Oscillation Variability Research Articles

Magnetic field study of the ultrasonic attenuation on textured YBCO

Ultrasonic and internal friction measurements were performed on textured YBCO samples in the presence of a magnetic field from 100K to room temperature. The attenuation was observed to decrease monotonically with increasing magnetic field. The relaxation time of carriers can be derived from a quantitative analysis. At higher frequencies and low temperatures, an oscillatory variation of the attenuation with magnetic field was observed that may be related to an effect called magnetoacoustic geometric resonance. The periodicity can be used to obtain the Fermi momentum in further experiments.

ASSESSMENT OF CORRELATED THERMAL DIFFUSE SCATTERING AS A DIRECT STRUCTURAL METHOD ON THE MULTIELEMENT SURFACE SYSTEM OF ${\rm Si}(111)(\sqrt3\times\sqrt3)\mbox{-}{\rm In}$

Correlated thermal diffuse scattering (CTDS), a direct structural technique using a simple oscillatory intensity variation in the medium energy electron diffraction, has been applied to the biatomic surface system of [Formula: see text]. A problem with the application of CTDS to multicomposition systems arises from the element-specific atomic scattering factors. The difference in atomic scattering factors disturbs the diffraction phase originating from the path length difference and causes the shift from the true atomic position in Patterson analysis. In order to recover the true atomic position, a numerical calibration method has been introduced. With the aid of the calibration, structural parameters for the topmost three layers of the [Formula: see text] surface have been determined with 0.1 Å accuracy. This shows that CTDS is applicable to multicomposition surface systems.

Atomic force microscopy study of oscillatory surface roughening in anodic dissolution of sputter-deposited nickel films

Using atomic force microscopy (AFM), the kinetic surface roughening in electrochemical dissolution of nickel films at a low constant current density was studied in order to reveal the scaling laws. The surface measurements of AFM exhibited the oscillatory variation of the interface width with time, which made it impossible to determine the growth exponent β. The oscillatory behavior of surface roughening was explained by the presence of unstable passive films formed on the nickel film surface. The roughness exponent α=0.94±0.04 calculated from the AFM images of the anodic dissolved surface was almost equal to that predicted by the diffusion-driven growth model.

Mirror Instability with Electron Temperature Effects**The project supported by National Natural Science Foundation of China under Grant Nos 49990452 and 19673019)

Linear kinetic mirror instabilities of a homogeneous magnetized plasma in which both ions and electrons have the bi-Maxwellian distributions are investigated in the lowfrequency and long-wavelength limit. It is shown that, in contrast to the case of cold electrons, the criterion for the mirror instability has an upper limit, above which the mirror mode becomes oscillating one. This can possibly account for the oscillatory variations of observed mirror waves in the space plasma. In addition it is also shown that the growth rate of the nonpropagation mirror mode increases rapidly with the anisotropy parameter and is slightly higher than its value under the cold electron assumption, but that the oscillating mirror mode remains nearly a constant growth rate.

Solar Flare Peculiarities: A Hypothesis for a New Phenomenological Model

An intensity time-profile of the hard X-ray emission in two cores of a small impulsive solar flare is analyzed. The emission in the cores proved to evolve in the opposite phases. The phases of growth and decay are also shown to be modulated by the slower oscillatory variations. It is suggested that acceleration processes may be oscillating and a collapsing acceleration process may occur above and below the photosphere.

Scanning and impedance properties of TEM horn arrays for transient radiation

A general concept for ultrawide-band array design using interconnected transverse electromagnetic (TEM) horns is described. At high frequencies (wavelength small compared to unit cell dimensions), the mutual coupling between elements is small and, consequently, the input impedance depends only on the lattice dimensions and not on either scan angle or frequency. At low frequencies (wavelength large compared to unit cell dimensions), the mutual coupling is purposefully made large, by interconnecting the elements to maximize the low-frequency performance. This paper presents the results of analyses using a periodic hybrid finite-element approach to calculate input impedance and scanning performance of generic TEM horn arrays. The limiting case, the planar bicone, is shown to have the frequency-independent property of a self-complementary antenna, making it a useful case for establishing the effects of feed region geometry. Although it radiates bidirectionally, it has the interesting property that its broadside-scan frequency response in the array environment is absolutely flat up to the grating lobe onset limit. A TEM horn array is more unidirectional, but as a consequence suffers both oscillatory variations in the input impedance with frequency and increased limits on minimum achievable rise time.

Intersubband collective spin-and charge-density excitations in a system of 2D electrons in the quantum Hall effect regime

Collective intersubband spin-and charge-density excitations in a system of 2D electrons and the dependence of the excitations on the perpendicular magnetic field are investigated by the inelastic light scattering method. Magnetooscillations of the energies of collective excitations are found, and it is shown that they are observed in the quantum Hall effect regime. The energy of the direct Coulomb interaction of the electrons and its oscillatory variation as a function of the perpendicular magnetic field are measured directly from the energy splitting of the spin and charge excitations.

Transient flow in bounded randomly heterogeneous domains: 2. Localization of conditional mean equations and temporal nonlocality effects

In randomly heterogeneous porous media one cannot predict flow behavior with certainty. One can, however, render optimum unbiased predictions of such behavior by means of conditional ensemble mean hydraulic heads and fluxes. We have shown in paper 1 [Tartakovsky and Neuman, this issue] that under transient flow, these optimum predictors are governed by nonlocal equations. In particular, the conditional mean flux is generally nonlocal in space‐time and therefore non‐Darcian. As such, it cannot be associated with an effective hydraulic conductivity except in special cases. Here we explore analytically situations under which localization is possible so that Darcy's law applies in real, Laplace, and/or infinite Fourier transformed spaces, approximately or exactly, with or without conditioning. We show that the corresponding conditional effective hydraulic conductivity tensor is generally nonsymmetric. An alternative to Darcy's law in each case, valid under mean no‐flow conditions along Neumann boundaries, is a quasi‐Darcian form that includes only a symmetric tensor which, however, does not constitute a bona fide effective hydraulic conductivity. Both lack of symmetry and differences between Darcian and quasi‐Darcian forms disappear to first (but not necessarily higher) order of approximation in the (conditional) variance of natural log hydraulic conductivity. We adopt such an approximation to investigate analytically the effect of temporal nonlocality on one‐and three‐dimensional mean flows in infinite, statistically homogeneous media. Our results show that temporal nonlocality may manifest itself under either monotonic or oscillatory time variations in the mean hydraulic gradient. The effect of temporal nonlocality increases with the variance of log hydraulic conductivity and is more pronounced in one dimension than in three.

An Analysis of Parameters of an Oscillatory Chemical Reaction by Holography Methods Involving a Transient Reference Wave

The results of an experimental study of an oscillatory chemical reaction (the Belousov-Zhabotinskii reaction) are reported. The measurements were performed for both the reaction proceeding in the regime of synchronization in the volume and the reaction proceeding without synchronization when the oscillations are less pronounced. Radiation passed through the sample and detected by the holography method with a transient reference wave was used in the analysis. This made it possible to obtain data on the time dependence of amplitudes and phases of the transmitted wave. The signal spectrum was reconstructed from the hologram. In this case, a spectrum rich in features was observed even when there was no synchronization. The shift of the zero-order component in the spectrum of oscillatory variations in the refractive index was measured and was found to be constant in the course of the reaction. The oscillation frequency decreased during the reaction. Special measurements with the use of interference were performed at the stage when the hologram was reconstructed and the signal-spectrum pattern was obtained; the time dependence of the signal in the course of the reaction was evaluated. Nonperiodic and periodic phase variations in the transmitted wave were studied; the parameters characterizing the variation of refractive index in the course of the reaction were determined. Variations in the refractive index of no less than 5 · 10−6 were measured to an accuracy of no lower than 0.2·106 and the rate of the refractive-index variation was measured to an accuracy of no lower than 10−8 s−1.

A predictability study of simulated North Atlantic multidecadal variability

The North Atlantic is one of the few places on the globe where the atmosphere is linked to the deep ocean through air–sea interaction. While the internal variability of the atmosphere by itself is only predictable over a period of one to two weeks, climate variations are potentially predictable for much longer periods of months or even years because of coupling with the ocean. This work presents details from the first study to quantify the predictability for simulated multidecadal climate variability over the North Atlantic. The model used for this purpose is the GFDL coupled ocean-atmosphere climate model used extensively for studies of global warming and natural climate variability. This model contains fluctuations of the North Atlantic and high-latitude oceanic circulation with variability concentrated in the 40–60 year range. Oceanic predictability is quantified through analysis of the time-dependent behavior of large-scale empirical orthogonal function (EOF) patterns for the meridional stream function, dynamic topography, 170 m temperature, surface temperature and surface salinity. The results indicate that predictability in the North Atlantic depends on three main physical mechanisms. The first involves the oceanic deep convection in the subpolar region which acts to integrate atmospheric fluctuations, thus providing for a red noise oceanic response as elaborated by Hasselmann. The second involves the large-scale dynamics of the thermohaline circulation, which can cause the oceanic variations to have an oscillatory character on the multidecadal time scale. The third involves nonlocal effects on the North Atlantic arising from periodic anomalous fresh water transport advecting southward from the polar regions in the East Greenland Current. When the multidecadal oscillatory variations of the thermohaline circulation are active, the first and second EOF patterns for the North Atlantic dynamic topography have predictability time scales on the order of 10–20 y, whereas EOF-1 of SST has predictability time scales of 5–7 y. When the thermohaline variability has weak multidecadal power, the Hasselmann mechanism is dominant and the predictability is reduced by at least a factor of two. When the third mechanism is in an extreme phase, the North Atlantic dynamic topography patterns realize a 10–20 year predictability time scale. Additional analysis of SST in the Greenland Sea, in a region associated with the southward propagating fresh water anomalies, indicates the potential for decadal scale predictability for this high latitude region as well. The model calculations also allow insight into regional variations of predictability, which might be useful information for the design of a monitoring system for the North Atlantic. Predictability appears to break down most rapidly in regions of active convection in the high-latitude regions of the North Atlantic.

Oscillatory variations of cell-mediated immunity parameters in patients with urogenital chlamydiosis (UGC)

Recently, several lines of evidence have suggested the possibility of immunological dysfunction in the pathogenesis of schizophrenia. We therefore investigated the ability to produce interferons and lymphokines in response to mitogenic or viral stimulation in a whole blood assay of 37 schizophrenic patients (DSM-III-R) and of 42 healthy blood donors. Phytohaemagglutinin (PHA) was used for the induction of interleukin-2 (IL-2), interferon gamma (IFN gamma), interleukin-6 (IL-6) and the soluble interleukin-2 receptor (sIL-2R) and Newcastle Disease Virus (NDV) for the induction of interferon α2 (IFN α2). All lymphokines and, in addition, the sIL-2R in the sera were determined by ELISA technique. The psychopathological status of the patients was assessed by psychiatrists according to internationally accepted standards. The patient group showed a trend to lower levels of the interferons a2 and gamma and a significant decrease of IL-2 production. The sIL-2R levels were significantly increased in the sera of schizophrenic patients. The latter increase was associated with a poor assessment of prognosis (Strauss and Carpenter). This association appears to be of interest. However, its significance is not understood, since longitudinal studies could not be performed.

Ferromagnetic Resonance in Co–Zr/Pd Multilayers

Co-Zr/Pd multilayers with different thicknesses of Pd layers have been prepared by rf sputtering and studied by ferromagnetic resonance (FMR) spectroscopy. The effective g-factor, g eff , of the multilayers has been obtained by FMR measurements. An oscillatory variation of g eff between 1.95 and 2.18 with the thickness of Pd layers is observed. The oscillation period in g eff is about 1 nm. This oscillatory behaviour of g eff has been interpreted in terms of a system of two magnetic sublattices, one is the Co-Zr layer system, the other is the polarized Pd layer system. Finally the dependence of the effective magnetic anisotropy K 0 of the Co-Zr/Pd multilayers on the thickness of Pd layers has been obtained according to the FMR results. A similar oscillatory behaviour in K c was obtained. This mainly originates from the oscillation of the polarization of Pd layers, which causes an oscillatory additional shape anisotropy.

Magnetic polarization of spacer Pd layer and magnetic properties of Co/Pd multilayers

Magnetic multilayers [Co(1.5 nm)/Pd(x nm)]40 grown by rf sputtering were studied by x-ray diffraction, vibrating sample magnetometer, torque magnetometer and magnetoresistance measurements. The dependences of the interfacial roughness and the structure perfectness of Co/Pd multilayers on the spacer Pd layer thickness have been revealed from x-ray diffraction data. An oscillatory variation of saturation magnetization versus the thickness of the Pd spacer was observed. A similar oscillatory behavior in the dependence of its magnetic anisotropy on the thickness of the Pd spacer was observed. It is suggested from these two phenomena that the magnetic polarization of Pd spacers oscillates between ferromagnetic and antiferromagnetic polarization with the increase of Pd spacer thickness under a RKKY-like interaction. Evidence is found for the antiferromagnetic polarization of the inner-part of the Pd spacer. The antiferromagnetic coupling between two Co layers and giant magnetoresistance effect in Co/Pd multilayer system were not observed. The relationship among structure, interlayer coupling and magnetic polarization effect of the Pd spacer was discussed.

Powder neutron diffraction studies of the thermal expansion, compressibility and dehydration of deuterated gypsum

The unit cell parameters of deuterated gypsum have been extracted from Rietveld analysis of powder neutron diffraction data between the temperature limits 4.2–320 K and pressures up to 5.4 GPa at 293 K. The thermal expansion is highly anisotropic along the b-axis. The high-temperature limits of the expansion coefficients for the unit cell edges a, b and c are 3.98 × 10 −6, 4.36 × 10 −5 and 2.53 × 10 −5 K −1. That for the unit cell volume is 6.96 × 10 −5 K −1. The β angle shows oscillatory variation, and empirical analysis results in α β = 1.251 × 10 −6 sin(0.0116 T + 0.311) K −1. The principal axes of the thermal expansion tensor at 300 K are α 22, 3.7 × 10 −5 K −1, parallel to the b-axis with α 11, 2.5 × 10 −5 K −1, and α 33, 1.1 × 10 −6 K −1, both in the ac-plane. α 11 is rotated by 12.1° towards a from c at 300 K. The static compressibility has been measured at room temperature and up to 5.4 GPa. The unit cell of gypsum compresses anisotropically, with the largest compression along the b-axis. Using a third-order Birch-Murnaghan equation of state values of 45 GPa and 2.0 are calculated for the bulk modulus and its pressure derivative.

Ferromagnetic resonance in Co - Nb/Pd multilayers

multilayers were prepared by the rf sputtering method. The polarization of Pd layers and the interlayer coupling through Pd layers were studied via magnetic and ferromagnetic resonance measurements. Magnetic measurement shows that the saturation magnetization of Co - Nb/Pd multilayers oscillates periodically when the Pd layer thickness increases, which is caused by the oscillatory polarization of the Pd layers. The spin-wave excitation indicates that a ferromagnetic interlayer coupling can exist until the thickness of the Pd layers is about 7 nm. An oscillatory variation between 2.00 and 2.12 of the effective g-factor, , with the thickness of Pd layers was observed for the first time. The oscillatory period of is about 1 nm. A similar oscillatory behaviour of the effective anisotropy, , was also obtained. This oscillatory behaviour of and was interpreted in terms of a model of two exchange-coupled sublattices: one sublattice is that of the Co - Nb magnetic layers, and the other is that of the polarized Pd layers. This model indicates that the oscillatory behaviour of and mainly originates from the oscillation of the polarization of the Pd layers.

Optical and magneto-optical properties of Co(001)/Ge/Co sandwiches

A series of bcc-Co(001)/Ge/Co trilayers was grown on a GaAs(001) substrate by the molecular beam epitaxy technique. The optical and magneto-optical properties of the samples were studied. An oscillatory variation of the magneto-optical Kerr effect (MOKE) with the thickness of the Ge spacers was observed. We conclude that the effective optical constants as well as the real and imaginary off-diagonal element of the dielectric tensor should be considered in explanation of the MOKE activities since both have a large influence on the MOKE oscillations. Moreover, the coercivity and magnetization also oscillate with the Ge layer thickness.

REEVALUATION OF THE HOMOGENEITY OF REE, THE AND U IN GEOCHEMICAL REFERENCE ZIRCON 61.308B

In a previous study of the reference sample zircon 61.308B, it has been suggested that either the sample is heterogeneous or inter‐method comparisons introduce analytical dispersions. New determinations by LA‐ICP‐MS show relative standard deviation in the order of 20% for Heavy Rare Earth Elements (HREE). This is four times the variation attributable to analytical method. A possible explanation is that HREE concentration varations in geochemical reference zircon were created by crystal fractionation or oscillatory variation in the host magma. This confirms that zircon 61.308B is heterogeneous for trace elements.

Thermal expansion of gypsum investigated by neutron powder diffraction

The cell parameters of deuterated gypsum have been extracted from Rietveld analysis of powder neutron diffraction data within the temperature range 4.2-320 K. The thermal expansion of gypsum is highly anisotropic along the b axis principally because of the effect of the D2.. .01 hydrogen bond. The high-temperature limits for the expansion coefficients for the cell edges a, b, and care 3.98 x 10-6,4.36 X 10-5, and 2.53 x 10-5 K-l, respectively, and for the cell volume the limit is 6.96 x 10-5 K-l. The (3angle displays oscillatory variation, reflecting a change in the influence of at least two coupled processes. Empirical data analysis, within this temperature range, results in a~ = 1.251 x 10-6 sin(0.0116T + 0.311) K-l.

The Baus elastic constants in interfaces of simple liquids

From molecular dynamics simulations of liquid–liquid and liquid–vapor interfaces at low temperatures between two simple liquids we determine the Baus elastic constants [M. Baus, J. Chem. Phys. 74, 2003 (1981)] and their variation across the interface. For certain cases the nonlocal stress–stress correlation functions were also calculated. A two-phase system with a planar interface is characterized by five independent elastic moduli. Two moduli show a dramatic decrease inside the liquid–liquid interface, similar to the drop in viscosity (‘‘lubricating effect’’) we found in sheared interfaces [P. Padilla, S. Toxvaerd, and J. Stecki, J. Chem. Phys. 103, 716 (1995)]. The other three, which are zero in the bulk region, show a oscillatory variation across the interface. One of these three is related to the surface tension.

Quantum oscillatory magnetostriction of the heavy fermion material CeB6

The first observations of magnetostrictive quantum oscillatory effects in a heavy fermion compound are presented. Using a capacitive dilatometric technique with resolution approaching 10−3A, measurements have been performed on CeB6 single crystals in magnetic fields up to 17T at millikelvin temperatures. The nonoscillatory magnetostriction is measured to be greatly enhanced over that for conventional metals, and is attributed to the large strain dependence of the conduction-4f electron hybridisation. This enhancement is not carried through to the oscillatory magnetostriction, rather, the amplitude of the oscillatory variation is comparable to that measured in conventional metals.