Non-local Transfer Research Articles

Nitrogen isotopic ratios in Barnard 1: a consistent study of the N2H+, NH3, CN, HCN, and HNC isotopologues

The 15N isotopologue abundance ratio measured today in different bodies of the solar system is thought to be connected to 15N-fractionation effects that would have occured in the protosolar nebula. The present study aims at putting constraints on the degree of 15N-fractionation that occurs during the prestellar phase, through observations of D, 13C and 15N-substituted isotopologues towards B1b. Both molecules from the nitrogen hydride family, i.e. N2H+ and NH3, and from the nitrile family, i.e. HCN, HNC and CN, are considered in the analysis. As a first step, we model the continuum emission in order to derive the physical structure of the cloud, i.e. gas temperature and H2 density. These parameters are subsequently used as an input in a non-local radiative transfer model to infer the radial abundances profiles of the various molecules. Our modeling shows that all the molecules are affected by depletion onto dust grains, in the region that encompasses the B1-bS and B1-bN cores. While high levels of deuterium fractionation are derived, we conclude that no fractionation occurs in the case of the nitrogen chemistry. Independently of the chemical family, the molecular abundances are consistent with 14N/15N~300, a value representative of the elemental atomic abundances of the parental gas. The inefficiency of the 15N-fractionation effects in the B1b region can be linked to the relatively high gas temperature ~17K which is representative of the innermost part of the cloud. Since this region shows signs of depletion onto dust grains, we can not exclude the possibility that the molecules were previously enriched in 15N, earlier in the B1b history, and that such an enrichment could have been incorporated into the ice mantles. It is thus necessary to repeat this kind of study in colder sources to test such a possibility.

Nonviolent nonlocality

If quantum mechanics governs nature, black holes must evolve unitarily, providing a powerful constraint on the dynamics of quantum gravity. Such evolution apparently must in particular be nonlocal, when described from the usual semiclassical geometric picture, in order to transfer quantum information into the outgoing state. While such transfer from a disintegrating black hole has the dangerous potential to be violent to generic infalling observers, this paper proposes the existence of a more innocuous form of information transfer, to relatively soft modes in the black hole atmosphere. Simplified models for such nonlocal transfer are described and parameterized, within a possibly more basic framework of networked Hilbert spaces. Sufficiently sensitive measurements by infalling observers may detect departures from Hawking's predictions, and in generic models black holes decay more rapidly. Constraints of consistency---internally and with known and expected features of physics---restrict the form of information transfer, and should provide important guides to discovery of the principles and mechanisms of the more fundamental nonlocal mechanics.

Effective eddy viscosity in stratified turbulence

This paper investigates the effective eddy viscosity inferred from direct numerical simulations of decaying stratified and non-stratified turbulence. It is shown that stratification affects the horizontal eddy viscosity dramatically, by increasing non-local energy transfer between large and small horizontal scales. This non-local horizontal energy transfer is around 20% of the local horizontal energy transfer at the cutoff wavenumber kc = 40. The non-local horizontal energy transfer occurs at large vertical wavenumbers, which may be larger than the buoyancy wavenumber kb = N/urms, where N is the buoyancy frequency and urms is the root-mean-square velocity. By increasing the value of the test cutoff wavenumber kc from large scales to the dissipation range, the non-local horizontal eddy viscosity decreases and the local eddy viscosity is dominant. Overall, the presence of stratification can significantly change the features of subgrid-scale (SGS) motions. Current SGS models should, therefore, be modified for use in large-eddy simulation of stratified turbulence.

Spectral non-uniform temperature and non-local heat transfer in the spin Seebeck effect

Recently discovered spin-dependent thermoelectric effects have merged spin, charge, and thermal physics, known as spin caloritronics, of which the spin Seebeck effect is its most puzzling. Here we present a theory of this effect driven by subthermal non-local phonon heat transfer and spectral non-uniform temperature. The theory explains its non-local behaviour from the fact that phonons that store the energy (thermal) and the phonons that transfer it (subthermal) are located in different parts of the spectrum and have different kinetics. This gives rise to a spectral phonon distribution that deviates from local equilibrium along the substrate and is sensitive to boundary conditions. The theory also predicts a non-magnon origin of the effect in ferromagnetic metals in agreement with observations in recent experiments. Equilibration of the heat flow from the substrate to the Pt probe and backwards leads to a vertical spin current produced by the spin-polarized electrons dragged by the thermal phonons.

Non-local radiative transfer in strongly inverted masers

Maser transitions are commonly observed in media exhibiting a large range of densities and temperatures. They can be used to obtain information on the dynamics and physical conditions of the observed regions. In order to obtain reliable constraints on the physical conditions prevailing in the masing regions, it is necessary to model the excitation mechanisms of the energy levels of the observed molecules. We present a numerical method that enables us to obtain self-consistent solutions for both the statistical equilibrium and radiative transfer equations. Using the standard maser theory, the method of Short Characteristics is extended to obtain the solution of the integro-differential radiative transfer equation, appropriate to the case of intense masing lines. We have applied our method to the maser lines of the H2O molecule and we compare with the results obtained with a less accurate approach. In the regime of large maser opacities we find large differences in the intensity of the maser lines that could be as high as several orders of magnitude. The comparison between the two methods shows, however, that the effect on the thermal lines is modest. Finally, the effect introduced by rate coefficients on the prediction of H2O masing lines and opacities is discussed, making use of various sets of rate coefficients involving He, o-H2 and p-H2. We find that the masing nature of a line is not affected by the selected collisional rates. However, from one set to the other the modelled line opacities and intensities can vary by up to a factor ~2 and ~10 respectively.

Nanoscale spin reversal by non-local angular momentum transfer following ultrafast laser excitation in ferrimagnetic GdFeCo

Ultrafast laser techniques have revealed extraordinary spin dynamics in magnetic materials that equilibrium descriptions of magnetism cannot explain. Particularly important for future applications is understanding non-equilibrium spin dynamics following laser excitation on the nanoscale, yet the limited spatial resolution of optical laser techniques has impeded such nanoscale studies. Here we present ultrafast diffraction experiments with an X-ray laser that probes the nanoscale spin dynamics following optical laser excitation in the ferrimagnetic alloy GdFeCo, which exhibits macroscopic all-optical switching. Our study reveals that GdFeCo displays nanoscale chemical and magnetic inhomogeneities that affect the spin dynamics. In particular, we observe Gd spin reversal in Gd-rich nanoregions within the first picosecond driven by the non-local transfer of angular momentum from larger adjacent Fe-rich nanoregions. These results suggest that a magnetic material's microstructure can be engineered to control transient laser-excited spins, potentially allowing faster (~ 1 ps) spin reversal than in present technologies.

Nonlocal effects in energy balance in an equilibrium plasma during its fast heating/cooling in tokamaks and stellarators

The long-standing problem of nonlocal energy transfer observed in a number of fast heating/cooling experiments in tokamaks and stellarators is discussed. The most representative and still unexplained are the results from cold-pulse experiments that demonstrate a rapid transient increase in the electron temperature in the plasma core in response to an abrupt cooling of the edge. This occurs on a timescale much faster than the diffusive one, which is incompatible with conventional local transport models. This paper contains a review of the most enigmatical observations and theoretical efforts to describe them, and offers an alternative theoretical approach to the problem. Its essential element is the incorporation of the induction effects and fast energy exchange between the plasma and the magnetic field into the traditional transport model. This makes an emphasis on the magnetic field as the main carrier of the interaction, which naturally explains the fast and nonlocal character of the process. The approach uses the ideas recently applied to the analysis of a closely related problem of ‘missing power’. Accordingly, the flux-conserving evolution of the plasma equilibrium and evaluation of the integral energy balance are parts of the analysis.

Calculation of Nonlocal Spin Transfer Torque

We microscopically derive the spin-transfer torque due to diffusive spin current arising from nonequilibrium spin accumulation as realized in systems with nonlocal spin valve structure. Spin relaxation effects in spin transport is taken into account by introducing magnetic impurities.

Spectral analysis of the transition to turbulence from a dipole in stratified fluid

AbstractWe investigate the spectral properties of the turbulence generated during the nonlinear evolution of a Lamb–Chaplygin dipole in a stratified fluid for a high Reynolds number $Re= 28\hspace{0.167em} 000$ and a wide range of horizontal Froude number ${F}_{h} \in [0. 0225~0. 135] $ and buoyancy Reynolds number $\mathscr{R}= Re{{F}_{h} }^{2} \in [14~510] $. The numerical simulations use a weak hyperviscosity and are therefore almost direct numerical simulations (DNS). After the nonlinear development of the zigzag instability, both shear and gravitational instabilities develop and lead to a transition to small scales. A spectral analysis shows that this transition is dominated by two kinds of transfer: first, the shear instability induces a direct non-local transfer toward horizontal wavelengths of the order of the buoyancy scale ${L}_{b} = U/ N$, where $U$ is the characteristic horizontal velocity of the dipole and $N$ the Brunt–Väisälä frequency; second, the destabilization of the Kelvin–Helmholtz billows and the gravitational instability lead to small-scale weakly stratified turbulence. The horizontal spectrum of kinetic energy exhibits a ${{\varepsilon }_{K} }^{2/ 3} { k}_{h}^{\ensuremath{-} 5/ 3} $ power law (where ${k}_{h} $ is the horizontal wavenumber and ${\varepsilon }_{K} $ is the dissipation rate of kinetic energy) from ${k}_{b} = 2\lrm{\pi} / {L}_{b} $ to the dissipative scales, with an energy deficit between the integral scale and ${k}_{b} $ and an excess around ${k}_{b} $. The vertical spectrum of kinetic energy can be expressed as $E({k}_{z} )= {C}_{N} {N}^{2} { k}_{z}^{\ensuremath{-} 3} + C{{\varepsilon }_{K} }^{2/ 3} { k}_{z}^{\ensuremath{-} 5/ 3} $ where ${C}_{N} $ and $C$ are two constants of order unity and ${k}_{z} $ is the vertical wavenumber. It is therefore very steep near the buoyancy scale with an ${N}^{2} { k}_{z}^{\ensuremath{-} 3} $ shape and approaches the ${{\varepsilon }_{K} }^{2/ 3} { k}_{z}^{\ensuremath{-} 5/ 3} $ spectrum for ${k}_{z} \gt {k}_{o} $, ${k}_{o} $ being the Ozmidov wavenumber, which is the cross-over between the two scaling laws. A decomposition of the vertical spectra depending on the horizontal wavenumber value shows that the ${N}^{2} { k}_{z}^{\ensuremath{-} 3} $ spectrum is associated with large horizontal scales $\vert {\mathbi{k}}_{h} \vert \lt {k}_{b} $ and the ${{\varepsilon }_{K} }^{2/ 3} { k}_{z}^{\ensuremath{-} 5/ 3} $ spectrum with the scales $\vert {\mathbi{k}}_{h} \vert \gt {k}_{b} $.

The Similarity of Non-local Triad Interactions in Energy Transfer of Isotropic Turbulence

The inter-scale energy transfer process is one of the key issues in the multi-scale nature of turbulent flows. A direct numerical simulation of homogeneous isotropic turbulent flows is conducted and the energy transfer is studied in detail in spectral space. The band-to-band energy transfer function involving non-local triad interactions with large scale modes peaks sharply. The similarity of this non-local energy transfer function is observed in both the shape and the amplitude. In addition, the similarity is satisfied in both the inertial subrange and dissipation range, implying that it is a general property of turbulence. The amplitude is determined by wave numbers p and q independently in a power law, with the power rates −3 and −2, respectively.

Observation and modelling of main-sequence star chromospheres - XIX. FIES and FEROS observations of dM1 stars

We present 187 high-resolution spectra for 62 different M1 dwarfs from observations obtained with the FIbre-fed Echelle Spectrograph (FIES) on the Nordic Optical Telescope (NOT) and from observations with the Fibre-fed Extended Range Echelle Spectrograph (FEROS) from the European Southern Observatory (ESO) data base. We also compiled other measurements available in the literature. We observed two stars, Gl 745A and Gl 745B, with no Ca ii line core emission and Hα line equivalent widths (EWs) of only 0.171 and 0.188 Å, respectively. We also observed another very low activity M1 dwarf, Gl 63, with an Hα line EW of only 0.199 Å. These are the lowest activity M dwarfs ever observed and are of particular interest for the non-local thermodynamic equilibrium radiative transfer modelling of M1 dwarfs. Thanks to the high signal-to-noise ratio of most of our spectra, we were able to measure the Ca ii H&K full width at half-maximum (FWHM) for most of our stars. We find good correlations between the FWHM values and the mean Ca ii line EW for dM1 stars. Then the FWHM seems to saturate for dM1e stars. Our previous models of M1 dwarfs can reproduce the FWHM for dM1e stars and the most active dM1 stars, but fail to reproduce the observations of lower activity M1 dwarfs. We believe this is due to an effect of metallicity. We also investigate the dependence of the Hα line FWHM as a function of its EW. We find that the models globally agree with the observations including subwarfs, but tend to produce too narrow profiles for dM1e stars. We re-investigate the correlation between the Ca ii line mean EW and the absolute magnitude. With our new data that notably include several M1 subdwarfs, we find a slightly different and better correlation with a slope of −0.779 instead of −0.909. We also re-investigate the variations of the Hα line EW as a function of radius and find that the EW increases continuously with increasing radius. This confirms our previous finding that the level of magnetic activity in M1 dwarfs increases with the radius. For the first time, we investigate the Wilson–Bappu correlation for a given spectral type. We find a rather linear correlation for stars of absolute magnitude greater than 9.6, but below this value the FWHM seems to saturate. In fact, we show that these Wilson–Bappu type correlations are activity–FWHM correlations and are due to the diminishing column mass of the transition region with decreasing activity level.

Atomic quantum information processing in low-Q cavity in the intermediate coupling region

We present an atomic-state entangler with single atoms trapped in separated low-Q cavities, a coherent optical pulse as a quantum channel, a photon detector that only distinguishes the vacuum and nonvacuum states, and basic optical elements based on the input–output process in the intermediate coupling region with a higher probability and fidelity. The atomic-state entangler is meaningful because it does not need a strong coupling cavity and a single-photon source and could be feasible for large-scale quantum computation and quantum communication in the future. Based on this entangler, quantum information nonlocal transfer without classical communication, the quantum controlled-NOT gate, the four-particle |χ〉 state, the N-particle Greenberger-Horne-Zeilinger (GHZ) state, and cluster-state generation can be realized completely, which is useful in large-scale and nonlocal quantum information processing.

KINEMATICS OF THE CO GAS IN THE INNER REGIONS OF THE TW Hya DISK

We present a detailed analysis of the spatially and spectrally resolved 12CO J=2-1 and J=3-2 emission lines from the TW Hya circumstellar disk, based on science verification data from the Atacama Large Millimeter/Submillimeter Array (ALMA). These lines exhibit substantial emission in their high-velocity wings (with projected velocities out to 2.1 km/s, corresponding to intrinsic orbital velocities >20 km/s) that trace molecular gas as close as 2 AU from the central star. However, we are not able to reproduce the intensity of these wings and the general spatio-kinematic pattern of the lines with simple models for the disk structure and kinematics. Using three-dimensional non-local thermodynamic equilibrium molecular excitation and radiative transfer calculations, we construct some alternative models that successfully account for these features by modifying either (1) the temperature structure of the inner disk (inside the dust-depleted disk cavity; r < 4 AU); (2) the intrinsic (Keplerian) disk velocity field; or (3) the distribution of disk inclination angles (a warp). The latter approach is particularly compelling because a representative warped disk model qualitatively reproduces the observed azimuthal modulation of optical light scattered off the disk surface. In any model scenario, the ALMA data clearly require a substantial molecular gas reservoir located inside the region where dust optical depths are known to be substantially diminished in the TW Hya disk, in agreement with previous studies based on infrared spectroscopy. The results from these updated model prescriptions are discussed in terms of their potential physical origins, which might include dynamical perturbations from a low-mass companion with an orbital separation of a few AU.

Non-local radiative transfer of SiO masers in Miras

Context. To properly understand the propagation of SiO masers within the shocked region of the circumstellar envelope of asymptotic giant branch stars, non-local radiative transfer calculations are required.Aims. The present study focuses on investigating how the non-linear velocity field affects the amplification of SiO masers in the circumstellar envelope of a Mira variable.Methods. We extend the capability of the coupled escape probability method to a spherical system and develop subroutines that are able to calculate the radiative transfer problems in an arbitrary velocity field. This method is applied to the model of a Mira variable that shows dramatic fluctuations in its physical conditions in the circumstellar envelope. We carry out the non-local calculations over the subset of whole epochs covering a complete stellar-pulsation cycle. We also include maser saturation in our calculations to properly treat the interaction of SiO maser radiation with the SiO molecules.Results. We reproduce the typical features of SiO masers in Mira variables and compare our results with previous large velocity gradient (LVG) calculations and observations. The region of SiO masers is very confined, at a distance of about one stellar radius from the photosphere, which implies that there has been a tangential amplification process. The relative strengths and positions of SiO masers of v = 1, J = 1−0,2−1 and v = 2, J = 1−0 transitions are shown. The temporal variability of a SiO maser, which is driven by stellar pulsations, is also examined in this study, and our results show some differences from those of previous LVG calculations.

Herschel/HIFI observations of CO, H2O and NH3in Monoceros R2

Context. Mon R2 is the only ultracompact HII region (UCHII) where the associated photon-dominated region (PDR) can be resolved with Herschel. Due to its brightness and proximity, it is the best source to investigate the chemistry and physics of highly UV-irradiated PDRs. Aims. Our goal is to estimate the abundance of H2O and NH3 in this region and investigate their origin. Methods. We present new observations obtained with HIFI and the IRAM-30m telescope. Using a large velocity gradient approach, we model the line intensities and derive an average abundance of H2O and NH3 across the region. Finally, we model the line profiles with a non-local radiative transfer model and compare these results with the abundance predicted by the Meudon PDR code. Results. The variations of the line profiles and intensities indicate complex geometrical and kinematical patterns. The H2O lines present a strong absorption at the ambient velocity and emission in high velocity wings towards the HII region. The spatial distribution of the o-H2^18O line shows that the its emission arises in the PDR surrounding the HII region. By modeling the o-H2^18O emission we derive a mean abundance of o-H2O of ~10^-8 relative to H2. The ortho-H2O abundance is however larger, ~1x10^-7, in the high velocity wings. Possible explanations for this larger abundance include an expanding hot PDR and/or an outflow. Ammonia seems to be present only in the envelope with an average abundance of ~2x10^-9 relative to H2. Conclusions. The Meudon PDR code can account for the measured water abundance in the high velocity gas as long as we assume that it originates from a <1 mag hot expanding layer of the PDR, i.e. that the outflow has only a minor contribution to this emission. To explain the abundances in the rest of the cloud the molecular freeze out and grain surface chemistry would need to be included.

Magnetic energy transfer at the top of the Earth’s core

SUMMARY We introduce a formalism to track magnetic energy transfer between spherical harmonic degrees due to the interaction of fluid flow and radial magnetic field at the top of the Earth’s core. Large-scale synthetic single harmonic flows are characterized by a fixed difference between harmonics participating in the transfer. Large-scale toroidal flows result in more local energy transfer than small-scale poloidal flows. Axisymmetric poloidal flows are most efficient in producing energy transfer and dipole changes. The azimuthal phase relation between the field and the flow may play a major role in the energy transfer. Geomagnetic energy transfer induced by core flow models exhibit a striking transfer spectrum pattern of alternating extrema suggestive of energy cascade, but the detailed transfer spectrum matrix reveals rich behaviour with both local Kolmogorov-like transfer and non-local transfer, the latter about twice larger. The transfer spectrum reverses from even maxima and odd minima between 1840 and 1910 to odd maxima and even minima between 1955 and 1990. The transfer spectrum matrix shows geomagnetic energy cascade from low to high degrees as well as non-local transfer from the dipole directly to higher degrees, explaining the simultaneous dipole decrease and non-dipole increase during the historical period.

Probing the properties of Be star discs with spectroastrometry and NLTE radiative transfer modelling: β CMi

ABSTRACT While the presence of discs around classical Be stars is well established, their origin is still uncertain. To understand what processes result in the creation of these discs and how angular momentum is transported within them, their physical properties must be constrained. This requires comparing high spatial and spectral resolution data with detailed radiative transfer modelling. We present a high spectral resolution, R∼ 80 000, sub-milliarcsecond precision, spectroastrometric study of the circumstellar disc around the Be star β CMi. The data are confronted with 3D, non-local thermodynamic equilibrium radiative transfer calculations to directly constrain the properties of the disc. Furthermore, we compare the data to disc models featuring two velocity laws: Keplerian, the prediction of the viscous disc model, and angular momentum conserving rotation. It is shown that the observations of β CMi can only be reproduced using Keplerian rotation. The agreement between the model and the observed spectral energy distribution, polarization and spectroastrometric signature of β CMi confirms that the discs around Be stars are well modelled as viscous decretion discs.

Implementation of nonlocal Bell-state measurement and quantum information transfer with weak Kerr nonlinearity

We propose a protocol to implement the nonlocal Bell-state measurement, which is nearly determinate with the help of weak cross-Kerr nonlinearities and quantum non-destructive photon number resolving detection. Based on the nonlocal Bell-state measurement, we implement the quantum information transfer from one place to another. The process is different from conventional teleportation but can be regarded as a novel form of teleportation without entangled channel and classic communication.

Quantum logic operations on two distant atoms trapped in two optical-fibre-connected cavities

Based on the coupling of two distant three-level atoms in two separate optical cavities connected with two optical fibres, schemes on the generation of several two-qubit logic gates are discussed under the conditions of Δ = δ − 2νcos πk/2 ≫ g/2 and ν ∼ g. Discussion and analysis of the fidelity, gate time and experimental setups show that our schemes are feasible with current optical cavity, atomic trap and optical fibre techniques. Moreover, the atom—cavity—fibre coupling can be used to generate an N-qubit nonlocal entanglement and transfer quantum information among N distant atoms by arranging N atom—cavity assemblages in a line and connecting each two adjacent cavities with two optical fibres.

ON THE GAS TEMPERATURE OF MOLECULAR CLOUD CORES

We investigate the uncertainties affecting the temperature profiles of dense cores of interstellar clouds. In regions shielded from external ultraviolet radiation, the problem is reduced to the balance between cosmic ray heating, line cooling, and the coupling between gas and dust. We show that variations in the gas phase abundances, the grain size distribution, and the velocity field can each change the predicted core temperatures by one or two degrees. We emphasize the role of non-local radiative transfer effects that often are not taken into account, for example, when modelling the core chemistry. These include the radiative coupling between regions of different temperature and the enhanced line cooling near the cloud surface. The uncertainty of the temperature profiles does not necessarily translate to a significant error in the column density derived from observations. However, depletion processes are very temperature sensitive and a two degree difference can mean that a given molecule no longer traces the physical conditions in the core centre.