Dominant Polarization Research Articles

Growth of Columnar Quantum Dots by Metalorganic Vapor-Phase Epitaxy for Semiconductor Optical Amplifiers

Growth of polarization-controlled quantum dots (QDs) by metalorganic vapor-phase epitaxy for semiconductor optical amplifiers (SOAs) is reported. Columnar QDs with small lateral sizes and high aspect ratios were formed using low growth temperatures and highly tensile-strained barriers. Dominant polarization sensitivities of columnar QDs were changed from the transverse-electric (TE) mode to the transverse-magnetic (TM) mode by controlling the heights of columnar QDs and tensile-strained barriers. TM-gain-dominant-QD SOAs were fabricated. A TM-mode gain of 17.3 dB was obtained at a wavelength of 1.55 µm. Polarization dependent gain was tuned by barrier thickness and reduced to 2.5 dB.

Shear-wave splitting of Sichuan Regional Seismic Network

Using seismic data recorded by the Chengdu Digital Seismic Network from May 1, 2000 to December 31, 2006, we obtain the dominant polarization directions of fast shear-waves at eight digital seismic stations adopting the SAM technique. The results show that the dominant directions of polarizations of fast shear-waves at most of stations are mainly in nearly NE-SW or NW-SE direction in Sichuan. The dominant polarization directions of the fast shear-waves at stations located at the active faults or intersection of several active faults are consistent with the strikes of active faults which control the earthquakes used in the analysis, and are basically consistent with the directions of regional compression axis. However, several stations show that the fast shear-waves are not consistent with the strikes of active faults and the directions of regional compression axis, due to the influence of local complicated crustal structure.

Electrical characteristics of (0 0 1)- and random-oriented Bi3.15Nd0.85Ti3O12 thin films: a comparative study

Highly (0 0 1)-oriented Bi3.15Nd0.85Ti3O12 (BNdT) films were deposited directly on single-crystalline Nb-doped SrTiO3 (STON) conductive substrates by chemical solution deposition. The electrical characteristics of BNdT films were studied and compared with random-oriented BNdT films on Pt/TiO2/SiO2/Si substrates. BNdT films on STON substrates show much smaller remanent polarization and ϵr values. This indicates that dominant polarization of BNdT is not along the (0 0 1)-axis. However, (0 0 1)-oriented BNdT films exhibit better retention characteristics, which can be ascribed to the better film/electrode interface between BNdT and STON.

Magnetic Flux Imbalance of the Solar and Heliospheric Magnetic Fields

A comparative analysis of solar and heliospheric magnetic fields in terms of their cumulative sums reveals cyclic and long-term changes that appear as a magnetic flux imbalance and alternations of dominant magnetic polarities. The global magnetic flux imbalance of the Sun manifests itself in the solar mean magnetic field (SMMF) signal. The north – south asymmetry of solar activity and the quadrupole mode of the solar magnetic field contribute the most to the observed magnetic flux imbalance. The polarity asymmetry exhibits the Hale magnetic cycle in both the radial and azimuthal components of the interplanetary magnetic field (IMF). Analysis of the cumulative sums of the IMF components clearly reveals cyclic changes in the IMF geometry. The accumulated deviations in the IMF spiral angle from its nominal value also demonstrate long-term changes resulting from a slow increase of the solar wind speed over 1965 – 2006. A predominance of the positive IMF Bz with a significant linear trend in its cumulative signal is interpreted as a manifestation of the relic magnetic field of the Sun. Long-term changes in the IMF Bz are revealed. They demonstrate decadal changes owing to the 11/22-year solar cycle. Long-duration time intervals with a dominant negative Bz component were found in temporal patterns of the cumulative sum of the IMF Bz.

Subsurface structure, physical properties, fault-zone characteristics and stress state in scientific drill holes of Taiwan Chelungpu Fault Drilling Project

Continuous cores and a suit of geophysical measurements were collected in two scientific drill holes to understand physical mechanisms involved in the large displacements during the 1999 Chi-Chi earthquake. Physical properties obtained from wire-line logs including P- and S-wave sonic velocity, gamma ray, electrical resistivity, density and temperature, are primarily dependent on parameters such as lithology, depth and fault zones. The average dip of bedding, identified from both cores and FMI (or FMS) logs, is about 30° towards SE. Nevertheless, local azimuthal variations and increasing or decreasing bedding dips appear across fault zones. A prominent increase of structural dip to 60°–80° below 1856 m could be due to deformation associated with propagation of the Sanyi fault. A total of 12 fault zones identified in hole-A are located in the Plio-Pleistocene Cholan Formation, Pliocene Chinshui Shale and Miocene Kueichulin Formation. The shallowest fault zone occurs at 1111 m depth (FZ1111). It is a 1 m gouge zone including 12 cm of thick indurate black material. We interpreted this zone as the slip zone during Chi-Chi earthquake. FZ1111 is characterized by: 1) bedding-parallel thrust fault with 30-degree dip; 2) the lowest resistivity; 3) low density, V p and V s, 4) high V p/ V s ratio and Poisson's ratio; 5) low energy and velocity anisotropy, and low permeability within the homogeneous 1 m gouge zone; 6) increasing gas (CO 2 and CH 4) emissions, and 7) appearance of smectite within the primary slip zone. In situ stresses at the drill site were inferred from leak-off tests, borehole breakouts and drilling-induced tensile fractures from borehole FMS/FMI logs, and shear seismic wave anisotropy from DSI logs. The dominant fast shear-wave polarization direction is in good agreement with regional maximum horizontal stress axis, particularly within the strongly anisotropic Kueichulin Formation. A conjugate set of secondary directions are parallel to microcrack orientations. A drastic change of orientation of fast shear-wave polarization across the Sanyi thrust fault at the depth of 1712 m reflects the change of stratigraphy, physical properties and structural geometry.

Design, morphometry and development of the secondary osteonal system in the femoral shaft of the rabbit

The architecture of the diaphyseal bone is closely correlated with the cortical vessel network, whose pattern develops in the course of growth. Various methods have been applied to clarify the three-dimensional anatomy of the cortical canal system, but there is still disagreement about the geometry, blood supply, flux dynamics and factors controlling canal geometry during bone growth and remodeling. A modification of the currently employed dye-injection method was applied to study the vessel network of the whole hemi-shaft of the rabbit femur in mature bones (8-month-old rabbits) and growing bones (1.5-month-old rabbits). The cortical vascular tree of the hemi-shaft of the femur was injected with black China ink and observed in full-thickness specimens of the cortex. The same specimens were then processed for histology. A comparative study of the middle diaphysis (mid-shaft) with the distal extremity (distal shaft) was performed in both young and old rabbit femurs. The longitudinally oriented pattern of the vessel network was seen to develop in the diaphysis of mature femurs, while at the extremity of the shaft of the same specimen the network showed a reticular organization without a dominant polarization. The vessels were significantly higher in the mid-shaft than in the distal shaft of the old femurs (P < 0.0001), as was their diameter (P < 0.05). In the group of young rabbits at mid-shaft level the longitudinally oriented pattern of the vessel network was not yet completely developed, without their being significant differences in length and diameter between the mid-shaft and distal shaft. The differentiation of the mid-shaft from the distal shaft was confirmed histologically by the presence, in the latter, of longitudinal calcified cartilage septa between osteons. This pattern of structural organization and development of the intracortical vascular network has not been previously reported. The cells primarily involved in polarization of the remodeling process were the osteoclasts at the top of the cutting cones advancing from the proximal and distal metaphyses toward the mid-shaft. This suggests, first, a relationship with the longitudinally oriented structures already present in the cortex near the metaphysis (the calcified cartilage septa) and then with the columns of interosteonic breccia, which were formed as a secondary effect of the longitudinal polarization of the remodeling process. Our observations did not enable us to substantiate the model of two different systems, one of longitudinal vessels (Havers) and the other of connecting transversal vessels (Volkmann), but suggested instead that there is a network whose loops lengthen in the direction of the major bone axis in the course of growth and secondary modeling. The associated morphology supported the view that the type of structural organization of the tubular bone cortex is primarily determined by an inherited constitutional factor rather than by mechanical strains.

Polarization characteristics of photonic quantum ring laser with three-dimensional whispering gallery resonances

We report polarization characteristics of light from a photonic quantum ring (PQR) laser of three-dimensional (3D) whispering gallery modes. The 3D polarization states of light from the PQR laser were studied with a home-built solid-angle scanner capable of detecting the spatial intensity distribution in a wide range of solid angles. The analysis shows that the dominant polarization vectors of the PQR laser emitting in the surface normal direction lie always tangential to the PQR perimeter, which means there is a strong carrier-photon coupling.

Ferromagnetic Interaction in an Asymmetric End‐to‐End Azido Double‐Bridged Copper(II) Dinuclear Complex: A Combined Structure, Magnetic, Polarized Neutron Diffraction and Theoretical Study

A new end-to-end azido double-bridged copper(II) complex [Cu(2)L(2)(N(3))2] (1) was synthesized and characterized (L=1,1,1-trifluoro-7-(dimethylamino)-4-methyl-5-aza-3-hepten-2-onato). Despite the rather long Cu-Cu distance (5.105(1) A), the magnetic interaction is ferromagnetic with J= +16 cm(-1) (H=-JS(1)S(2)), a value that has been confirmed by DFT and high-level correlated ab initio calculations. The spin distribution was studied by using the results from polarized neutron diffraction. This is the first such study on an end-to-end system. The experimental spin density was found to be localized mainly on the copper(II) ions, with a small degree of delocalization on the ligand (L) and terminal azido nitrogens. There was zero delocalization on the central nitrogen, in agreement with DFT calculations. Such a picture corresponds to an important contribution of the d(x2-y2) orbital and a small population of the d(z2) orbital, in agreement with our calculations. Based on a correlated wavefunction analysis, the ferromagnetic behavior results from a dominant double spin polarization contribution and vanishingly small ionic forms.

Environmental Control of Cloud-to-Ground Lightning Polarity in Severe Storms

Abstract In this study, it is hypothesized that the mesoscale environment can indirectly control the cloud-to-ground (CG) lightning polarity of severe storms by directly affecting their structural, dynamical, and microphysical properties, which in turn directly control cloud electrification and ground flash polarity. A more specific hypothesis, which has been supported by past observational and laboratory charging studies, suggests that broad, strong updrafts and associated large liquid water contents in severe storms lead to the generation of an inverted charge structure and enhanced +CG lightning production. The corollary is that environmental conditions favoring these kinematic and microphysical characteristics should support severe storms generating an anomalously high (&amp;gt;25%) percentage of +CG lightning (i.e., positive storms) while environmental conditions relatively less favorable should sustain storms characterized by a typical (≤25%) percentage of +CG lightning (i.e., negative storms). Forty-eight inflow proximity soundings were analyzed to characterize the environment of nine distinct mesoscale regions of severe storms (4 positive and 5 negative) on 6 days during May–June 2002 over the central United States. This analysis clearly demonstrated significant and systematic differences in the mesoscale environments of positive and negative storms, which were consistent with the stated hypothesis. When compared to negative storms, positive storms occurred in environments associated with a drier low to midtroposphere, higher cloud-base height, smaller warm cloud depth, stronger conditional instability, larger 0–3 km AGL wind shear, stronger 0–2 km AGL storm relative wind speed, and larger buoyancy in the mixed-phase zone, at a statistically significant level. Differences in the warm cloud depth of positive and negative storms were by far the most dramatic, suggesting an important role for this parameter in controlling CG lightning polarity. In this study, strong correlations between the mesoscale environment and CG lightning polarity were demonstrated. However, causality could not be verified due to a lack of in situ observations to confirm the hypothesized microphysical, dynamical, and electrical responses to variations in environmental conditions that ultimately determined the dominant CG polarity. Future observational field programs and cloud modeling studies should focus on these critical intermediary processes.

Subsurface Structure, Physical Properties, and Fault Zone Characteristics in the Scientific Drill Holes of Taiwan Chelungpu-Fault Drilling Project

1 Department of Earth Sciences and Institute of Geophysics, National Central University, Chung-Li, Taiwan, ROC 2 Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, Kochi, Japan 3 Department of Geosciences, National Taiwan University, Taipei, Taiwan, ROC 4 Exploration and Development Research Institute, Chinese Petroleum Corporation, Miaoli, Taiwan, ROC 5 Department of Earth Science, National Taiwan Normal University, Taipei, Taiwan, ROC * Corresponding author address: Prof. Jih-Hao Hung, Department of Earth Sciences and Institute of Geophysics, National Central University, Chung-Li, Taiwan, ROC; E-mail: jhhung@ncu.edu.tw doi: 10.3319/TAO.2007.18.2.271(TCDP) Continuous coring and a suite of geophysical measurements were collected in two scientific holes to understand physical mechanisms involved in large displacements in the 1999 Chi-Chi earthquake. Physical properties of formations obtained from wire-line logs including Pand S-wave sonic velocity, gamma ray, electrical resistivity, density and temperature, are primarily dependent on parameters such as lithology, depth and fault zones. The average dip of bedding, identified from both cores and FMI (or FMS) logs, is about 30 degrees towards the SE. Nevertheless, local azimuthal variations and increasing or decreasing bedding dips appear across fault zones. A prominent increase in structural dip to 60° 80° below 1856 m could be due to deformation associated with propagation of the Sanyi fault. A total of 12 fault zones identified in Hole-A are located in the PlioPleistocene Cholan Formation, Pliocene Chinshui Shale and Miocene Kueichulin Formation. The shallowest fault zone at 1111 m in depth, FZ1111, Terr. Atmos. Ocean. Sci., Vol. 18, No. 2, June 2007 272 is a 1-m long gouge zone that includes 12-cm thick indurate black material and has been interpreted as the slip zone during Chi-Chi earthquake. FZ1111 is characterized by: 1) a bedding-parallel thrust fault with a 30-degree dip; 2) the lowest resistivity; 3) low density, Vp and Vs ; 4) high Vp /Vs ratio and Poisson’s ratio; 5) low energy and velocity anisotropy, and low permeability or fluid mobility within the homogeneous gouge zone; 6) increasing gas (CO2 and CH4) emissions; and 7) being rich in smectite within the primary slip zone. Formation physical properties hold consistent relationships with either depth or lithology. Anisotropy of shear-wave velocity shows that the dominant fast shear polarization direction is in good agreement with an overall azimuth of the maximum horizontal stress axis, particularly within the strong anisotropic Kueichulin Formation. A drastic change in orientation of fast shear polarization across the Sanyi thrust fault at a depth of 1710 m reflects changes in stratigraphy, physical properties and structural geometry. (

Linearly polarized emission from GaInN lightemitting diodes with polarization-enhancing reflector

A polarization-enhancing reflector design, which is matched to the emission characteristics of GaInN/GaN 460 nm light-emitting diodes grown on (0001) oriented sapphire substrates, is reported. Side-emitted light from these devices is known to be highly polarized with the electric field in the plane of the active region. Through selective rotation of polarization by the reflector, the in-plane polarized side-emitted light is directed upwards with a single dominant linear polarization. Polarization ratios as high as 3.5:1 are measured in the farfield, and the average polarization ratio is 1.9:1. If only light that strikes the reflector is considered, the polarization ratio is 2.5:1. The concept of the polarization-enhancing reflector and the numerical algorithm used to generate the optimized shape are also described.

Inhibition of indoleamine 2,3-dioxygenase-mediated tryptophan catabolism accelerates collagen-induced arthritis in mice

Indoleamine 2,3-dioxygenase (IDO) is one of the initial and rate-limiting enzymes involved in the catabolism of the essential amino acid tryptophan. In cultured cells, the induction of IDO leads to depletion of tryptophan and tryptophan starvation. Recent studies suggest that modulation of tryptophan concentration via IDO plays a fundamental role in innate immune responses. Induction of IDO by interferon-γ in macrophages and dendritic cells results in tryptophan depletion and suppresses the immune-mediated activation of fibroblasts and T, B, and natural killer cells. To assess the role of IDO in collagen-induced arthritis (CIA), a model of rheumatoid arthritis characterized by a primarily Th1-like immune response, activity of IDO was inhibited by 1-methyl-tryptophan (1-MT) in vivo. The results showed significantly increased incidence and severity of CIA in mice treated with 1-MT. Activity of IDO, as determined by measuring the levels of kynurenine/tryptophan ratio in the sera, was increased in the acute phase of arthritis and was higher in collagen-immunized mice that did not develop arthritis. Treatment with 1-MT resulted in an enhanced cellular and humoral immune response and a more dominant polarization to Th1 in mice with arthritis compared with vehicle-treated arthritic mice. The results demonstrated that development of CIA was associated with increased IDO activity and enhanced tryptophan catabolism in mice. Blocking IDO with 1-MT aggravated the severity of arthritis and enhanced the immune responses. These findings suggest that IDO may play an important and novel role in the negative feedback of CIA and possibly in the pathogenesis of rheumatoid arthritis.

Long-term variations in the asymmetry of the magnetic field of the sun and heliosphere

The asymmetry of the magnetic field of the Sun and its manifestation in the interplanetary magnetic field (IMF) are studied. The dominant magnetic polarity of the radial component of the IMF alternates from cycle to cycle, but with an overall systematic dominance of polarity directed toward the Sun. The global asymmetry is also manifest in the component of the IMF perpendicular to the plane of the solar equator. The dominance of positive values of Bz together with an appreciable linear trend in the cumulative sum of this quantity is interpreted as a manifestation of a relic solar magnetic field. The strength of this relic magnetic field near the Earth is estimated to be 0.048 ± 0.015 nT, based on the growth of the linear component of the cumulative sum of Bz. Time intervals, in which negative values of the Bz component of the IMF dominate and enhanced geomagnetic activity is observed, are identified. Our analysis of solar and heliospheric magnetic fields in an integrated representation has enabled us to compare various types of measurements and estimate their stability.

Seismic anisotropy of the crust in Yunnan, China: Polarizations of fast shear-waves

Using seismic data recorded by Yunnan Telemetry Seismic Network from January 1, 2000 to December 31, 2003, the dominant polarization directions of fast shear-waves are obtained at 10 digital seismic stations by SAM technique, a systematic analysis method on shear-wave splitting, in this study. The results show that dominant directions of polarizations of fast shear-waves at most stations are mainly at nearly N-S or NNW direction in Yunnan. The dominant polarization directions of fast shear-waves at stations located on the active faults are consistent with the strike of active faults, directions of regional principal compressive strains measured from GPS data, and basically consistent with regional principal compressive stress. Only a few of stations show complicated polarization pattern of fast shear-waves, or are not consistent with the strike of active faults and the directions of principal GPS compressive strains, which are always located at junction of several faults. The result reflects complicated fault distribution and stress field. The dominant polarization direction of fast shear-wave indicates the direction of the in-situ maximum principal compressive stress is controlled by multiple tectonic aspects such as the regional stress field and faults.

The choice of basis set for calculations of linear and nonlinear optical properties of conjugated organic molecules in gas and in dielectric medium by the example of p-nitroaniline

In the present work the moderate-size basis sets suggested earlier – [4s3p Md/3s M′p], [5s3p Md/3s M′p] and [6s4p Md/4s M′p], with ( M/ M′) = (2/0), (2/2), (3/0), (3/3) – are used for the SCF level calculations of static molecular polarizability α ij and first hyperpolarizability β ijk of para-nitroaniline (PNA) both in gas and in two solvents (chloroform and acetone). Basis set dependencies of the nonlinear optical characteristics of PNA in gas and in condensed phase are shown to exhibit similar tendencies. It is demonstrated that for NLO chromophores, having a dominant π-electron polarization, one can obtain rather reliable results already with the [4s3p2d/3s] basis set. The obtained data are compared with the ones calculated with Dunning aug-cc-pVDZ basis set, these basis sets are shown to be of equal worth to obtain sufficiently reliable estimations of the (hyper)polarizability values, and they may be used in the study of the effect of the dielectric medium on NLO response of organic molecules at the SCF level.

Sequential Chromospheric Brightenings beneath a Transequatorial Halo Coronal Mass Ejection

Analyses of multiwavelength data sets for a solar eruption at ~21:30 UT on 2002 December 19 show evidence for the disappearance of a large-scale, transequatorial coronal loop (TL). In addition, coronal manifestations of the eruption (based on SOHO EIT and LASCO images) include large-scale coronal dimming, flares in each associated active region in the northern and southern hemispheres, and a halo CME. We present detailed observations of the chromospheric aspects of this event based on Hα images obtained with the ISOON telescope. The ISOON images reveal distant flare precursor brightenings, sympathetic flares, and, of most interest herein, four nearly cospatial propagating chromospheric brightenings. The speeds of the propagating disturbances causing these brightenings are 600-800 km s-1. The inferred propagating disturbances have some of the characteristics of Hα and EIT flare waves (e.g., speed, apparent emanation from the flare site, subsequent filament activation). However, they differ from typical Hα chromospheric flare waves (also known as Moreton waves) because of their absence in off-band Hα images, small angular arc of propagation (<30°), and their multiplicity. Three of the four propagating disturbances consist of a series of sequential chromospheric brightenings of network points that suddenly brighten in the area beneath the TL that disappeared earlier. SOHO MDI magnetograms show that the successively brightened points that define the inferred propagating disturbances were exclusively of one polarity, corresponding to the dominant polarity of the affected region. We speculate that the sequential chromospheric brightenings represent footpoints of field lines that extend into the corona, where they are energized in sequence by magnetic reconnection as coronal fields tear away from the chromosphere during the eruption of the transequatorial CME. We report briefly on three other events with similar narrow propagating disturbances that were confined to a single hemisphere.

Low‐latitude ELF‐whistlers observed in Taiwan

Detections of ELF whistler‐like events at a low latitude location are reported. Events with frequencies between 60 and 100 Hz were recorded by the ELF station at the Lulin Observatory in Taiwan from August 26, 2003 to July 13, 2004. The most distinguished feature for these events is the frequency descent in the frequency‐time spectrograms, resembling terrestrial whistlers. Other notable features include (a) a long event duration averaging up to two minutes, (b) a daytime diurnal maximum occurring around 10 am, (c) a dominant magnetic field polarization in the north‐south direction with strength of a few to tens of pT, and (d) no detection of vertical electric fields. Similar events were only reported twice for the past thirty years: one at an auroral latitude site in Alaska and the other at a mid‐latitude site in California. Possible source mechanisms including magnetosheath lion roars and lightning‐generated whistlers are discussed.

CMBB-mode polarization from Thomson scattering in the local universe

The polarization of the cosmic microwave background (CMB) is widely recognized as a potential source of information about primordial gravitational waves. The gravitational wave contribution can be separated from the dominant CMB polarization created by density perturbations at the times of recombination and reionization because it generates both $E$ and $B$ polarization modes, whereas the density perturbations create only $E$ polarization. The limits of our ability to measure gravitational waves are thus determined by statistical and systematic errors from CMB experiments, foregrounds, and nonlinear evolution effects such as gravitational lensing of the CMB. Usually it is assumed that most foregrounds can be removed because of their frequency dependence, however Thomson scattering of the CMB quadrupole by electrons in the Galaxy or nearby structures shares the blackbody frequency dependence of the CMB. If the optical depth from these nearby electrons is anisotropic, the polarization generated can include $B$ modes even if no tensor perturbations are present. We estimate this effect for the Galactic disk and nearby extragalactic structures, and find that it contributes to the $B$ polarization at the level of $\ensuremath{\sim}(1--2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\text{ }\text{ }\ensuremath{\mu}\mathrm{K}$ per logarithmic interval in multipole $\ensuremath{\ell}$ for $\ensuremath{\ell}&lt;30$. This is well below the detectability level even for a future CMB polarization satellite and hence is negligible. Depending on its structure and extent, the Galactic corona may be a source of $B$-modes comparable to the residual large-scale lensing $B$-mode after the latter has been cleaned using lensing reconstruction techniques. For an extremely ambitious post-Planck CMB experiment, Thomson scattering in the Galactic corona is thus a potential contaminant of the gravitational wave signal; conversely, if the other foregrounds can be cleaned out, such an experiment might be able to constrain models of the corona.

Candidate Type II Quasars from the Sloan Digital Sky Survey. III. Spectropolarimetry Reveals Hidden Type I Nuclei

We have conducted spectropolarimetry of 12 type II (obscured) quasar candidates selected from the spectroscopic database of the Sloan Digital Sky Survey on the basis of their emission-line properties. Polarization was detected in all objects, with nine being highly polarized (>3%) and with polarization reaching as high as 17% in two objects. Broad lines were detected in the polarized spectra of five objects. These observations prove beyond a reasonable doubt that the objects in our sample are indeed type II quasars in that they harbor luminous UV-excess active galactic nuclei (AGNs) in their centers and that the direct view to the AGN is highly obscured. For three of the objects in this paper, we have obtained Hubble Space Telescope (HST) images in three bands. The HST observations combined with the spectropolarimetry data imply that scattering off material outside the obscuration plane is the dominant polarization mechanism. In all three objects the sizes of scattering regions are a few kiloparsecs. For one object, the extent of the scattering region coupled with the characteristics of the polarized spectrum argues strongly that dust scattering rather than electron scattering dominates the polarized light. Our observations are well described by the basic orientation-based unification model of toroidal obscuration and off-plane scattering, implying that the model can be extended to include at least some high-luminosity AGNs.

Population genetic structure of annual and perennial populations ofZostera marinaL. along the Pacific coast of Baja California and the Gulf of California

The Baja California peninsula represents a biogeographical boundary contributing to regional differentiation among populations of marine animals. We investigated the genetic characteristics of perennial and annual populations of the marine angiosperm, Zostera marina, along the Pacific coast of Baja California and in the Gulf of California, respectively. Populations of Z. marina from five coastal lagoons along the Pacific coast and four sites in the Gulf of California were studied using nine microsatellite loci. Analyses of variance revealed significant interregional differentiation, but no subregional differentiation. Significant spatial differentiation, assessed using theta(ST) values, was observed among all populations within the two regions. Z. marina populations along the Pacific coast are separated by more than 220 km and had the greatest theta(ST) (0.13-0.28) values, suggesting restricted gene flow. In contrast, lower but still significant genetic differentiation was observed among populations within the Gulf of California (theta(ST) = 0.04-0.18), even though populations are separated by more than 250 km. This suggests higher levels of gene flow among Gulf of California populations relative to Pacific coast populations. Direction of gene flow was predominantly southward among Pacific coast populations, whereas no dominant polarity in the Gulf of California populations was observed. The test for isolation by distance (IBD) showed a significant correlation between genetic and geographical distances in Gulf of California populations, but not in Pacific coast populations, perhaps because of shifts in currents during El Niño Southern Oscillation (ENSO) events along the Pacific coast.