Global Polarization Research Articles

Depositional chronology and fabric of Siwalik group sediments in Central Nepal from magnetostratigraphy and magnetic anisotropy

Magnetostratigraphic research, undertaken within the past 15 years in the Siwaliks distributed along 400 km of the Sub-Himalaya in central Nepal, has proved that the sediments possess highly reliable hematite-based primary detrital remanent magnetization suitable to determine depositional chronology. In order to bring out the polarity sequences in a common chronological frame, all available data are newly correlated to the latest global magnetic polarity time scale of Cande and Kent (S.C. Cande, D.V. Kent (1995) Revised calibration of the geomagnetic polarity timescale for the Late Cretaceous and Cenozoic. Journal of Geophysical Research 100, 6093–6095). Chronological data presented are referred, in relation to the diverse lithological nomenclature, to the formations whose ages are not constrained by isotopic or paleontologic ages. The age of the sections dated by magnetostratigraphy ranges between 14 and <2 Ma. Sediment accumulation rates average to 32–50 cm kyr −1. Rock-magnetic parameters, e.g. initial susceptibility and isothermal remanent magnetization ratios, allow correlation with an accuracy of up to a few hundred meters among several kilometers thick adjacent sections. Anisotropy of magnetic susceptibility (AMS) data reveal a well-defined fabric contributed to by paramagnetic ( k=10 −5 to 3×10 −4 SI) as well as ferromagnetic minerals ( k=3×10 −4 to 10 −2 SI). AMS ellipsoids are mainly oblate along with some prolate ones and the degree of anisotropy is mostly low ( P′<1.2). The magnetic fabric is of pre-folding origin with tilt-corrected sub-vertical magnetic foliation poles. The magnetic lineations do not show parallelism to the expected paleocurrent directions. Rather, sub-parallelism between the clusters of magnetic lineation and the fold axes/bedding strikes/thrust fronts is observed. A superimposed fabric consisting of a sedimentary-compactional and an overprint induced by a mild deformation process is suggested. The latter process was active during, and subsequent to, the deposition in the compressive tectonic setting of the foreland basin. The magnetic lineations for Tinau Khola and Surai Khola sections cluster around N80°W and N88°W respectively, whereas N27°W trend characterizes the Amiliya-Tui area south of Dang. The peak clusters in lineations are probably orthogonal to the true shortening axes. Their variation along the Sub-Himalaya, together with the fold axes or thrust front trends, may be used for accurate tectonic reconstruction. It is especially important when the orthogonality of the latter to the shortening axes may not hold true in the sectors with imbricate fold-and-thrust structures.

Evolution of a two-dimensional quantum cellular neural network driven by an external field

A model of a two-dimensional quantum cellular neural network (QCNN) is presented in this article. The eigenvalues and eigenvectors for the Hamiltonian of a cell (neuron) are obtained, and we confirm that the ground or memory states are approximately two polarization states of 16 possible states in a cell (neuron) only when electron tunneling is relatively weak compared with the Coulomb repulsion. The evolution of the QCNN driven by a local external magnetic field is studied by solving the Liouville equation of the corresponding two-dimensional Ising model. The formula for the evolution of the density operator is given by using a subdynamics approach. We show that the local external magnetic field can drive the system to a global polarization state and induce a dynamical response in the original QCNN. This dynamical response can be interpreted as a computable function and measured by the system output.

Thermal compensation of a cw-pumped Nd:YAG laser

Thermally induced lensing and birefringence modify the transverse laser profile and may eliminate any global polarization state in systems utilizing Nd:YAG as a gain medium. This creates fundamental difficulties in obtaining a high-power, polarized output beam. Although abundant literature exists regarding thermal lensing, only one birefringence compensation scheme is prevalent in the literature. A modification of this scheme is given that eliminates residual birefringence. Experimental data verify the model's validity. A theoretical model is then presented that modifies the birefringence-compensated amplifier as a single power-dependent lens. After showing that solutions exist for a power-independent resonator consisting of a power-dependent lens between two flat mirrors, this amplifier is inserted into the resonator solution to produce, to first order, a resonator that is insensitive to thermally induced fluctuations in the rod focal length.

Differentiating glacio‐eustacy and tectonics; a case study involving dinoflagellate cysts from the Eocene–Oligocene transition of the Pindos Foreland Basin (NW Greece)

In an attempt to discriminate between tectonically induced sea‐level changes and glacio‐eustacy, the Ekklissia and Arakthos sections (Epirus, NW Greece) are examined, applying (dinocyst) palynology, sedimentology and magnetostratigraphy. The sections, located in the Pindos Foreland Basin, both comprise the transition from pelagic limestones to hemipelagic silty clays and turbidite sandstones, reflecting the onset of flysch sedimentation as a result of the Pindos thrust activity. Despite an overall tectonic overprint, relative changes of sea level can be reconstructed, using (i) continental/marine palynomorph ratios, (ii) relative abundance of inshore and offshore dinoflagellate cysts, and (iii) taxa indicative of relatively cold and warm sea‐surface temperature, that can be calibrated against the Global Polarity Time Scale (GPTS). Increased fluxes of marginal marine and continental palynomorphs coincide with colder periods on a ‘third‐order’ scale, which thus appear to be related to glacio‐eustatic trends in sea‐level. The larger scale is attributed to the increasing effect of tectonics and acts on a ‘second‐order scale’.

Periodicity of magnetic intensities in magnetic anomaly profiles: the Cretaceous of the Central Pacific

SUMMARY Spectral analyses of long magnetic anomaly profiles of Cretaceous age in the Phoenix and Hawaiian lineations within the Pacific Basin show two to five non-harmonic wavelength peaks, with probabilities >90 per cent, within the range of several tens to hundreds of kilometres for each profile. For each profile with four peak wavelengths, their ratios correlate strongly (r>0.98) with the ratios for the Earth’s orbital eccentricity periodicities for this time, and hence the profile peaks necessarily correlate with each other. These observations suggest that the magnetic anomaly signal is influenced by the Earth’s changing orbital parameters, probably through their influence on the internal geomagnetic field. This implies that assumptions usually made to convert the magnetic signal to the magnetization of the oceanic crust may be suspect. The observations, if confirmed, indicate that orbital periodicities can assist in improving the age calibration of the global polarity timescale and that the predicted orbital behaviour of the Earth is confirmed for the last 150 Ma.

Statistical prediction and experimental verification of concatenations of fiber optic components with polarization dependent loss

Due to the statistical nature of the evolution of the polarization state in optical fibers and components, it is difficult to measure the global polarization dependent loss (PDL) of a series of concatenated components, each having a different PDL value. The global PDL of concatenated components with PDL cannot be obtained by a simple addition of the single PDL values, moreover, it requires a statistical description. In the present work the statistics of the PDL resulting from the concatenation of several components with PDL, connected by standard optical fibers or by elements having some polarization mode dispersion (PMD) is discussed. Simulations and experimental results supporting the existing theory are presented.

VLBI Observations of Intraday Variability

AbstractIntegrated VLA measurements during our 6 cm global VLBI polarization observations of the intraday variable sources 0716+714, 0917+624, and 0954+658 indicate that although there were no significant total intensity variations during the 24-hour VLBI experiment, the polarization for all three sources varied substantially. Independent polarization images made for 2–3 hour segments show that there were no variations on VLBI scales for 0716+714 or 0954+658, but that there were appreciable variations in the VLBI core of 0917+624, which correlate well with the integrated variations in the simultaneous VLA data.

Sydney, Australia: A Global City? Testing the Social Polarisation Thesis

It has been argued that the global city-social polarisation thesis put forward by scholars looking at North American cities cannot be easily transferred to global cities in other parts of the world. Recent research has illustrated that whilst there may be some change in levels of social polarisation in global cities outside the US, the form, structure and causes of social polarisation are different. This paper extends the debate by looking at Sydney, Australia. It is argued that whilst changes in occupational structure and income polarisation are partially explained by economic restructuring associated with globalisation, global processes alone cannot fully explain these changes. The paper points to the significance of the inclusion of factors such as the unemployed, the gendered structure of occupations and migration.

Magnetostratigraphy of Early Cretaceous Maiolica sections of the Southern Alps (Cismon and Pra da Stua, Italy)

The bottom part of the Cretaceous Cismon section in the Southern Alps was sampled for high-resolution magnetostratigraphy. Although the almost pure pelagic nannofossil limestones (c. 90 per cent CaCO3) of the Maiolica/Biancone Formation are extremely weakly magnetized, stepwise thermal and alternating-field demagnetization removed overprints and isolated a characteristic remanent magnetization which is interpreted as a primary magnetization. The dominant magnetic carrier mineral is magnetite; a small fraction of haematite may be present. A clear reversal pattern can be correlated unambiguously with Mesozoic polarity chrons CM10N to CM8. A less well-constrained magnetostratigraphy from the Pra da Stua section could not be directly correlated with the global polarity scale, but biostratigraphic information allows its assignment to the interval CM10-CM5. A counterclockwise rotation of 56° and a northward translation of 28° latitude for the Cismon locality since the Early Cretaceous are derived from the palaeomagnetic data, consistent with previous results from the Southern Alps. The high-resolution magnetostratigraphy of the Cismon section is used in an effort to refine the Cretaceous timescale by the combination of magnetostratigraphic and cyclostratigraphic results from the same section. The cyclostratigraphic duration estimates of chrons CM10N to CM8 are compared to their equivalents in a number of traditional timescales and found to be shorter by a factor of 1.26–2.58.

The Dissemination of Culture

Despite tendencies toward convergence, differences between individuals and groups continue to exist in beliefs, attitudes, and behavior. An agent-based adaptive model reveals the effects of a mechanism of convergent social influence. The actors are placed at fixed sites. The basic premise is that the more similar an actor is to a neighbor, the more likely that that actor will adopt one of the neighbor's traits. Unlike previous models of social influence or cultural change that treat features one at a time, the proposed model takes into account the interaction between different features. The model illustrates how local convergence can generate global polarization. Simulations show that the number of stable homogeneous regions decreases with the number of features, increases with the number of alternative traits per feature, decreases with the range of interaction, and (most surprisingly) decreases when the geographic territory grows beyond a certain size.

Experimental investigation of the speckle polarization for a polished aluminium sample

As speckles carry information about polarization, we have perfected a polarimeter using the Stokes - Mueller formalism from which we exploit the matrix to analyse speckle polarization. The noise effects on the Mueller matrix are minimized to separate experimental noise from the depolarization phenomenon. In order to simplify this depolarization phenomenon, we used a polished aluminium sample. We describe a statistical polarization analysis of the speckle grains which show the depolarization evolution of the speckle field. A global polarization analysis of the clipped speckle is then performed. The experimental results show that it remains polarized, independently of the observation direction, and only shows a slight polarization dispersion.

VLBI polarization observations of intraday variability

Global λ6 cm VLBI polarization observations of the intraday variable sources 0716+714, 0917+624, and 0954+658 are analyzed. Integrated VLA measurements during the VLBI observations suggest that although there were no substantial total intensity variations, the polarization for all three sources varied significantly during the 24 h VLBI experiment. The VLBI data were divided into 2–3 h segments in order to identify corresponding rapid variability in the VLBI structure. There is evidence that the polarization variability indicated by the VLA measurements of 0917+624 is present in the VLBI data (i.e. it occurred on mas scales), but this is not the case for the other two sources.

Late Cenozoic magnetostratigraphy (11 – 0 Ma) of the Dongshanding and Wangjiashan sections in the Longzhong Basin, western China

A paleomagnetic study of the 510-m-thick Wangjiashan section of Late Miocene and Pliocene terrestrial sediments reveals a fairly complete reversal record with ages from 11 to 1.8 Ma. The magnetostratigraphy of the Dongshanding section, located nearby, reveals a partially overlapping reversal record with ages from 2.2 to 0 Ma, and facilitates correlation of the Wangjiashan section with the global polarity time scale. A new stratigraphic division of the Wangjiashan section replaces the name Linxia formation by five new formation names, based on lithologic variation and mammalian fossil finds. The new formations and their magnetostratigraphically determined ages are: Dongshan Formation (c. 1.75–2.6 Ma), Jishi Fm. (c. 2.6–3.6 Ma), Hewangjia Fm. (4.5–6.0 Ma), Liushu Fm. (6.0–7.6 Ma), and Dongxiang Fm. (7.6–c. 12 Ma). The Neogene stratigraphy and fossil mammals suggest that the nearby part of the Tibetan Plateau experienced a persistent denudation during the Late Miocene and Early Pliocene, but that it was uplifted more rapidly at about 3.6 Ma.

Explanation of Anomalous Gas-Chromatographic (Gc) Behaviour in a Homologous Series of 2-Chloroethyl Phosphonic Acid Dialkyl Esters

Abstract The study of GC separation of 2-chloroethylphosphonic acid di-n-alkyl (1–5 C atoms) esters (synthesised by us) on silicone stationary phases (OV-1, OV-17, OV-225) revealed a deviation from the expected linear dependence of retention indexes (RI) versus the number of C atoms of the alkyl chain: the first member of the series presents stronger retention than one can expect. This anomalous behaviour was observed especially on polar stationary phase (OV-225, see Figure l), and was emphasised with the increase of the column temperature. In an attempt to rationalise the above mentioned facts, we tried to relate the RI values to a global polarity parameter: the dipole moment, μ. The μ values for ClC2H4P(O)(OR)2 were calculated by a method described in [1] (tested by comparing the calculated μ values with experimental ones for alkyl phosphonic acid dialkylesters), using molecular mechanics (COSMIC package) in the search of the conformational space, AM1 method (MOPAC 6.0) for the μ values of the conformer...

Cellular Polarity in Ciliates: Persistence of Global Polarity in a disorganized Mutant of Tetrahymena thermophila That Disrupts Cytoskeletal Organization

Much of the cell surface on the ciliate Tetrahymena thermophila is covered by a polarized lattice of cytoskeletal structures that are associated with basal bodies of the ciliary rows. Unique structural landmarks, including an oral apparatus and contractile vacuole pores, develop before cell division in localized domains located, respectively, posterior and anterior to the transverse fission zone. All of these structures can be visualized by specific monoclonal antibodies. A single-locus recessive mutation, disorganized-A (disA), primarily affects the striated rootlets of the ciliary-row basal bodies and brings about a severe disorganization in the positioning and orientation of these basal bodies and associated cytoskeletal elements. Nonetheless, the new oral apparatus, contractile vacuole pores, and other unique structures appeared at or near their normal sites along the anteroposterior axis of disA cells, indicating that the positioning of these localized structures is not dependent on the integrity of the ciliary rows. Abnormalities were present in the details of construction of some of the localized structures and in aspects of cell shape that may be influenced by these details. In the main, however, analysis of disA mutant cells indicates that intracellular domains near the cell poles develop independently of the vectorial polarity of the ciliary rows.

Generation of waves by the solar magnetic field polarity reversal

In this paper an excitation of waves is considered during the time interval in which the undisturbed magnetic field changes its direction. If this interval is taken to be 2 years, which is shorter than the 11-year cycle, then the undisturbed components of the magnetic field may be linearly dependent on time and independent of the coordinates. The excitation of waves is due to the undisturbed stationaryV 0 flow with divV 0 = 0 and with (V 0 rot0) = constant. We use the local Cartesian coordinate system, which is immovable towards the solar centre, and consider the case when the toroidal component of the undisturbed magnetic field changes its sign simultaneously with one of the axial components. The third component does not change its direction. The efficiency of the enhancement of the magnetic field and velocity disturbances depends on the Alfven wave frequency,ω A. Whenω A = 0, the component of the disturbed velocity, which is directed along the constant component of the undisturbed magnetic field, increases. In this case the shear waves excite the carrier (high) frequency (KV 0), whereK is the wave vector. Due to the shear instability the amplitude of the velocity increases during 1 year before the moment of reversal of the global magnetic field polarity (RGMFP) for an arbitrary latitude. It reaches a maximum at RGMFP and decreases in the next year. Whenω A > 0, then the amplitudes of the disturbed values reach maxima before the moment of RGMFP, and whenω A < 0, they reach maxima after it. We argue that the shear waves propagate from middle latitudes to the pole and equator. Using the results of the analytical solutions and leaning on the evidence of the observational data (Gigolashvili and Japaridze, 1992), we derive the result that the component of the undisturbed magnetic field, which is perpendicular to the solar surface, changes its sign simultaneously with the toroidal component.

Application of a palaeomagnetic reversal stratigraphy to constrain well correlation and sequence stratigraphic interpretation of the Eocene C1 Sands, Maui Field, New Zealand

Abstract The giant, offshore Maui gas condensate field covers an area of 160 km 2 that straddled NE-SW oriented shorelines during the deposition of the main reservoir interval (C1 Sands) in the mid-late Eocene. These sands were deposited as highstand shoreline deposits and lowstand channel-fills that are vertically partitioned by thin, tight transgressive deposits. Correlation of shelf mudstones basinward of the shoreline with equivalent, tight coastal sands is important to define the distribution of barriers to vertical permeability within this approximately 100 m thick interval, but is ambiguous using a lithostratigraphic approach alone. A palaeomagnetic study of 273 samples of shales, siltstones and sandstones was undertaken from three cored wells, Maui-6, -7 and -A1, to place further constraints on well correlation. A variety of magnetic behaviour was observed: from strong, stable primary remanent magnetization, to weak magnetization carrying secondary overprints which sometimes could not be removed completely. Primary polarities were retrieved from about 950f samples. Maui-6, the most basinward well, contains a significant proportion of marine shales and is considered to provide the most complete record. The upper and lowermost parts of the magnetostratigraphic records from the other two wells correlate well with that from Maui-6. Incision of a channel system in the area of Maui-A1 is interpreted to have removed significant parts of the record from the middle C1 interval of this well. The palaeomagnetic data support the correlation of the high permeability, tidally influenced fill of this valley with time-equivalent, tight transgressive sands in interfluve areas. The composite magnetostratigraphic record shows a high frequency of reversals: it is of predominantly normal polarity and contains 10 intervals of reversed polarity. Five of these reversed intervals are apparently less than about 30 000 years in duration. On the basis of biostratigraphic evidence that the interval studied is Bortonian (Mid-Eocene) in age, the magnetostratigraphic record is correlated with Chrons 17 and 18 of the global polarity time-scale.

High-resolution magnetic stratigraphy across the Oligocene-Miocene boundary in an alluvial-lacustrine succession (Ebro Basin, northeast Spain)

The study of a late Oligocene-early Miocene, 300 m thick section of alluvial and shallow lacustrine sediments in the Ebro Basin, has allowed a high-resolution magnetic polarity stratigraphy for the Oligocene-Miocene boundary to be established. The samples studied include alluvial sandstones and mudstones as well as shallow lacustrine and paludine, micritic and microsparitic limestones. Two-hundred-and-fifty specimens were stepwise thermally or magnetically demagnetized following standard procedures. Magnetic imprints of the distinct lithologies present sharp contrasts, especially for the stability of the secondary components. The VGP data show 18 reversal events, defining a sequence of 16 polarity intervals. Lateral and vertical continuity of the sequences studied has enabled a correspondence between the local paleomastological biozones and the magnetostratigraphic succession to be established. The high-resolution chronology of this magnetostratigraphic succession provides valuable information that allows the non-marine European biochronological scales to be correlated to the global polarity time scale (GPTS). The magnetic polarity zonation of the section has been correlated to the GPTS using the distinct sequence and pattern polarity reversals as well as by considering the fossil mammal assemblages. As a preliminary result, chrons 8, 7A, 7 and 6C have been identified.

Magnetohydrodynamic processes in the solar corona: Flares, coronal mass ejections, and magnetic helicity*

The magnetized, million-degree solar corona evolves in cycles of about 11 years, in dynamical response to newly generated magnetic fluxes emerging from below to eventually reverse the global magnetic polarity. Over the larger scales, the corona does not erupt violently all the time. Violent events like the flares and episodic ejections of material into interplanetary space occur frequently, several times a day, but they often originate in long-lived magnetic structures that form continually throughout the solar cycle. In this paper, the creation, stability, and eventual eruption of these structures are discussed from basic principles, drawing on recent advances in observation and theory. A global view is offered in which different pieces of observation relate physically, with distinct roles for the conservation of magnetic helicity and the release of magnetic energy in dissipated and ordered forms.

Polarization Michelson interferometer as a global polarization state generator and for measurement of the coherence and spectral properties of quasimonochromatic light

For a quasimonochromatic light source with a known spectrum, the polarization Michelson interferometer (POLMINT) can be used as a global polarization state generator that produces totally or partially polarized light at its output in states of known degree of polarization that correspond to points on and within the Poincaré sphere. Conversely, the spectral and coherence properties of a quasimonochromatic source can be determined from the Stokes parameters of light at the output of the POLMINT measured by a complete polarization state detector as functions of a mirror displacement. Applications of the POLMINT as an ellipsometer are also discussed.