Differentially-rotating neutron star models with a parametrized rotation profile
Galeazzi, Filippo; Eriguchi, Yoshiharu
2011-01-01
We analyze the impact of the choice rotation law on equilibrium sequences of relativistic differentially-rotating neutron stars in axisymmetry. The maximum allowed mass for each model is strongly affected by the distribution of angular velocity along the radial direction and by the consequent degree of differential rotation. In order to study the wide parameter space implied by the choice of rotation law, we introduce a functional form that generalizes the so called "j-const. law" adopted in all previous work. Using this new rotation law we reproduce the angular velocity profile of differentially-rotating remnants from the coalescence of binary neutron stars in various 3-dimensional dynamical simulations. We compute equilibrium sequences of differentially rotating stars with a polytropic equation of state starting from the spherically symmetric static case. By analyzing the sequences at constant ratio, T/|W|, of rotational kinetic energy to gravitational binding energy, we find that the parameters that best d...
Differentially rotating magnetised neutron stars: production of toroidal magnetic fields
Thampan, A V
2004-01-01
We initiate numerical studies of differentially rotating magnetised (proto) neutron stars by studying - through construction from first principles - the coupling between an assumed differential rotation and an impressed magnetic field. For a perfect incompressible, homogeneous, non-dissipative fluid sphere immersed in an ambient plasma, we solve the (coupled) azimuthal components of the Navier-Stokes equation and the Maxwell induction equation. The assumed time--independent poloidal field lines get dragged by the rotating fluid and produce toroidal magnetic fields. Surface magnetic fields take away energy redistributing the angular momentum to produce rigid rotation along poloidal field lines. Due to absence of viscous dissipation, sustained torsional oscillations are set up within the star. However, the perpetual oscillations of neighbouring `closed' field lines get increasingly out of phase with time, leading to structure build up as in Liu & Shapiro (2004) implying the importance of taking into account...
Chirenti, Cecilia; Yoshida, Shin'ichirou
2013-01-01
Newly born neutron stars can present differential rotation, even if later it should be suppressed by viscosity or a sufficiently strong magnetic field. And in this early stage of its life, a neutron star is expected to have a strong emission of gravitational waves, which could be influenced by the differential rotation. We present here a new formalism for modelling differentially rotating neutron stars: working on the slow rotation approximation and assuming a small degree of differential rotation, we show that it is possible to separate variables in the Einstein field equations. The dragging of inertial frames is determined by solving three decoupled ODEs. After we establish our equilibrium model, we explore the influence of the differential rotation on the f and r-modes of oscillation of the neutron star in the Cowling approximation, and we also analyze an effect of the differential rotation on the emission of gravitational radiation from the f-modes. We see that the gravitational radiation from the f-modes...
Three dimensional evolution of differentially rotating magnetized neutron stars
Kiuchi, Kenta; Shibata, Masaru
2012-01-01
We construct a new three-dimensional general relativistic magnetohydrodynamics code, in which a fixed mesh refinement technique is implemented. To ensure the divergence-free condition as well as the magnetic flux conservation, we employ the method by Balsara (2001). Using this new code, we evolve differentially rotating magnetized neutron stars, and find that a magnetically driven outflow is launched from the star exhibiting a kink instability. The matter ejection rate and Poynting flux are still consistent with our previous finding (Shibata et al., 2011) obtained in axisymmetric simulations.
Four-Hair Relations for Differentially Rotating Neutron Stars in the Weak-Field Limit
Bretz, Joseph; Yunes, Nicolas
2015-01-01
The opportunity to study physics at supra-nuclear densities through X-ray observations of neutron stars has led to in-depth investigations of certain approximately universal relations that can remove degeneracies in pulse profile models. One such set of relations determines all of the multipole moments of a neutron star just from the first three (the mass monopole, the current dipole and the mass quadrupole moment) approximately independently of the equation of state. These three-hair relations were found to hold in neutron stars that rotate rigidly, as is the case in old pulsars, but neutron stars can also rotate differentially, as is the case for proto-neutron stars and hypermassive transient remnants of binary mergers. We here extend the three-hair relations to differentially rotating stars for the first time with a generic rotation law using two approximations: a weak-field scheme (an expansion in powers of the neutron star compactness) and a perturbative differential rotation scheme (an expansion about r...
A New View on the Maximum Mass of Differentially Rotating Neutron Stars
Gondek-Rosińska, D.; Kowalska, I.; Villain, L.; Ansorg, M.; Kucaba, M.
2017-03-01
We study the main astrophysical properties of differentially rotating neutron stars described as stationary and axisymmetric configurations of a moderately stiff {{Γ }}=2 polytropic fluid. The high level of accuracy and of stability of our relativistic multidomain pseudo-spectral code enables us to explore the whole solution space for broad ranges of the degree of differential rotation, but also of the stellar density and oblateness. Staying within an astrophysically motivated range of rotation profiles, we investigate the characteristics of neutron stars with maximal mass for all types of families of differentially rotating relativistic objects identified in a previous article. We find that the maximum mass depends on both the degree of differential rotation and the type of solution. It turns out that the maximum allowed mass can be up to 4 times higher than what it is for nonrotating stars with the same equation of state. Such values are obtained for a modest degree of differential rotation but for one of the newly discovered types of solutions. Since such configurations of stars are not that extreme, this result may have important consequences for the gravitational wave signal expected from coalescing neutron star binaries or from some supernova events.
Effect of the equation of state on the maximum mass of differentially rotating neutron stars
Studzińska, A. M.; Kucaba, M.; Gondek-Rosińska, D.; Villain, L.; Ansorg, M.
2016-12-01
Knowing the value of the maximum mass of a differentially rotating relativistic star is a key step towards the understanding of the signals to be expected from the merger of binary neutron stars, one of the most awaited alternative sources of gravitational waves after binary black holes. In this paper, we study the effects of differential rotation and of the equation of state on the maximum mass of rotating neutron stars modelled as relativistic polytropes with various adiabatic indices. Calculations are performed using a highly accurate numerical code, based on a multidomain spectral method. We thoroughly explore the parameter space and determine how the maximum mass depends on the stiffness, on the degree of differential rotation and on the maximal density, taking into account all the types of solutions that were proven to exist in a preceding paper. The highest increase with respect to the maximum mass for non-rotating stars with the same equation of state is reached for a moderate stiffness. With differential rotation, the maximum mass can even be 3-4 times higher than it is for static stars. This result may have important consequences for the gravitational wave signal from coalescing neutron star binaries or for some supernovae events.
A new view on the maximum mass of differentially rotating neutron stars
Gondek-Rosinska, Dorota; Villain, Loic; Ansorg, Marcus; Kucaba, Marcin
2016-01-01
We study the main astrophysical properties of differentially rotating neutron stars described as stationary and axisymmetric configurations of a moderately stiff $\\Gamma=2$ polytropic fluid. The high level of accuracy and of stability of our relativistic multidomain pseudo-spectral code enables us to explore the whole solution space for broad ranges of the degree of differential rotation, but also of the stellar density and oblateness. Staying within an astrophysicaly motivated range of rotation profiles, we investigate the characteristics of neutron stars with maximal mass for all types of families of differentially rotating relativistic objects identified in a previous article Ansorg, Gondek-Rosinsla, Villain (2009). We find that the maximum mass depends on both the degree of differential rotation and on the type of solution. It turns out that the maximum allowed mass can be up to 4 times higher than what it is for non-rotating stars with the same equation of state. Such values are obtained for a modest deg...
R-mode frequencies of rapidly and differentially rotating relativistic neutron stars
Chirenti, Cecilia; Jasiulek, Michael
2017-01-01
R-modes are a promising source of gravitational waves for ground based detectors. If the precise frequency is known, guided gravitational wave searches with higher detectability are possible. Many authors have calculated the r-mode frequency because of its physical importance. For the dominant mode its value is 4/3 times the angular velocity of the star, subject to various corrections, of which the most important are relativistic and rotational corrections. Here we extend the results from previous works and investigate the effect of rapid rotation and differential rotation on the r-mode frequency. We evolve the perturbation equations in Cowling approximation in time using finite differencing methods to compute the r-mode frequency for sequences of rotating neutron stars with polytropic equations of state. The results presented here are relevant to the design of gravitational wave and electromagnetic r-mode searches.
R-mode frequencies of rapidly and differentially rotating relativistic neutron stars
Jasiulek, Michael
2016-01-01
R-modes of neutron stars could be a source of gravitational waves for ground based detectors. If the precise frequency $\\sigma$ is known, guided gravitational wave searches with enhanced detectability are possible. Because of its physical importance many authors have calculated the r-mode frequency. For the dominant mode, the associated gravitational wave frequency is 4/3 times the angular velocity of the star $\\Omega$, subject to various corrections of which relativistic and rotational corrections are the most important. This has led several authors to investigate the dependence of the r-mode frequency on factors such as the relativistic compactness parameter ($M/R$) and the angular velocity of stars with different equations of state. The results found so far, however, are almost independent of the equation of state. Here we investigate the effect of rapid rotation and differential rotation on $\\sigma$. We evolve the perturbation equations using the Cowling approximation by applying finite differencing metho...
Uniformly rotating neutron stars
Boshkayev, Kuantay
2016-01-01
In this chapter we review the recent results on the equilibrium configurations of static and uniformly rotating neutron stars within the Hartle formalism. We start from the Einstein-Maxwell-Thomas-Fermi equations formulated and extended by Belvedere et al. (2012, 2014). We demonstrate how to conduct numerical integration of these equations for different central densities ${\\it \\rho}_c$ and angular velocities $\\Omega$ and compute the static $M^{stat}$ and rotating $M^{rot}$ masses, polar $R_p$ and equatorial $R_{\\rm eq}$ radii, eccentricity $\\epsilon$, moment of inertia $I$, angular momentum $J$, as well as the quadrupole moment $Q$ of the rotating configurations. In order to fulfill the stability criteria of rotating neutron stars we take into considerations the Keplerian mass-shedding limit and the axisymmetric secular instability. Furthermore, we construct the novel mass-radius relations, calculate the maximum mass and minimum rotation periods (maximum frequencies) of neutron stars. Eventually, we compare a...
Superfluid instability of r-modes in "differentially rotating" neutron stars
Andersson, N; Hogg, M
2012-01-01
Superfluid hydrodynamics affects the spin-evolution of mature neutron stars, and may be key to explaining timing irregularities such as pulsar glitches. However, most models for this phenomenon exclude the global instability required to trigger the event. In this paper we discuss a mechanism that may fill this gap. We establish that small scale inertial r-modes become unstable in a superfluid neutron star that exhibits a rotational lag, expected to build up due to vortex pinning as the star spins down. Somewhat counterintuitively, this instability arises due to the (under normal circumstances dissipative) vortex-mediated mutual friction. We explore the nature of the superfluid instability for a simple incompressible model, allowing for entrainment coupling between the two fluid components. Our results recover a previously discussed dynamical instability in systems where the two components are strongly coupled. In addition, we demonstrate for the first time that the system is secularly unstable (with a growth ...
Siegel, Daniel M.; Ciolfi, Riccardo; Rezzolla, Luciano [Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Am Mühlenberg 1, D-14476 Potsdam-Golm (Germany)
2014-04-10
Besides being among the most promising sources of gravitational waves, merging neutron star binaries also represent a leading scenario to explain the phenomenology of short gamma-ray bursts (SGRBs). Recent observations have revealed a large subclass of SGRBs with roughly constant luminosity in their X-ray afterglows, lasting 10-10{sup 4} s. These features are generally taken as evidence of a long-lived central engine powered by the magnetic spin-down of a uniformly rotating, magnetized object. We propose a different scenario in which the central engine powering the X-ray emission is a differentially rotating hypermassive neutron star (HMNS) that launches a quasi-isotropic and baryon-loaded wind driven by the magnetic field, which is built-up through differential rotation. Our model is supported by long-term, three-dimensional, general-relativistic, and ideal magnetohydrodynamic simulations, showing that this isotropic emission is a very robust feature. For a given HMNS, the presence of a collimated component depends sensitively on the initial magnetic field geometry, while the stationary electromagnetic luminosity depends only on the magnetic energy initially stored in the system. We show that our model is compatible with the observed timescales and luminosities and express the latter in terms of a simple scaling relation.
Siegel, Daniel M; Rezzolla, Luciano
2014-01-01
Besides being among the most promising sources of gravitational waves, merging neutron-star binaries also represent a leading scenario to explain the phenomenology of short gamma-ray bursts (SGRBs). Recent observations have revealed a large subclass of SGRBs with roughly constant luminosity in their X-ray afterglows lasting 10-10^4 s. These features are generally taken as evidence for a long-lived central engine powered by the magnetic spin-down of a uniformly rotating magnetized object. We propose a different scenario in which the central engine powering the X-ray emission is a differentially rotating hypermassive neutron star (HMNS) that launches a quasi-isotropic and baryon-loaded wind driven by the magnetic field built-up through differential rotation. Our model is supported by long-term, three-dimensional, general-relativistic and ideal magnetohydrodynamic simulations showing that this isotropic emission is a very robust feature. For a given HMNS, the presence of a collimated component depends sensitivel...
Properties of Rotating Neutron Star
Shailesh K. Singh
2015-08-01
Full Text Available Using the nuclear equation of states for a large variety of relativistic and non-relativistic force parameters, we calculate the static and rotating masses and radii of neutron stars. From these equation of states, we evaluate the properties of rotating neutron stars, such as rotational frequencies, moment of inertia, quadrupole deformation parameter, rotational ellipticity and gravitational wave strain amplitude. The estimated gravitational wave strain amplitude of the star is found to be~sim 10-23.
Rapidly rotating neutron star progenitors
Postnov, K. A.; Kuranov, A. G.; Kolesnikov, D. A.; Popov, S. B.; Porayko, N. K.
2016-12-01
Rotating proto-neutron stars can be important sources of gravitational waves to be searched for by present-day and future interferometric detectors. It was demonstrated by Imshennik that in extreme cases the rapid rotation of a collapsing stellar core may lead to fission and formation of a binary proto-neutron star which subsequently merges due to gravitational wave emission. In this paper, we show that such dynamically unstable collapsing stellar cores may be the product of a former merger process of two stellar cores in a common envelope. We applied population synthesis calculations to assess the expected fraction of such rapidly rotating stellar cores which may lead to fission and formation of a pair of proto-neutron stars. We have used the BSE (Binary Star Evolution) population synthesis code supplemented with a new treatment of stellar core rotation during the evolution via effective core-envelope coupling, characterized by the coupling time, τc. The validity of this approach is checked by direct MESA calculations of the evolution of a rotating 15 M⊙ star. From comparison of the calculated spin distribution of young neutron stars with the observed one, reported by Popov and Turolla, we infer the value τc ≃ 5 × 105 yr. We show that merging of stellar cores in common envelopes can lead to collapses with dynamically unstable proto-neutron stars, with their formation rate being ˜0.1-1 per cent of the total core collapses, depending on the common envelope efficiency.
Rapidly rotating neutron star progenitors
Postnov, K. A.; Kuranov, A. G.; Kolesnikov, D. A.; Popov, S. B.; Porayko, N. K.
2016-08-01
Rotating proto-neutron stars can be important sources of gravitational waves to be searched for by present-day and future interferometric detectors. It was demonstrated by Imshennik that in extreme cases the rapid rotation of a collapsing stellar core may lead to fission and formation of a binary proto-neutron star which subsequently merges due to gravitational wave emission. In the present paper, we show that such dynamically unstable collapsing stellar cores may be the product of a former merger process of two stellar cores in a common envelope. We applied population synthesis calculations to assess the expected fraction of such rapidly rotating stellar cores which may lead to fission and formation of a pair of proto-neutron stars. We have used the BSE population synthesis code supplemented with a new treatment of stellar core rotation during the evolution via effective core-envelope coupling, characterized by the coupling time, τc. The validity of this approach is checked by direct MESA calculations of the evolution of a rotating 15 M⊙ star. From comparison of the calculated spin distribution of young neutron stars with the observed one, reported by Popov and Turolla, we infer the value τc ≃ 5 × 105 years. We show that merging of stellar cores in common envelopes can lead to collapses with dynamically unstable proto-neutron stars, with their formation rate being ˜0.1 - 1% of the total core collapses, depending on the common envelope efficiency.
Rapidly rotating neutron star progenitors
Postnov, K A; Kolesnikov, D A; Popov, S B; Porayko, N K
2016-01-01
Rotating proto-neutron stars can be important sources of gravitational waves to be searched for by present-day and future interferometric detectors. It was demonstrated by Imshennik that in extreme cases the rapid rotation of a collapsing stellar core may lead to fission and formation of a binary proto-neutron star which subsequently merges due to gravitational wave emission. In the present paper, we show that such dynamically unstable collapsing stellar cores may be the product of a former merger process of two stellar cores in a common envelope. We applied population synthesis calculations to assess the expected fraction of such rapidly rotating stellar cores which may lead to fission and formation of a pair of proto-neutron stars. We have used the BSE population synthesis code supplemented with a new treatment of stellar core rotation during the evolution via effective core-envelope coupling, characterized by the coupling time, $\\tau_c$. The validity of this approach is checked by direct MESA calculations ...
Dynamics of Rotating, Magnetized Neutron Stars
Liebling, Steven L.
2010-01-01
Using a fully general relativistic implementation of ideal magnetohydrodynamics with no assumed symmetries in three spatial dimensions, the dynamics of magnetized, rigidly rotating neutron stars are studied. Beginning with fully consistent initial data constructed with Magstar, part of the Lorene project, we study the dynamics and stability of rotating, magnetized polytropic stars as models of neutron stars. Evolutions suggest that some of these rotating, magnetized stars may be minimally uns...
Quark Deconfinement in Rotating Neutron Stars
Richard D. Mellinger
2017-01-01
Full Text Available In this paper, we use a three flavor non-local Nambu–Jona-Lasinio (NJL model, an improved effective model of Quantum Chromodynamics (QCD at low energies, to investigate the existence of deconfined quarks in the cores of neutron stars. Particular emphasis is put on the possible existence of quark matter in the cores of rotating neutron stars (pulsars. In contrast to non-rotating neutron stars, whose particle compositions do not change with time (are frozen in, the type and structure of the matter in the cores of rotating neutron stars depends on the spin frequencies of these stars, which opens up a possible new window on the nature of matter deep in the cores of neutron stars. Our study shows that, depending on mass and rotational frequency, up to around 8% of the mass of a massive neutron star may be in the mixed quark-hadron phase, if the phase transition is treated as a Gibbs transition. We also find that the gravitational mass at which quark deconfinement occurs in rotating neutron stars varies quadratically with spin frequency, which can be fitted by a simple formula.
Rotational properties of hypermassive neutron stars from binary mergers
Hanauske, Matthias; Bovard, Luke; Rezzolla, Luciano; Font, José A; Galeazzi, Filippo; Stöcker, Horst
2016-01-01
Determining the differential-rotation law of compact stellar objects produced in binary neutron stars mergers or core-collapse supernovae is an old problem in relativistic astrophysics. Addressing this problem is important because it impacts directly on the maximum mass these objects can attain and hence on the threshold to black-hole formation under realistic conditions. Using the results from a large number of numerical simulations in full general relativity of binary neutron star mergers described with various equations of state and masses, we study the rotational properties of the resulting hypermassive neutron stars. We find that the angular-velocity distribution shows only a modest dependence on the equation of state, thus exhibiting the traits of "quasi-universality" found in other aspects of compact stars, both isolated and in binary systems. The distributions are characterized by an almost uniformly rotating core and a quasi-Keplerian "disk". Such a configuration is significantly different from the $...
Differentiating the differential rotation effect.
Boyarskaya, Evgenia; Hecht, Heiko
2012-07-01
As an observer views a picture from different viewing angles, objects in the picture appear to maintain their orientation relative to the observer. For instance, the eyes of a portrait appear to follow the observer as he or she views the image from different angles. We have explored this rotation effect, often called the Mona Lisa effect. We report three experiments that used portrait photographs to test variations of the Mona Lisa effect. The first experiment introduced picture displacements relative to the observer in directions beyond the horizontal plane. The Mona Lisa effect remained robust for vertical and/or diagonal observer displacements. The experiment also included conditions in which the portrait had averted gaze directions. An interaction between picture position relative to the observer and gaze direction was found. The second experiment followed up on very pronounced individual differences, suggesting that the Mona Lisa effect is even stronger than it should be for half of all observers (over-rotators). These individual differences do not correlate with any of the standard personality dimensions (Big Five) or with spatial intelligence. In the third experiment, we extended the experiment to virtual 3D heads using the same gaze directions and picture displacements as for the 2D portrait faces. Besides the picture displacements relative to the observer, we also added observer displacements relative to the picture. 3D pictures showed the Mona Lisa effect, but to a smaller extent than did 2D pictures. Copyright © 2012 Elsevier B.V. All rights reserved.
FAST FOSSIL ROTATION OF NEUTRON STAR CORES
Melatos, A., E-mail: amelatos@unimelb.edu.au [School of Physics, University of Melbourne, Parkville, VIC 3010 (Australia)
2012-12-10
It is argued that the superfluid core of a neutron star super-rotates relative to the crust, because stratification prevents the core from responding to the electromagnetic braking torque, until the relevant dissipative (viscous or Eddington-Sweet) timescale, which can exceed {approx}10{sup 3} yr and is much longer than the Ekman timescale, has elapsed. Hence, in some young pulsars, the rotation of the core today is a fossil record of its rotation at birth, provided that magnetic crust-core coupling is inhibited, e.g., by buoyancy, field-line topology, or the presence of uncondensed neutral components in the superfluid. Persistent core super-rotation alters our picture of neutron stars in several ways, allowing for magnetic field generation by ongoing dynamo action and enhanced gravitational wave emission from hydrodynamic instabilities.
A mechanical rotator for neutron scattering measurements
Thaler, A.; Northen, E.; Aczel, A. A.; MacDougall, G. J.
2016-12-01
We have designed and built a mechanical rotation system for use in single crystal neutron scattering experiments at low temperatures. The main motivation for this device is to facilitate the application of magnetic fields transverse to a primary training axis, using only a vertical cryomagnet. Development was done in the context of a triple-axis neutron spectrometer, but the design is such that it can be generalized to a number of different instruments or measurement techniques. Here, we discuss some of the experimental constraints motivating the design, followed by design specifics, preliminary experimental results, and a discussion of potential uses and future extension possibilities.
Relativistic superfluid models for rotating neutron stars
Carter, B
2001-01-01
This article starts by providing an introductory overview of the theoretical mechanics of rotating neutron stars as developped to account for the frequency variations, and particularly the discontinuous glitches, observed in pulsars. The theory suggests, and the observations seem to confirm, that an essential role is played by the interaction between the solid crust and inner layers whose superfluid nature allows them to rotate independently. However many significant details remain to be clarified, even in much studied cases such as the Crab and Vela. The second part of this article is more technical, concentrating on just one of the many physical aspects that needs further development, namely the provision of a satisfactorily relativistic (local but not microscopic) treatment of the effects of the neutron superfluidity that is involved.
Limiting rotational period of neutron stars
Glendenning, Norman K.
1992-11-01
We seek an absolute limit on the rotational period for a neutron star as a function of its mass, based on the minimal constraints imposed by Einstein's theory of relativity, Le Chatelier's principle, causality, and a low-density equation of state, uncertainties in which can be evaluated as to their effect on the result. This establishes a limiting curve in the mass-period plane below which no pulsar that is a neutron star can lie. For example, the minimum possible Kepler period, which is an absolute limit on rotation below which mass shedding would occur, is 0.33 ms for a M=1.442Msolar neutron star (the mass of PSR1913+16). A still lower curve, based only on the structure of Einstein's equations, limits any star whatsoever to lie in the plane above it. Hypothetical stars such as strange stars, if the matter of which they are made is self-bound in bulk at a sufficiently large equilibrium energy density, can lie in the region above the general-relativistic forbidden region, and in the region forbidden to neutron stars.
Slowly Rotating General Relativistic Superfluid Neutron Stars
Andersson, N
2001-01-01
We present a general formalism to treat slowly rotating general relativistic superfluid neutron stars. As a first approximation, their matter content can be described in terms of a two-fluid model, where one fluid is the neutron superfluid, which is believed to exist in the core and inner crust of mature neutron stars, and the other fluid represents a conglomerate of all other constituents (crust nuclei, protons, electrons, etc.). We obtain a system of equations, good to second-order in the rotational velocities, that determines the metric and the matter variables, irrespective of the equation of state for the two fluids. In particular, allowance is made for the so-called entrainment effect, whereby the momentum of one constituent (e.g. the neutrons) carries along part of the mass of the other constituent. As an illustration of the developed framework, we consider a simplified equation of state for which the two fluids are described by different polytropes. We determine numerically the effects of the two flui...
Gravitational wave background from rotating neutron stars
Rosado, Pablo A.
2012-11-01
The background of gravitational waves produced by the ensemble of rotating neutron stars (which includes pulsars, magnetars, and gravitars) is investigated. A formula for Ω(f) (a function that is commonly used to quantify the background, and is directly related to its energy density) is derived, without making the usual assumption that each radiating system evolves on a short time scale compared to the Hubble time; the time evolution of the systems since their formation until the present day is properly taken into account. Moreover, the formula allows one to distinguish the different parts of the background: the unresolvable (which forms a stochastic background or confusion noise, since the waveforms composing it cannot be either individually observed or subtracted out of the data of a detector) and the resolvable. Several estimations of the background are obtained, for different assumptions on the parameters that characterize neutron stars and their population. In particular, different initial spin period distributions lead to very different results. For one of the models, with slow initial spins, the detection of the background by present or planned detectors can be rejected. However, other models do predict the detection of the background, that would be unresolvable, by the future ground-based gravitational wave detector ET. A robust upper limit for the background of rotating neutron stars is obtained; it does not exceed the detection threshold of two cross-correlated Advanced LIGO interferometers. If gravitars exist and constitute more than a few percent of the neutron star population, then they produce an unresolvable background that could be detected by ET. Under the most reasonable assumptions on the parameters characterizing a neutron star, the background is too faint to be detected. Previous papers have suggested neutron star models in which large magnetic fields (like the ones that characterize magnetars) induce big deformations in the star, which
Light curves from rapidly rotating neutron stars
Numata, Kazutoshi
2010-01-01
We calculate light curves produced by a hot spot of a rapidly rotating neutron star, assuming that the spot is perturbed by a core $r$-mode, which is destabilized by emitting gravitational waves. To calculate light curves, we take account of relativistic effects such as the Doppler boost due to the rapid rotation and light bending assuming the Schwarzschild metric around the neutron star. We assume that the core $r$-modes penetrate to the surface fluid ocean to have sufficiently large amplitudes to disturb the spot. For a $l'=m$ core $r$-mode, the oscillation frequency $\\omega\\approx2m\\Omega/[l'(l'+1)]$ defined in the co-rotating frame of the star will be detected by a distant observer, where $l'$ and $m$ are respectively the spherical harmonic degree and the azimuthal wave number of the mode, and $\\Omega$ is the spin frequency of the star. In a linear theory of oscillation, using a parameter $A$ we parametrize the mode amplitudes such that ${\\rm max}\\left(|\\xi_\\theta|,|\\xi_\\phi|\\right)/R=A$ at the surface, w...
HOW CAN NEWLY BORN RAPIDLY ROTATING NEUTRON STARS BECOME MAGNETARS?
Cheng, Quan; Yu, Yun-Wei, E-mail: yuyw@mail.ccnu.edu.cn [Institute of Astrophysics, Central China Normal University, Wuhan 430079 (China)
2014-05-10
In a newly born (high-temperature and Keplerian rotating) neutron star, r-mode instability can lead to stellar differential rotation, which winds the seed poloidal magnetic field (∼10{sup 11} G) to generate an ultra-high (∼10{sup 17} G) toroidal field component. Subsequently, by succumbing to the Tayler instability, the toroidal field could be partially transformed into a new poloidal field. Through such dynamo processes, the newly born neutron star with sufficiently rapid rotation could become a magnetar on a timescale of ∼10{sup 2} {sup –} {sup 3} s, with a surface dipolar magnetic field of ∼10{sup 15} G. Accompanying the field amplification, the star could spin down to a period of ∼5 ms through gravitational wave radiation due to the r-mode instability and, in particular, the non-axisymmetric stellar deformation caused by the toroidal field. This scenario provides a possible explanation for why the remnant neutron stars formed in gamma-ray bursts and superluminous supernovae could be millisecond magnetars.
Light Curves of Rapidly Rotating Neutron Stars
Braje, T M; Rauch, K P; Braje, Timothy M.; Romani, Roger W.; Rauch, Kevin P.
2000-01-01
We consider the effect of rapid rotation on the light curves of neutron stars with hot polar caps. For $P \\approx 3$ms spin periods, the pulse fractions can be as much as an order of magnitude larger than with simple slowly-rotating (Schwarzschild) estimates. Doppler boosting, in particular, leads to characteristic distortion and ``soft lags'' in the pulse profiles, which are easily measurable in light curves with moderate energy resolution. With $\\sim 10^5$ photons it should also be possible to isolate the more subtle distortions of light travel time variations and frame dragging. Detailed analysis of high quality millisecond pulsar data from upcoming X-ray missions must include these effects.
Differential rotation of geomagnetic field
WEI Zigang; XU Wenyao
2003-01-01
The latitudinal dependence of the westward drift in the main geomagnetic field is examined by using the correlation analysis of moving random pattern. The study reveals the characteristics in the differential rotation of the main field. The results show that the global geomagnetic field drifts westward with an average speed of 0.18°/a during 1900-2000. The westward drift rate is not symmetrical with respect to the equator. The maximum westward drift rate, 0.31°/a, occurs at the latitude --= -15°, forming a Rapid Westward Drift Belt (RDB) around this latitude. Going northward and southward from this belt, the drift rate decreases and reaches the minimum (0.12°/a) at --= 50° and the minimum (0.14°/a) at --= -56°, forming a Northern Hemisphere Slow Westward Drift Belt (N-SDB) and a Southern Hemisphere Slow Westward Drift Belt (S-SDB). Three phases can be detected in the evolution of the westward drift. In the first phase (1900-1940), the RDB dominates the global drift pattern. The westward drifts in this belt are much faster than those in other areas. In the second phase (1940-1960), the drift rates in the RDB are less than those in the first phase, while the drifts in the N-SDB and S-SDB are relatively large. In this phase, the differential rotation becomes less obvious. In the third phase (1960-2000), the westward drift in the RDB increases again and the differential rotation gradually becomes apparent.
Differentially Rotating White Dwarfs I: Regimes of Internal Rotation
Ghosh, Pranab; Wheeler, J. Craig
2017-01-01
Most viable models of Type Ia supernovae (SNe Ia) require the thermonuclear explosion of a carbon/oxygen white dwarf that has evolved in a binary system. Rotation could be an important aspect of any model for SNe Ia, whether single or double degenerate, with the white dwarf mass at, below, or above the Chandrasekhar limit. Differential rotation is specifically invoked in attempts to account for the apparent excess mass in the super-Chandrasekhar events. Some earlier work has suggested that only uniform rotation is consistent with the expected mechanisms of angular momentum transport in white dwarfs, while others have found pronounced differential rotation. We show that if the baroclinic instability is active in degenerate matter and the effects of magnetic fields are neglected, both nearly uniform rotation and strongly differential rotation are possible. We classify rotation regimes in terms of the Richardson number, Ri. At small values of Ri ≤slant 0.1, we find both the low-viscosity Zahn regime with a nonmonotonic angular velocity profile and a new differential rotation regime for which the viscosity is high and scales linearly with the shear, σ. Employment of Kelvin–Helmholtz viscosity alone yields differential rotation. Large values of Ri ≫ 1 produce a regime of nearly uniform rotation for which the baroclinic viscosity is of intermediate value and scales as {σ }3. We discuss the gap in understanding of the behavior at intermediate values of Ri and how observations may constrain the rotation regimes attained by nature.
Gravitational waves from rapidly rotating neutron stars
Haskell, Brynmor; D`Angelo, Caroline; Degenaar, Nathalie; Glampedakis, Kostas; Ho, Wynn C G; Lasky, Paul D; Melatos, Andrew; Oppenoorth, Manuel; Patruno, Alessandro; Priymak, Maxim
2014-01-01
Rapidly rotating neutron stars in Low Mass X-ray Binaries have been proposed as an interesting source of gravitational waves. In this chapter we present estimates of the gravitational wave emission for various scenarios, given the (electromagnetically) observed characteristics of these systems. First of all we focus on the r-mode instability and show that a 'minimal' neutron star model (which does not incorporate exotica in the core, dynamically important magnetic fields or superfluid degrees of freedom), is not consistent with observations. We then present estimates of both thermally induced and magnetically sustained mountains in the crust. In general magnetic mountains are likely to be detectable only if the buried magnetic field of the star is of the order of $B\\approx 10^{12}$ G. In the thermal mountain case we find that gravitational wave emission from persistent systems may be detected by ground based interferometers. Finally we re-asses the idea that gravitational wave emission may be balancing the ac...
Light Curves for Rapidly-Rotating Neutron Stars
Cadeau, C; Leahy, D; Campbell, S S; Cadeau, Coire; Morsink, Sharon M.; Leahy, Denis; Campbell, Sheldon S.
2006-01-01
We present raytracing computations for light emitted from the surface of a rapidly-rotating neutron star in order to construct light curves for X-ray pulsars and bursters. These calculations are for realistic models of rapidly-rotating neutron stars which take into account both the correct exterior metric and the oblate shape of the star. We find that the most important effect arising from rotation comes from the oblate shape of the rotating star. We find that approximating a rotating neutron star as a sphere introduces serious errors in fitted values of the star's radius and mass if the rotation rate is very large. However, in most cases acceptable fits to the ratio M/R can be obtained with the spherical approximation.
Rotating neutron stars with exotic cores: masses, radii, stability
Haensel, P.; Bejger, M.; Fortin, M.; Zdunik, L. [Polish Academy of Sciences, N. Copernicus Astronomical Center, Warszawa (Poland)
2016-03-15
A set of theoretical mass-radius relations for rigidly rotating neutron stars with exotic cores, obtained in various theories of dense matter, is reviewed. Two basic observational constraints are used: the largest measured rotation frequency (716Hz) and the maximum measured mass (2M {sub CircleDot}). The present status of measuring the radii of neutron stars is described. The theory of rigidly rotating stars in general relativity is reviewed and limitations of the slow rotation approximation are pointed out. Mass-radius relations for rotating neutron stars with hyperon and quark cores are illustrated using several models. Problems related to the non-uniqueness of the crust-core matching are mentioned. Limits on rigid rotation resulting from the mass-shedding instability and the instability with respect to the axisymmetric perturbations are summarized. The problem of instabilities and of the back-bending phenomenon are discussed in detail. Metastability and instability of a neutron star core in the case of a first-order phase transition, both between pure phases, and into a mixed-phase state, are reviewed. The case of two disjoint families (branches) of rotating neutron stars is discussed and generic features of neutron-star families and of core-quakes triggered by the instabilities are considered. (orig.)
Searching for gravitational waves from rotating neutron stars
S V Dhurandhar
2000-10-01
Rotating neutron stars are one of the important sources of gravitational waves (GW) for the ground based as well as space based detectors. Since the waves are emitted continuously, the source is termed as a continuous gravitational wave (CGW) source. The expected weakness of the signal requires long integration times (∼ year). The data analysis problem involves tracking the phase coherently over such large integration times, which makes it the most computationally intensive problem among all GW sources envisaged. In this article, the general problem of data analysis is discussed, and more so, in the context of searching for CGW sources orbiting another companion object. The problem is important because there are several pulsars, which could be deemed to be CGW sources orbiting another companion star. Differential geometric techniques for data analysis are described and used to obtain computational costs. These results are applied to known systems to assess whether such systems are detectable with current (or near future) computing resources.
Regimes of Internal Rotation in Differentially Rotating White Dwarfs
Wheeler, J. Craig; Ghosh, Pranab
2017-01-01
Most viable models of Type Ia supernovae (SN Ia) require the thermonuclear explosion of a carbon/oxygen white dwarf that has evolved in a binary system. Rotation could be an important aspect of any model for SN Ia, whether single or double degenerate, with the white dwarf mass at, below, or above the Chandrasekhar limit. Differential rotation is specifically invoked in attempts to account for the apparent excess mass in the super--Chandrasekhar events. Some earlier work has suggested that only uniform rotation is consistent with the expected mechanisms of angular momentum transport in white dwarfs, while others have found pronounced differential rotation. We show that if the baroclinic instability is active in degenerate matter and the effects of magnetic fields are neglected, both nearly-uniform and strongly-differential rotation are possible. We classify rotation regimes in terms of the Richardson number, Ri. At small values of Ri > 1 produce a regime of nearly-uniform rotation for which the baroclinic viscosity is of intermediate value and scales as σ3. We discuss the gap in understanding of the behavior at intermediate values of Ri and how observations may constrain the rotation regimes attained by nature.
Confirmation of bistable stellar differential rotation profiles
Käpylä, P J; Brandenburg, A
2014-01-01
(abridged) Context: Solar-like differential rotation is characterized by a rapidly rotating equator and slower poles. However, theoretical models and numerical simulations can also result in a slower equator and faster poles when the overall rotation is slow. Aims: We study the critical rotational influence under which differential rotation flips from solar-like (fast equator, slow poles) to an anti-solar one (slow equator, fast poles). We also estimate the non-diffusive ($\\Lambda$-effect) and diffusive (turbulent viscosity) contributions to the Reynolds stress. Methods: We perform three-dimensional numerical simulations of mildly turbulent convection in spherical wedge geometry. We regulate the convective velocities by varying the amount of heat transported by thermal conduction, turbulent diffusion, and resolved convection. Results: Increasing the efficiency of resolved convection leads to a reduction of the rotational influence on the flow and a sharp transition from solar-like to anti-solar differential r...
Maldonado-Velázquez, M.; Barrón-Palos, L.; Crawford, C.; Snow, W. M.
2017-05-01
The neutron spin is a critical degree of freedom for many precision measurements using low-energy neutrons. Fundamental symmetries and interactions can be studied using polarized neutrons. Parity-violation (PV) in the hadronic weak interaction and the search for exotic forces that depend on the relative spin and velocity, are two questions of fundamental physics that can be studied via the neutron spin rotations that arise from the interaction of polarized cold neutrons and unpolarized matter. The Neutron Spin Rotation (NSR) collaboration developed a neutron polarimeter, capable of determining neutron spin rotations of the order of 10-7 rad per meter of traversed material. This paper describes two key components of the NSR apparatus, responsible for the transport and manipulation of the spin of the neutrons before and after the target region, which is surrounded by magnetic shielding and where residual magnetic fields need to be below 100 μG. These magnetic field devices, called input and output coils, provide the magnetic field for adiabatic transport of the neutron spin in the regions outside the magnetic shielding while producing a sharp nonadiabatic transition of the neutron spin when entering/exiting the low-magnetic-field region. In addition, the coils are self contained, forcing the return magnetic flux into a compact region of space to minimize fringe fields outside. The design of the input and output coils is based on the magnetic scalar potential method.
Differentially Rotating White Dwarfs I: Regimes of Internal Rotation
Ghosh, Pranab
2016-01-01
Most viable models of Type Ia supernovae (SN~Ia) require the thermonuclear explosion of a carbon/oxygen white dwarf that has evolved in a binary system. Rotation could be an important aspect of any model for SN~Ia, whether single or double degenerate, with the white dwarf mass at, below, or above the Chandrasekhar limit. {\\sl Differential rotation} is specifically invoked in attempts to account for the apparent excess mass in the super--Chandrasekhar events. Some earlier work has suggested that only uniform rotation is consistent with the expected mechanisms of angular momentum transport in white dwarfs, while others have found pronounced differential rotation. We show that if the baroclinic instability is active in degenerate matter and the effects of magnetic fields are neglected, both nearly-uniform and strongly-differential rotation are possible. We classify rotation regimes in terms of the Richardson number, Ri. At small values of Ri $\\leq$ 0.1, we find both the low-viscosity Zahn regime with a non-monot...
Rotating neutron stars with exotic cores: masses, radii, stability
Haensel, P; Fortin, M; Zdunik, J L
2016-01-01
A set of theoretical mass-radius relations for rigidly rotating neutron stars with exotic cores, obtained in various theories of dense matter, is reviewed. Two basic observational constraints are used: the largest measured rotation frequency is 716 Hz and the maximum measured mass is $2\\;{\\rm M}_\\odot$. Present status of measuring the radii of neutron stars is described. The theory of rigidly rotating stars in general relativity is reviewed and limitations of the slow rotation approximation are pointed out. Mass-radius relations for rotating neutron stars with hyperon and quark cores are illustrated using several models. Problems related to the non-uniqueness of the crust-core matching are mentioned. Limits on rigid rotation resulting from the mass-shedding instability and the instability with respect to the axisymmetric perturbations are summarized. The problem of instabilities and of the back-bending phenomenon are discussed in detail. Metastability and instability of a neutron star core in the case of a fi...
Rapidly rotating neutron stars in $R$-squared gravity
Yazadjiev, Stoytcho S; Kokkotas, Kostas D
2015-01-01
$f(R)$ theories of gravity are one of the most popular alternative explanations for dark energy and therefore studying the possible astrophysical implications of these theories is an important task. In the present paper we make a substantial advance in this direction by considering rapidly rotating neutron stars in $R^2$ gravity. The results are obtained numerically and the method we use is non-perturbative and self-consistent. The neutron star properties, such as mass, radius and moment of inertia, are studied in detail and the results show that rotation magnifies the deviations from general relativity and the maximum mass and moment of inertia can reach very high values. This observation is similar to previous studies of rapidly rotating neutron stars in other alternative theories of gravity, such as the scalar-tensor theories, and it can potentially lead to strong astrophysical manifestations.
Instability windows and evolution of rapidly rotating neutron stars
Gusakov, Mikhail E; Kantor, Elena M
2013-01-01
We consider an instability of rapidly rotating neutron stars in low-mass X-ray binaries (LMXBs) with respect to excitation of r-modes (which are analogous to Earth's Rossby waves controlled by the Coriolis force). We argue that finite temperature effects in the superfluid core of a neutron star lead to a resonance coupling and enhanced damping (and hence stability) of oscillation modes at certain stellar temperatures. We demonstrate that neutron stars with high spin frequency spend a substantial amount of time at these `resonance' temperatures. This finding allows us to explain puzzling observations of hot rapidly rotating neutron stars in LMXBs and to predict a new class of hot non-accreting rapidly rotating neutron stars, some of which may have already been observed and tentatively identified as quiescent LMXB (qLMXB) candidates. We also impose a new theoretical limit on the neutron star spin frequency, explaining the cut-off spin frequency ~730 Hz, following from the statistical analysis of accreting milli...
Differential Rotation in Solar Convective Dynamo Simulations
Fan, Yuhong
2015-01-01
We carry out a magneto-hydrodynamic (MHD) simulation of convective dynamo in the rotating solar convective envelope driven by the solar radiative diffusive heat flux. The simulation is similar to that reported in Fan & Fang (2014) but with further reduced viscosity and magnetic diffusion. The resulting convective dynamo produces a large scale mean field that exhibits similar irregular cyclic behavior and polarity reversals, and self-consistently maintains a solar-like differential rotation. The main driver for the solar-like differential rotation (with faster rotating equator) is a net outward transport of angular momentum away from the rotation axis by the Reynolds stress, and we found that this transport is enhanced with reduced viscosity and magnetic diffusion.
Differential rotation in solar convective dynamo simulations
Fan, Yuhong; Fang, Fang
2016-10-01
We carry out a magneto-hydrodynamic (MHD) simulation of convective dynamo in the rotating solar convective envelope driven by the solar radiative diffusive heat flux. The simulation is similar to that reported in Fan and Fang (2014) but with further reduced viscosity and magnetic diffusion. The resulting convective dynamo produces a large scale mean field that exhibits similar irregular cyclic behavior and polarity reversals, and self-consistently maintains a solar-like differential rotation. The main driver for the solar-like differential rotation (with faster rotating equator) is a net outward transport of angular momentum away from the rotation axis by the Reynolds stress, and we found that this transport is enhanced with reduced viscosity and magnetic diffusion.
On obliquely magnetized and differentially rotating stars
Wei, Xing
2015-01-01
We investigate the interaction of differential rotation and a misaligned magnetic field. The incompressible magnetohydrodynamic equations are solved numerically for a free-decay problem. In the kinematic limit, differential rotation annihilates the non-axisymmetric field on a timescale proportional to the cube root of magnetic Reynolds number ($Rm$), as predicted by R\\"adler. Nonlinearly, the outcome depends upon the initial energy in the non-axisymmetric part of the field. Sufficiently weak fields approach axisymmetry as in the kinematic limit; some differential rotation survives across magnetic surfaces, at least on intermediate timescales. Stronger fields enforce uniform rotation and remain non-axisymmetric. The initial field strength that divides these two regimes does not follow the scaling $Rm^{-1/3}$ predicted by quasi-kinematic arguments, perhaps because our $Rm$ is never sufficiently large or because of reconnection. We discuss the possible relevance of these results to tidal synchronization and tida...
Rotating proto-neutron stars under strong magnetic fields
Franzon, B; Schramm, S
2016-01-01
In this work, we study the effects of magnetic fields and rotation on the structure and composition of proto-neutron stars (PNSs). A hadronic chiral SU(3) model is applied to cold neutron stars (NS) and proto-neutron stars with trapped neutrinos and at fixed entropy per baryon. We obtain general relativistic solutions for neutron and proto-neutron stars endowed with a poloidal magnetic field by solving Einstein-Maxwell field equations in a self-consistent way. As the neutrino chemical potential decreases in value over time, this alters the chemical equilibrium and the composition inside the star, leading to a change in the structure and in the particle population of these objects. We find that the magnetic field deforms the star and significantly alters the number of trapped neutrinos in the stellar interior, together with strangeness content and temperature in each evolution stage.
Rotational and magnetic field instabilities in neutron stars
Kokkotas, Kostas D. [Theoretical Astrophysics, IAAT, Eberhard Karls University of Tübingen, Tübingen 72076 (Germany)
2014-01-14
In this short review we present recent results on the dynamics of neutron stars and their magnetic fields. We discuss the progress that has been made, during the last 5 years, in understanding the rotational instabilities with emphasis to the one due to the f-mode, the possibility of using gravitational wave detection in constraining the parameters of neutron stars and revealing the equation of state as well as the detectability of gravitational waves produced during the unstable phase of a neutron star’s life. In addition we discuss the dynamics of extremely strong magnetic fields observed in a class of neutron stars (magnetars). Magnetic fields of that strength are responsible for highly energetic phenomena (giant flares) and we demonstrate that the analysis of the emitted electromagnetic radiation can lead in constraining the parameters of neutron stars. Furthermore, we present our results from the study of such violent phenomena in association with the emission of gravitational radiation.
Axially symmetric equations for differential pulsar rotation with superfluid entrainment
Antonelli, Marco
2016-01-01
We propose an analytical two-components model for pulsar rotational dynamics: the aim is to reduce the 3D hydrodynamical problem to a 1D (radial) problem, using the hypothesis of negligible azimuthal inhomogeneities. The result is the construction of a computationally simple model that takes into account for the non-uniform structure of the star, entrainment effect and differential rotation of the superfluid component. For the first time all these ingredients are treated in a fully consistent way within the picture provided by our initial hypotheses. Our treatment clarifies which are the physical inputs needed to build, to current knowledge, more realistic simulations of rotating neutron stars and gives a neat description of the effect of entrainment when straight vortex lines are considered. Moreover, on this basis, we briefly introduce a new method that can be used to put a constraint to the mass of the pulsars that display very large glitches and to the relative spin up timescales.
Gravitational waves from rotating proto-neutron stars
Ferrari, V [Dipartimento di Fisica ' G Marconi' , Universita di Roma ' La Sapienza' and Sezione INFN ROMA 1, piazzale Aldo Moro 2, I-00185 Rome (Italy); Gualtieri, L [Dipartimento di Fisica ' G Marconi' , Universita di Roma ' La Sapienza' and Sezione INFN ROMA 1, piazzale Aldo Moro 2, I-00185 Rome (Italy); Pons, J A [Departament d' Astronomia i AstrofIsica, Universitat de Valencia, 46100 Burjassot, Valencia (Spain); Stavridis, A [Dipartimento di Fisica ' G Marconi' , Universita di Roma ' La Sapienza' and Sezione INFN ROMA 1, piazzale Aldo Moro 2, I-00185 Rome (Italy)
2004-03-07
We study the effects of rotation on the quasi-normal modes (QNMs) of a newly born proto-neutron star (PNS) at different evolutionary stages, until it becomes a cold neutron star (NS). We use the Cowling approximation, neglecting spacetime perturbations, and consider different models of evolving PNS. The frequencies of the modes of a PNS are considerably lower than those of a cold NS, and are further lowered by rotation; consequently, if QNMs were excited in a sufficiently energetic process, they would radiate waves that could be more easily detectable by resonant-mass and interferometric detectors than those emitted by a cold NS. We find that for high rotation rates, some of the g-modes become unstable via the CFS instability; however, this instability is likely to be suppressed by competing mechanisms before emitting a significant amount of gravitational waves.
Rotation, differential rotation, and gyrochronology of active Kepler stars
Reinhold, Timo
2015-01-01
The high-precision photometry from the CoRoT and Kepler satellites has led to measurements of surface rotation periods for tens of thousands of stars. Our main goal is to derive ages of thousands of field stars using consistent rotation period measurements in different gyrochronology relations. Multiple rotation periods are interpreted as surface differential rotation (DR). We re-analyze the sample of 24,124 Kepler stars from Reinhold et al. (2013) using different approaches based on the Lomb-Scargle periodogram. Each quarter (Q1-Q14) is treated individually using a prewhitening approach. Additionally, the full time series, and different segments thereof are analyzed. For more than 18,500 stars our results are consistent with the rotation periods from McQuillan et al. (2014). Thereof, more than 12,300 stars show multiple significant peaks, which we interpret as DR. Gyrochronology ages between 100 Myr and 10 Gyr were derived for more than 17,000 stars using different gyrochronology relations. We find a bimodal...
Keplerian frequency of uniformly rotating neutron stars and quark stars
Haensel, P; Bejger, M; Lattimer, J M
2009-01-01
We calculate Keplerian (mass shedding) configurations of rigidly rotating neutron stars and quark stars with crusts. We check the validity of empirical formula for Keplerian frequency, f_K, proposed by Lattimer & Prakash, f_K(M)=C (M/M_sun)^1/2 (R/10km)^-3/2, where M is the (gravitational) mass of Keplerian configuration, R is the (circumferential) radius of the non-rotating configuration of the same gravitational mass, and C = 1.04 kHz. Numerical calculations are performed using precise 2-D codes based on the multi-domain spectral methods. We use a representative set of equations of state (EOSs) of neutron stars and quark stars. We show that the empirical formula for f_K(M) holds within a few percent for neutron stars with realistic EOSs, provided 0.5 M_sun < M < 0.9 M_max,stat, where M_max,stat is the maximum allowable mass of non-rotating neutron stars for an EOS, and C=C_NS=1.08 kHz. Similar precision is obtained for quark stars with 0.5 M_sun < M < 0.9 M_max,stat. For maximal crust masses...
Rotation at 1122 Hz and the neutron star structure
Bejger, M; Zdunik, J L
2006-01-01
Recent observations of XTE J1739-285 suggest that it contains a neutron star rotating at 1122 Hz. Such rotation imposes bounds on the structure of neutron star in XTE J1739-285. These bounds may be used to constrain poorly known equation of state of dense matter. One-parameter families of stationary configurations rotating rigidly at 1122 Hz are constructed, using a precise 2-D code solving Einstein equations. Hydrostatic equilibrium solutions are tested for stability with respect to axi-symmetric perturbations. A set of ten diverse EOSs of neutron stars is considered. Hypothetical strange stars are also studied. For each EOS, the family of possible neutron star models is limited by the mass shedding limit, corresponding to maximum allowed equatorial radius, R_max, and by the instability with respect to the axi-symmetric perturbations, reached at the minimum allowed equatorial radius, R_min. We get R_min \\simeq 10-13km, and R_max \\simeq 16-18km, with allowed mass 1.4-2.3 M_\\odot. Allowed stars with hyperonic ...
An accurate metric for the spacetime around rotating neutron stars
Pappas, George
2017-04-01
The problem of having an accurate description of the spacetime around rotating neutron stars is of great astrophysical interest. For astrophysical applications, one needs to have a metric that captures all the properties of the spacetime around a rotating neutron star. Furthermore, an accurate appropriately parametrized metric, i.e. a metric that is given in terms of parameters that are directly related to the physical structure of the neutron star, could be used to solve the inverse problem, which is to infer the properties of the structure of a neutron star from astrophysical observations. In this work, we present such an approximate stationary and axisymmetric metric for the exterior of rotating neutron stars, which is constructed using the Ernst formalism and is parametrized by the relativistic multipole moments of the central object. This metric is given in terms of an expansion on the Weyl-Papapetrou coordinates with the multipole moments as free parameters and is shown to be extremely accurate in capturing the physical properties of a neutron star spacetime as they are calculated numerically in general relativity. Because the metric is given in terms of an expansion, the expressions are much simpler and easier to implement, in contrast to previous approaches. For the parametrization of the metric in general relativity, the recently discovered universal 3-hair relations are used to produce a three-parameter metric. Finally, a straightforward extension of this metric is given for scalar-tensor theories with a massless scalar field, which also admit a formulation in terms of an Ernst potential.
Differential rotation on early G dwarfs
Jeffers, S.V.; Donati, J.F.
2007-01-01
In this paper we present the latest results in our long-term program to understand how differential rotation depends on fundamental stellar parameters such as spectral type, mass and radius. In this paper we focus on early G dwarf spectral types by presenting our latest surface brightness image and
Effects of Uniform and Differential Rotation on Stellar Pulsations
Lovekin, C. C.; Deupree, R. G.; Clement, M.J.
2008-01-01
We have investigated the effects of uniform rotation and a specific model for differential rotation on the pulsation frequencies of 10 \\Msun\\ stellar models. Uniform rotation decreases the frequencies for all modes. Differential rotation does not appear to have a significant effect on the frequencies, except for the most extreme differentially rotating models. In all cases, the large and small separations show the effects of rotation at lower velocities than do the individual frequencies. Unf...
On Obliquely Magnetized and Differentially Rotating Stars
Wei, Xing; Goodman, Jeremy
2015-06-01
We investigate the interaction of differential rotation and a misaligned magnetic field. The incompressible magnetohydrodynamic equations are solved numerically for a free-decay problem. In the kinematic limit, differential rotation annihilates the non-axisymmetric field on a timescale proportional to the cube root of magnetic Reynolds number (Rm), as predicted by Rädler. Nonlinearly, the outcome depends upon the initial energy in the non-axisymmetric part of the field. Sufficiently weak fields approach axisymmetry as in the kinematic limit; some differential rotation survives across magnetic surfaces, at least on intermediate timescales. Stronger fields enforce uniform rotation and remain non-axisymmetric. The initial field strength that divides these two regimes does not follow the scaling R{{m}-1/3} predicted by quasi-kinematic arguments, perhaps because our Rm is never sufficiently large or because of reconnection. We discuss the possible relevance of these results to tidal synchronization and tidal heating of close binary stars, particularly double white dwarfs.
Does a neutron know that the earth is rotating?
Werner, Sam
2008-05-01
In 1979 we observed the quantum mechanical phase shift of neutron deBroglie waves due to the Earth’s rotation. After the result was published, a number of very nice theoretical papers on the experiment appeared. I have two favorites: The one by M. Dresden and C. N. Yang in which they view the effect as due to the Doppler shift created by reflection from moving mirrors; and the other one by J. J. Sakurai in which he views the origin of the effect as being due to a flux of rotation threading the neutron interferometer loop, in much the same way that magnetic flux threads the electron interferometer loop to create the topological Aharonov-Bohm effect. Here, I would like to place their explanations of the physics of this experiment in juxtaposition with my own understanding of it.
Nonmodal phenomena in differentially rotating dusty plasmas
Poedts, Stefaan; Rogava, Andria D.
2000-10-01
In this paper the foundation is layed for the nonmodal investigation of velocity shear induced phenomena in a differentially rotating flow of a dusty plasma. The simplest case of nonmagnetized flow is considered. It is shown that, together with the innate properties of the dusty plasma, the presence of differential rotation, Coriolis forces, and self-gravity casts a considerable richness on the nonmodal dynamics of linear perturbations in the flow. In particular: (i) dust-acoustic waves acquire the ability to extract energy from the mean flow and (ii) shear-induced, nonperiodic modes of collective plasma behavior-shear-dust-acoustic vortices-are generated. The presence of self-gravity and the nonzero Coriolis parameter (``epicyclic shaking'') makes these collective modes transiently unstable. .
MHD Modeling of Differential Rotation in Coronal Holes
Lionello, Roberto; Linker, Jon A.; Mikic, Zoran; Riley, Pete
2004-01-01
The photosphere and the magnetic flux therein undergo differential rotation. Coronal holes appear to rotate almost rigidly. Magnetic reconnection has been invoked to reconcile these phenomena. Mechanism relevant to the formation of the slow solar wind. We have used our MHD model in spherical coordinates to study the effect of differential rotation on coronal holes. We have imposed a magnetic flux distribution similar to and applied differential rotation for the equivalent of 5 solar rotations.
Axially symmetric equations for differential pulsar rotation with superfluid entrainment
Antonelli, M.; Pizzochero, P. M.
2017-01-01
In this article we present an analytical two-component model for pulsar rotational dynamics. Under the assumption of axial symmetry, implemented by a paraxial array of straight vortices that thread the entire neutron superfluid, we are able to project exactly the 3D hydrodynamical problem to a 1D cylindrical one. In the presence of density-dependent entrainment the superfluid rotation is non-columnar: we circumvent this by using an auxiliary dynamical variable directly related to the areal density of vortices. The main result is a system of differential equations that take consistently into account the stratified spherical structure of the star, the dynamical effects of non-uniform entrainment, the differential rotation of the superfluid component and its coupling to the normal crust. These equations represent a mathematical framework in which to test quantitatively the macroscopic consequences of the presence of a stable vortex array, a working hypothesis widely used in glitch models. Even without solving the equations explicitly, we are able to draw some general quantitative conclusions; in particular, we show that the reservoir of angular momentum (corresponding to recent values of the pinning forces) is enough to reproduce the largest glitch observed in the Vela pulsar, provided its mass is not too large.
Stellar Differential Rotation and Coronal Timescales
Gibb, G P S; Mackay, D H
2014-01-01
We investigate the timescales of evolution of stellar coronae in response to surface differential rotation and diffusion. To quantify this we study both the formation time and lifetime of a magnetic flux rope in a decaying bipolar active region. We apply a magnetic flux transport model to prescribe the evolution of the stellar photospheric field, and use this to drive the evolution of the coronal magnetic field via a magnetofrictional technique. Increasing the differential rotation (i.e. decreasing the equator-pole lap time) decreases the flux rope formation time. We find that the formation time is dependent upon the geometric mean of the lap time and the surface diffusion timescale. In contrast, the lifetime of flux ropes are proportional to the lap time. With this, flux ropes on stars with a differential rotation of more than eight times the solar value have a lifetime of less than two days. As a consequence, we propose that features such as solar-like quiescent prominences may not be easily observable on s...
Constraining properties of rapidly rotating neutron stars using data from heavy-ion collisions
Krastev, Plamen G; Worley, Aaron
2007-01-01
Aims.- Properties, structure, and thermal evolution of neutron stars are determined by the equation of state of stellar matter. Recent data on isospin-diffusion in heavy-ion collisions at intermediate energies and the size of neutron skin in $^{208}Pb$ have constrained considerably the density dependence of the nuclear symmetry energy and, in turn, the equation of state of neutron-rich nucleonic matter. These constraints could provide useful information about the global properties of rapidly rotating neutron stars. Methods.- Models of rapidly rotating neutron stars are constructed applying several nucleonic equations of state. Particular emphasis is placed on configurations rotating rigidly at 716 and 1122Hz. The range of allowed hydrostatic equilibrium solutions is determined and tested for stability. The effect of rotation on the internal composition and thermal properties of neutron stars is also examined. Results.- At a given rotational frequency, each equation of state yields a range of possible neutron ...
Wen, D; Wang, X; Ai, B; Liu, G; Dong, D; Liu, L; Wen, De-hua; Chen, Wei; Wang, Xian-ju; Ai, Bao-quan; Liu, Guo-tao; Dong, Dong-qiao; Liu, Liang-gang
2003-01-01
The influence of the rotation on the total masses and radii of the neutron stars are calculated by the Hartle's slow rotation formalism, while the equation of state is considered in a relativistic $\\sigma-\\omega$ model. Comparing with the observation, the calculating result shows that the double neutron star binaries are more like hyperon stars and the neutron stars of X-ray binaries are more like traditional neutron stars. As the changes of the mass and radius to a real neutron star caused by the rotation are very small comparing with the total mass and radius, one can see that Hartle's approximate method is rational to deal with the rotating neutron stars. If three property values: mass, radius and period are observed to the same neutron star, then the EOS of this neutron star could be decided entirely.
Asteroseismology of rapidly rotating neutron stars - an alternative approach
Doneva, Daniela D
2015-01-01
In the present paper we examine gravitational wave asteroseismology relations for f-modes of rapidly rotating neutron stars. An approach different to the previous studies is employed - first, the moment of inertia is used instead of the stellar radius, and second, the normalization of the oscillation frequencies and damping times is different. It was shown that in the non-rotating case this can lead to a much stronger equation of state independence and our goal is to generalize the static relations to the rapidly rotating case and values of the spherical mode number $l\\ge2$. We employ realistic equations of state that cover a very large range of stiffness in order to check better the universality of the relations. At the end we explore the inverse problem, i.e. obtain the neutron star parameters from the observed gravitational frequencies and damping times. It turns out that with this new set of relations we can solve the inverse problem with a very good accuracy using three frequencies that was not possible ...
Slowly rotating superfluid neutron stars with isospin dependent entrainment in a two-fluid model
Kheto, Apurba
2015-01-01
We investigate the slowly rotating general relativistic superfluid neutron stars including the entrainment effect in a two-fluid model, where one fluid represents the superfluid neutrons and the other is the charge-neutral fluid called the proton fluid, made of protons and electrons. The equation of state and the entrainment effect between the superfluid neutrons and the proton fluid are computed using a relativistic mean field (RMF) model where baryon-baryon interaction is mediated by the exchange of $\\sigma$, $\\omega$, and $\\rho$ mesons and scalar self interactions are also included. The equations governing rotating neutron stars in the slow rotation approximation are second order in rotational velocities of neutron and proton fluids. We explore the effects of the isospin dependent entrainment and the relative rotation between two fluids on the global properties of rotating superfluid neutron stars such as mass, shape, and the mass shedding (Kepler) limit within the RMF model with different parameter sets. ...
Properties of Neutron Stars Rotating at Kepler Frequency with Uniform Strong Magnetic Field
WEN De-Hua; CHEN Wei; LU Yi-Gang; LIU Liang-Gang
2007-01-01
A uniform strong magnetic field is considered in calculating the properties of neutron star rotating at the Kepler frequency. The results show that the effect of the magnetic field on the properties of neutron star is evident, and the properties of the neutron stars rotating at the Kepler frequency can be used as a criterion to the equations of states of the neutron star matters.
Dynamical Tidal Response of a Rotating Neutron Star
Landry, Philippe; Poisson, Eric
2017-01-01
The gravitational wave phase of a neutron star (NS) binary is sensitive to the deformation of the NS that results from its companion's tidal influence. In a perturbative treatment, the tidal deformation can be characterized by a set of dimensionless constants, called Love numbers, which depend on the NS equation of state. For static NSs, one type of Love number encodes the response to gravitoelectric tidal fields (associated with mass multipole moments), while another does likewise for gravitomagnetic fields (associated with mass currents). A NS subject to a gravitomagnetic tidal field develops internal fluid motions through gravitomagnetic induction; the fluid motions are irrotational, provided the star is non-rotating. When the NS is allowed to rotate, the situation is complicated by couplings between the tidal field and the star's spin. The problem becomes tractable in the slow-rotation limit. In this case, the fluid motions induced by an external gravitomagnetic field are fully dynamical, even if the tidal field is stationary: interior metric and fluid variables are time-dependent, and vary on the timescale of the rotation period. Remarkably, the exterior geometry of the NS remains time-independent.
Neutron Scattering Differential Cross Sections for 12C
Byrd, Stephen T.; Hicks, S. F.; Nickel, M. T.; Block, S. G.; Peters, E. E.; Ramirez, A. P. D.; Mukhopadhyay, S.; McEllistrem, M. T.; Yates, S. W.; Vanhoy, J. R.
2016-09-01
Because of the prevalence of its use in the nuclear energy industry and for our overall understanding of the interactions of neutrons with matter, accurately determining the effects of fast neutrons scattering from 12C is important. Previously measured 12C inelastic neutron scattering differential cross sections found in the National Nuclear Data Center (NNDC) show significant discrepancies (>30%). Seeking to resolve these discrepancies, neutron inelastic and elastic scattering differential cross sections for 12C were measured at the University of Kentucky Acceleratory Laboratory for incident neutron energies of 5.58, 5.83, and 6.04 MeV. Quasi mono-energetic neutrons were scattered off an enriched 12C target (>99.99%) and detected by a C6D6 liquid scintillation detector. Time-of-flight (TOF) techniques were used to determine scattered neutron energies and allowed for elastic/inelastic scattering distinction. Relative detector efficiencies were determined through direct measurements of neutrons produced by the 2H(d,n) and 3H(p,n) source reactions, and absolute normalization factors were found by comparing 1H scattering measurements to accepted NNDC values. This experimental procedure has been successfully used for prior neutron scattering measurements and seems well-suited to our current objective. Significant challenges were encountered, however, with measuring the neutron detector efficiency over the broad incident neutron energy range required for these measurements. Funding for this research was provided by the National Nuclear Security Administration (NNSA).
General relativistic spectra of accretion disks around rotating neutron stars
Bhattacharya, S; Thampan, A V
2000-01-01
General relativistic spectra from accretion disks around rotating neutron stars in the appropriate space-time geometry for several different equation of state, spin rates and mass of the compact object have been computed. The analysis involves the computation of the relativistically corrected radial temperature profiles and the effect of Doppler and gravitational red-shifts on the spectra. Light bending effects have been omitted for simplicity. The relativistic spectrum is compared with the Newtonian one and it is shown that the difference between the two is primarily due to the different radial temperature profile for the relativistic and Newtonian disk solutions. To facilitate direct comparison with observations, a simple empirical function has been presented which describes the numerically computed relativistic spectra well. This empirical function (which has three parameters including normalization) also describes the Newtonian spectrum adequately. Thus the function can in principle be used to distinguish...
Polarized neutron beam properties for measuring parity-violating spin rotation in liquid {sup 4}He
Micherdzinska, A.M., E-mail: amicherd@gwu.ed [Indiana University/IU Center for Exploration of Energy and Matter, Bloomington, IN 47408 (United States); George Washington University, Washington, DC 20052 (United States); Bass, C.D. [Indiana University/IU Center for Exploration of Energy and Matter, Bloomington, IN 47408 (United States); National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States); Bass, T.D. [Indiana University/IU Center for Exploration of Energy and Matter, Bloomington, IN 47408 (United States); Gan, K. [George Washington University, Washington, DC 20052 (United States); Luo, D. [Indiana University/IU Center for Exploration of Energy and Matter, Bloomington, IN 47408 (United States); Markoff, D.M. [North Carolina Central University, Durham, NC 27707 (United States); Mumm, H.P.; Nico, J.S. [National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States); Opper, A.K. [George Washington University, Washington, DC 20052 (United States); Sharapov, E.I. [Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation); Snow, W.M. [Indiana University/IU Center for Exploration of Energy and Matter, Bloomington, IN 47408 (United States); Swanson, H.E. [University of Washington/CENPA, Seattle, WA 98195 (United States); Zhumabekova, V. [Al-Farabi Kazakh National University, Al-Farabi Ave. 71, 050038 Almaty (Kazakhstan)
2011-03-01
Measurements of parity-violating neutron spin rotation can provide insight into the poorly understood nucleon-nucleon weak interaction. Because the expected rotation angle per unit length is small (10{sup -7} rad/m), several properties of the polarized cold neutron beam phase space and the neutron optical elements of the polarimeter must be measured to quantify possible systematic effects. This paper presents (1) an analysis of a class of possible systematic uncertainties in neutron spin rotation measurements associated with the neutron polarimetry, and (2) measurements of the relevant neutron beam properties (intensity distribution, energy spectrum, and the product of the neutron beam polarization and the analyzing power as a function of the beam phase space properties) on the NG-6 cold neutron beam-line at the National Institute of Standards and Technology Center for Neutron Research. We conclude that the phase space nonuniformities of the polarimeter in this beam are small enough that a parity-violating neutron spin rotation measurement in n-{sup 4}He with systematic uncertainties at the 10{sup -7} rad/m level is possible.
Simulation of MHD collimation from differential rotation
Carey, Christopher
2005-10-01
Recent observations indicate that astrophysical outflows from active galactic nuclei are permeated with helical magnetic fields[1]. The most promising theory for the formation of the magnetic configurations in these magnetically driven jets is the coiling of an initial seed field by the differential rotation of the accretion disk surrounding the central object. We have begun simulations that are relevant to these Poynting jets using the NIMROD code[2]. To simulate dynamics on length scales that are significantly larger than the accretion disk, the non-relativistic MHD equations are evolved on a hemispherical logarithmic mesh. The accretion disk is treated as a condition on the lower boundary by applying a Keplerian velocity to the azimuthal component of the fluid velocity and a prescribed flux of mass through the boundary. The magnetic field configuration is initialized to a dipole like field. Formation of a jet outflow is observed later in time. The initial field is coiled up and collimated, driving a large current density on the axis of symmetry. Slipping of magnetic field lines due to non-ideal effects has been investigated. 1. Asada K. et. al., Pub. of the Astr. Soc. of Japan, 54, L39-L43, 2002 2. Sovinec C. et. al., J. Comp. Phys., 195, 355-386, 2004
Parity-violating neutron spin rotation in hydrogen and deuterium
Grießhammer, H. W.; Schindler, M. R.; Springer, R. P.
2012-01-01
We calculate the (parity-violating) spin-rotation angle of a polarized neutron beam through hydrogen and deuterium targets, using pionless effective field theory up to next-to-leading order. Our result is part of a program to obtain the five leading independent low-energy parameters that characterize hadronic parity violation from few-body observables in one systematic and consistent framework. The two spin-rotation angles provide independent constraints on these parameters. Our result for np spin rotation is frac{1} {ρ }frac{{d\\varphi _{PV}^{np} }} {{dl}} = left[ {4.5 ± 0.5} right] rad MeV^{ - frac{1} {2}} left( {2g^{left( {^3 S_1 - ^3 P_1 } right)} + g^{left( {^3 S_1 - ^3 P_1 } right)} } right) - left[ {18.5 ± 1.9} right] rad MeV^{ - frac{1} {2}} left( {g_{left( {Δ I = 0} right)}^{left( {^1 S_0 - ^3 P_0 } right)} - 2g_{left( {Δ I = 2} right)}^{left( {^1 S_0 - ^3 P_0 } right)} } right), while for nd spin rotation we obtain frac{1} {ρ }frac{{d\\varphi _{PV}^{nd} }} {{dl}} = left[ {8.0 ± 0.8} right] rad MeV^{ - frac{1} {2}} g^{left( {^3 S_1 - ^1 P_1 } right)} + left[ {17.0 ± 1.7} right] rad MeV^{ - frac{1} {2}} g^{left( {^3 S_1 - ^3 P_1 } right)} + left[ {2.3 ± 0.5} right] rad MeV^{ - frac{1} {2}} left( {3g_{left( {Δ I = 0} right)}^{left( {^1 S_0 - ^3 P_0 } right)} - 2g_{left( {Δ I = 1} right)}^{left( {^1 S_0 - ^3 P_0 } right)} } right), where the g (X-Y), in units of MeV^{ - frac{3} {2}}, are the presently unknown parameters in the leading-order parity-violating Lagrangian. Using naıve dimensional analysis to estimate the typical size of the couplings, we expect the signal for standard target densities to be left| {frac{{d\\varphi _{PV} }} {{dl}}} right| ≈ left[ {10^{ - 7} ldots 10^{ - 6} } right]frac{{rad}} {m} for both hydrogen and deuterium targets. We find no indication that the nd observable is enhanced compared to the np one. All results are properly renormalized. An estimate of the numerical and systematic uncertainties of our calculations
Rotational Viscosity in Linear Irreversible Thermodynamics and its Application to Neutron Stars
Sandoval-Villalbazo, A; García-Colin, L S; Sandoval-Villalbazo, Alfredo; Garcia-Perciante, Ana; Garcia-Colin, LS
2001-01-01
A generalized analysis of the local entropy production of a simple fluid is used to show that, if intrinsic angular momentum is taken into account, rotational viscosity must arise in the linear non-equilibrium regime. As a consequence, the stress tensor of dense rotating matter, such as the one present in neutron stars, posseses a significant non-vansishing antisymmetrical part. A simple argument suggests that, due to the extreme magnetic fields present in neutron stars, the relaxation time associated to rotational viscosity is large (approx 10^{21} s). The formalism leads to generalized Navier-Stokes equations useful in neutron star physics which involve vorticity in the linear regime.
Frame Dragging Effect on Properties of Rotating Neutron Stars with Strong Magnetic Field
GUO Yu-Wu; WEN De-Hua; HU Jian-Xun
2008-01-01
The general relativistic frame dragging effect on the properties, such as the moments of inertia and the radii of gyration of fast rotating neutron stars with a uniform strong magnetic field, is calculated accurate to the first order in the uniform angular velocity. The results show that compared with the corresponding non-rotating static spherical symmetric neutron star with a weaker magnetic field, a fast rotating neutron star (millisecond pulsar) with a stronger magnetic field has a relative smaller moment of inertia and radius of gyration.
Numerical solutions of general-relativistic field equations for rapidly rotating neutron stars
吴雪君; 须重明
1997-01-01
Stationary axial symmetric equilibrium configurations rapidly rotating with uniform angular velocity in the framework of genera! relativity are considered. Sequences of models are numerically computed by means of a computer code that solves the full Einstein equations exactly. This code employs Neugebauer’s minimal surface formalism, where the field equations are equivalent to two-dimensional minimal surface equations for 4 metric potentials. The calculations are based upon 10 different equations of state. Results of various structures of neutron stars and the rotational effects on stellar structures and properties are reported. Finally some limits to equations of state of neutron stars and the stability for rapidly rotating relativistic neutron stars are discussed.
Rapidly Rotating Neutron Stars in Dilatonic Einstein-Gauss-Bonnet Theory
Kleihaus, Burkhard; Mojica, Sindy; Zagermann, Marco
2016-01-01
We construct sequences of rapidly rotating neutron stars in dilatonic Einstein-Gauss-Bonnet theory, employing two equations of state for the nuclear matter. We analyze the dependence of the physical properties of these neutron stars on the Gauss-Bonnet coupling strength. For a given equation of state we determine the physically relevant domain of rapidly rotating neutron stars, which is delimited by the set of neutron stars rotating at the Kepler limit, the set of neutron stars along the secular instability line, and the set of static neutron stars. As compared to Einstein gravity, the presence of the Gauss-Bonnet term decreases this domain, leading to lower values for the maximum mass as well as to smaller central densities. The quadrupole moment is decreased by the Gauss-Bonnet term for rapidly rotating neutron stars, while it is increased for slowly rotating neutron stars. The universal relation between the quadrupole moment and the moment of inertia found in General Relativity appears to extend to dilaton...
A Diagnostic for Localizing Red Giant Differential Rotation
Klion, Hannah
2016-01-01
We present a simple diagnostic that can be used to constrain the location of the differential rotation in red giants with measured mixed mode rotational splittings. Specifically, in red giants with radii $\\sim 4R_\\odot$, the splittings of p-dominated modes (sound wave dominated) relative to those of g-dominated modes (internal gravity wave dominated) are sensitive to how much of the differential rotation resides in the outer convection zone versus the radiative interior of the red giant. An independently measured surface rotation rate significantly aids breaking degeneracies in interpreting the measured splittings. We apply our results to existing observations of red giants, particularly those of Kepler-56, and find that most of the differential rotation resides in the radiative region rather than in the convection zone. This conclusion is consistent with results in the literature from rotational inversions, but our results are insensitive to some of the uncertainties in the inversion process and can be readi...
Differential rotation of the unstable nonlinear r -modes
Friedman, John L.; Lindblom, Lee; Lockitch, Keith H.
2016-01-01
At second order in perturbation theory, the r -modes of uniformly rotating stars include an axisymmetric part that can be identified with differential rotation of the background star. If one does not include radiation reaction, the differential rotation is constant in time and has been computed by Sá. It has a gauge dependence associated with the family of time-independent perturbations that add differential rotation to the unperturbed equilibrium star: For stars with a barotropic equation of state, one can add to the time-independent second-order solution arbitrary differential rotation that is stratified on cylinders (that is a function of distance ϖ to the axis of rotation). We show here that the gravitational radiation-reaction force that drives the r -mode instability removes this gauge freedom; the exponentially growing differential rotation of the unstable second-order r -mode is unique. We derive a general expression for this rotation law for Newtonian models and evaluate it explicitly for slowly rotating models with polytropic equations of state.
Zhang, Nai-Bo; Wang, Shou-Yu; Qi, Bin; Gao, Jian-Hua; Sun, Bao-Yuan
2017-07-01
Based on covariant density functional theory, we study the effects of rotation on the nucleon direct URCA (N-DURCA) process for traditional and hyperonic neutron stars. The calculated results indicate that, for a fixed mass sequence of rotational traditional neutron stars, the neutrino emissivity of the star is nearly invariant with increasing frequency, while it always increases for rotational hyperonic neutron stars. Thus, rotation has different effects on the N-DURCA process for these two kinds of neutron stars. Supported by National Natural Science Foundation of China (11545011, 11405096), the Shandong Natural Science Foundation (ZR2014AQ012), the Young Scholars Program of Shandong University, Weihai (2015WHWLJH01) and the Fundamental Research Funds for the Central Universities (lzujbky-2016-30)
Differential rotation of the unstable nonlinear r-modes
Friedman, John L; Lockitch, Keith H
2016-01-01
At second order in perturbation theory, the $r$-modes of uniformly rotating stars include an axisymmetric part that can be identified with differential rotation of the background star. If one does not include radiation-reaction, the differential rotation is constant in time and has been computed by S\\'a. It has a gauge dependence associated with the family of time-independent perturbations that add differential rotation to the unperturbed equilibrium star: For stars with a barotropic equation of state, one can add to the time-independent second-order solution arbitrary differential rotation that is stratified on cylinders (that is a function of distance $\\varpi$ to the axis of rotation). We show here that the gravitational radiation-reaction force that drives the $r$-mode instability removes this gauge freedom: The expontially growing differential rotation of the unstable second-order $r$-mode is unique. We derive a general expression for this rotation law for Newtonian models and evaluate it explicitly for s...
ON THE DIFFERENTIAL ROTATION OF MASSIVE MAIN-SEQUENCE STARS
Rogers, T. M. [Department of Mathematics and Statistics, Newcastle University (United Kingdom); Planetary Science Institute, Tucson, AZ 85721 (United States)
2015-12-20
To date, asteroseismology has provided core-to-surface differential rotation measurements in eight main-sequence stars. These stars, ranging in mass from ∼1.5–9 M{sub ⊙}, show rotation profiles ranging from uniform to counter-rotation. Although they have a variety of masses, these stars all have convective cores and overlying radiative regions, conducive to angular momentum transport by internal gravity waves (IGWs). Using two-dimensional numerical simulations, we show that angular momentum transport by IGWs can explain all of these rotation profiles. We further predict that, should high mass, faster rotating stars be observed, the core-to-envelope differential rotation will be positive, but less than one.
Differential Rotation and Magnetism in Simulations of Fully Convective Stars
Browning, Matthew
2010-01-01
Stars of sufficiently low mass are convective throughout their interiors, and so do not possess an internal boundary layer akin to the solar tachocline. Because that interface figures so prominently in many theories of the solar magnetic dynamo, a widespread expectation had been that fully convective stars would exhibit surface magnetic behavior very different from that realized in more massive stars. Here I describe how recent observations and theoretical models of dynamo action in low-mass stars are partly confirming, and partly confounding, this basic expectation. In particular, I present the results of 3--D MHD simulations of dynamo action by convection in rotating spherical shells that approximate the interiors of 0.3 solar-mass stars at a range of rotation rates. The simulated stars can establish latitudinal differential rotation at their surfaces which is solar-like at ``rapid'' rotation rates (defined within) and anti-solar at slower rotation rates; the differential rotation is greatly reduced by feed...
Rotating proto-neutron stars: spin evolution, maximum mass and I-Love-Q relations
Martinon, Grégoire; Gualtieri, Leonardo; Ferrari, Valeria
2014-01-01
Shortly after its birth in a gravitational collapse, a proto-neutron star enters in a phase of quasi-stationary evolution characterized by large gradients of the thermodynamical variables and intense neutrino emission. In few tens of seconds the gradients smooth out while the star contracts and cools down, until it becomes a neutron star. In this paper we study this phase of the proto-neutron star life including rotation, and employing finite temperature equations of state. We model the evolution of the rotation rate, and determine the relevant quantities characterizing the star. Our results show that an isolated neutron star cannot reach, at the end of the evolution, the maximum values of mass and rotation rate allowed by the zero-temperature equation of state. Moreover, a mature neutron star evolved in isolation cannot rotate too rapidly, even if it is born from a proto-neutron star rotating at the mass-shedding limit. We also show that the I-Love-Q relations are violated in the first second of life, but th...
22-Year Periodicity in the Solar Differential Rotation
J. Javaraiah
2000-09-01
Using the data on sunspot groups compiled during 1879-1975, we determined variations in the differential rotation coefficients and during the solar cycle. The variation in the equatorial rotation rate is found to be significant only in the odd numbered cycles, with an amplitude ∼ 0.01 rads-1. There exists a good anticorrelation between the variations of the differential rotation rate derived from the odd and even numbered cycles, suggesting existence of a `22-year' periodicity in . The amplitude of the variation of is ∼ 0.05 rad s-1.
Fast rotation of neutron stars and equation of state of dense matter
Haensel, P; Bejger, M
2008-01-01
Fast rotation of compact stars (at submillisecond period) and, in particular, their stability, are sensitive to the equation of state (EOS) of dense matter. Recent observations of XTE J1739-285 suggest that it contains a neutron star rotating at 1122 Hz (Kaaret et al. 2007). At such rotational frequency the effects of rotation on star's structure are significant. We study the interplay of fast rotation, EOS and gravitational mass of a submillisecond pulsar. We discuss the EOS dependence of spin-up to a submillisecond period, via mass accretion from a disk in a low-mass X-ray binary.
HERSCHEL AND SPITZER OBSERVATIONS OF SLOWLY ROTATING, NEARBY ISOLATED NEUTRON STARS
Posselt, B.; Pavlov, G. G. [Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States); Popov, S. [Sternberg Astronomical Institute, Lomonosov Moscow State University, Moscow 119992 (Russian Federation); Wachter, S., E-mail: posselt@psu.edu [Max Planck Institute for Astronomy, Königsstuhl 17, D-69117 Heidelberg (Germany)
2014-11-01
Supernova fallback disks around neutron stars have been suspected to influence the evolution of the diverse neutron star populations. Slowly rotating neutron stars are the most promising places to find such disks. Searching for the cold and warm debris of old fallback disks, we carried out Herschel PACS (70 μm, 160 mu m) and Spitzer IRAC (3.6 μm, 4.5 μm) observations of eight slowly rotating (P ≈ 3-11 s) nearby (<1 kpc) isolated neutron stars. Herschel detected 160 μm emission (>5σ) at locations consistent with the positions of the neutron stars RX J0806.4-4123 and RX J2143.0+0654. No other significant infrared emission was detected from the eight neutron stars. We estimate probabilities of 63%, 33%, and 3% that, respectively, none, one, or both Herschel PACS 160 μm detections are unrelated excess sources due to background source confusion or an interstellar cirrus. If the 160 μm emission is indeed related to cold (10-22 K) dust around the neutron stars, this dust is absorbing and re-emitting ∼10% to ∼20% of the neutron stars' X-rays. Such high efficiencies would be at least three orders of magnitude larger than the efficiencies of debris disks around nondegenerate stars. While thin dusty disks around the neutron stars can be excluded as counterparts of the 160 μm emission, dusty asteroid belts constitute a viable option.
Flare differentially rotates sunspot on Sun's surface
Liu, Chang; Xu, Yan; Cao, Wenda; Deng, Na; Lee, Jeongwoo; Hudson, Hugh S.; Gary, Dale E.; Wang, Jiasheng; Jing, Ju; Wang, Haimin
2016-10-01
Sunspots are concentrations of magnetic field visible on the solar surface (photosphere). It was considered implausible that solar flares, as resulted from magnetic reconnection in the tenuous corona, would cause a direct perturbation of the dense photosphere involving bulk motion. Here we report the sudden flare-induced rotation of a sunspot using the unprecedented spatiotemporal resolution of the 1.6 m New Solar Telescope, supplemented by magnetic data from the Solar Dynamics Observatory. It is clearly observed that the rotation is non-uniform over the sunspot: as the flare ribbon sweeps across, its different portions accelerate (up to ~50° h-1) at different times corresponding to peaks of flare hard X-ray emission. The rotation may be driven by the surface Lorentz-force change due to the back reaction of coronal magnetic restructuring and is accompanied by a downward Poynting flux. These results have direct consequences for our understanding of energy and momentum transportation in the flare-related phenomena.
Flare differentially rotates sunspot on Sun's surface
Liu, Chang; Cao, Wenda; Deng, Na; Lee, Jeongwoo; Hudson, Hugh S; Gary, Dale E; Wang, Jiasheng; Jing, Ju; Wang, Haimin
2016-01-01
Sunspots are concentrations of magnetic field visible on the solar surface (photosphere). It was considered implausible that solar flares, as resulted from magnetic reconnection in the tenuous corona, would cause a direct perturbation of the dense photosphere involving bulk motion. Here we report the sudden flare-induced rotation of a sunspot using the unprecedented spatiotemporal resolution of the 1.6 m New Solar Telescope, supplemented by magnetic data from the Solar Dynamics Observatory. It is clearly observed that the rotation is non-uniform over the sunspot: as the flare ribbon sweeps across, its different portions accelerate (up to 50 deg per hr) at different times corresponding to peaks of flare hard X-ray emission. The rotation may be driven by the surface Lorentz-force change due to the back reaction of coronal magnetic restructuring and is accompanied by a downward Poynting flux. These results have direct consequences for our understanding of energy and momentum transportation in the flare-related p...
Flare differentially rotates sunspot on Sun's surface.
Liu, Chang; Xu, Yan; Cao, Wenda; Deng, Na; Lee, Jeongwoo; Hudson, Hugh S; Gary, Dale E; Wang, Jiasheng; Jing, Ju; Wang, Haimin
2016-10-10
Sunspots are concentrations of magnetic field visible on the solar surface (photosphere). It was considered implausible that solar flares, as resulted from magnetic reconnection in the tenuous corona, would cause a direct perturbation of the dense photosphere involving bulk motion. Here we report the sudden flare-induced rotation of a sunspot using the unprecedented spatiotemporal resolution of the 1.6 m New Solar Telescope, supplemented by magnetic data from the Solar Dynamics Observatory. It is clearly observed that the rotation is non-uniform over the sunspot: as the flare ribbon sweeps across, its different portions accelerate (up to ∼50° h(-1)) at different times corresponding to peaks of flare hard X-ray emission. The rotation may be driven by the surface Lorentz-force change due to the back reaction of coronal magnetic restructuring and is accompanied by a downward Poynting flux. These results have direct consequences for our understanding of energy and momentum transportation in the flare-related phenomena.
Herschel and Spitzer Observations of Slowly Rotating, Nearby Isolated Neutron Stars
Posselt, B.; Pavlov, G. G.; Popov, S.; Wachter, S.
2014-11-01
Supernova fallback disks around neutron stars have been suspected to influence the evolution of the diverse neutron star populations. Slowly rotating neutron stars are the most promising places to find such disks. Searching for the cold and warm debris of old fallback disks, we carried out Herschel PACS (70 μm, 160 μm) and Spitzer IRAC (3.6 μm, 4.5 μm) observations of eight slowly rotating (P ≈ 3-11 s) nearby (5σ) at locations consistent with the positions of the neutron stars RX J0806.4-4123 and RX J2143.0+0654. No other significant infrared emission was detected from the eight neutron stars. We estimate probabilities of 63%, 33%, and 3% that, respectively, none, one, or both Herschel PACS 160 μm detections are unrelated excess sources due to background source confusion or an interstellar cirrus. If the 160 μm emission is indeed related to cold (10-22 K) dust around the neutron stars, this dust is absorbing and re-emitting ~10% to ~20% of the neutron stars' X-rays. Such high efficiencies would be at least three orders of magnitude larger than the efficiencies of debris disks around nondegenerate stars. While thin dusty disks around the neutron stars can be excluded as counterparts of the 160 μm emission, dusty asteroid belts constitute a viable option.
Large Scale Magnetohydrodynamic Dynamos from Cylindrical Differentially Rotating Flows
Ebrahimi, F
2015-01-01
For cylindrical differentially rotating plasmas threaded with a uniform vertical magnetic field, we study large-scale magnetic field generation from finite amplitude perturbations using analytic theory and direct numerical simulations. Analytically, we impose helical fluctuations, a seed field, and a background flow and use quasi-linear theory for a single mode. The predicted large-scale field growth agrees with numerical simulations in which the magnetorotational instability (MRI) arises naturally. The vertically and azimuthally averaged toroidal field is generated by a fluctuation-induced EMF that depends on differential rotation. Given fluctuations, the method also predicts large-scale field growth for MRI-stable rotation profiles and flows with no rotation but shear.
Seo, P -N; Bowman, J D; Chupp, T E; Crawford, C; Dabaghyan, M; Dawkins, M; Freedman, S J; Gentile, T; Gericke, M T; Gillis, R C; Greene, G L; Hersman, F W; Jones, G L; Kandes, M; Lamoreaux, S; Lauss, B; Leuschner, M B; Mahurin, R; Mason, M; Mei, J; Mitchell, G S; Nann, H; Page, S A; Penttila, S I; Ramsay, W D; Bacci, A Salas; Santra, S; Sharma, M; Smith, T B; Snow, W M; Wilburn, W S; Zhu, H
2007-01-01
We have developed a radio-frequency resonant spin rotator to reverse the neutron polarization in a 9.5 cm x 9.5 cm pulsed cold neutron beam with high efficiency over a broad cold neutron energy range. The effect of the spin reversal by the rotator on the neutron beam phase space is compared qualitatively to RF neutron spin flippers based on adiabatic fast passage. The spin rotator does not change the kinetic energy of the neutrons and leaves the neutron beam phase space unchanged to high precision. We discuss the design of the spin rotator and describe two types of transmission-based neutron spin-flip efficiency measurements where the neutron beam was both polarized and analyzed by optically-polarized 3He neutron spin filters. The efficiency of the spin rotator was measured to be 98.0+/-0.8% on resonance for neutron energies from 3.3 to 18.4 meV over the full phase space of the beam. As an example of the application of this device to an experiment we describe the integration of the RF spin rotator into an app...
Differential rotation of main-sequence dwarfs and its dynamo-efficiency
Kitchatinov, L L
2010-01-01
A new version of a numerical model of stellar differential rotation based on mean-field hydrodynamics is presented and tested by computing the differential rotation of the Sun. The model is then applied to four individual stars including two moderate and two fast rotators to reproduce their observed differential rotation quite closely. A series of models for rapidly rotating ($P_{rot} = 1$~day) stars of different masses and compositions is generated. The effective temperature is found convenient to parameterize the differential rotation: variations with metallicity, that are quite pronounced when the differential rotation is considered as a function of the stellar mass, almost disappear in the dependence of differential rotation on temperature. The differential rotation increases steadily with surface temperature to exceed the largest differential rotation observed to date for the hottest F-stars we considered. This strong differential rotation is, however, found not to be efficient for dynamos when the effic...
Magnetic field tomography and differential Faraday rotation
Horellou, Cathy
2014-01-01
Wide-band radio polarization observations offer the possibility to recover information about the magnetic fields in synchrotron sources, such as details of their three dimensional configuration, that has previously been inaccessible. The key physical process involved is the Faraday rotation of the polarized emission in the source (and elsewhere along its propagation path). In order to proceed reliable methods are required for inverting the signals observed in wavelength space into useful data in Faraday space, with robust estimates of their uncertainty. In this paper we examine how variations of the intrinsic angle of polarized emission chi0 with the Faraday depth phi within a source affect the observable quantities. Using simple models for the Faraday dispersion F(phi) and chi0(phi), along with the current and planned properties of the main radio interferometers, we demonstrate how degeneracies among the parameters describing the magneto-ionic medium can be minimised by combining observations in different wa...
Differential rotation in solar-like stars from global simulations
Guerrero, G.; Kosovichev, A. G. [Solar Physics, HEPL, Stanford University, 452 Lomita Mall, Stanford, CA 94305-4085 (United States); Smolarkiewicz, P. K. [European Centre for Medium-Range Weather Forecasts, Reading RG2 9AX (United Kingdom); Mansour, N. N., E-mail: gag@stanford.edu, E-mail: sasha@sun.stanford.edu, E-mail: smolar@ecmwf.int, E-mail: nagi.n.mansour@nasa.gov [NASA, Ames Research Center, Moffett Field, Mountain View, CA 94040 (United States)
2013-12-20
To explore the physics of large-scale flows in solar-like stars, we perform three-dimensional anelastic simulations of rotating convection for global models with stratification resembling the solar interior. The numerical method is based on an implicit large-eddy simulation approach designed to capture effects from non-resolved small scales. We obtain two regimes of differential rotation, with equatorial zonal flows accelerated either in the direction of rotation (solar-like) or in the opposite direction (anti-solar). While the models with the solar-like differential rotation tend to produce multiple cells of meridional circulation, the models with anti-solar differential rotation result in only one or two meridional cells. Our simulations indicate that the rotation and large-scale flow patterns critically depend on the ratio between buoyancy and Coriolis forces. By including a sub-adiabatic layer at the bottom of the domain, corresponding to the stratification of a radiative zone, we reproduce a layer of strong radial shear similar to the solar tachocline. Similarly, enhanced super-adiabaticity at the top results in a near-surface shear layer located mainly at lower latitudes. The models reveal a latitudinal entropy gradient localized at the base of the convection zone and in the stable region, which, however, does not propagate across the convection zone. In consequence, baroclinicity effects remain small, and the rotation isocontours align in cylinders along the rotation axis. Our results confirm the alignment of large convective cells along the rotation axis in the deep convection zone and suggest that such 'banana-cell' pattern can be hidden beneath the supergranulation layer.
Seo, P. -N. [Los Alamos National Laboratory (LANL); Barron-Palos, L. [Arizona State University; Bowman, J. D. [Los Alamos National Laboratory (LANL); Chupp, T. E. [University of Michigan; Crawford, C. [University of Tennessee, Knoxville (UTK); Dabaghyan, M. [University of New Hampshire; Dawkins, M. [Indiana University; Freedman, S. J. [University of California; Gentile, T. R. [National Institute of Standards and Technology (NIST); Gericke, M. T. [University of Manitoba, Canada; Gillis, R. C. [University of Manitoba, Canada; Greene, G. L. [University of Tennessee, Knoxville (UTK) & Oak Ridge National Laboratory (ORNL); Hersman, F. W. [University of New Hampshire; Jones, G. L. [Hamilton College, New York; Kandes, M. [University of Michigan; Lamoreaux, S. [Los Alamos National Laboratory (LANL); Lauss, B. [University of California, Berkeley; Leuschner, M. B. [Indiana University; Mahurin, R. [University of Tennessee, Knoxville (UTK); Mason, M. [University of New Hampshire; Mei, J. [Indiana University; Mitchell, G. S. [Los Alamos National Laboratory (LANL); Nann, H. [Indiana University; Page, S. A. [University of Manitoba, Canada; Penttila, S. I. [Los Alamos National Laboratory (LANL); Ramsay, W. D. [University of Manitoba & TRIUMF, Canada; Salas Bacci, A. [Los Alamos National Laboratory (LANL); Santra, S. [Indiana University; Sharma, M. [University of Michigan; Smith, T. B. [University of Dayton, Ohio; Snow, W. [Indiana University; Wilburn, W. S. [Los Alamos National Laboratory (LANL); Zhu, H. [University of New Hampshire
2008-01-01
High precision fundamental neutron physics experiments have been proposed for the intense pulsed spallation neutron beams at JSNS, LANSCE, and SNS to test the standard model and search for new physics. Certain systematic effects in some of these experiments have to be controlled at the few ppb level. The NPD Gamma experiment, a search for the small parity-violating {gamma}-ray asymmetry A{sub Y} in polarized cold neutron capture on parahydrogen, is one example. For the NPD Gamma experiment we developed a radio-frequency resonant spin rotator to reverse the neutron polarization in a 9.5 cm x 9.5 cm pulsed cold neutron beam with high efficiency over a broad cold neutron energy range. The effect of the spin reversal by the rotator on the neutron beam phase space is compared qualitatively to rf neutron spin flippers based on adiabatic fast passage. We discuss the design of the spin rotator and describe two types of transmission-based neutron spin-flip efficiency measurements where the neutron beam was both polarized and analyzed by optically polarized {sup 3}He neutron spin filters. The efficiency of the spin rotator was measured at LANSCE to be 98.8 {+-} 0.5% for neutron energies from 3 to 20 meV over the full phase space of the beam. Systematic effects that the rf spin rotator introduces to the NPD Gamma experiment are considered.
Geroyannis, Vassilis S
2014-01-01
We develop a "hybrid approximative scheme" in the framework of the post-Newtonian approximation for computing general-relativistic polytropic models simulating neutron stars in critical rigid rotation. We treat the differential equations governing such a model as a "complex initial value problem", and we solve it by using the so-called "complex-plane strategy". We incorporate into the computations the complete solution for the relativistic effects, this issue representing a significant improvement with regard to the classical post-Newtonian approximation, as verified by extended comparisons of the numerical results.
Differential rotation in solar-like stars from global simulations
Guerrero, G; Kosovichev, A G; Mansour, N N
2013-01-01
To explore the physics of large-scale flows in solar-like stars, we perform 3D anelastic simulations of rotating convection for global models with stratification resembling the solar interior. The numerical method is based on an implicit large-eddy simulation approach designed to capture effects from non-resolved small scales. We obtain two regimes of differential rotation, with equatorial zonal flows accelerated either in the direction of rotation (solar-like) or in the opposite direction (anti-solar). While the models with the solar-like differential rotation tend to produce multiple cells of meridional circulation, the models with anti-solar differential rotation result in only one or two meridional cells. Our simulations indicate that the rotation and large-scale flow patterns critically depend on the ratio between buoyancy and Coriolis forces. By including a subadiabatic layer at the bottom of the domain, corresponding to the stratification of a radiative zone, we reproduce a layer of strong radial shear...
A phased rotating collimator for a pulsed-neutron fixed scattering angle spectrometer
Wahba, M. (Ain Shams Univ., Cairo (Egypt). Dept. of Engineering Physics and Mathematics)
1991-06-01
The design principle of a phased rotating collimator for a pulsed-neutron fixed scattering angle spectrometer is given. The collimator's dimensions were selected to match the curved slot rotor of the spectrometer which is in operation at the ET-RR-1 reactor. The collimator has one slot, whose shape was determined to satisfy a 100% transmission of the polyenergetic neutron bursts produced by the curved slot rotor. (orig.).
Effect of heat flux on differential rotation in turbulent convection
Kleeorin, N
2006-01-01
We studied the effect of the turbulent heat flux on the Reynolds stresses in a rotating turbulent convection. To this end we solved a coupled system of dynamical equations which includes the equations for the Reynolds stresses, the entropy fluctuations and the turbulent heat flux. We used a spectral $\\tau$ approximation in order to close the system of dynamical equations. We found that the ratio of the contributions to the Reynolds stresses caused by the turbulent heat flux and the anisotropic eddy viscosity is of the order of $\\sim 10 (L_\\rho / l_0)^2$, where $l_{0}$ is the maximum scale of turbulent motions and $L_\\rho$ is the fluid density variation scale. This effect is crucial for the formation of the differential rotation and should be taken into account in the theories of the differential rotation of the Sun, stars and planets. In particular, we demonstrated that this effect may cause the differential rotation which is comparable with the typical solar differential rotation.
Herschel and Spitzer observations of slowly rotating, nearby isolated neutron stars
Posselt, B; Popov, S B; Wachter, S
2014-01-01
Supernova fallback disks around neutron stars have been discussed to influence the evolution of the diverse neutron star populations. Slowly rotating neutron stars are most promising to find such disks. Searching for the cold and warm debris of old fallback disks, we carried out Herschel PACS (70 $\\mu$m, 160 $\\mu$m) and Spitzer IRAC (3.6 $\\mu$m, 4.5 $\\mu$m) observations of eight slowly rotating ($P\\approx 3 - 11$ s) nearby ($5\\sigma$) at locations consistent with the positions of the neutron stars RX J0806.4-4123 and RX J2143.0+0654. No other significant infrared emission was detected from the eight neutron stars. We estimate probabilities of 63%, 33% and 3% that, respectively, none, one, or both Herschel PACS 160 $\\mu$m detections are unrelated excess sources due to background source confusion or an interstellar cirrus. If the 160 $\\mu$m emission is indeed related to cold (10 K to 22 K) dust around the neutron stars, this dust is absorbing and re-emitting $\\sim 10$% to $\\sim 20$% of the neutron stars' X-rays...
Inertial waves in a differentially rotating spherical shell
Baruteau, C
2012-01-01
We investigate the properties of small-amplitude inertial waves propagating in a differentially rotating incompressible fluid contained in a spherical shell. For cylindrical and shellular rotation profiles and in the inviscid limit, inertial waves obey a second-order partial differential equation of mixed type. Two kinds of inertial modes therefore exist, depending on whether the hyperbolic domain where characteristics propagate covers the whole shell or not. The occurrence of these two kinds of inertial modes is examined, and we show that the range of frequencies at which inertial waves may propagate is broader than with solid-body rotation. Using high-resolution calculations based on a spectral method, we show that, as with solid-body rotation, singular modes with thin shear layers following short-period attractors still exist with differential rotation. They exist even in the case of a full sphere. In the limit of vanishing viscosities, the width of the shear layers seems to weakly depend on the global bac...
Differential Rotation in Magnetized and Non-magnetized Stars
Mabuchi, Jun; Kageyama, Akira
2015-01-01
Effects of magnetic field on stellar differential rotation are studied by comparing magnetohydrodynamic (MHD) models and their hydrodynamic (HD) counterparts in the broad range of rotation rate and in varying initial rotation profile. Fully-compressible MHD simulations of rotating penetrative convection are performed in a full-spherical shell geometry. Critical conditions for the transition of the differential rotation between faster equator (solar-type) and slower equator (anti-solar type) are explored with focusing on the "Rossby number (${\\rm Ro}$)" and the "convective Rossby number (${\\rm Ro}_{\\rm conv}$)". It is confirmed that the transition is more gradual and the critical value for it is higher in the MHD model than the HD model in the view of the ${\\rm Ro}_{\\rm conv}$-dependence. The rotation profile shows, as observed in earlier studies, the bistability near the transition in the HD model, while it disappears when allowing the growth of magnetic fields except for the model with taking anti-solar type...
On Differential Rotation and Overshooting in Solar-like Stars
Brun, Allan Sacha; Strugarek, Antoine; Varela, Jacobo; Matt, Sean P.; Augustson, Kyle C.; Emeriau, Constance; DoCao, Olivier Long; Brown, Benjamin; Toomre, Juri
2017-02-01
We seek to characterize how the change of global rotation rate influences the overall dynamics and large-scale flows arising in the convective envelopes of stars covering stellar spectral types from early G to late K. We do so through numerical simulations with the ASH code, where we consider stellar convective envelopes coupled to a radiative interior with various global properties. As solar-like stars spin down over the course of their main sequence evolution, such a change must have a direct impact on their dynamics and rotation state. We indeed find that three main states of rotation may exist for a given star: anti-solar-like (fast poles, slow equator), solar-like (fast equator, slow poles), or a cylindrical rotation profile. Under increasingly strict rotational constraints, the last profile can further evolve into a Jupiter-like profile, with alternating prograde and retrograde zonal jets. We have further assessed how far the convection and meridional flows overshoot into the radiative zone and investigated the morphology of the established tachocline. Using simple mixing length arguments, we are able to construct a scaling of the fluid Rossby number {R}{of}=\\tilde{ω }/2{{{Ω }}}* ∼ \\tilde{v}/2{{{Ω }}}* {R}* , which we calibrate based on our 3D ASH simulations. We can use this scaling to map the behavior of differential rotation versus the global parameters of stellar mass and rotation rate. Finally, we isolate a region on this map (R of ≳ 1.5–2) where we posit that stars with an anti-solar differential rotation may exist in order to encourage observers to hunt for such targets.
Exact Solution for the Exterior Field of a Rotating Neutron Star
Man'ko, V I; Sanabria-Gómez, J D; Manko, Vladimir S.; Mielke, Eckehard W.; Sanabria-Gómez, José D.
2000-01-01
A four-parameter class of exact asymptotically flat solutions of the Einstein-Maxwell equations involving only rational functions is presented. It is able to describe the exterior field of a slowly or rapidly rotating neutron star with poloidal magnetic field.
Flavor oscillations of low energy neutrinos in the rotating neutron star
Dvornikov, Maxim
2010-01-01
We study flavor oscillations of low energy neutrinos propagating in dense matter of a rotating neutron star. On the basis of the exact solutions of the wave equations for neutrinos mass eigenstates we derive the transition probability for neutrinos having big initial angular momentum. It is found that flavor oscillations of neutrinos with energies of several electron-Volts can be resonancely enhanced.
Pareja, M J
2004-01-01
For general relativistic equilibrium stellar models (stationary axisymmetric asymptotically flat and convection-free) with differential rotation, it is shown that for a wide class of rotation laws the distribution of angular velocity of the fluid has a sign, say "positive", and then both the dragging rate and the angular momentum density are positive. In addition, the "mean value" (with respect to an intrinsic density) of the dragging rate is shown to be less than the mean value of the fluid angular velocity (in full general, without having to restrict the rotation law, nor the uniformity in sign of the fluid angular velocity); this inequality yields the positivity and an upper bound of the total rotational energy.
From solar-like to anti-solar differential rotation in cool stars
Gastine, T; Morin, J; Reiners, A; Wicht, J
2013-01-01
Stellar differential rotation can be separated into two main regimes: solar-like when the equator rotates faster than the poles and anti-solar when the polar regions rotate faster than the equator. We investigate the transition between these two regimes with 3-D numerical simulations of rotating spherical shells. We conduct a systematic parameter study which also includes models from different research groups. We find that the direction of the differential rotation is governed by the contribution of the Coriolis force in the force balance, independently of the model setup (presence of a magnetic field, thickness of the convective layer, density stratification). Rapidly-rotating cases with a small Rossby number yield solar-like differential rotation, while weakly-rotating models sustain anti-solar differential rotation. Close to the transition, the two kinds of differential rotation are two possible bistable states. This study provides theoretical support for the existence of anti-solar differential rotation i...
Neutrons and numerical methods. A new look at rotational tunneling
Johnson, M.R.; Kearley, G.J. [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France)
1997-04-01
Molecular modelling techniques are easily adapted to calculate rotational potentials in crystals of simple molecular compounds. A comparison with the potentials obtained from the tunnelling spectra provides a stringent means for validating current methods of calculating Van der Waals, Coulomb and covalent terms. (author). 5 refs.
Differential rotation, flares and coronae in A to M stars
Balona, L. A.; Švanda, M.; Karlický, M.
2016-08-01
Kepler data are used to investigate flares in stars of all spectral types. There is a strong tendency across all spectral types for the most energetic flares to occur among the most rapidly rotating stars. Differential rotation could conceivably play an important role in enhancing flare energies. This idea was investigated, but no correlation could be found between rotational shear and the incidence of flares. Inspection of Kepler light curves shows that rotational modulation is very common over the whole spectral type range. Using the rotational light amplitude, the size distribution of starspots was investigated. Our analysis suggests that stars with detectable flares have spots significantly larger than non-flare stars, indicating that flare energies are correlated with the size of the active region. Further evidence of the existence of spots on A stars is shown by the correlation between the photometric period and the projected rotational velocity. The existence of spots indicates the presence of magnetic fields, but the fact that A stars lack coronae implies that surface convection is a necessary condition for the formation of the corona.
Growth of black holes in the interior of rotating neutron stars
Kouvaris, C.; Tinyakov, P.
2014-01-01
Mini-black holes made of dark matter that can potentially form in the interior of neutron stars always have been thought to grow by accreting the matter of the core of the star via a spherical Bondi accretion. However, neutron stars have sometimes significant angular velocities that can...... in principle stall the spherical accretion and potentially change the conclusions derived about the time it takes for black holes to destroy a star. We study the effect of the star rotation on the growth of such black holes and the evolution of the black hole spin. Assuming no mechanisms of angular momentum...... evacuation, we find that even moderate rotation rates can in fact destroy spherical accretion at the early stages of the black hole growth. However, we demonstrate that the viscosity of nuclear matter can alleviate the effect of rotation, making it possible for the black hole to maintain spherical accretion...
Stationary Electromagnetic Fields of a Slowly Rotating Magnetized Neutron Star in General Relativity
Rezzolla, L; Miller, J C
2001-01-01
Following the general formalism presented by Rezzolla, Ahmedov and Miller (MNRAS, 322, 723 2001), we here derive analytic solutions of the electromagnetic fields equations in the internal and external background spacetime of a slowly rotating highly conducting magnetized neutron star. The star is assumed to be isolated and in vacuum, with a dipolar magnetic field not aligned with the axis of rotation. Our results indicate that the electromagnetic fields of a slowly rotating neutron star are modified by general relativistic effects arising from both the monopolar and the dipolar parts of the gravitational field. The results presented here differ from the ones discussed by Rezzolla, Ahmedov and Miller (MNRAS, 322, 723 2001) mainly in that we here consider the interior magnetic field to be dipolar with the same radial dependence as the external one. While this assumption might not be a realistic one, it should be seen as the application of our formalism to a case often discussed in the literature.
Quasi-periodical variations of pulsars spin as mimicry of differential rotation
Kitiashvili, I.; Gusev, A.
2008-09-01
164203 [2,3,6,]. The rotation of the terrestrial planets having rigid mantle, outer liquid and inner solid cores is characterized by Chandler wobble, Inner core wobble, Free Core Nutation, Free Inner Core Nutation. Like the Earth, a neutron star can undergo a free precession [4]. The period of precession is defined by deformation of a pulsar and tension in crust and mantle. If the crust and the core of pulsar have differential rotation then axis of a pulsar rotation will be precess, because axis of deformation will not coincide with axis of rotation. The three-layer model is more complicated than the previous case therefore classical methods fail. Escapa, Getino and Ferrandiz [1] developed a canonical formulation for an three-layer Earth model. We research model of pulsar, which includes three layers (fig. 1): an axis symmetrical rigid mantle, a fluid outer core (FOC) and a solid inner core (SIC). Flattened of the pulsar, it's FOC and SIC are Here A;C;Af ;Cf ;As;Cs;Ac;Cc are moments of inertia of the pulsar, FOC, SIC and total core accordingly; e, ef , ec are the flattening of total pulsar, FOC, core and SIC accordingly. In case rotation of a three-layer neutron star we have variations of next types: the Chandler Wobble (CW) is a motion of the pulsar rotation axis around its dynamical figure due to the bulges of the pulsar (it is the only global rotational mode for completely solid pulsar); the Free Core Nutation (FCN) is a differential rotation of the liquid core relatively the crust rotation; This mode does exist only if the core is liquid; the Free Inner Core Nutation (FICN) is a mode related to the differential rotation of the inner core with respect to the other layers of the pulsar. The mode exists only if the pulsar has two-layer core contains outer liquid and inner solid components; the Inner Core Wobble (ICW) is a differential rotation of the figure axis of the pulsar core with respect to the rotation axis of the pulsar and is due to the flattened of the inner
Takehiro, S.; Sasaki, Y.; Hayashi, Y.-Y.; Yamada, M.
2013-12-01
We investigate generation mechanisms of differential rotation and angular momentum transport caused by Boussinesq thermal convection in a rotating spherical shell based on weakly nonlinear numerical calculations for various values of the Prandtl and Ekman numbers under a setup similar to the solar convection layer. When the Prandtl number is of order unity or less and the rotation rate of the system is small (the Ekman number is larger than O(10-2)), the structure of thermal convection is not governed by the Taylor-Proudman theorem; banana-type convection cells emerge which follow the spherical shell boundaries rather than the rotation axis. Due to the Coriolis effect, the velocity field associated with those types of convection cells accompanies the Reynolds stress which transports angular momentum from high-latitudes to the equatorial region horizontally, and equatorial prograde flows are produced. The surface and internal distributions of differential rotation realized in this regime are quite similar to those observed in the Sun with helioseismology. These results may suggest that we should apply larger values of the eddy diffusivities than those believed so far when we use a low resolution numerical model for thermal convection in the solar interior.
Prototype Spallation Neutron Source Rotating Target Assembly Final Test Report
McManamy, Thomas J [ORNL; Graves, Van [Oak Ridge National Laboratory (ORNL); Garmendia, Amaia Zarraoa [IDOM Bilbao; Sorda, Fernando [ESS Bilbao; Etxeita, Borja [IDOM Bilbao; Rennich, Mark J [ORNL
2011-01-01
A full-scale prototype of an extended vertical shaft, rotating target assembly based on a conceptual target design for a 1 to 3-MW spallation facility was built and tested. Key elements of the drive/coupling assembly implemented in the prototype include high integrity dynamic face seals, commercially available bearings, realistic manufacturing tolerances, effective monitoring and controls, and fail-safe shutdown features. A representative target disk suspended on a 3.5 meter prototypical shaft was coupled with the drive to complete the mechanical tests. Successful operation for 5400 hours confirmed the overall mechanical feasibility of the extended vertical shaft rotating target concept. The prototype system showed no indications of performance deterioration and the equipment did not require maintenance or relubrication.
Geometric Optimization of Hydraulic Rotation Device for Neutron Transmutation Doping
Park, Yongsoo; Kang, Hanok; Park, Kijung; Kim, Seong Hoon; Park, Cheol [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)
2014-05-15
The Korea Atomic Energy Research Institute (KAERI) is developing a Hydraulic Rotation Device (HRD) for NTD facilities (NTDHRD) as a part of the Kijang Research Reactor (KJRR) project. This concept has many advantages when compared to the motor driven method, which is currently used in the HANARO research reactor located at KAERI. The OPAL research reactor located at ANSTO has already applied this method. To achieve a constant rotation speed, which is substantial for uniform doping, with a minimal amount of fluid flow, certain geometric requirements should be satisfied. This paper describes the approach we used while determining the number of impulse jet nozzles used to rotate the NTDHRD at a set number of blades as well as the angle of the nozzles of the NTDHRD. The approach that our group has used to geometrically optimize the design of a NTDHRD was described. The adaptation of this approach allows one to predict the required amount of inlet fluid flow and to determine the number of nozzles based on the rule that it should avoid being a divisor of the number of blades, and provides a reference while determining the tile angle of the nozzles. A CFD analysis will be performed as a future study.
On the reliability of measuring differential rotation of spotted stars
Kővári, Zsolt; Kriskovics, Levente; Vida, Krisztián; Oláh, Katalin
2013-01-01
Cross-correlation of consecutive Doppler images is one of the most common techniques used to detect surface differential rotation (hereafter DR) on spotted stars. The disadvantage of a single cross-correlation is, however, that the expected DR pattern can be overwhelmed by sudden changes in the apparent spot configuration. Another way to reconstruct the image shear using Doppler imaging is to include a predefined latitude-dependent rotation law in the inversion code (`sheared image method'). However, special but not unusual spot distributions, such like a large polar cap or an equatorial belt (e.g., small random spots evenly distributed along the equator), can distort the rotation profile similarly as the DR does, consequently, yielding incorrect measure of the DR from the sheared image method. To avoid these problems, the technique of measuring DR from averaged cross-correlations using time-series Doppler images (`ACCORD') is introduced and the reliability of this tool is demonstrated on artificial data.
Differential rotation on the young solar analogue V889 Herculis
Koari, Zsolt; Biazzo, Katia; Vida, Krisztian; Marilli, Ettore; Cakirli, Omur
2010-01-01
V889 Herculis is one of the brightest single early-G type stars, a young Sun, that is rotating fast enough (P_rot =1.337 days) for mapping its surface by Doppler Imaging. The 10 FOCES spectra collected between 13-16 Aug 2006 at Calar Alto Observatory allowed us to reconstruct one single Doppler image for two mapping lines. The FeI-6411 and CaI-6439 maps, in a good agreement, revealed an asymmetric polar cap and several weaker features at lower latitudes. Applying the sheared-image method with our Doppler reconstruction we perform an investigation to detect surface differential rotation (DR). The resulting DR parameter, deltaOmega/Omega~0.009 of solar type, is compared to previous studies which reported either much stronger shear or comparably weak DR, or just preferred rigid rotation. Theoretical aspects are also considered and discussed.
Stellar Coronal Response to Differential Rotation and Flux Emergence
Gibb, G P S; Jardine, M M; Yeates, A R
2016-01-01
We perform a numerical parameter study to determine what effect varying differential rotation and flux emergence has on a star's non-potential coronal magnetic field. In particular we consider the effects on the star's surface magnetic flux, open magnetic flux, mean azimuthal field strength, coronal free magnetic energy, coronal heating and flux rope eruptions. To do this, we apply a magnetic flux transport model to describe the photospheric evolution, and couple this to the non-potential coronal evolution using a magnetofrictional technique. A flux emergence model is applied to add new magnetic flux onto the photosphere and into the corona. The parameters of this flux emergence model are derived from the solar flux emergence profile, however the rate of emergence can be increased to represent higher flux emergence rates than the Sun's. Overall we find that flux emergence has a greater effect on the non-potential coronal properties compared to differential rotation, with all the aforementioned properties incr...
Magneto-rotational and thermal evolution of young neutron stars
Popov, S B
2015-01-01
After a brief review of population synthesis of close-by cooling neutron stars, I focus on the interpretation of dichotomy of spin periods of near-by coolers. The existence of two well separated groups -- short period ($\\sim$0.1-0.3 s) radio pulsars and long period ($\\sim$3-10 s) radio quiet sources, aka the Magnificent seven, -- can not be easily explained in unified models developed recently (Popov et al. 2010, Gull{\\'o}n et al. 2014). I speculate that the most natural solution of the problem can be in bimodal initial magnetic field distribution related to the existence of an additional mechanism of field generation in magnetars.
ROTATION CONSTELLATION FOR DIFFERENTIAL UNITARY SPACE-TIME MODULATION
Li Jun; Cao Haiyan; Wei Gang
2006-01-01
A new constellation which is the multiplication of the rotation matrix and the diagonal matrix according to the number of transmitters is proposed to increase the diversity product, the key property to the performance of the differential unitary space-time modulation. Analyses and the simulation results show that the proposed constellation performs better and 2dB or more coding gain can be achieved over the traditional cyclic constellation.
Stellar Coronal Response to Differential Rotation and Flux Emergence
Gibb, G. P. S.; Mackay, D. H.; Jardine, M. M.; Yeates, A. R.
2016-01-01
GPSG would like to thank the STFC for financial support. DHM would like to thank the STFC and the Leverhulme Trust for financial support. Simulations were carried out on a STFC/SRIF funded UKMHD cluster at St Andrews. We perform a numerical parameter study to determine what effect varying differential rotation and flux emergence has on a star's non-potential coronal magnetic field. In particular we consider the effects on the star's surface magnetic flux, open magnetic flux, mean azimuthal...
Appearance of innermost stable circular orbits of accretion discs around rotating neutron stars
Torok, G; Adamek, K; Urbancova, G
2014-01-01
The innermost stable cicular orbit (ISCO) of an accretion disc orbiting a neutron star (NS) is often assumed a unique prediction of general relativity. However, it has been argued that ISCO also appears around highly elliptic bodies described by Newtonian theory. In this sense, the behaviour of an ISCO around a rotating oblate neutron star is formed by the interplay between relativistic and Newtonian effects. Here we briefly explore the consequences of this interplay using a straightforward analytic approach as well as numerical models that involve modern NS equations of state. We examine the ratio K between the ISCO radius and the radius of the neutron star. We find that, with growing NS spin, the ratio K first decreases, but then starts to increase. This non-monotonic behaviour of K can give rise to a neutron star spin interval in which ISCO appears for two very different ranges of NS mass. This may strongly affect the distribution of neutron stars that have an ISCO (ISCO-NS). When (all) neutron stars are d...
Pareja, M J
2003-01-01
For relativistic stars rotating slowly and differentially with a positive angular velocity, some properties in relation to the positiveness of the rate of rotational dragging and of the angular momentum density are derived. Also, a new proof for the bounds on the rotational mass-energy is given.
Plasma Magnetosphere of Oscillating and Rotating Neutron Stars in General Relativity
Ahmedov, Bobomurat; Morozova, Viktoriya; Zanotti, Olindo
2016-07-01
We discuss a number of analytical studies, aimed at adding the influence of oscillations experienced by a pulsar/magnetar on its plasma magnetopshere. We show that particular modes of oscillations may considerably increase the pulsar/magnetar luminosity and apply the obtained theoretical results on the plasma magnetosphere of oscillating and rotating neutron stars i) to propose a qualitative model for the explanation of the phenomenology of intermittent part time pulsars, ii) to study the conditions for radio emission in rotating and oscillating magnetars by focusing on the main physical processes determining the position of their death lines, i.e. of those lines that separate the regions where the neutron star may be radio loud or radio quiet, iii) to explain the subpulse drift phenomena adopting the space-charge limited flow model and comparing the plasma drift velocity in the inner region of pulsar magnetospheres with the observed velocity of drifting subpulses.
Impact of Rotation on the Structure and Composition of Neutron Stars
Weber, Fridolin; Negreiros, Rodrigo
2013-01-01
Depending on mass and rotational frequency, gravity compresses the matter in the core regions of neutron stars to densities that are several times higher than the density of ordinary atomic nuclei. At such huge densities atoms themselves collapse, and atomic nuclei are squeezed so tightly together that new particle states may appear and novel states of matter, foremost quark matter, may be created. This feature makes neutron stars superb astrophysical laboratories for a wide range of physical studies. And with observational data accumulating rapidly from both orbiting and ground based observatories spanning the spectrum from X-rays to radio wavelengths, there has never been a more exiting time than today to study neutron stars. The Hubble Space Telescope and X-ray satellites such as Chandra and XMM-Newton in particular have proven especially valuable. New astrophysical instruments such as the Five hundred meter Aperture Spherical Telescope (FAST), the square kilometer Array (skA), Fermi Gamma-ray Space Telesc...
Manko, V S
2016-01-01
The 4-parameter exact solution presumably describing the exterior gravitational field of a generic neutron star is presented in a concise explicit form defined by only three potentials. In the equatorial plane, the metric functions of the solution are found to be given by particularly simple expressions that make them very suitable for the use in concrete applications. Following Pappas and Apostolatos, we perform a comparison of the multipole structure of the solution with the multipole moments of the known physically realistic Berti-Stergioulas numerical models of neutron stars to argue that the hyperextreme sectors of the solution are not less (but possibly even more) important for the correct description of rapidly rotating neutron stars than the subextreme sector involving exclusively the black-hole constituents. We have also worked out in explicit form an exact analog of the well-known Hartle-Thorne approximate metric.
Impact of triaxiality on the rotational structure of neutron-rich rhenium isotopes
M.W. Reed
2016-01-01
Full Text Available A number of 3-quasiparticle isomers have been found and characterised in the odd-mass, neutron-rich, 187Re, 189Re and 191Re nuclei, the latter being four neutrons beyond stability. The decay of the isomers populates states in the rotational bands built upon the 9/2−[514] Nilsson orbital. These bands exhibit a degree of signature splitting that increases with neutron number. This splitting taken together with measurements of the M1/E2 mixing ratios and with the changes observed in the energy of the gamma-vibrational band coupled to the 9/2−[514] state, suggests an increase in triaxiality, with γ values of 5°, 18° and 25° deduced in the framework of a particle-rotor model.
Turbulent Compressible Convection with Rotation. 2; Mean Flows and Differential Rotation
Brummell, Nicholas H.; Hurlburt, Neal E.; Toomre, Juri
1998-01-01
The effects of rotation on turbulent, compressible convection within stellar envelopes are studied through three-dimensional numerical simulations conducted within a local f-plane model. This work seeks to understand the types of differential rotation that can be established in convective envelopes of stars like the Sun, for which recent helioseismic observations suggest an angular velocity profile with depth and latitude at variance with many theoretical predictions. This paper analyzes the mechanisms that are responsible for the mean (horizontally averaged) zonal and meridional flows that are produced by convection influenced by Coriolis forces. The compressible convection is considered for a range of Rayleigh, Taylor, and Prandtl (and thus Rossby) numbers encompassing both laminar and turbulent flow conditions under weak and strong rotational constraints. When the nonlinearities are moderate, the effects of rotation on the resulting laminar cellular convection leads to distinctive tilts of the cell boundaries away from the vertical. These yield correlations between vertical and horizontal motions that generate Reynolds stresses that can drive mean flows, interpretable as differential rotation and meridional circulations. Under more vigorous forcing, the resulting turbulent convection involves complicated and contorted fluid particle trajectories, with few clear correlations between vertical and horizontal motions, punctuated by an evolving and intricate downflow network that can extend over much of the depth of the layer. Within such networks are some coherent structures of vortical downflow that tend to align with the rotation axis. These yield a novel turbulent alignment mechanism, distinct from the laminar tilting of cellular boundaries, that can provide the principal correlated motions and thus Reynolds stresses and subsequently mean flows. The emergence of such coherent structures that can persist amidst more random motions is a characteristic of turbulence
The Collapse of Differentially Rotating Supermassive Stars: Conformally Flat Simulations
Saijo, M
2004-01-01
We investigate the gravitational collapse of rapidly rotating relativistic supermassive stars by means of a 3+1 hydrodynamical simulations in conformally flat spacetime of general relativity. We study the evolution of differentially rotating supermassive stars of $q \\equiv J/M^{2} \\sim 1$ ($J$ is the angular momentum and $M$ is the gravitational mass of the star) from the onset of radial instability at $R/M \\sim 65$ ($R$ is the circumferential radius of the star) to the point where the conformally flat approximation breaks down. We find that the collapse of the star of $q \\gtrsim 1$, a radially unstable differentially rotating star form a black hole of $q \\lesssim 1$. The main reason to prevent formation of a black hole of $q \\gtrsim 1$ is that quite a large amount of angular momentum stays at the surface. We also find that most of the mass density collapses coherently to form a supermassive black hole with no appreciable disk nor bar. In the absence of nonaxisymmetric deformation, the collapse of differentia...
Dark matter seeding and the kinematics and rotation of neutron stars
Perez-Garcia, M. Angeles, E-mail: mperezga@usal.es [Departamento de Fisica Fundamental and IUFFyM, Universidad de Salamanca, Plaza de la Merced s/n, 37008 Salamanca (Spain); Silk, Joseph, E-mail: j.silk1@physics.ox.ac.uk [Institut d' Astrophysique, UPMC, 98 bis Boulevard Arago, Paris 75014 (France); Department of Physics and Astronomy, Johns Hopkins University, Homewood Campus, Baltimore, MD 21218 (United States); Beecroft Institute for Particle Astrophysics and Cosmology, University of Oxford, Keble Road, Oxford OX1 3RH (United Kingdom)
2012-05-01
Self-annihilation of dark matter accreted from the galactic halo in the inner regions of neutron stars may significantly affect their kinematical properties, namely velocity kicks and rotation patterns. We find that if a stable long-lived single or multiple strangelet off-center seed forms leading to an asymmetric ejection of matter and radiation, there is a significant modification in linear and angular momentum observables of the star.
On Differential Rotation and Convection in the Sun
Balbus, S A; Latter, H N; Weiss, N O
2009-01-01
We show that the differential rotation profile of the solar convection zone, apart from inner and outer boundary layers, can be reproduced with great accu- racy if the isorotation contours correspond to characteristics of the thermal wind equation. This requires that there be a formal quantitative relationship involving the entropy and the angular velocity. Earlier work has suggested that this could arise from magnetohydrodynamic stability constraints; here we argue that purely hydrodynamical processes could also lead to such a result. Of special importance to the hydrodynamical solution is the fact that the thermal wind equation is insensitive to radial entropy gradients. This allows a much more general class of solutions to fit the solar isorotation contours, beyond just those in which the entropy itself must be a function of the angular velocity. In particular, for this expanded class, the thermal wind solution of the solar rotation profile remains valid even when large radial entropy gradients are present...
An algorithm for computing thick target differential p-Li neutron yields near threshold
Lee, C. L.; Zhou, X.-L.
1999-06-01
The 7Li(p,n)7Be reaction is a good source of neutrons for accelerator boron neutron capture therapy (BNCT). Both reactor and accelerator neutron sources produce fast neutrons, which must be moderated since BNCT uses epithermal neutrons. Near-threshold BNCT uses proton energies only tens of keV above the reaction threshold, which reduces the thick target neutron yield but also produces neutrons closer to epithermal energies, so that less moderation is required. Accurate methods for calculating near-threshold differential neutron yields from thick targets of lithium, as well as certain low weight lithium compounds, were developed for BNCT source design. Neutron yields for proton beams up to 2.8 MeV will be presented. Good agreement with yields from several targets will be demonstrated.
M. Narendra Kumar
2016-01-01
Full Text Available Natural convection heat transfer in a two dimensional unsteady rotating differentially heated enclosure is studied numerically in this paper. The enclosure is filled with air and executes a steady counterclockwise rotation about the centre of the enclosure. A finite volume code on a staggered grid arrangement with TDMA algorithm is developed and employed to solve the governing equations subject to Boussinesq approximation. The numerical investigation is carried out for fixed Prandtl number equal to 0.71, Rayleigh number equal to1.1×〖10〗^5 while Taylors number vary from5.2×〖10〗^4 to 3.3×〖10〗^5and Rotational Rayleigh number from 4.9×〖10〗^2 to 3.1×〖10〗^3.Results reveal that there are considerable change in heat transfer rates beyond 15 rpm. The effect of rotation on the Nusselt number for a given Rayleigh number is shown in the present work which is not normally indicated and discussed in the available literature
Timokhin, Andrey
2007-01-01
In this paper we consider stationary force-free magnetosphere of an aligned rotator when plasma in the open field line region rotates differentially due to presence of a zone with the accelerating electric field in the polar cap of pulsar. We study the impact of differential rotation on the current density distribution in the magnetosphere. Using split-monopole approximation we obtain analytical expressions for physical parameters of differentially rotating magnetosphere. We find the range of admitted current density distributions under the requirement that the potential drop in the polar cap is less than the vacuum potential drop. We show that the current density distribution could deviate significantly from the ``classical'' Michel distribution and could be made almost constant over the polar cap even when the potential drop in the accelerating zone is of the order of 10 per cents of the vacuum potential drop. We argue that differential rotation of the open magnetic field lines could play an important role ...
Rapidly rotating neutron stars with a massive scalar field—structure and universal relations
Doneva, Daniela D.; Yazadjiev, Stoytcho S.
2016-11-01
We construct rapidly rotating neutron star models in scalar-tensor theories with a massive scalar field. The fact that the scalar field has nonzero mass leads to very interesting results since the allowed range of values of the coupling parameters is significantly broadened. Deviations from pure general relativity can be very large for values of the parameters that are in agreement with the observations. We found that the rapid rotation can magnify the differences several times compared to the static case. The universal relations between the normalized moment of inertia and quadrupole moment are also investigated both for the slowly and rapidly rotating cases. The results show that these relations are still EOS independent up to a large extend and the deviations from pure general relativity can be large. This places the massive scalar-tensor theories amongst the few alternative theories of gravity that can be tested via the universal I-Love-Q relations.
Rapidly rotating neutron stars with a massive scalar field - structure and universal relations
Doneva, Daniela D
2016-01-01
We construct rapidly rotating neutron star models in scalar-tensor theories with a massive scalar field. The fact that the scalar field has nonzero mass leads to very interesting results since the allowed range of values of the coupling parameters is significantly broadened. These deviations from pure general relativity can be very large for values of the parameters that are in agreement with the observations. The rapid rotation can magnify the differences several times compared to the static case. The universal relations between the normalized moment of inertia and quadrupole moment are also investigated both for the slowly and rapidly rotating cases. The results show that these relations are still EOS independent up to a large extend and the deviations from pure general relativity can be large. This places the massive scalar-tensor theories amongst the few alternative theories of gravity that can be tested via the universal $I$-Love-$Q$ relations.
The effect of rotation in the neutrino emission from a neutron star
Dvornikov, Maxim
2009-01-01
We study the interaction of neutrinos with matter of a rotating neutron star. First we examine the effect of the rotation on neutrino flavor oscillations and possible existence of bound states of low energy neutrinos in rotating matter. Then we consider the spin-down of a star during its early stages due to the neutrino emission. We find that low energy neutrinos indeed can get trapped, although the effect my not have observable consequences. Concerning flavor oscillations, only for neutrinos emitted with high angular momentum is there a small shift in the value of the electron density for the Mikheyev-Smirnov-Wolfenstein resonance. Finally, the spin-down due to neutrino emission was estimated be to near 10 % and occurs only in the first few seconds of the core formation.
Matching of analytical and numerical solutions for neutron stars of arbitrary rotation
Pappas, George, E-mail: gpappas@phys.uoa.g [Section of Astrophysics, Astronomy, and Mechanics, Department of Physics, University of Athens, Panepistimiopolis Zografos GR15783, Athens (Greece)
2009-10-01
We demonstrate the results of an attempt to match the two-soliton analytical solution with the numerically produced solutions of the Einstein field equations, that describe the spacetime exterior of rotating neutron stars, for arbitrary rotation. The matching procedure is performed by equating the first four multipole moments of the analytical solution to the multipole moments of the numerical one. We then argue that in order to check the effectiveness of the matching of the analytical with the numerical solution we should compare the metric components, the radius of the innermost stable circular orbit (R{sub ISCO}), the rotation frequency and the epicyclic frequencies {Omega}{sub {rho}}, {Omega}{sub z}. Finally we present some results of the comparison.
Gravito-inertial waves in a differentially rotating spherical shell
Mirouh, Giovanni M; Rieutord, Michel; Ballot, Jérôme
2015-01-01
We study the properties of gravito-inertial waves in a differentially rotating fluid inside a spherical shell. The fluid is modeled with the Boussinesq approximation and has a shellular steady rotation profile that stems from the combined effects of stratification, rotation, and no-slip boundary conditions. The waves properties are examined by computing paths of characteristics in the non-dissipative limit, and by solving the full dissipative eigenvalue problem using a high-resolution spectral method. Gravito-inertial waves are found to obey a mixed-type second-order operator and to be often focused around short-period attractors of characteristics or trapped in a wedge formed by turning surfaces and boundaries. We also find eigenmodes that show a weak dependence with respect to viscosity and heat diffusion just like truly regular modes. Some axisymmetric modes are found unstable and likely destabilized by baroclinic instabilities. Similarly, some non-axisymmetric modes that meet a critical layer (or corotati...
Experimental studies of magnetorotational instability in differentially rotating cylindrical flows
Brawn, Barbara; Lathrop, Daniel
2006-11-01
Given the ubiquity of rotating disks in the observable universe (e.g., galaxies, planetary rings, protoplanetary disks and accretion disks around compact objects), understanding differentially rotating, electrically conducting flows is of considerable astrophysical interest. Theoretical and numerical studies indicate that infall and accretion of orbiting material can result from a so-called magnetorotational instability (MRI) arising in such flows. Recent experimental work suggests that MRI is observable in a laboratory setting; inspired by these observations, we are building a sodium Taylor-Couette experiment, comprised of a stationary 30 cm diameter outer cylinder and a rotating 15 cm diameter inner cylinder, with liquid sodium filling the gap between the cylinders. Numerical studies indicate that MRI arises in this geometry in the presence of an external magnetic field; we will impose on the sodium flow a uniform axial magnetic field produced by Helmholtz coils at either end of the experiment. We will use ultrasound Doppler velocimetry to examine the turbulent sodium flow, and a Hall probe array to examine the induced magnetic field of the system, and will relate our observations to theoretical and numerical expectations.
Uniformly rotating neutron stars in the global and local charge neutrality cases
Belvedere, Riccardo, E-mail: riccardo.belvedere@icra.it [Dipartimento di Fisica and ICRA, Sapienza Universita' di Roma, P.le Aldo Moro 5, I-00185 Rome (Italy); ICRANet, P.zza della Repubblica 10, I-65122 Pescara (Italy); Boshkayev, Kuantay, E-mail: kuantay@icra.it [Physical–Technical Faculty, Al-Farabi Kazakh National University, Al-Farabi ave. 71, 050040 Almaty (Kazakhstan); Rueda, Jorge A., E-mail: jorge.rueda@icra.it [Dipartimento di Fisica and ICRA, Sapienza Universita' di Roma, P.le Aldo Moro 5, I-00185 Rome (Italy); ICRANet, P.zza della Repubblica 10, I-65122 Pescara (Italy); Ruffini, Remo, E-mail: ruffini@icra.it [Dipartimento di Fisica and ICRA, Sapienza Universita' di Roma, P.le Aldo Moro 5, I-00185 Rome (Italy); ICRANet, P.zza della Repubblica 10, I-65122 Pescara (Italy); ICRANet, University of Nice-Sophia Antipolis, 28 Av. de Valrose, 06103 Nice Cedex 2 (France)
2014-01-15
In our previous treatment of neutron stars, we have developed the model fulfilling global and not local charge neutrality. In order to implement such a model, we have shown the essential role by the Thomas–Fermi equations, duly generalized to the case of electromagnetic field equations in a general relativistic framework, forming a coupled system of equations that we have denominated Einstein–Maxwell–Thomas–Fermi (EMTF) equations. From the microphysical point of view, the weak interactions are accounted for by requesting the β stability of the system, and the strong interactions by using the σ–ω–ρ nuclear model, where σ, ω and ρ are the mediator massive vector mesons. Here we examine the equilibrium configurations of slowly rotating neutron stars by using the Hartle formalism in the case of the EMTF equations indicated above. We integrate these equations of equilibrium for different central densities ρ{sub c} and circular angular velocities Ω and compute the mass M, polar R{sub p} and equatorial R{sub eq} radii, angular momentum J, eccentricity ϵ, moment of inertia I, as well as quadrupole moment Q of the configurations. Both the Keplerian mass-shedding limit and the axisymmetric secular instability are used to construct the new mass–radius relation. We compute the maximum and minimum masses and rotation frequencies of neutron stars. We compare and contrast all the results for the global and local charge neutrality cases.
Pappas, George; Apostolatos, Theocharis A
2014-03-28
Recently, it was shown that slowly rotating neutron stars exhibit an interesting correlation between their moment of inertia I, their quadrupole moment Q, and their tidal deformation Love number λ (the I-Love-Q relations), independently of the equation of state of the compact object. In the present Letter a similar, more general, universality is shown to hold true for all rotating neutron stars within general relativity; the first four multipole moments of the neutron star are related in a way independent of the nuclear matter equation of state we assume. By exploiting this relation, we can describe quite accurately the geometry around a neutron star with fewer parameters, even if we don't know precisely the equation of state. Furthermore, this universal behavior displayed by neutron stars could promote them to a more promising class of candidates (next to black holes) for testing theories of gravity.
Global properties of rotating neutron stars with QCD equations of state
Gorda, Tyler
2016-01-01
We numerically investigate global properties of rotating neutron stars using the allowed band of QCD equations of state derived by Kurkela et al. This band is constrained by chiral effective theory at low densities and perturbative QCD at high densities, and is thus, in essence, a controlled constraint from first-principles physics. Previously, this band of equations of state was used to investigate non-rotating neutron stars only; in this work, we extend these results to any rotation frequency below the mass-shedding limit. We investigate mass--radius curves, allowed mass--frequency regions, radius--frequency curves for a typical 1.4-solar-mass star, and the values of the moment of inertia of the double pulsar PSR J0737-3039A, a pulsar whose moment of inertia may be constrained observationally in a few years. We present limits on observational data coming from these constraints, and identify values of observationally-relevant parameters that would further constrain the allowed region for the QCD equation of ...
Core-crust transition pressure for relativistic slowly rotating neutron stars
González-Romero, L M
2013-01-01
We study the influence of core-\\textit{crust} transition pressure changes on the general dynamical properties of neutron star configurations. First we study the matching conditions in core-\\textit{crust} transition pressure region, where phase transitions in the equation of state causes energy density jumps. Then using a surface \\textit{crust} approximation, we can construct configurations where the matter is described by the equation of state of the core of the star and the core-\\textit{crust} transition pressure. We will consider neutron stars in the slow rotation limit, considering perturbation theory up to second order in the angular velocity so that the deformation of the star is also taken into account. The junction determines the parameters of the star such as total mass, angular and quadrupolar momentum.
Rezzolla, L; Markovic, D M; Shapiro, S L; Rezzolla, Luciano; Lamb, Frederick L.; Markovic, Dragoljub; Shapiro, Stuart L.
2001-01-01
The evolution of the r-mode instability is likely to be accompanied by secular kinematic effects which will produce differential rotation with large scale drifts of fluid elements, mostly in the azimuthal direction. As first discussed by Rezzolla, Lamb and Shapiro 2000, the interaction of these secular velocity fields with a pre-existing neutron star magnetic field could result in the generation of intense and large scale toroidal fields. Following their derivation in the companion paper, we here discuss the numerical solution of the evolution equations for the magnetic field. The values of the magnetic fields obtained in this way are used to estimate the conditions under which the r-mode instability might be prevented or suppressed. We also assess the impact of the generation of large magnetic fields on the gravitational wave detectability of r-mode unstable neutron stars. Our results indicate that the signal to noise ratio in the detection of gravitational waves from the r-mode instability might be consider...
Measurement of the neutron electric dipole moment via spin rotation in a non-centrosymmetric crystal
Fedorov, V.V. [Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg (Russian Federation); Jentschel, M. [Institut Laue-Langevin, Grenoble (France); Kuznetsov, I.A.; Lapin, E.G. [Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg (Russian Federation); Lelievre-Berna, E.; Nesvizhevsky, V.; Petoukhov, A. [Institut Laue-Langevin, Grenoble (France); Semenikhin, S.Yu. [Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg (Russian Federation); Soldner, T., E-mail: soldner@ill.f [Institut Laue-Langevin, Grenoble (France); Voronin, V.V., E-mail: vvv@pnpi.spb.r [Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg (Russian Federation); Braginetz, Yu.P. [Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg (Russian Federation)
2010-10-25
We have measured the neutron electric dipole moment using spin rotation in a non-centrosymmetric crystal. Our result is d{sub n}=(2.5{+-}6.5{sup stat{+-}}5.5{sup syst}).10{sup -24}ecm. The dominating contribution to the systematic uncertainty is statistical in nature and will reduce with improved statistics. The statistical sensitivity can be increased to 2.10{sup -26}ecm in 100 days data taking with an improved setup. We state technical requirements for a systematic uncertainty at the same level.
Measurement of the neutron electric dipole moment via spin rotation in a non-centrosymmetric crystal
Fedorov, V V; Kuznetsov, I A; Lapin, E G; Lelievre-Berna, E; Nesvizhevsky, V; Petoukhov, A; Semenikhin, S Yu; Soldner, T; Voronin, V V; Braginetz, Yu P
2010-01-01
We have measured the neutron electric dipole moment using spin rotation in a non-centrosymmetric crystal. Our result is d_n = (2.5 +- 6.5(stat) +- 5.5(syst)) 10^{-24} e cm. The dominating contribution to the systematic uncertainty is statistical in nature and will reduce with improved statistics. The statistical sensitivity can be increased to 2 10^{-26} e cm in 100 days data taking with an improved setup. We state technical requirements for a systematic uncertainty at the same level.
Modeling of non-rotating neutron stars in minimal dilatonic gravity
Fiziev, Plamen
2016-01-01
The model of minimal dilatonic gravity (MDG), called also the massive Branse-Dicke model with $\\omega =0$, is an alternative model of gravitation, which uses one Branse-Dicke gravitation-dilaton field $\\Phi$ and offers a simultaneous explanation of the effects of dark energy (DE) and dark matter (DM). Here we present an extensive research of non-rotating neutron star models in MDG with four different realistic equations of state (EOS), which are in agreement with the latest observational data. The equations describing static spherically symmetric stars in MDG are solved numerically. The effects corresponding to DE and DM are clearly seen and discussed.
Gravitational waves and mass ejecta from binary neutron star mergers: Effect of the stars' rotation
Dietrich, Tim; Ujevic, Maximiliano; Tichy, Wolfgang
2016-01-01
We present new (3+1) dimensional numerical relativity simulations of the binary neutron star (BNS) mergers that take into account the NS spins. We consider different spin configurations, aligned or antialigned to the orbital angular momentum, for equal and unequal mass BNS and for two equations of state. All the simulations employ quasiequilibrium circular initial data in the constant rotational velocity approach, i.e. they are consistent with Einstein equations and in hydrodynamical equilibrium. We study the NS rotation effect on the energetics, the gravitational waves (GWs) and on the possible electromagnetic (EM) emission associated to dynamical mass ejecta. For dimensionless spin magnitudes of $\\chi\\sim0.1$ we find that spin-orbit interactions and also spin-induced-quadrupole deformations affect the late-inspiral-merger dynamics. The latter is, however, dominated by finite-size effects. Spin (tidal) effects contribute to GW phase differences up to 5 (20) radians accumulated during the last eight orbits to...
Observation of Rotational Bands in Neutron-Rich 106Mo Nucleus
许瑞清; 甘翠云; 张征; 姜卓; 肖树冬; W.C.Ma; J.Kormicki; E. F. Jones; J. D. Cole; R. Aryaeinejad; M. W. Drigert; 朱胜江; I. Y. Lee; J. O. Rasmussen; M. A. Stoyer; G. M. Ter-Akopian; A. V. Daniel; J.H.Hamilton; A.V.Ramayya; J K.Hwang; X.Q.Zhang; 李科; 杨利明; 朱凌燕
2002-01-01
The rotational bands up to a spin of 16h in the neutron-rich 106Mo nucleus have been investigated by measuring high-fold prompt γ-ray coincidence events following spontaneous fission of 252 Cf with a Gammasphere detector array. The ground-state band, the one-phonon and two-phonon γ-vibrational bands, as well as a quasi-particle band have been confirmed and expanded. The other four collective rotational bands, three proposed as twoquasi-particle bands and one proposed as a β-vibrational band, have been newly observed. The characteristics of these collective bands and the possible configurations for the quasi-particle bands are discussed.
General relativistic models for rotating magnetized neutron stars in conformally flat space-time
Pili, A. G.; Bucciantini, N.; Del Zanna, L.
2017-09-01
The extraordinary energetic activity of magnetars is usually explained in terms of dissipation of a huge internal magnetic field of the order of 1015-16 G. How such a strong magnetic field can originate during the formation of a neutron star (NS) is still subject of active research. An important role can be played by fast rotation: if magnetars are born as millisecond rotators dynamo mechanisms may efficiently amplify the magnetic field inherited from the progenitor star during the collapse. In this case, the combination of rapid rotation and strong magnetic field determine the right physical condition not only for the development of a powerful jet-driven explosion, manifesting as a gamma-ray burst, but also for a copious gravitational waves emission. Strong magnetic fields are indeed able to induce substantial quadrupolar deformations in the star. In this paper, we analyse the joint effect of rotation and magnetization on the structure of a polytropic and axisymmetric NS, within the ideal magneto-hydrodynamic regime. We will consider either purely toroidal or purely poloidal magnetic field geometries. Through the sampling of a large parameter space, we generalize previous results in literature, inferring new quantitative relations that allow for a parametrization of the induced deformation, that takes into account also the effects due to the stellar compactness and the current distribution. Finally, in the case of purely poloidal field, we also discuss how different prescription on the surface charge distribution (a gauge freedom) modify the properties of the surrounding electrosphere and its physical implications.
Characterizing the feedback of magnetic field on the differential rotation of solar-like stars
Varela, J; Brun, A S
2016-01-01
The aim of this article is to study how the differential rotation of solar-like stars is influenced by rotation rate and mass in presence of magnetic fields generated by a convective dynamo. We use the ASH code to model the convective dynamo of solar-like stars at various rotation rates and masses, hence different effective Rossby numbers. We obtained models with either prograde (solar-like) or retrograde (anti-solar-like) differential rotation. The trends of differential rotation versus stellar rotation rate obtained for simulations including the effect of the magnetic field are weaker compared with hydro simulations ($\\Delta \\Omega \\propto (\\Omega/\\Omega_{\\odot})^{0.44}$ in the MHD case and $\\Delta \\Omega \\propto (\\Omega/\\Omega_{\\odot})^{0.89}$ in the hydro case), hence showing a better agreement with the observations. Analysis of angular momentum transport revealed that the simulations with retrograde and prograde differential rotation have opposite distribution of the viscous, turbulent Reynolds stresses ...
A Differential Time-of-flight Spectrometer of Very Slow Neutrons
Pokotilovski, Yu N; Geltenbort, P; Brenner, Th
2011-01-01
A time-of-flight spectrometer of neutrons in the energy range (0.05 -- 2.5)$\\mu$eV is described. This spectrometer has been tested my measuring the total and differential neutron cross sections for a number of materials: Al, Cu, $^{6}$LiF, Si, Zr, teflon, polyethylene and liquid fluoropolymers, that are essential for experiments in the physics of ultracold neutrons.
Viscosity of neutron star matter and $r$-modes in rotating pulsars
Kolomeitsev, E E
2014-01-01
We study viscosity of the neutron star matter and $r$-mode instability in rotating neutron stars. Contributions to the shear and bulk viscosities from various processes are calculated with account of in-medium modifications of the nucleon-nucleon interaction. A softening of the pion mode and a possibility of the pion condensation are included. The nucleon pairing is incorporated. In the shear viscosity we include the lepton contribution calculated with account of the Landau damping in the photon exchange, the nucleon contribution described by the medium-modified one pion exchange, and other terms, such as the novel phonon contribution in the 1S$_0$ superfluid neutron phase, and the neutrino term in the neutrino opacity region. The nucleon shear viscosity depends on the density rather moderately and proves to be much less than the lepton term. Among the terms contributing to the bulk viscosity, the term from the medium modified Urca reactions possesses strongest density dependence because of the pion softening...
Slowly rotating neutron stars in the nonminimal derivative sector of Horndeski gravity
Cisterna, Adolfo; Ducobu, Ludovic; Rinaldi, Massimiliano
2016-01-01
This work is devoted to the construction of slowly rotating neutron stars in the context of the nonminimal derivative coupling sector of Horndeski theory. Using tabulated (realistic) equations of state (TEOS) we construct neutron stars with the maximum observed mass to date for these kind of objects, namely the mass of the pulsar PSR J0348+0432 ($2.01 \\pm 0.04 M_\\odot$ and with an orbital period of $2$ hours and $27$ minutes). Following the procedure stated in Phys.Rev. D92 (2015) 4, 044050 we show that depending on the value of the only free parameter our model possesses, $Q_p$, and depending on the sing of the coupling constant, $\\eta$, controlling the nonminimal derivative coupling, all the proposed TEOS can rich the proposed bound. We give the maximal allowed value of $Q_p$ for which we can construct the desired neutron stars for a given TEOS, when $\\eta$ is positive, showing that the mass of the stars decrease while increasing $Q_p$. On the other hand for negatives values of $\\eta$ we show that there is ...
Slowly rotating neutron stars in scalar-tensor theories with a massive scalar field
Yazadjiev, Stoytcho S; Popchev, Dimitar
2016-01-01
In the scalar-tensor theories with a massive scalar field the coupling constants, and the coupling functions in general, which are observationally allowed, can differ significantly from those in the massless case. This fact naturally implies that the scalar-tensor neutron stars with a massive scalar field can have rather different structure and properties in comparison with their counterparts in the massless case and in general relativity. In the present paper we study slowly rotating neutron stars in scalar-tensor theories with a massive gravitational scalar. Two examples of scalar-tensor theories are examined - the first example is the massive Brans-Dicke theory and the second one is a massive scalar-tensor theory indistinguishable from general relativity in the weak field limit. In the later case we study the effect of the scalar field mass on the spontaneous scalarization of neutron stars. Our numerical results show that the inclusion of a mass term for the scalar field indeed changes the picture drastica...
A unified approach to the helioseismic forward and inverse problems of differential rotation
Ritzwoller, M.H.; Lavely, E.M. (Colorado Univ., Boulder (USA) MIT, Cambridge, MA (USA))
1991-03-01
A general, degenerate perturbation theoretic treatment of the helioseismic forward and inverse problem for solar differential rotation is presented. For the forward problem, differential rotation is represented as the axisymmetric component of a general toroidal flow field using velocity spherical harmonics. This approach allows each degree of differential rotation to be estimated independently from all other degrees. In the inverse problem, the splitting caused by differential rotation is expressed as an expansion in a set of orthonormal polynomials that are intimately related to the solution of the forward problem. The combined use of vector spherical harmonics as basis functions for differential ratio and the Clebsch-Gordon coefficients to represent splitting provides a unified approach to the forward and inverse problems of differential rotation which greatly simplify inversion. 43 refs.
Spots, activity cycles, and differential rotation on cool stars
Alekseev, I. Yu.
2005-01-01
The first results are reported from a search for activity cycles in stars similar to the sun based on modelling their spotting with an algorithm developed at the Crimean Astrophysical Observatory. Of the more than thirty program stars, 10 manifested a cyclical variation in their central latitudes and total starspot area. The observed cycles have durations of 4-15 years, i.e., analogous to the 11 year Schwabe sunspot cycle. Most of the stars have a rough analog of the solar butterfly pattern, with a reduction in the average latitude of the spots as their area increases. A flip-flop effect during the epoch of the maximum average latitude is noted in a number of these objects (e.g., the analog LQ Hya of the young sun or the RS CVn-type variable V711 Tau), as well as a reduction in the photometric rotation period of a star as the spots drift toward the equator, an analog of the differential rotation effect in the sun. Unlike in the sun, the observed spot formation cycles do not correlate uniquely with other indicators of activity— chromospheric emission in the CaII HK lines (Be Cet, EK Dra, Dx Leo), H line emission (LQ Hya, VY Ari, EV Lac), or cyclical flare activity (EV Lac). In V833 Tau, BY Dra, EK Dra, and VY Ari short Schwabe cycles coexist with long cycles that are analogous to the Gleissberg solar cycle, in which the spotted area can approach half the entire area of the star.
Inelastic neutron scattering study of methyl groups rotation in some methylxanthines
Prager, M.; Pawlukojc, A.; Wischnewski, A.; Wuttke, J.
2007-12-01
The three isomeric dimethylxanthines and trimethylxanthine are studied by neutron spectroscopy up to energy transfers of 100meV at energy resolutions ranging from 0.7μeV to some meV. The loss of elastic intensity with increasing temperature can be modeled by quasielastic methyl rotation. The number of inequivalent methyl groups is in agreement with those of the room temperature crystal structures. Activation energies are obtained. In the case of theophylline, a doublet tunneling band is observed at 15.1 and 17.5μeV. In theobromine, a single tunneling band at 0.3μeV is found. Orientational disorder in caffeine leads to a 2.7μeV broad distribution of tunneling bands around the elastic line. At the same time, broad low energy phonon spectra characterize an orientational glassy state with weak methyl rotational potentials. Librational energies of the dimethylxanthines are clearly seen in the phonon densities of states. Rotational potentials can be derived which explain consistently all observables. While their symmetry in general is threefold, theophylline shows a close to sixfold potential reflecting a mirror symmetry.
Self-Similar Hot Accretion Flow onto a Rotating Neutron Star Structure and Stability
Medvedev, M V; Medvedev, Mikhail; Narayan, Ramesh
2001-01-01
We present analytical and numerical solutions which describe a hot, viscous, two-temperature accretion flow onto a rotating neutron star or any other rotating compact star with a surface. We assume Coulomb coupling between the protons and electrons, and free-free cooling from the electrons. Outside a thin boundary layer, where the accretion flow meets the star, we show that there is an extended settling region which is well-described by two self-similar solutions: (i) a two-temperature solution which is valid in an inner zone $r\\le10^{2.5}$ ($r$ is in Schwarzchild units), and (ii) a one-temperature solution at larger radii. In both zones, $\\rho\\propto r^{-2}, \\Omega\\propto r^{-3/2}, v\\propto r^0, T_p\\propto r^{-1}$; in the two-temperature zone, $T_e\\propto r^{-1/2}$. The luminosity of the settling zone arises from the rotational energy of the star as the star is braked by viscosity. Hence the luminosity and the flow parameters (density, temperature, angular velocity) are independent of $\\dot M$. The settling ...
Li, A; Qi, B; Burgio, G F
2016-01-01
We study the crust effects on fast-rotating configurations of neutron stars (NSs). For this aim, we employ four unified equations of state (EoS) for both the cores and crusts, namely BCPM, BSk20, BSk21, Shen-TM1, as well as two non-unified EoS widely used in the literature, i.e. APR and GM1 EoS. All the core EoSs satisfy the recent observational constraints of the two massive pulsars whose masses are precisely measured. We show that the NS mass-equatorial radius relations are slightly affected by the smoothness at the core-crust matching interface. However, the uncertainties in the crust EoS and the matching interface bring insignificant changes, even at maximally rotating (Keplerian) configurations. For all four unified EoS, rotations can increase the star's gravitational mass up to $18\\%-19\\%$ and the equatorial radius by $29\\%-36\\%$. For stars as heavy as 1.4 M$_{\\odot}$, the radius increase is more pronounced, reaching $41\\%-43\\%$, i.e. 5 - 6 km. Moreover, by comparing the present calculations with recent...
Global Properties of Rotating Neutron Stars with QCD Equations of State
Gorda, Tyler
2016-11-01
We numerically investigate global properties of rotating neutron stars (NSs) using the allowed band of QCD equations of state derived by Kurkela et al. This band is constrained by chiral effective theory at low densities and perturbative QCD at high densities, and is thus, in essence, a controlled constraint from first-principles physics. Previously, this band of equations of state was used to investigate non-rotating NSs only; in this work, we extend these results to any rotation frequency below the mass-shedding limit. We investigate mass–radius curves, allowed mass–frequency regions, radius–frequency curves for a typical 1.4{M}ȯ star, and the values of the moment of inertia of the double pulsar PSR J0737-3039A, a pulsar for which the moment of inertia may be constrained observationally in a few years. We present limits on observational data coming from these constraints, and identify values of observationally relevant parameters that would further constrain the allowed region for the QCD equation of state. We also discuss how much this region would be constrained by a measurement of the moment of inertia of the double pulsar PSR J0737-3039A.
Nievaart, V A; Moss, R L; Kloosterman, J L; van der Hagen, T H J J; van Dam, H; Wittig, A; Malago, M; Sauerwein, W
2006-07-01
In 2001, at the TRIGA reactor of the University of Pavia (Italy), a patient suffering from diffuse liver metastases from an adenocarcinoma of the sigmoid was successfully treated by boron neutron capture therapy (BNCT). The procedure involved boron infusion prior to hepatectomy, irradiation of the explanted liver at the thermal column of the reactor, and subsequent reimplantation. A complete response was observed. This encouraging outcome stimulated the Essen/Petten BNCT group to investigate whether such an extracorporal irradiation could be performed at the BNCT irradiation facility at the HFR Petten (The Netherlands), which has very different irradiation characteristics than the Pavia facility. A computational study has been carried out. A rotating PMMA container with a liver, surrounded by PMMA and graphite, is simulated using the Monte Carlo code MCNP. Due to the rotation and neutron moderation of the PMMA container, the initial epithermal neutron beam provides a nearly homogeneous thermal neutron field in the liver. The main conditions for treatment as reported from the Pavia experiment, i.e. a thermal neutron fluence of 4 x 10(12) +/- 20% cm(-2), can be closely met at the HFR in an acceptable time, which, depending on the defined conditions, is between 140 and 180 min.
Bejger, M; Haensel, P; Zdunik, J L; Fortin, M
2016-01-01
We explore the implications of a strong first-order phase transition region in the dense matter equation of state in the interiors of rotating neutron stars, and the resulting creation of two disjoint families of neutron-stars' configurations (the so-called high-mass twins). Rotating, axisymmetric and stationary stellar configurations are obtained numerically in the framework of general relativity, and their global parameters and stability are studied. The equation of state-induced instability divides stable neutron star configurations into two disjoint families: neutron stars (second family) and hybrid stars (third family), with an overlapping region in mass, the high-mass twin star region. These two regions are divided by an instability strip. Its existence has interesting astrophysical consequences for rotating neutron stars. We note that it provides a "natural" explanation for the rotational frequency cutoff in the observed distribution of neutron stars spins, and for the apparent lack of back-bending in ...
Angle and energy differential neutron spectrometry for the SPES BNCT facility
D' Errico, F. [Department of Mechanical, Nuclear and Production Engineering, University of Pisa (Italy); Ciolini, R. [Department of Mechanical, Nuclear and Production Engineering, University of Pisa (Italy)], E-mail: r.ciolini@ing.unipi.it; Di Fulvio, A. [Department of Mechanical, Nuclear and Production Engineering, University of Pisa (Italy); Reginatto, M. [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany); Esposito, J.; Ceballos Sanchez, C.; Colautti, P. [National Institute of Nuclear Physics (INFN), Legnaro National Laboratories, Legnaro (Italy)
2009-07-15
An accelerator-driven thermal neutron facility for boron neutron capture therapy of skin melanoma is currently under construction at the Legnaro National Laboratories, Italy. The installation relies on the production of neutrons from a thick beryllium target bombarded with 5 MeV protons. A complete set of double differential data, i.e. angle- and energy-differential neutron spectra produced by the beryllium target, is necessary for the Monte Carlo-based design of the installation. For this purpose, double differential fluence measurements are currently performed with the 'BINS' neutron spectrometer using 5 MeV protons at the 'CN' Van de Graaf accelerator. This spectrometer uses a superheated emulsion of dichlorotetrafluoroethane which is sequentially operated at 25, 30, 35, 40, 45, 50 and 55 deg. C and thus provides a series of seven sharp thresholds covering the 0.1-10 MeV neutron energy interval. Deconvolution of the data is performed with the code 'MAXED', which is based on the maximum entropy principle. The analysis of our first neutron spectrometry measurements at angles of 0 deg., 40 deg., 80 deg. and 120 deg. supports the viability of the BINS spectrometry method for the generation of the required double differential data.
Atanackovic, J; Matysiak, W; Hakmana Witharana, S S; Aslam, I; Dubeau, J; Waker, A J
2013-01-01
Neutron spectrometry and subsequent dosimetry measurements were undertaken at the McMaster Nuclear Reactor (MNR) and AECL Chalk River National Research Universal (NRU) Reactor. The instruments used were a Bonner sphere spectrometer (BSS), a cylindrical nested neutron spectrometer (NNS) and a commercially available rotational proton recoil spectrometer. The purposes of these measurements were to: (1) compare the results obtained by three different neutron measuring instruments and (2) quantify neutron fields of interest. The results showed vastly different neutron spectral shapes for the two different reactors. This is not surprising, considering the type of the reactors and the locations where the measurements were performed. MNR is a heavily shielded light water moderated reactor, while NRU is a heavy water moderated reactor. The measurements at MNR were taken at the base of the reactor pool, where a large amount of water and concrete shielding is present, while measurements at NRU were taken at the top of the reactor (TOR) plate, where there is only heavy water and steel between the reactor core and the measuring instrument. As a result, a large component of the thermal neutron fluence was measured at MNR, while a negligible amount of thermal neutrons was measured at NRU. The neutron ambient dose rates at NRU TOR were measured to be between 0.03 and 0.06 mSv h⁻¹, while at MNR, these values were between 0.07 and 2.8 mSv h⁻¹ inside the beam port and <0.2 mSv h⁻¹ between two operating beam ports. The conservative uncertainty of these values is 15 %. The conservative uncertainty of the measured integral neutron fluence is 5 %. It was also found that BSS over-responded slightly due to a non-calibrated response matrix.
Acosta Urdaneta, Gabriela Carolina; Bisello, Dario; Esposito, Juan; Mastinu, Pierfrancesco; Prete, Gianfranco; Silvestrin, Luca; Wyss, Jeffery
2016-09-01
A fast neutron (E> MeV) irradiation facility is under development at the 70 MeV SPES proton cyclotron at LNL (Legnaro, Italy) to investigate neutron-induced Single Event Effects (SEE) in microelectronic devices and systems. After an overview on neutron-induced SEE in electronics, we report on the progress in the design of ANEM (Atmospheric Neutron EMulator), a water-cooled rotating target made of Be and W to produce neutrons with an energy spectrum similar to that of neutrons produced by cosmic rays at sea-level. In ANEM, the protons from the cyclotron alternatively impinge on two circular sectors of Be and W of different areas; the effective neutron spectrum is a weighted combination of the spectra from the two sectors. In this contribution, we present the results of thermal-mechanical Finite Element Analysis (ANSYS) calculations of the performance of the ANEM prototype. The calculations at this stage indicate that ANEM can deliver fast neutrons with an atmospheric-like energy spectrum and with an integral flux Φn(1-70 MeV) ˜107 n cm-2s-1 that is 3×109 more intense than the natural one at sea-level: a very competitive flux for SEE testing.
Differential rotation in K, G, F and A stars
Balona, Luis A
2016-01-01
Rotational light modulation in Kepler photometry of K - A stars is used to estimate the absolute rotational shear. The rotation frequency spread in 2562 carefully selected stars with known rotation periods is measured using time-frequency diagrams. The variation of rotational shear as a function of effective temperature in restricted ranges of rotation period is determined. The shear increases to a maximum in F stars, but decreases somewhat in the A stars. Theoretical models reproduce the temperature variation quite well. The dependence of rotation shear on rotation rate in restricted temperature ranges is also determined. The dependence of the shear on the rotation rate is weak in K and G stars, increases rapidly for F stars and is strongest in A stars. For stars earlier than type K, a discrepancy exists between the predicted and observed variation of shear with rotation rate. There is a strong increase in the fraction of stars with zero frequency spread with increasing effective temperature. The time-freque...
Dietrich, Tim
2014-01-01
We reexamine the gravitational collapse of rotating neutron stars to black holes by new 3+1 numerical relativity simulations employing the Z4c formulation of Einstein equations, the moving puncture gauge conditions, and a conservative mesh refinement scheme or the general relativistic hydrodynamics. The end state of the collapse is compared to the vacuum spacetime resulting from the evolution of spinning puncture initial data. Using a local analysis for the metric fields, we demonstrate that the two spacetimes atually agree. Gravitational waveforms are analyzed in some detail. We connect the emission of radiation to the collapse dynamics using simplified spacetime diagrams, and discuss the similarity of the waveform structure with the one of black hole perturbation theory.
Bednarek, W
2015-01-01
We consider a simple scenario for the accretion of matter onto a neutron star in order to understand processes in the inner pulsar magnetosphere during the transition stage between different accretion modes. A simple quasi-spherical accretion process onto rotating, magnetized compact object is analyzed in order to search for the radiative signatures which could appear during transition between ejecting and accreting modes. It is argued that different accretion modes can be present in a single neutron star along different magnetic field lines for specific range of parameters characterising the pulsar (rotational period, surface magnetic field strength) and the density of surrounding medium. The radiation processes characteristic for the ejecting pulsar, i.e. curvature and synchrotron radiation produced by primary electrons in the pulsar outer gap, are expected to be modified by the presence of additional thermal radiation from the neutron star surface. We predict that during the transition from the pure ejecto...
New Suns in the Cosmos II: Differential rotation in $Kepler$ Sun-like stars
Chagas, M L Das; Costa, A D; Lopes, C E Ferreira; Sobrinho, R Silva; Paz-Chinchón, F; Leão, I C; Valio, A; de Freitas, D B; Martins, B L Canto; Lanza, A F; De Medeiros, J R
2016-01-01
The present study reports the discovery of Sun-like stars, namely main-sequence stars with $T_{\\rm eff}$, $\\log g$ and rotation periods $P_{rot}$ similar to solar values, presenting evidence of surface differential rotation. An autocorrelation of the time series was used to select stars presenting photometric signal stability from a sample of 881 stars with light curves collected by the $Kepler$ space-borne telescope, in which we have identified 17 stars with stable signals. A simple two-spot model together with a Bayesian information criterion were applied to these stars in the search for indications of differential rotation; in addition, for all 17 stars, it was possible to compute the spot rotation period $P$, the mean values of the individual spot rotation periods and their respective colatitudes, and the relative amplitude of the differential rotation.
Kővári, Zs; Strassmeier, K G; Carroll, T A; Weber, M; Kriskovics, L; Oláh, K; Vida, K; Granzer, T
2016-01-01
According to most stellar dynamo theories, differential rotation (DR) plays a crucial role for the generation of toroidal magnetic fields. Numerical models predict surface differential rotation to be anti-solar for rapidly-rotating giant stars, i.e., their surface angular velocity could increase with stellar latitude. However, surface differential rotation has been derived only for a handful of individual giant stars to date. The spotted surface of the K-giant KU Pegasi is investigated in order to detect its time evolution and quantify surface differential rotation. We present altogether 11 Doppler images from spectroscopic data collected with the robotic telescope STELLA between 2006--2011. All maps are obtained with the surface reconstruction code iMap. Differential rotation is extracted from these images by detecting systematic (latitude-dependent) spot displacements. We apply a cross-correlation technique to find the best differential rotation law. The surface of KU Peg shows cool spots at all latitudes a...
I-Love-Q, Spontaneously: Slowly Rotating Neutron Stars in Scalar-Tensor Theories
Pani, Paolo
2014-01-01
We construct models of slowly rotating, perfect-fluid neutron stars by extending the classical Hartle-Thorne formalism to generic scalar-tensor theories of gravity. Working at second order in the dimensionless angular momentum, we compute the mass $M$, radius $R$, scalar charge $q$, moment of inertia $I$ and spin-induced quadrupole moment $Q$, as well as the tidal and rotational Love numbers. Our formalism applies to generic scalar-tensor theories, but we focus in particular on theories that allow for spontaneous scalarization. It was recently discovered that the moment of inertia, quadrupole moment and Love numbers are connected by approximately universal (i.e., equation-of-state independent) "I-Love-Q" relations. We find that similar relations hold also for spontaneously scalarized stars. More interestingly, the I-Love-Q relations in scalar-tensor theories coincide with the general relativistic ones within less than a few percent, even for spontaneously scalarized stars with the largest couplings allowed by...
The effect of magnetic fields on the r-modes of slowly rotating relativistic neutron stars
Chirenti, Cecilia
2013-01-01
We study here the r-modes in the Cowling approximation of a simple slowly rotating and magnetized neutron star, where we neglect any deformations of the spherical symmetry of the star. We were able to quantify the influence of the magnetic field in both the oscillation frequency $\\sigma_r$ of the r-modes and the growth time $t_{GW}$ of the gravitational radiation emission. We conclude that magnetic fields of the order $10^{15}$ G at the center of the star are necessary to produce any changes. Our results for $\\sigma_r$ show a decrease of up to $\\sim$ 5% in the frequency with increasing magnetic field, with a $B^2$ dependence for rotation rates $\\Omega/\\Omega_K \\gtrsim 0.07$ and $B^4$ for $\\Omega/\\Omega_K \\lesssim 0.07$. For $t_{GW}$, we find that it is approximately 30% smaller than previous Newtonian results for non-magnetized stars, which would mean a faster growth of the emission of gravitational radiation. The effect of the magnetic field in $t_{GW}$ causes a non-monotonic effect, that first slightly incr...
Spread of Matter over a Neutron-Star Surface During Disk Accretion: Deceleration of Rapid Rotation
Sunyaev, R A
2011-01-01
The problem of disk accretion onto the surface of a neutron star with a weak magnetic field at a luminosity exceeding several percent of Eddington is reduced to the problem of the braking of a hypersonic flow with a velocity that is 0.4-0.5 of the speed of light above the base of the spreading layer -- a dense atmosphere made up of previously fallen matter. We show that turbulent braking in the Prandtl-Karman model with universally accepted coefficients for terrestrial conditions and laboratory experiments and a ladder of interacting gravity waves in a stratified quasi-exponential atmosphere at standard Richardson numbers lead to a spin-up of the massive zone that extends to the ocean made up of a plasma with degenerate electrons. Turbulent braking in the ocean at the boundary with the outer solid crust reduces the rotation velocity to the solid-body rotation velocity of the star. This situation should lead to strong heating of deep atmospheric layers and to the switch-off of the explosive helium burning mech...
Differential rotation on both components of the pre main-sequence binary system HD 155555
Dunstone, N. J.; Hussain, G A J; Cameron, A. Collier; Marsden, S. C.; Jardine, M.; Barnes, J. R.; Vlex, J. C. Ramirez; Donati, J.-F.
2008-01-01
We present the first measurements of surface differential rotation on a pre-main sequence binary system. Using intensity (Stokes I) and circularly polarised (Stokes V) timeseries spectra, taken over eleven nights at the Anglo-Australian Telescope (AAT), we incorporate a solar-like differential rotation law into the surface imaging process. We find that both components of the young, 18 Myr, HD 155555 (V824 Ara, G5IV + K0IV) binary system show significant differential rotation. The equator-pole...
Differential rotation on both components of the pre main-sequence binary system HD 155555
Dunstone, N. J.; Hussain, G. A. J.; Cameron, A. Collier; Marsden, S. C.; Jardine, M.; Barnes, J.R.; Vlex, J. C. Ramirez; Donati, J. -F.
2008-01-01
We present the first measurements of surface differential rotation on a pre-main sequence binary system. Using intensity (Stokes I) and circularly polarised (Stokes V) timeseries spectra, taken over eleven nights at the Anglo-Australian Telescope (AAT), we incorporate a solar-like differential rotation law into the surface imaging process. We find that both components of the young, 18 Myr, HD 155555 (V824 Ara, G5IV + K0IV) binary system show significant differential rotation. The equator-pole...
Thermal Neutron Point Source Imaging using a Rotating Modulation Collimator (RMC)
2010-03-01
2.5 Neutron Attenuation Neutron attenuation is an important physical aspect that influences the design of the RMC components. The narrow- beam ...29 3.3 Mask Designs .......................................................................................................36 3.4 Neutron ...detection efficiency is very high for thermal and epithermal neutrons but begins to approach zero at 1 MeV and above. For this reason the detector is
Smith, D.L.
1979-11-01
Effects of finite resolution in differential neutron measurements are examined. General procedures for deriving the experimental resolution functions from a knowledge of the experimental parameters are presented. Problems encountered in the comparison of different data sets, when the measured cross section is known to fluctuate with energy, are discussed. The objective is to encourage closer attention to the matter of resolution by experimenters, evaluators and users of neutron nuclear data.
Faraday resonance in dynamical bar instability of differentially rotating stars
Saijo, Motoyuki
2008-01-01
We investigate the nonlinear behaviour of the dynamically unstable rotating star for the bar mode by three-dimensional hydrodynamics in Newtonian gravity. We find that an oscillation along the rotation axis is induced throughout the growth of the unstable bar mode, and that its characteristic frequency is twice as that of the bar mode, which oscillates mainly along the equatorial plane. A possibility to observe Faraday resonance in gravitational waves is demonstrated and discussed.
Characterizing the feedback of magnetic field on the differential rotation of solar-like stars
Varela, J.; Strugarek, A.; Brun, A. S.
2016-10-01
The aim of this article is to study how the differential rotation of solar-like stars is influenced by rotation rate and mass in presence of magnetic fields generated by a convective dynamo. We use the ASH code to model the convective dynamo of solar-like stars at various rotation rates and masses, hence different effective Rossby numbers. We obtained models with either prograde (solar-like) or retrograde (anti-solar-like) differential rotation. The trends of differential rotation versus stellar rotation rate obtained for simulations including the effect of the magnetic field are weaker compared with hydro simulations (ΔΩ ∝(Ω /Ω⊙) 0.44 in the MHD case and ΔΩ ∝(Ω /Ω⊙) 0.89 in the hydro case), hence showing a better agreement with the observations. Analysis of angular momentum transport revealed that the simulations with retrograde and prograde differential rotation have opposite distribution of the viscous, turbulent Reynolds stresses and meridional circulation contributions. The thermal wind balance is achieved in the prograde cases. However, in retrograde cases Reynolds stresses are dominant for high latitudes and near the top of the convective layer. Baroclinic effects are stronger for faster rotating models.
无
2010-01-01
The instability of forced flow in a rotating cylindrical pool with a differentially rotating disk on the free surface is investigated through a series of unsteady three-dimensional numerical simulations.The results show that the basic flow state of this system is axisymmetric and steady,but has rich structures at the meridian plane.However,when the rotation Reynolds number exceeds a critical value,the flow will undergo a transition to three-dimensional oscillatory flow,characterized by the velocity fluctuation waves traveling in the azimuthal direction.The main characteristics of the flow patterns are presented,including the propagating direction,velocity,amplitude and wave number,which depend on the rotation rates and directions of the disk and the cylindrical pool,and the critical conditions for the onset of oscillatory flow are also determined.For the case of disk-only rotation,the centrifugal instability is responsible for the flow transition,and when the disk isoand counter-rotates with the cylindrical pool,the mechanisms for the transition are elliptic and of circular shear instabilities,respectively.
Differential rotation of solar background magnetic fields during the 20th solar cycle
Hejna, L.
1983-11-01
The study demonstrates the possibility of using the autocorrelation analysis for studies of the differential rotation of the solar background magnetic fields. For that purpose the time series obtained from the synoptic Hα charts published by McIntosh were subjected to an analysis. On their basis the distribution of the synodic angular velocity in time - during the cycle - and in the heliographic latitude - for |φ| smaller than 60° - was determined. After that the parameters A and B from the relation for differential rotation ω = A+B sin2φ could be determined, both for the entire cycle and for individual Carrington rotations.
Pétri, J
2014-01-01
Pulsars are believed to loose their rotational kinetic energy primarily by a large amplitude low frequency electromagnetic wave which is eventually converted into particle creation, acceleration and followed by a broad band radiation spectrum. To date, there exist no detailed calculation of the exact spin-down luminosity with respect to the neutron star magnetic moment and spin frequency, including general-relativistic effects. Estimates are usually given according to the flat spacetime magnetodipole formula. The present paper pursue our effort to look for accurate solutions of the general-relativistic electromagnetic field around a slowly rotating magnetized neutron star. In a previous work, we already found approximate stationary solutions to this problem. Here we address again this problem but using a more general approach. We indeed solve the full set of time-dependent Maxwell equations in a curved vacuum space-time following the 3+1 formalism. The numerical code is based on our pseudo-spectral method exp...
Role of neutrons in the coexistence of magnetic and antimagnetic rotation bands in 107Cd
Choudhury, Deepika; Palit, R.; Singh, P.; Sethi, J.; Saha, S.; Biswas, S.; Jain, H. C.; Nanal, V.; Pillay, R. G.; Donthi, R.; Jadhav, S. K.; Naidu, B. S.; Maheshwari, B.; Jain, A. K.; Pancholi, S. C.; Singh, R. P.; Mukhopadhyay, S.; Biswas, D. C.; Danu, L. S.; Tandel, S. K.; Chaturvedi, L.; Rojeeta Devi, K.; Singh, Sukhjeet
2015-01-01
Negative parity high-spin states of 107Cd have been investigated using the reaction 94Zr(18O ,5n), from the γ -ray coincidence events recorded by the Indian National Gamma Array. A magnetic dipole (M 1 ) band structure was established for the first time in this nucleus decaying to the low-spin states via several paths. Lifetimes of five in-band levels in this band have been measured using the Doppler shift attenuation method. The experimentally deduced B (M 1 ) values are found to decrease with increasing spin. The experimental observations, interpreted by the tilted axis cranking calculations, suggest that the M 1 band is developed from the shears mechanism based on the 5qp configuration π (g9/2 -2) ⊗ν (h11 /2g7/2 2) , which is then crossed by another 5qp configuration π (g9/2 -2) ⊗ν (h11/2 3) . The semiclassical model of the shears mechanism also reasonably reproduces the decreasing trend of the observed B (M 1 ) values as a function of spin, supporting the above interpretation. The present work highlights the unique coexistence of both magnetic and antimagnetic (observed by us earlier) rotation bands in one nucleus arising from the same proton configuration, but different neutron configurations.
Caleo, Andrea
2016-01-01
Barotropic rotation and radiative equilibrium are mutually incompatible in stars. The issue is often addressed by allowing for a meridional circulation, but this is not devoid of theoretical complications. Models of rotation in the Sun which maintain strict radiative equilibrium, making use of the observation that the Sun is not in a state of barotropic rotation, have recently been suggested. To investigate the dynamical behaviour of these solutions, we study the local stability of stratified, weakly magnetized, differentially rotating fluids to non-axisymmetric perturbations. Finite heat conductivity, kinematic viscosity, and resistivity are present. The evolution of local embedded perturbations is governed by a set of coupled, ordinary differential equations with time-dependent coefficients. Two baroclinic models of rotation for the upper radiative zone and tachocline are studied: (i) an interpolation based on helioseismology data, (ii) a theoretical solution directly compatible with radiative equilibrium. ...
Rotational Bands of Some Neutron Deficient Odd-A Pt Isotopes in Particle-Triaxial-Rotor Model
WU Xian-Ming; LIU Yu-Xin
2008-01-01
Theoretical calculations are performed for neutron deficient Pt isotopes 177pt and 175,173,171pt in the particle-triaxial-rotor model with variable moment of inertia. The obtained energy spectra agree with experimental data quite well. The calculated results indicate that all these nuclei are in triaxial rotation with 177pt being in prolate and 175,173,171pt in oblate. Several levels are predicted for the 13/2+ band in 169pt.
Measuring stellar differential rotation with high-precision space-borne photometry
Lanza, A F; De Medeiros, J R
2014-01-01
We introduce a method of measuring a lower limit to the amplitude of surface differential rotation from high-precision, evenly sampled photometric time series. It is applied to main-sequence late-type stars whose optical flux modulation is dominated by starspots. An autocorrelation of the time series was used to select stars that allow an accurate determination of starspot rotation periods. A simple two-spot model was applied together with a Bayesian information criterion to preliminarily select intervals of the time series showing evidence of differential rotation with starspots of almost constant area. Finally, the significance of the differential rotation detection and a measurement of its amplitude and uncertainty were obtained by an a posteriori Bayesian analysis based on a Monte Carlo Markov Chain approach. We applied our method to the Sun and eight other stars for which previous spot modelling had been performed to compare our results with previous ones. We find that autocorrelation is a simple method ...
Ibaraki, Masanobu; Matsuyama, Shigeo; Soda, Daisuke; Baba, Mamoru; Hirakawa, Naohiro [Tohoku Univ., Sendai (Japan). Faculty of Engineering
1997-03-01
Double-differential neutron emission cross sections (DDXs) of Nb and Bi have been measured for 11.5MeV neutrons using the {sup 15N}(d,n){sup 16}O quasi-monoenergetic neutron source at Tohoku University 4.5MV Dynamitron facility. For En`>6MeV, DDXs were measured by the conventional TOF method (single-TOF:S-TOF). For En`<6MeV, where the S-TOF spectra were distorted by the background neutrons, we adopted a double-TOF method (D-TOF). By applying D-TOF method, we obtained DDXs down to 1MeV. (author)
Ibaraki, Masanobu; Baba, Mamoru; Matsuyama, Shigeo; Sanami, Toshiya; Win, T.; Miura, Takako; Hirakawa, Naohiro [Tohoku Univ., Sendai (Japan). Faculty of Engineering
1997-03-01
Double-differential neutron emission cross sections of {sup 6}Li and {sup 7}Li were measured for 18 MeV neutrons at Tohoku University 4.5 MV Dynamitron facility. Neutron emission spectra were obtained down to 1 MeV at 13 angles with energy resolution good enough to separate discrete levels. A care was taken to eliminate the sample-dependent background due to parasitic neutrons. Experimental results were in fair agreement with the JENDL-3.2 data and a simple model considering a three-body breakup process and discrete level excitations. (author)
Pashitskii, E. A.
2017-07-01
On the basis of a two-component (two-fluid) hydrodynamic model, it is shown that the probable phenomenon of solar core rotation with a velocity higher than the average velocity of global rotation of the Sun, discovered by the SOHO mission, can be related to fast solid-body rotation of the light hydrogen component of the solar plasma, which is caused by thermonuclear fusion of hydrogen into helium inside the hot dense solar core. Thermonuclear fusion of four protons into a helium nucleus (α-particle) creates a large free specific volume per unit particle due to the large difference between the densities of the solar plasma and nuclear matter. As a result, an efficient volumetric sink of one of the components of the solar substance—hydrogen—forms inside the solar core. Therefore, a steady-state radial proton flux converging to the center should exist inside the Sun, which maintains a constant concentration of hydrogen as it burns out in the solar core. It is demonstrated that such a converging flux of hydrogen plasma with the radial velocity v r ( r) = -β r creates a convective, v r ∂ v φ/∂ r, and a local Coriolis, v r v φ/ r,φ nonlinear hydrodynamic forces in the solar plasma, rotating with the azimuthal velocity v φ. In the absence of dissipation, these forces should cause an exponential growth of the solid-body rotation velocity of the hydrogen component inside the solar core. However, friction between the hydrogen and helium components of the solar plasma due to Coulomb collisions of protons with α-particles results in a steady-state regime of rotation of the hydrogen component in the solar core with an angular velocity substantially exceeding the global rotational velocity of the Sun. It is suggested that the observed differential (liquid-like) rotation of the visible surface of the Sun (photosphere) with the maximum angular velocity at the equator is caused by sold-body rotation of the solar plasma in the radiation zone and strong turbulence in
Measuring differential rotation of the K-giant $\\zeta$\\,And
K\\Hovári, Zs; Kriskovics, L; Vida, K; Donati, J -F; Coroller, H Le; Pedretti, J D Monnier E; Petit, P
2012-01-01
We investigate the temporal spot evolution of the K-giant component in the RS CVn-type binary system $\\zeta$\\,Andromedae to establish its surface differential rotation. Doppler imaging is used to study three slightly overlapping spectroscopic datasets, obtained independently at three different observing sites. Each dataset covers one full stellar rotation with good phase coverage, and in total, results in a continuous coverage of almost three stellar rotations ($P_{\\rm rot}=$17.8\\,d). Therefore, these data are well suited for reconstructing surface temperature maps and studying temporal evolution in spot configurations. Surface differential rotation is measured by the means of cross-correlation of all the possible image pairs. The individual Doppler reconstructions well agree in the revealed spot pattern, recovering numerous low latitude spots with temperature contrasts of up to $\\approx$1000\\,K with respect to the unspotted photosphere, and also an asymmetric polar cap which is diminishing with time. Our det...
Magnetic Effects and Differential Rotation Near Transition from Solar to Anti-Solar Profiles
Simitev, Radostin D; Busse, Friedrich H
2015-01-01
We present a set of convective dynamo simulations in rotating spherical fluid shells based on an anelastic approximation of compressible fluids. The simulations extend into a "buoyancy-dominated" regime where the buoyancy forcing is dominant while the Coriolis force is no longer balanced by pressure gradients and strong anti-solar differential rotation develops as a result. Dynamos in this regime are strongly dominated by dipole components but at the same time their magnetic energies are relatively small compared to the corresponding kinetic energies of the flow. Despite being relatively weak the self-sustained magnetic fields are able to reverse the direction of differential rotation to solar-like. We find that the convection in the buoyancy-dominated regime is significantly stronger near the pole than in the equatorial region, leading to non-oscillatory dipolar dynamo solutions. The results are obtained with a new simulation code for modelling of convection and MHD dynamo generation in rotating spherical sh...
Differential rotation of stretched and twisted thick magnetic flux tube dynamos in Riemannian spaces
de Andrade, Garcia
2007-01-01
The topological mapping between a torus of big radius and a sphere is applied to the Riemannian geometry of a stretched and twisted very thick magnetic flux tube, to obtain spherical dynamos solving the magnetohydrodynamics (MHD) self-induction equation for the magnetic flux tubes undergoing differential (non-uniform) rotation along the tube magnetic axis. Constraints on the shear is also computed. It is shown that when the hypothesis of the convective cyclonic dynamo is used the rotation is ...
Tidal instability in a rotating and differentially heated ellipsoidal shell
Cébron, David; Bars, Michael Le; 10.1111/j.1365-246X.2010.04712.x
2010-01-01
The stability of a rotating flow in a triaxial ellipsoidal shell with an imposed temperature difference between inner and outer boundaries is studied numerically. We demonstrate that (i) a stable temperature field encourages the tidal instability, (ii) the tidal instability can grow on a convective flow, which confirms its relevance to geo- and astrophysical contexts and (iii) its growth rate decreases when the intensity of convection increases. Simple scaling laws characterizing the evolution of the heat flux based on a competition between viscous and thermal boundary layers are derived analytically and verified numerically. Our results confirm that thermal and tidal effects have to be simultaneously taken into account when studying geophysical and astrophysical flows.
Linear Instabilities Driven by Differential Rotation in Very Weakly Magnetized Plasmas
Quataert, Eliot; Spitkovsky, Anatoly
2014-01-01
We study the linear stability of weakly magnetized differentially rotating plasmas in both collisionless kinetic theory and Braginskii's theory of collisional, magnetized plasmas. We focus on the very weakly magnetized limit that is important for understanding how astrophysical magnetic fields originate and are amplified at high redshift. We show that the single instability of fluid theory - the magnetorotational instability mediated by magnetic tension - is replaced by two distinct instabilities, one associated with ions and one with electrons. Each of these has a different way of tapping into the free energy of differential rotation. The ion instability is driven by viscous transport of momentum across magnetic field lines due to a finite ion cyclotron frequency (gyroviscosity); the fastest growing modes have wavelengths significantly longer than MHD and Hall MHD predictions. The electron instability is a whistler mode driven unstable by the temperature anisotropy generated by differential rotation; the gro...
Stevens, Adam R H
2013-01-01
Finite-source effects of gravitationally microlensed stars have been well discussed in the literature, but the role that stellar rotation plays has been neglected. A differential magnification map applied to a differentially Doppler-shifted surface alters the profiles of absorption lines, compromising their ordinarily symmetric nature. Herein, we assess the degree to which this finite-source effect of differential limb magnification (DLM), in combination with stellar rotation, alters spectroscopically derived stellar properties. To achieve this, we simulated a grid of high-magnification microlensing events using synthetic spectra. Our analysis shows that rotation of the source generates differences in the measured equivalent widths of absorption lines supplementary to DLM alone, but only of the order of a few percent. Using the wings of H alpha from the same simulated data, we confirmed the result of Johnson et al. (2010) that DLM alters measurements of effective temperature by < 100 K for dwarf stars, whi...
Masuda, Akihiko; Matsumoto, Tetsuro; Iwamoto, Yosuke; Hagiwara, Masayuki; Satoh, Daiki; Sato, Tatsuhiko; Iwase, Hiroshi; Yashima, Hiroshi; Nakane, Yoshihiro; Nishiyama, Jun; Shima, Tatsushi; Tamii, Atsushi; Hatanaka, Kichiji; Harano, Hideki; Nakamura, Takashi
2017-03-01
Quasi-monoenergetic high-energy neutron fields induced by 7Li(p,n) reactions are used for the response evaluation of neutron-sensitive devices. The quasi-monoenergetic high-energy field consists of high-energy monoenergetic peak neutrons and unwanted continuum neutrons down to the low-energy region. A two-angle differential method has been developed to compensate for the effect of the continuum neutrons in the response measurements. In this study, the two-angle differential method was demonstrated for Bonner sphere detectors, which are typical examples of moderator-based neutron-sensitive detectors, to investigate the method's applicability and its dependence on detector characteristics. Experiments were performed under 96-387 MeV quasi-monoenergetic high-energy neutron fields at the Research Center for Nuclear Physics (RCNP), Osaka University. The measurement results for large high-density polyethylene (HDPE) sphere detectors agreed well with Monte Carlo calculations, which verified the adequacy of the two-angle differential method. By contrast, discrepancies were observed in the results for small HDPE sphere detectors and metal-induced sphere detectors. The former indicated that detectors that are particularly sensitive to low-energy neutrons may be affected by penetrating neutrons owing to the geometrical features of the RCNP facility. The latter discrepancy could be consistently explained by a problem in the evaluated cross-section data for the metals used in the calculation. Through those discussions, the adequacy of the two-angle differential method was experimentally verified, and practical suggestions were made pertaining to this method.
Surface differential rotation of IL Hya from time-series Doppler images
Kővári, Zsolt; Oláh, Katalin; Vida, Krisztián; Bartus, János; Strassmeier, Klaus G; Weber, Michael
2013-01-01
We present a time-series Doppler imaging study of the K-subgiant component in the RS CVn-type binary system IL Hya (P orb=12.905 d). From re-processing the unique long-term spectroscopic dataset of 70 days taken in 1996/97, we perform a thorough cross-correlation analysis to derive surface differential rotation. As a result we get solar-type differential rotation with a shear value alpha of 0.05, in agreement with preliminary suggestions from previous attempts. A possible surface pattern of meridional circulation is also detected.
Initial data for black hole-neutron star binaries, with rotating stars
Tacik, Nick; Pfeiffer, Harald P; Muhlberger, Curran; Kidder, Lawrence E; Scheel, Mark A; Szilagyi, Bela
2016-01-01
The coalescence of a neutron star with a black hole is a primary science target of ground-based gravitational wave detectors. Constraining or measuring the neutron star spin directly from gravitational wave observations requires knowledge of the dependence of the emission properties of these systems on the neutron star spin. This paper lays foundations for this task, by developing a numerical method to construct initial data for black hole--neutron star binaries with arbitrary spin on the neutron star. We demonstrate the robustness of the code by constructing initial-data sets in large regions of the parameter space. In addition to varying the neutron star spin-magnitude and spin-direction, we also explore neutron star compactness, mass-ratio, black hole spin, and black hole spin-direction. Specifically, we are able to construct initial data sets with neutron stars spinning near centrifugal break-up, and with black hole spins as large as $S_{\\rm BH}/M_{\\rm BH}^2=0.99$.
Initial data for black hole–neutron star binaries, with rotating stars
Tacik, Nick; Foucart, Francois; Pfeiffer, Harald P.; Muhlberger, Curran; Kidder, Lawrence E.; Scheel, Mark A.; Szilágyi, Béla
2016-11-01
The coalescence of a neutron star with a black hole is a primary science target of ground-based gravitational wave detectors. Constraining or measuring the neutron star spin directly from gravitational wave observations requires knowledge of the dependence of the emission properties of these systems on the neutron star spin. This paper lays foundations for this task, by developing a numerical method to construct initial data for black hole–neutron star binaries with arbitrary spin on the neutron star. We demonstrate the robustness of the code by constructing initial-data sets in large regions of the parameter space. In addition to varying the neutron star spin-magnitude and spin-direction, we also explore neutron star compactness, mass-ratio, black hole spin, and black hole spin-direction. Specifically, we are able to construct initial data sets with neutron stars spinning near centrifugal break-up, and with black hole spins as large as {S}{BH}/{M}{BH}2=0.99.
Kelsall, N. S.; Wadsworth, R.; Wilson, A. N.; Fallon, P.; Macchiavelli, A. O.; Clark, R. M.; Sarantites, D. G.; Seweryniak, D.; Svensson, C. E.; Vincent, S. M. (and others)
2001-08-01
High-spin states in the N=Z nucleus {sup 72}Kr were populated using the {sup 40}Ca({sup 36}Ar,2p2n) reaction at a beam energy of 145 MeV. The yrast band has been observed up to a tentative spin of 20{Dirac_h}. Nonyrast rotational structures have also been observed for the first time. The alignment of g{sub 9/2} protons and neutrons in the yrast band is observed to be significantly delayed relative to the heavier even-even Kr isotopes. Exact deformed cranked shell model calculations suggest that this could be due to the combined effect of isovector (T=1) and isoscalar (T=0) neutron-proton pairing correlations.
On the Cause of Solar Differential Rotations in the Solar Interior and Near the Solar Surface
Lyu, L.
2012-12-01
A theoretical model is proposed to explain the cause of solar differential rotations observed in the solar interior and near the solar surface. We propose that the latitudinal differential rotation in the solar convection zone is a manifestation of an easterly wind in the mid latitude. The speed of the easterly wind is controlled by the magnitude of the poleward temperature gradient in the lower part of the solar convection zone. The poleward temperature gradient depends on the orientation and strength of the magnetic fields at different latitudes in the solar convection zone. The north-south asymmetry in the wind speed can lead to north-south asymmetry in the evolution of the solar cycle. The easterly wind is known to be unstable for a west-to-east rotating star or planet. Based on the observed differential rotations in the solar convection zone, we can estimate the easterly wind speed at about 60-degree latitude and determine the azimuthal wave number of the unstable wave modes along the zonal flow. The lowest azimuthal wave number is about m=7~8. This result is consistent with the average width of the elephant-trunk coronal hole shown in the solar X-ray images. The nonlinear evolution of the unstable easterly wind can lead to transpolar migration of coronal holes and can change the poloidal magnetic field in a very efficient way. In the study of radial differential rotation near the solar surface, we propose that the radial differential rotation depends on the radial temperature gradient. The radial temperature gradient depends on the magnetic field structure above the solar surface. The non-uniform magnetic field distribution above the solar surface can lead to non-uniform radial convections and formation of magnetic flux rope at different spatial scales. The possible cause of continuous formation and eruption of prominences near an active region will also be discussed.
Gardner, A. B.; Howard, S.; Waddington, T. C.; Richardson, R. M.; Tomkinson, J.
1981-05-01
Incoherent quasi-elastic neutron scattering has been used to study the reorientational motions of the cyclopentadienyl rings in ferrocene, nickelocene and ruthenocene. The results for ferrocene show that the activation energy for ring rotation drops above the 164 K phase transition to 4.4 ± 0.5 kJ mol-1 (which is approximately half its low temperature value) but the rings still appear to jump between only five orientations on the observable time scale. At room temperature, the rings in nickelocene appear to behave the same as in ferrocene but in ruthenocene they reorientate much less frequently and resemble those in ferrocene below 164 K.
Gonzalez-Romero, L M; Blazquez-Salcedo, J L, E-mail: mgromero@fis.ucm.es, E-mail: joseluis.blazquez@fis.ucm.es [Depto. Fisica Teorica II, Facultad de Ciencias Fisicas, Universidad Complutense de Madrid, 28040-Madrid (Spain)
2011-09-22
Introducing a surface layer of matter on the edge of a neutron star in slow rigid rotation, we analyze, from an intrinsic point of view, the junction conditions that must be satisfied between the interior and exterior solutions of the Einstein equations. In our model the core-crust transition pressure arise as an essential parameter in the description of a configuration. As an application of this formalism, we describe giant glitches of the Vela pulsar as a result of variations in the transition pressure, finding that these small changes are compatible with the expected temperature variations of the inner crust during glitch time
The Effects of Differential Rotation on the Magnetic Structure of the Solar Corona: MHD Simulations
Lionello, Roberto; Riley, Pete; Linker, Jon A.; Mikic, Zoran
2004-01-01
Coronal holes are magnetically open regions from which the solar wind streams. Magnetic reconnection has been invoked to reconcile the apparently rigid rotation of coronal holes with the differential rotation of magnetic flux in the photosphere. This mechanism might also be relevant to the formation of the slow solar wind, the properties of which seem to indicate an origin from the opening of closed magnetic field lines. We have developed a global MHD model to study the effect of differential rotation on the coronal magnetic field. Starting from a magnetic flux distribution similar to that of Wang et al., which consists of a bipolar magnetic region added to a background dipole field, we applied differential rotation over a period of 5 solar rotations. The evolution of the magnetic field and of the boundaries of coronal holes are in substantial agreement with the findings of Wang et al.. We identified examples of interchange reconnection and other changes of topology of the magnetic field. Possible consequences for the origin of the slow solar wind are also discussed.
Spectral characterization and differential rotation study of active CoRoT stars
Nagel, E.; Czesla, S.; Schmitt, J. H. M. M.
2016-05-01
The CoRoT space telescope observed nearly 160 000 light curves. Among the most outstanding is that of the young, active planet host star CoRoT-2A. In addition to deep planetary transits, the light curve of CoRoT-2A shows strong rotational variability and a superimposed beating pattern. To study the stars that produce such an intriguing pattern of photometric variability, we identified a sample of eight stars with rotation periods between 0.8 and 11 days and photometric variability amplitudes of up to 7.5%, showing a similar CoRoT light curve. We also obtained high-resolution follow-up spectroscopy with TNG/SARG and carried out a spectral analysis with SME and MOOG. We find that the color dependence of the light curves is consistent with rotational modulation due to starspots and that latitudinal differential rotation provides a viable explanation for the light curves, although starspot evolution is also expected to play an important role. Our MOOG and SME spectral analyses provide consistent results, showing that the targets are dwarf stars with spectral types between F and mid-K. Detectable Li i absorption in four of the targets confirms a low age of 100-400 Myr also deduced from gyrochronology. Our study indicates that the photometric beating phenomenon is likely attributable to differential rotation in fast-rotating stars with outer convection zones.
Evidence of differential rotation inside Saturn from waves of its rings
El Moutamid, Maryame; Hedman, Matthew M.; Nicholson, Philip D.; Gierasch, Peter J.; Burns, Joseph A.
2016-10-01
Saturn's average interior rotation rate has been estimated based on various analyses of its shape (Anderson and Schubert, 2007; Read et al., 2009; Helled et al., 2015), but we still have no clear information on its exact value and the degree of differential rotation versus depth.However, Hedman et al., (2009), Hedman and Nicholson (2014) and El Moutamid et al., (2016) have identified several structures in the main rings of Saturn which appear to be related to the planet's rotation rate.These structures (waves and perturbed edges) appear to be generated by so-called Tesseral Resonances, which are associated with gravity anomalies that rotate with Saturn's interior, rather than being driven by a satellite. Their locations are given by the usual formula for inner or outer Lindblad resonances.We have searched for additional wave-like signatures in stellar occultation data for the main rings which are related to the rotation period of Saturn and have identified several signatures consistent with other differential rotation in Saturn's interior. Our study of the behavior of the A, B and C rings uses images and occultation data obtained by the Cassini spacecraft over a period of 10 years from 2006 to 2015.
Kovács, Z.; Harko, T.
2011-11-01
We present a full general relativistic numerical code for estimating the energy-momentum deposition rate (EMDR) from neutrino pair annihilation (?). The source of the neutrinos is assumed to be a neutrino-cooled accretion disc around neutron and quark stars. We calculate the neutrino trajectories by using a ray-tracing algorithm with the general relativistic Hamilton's equations for neutrinos and derive the spatial distribution of the EMDR due to the annihilations of neutrinos and antineutrinos around rotating neutron and quark stars. We obtain the EMDR for several classes of rotating neutron stars, described by different equations of state of the neutron matter, and for quark stars, described by the Massachusetts Institute of Technology (MIT) bag model equation of state and in the colour-flavour-locked (CFL) phase. The distribution of the total annihilation rate of the neutrino-antineutrino pairs around rotating neutron and quark stars is studied for isothermal discs and accretion discs in thermodynamical equilibrium. We demonstrate both the differences in the equations of state for neutron and quark matter and rotation with the general relativistic effects significantly modify the EMDR of the electrons and positrons generated by the neutrino-antineutrino pair annihilation around compact stellar objects, as measured at infinity.
Unstable normal modes of low T/W dynamical instabilities in differentially rotating stars
Saijo, Motoyuki
2016-01-01
We investigate the nature of low T/W dynamical instabilities in differentially rotating stars by means of linear perturbation. Here, T and W represent rotational kinetic energy and the gravitational binding energy of the star. This is the first attempt to investigate low T/W dynamical instabilities as a complete set of the eigenvalue problem. Our equilibrium configuration has "constant" specific angular momentum distribution, which potentially contains a singular solution in the perturbed enthalpy at corotation radius in linear perturbation. We find the unstable normal modes of differentially rotating stars by solving the eigenvalue problem along the equatorial plane of the star, imposing the regularity condition on the center and the vanished enthalpy at the oscillating equatorial surface. We find that the existing pulsation modes become unstable due to the existence of the corotation radius inside the star. The feature of the unstable mode eigenfrequency and its eigenfunction in the linear analysis roughly ...
Differential rotation on both components of the pre main-sequence binary system HD 155555
Dunstone, N J; Cameron, A Collier; Marsden, S C; Jardine, M; Barnes, J R; Vlex, J C Ramirez; Donati, J -F
2008-01-01
We present the first measurements of surface differential rotation on a pre-main sequence binary system. Using intensity (Stokes I) and circularly polarised (Stokes V) timeseries spectra, taken over eleven nights at the Anglo-Australian Telescope (AAT), we incorporate a solar-like differential rotation law into the surface imaging process. We find that both components of the young, 18 Myr, HD 155555 (V824 Ara, G5IV + K0IV) binary system show significant differential rotation. The equator-pole laptimes as determined from the intensity spectra are 80 days for the primary star and 163 days for the secondary. Similarly for the magnetic spectra we obtain equator-pole laptimes of 44 and 71 days respectively, showing that the shearing timescale of magnetic regions is approximately half that found for stellar spots. Both components are therefore found to have rates of differential rotation similar to those of the same spectral type main sequence single stars. The results for HD 155555 are therefore in contrast to tho...
Bursting and large-scale intermittency in turbulent convection with differential rotation
Garcia, O.E.; Bian, N.H.
2003-01-01
The tilting mechanism, which generates differential rotation in two-dimensional turbulent convection, is shown to produce relaxation oscillations in the mean flow energy integral and bursts in the global fluctuation level, akin to Lotka-Volterra oscillations. The basic reason for such behavior...
New Suns in the Cosmos II: differential rotation in Kepler Sun-like stars
Das Chagas, M. L.; Bravo, J. P.; Costa, A. D.; Ferreira Lopes, C. E.; Silva Sobrinho, R.; Paz-Chinchón, F.; Leão, I. C.; Valio, A.; de Freitas, D. B.; Canto Martins, B. L.; Lanza, A. F.; De Medeiros, J. R.
2016-12-01
The present study reports the discovery of Sun-like stars, namely main-sequence stars with Teff, log g and rotation periods Prot similar to solar values, presenting evidence of surface differential rotation (DR). An autocorrelation of the time series was used to select stars presenting photometric signal stability from a sample of 881 stars with light curves collected by the Kepler space-borne telescope, in which we have identified 17 stars with stable signals. A simple two-spot model together with a Bayesian information criterion were applied to these stars in the search for indications of DR; in addition, for all 17 stars, it was possible to compute the spot rotation period P, the mean values of the individual spot rotation periods and their respective colatitudes, and the relative amplitude of the DR.
Heyl, J S; Lloyd, D; CERN. Geneva; Heyl, Jeremy S.; Shaviv, Nir J.; Lloyd, Don
2003-01-01
In the presence of strong magnetic fields, the vacuum becomes a birefringent medium. We show that this QED effect decouples the polarization modes of photons leaving the NS surface. Both the total intensity and the intensity in each of the two modes is preserved along a ray's path through the neutron-star magnetosphere. We analyze the consequences that this effect has on aligning the observed polarization vectors across the image of the stellar surface to generate large net polarizations. Counter to previous predictions, we show that the thermal radiation of NSs should be highly polarized even in the optical. When detected, this polarization will be the first demonstration of vacuum birefringence. It could be used as a tool to prove the high magnetic field nature of AXPs and it could also be used to constrain physical NS parameters, such as $R/M$, to which the net polarization is sensitive.
Haseyama, T; Bowman, J D; Delheij, P P J; Funahashi, H; Ishimoto, S; Jones, G; Masaike, A; Masuda, Y; Matsuda, Y; Morimoto, K; Muto, S; Penttil\\"a, S I; Pomeroy, V R; Sakai, K; Sharapov, E I; Smith, D A; Yuan, V W
2002-01-01
The parity nonconserving spin rotation of neutrons in the 0.734-eV p-wave resonance of $^{139}La$ was measured with the neutron transmission method. Two optically polarized $^3He$ cells were used before and behind a a 5-cm long $^{139}La$ target as a polarizer and an analyzer of neutron spin. The rotation angle was carefully measured by flipping the direction of $^3He$ polarization in the polarizer in sequence. The peak-to-peak value of the spin rotation was found to be $ (7.4 \\pm 1.1) \\times 10^{-3} $ rad/cm which was consistent with the previous experiments. But the result was statisticallly improved. The s-p mixing model gives the weak matrix element as $xW = (1.71 \\pm 0.25)$ meV. The value agrees well with the one deduced from the parity-nonconserving longitudinal asymmetry in the same resonance.
A method to discriminate solar and antisolar differential rotation in high-precision light curves
Reinhold, T
2015-01-01
Surface differential rotation (DR) is one major ingredient of the magnetic field generation process in the Sun and likely in other stars. The term solar-like differential rotation describes the observation that solar equatorial regions rotate faster than polar ones. The opposite effect of polar regions rotating faster than equatorial ones (termed as antisolar DR) has only been observed in a few stars, although there is evidence from theoretical dynamo models. We present a new method to detect the sign of DR (i.e. solar-like or antisolar DR) by analyzing long-term high-precision light curves with the Lomb-Scargle periodogram.We compute the Lomb-Scargle periodogram and identify a set of significant periods $P_k$, which we associate with active regions located at different latitudes on the the stellar surface. If detectable, the first harmonics ($P_k'$) of these periods were identified to compute their peak-height-ratios $r_k:=h(P_k')/h(P_k)$. Spots rotating at lower latitudes generate less sine-shaped light cur...
Hill, Colin; Shahbaz, Tariq; Steeghs, Danny; Dhillon, Vik
2014-01-01
We present Roche tomograms of the K4V secondary star in the cataclysmic variable AE Aqr, reconstructed from two datasets taken 9 days apart, and measure the differential rotation of the stellar surface. The tomograms show many large, cool starspots, including a large high-latitude spot and a prominent appendage down the trailing hemisphere. We find two distinct bands of spots around 22$^{\\circ}$ and 43$^{\\circ}$ latitude, and estimate a spot coverage of 15.4-17% on the northern hemisphere. Assuming a solar-like differential rotation law, the differential rotation of AE Aqr was measured using two different techniques. The first method yields an equator-pole lap time of 269 d and the second yields a lap time of 262 d. This shows the star is not fully tidally locked, as was previously assumed for CVs, but has a co-rotation latitude of $\\sim 40^{\\circ}$. We discuss the implications that these observations have on stellar dynamo theory, as well as the impact that spot traversal across the first Lagrangian point ma...
Slow Differential Inner-core Rotation Inferred From Changes In Scattering Over Time
Xu, F.; Vidale, J.; Dodge, D.; Earle, P.
2001-12-01
Due to its important implications for our understanding of the core processes, including the generation and reversal of the Earth's magnetic field, the possibility that the inner core may be rotating faster than the mantle has been of wide interest. Attempts to constrain the speed of this differential rotation with differential times of core phases and spatial migration of inner core heterogeneity have yielded various discordant results. The detection of scattering in the inner core has enabled us to conduct a simple test for inner core motion. We compared scattered waves recorded at LASA in Montana from two nuclear tests at Novaya Zemlya in 1971 and 1974. This nearly co-located pair of events offered a rare opportunity of interpreting the variation in the inner core scattered waves in terms of relative inner-core rotation. The coda indeed shows small but coherent changes. The observation of earlier scattered arrivals from the west in 1974 compared to 1971, and later scattered arrivals from the east indicated an inner-core rotation rate of 0.15o per year (Vidale et al, Nature, 2000). This rate falls within the bounds set by other measurements, some of which find an upper limit of 0.1 to 0.2 per year for inner-core differential rotation. This year, we present further details of the comparison of 1971 and 1974 Novaya Zemlya explosions, and compare 1971 and 1973 Aleutian explosions. The latter pair is more difficult to use to constrain inner core rotation because the blasts were 10 km apart, rather than less than 1 km in the former case.
Taghipour-Darzi, Mohammad; Takamjani, Esmail Ebrahimi; Salavati, Mahyar; Mobini, Bahram; Zekavat, Hajar
2012-12-01
Lumbar segmental instability (LSI) is a sub-group of non-specific low back pain (NSLBP), without any accepted diagnostic tool as a golden standard. Some authors emphasize on clinical findings, and others focus on vertebral translation and rotation, but construct validity of these measures had not been approved. Therefore, the purpose of the study was to evaluate convergent and known group validity of vertebral translation and rotation in differentiating LSI from NSLBP and control subjects. Study variables included full-range and mid-range vertebral translation and rotation in sagittal plane. Five x-rays were taken in neutral, full flexion and extension and mid-flexion and mid-extension positions of lumbar spine. The variables were calculated using Computer Aided Radiographic Analysis of Spine (CARA) software after scanning. Sixty-six volunteered males participated in three groups. Twenty-two subjects were in the control group, and 44 NSLBP were divided into LSI and not LSI groups according to the criteria adopted by Hicks et al. The ANOVA and Tukey test were used in statistic analysis. ANOVA results demonstrated differences in three groups; for full-range translation and rotation, were not significant. However, the results of ANOVA demonstrated significant difference in L4-5 mid-range translation and rotation (p < 0/05). Tukey test showed significant difference for L4-5 mid-range translation between control (2.14 mm) and LSI (1.33 mm) groups (p < 0/05). Tukey test demonstrated difference between the control (14.18°) and LSI (11.65°) groups (p < 0/05); the control and not LSI (10.80) groups (p < 0/05) were significant for L4-5 mid-range rotation. On the basis of the study results, the full-range translation and rotation cannot differentiate LSI from not LSI and control groups. Moreover, the mid-range translation only differentiates control from LSI, whereas mid-range rotation differentiates control from both LSI and not LSI. Copyright © 2012
Guenel, M; Mathis, S; Rieutord, M
2015-01-01
Tidally-excited inertial waves in stellar convective regions are a key mechanism for tidal dissipation in stars and therefore the evolution of close-in binary or planetary systems. As a first step, we explore here the impact of latitudinal differential rotation on the properties of free inertial modes and identify the different families of modes. We show that they differ from the case of solid-body rotation. Using an analytical approach as well as numerical calculations, we conclude that critical layers (where the Doppler-shifted frequency vanishes) could play a very important role for tidal dissipation.
Planetary eclipse mapping of CoRoT-2a. Evolution, differential rotation, and spot migration
Huber, K F; Wolter, U; Schmitt, J H M M
2010-01-01
The lightcurve of CoRoT-2 shows substantial rotational modulation and deformations of the planet's transit profiles caused by starspots. We consistently model the entire lightcurve, including both rotational modulation and transits, stretching over approximately 30 stellar rotations and 79 transits. The spot distribution and its evolution on the noneclipsed and eclipsed surface sections are presented and analyzed, making use of the high resolution achievable under the transit path. We measure the average surface brightness on the eclipsed section to be (5\\pm1) % lower than on the noneclipsed section. Adopting a solar spot contrast, the spot coverage on the entire surface reaches up to 19 % and a maximum of almost 40 % on the eclipsed section. Features under the transit path, i.e. close to the equator, rotate with a period close to 4.55 days. Significantly higher rotation periods are found for features on the noneclipsed section indicating a differential rotation of $\\Delta \\Omega > 0.1$. Spotted and unspotted...
Li, Hua; Zhang, Li-Li; Yi, Zhou; Fratini, Emiliano; Baglioni, Piero; Chen, Sow-Hsin
2015-08-15
Cement is a widely used construction material in the world. The quality and durability of aged cement pastes have a strong relationship with the water contained in it. The translational and rotational dynamics of water in ordinary Portland cement (OPC) pastes cured for 7, 14 and 30days were studied by analyzing Quasi-elastic Neutron Scattering (QENS) data. The effect of a new super-plasticizer (SP) additive was also studied by comparing the samples with and without the additive. By fitting the QENS spectra with the Jump-diffusion and Rotation-diffusion Model (JRM), six important parameters including the bound water index (BWI), the self-diffusion coefficient, D(t), the average residence time, τ0, the rotational diffusion constant, D(r), the rotational residence time, τ(r), and the mean squared displacement (MSD), 〈u(2)〉, were obtained. From these parameters, we can quantitatively follow the evolution of the bound water fraction (BWI). We can clearly see the different time ranges for the translational and rotational dynamics of water contained in the OPC pastes by τ0 and τ(r). From the MSD values compared with those of molecular dynamics simulation, we can distinguish between immobile water (mainly bound water) and mobile water, which includes confined water and ultraconfined water. Furthermore, by the fitted parameters' values and their change of slopes with increasing setting time for cement pastes with and without additive SP, it becomes clear that the effect of additive SP is to make the mobile water more confined and induce a more uniform the aging process during the evolution of the OPC pastes.
The effect of rotation on the stability of nuclear burning in accreting neutron stars
Keek, L.; Langer, N.; in 't Zand, J.J.M.
2009-01-01
Hydrogen and/or helium accreted by a neutron star from a binary companion may undergo thermonuclear fusion. Different burning regimes are discerned at different mass accretion rates. Theoretical models predict helium fusion to proceed as a thermonuclear runaway for accretion rates below the
Dikpati, Mausumi
2013-01-01
Meridional circulation in stellar convection zones is not generally well observed, but may be critical for MHD dynamos. Coriolis forces from differential rotation (DR) play a large role in determining what the meridional circulation is. Here we consider whether a stellar DR that is constant on cylinders concentric with the rotation axis can drive a meridional circulation.Conventional wisdom says that it can not. Using two related forms of governing equations that respectively estimate the longitudinal components of the curl of meridional mass flux and the vorticity, we show that such DR will drive a meridional flow. This is because to satisfy anelastic mass conservation, non-spherically symmetric pressure contours must be present for all DRs, not just ones that depart from constancy on cylinders concentric with the rotation axis. Therefore the fluid is always baroclinic if DR is present, because, in anelastic systems, the perturbation pressure must satisfy a Poisson type equation, as well as an equation of st...
Caleo, Andrea; Balbus, Steven A.
2016-04-01
Barotropic rotation and radiative equilibrium are mutually incompatible in stars. The issue is often addressed by allowing for a meridional circulation, but this is not devoid of theoretical complications. Models of rotation in the Sun which maintain strict radiative equilibrium, making use of the observation that the Sun is not in a state of barotropic rotation, have recently been suggested. To investigate the dynamical behaviour of these solutions, we study the local stability of stratified, weakly magnetized, differentially rotating fluids to non-axisymmetric perturbations. Finite heat conductivity, kinematic viscosity, and resistivity are present. The evolution of local embedded perturbations is governed by a set of coupled, ordinary differential equations with time-dependent coefficients. Two baroclinic models of rotation for the upper radiative zone and tachocline are studied: (i) an interpolation based on helioseismology data, (ii) a theoretical solution directly compatible with radiative equilibrium. The growth of the local Goldreich-Schubert-Fricke instability appears to be suppressed, largely because of the viscosity. An extensive exploration of wavenumber space is carried out, with and without a magnetic field. Although we easily find classical local instabilities when they ought formally to be present, for the Sun the analysis reveals neither unstable solutions, nor even solutions featuring a large transient growth. We have not ruled out larger scale or non-linear instabilities, nor have we rigorously proven local stability. But rotational configurations in close agreement with observations, generally thought to be vulnerable to the classic local Goldreich-Schubert-Fricke instability, do appear to be locally stable under rather general circumstances.
Wang Wei-Li; Miao Gang; Chen Yue-Hui; Tang Dan; Ma Feng-Cai
2008-01-01
Collisional quantum interference (CQI) in the intramolecular rotational energy transfer was observed in experiment by Sha and co-workers.[1] The interference angle, which measuring the degree of the coherence, were measured in the experiment of the static cell. Based on the first Born approximation of time dependent perturbation theory, taking into accounts the anisotropic Lennard-Jones interaction potentials, this paper describes the theoretical model of CQI in intramolecular rotational energy transfer in an atom-diatom collision system. In the model, the differential interference angle for the experiment of the molecular beam is calculated, the changing tendencies of the differential interference angle with the impact parameter and collision partners are obtained. This theoretical model is important for understanding or performing this kind of experiments.
Saeed Talebi
2015-07-01
Full Text Available This study introduces the Differential Transform Method (DTM to analyse the free vibration response of a rotating, closed section, composite, Timoshenko beam which features material coupling between flapwise bending and torsional vibrations due to ply orientation. The governing differential equations of motion are derived using Hamilton’s principle and solved by applying DTM. The natural frequencies are calculated and the effects of the bending-torsion coupling, the slenderness ratio and several other parameters on the natural frequencies are investigated using the computer package, Mathematica. Wherever possible, comparisons are made with the studies in open literature.
Sustained Turbulence in Differentially Rotating Magnetized Fluids at Low Magnetic Prandtl Number
Nauman, Farrukh
2016-01-01
We show for the first time that sustained turbulence is possible at low magnetic Prandtl number for Keplerian flows with no mean magnetic flux. Our results indicate that increasing the vertical domain size is equivalent to increasing the dynamical range between the energy injection scale and the dissipative scale. This has important implications for a large variety of differentially rotating systems with low magnetic Prandtl number such as protostellar disks and laboratory experiments.
Sustained Turbulence in Differentially Rotating Magnetized Fluids at Low Magnetic Prandtl Number
Nauman, Farrukh; Pessah, Martin E.
2016-01-01
We show for the first time that sustained turbulence is possible at low magnetic Prandtl number for Keplerian flows with no mean magnetic flux. Our results indicate that increasing the vertical domain size is equivalent to increasing the dynamical range between the energy injection scale...... and the dissipative scale. This has important implications for a large variety of differentially rotating systems with low magnetic Prandtl number such as protostellar disks and laboratory experiments....
Some exploratory experiments with a new type of rotating, differentially-heated fluid annulus
Davies, Peter A; Walin, Gösta
2011-01-01
Some experiments with a rotating differentially heated annulus are presented. It is demonstrated that with suitable construction of the annulus the strength of the zonal baroclinic motion may be chosen independently of the basic density stratification. In the experiment reported it was found that baroclinic instability occurred in a state characterized by small isotherm slopes. Certain aspects of the observed flow and temperature fields—in particular the basic stratification and the slope of ...
Numerical Analysis of Nanofluids in Differentially Heated Enclosure Undergoing Orthogonal Rotation
H. Saleh
2014-01-01
Full Text Available Natural convection heat transfer in a rotating, differentially heated enclosure is studied numerically in this paper. The rotating enclosure is filled with water-Ag, water-Cu, water-Al2O3, or water-TiO2 nanofluids. The governing equations are in velocity, pressure, and temperature formulation and solved using the staggered grid arrangement together with MAC method. The governing parameters considered are the solid volume fraction, 0.0 ≤ ϕ ≤ 0.05, and the rotational speeds, 3.5≤ Ω ≤ 17.5 rpm, and the centrifugal force is smaller than the Coriolis force and both forces were kept below the buoyancy force. It is found that the angular locations of the local maximums heat transfer were sensitive to rotational speeds and nanoparticles concentration. The global quantity of heat transfer rate increases about 1.5%, 1.1%, 0.8%, and 0.6% by increasing 1% ϕ of the nanoparticles Ag, Cu, Al2O3, and TiO2, respectively, for the considered rotational speeds.
LO Peg: surface differential rotation, flares, and spot-topographic evolution
Karmakar, Subhajeet; Savanov, I S; Taş, G; Pandey, S B; Misra, K; Joshi, S; Dmitrienko, E S; Sakamoto, T; Gehrels, N; Okajima, T
2016-01-01
Using the wealth of ~24 yr multiband data, we present an in-depth study of the star-spot cycles, surface differential rotations (SDR), optical flares, evolution of star-spot distributions, and coronal activities on the surface of young, single, main-sequence, ultrafast rotator (UFR) LO Peg. From the long-term V -band photometry, we derive rotational period of LO Peg to be 0.4231 +/- 0.0001 d. Using the seasonal variations on the rotational period, the SDR pattern is investigated, and shows a solar-like pattern of SDR. A cyclic pattern with period of ~2.7 yr appears to be present in rotational period variation. During the observations, 20 optical flares are detected with a flare frequency of 1 flare per two days and with flare energy of 10^{31-34} erg. The surface coverage of cool spots is found to be in the range of 9-26 per cent. It appears that the high- and low-latitude spots are interchanging their positions. Quasi-simultaneous observations in X-ray, UV, and optical photometric bands show a signature of a...
Chaudhury, Salma; Holland, Christopher; Porter, David; Tirlapur, Uday K; Vollrath, Fritz; Carr, Andrew J
2011-12-01
The cause of the high failure rates often observed following rotator cuff tendon repairs, particularly massive tears, is not fully understood. Collagen structural changes have been shown to alter tendon thermal and mechanical properties. This study aimed to form a quantitative rather than qualitative assessment, of whether differences in collagen structure and integrity existed between small biopsies of normal, small, and massive rotator cuff tears using differential scanning calorimetry. Thermal properties were measured for 28 human biopsies taken intra-operatively from normal, small, and massive rotator cuff tendon tears in this powered study. Denaturation temperatures are represented by T(onset) (°C) and T(peak) (°C). The T(onset) is proposed to represent water-amide hydrogen bond breakage and resulting protein backbone mobility. T(peak) reportedly corresponds to the temperature at which the majority of proteins fall out of solution. Denaturation enthalpy (ΔH) should correlate with the amount of triple helical structure that is denatured. Fluorescence and confocal microscopy allowed quantitative validation. Small and massive rotator cuff tears had significantly higher T(onset), T(peak), and ΔH compared to controls. Polarized light microscopy of torn tendons confirmed greater collagen structural disruption compared to controls. These novel findings suggest greater quantifiable collagen structural disruption in rotator cuff tears, compared to controls. This study offers insight into possible mechanisms for the reduced strength of torn tendons and may explain why repaired tendons fail to heal.
Anti-solar differential rotation on the active sub-giant HU Virginis
Harutyunyan, G; Künstler, A; Carroll, T A; Weber, M
2016-01-01
Measuring surface differential rotation (DR) on different types of stars is important when characterizing the underlying stellar dynamo. It has been suggested that anti-solar DR laws can occur when strong meridional flows exist. We aim to investigate the differential surface rotation on the primary star of the RS CVn binary HU Vir by tracking its starspot distribution as a function of time. We also aim to recompute and update the values for several system parameters of the triple system HU Vir (close and wide orbits). Time-series high-resolution spectroscopy for four continuous months was obtained with the 1.2-m robotic STELLA telescope. Nine consecutive Doppler images were reconstructed from these data, using our line-profile inversion code iMap. An image cross-correlation method was applied to derive the surface differential-rotation law for HU Vir. New orbital elements for the close and the wide orbits were computed using our new STELLA radial velocities (RVs) combined with the RV data available in the lit...
Antisolar differential rotation of the K1-giant sigma Geminorum revisited
Kovari, Zs; Künstler, A; Carroll, T A; Strassmeier, K G; Vida, K; Olah, K; Bartus, J; Weber, M
2014-01-01
Context. Surface differential rotation and other global surface flows on magnetically active stars are among the observable manifestations of the stellar dynamo working underneath. Therefore, such observations are important for stellar dynamo theory and useful constraints for solar dynamo studies as well. Aims. The active K1-giant component of the long-period RS CVn-type binary system sigma Gem and its global surface flow pattern is revisited. Methods. We refine the differential rotation law from recovering the spot migration pattern. We apply a detailed cross-correlation technique to a unique set of 34 time-series Doppler images recovered using data from 1996/97. By increasing the number of the available cross-correlation function maps from the formerly used 4 to 17 we expect a more robust determination of the differential surface rotation law. In addition, we present a new time-series Doppler imaging study of sigma Gem using our advanced surface reconstruction code iMap for a dataset collected in 2006/07. R...
Anti-solar differential rotation on the active sub-giant HU Virginis
Harutyunyan, G.; Strassmeier, K. G.; Künstler, A.; Carroll, T. A.; Weber, M.
2016-08-01
Context. Measuring surface differential rotation (DR) on different types of stars is important when characterizing the underlying stellar dynamo. It has been suggested that anti-solar DR laws can occur when strong meridional flows exist. Aims: We aim to investigate the differential surface rotation on the primary star of the RS CVn binary, HU Vir, by tracking its starspot distribution as a function of time. We also aim to recompute and update the values for several system parameters of the triple system HU Vir (close and wide orbits). Methods: Time-series high-resolution spectroscopy for four continuous months was obtained with the 1.2-m robotic STELLA telescope. Nine consecutive Doppler images were reconstructed from these data, using our line-profile inversion code iMap. An image cross-correlation method was applied to derive the surface differential-rotation law for HU Vir. New orbital elements for the close and the wide orbits were computed using our new STELLA radial velocities (RVs) combined with the RV data available in the literature. Photometric observations were performed with the Amadeus Automatic Photoelectric Telescope (APT), providing contemporaneous Johnson-Cousins V and I data for approximately 20 yrs. This data was used to determine the stellar rotation period and the active longitudes. Results: We confirm anti-solar DR with a surface shear parameter α of -0.029 ± 0.005 and -0.026 ± 0.009, using single-term and double-term differential rotation laws, respectively. These values are in good agreement with previously claimed results. The best fit is achieved assuming a solar-like double-term law with a lap time of ≈400 d. Our orbital solutions result in a period of 10.387678 ± 0.000003 days for the close orbit and 2726 ± 7 d (≈7.5 yr) for the wide orbit. A Lomb-Scarge (L-S) periodogram of the pre-whitened V-band data reveals a strong single peak providing a rotation period of 10.391 ± 0.008 d, well synchronized to the short orbit. Based on
The T=0 neutron-proton pairing correlations in the superdeformed rotational bands around 60Zn
Dobaczewski, J.; Dudek, J.; Wyss, R.
2002-01-01
The superdeformed bands in 58Cu, 59Cu, 60Zn, and 61Zn are analyzed within the frameworks of the Skyrme-Hartree-Fock as well as Strutinsky-Woods-Saxon total routhian surface methods with and without the T=1 pairing correlations. It is shown that a consistent description within these standard approaches cannot be achieved. A T=0 neutron-proton pairing configuration mixing of signature-separated bands in 60Zn is suggested as a possible solution to the problem.
Optimization of a mirror-based neutron source using differential evolution algorithm
Yurov, D. V.; Prikhodko, V. V.
2016-12-01
This study is dedicated to the assessment of capabilities of gas-dynamic trap (GDT) and gas-dynamic multiple-mirror trap (GDMT) as potential neutron sources for subcritical hybrids. In mathematical terms the problem of the study has been formulated as determining the global maximum of fusion gain (Q pl), the latter represented as a function of trap parameters. A differential evolution method has been applied to perform the search. Considered in all calculations has been a configuration of the neutron source with 20 m long distance between the mirrors and 100 MW heating power. It is important to mention that the numerical study has also taken into account a number of constraints on plasma characteristics so as to provide physical credibility of searched-for trap configurations. According to the results obtained the traps considered have demonstrated fusion gain up to 0.2, depending on the constraints applied. This enables them to be used either as neutron sources within subcritical reactors for minor actinides incineration or as material-testing facilities.
Flame Propagation on the Surfaces of Rapidly Rotating Neutron Stars during Type I X-ray Bursts
Cavecchi, Yuri; Braithwaite, Jonathan; Levin, Yuri
2012-01-01
We present the first vertically resolved hydrodynamic simulations of a laterally propagating, deflagrating flame in the thin helium ocean of a rotating accreting neutron star. We use a new hydrodynamics solver tailored to deal with the large discrepancy in horizontal and vertical length scales typical of neutron star oceans, and which filters out sound waves that would otherwise limit our timesteps. We find that the flame moves horizontally with velocities of order $10^5$ cm s$^{-1}$, crossing the ocean in few seconds, broadly consistent with the rise times of Type I X-ray bursts. We address the open question of what drives flame propagation, and find that heat is transported from burning to unburnt fuel by a combination of top-to-bottom conduction and mixing driven by a baroclinic instability. The speed of the flame propagation is therefore a sensitive function of the ocean conductivity and spin: we explore this dependence for an astrophysically relevant range of parameters and find that in general flame pro...
Li Yong-Qing; Li Jian; Ma Feng-Cai
2006-01-01
Collisional quantum interference (CQI) on the intramolecular rotational energy transfer is observed in an experiment with a static cell, and the integral interference angles are measured. To obtain more accurate information, an experiment with a molecular beam is carried out, and thereby the relationship between the differential interference angle and the scattering angle is obtained. Based on the first-Born approximation of time-dependent perturbation theory,the theoretical model of CQI is developed in an atom-diatom system in the condition of the molecular beam, with the long-range interaction potential taken into account. The method of measuring correctly the differential interference angle is presented. The tendencies of the differential interference angle changing with the impact parameter and relative velocity are discussed. The theoretical model presented here is important for understanding or performing the experiment in the molecular beam.
T=0 neutron-proton pairing correlations in the superdeformed rotational bands around 60Zn
Dobaczewski, J.; Dudek, J.; Wyss, R.
2003-03-01
The superdeformed bands in 58Cu, 59Cu, 60Zn, and 61Zn are analyzed within the frameworks of the Skyrme-Hartree-Fock as well as Strutinsky-Woods-Saxon total Routhian surface methods with and without T=1 pairing correlations between like particles. It is shown that a consistent description within these standard approaches cannot be achieved. A T=0 neutron-proton pairing configuration mixing of signature-separated bands in 60Zn is suggested as a possible solution to the problem.
Detecting Differential Rotation and Starspot Evolution on the M dwarf GJ 1243 with Kepler
Davenport, James R A; Hawley, Suzanne L
2015-01-01
We present an analysis of the starspots on the active M4 dwarf GJ 1243, using four years of time series photometry from Kepler. A rapid $P = 0.592596\\pm0.00021$ day rotation period is measured due to the $\\sim$2.2\\% starspot-induced flux modulations in the light curve. We first use a light curve modeling approach, using a Monte Carlo Markov Chain sampler to solve for the longitudes and radii of the two spots within 5-day windows of data. Within each window of time the starspots are assumed to be unchanging. Only a weak constraint on the starspot latitudes can be implied from our modeling. The primary spot is found to be very stable over many years. A secondary spot feature is present in three portions of the light curve, decays on 100-500 day timescales, and moves in longitude over time. We interpret this longitude shearing as the signature of differential rotation. Using our models we measure an average shear between the starspots of 0.0047 rad day$^{-1}$, which corresponds to a differential rotation rate of...
Slow differential rotation of the Earth's inner core indicated by temporal changes in scattering
Vidale; Dodge; Earle
2000-05-25
The finding that the Earth's inner core might be rotating faster than the mantle has important implications for our understanding of core processes, including the generation of the Earth's magnetic field. But the reported signal is subtle--a change of about 0.01 s per year in the separation of two seismic waves with differing paths through the core. Subsequent studies of such data have generally supported the conclusion that differential rotation exists, but the difficulty of accurately locating historic earthquakes and possible biases induced by strong lateral variations in structure near the core-mantle boundary have raised doubt regarding the proposed inner-core motion. Also, a study of free oscillations constrained the motion to be relatively small compared to previous estimates and it has been proposed that the interaction of inner-core boundary topography and mantle heterogeneity might lock the inner core to the mantle. The recent detection of seismic waves scattered in the inner core suggests a simple test of inner-core motion. Here we compare scattered waves recorded in Montana, USA, from two closely located nuclear tests at Novaya Zemlya, USSR, in 1971 and 1974. The data show small but coherent changes in scattering which point toward an inner-core differential rotation rate of 0.15 degrees per year--consistent with constraints imposed by the free-oscillation data.
Wu, Xin-Yi; Ghorui, S. K.; Wang, Long-Jun; Kaneko, K.; Sun, Yang
2017-01-01
We analyze the high-spin structure of the even-even 72-80Kr isotopes using the Projected Shell Model (PSM). With the help of the Pfaffian formulas, we have vigorously extended the quasi-particle (qp) basis of the PSM code and applied in this mass region for the first time. We consider a sufficiently large multi-qp configuration space in order to describe high-spin rotational behavior. The results show that the calculation can reproduce most of the known rotational bands with positive- or negative-parity. Moreover, some side bands appearing in the near-yrast region are predicted. The main structure for each band is discussed in terms of multi-qp configurations. The variations in moment of inertia with spin are explained in terms of successive band crossings among the 2-qp, 4-qp, 6-qp, and 8-qp states. The B (E 2) transition probabilities in these bands are also calculated. To further understand the high-spin behavior of these neutron-deficient nuclei and to confirm predictions of the present work, good high-spin data, especially for B (E 2) transitions, are called for.
Wood, Kathleen; Tobias, Douglas J; Kessler, Brigitte; Gabel, Frank; Oesterhelt, Dieter; Mulder, Frans A A; Zaccai, Giuseppe; Weik, Martin
2010-04-14
There is increasing interest in the contribution of methyl groups to the overall dynamics measured by neutron scattering experiments of proteins. In particular an inflection observed in atomic mean square displacements measured as a function of temperature on high resolution spectrometers (approximately 1 microeV) was explained by the onset of methyl group rotations. By specifically labeling a non-methyl-containing side-chain in a native protein system, the purple membrane, and performing neutron scattering measurements, we here provide direct experimental evidence that the observed inflection is indeed due to methyl group rotations. Molecular dynamics simulations reproduce the experimental data, and their analysis suggests that the apparent transition is due to methyl group rotation entering the finite instrumental resolution of the spectrometer. Methyl group correlation times measured by solid state NMR in the purple membrane, taken from previous work, support the interpretation.
Spectral characterization and differential rotation study of active CoRoT stars
Nagel, Evangelos; Schmitt, Jürgen H M M
2016-01-01
The CoRoT space telescope observed nearly 160 000 light curves. Among the most outstanding is that of the young, active planet host star CoRoT-2A. In addition to deep planetary transits, the light curve of CoRoT-2A shows strong rotational variability and a superimposed beating pattern. To study the stars that produce such an intriguing pattern of photometric variability, we identified a sample of eight stars with rotation periods between 0.8 and 11 days and photometric variability amplitudes of up to 7.5 %, showing a similar CoRoT light curve. We also obtained high-resolution follow-up spectroscopy with TNG/SARG and carried out a spectral analysis with SME and MOOG. We find that the color dependence of the light curves is consistent with rotational modulation due to starspots and that latitudinal differential rotation provides a viable explanation for the light curves, although starspot evolution is also expected to play an important role. Our MOOG and SME spectral analyses provide consistent results, showing...
Lower limit for differential rotation in members of young loose stellar associations
Distefano, E; Lanza, A F; Messina, S; Spada, F
2016-01-01
Surface differential rotation (SDR) plays a key role in dynamo models. SDR estimates are therefore essential for constraining theoretical models. We measure a lower limit to SDR in a sample of solar-like stars belonging to young associations with the aim of investigating how SDR depends on global stellar parameters in the age range (4-95 Myr). The rotation period of a solar-like star can be recovered by analyzing the flux modulation caused by dark spots and stellar rotation. The SDR and the latitude migration of dark-spots induce a modulation of the detected rotation period. We employ long-term photometry to measure the amplitude of such a modulation and to compute the quantity DeltaOmega_phot =2p/P_min -2pi/P_max that is a lower limit to SDR. We find that DeltaOmega_phot increases with the stellar effective temperature and with the global convective turn-over time-scale tau_c. We find that DeltaOmega_phot is proportional to Teff^2.18pm 0.65 in stars recently settled on the ZAMS. This power law is less steep ...
Solar coronal differential rotation from XBPs in Hinode/XRT and Yohkoh/SXT images
Kariyappa, R
2008-01-01
Our aim is to identify and trace the X-ray Bright Points (XBPs) over the disk and use them as tracers to determine the coronal rotation. This investigation will help to clarify and understand several issues: whether (i) the corona rotates differentially; (ii) the rotation depends on the sizes of the XBPs; and (iii) dependence on phases of the solar magnetic cycle. We analysed the daily full-disk soft X-ray images observed with (i) X-Ray Telescope (XRT) on-board the Hinode mission during January, March and April, 2007 and (ii) Soft X-ray Telescope (SXT) on-board the Yohkoh from 1992 to 2001 using SSW in IDL. We have used the tracer method to trace the passage of XBPs over the solar disk with the help of overlaying grids and derived the sidereal angular rotation velocity and the coordinates (latitude and longitude) of the XBPs. We have determined the position of a large number of XBPs both in Hinode/XRT and Yohkoh/SXT images and followed them over the solar disk as a function of time. We derived the coronal sid...
Lower limit for differential rotation in members of young loose stellar associations
Distefano, E.; Lanzafame, A. C.; Lanza, A. F.; Messina, S.; Spada, F.
2016-06-01
Context. Surface differential rotation (SDR) plays a key role in dynamo models and determines a lower limit on the accuracy of stellar rotation period measurements. SDR estimates are therefore essential to constrain theoretical models and infer realistic rotation period uncertainties. Aims: We measure a lower limit to SDR in a sample of solar-like stars belonging to young loose stellar associations with the aim of investigating how SDR depends on global stellar parameters in the age range (4 - 95 Myr). Methods: The rotation period of a solar-like star can be recovered by analyzing the flux modulation caused by dark spots and stellar rotation. The SDR and the latitude migration of dark-spots induce a modulation of the detected rotation period. We employed long-term photometry to measure the amplitude of such a modulation and to compute the quantity ΔΩphot = 2π/Pmin - 2π/Pmax that is a lower limit to SDR. Results: We find that ΔΩphot increases with the stellar effective temperature and with the global convective turn-over timescale τc, which is the characteristic time for the rise of a convective element through the stellar convection zone. We find that ΔΩphot is proportional to Teff2.18±0.65 in stars recently settled on the ZAMS. This power law is less steep than those found by previous authors, but closest to recent theoretical models. We investigate how ΔΩphot changes in time in a ~1 M⊙ star. We find that ΔΩphot steeply increases between 4 and 30 Myr and that it is almost constant between 30 and 95 Myr. We find also that the relative shear increases with the Rossby number Ro. Although our results are qualitatively in agreement with hydrodynamical mean-field models, our measurements are systematically higher than the values predicted by these models. The discrepancy between ΔΩphot measurements and theoretical models is particularly large in stars with periods between 0.7 and 2 d. Such a discrepancy, together with the anomalous SDR measured by
Coherent population trapping magnetometer by differential detecting magneto-optic rotation effect
Zhang, Fan; Tian, Yuan; Zhang, Yi; Gu, Si-Hong
2016-09-01
A pocket coherent population trapping (CPT) atomic magnetometer scheme that uses a vertical cavity surface emitting laser as a light source is proposed and experimentally investigated. Using the differential detecting magneto-optic rotation effect, a CPT spectrum with the background canceled and a high signal-to-noise ratio is obtained. The experimental results reveal that the sensitivity of the proposed scheme can be improved by half an order, and the ability to detect weak magnetic fields is extended one-fold. Therefore, the proposed scheme is suited to realize a pocket-size CPT magnetometer. Project supported by the National Natural Science Foundation of China (Grant Nos. 11304362 and 61434005).
Hansen, Ulrich; Maas, Christian
2017-04-01
About 4.5 billion years ago the early Earth experienced several giant impacts that lead to one or more deep terrestrial magma oceans of global extent. The crystallization of these vigorously convecting magma oceans is of key importance for the chemical structure of the Earth, the subsequent mantle evolution as well as for the initial conditions for the onset of plate tectonics. Due to the fast planetary rotation of the early Earth and the small magma viscosity, rotation probably had a profound effect on early differentiation processes and could for example influence the presence and distribution of chemical heterogeneities in the Earth's mantle [e.g. Matyska et al., 1994, Garnero and McNamara, 2008]. Previous work in Cartesian geometry revealed a strong influence of rotation as well as of latitude on the crystal settling in a terrestrial magma ocean [Maas and Hansen, 2015]. Based on the preceding study we developed a spherical shell model that allows to study crystal settling in-between pole and equator as well as the migration of crystals between these regions. Further we included centrifugal forces on the crystals, which significantly affect the lateral and radial distribution of the crystals. Depending on the strength of rotation the particles accumulate at mid-latitude or at the equator. At high rotation rates the dynamics of fluid and particles are dominated by jet-like motions in longitudinal direction that have different directions on northern and southern hemisphere. All in all the first numerical experiments in spherical geometry agree with Maas and Hansen [2015] that the crystal distribution crucially depends on latitude, rotational strength and crystal density. References E. J. Garnero and A. K. McNamara. Structure and dynamics of earth's lower mantle. Science, 320(5876):626-628, 2008. C. Maas and U. Hansen. Eff ects of earth's rotation on the early di erentiation of a terrestrial magma ocean. Journal of Geophysical Research: Solid Earth, 120
AlMuhammad, Anwar S
2002-01-01
Relying on the magnetic dipole model of the pulsar, we use the extension of the work of Haxton-Ruffini [31] for single charges by DePaolis-Ingrosso-Qadir [32] for an obliquely rotating magnetic dipole, to incorporate the effect of the gravitational mass. So, by using the numerical and analytical solutions of the differential equation for the radiation, we construct the energy spectra for different masses of the dipole-NS. These spectra show that, in relatively low angular momentum l, the effect of the gravitational mass is very significant in suppressing the relativistic enhancement factor, which had been found [27, 28, 32], by two to three orders of magnitude, as the mass changes from 0.5 solar mass to 3 solar masses. It is an indication that most of the angular momentum of the NS is retained as rotational kinetic energy instead of being radiated as an electromagnetic energy. Also, the suppressing in radiation energy is more or less independent of the angular momentum, and the high rotational velocity. We al...
Evolution of a magnetic field in a differentially rotating radiative zone
Gaurat, Mathieu; Lignières, François; Gastine, Thomas
2015-01-01
Recent spectropolarimetric surveys of main-sequence intermediate-mass stars have exhibited a dichotomy in the distribution of the observed magnetic field between the kG dipoles of Ap/Bp stars and the sub-Gauss magnetism of Vega and Sirius. We would like to test whether this dichotomy is linked to the stability versus instability of large-scale magnetic configurations in differentially rotating radiative zones. We computed the axisymmetric magnetic field obtained from the evolution of a dipolar field threading a differentially rotating shell. A full parameter study including various density profiles and initial and boundary conditions was performed with a 2D numerical code. We then focused on the ratio between the toroidal and poloidal components of the magnetic field and discuss the stability of the configurations dominated by the toroidal component using local stability criteria and insights from recent 3D numerical simulations. The numerical results and a simple model show that the ratio between the toroida...
Danilyan, G. V.; Klenke, J.; Kopach, Yu. N.; Krakhotin, V. A.; Novitsky, V. V.; Pavlov, V. S.; Shatalov, P. B.
2014-06-01
The results of an experiment devoted to searches for effects of rotation of fissioning nuclei in the angular distributions of prompt neutrons and gamma rays originating from the polarized-neutron-induced fission of 233U nuclei are presented. The effects discovered in these angular distributions are opposite in sign to their counterparts in the polarized-neutron-induced fission of 235U nuclei. This is at odds with data on the relative signs of respective effects in the angular distribution of alpha particles from the ternary fission of the same nuclei and may be indicative of problems in the model currently used to describe the effect in question. The report on which this article is based was presented at the seminar held at the Institute of Theoretical and Experimental Physics and dedicated to the 90th anniversary of the birth of Yu.G. Abov, corresponding member of Russian Academy of Sciences, Editor in Chief of the journal Physics of Atomic Nuclei.
Rezzolla, L; Markovic, D M; Shapiro, S L; Rezzolla, Luciano; Lamb, Frederick L.; Markovic, Dragoljub; Shapiro, Stuart L.
2001-01-01
The instability of r-mode oscillations in rapidly rotating neutron stars has attracted attention as a potential mechanism for producing high frequency, almost periodic gravitational waves. The analyses carried so far have shown the existence of these modes and have considered damping by shear and bulk viscosity. However, the magnetohydrodynamic coupling of the modes with a stellar magnetic field and its role in the damping of the instability has not been fully investigated yet. Following our introductory paper (Rezzolla, Lamb and Shapiro 2000), we here discuss in more detail the existence of secular higher-order kinematical effects which will produce toroidal fluid drifts. We also define the sets of equations that account for the time evolution of the magnetic fields produced by these secular velocity fields and show that the magnetic fields produced can reach equipartition in less than a year. The full numerical calculations as well as the evaluation of the impact of strong magnetic fields on the onset and e...
Linares, Manuel; Heinke, Craig; Wijnands, Rudy; Patruno, Alessandro; Altamirano, Diego; Homan, Jeroen; Bogdanov, Slavko; Pooley, David
2013-01-01
The X-ray transient IGR J18245-2452 in the globular cluster M28 contains the first neutron star (NS) seen to switch between rotation-powered and accretion-powered pulsations. We analyse its 2013 March-April 25d-long outburst as observed by Swift, which had a peak bolometric luminosity of ~6% of the Eddington limit (L$_{E}$), and give detailed properties of the thermonuclear burst observed on 2013 April 7. We also present a detailed analysis of new and archival Chandra data, which we use to study quiescent emission from IGR J18245-2452 between 2002 and 2013. Together, these observations cover almost five orders of magnitude in X-ray luminosity (L$_X$, 0.5-10 keV). The Swift spectrum softens during the outburst decay (photon index $\\Gamma$ from 1.3 above L$_X$/L$_{E}$=10$^{-2}$ to ~2.5 at L$_X$/L$_{E}$=10$^{-4}$), similar to other NS and black hole (BH) transients. At even lower luminosities, deep Chandra observations reveal hard ($\\Gamma$=1-1.5), purely non-thermal and highly variable X-ray emission in quiesce...
Teixeira, Paulo Cleber Mendonca
2002-12-01
In this study, an analytical solution of the neutron transport equation in an annular reactor is presented with a short and rotating neutron source of the type S(x) {delta} (x- Vt), where V is the speed of annular pulsed reactor. The study is an extension of a previous study by Williams [12] carried out with a pulsed source of the type S(x) {delta} (t). In the new concept of annular pulsed reactor designed to produce continuous high flux, the core consists of a subcritical annular geometry pulsed by a rotating modulator, producing local super prompt critical condition, thereby giving origin to a rotating neutron pulse. An analytical solution is obtained by opening up of the annular geometry and applying one energy group transport theory in one dimension using applied mathematical techniques of Laplace transform and Complex Variables. The general solution for the flux consists of a fundamental mode, a finite number of harmonics and a transient integral. A condition which limits the number of harmonics depending upon the circumference of the annular geometry has been obtained. Inverse Laplace transform technique is used to analyse instability condition in annular reactor core. A regenerator parameter in conjunction with perimeter of the ring and nuclear properties is used to obtain stable and unstable harmonics and to verify if these exist. It is found that the solution does not present instability in the conditions stated in the new concept of annular pulsed reactor. (author)
Inertial modes and their transition to turbulence in a differentially rotating spherical gap flow
Hoff, Michael; Harlander, Uwe; Andrés Triana, Santiago; Egbers, Christoph
2016-04-01
We present a study of inertial modes in a spherical shell experiment. Inertial modes are Coriolis-restored linear wave modes, often arise in rapidly-rotating fluids (e.g. in the Earth's liquid outer core [1]). Recent experimental works showed that inertial modes exist in differentially rotating spherical shells. A set of particular inertial modes, characterized by (l,m,ˆω), where l, m is the polar and azimuthal wavenumber and ˆω = ω/Ωout the dimensionless frequency [2], has been found. It is known that they arise due to eruptions in the Ekman boundary layer of the outer shell. But it is an open issue why only a few modes develop and how they get enhanced. Kelley et al. 2010 [3] showed that some modes draw their energy from detached shear layers (e.g. Stewartson layers) via over-reflection. Additionally, Rieutord et al. (2012) [4] found critical layers within the shear layers below which most of the modes cannot exist. In contrast to other spherical shell experiments, we have a full optical access to the flow. Therefore, we present an experimental study of inertial modes, based on Particle-Image-Velocimetry (PIV) data, in a differentially rotating spherical gap flow where the inner sphere is subrotating or counter-rotating at Ωin with respect to the outer spherical shell at Ωout, characterized by the Rossby number Ro = (Ωin - Ωout)/Ωout. The radius ratio of η = 1/3, with rin = 40mm and rout = 120mm, is close to that of the Earth's core. Our apparatus is running at Ekman numbers (E ≈ 10-5, with E = ν/(Ωoutrout2), two orders of magnitude higher than most of the other experiments. Based on a frequency-Rossby number spectrogram, we can partly confirm previous considerations with respect to the onset of inertial modes. In contrast, the behavior of the modes in the counter-rotation regime is different. We found a triad interaction between three dominant inertial modes, where one is a slow axisymmetric Rossby mode [5]. We show that the amplitude of the most
Parity-Violating Neutron Spin Rotation in Hydrogen and Deuterium and the Predictive Power of EFT
Griesshammer, Harald W.
2013-10-01
One of the least-explored sectors of the Standard Model is the weak part of the nuclear force. Experiments on hadronic parity-violation (PV) at low energies require one comprehensive theoretical framework with reliable error-estimates to: check data consistency; subtract binding effects; and extract the PV interaction strengths. ``Pion-less'' Effective Field Theory is such a method with minimal theoretical bias. Different PV parameters are probed in np and nd spin rotation. Using naïve dimensional analysis, the signal for standard target densities is. An estimate of the numerical and systematic uncertainties of our calculations indicates excellent convergence. We also show that PV 3-nucleon interactions are suppressed in the nd -system, despite the non-perturbative renormalisation of parity-conserving 3-nucleon interactions. Therefore, few-nucleon experiments can dis-entangle PV 2-nucleon interactions at the 10%-level without introducing new unknowns. Supported in part by the US National Science Foundation under CAREER award PHY- 0645498, by the US Department of Energy under contract DE-FG02-95ER-40907, and by University Facilitating Funds of the George Washington University.
Domiciano de Souza, A.; Hadjara, M.; Vakili, F.; Bendjoya, P.; Millour, F.; Abe, L.; Carciofi, A. C.; Faes, D. M.; Kervella, P.; Lagarde, S.; Marconi, A.; Monin, J.-L.; Niccolini, G.; Petrov, R. G.; Weigelt, G.
2012-09-01
Context. Spectrally resolved long-baseline optical/IR interferometry of rotating stars opens perspectives to investigate their fundamental parameters and the physical mechanisms that govern their interior, photosphere, and circumstellar envelope structures. Aims: Based on the signatures of stellar rotation on observed interferometric wavelength-differential phases, we aim to measure angular diameters, rotation velocities, and orientation of stellar rotation axes. Methods: We used the AMBER focal instrument at ESO-VLTI in its high-spectral resolution mode to record interferometric data on the fast rotator Achernar. Differential phases centered on the hydrogen Br γ line (K band) were obtained during four almost consecutive nights with a continuous Earth-rotation synthesis during ~5 h/night, corresponding to ~60° position angle coverage per baseline. These observations were interpreted with our numerical code dedicated to long-baseline interferometry of rotating stars. Results: By fitting our model to Achernar's differential phases from AMBER, we could measure its equatorial radius Req = 11.6 ± 0.3 R⊙, equatorial rotation velocity Veq = 298 ± 9 km s-1, rotation axis inclination angle i = 101.5 ± 5.2°, and rotation axis position angle (from North to East) PArot = 34.9 ± 1.6°. From these parameters and the stellar distance, the equatorial angular diameter ⌀eq of Achernar is found to be 2.45 ± 0.09 mas, which is compatible with previous values derived from the commonly used visibility amplitude. In particular, ⌀eq and PArot measured in this work with VLTI/AMBER are compatible with the values previously obtained with VLTI/VINCI. Conclusions: The present paper, based on real data, demonstrates the super-resolution potential of differential interferometry for measuring sizes, rotation velocities, and orientation of rotating stars in cases where visibility amplitudes are unavailable and/or when the star is partially or poorly resolved. In particular, we showed
Time-series Doppler imaging of the red giant HD 208472. Active longitudes and differential rotation
Özdarcan, O.; Carroll, T. A.; Künstler, A.; Strassmeier, K. G.; Evren, S.; Weber, M.; Granzer, T.
2016-10-01
Context. HD 208472 is among the most active RS CVn binaries with cool starspots. Decade-long photometry has shown that the spots seem to change their longitudinal appearance with a period of about six years, coherent with brightness variations. Aims: Our aim is to spatially resolve the stellar surface of HD 208472 and relate the photometric results to the true longitudinal and latitudinal spot appearance. Furthermore, we investigate the surface differential rotation pattern of the star. Methods: We employed three years of high-resolution spectroscopic data with a high signal-to-noise ratio (S/N) from the STELLA robotic observatory and determined new and more precise stellar physical parameters. Precalculated synthetic spectra were fit to each of these spectra, and we provide new spot-corrected orbital elements. A sample of 34 absorption lines per spectrum was used to calculate mean line profiles with a S/N of several hundred. A total of 13 temperature Doppler images were reconstructed from these line profiles with the inversion code iMap. Differential rotation was investigated by cross-correlating successive Doppler images in each observing season. Results: Spots on HD 208472 are distributed preferably at high latitudes and less frequently around mid-to-low latitudes. No polar-cap like structure is seen at any epoch. We observed a flip-flop event between 2009 and 2010, manifested as a flip of the spot activity from phase 0.0 to phase 0.5, while the overall brightness of the star continued to increase and reached an all-time maximum in 2014. Cross-correlation of successive Doppler images suggests a solar-like differential rotation that is ≈15 times weaker than that of the Sun. Based on data obtained with the STELLA robotic telescope in Tenerife, an AIP facility jointly operated by AIP and IAC, and the Potsdam Automatic Photoelectric Telescopes (APT) in Arizona, jointly operated by AIP and Fairborn Observatory.Radial velocity measurements are only available at the
Guarini, E
2003-01-01
A review of the available tools for the calculation of the neutron double-differential cross-section of fundamental molecules, such as hydrogen and methane, is reported here. The most common cases occurring in neutron data analysis are treated in detail with the aim of providing the reader with intelligible and efficient procedures. The utility nowadays of these kinds of computation are widely described, and applications discussed, with examples based on the comparison with experimental data. New advances and refinement/corrections of earlier work are given throughout the paper, as well as suggestions for practical implementation. (topical review)
Kriskovics, L; Vida, K; Granzer, T; Oláh, K
2014-01-01
We investigate the surface spot activity of the rapidly rotating, lithium-rich active single K-giant DI Psc to measure the surface differential rotation and understand the mechanisms behind the Li-enrichment. Doppler imaging was applied to recover the surface temperature distribution of DI Psc in two subsequent rotational cycles using the individual mapping lines Ca I 6439, Fe I 6430, Fe I 6421 and Li I 6708. Surface differential rotation was derived by cross-correlation of the subsequent maps. Difference maps are produced to study the uniformity of Li-enrichment on the surface. These maps are compared with the rotational modulation of the Li I 6708 line equivalent width. Doppler images obtained for the Ca and Fe mapping lines agree well and reveal strong polar spottedness, as well as cool features at lower latitudes. Cross-correlating the consecutive maps yields antisolar differential rotation with shear coefficient -0.083 +- 0.021. The difference of the average and the Li maps indicates that the lithium abu...
Blanc, Pauline [Los Alamos National Laboratory; Tobin, Stephen J [Los Alamos National Laboratory; Croft, Stephen [Los Alamos National Laboratory; Menlove, Howard O [Los Alamos National Laboratory; Swinhoe, M [Los Alamos National Laboratory; Lee, T [NON LANL
2010-12-02
The Next Generation Safeguards Initiative (NGSI) of the U.S. Department of Energy (DOE) has funded multiple laboratories and universities to develop a means to accurately quantify the Plutonium (Pu) mass in spent nuclear fuel assemblies and ways to also detect potential diversion of fuel pins. Delayed Neutron (DN) counting provides a signature somewhat more sensitive to {sup 235}U than Pu while Differential Die-Away (DDA) is complementary in that it has greater sensitivity to Pu. The two methods can, with care, be combined into a single instrument which also provides passive neutron information. Individually the techniques cannot robustly quantify the Pu content but coupled together the information content in the signatures enables Pu quantification separate to the total fissile content. The challenge of merging DN and DDA, prompt neutron (PN) signal, capabilities in the same design is the focus of this paper. Other possibilities also suggest themselves, such as a direct measurement of the reactivity (multiplication) by either the boost in signal obtained during the active interrogation itself or by the extension of the die-away profile. In an early study, conceptual designs have been modeled using a neutron detector comprising fission chambers or 3He proportional counters and a {approx}14 MeV neutron Deuterium-Tritium (DT) generator as the interrogation source. Modeling was performed using the radiation transport code Monte Carlo N-Particles eXtended (MCNPX). Building on this foundation, the present paper quantifies the capability of a new design using an array of {sup 3}He detectors together with fission chambers to optimize both DN and PN detections and active characterization, respectively. This new design was created in order to minimize fission in {sup 238}U (a nuisance DN emitter), to use a realistic neutron generator, to reduce the cost and to achieve near spatial interrogation and detection of the DN and PN, important for detection of diversion, all within
Magnetic Exchange Couplings in Heterodinuclear Complexes Based on Differential Local Spin Rotations.
Joshi, Rajendra P; Phillips, Jordan J; Peralta, Juan E
2016-04-12
We analyze the performance of a new method for the calculation of magnetic exchange coupling parameters for the particular case of heterodinuclear transition metals complexes of Cu, Ni, and V. This method is based on a generalized perturbative approach which uses differential local spin rotations via formal Lagrange multipiers (Phillips, J. J.; Peralta, J. E. J. Chem. Phys. 2013, 138, 174115). The reliability of the calculated couplings has been assessed by comparing with results from traditional energy differences with different density functional approximations and with experimental values. Our results show that this method to calculate magnetic exchange couplings can be reliably used for heteronuclear transition metal complexes, and at the same time, that it is independent from the different mapping schemes used in energy difference methods.
Schekochihin, A A; Cowley, S C
2011-01-01
Differential rotation is known to suppress linear instabilities in fusion plasmas. However, even in the absence of growing eigenmodes, subcritical fluctuations that grow transiently can lead to sustained turbulence. Here transient growth of electrostatic fluctuations driven by the parallel velocity gradient (PVG) and the ion temperature gradient (ITG) in the presence of a perpendicular ExB velocity shear is considered. The maximally simplified case of zero magnetic shear is treated in the framework of a local shearing box. There are no linearly growing eigenmodes, so all excitations are transient. The maximal amplification factor of initial perturbations and the corresponding wavenumbers are calculated as functions of q/\\epsilon (=safety factor/aspect ratio), temperature gradient and velocity shear. Analytical results are corroborated and supplemented by linear gyrokinetic numerical tests. For sufficiently low values of q/\\epsilon (<7 in our model), regimes with fully suppressed ion-scale turbulence are po...
A differentially rotating disc in a high-mass protostellar system
Pestalozzi, M; Conway, J
2009-01-01
A strong signature of a circumstellar disc around a high-mass protostar has been inferred from high resolution methanol maser observations in NGC7538-IRS1 N. This interpretation has however been challenged with a bipolar outflow proposed as an alternative explanation. We compare the two proposed scenarios for best consistency with the observations. Using a newly developed formalism we model the optical depth of the maser emission at each observed point in the map and LOS velocity for the two scenarios. We find that if the emission is symmetric around a central peak in both space and LOS velocity then it has to arise from an edge-on disc in sufficiently fast differential rotation. Disc models successfully fit ~100 independent measurement points in position-velocity space with 4 free parameters to an overall accuracy of 3-4%. Solutions for Keplerian rotation require a central mass of at least 4 solar masses. Close to best-fitting models are obtained if Keplerian motion is assumed around a central mass equaling ...
Experiments on transitions of baroclinic waves in a differentially heated rotating annulus
Th. von Larcher
2005-01-01
Full Text Available Experiments of baroclinic waves in a rotating, baroclinic annulus of fluid are presented for two gap widths. The apparatus is a differentially heated cylindrical gap, rotated around its vertical axis of symmetry, cooled from within, with a free surface, and filled with de-ionised water as working fluid. The surface flow was observed with visualisation technique while thermographic measurements gave a detailed understanding of the temperature distribution and its time-dependent behaviour. We focus in particular on transitions between different flow regimes. Using a wide gap, the first transition from axisymmetric flow to the regular wave regime was characterised by complex flows. The transition to irregular flows was smooth, where a coexistence of the large-scale jet-stream and small-scale vortices was observed. Furthermore, temperature measurements showed a repetitive separation of cold vortices from the inner wall. Experiments using a narrow gap showed no complex flows but strong hysteresis in the steady wave regime, with up to five different azimuthal wave modes as potential steady and stable solutions.
Morphological Differentiation of Colon Carcinoma Cell Lines in Rotating Wall Vessels
Jessup, J. M.
1994-01-01
The objectives of this project were to determine whether (1) microgravity permits unique, three-dimensional cultures of neoplastic human colon tissues and (2) this culture interaction produces novel intestinal growth and differentiation factors. The initial phase of this project tested the efficacy of simulated microgravity for the cultivation and differentiation of human colon carcinoma in rotating wall vessels (RWV's) on microcarrier beads. The RWV's simulate microgravity by randomizing the gravity vector in an aqueous medium under a low shear stress environment in unit gravity. This simulation achieves approximately a one-fifth g environment that allows cells to 'float' and form three-dimensional relationships with less shear stress than in other stirred aqueous medium bioreactors. In the second phase of this project we assessed the ability of human colon carcinoma lines to adhere to various substrates because adhesion is the first event that must occur to create three-dimensional masses. Finally, we tested growth factor production in the last phase of this project.
Educing the emission mechanism of internal gravity waves in the differentially heat rotating annulus
Rolland, Joran; Hien, Steffen; Achatz, Ulrich; Borchert, Sebastian; Fruman, Mark
2016-04-01
Understanding the lifecycle of gravity waves is fundamental to a good comprehension of the dynamics of the atmosphere. In this lifecycle, the emission mechanisms may be the most elusive. Indeed, while the emission of gravity waves by orography or convection is well understood, the so-called spontaneous emission is still a quite open topic of investigation [1]. This type of emission usually occur very near jet-front systems in the troposphere. In this abstract, we announce our numerical study of the question. Model systems of the atmosphere which can be easily simulated or built in a laboratory have always been an important part of the study of atmospheric dynamics, alongside global simulations, in situ measurements and theory. In the case of the study of the spontaneous emission of gravity waves near jet-front systems, the differentially heated rotating annulus set up has been proposed and extensively used. It comprises of an annular tank containing water: the inner cylinder is kept at a cold temperature while the outer cylinder is kept at a warm temperature. The whole system is rotating. Provided the values of the control parameters (temperature, rotation rate, gap between the cylinders, height of water) are well chosen, the resulting flow mimics the troposphere at midlatitudes: it has a jet stream, and a baroclinic lifecycle develops on top of it. A very reasonable ratio of Brunt-Väisälä frequency over rotation rate of the system can be obtained, so as to be as close to the atmosphere as possible. Recent experiments as well as earlier numerical simulations in our research group have shown that gravity waves are indeed emitted in this set up, in particular near the jet front system of the baroclinic wave [2]. After a first experimental stage of characterising the emitted wavepacket, we focused our work on testing hypotheses on the gravity wave emission mechanism: we have tested and validated the hypothesis of spontaneous imbalance generated by the flow in
Differential rotation rates for short-lived regions of emerging magnetic flux. [in sun
Golub, L.; Vaiana, G. S.
1978-01-01
We have measured the synodic rotation rates of a sample of compact X-ray emission features lasting from 1 day to 7 days, thus bridging the transition between X-ray bright points and active regions. The rotation rate is found to be a function of the lifetime, or size, of the feature; shorter-lived smaller features rotate more slowly than long-lived ones. The rotation rate for features lasting 2 days or less is consistent with that of the photospheric gas. The longest-lived features rotate at a rate about 5% higher, consistent with the sunspot rotation rate.
Karino, S; Eriguchi, Y; Karino, Shigeyuki; Yoshida, Shin'ichirou; Yoshida, Shijun; Eriguchi, Yoshiharu
2000-01-01
We have developed a new numerical scheme to solve r-mode oscillations of {\\it rapidly rotating polytropic stars} in Newtonian gravity. In this scheme, Euler perturbations of the density, three components of the velocity are treated as four unknown quantities together with the oscillation frequency. For the basic equations of oscillations, the compatibility equations are used instead of the linearized equations of motion. By using this scheme, we have solved the classical r-mode oscillations of rotational equilibrium sequences of polytropes with the polytropic indices $N = 0.5, 1.0$ and 1.5 for $m = 2, 3$ and 4 modes. Here $m$ is the rank of the spherical harmonics $Y_l^m$. These results have been applied to investigate evolution of uniformly rotating hot young neutron stars by considering the effect of gravitational radiation and viscosity. We have found that the maximum angular velocities of neutron stars are around 10-20% of the Keplerian angular velocity irrespective of the softness of matter. This confirm...
Theoretical Analysis of Neutron Double-Differential Cross Section of n+11B at 14.2 MeV
ZHANG Jing-Shang
2003-01-01
A new reaction model for light nuclei is proposed to analyze the measured data, especially for the doubledifferential cross sections. In this paper the calculation with this model is employed to analyze measurements of the total outgoing neutron double-differential cross sections for n+11B reactions at En = 14.2 MeV. The representation of the double-differential cross sections of the second emitted particles is given in detail. The calculation results indicate that the recoil effect in light nuclear reaction is essentially important. The reaction channels are discussed in detail.
Bartkowiak, M.; Hofmann, T.; Stüßer, N.
2017-02-01
Energy resolution is an important design goal for time-of-flight instruments and neutron spectroscopy. For high-resolution applications, it is required that the burst times of choppers be short, going down to the μs-range. To produce short pulses while maintaining high neutron flux, we propose beam masks with more than two slits on a counter-rotating 2-disc chopper, behind specially adapted focusing multi-channel guides. A novel non-regular arrangement of the slits ensures that the beam opens only once per chopper cycle, when the masks are congruently aligned. Additionally, beam splitting and intensity focusing by guides before and after the chopper position provide high intensities even for small samples. Phase-space analysis and Monte Carlo simulations on examples of four-slit masks with adapted guide geometries show the potential of the proposed setup.
Taghipour-Darzi, Mohammad; Ebrahimi-Takamjani, Esmail; Salavati, Mahyar; Mobini, Bahram; Zekavat, Hajar; Beneck, George J
2015-01-01
Lumbar Segmental Instability (LSI) is a subgroup of nonspecific Low Back Pain (NSLBP) without any accepted diagnostic tool as a gold standard. Some authors emphasize on quality measure such as centre of rotation (COR) but construct validity of this measure had not been approved. Therefore the purpose of the present study was to evaluate Concurrent and Convergent validity of COR in differentiating LSI. A total of 66 volunteered males participated in three groups named control, NSLBP and LSI groups based on clinical examination. Patients were diagnosed as LSI according to screening criteria adopted by Hicks et al. Study variables included CORs of lumbar segments in sagittal plane. Three x-rays were taken in neutral, flexion and extension positions. The variables were calculated using CARA software. The ANOVA and Tukey test were utilized in statistic analysis. ANOVA results demonstrated mean differences between three groups for COR of L4 motion segment in y axis (p= 0/008) and L5 motion segment in y axis (p= 0/005) were significant. Tukey test showed significant difference for COR of L4 motion segment in y axis between LSI and healthy groups (p= 0/038) and between LSI and NSLBP groups (p= 0/009). For COR of L5 motion segment in y axis, tukey test demonstrated mean difference between LSI and healthy groups (p= 0/028) and between LSI and NSLBP groups (p= 0/007) were significant. Tukey test did't show any significant difference between NSLBP and healthy groups for COR of L4 (p= 0/852) and L5 (p= 0/871) motion segments in y-axis. The COR has ability to differentiate patients with signs and symptoms of LSI from other NSLBP and healthy subjects based on the present study results. However, more researches are needed to develop and support results of this study.
Harlander, Uwe; Alexandrov, Kiril; Wang, Yongtai; Egbers, Christoph [Brandenburg University of Technology Cottbus, Department of Aerodynamics and Fluid Mechanics, Cottbus (Germany); Wenzel, Julia [University of Leipzig, Institute of Meteorology, Leipzig (Germany)
2012-04-15
A radial barrier has been mounted in a differentially heated rotating annulus that partially blocks the azimuthal flow component. The experiment can be seen as an analog to geophysical flows with constrictions, e.g., the Antarctic Circumpolar Current. However, the experiment has been carried out without a particular natural flow in mind. The main interest was to observe a baroclinic annulus flow that does not become saturated. Hence, in contrast to the annulus flow without a barrier, the partially blocked flow remains transient and surface heat fluxes associated with baroclinic life cycles can be studied. The annulus can be subdivided into the upstream half of the barrier, where waves amplify, and the downstream half of the barrier, where waves decay. In the upstream half, the azimuthal mean flow is moderate but with a significant positive eddy radial heat flux. In the downstream half, we find a strong jet in the mean azimuthal flow and furthermore an increased radial mean temperature gradient. The latter points to a weakened or even reversed radial eddy heat flux in the lee side of the barrier. Temperature anomalies appear as large bulges in the outer part of the annulus. Moreover, an outward shift of vortex centers can be observed with respect to centers of temperature anomalies. This phase shift between pressure and temperature anomalies differs from that of classical Eady modes of baroclinic instability. (orig.)
Time-series Doppler imaging of the red giant HD 208472. Active longitudes and differential rotation
Özdarcan, O; Künstler, A; Strassmeier, K G; Evren, S; Weber, M; Granzer, T
2016-01-01
HD 208472 is among the most active RS~CVn binaries with cool starspots. Decade-long photometry has shown that the spots seem to change their longitudinal appearance with a period of about six years, coherent with brightness variations. Our aim is to spatially resolve the stellar surface of HD 208472 and relate the photometric results to the true longitudinal and latitudinal spot appearance. Furthermore, we investigate the surface differential rotation pattern of the star. We employed three years of high-resolution spectroscopic data with a high signal-to-noise ratio (S/N) from the STELLA robotic observatory and determined new and more precise stellar physical parameters. Precalculated synthetic spectra were fit to each of these spectra, and we provide new spot-corrected orbital elements. A sample of 34 absorption lines per spectrum was used to calculate mean line profiles with a S/N of several hundred. A total of 13 temperature Doppler images were reconstructed from these line profiles with the inversion code...
Weisberg, David
2016-10-01
Differentially rotating plasma flow has been measured in the Madison Plasma Dynamo Experiment (MPDX). Spherical cusp-confined plasmas have been stirred both from the plasma boundary using electrostatic stirring in the magnetized edge and in the plasma core using weak global fields and cross-field currents to impose a body-force torque. Laminar velocity profiles conducive to shear-driven MHD instabilities like the dynamo and the MRI are now being generated and controlled with magnetic Reynolds numbers of Rm method for plasma heating, but limits on input heating power have been observed (believed to be caused by the formation of double-layers at anodes). These confinement studies have culminated in large (R = 1.4 m), warm (Te 1), steady-state plasmas. Results of the ambipolar transport model are good fits to measurements of pressure gradients and fluid drifts in the cusp, and offer a predictive tool for future cusp-confined devices. Hydrodynamic modeling is shown to be a good description for measured plasma flows, where ion viscosity proves to be an efficient mechanism for transporting momentum from the magnetized edge into the unmagnetized core. In addition, the body-force stirring technique produces velocity profiles conducive to MRI experiments where dΩ / dr research of flow-driven astrophysical MHD instabilities.
Gellert, M; Elstner, D
2007-01-01
We investigate in isothermal MHD simulations the instability of toroidal magnetic fields resulting by the action of z-dependent differential rotation on a given axial field B^0 in a cylindrical enclosure where in particular the helicity of the resulting nonaxisymmetric flow is of interest. The idea is probed that helicity H is related to the external field and the differential rotation as H ~ B^0_i B^0_j Omega_i,j. The observed instability leads to a nonaxisymmetric solution with dominating mode m=1. With the onset of instability both kinematic and current helicity are produced which fulfill the suggested relation. Obviously, differential rotation dOmega/dz only needs an external axial field B^0_z to produce remarkable amounts of the helicities. Any regular time-dependency of the helicity could not be found. The resulting axial alpha-effect is mainly due to the current helicity, the characteristic time scale between both the values is of order of the rotation time. If the axial field is switched off then the ...
Park, Seoung Hoon; Kim, Seonjin; Kwon, MinHyuk; Christou, Evangelos A
2016-03-01
Vision and auditory information are critical for perception and to enhance the ability of an individual to respond accurately to a stimulus. However, it is unknown whether visual and auditory information contribute differentially to identify the direction and rotational motion of the stimulus. The purpose of this study was to determine the ability of an individual to accurately predict the direction and rotational motion of the stimulus based on visual and auditory information. In this study, we recruited 9 expert table-tennis players and used table-tennis service as our experimental model. Participants watched recorded services with different levels of visual and auditory information. The goal was to anticipate the direction of the service (left or right) and the rotational motion of service (topspin, sidespin, or cut). We recorded their responses and quantified the following outcomes: (i) directional accuracy and (ii) rotational motion accuracy. The response accuracy was the accurate predictions relative to the total number of trials. The ability of the participants to predict the direction of the service accurately increased with additional visual information but not with auditory information. In contrast, the ability of the participants to predict the rotational motion of the service accurately increased with the addition of auditory information to visual information but not with additional visual information alone. In conclusion, this finding demonstrates that visual information enhances the ability of an individual to accurately predict the direction of the stimulus, whereas additional auditory information enhances the ability of an individual to accurately predict the rotational motion of stimulus.
Serebrov, A. P., E-mail: serebrov@pnpi.spb.ru; Kolomenskiy, E. A.; Pirozhkov, A. N.; Krasnoshchekova, I. A.; Vasiliev, A. V.; Polyushkin, A. O.; Lasakov, M. S.; Murashkin, A. N.; Solovey, V. A.; Fomin, A. K.; Shoka, I. V.; Zherebtsov, O. M. [National Research Center Kurchatov Institute, Petersburg Nuclear Physics Institute (Russian Federation); Alexandrov, E. B.; Dmitriev, S. P.; Dovator, N. A. [Russian Academy of Sciences, Ioffe Physical Technical Institute (Russian Federation); Geltenbort, P.; Ivanov, S. N.; Zimmer, O. [Institut Max von Laue–Paul Langevin (France)
2015-12-15
In this work, the double chamber magnetic resonance spectrometer of the Petersburg Nuclear Physics Institute (PNPI) designed to measure the neutron electric dipole moment (EDM) is briefly described. A method for long storage of polarized ultracold neutrons in a resonance space with a superposed electric field collinear to the leading magnetic field is used. The results of the measurements carried out on the ILL reactor (Grenoble, France) are interpreted as the upper limit of the value of neutron EDM vertical bar d{sub n} vertical bar < 5.5 × 10{sup –26}e cm at the 90% confidence level.
Differential Hanbury-Brown-Twiss for an exact hydrodynamic model with rotation
Velle, S
2015-01-01
We study an exact rotating and expanding solution of the fluid dynamical model of heavy ion reactions, that take into account the rate of slowing down of the rotation due to the longitudinal and transverse expansion of the system. The parameters of the model are set on the basis of realistic 3+1D fluid dynamical calculation at TeV energies, where the rotation is enhanced by the build up of the Kelvin Helmholtz Instability in the flow.
Theoretical Analysis of Neutron Double-Differential Cross Section of n + 19F at 14.2 MeV
DUAN Jun-Feng; YAN Yu-Liang; SUN Xiao-Jun; ZHANG Yue; ZHANG Jing-Shang
2007-01-01
A new light nuclear reaction model has been developed and the double-differential measurements of 1p shell nuclei have been analyzed successfully. Now, the application of this model is expanded to 19F of the 2s-1d shell nucleus. The double-differential cross section of total outgoing neutron for n + 19F reactions at En = 14.2 MeV has been calculated and analyzed, which agrees fairly well with the experimental measurements. In this paper, the contributions from different reaction channels to the double-differential cross sections have been analyzed in detail. The calculations indicate that this light nuclear reaction model is also able to be used for the 2s-1d shell nucleus so long as the related level scheme could be provided sufficiently.
Duke, P.; Oakley, C.; Montufar-Solis, D.
The embryonic mammalian limb is sensitive both in vivo and in vitro to changes in gravitational force. Hypergravity of centrifugation and microgravity of space decreased size of elements due to precocious or delayed chondrogenesis respectively. In recapitulating spaceflight experiments, premetatarsals were cultured in suspension in a low stress, low sheer rotating bioreactor, and found to be shorter than those cultured in standard culture dishes, and cartilage development was delayed. This study only measured length of the metatarsals, and did not account for possible changes in width and/or in form of the skeletal elements. Shorter cartilage elements in limbbuds cultured in the bioreactor may be due to the ability of the system to reproduce a more in vivo 3D shape than traditional organ cultures. Tissues subjected to traditional organ cultures become flattened by their own weight, attachment to the filter, and restrictions imposed by nutrient diffusion. The purpose of the current experiment was to determine if entire limb buds could be successfully cultured in the bioreactor, and to compare the effects on 3D shape with that of culturing in a culture dish system. Fore and hind limbs from E11-E13 ICR mouse embryos were placed either in the bioreactor, in Trowell culture, or fixed as controls. Limbbuds were cultured for six days, fixed, and processed either as whole mounts or embedded for histology. Qualitative analysis revealed that the Trowell culture specimens were flattened, while bioreactor culture specimens had a more in vivo-like 3D limb shape. Sections of limbbuds from both types of cultures had excellent cartilage differentiation, with apparently more cell maturation, and hypertrophy in the specimens cultured in the bioreactor. Morphometric quantitation of the cartilaginous elements for comparisons of the two culture systems was complicated due to some limb buds fusing together during culture. This problem was especially noticeable in the younger limbs, and
Guenel, M; Mathis, S; Rieutord, M
2016-01-01
Star-planet tidal interactions may result in the excitation of inertial waves in the convective region of stars. In low-mass stars, their dissipation plays a prominent role in the long-term orbital evolution of short-period planets. Turbulent convection can sustain differential rotation in their envelope, with an equatorial acceleration (as in the Sun) or deceleration, which can modify the waves' propagation properties. We explore in this first paper the general propagation properties of free linear inertial waves in a differentially rotating homogeneous fluid inside a spherical shell. We assume that the angular velocity background flow depends on the latitudinal coordinate only, close to what is expected in the external convective envelope of low-mass stars. We use i) an analytical approach in the inviscid case to get the dispersion relation, from which we compute the characteristic trajectories along which energy propagates. This allows us to study the existence of attractor cycles and infer the different f...
Asteroseismology of Red-Giant Stars: Mixed Modes, Differential Rotation, and Eccentric Binaries
Beck, Paul G.
2013-12-01
Astronomers are aware of rotation in stars since Galileo Galilei attributed the movement of sunspots to rotation of the Sun in 1613. In contrast to the Sun, whose surface can be resolved by small telescopes or even the (protected) eye, we detect stars as point sources with no spatial information. Numerous techniques have been developed to derive information about stellar rotation. Unfortunately, most observational data allow only for the surface rotational rate to be inferred. The internal rotational profile, which has a great effect on the stellar structure and evolution, remains hidden below the top layers of the star - the essential is hidden to the eyes. Asteroseismology allows us to "sense" indirectly deep below the stellar surface. Oscillations that propagate through the star provide information about the deep stellar interiors while they also distort the stellar surface in characteristic patterns leading to detectable brightness or velocity variations. Also, certain oscillation modes are sensitive to internal rotation and carry information on how the star is spinning deep inside. Thanks to the unprecedented quality of NASA's space telescope Kepler, numerous detailed observations of stars in various evolutionary stages are available. Such high quality data allow that for many stars, rotation can not only be constrained from surface rotation, but also investigated through seismic studies. The work presented in this thesis focuses on the oscillations and internal rotational gradient of evolved single and binary stars. It is shown that the seismic analysis can reach the cores of oscillating red-giant stars and that these cores are rapidly rotating, while nested in a slowly rotating convective envelope.
Differential Effects of the Rod-and-Frame Illusion on the Timing of Forearm Rotations
Lommertzen, J.; Zuijlen, A.M.J. van; Meulenbroek, R.G.J.; Lier, R.J. van
2009-01-01
The present study focused on the time course of the effects of the Rod-and-Frame Illusion (RFI) on the kinematics of targeted forearm rotations. Participants were asked to reproduce perceived rod orientations by propelling a hand-held cylinder forward while rotating it to the target orientation. Rod
Michael Hoff
2015-01-01
Full Text Available Instability is related to exponentially growing eigenmodes. Interestingly, when finite time intervals are considered, growth rates of certain initial perturbations can exceed the growth rates of the most unstable modes. Moreover, even when all modes are damped, such particular initial perturbations can still grow during finite time intervals. The perturbations with the largest growth rates are called singular vectors (SVs or optimal perturbations. They not only play an important role in atmospheric ensemble predictions, but also for the theory of instability and turbulence. Starting point for a classical SV-analysis is a linear dynamical system with a known system matrix. In contrast to this traditional approach, measured data are used here to estimate the linear propagator. For this estimation, a method is applied that uses the covariances of the measured time series to find the principal oscillation patterns (POPs that are the empirically estimated linear eigenmodes of the system. By using the singular value decomposition (SVD, we can estimate the modes of maximal growth of the propagator which are thus the empirically estimated SVs. These modes can be understood as a superposition of POPs that form a complete but in general non-orthogonal basis. The data used, originate from a differentially heated rotating annulus laboratory experiment. This experiment is an analogue of the earth's atmosphere and is used to study the development of baroclinic waves in a well controlled and reproducible way without the need of numerical approximations. Baroclinic waves form the background for many studies on SV growth and it is thus straight forward to apply the technique of empirical SV estimation to these laboratory data. To test the method of SV estimation, we use a quasi-geostrophic barotropic model and compare the known SVs from that model with SVs estimated from a surrogate data set that was generated with the help of the exact model propagator and some
Blanchard, Didier; Maronsson, Jon Bergmann; Riktor, M.D.;
2012-01-01
In this work, hindered rotations of the BH4- tetrahedra in Mg(BH4)2 were studied by quasielastic neutron scattering, using two instruments with different energy resolution, in combination with density functional theory (DFT) calculations. Two thermally activated reorientations of the BH4- units......, around the 2-fold (C2) and 3-fold (C3) axes were observed at temperatures from 120 to 440 K. The experimentally obtained activation energies (EaC2 = 39 and 76 meV and EaC3 = 214 meV) and mean residence times between reorientational jumps are comparable with the energy barriers obtained from DFT...... calculations. A linear dependency of the energy barriers for rotations around the C2 axis parallel to the Mg-Mg axis with the distance between these two axes was revealed by the DFT calculations. At the lowest temperature (120 K) only 15% of the BH4- units undergo rotational motion and from comparison with DFT...
Iga, Kiminori; Ishibashi, Kenji; Shigyo, Nobuhiro [Kyushu Univ., Fukuoka (Japan)] [and others
1998-03-01
Neutron and gamma-ray production double differential cross sections were measured for iron by the use of 1.5 GeV {pi}{sup +} mesons. The measured cross sections were compared with the calculated values by HETC-KFA2. For the neutrons, the calculated results deviate from the experimental data in the neutron energy region below 30 MeV. The calculated values of gamma-ray production agree with the experimental data at gamma-ray energies from 1 to 7 MeV within a factor of three. (author)
Ober, Christopher P
2017-03-01
When confronted with various findings on thoracic radiographs, fourth-year veterinary students often have difficulty generating appropriate lists of differential diagnoses. The purpose of this one-group, pretest, posttest experimental study was to determine if a game could be used as an adjunct teaching method to improve students' understanding of connections between imaging findings and differential diagnoses. A novel board game focusing on differential diagnoses in thoracic radiography was developed. One hundred fourth-year veterinary students took a brief pretest, played the board game, and took a brief posttest as a part of their respective clinical radiology rotations. Pretest results were compared to posttest results using a paired t-test to determine if playing the game impacted student understanding. Students' mean scores on the posttest were significantly higher than mean pretest scores (P game resulted in improved short-term understanding of thoracic differential diagnoses by fourth-year students, and use of the board game on a clinical rotation seems to be a beneficial part of the learning process. © 2016 American College of Veterinary Radiology.
Mixing of a passive scalar by the instability of a differentially rotating axial pinch
Paredes, A; Rüdiger, G
2016-01-01
The mixing of a passive scalar like lithium, beryllium or temperature fluctuations due to the magnetic Tayler instability of a rotating axial pinch is considered. Our study is carried out within a Taylor-Couette setup for two rotation laws: quasi-Kepler and solid-body rotation. The minimum magnetic Prandtl number used is 0.05 while the molecular Schmidt number Sc of the fluid varies between 0.1 and 2. An effective diffusivity coefficient for the mixing is numerically measured by the decay process of a global concentration peak located between the cylinder walls. We find that only models with Sc>0.1 do provide finite eddy diffusivity values. We also find that for quasi-Kepler rotation at a magnetic Mach number Mm~2 the flow transits from the slow-rotation regime to the fast-rotation regime. For fixed Reynolds number the relation between the normalized eddy diffusivity and the Schmidt number of the fluid is always linear so that also a linear relation between the instability-induced diffusivity and the molecula...
Validation of neutron data libraries by differential and integral cross sections
Kiraly, B.; Csikai, J.; Doczi, R. [University of Debrecen, Institute of Experimental Physics, Debrecen (Hungary)
2001-03-01
Some new activation cross sections were measured in the discrepant regions of the excitation functions of the following reactions: Hg-198(n,2n)Hg-197m, Hf-176(n,2n)Hf-175, Tl-203(n,2n)Tl-202, Nb-93(n,2n)Nb-92m, Zr-90(n,2n)Zr-89, Re-185(n,2n)Re-184g, Re-185(n,2n)Re-184m. Results obtained for these reactions could contribute to the improvement of the IAEA Reference Neutron Activation Library and through it to the quality of neutron data. The relative values of reflection R{sub {beta}}={sigma}{sub {beta}}{sub ,X}/{sigma}{sub {beta}}{sub ,H} and elastic scattering R{sub EL}={sigma}{sub EL,X}/{sigma}{sub EL,H} cross sections of the thermal neutrons normalized to hydrogen render possible the validation of different neutron data libraries taking to {sigma}{sub EL} data from the JEF Report 14. From the R{sub {beta}}/R{sub EL} values the recommended libraries for the {sigma}{sub EL} elastic scattering cross sections of elements could be deduced. (author)
Wang, Jialei; Wang, Zheng-Xiong; Wei, Lai; Liu, Yue
2017-04-01
The control of neo-classical tearing modes (NTMs) by the differential rotation in the reversed magnetic shear (RMS) configuration with different separations Δ {{r}\\text{s}} between two rational surfaces is numerically studied by means of reduced magnetohydrodynamic (MHD) simulations. It is found that the differential rotation with a strong shear at the outer resonant surface can effectively suppress the explosive burst of double tearing modes (DTMs)/NTMs. Critical values of the strength of rotation to suppress the burst are also presented for different bootstrap current fractions {{f}\\text{b}} . Furthermore, a couple of measurable parameters ≤ft(δ, κ \\right) , corresponding respectively to the triangularity and elongation of the magnetic islands at the outer resonant surface, are introduced to characterize the deformation of islands in the nonlinear phase. It is found that the triangularity δ is more likely to precisely predict the onset of burst than the island width w and elongation κ . For a given Δ {{r}\\text{s}} , the critical value of triangularity {δ\\text{crit}} is obtained by scanning different plasma parameters. Establishing such a database of ≤ft(δ,κ \\right) is helpful to effectively control the development of NTMs in the RMS experimental discharges.
Yoshida, Shin'ichirou; Saijo, Motoyuki
2017-04-01
We investigate the nature of so-called low T/W dynamical instability in a differentially rotating star, by focusing on the role played by the corotation radius of the unstable oscillation modes. A one-dimensional model of linear perturbation, which neglects dependence of variables on the coordinate along the rotational axis of the star, is solved to obtain stable and unstable eigenmodes. A linear eigenmode having a corotation radius, at which azimuthal pattern speed of the mode coincides with the stellar angular velocity, is categorized to either a complex (growing or damping) mode or a purely real mode belonging to a continuous spectrum of frequency. We compute canonical angular momentum and its flux to study eigenmodes with corotation radius. In a dynamically unstable mode, sound wave transports its angular momentum in such a way that the absolute value of the angular momentum is increased on both sides of the corotation radius. We further evaluate growth of amplitude of reflected sound wave incident to a corotation point, and find that the overreflection of the wave and the trapping of it between the corotation radius and the surface of the star may qualitatively explain dependences of eigenfrequencies on the stellar differential rotation. The results suggest that the low T/W instability may be caused by overreflection of sound waves trapped mainly between the surface of the star and a corotation radius.
Magnetic fields and differential rotation on the pre-main sequence III: The early-G star HD 106506
Waite, I A; Carter, B D; Hart, R; Donati, J -F; Vélez, J C Ramírez; Semel, M; Dunstone, N
2011-01-01
We present photometry and spectropolarimetry of the pre-main sequence star HD 106506. A photometric rotational period of ~1.416 +/- 0.133 days has been derived using observations at Mount Kent Observatory (MKO). Spectropolarimetric data taken at the 3.9-m Anglo-Australian Telescope (AAT) were used to derive spot occupancy and magnetic maps of the star through the technique of Zeeman Doppler imaging (ZDI). The resulting brightness maps indicate that HD 106506 displays photospheric spots at all latitudes including a predominant polar spot. Azimuthal and radial magnetic images of this star have been derived, and a significant azimuthal magnetic field is indicated, in line with other active young stars. A solar-like differential rotation law was incorporated into the imaging process. Using Stokes I information the equatorial rotation rate, $\\Omega_{eq}$, was found to be 4.54 +/- 0.01 rad/d, with a photospheric shear $\\delta\\Omega$ of $0.21_{-0.03}^{+0.02}$ rad/d. This equates to an equatorial rotation period of ~...
Papaloizou, J C B
2004-01-01
We carry out a general study of the stability of astrophysical flows that appear steady in a uniformly rotating frame. Such a flow might correspond to a stellar pulsation mode or an accretion disk with a free global distortion giving it finite eccentricity. We consider perturbations arbitrarily localized in the neighbourhood of unperturbed fluid streamlines.When conditions do not vary around them, perturbations take the form of oscillatory inertial or gravity modes. However, when conditions do vary so that a circulating fluid element is subject to periodic variations, parametric instability may occur. For nearly circular streamlines, the dense spectra associated with inertial or gravity modes ensure that resonance conditions can always be satisfied when twice the period of circulation round a streamline falls within. We apply our formalism to a differentially rotating disk for which the streamlines are Keplerian ellipses, with free eccentricity up to 0.7, which do not precess in an inertial frame. We show tha...
Fundamental physics research and neutron interferometry
Ioffe, A. [Hahn-Meitner-Institut Berlin GmbH (Germany)
1996-08-01
The possibility of the use of an extremely sensitive neutron interferometry technique for the study of electromagnetic structure of the neutron and the parity non-conservative effects in neutron spin rotation is discussed. (author)
Leahy, Brian; Ong, Desmond; Cheng, Xiang; Cohen, Itai
2013-03-01
The idea of Taylor dispersion - enhancement of translational diffusion under shear - has found applications in fields from pharmacology to chemical engineering. Here, in a combination of experiment and simulations, we study the translational and rotational diffusion of colloidal dimers under triangle-wave oscillatory shear. We find that the rotational diffusion is enhanced, in addition to the enhanced translational diffusion. This ``rotational Taylor dispersion'' depends strongly on the strain rate (Peclet number), aspect ratio, and the shear strain, in contradistinction to translational Taylor dispersion in a shear flow, which depends only weakly on strain rate and aspect ratio. This separate tunability of translations and orientations promises important applications in mixing and self-assembly of solutions of anisometric colloids. We discuss the corresponding effect on the structure and rheology of denser suspensions of rod-like particles. B. L. acknowledges supported by the Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program.
Tenorio-Tagle, G.; Palous, J.
1987-01-01
The evolution of remnants produced by the total supernova power from an evolved OB association in a differentially rotating galactic disk is presented. The calculations at 5 kpc and 10 kpc from the galactic center lead to column densities across the remnant shell, or across sections of the remnants, which eventually exceed the opacity criterion of Franco and Cox (1986) and thus form molecular clouds. The resultant clouds have masses larger than 100,000 solar masses, dimensions of several hundred parsecs, and a separation larger than 1 kpc. In contrast, at 20 kpc from the galactic center the opacity criterion is never fulfilled.
High levels of surface differential rotation on the young G0 dwarf HD 171488
Jeffers, S.V.; Donati, J.F.
2008-01-01
We present high-resolution images of the young, rapidly rotating G0 dwarf HD 171488, using both Stokes I and Stokes V data. The observations were secured with the MuSiCoS spectropolarimeter at Telescope Bernard Lyot from 2005 May 31 to June 10. The photospheric surface brightness distributions show
Marsden, S C; Vélez, J C Ramírez; Alecian, E; Brown, C J; Carter, B D; Donati, J F; Dunstone, N; Hart, R; Semel, M; Waite, I A
2011-01-01
Spectropolarimetric observations of the pre-main sequence early-G star HD 141943 were obtained at three observing epochs (2007, 2009 and 2010). The observations were obtained using the 3.9-m Anglo-Australian telescope with the UCLES echelle spectrograph and the SEMPOL spectropolarimeter visitor instrument. The brightness and surface magnetic field topologies (given in Paper I) were used to determine the star's surface differential rotation and reconstruct the coronal magnetic field of the star. The coronal magnetic field at the 3 epochs shows on the largest scales that the field structure is dominated by the dipole component with possible evidence for the tilt of the dipole axis shifting between observations. We find very high levels of differential rotation on HD 141943 (~8 times the solar value for the magnetic features and ~5 times solar for the brightness features) similar to that evidenced by another young early-G star, HD 171488. These results indicate that a significant increase in the level of differe...
Ziavra, Despina; Makri, Georgia; Giompres, Panagiotis; Taraviras, Stavros; Thomaidou, Dimitra; Matsas, Rebecca; Mitsacos, Ada; Kouvelas, Elias D
2012-11-01
The most prominent pathological feature in Parkinson's disease (PD) is the progressive and selective loss of mesencephalic dopaminergic neurons of the nigrostriatal tract. The present study was conducted in order to investigate whether naive and or genetically modified neural stem/precursor cells (NPCs) can survive, differentiate and functionally integrate in the lesioned striatum. To this end, stereotaxic injections of 6-OHDA in the right ascending nigrostriatal dopaminergic pathway of mice and subsequent NPC transplantations were performed, followed by apomorphine-induced rotations and double-immunofluorescence experiments. Our results demonstrate that transplanted embryonic NPCs derived from the cortical ventricular zone of E14.5 transgenic mouse embryos expressing the green fluorescent protein (GFP) under control of the beta-actin promoter and cultured as neurospheres can survive in the host striatum for at least three weeks after transplantation. The percentage of surviving GFP-positive cells in the host striatum ranges from 0.2% to 0.6% of the total transplanted NPCs. Grafted cells functionally integrate in the striatum, as indicated by the statistically significant decrease of contralateral rotations after apomorphine treatment. Furthermore, we show that within the striatal environment GFP-positive cells differentiate into beta-III tubulin-expressing neurons, but not glial cells. Most importantly, GFP-positive cells further differentiate to dopaminergic (TH-positive) and medium size spiny (DARPP-32- positive) neuronal phenotypes. Over-expression of the cell cycle exit and neuronal differentiation protein Cend1 in NPCs enhances the generation of GABAergic, but not dopaminergic, neuronal phenotypes after grafting in the lesioned striatum. Our results encourage the development of strategies involving NPC transplantation for the treatment of neurodegenerative diseases.
Agosteo, S; Mereghetti, A; Silari, M; Zajacova, Z
2007-01-01
Double differential distributions of neutrons produced by 100, 150, 200 and 250 MeV protons stopped in a thick iron target were simulated with the FLUKA Monte Carlo code at four emission angles: forward, 45°, transverse and 135° backwards. The attenuation in ordinary concrete of the dose equivalent due to secondary neutrons, protons, photons and electrons was calculated. Some of the resulting attenuation curves are best fitted by a double-exponential function rather than a single-exponential. The effect of various approximations introduced in the simulations is thoroughly discussed. The contribution to the total ambient dose equivalent from photons and protons is usually limited to a few percent, except in the backward direction where photons contribute more than 10% and up to 35% to the total dose for a shield thickness of 1 – 2 m. Source terms and attenuation lengths are given as a function of energy and emission angle, along with fit to the Monte Carlo data. An extensive comparison is made of values ob...
PRAJAPATI P M; PANDEY BHAWNA; GUPTA N C; KUMAR SURESH; NAYAK B K; SAXENA A; SURYANARAYANA S V; JAKHAR S; VALA SUDHIRSINH; RAO C V S; BASU T K
2016-06-01
Measurement of double-differential cross-sections of 14 MeV neutron-inducedcharged-particle productions is very important for estimating the nuclear heating and radiation damage of a fusion reactor. Only a few experimental data are available even though the nuclear reaction cross-section data of structural materials are important in fusion nuclear technology. In this context,general purpose scattering chamber facility has been developed for accelerator-based 14 MeV DT neutron generator to measure double-differential nuclear reaction cross-section at Fusion Neutronics Laboratory, IPR. It has been designed for experiments using silicon surface barrier detectors forthe online detection of charged particles. It offers flexibility in the arrangement of silicon surface barrier detectors.
Ioannidis, P.; Schmitt, J. H. M. M.
2016-10-01
We use high accuracy photometric data obtained with the Kepler satellite to monitor the activity modulations of the Kepler-210 planet host star over a time span of more than four years. Following the phenomenology of the star's light curve in combination with a five spot model, we identify six different so-called spot seasons. A characteristic, which is common in the majority of the seasons, is the persistent appearance of spots in a specific range of longitudes on the stellar surface. The most prominent period of the observed activity modulations is different for each season and appears to evolve following a specific pattern, resembling the changes in the sunspot periods during the solar magnetic cycle. Under the hypothesis that the star exhibits solar-like differential rotation, we suggest differential rotation values of Kepler-210 that are similar to or smaller than that of the Sun. Finally, we estimate spot life times between ~60 days and ~90 days, taking into consideration the evolution of the total covered stellar surface computed from our model.
Ioannidis, P
2016-01-01
We use high accuracy photometric data obtained with the Kepler satellite to monitor the activity modulations of the Kepler-210 planet host star over a time span of more than four years. Following the phenomenology of the star's light curve in combination with a five spot model, we identify six different so-called spot seasons. A characteristic, which is common in the majority of the seasons, is the persistent appearance of spots in a specific range of longitudes on the stellar surface. The most prominent period of the observed activity modulations is different for each season and appears to evolve following a specific pattern, resembling the changes in the sunspot periods during the solar magnetic cycle. Under the hypothesis that the star exhibits solar-like differential rotation, we suggest differential rotation values of Kepler-210 that are similar to or smaller than that of the Sun. Finally, we estimate spot life times between 60 days and 90 days, taking into consideration the evolution of the total covere...
Sytkowski, A. J.; Davis, K. L.
2001-01-01
Prolonged exposure of humans and experimental animals to the altered gravitational conditions of space flight has adverse effects on the lymphoid and erythroid hematopoietic systems. Although some information is available regarding the cellular and molecular changes in lymphocytes exposed to microgravity, little is known about the erythroid cellular changes that may underlie the reduction in erythropoiesis and resultant anemia. We now report a reduction in erythroid growth and a profound inhibition of erythropoietin (Epo)-induced differentiation in a ground-based simulated microgravity model system. Rauscher murine erythroleukemia cells were grown either in tissue culture vessels at 1 x g or in the simulated microgravity environment of the NASA-designed rotating wall vessel (RWV) bioreactor. Logarithmic growth was observed under both conditions; however, the doubling time in simulated microgravity was only one-half of that seen at 1 x g. No difference in apoptosis was detected. Induction with Epo at the initiation of the culture resulted in differentiation of approximately 25% of the cells at 1 x g, consistent with our previous observations. In contrast, induction with Epo at the initiation of simulated microgravity resulted in only one-half of this degree of differentiation. Significantly, the growth of cells in simulated microgravity for 24 h prior to Epo induction inhibited the differentiation almost completely. The results suggest that the NASA RWV bioreactor may serve as a suitable ground-based microgravity simulator to model the cellular and molecular changes in erythroid cells observed in true microgravity.
Guenel, M.; Baruteau, C.; Mathis, S.; Rieutord, M.
2016-05-01
Context. Star-planet tidal interactions may result in the excitation of inertial waves in the convective region of stars. In low-mass stars, their dissipation plays a prominent role in the long-term orbital evolution of short-period planets. Turbulent convection can sustain differential rotation in their envelopes with an equatorial acceleration (as in the Sun) or deceleration, which can modify the propagation properties of the waves. Aims: We explore in this first paper the general propagation properties of free linear inertial waves in a differentially rotating homogeneous fluid inside a spherical shell. We assume that the angular velocity background flow depends on the latitudinal coordinate alone, close to what is expected in the external convective envelope of low-mass stars. Methods: We use an analytical approach in the inviscid case to get the dispersion relation, from which we compute the characteristic trajectories along which energy propagates. This allows us to study the existence of attractor cycles and infer the different families of inertial modes. We also use high-resolution numerical calculations based on a spectral method for the viscous problem. Results: We find that modes that propagate in the whole shell (D modes) behave the same way as with solid-body rotation. However, another family of inertial modes exists (DT modes), which can only propagate in a restricted part of the convective zone. Our study shows that they are less common than D modes and that the characteristic rays and shear layers often focus towards a wedge - or point-like attractor. More importantly, we find that for non-axisymmetric oscillation modes, shear layers may cross a corotation resonance with a local accumulation of kinetic energy. Their damping rate scales very differently from the value we obtain for standard D modes, and we show an example where it is independent of viscosity (Ekman number) in the astrophysical regime in which it is small.
Lekner, John
2008-01-01
Any free-particle wavepacket solution of Schrodinger's equation can be converted by differentiations to wavepackets rotating about the original direction of motion. The angular momentum component along the motion associated with this rotation is an integral multiple of [h-bar]. It is an "intrinsic" angular momentum: independent of origin and…
Nobili, A. M.; Bramanti, D.; Comandi, G. L.; Toncelli, R.; Polacco, E.
2003-07-01
We have proposed to test the equivalence principle (EP) in low Earth orbit with a rapidly rotating differential accelerometer (made of weakly coupled concentric test cylinders) whose rotation provides high frequency signal modulation and avoids severe limitations otherwise due to operation at room temperature [PhRvD 63 (2001) 101101]. Although the accelerometer has been conceived for best performance in absence of weight, we have designed, built and tested a variant of it at 1-g. Here we report the results of measurements performed so far. Losses measured with the full system in operation yield a quality factor only four times smaller than the value required for the proposed high accuracy EP test in space. Unstable whirl motions, which are known to arise in the system and might be a matter of concern, are found to grow as slowly as predicted and can be stabilized. The capacitance differential read-out (the mechanical parts, electronics and software for data analysis) is in all similar to what is needed in the space experiment. In the instrument described here the coupling of the test masses is 24 000 times stiffer than in the one proposed for flight, which makes it 24 000 times less sensitive to differential displacements. With this stiffness it should detect test masses separations of 1.5·10 -2 μm, while so far we have achieved only 1.5 μm, because of large perturbations—due to the motor, the ball bearings, the non-perfect verticality of the system—all of which, however, are absent in space. The effects of these perturbations should be reduced by 100 times in order to perform a better demonstration. Further instrument improvements are underway to fill this gap and also to reduce its stiffness, thus increasing its significance as a prototype of the space experiment.
Goodsell, Alison Victoria [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Swinhoe, Martyn Thomas [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Henzl, Vladimir [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Ianakiev, Kiril Dimitrov [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Iliev, Metodi [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Rael, Carlos D. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Desimone, David J. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2014-09-22
Four helium-3 (^{3}He) detector/preamplifier packages (¾”/KM200, DDSI/PDT-A111, DDA/PDT-A111, and DDA/PDT10A) were experimentally tested to determine the deadtime effects at different DT neutron generator output settings. At very high count rates, the ¾”/KM200 package performed best. At high count rates, the ¾”/KM200 and the DDSI/PDT-A111 packages performed very well, with the DDSI/PDT-A111 operating with slightly higher efficiency. All of the packages performed similarly at mid to low count rates. Proposed improvements include using a fast recovery LANL-made dual channel preamplifier, testing smaller diameter ^{3}He tubes, and further investigating quench gases.
Eigenoscillations of the Differentially Rotating Sun I. 22-year, 4000-year, and quasi-biennial modes
Dzhalilov, N S; Oraevsky, V N
2002-01-01
Retrograde waves with frequencies much lower than the rotation frequency become trapped in the solar radiative interior. The eigenfunctions of the compressible, nonadiabatic, Rossby-like modes ($\\epsilon$-mechanism and radiative losses taken into account) are obtained by an asymptotic method assuming a very small latitudinal gradient of rotation, without an arbitrary choice of other free parameters. An integral dispersion relation for the complex eigenfrequencies is derived as a solution of the boundary value problem. The discovered resonant cavity modes (called R-modes) are fundamentally different from the known r-modes: their frequencies are functions of the solar interior structure, and the reason for their existence is not related to geometrical effects. The most unstable R-modes are those with periods of 1--3 yr, 18--30 yr, and 1500--20000 yrs; these three separate period ranges are known from solar and geophysical data. The growing times of those modes which are unstable with respect to the $\\epsilon$-m...
Degroote, P; Samadi, R; Aerts, C; Kurtz, D W; Noels, A; Miglio, A; Montalban, J; Bloemen, S; Baglin, A; Baudin, F; Catala, C; Michel, E; Auvergne, M
2011-01-01
Context. There exist few variability studies of stars in the region in the Hertzsprung-Russell diagram between the A and B-star pulsational instability strips. With the aid of the high precision continuous measurements of the CoRoT space satellite, low amplitudes are more easily detected, making a study of this neglected region worthwhile. Aims. We collected a small sample of B stars observed by CoRoT to determine the origin of the different types of variability observed. Methods. We combine literature photometry and spectroscopy to measure the fundamental parameters of the stars in the sample, and compare asteroseismic modelling of the light curves with (differentially rotating) spotted star models. Results. We found strong evidence for the existence of spots and differential rotation in HD 174648, and formulated hypotheses for their origin. We show that the distinction between pulsations and rotational modulation is difficult to make solely based on the light curve, especially in slowly rotating stars.
Morphologic differentiation of colon carcinoma cell lines HT-29 and HT-29KM in rotating-wall vessels
Goodwin, T. J.; Jessup, J. M.; Wolf, D. A.
1992-01-01
A new low shear stress microcarrier culture system has been developed at NASA's Johnson Space Center that permits three-dimensional tissue culture. Two established human colon adenocarcinoma cell lines, HT-29, an undifferentiated, and HT-29KM, a stable, moderately differentiated subline of HT-29, were grown in new tissue culture bioreactors called Rotating-Wall Vessels (RWVs). RWVs are used in conjunction with multicellular cocultivation to develop a unique in vitro tissue modeling system. Cells were cultivated on Cytodex-3 microcarrier beads, with and without mixed normal human colonic fibroblasts, which served as the mesenchymal layer. Culture of the tumor lines in the absence of fibroblasts produced spheroidlike growth and minimal differentiation. In contrast, when tumor lines were co-cultivated with normal colonic fibroblasts, initial growth was confined to the fibroblast population until the microcarriers were covered. The tumor cells then commenced proliferation at an accelerated rate, organizing themselves into three-dimensional tissue masses that achieved 1.0- to 1.5-cm diameters. The masses displayed glandular structures, apical and internal glandular microvilli, tight intercellular junctions, desmosomes, cellular polarity, sinusoid development, internalized mucin, and structural organization akin to normal colon crypt development. Differentiated samples were subjected to transmission and scanning electron microscopy and histologic analysis, revealing embryoniclike mesenchymal cells lining the areas around the growth matrices. Necrosis was minimal throughout the tissue masses. These data suggest that the RWV affords a new model for investigation and isolation of growth, regulatory, and structural processes within neoplastic and normal tissue.
Dagrosa, A., E-mail: dagrosa@cnea.gov.ar [Department of Radiobiology, National Atomic Energy Commission (CNEA), Av General Paz 1499, San Martin (1560) (Argentina)] [National Research Council of Argentina (CONICET), Rivadavia 1917, (1033) Buenos Aires (Argentina); Carpano, M. [Department of Radiobiology, National Atomic Energy Commission (CNEA), Av General Paz 1499, San Martin (1560) (Argentina); Perona, M. [Department of Radiobiology, National Atomic Energy Commission (CNEA), Av General Paz 1499, San Martin (1560) (Argentina)] [National Research Council of Argentina (CONICET), Rivadavia 1917, (1033) Buenos Aires (Argentina); Thomasz, L. [Department of Radiobiology, National Atomic Energy Commission (CNEA), Av General Paz 1499, San Martin (1560) (Argentina); Nievas, S. [Department of Chemistry, National Atomic Energy Commission (CNEA), Av General Paz 1499, San Martin (1560) (Argentina); Cabrini, R. [Department of Radiobiology, National Atomic Energy Commission (CNEA), Av General Paz 1499, San Martin (1560) (Argentina); Juvenal, G. [Department of Radiobiology, National Atomic Energy Commission (CNEA), Av General Paz 1499, San Martin (1560) (Argentina)] [National Research Council of Argentina (CONICET), Rivadavia 1917, (1033) Buenos Aires (Argentina); Pisarev, M. [Department of Radiobiology, National Atomic Energy Commission (CNEA), Av General Paz 1499, San Martin (1560) (Argentina)] [National Research Council of Argentina (CONICET), Rivadavia 1917, (1033) Buenos Aires (Argentina)] [Department of Biochemistry, UBA School of Medicine (Argentina)
2011-12-15
The aim of these studies was to evaluate the possibility of treating differentiated thyroid cancer by BNCT. These carcinomas are well controlled with surgery followed by therapy with {sup 131}I; however, some patients do not respond to this treatment. BPA uptake was analyzed both in vitro and in nude mice implanted with cell lines of differentiated thyroid carcinoma. The boron intracellular concentration in the different cell lines and the biodistribution studies showed the selectivity of the BPA uptake by this kind of tumor.
Enoto, Teruaki; Corbet, Robin H. D. [NASA Goddard Space Flight Center, Astrophysics Science Division, Code 662, Greenbelt, MD 20771 (United States); Sasano, Makoto [Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Yamada, Shin' ya; Tamagawa, Toru; Makishima, Kazuo [High Energy Astrophysics Laboratory, RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Pottschmidt, Katja; Marcu, Diana [NASA Goddard Space Flight Center, Astrophysics Science Division, Code 661, Greenbelt, MD 20771 (United States); Fuerst, Felix [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States); Wilms, Jörn, E-mail: teruaki.enoto@nasa.gov [Dr. Remeis-Sternwarte and Erlangen Centre for Astroparticle Physics, Universität Erlangen-Nürnberg, Sternwartstr. 7, D-96049 Bamberg (Germany)
2014-05-10
The symbiotic X-ray binary (SyXB) 4U 1954+319 is a rare system hosting a peculiar neutron star (NS) and an M-type optical companion. Its ∼5.4 hr NS spin period is the longest among all known accretion-powered pulsars and exhibited large (∼7%) fluctuations over 8 yr. A spin trend transition was detected with Swift/BAT around an X-ray brightening in 2012. The source was in quiescent and bright states before and after this outburst based on 60 ks Suzaku observations in 2011 and 2012. The observed continuum is well described by a Comptonized model with the addition of a narrow 6.4 keV Fe-Kα line during the outburst. Spectral similarities to slowly rotating pulsars in high-mass X-ray binaries, its high pulsed fraction (∼60%-80%), and the location in the Corbet diagram favor high B-field (≳ 10{sup 12} G) over a weak field as in low-mass X-ray binaries. The observed low X-ray luminosity (10{sup 33}-10{sup 35} erg s{sup –1}), probable wide orbit, and a slow stellar wind of this SyXB make quasi-spherical accretion in the subsonic settling regime a plausible model. Assuming a ∼10{sup 13} G NS, this scheme can explain the ∼5.4 hr equilibrium rotation without employing the magnetar-like field (∼10{sup 16} G) required in the disk accretion case. The timescales of multiple irregular flares (∼50 s) can also be attributed to the free-fall time from the Alfvén shell for a ∼10{sup 13} G field. A physical interpretation of SyXBs beyond the canonical binary classifications is discussed.
Enoto, Teruaki; Sasano, Makoto; Yamada, Shin'Ya; Tamagawa, Toru; Makishima, Kazuo; Pottschmidt, Katja; Marcu, Diana; Corbet, Robin H. D.; Fuerst, Felix; Wilms, Jorn
2014-01-01
The symbiotic X-ray binary (SyXB) 4U 1954+319 is a rare system hosting a peculiar neutron star (NS) and an M-type optical companion. Its approx. 5.4 hr NS spin period is the longest among all known accretion-powered pulsars and exhibited large (is approx. 7%) fluctuations over 8 yr. A spin trend transition was detected with Swift/BAT around an X-ray brightening in 2012. The source was in quiescent and bright states before and after this outburst based on 60 ks Suzaku observations in 2011 and 2012. The observed continuum is well described by a Comptonized model with the addition of a narrow 6.4 keV Fe-K alpha line during the outburst. Spectral similarities to slowly rotating pulsars in high-mass X-ray binaries, its high pulsed fraction (approx. 60%-80%), and the location in the Corbet diagram favor high B-field (approx. greater than 10(exp12) G) over a weak field as in low-mass X-ray binaries. The observed low X-ray luminosity (10(exp33)-10(exp35) erg s(exp-1)), probable wide orbit, and a slow stellar wind of this SyXB make quasi-spherical accretion in the subsonic settling regime a plausible model. Assuming a approx. 10(exp13) G NS, this scheme can explain the approx. 5.4 hr equilibrium rotation without employing the magnetar-like field (approx. 10(exp16) G) required in the disk accretion case. The timescales of multiple irregular flares (approx. 50 s) can also be attributed to the free-fall time from the Alfv´en shell for a approx. 10(exp13) G field. A physical interpretation of SyXBs beyond the canonical binary classifications is discussed.
Eta photoproduction on the neutron at GRAAL: Measurement of the differential cross section
Rebreyend, D
2005-01-01
In this contribution, we will present our first preliminary measurement of the differential cross section for the reaction gamma+n->eta+n. Comparison of the reactions gamma+p->eta+p for free and bound proton (D2 target) will also be discussed.
MacGregor, K B; Skumanich, Andrew; Metcalfe, T S
2007-01-01
We conduct a systematic examination of the properties of models for chemically homogeneous, differentially rotating, main-sequence stars of mass 1-2 M_sun. The models were constructed using a code based on a reformulation of the self-consistent field method of computing the equilibrium stellar structure for a specified conservative internal rotation law. [abridged] Relative to nonrotating stars of the same mass, these models all have reduced luminosities and effective temperatures, and flattened photospheric shapes (i.e., decreased polar radii) with equatorial radii that can be larger or smaller, depending on the degree of differential rotation. For a fixed ratio of the axial rotation rate to the surface equatorial rotation rate, increasingly rapid rotation generally deepens convective envelopes, shrinks convective cores, and can lead to the presence of a convective core (envelope) in a 1 M_sun (2 M_sun) model, a feature that is absent in a nonrotating star of the same mass. The positions of differentially ro...
Vincze, Miklos; Harlander, Uwe; Gal, Patrice Le
2016-01-01
A water-filled differentially heated rotating annulus with initially prepared stable vertical salinity profiles is studied in the laboratory. Based on two-dimensional horizontal particle image velocimetry (PIV) data, and infrared camera visualizations, we describe the appearance and the characteristics of the baroclinic instability in this original configuration. First, we show that when the salinity profile is linear and confined between two non stratified layers at top and bottom, only two separate shallow fluid layers can be destabilized. These unstable layers appear nearby the top and the bottom of the tank with a stratified motionless zone between them. This laboratory arrangement is thus particularly interesting to model geophysical or astrophysical situations where stratified regions are often juxtaposed to convective ones. Then, for more general but stable initial density profiles, statistical measures are introduced to quantify the extent of the baroclinic instability at given depths and to analyze t...
Yoshida, Shin'ichirou
2016-01-01
We investigate the nature of so-called low $T/W$ dynamical instability in a differentially rotating star by focusing on the role played by the corotation radius of the unstable oscillation modes. An one dimensional model of linear perturbation, which neglects dependence of variables on the coordinate along the rotational axis of the star, is solved to obtain stable and unstable eigenmodes. A linear eigenmode having a corotation radius, at which azimuthal pattern speed of the mode coincides with the stellar angular velocity, is categorized to either a complex (growing or damping) mode or a purely real mode belonging to a continuous spectrum of frequency. We compute canonical angular momentum and its flux to study eigenmodes with corotation radius. In a dynamically unstable mode, sound wave transports its angular momentum in such a way that the absolute value of the angular momentum is increased on both sides of the corotation radius. We further evaluate growth of amplitude of reflected sound wave incident to a...
Hicks, Andy S.; Larese, J. Z.
2013-12-01
High resolution inelastic neutron scattering (INS) measurements of the low temperature (T ∼ 2.0 K) rotational dynamics of isotopically substituted methane monolayers adsorbed on MgO(1 0 0) are presented. These spectra, obtained using BASIS at SNS, represent the most detailed measurements available for surface-adsorbed monolayer films of methane. Distinct excitations are readily observed at 15, 31, 45 and 127 μeV for the CH2D2 on MgO monolayer and at 40, 51, 95 and 138 μeV for CH3D/MgO. These features are attributed to tunneling transitions between sublevels within the ground librational state and are interpreted using the pocket state (PS) formalism first proposed by Hüller. This theoretical analysis employs the findings of earlier studies of CH4 on MgO(1 0 0) which suggest that molecules adsorb with their C2v axes normal to the surface plane. The comparison between theory and experiment provides direct insight into the impact of molecular versus surface symmetry on the observed tunneling spectra.
A Rotating Bioreactor for Scalable Culture and Differentiation of Respiratory Epithelium.
Raredon, Micha Sam Brickman; Ghaedi, Mahboobe; Calle, Elizabeth A; Niklason, Laura E
2015-10-01
Respiratory epithelium is difficult to grow in vitro, as it requires a well-maintained polarizing air-liquid interface (ALI) to maintain differentiation. Traditional methods rely on permeable membrane culture inserts, which are difficult to work with and are ill-suited for the production of large numbers of cells, such as the quantities required for cell-based clinical therapies. Herein, we investigate an alternative form of culture in which the cells are placed on a porous substrate that is continuously rolled, such that the monolayer of cells is alternately submerged in media or apically exposed to air. Our prototype bioreactor is reliable for up to 21 days of continuous culture and is designed for scale-up for large-scale cell culture with continuous medium and gas exchange. Normal human bronchial epithelial (NHBE) cells were cultured on an absorbent substrate in the reactor for periods of 7, 14, and 21 days and were compared to static controls that were submerged in media. Quantification by immunohistochemistry and quantitative PCR of markers specific to differentiated respiratory epithelium indicated increased cilia, mucous production, and tight junction formation in the rolled cultures, compared to static. Together with scanning electron microscopy and paraffin histology, the data indicate that the intermittent ALI provided by the rolling bioreactor promotes a polarized epithelial phenotype over a period of 21 days.
Thomas, Kelsey A; Gibbons, Michael C; Lane, John G; Singh, Anshuman; Ward, Samuel R; Engler, Adam J
2017-08-01
Full thickness rotator cuff tendon (RCT) tears have long-term effects on RC muscle atrophy and fatty infiltration, with lasting damage even after surgical tendon repair. Skeletal muscle progenitor cells (SMPs) are critical for muscle repair in response to injury, but the inability of RC muscles to recover from chronic RCT tear indicates possible deficits in repair mechanisms. Here we investigated if muscle injury state was a crucial factor during human SMP expansion and differentiation ex vivo. SMPs were isolated from muscles in patients with no, partial-thickness (PT), or full-thickness (FT) RCT tears. Despite using growth factors, physiological niche stiffness, and muscle-mimetic extracellular matrix (ECM) proteins, we found that SMPs isolated from human RC muscle with RCT tears proliferated slower but fused into myosin heavy chain (MHC)-positive myotubes at higher rates than SMPs from untorn RCTs. Proteomic analysis of RC muscle tissue revealed shifts in muscle composition with pathology, as muscle from massive RCT tears had increased ECM deposition compared with no tear RC muscle. Together these data imply that the remodeled niche in a torn RCT primes SMPs not for expansion but for differentiation, thus limiting longer-term self-renewal necessary for regeneration after surgical repair. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1816-1823, 2017. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.
Static magnetic Faraday rotation spectroscopy combined with a differential scheme for OH detection
Zhao, Weixiong; Deng, Lunhua; Qian, Xiaodong; Fang, Bo; Gai, Yanbo; Chen, Weidong; Gao, Xiaoming; Zhang, Weijun
2015-04-01
The hydroxyl (OH) radical plays a critical role in atmospheric chemistry due to its high reactivity with volatile organic compounds (VOCs) and other trace gaseous species. Because of its very short life time and very low concentration in the atmosphere, interference-free high sensitivity in-situ OH monitoring by laser spectroscopy represents a real challenge. Faraday rotation spectroscopy (FRS) relies on the particular magneto-optic effect observed for paramagnetic species, which makes it capable of enhancing the detection sensitivity and mitigation of spectral interferences from diamagnetic species in the atmosphere. When an AC magnetic field is used, the Zeeman splitting of the molecular absorption line (and thus the magnetic circular birefringence) is modulated. This provides an 'internal modulation' of the sample, which permits to suppress the external noise like interference fringes. An alternative FRS detection scheme is to use a static magnetic field (DC-field) associated with laser wavelength modulation to effectively modulate the Zeeman splitting of the absorption lines. In the DC field case, wavelength modulation of the laser frequency can provide excellent performance compared to most of the sensing systems based on direct absorption and wavelength modulation spectroscopy. The dimension of the DC solenoid is not limited by the resonant frequency of the RLC circuit, which makes large dimension solenoid coil achievable and the absorption base length could be further increased. By employing a combination of the environmental photochemical reactor or smog chamber with multipass absorption cell, one can lower the minimum detection limit for high accuracy atmospheric chemistry studies. In this paper, we report on the development of a DC field based FRS in conjunction with a balanced detection scheme for OH radical detection at 2.8 μm and the construction of OH chemistry research platform which combined a large dimension superconducting magnetic coil with the
First results of micro-neutron tomography by use of a focussing neutron lens
Masschaele, B; Cauwels, P; Dierick, M; Jolie, J; Mondelaers, W
2001-01-01
Since the appearance of high flux neutron beams, scientists experimented with neutron radiography. This high beam flux combined with modern neutron to visible light converters leads to the possibility of performing fast neutron micro-tomography. The first results of cold neutron tomography with a neutron lens are presented in this article. Samples are rotated in the beam and the projections are recorded with a neutron camera. The 3D reconstruction is performed with cone beam reconstruction software.
Duncan, Fraser Andrew
There is considerable interest in the pn to pi^-pp reaction which can proceed by a nonresonant channel from the isospin 0 pn initial state (an NDelta intermediate state cannot be formed). This thesis describes a measurement of analyzing powers and triple differential cross sections for a subset of this reaction, pn to pi^-pp(^1S_0) by isolating the quasifree process in pd to pi^-ppp_{s}. The experimental arrangement selects the relative S-wave component of the outgoing "diproton". The experiment was done on TRIUMF beam line 1B using a LD_2 target; the pion was detected in a magnetic spectrometer, the two outgoing protons in a scintillator bar array. The spectator proton was undetected. Data were taken in August 1989 at 353, 403 and 440 MeV beam energies. Of these the 403 and 440 MeV data are analysed in this thesis and analyzing powers and triple differential cross sections as a function of pion scattering angle extracted at centre of mass kinetic energies, T_{CM}, of 55 and 70 MeV (corresponding to the 403 and 440 MeV beam energies respectively). Partial wave analysis of the data shows that, while the isospin 0 channel dominates the reaction, contributing approximately 75% of the cross section at the energies studied here, there are significant contributions from the s and d-wave pion, isospin 1 channels. Of particular importance is the contribution from the s-wave pion, isospin 1, channel whose interference with the isospin 0 channels produces the characteristic shapes of the cross sections and analyzing powers observed in the data. The d-wave pion, isospin 1 channels, are also required to fully explain the observed analyzing power distributions, and are essential for the T_{CM} = 70MeV data. Comparisons of the pion production data measured in this experiment with pion absorption measurements on ^3He, where the absorption process is pi^-pp(^1S_0) to pn, show a shift in the shape of the differential cross section which can be interpreted as due to differences in
Nauchi, Yasushi; Baba, Mamoru; Iwasaki, Tomohiko [Tohoku Univ., Sendai (Japan). Faculty of Engineering] [and others
1998-03-01
The (n,xp) and (n,xd) double differential cross sections (DDXs) of Al and C were measured at 6 angles (12deg, 17deg, 25deg, 40deg, 55deg and 70deg) for neutrons En=65 and 75 MeV. These data are compared with theoretical calculations of ISOBAR and GNASH. A new wide range spectrometer under fabrication to down the detection threshold is also described. (author)
Towards rotationally state-resolved differential cross sections for the hydrogen exchange reaction
Vrakking, M.J.J.
1992-11-01
The hydrogen exchange reaction H + H{sub 2} {yields} H{sub 2} + H (and its isotopic variants) plays a pivotal role in chemical reaction dynamics. It is the only chemical reaction for which fully converged quantum scattering calculations have been carried out using a potential energy surface which is considered to be chemically accurate. To improve our ability to test the theory, a `perfect experiment`, measuring differential cross sections with complete specification of the reactant and product states, is called for. In this thesis, the design of an experiment is described that aims at achieving this goal for the D + H{sub 2} reaction. A crossed molecular beam arrangement is used, in which a photolytic D atom beam is crossed by a pulsed beam of H{sub 2} molecules. DH molecules formed in the D + H{sub 2} reaction are state-specifically ionized using Doppler-free (2+1) Resonance-Enhanced Multi-Photon Ionization (REMPI) and detected using a Position-sensitive microchannel plate detector. This detection technique has an unprecedented single shot detection sensitivity of 6.8 10{sup 3} molecules/cc. This thesis does not contain experimental results for the D + H{sub 2} reaction yet, but progress that has been made towards achieving this goal is reported. In addition, results are reported for a study of the Rydberg spectroscopy of the water molecule.
Towards rotationally state-resolved differential cross sections for the hydrogen exchange reaction
Vrakking, M.J.J.
1992-11-01
The hydrogen exchange reaction H + H[sub 2] [yields] H[sub 2] + H (and its isotopic variants) plays a pivotal role in chemical reaction dynamics. It is the only chemical reaction for which fully converged quantum scattering calculations have been carried out using a potential energy surface which is considered to be chemically accurate. To improve our ability to test the theory, a 'perfect experiment', measuring differential cross sections with complete specification of the reactant and product states, is called for. In this thesis, the design of an experiment is described that aims at achieving this goal for the D + H[sub 2] reaction. A crossed molecular beam arrangement is used, in which a photolytic D atom beam is crossed by a pulsed beam of H[sub 2] molecules. DH molecules formed in the D + H[sub 2] reaction are state-specifically ionized using Doppler-free (2+1) Resonance-Enhanced Multi-Photon Ionization (REMPI) and detected using a Position-sensitive microchannel plate detector. This detection technique has an unprecedented single shot detection sensitivity of 6.8 10[sup 3] molecules/cc. This thesis does not contain experimental results for the D + H[sub 2] reaction yet, but progress that has been made towards achieving this goal is reported. In addition, results are reported for a study of the Rydberg spectroscopy of the water molecule.
Hanson, Mark D.; Szatmari, Peter; Eva, Kevin W.
2011-01-01
Objective: The authors evaluated the differential impact of clerk interest and participation in a Child and Adolescent Psychiatry (CAP) clerkship rotation upon psychiatry and pediatrics residency matches. Method: Authors studied clerks from the McMaster University M.D. program graduating years of 2005-2007. Participants were categorized as 1)…
Hanson, Mark D.; Szatmari, Peter; Eva, Kevin W.
2011-01-01
Objective: The authors evaluated the differential impact of clerk interest and participation in a Child and Adolescent Psychiatry (CAP) clerkship rotation upon psychiatry and pediatrics residency matches. Method: Authors studied clerks from the McMaster University M.D. program graduating years of 2005-2007. Participants were categorized as 1)…
Sahan Muhittin
2017-01-01
Full Text Available In this preset study, calculations of neutron-induced alpha particle emission double-differential cross section of fluorine (19F at 14.2 MeV have been calculated by using ALICE and EMPIRE model programs for six different emission angles ranging from 30° to 150°. Calculated results from the Hybrid Monte Carlo pre-equilibrium emission and the full featured Hauser-Feshbach model have been compared with the experimental (EXFOR. The calculated double-differential cross section results using three codes are in good agreement with experimental data.
Vincze, Miklos; Borcia, Ion; Harlander, Uwe; Le Gal, Patrice
2016-12-01
A water-filled differentially heated rotating annulus with initially prepared stable vertical salinity profiles is studied in the laboratory. Based on two-dimensional horizontal particle image velocimetry data and infrared camera visualizations, we describe the appearance and the characteristics of the baroclinic instability in this original configuration. First, we show that when the salinity profile is linear and confined between two non-stratified layers at top and bottom, only two separate shallow fluid layers can be destabilized. These unstable layers appear nearby the top and the bottom of the tank with a stratified motionless zone between them. This laboratory arrangement is thus particularly interesting to model geophysical or astrophysical situations where stratified regions are often juxtaposed to convective ones. Then, for more general but stable initial density profiles, statistical measures are introduced to quantify the extent of the baroclinic instability at given depths and to analyze the connections between this depth-dependence and the vertical salinity profiles. We find that, although the presence of stable stratification generally hinders full-depth overturning, double-diffusive convection can lead to development of multicellular sideways convection in shallow layers and subsequently to a multilayered baroclinic instability. Therefore we conclude that by decreasing the characteristic vertical scale of the flow, stratification may even enhance the formation of cyclonic and anticyclonic eddies (and thus, mixing) in a local sense.
Halari, Rozmin; Sharma, Tonmoy; Hines, Melissa; Andrew, Chris; Simmons, Andy; Kumari, Veena
2006-02-01
To explicate the neural correlates of sex differences in visuospatial and verbal fluency tasks, we examined behavioural performance and blood-oxygenation-level-dependent (BOLD) regional brain activity, using functional magnetic resonance imaging, during a three-dimensional (3D) mental rotation task and a compressed sequence overt verbal fluency task in a group of healthy men (n=9) and women (n=10; tested during the low-oestrogen phase of the menstrual cycle). Men outperformed women on the mental rotation task, and women outperformed men on the verbal fluency task. For the mental rotation task, men and women activated areas in the right superior parietal lobe and the bilateral middle occipital gyrus in association with the rotation condition. In addition, men activated the left middle temporal gyrus and the right angular gyrus. For verbal fluency, men activated areas in the bilateral superior frontal gyrus, right cingulate gyrus, left precentral gyrus, left medial frontal gyrus, left inferior frontal gyrus, thalamus, left parahippocampal gyrus and bilateral lingual gyrus, and women activated areas in the bilateral inferior frontal gyrus and left caudate. Despite observing task related activation in the hypothesised areas in men and women, no areas significantly differentiated the two sexes. Our results demonstrate comparable brain activation in men and women in association with mental rotation and verbal fluency function with differential performance, and provide support for sex differences in brain-behaviour relationships.
Uddin, M.S.; Hossain, S.M.; Khan, R. [Atomic Energy Research Establishment, Dhaka (Bangladesh). Inst. of Nuclear Science and Technology (INST); Sudar, S. [Debrecen Univ. (Hungary). Inst. of Experimental Physics; Zulquarnain, M.A. [Bangladesh Atomic Energy Commission, Dhaka (Bangladesh); Qaim, S.M. [Forschungszentrum Juelich (Germany). Inst. fuer Neurowissenschaften und Medizin (INM-5)
2013-07-01
The spectrum of fast neutrons having energies from 0.5 to 20 MeV in the core of the 3MW TRIGA Mark II reactor at Savar, Dhaka, Bangladesh, was unfolded by activating several metal foils to induce threshold nuclear reactions covering the whole spectrum, and then doing necessary iterative calculations utilizing the activation results and the code SULSA. The analysed shape of the spectrum in the TRIGA core was found to be similar to that of the pure {sup 235}U-fission spectrum, except for the energies between 0.5 and 1.5 MeV, where it was slightly higher than the fission spectrum. Spectrum-averaged cross sections were determined by integral measurements. The integral values measured in this work were compared with the recommended values for a pure fission spectrum as well as with the integrated data deduced from measured and evaluated excitation functions of a few reactions given in some data files. The good agreement between integral measurements and integrated data in case of well-investigated reactions shows that the fast neutron field at the TRIGA Mark II reactor can be used for validation of evaluated data of neutron threshold reactions. (orig.)
American Society for Testing and Materials. Philadelphia
2009-01-01
1.1 This test method covers a system that performs nondestructive assay (NDA) of uranium or plutonium, or both, using the active, differential die-away technique (DDT), and passive neutron coincidence counting. Results from the active and passive measurements are combined to determine the total amount of fissile and spontaneously-fissioning material in drums of scrap or waste. Corrections are made to the measurements for the effects of neutron moderation and absorption, assuming that the effects are averaged over the volume of the drum and that no significant lumps of nuclear material are present. These systems are most widely used to assay low-level and transuranic waste, but may also be used for the measurement of scrap materials. The examples given within this test method are specific to the second-generation Los Alamos National Laboratory (LANL) passive-active neutron assay system. 1.1.1 In the active mode, the system measures fissile isotopes such as 235U and 239Pu. The neutrons from a pulsed, 14-MeV ne...
Mascarenhas, Nicholas; Marleau, Peter; Brennan, James S.; Krenz, Kevin D.
2010-06-22
An instrument that will directly image the fast fission neutrons from a special nuclear material source has been described. This instrument can improve the signal to background compared to non imaging neutron detection techniques by a factor given by ratio of the angular resolution window to 4.pi.. In addition to being a neutron imager, this instrument will also be an excellent neutron spectrometer, and will be able to differentiate between different types of neutron sources (e.g. fission, alpha-n, cosmic ray, and D-D or D-T fusion). Moreover, the instrument is able to pinpoint the source location.
Time Evolution of Relativistic Force-Free Fields Connecting a Neutron Star and its Disk
Asano, E; Matsumoto, R; Asano, Eiji; Uchida, Toshio; Matsumoto, Ryoji
2005-01-01
We study the magnetic interaction between a neutron star and its disk by solving the time-dependent relativistic force-free equations. At the initial state, we assume that the dipole magnetic field of the neutron star connects the neutron star and its equatorial disk, which deeply enters into the magnetosphere of the neutron star. Magnetic fields are assumed to be frozen to the star and the disk. The rotation of the neutron star and the disk is imposed as boundary conditions. We apply Harten-Lax-van Leer (HLL) method to simulate the evolution of the star-disk system. We carry out simulations for (1) a disk inside the corotation radius, in which the disk rotates faster than the star, and (2) a disk outside the corotation radius, in which the neutron star rotates faster than the disk. Numerical results indicate that for both models, the magnetic field lines connecting the disk and the star inflate as they are twisted by the differential rotation between the disk and the star. When the twist angle exceeds pi rad...
Platais, I; Quinn, S N; Clem, J L; de Mink, S E; Dotter, A; Kozhurina-Platais, V; Latham, D W; Bellini, A
2012-01-01
We present a detailed analysis of the upper main sequence of the 1.3 Gyr old open cluster Trumpler 20. High accuracy BV photometry combined with the Very Large Telescope/FLAMES medium-resolution spectroscopy of 954 stars is essential to understanding the unusual appearance of the color-magnitude diagram (CMD), initially suggesting multiple populations in Trumpler 20. We show that differential reddening is a dominant contributor to the apparent splitting/widening of the main-sequence turnoff region. At its extreme, the excess differential reddening reaches Delta(B-V)=0.1 while the adopted minimum reddening for the cluster is E(B-V)=0.36. A unique sample of measured projected rotational velocities indicates that stellar rotation is high near the main-sequence turnoff, reaching vsin i=180 km/s. By dividing the upper main-sequence stars into equal groups of slow and fast rotators, we find that fast rotators have a marginal blueshift of delta(V-I)=-0.01, corresponding to a difference in the median vsin i of 60 km/...
Satoh, D; Ishibashi, K
2003-01-01
Neutron-production double-differential cross sections of iron and lead for 0.8 and 1.5 GeV protons incidences were measured in the most-forward direction. Neutrons were measured by the time-of-flight (TOF) method. An NE213 liquid organic scintillator was set at 0deg as a neutron detector. Neutron detection efficiencies were obtained by calculations with a Monte Carlo simulation code SCINFUL-QMD. The present experimental data were compared with other reported experimental data and the results of calculation codes based on Intranuclear-Cascade-Evaporation (INC/E) and Quantum Molecular Dynamics (QMD) models. For neutrons associated with DELTA formation, the present data deviated from predictions of these codes, and gave magnitudes between them in both 0.8 and 1.5 GeV incidences. (author)
Drosg, Manfred
2016-01-01
Estimated cross sections for neutron production from triton bombardment of gold are deduced from measurements of triton interactions with gas targets that used gold as a triton beam stop material. Differential cross sections for production of neutrons from 5.97-, 7.47-, 10.45-, 16.41- and 19.14-MeV tritons on 197Au were evaluated. Corrections for the neutron interaction in gold, in the target structure and in the air of the flight path were obtained by means of a Monte Carlo technique. Uncorrelated scale uncertainties range from 24 to 41% whereas those of double differential cross sections range from 0.2 to 5%. Based on these cross section data, calculation of neutron yield at 0o from fully stopped tritons at 20.22 MeV agree with an independent measurement. Least-squares fits with a gamma distribution model indicate an anisotropy in the high energy portion of the neutron spectra. Legendre polynomial fits of differential cross sections are reported. All neutron cross section data are made available through the...
Jets from Merging Neutron Stars
Kohler, Susanna
2016-06-01
With the recent discovery of gravitational waves from the merger of two black holes, its especially important to understand the electromagnetic signals resulting from mergers of compact objects. New simulations successfully follow a merger of two neutron stars that produces a short burst of energy via a jet consistent with short gamma-ray burst (sGRB) detections.Still from the authors simulation showing the two neutron stars, and their magnetic fields, before merger. [Adapted from Ruiz et al. 2016]Challenging SystemWe have long suspected that sGRBs are produced by the mergers of compact objects, but this model has been difficult to prove. One major hitch is that modeling the process of merger and sGRB launch is very difficult, due to the fact that these extreme systems involve magnetic fields, fluids and full general relativity.Traditionally, simulations are only able to track such mergers over short periods of time. But in a recent study, Milton Ruiz (University of Illinois at Urbana-Champaign and Industrial University of Santander, Colombia) and coauthors Ryan Lang, Vasileios Paschalidis and Stuart Shapiro have modeled a binary neutron star system all the way through the process of inspiral, merger, and the launch of a jet.A Merger TimelineHow does this happen? Lets walk through one of the teams simulations, in which dipole magnetic field lines thread through the interior of each neutron star and extend beyond its surface(like magnetic fields found in pulsars). In this example, the two neutron stars each have a mass of 1.625 solar masses.Simulation start (0 ms)Loss of energy via gravitational waves cause the neutron stars to inspiral.Merger (3.5 ms)The neutron stars are stretched by tidal effects and make contact. Their merger produces a hypermassive neutron star that is supported against collapse by its differential (nonuniform) rotation.Delayed collapse into a black hole (21.5 ms)Once the differential rotation is redistributed by magnetic fields and partially
Alam, Muntasir; Kamruzzaman, Ahsan, Faraz; Hasan, Mohammad Nasim
2016-07-01
A numerical study of mixed convection heat transfer phenomena in a square cavity containing a heat conducting rotating cylinder has been investigated. A discrete isoflux heater is placed at the bottom wall of the enclosure while the top wall is kept adiabatic. Left and right sidewalls of the enclosure are assumed to be maintained at constant low temperature. A two-dimensional solution for steady laminar mixed convection flow is obtained by using the finite element scheme based on the Galerkin method of weighted residuals for different rotating speeds of the cylinder varying over the range of 0-1000 keeping the Rayleigh number fixed at 5×104 and the Prandtl number at 0.7. The effects of rotating speeds of the cylinder, its radius and conductivity ratio of the rotating cylinder and working fluid on the streamlines, isotherms, local Nusselt number, average Nusselt number and other heat transfer and fluid flow phenomena are investigated. The results indicate that the flow field, temperature distribution and heat transfer rate are dependent on rotating speeds and cylinder size. However, it has been observed that the effect of conductivity ratio is not so prominent.
Neutron stars - General review
Cameron, A. G. W.; Canuto, V.
1974-01-01
A review is presented of those properties of neutron stars upon which there is general agreement and of those areas which currently remain in doubt. Developments in theoretical physics of neutron star interiors are summarized with particular attention devoted to hyperon interactions and the structure of interior layers. Determination of energy states and the composition of matter is described for successive layers, beginning with the surface and proceeding through the central region into the core. Problems encountered in determining the behavior of matter in the ultra-high density regime are discussed, and the effects of the magnetic field of a neutron star are evaluated along with the behavior of atomic structures in the field. The evolution of a neutron star is outlined with discussion centering on carbon detonation, cooling, vibrational damping, rotation, and pulsar glitches. The role of neutron stars in cosmic-ray propagation is considered.
Fast-neutron total and scattering cross sections of sup 58 Ni and nuclear models
Smith, A.B.; Guenther, P.T.; Whalen, J.F. (Argonne National Lab., IL (United States)); Chiba, S. (Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment)
1991-07-01
The neutron total cross sections of {sup 58}Ni were measured from {approx} 1 to > 10 MeV using white-source techniques. Differential neutron elastic-scattering cross sections were measured from {approx} 4.5 to 10 MeV at {approx} 0.5 MeV intervals with {ge} 75 differential values per distribution. Differential neutron inelastic-scattering cross sections were measured, corresponding to fourteen levels with excitations up to 4.8 MeV. The measured results, combined with relevant values available in the literature, were interpreted in terms of optical-statistical and coupled-channels model using both vibrational and rotational coupling schemes. The physical implications of the experimental results nd their interpretation are discussed in the contexts of optical-statistical, dispersive-optical, and coupled-channels models. 61 refs.
Kallinger, T.; Weiss, W. W.; Beck, P. G.; Pigulski, A.; Kuschnig, R.; Tkachenko, A.; Pakhomov, Y.; Ryabchikova, T.; Lüftinger, T.; Palle, , P. L.; Semenko, E.; Handler, G.; Koudelka, O.; Matthews, J. M.; Moffat, A. F. J.; Pablo, H.; Popowicz, A.; Rucinski, S.; Wade, G. A.; Zwintz, K.
2017-07-01
Context. Stellar rotation affects the transport of chemical elements and angular momentum and is therefore a key process during stellar evolution, which is still not fully understood. This is especially true for massive OB-type stars, which are important for the chemical enrichment of the Universe. It is therefore important to constrain the physical parameters and internal angular momentum distribution of massive OB-type stars to calibrate stellar structure and evolution models. Stellar internal rotation can be probed through asteroseismic studies of rotationally split non radial oscillations but such results are still quite rare, especially for stars more massive than the Sun. The slowly pulsating B9V star HD 201433 is known to be part of a single-lined spectroscopic triple system, with two low-mass companions orbiting with periods of about 3.3 and 154 days. Aims: Our goal is to measure the internal rotation profile of HD 201433 and investigate the tidal interaction with the close companion. Methods: We used probabilistic methods to analyse the BRITE - Constellation photometry and radial velocity measurements, to identify a representative stellar model, and to determine the internal rotation profile of the star. Results: Our results are based on photometric observations made by BRITE - Constellation and the Solar Mass Ejection Imager on board the Coriolis satellite, high-resolution spectroscopy, and more than 96 yr of radial velocity measurements. We identify a sequence of nine frequency doublets in the photometric time series, consistent with rotationally split dipole modes with a period spacing of about 5030 s. We establish that HD 201433 is in principle a solid-body rotator with a very slow rotation period of 297 ± 76 days. Tidal interaction with the inner companion has, however, significantly accelerated the spin of the surface layers by a factor of approximately one hundred. The angular momentum transfer onto the surface of HD 201433 is also reflected by the
Henzl, Vladimir [Los Alamos National Laboratory; Croft, Stephen [Los Alamos National Laboratory; Swinhoe, Martyn T. [Los Alamos National Laboratory; Tobin, Stephen J. [Los Alamos National Laboratory
2012-07-18
A key objective of the Next Generation Safeguards Initiative (NGSI) is to evaluate and develop non-destructive assay (NDA) techniques to determine the elemental plutonium content in a commercial-grade nuclear spent fuel assembly (SFA) [1]. Within this framework, we investigate by simulation a novel analytical approach based on combined information from passive measurement of the total neutron count rate of a SFA and its multiplication determined by the active interrogation using an instrument based on a Differential Die-Away technique (DDA). We use detailed MCNPX simulations across an extensive set of SFA characteristics to establish the approach and demonstrate its robustness. It is predicted that Pu content can be determined by the proposed method to a few %.
Magnetized Hypermassive Neutron Star Collapse: a candidate central engine for short-hard GRBs
Stephens, Branson C; Liu, Yuk Tung; Shapiro, Stuart L; Shibta, Masaru
2016-01-01
Hypermassive neutron stars (HMNSs) are equilibrium configurations supported against collapse by rapid differential rotation and likely form as transient remnants of binary neutron star mergers. Though HMNSs are dynamically stable, secular effects such as viscosity or magnetic fields tend to bring HMNSs into uniform rotation and thus lead to collapse. We simulate the evolution of magnetized HMNSs in axisymmetry using codes which solve the Einstein-Maxwell-MHD system of equations. We find that magnetic braking and the magnetorotational instability (MRI) both contribute to the eventual collapse of HMNSs to rotating black holes surrounded by massive, hot accretion tori and collimated magnetic fields. Such hot tori radiate strongly in neutrinos, and the resulting neutrino-antineutrino annihilation could power short-hard GRBs.
Neutron Stars Recent Developments
Heiselberg, H
1999-01-01
Recent developments in neutron star theory and observation are discussed. Based on modern nucleon-nucleon potentials more reliable equations of state for dense nuclear matter have been constructed. Furthermore, phase transitions such as pion, kaon and hyperon condensation, superfluidity and quark matter can occur in cores of neutron stars. Specifically, the nuclear to quark matter phase transition and its mixed phases with intriguing structures is treated. Rotating neutron stars with and without phase transitions are discussed and compared to observed masses, radii and glitches. The observations of possible heavy $\\sim 2M_\\odot$ neutron stars in X-ray binaries and QPO's require relatively stiff equation of states and restrict strong phase transitions to occur at very high nuclear densities only.
Passamonti, A; Gualtieri, L; Nagar, A; Sopuerta, C F
2006-01-01
We investigate the non-linear coupling between radial and non-radial oscillations of static spherically symmetric neutron stars as a possible mechanism for the generation of gravitational waves that may lead to observable signatures. In this paper we concentrate on the axial sector of the non-radial perturbations. By using a multi-parameter perturbative framework we introduce a complete description of the non-linear coupling between radial and axial non-radial oscillations; we study the gauge invariant character of the associated perturbative variables and develop a computational scheme to evolve the non-linear coupling perturbations in the time domain. We present results of simulations corresponding to different physical situations and discuss the dynamical behaviour of this non-linear coupling. Of particular interest is the occurrence of signal amplifications in the form of resonance phenomena when a frequency associated with the radial pulsations is close to a frequency associated with one of the axial w-m...
McIntyre, M. E.
2003-04-01
The tachocline is characterized by large gradient Richardson number and a fluid-dynamical parameter regime like that of the Earth's stratosphere. It follows that any turbulence present will be layerwise-two-dimensional and potential-vorticity-transporting, not momentum-transporting. Such regimes are well understood from terrestrial ozone-layer studies. In particular, if horizontal Reynolds stresses are significant in such regimes, then they are unlikely to conform to any "horizontal eddy viscosity" paradigm (as fully explained in McIntyre 2003, Gough Festschrift paper at www.atm.damtp.cam.ac.uk/people/mem/). It follows, as argued in Gough and McIntyre 1998 (same website, and Nature 394, 755) that the helioseismically-inferred near-solid rotation beneath the tachocline can only be due to a poloidal, probably primordial dipolar, interior magnetic field. Gough and McIntyre estimated its strength as very roughly of order 1 gauss. The existence of this field allows several other pieces of the convection-zone/tachocline jigsaw puzzle to fall into place. They include "tachocline sound-speed anomaly" and the confinement of the tachocline ventilation circulation, which must be gyroscopically pumped from above by the turbulent Reynolds and Maxwell stresses interior to the convection zone and which would therefore burrow further downwards in the absence of the interior poloidal field. The talk will summarize these ideas and try to carry them forward by formulating and discussing the simplest tenable model of the dynamical coupling between convection zone and tachocline, taking account of magneto-rotational instabilities.
Kokooo; Murata, Isao; Takahashi, Akito [Osaka Univ., Suita (Japan). Faculty of Engineering
1997-03-01
The double differential cross sections of V(n,xp) and V(n,x{alpha}) reactions have been measured by using the E-TOF spectrometer. The measured data were compared with other experimental data and evaluated nuclear data of JENDL Fusion-File. (author)
Zhai, Yong; Chong, Parkson Lee-Gau; Taylor, Leeandrew Jacques-Asa; Erlkamp, Mirko; Grobelny, Sebastian; Czeslik, Claus; Watkins, Erik; Winter, Roland
2012-03-20
The polar lipid fraction E (PLFE) is a major tetraether lipid component in the thermoacidophilic archaeon Sulfolobus acidocaldarius. Using differential scanning and pressure perturbation calorimetry as well as ultrasound velocity and density measurements, we have determined the compressibilities and volume fluctuations of PLFE liposomes derived from different cell growth temperatures (T(g) = 68, 76, and 81 °C). The compressibility and volume fluctuation values of PLFE liposomes, which are substantially less than those detected from diester lipid membranes (e.g., DPPC), exhibit small but significant differences with T(g). Among the three T(g)s employed, 76 °C leads to the least compressible and most tightly packed PLFE membranes. This temperature is within the range for optimal cell growth (75-80 °C). It is known that a decrease in T(g) decreases the number of cyclopentane rings in archael tetraether lipids. Thus, our data enable us to present the new view that membrane packing in PLFE liposomes varies with the number of cyclopentane rings in a nonlinear manner, reaching maximal tightness when the tetraether lipids are derived from cells grown at optimal T(g)s. In addition, we have studied the effects of pressure on total layer thickness, d, and neutron scattering length density, ρ(n), of a silicon-D(2)O interface that is covered with a PLFE membrane using neutron reflectometry (NR). At 55 °C, d and ρ(n) are found to be rather insensitive to pressure up to 1800 bar, suggesting minor changes of the thickness of the membrane's hydrophobic core and headgroup orientation upon compression only.
Söderström, P.-A., E-mail: pasoder@ribf.riken.jp; Doornenbal, P.; Nishimura, S.; Baba, H.; Fukuda, N.; Inabe, N.; Isobe, T.; Kubo, T.; Kubono, S.; Suzuki, H.; Takeda, H. [RIKEN Nishina Center, 2-1 Hirosawa, Wako-shi, Saitama 351-0198 (Japan); Regan, P. H. [Department of Physics, University of Surrey, Guildford, GU2 7XH (United Kingdom); National Physical Laboratory, Teddington, Middlesex, TW11 0LW (United Kingdom); Walker, P. M.; Carroll, R.; Lalkovski, S.; Lotay, G.; Patel, Z.; Podolyák, Zs.; Shand, C. M. [Department of Physics, University of Surrey, Guildford, GU2 7XH (United Kingdom); Watanabe, H. [IRCNPC, Beihang University, Beijing 100191 (China); School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191 (China); and others
2015-10-15
In this contribution the low-excitation structural properties of the doubly mid-shell nucleus {sup 170}Dy are discussed, with a special empasis on the evolution of the ground state rotational band within the dysprosium isotopic chain. Recent results from an experiment with the EURICA setup at RIKEN are shown in the context of previous measurements at the PRISMA+CLARA as well as the PRISMA+AGATA setups at Laboratori Nazionali di Legnaro. A brief outlook on future planned measurements is also given.
Multi-messenger observations of neutron rich matter
Horowitz, C J
2011-01-01
Neutron rich matter is central to many fundamental questions in nuclear physics and astrophysics. Moreover, this material is being studied with an extraordinary variety of new tools such as the Facility for Rare Isotope Beams (FRIB) and the Laser Interferometer Gravitational Wave Observatory (LIGO). We describe the Lead Radius Experiment (PREX) that uses parity violating electron scattering to measure the neutron radius in $^{208}$Pb. This has important implications for neutron stars and their crusts. We discuss X-ray observations of neutron star radii. These also have important implications for neutron rich matter. Gravitational waves (GW) open a new window on neutron rich matter. They come from sources such as neutron star mergers, rotating neutron star mountains, and collective r-mode oscillations. Using large scale molecular dynamics simulations, we find neutron star crust to be very strong. It can support mountains on rotating neutron stars large enough to generate detectable gravitational waves. Finally...
Shahamatnia Ehsan
2016-01-01
Full Text Available Developing specialized software tools is essential to support studies of solar activity evolution. With new space missions such as Solar Dynamics Observatory (SDO, solar images are being produced in unprecedented volumes. To capitalize on that huge data availability, the scientific community needs a new generation of software tools for automatic and efficient data processing. In this paper a prototype of a modular framework for solar feature detection, characterization, and tracking is presented. To develop an efficient system capable of automatic solar feature tracking and measuring, a hybrid approach combining specialized image processing, evolutionary optimization, and soft computing algorithms is being followed. The specialized hybrid algorithm for tracking solar features allows automatic feature tracking while gathering characterization details about the tracked features. The hybrid algorithm takes advantages of the snake model, a specialized image processing algorithm widely used in applications such as boundary delineation, image segmentation, and object tracking. Further, it exploits the flexibility and efficiency of Particle Swarm Optimization (PSO, a stochastic population based optimization algorithm. PSO has been used successfully in a wide range of applications including combinatorial optimization, control, clustering, robotics, scheduling, and image processing and video analysis applications. The proposed tool, denoted PSO-Snake model, was already successfully tested in other works for tracking sunspots and coronal bright points. In this work, we discuss the application of the PSO-Snake algorithm for calculating the sidereal rotational angular velocity of the solar corona. To validate the results we compare them with published manual results performed by an expert.
Differential rotation of the active G5V star Kappa1 Ceti: Photometry from the MOST satellite
Rucinski, S M; Matthews, J M; Kuschnig, R; Shkolnik, E; Marchenko, S; Bohlender, D A; Günther, D B; Moffat, A F J; Sasselov, D; Weiss, W W; Rucinski, Slavek M.; Walker, Gordon A.H.; Matthews, Jaymie M.; Kuschnig, Rainer; Shkolnik, Evgenya; Marchenko, Sergey; Bohlender, David A.; Moffat, Anthony F.J.; Sasselov, Dimitar; Weiss, Werner W.
2004-01-01
About 30.5 days of nearly uninterrupted broadband photometry of the solar-type star Kappa1 Ceti, obtained with the MOST (Microvariability & Oscillations of STars) satellite, shows evidence for two large starspots with different rotation periods of 8.9 and approximately 9.3 days (DeltaOmega/Omega~4%). Ground based measurements in 2002 and 2003 of Ca II H & K emission reveal variations in chromospheric activity with a period of about 9.3 days. The data were obtained during the MOST commissioning phase. When the data are combined with historical observations, they indicate that the 9.3-day spot has been stable in its period for over 30 years. The photometry, with a sampling rate of approximately once per minute, was also used to search for acoustic (p-mode) oscillations in the star. We detect no clear evidence for p-modes in the Kappa1 Ceti photometry, with a noise level around 7-9 mu_mag at frequencies in the range 0.5-4 mHz (3-sigma detection limit of 21 - 27 mu_mag). There were no flares or planetary ...
Henry, Gregory W.; Eaton, Joel A.; Hamer, Jamesia; Hall, Douglas S.
1995-01-01
We have analyzed 15-19 yr of photoelectric photometry, obtained manually and with automated telescopes, of the chromospherically active binaries lambda And, sigma Gem, II Peg, and V711 Tau. These observations let us identify individual dark starspots on the stellar surfaces from periodic dimming of the starlight, follow the evolution of these spots, and search for long-term cyclic changes in the properties of these starspots that might reveal magnetic cycles analogous to the Sun's 11 yr sunspot cycle. We developed a computer code to fit a simple two-spot model to our observed light curves that allows us to extract the most easily determinable and most reliable spot parameters from the light curves, i.e., spot longitudes and radii. We then used these measured properties to identify individual spots and to chart their life histories by constructing migration and amplitude curves. We identified and followed 11 spots in lambda And, 16 in sigma Gem, 12 in II Peg, and 15 in V711 Tau. Lifetimes of individual spots ranged from a few months to longer than 6 yr. Differential rotation coefficients, estimated from the observed range of spot rotation periods for each star and defined by equation (2), were 0.04 for lambda And, 0.038 for sigma Gem, 0.005 for II Peg, and 0.006 for V711 Tau, versus 0.19 for the Sun. We searched for cyclic changes in mean brightness, B-V color index, and spot rotation period as evidence for long-term cycles. Of these, long-term variability in mean brightness appears to offer the best evidence for such cycles in these four stars. Cycles of 11.1 yr for lambda And, 8.5 yr for sigma Gem, 11 yr for II Peg, and 16 yr V711 Tau are implied by these mean brightness changes. Cyclic changes in spot rotation period were found in lambda And and possibly II Peg. Errors in B-V were too large for any long-term changes to be detectable.
Implications of the r-mode instability of rotating relativistic stars
Friedman, J L; Friedman, John L.; Lockitch, Keith H.
2002-01-01
Several recent surprises appear dramatically to have improved the likelihood that the spin of rapidly rotating, newly formed neutron stars (and, possibly, of old stars spun up by accretion) is limited by a nonaxisymmetric instability driven by gravitational waves. Except for the earliest part of the spin-down, the axial l=m=2 mode (an r-mode) dominates the instability, and the emitted waves may be observable by detectors with the sensitivity of LIGO II. A review of these hopeful results is followed by a discussion of constraints on the instability set by dissipative mechanisms, including viscosity, nonlinear saturation, and energy loss to a magnetic field driven by differential rotation.
Yachmenev, Andrey; Yurchenko, Sergei N
2015-07-07
We present a new numerical method to construct a rotational-vibrational Hamiltonian of a general polyatomic molecule in the Eckart frame as a power series expansion in terms of curvilinear internal coordinates. The expansion of the kinetic energy operator of an arbitrary order is obtained numerically using an automatic differentiation (AD) technique. The method is applicable to molecules of arbitrary size and structure and is flexible for choosing various types of internal coordinates. A new way of solving the Eckart-frame equations for curvilinear coordinates also based on the AD technique is presented. The resulting accuracy of the high-order expansion coefficients for the kinetic energy operator using our numerical technique is comparable to that obtained by symbolic differentiation, with the advantage of being faster and less demanding in memory. Examples for H2CO, NH3, PH3, and CH3Cl molecules demonstrate the advantages of the curvilinear internal coordinates and the Eckart molecular frame for accurate ro-vibrational calculations. Our results show that very high accuracy and quick convergence can be achieved even with moderate expansions if curvilinear coordinates are employed, which is important for applications involving large polyatomic molecules.
Yachmenev, Andrey; Yurchenko, Sergei N.
2015-07-01
We present a new numerical method to construct a rotational-vibrational Hamiltonian of a general polyatomic molecule in the Eckart frame as a power series expansion in terms of curvilinear internal coordinates. The expansion of the kinetic energy operator of an arbitrary order is obtained numerically using an automatic differentiation (AD) technique. The method is applicable to molecules of arbitrary size and structure and is flexible for choosing various types of internal coordinates. A new way of solving the Eckart-frame equations for curvilinear coordinates also based on the AD technique is presented. The resulting accuracy of the high-order expansion coefficients for the kinetic energy operator using our numerical technique is comparable to that obtained by symbolic differentiation, with the advantage of being faster and less demanding in memory. Examples for H2CO, NH3, PH3, and CH3Cl molecules demonstrate the advantages of the curvilinear internal coordinates and the Eckart molecular frame for accurate ro-vibrational calculations. Our results show that very high accuracy and quick convergence can be achieved even with moderate expansions if curvilinear coordinates are employed, which is important for applications involving large polyatomic molecules.
Jernigan, J G
2001-01-01
The basic theory of torque free precession (TFP) of the outer crust of a neutron star (NS) as the signature of the approach to NS breakup is a viable explanation of the uniform properties of kHz Quasi-periodic Oscillations (QPO) observed in X-rays emitted by Low Mass X-ray Binary (LMXB) sources. The theory outlined in this paper relates the intrinsic properties of NS structure to the observed kHz frequencies. The range of kHz frequencies and the observed quality factors (Qs) are also explained by this simple dynamical model. A scenario that begins with the melting of the inner crust of an LMXB NS creates the conditions necessary for the generation of kHz QPO. The theory relates the ratio of the observed kHz frequencies to the ratios of the components of the moments of inertia of the NS, thereby tightly constraining the equation of state (EOS) of NS matter (polytrope index ~1.0). The TFP model is in strong contrast to existing models which primarily relate the kHz QPO phenomenon to the physics of gas dynamics ...
DeWyngaert, J.K.; Leith, J.T.; Peck, R.A.; Bliven, S.F.
1981-10-01
For tumor cell subpopulations which were isolated from a single mouse mammary adenocarcinoma were examined for their relative sensitivities to 250-kVp x irradiation and 14.8-MeV neutron irradiation. The sublines are designated 66, 67, 4.10, and 68H and differ significantly in their biological characteristics. Exponentially growing cells were exposed at the Radiological Research Accelerator Facility (RARAF) at Brookhaven National Laboratories, Upton, NY. The purpose of these studies was to compare the response of these cell lines to ionizing radiation, for high-linear-energy-transfer radiation as well as for low. The interest of such an intercomparison lies in the fact that these different cell lines, while closely related, were biologically distinguishable. Survival curve parameters obtained by fitting the single dose-response curves to a linear-quadratic equation using linear least-squares regression analysis gave values for sublines 66, 67, 4.10, and 68H, respectively, of: ..cap alpha../sub n/ (G/sub 8//sup -1/) = 0.00. 0.150, 0.041, and 0.182; ..cap alpha../sub x/ (G/sub 8//sup -1/) = 0.672, 0.845, 0.787, and 0.709; ..beta../sub x/ (G/sub 8//sup -2/) = 0.0462, 0.0345, 0.0576, and 0.0503; and ..beta../sub n/ (G/sub 8//sup -2/) = 0.0253, 0.0000, 0.0156, and 0.0666. Different relative biological effectiveness (RBE) values were obtained for sublines 66, 67, 4.10, and 68H of 4.0, 3.6, 3.9, and 2.7 at the 50% level of survival and 2.4, 2.4, 2.2, and 2.0 at the 10% level. Sublines 67 and 68H show responses which suggest a constant RBE at low values of dose, while sublines 66 and 4.10 do not. It is felt that these data illustrate the need to consider biological information as well as microdosimetric considerations in attempts to relate celluar inactivation responses to radiation quality. Further implications of these data in relation to the dual-action model of radiation inactivation are discussed.
Litaize, O
2000-07-01
The goal of this thesis is to study the neutron propagation by reflection from lacunar medium interfaces. The most efficient method to calculate this type of propagation is to use the concept of albedo. Actual version of NARCISSE code uses a simple formulation of angular differential albedos and so, can only treat single reflections. Multiple reflections treatment needs the knowledge of neutron spectrum after reflection. This energetic information is contained in double angular and energy differential albedos. The first step of this study consists to generate these albedos for various materials. Several methods have been tested and the Monte Carlo method was retained. A new estimator has been developed and validated in the Mote Carlo transport code TRIPOLI-4. It computes, during the simulation of the neutron history, the angular and energy reflection probability at each collision site. The second step consists to generate an interpolation scheme and albedo libraries for various materials. A new version of NARCISSE was developed to use these libraries and the interpolation module. Spectrum and dose rates comparisons were made between codes to validate these albedos. The neutron propagation by multiple reflections can be studied now, by using this new version of Narcisse. (author)
Gomez, Alice; Cerles, Mélanie; Rousset, Stéphane; Rémy, Chantal; Baciu, Monica
2014-01-01
The way new spatial information is encoded seems to be crucial in disentangling the role of decisive regions within the spatial memory network (i.e., hippocampus, parahippocampal, parietal, retrosplenial,…). Several data sources converge to suggest that the hippocampus is not always involved or indeed necessary for allocentric processing. Hippocampal involvement in spatial coding could reflect the integration of new information generated by "online" self-related changes. In this fMRI study, the participants started by encoding several object locations in a virtual reality environment and then performed a pointing task. Allocentric encoding was maximized by using a survey perspective and an object-to-object pointing task. Two egocentric encoding conditions were used, involving self-related changes processed under a first-person perspective and implicating a self-to-object pointing task. The Egocentric-updating condition involved navigation whereas the Egocentric with rotation only condition involved orientation changes only. Conjunction analysis of spatial encoding conditions revealed a wide activation of the occipito-parieto-frontal network and several medio-temporal structures. Interestingly, only the cuneal areas were significantly more recruited by the allocentric encoding in comparison to other spatial conditions. Moreover, the enhancement of hippocampal activation was found during Egocentric-updating encoding whereas the retrosplenial activation was observed during the Egocentric with rotation only condition. Hence, in some circumstances, hippocampal and retrosplenial structures-known for being involved in allocentric environmental coding-demonstrate preferential involvement in the egocentric coding of space. These results indicate that the raw differentiation between allocentric versus egocentric representation seems to no longer be sufficient in understanding the complexity of the mechanisms involved during spatial encoding.
Fomina, Margarita; Schirò, Giorgio; Cupane, Antonio
2014-01-01
In this work we present a thorough investigation of the hydration dependence of myoglobin dynamics. The study is performed on D2O-hydrated protein powders in the hydration range 0Differential Scanning Calorimetry is used to obtain a thermodynamic description of the system. The effect of increasing hydration is to speed up the relaxations of the myoglobin+hydration water system and, thermodynamically, to decrease the glass transition temperature; these effects tend to saturate at h values greater than ~0.3. Moreover, the calorimetric scans put in evidence the occurrence of an endothermic peak whose onset temperature is located at ~230K independent of hydration. From the point of view of the protein equilibrium fluctuations, while the amplitude of anharmonic mean square displacements is found to increase with hydration, their onset temperature (i.e. the onset temperature of the well known "protein dynamical transition") is hydration independent. On the basis of the above results, the relevance of protein+hydration water relaxations and of the thermodynamic state of hydration water to the onset of the protein dynamical transition is discussed. Copyright © 2013 Elsevier B.V. All rights reserved.
Grand Unification in Neutron Stars
Kaspi, Victoria M
2010-01-01
The last decade has shown us that the observational properties of neutron stars are remarkably diverse. From magnetars to rotating radio transients, from radio pulsars to `isolated neutron stars,' from central compact objects to millisecond pulsars, observational manifestations of neutron stars are surprisingly varied, with most properties totally unpredicted. The challenge is to establish an overarching physical theory of neutron stars and their birth properties that can explain this great diversity. Here I survey the disparate neutron stars classes, describe their properties, and highlight results made possible by the Chandra X-ray Observatory, in celebration of its tenth anniversary. Finally, I describe the current status of efforts at physical `grand unification' of this wealth of observational phenomena, and comment on possibilities for Chandra's next decade in this field.
Grand unification of neutron stars.
Kaspi, Victoria M
2010-04-20
The last decade has shown us that the observational properties of neutron stars are remarkably diverse. From magnetars to rotating radio transients, from radio pulsars to isolated neutron stars, from central compact objects to millisecond pulsars, observational manifestations of neutron stars are surprisingly varied, with most properties totally unpredicted. The challenge is to establish an overarching physical theory of neutron stars and their birth properties that can explain this great diversity. Here I survey the disparate neutron stars classes, describe their properties, and highlight results made possible by the Chandra X-Ray Observatory, in celebration of its 10th anniversary. Finally, I describe the current status of efforts at physical "grand unification" of this wealth of observational phenomena, and comment on possibilities for Chandra's next decade in this field.
Grand unification of neutron stars
Kaspi, Victoria M.
2010-01-01
The last decade has shown us that the observational properties of neutron stars are remarkably diverse. From magnetars to rotating radio transients, from radio pulsars to isolated neutron stars, from central compact objects to millisecond pulsars, observational manifestations of neutron stars are surprisingly varied, with most properties totally unpredicted. The challenge is to establish an overarching physical theory of neutron stars and their birth properties that can explain this great diversity. Here I survey the disparate neutron stars classes, describe their properties, and highlight results made possible by the Chandra X-Ray Observatory, in celebration of its 10th anniversary. Finally, I describe the current status of efforts at physical “grand unification” of this wealth of observational phenomena, and comment on possibilities for Chandra’s next decade in this field. PMID:20404205
Manuel, Oliver K.
2011-01-01
Earth is connected gravitationally, magnetically and electrically to its heat source - a neutron star that is obscured from view by waste products in the photosphere. Neutron repulsion is like the hot filament in an incandescent light bulb. Excited neutrons are emitted from the solar core and decay into hydrogen that glows in the photosphere like a frosted light bulb. Neutron repulsion was recognized in nuclear rest mass data in 2000 as the overlooked source of energy, the keystone of an arch...
Accretion Models for Young Neutron Stars
Alpar, M. Ali
2003-01-01
Interaction with possible fallback material, along with the magnetic fields and rotation rates at birth should determine the fates and categories of young neutron stars. This paper addresses some issues related to pure or hybrid accretion models for explaining the properties of young neutron stars.
Recycling of Neutron Stars in Common Envelopes and Hypernova Explosions
Barkov, Maxim V
2010-01-01
In this paper we propose a new plausable mechanism of supernova explosions specific to close binary systems. The starting point is the common envelope phase in the evolution of a binary consisting of a red super giant and a neutron star. As the neutron star spirals towards the center of its companion it spins up via disk accretion. Depending on the specific angular momentum of gas captured by the neutron star via the Bondi-Hoyle mechanism, it may reach millisecond periods either when it is still inside the common envelope or after it has merged with the companion core. Then it can generate magnetar strength magnetic field via becoming unstable to emission of gravitational waves and developing strong differential rotation, as this has been recently proposed by H.Spruit. The magnetar wind can blow away the common envelope if its magnetic field is as strong as $10^{15}\\,$G, and can destroy the entire companion if it is as strong as $10^{16}\\,$G. The total explosion energy can be comparable to the rotational ener...
Solar rotation gravitational moments
A. Ajabshirizadeh
2005-09-01
Full Text Available Gravitational multipole moments of the Sun are still poorly known. Theoretically, the difficulty is mainly due to the differential rotation for which the velocity rate varies both on the surface and with the depth. From an observational point of view, the multipole moments cannot be directly measured. However, recent progresses have been made proving the existence of a strong radial differential rotation in a thin layer near the solar surface (the leptocline. Applying the theory of rotating stars, we will first compute values of J2 and J4 taking into account the radial gradient of rotation, then we will compare these values with the existing ones, giving a more complete review. We will explain some astrophysical outcomes, mainly on the relativistic Post Newtonian parameters. Finally we will conclude by indicating how space experiments (balloon SDS flights, Golf NG, Beppi-Colombo, Gaia... will be essential to unambiguously determine these parameters.
A slow neutron polarimeter for the measurement of parity-odd neutron rotary power
Snow, W. M.; Anderson, E.; Bass, T. D.; Dawkins, J. M.; Fry, J.; Haddock, C.; Horton, J. C.; Luo, D.; Micherdzinska, A. M.; Walbridge, S. B. [Indiana University and Center for the Exploration of Energy and Matter, 2401 Milo B. Sampson Lane, Bloomington, Indiana 47408 (United States); Barrón-Palos, L.; Maldonado-Velázquez, M. [Instituto de Física, Universidad Nacional Autónoma de México, Ciudad de México, D.F. 04510, México (Mexico); Bass, C. D. [LeMoyne College, 1419 Salt Springs Road, Syracuse, New York 13214 (United States); Crawford, B. E. [Gettysburg College, 300 North Washington Street, Gettysburg, Pennsylvania 17325 (United States); Crawford, C. [University of Kentucky, 177 Chem.-Phys. Building, 505 Rose Street, Lexington, Kentucky 40506-0055 (United States); Esposito, D. [University of Dayton, 300 College Park, Dayton, Ohio 45469 (United States); Gardiner, H. [Louisiana State University, Baton Rouge, Louisiana 70803 (United States); Gan, K. [The George Washington University, 2121 I Street N.W., Washington, District of Columbia 20052 (United States); Heckel, B. R.; Swanson, H. E., E-mail: swanson@npl.washington.edu [University of Washington/Center for Experimental Nuclear Physics and Astrophysics, Box 354290, Seattle, Washington 98195 (United States); and others
2015-05-15
We present the design, description, calibration procedure, and an analysis of systematic effects for an apparatus designed to measure the rotation of the plane of polarization of a transversely polarized slow neutron beam as it passes through unpolarized matter. This device is the neutron optical equivalent of a crossed polarizer/analyzer pair familiar from light optics. This apparatus has been used to search for parity violation in the interaction of polarized slow neutrons in matter. Given the brightness of existing slow neutron sources, this apparatus is capable of measuring a neutron rotary power of dϕ/dz = 1 × 10{sup −7} rad/m.
The Electromagnetic Spectrum of Neutron Stars
Baykal, Altan; Inam, Sitki C; Grebenev, Sergei
2005-01-01
Neutron stars hold a central place in astrophysics, not only because they are made up of the most extreme states of the condensed matter, but also because they are, along with white dwarfs and black holes, one of the stable configurations that stars reach at the end of stellar evolution. Neutron stars posses the highest rotation rates and strongest magnetic fields among all stars. They radiate prolifically, in high energy electromagnetic radiation and in the radio band. This book is devoted to the selected lectures presented in the 6th NATO-ASI series entitled "The Electromagnetic Spectrum of Neutron Stars" in Marmaris, Turkey, on 7-18 June 2004. This ASI is devoted to the spectral properties of neutron stars. Spectral observations of neutron stars help us to understand the magnetospheric emission processes of isolated radio pulsars and the emission processes of accreting neutron stars. This volume includes spectral information from the neutron stars in broadest sense, namely neutrino and gravitational radiat...
Heller, A. K.; Brenizer, J. S.
Neutron radiography and its related two-dimensional (2D) neutron imaging techniques have been established as invaluable nondestructive inspection methods and quantitative measurement tools. They have been used in a wide variety of applications ranging from inspection of aircraft engine turbine blades to study of two-phase fluid flow in operating proton exchange membrane fuel cells. Neutron radiography is similar to X-ray radiography in that the method produces a 2D attenuation map of neutron radiation that has penetrated the object being examined. However, the images produced differ and are often complementary due to the differences between X-ray and neutron interaction mechanisms. The uses and types of 2D neutron imaging have expanded over the past 15 years as a result of advances in imaging technology and improvements in neutron generators/sources and computers. Still, high-intensity sources such as those from reactors and spallation neutron sources, together with conventional film radiography, remain the mainstay of high-resolution, large field-of-view neutron imaging. This chapter presents a summary of the history, methods, and related variations of neutron radiography techniques.
High-resolution neutron microtomography with noiseless neutron counting detector
Tremsin, A.S., E-mail: ast@ssl.berkeley.edu [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States); McPhate, J.B.; Vallerga, J.V.; Siegmund, O.H.W. [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States); Feller, W.B. [Nova Scientific Inc., 10 Picker Road, Sturbridge, MA 01566 (United States); Lehmann, E. [Paul Scherrer Institute, CH-5232 Villigen (Switzerland); Butler, L.G. [Louisiana State University, Baton Rouge, LA 70803 (United States); Dawson, M. [Helmholtz Centre Berlin for Materials and Energy (Germany)
2011-10-01
The improved collimation and intensity of thermal and cold neutron beamlines combined with recent advances in neutron imaging devices enable high-resolution neutron radiography and microtomography, which can provide information on the internal structure of objects not achievable with conventional X-ray imaging techniques. Neutron detection efficiency, spatial and temporal resolution (important for the studies of dynamic processes) and low background count rate are among the crucial parameters defining the quality of radiographic images and tomographic reconstructions. The unique capabilities of neutron counting detectors with neutron-sensitive microchannel plates (MCPs) and with Timepix CMOS readouts providing high neutron detection efficiency ({approx}70% for cold neutrons), spatial resolutions ranging from 15 to 55 {mu}m and a temporal resolution of {approx}1 {mu}s-combined with the virtual absence of readout noise-make these devices very attractive for high-resolution microtomography. In this paper we demonstrate the capabilities of an MCP-Timepix detection system applied to microtomographic imaging, performed at the ICON cold neutron facility of the Paul Scherrer Institute. The high resolution and the absence of readout noise enable accurate reconstruction of texture in a relatively opaque wood sample, differentiation of internal tissues of a fly and imaging of individual {approx}400 {mu}m grains in an organic powder encapsulated in a {approx}700 {mu}m thick metal casing.
Beer, A. de; Hershcovitch, A.; Franklyn, C.B.; Straaten, S. van; Guzek, J. E-mail: jguzek@debeers.co.za
2000-09-01
The reactions D(d,n){sup 3}He and T(d,n){sup 4}He are frequently used for production of the mono-energetic or quasi mono-energetic neutron beams but successful applications are often limited by the intensity of the generated neutron beams. The development of a suitable neutron source for such applications as studies of resonance phenomena, fast neutron radiography, selective fast neutron activation, explosives and contraband detection and others, depends on the output ion current of the accelerator and the design of the target system. A practical solution for a high pressure gas target was previously developed and successfully implemented at De Beers Diamond Research Laboratory in Johannesburg (Guzek et al., 1999), but it is limited to applications using low (<20%) duty cycle accelerators. The concept of a plasma window for the separation of a high pressure gas target region and accelerator vacuum, that was originally developed by Hershcovitch (1995) for electron welding applications, may be suitable for operation with continuous wave accelerators at high particle current output. Preliminary test results, which have been performed with various gases (argon, helium and deuterium), indicate that implementation of the plasma window into a gas target system, for the production of intense mono-energetic fast neutron beams will be achievable.
Hadron star models. [neutron stars
Cohen, J. M.; Boerner, G.
1974-01-01
The properties of fully relativistic rotating hadron star models are discussed using models based on recently developed equations of state. All of these stable neutron star models are bound with binding energies as high as about 25%. During hadron star formation, much of this energy will be released. The consequences, resulting from the release of this energy, are examined.
Wu, Yican
2017-01-01
This book provides a systematic and comprehensive introduction to fusion neutronics, covering all key topics from the fundamental theories and methodologies, as well as a wide range of fusion system designs and experiments. It is the first-ever book focusing on the subject of fusion neutronics research. Compared with other nuclear devices such as fission reactors and accelerators, fusion systems are normally characterized by their complex geometry and nuclear physics, which entail new challenges for neutronics such as complicated modeling, deep penetration, low simulation efficiency, multi-physics coupling, etc. The book focuses on the neutronics characteristics of fusion systems and introduces a series of theories and methodologies that were developed to address the challenges of fusion neutronics, and which have since been widely applied all over the world. Further, it introduces readers to neutronics design’s unique principles and procedures, experimental methodologies and technologies for fusion systems...
Rotation and Magnetic Fields in Supernovae and Gamma-ray Bursts
Wheeler, J. Craig
2005-10-01
Spectropolarimetry of core collapse supernovae has shown that they are asymmetric and often, but not universally, bi-polar; in some the dominant axes associated with hydrogen, oxygen, and calcium are oriented substantially differently. Jet-induced supernova models give a typical jet/torus structure that is reminiscent of some objects like the Crab nebula, SN 1987A and perhaps Cas A. Jets, in turn, may arise from the intrinsic rotation and magnetic fields that are expected to accompany core collapse. We summarize the potential importance of the magneto-rotational instability for the core collapse problem, stress the non- monotonic response of the final rotation and magnetic field to the initial iron core rotation, and the potential role of non-axisymmetric instabilities in the new-born neutron star. We sketch some of the effects that large magnetic fields, ˜10^15 - 10^17 G, may have on the physics at core bounce and in the subsequent cooling, de-leptonization phase. Production and dissipation of MHD waves in this strongly differentially rotating environment may affect the success of the supernova explosion, the nature of the compact remnant -- neutron star or black hole, pulsar or magnetar -- and whether the outcome is a normal supernova or a gamma-ray burst. In collaboration with Shizuka Akiyama, University of Texas at Austin.
Ignatovich, V K
2005-01-01
A new, algebraic, method is applied to calculation of neutron albedo from substance to check the claim that use of ultradispersive fuel and moderator of an active core can help to gain in size and mass of the reactor. In a model of isotropic distribution of incident and reflected neutrons it is shown that coherent scattering on separate grains in the case of thermal neutrons increases transport cross section negligibly, however it decreases albedo from a wall of finite thickness because of decrease of substance density. A visible increase of albedo takes place only for neutrons with wave length of the order of the size of a single grain.
Neutron dosimetry; Dosimetria de neutrons
Fratin, Luciano
1993-12-31
A neutron irradiation facility was designed and built in order to establish a procedure for calibrating neutron monitors and dosemeters. A 185 GBq {sup 241} Am Be source of known is used as a reference source. The irradiation facility using this source in the air provides neutron dose rates between 9 nSv s{sup -1} and 0,5 {sup {mu}}Sv s{sup -1}. A calibrated 50 nSv s{sup -1} thermal neutron field is obtained by using a specially designed paraffin block in conjunction with the {sup 241} Am Be source. A Bonner multisphere spectrometer was calibrated, using a procedure based on three methods proposed by international standards. The unfold {sup 241} Am Be neutron spectrum was determined from the Bonner spheres data and resulted in a good agreement with expected values for fluence rate, dose rate and mean energy. A dosimetric system based on the electrochemical etching of CR-39 was developed for personal dosimetry. The dosemeter badge using a (n,{alpha}) converter, the etching chamber and high frequency power supply were designed and built specially for this project. The electrochemical etching (ECE) parameters used were: a 6N KOH solution, 59 deg C, 20 kV{sub pp} cm{sup -1}, 2,0 kHz, 3 hours of ECE for thermal and intermediate neutrons and 6 hours for fast neutrons. The calibration factors for thermal, intermediate and fast neutrons were determined for this personal dosemeter. The sensitivities determined for the developed dosimetric system were (1,46{+-} 0,09) 10{sup 4} tracks cm{sup -2} mSv{sup -1} for thermal neutrons, (9{+-}3) 10{sup 2} tracks cm{sup -2} mSV{sup -1} for intermediate neutrons and (26{+-}4) tracks cm{sup -2} mSv{sup -1} for fast neutrons. The lower and upper limits of detection were respectively 0,002 mSv and 0,6 mSv for thermal neutrons, 0,04 mSv and 8 mSv for intermediate neutrons and 1 mSv and 12 mSv for fast neutrons. In view of the 1990`s ICRP recommendations, it is possible to conclude that the personal dosemeter described in this work is
Klösgen-Buchkremer, Beate Maria
2014-01-01
films or films with magnetic properties. The reason is the peculiar property of neutron light since the mass of a neutron is close to the one of a proton, and since it bears a magnetic moment. The optical properties of matter, when interacting with neutrons, are described by a refractive index......Neutron (and X-ray) reflectometry constitute complementary interfacially sensitive techniques that open access to studying the structure within thin films of both soft and hard condensed matter. Film thickness starts oxide surfaces on bulk substrates, proceeding to (pauci-)molecular layers and up...... to hundreds of nanometers. Thickness resolution for flat surfaces is in the range of few Ǻngstrøm, and as a peculiar benefit, the presence and properties of buried interfaces are accessible. Focus here will be on neutron reflectometry, a technique that is unique in applications involving composite organic...
Henzl, Vladimir [Los Alamos National Laboratory; Croft, Stephen [Los Alamos National Laboratory; Swinhoe, Martyn T. [Los Alamos National Laboratory; Tobin, Stephen J. [Los Alamos National Laboratory
2012-07-13
Inspired by approach of Bignan and Martin-Didier (ESARDA 1991) we introduce novel (instrument independent) approach based on multiplication and passive neutron. Based on simulations of SFL-1 the accuracy of determination of {sup tot}Pu content with new approach is {approx}1.3-1.5%. Method applicable for DDA instrument, since it can measure both multiplication and passive neutron count rate. Comparison of pro's & con's of measuring/determining of {sup 239}Pu{sub eff} and {sup tot}Pu suggests a potential for enhanced diversion detection sensitivity.
Nolte, R; Plompen, A; Röttger, S
2014-01-01
The angular distribution of neutron-deuteron scattering was investigated using the proportional counter P2 simultaneously as scattering target and detector for the recoil deuterons. The measurements were carried out using monoenergetic neutrons in the energy range from 150 keV to 500 keV. Various techniques were employed to reduce distortions of the experimental pulse-height distribution by photon-induced events. The experimental data were compared with realistic simulations which were carried out using different evaluated data sets. This comparison allows to conclude on inconsistencies in the evaluations.
The Fate of Merging Neutron Stars
Kohler, Susanna
2017-08-01
A rapidly spinning, highly magnetized neutron star is one possible outcome when two smaller neutron stars merge. [Casey Reed/Penn State University]When two neutron stars collide, the new object that they make can reveal information about the interior physics of neutron stars. New theoretical work explores what we should be seeing, and what it can teach us.Neutron Star or Black Hole?So far, the only systems from which weve detected gravitational waves are merging black holes. But other compact-object binaries exist and are expected to merge on observable timescales in particular, binary neutron stars. When two neutron stars merge, the resulting object falls into one of three categories:a stable neutron star,a black hole, ora supramassive neutron star, a large neutron star thats supported by its rotation but will eventually collapse to a black hole after it loses angular momentum.Histograms of the initial (left) and final (right) distributions of objects in the authors simulations, for five different equations of state. Most cases resulted primarily in the formation of neutron stars (NSs) or supramassive neutron stars (sNSs), not black holes (BHs). [Piro et al. 2017]Whether a binary-neutron-star merger results in another neutron star, a black hole, or a supramassive neutron star depends on the final mass of the remnant and what the correct equation of state is that describes the interiors of neutron stars a longstanding astrophysical puzzle.In a recent study, a team of scientists led by Anthony Piro (Carnegie Observatories) estimated which of these outcomes we should expect for mergers of binary neutron stars. The teams results along with future observations of binary neutron stars may help us to eventually pin down the equation of state for neutron stars.Merger OutcomesPiro and collaborators used relativistic calculations of spinning and non-spinning neutron stars to estimate the mass range that neutron stars would have for several different realistic equations of
Hermes, J. J.; Kawaler, Steven D.; Bischoff-Kim, A.; Provencal, J. L.; Dunlap, B. H.; Clemens, J. C.
2017-02-01
We present the detection of non-radial oscillations in a hot, helium-atmosphere white dwarf using 78.7 days of nearly uninterrupted photometry from the Kepler space telescope. With an effective temperature >30,000 K, PG 0112+104 becomes the hottest helium-atmosphere white dwarf known to pulsate. The rich oscillation spectrum of low-order g-modes includes clear patterns of rotational splittings from consecutive sequences of dipole and quadrupole modes, which can be used to probe the rotation rate with depth in this highly evolved stellar remnant. We also measure a surface rotation rate of 10.17404 hr from an apparent spot modulation in the K2 data. With two independent measures of rotation, PG 0112+104 provides a remarkable test of asteroseismic inference.
Quasilocal rotating conformal Killing horizons
Chatterjee, Ayan
2015-01-01
The formulation of quasi-local conformal Killling horizons(CKH) is extended to include rotation. This necessitates that the horizon be foliated by 2-spheres which may be distorted. Matter degrees of freedom which fall through the horizon is taken to be a real scalar field. We show that these rotating CKHs also admit a first law in differential form.
邹润莉
2012-01-01
As the earth's main magnetic field is stationary relative to the earth's axis, the earth autorotation drives the electrostatic charges to move along the vertical direction of the earth's main magnetic field,and causes charged particles subject to Lorentz force. According to the right-hand screw rule, the Lorentz force lies in meridian plane, perpendicular to the earth's rotation speed,with the directions of positively charged particles pointing to the earth's axis and the negatively charged to the opposite in normal phase of geomagnetic field while in abnormal phase, they point to the opposite. This force is proportional to the earth' s rotation speed and is referred to as normal Lorentz force. The normal Lorentz force forces the charges to drift along the normal and causes the normal drift velocity. Similarly.it is deduced that the Lorentz force, corresponding to the normal drift velocity of the charged particles, is always to the west along the tangent whether normal or abnormal phase of geomagnetic field. This force is proportional to the normal drift velocity and is referred to as tangent Lorentz force. The tangential Lorentz force causes charged particles to produce tangent acceleration,and thus forms westward drift which drives the solid medium containing charged particles drift westward. It hinders the earth's rotation that the torque of the tangential Lorentz force relative to the earth's axis,which is the electromagnetic torquen M of the earth's main magnetic field. This leads to the earth's rotation rate long-term slowdown in single-valued,as well as differential rotation of the earth. To explore the law of the earth's differential rotation, the whole earth was studied as the object and the earth's axis was as the central axis for the cylindrical coordinate system. With application of the classical physics theory and analyzing method, the formulas were deduced to calculate the rotary inertia J of thin cylinder in the earth's sphere, the electromagnetic
Kerveno, M
2000-09-27
In order to develop new options for nuclear waste management, studies are carrying out on the perfecting of hybrid systems (sub-critical reactor driven by accelerator). This thesis work takes place more precisely in the framework of nuclear data linked to hybrid systems development. Increasing the upper limit energy value (from 20 to 150 MeV) of data bases supposes that theoretical codes could have sufficient predictive power in this energy range. Thus it's necessary to measure new cross sections to constrain these codes. The experiment, performed at Louvain-la-Neuve Cyclotron, aims to determine the double differential cross sections for light charged particles production in neutron induced reactions at 62.7 MeV on natural lead target. The detection device consists of 6 NE102-CsI telescopes. Time of flight measurements are used to reconstruct the neutron energy spectra. The general framework (hybrid systems and associated nuclear data problematic) in which this work takes place is presented in a first part. The experimental set up used for our measurements is described in a second part. The three following parts are dedicated to the data analysis and double differential cross sections extraction. The particle discrimination, the energy calibration of detectors as the different corrections applied to the experimental spectra are related in details. And finally a comparative study between our experimental results and some theoretical predictions is presented. (author)
Childs, Peter R N
2010-01-01
Rotating flow is critically important across a wide range of scientific, engineering and product applications, providing design and modeling capability for diverse products such as jet engines, pumps and vacuum cleaners, as well as geophysical flows. Developed over the course of 20 years' research into rotating fluids and associated heat transfer at the University of Sussex Thermo-Fluid Mechanics Research Centre (TFMRC), Rotating Flow is an indispensable reference and resource for all those working within the gas turbine and rotating machinery industries. Traditional fluid and flow dynamics
Beckmann, Peter A; McGhie, Andrew R; Rheingold, Arnold L; Sloan, Gilbert J; Szewczyk, Steven T
2017-08-24
Using solid-state (1)H nuclear magnetic resonance (NMR) spin-lattice relaxation experiments, we have investigated the effects of several solid-solid phase transitions on tert-butyl and methyl group rotation in solid 1,3,5-tri-tert-butylbenzene. The goal is to relate the dynamics of the tert-butyl groups and their constituent methyl groups to properties of the solid determined using single-crystal X-ray diffraction and differential scanning calorimetry (DSC). On cooling, the DSC experiments see a first-order, solid-solid phase transition at either 268 or 155 K (but not both) depending on thermal history. The 155 K transition (on cooling) is identified by single-crystal X-ray diffraction to be one from a monoclinic phase (above 155 K), where the tert-butyl groups are disordered (that is, with a rotational 6-fold intermolecular potential dominating), to a triclinic phase (below 155 K), where the tert-butyl groups are ordered (that is, with a rotational 3-fold intermolecular potential dominating). This transition shows very different DSC scans when both a 4.7 mg polycrystalline sample and a 19 mg powder sample are used. The (1)H spin-lattice relaxation experiments with a much larger 0.7 g sample are very complicated and, depending on thermal history, can show hysteresis effects over many hours and over very large temperature ranges. In the high-temperature monoclinic phase, the tert-butyl groups rotate with NMR activation energies (closely related to rotational barriers) in the 17-23 kJ mol(-1) range, and the constituent methyl groups rotate with NMR activation energies in the 7-12 kJ mol(-1) range. In the low-temperature triclinic phase, the rotations of the tert-butyl groups and their methyl groups in the aromatic plane are quenched (on the NMR time scale). The two out-of-plane methyl groups in the tert-butyl groups are rotating with activation energies in the 5-11 kJ mol(-1) range.
Cross-section model for cold neutron scattering in solid and liquid methane
Morishima, N
2002-01-01
Incoherent neutron scattering cross-sections for solid CH sub 4 in the temperature range of 20.4-90.7 K and liquid CH sub 4 at temperatures between 90.7 and 111.7 K are evaluated. A space-time correlation approach is used to describe a double-differential scattering cross-section which is basically expressed by a generalized frequency distribution. The cross-section model includes molecular translations and rotations as well as intramolecular vibrations. The former are concerned with very short-time free-gas like translation, short-lived vibration and long-time diffusion (only in liquid state). The latter consists of short-time free rotation and long-time isotropic rotational diffusion. Numerical calculations on double-differential and total cross-sections are carried out for incident neutron energies covered 0.1 mu eV to 10 eV. Good agreement with experimental results at many different temperatures is found.
Effect of the Quadrupole Moment of a Rotating Massive Object on the Gravitational Faraday Rotation
陈贻汉; 邵常贵
2002-01-01
We study the rotation of the polarization plane for a ray of electromagnetic radiation propagating in the grav-itoelectromagnetic field caused by a rotating massive object with the quadrupole moment. The effect of thequadrupole moment on the gravitational Faraday rotation is investigated. It is found that the gravitational Fara-day effect of the quadrupole moment is negligible for Kerr black holes, but this effect is important for rapidlyrotating neutron stars.
Nauchi, Yasushi; Baba, Mamoru; Kiyosumi, Takehide [Tohoku Univ., Sendai (Japan). Faculty of Engineering] [and others
1997-03-01
We measured (n,xp), (n,xd) cross sections of C and Al for En=64.3 MeV neutrons at the {sup 7}Li(p,n) neutron sources facility at TIARA (Takasaki Establishment, JAERI) by using a conventional SSD-NaI telescope placed in the air. They show characteristic energy and angular dependence in high energy regions. In order to extend the measurements to low energy protons and {alpha} particles, a new spectrometer consisting of low pressure gas counters and BaF{sub 2} scintillators is now under development. A low threshold for low energy {alpha} particles will be achieved by using the gas counters. The particle identification over a wide energy range will be achieved by combining the {Delta}E-E method for low energy particles with the pulse shape discrimination (PSD) method of BaF{sub 2} for high energy particles. (author)
Cegla, H. M.; Lovis, C.; Bourrier, V.; Beeck, B.; Watson, C. A.; Pepe, F.
2016-04-01
When a planet transits its host star, it blocks regions of the stellar surface from view; this causes a distortion of the spectral lines and a change in the line-of-sight (LOS) velocities, known as the Rossiter-McLaughlin (RM) effect. Since the LOS velocities depend, in part, on the stellar rotation, the RM waveform is sensitive to the star-planet alignment (which provides information on the system's dynamical history). We present a new RM modelling technique that directly measures the spatially-resolved stellar spectrum behind the planet. This is done by scaling the continuum flux of the (HARPS) spectra by the transit light curve, and then subtracting the in- from the out-of-transit spectra to isolate the starlight behind the planet. This technique does not assume any shape for the intrinsic local profiles. In it, we also allow for differential stellar rotation and centre-to-limb variations in the convective blueshift. We apply this technique to HD 189733 and compare to 3D magnetohydrodynamic (MHD) simulations. We reject rigid body rotation with high confidence (>99% probability), which allows us to determine the occulted stellar latitudes and measure the stellar inclination. In turn, we determine both the sky-projected (λ ≈ -0.4 ± 0.2°) and true 3D obliquity (ψ ≈ 7+12-4°). We also find good agreement with the MHD simulations, with no significant centre-to-limb variations detectable in the local profiles. Hence, this technique provides a new powerful tool that can probe stellar photospheres, differential rotation, determine 3D obliquities, and remove sky-projection biases in planet migration theories. This technique can be implemented with existing instrumentation, but will become even more powerful with the next generation of high-precision radial velocity spectrographs.
Neutron scattering and models: Iron. Nuclear data and measurements series
Smith, A.B. [Argonne National Lab., IL (United States)
1995-08-01
Differential elastic and inelastic neutron-scattering cross sections of elemental iron are measured from 4.5 to 10 MeV in increments of {approx} 0.5 MeV. At each incident energy the measurements are made at forty or more scattering angles distributed between {approx} 17{degrees} and 160{degrees}, with emphasis on elastic scattering and inelastic scattering due to the excitation of the yrast 2{sup +} state. The measured data is combined with earlier lower-energy results from this laboratory, with recent high-precision {approx} 9.5 {yields} 15 MeV results from the Physilalisch Technische Bundesanstalt and with selected values from the literature to provide a detailed neutron-scattering data base extending from {approx} 1.5 to 26 MeV. This data is interpreted in the context of phenomenological spherical-optical and coupled-channels (vibrational and rotational) models, and physical implications discussed. Deformation, coupling, asymmetry and dispersive effects are explored. It is shown that, particularly in a collective context, a good description of the interaction of neutrons with iron is achieved over the energy range {approx} 0 {yields} 26 MeV, avoiding the dichotomy between high and low-energy interpretations found in previous work.
Methods for Neutron Spectrometry
Brockhouse, Bertram N.
1961-01-09
The appropriate theories and the general philosophy of methods of measurement and treatment of data neutron spectrometry are discussed. Methods of analysis of results for liquids using the Van Hove formulation, and for crystals using the Born-von Karman theory, are reviewed. The most useful of the available methods of measurement are considered to be the crystal spectrometer methods and the pulsed monoenergetic beam/time-of-flight method. Pulsed-beam spectrometers have the advantage of higher counting rates than crystal spectrometers, especially in view of the fact that simultaneous measurements in several counters at different angles of scattering are possible in pulsed-beam spectrometers. The crystal spectrometer permits several valuable new types of specialized experiments to be performed, especially energy distribution measurements at constant momentum transfer. The Chalk River triple-axis crystal-spectrometer is discussed, with reference to its use in making the specialized experiments. The Chalk River rotating crystal (pulsed-beam) spectrometer is described, and a comparison of this type instrument with other pulsed-beam spectrometers is made. A partial outline of the theory of operation of rotating-crystal spectrometers is presented. The use of quartz-crystal filters for fast neutron elimination and for order elimination is discussed. (auth)
Structural behaviour of AgNO3 at low temperatures by neutron diffraction
P U Sastry; P S R Krishna; Lata Panicker; A B Shinde
2008-11-01
Structural behaviour of silver nitrate (AgNO3) at low temperatures has been investigated by neutron powder diffraction and differential scanning calorimetry (DSC). Analysis showed abnormal changes in the rotations of nitrate (NO3) anions and thermal displacement parameters of the atoms near 220 K and 125 K. However, the basic lattice is compatible with the orthorhombic symmetry (space group Pbca) till 12 K. The fine, small-scale structural anomalies probably originate from freezing of reorientation of NO3 ions from high-temperature disordered phase.
Ouazzani, R-M
2012-01-01
Information about the rotation rate is contained in the low frequency part of power spectra, where signatures of nonuniform surface rotation are expected, as well as in the frequency splittings induced by the internal rotation rate. We wish to figure out whether the differences between the seismic rotation period as determined by a mean rotational splitting, and the rotation period measured from the low frequency peak in the Fourier spectrum (observed for some of CoRoT's targets) can provide constraints on the rotation profile. For uniform moderate rotators,perturbative corrections to second and third order in terms of the rotation angular velocity \\Omega, may mimic differential rotation. We apply our perturbation method to evaluate mode frequencies accurate up to \\Omega^3 for uniform rotation. Effects of latitudinal dependence are calculated in the linear approximation. In \\beta Cephei pulsators models, third order effects become comparable to that of a horizontal shear similar to the solar one at rotation r...
Vassiliev, Dmitri
2017-04-01
We consider an infinite three-dimensional elastic continuum whose material points experience no displacements, only rotations. This framework is a special case of the Cosserat theory of elasticity. Rotations of material points are described mathematically by attaching to each geometric point an orthonormal basis that gives a field of orthonormal bases called the coframe. As the dynamical variables (unknowns) of our theory, we choose the coframe and a density. We write down the general dynamic variational functional for our rotational theory of elasticity, assuming our material to be physically linear but the kinematic model geometrically nonlinear. Allowing geometric nonlinearity is natural when dealing with rotations because rotations in dimension three are inherently nonlinear (rotations about different axes do not commute) and because there is no reason to exclude from our study large rotations such as full turns. The main result of the talk is an explicit construction of a class of time-dependent solutions that we call plane wave solutions; these are travelling waves of rotations. The existence of such explicit closed-form solutions is a non-trivial fact given that our system of Euler-Lagrange equations is highly nonlinear. We also consider a special case of our rotational theory of elasticity which in the stationary setting (harmonic time dependence and arbitrary dependence on spatial coordinates) turns out to be equivalent to a pair of massless Dirac equations. The talk is based on the paper [1]. [1] C.G.Boehmer, R.J.Downes and D.Vassiliev, Rotational elasticity, Quarterly Journal of Mechanics and Applied Mathematics, 2011, vol. 64, p. 415-439. The paper is a heavily revised version of preprint https://arxiv.org/abs/1008.3833
Manuel, Oliver K
2011-01-01
Earth is connected gravitationally, magnetically and electrically to its heat source - a neutron star that is obscured from view by waste products in the photosphere. Neutron repulsion is like the hot filament in an incandescent light bulb. Excited neutrons are emitted from the solar core and decay into hydrogen that glows in the photosphere like a frosted light bulb. Neutron repulsion was recognized in nuclear rest mass data in 2000 as the overlooked source of energy, the keystone of an arch that locked together these puzzling space-age observations: 1.) Excess 136Xe accompanied primordial helium in the stellar debris that formed the solar system (Fig. 1); 2.) The Sun formed on the supernova core (Fig. 2); 3.) Waste products from the core pass through an iron-rich mantle, selectively carrying lighter elements and lighter isotopes of each element into the photosphere (Figs. 3-4); and 4.) Neutron repulsion powers the Sun and sustains life (Figs. 5-7). Together these findings offer a framework for understanding...
Heger, G. [Rheinisch-Westfaelische Technische Hochschule Aachen, Inst. fuer Kristallographie, Aachen (Germany)
1996-12-31
X-ray diffraction using conventional laboratory equipment and/or synchrotron installations is the most important method for structure analyses. The purpose of this paper is to discuss special cases, for which, in addition to this indispensable part, neutrons are required to solve structural problems. Even though the huge intensity of modern synchrotron sources allows in principle the study of magnetic X-ray scattering the investigation of magnetic structures is still one of the most important applications of neutron diffraction. (author) 15 figs., 1 tab., 10 refs.
Neutronics of pulsed spallation neutron sources
Watanabe, N
2003-01-01
Various topics and issues on the neutronics of pulsed spallation neutron sources, mainly for neutron scattering experiments, are reviewed to give a wide circle of readers a better understanding of these sources in order to achieve a high neutronic performance. Starting from what neutrons are needed, what the spallation reaction is and how to produce slow-neutrons more efficiently, the outline of the target and moderator neutronics are explained. Various efforts with some new concepts or ideas have already been devoted to obtaining the highest possible slow-neutron intensity with desired pulse characteristics. This paper also reviews the recent progress of such efforts, mainly focused on moderator neutronics, since moderators are the final devices of a neutron source, which determine the source performance. Various governing parameters for neutron-pulse characteristics such as material issues, geometrical parameters (shape and dimensions), the target-moderator coupling scheme, the ortho-para-hydrogen ratio, po...
Spallation neutron experiment at SATURNE
Meigo, Shin-ichiro [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment
1998-11-01
The double differential cross sections for (p,xn) reactions and the spectra of neutrons produced from the thick target have been measured at SATURNE in SACLAY from 1994 to 1997. The status of the experiment and the preliminary experimental results are presented. (author)
Mikuli, E.; Migdał-Mikuli, A.; Natkaniec, I.; Mayer, J.
2000-10-01
DSC measurements performed at 95 -290 K have shown that [Mn(H 2 O) 6 ](CIO 4) 2 possesses, besides a high-temperature phase, existing above 323 K, four low-temperature solid phases. The inelastic incoherent neutron scattering (IINS) spectra and neutron powder diffraction (NPD) pat-terns registered at 20 -290 K have supported the DSC results and provided evidence that the investigated substance possesses even more than five solid phases. The IINS spectra have shown that in the room-temperature phase, water molecules perform fast stochastic reorientation at the picosecond scale. The orientational disorder characteristic for the room-temperature phase can be easily overcooled and frozen. Even by relatively slow cooling at ca. 40 K/hour a metastable, orientational (protonic) glass phase is formed below ca. 160 K. Below ca. 100 K, a structural phase transition was observed by the NPD, however the IINS spectra indicate existence of the pure ordered low-temperature phase only after annealing the sample for a few hours at 100 K. On heating, a structural phase transition takes place at ca. 120 K, and at ca. 225 K water molecules begin fast reorientation.
Preliminary Study on Method of Quantitative Measurement of Nuclear Fuel Rod by Neutron CT at CARR
WEI; Guo-hai; HAN; Song-bai; WANG; Hong-li; HE; Lin-feng; WANG; Yu; WU; Mei-mei; LIU; Yun-tao; CHEN; Dong-feng
2015-01-01
Neutron CT technique was applied to the quantitative measurement of the key parameters of nuclear fuel rods at China Advanced Research Reactor(CARR).The sample of dummy nuclear fuel rod was rotated in 180°range,and 900neutron projections were obtained.The 3-D neutron
Crump, James C., III; Richards, Wade J.; Shields, Kevin C.
1995-07-01
The McClellan Nuclear Radiation Center's (MNRC) staff in conjunction with a Cooperative Research and Development Agreement (CRDA) with the U.C. Santa Barbara facility has developed a system that can be used for aircraft inspection of jet engine blades. The problem was to develop an inspection system that can detect very low concentrations of hydrogen (i.e., greater than 100 ppm) in metal matricies. Specifically in Titanium alloy jet engine blades. Entrapment and precipitation of hydrogen in metals is an undesirable phenomenon which occurs in many alloys of steel and titanium. In general, metals suffer a loss of mechanical properties after long exposures to hydrogen, especially at high temperatures and pressures, thereby becoming embrittled. Neutron radiography has been used as a nondestructive testing technique for many years. Neutrons, because of their unique interactions with materials, are especially useful in the detection of hydrogen. They have an extremely high interaction cross section for low atomic number nuclei (i.e., hydrogen). Thus hydrogen in a metal matrix can be visualized using neutrons. Traditional radiography is sensitive to the total attenuation integrated over the path of radiation through the material. Increased sensitivity and quantitative cross section resolution can be obtained using three-dimensional volumetric imaging techniques such as tomography. The solution used to solve the problem was to develop a neutron tomography system. The neutron source is the McClellan Nuclear Radiation Center's 1 MW TRIGA reactor. This paper describes the hardware used in the system as well as some of the preliminary results.
Optical timing studies of isolated neutron stars: Current Status
Mignani, R P
2010-01-01
Being fast rotating objects, Isolated Neutron Stars (INSs) are natural targets for high-time resolution observations across the whole electromagnetic spectrum. With the number of objects detected at optical (plus ultraviolet and infrared) wavelengths now increased to 24, high-time resolution observations of INSs at these wavelengths are becoming more and more important. While classical rotation-powered radio pulsars, like the Crab and Vela pulsars, have been the first INSs studied at high-time resolution in the optical domain, observations performed in the last two decades have unveiled potential targets in other types of INSs which are not rotation powered, although their periodic variability is still related to the neutron star rotation. In this paper I review the current status of high-time resolution observations of INSs in the optical domain for different classes of objects: rotation-powered pulsars, magnetars, thermally emitting neutron stars, and rapid radio transients, I describe their timing properti...
Inertial modes of non-stratified superfluid neutron stars
Prix, R; Andersson, N
2004-01-01
We present results concerning adiabatic inertial-mode oscillations of non-stratified superfluid neutron stars in Newtonian gravity, using the anelastic and slow-rotation approximations. We consider a simple two-fluid model of a superfluid neutron star, where one fluid consists of the superfluid neutrons and the second fluid contains all the comoving constituents (protons, electrons). The two fluids are assumed to be ``free'' in the sense that vortex-mediated forces like mutual friction or pinning are absent, but they can be coupled by the equation of state, in particular by entrainment. The stationary background consists of the two fluids rotating uniformly around the same axis with potentially different rotation rates. We study the special cases of co-rotating backgrounds, vanishing entrainment, and the purely toroidal r-modes, analytically. We calculate numerically the eigenfunctions and frequencies of inertial modes in the general case of non co-rotating backgrounds, and study their dependence on the relat...
Invalidity of Geometrical Interpretation of F-Spin Structure of Nuclear Rotations by Otsuka's View
Long, Guilu
1995-06-01
In Otsuka's view of nuclear rotations neutrons and protons are not rotating around a common axis, but rather around separate axis. In this letter, we pointed out that this invalidates the geometrical interpretation of F-spin structure of the neutron-proton interacting boson model, where the angle between the axis of symmetries of neutron ellipsoid and proton ellipsoid is used to determine whether a state is F-spin symmetric or mixed symmetric.
The neutron-deuteron elastic scattering angular distribution at 95 MeV
Mermod, Philippe
2004-04-01
The neutron-deuteron elastic scattering differential cross section has been measured at 95 MeV incident neutron energy, with the Medley setup at TSL in Uppsala. The neutron-proton differential cross section has also been measured for normalization purposes. The data are compared with theoretical calculations to investigate the role of three-nucleon force effects.
Peralta, C; Giacobello, M; Ooi, A
2006-01-01
We investigate the global transition from a turbulent state of superfluid vorticity to a laminar state, and vice versa, in the outer core of a neutron star. By solving numerically the hydrodynamic Hall-Vinen-Bekarevich-Khalatnikov equations for a rotating superfluid in a differentially rotating spherical shell, we find that the meridional counterflow driven by Ekman pumping exceeds the Donnelly-Glaberson threshold throughout most of the outer core, exciting unstable Kelvin waves which disrupt the rectilinear vortex array, creating a vortex tangle. In the turbulent state, the torque exerted on the crust oscillates, and the crust-core coupling is weaker than in the laminar state. This leads to a new scenario for the rotational glitches observed in radio pulsars: a vortex tangle is sustained in the differentially rotating outer core by the meridional counterflow, a sudden spin-up event brings the crust and core into corotation, the vortex tangle relaxes back to a rectilinear vortex array, then the crust spins do...
Gravitational radiation from a rotating magnetic dipole
Hacyan, Shahen
2016-01-01
The gravitational radiation emitted by a rotating magnetic dipole is calculated. Formulas for the polarization amplitudes and the radiated power are obtained in closed forms, considering both the near and radiation zones of the dipole. For a neutron star, a comparison is made with other sources of gravitational and electromagnetic radiation.
The Influence of Thermal Pressure on Hypermassive Neutron Star Merger Remnants
Kaplan, J D; O'Connor, E P; Kiuchi, K; Roberts, L; Duez, M
2013-01-01
The merger of two neutron stars leaves behind a rapidly spinning hypermassive object whose survival is believed to depend on the maximum mass supported by the nuclear equation of state, angular momentum redistribution by (magneto-)rotational instabilities, and spindown by gravitational waves. The high temperatures (~5-40 MeV) prevailing in the merger remnant may provide thermal pressure support that could increase its maximum mass and, thus, its life on a neutrino-cooling timescale. We investigate the role of thermal pressure support in hypermassive merger remnants by computing sequences of spherically-symmetric and axisymmetric uniformly and differentially rotating equilibrium solutions to the general-relativistic stellar structure equations. Using a set of finite-temperature nuclear equations of state, we find that hot maximum-mass critically spinning configurations generally do not support larger baryonic masses than their cold counterparts. However, subcritically spinning configurations with mean density ...
Klösgen-Buchkremer, Beate Maria
2014-01-01
to hundreds of nanometers. Thickness resolution for flat surfaces is in the range of few Ǻngstrøm, and as a peculiar benefit, the presence and properties of buried interfaces are accessible. Focus here will be on neutron reflectometry, a technique that is unique in applications involving composite organic...... of desired information. In the course, an introduction into the method and an overview on selected instruments at large scale facilities will be presented. Examples will be given that illustrate the potential of the method, mostly based on organic films. Results from the investigation of layered films...... and the detection on nanoscopic roughnesses will be shown. The potential of neutron reflectometry is not only of academic origin. It may turn out to be useful in the design and development of new functional materials even though it will never develop into a standard method to be applied in the product control...
Neutron Polarization Measurements with a 3He Spin Filter for the NPDGamma Experiment
Musgrave, Matthew
2012-10-01
The Fundamental Neutron Physics Beamline (FNPB) at the Spallation Neutron Source (SNS) provides a pulsed beam of polarized cold neutrons for the NPDGamma experiment which intends to measure the parity violating asymmetry in the emitted gamma rays from the capture of polarized neutrons on protons in a para-hydrogen target. The neutrons are polarized by a multi-channel super mirror polarizer, and the polarization of each neutron pulse can be flipped with an RF spin rotator. The accuracy of the NPDGamma experiment and various commissioning experiments is dependent on the polarization of the neutron beam and the efficiency of the RF spin rotator. These parameters are measured with a polarized 3He spin filter at multiple points in the beam cross section and with multiple 3He polarizations. The measured neutron polarization is compared to a McStas model to validate our results and our beam averaging technique. The analysis methods, background effects, and results will be discussed.
Sheared and unsheared rotation of driven dust clusters
Schablinski, Jan; Block, Dietmar; Carstensen, Jan; Greiner, Franko; Piel, Alexander [Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universitaet Kiel, Leibnizstraße 19-Kiel, SH 24098 (Germany)
2014-07-15
Finite size plasma crystals confined in an anisotropic potential well were studied under a rotating and radially unsheared drive in experiment and simulation at moderate rotational frequencies. A radially sheared rotation of these strongly coupled systems is observed for most cluster configurations with a low symmetry. The results show that a differential rotation can be effected by a non-sheared driving force.
Precision manipulation of the neutron polarisation vector
Lelievre-Berna, E. [Institut Laue Langevin, 6 rue Jules Horowitz, 38042 Grenoble Cedex 9 (France)]. E-mail: lelievre@ill.fr; Brown, P.J. [Institut Laue Langevin, 6 rue Jules Horowitz, 38042 Grenoble Cedex 9 (France); Tasset, F. [Institut Laue Langevin, 6 rue Jules Horowitz, 38042 Grenoble Cedex 9 (France); Kakurai, K. [Quantum Beam Science Directorate, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Takeda, M. [Quantum Beam Science Directorate, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Regnault, L.-P. [CEA - DRFMC/SPSMS/MDN, 17 avenue des Martyrs, 38054 Grenoble Cedex 9 (France)
2007-07-15
The rotation of the neutron polarisation vector that takes place on scattering is determined with polarimeters which can measure the three components of the scattered polarisation for any chosen incident polarisation direction. Cryopad zero-field polarimeters are used on the D3/ILL diffractometer and the IN14/ILL, IN20/ILL, IN22/CEA and TAS-1/JAEA three-axis spectrometers. MuPAD zero-field polarimeters have also recently been built for use at the cold neutron beam MIRA/FRM-II and the three-axis spectrometer TASP/SINQ. We present the experimental strategy of this technique called spherical neutron polarimetry (SNP), develop the equations that relate the polarisation components to the CRYOPAD rotation angles, and explain the uncertainties that must be taken into account when carrying out SNP experiments.
Neutron Stars in Supernovae and Their Remnants
Chevalier, Roger A
2010-01-01
The magnetic fields of neutron stars have a large range (~3e10 - 1e15 G). There may be a tendency for more highly magnetized neutron stars to come from more massive stellar progenitors, but other factors must also play a role. When combined with the likely initial periods of neutron stars, the magnetic fields imply a spindown power that covers a large range and is typically dominated by other power sources in supernovae. Distinctive features of power input from pulsar spindown are the time dependence of power and the creation of a low density bubble in the interior of the supernova; line profiles in the late phases are not centrally peaked after significant pulsar rotational energy has been deposited. Clear evidence for pulsar power in objects <300 years old is lacking, which can be attributed to large typical pulsar rotation periods at birth.
Manoshin, S. A.; Belushkin, A. V.; Ioffe, A. I.
2016-07-01
Reviewed are the results of simulating the neutron scattering instruments with the program package VITESS upgraded by the routines for treating the polarized neutrons, as developed by the authors. The reported investigations have been carried out at the Frank Laboratory for Neutron Physics at JINR in collaboration with the Juelich research center (Germany). The performance of the resonance and gradient adiabatic spin flippers, the Drabkin resonator, the classical and resonance spin-echo spectrometers, the spin-echo diffractometer for the small-angle neutron scattering, and the spin-echo spectrometer with rotating magnetic fields is successfully modeled. The methods for using the 3D map of the magnetic field from the input file, either mapped experimentally or computed using the finite-elements technique, in the VITESS computer code, are considered in detail. The results of neutron-polarimetry experiments are adequately reproduced by our simulations.
Effects of rotation in AGB stars
Luciano, Piersanti; Oscar, Straniero
2013-01-01
In this paper we analyze the effects induced by rotation on low mass Asymptotic Giant Branch stars. We compute two sets of models, M=2.0 Msun at [Fe/H]=0 and M=1.5 Msun at [Fe/H]=-1.7, respectively, by adopting Main Sequence rotation velocities in the range 0 - 120 km/s. At high metallicity, we find that the Goldreich-Schubert-Fricke instability, active at the interface between the convective envelope and the rapid rotating core, contaminates the 13C-pocket (the major neutron source) with 14N (the major neutron poison), thus reducing the neutron flux available for the synthesis of heavy elements. As a consequence, the yields of heavy-s elements (Ba, La, Nd, Sm) and, to a less extent, those of light-s elements (Sr, Y, Zr) decrease with increasing rotation velocities up to 60 km/s. However, for larger initial rotation velocities, the production of light-s and, to a less extent, that of heavy-s begins again to increase, due to mixing induced by meridional circulations. At low metallicity, the effects of meridion...
Cegla, H M; Bourrier, V; Beeck, B; Watson, C A; Pepe, F
2016-01-01
When a planet transits its host star, it blocks regions of the stellar surface from view; this causes a distortion of the spectral lines and a change in the line-of-sight (LOS) velocities, known as the Rossiter-McLaughlin (RM) effect. Since the LOS velocities depend, in part, on the stellar rotation, the RM waveform is sensitive to the star-planet alignment (which provides information on the system's dynamical history). We present a new RM modelling technique that directly measures the spatially-resolved stellar spectrum behind the planet. This is done by scaling the continuum flux of the (HARPS) spectra by the transit light curve, and then subtracting the in- from the out-of-transit spectra to isolate the starlight behind the planet. This technique does not assume any shape for the intrinsic local profiles. In it, we also allow for differential stellar rotation and centre-to-limb variations in the convective blueshift. We apply this technique to HD189733 and compare to 3D magnetohydrodynamic (MHD) simulation...
Spallation Neutron Source (SNS)
Federal Laboratory Consortium — The SNS at Oak Ridge National Laboratory is a next-generation spallation neutron source for neutron scattering that is currently the most powerful neutron source in...
Neutron multiplication error in TRU waste measurements
Veilleux, John [Los Alamos National Laboratory; Stanfield, Sean B [CCP; Wachter, Joe [CCP; Ceo, Bob [CCP
2009-01-01
Total Measurement Uncertainty (TMU) in neutron assays of transuranic waste (TRU) are comprised of several components including counting statistics, matrix and source distribution, calibration inaccuracy, background effects, and neutron multiplication error. While a minor component for low plutonium masses, neutron multiplication error is often the major contributor to the TMU for items containing more than 140 g of weapons grade plutonium. Neutron multiplication arises when neutrons from spontaneous fission and other nuclear events induce fissions in other fissile isotopes in the waste, thereby multiplying the overall coincidence neutron response in passive neutron measurements. Since passive neutron counters cannot differentiate between spontaneous and induced fission neutrons, multiplication can lead to positive bias in the measurements. Although neutron multiplication can only result in a positive bias, it has, for the purpose of mathematical simplicity, generally been treated as an error that can lead to either a positive or negative result in the TMU. While the factors that contribute to neutron multiplication include the total mass of fissile nuclides, the presence of moderating material in the matrix, the concentration and geometry of the fissile sources, and other factors; measurement uncertainty is generally determined as a function of the fissile mass in most TMU software calculations because this is the only quantity determined by the passive neutron measurement. Neutron multiplication error has a particularly pernicious consequence for TRU waste analysis because the measured Fissile Gram Equivalent (FGE) plus twice the TMU error must be less than 200 for TRU waste packaged in 55-gal drums and less than 325 for boxed waste. For this reason, large errors due to neutron multiplication can lead to increased rejections of TRU waste containers. This report will attempt to better define the error term due to neutron multiplication and arrive at values that are
Brueckel, Thomas; Heger, Gernot; Richter, Dieter; Roth, Georg; Zorn, Reiner (eds.)
2010-07-01
The following topics are dealt with: Neutron sources, neutron properties and elastic scattering, correlation functions measured by scattering experiments, symmetry of crystals, applications of neutron scattering, polarized-neutron scattering and polarization analysis, structural analysis, magnetic and lattice excitation studied by inelastic neutron scattering, macromolecules and self-assembly, dynamics of macromolecules, correlated electrons in complex transition-metal oxides, surfaces, interfaces, and thin films investigated by neutron reflectometry, nanomagnetism. (HSI)
Dupre, Kristin B; Eskow, Karen L; Negron, Giselle; Bishop, Christopher
2007-07-16
Serotonin 1A receptor (5-HT(1A)R) agonists have emerged as valuable supplements to l-DOPA therapy, demonstrating that they can decrease side effects and enhance motor function in animal models of Parkinson's disease (PD) and human PD patients. The precise mechanism by which these receptors act remains unknown and there is limited information on how 5-HT(1A)R stimulation impacts striatal dopamine (DA) D1 receptor (D1R) and D2 receptor (D2R) function. The current study examined the effects of 5-HT(1A)R stimulation on DA receptor-mediated behaviors. Male Sprague-Dawley rats were rendered hemiparkinsonian by unilateral 6-OHDA lesions and primed with the D1R agonist SKF81297 (0.8 mg/kg, i.p.) in order to sensitize DA receptors. Using a randomized within subjects design, rats received a first injection of: Vehicle (dH(2)O) or the 5-HT(1A)R agonist +/-8-OH-DPAT (0.1 or 1.0 mg/kg, i.p.), followed by a second injection of: Vehicle (dimethyl sulfoxide), the D1R agonist SKF81297 (0.8 mg/kg, i.p.), the D2R agonist quinpirole (0.2 mg/kg, i.p.), or l-DOPA (12 mg/kg+benserazide, 15 mg/kg, i.p.). On test days, rats were monitored over a 2-h period immediately following the second injection for abnormal involuntary movements (AIMs), analogous to dyskinesia observed in PD patients, and contralateral rotations. The present findings indicate that 5-HT(1A)R stimulation reduces AIMs induced by D1R, D2R and l-DOPA administration while its effects on DA agonist-induced rotations were receptor-dependent, suggesting that direct 5-HT(1A)R and DA receptor interactions may contribute to the unique profile of 5-HT(1A)R agonists for the improvement of PD treatment.
Federal Laboratory Consortium — The Neutron Therapy Facility provides a moderate intensity, broad energy spectrum neutron beam that can be used for short term irradiations for radiobiology (cells)...
Non-Spherical Models of Neutron Stars
Zubairi, O; Romero, A; Mellinger, R; Weber, F; Orsaria, M; Contrera, G
2015-01-01
Non-rotating neutron stars are generally treated in theoretical studies as perfect spheres. Such a treatment, however, may not be correct if strong magnetic fields are present (such as for magnetars) and/or the pressure of the matter in the cores of neutron stars is non-isotropic (e.g., color superconducting). In this paper, we investigate the structure of non-spherical neutron stars in the framework of general relativity. Using a parameterized metric to model non-spherical mass distributions, we first derive a stellar structure equation for deformed neutron stars. Numerical investigations of this model equation show that the gravitational masses of deformed neutron stars depend rather strongly on the degree and type (oblate or prolate) of stellar deformation. In particular, we find that the mass of a neutron star increases with increasing oblateness but decreases with increasing prolateness. If this feature carries over to a full two-dimensional treatment of deformed neutron stars, this opens up the possibil...
A new polarized neutron interferometry facility at the NCNR
Shahi, C. B.; Arif, M.; Cory, D. G.; Mineeva, T.; Nsofini, J.; Sarenac, D.; Williams, C. J.; Huber, M. G.; Pushin, D. A.
2016-03-01
A new monochromatic beamline and facility has been installed at the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR) devoted to neutron interferometry in the research areas of spin control, spin manipulation, quantum mechanics, quantum information science, spintronics, and material science. This facility is possible in part because of advances in decoherence free subspace interferometer designs that have demonstrated consistent contrast in the presence of vibrational noise; a major environmental constraint that has prevented neutron interferometry from being applied at other neutron facilities. Neutron interferometry measures the phase difference between a neutron wave function propagating along two spatially separated paths. It is a practical example of self interference and due to its modest path separation of a few centimeters allows the insertion of samples and macroscopic neutron spin rotators. Phase shifts can be caused by gravitational, magnetic and nuclear interactions as well as purely quantum mechanical effects making interferometer a robust tool in neutron research. This new facility is located in the guide hall of the NCNR upstream of the existing Neutron Interferometry and Optics Facility (NIOF) and has several advantages over the NIOF including higher incident flux, better neutron polarization, and increased accessibility. The long term goal for the new facility is to be a user supported beamline and makes neutron interferometer more generally available to the scientific community. This paper addresses both the capabilities and characteristics of the new facility.
A new polarized neutron interferometry facility at the NCNR
Shahi, C.B. [Physics and Engineering Physics Department, Tulane University, New Orleans, LA 70188 (United States); Arif, M. [National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States); Cory, D.G. [Department of Chemistry, University of Waterloo, Waterloo, ON, Canada N2L 3G1 (Canada); Perimeter Institute for Theoretical Physics, Waterloo, ON, Canada N2L 2Y5 (Canada); Institute for Quantum Computing, University of Waterloo, Waterloo, ON, Canada N2L 3G1 (Canada); Canadian Institute for Advanced Research, Toronto, ON, Canada M5G 1Z8 (Canada); Mineeva, T. [Department of Physics and Astronomy, University of Waterloo, Waterloo, ON, Canada N2L 3G1 (Canada); Canadian Institute for Advanced Research, Toronto, ON, Canada M5G 1Z8 (Canada); Nsofini, J.; Sarenac, D. [Institute for Quantum Computing, University of Waterloo, Waterloo, ON, Canada N2L 3G1 (Canada); Department of Physics and Astronomy, University of Waterloo, Waterloo, ON, Canada N2L 3G1 (Canada); Williams, C.J. [National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States); Huber, M.G., E-mail: michael.huber@nist.gov [National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States); Pushin, D.A., E-mail: dmitry.pushin@uwaterloo.ca [Institute for Quantum Computing, University of Waterloo, Waterloo, ON, Canada N2L 3G1 (Canada); Department of Physics and Astronomy, University of Waterloo, Waterloo, ON, Canada N2L 3G1 (Canada)
2016-03-21
A new monochromatic beamline and facility has been installed at the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR) devoted to neutron interferometry in the research areas of spin control, spin manipulation, quantum mechanics, quantum information science, spintronics, and material science. This facility is possible in part because of advances in decoherence free subspace interferometer designs that have demonstrated consistent contrast in the presence of vibrational noise; a major environmental constraint that has prevented neutron interferometry from being applied at other neutron facilities. Neutron interferometry measures the phase difference between a neutron wave function propagating along two spatially separated paths. It is a practical example of self interference and due to its modest path separation of a few centimeters allows the insertion of samples and macroscopic neutron spin rotators. Phase shifts can be caused by gravitational, magnetic and nuclear interactions as well as purely quantum mechanical effects making interferometer a robust tool in neutron research. This new facility is located in the guide hall of the NCNR upstream of the existing Neutron Interferometry and Optics Facility (NIOF) and has several advantages over the NIOF including higher incident flux, better neutron polarization, and increased accessibility. The long term goal for the new facility is to be a user supported beamline and makes neutron interferometer more generally available to the scientific community. This paper addresses both the capabilities and characteristics of the new facility.
Neutron Time-of-Flight Quantification of Water Desorption Isotherms of Montmorillonite
Gates, Will P.; Bordallo, Heloisa N.; Aldridge, Laurence P.
2012-01-01
enabled us to differentiate at least two water motions during dehydration of Ca- and Na-SAz-1 (initially equilibrated at RH = 55%) by using a "controlled water loss" time-of-flight procedure. This work confirms that (a) interlayer and cationic water in dioctahedral smectites are characterized by slower......The multiple energy states of water held by surfaces of a clay mineral can be effectively probed with time-of-flight and fixed elastic window neutron scattering. We used these techniques to quantitatively differentiate water types, including rotational and translational diffusions, in Ca- and Na...... motions than interparticle water, (b) interlayer cations influenced the dynamics of water loss, probably through its affect on clay fabric, and (c) interparticle water behaves more like bulk water. At 55% RH the Ca montmorillonite held more interparticle water, but on dehydration under controlled...
Guzek, J. E-mail: jguzek@debeers.co.za; Richardson, K.; Franklyn, C.B.; Waites, A.; McMurray, W.R.; Watterson, J.I.W.; Tapper, U.A.S
1999-06-01
Two different technical solutions to the problem of generation of mono-energetic fast neutron beams on the gaseous targets are presented here. A simple and cost-effective design of a cooled windowed gas target system is described in the first part of this paper. It utilises a thin metallic foil window and circulating deuterium gas cooled down to 100 K. The ultimate beam handling capability of such target is determined by the properties of the window. Reliable performance of this gas target system was achieved at 1 bar of deuterium gas, when exposed to a 45 {mu}A beam of 5 MeV deuterons, for periods in excess of 6 h. Cooling of the target gas resulted in increased fast neutron output and improved neutron to gamma-ray ratio. The second part of this paper discusses the design of a high pressure, windowless gas target for use with pulsed, low duty cycle accelerators. A rotating seal concept was applied to reduce the gas load in a differentially pumped system. This allows operation at 1.23 bar of deuterium gas pressure in the gas cell region. Such a gas target system is free from the limitations of the windowed target but special attention has to be paid to the heat dissipation capability of the beam dump, due to the use of a thin target. The rotating seal concept is particularly suitable for use with accelerators such as radio-frequency quadrupole (RFQ) linacs that operate with a very high peak current at low duty cycle. The performance of both target systems was comprehensively characterized using the time-of-flight (TOF) technique. This demonstrated that very good quality mono-energetic fast neutron beams were produced with the slow neutron and gamma-ray component below 10% of the total target output.
Utilization of low voltage D-T neutron generators in neutron physics studies
Singkarat, S.
1995-08-01
In a small nuclear laboratory of a developing country a low voltage D-T neutron generator can be a very useful scientific apparatus. Such machines have been used successfully for more than 40 years in teaching and scientific research. The original continuous mode 150-kV D-T neutron generator has been modified to have also a capability of producing 2-ns pulsed neutrons. Together with a carefully designed 10 m long flight path collimator and shielding of a 25 cm diameter {center_dot} 10 cm thick BC-501 neutron detector, the pulsing system was successfully used for measuring the double differential cross-section (DDX) of natural iron for 14.1-MeV neutron from the angle of 30 deg to 150 deg in 10 deg steps. In order to extend the utility of the generator, two methods for converting the almost monoenergetic 14-MeV neutrons to monoenergetic neutrons of lower energy were proposed and tested. The first method uses a pulsed neutron generator and the second method uses an ordinary continuous mode generator. The latter method was successfully used to measure the scintillation light output of a 1.4 cm diameter spherical NE-213 scintillation detector. The neutron generator has also been used in the continuous search for improved neutron detection techniques. There is a proposal, based on Monte Carlo calculations, of using a scintillation fiber for a fast neutron spectrometer. Due to the slender shape of the fiber, the pattern of produced light gives a peak in the pulse height spectrum instead of the well-known rectangular-like distribution, when the fiber is bombarded end-on by a beam of 14-MeV neutrons. Experimental investigations were undertaken. Detailed investigations on the light transportation property of a short fiber were performed. The predicted peak has not yet been found but the fiber detector may be developed as a directional discrimination fast neutron detector. 18 refs.
Nayak, R C
2015-01-01
We identify here possible occurrence of large deformations in the neutron- and proton-rich regions of the nuclear chart from extensive predictions of the values of the reduced quadrupole transition probability B-E2 for the transition from the ground state to the first 2+ state and the corresponding excitation energy E2 of even-even nuclei in the recently developed Generalized Differential Equation model exclusively meant for these physical quantities. This is made possible from our analysis of the predicted values of these two physical quantities and the corresponding deformation parameters derived from them such as the quadrupole deformation beta-2, the ratio of beta-2 to the Weisskopf single-particle beta-2 and the intrinsic electric quadruplole moment , calculated for a large number of both known as well as hitherto unknown even-even isotopes of Oxygen to Fermium (Z=8 to 100). Our critical analysis of the resulting data convincingly support possible existence of large collectivity for the nuclides 30,32 Ne...
Rotational evolution of slow-rotators sequence stars
Lanzafame, Alessandro C
2015-01-01
The observed mass-age-rotation relationship in open clusters shows the progressive development of a slow-rotators sequence at masses lower than 1.2 $M_{\\odot}$. After 0.6 Gyr, almost all stars have settled on this sequence. The observed clustering on this sequence suggests that it corresponds to some equilibrium or asymptotic condition that still lacks a complete theoretical interpretation, crucial to our understanding of the stellar angular momentum evolution. We couple a rotational evolution model that takes into account internal differential rotation with classical and new proposals for the wind braking law, and fit models to the data using a Monte Carlo Markov Chain method tailored to the case at hand. We explore the extent to which these models are able to reproduce the mass and time dependence of the stellar rotational evolution on the slow-rotators sequence. The description of the early evolution (0.1-0.6 Gyr) of the slow-rotators sequence requires taking into account the transfer of angular momentum f...
Neutron transport study of a beam port based dynamic neutron radiography facility
Khaial, Anas M.
Neutron radiography has the ability to differentiate between gas and liquid in two-phase flow due both to the density difference and the high neutron scattering probability of hydrogen. Previous studies have used dynamic neutron radiography -- in both real-time and high-speed -- for air-water, steam-water and gas-liquid metal two-phase flow measurements. Radiography with thermal neutrons is straightforward and efficient as thermal neutrons are easier to detect with relatively higher efficiency and can be easily extracted from nuclear reactor beam ports. The quality of images obtained using neutron radiography and the imaging speed depend on the neutron beam intensity at the imaging plane. A high quality neutron beam, with thermal neutron intensity greater than 3.0x 10 6 n/cm2-s and a collimation ratio greater than 100 at the imaging plane, is required for effective dynamic neutron radiography up to 2000 frames per second. The primary objectives of this work are: (1) to optimize a neutron radiography facility for dynamic neutron radiography applications and (2) to investigate a new technique for three-dimensional neutron radiography using information obtained from neutron scattering. In this work, neutron transport analysis and experimental validation of a dynamic neutron radiography facility is studied with consideration of real-time and high-speed neutron radiography requirements. A beam port based dynamic neutron radiography facility, for a target thermal neutron flux of 1.0x107 n/cm2-s, has been analyzed, constructed and experimentally verified at the McMaster Nuclear Reactor. The neutron source strength at the beam tube entrance is evaluated experimentally by measuring the thermal and fast neutron fluxes using copper activation flux-mapping technique. The development of different facility components, such as beam tube liner, gamma ray filter, beam shutter and biological shield, is achieved analytically using neutron attenuation and divergence theories. Monte
Brueckel, Thomas; Heger, Gernot; Richter, Dieter; Roth, Georg; Zorn, Reiner (eds.)
2010-07-01
The following topics are dealt with: Neutron sources, symmetry of crystals, diffraction, nanostructures investigated by small-angle neutron scattering, the structure of macromolecules, spin dependent and magnetic scattering, structural analysis, neutron reflectometry, magnetic nanostructures, inelastic scattering, strongly correlated electrons, dynamics of macromolecules, applications of neutron scattering. (HSI)
Neutron Capture Nucleosynthesis
Kiss, Miklos
2016-01-01
Heavy elements (beyond iron) are formed in neutron capture nucleosynthesis processes. We have proposed a simple unified model to investigate the neutron capture nucleosynthesis in arbitrary neutron density environment. We have also investigated what neutron density is required to reproduce the measured abundance of nuclei assuming equilibrium processes. We found both of these that the medium neutron density has a particularly important role at neutron capture nucleosynthesis. About these results most of the nuclei can formed at medium neutron capture density environment e.g. in some kind of AGB stars. Besides these observations our model is capable to use educational purpose.
Mathematical Minute: Rotating a Function Graph
Bravo, Daniel; Fera, Joseph
2013-01-01
Using calculus only, we find the angles you can rotate the graph of a differentiable function about the origin and still obtain a function graph. We then apply the solution to odd and even degree polynomials.
Biological Augmentation of Rotator Cuff Tendon Repair
Kovacevic, David; Rodeo, Scott A
2008-01-01
A histologically normal insertion site does not regenerate following rotator cuff tendon-to-bone repair, which is likely due to abnormal or insufficient gene expression and/or cell differentiation at the repair site...
Nuclear reactor neutron shielding
Speaker, Daniel P; Neeley, Gary W; Inman, James B
2017-09-12
A nuclear reactor includes a reactor pressure vessel and a nuclear reactor core comprising fissile material disposed in a lower portion of the reactor pressure vessel. The lower portion of the reactor pressure vessel is disposed in a reactor cavity. An annular neutron stop is located at an elevation above the uppermost elevation of the nuclear reactor core. The annular neutron stop comprises neutron absorbing material filling an annular gap between the reactor pressure vessel and the wall of the reactor cavity. The annular neutron stop may comprise an outer neutron stop ring attached to the wall of the reactor cavity, and an inner neutron stop ring attached to the reactor pressure vessel. An excore instrument guide tube penetrates through the annular neutron stop, and a neutron plug comprising neutron absorbing material is disposed in the tube at the penetration through the neutron stop.
Rotational properties of strange-pulsar models
Benvenuto, O.G. (Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata, Paseo del Bosque S/N, (1900) La Plata, Argentina (AR)); Horvath, J.E. (Instituto Astronomico e Geofisico, Departamento de Astronomia, Universidade de Sao Paulo, Caixa Postal 30627, 01051 Sao Paulo, Brazil (BR)); Vucetich, H. (Departamento de Fisica, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, C.C. 67, (1900) La Plata, Argentina (AR))
1991-07-15
We present a study of the rotational properties of strange pulsars: strange-matter stars capable of supporting glitches. It is shown that their differentiated internal structure implies a lower maximum rotational frequency than that of homogeneous strange stars. Nevertheless, they are able to fit the known pulsar properties.
Rotational properties of strange-pulsar models
Benvenuto, O.G. (Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata, Paseo del Bosque S/N, (1900) La Plata (Argentina)); Horvath, J.E. (Instituto Astronomico e Geofisico, Departamento de Astronomia, Universidade de Sao Paulo, Caixa Postal 30627, 01051 Sao Paulo (Brazil)); Vucetich, H. (Departamento de Fisica, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, C.C. 67, (1900) La Plata (Argentina))
1991-08-15
We present a study of the rotational properties of strange pulsars: strange-matter stars capable of supporting glitches. It is shown that their differentiated internal structure implies a lower maximum rotational frequency than that of homogeneous strange stars. Nevertheless, they are able to fit the known pulsar properties.
Ishikawa, Masao, E-mail: ishikawa.masao@jaea.go.jp [Fusion Research and Development Directorate, Japan Atomic Energy Agency, Ibaraki 311-0193 (Japan); Kondoh, Takashi; Kusama, Yoshinori [Fusion Research and Development Directorate, Japan Atomic Energy Agency, Ibaraki 311-0193 (Japan); Bertalot, Luciano [ITER Organization, Route de Vinon sur Verdon, 13115 Saint Paul Lez Durance (France)
2013-10-15
Highlights: ► Neutronic analysis is performed for in situ calibration of the microfission chamber (MFC). ► The source transfer system deigned in this study does not affect MFC detection efficiency. ► The rotation method is appropriate for full calibration because the calibration time is shorter. ► But, point-by-point method should be performed to check the accuracy of the MCNP model. ► Combination of two methods are important to perform in situ calibration efficiently. -- Abstract: Neutronic analysis is performed for in situ calibration of the microfission chamber (MFC), which is the in-vessel neutron-flux monitor at the International Thermonuclear Experimental Reactor (ITER). We present the design of the transfer system for a neutron generator, which consists of two toroidal rings and a neutron-generator holder, and estimate the effect of the system on MFC detection efficiency through neutronic analysis with the Monte Carlo N-particle (MCNP) code. The result indicates that the designed transfer system does not affect MFC detection efficiency. In situ calibrations by the point-by-point method and by the rotation method are also simulated and compared by neutronic analysis. The results indicate that the rotation method is appropriate for full calibration because the calibration time is shorter (all neutron-flux monitors can be calibrated simultaneously). However, the rotation method makes it difficult to compare the results with neutronic analysis, so the point-by-point method should be performed prior to full calibration to check the accuracy of the MCNP model.
Weapons Neutron Research Facility (WNR)
Federal Laboratory Consortium — The Weapons Neutron Research Facility (WNR) provides neutron and proton beams for basic, applied, and defense-related research. Neutron beams with energies ranging...
Neutron kinetics in moderators and SNM detection through epithermal-neutron-induced fissions
Gozani, Tsahi; King, Michael J.
2016-01-01
Extension of the well-established Differential Die Away Analysis (DDAA) into a faster time domain, where more penetrating epithermal neutrons induce fissions, is proposed and demonstrated via simulations and experiments. In the proposed method the fissions stimulated by thermal, epithermal and even higher-energy neutrons are measured after injection of a narrow pulse of high-energy 14 MeV (d,T) or 2.5 MeV (d,D) source neutrons, appropriately moderated. The ability to measure these fissions stems from the inherent correlation of neutron energy and time ("E-T" correlation) during the process of slowing down of high-energy source neutrons in common moderating materials such as hydrogenous compounds (e.g., polyethylene), heavy water, beryllium and graphite. The kinetic behavior following injection of a delta-function-shaped pulse (in time) of 14 MeV neutrons into such moderators is studied employing MCNPX simulations and, when applicable, some simple "one-group" models. These calculations served as a guide for the design of a source moderator which was used in experiments. Qualitative relationships between slowing-down time after the pulse and the prevailing neutron energy are discussed. A laboratory system consisting of a 14 MeV neutron generator, a polyethylene-reflected Be moderator, a liquid scintillator with pulse-shape discrimination (PSD) and a two-parameter E-T data acquisition system was set up to measure prompt neutron and delayed gamma-ray fission signatures in a 19.5% enriched LEU sample. The measured time behavior of thermal and epithermal neutron fission signals agreed well with the detailed simulations. The laboratory system can readily be redesigned and deployed as a mobile inspection system for SNM in, e.g., cars and vans. A strong pulsed neutron generator with narrow pulse (<75 ns) at a reasonably high pulse frequency could make the high-energy neutron induced fission modality a realizable SNM detection technique.
Neutron kinetics in moderators and SNM detection through epithermal-neutron-induced fissions
Gozani, Tsahi, E-mail: tgmaven@gmail.com [1050 Harriet St., Palo Alto, CA 94301 (United States); King, Michael J. [Rapiscan Laboratories Inc., 520 Almanor Ave., Sunnyvale, CA 94085 (United States)
2016-01-01
Extension of the well-established Differential Die Away Analysis (DDAA) into a faster time domain, where more penetrating epithermal neutrons induce fissions, is proposed and demonstrated via simulations and experiments. In the proposed method the fissions stimulated by thermal, epithermal and even higher-energy neutrons are measured after injection of a narrow pulse of high-energy 14 MeV (d,T) or 2.5 MeV (d,D) source neutrons, appropriately moderated. The ability to measure these fissions stems from the inherent correlation of neutron energy and time (“E–T” correlation) during the process of slowing down of high-energy source neutrons in common moderating materials such as hydrogenous compounds (e.g., polyethylene), heavy water, beryllium and graphite. The kinetic behavior following injection of a delta-function-shaped pulse (in time) of 14 MeV neutrons into such moderators is studied employing MCNPX simulations and, when applicable, some simple “one-group” models. These calculations served as a guide for the design of a source moderator which was used in experiments. Qualitative relationships between slowing-down time after the pulse and the prevailing neutron energy are discussed. A laboratory system consisting of a 14 MeV neutron generator, a polyethylene-reflected Be moderator, a liquid scintillator with pulse-shape discrimination (PSD) and a two-parameter E–T data acquisition system was set up to measure prompt neutron and delayed gamma-ray fission signatures in a 19.5% enriched LEU sample. The measured time behavior of thermal and epithermal neutron fission signals agreed well with the detailed simulations. The laboratory system can readily be redesigned and deployed as a mobile inspection system for SNM in, e.g., cars and vans. A strong pulsed neutron generator with narrow pulse (<75 ns) at a reasonably high pulse frequency could make the high-energy neutron induced fission modality a realizable SNM detection technique.
Exploring properties of high-density matter through remnants of neutron-star mergers
Bauswein, Andreas [Aristotle University of Thessaloniki, Department of Physics, Thessaloniki (Greece); Heidelberger Institut fuer Theoretische Studien, Heidelberg (Germany); Stergioulas, Nikolaos [Aristotle University of Thessaloniki, Department of Physics, Thessaloniki (Greece); Janka, Hans-Thomas [Max-Planck-Institut fuer Astrophysik, Garching (Germany)
2016-03-15
Remnants of neutron-star mergers are essentially massive, hot, differentially rotating neutron stars, which are initially strongly oscillating. As such they represent a unique probe for high-density matter because the oscillations are detectable via gravitational-wave measurements and are strongly dependent on the equation of state. The impact of the equation of state for instance is apparent in the frequency of the dominant oscillation mode of the remnant. For a fixed total binary mass a tight relation between the dominant postmerger oscillation frequency and the radii of nonrotating neutron stars exists. Inferring observationally the dominant postmerger frequency thus determines neutron star radii with high accuracy of the order of a few hundred meters. By considering symmetric and asymmetric binaries of the same chirp mass, we show that the knowledge of the binary mass ratio is not critical for this kind of radius measurements. We perform simulations which show that initial intrinsic neutron star rotation is unlikely to affect this method of constraining the high-density equation of state. We also summarize different possibilities about how the postmerger gravitational-wave emission can be employed to deduce the maximum mass of nonrotating neutron stars. We clarify the nature of the three most prominent features of the postmerger gravitational-wave spectrum and argue that the merger remnant can be considered to be a single, isolated, self-gravitating object that can be described by concepts of asteroseismology. We sketch how the consideration of the strength of secondary gravitational-wave peaks leads to a classification scheme of the gravitational-wave emission and postmerger dynamics. The understanding of the different mechanisms shaping the gravitational-wave signal yields a physically motivated analytic model of the gravitational-wave emission, which may form the basis for template-based gravitational-wave data analysis. We explore the observational
Zeitelhack, K.; Schanzer, C.; Kastenmüller, A.; Röhrmoser, A.; Daniel, C.; Franke, J.; Gutsmiedl, E.; Kudryashov, V.; Maier, D.; Päthe, D.; Petry, W.; Schöffel, T.; Schreckenbach, K.; Urban, A.; Wildgruber, U.
2006-05-01
A sophisticated neutron guide system has been installed at the new Munich neutron source FRM-II to transport neutrons from the D 2 cold neutron source to several instruments, which are situated in a separate neutron guide hall. The guide system takes advantage of supermirror coatings and includes a worldwide unique "twisted" guide for a desired phase space transformation of the neutron beam. During the initial reactor commissioning in summer 2004, the integral and differential neutron flux as well as the distribution of beam divergence at the exit of two representative and the twisted neutron guide were measured using time-of-flight spectroscopy and gold-foil activation. The experimental results can be compared to extensive simulation calculations based on MCNP and McStas. The investigated guides fulfill the expectations of providing high neutron fluxes and reveal good quality with respect to the reflective coatings and the installation precision.
Zeitelhack, K. [ZWE FRM-II, TU Muenchen, D-85747 Garching (Germany)]. E-mail: karl.zeitelhack@frm2.tum.de; Schanzer, C. [Physik-Department E21, TU Muenchen, D-85747 Garching (Germany); Kastenmueller, A. [ZWE FRM-II, TU Muenchen, D-85747 Garching (Germany); Roehrmoser, A. [ZWE FRM-II, TU Muenchen, D-85747 Garching (Germany); Daniel, C. [Physik-Department E22, TU Muenchen, D-85747 Garching (Germany); Franke, J. [Max-Planck-Institut fuer Metallforschung, D-70569 Stuttgart (Germany); Gutsmiedl, E. [ZWE FRM-II, TU Muenchen, D-85747 Garching (Germany); Kudryashov, V. [GKSS Forschungszentrum GmbH, D-21502 Geesthacht (Germany); Maier, D. [ZWE FRM-II, TU Muenchen, D-85747 Garching (Germany); Paethe, D. [ZWE FRM-II, TU Muenchen, D-85747 Garching (Germany); Petry, W. [ZWE FRM-II, TU Muenchen, D-85747 Garching (Germany); Schoeffel, T. [ZWE FRM-II, TU Muenchen, D-85747 Garching (Germany); Schreckenbach, K. [ZWE FRM-II, TU Muenchen, D-85747 Garching (Germany); Urban, A. [ZWE FRM-II, TU Muenchen, D-85747 Garching (Germany); Wildgruber, U. [Max-Planck-Institut fuer Metallforschung, D-70569 Stuttgart (Germany)
2006-05-10
A sophisticated neutron guide system has been installed at the new Munich neutron source FRM-II to transport neutrons from the D{sub 2} cold neutron source to several instruments, which are situated in a separate neutron guide hall. The guide system takes advantage of supermirror coatings and includes a worldwide unique 'twisted' guide for a desired phase space transformation of the neutron beam. During the initial reactor commissioning in summer 2004, the integral and differential neutron flux as well as the distribution of beam divergence at the exit of two representative and the twisted neutron guide were measured using time-of-flight spectroscopy and gold-foil activation. The experimental results can be compared to extensive simulation calculations based on MCNP and McStas. The investigated guides fulfill the expectations of providing high neutron fluxes and reveal good quality with respect to the reflective coatings and the installation precision.
Plasma physics of accreting neutron stars
Ghosh, Pranab; Lamb, Frederick K.
1991-01-01
Plasma concepts and phenomena that are needed to understand X- and gamma-ray sources are discussed. The capture of material from the wind or from the atmosphere or envelope of a binary companion star is described and the resulting types of accretion flows discussed. The reasons for the formation of a magnetosphere around the neutron star are explained. The qualitative features of the magnetospheres of accreting neutron stars are then described and compared with the qualitative features of the geomagnetosphere. The conditions for stable flow and for angular and linear momentum conservation are explained in the context of accretion by magnetic neutron stars and applied to obtain rough estimates of the scale of the magnetosphere. Accretion from Keplerian disks is then considered in some detail. The radial structure of geometrically thin disk flows, the interaction of disk flows with the neutron star magnetosphere, and models of steady accretion from Keplerian disks are described. Accretion torques and the resulting changes in the spin frequencies of rotating neutron stars are considered. The predicted behavior is then compared with observations of accretion-powered pulsars. Magnetospheric processes that may accelerate particles to very high energies, producing GeV and, perhaps, TeV gamma-rays are discussed. Finally, the mechanisms that decelerate and eventually stop accreting plasma at the surfaces of strongly magnetic neutron stars are described.
Nuclear data measurements for 40-90 MeV neutrons at TIARA
Baba, M. [Tohoku Univ., Sendai (Japan). Cyclotron and Radioisotope Center
2000-03-01
Experimental activities at the {sup 7}Li neutron source of TIARA, Japan Atomic Energy Research Institute, Takasaki Establishment are reviewed briefly. Experiments on (1) double-differential charged particle production cross sections for 40-90 MeV neutrons and protons, and (2) neutron elastic scattering and non-elastic cross sections are described as well as the frame of the research. (author)
Superheated drop neutron spectrometer
Das, M; Roy, B; Roy, S C; Das, Mala
2000-01-01
Superheated drops are known to detect neutrons through the nucleation caused by the recoil nuclei produced by the interactions of neutrons with the atoms constituting the superheated liquid molecule. A novel method of finding the neutron energy from the temperature dependence response of SDD has been developed. From the equivalence between the dependence of threshold energy for nucleation on temperature of SDD and the dependence of dE/dx of the recoil ions with the energy of the neutron, a new method of finding the neutron energy spectrum of a polychromatic as well as monochromatic neutron source has been developed.
Wang, Ching L.
1983-09-13
Apparatus for improved sensitivity and time resolution of a neutron measurement. The detector is provided with an electrode assembly having a neutron sensitive cathode which emits relatively low energy secondary electrons. The neutron sensitive cathode has a large surface area which provides increased sensitivity by intercepting a greater number of neutrons. The cathode is also curved to compensate for differences in transit time of the neutrons emanating from the point source. The slower speeds of the secondary electrons emitted from a certain portion of the cathode are matched to the transit times of the neutrons impinging thereupon.
Resistivity damage rates in fusion-neutron-irradiated metals at 4. 2 K
Guinan, M.W.; Kinney, J.H.
1981-01-01
Changes in electrical resistivity at liquid helium temperature have been used to monitor the production of damage in dilute alloys of vanadium, niobium and molybdenum, and pure tungsten, aluminum and copper irradiated with high energy neutrons. The neutrons were produced at the Livermore rotating-target neutron sources (RTNS-I and RTNS-II). Further experiments on V, Nb and Mo were carried out with 30 MeV d-Be neutrons and slightly degraded fission-spectra neutrons. The results for all six materials are compared to those obtained in a pure fission spectrum. The relative damage production rates are in agreement with predictions based on damage energy calculations.
Of Mountains and Molehills : Gravitational Waves from Neutron Stars
Konar, Sushan; Bhattacharya, Dipankar; Sarkar, Prakash
2016-01-01
Surface asymmetries of accreting neutron stars are investigated for their mass quadrupole moment content. Though the amplitude of the gravitational waves from such asymmetries seem to be beyond the limit of detectability of the present generation of detectors, it appears that rapidly rotating neutron stars with strong magnetic fields residing in HMXBs would be worth considering for targeted search for continuous gravitational waves with the next generation of instruments.
Gravitational waves from surface inhomogeneities of neutron stars
Konar, Sushan; Mukherjee, Dipanjan; Bhattacharya, Dipankar; Sarkar, Prakash
2016-11-01
Surface asymmetries of accreting neutron stars are investigated for their mass quadrupole moment content. Though the amplitude of the gravitational waves from such asymmetries seems to be beyond the limit of detectability of the present generation of detectors, it appears that rapidly rotating neutron stars with strong magnetic fields residing in high-mass x-ray binaries would be worth considering for a targeted search for continuous gravitational waves with the next generation of instruments.
Proteomics perspectives in rotator cuff research
Sejersen, Maria Hee Jung; Frost, Poul; Hansen, Torben Bæk
2015-01-01
Background Rotator cuff tendinopathy including tears is a cause of significant morbidity. The molecular pathogenesis of the disorder is largely unknown. This review aimed to present an overview of the literature on gene expression and protein composition in human rotator cuff tendinopathy and other...... studies on objectively quantified differential gene expression and/or protein composition in human rotator cuff tendinopathy and other tendinopathies as compared to control tissue. Results We identified 2199 studies, of which 54 were included; 25 studies focussed on rotator cuff or biceps tendinopathy......, which only allowed simultaneous quantification of a limited number of prespecified mRNA molecules or proteins, several proteins appeared to be differentially expressed/represented in rotator cuff tendinopathy and other tendinopathies. No proteomics studies fulfilled our inclusion criteria, although...
The s-Process in Rotating Asymptotic Giant Branch Stars
Herwig, F; Lugaro, M
2003-01-01
(abridged) We model the nucleosynthesis during the thermal pulse phase of a rotating, solar metallicity AGB star of 3M_sun. Rotationally induced mixing during the thermal pulses produces a layer (~2E-5M_sun) on top of the CO-core where large amounts of protons and C12 co-exist. We follow the abundance evolution in this layer, in particular that of the neutron source C13 and of the neutron poison N14. In our AGB model mixing persists during the entire interpulse phase due to the steep angular velocity gradient at the core-envelope interface. We follow the neutron production during the interpulse phase, and find a resulting maximum neutron exposure of tau_max =0.04 mbarn^-1, which is too small to produce any significant s-process. In parametric models, we then investigate the combined effects of diffusive overshooting from the convective envelope and rotationally induced mixing. Models with overshoot and weaker interpulse mixing - as perhaps expected from more slowly rotating stars - yield larger neutron exposu...
The Fastest Rotating Pulsar: a Strange Star?
徐仁新; 徐轩彬; 吴鑫基
2001-01-01
According to the observational limits on the radius and mass, the fastest rotating pulsar (PSR 1937+21) is probably a strange star, or at least some neutron star equations of state should be ruled out, if we suggest that a dipole magnetic field is relevant to its radio emission. We presume that the millisecond pulsar is a strange star with much low mass, small radius and weak magnetic moment.
Modeling magnetized neutron stars using resistive MHD
Palenzuela, Carlos
2013-01-01
This work presents an implementation of the resistive MHD equations for a generic algebraic Ohm's law which includes the effects of finite resistivity within full General Relativity. The implementation naturally accounts for magnetic-field-induced anisotropies and, by adopting a phenomenological current, is able to accurately describe electromagnetic fields in the star and in its magnetosphere. We illustrate the application of this approach in interesting systems with astrophysical implications; the aligned rotator solution and the collapse of a magnetized rotating neutron star to a black hole.
Electromagnetic multipole fields of neutron stars
Roberts, W. J.
1979-01-01
A formalism is developed for treating general multipole electromagnetic fields of neutron stars. The electric multipoles induced in a neutron star by its rotation with an arbitrary magnetic multipole at its center are presented. It is shown how to express a family of off-centered multipoles having the same l weight as an infinite array of centered multipoles of increasing l weight referred to the rotational axis. General expressions are given for the linear momentum present in the superposition of arbitrary multipole fields, and the results are combined to compute the radiation rate of linear momentum by an off-centered dipole to zeroth order in the parameter Omega x R/c. The general Deutsch (1955) solution is then rederived in a clear consistent manner, and some minor additions and corrections are provided.
The Neutron Star Interior Composition Explorer (NICER)
Wilson-Hodge, Colleen A.; Gendreau, K.; Arzoumanian, Z.
2014-01-01
The Neutron Star Interior Composition Explorer (NICER) is an approved NASA Explorer Mission of Opportunity dedicated to the study of the extraordinary gravitational, electromagnetic, and nuclear-physics environments embodied by neutron stars. Scheduled to be launched in 2016 as an International Space Station payload, NICER will explore the exotic states of matter, using rotation-resolved spectroscopy of the thermal and non-thermal emissions of neutron stars in the soft (0.2-12 keV) X-ray band. Grazing-incidence "concentrator" optics coupled with silicon drift detectors, actively pointed for a full hemisphere of sky coverage, will provide photon-counting spectroscopy and timing registered to GPS time and position, with high throughput and relatively low background. The NICER project plans to implement a Guest Observer Program, which includes competitively selected user targets after the first year of flight operations. I will describe NICER and discuss ideas for potential Be/X-ray binary science.
Soft rotator model and {sup 246}Cm low-lying level scheme
Porodzinskij, Yu.V.; Sukhovitskij, E.Sh. [Radiation Physics and Chemistry Problems Inst., Minsk-Sosny (Belarus)
1997-03-01
Non-axial soft rotator nuclear model is suggested as self-consistent approach for interpretation of level schemes, {gamma}-transition probabilities and neutron interaction with even-even nuclei. (author)
Soft rotator model and {sup 246}Cm low-lying level scheme
Porodzinskij, Yu.V.; Sukhovitskij, E.Sh. [Radiation Physics and Chemistry Problems Inst., Minsk-Sosny (Belarus)
1997-03-01
Non-axial soft rotator nuclear model is suggested as self-consistent approach for interpretation of level schemes, {gamma}-transition probabilities and neutron interaction with even-even nuclei. (author)
Determination of spallation neutron flux through spectral adjustment techniques
Mosby, M.A., E-mail: mosbym@lanl.gov; Engle, J.W.; Jackman, K.R.; Nortier, F.M.; Birnbaum, E.R.
2016-08-15
The Los Alamos Isotope Production Facility (IPF) creates medical isotopes using a proton beam impinged on a target stack. Spallation neutrons are created in the interaction of the beam with target. The use of these spallation neutrons to produce additional radionuclides has been proposed. However, the energy distribution and magnitude of the flux is not well understood. A modified SAND-II spectral adjustment routine has been used with radioactivation foils to determine the differential neutron fluence for these spallation neutrons during a standard IPF production run.
Determination of spallation neutron flux through spectral adjustment techniques
Mosby, M. A.; Engle, J. W.; Jackman, K. R.; Nortier, F. M.; Birnbaum, E. R.
2016-08-01
The Los Alamos Isotope Production Facility (IPF) creates medical isotopes using a proton beam impinged on a target stack. Spallation neutrons are created in the interaction of the beam with target. The use of these spallation neutrons to produce additional radionuclides has been proposed. However, the energy distribution and magnitude of the flux is not well understood. A modified SAND-II spectral adjustment routine has been used with radioactivation foils to determine the differential neutron fluence for these spallation neutrons during a standard IPF production run.
Bacon, G.E. [Univ. of Sheffield (United Kingdom)
1994-12-31
The familiar extremes of crystalline material are single-crystals and random powders. In between these two extremes are polycrystalline aggregates, not randomly arranged but possessing some preferred orientation and this is the form taken by constructional materials, be they steel girders or the bones of a human or animal skeleton. The details of the preferred orientation determine the ability of the material to withstand stress in any direction. In the case of bone the crucial factor is the orientation of the c-axes of the mineral content - the crystals of the hexagonal hydroxyapatite - and this can readily be determined by neutron diffraction. In particular it can be measured over the volume of a piece of bone, utilizing distances ranging from 1mm to 10mm. The major practical problem is to avoid the intense incoherent scattering from the hydrogen in the accompanying collagen; this can best be achieved by heat-treatment and it is demonstrated that this does not affect the underlying apatite. These studies of bone give leading anatomical information on the life and activities of humans and animals - including, for example, the life history of the human femur, the locomotion of sheep, the fracture of the legs of racehorses and the life-styles of Neolithic tribes. We conclude that the material is placed economically in the bone to withstand the expected stresses of life and the environment. The experimental results are presented in terms of the magnitude of the 0002 apatite reflection. It so happens that for a random powder the 0002, 1121 reflections, which are neighboring lines in the powder pattern, are approximately equal in intensity. The latter reflection, being of manifold multiplicity, is scarcely affected by preferred orientation so that the numerical value of the 0002/1121 ratio serves quite accurately as a quantitative measure of the degree of orientation of the c-axes in any chosen direction for a sample of bone.
Neutron laminography-a novel approach to three-dimensional imaging of flat objects with neutrons
Helfen, L., E-mail: Lukas.Helfen@kit.edu [Institute for Synchrotron Radiation (ISS/ANKA), Karlsruhe Institute of Technology (KIT), Kaiserstr. 12, D-76131 Karlsruhe (Germany); Xu, F. [Institute for Synchrotron Radiation (ISS/ANKA), Karlsruhe Institute of Technology (KIT), Kaiserstr. 12, D-76131 Karlsruhe (Germany); Schillinger, B.; Calzada, E. [FRM-II, Technische Universitaet Muenchen, Lichtenbergstr. 1, D-85747 Garching (Germany); Zanette, I. [European Synchrotron Radiation Facility (ESRF), 6 rue Jules Horowitz, BP 220, F-38043 Grenoble (France); Weitkamp, T. [Synchrotron Soleil, L' Orme des Merisiers, Saint-Aubin, 91190 Gif-sur-Yvette (France); Baumbach, T. [Institute for Synchrotron Radiation (ISS/ANKA), Karlsruhe Institute of Technology (KIT), Kaiserstr. 12, D-76131 Karlsruhe (Germany)
2011-09-21
Computed tomography (CT) is a three-dimensional (3D) imaging method which, for compact or prolate (i.e. rather isotropically extended around the rotation axis) specimens, can yield artefact-free reconstructed cross-sections. Laterally extended specimens like plate-like objects, however, are much less amenable to CT since reliable projection data cannot be acquired from angles where the plate is oriented parallel to the irradiation direction. To overcome this drawback, computed laminography (CL) was introduced recently to imaging set-ups at synchrotron storage rings. Here, we report on the first implementation of computed laminography with neutron radiation, showing measurements that were performed at the ANTARES neutron imaging facility at the FRM II research reactor of Technische Universitaet Muenchen. In general, neutrons are highly interesting probes for imaging since they provide a sensitivity to chemical elements very different from X-rays, yielding complementary information about the specimens investigated. Like for X-ray laminography, we avoid the projection directions where the beam is parallel to the long extensions of the specimen. We accomplish this by tilting of the rotation axis with respect to the transmitted-beam to an angle smaller than 90{sup o} (which would be the limiting case of CT) and roughly aligning the specimen's surface normal parallel to this rotation axis. The principles of neutron laminography are introduced and first test experiments are described.
Gravitational radiation and gamma-ray bursts from accreting neutron stars
Mosquera Cuesta, H.J.; Araujo, J.C.N. de; Aguiar, O.D. [Instituto Nacional de Pesquisas Espaciais (INPE), Sao Jose dos Campos, SP (Brazil). Div. de Astrofisica]. E-mail: herman@das.inpe.br; jcarlos@das.inpe.br; odylio@das.inpe.br; Horvath, J.E. [Sao Paulo Univ., SP (Brazil). Inst. Astronomico e Geofisico]. E-mail: foton@orion.iagusp.usp.br
2000-07-01
It is well known that hydrodynamic instabilities can be induced in rapidly rotating low magnetic field neutron stars, which accrete mass from a companion in both high and low mass X-ray binaries. (author)
Observational constraints on neutron star masses and radii
Coleman Miller, M. [University of Maryland, Department of Astronomy and Joint Space-Science Institute, College Park, MD (United States); Lamb, Frederick K. [University of Illinois at Urbana-Champaign, Center for Theoretical Astrophysics and Department of Physics, Urbana, IL (United States); University of Illinois at Urbana-Champaign, Department of Astronomy, Urbana, IL (United States)
2016-03-15
Precise and reliable measurements of the masses and radii of neutron stars with a variety of masses would provide valuable guidance for improving models of the properties of cold matter with densities above the saturation density of nuclear matter. Several different approaches for measuring the masses and radii of neutron stars have been tried or proposed, including analyzing the X-ray fluxes and spectra of the emission from neutron stars in quiescent low-mass X-ray binary systems and thermonuclear burst sources; fitting the energy-dependent X-ray waveforms of rotation-powered millisecond pulsars, burst oscillations with millisecond periods, and accretion-powered millisecond pulsars; and modeling the gravitational radiation waveforms of coalescing double neutron star and neutron star - black hole binary systems. We describe the strengths and weaknesses of these approaches, most of which currently have substantial systematic errors, and discuss the prospects for decreasing the systematic errors in each method. (orig.)
Observational Constraints on Neutron Star Masses and Radii
Miller, M Coleman
2016-01-01
Precise and reliable measurements of the masses and radii of neutron stars with a variety of masses would provide valuable guidance for improving models of the properties of cold matter with densities above the saturation density of nuclear matter. Several different approaches for measuring the masses and radii of neutron stars have been tried or proposed, including analyzing the X-ray fluxes and spectra of the emission from neutron stars in quiescent low-mass X-ray binary systems and thermonuclear burst sources; fitting the energy-dependent X-ray waveforms of rotation-powered millisecond pulsars, burst oscillations with millisecond periods, and accretion-powered millisecond pulsars; and modeling the gravitational radiation waveforms of coalescing double neutron star and neutron star -- black hole binary systems. We describe the strengths and weaknesses of these approaches, most of which currently have substantial systematic errors, and discuss the prospects for decreasing the systematic errors in each method...
Observation of Aharonov-Bohm effects by neutron interferometry
Werner, Samuel A [Physics Laboratory, NIST, Gaithersburg, MD 20899 (United States); Klein, Anthony G, E-mail: sam.werner@verizon.ne [School of Physics, University of Melbourne, Parkville, Victoria 3010 (Australia)
2010-09-03
The special and unique techniques of neutron interferometry have been used to observe a number of topological effects. These include the quantum mechanical phase shift of a neutron due to the Earth's rotation (the quantum analog of the Michelson-Gale-Pearson experiment with light), the phase shift of a particle carrying a magnetic moment (a neutron) encircling a line charge (the Aharonov-Casher effect) and the scalar Aharonov-Bohm effect, observed with a pulsed magnetic field solenoid and time-of-flight neutron detection. On the occasion of the 50th anniversary of the Aharonov-Bohm paper, we provide an overview of the neutron interferometry technique and a description of these three historic experiments.
Observation of Aharonov-Bohm effects by neutron interferometry
Werner, Samuel A.; Klein, Anthony G.
2010-09-01
The special and unique techniques of neutron interferometry have been used to observe a number of topological effects. These include the quantum mechanical phase shift of a neutron due to the Earth's rotation (the quantum analog of the Michelson-Gale-Pearson experiment with light), the phase shift of a particle carrying a magnetic moment (a neutron) encircling a line charge (the Aharonov-Casher effect) and the scalar Aharonov-Bohm effect, observed with a pulsed magnetic field solenoid and time-of-flight neutron detection. On the occasion of the 50th anniversary of the Aharonov-Bohm paper, we provide an overview of the neutron interferometry technique and a description of these three historic experiments.
Neutron interferometry for precise characterization of quantum systems
Sarenac, Dusan; Shahi, Chandra; Mineeva, Taisiya; Wood, Christopher J.; Huber, Michael G.; Arif, Muhammad; Clark, Charles W.; Cory, David G.; Pushin, Dmitry A.
Neutron interferometry (NI) is among the most precise techniques used to test the postulates of quantum mechanics. It has demonstrated coherent spinor rotation and superposition, gravitationally induced quantum interference, the Aharonov-Casher effect, violation of a Bell-like inequality, and generation of a single-neutron entangled state. As massive, penetrating and neutral particles neutrons now provide unique capabilities in classical imaging applications that we seek to extend to the quantum domain. We present recent results on NI measurements of quantum discord in a bipartite quantum system and neutron orbital angular momentum multiplexing, and review progress on our commissioning of a decoherence-free-subspace NI user facility at the NIST Center for Neutron Research. Supported in part by CERC, CIFAR, NSERC and CREATE.
A gravitational wave afterglow in binary neutron star mergers
Doneva, Daniela D; Pnigouras, Pantelis
2015-01-01
We study in detail the f-mode secular instability for rapidly rotating neutron stars, putting emphasis on supermassive models which do not have a stable nonrotating counterpart. Such neutron stars are thought to be the generic outcome of the merger of two standard mass neutron stars. In addition we take into account the effects of strong magnetic field and r-mode instability, that can drain a substantial amount of angular momentum. We find that the gravitational wave signal emitted by supramassive neutron stars can reach above the Advance LIGO sensitivity at distance of about 20Mpc and the detectability is substantially enhanced for the Einstein Telescope. The event rate will be of the same order as the merging rates, while the analysis of the signal will carry information for the equation of state of the post-merging neutron stars and the strength of the magnetic fields.
Imaging with Scattered Neutrons
Ballhausen, H.; Abele, H.; Gaehler, R.; Trapp, M.; Van Overberghe, A.
2006-01-01
We describe a novel experimental technique for neutron imaging with scattered neutrons. These scattered neutrons are of interest for condensed matter physics, because they permit to reveal the local distribution of incoherent and coherent scattering within a sample. In contrast to standard attenuation based imaging, scattered neutron imaging distinguishes between the scattering cross section and the total attenuation cross section including absorption. First successful low-noise millimeter-re...
Intense fusion neutron sources
Kuteev, B. V.; Goncharov, P. R.; Sergeev, V. Yu.; Khripunov, V. I.
2010-04-01
The review describes physical principles underlying efficient production of free neutrons, up-to-date possibilities and prospects of creating fission and fusion neutron sources with intensities of 1015-1021 neutrons/s, and schemes of production and application of neutrons in fusion-fission hybrid systems. The physical processes and parameters of high-temperature plasmas are considered at which optimal conditions for producing the largest number of fusion neutrons in systems with magnetic and inertial plasma confinement are achieved. The proposed plasma methods for neutron production are compared with other methods based on fusion reactions in nonplasma media, fission reactions, spallation, and muon catalysis. At present, intense neutron fluxes are mainly used in nanotechnology, biotechnology, material science, and military and fundamental research. In the near future (10-20 years), it will be possible to apply high-power neutron sources in fusion-fission hybrid systems for producing hydrogen, electric power, and technological heat, as well as for manufacturing synthetic nuclear fuel and closing the nuclear fuel cycle. Neutron sources with intensities approaching 1020 neutrons/s may radically change the structure of power industry and considerably influence the fundamental and applied science and innovation technologies. Along with utilizing the energy produced in fusion reactions, the achievement of such high neutron intensities may stimulate wide application of subcritical fast nuclear reactors controlled by neutron sources. Superpower neutron sources will allow one to solve many problems of neutron diagnostics, monitor nano-and biological objects, and carry out radiation testing and modification of volumetric properties of materials at the industrial level. Such sources will considerably (up to 100 times) improve the accuracy of neutron physics experiments and will provide a better understanding of the structure of matter, including that of the neutron itself.
Physics, Formation and Evolution of Rotating Stars
Maeder, André
2009-01-01
Rotation is ubiquitous at each step of stellar evolution, from star formation to the final stages, and it affects the course of evolution, the timescales and nucleosynthesis. Stellar rotation is also an essential prerequisite for the occurrence of Gamma-Ray Bursts. In this book the author thoroughly examines the basic mechanical and thermal effects of rotation, their influence on mass loss by stellar winds, the effects of differential rotation and its associated instabilities, the relation with magnetic fields and the evolution of the internal and surface rotation. Further, he discusses the numerous observational signatures of rotational effects obtained from spectroscopy and interferometric observations, as well as from chemical abundance determinations, helioseismology and asteroseismology, etc. On an introductory level, this book presents in a didactical way the basic concepts of stellar structure and evolution in "track 1" chapters. The other more specialized chapters form an advanced course on the gradua...
An intense 14 MeV neutron source
Su Tongling; Sun Biehe; Yang Baotai; Piao Yubo; Shui Yongqing; Chen Kefan; Wang Xuezhi; Yang Cheng; Niu Zhanqi; Liu Yanton; Pan Minshen; Hong Zhongti; Chen Qin (Lanzhou Univ., GS (China). Inst. of Nuclear Research)
1990-02-15
A 3x10{sup 12} n/s source of 14 MeV neutrons is described in this paper. The neutrons are produced by the T(d,n){sup 4}He reaction under a 30 mA, 300 keV deuteron beam bombarding a water-cooled, rotating titanium-tritide target. The size of the beam spot on the target is 1.8 cm, and at the distance of closest approach to the source a neutron flux of 5x10{sup 11} n/cm{sup 2} s is obtained. (orig.).
... this page: //medlineplus.gov/ency/patientinstructions/000357.htm Rotator cuff exercises To use the sharing features on this ... gov/pubmed/25560729 . Read More Frozen shoulder Rotator cuff problems Rotator cuff repair Shoulder arthroscopy Shoulder CT scan Shoulder ...
International Neutron Radiography Newsletter
Domanus, Joseph Czeslaw
1986-01-01
At the First World Conference on Neutron Radiography i t was decided to continue the "Neutron Radiography Newsletter", published previously by J.P. Barton, as the "International Neutron Radiography Newsletter" (INRNL), with J.C. Doraanus as editor. The British Journal of Non-Destructive Testing...
Advanced neutron absorber materials
Branagan, Daniel J.; Smolik, Galen R.
2000-01-01
A neutron absorbing material and method utilizing rare earth elements such as gadolinium, europium and samarium to form metallic glasses and/or noble base nano/microcrystalline materials, the neutron absorbing material having a combination of superior neutron capture cross sections coupled with enhanced resistance to corrosion, oxidation and leaching.
Prototype Neutron Energy Spectrometer
Stephen Mitchell, Sanjoy Mukhopadhyay, Richard Maurer, Ronald Wolff
2010-06-16
The project goals are: (1) Use three to five pressurized helium tubes with varying polyethylene moderators to build a neutron energy spectrometer that is most sensitive to the incident neutron energy of interest. Neutron energies that are of particular interest are those from the fission neutrons (typically around 1-2 MeV); (2) Neutron Source Identification - Use the neutron energy 'selectivity' property as a tool to discriminate against other competing processes by which neutrons are generated (viz. Cosmic ray induced neutron production [ship effect], [a, n] reactions); (3) Determine the efficiency as a function of neutron energy (response function) of each of the detectors, and thereby obtain the composite neutron energy spectrum from the detector count rates; and (4) Far-field data characterization and effectively discerning shielded fission source. Summary of the presentation is: (1) A light weight simple form factor compact neutron energy spectrometer ready to be used in maritime missions has been built; (2) Under laboratory conditions, individual Single Neutron Source Identification is possible within 30 minutes. (3) Sources belonging to the same type of origin viz., (a, n), fission, cosmic cluster in the same place in the 2-D plot shown; and (4) Isotopes belonging to the same source origin like Cm-Be, Am-Be (a, n) or Pu-239, U-235 (fission) do have some overlap in the 2-D plot.
X-ray Measurements of a Thermo Scientific P385 DD Neutron Generator
E.H. Seabury; D.L. Chichester; A.J. Caffrey; J. Simpson; M. Lemchak; C.J. Wharton
2001-08-01
Idaho National Laboratory is experimenting with electrical neutron generators, as potential replacements for californium-252 radioisotopic neutron sources in its PINS prompt gamma-ray neutron activation analysis (PGNAA) system for the identification of military chemical warfare agents and explosives. In addition to neutron output, we have recently measured the x-ray output of the Thermo Scientific P385 deuterium-deuterium neutron generator. X-rays are a normal byproduct from a neutron generator and depending on their intensity and energy they can interfere with gamma rays from the object under test, increase gamma-spectrometer dead time, and reduce PGNAA system throughput. The P385 x-ray energy spectrum was measured with a high-purity germanium (HPGe) detector, and a broad peak is evident at about 70 keV. To identify the source of the x-rays within the neutron generator assembly, it was scanned by collimated scintillation detectors along its long axis. At the strongest x-ray emission points, the generator also was rotated 60° between measurements. The scans show the primary source of x-ray emission from the P385 neutron generator is an area 60 mm from the neutron production target, in the vicinity of the ion source. Rotation of the neutron generator did not significantly alter the x-ray count rate, and the x-ray emission appears to be axially symmetric within the neutron generator.
Rotating Cavitation Supression Project
National Aeronautics and Space Administration — FTT proposes development of a rotating cavitation (RC) suppressor for liquid rocket engine turbopump inducers. Cavitation instabilities, such as rotating...
Low-mass neutron stars: universal relations, the nuclear symmetry energy and gravitational radiation
Silva, Hector O.; Sotani, Hajime; Berti, Emanuele
2016-07-01
The lowest neutron star masses currently measured are in the range 1.0-1.1 M⊙, but these measurement have either large uncertainties or refer to isolated neutron stars. The recent claim of a precisely measured mass M/M⊙ = 1.174 ± 0.004 (Martinez et al. 2015) in a double neutron star system suggests that low-mass neutron stars may be an interesting target for gravitational-wave detectors. Furthermore, Sotani et al. recently found empirical formulas relating the mass and surface redshift of non-rotating neutron stars to the star's central density and to the parameter η ≡ (K0L2)1/3, where K0 is the incompressibility of symmetric nuclear matter and L is the slope of the symmetry energy at saturation density. Motivated by these considerations, we extend the work by Sotani et al. to slowly rotating and tidally deformed neutron stars. We compute the moment of inertia, quadrupole moment, quadrupole ellipticity, tidal and rotational Love number and apsidal constant of slowly rotating neutron stars by integrating the Hartle-Thorne equations at second order in rotation, and we fit all of these quantities as functions of η and of the central density. These fits may be used to constrain η, either via observations of binary pulsars in the electromagnetic spectrum, or via near-future observations of inspiralling compact binaries in the gravitational-wave spectrum.
Manifestation of the geometric phase in neutron spin-echo experiments
Kraan, W.H.; Grigoriev, S.V.; Rekveldt, M.T.
2010-01-01
We show how the geometric (Berry’s) phase becomes manifest on adiabatic rotation of the polarization vector in the magnetic field configuration in the arms in a neutron spin echo (NSE) experiment.When the neutron beam used is monochromatic, a geometric phase collected in one spin-echo arm can be exa
Massive and massless modes of the triplet phase of neutron matter
Bedaque, Paulo F; Sen, Srimoyee
2014-01-01
Neutron matter at densities of the order of the nuclear saturation density is believed to have neutrons paired in the 3P2 channel. We study the low lying modes of this phase and find two massless modes (angulons), resulting from the spontaneous breaking of rotational symmetry as well as three other, gapped modes. We compute their masses at arbitrary temperatures.
Neutron scattering. Experiment manuals
Brueckel, Thomas; Heger, Gernot; Richter, Dieter; Roth, Georg; Zorn, Reiner (eds.)
2010-07-01
The following topics are dealt with: The thermal triple axis spectrometer PUMA, the high-resolution powder diffractometer SPODI, the hot single-crystal diffractometer HEiDi for structure analysis with neutrons, the backscattering spectrometer SPHERES, neutron polarization analysis with tht time-of-flight spectrometer DNS, the neutron spin-echo spectrometer J-NSE, small-angle neutron scattering with the KWS-1 and KWS-2 diffractometers, the very-small-angle neutron scattering diffractrometer with focusing mirror KWS-3, the resonance spin-echo spectrometer RESEDA, the reflectometer TREFF, the time-of-flight spectrometer TOFTOF. (HSI)
Grazing Incidence Neutron Optics
Gubarev, Mikhail V. (Inventor); Ramsey, Brian D. (Inventor); Engelhaupt, Darell E. (Inventor)
2013-01-01
Neutron optics based on the two-reflection geometries are capable of controlling beams of long wavelength neutrons with low angular divergence. The preferred mirror fabrication technique is a replication process with electroform nickel replication process being preferable. In the preliminary demonstration test an electroform nickel optics gave the neutron current density gain at the focal spot of the mirror at least 8 for neutron wavelengths in the range from 6 to 20.ANG.. The replication techniques can be also be used to fabricate neutron beam controlling guides.
Advances in neutron tomography
W Treimer
2008-11-01
In the last decade neutron radiography (NR) and tomography (NCT) have experienced a number of improvements, due to the well-known properties of neutrons interacting with matter, i.e. the low attenuation by many materials, the strong attenuation by hydrogenous constituent in samples, the wavelength-dependent attenuation in the neighbourhood of Bragg edges and due to better 2D neutron detectors. So NR and NCT were improved by sophisticated techniques that are based on the attenuation of neutrons or on phase changes of the associated neutron waves if they pass through structured materials. Up to now the interaction of the neutron spin with magnetic fields in samples has not been applied to imaging techniques despite the fact that it was proposed many years ago. About ten years ago neutron depolarization as imaging signal for neutron radiography or tomography was demonstrated and in principle it works. Now one can present much improved test experiments using polarized neutrons for radiographic imaging. For this purpose the CONRAD instrument of the HMI was equipped with polarizing and analysing benders very similar to conventional scattering experiments using polarized neutrons. Magnetic fields in different coils and in samples (superconductors) at low temperatures could be visualized. In this lecture a summary about standard signals (attenuation) and the more `sophisticated' imaging signals as refraction, small angle scattering and polarized neutrons will be given.
Fermi, Enrico; Zinn, Walter H.
The argument of the present Patent is a radiation shield suitable for protection of personnel from both gamma rays and neutrons. Such a shield from dangerous radiations is achieved to the best by the combined action of a neutron slowing material (a moderator) and a neutron absorbing material. Hydrogen is particularly effective for this shield since it is a good absorber of slow neutrons and a good moderator of fast neutrons. The neutrons slowed down by hydrogen may, then, be absorbed by other materials such as boron, cadmium, gadolinium, samarium or steel. Steel is particularly convenient for the purpose, given its effectiveness in absorbing also the gamma rays from the reactor (both primary gamma rays and secondary ones produced by the moderation of neutrons). In particular, in the present Patent a shield is described, made of alternate layers of steel and Masonite (an hydrolized ligno-cellulose material). The object of the present Patent is not discussed in any other published paper.