Time dependent correlations in marine stratocumulus cloud base height records

The scaling ranges of time correlations in the cloud base height records of marine boundary layer stratocumulus are studied applying the Detrended Fluctuation Analysis statistical method. We have found that time dependent variations in the evolution of the $\alpha$ exponent reflect the diurnal dynamics of cloud base height fluctuations in the marine boundary layer. In general, a more stable structure of the boundary layer corresponds to a lower value of the $\alpha$ - indicator, i.e. larger anti-persistence, thus a set of fluctuations tending to induce a greater stability of the stratocumulus. In contrast, during periods of higher instability in the marine boundary, less anti-persistent (more persistent like) behavior of the system drags it out of equilibrium, corresponding to larger $\alpha$ values. From an analysis of the frequency spectrum, the stratocumulus base height evolution is found to be a non-stationary process with stationary increments. The occurrence of these statistics in cloud base height fluctuations suggests the usefulness of similar studies for the radiation transfer dynamics modeling.Comment: 12 pages, 6 figures; to appear in Int. J. Mod. Phys. C, Vol. 13, No. 2 (2002

207Pb and 17O NMR Study of the Electron Density Distribution in Metal Phase of BaPb_{1-x}Bi_xO_3

The 17O and 207Pb NMR spectra were measured in ceramic samples in the metallic phase of BaPb_{1-x}Bi_{x}O_3 oxides (0<x< 0.33). The inhomogeneous magnetic broadening which appears due to a distribution of the Knight shifts was analyzed in detail. It is shown that Bi atoms, which are randomly incorporated in BaPbO_3 parent compound give rise to an increased conduction electron spin density within an area which is delimited by its two first cation shells. According to NMR data the percolative overlap of these areas occurs in superconducting compositions and it is accompanied by a sharp growth of the average Knight shift . The decrease of with temperature revealed for x=0.33 evidences for an opening of the energy gap near E_F near the metal-semiconductor transition (x=0.35).Comment: submitted to Phys. Rev.

The charge ordered state in half-doped Bi-based manganites studied by 17^{17}O and 209^{209}Bi NMR

We present a $^{209}$Bi and $^{17}$O NMR study of the Mn electron spin correlations developed in the charge ordered state of Bi$_{0.5}$Sr$_{0.5}$MnO$_{3}$ and Bi$_{0.5}$Ca$_{0.5}$MnO$_{3}$. The unusually large local magnetic field $^{209}H_{loc}$ indicates the dominant $6s^{2}$ character of the lone electron pair of Bi$^{3+}$-ions in both compounds. The mechanism connecting the $s$ character of the lone pairs to the high temperature of charge ordering $T_{CO}$ is still not clarified. The observed difference in $^{209}H_{loc}$ for Bi$_{0.5}$Sr$_{0.5}$MnO$_{3}$ to Bi$_{0.5}$Ca$_{0.5}$MnO$_{3}$ is probably due to a decrease in the canting of the staggered magnetic moments of Mn$^{3+}$-ions from. The modification of the $^{17}$O spectra below $T_{CO}$ demonstrates that the line due to the apical oxygens is a unique local tool to study the development of the Mn spin correlations. In the AF state the analysis of the $^{17}$O spectrum of Pr$_{0.5}$Ca$_{0.5}$MnO$_{3}$ and Bi$_{0.5}$Sr$_{0.5}$MnO$_{3}$ prompts us to try two different theoretical descriptions of the charge-ordered state, a site-centered model for the first manganite and a bond-centered model for the second one.Comment: 10 pages, 7 figure

Spin Susceptibility of Ga-Stabilized delta-Pu Probed by {69}^Ga NMR

Spin susceptibility of stabilized \delta phase in the Pu-Ga alloy is studied by measuring {69,71}^Ga NMR spectra and nuclear spin-lattice relaxation rate {69}T_{1}^{-1} in the temperature range 5 - 350 K. The shift ({69}^K) of the {69,71}^Ga NMR line and {69}^T_{1}^{-1} are controlled correspondingly by the static and the fluctuating in time parts of local magnetic field arisen at nonmagnetic gallium due to transferred hyperfine coupling with the nearest f electron environment of the more magnetic Pu. The nonmonotonic with a maximum around 150 K behavior of {69}^K(T) \chi_{s,5f}(T) is attributed to the peculiarities in temperature dependence of the f electron spin susceptibility \chi_{s,5f}(T) in \delta phase of plutonium. The temperature reversibility being observed in {69}^K(T) data provides strong evidence for an electronic instability developed with T in f electron bands near the Fermi energy and accompanied with a pseudogap-like decrease of \chi_{s,5f}(T) at T<150 K. The NMR data at high temperature are in favor of the mainly localized character of 5f electrons in \delta phase of the alloy with characteristic spin-fluctuation energy \Gamma(T) T^{0.35(5)}, which is close to $\Gamma(T) T^{0.5} predicted by Cox et al. [J. Appl. Phys. 57, 3166 (1985)] for 3D Kondo-system above T_Kondo}. The dynamic spin correlations of 5f electrons become essential to consider for {69}^T_{1}^{-1}(T) only at T<100 K. However, no NMR evidences favoring formation of the static magnetic order in \delta-Pu were revealed down to 5K .Comment: 6 pages, 4 figure

Melting of the orbital order in LaMnO3 probed by NMR

The Mn spin correlations were studied near the O′-O phase transition at TJT=750 K up to 950 K with 17O and 139La NMR in a stoichiometric LaMnO3 crystalline sample. The measured local hyperfine fields originate from the electron density transferred from the eg and t2g orbitals to the 2s(O) and 6s(La) orbits, respectively. By probing the oxygen nuclei, we show that the correlations of the Mn spins are ferromagnetic in the ab plane and robust up to TJT, whereas along the c axis they are antiferromagnetic and start to melt below TJT, at about 550 K. Above TJT, the ferromagnetic Mn-Mn exchange interaction is found isotropic. The room-temperature orbital mixing angle, φNMR= 109±1.5â̂̃, of the eg ground state is close to the reported value which was deduced from structural data on Jahn-Teller distorted MnO6 octahedra. For T>TJT, LaMnO3 can be described in terms of nonpolarized eg orbitals since both eg orbitals are equally occupied. © 2013 American Physical Society