession frequency of the spin); (3) determining the frequencies of photons effectively acting on BS.  It is shown that the effect of BAS in ultra-low doses on BS can be replaced by the effect of a beam of low-intensity photons, if the frequency of photons equals the precession frequency of spin in spin structures created by BS. Consequently, the color of bodies placed near a biological system is able to exert an effective action on the biological system: that is "color therapy" is possible. It is also supposed that the spin-flip effect may be used not only for determining the precession frequency of spin in spin structures created by BS but also for therapeutic action on biological systems. The Faculty of Homeopathy.

Self-gravity and dissipation in polar rings

NASA Technical Reports Server (NTRS)

Dubinski, John; Christodoulou, Dimitris M.

1994-01-01

Studies of inclined rings inside galaxy potentials have mostly considered the influence of self-gravity and viscous dissipation separately. In this study, we construct models of highly inclined ('polar') rings in an external potential including both self-gravity and dissipation due to a drag force. We do not include pressure forces and thus ignore shock heating that dominates the evolution of gaseous rings inside strongly nonspherical potentials. We adopt an oblate spheroidal scale-free logarithmic potential with axis ratio q = 0.85 and an initial inclination of 80 deg for the self-gravitating rings. We find that stellar (dissipationless) rings suffer from mass loss during their evolution. Mass loss also drives a secular change of the mean inclination toward the poles of the potential. As much as half of the ring mass escapes in the process and forms an inner and an outer shell of precessing orbits. If the remaining mass is more than approximately 0.02 of the enclosed galaxy mass, rings remain bound and do not fall apart from differential precession. The rings precess at a constant rate for more than a precession period tau(sub p) finding the configuration predicted by Sparke in 1986 which warps at larger radii toward the poles of the potential. We model shear viscosity with a velocity-dependent drag force and find that nuclear inflow dominates over self-gravity if the characteristic viscous inflow time scale tau(sub vi) is shorter than approximately 25(tau(sub p)). Rings with (tau(sub vi))/(tau(sub p)) less than or approximately equal to 25 collapse toward the nucleus of the potential within one precession period independent of the amount of self-gravity. Our results imply that stars and gas in real polar rings exhibit markedly different dynamical evolutions.

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

Fast and Slow Precession of Gaseous Debris Disks around Planet-accreting White Dwarfs

NASA Astrophysics Data System (ADS)

Miranda, Ryan; Rafikov, Roman R.

2018-04-01

Spectroscopic observations of some metal-rich white dwarfs (WDs), believed to be polluted by planetary material, reveal the presence of compact gaseous metallic disks orbiting them. The observed variability of asymmetric, double-peaked emission-line profiles in about half of such systems could be interpreted as the signature of precession of an eccentric gaseous debris disk. The variability timescales—from decades down to 1.4 year (recently inferred for the debris disk around HE 1349–2305)—are in rough agreement with the rate of general relativistic (GR) precession in the test-particle limit. However, it has not been demonstrated that this mechanism can drive such a fast, coherent precession of a radially extended (out to 1 {R}ȯ ) gaseous disk mediated by internal stresses (pressure). Here, we use the linear theory of eccentricity evolution in hydrodynamic disks to determine several key properties of eccentric modes in gaseous debris disks around WDs. We find a critical dependence of both the precession period and radial eccentricity distribution of the modes on the inner disk radius, r in. For small inner radii, {r}in}≲ (0.2{--}0.4) {R}ȯ , the modes are GR-driven, with periods of ≈1–10 year. For {r}in}≳ (0.2{--}0.4) {R}ȯ , the modes are pressure dominated, with periods of ≈3–20 year. Correspondence between the variability periods and inferred inner radii of the observed disks is in general agreement with this trend. In particular, the short period of HE 1349–2305 is consistent with its small r in. Circum-WD debris disks may thus serve as natural laboratories for studying the evolution of eccentric gaseous disks.

Highly selective detection of individual nuclear spins with rotary echo on an electron spin probe

PubMed Central

Mkhitaryan, V. V.; Jelezko, F.; Dobrovitski, V. V.

2015-01-01

We consider an electronic spin, such as a nitrogen-vacancy center in diamond, weakly coupled to a large number of nuclear spins, and subjected to the Rabi driving with a periodically alternating phase. We show that by switching the driving phase synchronously with the precession of a given nuclear spin, the interaction to this spin is selectively enhanced, while the rest of the bath remains decoupled. The enhancement is of resonant character. The key feature of the suggested scheme is that the width of the resonance is adjustable, and can be greatly decreased by increasing the driving strength. Thus, the resonance can be significantly narrowed, by a factor of 10–100 in comparison with the existing detection methods. Significant improvement in selectivity is explained analytically and confirmed by direct numerical many-spin simulations. The method can be applied to a wide range of solid-state systems. PMID:26497777

Icosahedral quasicrystals as twins of cubic crystals containing large icosahedral clusters of atoms: The 1012-atom primitive cubic structure of Al(6)CuLi(3), the C-phase Al(37)Cu(3)Li(21)Mg(3), and GaMg(2)Zn(3).

PubMed

Pauling, L

1988-06-01

Single-grain precession x-ray diffraction photographs of Al(6)CuLi(3) have been successfully indexed on the basis of icosahedral twinning of cubic crystals with a 1012-atom primitive cubic unit with edge 25.70 A, giving support to the proposal that the so-called icosahedral quasicrystals are twins of crystals containing eight large icosahedral clusters in the beta-W arrangement. In this compound two of the clusters consist of 104 atoms and six consist of 136 atoms, with 24 atoms shared. The same structure is assigned to the C-phase, Al(37)Cu(3)Li(21)Mg(3), and to GaMg(2)Zn(3). A theory of icosahedral quasicrystals and amorphous metals is described.

Icosahedral quasicrystals as twins of cubic crystals containing large icosahedral clusters of atoms: The 1012-atom primitive cubic structure of Al6CuLi3, the C-phase Al37Cu3Li21Mg3, and GaMg2Zn3

PubMed Central

Pauling, Linus

1988-01-01

Single-grain precession x-ray diffraction photographs of Al6CuLi3 have been successfully indexed on the basis of icosahedral twinning of cubic crystals with a 1012-atom primitive cubic unit with edge 25.70 Å, giving support to the proposal that the so-called icosahedral quasicrystals are twins of crystals containing eight large icosahedral clusters in the β-W arrangement. In this compound two of the clusters consist of 104 atoms and six consist of 136 atoms, with 24 atoms shared. The same structure is assigned to the C-phase, Al37Cu3Li21Mg3, and to GaMg2Zn3. A theory of icosahedral quasicrystals and amorphous metals is described. PMID:16593929

Analogies of the classical Euler top with a rotor to spin squeezing and quantum phase transitions in a generalized Lipkin-Meshkov-Glick model.

PubMed

Opatrný, Tomáš; Richterek, Lukáš; Opatrný, Martin

2018-01-31

We show that the classical model of Euler top (freely rotating, generally asymmetric rigid body), possibly supplemented with a rotor, corresponds to a generalized Lipkin-Meshkov-Glick (LMG) model describing phenomena of various branches of quantum physics. Classical effects such as free precession of a symmetric top, Feynman's wobbling plate, tennis-racket instability and the Dzhanibekov effect, attitude control of satellites by momentum wheels, or twisting somersault dynamics, have their counterparts in quantum effects that include spin squeezing by one-axis twisting and two-axis countertwisting, transitions between the Josephson and Rabi regimes of a Bose-Einstein condensate in a double-well potential, and other quantum critical phenomena. The parallels enable us to expand the range of explored quantum phase transitions in the generalized LMG model, as well as to present a classical analogy of the recently proposed LMG Floquet time crystal.

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.

On the origin of the Z-shaped narrow-line region in the Seyfert galaxy NGC 3516

NASA Technical Reports Server (NTRS)

Veilleux, Sylvain; Tully, R. B.; Bland-Hawthorn, Jonathan

1993-01-01

A kinematic study has been carried out of the line-emitting gas in the Seyfert galaxy NGC 3516. The existence of two curved filaments in the central 2.5 kpc of this galaxy, which give Z-shaped appearance to its NLR. A precessing twin-jet model in which the line-emitting material is entrained by a precessing radio jet and kept ionized by the nuclear ionization field can explain the kinematic data of the brightest emission rather well. If this model is valid, this would make NGC 3516 the least luminous known active galaxy with a precessing jet. An alternative scenario assumes that the curved inner filaments represent gas entrained by a radio jet which is deflected by ram pressure from the rotation interstellar medium of the galaxy.

Maneuver Design and Calibration for the Genesis Spacecraft

NASA Technical Reports Server (NTRS)

Williams, Kenneth E.; Hong, Philip E.; Zietz, Richard P.; Han, Don

2000-01-01

Genesis is the fifth mission selected as part of NASA's Discovery Program. The objective of Genesis is to collect solar wind samples for a period of approximately two years while in a halo orbit about the Earth-Sun L I point. At the end of this period, the samples are to be returned to a specific recovery point on the Earth for subsequent analysis. This goal has never been attempted before and presents a formidable challenge in terms of mission design and operations, particularly planning and execution of propulsive maneuvers. To achieve a level of cost-effectiveness consistent with a Discovery-class mission, the Genesis spacecraft design was adapted to the maximum extent possible from designs used on earlier missions, such as Mars Global Surveyor (MGS) and Stardust, another sample collection mission. The spacecraft design for Genesis is shown. Spin stabilization was chosen for attitude control, in lieu of three-axis stabilization, with neither reaction wheels nor accelerometers included. This precludes closed-loop control of propulsive maneuvers and implies that any attitude changes, including spin changes and precessions, will behave like translational propulsive maneuvers and affect the spacecraft trajectory. Moreover, to minimize contamination risk to the samples collected, all thrusters were placed on the side opposite the sample collection canister. The orientation and characteristics of thrusters are indicated. For large maneuvers (>2.5 m/s), two 5 lbf thrusters will be used for delta v, with precession to the burn attitude, followed by spin-up from 1.6 to 10 rpm before the burn and spin down to 1.6 rpm afterwards, then precession back to the original spin attitude. For small maneuvers (<2.5 m/s), no spin change is needed and four 0.2 lbf thrusters are used for Av. Single or double 360 deg. precession changes are required whenever the desired delta v falls inside the two-way turn circle (about 0.4 m/s) based on the mass properties, spin rate and lever arm lengths based on thruster locations. In such instances, delta v resulting from spacecraft precession cannot be used effectively as a component of the desired delta v, and must therefore be removed by precessing at least one complete revolution around the turn circle. To eliminate cross-track execution errors, a second revolution in the opposite direction would also be performed. This paper will address the design of propulsive maneuvers in light of the aforementioned challenges and other constraints. Maneuver design will be performed jointly by the Navigation Team at JPL and the Spacecraft Team at LMA, based on the process indicated . Typical maneuver timelines will be presented which address considerations introduced by attitude changes. These include nutation, which is introduced by precessing or spinning down and must be given sufficient time to damp out prior to execution of subsequent events, as well as sun and earth pointing constraints, which must be considered to ensure sufficient spacecraft power and to minimize telecommunications interruptions, respectively. The paper will include a description of how individual propulsive maneuvers are resolved into components to account for delta v from translational burns and spacecraft attitude changes required to carry out such maneuvers. Contributions to maneuver delta v arising from attitude changes, based on mass properties for the period just after launch, are indicated. Similar curves will be presented spanning all mission phases from launch through return. A set of closed-form equations for resolving maneuver components, base on a specific delta v required for correction or deterministic changes to the spacecraft trajectory will be presented, as well. In addition to nominal maneuvers, special calibration maneuvers are planned to improve open-loop modeling of maneuvers and to reduce execution errors. Uncalibrated execution errors are indicated. Such errors could be reduced by 50% or more over the course of the mission. Special calibrations are of particular importance for the return leg of the mission, since the sample canister must be returned to a specific location within the Utah Test and Training Range (UTTR) for mid-air retrieval. An entry angle tolerance of no less than +/- 0.08 deg. is required to achieve this objective. Biasing of the final return maneuvers coupled with a specific maneuver mode to use a series of well-characterized spin changes to effect these maneuvers is part of the current Genesis baseline mission plan. Another important objective of calibrations is to better characterize precession maneuvers. Such maneuvers are part of most propulsive maneuvers, but are also required periodically to maintain sun-pointing for power or daily during solar-wind pointing during collection periods. Although relatively small, such maneuvers will have a significant cumulative impact on orbit determination, particularly in the halo portion of the mission. The current mission design also calls for three stationkeeping maneuvers during each halo orbit of approximately six months duration. These stationkeeping maneuvers may be sufficiently small that single or double 360 deg. precession changes may be required. Because there are no accelerometers on board the spacecraft, calibration can only be performed with the aid of ground-based radiometric tracking. To establish a high degree of accuracy in characterizing the magnitude of burns, the spacecraft spin axis should be along the line of sight to the Earth, providing Doppler measurements with <1 mm/sec accuracy in S-Band. Emission constraints allow such alignment only during certain portions of the mission when the Earth-spacecraft-sun geometry is favorable. The impact of precessions, or burns at times when geometry is not favorable, can be assessed by reconstruction of the spacecraft trajectory using tracking arcs of several days before and after the event.

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.

Does the Atmosphere Precess?

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.

General Relativistic Effects and QPOs in X-Ray Binaries

NASA Astrophysics Data System (ADS)

Markovic, D.; Lamb, F. K.

We have investigated whether general relativistic effects may be responsible for some of the quasi-periodic X-ray brightness oscillations (QPOs) observed in low-mass binary systems containing accreting neutron stars and black hole candidates. In particular, we have computed the motions of accreting gas in the strong gravitational fields near such objects and have explored possible mechanisms for producing X-ray flux oscillations. We have discovered a family of weakly damped global gravitomagnetic (Lense-Thirring) warping modes of the inner (viscous) accretion disk that have precession frequencies ranging up to the single-particle gravitomagnetic precession frequency at the inner edge of the disk, which is about 30 Hz if the disk extends inward to the innermost stable circular orbit around a compact object of solar mass with dimensionless angular momentum cJ/GM2 ~ 0.2. Precession of regions of enhanced viscous dissipation or modulation of the accretion flow by the precession may produce observable periodic variation of the X-ray flux. Detectable effects might also be produced if the gas in the inner disk breaks up into a collection of distinct clumps. We have analyzed the dynamics of such clumps as well as the conditions required for their formation and survival on time scales long enough to produce QPOs with the coherence observed in low-mass X-ray binaries.

POLARIZATION MODULATION FROM LENSE–THIRRING PRECESSION IN X-RAY BINARIES

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

Ingram, Adam; Maccarone, Thomas J.; Poutanen, Juri

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 themore » 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)« less

Formation of precessing jets by tilted black hole discs in 3D general relativistic MHD simulations

NASA Astrophysics Data System (ADS)

Liska, M.; Hesp, C.; Tchekhovskoy, A.; Ingram, A.; van der Klis, M.; Markoff, S.

2018-02-01

Gas falling into a black hole (BH) from large distances is unaware of BH spin direction, and misalignment between the accretion disc and BH spin is expected to be common. However, the physics of tilted discs (e.g. angular momentum transport and jet formation) is poorly understood. Using our new GPU-accelerated code H-AMR, we performed 3D general relativistic magnetohydrodynamic simulations of tilted thick accretion discs around rapidly spinning BHs, at the highest resolution to date. We explored the limit where disc thermal pressure dominates magnetic pressure, and showed for the first time that, for different magnetic field strengths on the BH, these flows launch magnetized relativistic jets propagating along the rotation axis of the tilted disc (rather than of the BH). If strong large-scale magnetic flux reaches the BH, it bends the inner few gravitational radii of the disc and jets into partial alignment with the BH spin. On longer time-scales, the simulated disc-jet system as a whole undergoes Lense-Thirring precession and approaches alignment, demonstrating for the first time that jets can be used as probes of disc precession. When the disc turbulence is well resolved, our isolated discs spread out, causing both the alignment and precession to slow down.

Noise suppression for the differential detection in nuclear magnetic resonance gyroscope

NASA Astrophysics Data System (ADS)

Yang, Dan; Zhou, Binquan; Chen, LinLin; Jia, YuChen; Lu, QiLin

2017-10-01

The nuclear magnetic resonance gyroscope is based on spin-exchange optical pumping of noble gases to detect and measure the angular velocity of the carrier, but it would be challenging to measure the precession signal of noble gas nuclei directly. To solve the problem, the primary detection method utilizes alkali atoms, the precession of nuclear magnetization modulates the alkali atoms at the Larmor frequency of nuclei, relatively speaking, and it is easier to detect the precession signal of alkali atoms. The precession frequency of alkali atoms is detected by the rotation angle of linearly polarized probe light; and differential detection method is commonly used in NMRG in order to detect the linearly polarized light rotation angle. Thus, the detection accuracy of differential detection system will affect the sensitivity of the NMRG. For the purpose of further improvement of the sensitivity level of the NMRG, this paper focuses on the aspects of signal detection, and aims to do an error analysis as well as an experimental research of the linearly light rotation angle detection. Through the theoretical analysis and the experimental illustration, we found that the extinction ratio σ2 and DC bias are the factors that will produce detective noise in the differential detection method.

How to Make Eccentricity Cycles in Stratigraphy: the Role of Compaction

NASA Astrophysics Data System (ADS)

Liu, W.; Hinnov, L.; Wu, H.; Pas, D.

2017-12-01

Milankovitch cycles from astronomically driven climate variations have been demonstrated as preserved in cyclostratigraphy throughout geologic time. These stratigraphic cycles have been identified in many types of proxies, e.g., gamma ray, magnetic susceptibility, oxygen isotopes, carbonate content, grayscale, etc. However, the commonly prominent spectral power of orbital eccentricity cycles in stratigraphy is paradoxical to insolation, which is dominated by precession index power. How is the spectral power transferred from precession to eccentricity in stratigraphy? Nonlinear sedimentation and bioturbation have long been identified as players in this transference. Here, we propose that in the absence of bioturbation differential compaction can generate the transference. Using insolation time series, we trace the steps by which insolation is transformed into stratigraphy, and how differential compaction of lithology acts to transfer spectral power from precession to eccentricity. Differential compaction is applied to unique values of insolation, which is assumed to control the type of deposited sediment. High compaction is applied to muds, and progressively lower compaction is applied to silts and sands, or carbonate. Linear differential compaction promotes eccentricity spectral power, but nonlinear differential compaction elevates eccentricity spectral power to dominance and precession spectral power to near collapse as is often observed in real stratigraphy. Keywords: differential compaction, cyclostratigraphy, insolation, eccentricity

Probing general relativistic precession around stellar-mass black holes with tomography and polarimetry

NASA Astrophysics Data System (ADS)

Ingram, A.

2017-10-01

Accreting stellar-mass black holes often show a quasi-periodic oscillation (QPO) in their X-ray flux, and an iron emission line in their X-ray spectrum. The iron line is generated through disc reflection, and its shape is distorted by rapid orbital motion and gravitational redshift. The physical origin of the QPO has long been debated, but is often attributed to 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 blueshift as the receding and approaching sides of the disc are respectively illuminated. I will first talk about our XMM-Newton and NuSTAR observations of the black hole binary H 1743-322 in which the line energy varies systematically over the ˜ 4 s QPO cycle, as predicted. This result has enabled us to map the inner accretion disc using tomographic techniques for the first time. I will then talk about the quasi-periodic swings in X-ray polarisation angle predicted by the precession model, and show how we can go about measuring such swings with the recently selected NASA Small explorer mission IXPE and proposed missions such as XIPE and eXTP.

Measurement of phase difference for micromachined gyros driven by rotating aircraft.

PubMed

Zhang, Zengping; Zhang, Fuxue; Zhang, Wei

2013-08-21

This paper presents an approach for realizing a phase difference measurement of a new gyro. A silicon micromachined gyro was mounted on rotating aircraft for aircraft attitude control. Aircraft spin drives the silicon pendulum of a gyro rotating at a high speed so that it can sense the transverse angular velocity of the rotating aircraft based on the gyroscopic precession principle when the aircraft has transverse rotation. In applications of the rotating aircraft single channel control system, such as damping in the attitude stabilization loop, the gyro signal must be kept in sync with the control signal. Therefore, the phase difference between both signals needs to be measured accurately. Considering that phase difference is mainly produced by both the micromachined part and the signal conditioning circuit, a mathematical model has been established and analyzed to determine the gyro's phase frequency characteristics. On the basis of theoretical analysis, a dynamic simulation has been done for a case where the spin frequency is 15 Hz. Experimental results with the proposed measurement method applied to a silicon micromachined gyro driven by a rotating aircraft demonstrate that it is effective in practical applications. Measured curve and numerical analysis of phase frequency characteristic are in accordance, and the error between measurement and simulation is only 5.3%.

Probing Collimated Jets and Dusty Waists in Dying Stars with Keck LGSAO

NASA Astrophysics Data System (ADS)

Sahai, R.; Le Mignant, D.; Sanchez Contreras, C.; Stute, M.; Morris, M.

2005-12-01

The shaping of planetary nebulae (PNs) is probably the most exciting yet least understood problem in the late evolution of intermediate mass stars. PNs evolve from the envelopes of AGB stars via a supposedly short ( ˜1000 yr) pre-planetary nebula (PPN) phase. HST imaging of PPNs and PNs has shown the widespread presence of diverse bipolar and multipolar morphologies. In 1998, in a radical departure from the long-standing theoretical paradigm for PN formation, Sahai & Trauger proposed that as most stars evolve off the AGB, they drive collimated fast winds that sweep up and shock the AGB circumstellar envelope, producing the observed dramatic changes in circumstellar geometry and kinematics from the AGB to the PN phase. The search for these collimated jets has proved to be rather elusive, partly because these are most likely episodic and operate only for a few x 100 years in the early PPN phase. During this phase, much of the circumstellar environment, including the central dusty waist of these nebulae, is optically-thick at visible wavelengths. We are therefore carrying out a program of observing PPNs with the LGSAO system on Keck II at near-infrared (1.1-4.7 micron) wavelengths. Our very first attempt met with remarkable success -- observations of the bipolar young PPN, IRAS16342-3814, revealed a remarkable corkscrew-shaped structure apparently etched into the lobe walls -- direct signature of an underlying precessing jet. Here we present results from new high-resolution (55 mas at 2 micron) observations of a small sample of PPNs with the LGSAO system. As in their HST images, our objects display bipolar/multipolar morphologies, but in addition, the bubble-like ``wind-swept" structure of the lobes is clearly revealed. Furthermore, the dusty waists appear much thinner geometrically than in the HST images, but surprisingly, in some PPNs, the central stars still remain obscured, with important implications for the poorly-known physical structure of the waists. We discuss some preliminary results from our data such as the nature of the illuminating sources, quantitative analysis of the mass and dynamics of different nebular components by combining our AO data with complementary data from our multi-wavelength survey of PPNs, and numerical simulations of precessing jets interacting with AGB winds.

Electromagnetic dipole moments of charged baryons with bent crystals at the LHC

NASA Astrophysics Data System (ADS)

Bagli, E.; Bandiera, L.; Cavoto, G.; Guidi, V.; Henry, L.; Marangotto, D.; Martinez Vidal, F.; Mazzolari, A.; Merli, A.; Neri, N.; Ruiz Vidal, J.

2017-12-01

We propose a unique program of measurements of electric and magnetic dipole moments of charm, beauty and strange charged baryons at the LHC, based on the phenomenon of spin precession of channeled particles in bent crystals. Studies of crystal channeling and spin precession of positively- and negatively-charged particles are presented, along with feasibility studies and expected sensitivities for the proposed experiment using a layout based on the LHCb detector.

Dynamics of the precessing vortex rope and its interaction with the system at Francis turbines part load operating conditions

NASA Astrophysics Data System (ADS)

Favrel, A.; Müller, A.; Landry, C.; Gomes, J.; Yamamoto, K.; Avellan, F.

2017-04-01

At part load conditions, Francis turbines experience the formation of a cavitation vortex rope at the runner outlet whose precession acts as a pressure excitation source for the hydraulic circuit. This can lead to hydro-acoustic resonances characterized by high pressure pulsations, as well as torque and output power fluctuations. This study highlights the influence of the discharge factor on both the vortex parameters and the pressure excitation source by performing Particle Image Velocimetry (PIV) and pressure measurements. Moreover, it is shown that the occurrence of hydro-acoustic resonances in cavitation conditions mainly depend on the swirl degree of the flow independently of the speed factor. Empirical laws linking both natural and precession frequencies with the operating parameters of the machine are, then, derived, enabling the prediction of resonance conditions on the complete part load operating range of the turbine.

Non-rigid precession of magnetic stars

NASA Astrophysics Data System (ADS)

Lander, S. K.; Jones, D. I.

2017-06-01

Stars are, generically, rotating and magnetized objects with a misalignment between their magnetic and rotation axes. Since a magnetic field induces a permanent distortion to its host, it provides effective rigidity even to a fluid star, leading to bulk stellar motion that resembles free precession. This bulk motion is, however, accompanied by induced interior velocity and magnetic field perturbations, which are oscillatory on the precession time-scale. Extending previous work, we show that these quantities are described by a set of second-order perturbation equations featuring cross-terms scaling with the product of the magnetic and centrifugal distortions to the star. For the case of a background toroidal field, we reduce these to a set of differential equations in radial functions, and find a method for their solution. The resulting magnetic field and velocity perturbations show complex multipolar structure and are strongest towards the centre of the star.

Evidence for free precession in a pulsar

PubMed

Stairs; Lyne; Shemar

2000-08-03

Pulsars are rotating neutron stars that produce lighthouse-like beams of radio emission from their magnetic poles. The observed pulse of emission enables their rotation rates to be measured with great precision. For some young pulsars, this provides a means of studying the interior structure of neutron stars. Most pulsars have stable pulse shapes, and slow down steadily (for example, see ref. 20). Here we report the discovery of long-term, highly periodic and correlated variations in both the pulse shape and the rate of slow-down of the pulsar PSR B1828-11. The variations are best described as harmonically related sinusoids, with periods of approximately 1,000, 500 and 250 days, probably resulting from precession of the spin axis caused by an asymmetry in the shape of the pulsar. This is difficult to understand theoretically, because torque-free precession of a solitary pulsar should be damped out by the vortices in its superfluid interior.

Application of spin-exchange relaxation-free magnetometry to the Cosmic Axion Spin Precession Experiment

NASA Astrophysics Data System (ADS)

Wang, Tao; Kimball, Derek F. Jackson; Sushkov, Alexander O.; Aybas, Deniz; Blanchard, John W.; Centers, Gary; Kelley, Sean R. O.'; Wickenbrock, Arne; Fang, Jiancheng; Budker, Dmitry

2018-03-01

The Cosmic Axion Spin Precession Experiment (CASPEr) seeks to measure oscillating torques on nuclear spins caused by axion or axion-like-particle (ALP) dark matter via nuclear magnetic resonance (NMR) techniques. A sample spin-polarized along a leading magnetic field experiences a resonance when the Larmor frequency matches the axion/ALP Compton frequency, generating precessing transverse nuclear magnetization. Here we demonstrate a Spin-Exchange Relaxation-Free (SERF) magnetometer with sensitivity ≈ 1 fT /√{ Hz } and an effective sensing volume of 0.1 cm3 that may be useful for NMR detection in CASPEr. A potential drawback of SERF-magnetometer-based NMR detection is the SERF's limited dynamic range. Use of a magnetic flux transformer to suppress the leading magnetic field is considered as a potential method to expand the SERF's dynamic range in order to probe higher axion/ALP Compton frequencies.

Mapping the magnetic and crystal structure in cobalt nanowires

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

Cantu-Valle, Jesus; Betancourt, Israel; Sanchez, John E.

2015-07-14

Using off-axis electron holography under Lorentz microscopy conditions to experimentally determine the magnetization distribution in individual cobalt (Co) nanowires, and scanning precession-electron diffraction to obtain their crystalline orientation phase map, allowed us to directly visualize with high accuracy the effect of crystallographic texture on the magnetization of nanowires. The influence of grain boundaries and disorientations on the magnetic structure is correlated on the basis of micromagnetic analysis in order to establish the detailed relationship between magnetic and crystalline structure. This approach demonstrates the applicability of the method employed and provides further understanding on the effect of crystalline structure on magneticmore » properties at the nanometric scale.« less

SELF-TRAPPING OF DISKOSEISMIC CORRUGATION MODES IN NEUTRON STAR SPACETIMES

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

Tsang, David; Pappas, George

2016-02-10

We examine the effects of higher-order multipole contributions of rotating neutron star (NS) spacetimes on the propagation of corrugation (c-)modes within a thin accretion disk. We find that the Lense–Thirring precession frequency, which determines the propagation region of the low-frequency fundamental corrugation modes, can experience a turnover allowing for c-modes to become self-trapped for sufficiently high dimensionless spin j and quadrupole rotational deformability α. If such self-trapping c-modes can be detected, e.g., through phase-resolved spectroscopy of the iron line for a high-spin low-mass accreting neutron star, this could potentially constrain the spin-induced NS quadrupole and the NS equation of state.

Multislice imaging of integrated circuits by precession X-ray ptychography.

PubMed

Shimomura, Kei; Hirose, Makoto; Takahashi, Yukio

2018-01-01

A method for nondestructively visualizing multisection nanostructures of integrated circuits by X-ray ptychography with a multislice approach is proposed. In this study, tilt-series ptychographic diffraction data sets of a two-layered circuit with a ∼1.4 µm gap at nine incident angles are collected in a wide Q range and then artifact-reduced phase images of each layer are successfully reconstructed at ∼10 nm resolution. The present method has great potential for the three-dimensional observation of flat specimens with thickness on the order of 100 µm, such as three-dimensional stacked integrated circuits based on through-silicon vias, without laborious sample preparation.

Astronomical calibration of Gauss to Matuyama sapropels in the Mediterranean and implication for the Geomagnetic Polarity Time Scale

NASA Astrophysics Data System (ADS)

Hilgen, F. J.

1991-06-01

The astronomically calibrated age of the Olduvai Subchron is established by correlating the cyclic sapropel patterns in the Vrica section and in the sections of Semaforo (Italy), Singa (Italy), Punta Piccola (Sicily), and Francocastello (Crete) to the new astronomical solutions for the precession of the equinox and eccentricity of the earth's orbit, using inferred phase relationships between the sapropel cycles and orbital cycles. The resultant ages for the Olduvai and for older boundaries are then compared with conventional, as well as other orbitally tuned ages, for these polarity transitions. It is shown that this astronomically calibrated time scale can be extended back to the Miocene/Pliocene boundary.

Self-Trapping of Diskoseismic Corrugation Modes in Neutron Star Spacetimes

NASA Astrophysics Data System (ADS)

Tsang, David; Pappas, George

2016-02-01

We examine the effects of higher-order multipole contributions of rotating neutron star (NS) spacetimes on the propagation of corrugation (c-)modes within a thin accretion disk. We find that the Lense-Thirring precession frequency, which determines the propagation region of the low-frequency fundamental corrugation modes, can experience a turnover allowing for c-modes to become self-trapped for sufficiently high dimensionless spin j and quadrupole rotational deformability α. If such self-trapping c-modes can be detected, e.g., through phase-resolved spectroscopy of the iron line for a high-spin low-mass accreting neutron star, this could potentially constrain the spin-induced NS quadrupole and the NS equation of state.

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 also considered tilt of Earth's spin axis; eccentricity of Earth's orbit; and precession of equinoxes:Together these, yield a complex curve for the solar constant at different latitudes,as first suggested by Croll( 1875) y Milankovitch (1920, 1930), Zeuner ( e. g. 1945), and other.

Jetted Tidal Disruption Gone MAD: Case of Dynamically Important Magnetic Field Near the Black Hole in Sw J1644+57

NASA Astrophysics Data System (ADS)

Tchekhovskoy, Alexander; Metzger, B.; Giannios, D.; Kelley, L. Z.

2013-04-01

It is likely that the unusual gamma-ray/X-ray/radio transient Swift J1644+57 was produced by a collimated relativistic jet formed in the aftermath of a tidal disruption (TD) of a star by a massive black hole (BH). Some of the properties of the event are, however, difficult to explain within the TD scenario: (1) extreme flaring and `plateau' shape of the gamma-ray/X-ray light curve during the first 10 days after the gamma-ray trigger; (2) unexpected rebrightening of the forward shock radio emission months after trigger; (3) no obvious evidence for jet precession, despite misalignment typically expected between the angular momentum of the accretion disk and BH; (4) recent abrupt shut-off in jet X-ray emission after 1.5 years. Here we show that all of these seemingly disparate mysteries are naturally resolved by one assumption: the presence of strong magnetic flux Phi threading the BH. Initially, Phi is weak relative to high fall-back mass accretion rate, Mdot, and the disk and jets precess about the BH axis = our line of sight. As Mdot drops, Phi becomes dynamically important and leads to a magnetically-arrested disk (MAD). MAD naturally aligns disk and jet axis along the BH spin axis, but only after a violent rearrangement phase (jet wobbling). This explains the erratic light curve at early times and the lack of precession at later times. We use our model for Swift J1644+57 to constrain BH and disrupted star properties, finding that a solar-mass main sequence star disrupted by a relatively low mass, 10^5-10^6 Msun, BH is consistent with the data, while a WD disruption (though still possible) is disfavored. The magnetic flux required to power Swift J1644+57 is too large to be supplied by the star itself, but it could be collected from a quiescent `fossil' accretion disk present in the galactic nucleus prior to the TD. The presence (lack of) of such a fossil disk could be a deciding factor in what TD events are accompanied by powerful jets.

Past environmental/climatic changes in the northern part of the South China Sea, input from multi-proxy analysis of core MD12-3432

NASA Astrophysics Data System (ADS)

Chen, Quan; Kissel, Catherine; Liu, Zhifei

2017-04-01

In the South China Sea, the magnetic component of marine sediment is a powerful recorder of paleoenvironmental changes linked to the regional and global climate. Based on the knowledge of the sedimentary signature of the potential sources for terrigenous sediments, the composition of marine sediments can be used to decipher the different mechanisms, forcing, and transport vectors. We report here the analysis of the magnetic properties combined with sortable silt and clay mineralogy of a 51 m long sedimentary sequence retrieved from the northern South China Sea and covering the last 400 ka. Magnetic minerals with different coercivities (magnetite, pyrrhotite and hematite) are mixed in the sequence and their relative concentration varies with time. Glacial low sea-levels reduce the land-site distance and they are illlustrated by higher concentrations in magnetites and iron-sulfides (pyrrhotite) related to the sediments previously deposited on the continental shelf and re-worked by the river. This is accompanied by increasing kaolinite content within the clay assemblage (Pearl River signature) and by coarser grains. Superimposed to this eccentricity periodicity, hematite content and smectite/(illite+chlorite) ratio present a predominant precession periodicity synchronous with the northern hemisphere summer insolation changes and therefore with that of the East Asian summer monsoon. Events of high hematite content, in phase with finer grains, coincide with precession lows, while smectite/(illite+chlorite) ratio is maximum during precession highs. Knowing that smectite is mainly produced by contemporaneous chemical weathering intensity in Luzon, we use the smectite/(illite+chlorite) ratio as a tracer for increasing weathering rate in Luzon, in turn related to enhanced East Asian summer monsoon. Hematite is not produced in large amount on adjacent lands and its association with fine sediment grains suggests that its periodic supply is related to the eolian dust transported from the Central China deserts to the studied site. Higher hematite content at this latitude may therefore be used as a tracer for weak East Asian summer monsoon intensity.

Noncircular features in Saturn's rings IV: Absolute radius scale and Saturn's pole direction

NASA Astrophysics Data System (ADS)

French, Richard G.; McGhee-French, Colleen A.; Lonergan, Katherine; Sepersky, Talia; Jacobson, Robert A.; Nicholson, Philip D.; Hedman, Mathew M.; Marouf, Essam A.; Colwell, Joshua E.

2017-07-01

We present a comprehensive solution for the geometry of Saturn's ring system, based on orbital fits to an extensive set of occultation observations of 122 individual ring edges and gaps. We begin with a restricted set of very high quality Cassini VIMS, UVIS, and RSS measurements for quasi-circular features in the C and B rings and the Cassini Division, and then successively add suitably weighted additional Cassini and historical occultation measurements (from Voyager, HST and the widely-observed 28 Sgr occultation of 3 Jul 1989) for additional non-circular features, to derive an absolute radius scale applicable across the entire classical ring system. As part of our adopted solution, we determine first-order corrections to the spacecraft trajectories used to determine the geometry of individual occultation chords. We adopt a simple linear model for Saturn's precession, and our favored solution yields a precession rate on the sky n^˙P = 0.207 ± 0 .006‧‧yr-1 , equivalent to an angular rate of polar motion ΩP = 0.451 ± 0 .014‧‧yr-1 . The 3% formal uncertainty in the fitted precession rate is approaching the point where it can provide a useful constraint on models of Saturn's interior, although realistic errors are likely to be larger, given the linear approximation of the precession model and possible unmodeled systematic errors in the spacecraft ephemerides. Our results are largely consistent with independent estimates of the precession rate based on historical RPX times (Nicholson et al., 1999 AAS/Division for Planetary Sciences Meeting Abstracts #31 31, 44.01) and from theoretical expectations that account for Titan's 700-yr precession period (Vienne and Duriez 1992, Astronomy and Astrophysics 257, 331-352). The fitted precession rate based on Cassini data only is somewhat lower, which may be an indication of unmodeled shorter term contributions to Saturn's polar motion from other satellites, or perhaps the result of inconsistencies in the assumed direction of Saturn's pole in the reconstructed Cassini spacecraft ephemerides. Overall, the agreement of our results with the widely-used French et al. (1993, Icarus 103, 163-214) radius scale is excellent, with very small (≲ 0.1 km) systematic differences, although differences in a few individual feature radii are as large as 6 km. Our new solution incorporates many more features across the ring system, and the fitted orbital elements correct for the several-km biases in the radii of many ring features in the French et al. (1993) catalog that were unresolved because of the large projected diameter of the occulted star in the 28 Sgr event. The formal errors in the fitted radii are generally quite small - on the order of tens of meters. Systematic errors stemming from uncertainty in the precession rate of Saturn's pole and its effect on the accuracy of the reconstructed Cassini trajectories are somewhat larger, but the absolute radius scale is relatively insensitive to 5-σ changes in the pole direction or precession rate, and we estimate the combined magnitude of these systematic errors and pole uncertainties to be of order 250 m. This estimate is likely to be improved once a new set of reconstructed Cassini trajectories has been developed, based on a self-consistent model for Saturn's pole. We demonstrate the utility of the new radius scale and the associated trajectory corrections in the analysis of short-wavelength density waves in the C ring. In online supplementary material, we provide in machine-readable form the more than 15,000 individual ring measurements used in this study, as well as details of the ring orbit fits underlying this work.

WASP-12b and Its Possible Fiery Demise

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-07-01

Jupiter-like planets on orbits close to their hosts are predicted to spiral ever closer to their hosts until they meet their eventual demise and yet weve never observed orbital decay. Could WASP-12b provide the first evidence?Undetected PredictionsSince the discovery of the first hot Jupiter more than 20 years ago, weve studied a number of these peculiar exoplanets. Despite our many observations, two phenomena predicted of hot Jupiters have not yet been detected, due to the long timescales needed to identify them:Tidal orbital decayTidal forces should cause a hot Jupiters orbit to shrink over time, causing the planet to eventually spiral into its host star. This phenomenon would explain a number of statistical properties of observed star-planet systems (for instance, the scarcity of gas giants with periods less than a day).An illustration of apsidal precession. [Mpfiz]Apsidal precessionThe orbits of hot Jupiters should be apsidally precessing on timescales of decades, as long as they are at least slightly eccentric. Since the precession rate depends on the planets tidally deformed mass distribution, measuring this would allow us to probe the interior of the planet.A team of scientists led by Kishore Patra (Massachusetts Institute of Technology) think that the hot Jupiter WASP-12b may be our first chance to study one of these two phenomena. The question is, which one?WASP-12bWASP-12b has orbital period of 1.09 days one of the shortest periods observed for a giant planet and weve monitored it for a decade, making it a great target to test for both of these long-term effects.Timing residuals for WASP-12b. Squares show the new data points, circles show previous data from the past decade. The data are better fit by the decay model than the precession model, but both are still consistent. [Patra et al. 2017]Patra and collaborators made transit observations with the 1.2-m telescope at the Fred Lawrence Whipple Observatory in Arizona and occultation observations with the Spitzer Space Telescope. These two new sets of observations, combined with the decade of previous observations, allowed the authors to fit models to WASP-12bs orbit over time.The results show that a constant period for WASP-12b is firmly ruled out this planets orbit is definitely changing over time. The observations are best fit by a model in which the planets orbit is tidally decaying, but a 14-year apsidal precession cycle cant be definitively ruled out.Future ProspectsPossible futures for WASP-12bs orbit, based on the decay model (red) and the precession model (blue). We should be able to differentiate between these models with a few more years of observations. [Patra et al. 2017]If the planets orbit is decaying, then the authors show that its period will shrink to zero within 3.2 million years, suggesting that were currently witnessing the last 0.2% of the planets lifetime. Supporting the orbital-decay hypothesis are independent observations that suggest WASP-12b is approaching a point of tidal disruption it appears to have an extended and escaping exosphere, for instance.While we cant yet state for certain that WASP-12bs orbit is decaying, the authors argue that we should be able to tell conclusively with a few more years of observations. Either of the two outcomes above orbital decay or apsidal precession would have exciting scientific implications, however: if WASP-12bs orbit is decaying, we can measure the tidal dissipation rate of the star. If its orbit is apsidally precessing, we may be able to measure the tidal deformability of an exoplanet. Future observations of this hot Jupiter should prove interesting!CitationKishore C. Patra et al 2017 AJ 154 4. doi:10.3847/1538-3881/aa6d75

Oriented Polar Molecules in a Solid Inert-Gas Matrix: A Proposed Method for Measuring the Electric Dipole Moment of the Electron

NASA Astrophysics Data System (ADS)

Vutha, A.; Horbatsch, M.; Hessels, E.

2018-01-01

We propose a very sensitive method for measuring the electric dipole moment of the electron using polar molecules embedded in a cryogenic solid matrix of inert-gas atoms. The polar molecules can be oriented in the $\\hat{\\rm{z}}$ direction by an applied electric field, as has recently been demonstrated by Park, et al. [Angewandte Chemie {\\bf 129}, 1066 (2017)]. The trapped molecules are prepared into a state which has its electron spin perpendicular to $\\hat{\\rm{z}}$, and a magnetic field along $\\hat{\\rm{z}}$ causes precession of this spin. An electron electric dipole moment $d_e$ would affect this precession due to the up to 100~GV/cm effective electric field produced by the polar molecule. The large number of polar molecules that can be embedded in a matrix, along with the expected long coherence times for the precession, allows for the possibility of measuring $d_e$ to an accuracy that surpasses current measurements by many orders of magnitude. Because the matrix can inhibit molecular rotations and lock the orientation of the polar molecules, it may not be necessary to have an electric field present during the precession. The proposed technique can be applied using a variety of polar molecules and inert gases, which, along with other experimental variables, should allow for careful study of systematic uncertainties in the measurement.

Numerical Simulations of Naturally Tilted, Retrogradely Precessing, Nodal Superhumping Accretion Disks

NASA Astrophysics Data System (ADS)

Montgomery, M. M.

2012-02-01

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.

Precessional Instability in Binary Black Holes with Aligned Spins.

PubMed

Gerosa, Davide; Kesden, Michael; O'Shaughnessy, Richard; Klein, Antoine; Berti, Emanuele; Sperhake, Ulrich; Trifirò, Daniele

2015-10-02

Binary black holes on quasicircular orbits with spins aligned with their orbital angular momentum have been test beds for analytic and numerical relativity for decades, not least because symmetry ensures that such configurations are equilibrium solutions to the spin-precession equations. In this work, we show that these solutions can be unstable when the spin of the higher-mass black hole is aligned with the orbital angular momentum and the spin of the lower-mass black hole is antialigned. Spins in these configurations are unstable to precession to large misalignment when the binary separation r is between the values r(ud±)=(√(χ(1))±√(qχ(2)))(4)(1-q)(-2)M, where M is the total mass, q≡m(2)/m(1) is the mass ratio, and χ(1) (χ(2)) is the dimensionless spin of the more (less) massive black hole. This instability exists for a wide range of spin magnitudes and mass ratios and can occur in the strong-field regime near the merger. We describe the origin and nature of the instability using recently developed analytical techniques to characterize fully generic spin precession. This instability provides a channel to circumvent astrophysical spin alignment at large binary separations, allowing significant spin precession prior to merger affecting both gravitational-wave and electromagnetic signatures of stellar-mass and supermassive binary black holes.

Phase-space networks of geometrically frustrated systems.

PubMed

Han, Yilong

2009-11-01

We illustrate a network approach to the phase-space study by using two geometrical frustration models: antiferromagnet on triangular lattice and square ice. Their highly degenerated ground states are mapped as discrete networks such that the quantitative network analysis can be applied to phase-space studies. The resulting phase spaces share some comon features and establish a class of complex networks with unique Gaussian spectral densities. Although phase-space networks are heterogeneously connected, the systems are still ergodic due to the random Poisson processes. This network approach can be generalized to phase spaces of some other complex systems.

The Effects of Theta Precession on Spatial Learning and Simplicial Complex Dynamics in a Topological Model of the Hippocampal Spatial Map

PubMed Central

Arai, Mamiko; Brandt, Vicky; Dabaghian, Yuri

2014-01-01

Learning arises through the activity of large ensembles of cells, yet most of the data neuroscientists accumulate is at the level of individual neurons; we need models that can bridge this gap. We have taken spatial learning as our starting point, computationally modeling the activity of place cells using methods derived from algebraic topology, especially persistent homology. We previously showed that ensembles of hundreds of place cells could accurately encode topological information about different environments (“learn” the space) within certain values of place cell firing rate, place field size, and cell population; we called this parameter space the learning region. Here we advance the model both technically and conceptually. To make the model more physiological, we explored the effects of theta precession on spatial learning in our virtual ensembles. Theta precession, which is believed to influence learning and memory, did in fact enhance learning in our model, increasing both speed and the size of the learning region. Interestingly, theta precession also increased the number of spurious loops during simplicial complex formation. We next explored how downstream readout neurons might define co-firing by grouping together cells within different windows of time and thereby capturing different degrees of temporal overlap between spike trains. Our model's optimum coactivity window correlates well with experimental data, ranging from ∼150–200 msec. We further studied the relationship between learning time, window width, and theta precession. Our results validate our topological model for spatial learning and open new avenues for connecting data at the level of individual neurons to behavioral outcomes at the neuronal ensemble level. Finally, we analyzed the dynamics of simplicial complex formation and loop transience to propose that the simplicial complex provides a useful working description of the spatial learning process. PMID:24945927

SEEING THROUGH THE RING: NEAR-INFRARED PHOTOMETRY OF V582 MON (KH 15D)

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

Arulanantham, Nicole A.; Herbst, William; Cody, Ann Marie

2016-04-15

We examine the light and color evolution of the T Tauri binary KH 15D through photometry obtained at wavelengths between 0.55 and 8.0 μm. The data were collected with A Novel Dual Imaging CAMera (ANDICAM) on the 1.3 m SMARTS telescope at Cerro-Tololo Inter-American Observatory and with InfraRed Array Camera on the Spitzer Space Telescope. We show that the system’s circumbinary ring, which acts as a screen that covers and uncovers different portions of the binary orbit as the ring precesses, has reached an orientation where the brighter component (star B) fully or nearly fully emerges during each orbital cycle.more » The fainter component (star A) remains fully occulted by the screen at all phases. The leading and trailing edges of the screen move across the sky at the same rate of ∼15 m s{sup −1}, consistent with expectation for a ring with a radius and width of ∼4 au and a precession period of ∼6500 years. Light and color variations continue to indicate that the screen is sharp edged and opaque at VRIJH wavelengths. However, we find an increasing transparency of the ring edge at 2.2, 3.6, and 4.5 μm. Reddening seen at the beginning of the eclipse that occurred during the CSI 2264 campaign particularly suggests selective extinction by a population of large dust grains. Meanwhile, the gradual bluing observed while star B is setting is indicative of forward scattering effects at the edge of the ring. The spectral energy distribution of the system at its bright phase shows no evidence of infrared excess emission that can be attributed to radiation from the ring or other dust component out to 8 μm.« less

Indian monsoon variations during three contrasting climatic periods: The Holocene, Heinrich Stadial 2 and the last interglacial-glacial transition

NASA Astrophysics Data System (ADS)

Zorzi, Coralie; Sanchez Goñi, Maria Fernanda; Anupama, Krishnamurthy; Prasad, Srinivasan; Hanquiez, Vincent; Johnson, Joel; Giosan, Liviu

2015-10-01

In contrast to the East Asian and African monsoons the Indian monsoon is still poorly documented throughout the last climatic cycle (last 135,000 years). Pollen analysis from two marine sediment cores (NGHP-01-16A and NGHP-01-19B) collected from the offshore Godavari and Mahanadi basins, both located in the Core Monsoon Zone (CMZ) reveals changes in Indian summer monsoon variability and intensity during three contrasting climatic periods: the Holocene, the Heinrich Stadial (HS) 2 and the Marine Isotopic Stage (MIS) 5/4 during the ice sheet growth transition. During the first part of the Holocene between 11,300 and 4200 cal years BP, characterized by high insolation (minimum precession, maximum obliquity), the maximum extension of the coastal forest and mangrove reflects high monsoon rainfall. This climatic regime contrasts with that of the second phase of the Holocene, from 4200 cal years BP to the present, marked by the development of drier vegetation in a context of low insolation (maximum precession, minimum obliquity). The historical period in India is characterized by an alternation of strong and weak monsoon centennial phases that may reflect the Medieval Climate Anomaly and the Little Ice Age, respectively. During the HS 2, a period of low insolation and extensive iceberg discharge in the North Atlantic Ocean, vegetation was dominated by grassland and dry flora indicating pronounced aridity as the result of a weak Indian summer monsoon. The MIS 5/4 glaciation, also associated with low insolation but moderate freshwater fluxes, was characterized by a weaker reduction of the Indian summer monsoon and a decrease of seasonal contrast as recorded by the expansion of dry vegetation and the development of Artemisia, respectively. Our results support model predictions suggesting that insolation changes control the long term trend of the Indian monsoon precipitation, but its millennial scale variability and intensity are instead modulated by atmospheric teleconnections to remote phenomena in the North Atlantic, Eurasia or the Indian Ocean.

Stability of rotors and focal sources for human atrial fibrillation: focal impulse and rotor mapping (FIRM) of AF sources and fibrillatory conduction.

PubMed

Swarup, Vijay; Baykaner, Tina; Rostamian, Armand; Daubert, James P; Hummel, John; Krummen, David E; Trikha, Rishi; Miller, John M; Tomassoni, Gery F; Narayan, Sanjiv M

2014-12-01

Several groups report electrical rotors or focal sources that sustain atrial fibrillation (AF) after it has been triggered. However, it is difficult to separate stable from unstable activity in prior studies that examined only seconds of AF. We applied phase-based focal impulse and rotor mapping (FIRM) to study the dynamics of rotors/sources in human AF over prolonged periods of time. We prospectively mapped AF in 260 patients (169 persistent, 61 ± 12 years) at 6 centers in the FIRM registry, using baskets with 64 contact electrodes per atrium. AF was phase mapped (RhythmView, Topera, Menlo Park, CA, USA). AF propagation movies were interpreted by each operator to assess the source stability/dynamics over tens of minutes before ablation. Sources were identified in 258 of 260 of patients (99%), for 2.8 ± 1.4 sources/patient (1.8 ± 1.1 in left, 1.1 ± 0.8 in right atria). While AF sources precessed in stable regions, emanating activity including spiral waves varied from collision/fusion (fibrillatory conduction). Each source lay in stable atrial regions for 4,196 ± 6,360 cycles, with no differences between paroxysmal versus persistent AF (4,290 ± 5,847 vs. 4,150 ± 6,604; P = 0.78), or right versus left atrial sources (P = 0.26). Rotors and focal sources for human AF mapped by FIRM over prolonged time periods precess ("wobble") but remain within stable regions for thousands of cycles. Conversely, emanating activity such as spiral waves disorganize and collide with the fibrillatory milieu, explaining difficulties in using activation mapping or signal processing analyses at fixed electrodes to detect AF rotors. These results provide a rationale for targeted ablation at AF sources rather than fibrillatory spiral waves. © 2014 Wiley Periodicals, Inc.

The variations in eccentricity and apse precession rate of a narrow ring perturbed by a close satellite

NASA Technical Reports Server (NTRS)

Borderies, N.; Goldreich, P.; Tremaine, S.

1983-01-01

The first-order perturbations of orbital eccentricity and apse precession rate for the case of a narrow ring, due to a close satellite whose orbit is also eccentric, are described by means of a Hamiltonian. The present treatment covers cases in which the satellite crosses the ring, and the level curves of the Hamiltonian are displayed for several parameter values. The results obtained are applied to the interaction of Saturn's F ring with its inner shepherd satellite.

Abiotic and biotic responses to Milankovitch-forced megamonsoon and glacial cycles recorded in South China at the end of the Late Paleozoic Ice Age

NASA Astrophysics Data System (ADS)

Fang, Qiang; Wu, Huaichun; Hinnov, Linda A.; Tian, Wenqian; Wang, Xunlian; Yang, Tianshui; Li, Haiyan; Zhang, Shihong

2018-04-01

At the end of the Late Paleozoic Ice Age (LPIA) from late Early Permian to early Late Permian, the global climate was impacted by a prevailing megamonsoon and Gondwanan deglaciation. To better understand the abiotic and biotic responses to Milankovitch-forced climate changes during this time period, multi-element X-ray fluorescence (XRF) geochemistry analyses were conducted on 948 samples from the late Early-late Middle Permian Maokou Formation at Shangsi, South China. The Fe/Ti, S/Ti, Ba/Ti and Ca time series, which were calibrated with an existing "floating" astronomical time scale (ATS), show the entire suite of Milankovitch rhythms including 405 kyr long eccentricity, 128 and 95 kyr short eccentricity, 33 kyr obliquity and 20 kyr precession. Spectral coherency and cross-phase analysis reveals that chemical weathering (monitored by Fe/Ti) and upwelling (captured by S/Ti and Ba/Ti) are nearly antiphase in the precession band, which suggests a contrast between summer and winter monsoon intensities. Strong obliquity signal in the Ba/Ti series is proposed to derive from changes in thermohaline circulation intensity from glaciation dynamics in southern Gondwana. The abundance of foraminifer, brachiopod and ostracod faunas within the Maokou Formation were mainly controlled by the 1.1 Myr obliquity modulation cycle. The obliquity-forced high-nutrient and oxygen-depleted conditions generally produced a benthic foraminifer bloom, but threatened the brachiopod and ostracod faunas.

Single and double acquisition strategies for compensation of artifacts from eddy current and transient oscillation in balanced steady-state free precession.

PubMed

Lee, Hyun-Soo; Choi, Seung Hong; Park, Sung-Hong

2017-07-01

To develop single and double acquisition methods to compensate for artifacts from eddy currents and transient oscillations in balanced steady-state free precession (bSSFP) with centric phase-encoding (PE) order for magnetization-prepared bSSFP imaging. A single and four different double acquisition methods were developed and evaluated with Bloch equation simulations, phantom/in vivo experiments, and quantitative analyses. For the single acquisition method, multiple PE groups, each of which was composed of N linearly changing PE lines, were ordered in a pseudocentric manner for optimal contrast and minimal signal fluctuations. Double acquisition methods used complex averaging of two images that had opposite artifact patterns from different acquisition orders or from different numbers of dummy scans. Simulation results showed high sensitivity of eddy-current and transient-oscillation artifacts to off-resonance frequency and PE schemes. The artifacts were reduced with the PE-grouping with N values from 3 to 8, similar to or better than the conventional pairing scheme of N = 2. The proposed double acquisition methods removed the remaining artifacts significantly. The proposed methods conserved detailed structures in magnetization transfer imaging well, compared with the conventional methods. The proposed single and double acquisition methods can be useful for artifact-free magnetization-prepared bSSFP imaging with desired contrast and minimized dummy scans. Magn Reson Med 78:254-263, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

Study of magnetic resonance with parametric modulation in a potassium vapor cell

NASA Astrophysics Data System (ADS)

Zhang, Rui; Wang, Zhiguo; Peng, Xiang; Li, Wenhao; Li, Songjian; Guo, Hong; Cream Team

2017-04-01

A typical magnetic-resonance scheme employs a static bias magnetic field and an orthogonal driving magnetic field oscillating at the Larmor frequency, at which the atomic polarization precesses around the static magnetic field. We demonstrate in a potassium vapor cell the variations of the resonance condition and the spin precession dynamics resulting from the parametric modulation of the bias field, which are in well agreement with theoretical predictions from the Bloch equation. We show that, the driving magnetic field with the frequency detuned by different harmonics of the parametric modulation frequency can lead to resonance as well. Also, a series of frequency sidebands centered at the driving frequency and spaced by the parametric modulation frequency can be observed in the precession of the atomic polarization. These effects could be used in different atomic magnetometry applications. This work is supported by the National Science Fund for Distinguished Young Scholars of China (Grant No. 61225003) and the National Natural Science Foundation of China (Grant Nos. 61531003 and 61571018).

Gas dynamics and mixture formation in swirled flows with precession of air flow

NASA Astrophysics Data System (ADS)

Tretyakov, V. V.; Sviridenkov, A. A.

2017-10-01

The effect of precessing air flow on the processes of mixture formation in the wake of the front winding devices of the combustion chambers is considered. Visual observations have shown that at different times the shape of the atomized jet is highly variable and has signs of precessing motion. The experimental data on the distribution of the velocity and concentration fields of the droplet fuel in the working volume of the flame tube of a typical combustion chamber are obtained. The method of calculating flows consisted in integrating the complete system of Reynolds equations written in Euler variables and closed with the two-parameter model of turbulence k-ε. Calculation of the concentration fields of droplet and vapor fuel is based on the use of models for disintegration into droplets of fuel jets, fragmentation of droplets and analysis of motion and evaporation of individual droplets in the air flow. Comparison of the calculation results with experimental data showed their good agreement.

Nonlinear Large Scale Flow in a Precessing Cylinder and Its Ability To Drive Dynamo Action

NASA Astrophysics Data System (ADS)

Giesecke, André; Vogt, Tobias; Gundrum, Thomas; Stefani, Frank

2018-01-01

We have conducted experimental measurements and numerical simulations of a precession-driven flow in a cylindrical cavity. The study is dedicated to the precession dynamo experiment currently under construction at Helmholtz-Zentrum Dresden-Rossendorf and aims at the evaluation of the hydrodynamic flow with respect to its ability to drive a dynamo. We focus on the strongly nonlinear regime in which the flow is essentially composed of the directly forced primary Kelvin mode and higher modes in terms of standing inertial waves arising from nonlinear self-interactions. We obtain an excellent agreement between experiment and simulation with regard to both flow amplitudes and flow geometry. A peculiarity is the resonance-like emergence of an axisymmetric mode that represents a double roll structure in the meridional plane. Kinematic simulations of the magnetic field evolution induced by the time-averaged flow yield dynamo action at critical magnetic Reynolds numbers around Rmc≈430 , which is well within the range of the planned liquid sodium experiment.

Non-equilibrium dynamics of 2D liquid crystals driven by transmembrane gas flow.

PubMed

Seki, Kazuyoshi; Ueda, Ken; Okumura, Yu-ichi; Tabe, Yuka

2011-07-20

Free-standing films composed of several layers of chiral smectic liquid crystals (SmC*) exhibited unidirectional director precession under various vapor transfers across the films. When the transferred vapors were general organic solvents, the precession speed linearly depended on the momentum of the transmembrane vapors, where the proportional constant was independent of the kind of vapor. In contrast, the same SmC* films under water transfer exhibited precession in the opposite direction. As a possible reason for the rotational inversion, we suggest the competition of two origins for the torques, one of which is microscopic and the other macroscopic. Next, we tried to move an external object by making use of the liquid crystal (LC) motion. When a solid or a liquid particle was set on a film under vapor transfer, the particle was rotated in the same direction as the LC molecules. Using home-made laser tweezers, we measured the force transmitted from the film to the particle, which we found to be several pN.

Nonlinear Large Scale Flow in a Precessing Cylinder and Its Ability To Drive Dynamo Action.

PubMed

Giesecke, André; Vogt, Tobias; Gundrum, Thomas; Stefani, Frank

2018-01-12

We have conducted experimental measurements and numerical simulations of a precession-driven flow in a cylindrical cavity. The study is dedicated to the precession dynamo experiment currently under construction at Helmholtz-Zentrum Dresden-Rossendorf and aims at the evaluation of the hydrodynamic flow with respect to its ability to drive a dynamo. We focus on the strongly nonlinear regime in which the flow is essentially composed of the directly forced primary Kelvin mode and higher modes in terms of standing inertial waves arising from nonlinear self-interactions. We obtain an excellent agreement between experiment and simulation with regard to both flow amplitudes and flow geometry. A peculiarity is the resonance-like emergence of an axisymmetric mode that represents a double roll structure in the meridional plane. Kinematic simulations of the magnetic field evolution induced by the time-averaged flow yield dynamo action at critical magnetic Reynolds numbers around Rm^{c}≈430, which is well within the range of the planned liquid sodium experiment.

WASP-12b: Orbital Decay or Apsidal Precession?

NASA Astrophysics Data System (ADS)

Winn, Joshua; Knutson, Heather

2018-05-01

Over the last decade, the interval between the transits of the hot Jupiter WASP-12b has been steadily shrinking by 29 milliseconds per year. This may represent the first direct detection of tidal orbital decay, a phenomenon that has long been predicted to occur for hot Jupiters and that features in many theories to explain their properties. Another viable explanation for the apparent period decrease is that the orbit is slightly eccentric and apsidally precessing, in which case the data could be used to measure the planet's Love number. This would be a rare and precious constraint on its interior density distribution. The best way to tell the difference is to combine new Spitzer observations of secondary eclipses with ongoing ground-based transit observations. Orbital decay predicts that the transit and eclipse timing residuals will have the same sign, while apsidal precession would produce anti-correlated residuals. We propose to observe 4 eclipses with Spitzer during Cycle 14, which will allow the two hypotheses to be distinguished with high confidence.

General Relativistic Effects and QPOs in X-Ray Binaries

NASA Astrophysics Data System (ADS)

Markovic, D.; Lamb, F.

1999-05-01

We have investigated whether general relativistic effects may be responsible for some of the quasi-periodic X-ray brightness oscillations (QPOs) with frequencies 20--300 Hz observed in low-mass binary systems containing accreting neutron stars and black hole candidates. In particular, we have computed the motions of accreting gas in the strong gravitational fields near such objects and have explored possible mechanisms for producing X-ray flux oscillations. We have discovered a family of global gravitomagnetic (Lense-Thirring) warping modes of the inner accretion disk that have precession frequencies ranging up to the single-particle gravitomagnetic precession frequency at the inner edge of the disk, which is 30 Hz if the disk extends inward to the innermost stable circular orbit around a compact object of solar mass with dimensionless angular momentum cJ/GM2 0.2. The highest-frequency warping modes are very localized spiral corrugations of the inner disk and are weakly damped, with Q values 2--50. Precession of regions of enhanced viscous dissipation or modulation of the accretion flow by the precession may produce observable periodic variation of the X-ray flux. Detectable effects might also be produced if the gas in the inner disk breaks up into a collection of distinct clumps. We have analyzed the dynamics of such clumps as well as the conditions required for their formation and survival on time scales long enough to produce oscillations with the coherence observed in X-ray binaries.

Anxiety Sensitivity and Pre-Cessation Smoking Processes: Testing the Independent and Combined Mediating Effects of Negative Affect–Reduction Expectancies and Motives

PubMed Central

Farris, Samantha G.; Leventhal, Adam M.; Schmidt, Norman B.; Zvolensky, Michael J.

2015-01-01

Objective: Anxiety sensitivity appears to be relevant in understanding the nature of emotional symptoms and disorders associated with smoking. Negative-reinforcement smoking expectancies and motives are implicated as core regulatory processes that may explain, in part, the anxiety sensitivity–smoking interrelations; however, these pathways have received little empirical attention. Method: Participants (N = 471) were adult treatment-seeking daily smokers assessed for a smoking-cessation trial who provided baseline data; 157 participants provided within-treatment (pre-cessation) data. Anxiety sensitivity was examined as a cross-sectional predictor of several baseline smoking processes (nicotine dependence, perceived barriers to cessation, severity of prior withdrawal-related quit problems) and pre-cessation processes including nicotine withdrawal and smoking urges (assessed during 3 weeks before the quit day). Baseline negative-reinforcement smoking expectancies and motives were tested as simultaneous mediators via parallel multiple mediator models. Results: Higher levels of anxiety sensitivity were related to higher levels of nicotine dependence, greater perceived barriers to smoking cessation, more severe withdrawal-related problems during prior quit attempts, and greater average withdrawal before the quit day; effects were indirectly explained by the combination of both mediators. Higher levels of anxiety sensitivity were not directly related to pre-cessation smoking urges but were indirectly related through the independent and combined effects of the mediators. Conclusions: These empirical findings bolster theoretical models of anxiety sensitivity and smoking and identify targets for nicotine dependence etiology research and cessation interventions. PMID:25785807

Linear study of the precessional fishbone instability

NASA Astrophysics Data System (ADS)

Idouakass, M.; Faganello, M.; Berk, H. L.; Garbet, X.; Benkadda, S.

2016-10-01

The precessional fishbone instability is an m = n = 1 internal kink mode destabilized by a population of trapped energetic particles. The linear phase of this instability is studied here, analytically and numerically, with a simplified model. This model uses the reduced magneto-hydrodynamics equations for the bulk plasma and the Vlasov equation for a population of energetic particles with a radially decreasing density. A threshold condition for the instability is found, as well as a linear growth rate and frequency. It is shown that the mode frequency is given by the precession frequency of the deeply trapped energetic particles at the position of strongest radial gradient. The growth rate is shown to scale with the energetic particle density and particle energy while it is decreased by continuum damping.

Generation of a spin-polarized electron beam by multipole magnetic fields.

PubMed

Karimi, Ebrahim; Grillo, Vincenzo; Boyd, Robert W; Santamato, Enrico

2014-03-01

The propagation of an electron beam in the presence of transverse magnetic fields possessing integer topological charges is presented. The spin-magnetic interaction introduces a nonuniform spin precession of the electrons that gains a space-variant geometrical phase in the transverse plane proportional to the field's topological charge, whose handedness depends on the input electron's spin state. A combination of our proposed device with an electron orbital angular momentum sorter can be utilized as a spin-filter of electron beams in a mid-energy range. We examine these two different configurations of a partial spin-filter generator numerically. The results of this analysis could prove useful in the design of an improved electron microscope. Copyright © 2013 Elsevier B.V. All rights reserved.

Localized and delocalized motion of colloidal particles on a magnetic bubble lattice.

PubMed

Tierno, Pietro; Johansen, Tom H; Fischer, Thomas M

2007-07-20

We study the motion of paramagnetic colloidal particles placed above magnetic bubble domains of a uniaxial garnet film and driven through the lattice by external magnetic field modulation. An external tunable precessing field propels the particles either in localized orbits around the bubbles or in superdiffusive or ballistic motion through the bubble array. This motion results from the interplay between the driving rotating signal, the viscous drag force and the periodic magnetic energy landscape. We explain the transition in terms of the incommensurability between the transit frequency of the particle through a unit cell and the modulation frequency. Ballistic motion dynamically breaks the symmetry of the array and the phase locked particles follow one of the six crystal directions.

Investigation of the Magnetic Properties of Na0.7CoO2 Prepared by Electrochemical Reaction

NASA Astrophysics Data System (ADS)

Sassa, Y.; Umegaki, I.; Nozaki, H.; Forslund, O. K.; Delmas, C.; Orain, J.-C.; Amato, A.; Andreica, D.; Månsson, M.; Sugiyama, J.

We report a muon spin rotation and relaxation (μ+SR) study on Na0.7CoO2 powder samples, where the sodium (Na) has been intercalated via an electrochemical reaction inside a Na-ion battery. The zero field μ+SR measurement at T = 2 K shows a paramagnetic state for the as-grown sample whereas an antiferromagnetic (AF) ordered state is seen for the electrochemically cycled one. Furthermore, the temperature dependence of the muon-spin precession frequencies reveals a Néel transition temperature of TN = 22 K. The results demonstrate the importance of having high-quality homogenous samples, and put the existing NaxCoO2 magnetic phase diagram under debate.

The effect of support flexibility and damping on the dynamic response of a single mass flexible rotor in elastic bearings

NASA Technical Reports Server (NTRS)

Kirk, R. G.; Gunter, E. J.

1972-01-01

The dynamic unabalance response and transient motion of the single mass Jeffcott rotor in elastic bearings mounted on damped, flexible supports are discussed. A steady state analysis of the shaft and the bearing housing motion was made by assuming synchronous precession of the system. The conditions under which the support system would act as a dynamic vibration absorber at the rotor critical speed were studied. Plots of the rotor and support amplitudes, phase angles, and forces transmitted were evaluated by the computer and the performance curves were plotted by an automatic plotter unit. Curves are presented on the optimization of the support housing characteristics of attenuate the rotor synchronous unbalance response.

Low Frequency Quasi-periodic Oscillations in the High-eccentric LMXB Cir X-1: Extending the WK Correlation for Z Sources

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

Bu, Qingcui; Chen, Li; Belloni, T. M.

Using archival Rossi X-ray Timing Explorer ( RXTE ) data, we studied the low-frequency quasi-periodic oscillations (LFQPOs) in the neutron star low-mass X-ray binary (LMXB) Cir X-1 and examined their contribution to frequency–frequency correlations for Z sources. We also studied the orbital phase effects on the LFQPO properties and found them to be phase independent. Comparing LFQPO frequencies in different classes of LMXBs, we found that systems that show both Z and atoll states form a common track with atoll/BH sources in the so-called WK correlation, while persistent Z systems are offset by a factor of about two. We foundmore » that neither source luminosity nor mass accretion rate is related to the shift of persistent Z systems. We discuss the possibility of a misidentification of fundamental frequency for horizontal branch oscillations from persistent Z systems and interpreted the oscillations in terms of models based on relativistic precession.« less

Fundamental Phenomena on Fuel Decomposition and Boundary-Layer Combustion Precesses with Applications to Hybrid Rocket Motors. Part 1; Experimental Investigation

NASA Technical Reports Server (NTRS)

Kuo, Kenneth K.; Lu, Yeu-Cherng; Chiaverini, Martin J.; Johnson, David K.; Serin, Nadir; Risha, Grant A.; Merkle, Charles L.; Venkateswaran, Sankaran

1996-01-01

This final report summarizes the major findings on the subject of 'Fundamental Phenomena on Fuel Decomposition and Boundary-Layer Combustion Processes with Applications to Hybrid Rocket Motors', performed from 1 April 1994 to 30 June 1996. Both experimental results from Task 1 and theoretical/numerical results from Task 2 are reported here in two parts. Part 1 covers the experimental work performed and describes the test facility setup, data reduction techniques employed, and results of the test firings, including effects of operating conditions and fuel additives on solid fuel regression rate and thermal profiles of the condensed phase. Part 2 concerns the theoretical/numerical work. It covers physical modeling of the combustion processes including gas/surface coupling, and radiation effect on regression rate. The numerical solution of the flowfield structure and condensed phase regression behavior are presented. Experimental data from the test firings were used for numerical model validation.

Versatile low-Reynolds-number swimmer with three-dimensional maneuverability.

PubMed

Jalali, Mir Abbas; Alam, Mohammad-Reza; Mousavi, SeyyedHossein

2014-11-01

We design and simulate the motion of a swimmer, the Quadroar, with three-dimensional translation and reorientation capabilities in low-Reynolds-number conditions. The Quadroar is composed of an I-shaped frame whose body link is a simple linear actuator and four disks that can rotate about the axes of flange links. The time symmetry is broken by a combination of disk rotations and the one-dimensional expansion or contraction of the body link. The Quadroar propels on forward and transverse straight lines and performs full three-dimensional reorientation maneuvers, which enable it to swim along arbitrary trajectories. We find continuous operation modes that propel the swimmer on planar and three-dimensional periodic and quasiperiodic orbits. Precessing quasiperiodic orbits consist of slow lingering phases with cardioid or multiloop turns followed by directional propulsive phases. Quasiperiodic orbits allow the swimmer to access large parts of its neighboring space without using complex control strategies. We also discuss the feasibility of fabricating a nanoscale Quadroar by photoactive molecular rotors.

Highly selective detection of individual nuclear spins with rotary echo on an electron spin probe

DOE PAGES

Mkhitaryan, V. V.; Jelezko, F.; Dobrovitski, V. V.

2015-10-26

We consider an electronic spin, such as a nitrogen-vacancy center in diamond, weakly coupled to a large number of nuclear spins, and subjected to the Rabi driving with a periodically alternating phase. We show that by switching the driving phase synchronously with the precession of a given nuclear spin, the interaction to this spin is selectively enhanced, while the rest of the bath remains decoupled. The enhancement is of resonant character. The key feature of the suggested scheme is that the width of the resonance is adjustable, and can be greatly decreased by increasing the driving strength. Thus, the resonancemore » can be significantly narrowed, by a factor of 10–100 in comparison with the existing detection methods. Significant improvement in selectivity is explained analytically and confirmed by direct numerical many-spin simulations. As a result, the method can be applied to a wide range of solid-state systems.« less

THE NuSTAR X-RAY SPECTRUM OF HERCULES X-1: A RADIATION-DOMINATED RADIATIVE SHOCK

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

Wolff, Michael T.; Wood, Kent S.; Becker, Peter A.

2016-11-10

We report on new spectral modeling of the accreting X-ray pulsar Hercules X-1. Our radiation-dominated radiative shock model is an implementation of the analytic work of Becker and Wolff on Comptonized accretion flows onto magnetic neutron stars. We obtain a good fit to the spin-phase-averaged 4–78 keV X-ray spectrum observed by the Nuclear Spectroscopic Telescope Array during a main-on phase of the Her X-1 35 day accretion disk precession period. This model allows us to estimate the accretion rate, the Comptonizing temperature of the radiating plasma, the radius of the magnetic polar cap, and the average scattering opacity parameters inmore » the accretion column. This is in contrast to previous phenomenological models that characterized the shape of the X-ray spectrum, but could not determine the physical parameters of the accretion flow. We describe the spectral fitting details and discuss the interpretation of the accretion flow physical parameters.« less

Torques on a nearly rigid body in a relativistic gravitational field

NASA Technical Reports Server (NTRS)

Caporali, A.

1980-01-01

The effect of post-Newtonian potentials on the rotation of a nearly rigid body is shown to consist of a precession and a torque. The frequency of the precession can be exactly represented by means of suitable differential operators. The relativistic torques in the quadrupole approximation depend on the instantaneous orientation of the principal axes of one body with respect to the position like the classical torque and velocity of the other. For a relatively low mass body, such as a gyroscope, these velocity-dependent torques have no observable consequences.

Vortex rope instabilities in a model of conical draft tube

NASA Astrophysics Data System (ADS)

Skripkin, Sergey; Tsoy, Mikhail; Kuibin, Pavel; Shtork, Sergey

2017-10-01

We report on experimental studies of the formation of vortex ropes in a laboratory simplified model of hydroturbine draft tube. Work is focused on the observation of various flow patterns at the different rotational speed of turbine runner at fixed flow rate. The measurements involve high-speed visualization and pressure pulsations recordings. Draft tube wall pressure pulsations are registered by pressure transducer for different flow regimes. Vortex rope precession frequency were calculated using FFT transform. The experiments showed interesting features of precessing vortex rope like twin spiral and formation of vortex ring.

Research program in nuclear and solid state physics. [including pion absorption spectra and muon spin precession

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.

Integral equation theory study on the phase separation in star polymer nanocomposite melts.

PubMed

Zhao, Lei; Li, Yi-Gui; Zhong, Chongli

2007-10-21

The polymer reference interaction site model theory is used to investigate phase separation in star polymer nanocomposite melts. Two kinds of spinodal curves were obtained: classic fluid phase boundary for relatively low nanoparticle-monomer attraction strength and network phase boundary for relatively high nanoparticle-monomer attraction strength. The network phase boundaries are much more sensitive with nanoparticle-monomer attraction strength than the fluid phase boundaries. The interference among the arm number, arm length, and nanoparticle-monomer attraction strength was systematically investigated. When the arm lengths are short, the network phase boundary shows a marked shift toward less miscibility with increasing arm number. When the arm lengths are long enough, the network phase boundaries show opposite trends. There exists a crossover arm number value for star polymer nanocomposite melts, below which the network phase separation is consistent with that of chain polymer nanocomposite melts. However, the network phase separation shows qualitatively different behaviors when the arm number is larger than this value.

Flow-pattern identification and nonlinear dynamics of gas-liquid two-phase flow in complex networks.

PubMed

Gao, Zhongke; Jin, Ningde

2009-06-01

The identification of flow pattern is a basic and important issue in multiphase systems. Because of the complexity of phase interaction in gas-liquid two-phase flow, it is difficult to discern its flow pattern objectively. In this paper, we make a systematic study on the vertical upward gas-liquid two-phase flow using complex network. Three unique network construction methods are proposed to build three types of networks, i.e., flow pattern complex network (FPCN), fluid dynamic complex network (FDCN), and fluid structure complex network (FSCN). Through detecting the community structure of FPCN by the community-detection algorithm based on K -mean clustering, useful and interesting results are found which can be used for identifying five vertical upward gas-liquid two-phase flow patterns. To investigate the dynamic characteristics of gas-liquid two-phase flow, we construct 50 FDCNs under different flow conditions, and find that the power-law exponent and the network information entropy, which are sensitive to the flow pattern transition, can both characterize the nonlinear dynamics of gas-liquid two-phase flow. Furthermore, we construct FSCN and demonstrate how network statistic can be used to reveal the fluid structure of gas-liquid two-phase flow. In this paper, from a different perspective, we not only introduce complex network theory to the study of gas-liquid two-phase flow but also indicate that complex network may be a powerful tool for exploring nonlinear time series in practice.

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 methods are of similar efficiency, and both support equinox based as well as CIO based applications.

Basic spin physics.

PubMed

Pipe, J G

1999-11-01

Magnetic resonance imaging is fundamentally a measurement of the magnetism inherent in some nuclear isotopes; of these the proton, or hydrogen atom, is of particular interest for clinical applications. The magnetism in each nucleus is often referred to as spin. A strong, static magnetic field B0 is used to align spins, forming a magnetic density within the patient. A second, rotating magnetic field B1 (RF pulse) is applied for a short duration, which rotates the spins away from B0 in a process called excitation. After the spins are rotated away from B0, the RF pulse is turned off, and the spins precess about B0. As long as the spins are all pointing in the same direction at any one time (have phase coherence), they act in concert to create rapidly oscillating magnetic fields. These fields in turn create a current in an appropriately placed receiver coil, in a manner similar to that of an electrical generator. The precessing magnetization decays rapidly in a duration roughly given by the T2 time constant. At the same time, but at a slower rate, magnetization forms again along the direction of B0; the duration of this process is roughly expressed by the T1 time constant. The precessional frequency of each spin is proportional to the magnetic field experienced at the nucleus. Small variations in this magnetic field can have dramatic effects on the MR image, caused in part by loss of phase coherence. These magnetic field variations can arise because of magnet design, the magnetic properties (susceptibility) of tissues and other materials, and the nuclear environment unique to various sites within any given molecule. The loss of phase coherence can be effectively eliminated by the use of RF refocusing pulses. Conventional MR imaging experiments can be characterized as either gradient echo or spin echo, the latter indicating the use of a RF refocusing pulse, and by the parameters TR, TE, and flip angle alpha. Tissues, in turn, are characterized by their individual spin density, M0, and by the T1, T2, and T2* time constants. Knowledge of these parameters allows one to calculate the resulting signal from a given tissue for a given MR imaging experiment.

X-Ray Quasi-periodic Oscillations in the Lense–Thirring Precession Model. I. Variability of Relativistic Continuum

NASA Astrophysics Data System (ADS)

You, Bei; Bursa, Michal; Życki, Piotr T.

2018-05-01

We develop a Monte Carlo code to compute the Compton-scattered X-ray flux arising from a hot inner flow that undergoes Lense–Thirring precession. The hot flow intercepts seed photons from an outer truncated thin disk. A fraction of the Comptonized photons will illuminate the disk, and the reflected/reprocessed photons will contribute to the observed spectrum. The total spectrum, including disk thermal emission, hot flow Comptonization, and disk reflection, is modeled within the framework of general relativity, taking light bending and gravitational redshift into account. The simulations are performed in the context of the Lense–Thirring precession model for the low-frequency quasi-periodic oscillations, so the inner flow is assumed to precess, leading to periodic modulation of the emitted radiation. In this work, we concentrate on the energy-dependent X-ray variability of the model and, in particular, on the evolution of the variability during the spectral transition from hard to soft state, which is implemented by the decrease of the truncation radius of the outer disk toward the innermost stable circular orbit. In the hard state, where the Comptonizing flow is geometrically thick, the Comptonization is weakly variable with a fractional variability amplitude of ≤10% in the soft state, where the Comptonizing flow is cooled down and thus becomes geometrically thin, the fractional variability of the Comptonization is highly variable, increasing with photon energy. The fractional variability of the reflection increases with energy, and the reflection emission for low spin is counterintuitively more variable than the one for high spin.

Jet Precession Driven by a Supermassive Black Hole Binary System in the BL Lac Object PG 1553+113

NASA Astrophysics Data System (ADS)

Caproni, Anderson; Abraham, Zulema; Motter, Juliana Cristina; Monteiro, Hektor

2017-12-01

The recent discovery of a roughly simultaneous periodic variability in the light curves of the BL Lac object PG 1553+113 at several electromagnetic bands represents the first case of such odd behavior reported in the literature. Motivated by this, we analyzed 15 GHz interferometric maps of the parsec-scale radio jet of PG 1553+113 to verify the presence of a possible counterpart of this periodic variability. We used the Cross-entropy statistical technique to obtain the structural parameters of the Gaussian components present in the radio maps of this source. We kinematically identified seven jet components formed coincidentally with flare-like features seen in the γ-ray light curve. From the derived jet component positions in the sky plane and their kinematics (ejection epochs, proper motions, and sky position angles), we modeled their temporal changes in terms of a relativistic jet that is steadily precessing in time. Our results indicate a precession period in the observer’s reference frame of 2.24 ± 0.03 years, compatible with the periodicity detected in the light curves of PG 1553+113. However, the maxima of the jet Doppler boosting factor are systematically delayed relative to the peaks of the main γ-ray flares. We propose two scenarios that could explain this delay, both based on the existence of a supermassive black hole binary system in PG 1553+113. We estimated the characteristics of this putative binary system that also would be responsible for driving the inferred jet precession.

Comparing models of the periodic variations in spin-down and beamwidth for PSR B1828-11

NASA Astrophysics Data System (ADS)

Ashton, G.; Jones, D. I.; Prix, R.

2016-05-01

We build a framework using tools from Bayesian data analysis to evaluate models explaining the periodic variations in spin-down and beamwidth of PSR B1828-11. The available data consist of the time-averaged spin-down rate, which displays a distinctive double-peaked modulation, and measurements of the beamwidth. Two concepts exist in the literature that are capable of explaining these variations; we formulate predictive models from these and quantitatively compare them. The first concept is phenomenological and stipulates that the magnetosphere undergoes periodic switching between two metastable states as first suggested by Lyne et al. The second concept, precession, was first considered as a candidate for the modulation of B1828-11 by Stairs et al. We quantitatively compare models built from these concepts using a Bayesian odds ratio. Because the phenomenological switching model itself was informed by these data in the first place, it is difficult to specify appropriate parameter-space priors that can be trusted for an unbiased model comparison. Therefore, we first perform a parameter estimation using the spin-down data, and then use the resulting posterior distributions as priors for model comparison on the beamwidth data. We find that a precession model with a simple circular Gaussian beam geometry fails to appropriately describe the data, while allowing for a more general beam geometry provides a good fit to the data. The resulting odds between the precession model (with a general beam geometry) and the switching model are estimated as 102.7±0.5 in favour of the precession model.

Proterozoic Milankovitch cycles and the history of the solar system.

PubMed

Meyers, Stephen R; Malinverno, Alberto

2018-06-19

The geologic record of Milankovitch climate cycles provides a rich conceptual and temporal framework for evaluating Earth system evolution, bestowing a sharp lens through which to view our planet's history. However, the utility of these cycles for constraining the early Earth system is hindered by seemingly insurmountable uncertainties in our knowledge of solar system behavior (including Earth-Moon history), and poor temporal control for validation of cycle periods (e.g., from radioisotopic dates). Here we address these problems using a Bayesian inversion approach to quantitatively link astronomical theory with geologic observation, allowing a reconstruction of Proterozoic astronomical cycles, fundamental frequencies of the solar system, the precession constant, and the underlying geologic timescale, directly from stratigraphic data. Application of the approach to 1.4-billion-year-old rhythmites indicates a precession constant of 85.79 ± 2.72 arcsec/year (2σ), an Earth-Moon distance of 340,900 ± 2,600 km (2σ), and length of day of 18.68 ± 0.25 hours (2σ), with dominant climatic precession cycles of ∼14 ky and eccentricity cycles of ∼131 ky. The results confirm reduced tidal dissipation in the Proterozoic. A complementary analysis of Eocene rhythmites (∼55 Ma) illustrates how the approach offers a means to map out ancient solar system behavior and Earth-Moon history using the geologic archive. The method also provides robust quantitative uncertainties on the eccentricity and climatic precession periods, and derived astronomical timescales. As a consequence, the temporal resolution of ancient Earth system processes is enhanced, and our knowledge of early solar system dynamics is greatly improved.

Self-force correction to geodetic spin precession in Kerr spacetime

NASA Astrophysics Data System (ADS)

Akcay, Sarp

2017-08-01

We present an expression for the gravitational self-force correction to the geodetic spin precession of a spinning compact object with small, but non-negligible mass in a bound, equatorial orbit around a Kerr black hole. We consider only conservative backreaction effects due to the mass of the compact object (m1), thus neglecting the effects of its spin s1 on its motion; i.e., we impose s1≪G m12/c and m1≪m2, where m2 is the mass parameter of the background Kerr spacetime. We encapsulate the correction to the spin precession in ψ , the ratio of the accumulated spin-precession angle to the total azimuthal angle over one radial orbit in the equatorial plane. Our formulation considers the gauge-invariant O (m1) part of the correction to ψ , denoted by Δ ψ , and is a generalization of the results of Akcay et al. [Classical Quantum Gravity 34, 084001 (2017), 10.1088/1361-6382/aa61d6] to Kerr spacetime. Additionally, we compute the zero-eccentricity limit of Δ ψ and show that this quantity differs from the circular orbit Δ ψcirc by a gauge-invariant quantity containing the gravitational self-force correction to general relativistic periapsis advance in Kerr spacetime. Our result for Δ ψ is expressed in a manner that readily accommodates numerical/analytical self-force computations, e.g., in the radiation gauge, and paves the way for the computation of a new eccentric-orbit Kerr gauge invariant beyond the generalized redshift.

Measuring Relativistic effects in the field of the Earth with Laser Ranged Satellites and the LARASE research program

NASA Astrophysics Data System (ADS)

Lucchesi, David; Anselmo, Luciano; Bassan, Massimo; Magnafico, Carmelo; Pardini, Carmen; Peron, Roberto; Pucacco, Giuseppe; Stanga, Ruggero; Visco, Massimo

2017-04-01

The main goal of the LARASE (LAser RAnged Satellites Experiment) research program is to obtain refined tests of Einstein's theory of General Relativity (GR) by means of very precise measurements of the round-trip time among a number of ground stations of the International Laser Ranging Service (ILRS) network and a set of geodetic satellites. These measurements are guaranteed by means of the powerful and precise Satellite Laser Ranging (SLR) technique. In particular, a big effort of LARASE is dedicated to improve the dynamical models of the LAGEOS, LAGEOS II and LARES satellites, with the objective to obtain a more precise and accurate determination of their orbit. These activities contribute to reach a final error budget that should be robust and reliable in the evaluation of the main systematic errors sources that come to play a major role in masking the relativistic precession on the orbit of these laser-ranged satellites. These error sources may be of gravitational and non-gravitational origin. It is important to stress that a more accurate and precise orbit determination, based on more reliable dynamical models, represents a fundamental prerequisite in order to reach a sub-mm precision in the root-mean-square of the SLR range residuals and, consequently, to gather benefits in the fields of geophysics and space geodesy, such as stations coordinates knowledge, geocenter determination and the realization of the Earth's reference frame. The results reached over the last year will be presented in terms of the improvements achieved in the dynamical model, in the orbit determination and, finally, in the measurement of the relativistic precessions that act on the orbit of the satellites considered.

The default mode network and the working memory network are not anti-correlated during all phases of a working memory task.

PubMed

Piccoli, Tommaso; Valente, Giancarlo; Linden, David E J; Re, Marta; Esposito, Fabrizio; Sack, Alexander T; Di Salle, Francesco

2015-01-01

The default mode network and the working memory network are known to be anti-correlated during sustained cognitive processing, in a load-dependent manner. We hypothesized that functional connectivity among nodes of the two networks could be dynamically modulated by task phases across time. To address the dynamic links between default mode network and the working memory network, we used a delayed visuo-spatial working memory paradigm, which allowed us to separate three different phases of working memory (encoding, maintenance, and retrieval), and analyzed the functional connectivity during each phase within and between the default mode network and the working memory network networks. We found that the two networks are anti-correlated only during the maintenance phase of working memory, i.e. when attention is focused on a memorized stimulus in the absence of external input. Conversely, during the encoding and retrieval phases, when the external stimulation is present, the default mode network is positively coupled with the working memory network, suggesting the existence of a dynamically switching of functional connectivity between "task-positive" and "task-negative" brain networks. Our results demonstrate that the well-established dichotomy of the human brain (anti-correlated networks during rest and balanced activation-deactivation during cognition) has a more nuanced organization than previously thought and engages in different patterns of correlation and anti-correlation during specific sub-phases of a cognitive task. This nuanced organization reinforces the hypothesis of a direct involvement of the default mode network in cognitive functions, as represented by a dynamic rather than static interaction with specific task-positive networks, such as the working memory network.

The Default Mode Network and the Working Memory Network Are Not Anti-Correlated during All Phases of a Working Memory Task

PubMed Central

Piccoli, Tommaso; Valente, Giancarlo; Linden, David E. J.; Re, Marta; Esposito, Fabrizio; Sack, Alexander T.; Salle, Francesco Di

2015-01-01

Introduction The default mode network and the working memory network are known to be anti-correlated during sustained cognitive processing, in a load-dependent manner. We hypothesized that functional connectivity among nodes of the two networks could be dynamically modulated by task phases across time. Methods To address the dynamic links between default mode network and the working memory network, we used a delayed visuo-spatial working memory paradigm, which allowed us to separate three different phases of working memory (encoding, maintenance, and retrieval), and analyzed the functional connectivity during each phase within and between the default mode network and the working memory network networks. Results We found that the two networks are anti-correlated only during the maintenance phase of working memory, i.e. when attention is focused on a memorized stimulus in the absence of external input. Conversely, during the encoding and retrieval phases, when the external stimulation is present, the default mode network is positively coupled with the working memory network, suggesting the existence of a dynamically switching of functional connectivity between “task-positive” and “task-negative” brain networks. Conclusions Our results demonstrate that the well-established dichotomy of the human brain (anti-correlated networks during rest and balanced activation-deactivation during cognition) has a more nuanced organization than previously thought and engages in different patterns of correlation and anti-correlation during specific sub-phases of a cognitive task. This nuanced organization reinforces the hypothesis of a direct involvement of the default mode network in cognitive functions, as represented by a dynamic rather than static interaction with specific task-positive networks, such as the working memory network. PMID:25848951

Study of the turbocharger shaft motion by means of infrared sensors

NASA Astrophysics Data System (ADS)

Serrano, J. R.; Guardiola, C.; Dolz, V.; López, M. A.; Bouffaud, F.

2015-05-01

This work describes a technique for measuring the precession movement of the shaft of small automotive turbochargers. The main novelty is that the technique is based on infrared light diode sensors. With presented technique it is possible to perform secure mounting of electronics and also to measure, with good accuracy, far enough from the turbocharger shaft. Both advantages allow applying it even in critical lubrication conditions and when blade contact occurs. The technique's main difficulties arise from the small size of the turbocharger shaft and the high precession movement in critical conditions. In order to generate the optimum albedo reflection for infrared measurement, a special cylindrical nut with larger diameter than the original one is assembled at the shaft tip in the compressor side. Following, shaft balancing, the calibration of the sensors and the compensation of errors from different sources are needed steps before the method is able to identify the main frequencies of shaft motion. Once synchronous and sub-synchronous frequencies have been obtained it is possible to reconstruct the instantaneous position of the shaft to determine its precession movement.

Developing the Precision Magnetic Field for the E989 Muon g{2 Experiment

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

Smith, Matthias W.

The experimental value ofmore » $$(g\\hbox{--}2)_\\mu$$ historically has been and contemporarily remains an important probe into the Standard Model and proposed extensions. Previous measurements of $$(g\\hbox{--}2)_\\mu$$ exhibit a persistent statistical tension with calculations using the Standard Model implying that the theory may be incomplete and constraining possible extensions. The Fermilab Muon g-2 experiment, E989, endeavors to increase the precision over previous experiments by a factor of four and probe more deeply into the tension with the Standard Model. The $$(g\\hbox{--}2)_\\mu$$ experimental implementation measures two spin precession frequencies defined by the magnetic field, proton precession and muon precession. The value of $$(g\\hbox{--}2)_\\mu$$ is derived from a relationship between the two frequencies. The precision of magnetic field measurements and the overall magnetic field uniformity achieved over the muon storage volume are then two undeniably important aspects of the e xperiment in minimizing uncertainty. The current thesis details the methods employed to achieve magnetic field goals and results of the effort.« less

Precession technique and electron diffractometry as new tools for crystal structure analysis and chemical bonding determination.

PubMed

Avilov, A; Kuligin, K; Nicolopoulos, S; Nickolskiy, M; Boulahya, K; Portillo, J; Lepeshov, G; Sobolev, B; Collette, J P; Martin, N; Robins, A C; Fischione, P

2007-01-01

We have developed a new fast electron diffractometer working with high dynamic range and linearity for crystal structure determinations. Electron diffraction (ED) patterns can be scanned serially in front of a Faraday cage detector; the total measurement time for several hundred ED reflections can be tens of seconds having high statistical accuracy for all measured intensities (1-2%). This new tool can be installed to any type of TEM without any column modification and is linked to a specially developed electron beam precession "Spinning Star" system. Precession of the electron beam (Vincent-Midgley technique) reduces dynamical effects allowing also use of accurate intensities for crystal structure analysis. We describe the technical characteristics of this new tool together with the first experimental results. Accurate measurement of electron diffraction intensities by electron diffractometer opens new possibilities not only for revealing unknown structures, but also for electrostatic potential determination and chemical bonding investigation. As an example, we present detailed atomic bonding information of CaF(2) as revealed for the first time by precise electron diffractometry.

Black hole spin from wobbling and rotation of the M87 jet and a sign of a magnetically arrested disc

NASA Astrophysics Data System (ADS)

Sob'yanin, Denis Nikolaevich

2018-06-01

New long-term Very Long Baseline Array observations of the well-known jet in the M87 radio galaxy at 43 GHz show that the jet experiences a sideways shift with an approximately 8-10 yr quasi-periodicity. Such jet wobbling can be indicative of a relativistic Lense-Thirring precession resulting from a tilted accretion disc. The wobbling period together with up-to-date kinematic data on jet rotation opens up the possibility for estimating angular momentum of the central supermassive black hole. In the case of a test-particle precession, the specific angular momentum is J/Mc = (2.7 ± 1.5) × 1014 cm, implying moderate dimensionless spin parameters a = 0.5 ± 0.3 and 0.31 ± 0.17 for controversial gas-dynamic and stellar-dynamic black hole masses. However, in the case of a solid-body-like precession, the spin parameter is much smaller for both masses, 0.15 ± 0.05. Rejecting this value on the basis of other independent spin estimations requires the existence of a magnetically arrested disc in M87.

Swirling plumes and spinning tops

NASA Astrophysics Data System (ADS)

Frank, Daria; Landel, Julien; Dalziel, Stuart; Linden, Paul

2017-11-01

Motivated by potential effects of the Earth's rotation on the dynamics of the oil plume resulting from the Deepwater Horizon disaster in 2010, we conducted laboratory experiments on saltwater and bubble axisymmetric point plumes in a homogeneous rotating environment. The effect of rotation is conventionally characterized by a Rossby number, based on the source buoyancy flux, the rotation rate of the system and the total water depth and which ranged from 0.02 to 1.3 in our experiments. In the range of parameters studied, we report a striking new physical instability in the plume dynamics near the source. After approximately one rotation period, the plume axis tilts away laterally from the centreline and the plume starts to precess in the anticyclonic direction. We find that the mean precession frequency of the plume scales linearly with the rotation rate of the environment. Surprisingly, the precession frequency is found to be independent of the diameter of the plume nozzle, the source buoyancy flux, the water depth and the geometry of the domain. In this talk, we present our experimental results and develop simple theoretical toy models to explain the observed plume behaviour.

Model of inter-cell interference phenomenon in 10 nm magnetic tunnel junction with perpendicular anisotropy array due to oscillatory stray field from neighboring cells

NASA Astrophysics Data System (ADS)

Ohuchida, Satoshi; Endoh, Tetsuo

2018-06-01

In this paper, we propose a new model of inter-cell interference phenomenon in a 10 nm magnetic tunnel junction with perpendicular anisotropy (p-MTJ) array and investigated the interference effect between a program cell and unselected cells due to the oscillatory stray field from neighboring cells by Landau–Lifshitz–Gilbert micromagnetic simulation. We found that interference brings about a switching delay in a program cell and excitation of magnetization precession in unselected cells even when no programing current passes through. The origin of interference is ferromagnetic resonance between neighboring cells. During the interference period, the precession frequency of the program cell is 20.8 GHz, which synchronizes with that of the theoretical precession frequency f = γH eff in unselected cells. The disturbance strength of unselected cells decreased to be inversely proportional to the cube of the distance from the program cell, which is in good agreement with the dependence of stray field on the distance from the program cell calculated by the dipole approximation method.

Variations and controlling factors of the coccolith weight in the Western Pacific Warm Pool over the last 200 ka

NASA Astrophysics Data System (ADS)

Liang, Dan; Liu, Chuanlian

2016-06-01

Using a coccolith weight analytic software (Particle Analyser), we analyze most abundant coccolith species in a sediment core from the central Western Pacific Warm Pool (WPWP) and calculate coccolith size and weight variations over the last 200 ka. These variations are compared with the trends of sea surface temperature (SST), primary productivity (PP), sea surface salinity (SSS), and insolation. Our results demonstrate that the size and weight of the coccoliths varied in response to variations of these factors, and their average total weight is primarily related to the relative abundance of the dominant species GEO ( Gephyrocapsa oceanica). The variation in weight of EMI ( Emiliania huxleyi) and GEE ( Gephyrocapsa ericsonii) are mainly influenced by nutrients, and the variation of GEM ( G. muellerae conformis) and GEO ( G. oceanica) weight are mainly influenced by SST. For all of the taxa weight, PP and SST present apparent precession or semi-precession cycles, we consider that the mono-coccolith weight of the Equatorial Western Pacific is primarily affected by precession drived thermocline and nutricline variation.

Orbitally-forced Azolla blooms and middle Eocene Arctic hydrology; clues from palynology

NASA Astrophysics Data System (ADS)

Barke, Judith; Abels, Hemmo A.; Sangiorgi, Francesca; Greenwood, David R.; Sweet, Arthur R.; Donders, Timme; Lotter, Andre F.; Reichart, Gert-Jan; Brinkhuis, Henk

2010-05-01

The presence of high abundances of the freshwater fern Azolla in the early Middle Eocene central Arctic Ocean sediments recovered from the Lomonosov Ridge during IODP Expedition 302, have been related to the presence of a substantial freshwater cap. Azolla massulae, belonging to the newly described Eocene species Azolla arctica Collinson et al., have been found over at least a ~4 m-thick interval. There are strong indications that Azolla has bloomed and reproduced in situ in the Arctic Ocean for several hundreds of thousands of years. Possible causes for the sudden demise of Azolla at ~48.1 Ma include salinity changes due to evolving oceanic connections or sea-level change. Distinct cyclic fluctuation in the Azolla massulae abundances have previously been related to orbitally forced climate changes. In this study, we evaluate the possible underlying forcing mechanisms for these freshwater cycles and for the eventual demise of Azolla in an integrated palynological and cyclostratigraphical approach. Our results show two clear periodicities of ~1.3 and ~0.7 m in all major aquatic and terrestrial palynomorph associations, which we can relate to obliquity (41 ka) and precession (~21 ka), respectively. Cycles in the abundances of Azolla, freshwater-tolerant dinoflagellate cysts, and swamp vegetation pollen show co-variability in the obliquity domain. Their strong correlation suggests periods of enhanced rainfall and runoff during Azolla blooms, possibly associated with increased summer season length and insolation during obliquity maxima. Cycles in the angiosperm pollen record are in anti-phase with the Azolla cycles. We interpret this pattern as edaphically drier conditions on land and reduced associated runoff during Azolla lows, possibly corresponding to obliquity minima. The precession signal is distinctly weaker than that for obliquity, and is mainly detectable in the cold-temperate Larix and bisaccate conifer pollen abundances, which is interpreted as a response to stronger seasonality with colder winters and warmer summers during precession minima. Together with the Azolla demise at 48.1 Ma, a concurrent decline of swamp vegetation suggests drier local conditions on land, saltwater intrusion, and possibly decreased runoff into the Arctic Ocean, causing salinity changes which could have been fatal for Azolla blooms. After the Azolla demise, the cyclic distribution of freshwater tolerant dinoflagellate cysts suggests that runoff cycles continued to influence the central Arctic although at decreased intensity.

Reducing orbital eccentricity of precessing black-hole binaries

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

Buonanno, Alessandra; Taracchini, Andrea; Kidder, Lawrence E.

2011-05-15

Building initial conditions for generic binary black-hole evolutions which are not affected by initial spurious eccentricity remains a challenge for numerical-relativity simulations. This problem can be overcome by applying an eccentricity-removal procedure which consists of evolving the binary black hole for a couple of orbits, estimating the resulting eccentricity, and then restarting the simulation with corrected initial conditions. The presence of spins can complicate this procedure. As predicted by post-Newtonian theory, spin-spin interactions and precession prevent the binary from moving along an adiabatic sequence of spherical orbits, inducing oscillations in the radial separation and in the orbital frequency. For single-spinmore » binary black holes these oscillations are a direct consequence of monopole-quadrupole interactions. However, spin-induced oscillations occur at approximately twice the orbital frequency, and therefore can be distinguished and disentangled from the initial spurious eccentricity which occurs at approximately the orbital frequency. Taking this into account, we develop a new eccentricity-removal procedure based on the derivative of the orbital frequency and find that it is rather successful in reducing the eccentricity measured in the orbital frequency to values less than 10{sup -4} when moderate spins are present. We test this new procedure using numerical-relativity simulations of binary black holes with mass ratios 1.5 and 3, spin magnitude 0.5, and various spin orientations. The numerical simulations exhibit spin-induced oscillations in the dynamics at approximately twice the orbital frequency. Oscillations of similar frequency are also visible in the gravitational-wave phase and frequency of the dominant l=2, m=2 mode.« less

Constraints on the atmospheric circulation and variability of the eccentric hot Jupiter XO-3b

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

Wong, Ian; Knutson, Heather A.; Cowan, Nicolas B.

We report secondary eclipse photometry of the hot Jupiter XO-3b in the 4.5 μm band taken with the Infrared Array Camera on the Spitzer Space Telescope. We measure individual eclipse depths and center of eclipse times for a total of 12 secondary eclipses. We fit these data simultaneously with two transits observed in the same band in order to obtain a global best-fit secondary eclipse depth of 0.1580% ± 0.0036% and a center of eclipse phase of 0.67004 ± 0.00013. We assess the relative magnitude of variations in the dayside brightness of the planet by measuring the size of themore » residuals during ingress and egress from fitting the combined eclipse light curve with a uniform disk model and place an upper limit of 0.05%. The new secondary eclipse observations extend the total baseline from one and a half years to nearly three years, allowing us to place an upper limit on the periastron precession rate of 2.9 × 10{sup –3} deg day{sup –1}— the tightest constraint to date on the periastron precession rate of a hot Jupiter. We use the new transit observations to calculate improved estimates for the system properties, including an updated orbital ephemeris. We also use the large number of secondary eclipses to obtain the most stringent limits to date on the orbit-to-orbit variability of an eccentric hot Jupiter and demonstrate the consistency of multiple-epoch Spitzer observations.« less

Active edge control in the precessions polishing process for manufacturing large mirror segments

NASA Astrophysics Data System (ADS)

Li, Hongyu; Zhang, Wei; Walker, David; Yu, Gouyo

2014-09-01

The segmentation of the primary mirror is the only promising solution for building the next generation of ground telescopes. However, manufacturing segmented mirrors presents its own challenges. The edge mis-figure impacts directly on the telescope's scientific output. The `Edge effect' significantly dominates the polishing precision. Therefore, the edge control is regarded as one of the most difficult technical issues in the segment production that needs to be addressed urgently. This paper reports an active edge control technique for the mirror segments fabrication using the Precession's polishing technique. The strategy in this technique requires that the large spot be selected on the bulk area for fast polishing, and the small spot is used for edge figuring. This can be performed by tool lift and optimizing the dell time to compensate for non-uniform material removal at the edge zone. This requires accurate and stable edge tool influence functions. To obtain the full tool influence function at the edge, we have demonstrated in previous work a novel hybrid-measurement method which uses both simultaneous phase interferometry and profilometry. In this paper, the edge effect under `Bonnet tool' polishing is investigated. The pressure distribution is analyzed by means of finite element analysis (FEA). According to the `Preston' equation, the shape of the edge tool influence functions is predicted. With this help, the multiple process parameters at the edge zone are optimized. This is demonstrated on a 200mm crosscorners hexagonal part with a result of PV less than 200nm for entire surface.

Research of spin-orbit interaction in organic conjugated polymers

NASA Astrophysics Data System (ADS)

Li, H.; Zhou, M. Y.; Wu, S. Y.; Liang, X. R.

2017-06-01

The effect of spin-orbit interaction on the one-dimensional organic polymer was investigated theoretically. Spin-orbital interaction led to the spatial separation of energy band but did not eliminate spin degeneration, which was different from energy level splitting in the Zeeman Effect. Spin-orbit interaction had little effect on the energy band structure, charge density, and lattice position, etc.; Spin precession was obtained when a polaron was transported along the polymer chain, which theoretically proved that it was feasible to control the spin precession of polaron in organic polymers by the use of external electric field.

Interior structure and seasonal mass redistribution of Mars from radio tracking of Mars Pathfinder

NASA Technical Reports Server (NTRS)

Folkner, W. M.; Yoder, C. F.; Yuan, D. N.; Standish, E. M.; Preston, R. A.

1997-01-01

Doppler and range measurements to the Mars Pathfinder lander made using its radio communications system have been combined with similar measurements from the Viking landers to estimate improved values of the precession of Mars' pole of rotation and the variation in Mars' rotation rate. The observed precession of -7576 +/- 35 milliarc seconds of angle per year implies a dense core and constrains possible models of interior composition. The estimated annual variation in rotation is in good agreement with a model of seasonal mass exchange of carbon dioxide between the atmosphere and ice caps.

Interior structure and seasonal mass redistribution of Mars from radio tracking of Mars Pathfinder.

PubMed

Folkner, W M; Yoder, C F; Yuan, D N; Standish, E M; Preston, R A

1997-12-05

Doppler and range measurements to the Mars Pathfinder lander made using its radio communications system have been combined with similar measurements from the Viking landers to estimate improved values of the precession of Mars' pole of rotation and the variation in Mars' rotation rate. The observed precession of -7576 +/- 35 milliarc seconds of angle per year implies a dense core and constrains possible models of interior composition. The estimated annual variation in rotation is in good agreement with a model of seasonal mass exchange of carbon dioxide between the atmosphere and ice caps.

Regge calculus and observations. II. Further applications.

NASA Astrophysics Data System (ADS)

Williams, Ruth M.; Ellis, G. F. R.

1984-11-01

The method, developed in an earlier paper, for tracing geodesies of particles and light rays through Regge calculus space-times, is applied to a number of problems in the Schwarzschild geometry. It is possible to obtain accurate predictions of light bending by taking sufficiently small Regge blocks. Calculations of perihelion precession, Thomas precession, and the distortion of a ball of fluid moving on a geodesic can also show good agreement with the analytic solution. However difficulties arise in obtaining accurate predictions for general orbits in these space-times. Applications to other problems in general relativity are discussed briefly.

A Perspective on the Numerical and Experimental Characteristics of Multi-Mode Dry-Friction Whip and Whirl

DTIC Science & Technology

2008-06-01

different builds of the ALH; only the first of these ran according to plan . Following test 1, the development of large supersynchronous vibrations...Precession Frequency vs. Speed Case:20, Prox:1, Dn 0 50 100 150 200 250 0 50 100 150 200 Speed (rpm) A m pl itu de ( μ m ) Max Backward Precession...1 -2000 -1500 -1000 -500 0 500 1000 1500 2000 0 50 100 150 200 250 0 50 100 150 Waterfall Plot Frequency (Hz) Speed (rpm) A m pl itu de ( μ m

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

Milankovitch theory proposes that changes in insolation due to orbital perturbations dictate the waxing and waning of the ice sheets (Hays et al., 1976). However, variations in solar forcing alone are insufficient to produce the glacial oscillations observed in the climate record. Non-linear feedbacks in the Earth system likely work in concert with the orbital cycles to produce a modified signal (e.g. Berger and Loutre, 1996), but the nature of these feedbacks remain poorly understood. To gain a better understand of the ice dynamics and climate feedbacks associated with changes in orbital configuration, we use a complex Earth system model consisting of the GENESIS GCM and land surface model (Pollard and Thompson, 1997), the Pennsylvania State University ice sheet model (Pollard and DeConto, 2009), and the BIOME vegetation model (Kaplan et al., 2001). We began this study by investigating ice sheet sensitivity to a range of commonly used ice sheet model parameters, including mass balance and albedo, to optimize simulations for Pleistocene orbital cycles. Our tests indicate that choice of mass balance and albedo parameterizations can lead to significant differences in ice sheet behavior and volume. For instance, use of an insolation-temperature mass balance scheme (van den Berg, 2008) allows for a larger ice sheet response to orbital changes than the commonly employed positive degree-day method. Inclusion of a large temperature dependent ice albedo, representing phenomena such as melt ponds and dirty ice, also enhances ice sheet sensitivity. Careful tuning of mass balance and albedo parameterizations can help alleviate the problem of insufficient ice sheet retreat during periods of high summer insolation (Horton and Poulsen, 2007) while still accurately replicating the modern climate. Using our optimized configuration, we conducted a series of experiments with idealized transient orbits in an asynchronous coupling scheme to investigate the influence of obliquity and 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.

Replicating the Ice-Volume Signal of the Early Pleistocene with a Complex Earth System Model

NASA Astrophysics Data System (ADS)

Tabor, C. R.; Poulsen, C. J.; Pollard, D.

2013-12-01

Milankovitch theory proposes high-latitude summer insolation intensity paces the ice ages by controlling perennial snow cover amounts (Milankovitch, 1941). According to theory, the ~21 kyr cycle of precession should dominate the ice-volume records since it has the greatest influence on high-latitude summer insolation. Modeling experiments frequently support Milankovitch theory by attributing the majority of Northern Hemisphere high-latitude summer snowmelt to changes in the cycle of precession (e.g. Jackson and Broccoli, 2003). However, ice-volume proxy records, especially those of the Early Pleistocene (2.6-0.8 Ma), display variability with a period of ~41 kyr (Raymo and Lisiecki, 2005), indicative of insolation forcing from obliquity, which has a much smaller influence on summer insolation intensity than precession. Several hypotheses attempt to explain the discrepancies between Milkankovitch theory and the proxy records by invoking phenomena such as insolation gradients (Raymo and Nisancioglu, 2003), hemispheric offset (Raymo et al., 2006; Lee and Poulsen, 2009), and integrated summer energy (Huybers, 2006); however, all of these hypotheses contain caveats (Ruddiman, 2006) and have yet to be supported by modeling studies that use a complex GCM. To explore potential solutions to this '41 kyr problem,' we use an Earth system model composed of the GENESIS GCM and Land Surface model, the BIOME4 vegetation model, and the Pennsylvania State ice-sheet model. Using an asynchronous coupling technique, we run four idealized transient combinations of obliquity and precession, representing the orbital extremes of the Pleistocene (Berger and Loutre, 1991). Each experiment is run through several complete orbital cycles with a dynamic ice domain spanning North America and Greenland, and fixed preindustrial greenhouse-gas concentrations. For all orbital configurations, model results produce greater ice-volume spectral power at the frequency of obliquity despite significantly greater summer insolation variability from the cycle of precession. We find obliquity enhances the climate sensitivity to direct insolation forcing through positive high-latitude surface feedbacks between vegetation, sea-ice, and mean-annual insolation while the seasonal dichotomy of precessional forcing leads to climate counterbalancing that dampens the annual ice-volume response. Longer cycle duration further amplifies the ice-volume response to obliquity. Our results help remedy the discrepancies between Milankovitch theory and the ice-volume proxy records. However, summer insolation intensity remains the most important factor for determining ice-volume rate-of-change in our experiments. Consequently, we still find a significant ice-volume response to precession, which is inconsistent with the Early Pleistocene records. The disconnect is likely attributable to climate phenomena not accounted for in the model or our choice of initial conditions, which are poorly constrained for the Early Pleistocene and ice-sheet modeling in general. Future work will examine the importance of initial climate conditions on ice-volume response.

Magnetic resonance angiography: current status and future directions

PubMed Central

2011-01-01

With recent improvement in hardware and software techniques, magnetic resonance angiography (MRA) has undergone significant changes in technique and approach. The advent of 3.0 T magnets has allowed reduction in exogenous contrast dose without compromising overall image quality. The use of novel intravascular contrast agents substantially increases the image windows and decreases contrast dose. Additionally, the lower risk and cost in non-contrast enhanced (NCE) MRA has sparked renewed interest in these methods. This article discusses the current state of both contrast-enhanced (CE) and NCE-MRA. New CE-MRA methods take advantage of dose reduction at 3.0 T, novel contrast agents, and parallel imaging methods. The risks of gadolinium-based contrast media, and the NCE-MRA methods of time-of-flight, steady-state free precession, and phase contrast are discussed. PMID:21388544

Chaos in navigation satellite orbits caused by the perturbed motion of the Moon

NASA Astrophysics Data System (ADS)

Rosengren, Aaron J.; Alessi, Elisa Maria; Rossi, Alessandro; Valsecchi, Giovanni B.

2015-06-01

Numerical simulations carried out over the past decade suggest that the orbits of the Global Navigation Satellite Systems are unstable, resulting in an apparent chaotic growth of the eccentricity. Here, we show that the irregular and haphazard character of these orbits reflects a similar irregularity in the orbits of many celestial bodies in our Solar system. We find that secular resonances, involving linear combinations of the frequencies of nodal and apsidal precession and the rate of regression of lunar nodes, occur in profusion so that the phase space is threaded by a devious stochastic web. As in all cases in the Solar system, chaos ensues where resonances overlap. These results may be significant for the analysis of disposal strategies for the four constellations in this precarious region of space.

Temporal Order in Periodically Driven Spins in Star-Shaped Clusters

NASA Astrophysics Data System (ADS)

Pal, Soham; Nishad, Naveen; Mahesh, T. S.; Sreejith, G. J.

2018-05-01

We experimentally study the response of star-shaped clusters of initially unentangled N =4 , 10, and 37 nuclear spin-1 /2 moments to an inexact π -pulse sequence and show that an Ising coupling between the center and the satellite spins results in robust period-2 magnetization oscillations. The period is stable against bath effects, but the amplitude decays with a timescale that depends on the inexactness of the pulse. Simulations reveal a semiclassical picture in which the rigidity of the period is due to a randomizing effect of the Larmor precession under the magnetization of surrounding spins. The timescales with stable periodicity increase with net initial magnetization, even in the presence of perturbations, indicating a robust temporal ordered phase for large systems with finite magnetization per spin.

Torsion as a source of expansion in a Bianchi type-I universe in the self-consistent Einstein-Cartan theory of a perfect fluid with spin density

NASA Technical Reports Server (NTRS)

Bradas, James C.; Fennelly, Alphonsus J.; Smalley, Larry L.

1987-01-01

It is shown that a generalized (or 'power law') inflationary phase arises naturally and inevitably in a simple (Bianchi type-I) anisotropic cosmological model in the self-consistent Einstein-Cartan gravitation theory with the improved stress-energy-momentum tensor with the spin density of Ray and Smalley (1982, 1983). This is made explicit by an analytical solution of the field equations of motion of the fluid variables. The inflation is caused by the angular kinetic energy density due to spin. The model further elucidates the relationship between fluid vorticity, the angular velocity of the inertially dragged tetrads, and the precession of the principal axes of the shear ellipsoid. Shear is not effective in damping the inflation.

NCC Simulation Model: Simulating the operations of the network control center, phase 2

NASA Technical Reports Server (NTRS)

Benjamin, Norman M.; Paul, Arthur S.; Gill, Tepper L.

1992-01-01

The simulation of the network control center (NCC) is in the second phase of development. This phase seeks to further develop the work performed in phase one. Phase one concentrated on the computer systems and interconnecting network. The focus of phase two will be the implementation of the network message dialogues and the resources controlled by the NCC. These resources are requested, initiated, monitored and analyzed via network messages. In the NCC network messages are presented in the form of packets that are routed across the network. These packets are generated, encoded, decoded and processed by the network host processors that generate and service the message traffic on the network that connects these hosts. As a result, the message traffic is used to characterize the work done by the NCC and the connected network. Phase one of the model development represented the NCC as a network of bi-directional single server queues and message generating sources. The generators represented the external segment processors. The served based queues represented the host processors. The NCC model consists of the internal and external processors which generate message traffic on the network that links these hosts. To fully realize the objective of phase two it is necessary to identify and model the processes in each internal processor. These processes live in the operating system of the internal host computers and handle tasks such as high speed message exchanging, ISN and NFE interface, event monitoring, network monitoring, and message logging. Inter process communication is achieved through the operating system facilities. The overall performance of the host is determined by its ability to service messages generated by both internal and external processors.

Network traffic behaviour near phase transition point

NASA Astrophysics Data System (ADS)

Lawniczak, A. T.; Tang, X.

2006-03-01

We explore packet traffic dynamics in a data network model near phase transition point from free flow to congestion. The model of data network is an abstraction of the Network Layer of the OSI (Open Systems Interconnect) Reference Model of packet switching networks. The Network Layer is responsible for routing packets across the network from their sources to their destinations and for control of congestion in data networks. Using the model we investigate spatio-temporal packets traffic dynamics near the phase transition point for various network connection topologies, and static and adaptive routing algorithms. We present selected simulation results and analyze them.

New Insights into Hard Phases of CoCrMo Metal-on-Metal Hip Replacements

PubMed Central

Liao, Y.; Pourzal, R.; Stemmer, P.; Wimmer, M.A.; Jacobs, J.J.; Fischer, A.; Marks, L. D.

2012-01-01

The microstructural and mechanical properties of the hard phases in CoCrMo prosthetic alloys in both cast and wrought conditions were examined using transmission electron microscopy and nanoindentation. Besides the known carbides of M23C6-type (M=Cr, Mo, Co) and M6C-type which are formed by either eutectic solidification or precipitation, a new mixed-phase hard constituent has been found in the cast alloys, which is composed of ~100 nm fine grains. The nanosized grains were identified to be mostly of M23C6 type using nano-beam precession electron diffraction, and the chemical composition varied from grain to grain being either Cr- or Co-rich. In contrast, the carbides within the wrought alloy having the same M23C6 structure were homogeneous, which can be attributed to the repeated heating and deformation steps. Nanoindentation measurements showed that the hardness of the hard phase mixture in the cast specimen was ~15.7 GPa, while the M23C6 carbides in the wrought alloy were twice as hard (~30.7 GPa). The origin of the nanostructured hard phase mixture was found to be related to slow cooling during casting. Mixed hard phases were produced at a cooling rate of 0.2 °C/s, whereas single phase carbides were formed at a cooling rate of 50 °C/s. This is consistent with sluggish kinetics and rationalizes different and partly conflicting microstructural results in the literature, and could be a source of variations in the performance of prosthetic devices in-vivo. PMID:22659365

Hysteresis and precession of a swirling jet normal to a wall.

PubMed

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.

Constraints on the duration of the Paleocene-Eocene Thermal Maximum by orbitally-influenced fluvial sediment records of the northern Bighorn Basin, Wyoming, USA

NASA Astrophysics Data System (ADS)

van der Meulen, Bas; Abels, Hemmo; Meijer, Niels; Gingerich, Philip; Lourens, Lucas

2016-04-01

The addition of major amounts of carbon to the exogenic carbon pool caused rapid climate change and faunal turnover during the Paleocene-Eocene Thermal Maximum (PETM) around 56 million years ago. Constraints are still needed on the duration of the onset, main body, and recovery of the event. The Bighorn Basin in Wyoming provides expanded terrestrial sections spanning the PETM and lacking the carbonate dissolution present in many marine records. Here we provide new carbon isotope records for the Polecat Bench and Head of Big Sand Coulee sections, two parallel sites in the northern Bighorn Basin, at unprecedented resolution. Cyclostratigraphic analysis of these fluvial sediment records using descriptive sedimentology and proxy records allows subdivision into intervals dominated by avulsion deposits and intervals dominated by overbank deposits. These sedimentary sequences alternate in a regular fashion and are related to climatic precession. Correlation of the two, 8-km-spaced sections shows that the avulsion-overbank cycles are laterally consistent. The presence of longer-period alternations, related to modulation by the 100-kyr eccentricity cycle, corroborates the precession influence on the sediments. Sedimentary cyclicity is then used to develop a floating precession-scale age model for the PETM carbon isotope excursion (CIE). We find a CIE body encompassing 95 kyrs aligning with marine cyclostratigraphic age models. The duration of the CIE onset is estimated at 5 kyrs, but difficult to determine because sedimentation rates vary at the sub-precession scale. The CIE recovery starts with a 2 to 4 per mille step and lasts 40 or 90 kyrs, depending on what is considered the carbon isotope background state.

Wirelessly Networked Digital Phased Array: Analysis and Development of a Phase Synchronization Concept

DTIC Science & Technology

2007-09-01

NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA THESIS Approved for public release; distribution is unlimited WIRELESSLY NETWORKED...DIGITAL PHASED ARRAY: ANALYSIS AND DEVELOPMENT OF A PHASE SYNCHRONIZATION CONCEPT by Micael Grahn September 2007 Thesis Advisor...September 2007 3. REPORT TYPE AND DATES COVERED Master’s Thesis 4. TITLE AND SUBTITLE Wirelessly Networked Digital Phased Array: Analysis and

NASA/SPAN and DOE/ESnet-DECnet transition strategy for DECnet OSI/phase 5

NASA Technical Reports Server (NTRS)

Porter, Linda; Demar, Phil

1991-01-01

The technical issues are examined involved with the transition of very large DECnet networks from DECnet phase IV protocols to DECnet OSI/Phase V protocols. The networks involved are the NASA's Science Internet (NSI-DECnet) and the DOE's Energy Science network (ESnet-DECnet). These networks, along with the many universities and research institutions connected to them, combine to form a single DECnet network containing more than 20,000 transitions and crossing numerous organizational boundaries. Discussion of transition planning, including decisions about Phase V naming, addressing, and routing are presented. Also discussed are transition issues related to the use of non-DEC routers in the network.

A constraint optimization based virtual network mapping method

NASA Astrophysics Data System (ADS)

Li, Xiaoling; Guo, Changguo; Wang, Huaimin; Li, Zhendong; Yang, Zhiwen

2013-03-01

Virtual network mapping problem, maps different virtual networks onto the substrate network is an extremely challenging work. This paper proposes a constraint optimization based mapping method for solving virtual network mapping problem. This method divides the problem into two phases, node mapping phase and link mapping phase, which are all NP-hard problems. Node mapping algorithm and link mapping algorithm are proposed for solving node mapping phase and link mapping phase, respectively. Node mapping algorithm adopts the thinking of greedy algorithm, mainly considers two factors, available resources which are supplied by the nodes and distance between the nodes. Link mapping algorithm is based on the result of node mapping phase, adopts the thinking of distributed constraint optimization method, which can guarantee to obtain the optimal mapping with the minimum network cost. Finally, simulation experiments are used to validate the method, and results show that the method performs very well.

Analysis of structural patterns in the brain with the complex network approach

NASA Astrophysics Data System (ADS)

Maksimenko, Vladimir A.; Makarov, Vladimir V.; Kharchenko, Alexander A.; Pavlov, Alexey N.; Khramova, Marina V.; Koronovskii, Alexey A.; Hramov, Alexander E.

2015-03-01

In this paper we study mechanisms of the phase synchronization in a model network of Van der Pol oscillators and in the neural network of the brain by consideration of macroscopic parameters of these networks. As the macroscopic characteristics of the model network we consider a summary signal produced by oscillators. Similar to the model simulations, we study EEG signals reflecting the macroscopic dynamics of neural network. We show that the appearance of the phase synchronization leads to an increased peak in the wavelet spectrum related to the dynamics of synchronized oscillators. The observed correlation between the phase relations of individual elements and the macroscopic characteristics of the whole network provides a way to detect phase synchronization in the neural networks in the cases of normal and pathological activity.

Indian monsoon variations during three contrasting climatic periods: the Holocene, Heinrich Stadial 2 and the last interglacial-glacial transition

NASA Astrophysics Data System (ADS)

Zorzi, Coralie; Fernanda Sanchez Goñi, Maria; Anupama, Krishnamurthy; Prasad, Srinivasan; Hanquiez, Vincent; Johnson, Joel; Giosan, Liviu

2016-04-01

In contrast to the East Asian and African monsoons the Indian monsoon is still poorly documented throughout the last climatic cycle (last 135,000 years). Pollen analysis from two marine sediment cores (NGHP-01-16A and NGHP-01-19B) collected from the offshore Godavari and Mahanadi basins, both located in the Core Monsoon Zone (CMZ) reveals changes in Indian summer monsoon variability and intensity during three contrasting climatic periods: the Holocene, the Heinrich Stadial (HS) 2 and the Marine Isotopic Stage (MIS) 5/4 during the ice sheet growth transition. During the first part of the Holocene between 11,300 and 4,200 cal years BP, characterized by high insolation (minimum precession, maximum obliquity), the maximum extension of the coastal forest and mangrove reflects high monsoon rainfall. This climatic regime contrasts with that of the second phase of the Holocene, from 4,200 cal years BP to the present, marked by the development of drier vegetation in a context of low insolation (maximum precession, minimum obliquity). The historical period in India is characterized by an alternation of strong and weak monsoon centennial phases that may reflect the Medieval Climate Anomaly and the Little Ice Age, respectively. During the HS 2, a period of low insolation and extensive iceberg discharge in the North Atlantic Ocean, vegetation was dominated by grassland and dry flora indicating pronounced aridity as the result of a weak Indian summer monsoon. The MIS 5/4 glaciation, also associated with low insolation but moderate freshwater fluxes, was characterized by a weaker reduction of the Indian summer monsoon and a decrease of seasonal contrast as recorded by the expansion of dry vegetation and the development of Artemisia, respectively. Our results support model predictions suggesting that insolation changes control the long term trend of the Indian monsoon precipitation, but its millennial scale variability and intensity are instead modulated by atmospheric teleconnections to remote phenomena in the North Atlantic, Eurasia or the Indian Ocean.

Accuracy of right and left ventricular functional assessment by short-axis vs axial cine steady-state free-precession magnetic resonance imaging: intrapatient correlation with main pulmonary artery and ascending aorta phase-contrast flow measurements.

PubMed

James, Susan H; Wald, Rachel; Wintersperger, Bernd J; Jimenez-Juan, Laura; Deva, Djeven; Crean, Andrew M; Nguyen, Elsie; Paul, Narinder S; Ley, Sebastian

2013-08-01

The left ventricle (LV) is routinely assessed with cardiac magnetic resonance imaging (MRI) by using short-axis orientation; it remains unclear whether the right ventricle (RV) can also be adequately assessed in this orientation or whether dedicated axial orientation is required. We used phase-contrast (PC) flow measurements in the main pulmonary artery (MPA) and the ascending aorta (Aorta) as nonvolumetric standard of reference and compared RV and LV volumes in short-axis and axial orientations. A retrospective analysis identified 30 patients with cardiac MRI data sets. Patients underwent MRI (1.5 T or 3 T), with retrospectively gated cine steady-state free-precession in axial and short-axis orientations. PC flow analyses of MPA and Aorta were used as the reference measure of RV and LV output. There was a high linear correlation between MPA-PC flow and RV-stroke volume (SV) short axis (r = 0.9) and RV-SV axial (r = 0.9). Bland-Altman analysis revealed a mean offset of 1.4 mL for RV axial and -2.3 mL for RV-short-axis vs MPA-PC flow. There was a high linear correlation between Aorta-PC flow and LV-SV short-axis (r = 0.9) and LV-SV axial (r = 0.9). Bland-Altman analysis revealed a mean offset of 4.8 m for LV short axis and 7.0 mL for LV axial vs Aorta-PC flow. There was no significant difference (P = .6) between short-axis-LV SV and short-axis-RV SV. No significant impact of the slice acquisition orientation for determination of RV and LV stroke volumes was found. Therefore, cardiac magnetic resonance workflow does not need to be extended by an axial data set for patients without complex cardiac disease for assessment of biventricular function and volumes. Copyright © 2013 Canadian Association of Radiologists. Published by Elsevier Inc. All rights reserved.

Detecting phase transitions in a neural network and its application to classification of syndromes in traditional Chinese medicine

NASA Astrophysics Data System (ADS)

Chen, J.; Xi, G.; Wang, W.

2008-02-01

Detecting phase transitions in neural networks (determined or random) presents a challenging subject for phase transitions play a key role in human brain activity. In this paper, we detect numerically phase transitions in two types of random neural network(RNN) under proper parameters.

Spin pumping driven auto-oscillator for phase-encoded logic—device design and material requirements

NASA Astrophysics Data System (ADS)

Rakheja, S.; Kani, N.

2017-05-01

In this work, we propose a spin nano-oscillator (SNO) device where information is encoded in the phase (time-shift) of the output oscillations. The spin current required to set up the oscillations in the device is generated through spin pumping from an input nanomagnet that is precessing at RF frequencies. We discuss the operation of the SNO device, in which either the in-plane (IP) or out-of-plane (OOP) magnetization oscillations are utilized toward implementing ultra-low-power circuits. Using physical models of the nanomagnet dynamics and the spin transport through non-magnetic channels, we quantify the reliability of the SNO device using a "scaling ratio". Material requirements for the nanomagnet and the channel to ensure correct logic functionality are identified using the scaling ratio metric. SNO devices consume (2-5)× lower energy compared to CMOS devices and other spin-based devices with similar device sizes and material parameters. The analytical models presented in this work can be used to optimize the performance and scaling of SNO devices in comparison to CMOS devices at ultra-scaled technology nodes.

Magnetic resonance separation imaging using a divided inversion recovery technique (DIRT).

PubMed

Goldfarb, James W

2010-04-01

The divided inversion recovery technique is an MRI separation method based on tissue T(1) relaxation differences. When tissue T(1) relaxation times are longer than the time between inversion pulses in a segmented inversion recovery pulse sequence, longitudinal magnetization does not pass through the null point. Prior to additional inversion pulses, longitudinal magnetization may have an opposite polarity. Spatial displacement of tissues in inversion recovery balanced steady-state free-precession imaging has been shown to be due to this magnetization phase change resulting from incomplete magnetization recovery. In this paper, it is shown how this phase change can be used to provide image separation. A pulse sequence parameter, the time between inversion pulses (T180), can be adjusted to provide water-fat or fluid separation. Example water-fat and fluid separation images of the head, heart, and abdomen are presented. The water-fat separation performance was investigated by comparing image intensities in short-axis divided inversion recovery technique images of the heart. Fat, blood, and fluid signal was suppressed to the background noise level. Additionally, the separation performance was not affected by main magnetic field inhomogeneities.

On safe configurations of a natural-artificial space tether system

NASA Astrophysics Data System (ADS)

Rodnikov, A. V.

2018-05-01

We study the dynamics of a particle moving under gravitation of precessing dynamically symmetric rigid body if the particle motion is restricted by two unilateral (flexible) constraints realized by two weightless unstretchable tethers with ends fixed at body poles, formed as the intersection of the body surface with the axis of its dynamical symmetry. The system under consideration is a simple model of an original natural-artificial space construction consisting of an asteroid and a space station tethered to each other via two cables. We note that the problem is integrable for the system safe configurations, i.e. for motions along the constraints common boundary (both tethers are tensed) if the body gravitational potential is invariant with respect to rotation about the axis of dynamical symmetry. We study these motions depicting phase portraits for possible values of system parameters. We also deduce conditions for the particle coming off the boundary of constraint(s) (if the tether(s) are slackened) and analyze these conditions, eliminating corresponding areas from phase portraits. We also formulate some statements, concerning the particle safety.

Discriminative Cooperative Networks for Detecting Phase Transitions

NASA Astrophysics Data System (ADS)

Liu, Ye-Hua; van Nieuwenburg, Evert P. L.

2018-04-01

The classification of states of matter and their corresponding phase transitions is a special kind of machine-learning task, where physical data allow for the analysis of new algorithms, which have not been considered in the general computer-science setting so far. Here we introduce an unsupervised machine-learning scheme for detecting phase transitions with a pair of discriminative cooperative networks (DCNs). In this scheme, a guesser network and a learner network cooperate to detect phase transitions from fully unlabeled data. The new scheme is efficient enough for dealing with phase diagrams in two-dimensional parameter spaces, where we can utilize an active contour model—the snake—from computer vision to host the two networks. The snake, with a DCN "brain," moves and learns actively in the parameter space, and locates phase boundaries automatically.

Embedded Electro-Optic Sensor Network for the On-Site Calibration and Real-Time Performance Monitoring of Large-Scale Phased Arrays

DTIC Science & Technology

2005-07-09

This final report summarizes the progress during the Phase I SBIR project entitled Embedded Electro - Optic Sensor Network for the On-Site Calibration...network based on an electro - optic field-detection technique (the Electro - optic Sensor Network, or ESN) for the performance evaluation of phased

Electron Spin Dephasing and Decoherence by Interaction with Nuclear Spins in Self-Assembled Quantum Dots

NASA Technical Reports Server (NTRS)

Lee, Seungwon; vonAllmen, Paul; Oyafuso, Fabiano; Klimeck, Gerhard; Whale, K. Birgitta

2004-01-01

Electron spin dephasing and decoherence by its interaction with nuclear spins in self-assembled quantum dots are investigated in the framework of the empirical tight-binding model. Electron spin dephasing in an ensemble of dots is induced by the inhomogeneous precession frequencies of the electron among dots, while electron spin decoherence in a single dot arises from the inhomogeneous precession frequencies of nuclear spins in the dot. For In(x)Ga(1-x) As self-assembled dots containing 30000 nuclei, the dephasing and decoherence times are predicted to be on the order of 100 ps and 1 (micro)s.

Proposed new test of spin effects in general relativity.

PubMed

O'Connell, R F

2004-08-20

The recent discovery of a double-pulsar PSR J0737-3039A/B provides an opportunity of unequivocally observing, for the first time, spin effects in general relativity. Existing efforts involve detection of the precession of the spinning body itself. However, for a close binary system, spin effects on the orbit may also be discernible. Not only do they add to the advance of the periastron (by an amount which is small compared to the conventional contribution) but they also give rise to a precession of the orbit about the spin direction. The measurement of such an effect would also give information on the moment of inertia of pulsars.

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

Philippov, Alexander A.; Rafikov, Roman R., E-mail: rrr@astro.princeton.edu

The eclipsing binary DI Herculis (DI Her) is known to exhibit anomalously slow apsidal precession below the rate predicted by general relativity. Recent measurements of the Rossiter-McLaughlin effect indicate that stellar spins in DI Her are almost orthogonal to the orbital angular momentum, which explains the anomalous precession in agreement with the earlier theoretical suggestion by Shakura. However, these measurements yield only projections of the spin-orbit angles onto the sky plane, leaving the spin projection onto our line of sight unconstrained. Here we describe a method for determining the full three-dimensional spin orientation of the binary components relying on themore » use of the gravity-darkening effect, which is significant for the rapidly rotating stars in DI Her. Gravity darkening gives rise to a nonuniform brightness distribution over the stellar surface, the pattern of which depends on the stellar spin orientation. Using archival photometric data obtained during multiple eclipses over several decades, we are able to constrain the unknown spin angles in DI Her with this method, finding that the spin axes of both stars lie close to the plane of the sky. Our procedure fully accounts for the precession of stellar spins over the long time span of observations.« less

Monitoring Orbital Precession of EO-1 Hyperion with Three Atmospheric Correction Models in the Libya-4 PICS

NASA Technical Reports Server (NTRS)

Neigh, Christopher; McCorkel, Joel; Campbell, Petya; Ong, Laurence; Ly, Vuong; Landis, David; Fry, Stuart; Middleton, Elizabeth

2016-01-01

Spaceborne spectrometers require spectral-temporal stability characterization to aid validation of derived data products. EO-1 began orbital precession in 2011 after exhausting onboard fuel resources. In the Libya-4 Pseudo Invariant Calibration Site (PICS) this resulted in a progressive shift from a mean local equatorial crossing time of approx. 10:00 AM in 2011 to approx. 8:30 AM in late 2015. Here, we studied precession impacts to Hyperion surface reflectance products using three atmospheric correction approaches from 2004 to 2015. Combined difference estimates of surface reflectance were < 5% in the visible near infrared (VNIR) and < 10% for most of the shortwave infrared (SWIR). Combined coefficient of variation (CV) estimates in the VNIR ranged from 0.025 ? 0.095, and in the SWIR ranged from 0.025 ? 0.06, excluding bands near atmospheric absorption features. Reflectances produced with different atmospheric models were correlated (R2) in VNIR from 0.25 ? 0.94 and SWIR from 0.12 ? 0.88 (p < 0.01). The uncertainties in all models increased with terrain slope up to 15deg and selecting dune flats could reduce errors. We conclude that these data remain a useful resource over this period.

Sculpting a Pre-planetary Nebula with a Precessing Jet: IRAS 16342-3814

NASA Astrophysics Data System (ADS)

Sahai, R.; Le Mignant, D.; Sánchez Contreras, C.; Campbell, R. D.; Chaffee, F. H.

2005-03-01

We have imaged the bipolar pre-planetary nebula IRAS 16342-3814 with the Keck adaptive optics (AO) system in four near-infrared bands in the 1.6-4.7 μm range. The lobes, which showed smoothly varying brightness distributions in previous optical images taken with the Hubble Space Telescope, have a limb-brightened appearance in the AO images, with a remarkable corkscrew structure inscribed on the lobe walls. A well-collimated, precessing jet with a diameter <~100 AU and a precession period <~50 yr, interacting with ambient circumstellar material, is most likely responsible for the corkscrew structure and the lobes, as indicated by a detailed comparison of our observations with published numerical simulations. The very red colors of the lobes in the near-infrared, coupled with their visibility at optical wavelengths, require that at least half, but not all, of the light of the central star be trapped by a compact circumstellar dust cloud heated to ~600-700 K and reradiated in the infrared. The lobes are thus illuminated both by the infrared light from this dust cloud as well as by the optical light from the central star.

Experimental and Numerical Investigation of Vortical Structures in Lean Premixed Swirl-Stabilized Combustion

NASA Astrophysics Data System (ADS)

Taamallah, Soufien; Chakroun, Nadim; Shanbhogue, Santosh; Kewlani, Gaurav; Ghoniem, Ahmed

2015-11-01

A combined experimental and LES investigation is performed to identify the origin of major flow dynamics and vortical structures in a model gas turbine's swirl-stabilized turbulent combustor. Swirling flows in combustion lead to the formation of complex flow dynamics and vortical structures that can interact with flames and influence its stabilization. Our experimental results for non-reacting flow show the existence of large scale precession motion. The precessing vortex core (PVC) dynamics disappears with combustion but only above a threshold of equivalence ratio. In addition, large scale vortices along the inner shear layer (ISL) are observed. These structures interact with the ISL stabilized flame and contribute to its wrinkling. Next, the LES setup is validated against the flow field's low-order statistics and point temperature measurement in relevant areas of the chamber. Finally, we show that LES is capable of predicting the precession motion as well as the ISL vortices in the reacting case: we find that ISL vortices originate from a vortex core that is formed right downstream of the swirler's centerbody. The vortex core has a conical spiral shape resembling a corkscrew that interacts - as it winds out - with the flame when it reaches the ISL.

Sculpting a Pre-Planetary Nebula with a Precessing Jet: IRAS 16342-3814

NASA Technical Reports Server (NTRS)

Sahai, R.; Le Mignant, D.; Sanchez Contreras, C.; Campbell, R. D.; Chaffee, F. H.

2005-01-01

We have imaged the bipolar pre-planetary nebula IRAS 16342-3814 with the Keck adaptive optics (AO) system in four near-infrared bands in the 1.6-4.7 (micro)m range. The lobes, which showed smoothly varying brightness distributions in previous optical images taken with the Hubble Space Telescope, have a limb-brightened appearance in the AO images, with a remarkable corkscrew structure inscribed on the lobe walls. A well-collimated, precessing jet with a diameter less than or approximately equal to 100 AU and a precession period less than or approximately equal to 50 yr, interacting with ambient circumstellar material, is most likely responsible for the corkscrew structure and the lobes, as indicated by a detailed comparison of our observations with published numerical simulations. The very red colors of the lobes in the near-infrared, coupled with their visibility at optical wavelengths, require that at least half, but not all, of the light of the central star be trapped by a compact circumstellar dust cloud heated to approximately 600-700 K and reradiated in the infrared. The lobes are thus illuminated both by the infrared light from this dust cloud as well as by the optical light from the central star.

Failure of geometric electromagnetism in the adiabatic vector Kepler problem

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

Anglin, J.R.; Schmiedmayer, J.

2004-02-01

The magnetic moment of a particle orbiting a straight current-carrying wire may precess rapidly enough in the wire's magnetic field to justify an adiabatic approximation, eliminating the rapid time dependence of the magnetic moment and leaving only the particle position as a slow degree of freedom. To zeroth order in the adiabatic expansion, the orbits of the particle in the plane perpendicular to the wire are Keplerian ellipses. Higher-order postadiabatic corrections make the orbits precess, but recent analysis of this 'vector Kepler problem' has shown that the effective Hamiltonian incorporating a postadiabatic scalar potential ('geometric electromagnetism') fails to predict themore » precession correctly, while a heuristic alternative succeeds. In this paper we resolve the apparent failure of the postadiabatic approximation, by pointing out that the correct second-order analysis produces a third Hamiltonian, in which geometric electromagnetism is supplemented by a tensor potential. The heuristic Hamiltonian of Schmiedmayer and Scrinzi is then shown to be a canonical transformation of the correct adiabatic Hamiltonian, to second order. The transformation has the important advantage of removing a 1/r{sup 3} singularity which is an artifact of the adiabatic approximation.« less

Directly comparing GW150914 with numerical solutions of Einstein's equations for binary black hole coalescence

NASA Astrophysics Data System (ADS)

Abbott, B. P.; Abbott, R.; Abbott, T. D.; Abernathy, M. R.; Acernese, F.; Ackley, K.; Adams, C.; Adams, T.; Addesso, P.; Adhikari, R. X.; Adya, V. B.; Affeldt, C.; Agathos, M.; Agatsuma, K.; Aggarwal, N.; Aguiar, O. D.; Aiello, L.; Ain, A.; Ajith, P.; Allen, B.; Allocca, A.; Altin, P. A.; Anderson, S. B.; Anderson, W. G.; Arai, K.; Araya, M. C.; Arceneaux, C. C.; Areeda, J. S.; Arnaud, N.; Arun, K. G.; Ascenzi, S.; Ashton, G.; Ast, M.; Aston, S. M.; Astone, P.; Aufmuth, P.; Aulbert, C.; Babak, S.; Bacon, P.; Bader, M. K. M.; Baker, P. T.; Baldaccini, F.; Ballardin, G.; Ballmer, S. W.; Barayoga, J. C.; Barclay, S. E.; Barish, B. C.; Barker, D.; Barone, F.; Barr, B.; Barsotti, L.; Barsuglia, M.; Barta, D.; Bartlett, J.; Bartos, I.; Bassiri, R.; Basti, A.; Batch, J. C.; Baune, C.; Bavigadda, V.; Bazzan, M.; Bejger, M.; Bell, A. S.; Berger, B. K.; Bergmann, G.; Berry, C. P. L.; Bersanetti, D.; Bertolini, A.; Betzwieser, J.; Bhagwat, S.; Bhandare, R.; Bilenko, I. A.; Billingsley, G.; Birch, J.; Birney, R.; Biscans, S.; Bisht, A.; Bitossi, M.; Biwer, C.; Bizouard, M. A.; Blackburn, J. K.; Blair, C. D.; Blair, D. G.; Blair, R. M.; Bloemen, S.; Bock, O.; Boer, M.; Bogaert, G.; Bogan, C.; Bohe, A.; Bond, C.; Bondu, F.; Bonnand, R.; Boom, B. A.; Bork, R.; Boschi, V.; Bose, S.; Bouffanais, Y.; Bozzi, A.; Bradaschia, C.; Brady, P. R.; Braginsky, V. B.; Branchesi, M.; Brau, J. E.; Briant, T.; Brillet, A.; Brinkmann, M.; Brisson, V.; Brockill, P.; Broida, J. E.; Brooks, A. F.; Brown, D. A.; Brown, D. D.; Brown, N. M.; Brunett, S.; Buchanan, C. C.; Buikema, A.; Bulik, T.; Bulten, H. J.; Buonanno, A.; Buskulic, D.; Buy, C.; Byer, R. L.; Cabero, M.; Cadonati, L.; Cagnoli, G.; Cahillane, C.; Calderón Bustillo, J.; Callister, T.; Calloni, E.; Camp, J. B.; Cannon, K. C.; Cao, J.; Capano, C. D.; Capocasa, E.; Carbognani, F.; Caride, S.; Casanueva Diaz, J.; Casentini, C.; Caudill, S.; Cavaglià, M.; Cavalier, F.; Cavalieri, R.; Cella, G.; Cepeda, C. B.; Cerboni Baiardi, L.; Cerretani, G.; Cesarini, E.; Chamberlin, S. J.; Chan, M.; Chao, S.; Charlton, P.; Chassande-Mottin, E.; Cheeseboro, B. D.; Chen, H. Y.; Chen, Y.; Cheng, C.; Chincarini, A.; Chiummo, A.; Cho, H. S.; Cho, M.; Chow, J. H.; Christensen, N.; Chu, Q.; Chua, S.; Chung, S.; Ciani, G.; Clara, F.; Clark, J. A.; Cleva, F.; Coccia, E.; Cohadon, P.-F.; Colla, A.; Collette, C. G.; Cominsky, L.; Constancio, M.; Conte, A.; Conti, L.; Cook, D.; Corbitt, T. R.; Cornish, N.; Corsi, A.; Cortese, S.; Costa, C. A.; Coughlin, M. W.; Coughlin, S. B.; Coulon, J.-P.; Countryman, S. T.; Couvares, P.; Cowan, E. E.; Coward, D. M.; Cowart, M. J.; Coyne, D. C.; Coyne, R.; Craig, K.; Creighton, J. D. E.; Cripe, J.; Crowder, S. G.; Cumming, A.; Cunningham, L.; Cuoco, E.; Dal Canton, T.; Danilishin, S. L.; D'Antonio, S.; Danzmann, K.; Darman, N. S.; Dasgupta, A.; Da Silva Costa, C. F.; Dattilo, V.; Dave, I.; Davier, M.; Davies, G. S.; Daw, E. J.; Day, R.; De, S.; DeBra, D.; Debreczeni, G.; Degallaix, J.; De Laurentis, M.; Deléglise, S.; Del Pozzo, W.; Denker, T.; Dent, T.; Dergachev, V.; De Rosa, R.; DeRosa, R. T.; DeSalvo, R.; Devine, R. C.; Dhurandhar, S.; Díaz, M. C.; Di Fiore, L.; Di Giovanni, M.; Di Girolamo, T.; Di Lieto, A.; Di Pace, S.; Di Palma, I.; Di Virgilio, A.; Dolique, V.; Donovan, F.; Dooley, K. L.; Doravari, S.; Douglas, R.; Downes, T. P.; Drago, M.; Drever, R. W. P.; Driggers, J. C.; Ducrot, M.; Dwyer, S. E.; Edo, T. B.; Edwards, M. C.; Effler, A.; Eggenstein, H.-B.; Ehrens, P.; Eichholz, J.; Eikenberry, S. S.; Engels, W.; Essick, R. C.; Etzel, T.; Evans, M.; Evans, T. M.; Everett, R.; Factourovich, M.; Fafone, V.; Fair, H.; Fan, X.; Fang, Q.; Farinon, S.; Farr, B.; Farr, W. M.; Favata, M.; Fays, M.; Fehrmann, H.; Fejer, M. M.; Fenyvesi, E.; Ferrante, I.; Ferreira, E. C.; Ferrini, F.; Fidecaro, F.; Fiori, I.; Fiorucci, D.; Fisher, R. P.; Flaminio, R.; Fletcher, M.; Fournier, J.-D.; Frasca, S.; Frasconi, F.; Frei, Z.; Freise, A.; Frey, R.; Frey, V.; Fritschel, P.; Frolov, V. V.; Fulda, P.; Fyffe, M.; Gabbard, H. A. G.; Gair, J. R.; Gammaitoni, L.; Gaonkar, S. G.; Garufi, F.; Gaur, G.; Gehrels, N.; Gemme, G.; Geng, P.; Genin, E.; Gennai, A.; George, J.; Gergely, L.; Germain, V.; Ghosh, Abhirup; Ghosh, Archisman; Ghosh, S.; Giaime, J. A.; Giardina, K. D.; Giazotto, A.; Gill, K.; Glaefke, A.; Goetz, E.; Goetz, R.; Gondan, L.; González, G.; Gonzalez Castro, J. M.; Gopakumar, A.; Gordon, N. A.; Gorodetsky, M. L.; Gossan, S. E.; Gosselin, M.; Gouaty, R.; Grado, A.; Graef, C.; Graff, P. B.; Granata, M.; Grant, A.; Gras, S.; Gray, C.; Greco, G.; Green, A. C.; Groot, P.; Grote, H.; Grunewald, S.; Guidi, G. M.; Guo, X.; Gupta, A.; Gupta, M. K.; Gushwa, K. E.; Gustafson, E. K.; Gustafson, R.; Hacker, J. J.; Hall, B. R.; Hall, E. D.; Hammond, G.; Haney, M.; Hanke, M. M.; Hanks, J.; Hanna, C.; Hanson, J.; Hardwick, T.; Harms, J.; Harry, G. M.; Harry, I. W.; Hart, M. J.; Hartman, M. T.; Haster, C.-J.; Haughian, K.; Heidmann, A.; Heintze, M. C.; Heitmann, H.; Hello, P.; Hemming, G.; Hendry, M.; Heng, I. S.; Hennig, J.; Henry, J.; Heptonstall, A. W.; Heurs, M.; Hild, S.; Hoak, D.; Hofman, D.; Holt, K.; Holz, D. E.; Hopkins, P.; Hough, J.; Houston, E. A.; Howell, E. J.; Hu, Y. M.; Huang, S.; Huerta, E. A.; Huet, D.; Hughey, B.; Huttner, S. H.; Huynh-Dinh, T.; Indik, N.; Ingram, D. R.; Inta, R.; Isa, H. N.; Isac, J.-M.; Isi, M.; Isogai, T.; Iyer, B. R.; Izumi, K.; Jacqmin, T.; Jang, H.; Jani, K.; Jaranowski, P.; Jawahar, S.; Jian, L.; Jiménez-Forteza, F.; Johnson, W. W.; Jones, D. I.; Jones, R.; Jonker, R. J. G.; Ju, L.; Haris, K.; Kalaghatgi, C. V.; Kalogera, V.; Kandhasamy, S.; Kang, G.; Kanner, J. B.; Kapadia, S. J.; Karki, S.; Karvinen, K. S.; Kasprzack, M.; Katsavounidis, E.; Katzman, W.; Kaufer, S.; Kaur, T.; Kawabe, K.; Kéfélian, F.; Kehl, M. S.; Keitel, D.; Kelley, D. B.; Kells, W.; Kennedy, R.; Key, J. S.; Khalili, F. Y.; Khan, I.; Khan, Z.; Khazanov, E. A.; Kijbunchoo, N.; Kim, Chi-Woong; Kim, Chunglee; Kim, J.; Kim, K.; Kim, N.; Kim, W.; Kim, Y.-M.; Kimbrell, S. J.; King, E. J.; King, P. J.; Kissel, J. S.; Klein, B.; Kleybolte, L.; Klimenko, S.; Koehlenbeck, S. M.; Koley, S.; Kondrashov, V.; Kontos, A.; Korobko, M.; Korth, W. Z.; Kowalska, I.; Kozak, D. B.; Kringel, V.; Królak, A.; Krueger, C.; Kuehn, G.; Kumar, P.; Kumar, R.; Kuo, L.; Kutynia, A.; Lackey, B. D.; Landry, M.; Lange, J.; Lantz, B.; Lasky, P. D.; Laxen, M.; Lazzarini, A.; Lazzaro, C.; Leaci, P.; Leavey, S.; Lebigot, E. O.; Lee, C. H.; Lee, H. K.; Lee, H. M.; Lee, K.; Lenon, A.; Leonardi, M.; Leong, J. R.; Leroy, N.; Letendre, N.; Levin, Y.; Lewis, J. B.; Li, T. G. F.; Libson, A.; Littenberg, T. B.; Lockerbie, N. A.; Lombardi, A. L.; Lord, J. E.; Lorenzini, M.; Loriette, V.; Lormand, M.; Losurdo, G.; Lough, J. D.; Lück, H.; Lundgren, A. P.; Lynch, R.; Ma, Y.; Machenschalk, B.; MacInnis, M.; Macleod, D. M.; Magaña-Sandoval, F.; Zertuche, L. Magaña; Magee, R. M.; Majorana, E.; Maksimovic, I.; Malvezzi, V.; Man, N.; Mandic, V.; Mangano, V.; Mansell, G. L.; Manske, M.; Mantovani, M.; Marchesoni, F.; Marion, F.; Márka, S.; Márka, Z.; Markosyan, A. S.; Maros, E.; Martelli, F.; Martellini, L.; Martin, I. W.; Martynov, D. V.; Marx, J. N.; Mason, K.; Masserot, A.; Massinger, T. J.; Masso-Reid, M.; Mastrogiovanni, S.; Matichard, F.; Matone, L.; Mavalvala, N.; Mazumder, N.; McCarthy, R.; McClelland, D. E.; McCormick, S.; McGuire, S. C.; McIntyre, G.; McIver, J.; McManus, D. J.; McRae, T.; McWilliams, S. T.; Meacher, D.; Meadors, G. D.; Meidam, J.; Melatos, A.; Mendell, G.; Mercer, R. A.; Merilh, E. L.; Merzougui, M.; Meshkov, S.; Messenger, C.; Messick, C.; Metzdorff, R.; Meyers, P. M.; Mezzani, F.; Miao, H.; Michel, C.; Middleton, H.; Mikhailov, E. E.; Milano, L.; Miller, A. L.; Miller, A.; Miller, B. B.; Miller, J.; Millhouse, M.; Minenkov, Y.; Ming, J.; Mirshekari, S.; Mishra, C.; Mitra, S.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.; Moggi, A.; Mohan, M.; Mohapatra, S. R. P.; Montani, M.; Moore, B. C.; Moore, C. J.; Moraru, D.; Moreno, G.; Morriss, S. R.; Mossavi, K.; Mours, B.; Mow-Lowry, C. M.; Mueller, G.; Muir, A. W.; Mukherjee, Arunava; Mukherjee, D.; Mukherjee, S.; Mukund, N.; Mullavey, A.; Munch, J.; Murphy, D. J.; Murray, P. G.; Mytidis, A.; Nardecchia, I.; Naticchioni, L.; Nayak, R. K.; Nedkova, K.; Nelemans, G.; Nelson, T. J. N.; Neri, M.; Neunzert, A.; Newton, G.; Nguyen, T. T.; Nielsen, A. B.; Nissanke, S.; Nitz, A.; Nocera, F.; Nolting, D.; Normandin, M. E. N.; Nuttall, L. K.; Oberling, J.; Ochsner, E.; O'Dell, J.; Oelker, E.; Ogin, G. H.; Oh, J. J.; Oh, S. H.; Ohme, F.; Oliver, M.; Oppermann, P.; Oram, Richard J.; O'Reilly, B.; O'Shaughnessy, R.; Ottaway, D. J.; Overmier, H.; Owen, B. J.; Pai, A.; Pai, S. A.; Palamos, J. R.; Palashov, O.; Palomba, C.; Pal-Singh, A.; Pan, H.; Pankow, C.; Pant, B. C.; Paoletti, F.; Paoli, A.; Papa, M. A.; Paris, H. R.; Parker, W.; Pascucci, D.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Patricelli, B.; Patrick, Z.; Pearlstone, B. L.; Pedraza, M.; Pedurand, R.; Pekowsky, L.; Pele, A.; Penn, S.; Perreca, A.; Perri, L. M.; Phelps, M.; Piccinni, O. J.; Pichot, M.; Piergiovanni, F.; Pierro, V.; Pillant, G.; Pinard, L.; Pinto, I. M.; Pitkin, M.; Poe, M.; Poggiani, R.; Popolizio, P.; Post, A.; Powell, J.; Prasad, J.; Predoi, V.; Prestegard, T.; Price, L. R.; Prijatelj, M.; Principe, M.; Privitera, S.; Prodi, G. A.; Prokhorov, L.; Puncken, O.; Punturo, M.; Puppo, P.; Pürrer, M.; Qi, H.; Qin, J.; Qiu, S.; Quetschke, V.; Quintero, E. A.; Quitzow-James, R.; Raab, F. J.; Rabeling, D. S.; Radkins, H.; Raffai, P.; Raja, S.; Rajan, C.; Rakhmanov, M.; Rapagnani, P.; Raymond, V.; Razzano, M.; Re, V.; Read, J.; Reed, C. M.; Regimbau, T.; Rei, L.; Reid, S.; Reitze, D. H.; Rew, H.; Reyes, S. D.; Ricci, F.; Riles, K.; Rizzo, M.; Robertson, N. A.; Robie, R.; Robinet, F.; Rocchi, A.; Rolland, L.; Rollins, J. G.; Roma, V. J.; Romano, J. D.; Romano, R.; Romanov, G.; Romie, J. H.; Rosińska, D.; Rowan, S.; Rüdiger, A.; Ruggi, P.; Ryan, K.; Sachdev, S.; Sadecki, T.; Sadeghian, L.; Sakellariadou, M.; Salconi, L.; Saleem, M.; Salemi, F.; Samajdar, A.; Sammut, L.; Sanchez, E. J.; Sandberg, V.; Sandeen, B.; Sanders, J. R.; Sassolas, B.; Saulson, P. R.; Sauter, O. E. S.; Savage, R. L.; Sawadsky, A.; Schale, P.; Schilling, R.; Schmidt, J.; Schmidt, P.; Schnabel, R.; Schofield, R. M. S.; Schönbeck, A.; Schreiber, E.; Schuette, D.; Schutz, B. F.; Scott, J.; Scott, S. M.; Sellers, D.; Sengupta, A. S.; Sentenac, D.; Sequino, V.; Sergeev, A.; Setyawati, Y.; Shaddock, D. A.; Shaffer, T.; Shahriar, M. S.; Shaltev, M.; Shapiro, B.; Shawhan, P.; Sheperd, A.; Shoemaker, D. H.; Siellez, K.; Siemens, X.; Sieniawska, M.; Sigg, D.; Silva, A. D.; Singer, A.; Singer, L. P.; Singh, A.; Singh, R.; Singhal, A.; Sintes, A. M.; Slagmolen, B. J. J.; Smith, J. R.; Smith, N. D.; Smith, R. J. E.; Son, E. J.; Sorazu, B.; Sorrentino, F.; Souradeep, T.; Srivastava, A. K.; Staley, A.; Steinke, M.; Steinlechner, J.; Steinlechner, S.; Steinmeyer, D.; Stephens, B. C.; Stone, R.; Strain, K. A.; Straniero, N.; Stratta, G.; Strauss, N. A.; Strigin, S.; Sturani, R.; Stuver, A. L.; Summerscales, T. Z.; Sun, L.; Sunil, S.; Sutton, P. J.; Swinkels, B. L.; Szczepańczyk, M. J.; Tacca, M.; Talukder, D.; Tanner, D. B.; Tápai, M.; Tarabrin, S. P.; Taracchini, A.; Taylor, R.; Theeg, T.; Thirugnanasambandam, M. P.; Thomas, E. G.; Thomas, M.; Thomas, P.; Thorne, K. A.; Thorne, K. S.; Thrane, E.; Tiwari, S.; Tiwari, V.; Tokmakov, K. V.; Toland, K.; Tomlinson, C.; Tonelli, M.; Tornasi, Z.; Torres, C. V.; Torrie, C. I.; Töyrä, D.; Travasso, F.; Traylor, G.; Trifirò, D.; Tringali, M. C.; Trozzo, L.; Tse, M.; Turconi, M.; Tuyenbayev, D.; Ugolini, D.; Unnikrishnan, C. S.; Urban, A. L.; Usman, S. A.; Vahlbruch, H.; Vajente, G.; Valdes, G.; van Bakel, N.; van Beuzekom, M.; van den Brand, J. F. J.; Van Den Broeck, C.; Vander-Hyde, D. C.; van der Schaaf, L.; van Heijningen, J. V.; van Veggel, A. A.; Vardaro, M.; Vass, S.; Vasúth, M.; Vaulin, R.; Vecchio, A.; Vedovato, G.; Veitch, J.; Veitch, P. J.; Venkateswara, K.; Verkindt, D.; Vetrano, F.; Viceré, A.; Vinciguerra, S.; Vine, D. J.; Vinet, J.-Y.; Vitale, S.; Vo, T.; Vocca, H.; Vorvick, C.; Voss, D. V.; Vousden, W. D.; Vyatchanin, S. P.; Wade, A. R.; Wade, L. E.; Wade, M.; Walker, M.; Wallace, L.; Walsh, S.; Wang, G.; Wang, H.; Wang, M.; Wang, X.; Wang, Y.; Ward, R. L.; Warner, J.; Was, M.; Weaver, B.; Wei, L.-W.; Weinert, M.; Weinstein, A. J.; Weiss, R.; Wen, L.; Weßels, P.; Westphal, T.; Wette, K.; Whelan, J. T.; Whiting, B. F.; Williams, R. D.; Williamson, A. R.; Willis, J. L.; Willke, B.; Wimmer, M. H.; Winkler, W.; Wipf, C. C.; Wittel, H.; Woan, G.; Woehler, J.; Worden, J.; Wright, J. L.; Wu, D. S.; Wu, G.; Yablon, J.; Yam, W.; Yamamoto, H.; Yancey, C. C.; Yu, H.; Yvert, M.; ZadroŻny, A.; Zangrando, L.; Zanolin, M.; Zendri, J.-P.; Zevin, M.; Zhang, L.; Zhang, M.; Zhang, Y.; Zhao, C.; Zhou, M.; Zhou, Z.; Zhu, X. J.; Zucker, M. E.; Zuraw, S. E.; Zweizig, J.; Boyle, M.; Campanelli, M.; Chu, T.; Clark, M.; Fauchon-Jones, E.; Fong, H.; Healy, J.; Hemberger, D.; Hinder, I.; Husa, S.; Kalaghati, C.; Khan, S.; Kidder, L. E.; Kinsey, M.; Laguna, P.; London, L. T.; Lousto, C. O.; Lovelace, G.; Ossokine, S.; Pannarale, F.; Pfeiffer, H. P.; Scheel, M.; Shoemaker, D. M.; Szilagyi, B.; Teukolsky, S.; Vinuales, A. Vano; Zlochower, Y.; LIGO Scientific Collaboration; Virgo Collaboration

2016-09-01

We compare GW150914 directly to simulations of coalescing binary black holes in full general relativity, including several performed specifically to reproduce this event. Our calculations go beyond existing semianalytic models, because for all simulations—including sources with two independent, precessing spins—we perform comparisons which account for all the spin-weighted quadrupolar modes, and separately which account for all the quadrupolar and octopolar modes. Consistent with the posterior distributions reported by Abbott et al. [Phys. Rev. Lett. 116, 241102 (2016)] (at the 90% credible level), we find the data are compatible with a wide range of nonprecessing and precessing simulations. Follow-up simulations performed using previously estimated binary parameters most resemble the data, even when all quadrupolar and octopolar modes are included. Comparisons including only the quadrupolar modes constrain the total redshifted mass Mz∈[64 M⊙-82 M⊙] , mass ratio 1 /q =m2/m1∈[0.6 ,1 ], and effective aligned spin χeff∈[-0.3 ,0.2 ], where χeff=(S1/m1+S2/m2).L ^/M . Including both quadrupolar and octopolar modes, we find the mass ratio is even more tightly constrained. Even accounting for precession, simulations with extreme mass ratios and effective spins are highly inconsistent with the data, at any mass. Several nonprecessing and precessing simulations with similar mass ratio and χeff are consistent with the data. Though correlated, the components' spins (both in magnitude and directions) are not significantly constrained by the data: the data is consistent with simulations with component spin magnitudes a1 ,2 up to at least 0.8, with random orientations. Further detailed follow-up calculations are needed to determine if the data contain a weak imprint from transverse (precessing) spins. For nonprecessing binaries, interpolating between simulations, we reconstruct a posterior distribution consistent with previous results. The final black hole's redshifted mass is consistent with Mf ,z in the range 64.0 M⊙-73.5 M⊙ and the final black hole's dimensionless spin parameter is consistent with af=0.62 - 0.73 . As our approach invokes no intermediate approximations to general relativity and can strongly reject binaries whose radiation is inconsistent with the data, our analysis provides a valuable complement to Abbott et al. [Phys. Rev. Lett. 116, 241102 (2016)].

Fast isotropic banding-free bSSFP imaging using 3D dynamically phase-cycled radial bSSFP (3D DYPR-SSFP).

PubMed

Benkert, Thomas; Ehses, Philipp; Blaimer, Martin; Jakob, Peter M; Breuer, Felix A

2016-03-01

Dynamically phase-cycled radial balanced steady-state free precession (DYPR-SSFP) is a method for efficient banding artifact removal in bSSFP imaging. Based on a varying radiofrequency (RF) phase-increment in combination with a radial trajectory, DYPR-SSFP allows obtaining a banding-free image out of a single acquired k-space. The purpose of this work is to present an extension of this technique, enabling fast three-dimensional isotropic banding-free bSSFP imaging. While banding artifact removal with DYPR-SSFP relies on the applied dynamic phase-cycle, this aspect can lead to artifacts, at least when the number of acquired projections lies below a certain limit. However, by using a 3D radial trajectory with quasi-random view ordering for image acquisition, this problem is intrinsically solved, enabling 3D DYPR-SSFP imaging at or even below the Nyquist criterion. The approach is validated for brain and knee imaging at 3 Tesla. Volumetric, banding-free images were obtained in clinically acceptable scan times with an isotropic resolution up to 0.56mm. The combination of DYPR-SSFP with a 3D radial trajectory allows banding-free isotropic volumetric bSSFP imaging with no expense of scan time. Therefore, this is a promising candidate for clinical applications such as imaging of cranial nerves or articular cartilage. Copyright © 2015. Published by Elsevier GmbH.

Selective spectroscopic imaging of hyperpolarized pyruvate and its metabolites using a single-echo variable phase advance method in balanced SSFP

PubMed Central

Varma, Gopal; Wang, Xiaoen; Vinogradov, Elena; Bhatt, Rupal S.; Sukhatme, Vikas; Seth, Pankaj; Lenkinski, Robert E.; Alsop, David C.; Grant, Aaron K.

2015-01-01

Purpose In balanced steady state free precession (bSSFP), the signal intensity has a well-known dependence on the off-resonance frequency, or, equivalently, the phase advance between successive radiofrequency (RF) pulses. The signal profile can be used to resolve the contributions from the spectrally separated metabolites. This work describes a method based on use of a variable RF phase advance to acquire spatial and spectral data in a time-efficient manner for hyperpolarized 13C MRI. Theory and Methods The technique relies on the frequency response from a bSSFP acquisition to acquire relatively rapid, high-resolution images that may be reconstructed to separate contributions from different metabolites. The ability to produce images from spectrally separated metabolites was demonstrated in-vitro, as well as in-vivo following administration of hyperpolarized 1-13C pyruvate in mice with xenograft tumors. Results In-vivo images of pyruvate, alanine, pyruvate hydrate and lactate were reconstructed from 4 images acquired in 2 seconds with an in-plane resolution of 1.25 × 1.25mm2 and 5mm slice thickness. Conclusions The phase advance method allowed acquisition of spectroscopically selective images with high spatial and temporal resolution. This method provides an alternative approach to hyperpolarized 13C spectroscopic MRI that can be combined with other techniques such as multi-echo or fluctuating equilibrium bSSFP. PMID:26507361

Ultra fast polymer network blue phase liquid crystals

NASA Astrophysics Data System (ADS)

Hussain, Zakir; Masutani, Akira; Danner, David; Pleis, Frank; Hollfelder, Nadine; Nelles, Gabriele; Kilickiran, Pinar

2011-06-01

Polymer-stabilization of blue phase liquid crystal systems within a host polymer network are reported, which enables ultrafast switching flexible displays. Our newly developed method to stabilize the blue phase in an existing polymer network (e.g., that of a polymer network liquid crystal; PNLC) has shown wide temperature stability and fast response speeds. Systems where the blue phase is stabilized in an already existing polymer network are attractive candidates for ultrafast LCDs. The technology also promises to be applied to flexible PNLC and/or polymer dispersed liquid crystal (PDLC) displays using plastic substrate such as polyethylene terephthalate (PET).

The Classical Laplace Plane and Its use as a Stable Disposal Orbit for GEO

NASA Astrophysics Data System (ADS)

Rosengren, A.; Scheeres, D.; McMahon, J.

2013-09-01

The geosynchronous Earth orbit (GEO) is the most susceptible region to space debris because there is no natural cleansing mechanism, such as atmospheric drag. Placing satellites in super-synchronous disposal orbits at the ends of their operational lifetimes has been recommended and practiced as one possible means of protecting this environment. The discovery of the high area-to-mass ratio (HAMR) debris population in near geosynchronous orbit (ca. 2004) raises concern for the long-term sustainability of this unique resource. It is currently believed that HAMR objects are sheets of multilayer insulation detaching from satellites in GEO disposal orbits due to surface degradation and material deterioration. The low energy release of HAMR objects from aging satellites abandoned in disposal orbits is not directly addressed in the national policies that established the graveyard. The current disposal regions cannot account for the large solar radiation pressure (SRP) perturbations of HAMR objects, implying that these storage orbits are not well suited as a graveyard. The orbital dynamics of uncontrolled GEO satellites is governed by the oblateness of the Earth and luni-solar gravitational interactions. By itself, Earth's oblateness causes the pole of the orbital plane to precess around Earth's rotation pole. Lunisolar perturbations will have a similar effect, but the precession will now take place about the orbit poles of the Moon and the Sun, respectively. The classical Laplace plane is the mean reference plane about whose axis the satellite's orbit precesses. On the Laplace place, the secular orbital evolution driven by the combined effects of these perturbations is zero, so that the orbits are frozen. The Laplace plane at GEO lies between the plane of the Earth's equator and that of the ecliptic, passing through their intersection, and has an inclination of about 7.5 degrees relative to Earth's equator. The uncontrolled GEO satellites precess at a constant inclination about the pole of this plane with a period of nearly 53 years. The significance of the Laplace plane for use as a GEO disposal orbit is that the orbits of satellites placed in this stable equilibrium will be fixed on average, and that any orbit at small inclination to it regresses around this plane at nearly constant inclination and rate. This stable graveyard can be specified for a range of semi-major axes above GEO, and satellites placed in this region will have significantly reduced relative encounter velocities, compared to the current graveyard. Thus, if collisions were to occur between satellites in the stable graveyard, they would occur at very low velocities, thereby damping out the relative motion of these objects. We explore the use of the classical Laplace plane as a long-term GEO disposal orbit. We show that HAMR objects released from satellites located in this stable equilibrium will be trapped in inclination and node phase space, and will not likely cross the GEO protected region. This is followed by a discussion of the robustness of these solutions to more realistic SRP models and an investigation of the economic viability of our proposed GEO graveyard.

Dynamics of a network of phase oscillators with plastic couplings

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

Nekorkin, V. I.; Kasatkin, D. V.; Moscow Institute of Physics and Technology

The processes of synchronization and phase cluster formation are investigated in a complex network of dynamically coupled phase oscillators. Coupling weights evolve dynamically depending on the phase relations between the oscillators. It is shown that the network exhibits several types of behavior: the globally synchronized state, two-cluster and multi-cluster states, different synchronous states with a fixed phase relationship between the oscillators and chaotic desynchronized state.

The Fourth Law of Motion in Classical Mechanics and Electrodynamics

NASA Astrophysics Data System (ADS)

Pinheiro, Mario J.

2010-01-01

Newton's second law has limited scope of application when transient phenomena are at stake. We endeavor here to consider a modification of Newton's second law in order to take into account sudden change (surge) of angular momentum or linear momentum. It is shown that space react back according to a kind of induction law that is related to inertia, but also appears to give evidence of a "fluidic" nature of space itself. The back-reaction is quantified by the time rate of the angular momentum flux threading a surface, mass dependent, and bearing similarity to the quantum mechanics phase shift, present in the Aharonov-Bohm and Aharonov-Casher effects, thus giving evidence of the property of vacuum polarization, a phenomena which is relative to local space. It is formulated a kind of (qualitative) Lenz law that gives an explanation to precession.

Application of δ recycling to electron automated diffraction tomography data from inorganic crystalline nanovolumes.

PubMed

Rius, Jordi; Mugnaioli, Enrico; Vallcorba, Oriol; Kolb, Ute

2013-07-01

δ Recycling is a simple procedure for directly extracting phase information from Patterson-type functions [Rius (2012). Acta Cryst. A68, 399-400]. This new phasing method has a clear theoretical basis and was developed with ideal single-crystal X-ray diffraction data. On the other hand, introduction of the automated diffraction tomography (ADT) technique has represented a significant advance in electron diffraction data collection [Kolb et al. (2007). Ultramicroscopy, 107, 507-513]. When combined with precession electron diffraction, it delivers quasi-kinematical intensity data even for complex inorganic compounds, so that single-crystal diffraction data of nanometric volumes are now available for structure determination by direct methods. To check the tolerance of δ recycling to missing data-collection corrections and to deviations from kinematical behaviour of ADT intensities, δ recycling has been applied to differently shaped nanocrystals of various inorganic materials. The results confirm that it can phase ADT data very efficiently. In some cases even more complete structure models than those derived from conventional direct methods and least-squares refinement have been found. During this study it has been demonstrated that the Wilson-plot scaling procedure is largely insensitive to sample thickness variations and missing absorption corrections affecting electron ADT intensities.

Exploring the Middle Pleistocene Lake Suguta Sr-isotope Stratigraphic record

NASA Astrophysics Data System (ADS)

Vonhof, Hubert; Junginger, Annett; Agmon, Nadav; Trauth, Martin

2017-04-01

Several studies into the Quaternary stratigraphic record of the Sr-isotope composition of paleolake Turkana in the East African Rift System (EARS) show how variation of climate left a signal of changing lacustrine Sr isotope values. This Sr isotope signal was captured in the lacustrine fossil record of the Turkana Basin, and can be a useful chemostratigraphic tool (e.g. Joordens et al., 2011; van der Lubbe et al., submitted). Such lacustrine Sr-isotope changes are believed to be paced by orbital-forced insolation cyclicity, and interpreted to be the result of changing contribution of run-off from different sub-catchments of lake Turkana, as climate change shifted regional rainfall patterns. Here, we present a first set of data from a middle Pleistocene stratigraphical sequence in the Suguta Valley, South of the Turkana Basin in the EARS. This sequence spans a couple of sedimentological cycles that potentially represent precession-forced lake level variation. In this setting, the Sr-isotope data do not vary in phase with these sedimentological cycles, but demonstrate a long trend of Sr isotope change. This may suggest that the catchment configuration of the Suguta Valley in the Mid Pleistocene was less suitable to record precession-forced hydroclimate change in Lacustrine Sr isotope ratios. This may have implications for the Turkana Basin Sr isotope record as well, because the two basins are believed to have been hydrologically connected in the Middle Pleistocene. references: 1)Joordens, J.C.A. et al., 2011. An astronomically-tuned climate framework for hominins in the Turkana Basin. Earth and Planetary Science Letters 307, 1-8. 2)van der Lubbe et al., submitted. Gradual or abrupt? Changes in water source of Lake Turkana (Kenya) during the African Humid Period inferred from Sr isotope ratios

Tides and Decadal Variability

NASA Technical Reports Server (NTRS)

Ray, Richard D.

2003-01-01

This paper reviews the mechanisms by which oceanic tides and decadal variability in the oceans are connected. We distinguish between variability caused by tides and variability observed in the tides themselves. Both effects have been detected at some level. The most obvious connection with decadal timescales is through the 18.6-year precession of the moon's orbit plane. This precession gives rise to a small tide of the same period and to 18.6-year modulations in the phase and amplitudes of short-period tides. The 18.6-year "node tide" is very small, no more than 2 cm anywhere, and in sea level data it is dominated by the ocean's natural Variability. Some authors have naively attributed climate variations with periods near 19 years directly to the node tide, but the amplitude of the tide is too small for this mechanism to be operative. The more likely explanation (Loder and Garrett, JGR, 83, 1967-70, 1978) is that the 18.6-y modulations in short-period tides, especially h e principal tide M2, cause variations in ocean mixing, which is then observed in temperature and other climatic indicators. Tidally forced variability has also been proposed by some authors, either in response to occasional (and highly predictable) tidal extremes or as a nonlinear low-frequency oscillation caused by interactions between short-period tides. The former mechanism can produce only short-duration events hardly more significant than normal tidal ranges, but the latter mechanism can in principle induce low-frequency oscillations. The most recent proposal of this type is by Keeling and Whorf, who highlight the 1800-year spectral peak discovered by Bond et al. (1997). But the proposal appears contrived and should be considered, in the words of Munk et al. (2002), "as the most likely among unlikely candidates."

The Brightening of Saturn's F Ring

NASA Astrophysics Data System (ADS)

Showalter, Mark R.; French, R.; Sfair, R.; Argüelles, C.; Pajuelo, M.; Becerra, P.; Hedman, M.; Nicholson, P.

2009-09-01

A substantial secular increase in the brightness of Saturn's F ring has occurred in the last 25 years. The ring is twice as bright in the Cassini data as it was in the Voyager data from 1980 and 1981. However, no changes have been measured since the Cassini tour began in 2004. These conclusions are based on the photometric analysis of 3500 Cassini images taken primarily through clear filters, as compared to an earlier analysis of 67 Voyager images (Icarus 100, 394-411, 1992). Analysis of the large number of images has enabled us to average out the intrinsic longitudinal variations in the ring. The shapes of the phase curves from Cassini and Voyager are similar, suggesting that although the number of dust particles has increased, the overall distribution of sizes is unchanged. The color of the ring is neutral, and photometric models point to a power law size distribution with differential slope in the range 3 to 4. Eleven stellar occultation profiles from Cassini VIMS are consistent with the above factor-of-two change. They show consistently higher integrated optical depths than were measured by Voyager during its single stellar occultation. The F ring's peculiar dynamics are dominated by perturbations from Prometheus and Pandora, plus impacts from smaller clumps orbiting nearby. This work indicates that the amount of ring dust is highly variable on time scales of decades. This suggests that dust production is probably not dominated by the relatively frequent impacts of nearby clumps. The variations are consistent with the time scale for mutual precession of the nearby moons relative to the F ring. It implies a "seasonal" aspect to the dust production, in which dust increases whenever mutual precession allows a moon to rotate into a ring-approaching orbit.

Panoramic Electrophysiological Mapping but not Electrogram Morphology Identifies Stable Sources for Human Atrial Fibrillation

PubMed Central

Narayan, Sanjiv M.; Shivkumar, Kalyanam; Krummen, David E.; Miller, John M.; Rappel, Wouter-Jan

2013-01-01

Background The foundation for successful arrhythmia ablation is the mapping of electric propagation to identify underlying mechanisms. In atrial fibrillation (AF), however, mapping is difficult so that ablation has often targeted electrogram features, with mixed results. We hypothesized that wide field-of-view (panoramic) mapping of both atria would identify causal mechanisms for AF and allow interpretation of local electrogram features, including complex fractionated atrial electrograms (CFAE). Methods and Results Contact mapping was performed using biatrial multipolar catheters in 36 AF subjects (29 persistent). Stable AF rotors (spiral waves) or focal sources were seen in 35 of 36 cases and targeted for ablation (focal impulse and rotor modulation) before pulmonary vein isolation. In 31 of 36 subjects (86.1%), AF acutely terminated (n=20; 16 to sinus rhythm) or organized (n=11; 19±8% slowing) with 2.5 minutes focal impulse and rotor modulation (interquartile range, 1.0–3.1) at one source, defined as the primary source. Subjects exhibited 2.1±1.0 concurrent AF sources of which the primary, by phase mapping, precessed in limited areas (persistent 2.5±1.7 versus paroxysmal 1.7±0.5 cm2; P=0.30). Notably, source regions showed mixed electrogram amplitudes and CFAE grades that did not differ from surrounding atrium (P=NS). AF sources were not consistently surrounded by CFAE (P=0.67). Conclusions Stable rotors and focal sources for human AF were revealed by contact panoramic mapping (focal impulse and rotor modulation mapping), but not by electrogram footprints. AF sources precessed within areas of ≈2 cm2, with diverse voltage characteristics poorly correlated with CFAE. Most CFAE sites lie remote from AF sources and are not suitable targets for catheter ablation of AF. PMID:23392583

Life cycle assessment of second generation (2G) and third generation (3G) mobile phone networks.

PubMed

Scharnhorst, Wolfram; Hilty, Lorenz M; Jolliet, Olivier

2006-07-01

The environmental performance of presently operated GSM and UMTS networks was analysed concentrating on the environmental effects of the End-of-Life (EOL) phase using the Life Cycle Assessment (LCA) method. The study was performed based on comprehensive life cycle inventory and life cycle modelling. The environmental effects were quantified using the IMPACT2002+ method. Based on technological forecasts, the environmental effects of forthcoming mobile telephone networks were approximated. The results indicate that a parallel operation of GSM and UMTS networks is environmentally detrimental and the transition phase should be kept as short as possible. The use phase (i.e. the operation) of the radio network components account for a large fraction of the total environmental impact. In particular, there is a need to lower the energy consumption of those network components. Seen in relation to each other, UMTS networks provide an environmentally more efficient mobile communication technology than GSM networks. In assessing the EOL phase, recycling the electronic scrap of mobile phone networks was shown to have clear environmental benefits. Under the present conditions, material recycling could help lower the environmental impact of the production phase by up to 50%.

Analyzing phase diagrams and phase transitions in networked competing populations

NASA Astrophysics Data System (ADS)

Ni, Y.-C.; Yin, H. P.; Xu, C.; Hui, P. M.

2011-03-01

Phase diagrams exhibiting the extent of cooperation in an evolutionary snowdrift game implemented in different networks are studied in detail. We invoke two independent payoff parameters, unlike a single payoff often used in most previous works that restricts the two payoffs to vary in a correlated way. In addition to the phase transition points when a single payoff parameter is used, phase boundaries separating homogeneous phases consisting of agents using the same strategy and a mixed phase consisting of agents using different strategies are found. Analytic expressions of the phase boundaries are obtained by invoking the ideas of the last surviving patterns and the relative alignments of the spectra of payoff values to agents using different strategies. In a Watts-Strogatz regular network, there exists a re-entrant phenomenon in which the system goes from a homogeneous phase into a mixed phase and re-enters the homogeneous phase as one of the two payoff parameters is varied. The non-trivial phase diagram accompanying this re-entrant phenomenon is quantitatively analyzed. The effects of noise and cooperation in randomly rewired Watts-Strogatz networks are also studied. The transition between a mixed phase and a homogeneous phase is identify to belong to the directed percolation universality class. The methods used in the present work are applicable to a wide range of problems in competing populations of networked agents.

Mechanical critical phenomena and the elastic response of fiber networks

NASA Astrophysics Data System (ADS)

Mackintosh, Fred

The mechanics of cells and tissues are largely governed by scaffolds of filamentous proteins that make up the cytoskeleton, as well as extracellular matrices. Evidence is emerging that such networks can exhibit rich mechanical phase behavior. A classic example of a mechanical phase transition was identified by Maxwell for macroscopic engineering structures: networks of struts or springs exhibit a continuous, second-order phase transition at the isostatic point, where the number of constraints imposed by connectivity just equals the number of mechanical degrees of freedom. We present recent theoretical predictions and experimental evidence for mechanical phase transitions in in both synthetic and biopolymer networks. We show, in particular, excellent quantitative agreement between the mechanics of collagen matrices and the predictions of a strain-controlled phase transition in sub-isostatic networks.

Aperiodic pressure pulsation under non optimal hydraulic turbine regimes at low swirl number

NASA Astrophysics Data System (ADS)

Skripkin, S. G.; Tsoy, M. A.; Kuibin, P. A.; Shtork, S. I.

2017-09-01

Off-design operating conditions of hydraulic turbines is hindered by pressure fluctuations in the draft tube of the turbine. A precessing helical vortex rope develops, which imperils the mechanical structure and limits the operation flexibility of hydropower station. Understanding of the underlying instabilities of precessing vortex rope at low swirl number is incomplete. In this paper flow regimes with different residual swirl is analysed, particular attention is paid to the regime with a small swirl parameter. Study defines upper and low boundaries of regime where aperiodic pressure surge is observed. Flow field at the runner exit is investigated by Laser Doppler Velocimetry and high-speed visualizations, which are complemented draft tube wall pressure measurements.

Thermal diffusivity and nuclear spin relaxation: a continuous wave free precession NMR study.

PubMed

Venâncio, Tiago; Engelsberg, Mario; Azeredo, Rodrigo B V; Colnago, Luiz A

2006-07-01

Continuous wave free precession (CWFP) nuclear magnetic resonance is capable of yielding quantitative and easily obtainable information concerning the kinetics of processes that change the relaxation rates of the nuclear spins through the action of some external agent. In the present application, heat flow from a natural rubber sample to a liquid nitrogen thermal bath caused a large temperature gradient leading to a non-equilibrium temperature distribution. The ensuing local changes in the relaxation rates could be monitored by the decay of the CWFP signals and, from the decays, it was possible to ascertain the prevalence of a diffusive process and to obtain an average value for the thermal diffusivity.

The Orbital precession around oblate spheroids

NASA Astrophysics Data System (ADS)

Montanus, J. M. C.

2006-07-01

An exact series will be given for the gravitational potential generated by an oblate gravitating source. To this end the corresponding Epstein-Hubbell type elliptic integral is evaluated. The procedure is based on the Legendre polynomial expansion method and on combinatorial techniques. The result is of interest for gravitational models based on the linearity of the gravitational potential. The series approximation for such potentials is of use for the analysis of orbital motions around a nonspherical source. It can be considered advantageous that the analysis is purely algebraic. Numerical approximations are not required. As an important example, the expression for the orbital precession will be derived for an object orbiting around an oblate homogeneous spheroid.

Performance of a recoverable tug for planetary missions including use of perigee propulsion and corrections for nodal regression

NASA Technical Reports Server (NTRS)

Borsody, J.

1976-01-01

Mathematical equations are derived by using the Maximum Principle to obtain the maximum payload capability of a reusable tug for planetary missions. The mathematical formulation includes correction for nodal precession of the space shuttle orbit. The tug performs this nodal correction in returning to this precessed orbit. The sample case analyzed represents an inner planet mission as defined by the declination (fixed) and right ascension of the outgoing asymptote and the mission energy. Payload capability is derived for a typical cryogenic tug and the sample case with and without perigee propulsion. Optimal trajectory profiles and some important orbital elements are also discussed.

Dynamic functional-structural coupling within acute functional state change phases: Evidence from a depression recognition study.

PubMed

Bi, Kun; Hua, Lingling; Wei, Maobin; Qin, Jiaolong; Lu, Qing; Yao, Zhijian

2016-02-01

Dynamic functional-structural connectivity (FC-SC) coupling might reflect the flexibility by which SC relates to functional connectivity (FC). However, during the dynamic acute state change phases of FC, the relationship between FC and SC may be distinctive and embody the abnormality inherent in depression. This study investigated the depression-related inter-network FC-SC coupling within particular dynamic acute state change phases of FC. Magnetoencephalography (MEG) and diffusion tensor imaging (DTI) data were collected from 26 depressive patients (13 women) and 26 age-matched controls (13 women). We constructed functional brain networks based on MEG data and structural networks from DTI data. The dynamic connectivity regression algorithm was used to identify the state change points of a time series of inter-network FC. The time period of FC that contained change points were partitioned into types of dynamic phases (acute rising phase, acute falling phase,acute rising and falling phase and abrupt FC variation phase) to explore the inter-network FC-SC coupling. The selected FC-SC couplings were then fed into the support vector machine (SVM) for depression recognition. The best discrimination accuracy was 82.7% (P=0.0069) with FC-SC couplings, particularly in the acute rising phase of FC. Within the FC phases of interest, the significant discriminative network pair was related to the salience network vs ventral attention network (SN-VAN) (P=0.0126) during the early rising phase (70-170ms). This study suffers from a small sample size, and the individual acute length of the state change phases was not considered. The increased values of significant discriminative vectors of FC-SC coupling in depression suggested that the capacity to process negative emotion might be more directly related to the SC abnormally and be indicative of more stringent and less dynamic brain function in SN-VAN, especially in the acute rising phase of FC. We demonstrated that depressive brain dysfunctions could be better characterized by reduced FC-SC coupling flexibility in this particular phase. Copyright © 2015 Elsevier B.V. All rights reserved.

Parameter diagnostics of phases and phase transition learning by neural networks

NASA Astrophysics Data System (ADS)

Suchsland, Philippe; Wessel, Stefan

2018-05-01

We present an analysis of neural network-based machine learning schemes for phases and phase transitions in theoretical condensed matter research, focusing on neural networks with a single hidden layer. Such shallow neural networks were previously found to be efficient in classifying phases and locating phase transitions of various basic model systems. In order to rationalize the emergence of the classification process and for identifying any underlying physical quantities, it is feasible to examine the weight matrices and the convolutional filter kernels that result from the learning process of such shallow networks. Furthermore, we demonstrate how the learning-by-confusing scheme can be used, in combination with a simple threshold-value classification method, to diagnose the learning parameters of neural networks. In particular, we study the classification process of both fully-connected and convolutional neural networks for the two-dimensional Ising model with extended domain wall configurations included in the low-temperature regime. Moreover, we consider the two-dimensional XY model and contrast the performance of the learning-by-confusing scheme and convolutional neural networks trained on bare spin configurations to the case of preprocessed samples with respect to vortex configurations. We discuss these findings in relation to similar recent investigations and possible further applications.

Stress reduction in phase-separated, cross-linked networks: influence of phase structure and kinetics of reaction

PubMed Central

Szczepanski, Caroline R.; Stansbury, Jeffrey W.

2014-01-01

A mechanism for polymerization shrinkage and stress reduction was developed for heterogeneous networks formed via ambient, photo-initiated polymerization-induced phase separation (PIPS). The material system used consists of a bulk homopolymer matrix of triethylene glycol dimethacrylate (TEGDMA) modified with one of three non-reactive, linear prepolymers (poly-methyl, ethyl and butyl methacrylate). At higher prepolymer loading levels (10–20 wt%) an enhanced reduction in both shrinkage and polymerization stress is observed. The onset of gelation in these materials is delayed to a higher degree of methacrylate conversion (~15–25%), providing more time for phase structure evolution by thermodynamically driven monomer diffusion between immiscible phases prior to network macro-gelation. The resulting phase structure was probed by introducing a fluorescently tagged prepolymer into the matrix. The phase structure evolves from a dispersion of prepolymer at low loading levels to a fully co-continuous heterogeneous network at higher loadings. The bulk modulus in phase separated networks is equivalent or greater than that of poly(TEGDMA), despite a reduced polymerization rate and cross-link density in the prepolymer-rich domains. PMID:25418999

Three learning phases for radial-basis-function networks.

PubMed

Schwenker, F; Kestler, H A; Palm, G

2001-05-01

In this paper, learning algorithms for radial basis function (RBF) networks are discussed. Whereas multilayer perceptrons (MLP) are typically trained with backpropagation algorithms, starting the training procedure with a random initialization of the MLP's parameters, an RBF network may be trained in many different ways. We categorize these RBF training methods into one-, two-, and three-phase learning schemes. Two-phase RBF learning is a very common learning scheme. The two layers of an RBF network are learnt separately; first the RBF layer is trained, including the adaptation of centers and scaling parameters, and then the weights of the output layer are adapted. RBF centers may be trained by clustering, vector quantization and classification tree algorithms, and the output layer by supervised learning (through gradient descent or pseudo inverse solution). Results from numerical experiments of RBF classifiers trained by two-phase learning are presented in three completely different pattern recognition applications: (a) the classification of 3D visual objects; (b) the recognition hand-written digits (2D objects); and (c) the categorization of high-resolution electrocardiograms given as a time series (ID objects) and as a set of features extracted from these time series. In these applications, it can be observed that the performance of RBF classifiers trained with two-phase learning can be improved through a third backpropagation-like training phase of the RBF network, adapting the whole set of parameters (RBF centers, scaling parameters, and output layer weights) simultaneously. This, we call three-phase learning in RBF networks. A practical advantage of two- and three-phase learning in RBF networks is the possibility to use unlabeled training data for the first training phase. Support vector (SV) learning in RBF networks is a different learning approach. SV learning can be considered, in this context of learning, as a special type of one-phase learning, where only the output layer weights of the RBF network are calculated, and the RBF centers are restricted to be a subset of the training data. Numerical experiments with several classifier schemes including k-nearest-neighbor, learning vector quantization and RBF classifiers trained through two-phase, three-phase and support vector learning are given. The performance of the RBF classifiers trained through SV learning and three-phase learning are superior to the results of two-phase learning, but SV learning often leads to complex network structures, since the number of support vectors is not a small fraction of the total number of data points.

Revisiting the Potential of Alternating Repetition Time Balanced Steady-State Free Precession Imaging of the Abdomen at 3 T.

PubMed

Gurney-Champion, Oliver J; Nederveen, Aart J; Klaassen, Remy; Engelbrecht, Marc R; Bel, Arjan; van Laarhoven, Hanneke W M; Stoker, Jaap; Goncalves, Sonia I

2016-09-01

The aim was to investigate the value of optimized 3-dimensional alternating repetition time balanced steady-state free precession (ATR-SSFP), as an alternative to conventional segmented balanced steady-state free precession (bSSFP) with fat suppression prepulse (FS-bSSFP), in single breath-hold abdominal magnetic resonance imaging at 3 T. Bloch simulations were performed to determine the optimal flip angle (FA = 1-90 degrees) and τ (1-3) with respect to signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) between abdominal organs for ATR-SSFP. These were corroborated by phantom measurements for different T1/T2 values (5-47) as well as in a healthy volunteer. In addition, fat suppression efficiency was studied using phantom and volunteer measurements. The effect of resolution on image quality was studied in a healthy volunteer. Using the optimal settings, ATR-SSFP images as well as FS-bSSFP images were obtained in 15 pancreatic cancer patients. For 10 structures of interest, the signal ratio with respect to the pancreas was computed and compared between both sequences. Finally, 10 items on image quality (fat suppression, artifacts, and sharpness) and tissue conspicuity (ducts, vessels, and duodenum) were scored by 2 abdominal radiologists for both image sequences. The results of simulations, phantom measurements, and volunteer measurements showed that, considering scan time, fat suppression, and clinical relevance, the ideal settings for ATR-SSFP were as follows: τ = 3; TR1 = 3.46 milliseconds; radiofrequency phase cycling 0, 180, 180, 0 degrees; and FA = 13-16 degrees (highest SNR) and 24-26 degrees (highest CNR). The optimized feasible additional settings implemented for patient scans were FA = 18 degrees and resolution = 1.4 × 1.4 × 1.4 mm. In patients, the signal ratios of both ATR-SSFP and FS-bSSFP were comparable and had a T2-like contrast behavior, although more accentuated in ATR-SSFP. The ATR-SSFP scored significantly higher than FS-bSSFP for 9 of 10 items scored. For single breath-hold abdominal imaging at 3 T, ATR-SSFP performs best with τ = 3 and an FA between 13 degrees (highest SNR) and 26 degrees (highest CNR). The scoring of both abdominal radiologists indicated that, at τ = 3, FA = 18 degrees, and 1.4 × 1.4 × 1.4 mm resolution, ATR-SSFP was preferred over conventional FS-bSSFP with similar settings.

NCC simulation model. Phase 2: Simulating the operations of the Network Control Center and NCC message manual

NASA Technical Reports Server (NTRS)

Benjamin, Norman M.; Gill, Tepper; Charles, Mary

1994-01-01

The network control center (NCC) provides scheduling, monitoring, and control of services to the NASA space network. The space network provides tracking and data acquisition services to many low-earth orbiting spacecraft. This report describes the second phase in the development of simulation models for the FCC. Phase one concentrated on the computer systems and interconnecting network.Phase two focuses on the implementation of the network message dialogs and the resources controlled by the NCC. Performance measures were developed along with selected indicators of the NCC's operational effectiveness.The NCC performance indicators were defined in terms of the following: (1) transfer rate, (2) network delay, (3) channel establishment time, (4) line turn around time, (5) availability, (6) reliability, (7) accuracy, (8) maintainability, and (9) security. An NCC internal and external message manual is appended to this report.

Electronic properties of quasi one-dimensional quantum wire models under equal coupling strength superpositions of Rashba and Dresselhaus spin-orbit interactions in the presence of an in-plane magnetic field

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

Papp, E.; Micu, C.; Racolta, D.

In this paper one deals with the theoretical derivation of energy bands and of related wavefunctions characterizing quasi 1D semiconductor heterostructures, such as InAs quantum wire models. Such models get characterized this time by equal coupling strength superpositions of Rashba and Dresselhaus spin-orbit interactions of dimensionless magnitude a under the influence of in-plane magnetic fields of magnitude B. We found that the orientations of the field can be selected by virtue of symmetry requirements. For this purpose one resorts to spin conservations, but alternative conditions providing sensible simplifications of the energy-band formula can be reasonably accounted for. Besides the wavenumbermore » k relying on the 1D electron, one deals with the spin-like s=±1 factors in the front of the square root term of the energy. Having obtained the spinorial wavefunction, opens the way to the derivation of spin precession effects. For this purpose one resorts to the projections of the wavenumber operator on complementary spin states. Such projections are responsible for related displacements proceeding along the Ox-axis. This results in a 2D rotation matrix providing both the precession angle as well as the precession axis.« less

The warped disk of Centaurus A in the near-infrared

NASA Technical Reports Server (NTRS)

Quillen, A. C.; Graham, James R.; Frogel, Jay A.

1993-01-01

We present infrared images of Cen A (NGC 5128) in the J, H, and K bands. The infrared morphology is primarily determined by the presence of a thin absorptive warped disk. By integrating the light of the underlying prolate galaxy through such a disk, we construct models which we compare with infrared and X-ray data. The geometry of the warped disk needed to fit the IR data is consistent with a warped disk which has evolved as a result of differential precession in a prolate potential. The disk has an inclination, with respect to the principal axis of the underlying elliptical galaxy, that is higher at larger radii than in the inner region. A scenario is proposed where a small gas-rich galaxy infalling under the force of dynamical friction is tidally stripped. Stripping occurs at different times during its infall. The orientation of the resulting gas disk depends upon the angular momentum of the infalling galaxy. We find that the resulting precession angle of the disk is well described by the precession model, but that the inclination angle may vary as a function of radius. We propose an orbit for the infalling galaxy that is consistent with the geometry of the warped disk needed to fit our infrared data, and rotation observed in the outer part of the galaxy.

Precession-paced thermocline water temperature changes in response to upwelling conditions off southern Sumatra over the past 300,000 years

NASA Astrophysics Data System (ADS)

Wang, Xingxing; Jian, Zhimin; Lückge, Andreas; Wang, Yue; Dang, Haowen; Mohtadi, Mahyar

2018-07-01

Modern variations of sea surface temperature (SST) and thermocline water temperature (TWT) off southern Sumatra are responding to local upwelling conditions which are controlled by the Australian-Indonesian winter monsoon. The relationships between SST, TWT and upwelling during the past glacial-interglacial cycles are less clearly understood. In this study, SST and TWT variabilities over the past 300 kyr are reconstructed by using foraminiferal Mg/Ca-paleothermometry in sediment core SO139-74 KL off southern Sumatra (6°32.6‧S, 103°50‧E; 1690 m water depth). Whereas SST shows a clear glacial-interglacial cycle, TWT displays a predominant cycle at the precession band. Generally, the TWT record varies with total organic carbon content, revealing that similar to today, TWT and upwelling intensity off southern Sumatra vary in concert during the past 300 kyr. The lack of glacial-interglacial variability in the TWT suggests a limited role of glacial boundary conditions, such as changing sea level and ice volume, on the upwelling intensity in this region. The vertical gradients of upper water δ18O and temperature at this site also reveal precessional cyclicity. Our model simulation of air-sea interaction further supports the low TWTs during periods of enhanced upwelling and precession minimum.

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.

On the Obliquities of Planets in Close-in, Compact Systems

NASA Astrophysics Data System (ADS)

Millholland, Sarah; Laughlin, Gregory

2018-04-01

Secular spin-orbit resonances can be encountered when planets sweep through commensurabilities between nodal and spin-axis precession frequencies, for example, during disk-driven migration. These encounters can induce significant planetary spin-axis misalignment and capture into a “Cassini state”, a configuration involving synchronous precession of the planetary spin and orbital angular momentum vectors. We show that typical extrasolar systems – exemplified by the Kepler close-in, coplanar multiple-planet systems – frequently have nodal and spin-axis precession frequencies that are near-commensurable. This implies that obliquity-pumping should be common if the planets undergo any migration. We present analytic and numerical models of the spin evolution of typical Kepler-multi-type systems subject to the influences of disk migration, the quadrupole potential of an oblate young star, and tidal dissipation. Among other consequences of large obliquities, we find that the several orders of magnitude enhancement in tidal dissipation strength at non-zero obliquity may be able to generate the observed excess of planet pairs with period ratios just wide of 2:1 and 3:2. Though tidal origins of these excesses have previously been discussed, tidal dissipation is insufficient to reproduce the observations unless planets have non-negligible obliquities at some time in their history.

Investigating the temporal domain of massive ionized jets - I. A pilot study

NASA Astrophysics Data System (ADS)

Purser, S. J. D.; Lumsden, S. L.; Hoare, M. G.; Cunningham, N.

2018-03-01

We present sensitive (σ < 10 μJy beam- 1), radio continuum observations using the Australian Telescope Compact Array at frequencies of 6 and 9 GHz towards four massive young stellar objects (MYSOs). From a previous, less sensitive work, these objects are known to harbour ionized jets associated with radio lobes, which result from shock processes. In comparison with that work, further emission components are detected towards each MYSO. These include extended, direct, thermal emission from the ionized jet's stream, new radio lobes indicative of shocks close (<105 au) to the MYSO, three radio Herbig-Haro objects separated by up to 3.8 pc from the jet's launching site, and an IR-dark source coincident with CH3OH maser emission. No significant, integrated flux variability is detected towards any jets or shocked lobes, and only one proper motion is observed (1806± 596{{ km}{ s}^{-1}{ }} parallel to the jet axis of G310.1420+00.7583A). Evidence for precession is detected in all four MYSOs with precession periods and angles within the ranges 66-15 480 yr and 6°-36°, respectively. Should precession be the result of the influence from a binary companion, we infer orbital radii of 30-1800 au.

Rapid Evolution of the Gaseous Exoplanetary Debris around the White Dwarf Star HE 1349–2305

NASA Astrophysics Data System (ADS)

Dennihy, E.; Clemens, J. C.; Dunlap, B. H.; Fanale, S. M.; Fuchs, J. T.; Hermes, J. J.

2018-02-01

Observations of heavy metal pollution in white dwarf stars indicate that metal-rich planetesimals are frequently scattered into star-grazing orbits, tidally disrupted, and accreted onto the white dwarf surface, offering direct insight into the dynamical evolution of post-main-sequence exoplanetary systems. Emission lines from the gaseous debris in the accretion disks of some of these systems show variations on timescales of decades, and have been interpreted as the general relativistic precession of a recently formed, elliptical disk. Here we present a comprehensive spectroscopic monitoring campaign of the calcium infrared triplet emission in one system, HE 1349–2305, which shows morphological emission profile variations suggestive of a precessing, asymmetric intensity pattern. The emission profiles are shown to vary on a timescale of one to two years, which is an order of magnitude shorter than what has been observed in other similar systems. We demonstrate that this timescale is likely incompatible with general relativistic precession, and consider alternative explanations for the rapid evolution, including the propagation of density waves within the gaseous debris. We conclude with recommendations for follow-up observations, and discuss how the rapid evolution of the gaseous debris in HE 1349–2305 could be leveraged to test theories of exoplanetary debris disk evolution around white dwarf stars.

Two spinning ways for precession dynamo.

PubMed

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.

Design of a ground-water-quality monitoring network for the Salinas River basin, California

USGS Publications Warehouse

Showalter, P.K.; Akers, J.P.; Swain, L.A.

1984-01-01

A regional ground-water quality monitoring network for the entire Salinas River drainage basin was designed to meet the needs of the California State Water Resources Control Board. The project included phase 1--identifying monitoring networks that exist in the region; phase 2--collecting information about the wells in each network; and phase 3--studying the factors--such as geology, land use, hydrology, and geohydrology--that influence the ground-water quality, and designing a regional network. This report is the major product of phase 3. Based on the authors ' understanding of the ground-water-quality monitoring system and input from local offices, an ideal network was designed. The proposed network includes 317 wells and 8 stream-gaging stations. Because limited funds are available to implement the monitoring network, the proposed network is designed to correspond to the ideal network insofar as practicable, and is composed mainly of 214 wells that are already being monitored by a local agency. In areas where network wells are not available, arrangements will be made to add wells to local networks. The data collected by this network will be used to assess the ground-water quality of the entire Salinas River drainage basin. After 2 years of data are collected, the network will be evaluated to test whether it is meeting the network objectives. Subsequent network evaluations will be done very 5 years. (USGS)

Bootstrap percolation on spatial networks

NASA Astrophysics Data System (ADS)

Gao, Jian; Zhou, Tao; Hu, Yanqing

2015-10-01

Bootstrap percolation is a general representation of some networked activation process, which has found applications in explaining many important social phenomena, such as the propagation of information. Inspired by some recent findings on spatial structure of online social networks, here we study bootstrap percolation on undirected spatial networks, with the probability density function of long-range links’ lengths being a power law with tunable exponent. Setting the size of the giant active component as the order parameter, we find a parameter-dependent critical value for the power-law exponent, above which there is a double phase transition, mixed of a second-order phase transition and a hybrid phase transition with two varying critical points, otherwise there is only a second-order phase transition. We further find a parameter-independent critical value around -1, about which the two critical points for the double phase transition are almost constant. To our surprise, this critical value -1 is just equal or very close to the values of many real online social networks, including LiveJournal, HP Labs email network, Belgian mobile phone network, etc. This work helps us in better understanding the self-organization of spatial structure of online social networks, in terms of the effective function for information spreading.

Gravity field and solar component of the precession rate and nutation coefficients of Comet 67P/Churyumov-Gerasimenko

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 ɛ ≃ 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 Δɛ ≃ 0.5 arcmin.

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.

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

Yagi, Kent; Tanaka, Takahiro; Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502

We calculate how strongly one can put constraints on alternative theories of gravity such as Brans-Dicke and massive graviton theories with LISA. We consider inspiral gravitational waves from a compact binary composed of a neutron star and an intermediate mass black hole in Brans-Dicke (BD) theory and that composed of a super massive black hole in massive graviton theories. We use the restricted second post-Newtonian waveforms including the effects of spins. We also take both precession and eccentricity of the orbit into account. For simplicity, we set the fiducial value for the spin of one of the binary constituents tomore » zero so that we can apply the approximation called simple precession. We perform the Monte Carlo simulations of 10{sup 4} binaries, estimating the determination accuracy of binary parameters including the BD parameter {omega}{sub BD} and the Compton wavelength of graviton {lambda}{sub g} for each binary using the Fisher matrix method. We find that including both the spin-spin coupling {sigma} and the eccentricity e into the binary parameters reduces the determination accuracy by an order of magnitude for the Brans-Dicke case, while it has less influence on massive graviton theories. On the other hand, including precession enhances the constraint on {omega}{sub BD} only 20% but it increases the constraint on {lambda}{sub g} by several factors. Using a (1.4+1000)M{sub {center_dot}}neutron star/black hole binary of SNR={radical}(200), one can put a constraint {omega}{sub BD}>6944, while using a (10{sup 7}+10{sup 6})M{sub {center_dot}}black hole/black hole binary at 3 Gpc, one can put {lambda}{sub g}>3.10x10{sup 21} cm, on average. The latter is 4 orders of magnitude stronger than the one obtained from the solar system experiment. These results are consistent with previous results within uncontrolled errors and indicate that the effects of precession and eccentricity must be taken carefully in the parameter estimation analysis.« less

New method to control form and texture on industrially-sized lenses

NASA Astrophysics Data System (ADS)

Walker, D. D.

2003-05-01

Summary This paper provides a progress-report on the development of the Precessions polishing process. This is a new small-tool polishing technique for producing aspheric forms and correcting spherical forms. Precessions polishing has been developed by Zeeko Ltd in collaboration with the Optical Science Laboratory at University College London and Loh Optikmaschinen. The Zeeko/Loh All machine (see figure below) has a capacity of 200mm diameter, and is targeted at industrial lenses and mirrors. The baseline of the PrecessionsTM process is a sub-diameter physical tool working the surface with a polishing slurry. Position and orientation of the tooling is controlled by a 7-axis CNC polishing machine that has been custom-designed for the purpose. The tool comprises an inflated, bulged, rubber-membrane (the 'bonnet'), covered with one of the usual proprietary flexible polishing surfaces familiar to opticians. The membrane moulds itself around the local asphere, keeping good contact everywhere. It is spun about its axis to give high removal-rates, and attacks the surface of the part working on the side of the bulged surface, rather than the classical pole-down configuration. The contact area and polishing pressure can be varied independently by changing the degree to which the bonnet is compressed, and the internal fluid pressure. The rotation axis is precessed around the local normal to the part, and this averages surface texture and achieves a near-Gaussian tool removal-profile (Influence function'). For axially-symmetric parts, the part is rotated and the tool moved radially, thereby creating a spiral tool-path. An off- line software application analyses i) the surface error-profile, and ii) experimental data on the tool influence functions for different spot-sizes. An iterative numerical optimisation method is then used to compute the dwell-time and spot- size for each zone of the spiral on the surface, to rectify the form error.

Flow Pattern Identification of Horizontal Two-Phase Refrigerant Flow Using Neural Networks

DTIC Science & Technology

2015-12-31

AFRL-RQ-WP-TP-2016-0079 FLOW PATTERN IDENTIFICATION OF HORIZONTAL TWO-PHASE REFRIGERANT FLOW USING NEURAL NETWORKS (POSTPRINT) Abdeel J...Journal Article Postprint 01 October 2013 – 22 June 2015 4. TITLE AND SUBTITLE FLOW PATTERN IDENTIFICATION OF HORIZONTAL TWO-PHASE REFRIGERANT FLOW USING...networks were used to automatically identify two-phase flow patterns for refrigerant R-134a flowing in a horizontal tube. In laboratory experiments

Corkscrew Structures and Precessing Jets

NASA Astrophysics Data System (ADS)

Sahai, Raghvendra

2005-07-01

Collimated jets are one of the most intriguing, yet poorly understood phenomena in astrophysics. Jets have been found in a wide variety of object classes which include AGNs, YSOs, massive X-ray binaries {e.g. SS433}, black hole X-ray transients, symbiotic stars, supersoft X-ray sources, and finally, planetary and preplanetary nebulae {PNs & PPNs}. In the case of PNs and PPNs, we have propsoed that wobbling collimated jets are the universal mechanism which can shape the wide variety of bipolar and multipolar morphologies seen in these objects. Most of our knowledge of post-AGB jets is indirectly inferred from their effects on the circumstellar envelopes of the progenitor AGB stars and, for that reason, these jets remain very poorly understood. Thus the mechanism that powers and collimates these jet-like post-AGB outflows remains as one of the most important, unsolved issues in post-AGB evolution. We propose an archival study of two bipolar PPNs, motivated by two recent discoveries which indicate that precessing jets are likely to be operational in them, and that the properties of the jets and the bipolar lobes produced by them, may be directly measured. One of these is IRAS16342-3814 {IRAS1634}, previously imaged with WPFC2, in which new Adaptive Optics {AO} observations at near-IR wavelengths show a remarkable corkscrew-shaped structure, the tell-tale signature of a precessing jet. Inspection of WFPC2 images of another PPN, OH231.8+4.2 in which we have recently discovered a A-type companion to the central mass-losing star, shows a sinuous nebulosity in a broad-band continuum image, resembling a corkscrew structure. We will use the latter to constrain the phsyical properties of the jet {precession period, opening angle, jet beam diameter, temporal history} in OH231.8. Using the multi-wavelength data on both sources, we will build models of the density distribution of the lobes and their interiors. In the case of IRAS1634, these models will be used to investigate the hypothesis that the HST images do not show the corkscrew structure because of opacity effects. Under the assumption that the jets are driven by an accretion disk around the companion, we will use theoretical relationships between disk precession and binary rotation period to estimate the properties of the binary {period, separation}. The results of this study will provide quantitative constraints for jet-driven shaping of PNs and inspire new models for the launching of jets from accretion disks in dying stars with binary companions.

Competing dynamic phases of active polymer networks

NASA Astrophysics Data System (ADS)

Freedman, Simon; Banerjee, Shiladitya; Dinner, Aaron R.

Recent experiments on in-vitro reconstituted assemblies of F-actin, myosin-II motors, and cross-linking proteins show that tuning local network properties can changes the fundamental biomechanical behavior of the system. For example, by varying cross-linker density and actin bundle rigidity, one can switch between contractile networks useful for reshaping cells, polarity sorted networks ideal for directed molecular transport, and frustrated networks with robust structural properties. To efficiently investigate the dynamic phases of actomyosin networks, we developed a coarse grained non-equilibrium molecular dynamics simulation of model semiflexible filaments, molecular motors, and cross-linkers with phenomenologically defined interactions. The simulation's accuracy was verified by benchmarking the mechanical properties of its individual components and collective behavior against experimental results at the molecular and network scales. By adjusting the model's parameters, we can reproduce the qualitative phases observed in experiment and predict the protein characteristics where phase crossovers could occur in collective network dynamics. Our model provides a framework for understanding cells' multiple uses of actomyosin networks and their applicability in materials research. Supported by the Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program.

Synchronization and spatiotemporal patterns in coupled phase oscillators on a weighted planar network

NASA Astrophysics Data System (ADS)

Kagawa, Yuki; Takamatsu, Atsuko

2009-04-01

To reveal the relation between network structures found in two-dimensional biological systems, such as protoplasmic tube networks in the plasmodium of true slime mold, and spatiotemporal oscillation patterns emerged on the networks, we constructed coupled phase oscillators on weighted planar networks and investigated their dynamics. Results showed that the distribution of edge weights in the networks strongly affects (i) the propensity for global synchronization and (ii) emerging ratios of oscillation patterns, such as traveling and concentric waves, even if the total weight is fixed. In-phase locking, traveling wave, and concentric wave patterns were, respectively, observed most frequently in uniformly weighted, center weighted treelike, and periphery weighted ring-shaped networks. Controlling the global spatiotemporal patterns with the weight distribution given by the local weighting (coupling) rules might be useful in biological network systems including the plasmodial networks and neural networks in the brain.

Effects of RF pulse profile and intra-voxel phase dispersion on MR fingerprinting with balanced SSFP readout.

PubMed

Chiu, Su-Chin; Lin, Te-Ming; Lin, Jyh-Miin; Chung, Hsiao-Wen; Ko, Cheng-Wen; Büchert, Martin; Bock, Michael

2017-09-01

To investigate possible errors in T1 and T2 quantification via MR fingerprinting with balanced steady-state free precession readout in the presence of intra-voxel phase dispersion and RF pulse profile imperfections, using computer simulations based on Bloch equations. A pulse sequence with TR changing in a Perlin noise pattern and a nearly sinusoidal pattern of flip angle following an initial 180-degree inversion pulse was employed. Gaussian distributions of off-resonance frequency were assumed for intra-voxel phase dispersion effects. Slice profiles of sinc-shaped RF pulses were computed to investigate flip angle profile influences. Following identification of the best fit between the acquisition signals and those established in the dictionary based on known parameters, estimation errors were reported. In vivo experiments were performed at 3T to examine the results. Slight intra-voxel phase dispersion with standard deviations from 1 to 3Hz resulted in prominent T2 under-estimations, particularly at large T2 values. T1 and off-resonance frequencies were relatively unaffected. Slice profile imperfections led to under-estimations of T1, which became greater as regional off-resonance frequencies increased, but could be corrected by including slice profile effects in the dictionary. Results from brain imaging experiments in vivo agreed with the simulation results qualitatively. MR fingerprinting using balanced SSFP readout in the presence of intra-voxel phase dispersion and imperfect slice profile leads to inaccuracies in quantitative estimations of the relaxation times. Copyright © 2017 Elsevier Inc. All rights reserved.

Identification of a Debris Cloud from the Nuclear Powered SNAPSHOT Satellite with Haystack Radar Measurements

NASA Technical Reports Server (NTRS)

Stokely, C.; Stansbery, E.

2006-01-01

Data from the MIT Lincoln Laboratory (MIT/LL) Long Range Imaging Radar (known as the Haystack radar) have been used in the past to examine families of objects from individual satellite breakups or families of orbiting objects that can be isolated in altitude and inclination. This is possible because for some time after a breakup, the debris cloud of particles can remain grouped together in similar orbit planes. This cloud will be visible to the radar, in fixed staring mode, for a short time twice each day, as the orbit plane moves through the field of view. There should be a unique three-dimensional pattern in observation time, range, and range rate which can identify the cloud. Eventually, through slightly differing precession rates of the right ascension of ascending node of the debris cloud, the observation time becomes distributed so that event identification becomes much more difficult. Analyses of the patterns in observation time, range, and range rate have identified good debris candidates released from the polar orbiting SNAPSHOT satellite (International Identifier: 1965-027A). For orbits near 90o inclination, there is essentially no precession of the orbit plane. The SNAPSHOT satellite is a well known nuclear powered satellite launched in 1965 to a near circular 1300 km orbit with an inclination of 90.3o. This satellite began releasing debris in 1979 with new pieces being discovered and cataloged over the years. 51 objects are still being tracked by the United States Space Surveillance Network. An analysis of the Haystack data has identified at least 60 pieces of debris separate from the 51 known tracked debris pieces, where all but 2 of the 60 pieces have a size less than 10cm. The altitude and inclination (derived from range-rate with a circular orbit assumption) are consistent with the SNAPSHOT satellite and its tracked debris cloud.

Structural analysis of the epitaxial interface Ag/ZnO in hierarchical nanoantennas.

PubMed

Sanchez, John Eder; Santiago, Ulises; Benitez, Alfredo; Yacamán, Miguel José; González, Francisco Javier; Ponce, Arturo

2016-10-10

Detectors, photo-emitter, and other high order radiation devices work under the principle of directionality to enhance the power of emission/transmission in a particular direction. In order to understand such directionality, it is important to study their coupling mechanism of their active elements. In this work, we present a crystalline orientation analysis of ZnO nanorods grown epitaxially on the pentagonal faces of silver nanowires. The analysis of the crystalline orientation at the metal-semiconductor interface (ZnO/Ag) is performed with precession electron diffraction under assisted scanning mode. In addition, high resolution X-ray diffraction on a Bragg-Brentano configuration has been used to identify the crystalline phases of the arrangement between ZnO rods and silver nanowires. The work presented herein provides a fundamental knowledge to understand the metal-semiconductor behavior related to the receiving/transmitting mechanisms of ZnO/Ag nanoantennas.

Measurement of pulmonary arterial impedance and reflection from single-slice phase-contrast and steady-state free precession MRI

NASA Astrophysics Data System (ADS)

Leimbigler, Peter John

Pulmonary arterial hypertension (PAH) alters vessel wall mechanics and vasomotor tone, driving up pulmonary hemodynamic variables such as pulse wave velocity, input and characteristic impedance, and pulse wave reflection magnitude. Heterogeneous treatment response necessitates frequent hemodynamic evaluation, for which right-heart catheterization (RHC) remains the gold standard; however, several disadvantages limit its frequency of use. In this work, a non-invasive magnetic resonance (MR) imaging protocol is developed to address the shortcomings of invasive hemodynamic monitoring and may support existing diagnostic procedures. First, accuracy and precision of the proposed method is characterized through linear uncertainty propagation and numerical simulation of the data-processing pipeline. Second, the MR protocol is tested in seven healthy adult volunteers. Third, a rapid version of the MR protocol is tested in a healthy volunteer, yielding good agreement with mean values obtained in the seven-volunteer study.

High Accuracy Fuel Flowmeter, Phase 1

NASA Technical Reports Server (NTRS)

Mayer, C.; Rose, L.; Chan, A.; Chin, B.; Gregory, W.

1983-01-01

Technology related to aircraft fuel mass - flowmeters was reviewed to determine what flowmeter types could provide 0.25%-of-point accuracy over a 50 to one range in flowrates. Three types were selected and were further analyzed to determine what problem areas prevented them from meeting the high accuracy requirement, and what the further development needs were for each. A dual-turbine volumetric flowmeter with densi-viscometer and microprocessor compensation was selected for its relative simplicity and fast response time. An angular momentum type with a motor-driven, spring-restrained turbine and viscosity shroud was selected for its direct mass-flow output. This concept also employed a turbine for fast response and a microcomputer for accurate viscosity compensation. The third concept employed a vortex precession volumetric flowmeter and was selected for its unobtrusive design. Like the turbine flowmeter, it uses a densi-viscometer and microprocessor for density correction and accurate viscosity compensation.

Linear stability analysis of a levitated nanomagnet in a static magnetic field: Quantum spin stabilized magnetic levitation

NASA Astrophysics Data System (ADS)

Rusconi, C. C.; Pöchhacker, V.; Cirac, J. I.; Romero-Isart, O.

2017-10-01

We theoretically study the levitation of a single magnetic domain nanosphere in an external static magnetic field. We show that, apart from the stability provided by the mechanical rotation of the nanomagnet (as in the classical Levitron), the quantum spin origin of its magnetization provides two additional mechanisms to stably levitate the system. Despite the Earnshaw theorem, such stable phases are present even in the absence of mechanical rotation. For large magnetic fields, the Larmor precession of the quantum magnetic moment stabilizes the system in full analogy with magnetic trapping of a neutral atom. For low magnetic fields, the magnetic anisotropy stabilizes the system via the Einstein-de Haas effect. These results are obtained with a linear stability analysis of a single magnetic domain rigid nanosphere with uniaxial anisotropy in a Ioffe-Pritchard magnetic field.

Generation of maximally entangled states and coherent control in quantum dot microlenses

NASA Astrophysics Data System (ADS)

Bounouar, Samir; de la Haye, Christoph; Strauß, Max; Schnauber, Peter; Thoma, Alexander; Gschrey, Manuel; Schulze, Jan-Hindrik; Strittmatter, André; Rodt, Sven; Reitzenstein, Stephan

2018-04-01

The integration of entangled photon emitters in nanophotonic structures designed for the broadband enhancement of photon extraction is a major challenge for quantum information technologies. We study the potential of quantum dot (QD) microlenses as efficient emitters of maximally entangled photons. For this purpose, we perform quantum tomography measurements on InGaAs QDs integrated deterministically into microlenses. Even though the studied QDs show non-zero excitonic fine-structure splitting (FSS), polarization entanglement can be prepared with a fidelity close to unity. The quality of the measured entanglement is only dependent on the temporal resolution of the applied single-photon detectors compared to the period of the excitonic phase precession imposed by the FSS. Interestingly, entanglement is kept along the full excitonic wave-packet and is not affected by decoherence. Furthermore, coherent control of the upper biexcitonic state is demonstrated.

Spin transfer and spin pumping in disordered normal metal-antiferromagnetic insulator systems

NASA Astrophysics Data System (ADS)

Gulbrandsen, Sverre A.; Brataas, Arne

2018-02-01

We consider an antiferromagnetic insulator that is in contact with a metal. Spin accumulation in the metal can induce spin-transfer torques on the staggered field and on the magnetization in the antiferromagnet. These torques relate to spin pumping: the emission of spin currents into the metal by a precessing antiferromagnet. We investigate how the various components of the spin-transfer torque are affected by spin-independent disorder and spin-flip scattering in the metal. Spin-conserving disorder reduces the coupling between the spins in the antiferromagnet and the itinerant spins in the metal in a manner similar to Ohm's law. Spin-flip scattering leads to spin-memory loss with a reduced spin-transfer torque. We discuss the concept of a staggered spin current and argue that it is not a conserved quantity. Away from the interface, the staggered spin current varies around a 0 mean in an irregular manner. A network model explains the rapid decay of the staggered spin current.

Strange mechanics of the neutrino flavor pendulum

NASA Astrophysics Data System (ADS)

Johns, Lucas; Fuller, George M.

2018-01-01

We identify in the flavor transformation of astrophysical neutrinos a new class of phenomena, a common outcome of which is the suppression of flavor conversion. Appealing to the equivalence between a bipolar neutrino system and a gyroscopic pendulum, we find that these phenomena have rather striking interpretations in the mechanical picture: in one instance, the gyroscopic pendulum initially precesses in one direction, then comes to a halt and begins to precess in the opposite direction—a counterintuitive behavior that we analogize to the motion of a toy known as a rattleback. We analyze these behaviors in the early Universe, wherein a chance connection to sterile neutrino dark matter emerges, and we briefly suggest how they might manifest in compact-object environments.

Nonlinear gravitational recoil from the mergers of precessing black-hole binaries

NASA Astrophysics Data System (ADS)

Lousto, Carlos O.; Zlochower, Yosef

2013-04-01

We present results from an extensive study of 88 precessing, equal-mass black-hole binaries with large spins (83 with intrinsic spins |S→i/mi2| of 0.8 and 5 with intrinsic spins of 0.9), and use these data to model new nonlinear contributions to the gravitational recoil imparted to the merged black hole. We find a new effect, the cross kick, that enhances the recoil for partially aligned binaries beyond the hangup kick effect. This has the consequence of increasing the probabilities of recoils larger than 2000kms-1 by nearly a factor of 2, and consequently, of black holes getting ejected from galaxies, as well as the observation of large differential redshifts/blueshifts in the cores of recently merged galaxies.

Spin coherence and dephasing of localized electrons in monolayer MoS 2

DOE PAGES

Yang, Luyi; Chen, Weibing; McCreary, Kathleen M.; ...

2015-11-10

Here, we report a systematic study of coherent spin precession and spin dephasing in electron-doped monolayer MoS 2. Using time-resolved Kerr rotation spectroscopy and applied in-plane magnetic fields, a nanosecond time scale Larmor spin precession signal commensurate with g-factor |g 0| ≃ 1.86 is observed in several different MoS 2 samples grown by chemical vapor deposition. The dephasing rate of this oscillatory signal increases linearly with magnetic field, suggesting that the coherence arises from a subensemble of localized electron spins having an inhomogeneously broadened distribution of g-factors, g 0 + Δg. In contrast to g 0, Δg is sample-dependent andmore » ranges from 0.042 to 0.115.« less

Spin Hall and Spin Swapping Torques in Diffusive Ferromagnets

NASA Astrophysics Data System (ADS)

Pauyac, Christian Ortiz; Chshiev, Mairbek; Manchon, Aurelien; Nikolaev, Sergey A.

2018-04-01

A complete set of the generalized drift-diffusion equations for a coupled charge and spin dynamics in ferromagnets in the presence of extrinsic spin-orbit coupling is derived from the quantum kinetic approach, covering major transport phenomena, such as the spin and anomalous Hall effects, spin swapping, spin precession, and relaxation processes. We argue that the spin swapping effect in ferromagnets is enhanced due to spin polarization, while the overall spin texture induced by the interplay of spin-orbital and spin precession effects displays a complex spatial dependence that can be exploited to generate torques and nucleate or propagate domain walls in centrosymmetric geometries without the use of external polarizers, as opposed to the conventional understanding of spin-orbit mediated torques.

Hardware development for Gravity Probe-B

NASA Technical Reports Server (NTRS)

Bardas, D.; Cheung, W. S.; Gill, D.; Hacker, R.; Keiser, G. M.

1986-01-01

Gravity Probe-B (GP-B), also known as the Stanford Relativity Gyroscope Experiment, will test two fundamental predictions of Einstein's General Theory of Relativity by precise measurement of the precessions of nearly perfect gyroscopes in earth orbit. This endeavor embodies state-of-the-art technologies in many fields, including gyroscope fabrication and readout, cryogenics, superconductivity, magnetic shielding, precision optics and alignment methods, and satellite control systems. These technologies are necessary to enable measurement of the predicted precession rates to the milliarcsecond/year level, and to reduce to 'near zero' all non-General Relativistic torques on the gyroscopes. This paper provides a brief overview of the experiment followed by descriptions of several specific hardware items with highlights on progress to date and plans for future development and tests.

An Application of Social Network Analysis on Military Strategy, System Networks and the Phases of War

DTIC Science & Technology

2015-03-26

1977. [29] J. D. Guzman, R. F. Deckro, M. J. Robbins, J. F. Morris and N. A. Ballester, “An Analytical Comparison of Social Network Measures,” IEEE...AN APPLICATION OF SOCIAL NETWORK ANALYSIS ON MILITARY STRATEGY, SYSTEM NETWORKS AND THE PHASES OF...subject to copyright protection in the United States. AFIT-ENS-MS-15-M-117 AN APPLICATION OF SOCIAL NETWORK ANALYSIS ON MILITARY STRATEGY

QSAR modelling using combined simple competitive learning networks and RBF neural networks.

PubMed

Sheikhpour, R; Sarram, M A; Rezaeian, M; Sheikhpour, E

2018-04-01

The aim of this study was to propose a QSAR modelling approach based on the combination of simple competitive learning (SCL) networks with radial basis function (RBF) neural networks for predicting the biological activity of chemical compounds. The proposed QSAR method consisted of two phases. In the first phase, an SCL network was applied to determine the centres of an RBF neural network. In the second phase, the RBF neural network was used to predict the biological activity of various phenols and Rho kinase (ROCK) inhibitors. The predictive ability of the proposed QSAR models was evaluated and compared with other QSAR models using external validation. The results of this study showed that the proposed QSAR modelling approach leads to better performances than other models in predicting the biological activity of chemical compounds. This indicated the efficiency of simple competitive learning networks in determining the centres of RBF neural networks.

Analysis of the characteristics of the synchronous clusters in the adaptive Kuramoto network and neural network of the epileptic brain

NASA Astrophysics Data System (ADS)

Hramov, Alexander E.; Kharchenko, Alexander A.; Makarov, Vladimir V.; Khramova, Marina V.; Koronovskii, Alexey A.; Pavlov, Alexey N.; Dana, Syamal K.

2016-04-01

In the paper we study the mechanisms of phase synchronization in the adaptive model network of Kuramoto oscillators and the neural network of brain by consideration of the integral characteristics of the observed networks signals. As the integral characteristics of the model network we consider the summary signal produced by the oscillators. Similar to the model situation we study the ECoG signal as the integral characteristic of neural network of the brain. We show that the establishment of the phase synchronization results in the increase of the peak, corresponding to synchronized oscillators, on the wavelet energy spectrum of the integral signals. The observed correlation between the phase relations of the elements and the integral characteristics of the whole network open the way to detect the size of synchronous clusters in the neural networks of the epileptic brain before and during seizure.

A Two-Phase Coverage-Enhancing Algorithm for Hybrid Wireless Sensor Networks.

PubMed

Zhang, Qingguo; Fok, Mable P

2017-01-09

Providing field coverage is a key task in many sensor network applications. In certain scenarios, the sensor field may have coverage holes due to random initial deployment of sensors; thus, the desired level of coverage cannot be achieved. A hybrid wireless sensor network is a cost-effective solution to this problem, which is achieved by repositioning a portion of the mobile sensors in the network to meet the network coverage requirement. This paper investigates how to redeploy mobile sensor nodes to improve network coverage in hybrid wireless sensor networks. We propose a two-phase coverage-enhancing algorithm for hybrid wireless sensor networks. In phase one, we use a differential evolution algorithm to compute the candidate's target positions in the mobile sensor nodes that could potentially improve coverage. In the second phase, we use an optimization scheme on the candidate's target positions calculated from phase one to reduce the accumulated potential moving distance of mobile sensors, such that the exact mobile sensor nodes that need to be moved as well as their final target positions can be determined. Experimental results show that the proposed algorithm provided significant improvement in terms of area coverage rate, average moving distance, area coverage-distance rate and the number of moved mobile sensors, when compare with other approaches.

A Two-Phase Coverage-Enhancing Algorithm for Hybrid Wireless Sensor Networks

PubMed Central

Zhang, Qingguo; Fok, Mable P.

2017-01-01

Providing field coverage is a key task in many sensor network applications. In certain scenarios, the sensor field may have coverage holes due to random initial deployment of sensors; thus, the desired level of coverage cannot be achieved. A hybrid wireless sensor network is a cost-effective solution to this problem, which is achieved by repositioning a portion of the mobile sensors in the network to meet the network coverage requirement. This paper investigates how to redeploy mobile sensor nodes to improve network coverage in hybrid wireless sensor networks. We propose a two-phase coverage-enhancing algorithm for hybrid wireless sensor networks. In phase one, we use a differential evolution algorithm to compute the candidate’s target positions in the mobile sensor nodes that could potentially improve coverage. In the second phase, we use an optimization scheme on the candidate’s target positions calculated from phase one to reduce the accumulated potential moving distance of mobile sensors, such that the exact mobile sensor nodes that need to be moved as well as their final target positions can be determined. Experimental results show that the proposed algorithm provided significant improvement in terms of area coverage rate, average moving distance, area coverage–distance rate and the number of moved mobile sensors, when compare with other approaches. PMID:28075365

Water-maser emission from a planetary nebula with a magnetized torus.

PubMed

Miranda, L F; Gómez, Y; Anglada, G; Torrelles, J M

2001-11-15

A star like the Sun becomes a planetary nebula towards the end of its life, when the envelope ejected during the earlier giant phase becomes photoionized as the surface of the remnant star reaches a temperature of approximately 30,000 K. The spherical symmetry of the giant phase is lost in the transition to a planetary nebula, when non-spherical shells and powerful jets develop. Molecules that were present in the giant envelope are progressively destroyed by the radiation. The water-vapour masers that are typical of the giant envelopes therefore are not expected to persist in planetary nebulae. Here we report the detection of water-maser emission from the planetary nebula K3-35. The masers are in a magnetized torus with a radius of about 85 astronomical units and are also found at the surprisingly large distance of about 5,000 astronomical units from the star, in the tips of bipolar lobes of gas. The precessing jets from K3-35 are probably involved in the excitation of the distant masers, although their existence is nevertheless puzzling. We infer that K3-35 is being observed at the very moment of its transformation from a giant star to a planetary nebula.

Pulsed field gradients in simulations of one- and two-dimensional NMR spectra.

PubMed

Meresi, G H; Cuperlovic, M; Palke, W E; Gerig, J T

1999-03-01

A method for the inclusion of the effects of z-axis pulsed field gradients in computer simulations of an arbitrary pulsed NMR experiment with spin (1/2) nuclei is described. Recognizing that the phase acquired by a coherence following the application of a z-axis pulsed field gradient bears a fixed relation to its order and the spatial position of the spins in the sample tube, the sample is regarded as a collection of volume elements, each phase-encoded by a characteristic, spatially dependent precession frequency. The evolution of the sample's density matrix is thus obtained by computing the evolution of the density matrix for each volume element. Following the last gradient pulse, these density matrices are combined to form a composite density matrix which evolves through the rest of the experiment to yield the observable signal. This approach is implemented in a program which includes capabilities for rigorous inclusion of spin relaxation by dipole-dipole, chemical shift anisotropy, and random field mechanisms, plus the effects of arbitrary RF fields. Mathematical procedures for accelerating these calculations are described. The approach is illustrated by simulations of representative one- and two-dimensional NMR experiments. Copyright 1999 Academic Press.

A network of networks model to study phase synchronization using structural connection matrix of human brain

NASA Astrophysics Data System (ADS)

Ferrari, F. A. S.; Viana, R. L.; Reis, A. S.; Iarosz, K. C.; Caldas, I. L.; Batista, A. M.

2018-04-01

The cerebral cortex plays a key role in complex cortical functions. It can be divided into areas according to their function (motor, sensory and association areas). In this paper, the cerebral cortex is described as a network of networks (cortex network), we consider that each cortical area is composed of a network with small-world property (cortical network). The neurons are assumed to have bursting properties with the dynamics described by the Rulkov model. We study the phase synchronization of the cortex network and the cortical networks. In our simulations, we verify that synchronization in cortex network is not homogeneous. Besides, we focus on the suppression of neural phase synchronization. Synchronization can be related to undesired and pathological abnormal rhythms in the brain. For this reason, we consider the delayed feedback control to suppress the synchronization. We show that delayed feedback control is efficient to suppress synchronous behavior in our network model when an appropriate signal intensity and time delay are defined.

Quantitative phase microscopy using deep neural networks

NASA Astrophysics Data System (ADS)

Li, Shuai; Sinha, Ayan; Lee, Justin; Barbastathis, George

2018-02-01

Deep learning has been proven to achieve ground-breaking accuracy in various tasks. In this paper, we implemented a deep neural network (DNN) to achieve phase retrieval in a wide-field microscope. Our DNN utilized the residual neural network (ResNet) architecture and was trained using the data generated by a phase SLM. The results showed that our DNN was able to reconstruct the profile of the phase target qualitatively. In the meantime, large error still existed, which indicated that our approach still need to be improved.

Phase-locking and bistability in neuronal networks with synaptic depression

NASA Astrophysics Data System (ADS)

Akcay, Zeynep; Huang, Xinxian; Nadim, Farzan; Bose, Amitabha

2018-02-01

We consider a recurrent network of two oscillatory neurons that are coupled with inhibitory synapses. We use the phase response curves of the neurons and the properties of short-term synaptic depression to define Poincaré maps for the activity of the network. The fixed points of these maps correspond to phase-locked modes of the network. Using these maps, we analyze the conditions that allow short-term synaptic depression to lead to the existence of bistable phase-locked, periodic solutions. We show that bistability arises when either the phase response curve of the neuron or the short-term depression profile changes steeply enough. The results apply to any Type I oscillator and we illustrate our findings using the Quadratic Integrate-and-Fire and Morris-Lecar neuron models.

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

Hu, Chin-Ping; Ng, C.-Y.; Li, K. L.

NGC 7793 P13 is an ultraluminous X-ray source harboring an accreting pulsar. We report on the detection of a ∼65 day period X-ray modulation with Swift observations in this system. The modulation period found in the X-ray band is P = 65.05 ± 0.10 days and the profile is asymmetric with a fast rise and a slower decay. On the other hand, the u -band light curve collected by Swift UVOT confirmed an optical modulation with a period of P = 64.24 ± 0.13 days. We explored the phase evolution of the X-ray and optical periodicities and propose two solutions.more » A superorbital modulation with a period of ∼2700–4700 days probably caused by the precession of a warped accretion disk is necessary to interpret the phase drift of the optical data. We further discuss the implication if this ∼65 day periodicity is caused by the superorbital modulation. Estimated from the relationship between the spin-orbital and orbital-superorbital periods of known disk-fed high-mass X-ray binaries, the orbital period of P13 is roughly estimated as 3–7 days. In this case, an unknown mechanism with a much longer timescale is needed to interpret the phase drift. Further studies on the stability of these two periodicities with a long-term monitoring could help us to probe their physical origins.« less

Animal-to-animal variability in the phasing of the crustacean cardiac motor pattern: an experimental and computational analysis

PubMed Central

Williams, Alex H.; Kwiatkowski, Molly A.; Mortimer, Adam L.; Marder, Eve; Zeeman, Mary Lou

2013-01-01

The cardiac ganglion (CG) of Homarus americanus is a central pattern generator that consists of two oscillatory groups of neurons: “small cells” (SCs) and “large cells” (LCs). We have shown that SCs and LCs begin their bursts nearly simultaneously but end their bursts at variable phases. This variability contrasts with many other central pattern generator systems in which phase is well maintained. To determine both the consequences of this variability and how CG phasing is controlled, we modeled the CG as a pair of Morris-Lecar oscillators coupled by electrical and excitatory synapses and constructed a database of 15,000 simulated networks using random parameter sets. These simulations, like our experimental results, displayed variable phase relationships, with the bursts beginning together but ending at variable phases. The model suggests that the variable phasing of the pattern has important implications for the functional role of the excitatory synapses. In networks in which the two oscillators had similar duty cycles, the excitatory coupling functioned to increase cycle frequency. In networks with disparate duty cycles, it functioned to decrease network frequency. Overall, we suggest that the phasing of the CG may vary without compromising appropriate motor output and that this variability may critically determine how the network behaves in response to manipulations. PMID:23446690

Prediction of U-Mo dispersion nuclear fuels with Al-Si alloy using artificial neural network

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

Susmikanti, Mike, E-mail: mike@batan.go.id; Sulistyo, Jos, E-mail: soj@batan.go.id

2014-09-30

Dispersion nuclear fuels, consisting of U-Mo particles dispersed in an Al-Si matrix, are being developed as fuel for research reactors. The equilibrium relationship for a mixture component can be expressed in the phase diagram. It is important to analyze whether a mixture component is in equilibrium phase or another phase. The purpose of this research it is needed to built the model of the phase diagram, so the mixture component is in the stable or melting condition. Artificial neural network (ANN) is a modeling tool for processes involving multivariable non-linear relationships. The objective of the present work is to developmore » code based on artificial neural network models of system equilibrium relationship of U-Mo in Al-Si matrix. This model can be used for prediction of type of resulting mixture, and whether the point is on the equilibrium phase or in another phase region. The equilibrium model data for prediction and modeling generated from experimentally data. The artificial neural network with resilient backpropagation method was chosen to predict the dispersion of nuclear fuels U-Mo in Al-Si matrix. This developed code was built with some function in MATLAB. For simulations using ANN, the Levenberg-Marquardt method was also used for optimization. The artificial neural network is able to predict the equilibrium phase or in the phase region. The develop code based on artificial neural network models was built, for analyze equilibrium relationship of U-Mo in Al-Si matrix.« less

Spin dynamics of paramagnetic centers with anisotropic g tensor and spin of ½

PubMed Central

Maryasov, Alexander G.

2012-01-01

The influence of g tensor anisotropy on spin dynamics of paramagnetic centers having real or effective spin of 1/2 is studied. The g anisotropy affects both the excitation and the detection of EPR signals, producing noticeable differences between conventional continuous-wave (cw) EPR and pulsed EPR spectra. The magnitudes and directions of the spin and magnetic moment vectors are generally not proportional to each other, but are related to each other through the g tensor. The equilibrium magnetic moment direction is generally parallel to neither the magnetic field nor the spin quantization axis due to the g anisotropy. After excitation with short microwave pulses, the spin vector precesses around its quantization axis, in a plane that is generally not perpendicular to the applied magnetic field. Paradoxically, the magnetic moment vector precesses around its equilibrium direction in a plane exactly perpendicular to the external magnetic field. In the general case, the oscillating part of the magnetic moment is elliptically polarized and the direction of precession is determined by the sign of the g tensor determinant (g tensor signature). Conventional pulsed and cw EPR spectrometers do not allow determination of the g tensor signature or the ellipticity of the magnetic moment trajectory. It is generally impossible to set a uniform spin turning angle for simple pulses in an unoriented or ‘powder’ sample when g tensor anisotropy is significant. PMID:22743542

Spin dynamics of paramagnetic centers with anisotropic g tensor and spin of 1/2

NASA Astrophysics Data System (ADS)

Maryasov, Alexander G.; Bowman, Michael K.

2012-08-01

The influence of g tensor anisotropy on spin dynamics of paramagnetic centers having real or effective spin of 1/2 is studied. The g anisotropy affects both the excitation and the detection of EPR signals, producing noticeable differences between conventional continuous-wave (cw) EPR and pulsed EPR spectra. The magnitudes and directions of the spin and magnetic moment vectors are generally not proportional to each other, but are related to each other through the g tensor. The equilibrium magnetic moment direction is generally parallel to neither the magnetic field nor the spin quantization axis due to the g anisotropy. After excitation with short microwave pulses, the spin vector precesses around its quantization axis, in a plane that is generally not perpendicular to the applied magnetic field. Paradoxically, the magnetic moment vector precesses around its equilibrium direction in a plane exactly perpendicular to the external magnetic field. In the general case, the oscillating part of the magnetic moment is elliptically polarized and the direction of precession is determined by the sign of the g tensor determinant (g tensor signature). Conventional pulsed and cw EPR spectrometers do not allow determination of the g tensor signature or the ellipticity of the magnetic moment trajectory. It is generally impossible to set a uniform spin turning angle for simple pulses in an unoriented or 'powder' sample when g tensor anisotropy is significant.

A quasi-periodic modulation of the iron line centroid energy in the black hole binary H1743-322

NASA Astrophysics Data System (ADS)

Ingram, Adam; van der Klis, Michiel; Middleton, Matthew; Done, Chris; Altamirano, Diego; Heil, Lucy; Uttley, Phil; Axelsson, Magnus

2016-09-01

Accreting stellar-mass black holes often show a `Type-C' quasi-periodic oscillation (QPO) in their X-ray flux and an iron emission line in their X-ray spectrum. The iron line is generated through continuum photons reflecting off the accretion disc, and its shape is distorted by relativistic motion of the orbiting plasma and the gravitational pull of the black hole. The physical origin of the QPO has long been debated, but is often attributed to 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 blueshift as the receding and approaching sides of the disc are respectively illuminated. Here we report on XMM-Newton and NuSTAR observations of the black hole binary H1743-322 in which the line energy varies systematically over the ˜4 s QPO cycle (3.70σ significance), as predicted. This provides strong evidence that the QPO is produced by Lense-Thirring precession, constituting the first detection of this effect in the strong gravitation regime. There are however elements of our results harder to explain, with one section of data behaving differently than all the others. Our result enables the future application of tomographic techniques to map the inner regions of black hole accretion discs.

Monitoring Orbital Precession of EO-1 Hyperion With Three Atmospheric Correction Models in the Libya-4 PICS

NASA Technical Reports Server (NTRS)

Neigh, Christopher S. R.; McCorkel, Joel; Campbell, Petya K. E.; Ong, Lawrence; Ly, Vuong; Landis, David; Middleton, Elizabeth M.

2016-01-01

Spaceborne spectrometers require spectral-temporal stability characterization to aid in validation of derived data products. Earth Observation 1 (EO-1) began orbital precession in 2011 after exhausting onboard fuel resources. In the Libya-4 pseudo-invariant calibration site (PICS), this resulted in a progressive shift from a mean local equatorial crossing time of approximately10:00 A.M. in 2011 to approximately 8:30 A.M. in late 2015. Here, we studied precession impacts to Hyperion surface reflectance products using three atmospheric correction approaches from 2004 to 2015. Combined difference estimates of surface reflectance were less than 5 percent in the visible near infrared (VNIR) and less than 10 percent for most of the shortwave infrared (SWIR). Combined coefficient of variation estimates in the VNIR ranged from 0.025 to 0.095, and in the SWIR it ranged from 0.025 to 0.06, excluding bands near atmospheric absorption features. Reflectances produced with different atmospheric models were correlated (R squared) in VNIR from 0.25 to 0.94 and in SWIR from 0.12 to 0.88 (p value (calculated probability) less than 0.01). The uncertainties in all the models increased with a terrain slope up to 15 degrees and selecting dune flats could reduce errors. We conclude that these data remain a valuable resource over this period for sensor intercalibration despite orbital decay.

Present status of astronomical constants

NASA Astrophysics Data System (ADS)

Fukushima, T.

Given was the additional information to the previous report on the recent progress in the determinations of astronomical constants (Fukushima 2000). First noted was the revision of LG as 6.969290134×10-10 based on the proposal to shift its status from a primary to a defining constant (Petit 2000). Next focused was the significant update of the correction to the current precession constant, Δp, based on the recent LLR-based determination (Chapront et al. 2000) as -0.3164+/-0.0030"/cy. By combining this and the equal weighted average of VLBI determinations (Mathews et al. 2000; Petrov 2000; Shirai and Fukushima 2000; Vondrak and Ron 2000) as -0.2968+/-0.0043"/cy, we derived the best estimate of precession constant as p = 5028.790+/-0.005"/cy. Also redetermined were some other quantities related to the precession formula; namely the offsets of Celestial Ephemeris Pole of the International Celestial Reference System as &Deltaψ0sinɛ0 = (-17.0+/-0.3) mas and Δɛ0 = (-5.1+/-0.3) mas. As a result, the obliquity of the ecliptic at the epoch J2000.0 was estimated as ɛ0 = 23°26'21."4059+/-0."0003. As a summary, presented was the (revised) IAU 2000 File of Current Best Estimates of astronomical constants, which is to replace the former 1994 version (Standish 1995).

Reducing Field Distortion in Magnetic Resonance Imaging

NASA Technical Reports Server (NTRS)

Eom, Byeong Ho; Penanen, Konstantin; Hahn, Inseob

2010-01-01

A concept for a magnetic resonance imaging (MRI) system that would utilize a relatively weak magnetic field provides for several design features that differ significantly from the corresponding features of conventional MRI systems. Notable among these features are a magnetic-field configuration that reduces (relative to the conventional configuration) distortion and blurring of the image, the use of a superconducting quantum interference device (SQUID) magnetometer as the detector, and an imaging procedure suited for the unconventional field configuration and sensor. In a typical application of MRI, a radio-frequency pulse is used to excite precession of the magnetic moments of protons in an applied magnetic field, and the decaying precession is detected for a short time following the pulse. The precession occurs at a resonance frequency proportional to the strengths of the magnetic field and the proton magnetic moment. The magnetic field is configured to vary with position in a known way; hence, by virtue of the aforesaid proportionality, the resonance frequency varies with position in a known way. In other words, position is encoded as resonance frequency. MRI using magnetic fields weaker than those of conventional MRI offers several advantages, including cheaper and smaller equipment, greater compatibility with metallic objects, and higher image quality because of low susceptibility distortion and enhanced spin-lattice-relaxation- time contrast. SQUID MRI is being developed into a practical MRI method for applied magnetic flux densities of the order of only 100 T

A model for periodic blazars

NASA Astrophysics Data System (ADS)

Sobacchi, Emanuele; Sormani, Mattia C.; Stamerra, Antonio

2017-02-01

We describe a scenario to explain blazar periodicities with time-scales of ˜ few years. The scenario is based on a binary supermassive black hole (SMBH) system in which one of the two SMBHs carries a jet. We discuss the various mechanisms that can cause the jet to precess and produce corkscrew patterns through space with a scale of ˜ few pc. It turns out that the dominant mechanism responsible for the precession is simply the imprint of the jet-carrying SMBH orbital speed on the jet. Gravitational deflection and Lense-Thirring precession (due to the gravitational field of the other SMBH) are second-order effects. We complement the scenario with a kinematical jet model which is inspired to the spine-sheath structure observed in M87. One of the main advantages of such a structure is that it allows the peak of the synchrotron emission to scale with frequency according to νF ∝ νξ as the viewing angle is changed, where ξ is not necessarily 3 or 4 as in the case of jets with uniform velocity, but can be ξ ˜ 1. Finally, we apply the model to the source PG1553+113, which has been recently claimed to show a Tobs = (2.18 ± 0.08) yr periodicity. We are able to reproduce the optical and gamma-ray light curves and multiple synchrotron spectra simultaneously. We also give estimates of the source mass and size.

Revealing giant internal magnetic fields due to spin fluctuations in magnetically doped colloidal nanocrystals

DOE PAGES

Rice, William D.; Liu, Wenyong; Baker, Thomas A.; ...

2015-11-23

Strong quantum confinement in semiconductors can compress the wavefunctions of band electrons and holes to nanometre-scale volumes, significantly enhancing interactions between themselves and individual dopants. In magnetically doped semiconductors, where paramagnetic dopants (such as Mn 2+, Co 2+ and so on) couple to band carriers via strong sp–d spin exchange, giant magneto-optical effects can therefore be realized in confined geometries using few or even single impurity spins. Importantly, however, thermodynamic spin fluctuations become increasingly relevant in this few-spin limit. In nanoscale volumes, the statistical √N fluctuations of N spins are expected to generate giant effective magnetic fields B eff, whichmore » should dramatically impact carrier spin dynamics, even in the absence of any applied field. In this paper, we directly and unambiguously reveal the large B eff that exist in Mn 2+-doped CdSe colloidal nanocrystals using ultrafast optical spectroscopy. At zero applied magnetic field, extremely rapid (300–600 GHz) spin precession of photoinjected electrons is observed, indicating B eff ~ 15-30 T for electrons. Precession frequencies exceed 2 THz in applied magnetic fields. Finally, these signals arise from electron precession about the random fields due to statistically incomplete cancellation of the embedded Mn 2+ moments, thereby revealing the initial coherent dynamics of magnetic polaron formation, and highlighting the importance of magnetization fluctuations on carrier spin dynamics in nanomaterials.« less

Dating an 800,000 year Antarctic ice core record using the isotopic composition of trapped air

NASA Astrophysics Data System (ADS)

Dreyfus, Gabrielle Boissier

Here we measure the isotopic composition of air trapped in the European Project for Ice Coring in Antarctica Dome C (EDC) ice core, and use this geochemical information to improve the ice core agescale and our understanding of air enclosure processes. A first result is the detection of a flow anomaly in the bottom 500m of the EDC ice core using the delta18O of atmospheric oxygen (noted delta18Oatm). By tuning the measured delta18Oatm to the orbital precession signal, we correct the EDC agescale over 400-800 ka for flow-induced distortions in the duration of events. Uncertainty in delta 18Oatm phasing with respect to precession limits the accuracy of the tuned agescale to +/-6 ka. We use this improved agescale to date two 10Be peaks detected in the EDC ice core and associated with the Matuyama-Brunhes geomagnetic boundary. While the ice age of the "precursor" event agrees within uncertainty with the age of radioisotopically dated lavas, the volcanic age for the younger reversal is approximately 10 ka older than the mid-point of the 10 Be peak in the ice. Since 80% of the lavas recording the Matuyama-Brunhes reversal are located in the Central Pacific, the observed age difference may indicate that the magnetic field orientation at this location changed prior to the dipole intensity minimum recorded by the ice core 10Be, as suggested by recent geodynamo modeling. A particular challenge for ice core dating is accurately accounting for the age difference between the trapped air and surrounding ice. This gas age - ice age difference (noted Deltaage) depends on the age of the ice at the bottom of the firn. delta15N of N2 is constant in the atmosphere over the timescales considered here, so any deviation from atmospheric composition reflects fractionation processes in the firn. We show that delta15N is positively correlated with the ice deuterium content, a proxy for temperature, over the entire EDC record, and propose an accumulation-permeability-convection mechanism. While temporal resolution and noise in the available data limit our ability to constrain glacial Deltaage, these data suggest that delta15N may be used as a gas-phase climate proxy at EDC.

Organization of Anti-Phase Synchronization Pattern in Neural Networks: What are the Key Factors?

PubMed Central

Li, Dong; Zhou, Changsong

2011-01-01

Anti-phase oscillation has been widely observed in cortical neural network. Elucidating the mechanism underlying the organization of anti-phase pattern is of significance for better understanding more complicated pattern formations in brain networks. In dynamical systems theory, the organization of anti-phase oscillation pattern has usually been considered to relate to time delay in coupling. This is consistent to conduction delays in real neural networks in the brain due to finite propagation velocity of action potentials. However, other structural factors in cortical neural network, such as modular organization (connection density) and the coupling types (excitatory or inhibitory), could also play an important role. In this work, we investigate the anti-phase oscillation pattern organized on a two-module network of either neuronal cell model or neural mass model, and analyze the impact of the conduction delay times, the connection densities, and coupling types. Our results show that delay times and coupling types can play key roles in this organization. The connection densities may have an influence on the stability if an anti-phase pattern exists due to the other factors. Furthermore, we show that anti-phase synchronization of slow oscillations can be achieved with small delay times if there is interaction between slow and fast oscillations. These results are significant for further understanding more realistic spatiotemporal dynamics of cortico-cortical communications. PMID:22232576

Structural integration and performance of inter-sectoral public health-related policy networks: An analysis across policy phases.

PubMed

Peters, D T J M; Raab, J; Grêaux, K M; Stronks, K; Harting, J

2017-12-01

Inter-sectoral policy networks may be effective in addressing environmental determinants of health with interventions. However, contradictory results are reported on relations between structural network characteristics (i.e., composition and integration) and network performance, such as addressing environmental determinants of health. This study examines these relations in different phases of the policy process. A multiple-case study was performed on four public health-related policy networks. Using a snowball method among network actors, overall and sub-networks per policy phase were identified and the policy sector of each actor was assigned. To operationalise the outcome variable, interventions were classified by the proportion of environmental determinants they addressed. In the overall networks, no relation was found between structural network characteristics and network performance. In most effective cases, the policy development sub-networks were characterised by integration with less interrelations between actors (low cohesion), more equally distributed distances between the actors (low closeness centralisation), and horizontal integration in inter-sectoral cliques. The most effective case had non-public health central actors with less connections in all sub-networks. The results suggest that, to address environmental determinants of health, sub-networks should be inter-sectorally composed in the policy development rather than in the intervention development and implementation phases, and that policy development actors should have the opportunity to connect with other actors, without strong direction from a central actor. Copyright © 2017 Elsevier B.V. All rights reserved.

Technology for Transient Simulation of Vibration during Combustion Process in Rocket Thruster

NASA Astrophysics Data System (ADS)

Zubanov, V. M.; Stepanov, D. V.; Shabliy, L. S.

2018-01-01

The article describes the technology for simulation of transient combustion processes in the rocket thruster for determination of vibration frequency occurs during combustion. The engine operates on gaseous propellant: oxygen and hydrogen. Combustion simulation was performed using the ANSYS CFX software. Three reaction mechanisms for the stationary mode were considered and described in detail. The way for obtaining quick CFD-results with intermediate combustion components using an EDM model was found. The way to generate the Flamelet library with CFX-RIF was described. A technique for modeling transient combustion processes in the rocket thruster was proposed based on the Flamelet library. A cyclic irregularity of the temperature field like vortex core precession was detected in the chamber. Frequency of flame precession was obtained with the proposed simulation technique.

Conductance dips and spin precession in a nonuniform waveguide with spin–orbit coupling

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

Malyshev, A. I., E-mail: malyshev@phys.unn.ru; Kozulin, A. S.

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 effectivemore » magnetic field does not lead to a change in the direction of the average spin vector at the output of the system.« less

Neural Networks For Demodulation Of Phase-Modulated Signals

NASA Technical Reports Server (NTRS)

Altes, Richard A.

1995-01-01

Hopfield neural networks proposed for demodulating quadrature phase-shift-keyed (QPSK) signals carrying digital information. Networks solve nonlinear integral equations prior demodulation circuits cannot solve. Consists of set of N operational amplifiers connected in parallel, with weighted feedback from output terminal of each amplifier to input terminals of other amplifiers. Used to solve signal processing problems. Implemented as analog very-large-scale integrated circuit that achieves rapid convergence. Alternatively, implemented as digital simulation of such circuit. Also used to improve phase estimation performance over that of phase-locked loop.

Phase-locked patterns of the Kuramoto model on 3-regular graphs

NASA Astrophysics Data System (ADS)

DeVille, Lee; Ermentrout, Bard

2016-09-01

We consider the existence of non-synchronized fixed points to the Kuramoto model defined on sparse networks: specifically, networks where each vertex has degree exactly three. We show that "most" such networks support multiple attracting phase-locked solutions that are not synchronized and study the depth and width of the basins of attraction of these phase-locked solutions. We also show that it is common in "large enough" graphs to find phase-locked solutions where one or more of the links have angle difference greater than π/2.

Phase-locked patterns of the Kuramoto model on 3-regular graphs.

PubMed

DeVille, Lee; Ermentrout, Bard

2016-09-01

We consider the existence of non-synchronized fixed points to the Kuramoto model defined on sparse networks: specifically, networks where each vertex has degree exactly three. We show that "most" such networks support multiple attracting phase-locked solutions that are not synchronized and study the depth and width of the basins of attraction of these phase-locked solutions. We also show that it is common in "large enough" graphs to find phase-locked solutions where one or more of the links have angle difference greater than π/2.

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 obtained at different epochs suggests that the jet is expanding at a maximum speed on the plane of the sky of 300 km s-1. The proper motions of the H2O maser spots measured in the region also indicate expansion in a direction similar to that of the radio jet. Conclusions: We have revealed a binary system of high-mass young stellar objects embedded in the rotating disk in G35.20-0.74N. The presence of a massive binary system is in agreement with the theoretical predictions of high-mass star formation, according to which the gravitational instabilities during the collapse would produce the fragmentation of the disk and the formation of such a system. For the first time, we have detected a high-mass young star associated with an UC/HC Hii region and at the same time powering a radio jet. The reduced images (FITS files) is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/593/A49

Associative memory in phasing neuron networks

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

Nair, Niketh S; Bochove, Erik J.; Braiman, Yehuda

2014-01-01

We studied pattern formation in a network of coupled Hindmarsh-Rose model neurons and introduced a new model for associative memory retrieval using networks of Kuramoto oscillators. Hindmarsh-Rose Neural Networks can exhibit a rich set of collective dynamics that can be controlled by their connectivity. Specifically, we showed an instance of Hebb's rule where spiking was correlated with network topology. Based on this, we presented a simple model of associative memory in coupled phase oscillators.

Spike phase synchronization in multiplex cortical neural networks

NASA Astrophysics Data System (ADS)

Jalili, Mahdi

2017-01-01

In this paper we study synchronizability of two multiplex cortical networks: whole-cortex of hermaphrodite C. elegans and posterior cortex in male C. elegans. These networks are composed of two connection layers: network of chemical synapses and the one formed by gap junctions. This work studies the contribution of each layer on the phase synchronization of non-identical spiking Hindmarsh-Rose neurons. The network of male C. elegans shows higher phase synchronization than its randomized version, while it is not the case for hermaphrodite type. The random networks in each layer are constructed such that the nodes have the same degree as the original network, thus providing an unbiased comparison. In male C. elegans, although the gap junction network is sparser than the chemical network, it shows higher contribution in the synchronization phenomenon. This is not the case in hermaphrodite type, which is mainly due to significant less density of gap junction layer (0.013) as compared to chemical layer (0.028). Also, the gap junction network in this type has stronger community structure than the chemical network, and this is another driving factor for its weaker synchronizability.

Variations of the Milankovitch frequencies in time

NASA Technical Reports Server (NTRS)

Loutre, Marie-France; Berger, A.

1992-01-01

The sensitivity of the amplitudes and frequencies in the development of the Earth's orbital and rotational elements involved in the astronomical theory of paleoclimates (eccentricity, obliquity, and climate precession), to the Earth-Moon distance and consequently to the length of the day and to the dynamical ellipticity of the Earth has been discussed for the last billions of years. The shortening of the Earth-Moon distance and of the length of the day, as well as the lengthening of the dynamical ellipticity of the Earth back in time induce a shortening of the fundamental astronomical periods for precession and obliquity. At the same time, the amplitudes of the different terms in the development of the obliquity are undergoing a relative enlargement of about 50 percent at 2 x 10(exp 9) yr BP but the independent term is increasing very weakly (less than 0.1 percent). In other words, the value of the obliquity, which lies within a range of 21.7 to 24.9 deg over the Quarternary was restricted to a range of 22.5 to 24.1 deg at 2 x 10(exp 9) yr BP. On the other hand, the amplitudes in the development of the climatic precession do not change. Moreover, these changes in the frequencies and amplitudes for both obliquity and climatic precession are larger for longer period terms. Finally, the periods in the eccentricity development are not influenced by the variation of the lunar distance. But the motion of the solar system, especially of the inner planets, was shown to be chaotic. It means that it is impossible to compute the exact motion of the planets over more than about 100 Myr, and the fundamental frequencies of the systems are not fixed quantities, but are slowly varying with time. As long as we consider the most important terms, the maximum deviation from the present-day value of the 19-kyr precessional period due to the chaotic motion of the solar system only does not reach more than a few tens of years around 80 Myr BP. Therefore the shortening of the obliquity and climatic precession periods is mostly driven by the change in the lunar distance and the consequent variations in the dynamical ellipticity of the Earth's angular speed. At first sight, the deviation in the period for the eccentricity can be neglected, as the chaotic behavior of the solar system implies a relative change of the main periods by less than 0.2 percent, 1.4 percent, and 1.9 percent respectively, this maximum change being achieved around 80 Myr BP. This implies, in particular, that the eccentricity periods for Quarternary climate studies may be considered more or less constant for pre-Quaternay times and equal to their Quaternary values.

Microbially mediated carbon cycling at the Cenomanian-Turonian transition in lacustrine environments

NASA Astrophysics Data System (ADS)

Wu, H.; Zhang, S.; Jiang, G.; Underwood, M.; Wan, X.

2009-12-01

The Late Cretaceous Cenomanian-Turonian (C-T) transition records a major ocean anoxic event (OAE2) and a positive carbon isotope excursion. These events have been documented mostly from marine successions and their expression in terrestrial environments is highly desirable. Here we report a high-resolution organic carbon isotope record across the C-T boundary from the Qingshankou Formation (K2qn) of the terrestrial Songliao Basin (SLB) in northeastern China. Samples were collected from the drilled core (SK-1) and cover the bottom 60 m of the K2qn that has been correlated to the C-T transition using the astronomical time scale. The results show a long-term negative δ13Corg excursion superimposed on short-term δ13Corg cycles. Most δ13Corg cycles have a reverse relationship with total organic carbon (TOC) concentration, except at the beginning and the end of the long-term δ13Corg excursion. Spectral analysis of the δ13Corg, TOC and Gamma Ray Logging curves (GR) reveals three distinct cycle bands with the thickness of 14.5-9.0m, 5.8-3.4m and 2.2-1.5m, which were interpreted as the short eccentricity, obliquity, and precession cycles, respectively. The investigated section recorded about 7 short eccentricity and 39 precession cycles. The reverse relationship between TOC and δ13Corg is inconsistent with the general TOC-δ13Corg pattern seen in most lacustrine environments, in which increasing primary productivity (and thus TOC) in the epilimnion results in higher δ13Corg values. In combination with existing biomarker data from K2qn, the TOC-δ13Corg pattern in SLB is better explained by microbially mediated carbon cycling that is astronomically controlled by the precession cycles. During precession minima (summer insolation maxima) periods, intensified precipitation and increased chemical weathering may have led to sustained eutrophication in SLB and the bloom of chemoautotrophic and methanotrophic organisms in the basin. Significant biomass contribution from chemoautotrophic and methanotrophic organisms resulted in lower δ13Corg values. During precession maximum, seasonal changes and reduced nutrient supply kept better water circulation and a lower chemocline. Most organic carbon contribution was from photosynthetic organisms and has relatively higher δ13Corg values. The positive TOC-δ13Corg correlation at the beginning and end of the long-term negative δ13Corg excursion can be interpreted as resulting from the algal/diatom blooms at the onset and ending of the eccentricity cycle, during which high surface water production and a lower chemocline were maintained. The data indicate sustained anoxia/euxinia in the SLB during the time of OAE2, suggesting a paleoclimate event influencing both the marine and terrestrial systems.

Morphology effect on the light scattering and dynamic response of polymer network liquid crystal phase modulator.

PubMed

Xiangjie, Zhao; Cangli, Liu; Jiazhu, Duan; Jiancheng, Zeng; Dayong, Zhang; Yongquan, Luo

2014-06-16

Polymer network liquid crystal (PNLC) was one of the most potential liquid crystal for submillisecond response phase modulation, which was possible to be applied in submillisecond response phase only spatial light modulator. But until now the light scattering when liquid crystal director was reoriented by external electric field limited its phase modulation application. Dynamic response of phase change when high voltage was applied was also not elucidated. The mechanism that determines the light scattering was studied by analyzing the polymer network morphology by SEM method. Samples were prepared by varying the polymerization temperature, UV curing intensity and polymerization time. The morphology effect on the dynamic response of phase change was studied, in which high voltage was usually applied and electro-striction effect was often induced. The experimental results indicate that the polymer network morphology was mainly characterized by cross linked single fibrils, cross linked fibril bundles or even both. Although the formation of fibril bundle usually induced large light scattering, such a polymer network could endure higher voltage. In contrast, although the formation of cross linked single fibrils induced small light scattering, such a polymer network cannot endure higher voltage. There is a tradeoff between the light scattering and high voltage endurance. The electro-optical properties such as threshold voltage and response time were taken to verify our conclusion. For future application, the monomer molecular structure, the liquid crystal solvent and the polymerization conditions should be optimized to generate optimal polymer network morphology.

Participation of the Abastumani Astrophysical Observatory in Different Programs for Coordinated Investigation of Cyg X-1

NASA Astrophysics Data System (ADS)

Kumsiashvili, M. I.; Kochiashvili, N. T.

2000-10-01

Broad-band photometric observations of the black hole candidate Cyg X-1 were carried out in 1975-1998 at the Abastumani Astrophysical Observatory in the framework of coordinated observations, at the varies observatories of the former Soviet Union. All data have been reduced to a homogeneous set.Comparison of the optical and X-ray data clearly shows the existence of several kinds of variability. Analysis of the prolonged photoelectric observations of V 1357 Cyg=Cyg X-1 confirmed long-period optical variation of this X-ray binary system with the period of 294 d revealed by Kemp et al. This periodicity is most strongly pronounced at the orbital period phase when the optical star is in front of the X-ray source. Variations of the mean level of Cyg X-1 and of the light curve form with the phase of the period 294 d agree well with the model of the precessing accretion disk which radiates in the optical range mainly by scattering and processing of the optical star radiation. The direction of the disc precession coincides with that of the orbital motion and it is hard to understand this fact in the models with the forced precession. The triple system model is less probable. There are also observations of this objects made in the Abastumani Observatory in 1982-1988 which are represented the Table and light curves. These observations have not discussed by coordinators. The observations taken in the course of the International campaign "The Optical Monitoring of the Unique Astrophysical Objects" were realized by the observatories located on the territories of Georgia, Russia, Uzbekistan and Ukraine in 1994-1998. They are united in a single set, taking into account the systemic differences between them. Number of usual observations is 2247 in 399 nights in U B V R bands. The observations were performed simultaneously in X-ray band in the energy range of 2-10 keV (ASM/RXTE), and 20-100 keV (BASTE/CGRO), and also with radio observations at the Mullard radio observatory. Our optical data overlapped well the hard band at JD 2451000-040. Both outbursts did not coincide with any optical brightening or double wave orbital light curve changes. From two independent sets strong optical flare at JD 2450988, being a possible precursor of hard X-ray flare have been detected. Intrinsic variations of the system have the chaotic character with flares and dips in time scale of a day and the amplitude of 0.10 m. Fourier spectra show predominating secondary period of 147 d at high probability level, being a half of 294 d period found by Priedhorsky et al. in X-rays, and Kemp et al. in optics. We have identified near-by period of 150 d which predominates modern X-ray light curve. The period found in optics is close to the period of 142.7 d in modern Mullard radio data by Brooksopp et al. The light curve resembles a non-stationary process by the time changes of Fourier spectra. But some spectrum peaks can be stable for several seasons. The cross-correlation analysis confirms the time delay of the trends of the X-ray light curve relative to the optical one by 11.620 days. The weak relation of the short-time variations of X-ray and optical radiation are also found at high probability level with delay 3 days.

Predicting neural network firing pattern from phase resetting curve

NASA Astrophysics Data System (ADS)

Oprisan, Sorinel; Oprisan, Ana

2007-04-01

Autonomous neural networks called central pattern generators (CPG) are composed of endogenously bursting neurons and produce rhythmic activities, such as flying, swimming, walking, chewing, etc. Simplified CPGs for quadrupedal locomotion and swimming are modeled by a ring of neural oscillators such that the output of one oscillator constitutes the input for the subsequent neural oscillator. The phase response curve (PRC) theory discards the detailed conductance-based description of the component neurons of a network and reduces them to ``black boxes'' characterized by a transfer function, which tabulates the transient change in the intrinsic period of a neural oscillator subject to external stimuli. Based on open-loop PRC, we were able to successfully predict the phase-locked period and relative phase between neurons in a half-center network. We derived existence and stability criteria for heterogeneous ring neural networks that are in good agreement with experimental data.

A new approach to network heterogeneity: Polymerization Induced Phase Separation in photo-initiated, free-radical methacrylic systems

PubMed Central

Szczepanski, Caroline R.; Pfeifer, Carmem S.; Stansbury, Jeffrey W.

2012-01-01

Non-reactive, thermoplastic prepolymers (poly- methyl, ethyl and butyl methacrylate) were added to a model homopolymer matrix composed of triethylene glycol dimethacrylate (TEGDMA) to form heterogeneous networks via polymerization induced phase separation (PIPS). PIPS creates networks with distinct phase structure that can partially compensate for volumetric shrinkage during polymerization through localized internal volume expansion. This investigation utilizes purely photo-initiated, free-radical systems, broadening the scope of applications for PIPS since these processing conditions have not been studied previously. The introduction of prepolymer into TEGDMA monomer resulted in stable, homogeneous monomer formulations, most of which underwent PIPS upon photo-irradiation, creating heterogeneous networks. During polymerization the presence of prepolymer enhanced autoacceleration, allowing for a more extensive ambient cure of the material. Phase separation, as characterized by dynamic changes in sample turbidity, was monitored simultaneously with monomer conversion and either preceded or was coincident with network gelation. Dynamic mechanical analysis shows a broadening of the tan delta peak and secondary peak formation, characteristic of phase-separated materials, indicating one phase rich in prepolymer and another depleted form upon phase separation. In certain cases, PIPS leads to an enhanced physical reduction of volumetric shrinkage, which is attractive for many applications including dental composite materials. PMID:23109733

Geometrically Induced Interactions and Bifurcations

NASA Astrophysics Data System (ADS)

Binder, Bernd

2010-01-01

In order to evaluate the proper boundary conditions in spin dynamics eventually leading to the emergence of natural and artificial solitons providing for strong interactions and potentials with monopole charges, the paper outlines a new concept referring to a curvature-invariant formalism, where superintegrability is given by a special isometric condition. Instead of referring to the spin operators and Casimir/Euler invariants as the generator of rotations, a curvature-invariant description is introduced utilizing a double Gudermann mapping function (generator of sine Gordon solitons and Mercator projection) cross-relating two angular variables, where geometric phases and rotations arise between surfaces of different curvature. Applying this stereographic projection to a superintegrable Hamiltonian can directly map linear oscillators to Kepler/Coulomb potentials and/or monopoles with Pöschl-Teller potentials and vice versa. In this sense a large scale Kepler/Coulomb (gravitational, electro-magnetic) wave dynamics with a hyperbolic metric could be mapped as a geodesic vertex flow to a local oscillator singularity (Dirac monopole) with spherical metrics and vice versa. Attracting fixed points and dynamic constraints are given by special isometries with magic precession angles. The nonlinear angular encoding directly provides for a Shannon mutual information entropy measure of the geodesic phase space flow. The emerging monopole patterns show relations to spiral Fresnel holography and Berry/Aharonov-Bohm geometric phases subject to bifurcation instabilities and singularities from phase ambiguities due to a local (entropy) overload. Neutral solitons and virtual patterns emerging and mediating in the overlap region between charged or twisted holographic patterns are visualized and directly assigned to the Berry geometric phase revealing the role of photons, neutrons, and neutrinos binding repulsive charges in Coulomb, strong and weak interaction.