Relativistic theory for time and frequency transfer to order c^{-3}

This paper is motivated by the current development of several space missions (e.g. ACES on International Space Station) that will fly on Earth orbit laser cooled atomic clocks, providing a time-keeping accuracy of the order of 5~10^{-17} in fractional frequency. We show that to such accuracy, the theory of frequency transfer between Earth and Space must be extended from the currently known relativistic order 1/c^2 (which has been needed in previous space experiments such as GP-A) to the next relativistic correction of order 1/c^3. We find that the frequency transfer includes the first and second-order Doppler contributions, the Einstein gravitational red-shift and, at the order 1/c^3, a mixture of these effects. As for the time transfer, it contains the standard Shapiro time delay, and we present an expression also including the first and second-order Sagnac corrections. Higher-order relativistic corrections, at least O(1/c^4), are numerically negligible for time and frequency transfers in these experiments, being for instance of order 10^{-20} in fractional frequency. Particular attention is paid to the problem of the frequency transfer in the two-way experimental configuration. In this case we find a simple theoretical expression which extends the previous formula (Vessot et al. 1980) to the next order 1/c^3. In the Appendix we present the detailed proofs of all the formulas which will be needed in such experiments.Comment: 11 pages, 2 figures, to appear in Astronomy & Astrophysic

Tuning thermally treated graphitic carbon nitride for H₂ evolution and CO₂ photoreduction: The effects of material properties and mid-gap states

Graphitic carbon nitride (g-C3N4) is regarded as an attractive photocatalyst for solar fuel production, i.e., H2 evolution and CO2 photoreduction. Yet, its structural, chemical and optoelectronic properties are very much dependent on the synthesis method and are likely to contribute differently whether H2 evolution or CO2 reduction is considered. Little is known about this aspect making it difficult to tailor g-C3N4 structure and chemistry for a specific photoreaction. Herein, we create g-C3N4 of varying chemical, structural and optical features by applying specific thermal treatments and investigating the effects of the materials properties on solar fuel production. The samples were characterized across scales using spectroscopic, analytical and imaging tools, with particular attention given to the analyses of trap states. In the case of H2 evolution, the reaction is controlled by light absorption and charge separation enabled by the presence of trap states created by N vacancies. In the case of CO2 photoreduction, reactant adsorption appears as a dominating factor. The analyses also suggest that the thermal treatment leads to the formation of trap states located close to the valence band of g-C3N4

Longitudinal and Transverse Zeeman Ladders in the Ising-Like Chain Antiferromagnet BaCo2V2O8

We explore the spin dynamics emerging from the N\'eel phase of the chain compound antiferromagnet BaCo2V2O8. Our inelastic neutron scattering study reveals unconventional discrete spin excitations, so called Zeeman ladders, understood in terms of spinon confinement, due to the interchain attractive linear potential. These excitations consist in two interlaced series of modes, respectively with transverse and longitudinal polarization. The latter have no classical counterpart and are related to the zero-point fluctuations that weaken the ordered moment in weakly coupled quantum chains. Our analysis reveals that BaCo2V2O8, with moderate Ising anisotropy and sizable interchain interactions, remarkably fulfills the conditions necessary for the observation of these longitudinal excitations.Comment: 5 pages, 4 figures, 2 additional pages of supplemental material with 2 figures; Journal ref. added; 1 page erratum added at the end with 1 figur

Extragalactic database. VII Reduction of astrophysical parameters

The Lyon-Meudon Extragalactic database (LEDA) gives a free access to the main astrophysical parameters for more than 100,000 galaxies. The most common names are compiled allowing users to recover quickly any galaxy. All these measured astrophysical parameters are first reduced to a common system according to well defined reduction formulae leading to mean homogeneized parameters. Further, these parameters are also transformed into corrected parameters from widely accepted models. For instance, raw 21-cm line widths are transformed into mean standard widths after correction for instrumental effect and then into maximum velocity rotation properly corrected for inclination and non-circular velocity. This paper presents the reduction formulae for each parameter: coordinates, morphological type and luminosity class, diameter and axis ratio, apparent magnitude (UBV, IR, HI) and colors, maximum velocity rotation and central velocity dispersion, radial velocity, mean surface brightness, distance modulus and absolute magnitude, and group membership. For each of these parameters intermediate quantities are given: galactic extinction, inclination, K-correction etc.. All these parameters are available from direct connexion to LEDA (telnet lmc.univ-lyon1.fr, login: leda, no passwd OR http://www-obs.univ-lyon1.fr/leda ) and distributed on a standard CD-ROM (PGC-ROM 1996) by the Observatoire de Lyon via the CNRS (mail to [email protected]).Comment: 13 pages, 12 figures. The CDROM of the extragalactic database LEDA is available by mailing to: [email protected]

The Kuiper Belt Luminosity Function from m(R)=21 to 26

We have performed an ecliptic imaging survey of the Kuiper belt with our deepest and widest field achieving a limiting flux of m(g') = 26.4, with a sky coverage of 3.0 square-degrees. This is the largest coverage of any other Kuiper belt survey to this depth. We detect 72 objects, two of which have been previously observed. We have improved the Bayesian maximum likelihood fitting technique presented in Gladman et al. (1998) to account for calibration and sky density variations and have used this to determine the luminosity function of the Kuiper belt. Combining our detections with previous surveys, we find the luminosity function is well represented by a single power-law with slope alpha = 0.65 +/- 0.05 and an on ecliptic sky density of 1 object per square-degree brighter than m(R)=23.42 +/- 0.13. Assuming constant albedos, this slope suggests a differential size-distribution slope of 4.25 +/- 0.25, which is steeper than the Dohnanyi slope of 3.5 expected if the belt is in a state of collisional equilibrium. We find no evidence for a roll-over or knee in the luminosity function and reject such models brightward of m(R) ~ 24.6.Comment: 50 Pages, 8 Figure

Anisotropic interactions opposing magnetocrystalline anisotropy in Sr3_3NiIrO6_6

We report our investigation of the electronic and magnetic excitations of Sr$_3$NiIrO$_6$ by resonant inelastic x-ray scattering at the Ir L$_3$ edge. The intra-$t_{2g}$ electronic transitions are analyzed using an atomic model, including spin-orbit coupling and trigonal distortion of the IrO$_6$ octahedron, confronted to {\it ab initio} quantum chemistry calculations. The Ir spin-orbital entanglement is quantified and its implication on the magnetic properties, in particular in inducing highly anisotropic magnetic interactions, is highlighted. These are included in the spin-wave model proposed to account for the dispersionless magnetic excitation that we observe at 90 meV. By counterbalancing the strong Ni$^{2+}$ easy-plane anisotropy that manifests itself at high temperature, the anisotropy of the interactions finally leads to the remarkable easy-axis magnetism reported in this material at low temperature

Magneto-elastic coupling and unconventional magnetic ordering in triangular multiferroic AgCrS2

The temperature evolution of the crystal and magnetic structures of ferroelectric sulfide AgCrS2 have been investigated by means of neutron scattering. AgCrS2 undergoes at TN = 41.6 K a first-order phase transition, from a paramagnetic rhombohedral R3m to an antiferromagnetic monoclinic structure with a polar Cm space group. In addition to being ferroelectric below TN, the low temperature phase of AgCrS2 exhibits an unconventional collinear magnetic structure that can be described as double ferromagnetic stripes coupled antiferromagnetically, with the magnetic moment of Cr+3 oriented along b within the anisotropic triangular plane. The magnetic couplings stabilizing this structure are discussed using inelastic neutron scattering results. Ferroelectricity below TN in AgCrS2 can possibly be explained in terms of atomic displacements at the magneto-elastic induced structural distortion. These results contrast with the behavior of the parent frustrated antiferromagnet and spin-driven ferroelectric AgCrO2