Sun-synchronous orbits near critical inclination

The long period dynamics of Sun-synchronous orbits near the critical inclination 116.6° are investigated. It is known that, at the critical inclination, the average perigee location is unchanged by Earth oblateness. For certain values of semimajor axis and eccentricity, orbit plane precession caused by Earth oblateness is synchronous with the mean orbital motion of the apparent Sun (a Sun-synchronism). Sun-synchronous orbits have been used extensively in meteorological and remote sensing satellite missions. Gravitational perturbations arising from an aspherical Earth, the Moon, and the Sun cause long period fluctuations in the mean argument of perigee, eccentricity, inclination, and ascending node. Double resonance occurs because slow oscillations in the perigee and Sun-referenced ascending node are coupled through the solar gravity gradient. It is shown that the total number and infinitesimal stability of equilibrium solutions can change abruptly over the Sun-synchronous range of semimajor axis values (1.54 to 1.70 Earth radii). The effect of direct solar radiation pressure upon certain stable equilibria is investigated.     

Near-infrared imaging polarimetry of Cygnus A

We present a 2.2-μm polarization image of the nuclear regions of Cygnus A. The degree of polarization in the central 1 arcsec is (4.1±0.50) per cent, at a position angle of (23.6±3.6)°, approximately perpendicular to the axis of the radio jet.
Modelling of the results suggests that at this wavelength the polarization along the line of sight to the central source is most likely produced by dichroism, through an A _v∼40 mag, with the polarization in surrounding regions produced by scattering. For this model, the K -band luminosity of the central source is calculated to be ∼2×10⁴⁴ erg s⁻¹.     

Can One-Run-Fixed-Arrhenius Kerogen Analysis Provide Comparable Organofacies Results to Detailed Palynological Analysis? A Case Study from a Prospective Mississippian Source Rock Reservoir (Bowland Shale,UK)

Natural Resources Research - Organofacies analysis, a fundamental component within source rock appraisal based on the study of kerogen within a source rock, is typically produced from microscopy...     

GAUGE: the GrAnd Unification and Gravity Explorer

The GAUGE (GrAnd Unification and Gravity Explorer) mission proposes to use a drag-free spacecraft platform onto which a number of experiments are attached. They are designed to address a number of key issues at the interface between gravity and unification with the other forces of nature. The equivalence principle is to be probed with both a high-precision test using classical macroscopic test bodies, and, to lower precision, using microscopic test bodies via cold-atom interferometry. These two equivalence principle tests will explore string-dilaton theories and the effect of space–time fluctuations respectively. The macroscopic test bodies will also be used for intermediate-range inverse-square law and an axion-like spin-coupling search. The microscopic test bodies offer the prospect of extending the range of tests to also include short-range inverse-square law and spin-coupling measurements as well as looking for evidence of quantum decoherence due to space–time fluctuations at the Planck scale.     

Circumstellar structure of RU Lupi down to au scales

We have used the technique of spectro-astrometry to study the milliarcsecond scale structure of the emission lines in the T Tauri star RU Lupi. The wings of the H α emission are found to be displaced from the star towards the south-west (blue wing) and north-east (red wing) with angular scales of 20–30 mas. This structure is consistent with a bipolar outflow from the star. From a study of the variability of the intensity and position spectra, we argue that a combination of magnetically driven bipolar outflow and accreting gas contributes to the H α emission. On the other hand, the [O  i ] and [S  ii ] emission are displaced from the star to the south-west but at much larger distances than the H α , hundreds of milliarcseconds for the high-velocity component (HVC) and down to 30 mas for the low-velocity components (LVCs). The presence of both redshifted and blueshifted outflows in H α but only a blueshifted outflow in the forbidden lines can be explained if the disc obscures the redshifted forbidden line outflow, but a disc gap with outer radius 3–4 au allows the redshifted H α to be seen. This gap could be induced by an unseen companion.     

Earthquake intensity distributions: a new view

Pioneering work by Nicolas Ambraseys and many collaborators demonstrates both the tremendous value of macroseismic data and the perils of its uncritical assessment. In numerous publications he shows that neglect of original sources and/or failure to appreciate the context of historical accounts, as well as use of unreliable indicators such as landsliding to determine intensities, commonly leads to inflated magnitude estimates for historical earthquakes. The U.S. Geological Survey “Did You Feel It?” (DYFI) system, which now collects and systematically interprets thousands of first-hand reports from felt earthquakes, provides the opportunity to explore further the biases associated with traditional intensity distributions determined from written (media or archival) accounts. I briefly summarize and further develop the results of Hough (2013), who shows that traditional intensity distributions imply more dramatic damage patterns than are documented by more spatially rich DYFI data, even when intensities are assigned according to the conservative practices established by Ambraseys’ work. I further consider the separate intensity–attenuation relations that have been developed to characterize intensities for historical and modern earthquakes in California, using traditionally assigned intensities and DYFI intensities, respectively. The results support the conclusion that traditionally assigned intensity values tend to be inflated by a fundamental bias towards reporting of dramatic rather than representative effects. I introduce an empirical correction-factor approach to correct for these biases. This allows the growing wealth of well-calibrated DYFI data to be used as calibration events in the analysis of historical earthquakes.     

Constraints on the nuclear emission of the Circinus galaxy: the torus

In the context of the unified model of Seyfert galaxies, we use observations from the literature and a radiative transfer model to investigate the near-IR to mm emission produced by the presumed torus in the Circinus galaxy, from 2 μm to 1.3 mm. From the infrared SED modelling, we find that the total luminosity ( L _IR) in this wavelength range consists of similar contributions from the torus and starburst with a ratio of nuclear luminosity to starburst luminosity ( L _NUC/ L _SB)∼0.8 .
By using a similar torus model to that of NGC 1068, but without the conical dust , we find an upper limit to the outer torus radius of ∼12 pc with a best fit of ∼2 pc. The upper limit torus size estimated from the radiative transfer modelling is consistent with the 16-pc torus radius estimated from near-IR imaging polarimetry of Circinus.     

Time-resolved,defect-hosted,trace element mobility in deformed Witwatersrand pyrite

The Pb isotopic composition of rocks is widely used to constrain the sources and mobility of melts and hydrothermal fluids in the Earth's crust. In many cases, the Pb isotopic composition appears to represent mixing of multiple Pb reservoirs. However, the nature, scale and mechanisms responsible for isotopic mixing are not well known. Additionally, the trace element composition of sulphide minerals are routinely used in ore deposit research, mineral exploration and environmental studies, though little is known about element mobility in sulphides during metamorphism and deformation. To investigate the mechanisms of trace element mobility in a deformed Witwatersrand pyrite(FeS_2), we have combined electron backscatter diffraction(EBSD) and atom probe microscopy(APM). The results indicate that the pyrite microstructural features record widely different Pb isotopic compositions, covering the entire range of previously published sulphide Pb compositions from the Witwatersrand basin. We show that entangled dislocations record enhanced Pb, Sb, Ni, Tl and Cu composition likely due to entrapment and short-circuit diffusion in dislocation cores. These dislocations preserve the Pb isotopic composition of the pyrite at the time of growth(~3 Ga) and show that dislocation intersections, likely to be common in deforming minerals, limit trace element mobility. In contrast, Pb, As, Ni, Co, Sb and Bi decorate a highangle grain boundary which formed soon after crystallisation by sub-grain rotation recrystallization.Pb isotopic composition within this boundary indicates the addition of externally-derived Pb and trace elements during greenschist metamorphism at ~2 Ga. Our results show that discrete Pb reservoirs are nanometric in scale, and illustrate that grain boundaries may remain open systems for trace element mobility over 1 billion years after their formation.     

Some Aspects of Diet and Foraging Behavior of Octopus dofleini Wülker, 1910 in its Northernmost Range

Abstract. Diet and foraging behavior of Octopus dofleini in Prince William Sound and Port Graham, Alaska, were studied from collections of den litter, measurements of octopuses and estimates of live prey abundance. Based on 193 den collections from depths of - 31 to + 1.3 m, a diet of hard-bodied prey could be identified. The five most common litter species made up 80% of the litter remains, with nearly 30 species of various taxa malung up the rest. The proportions of major hard-bodied prey species in each litter pile significantly differed with depth of den, associated substrata, presence of cobble and geographical location but not with the presence of boulders or outcrop, the density of kelp or season of litter collection. Octopus weight was not significantly correlated with the size of prey remains although O. dofleini may take a wide range of prey sizes once it reaches 2.5 kg. O. dofleini was more likely to be found at sites with crabs, although no litter species was significantly preferred over its estimated abundance, and one species was significantly avoided. These results suggest that O. dofleini includes suitable bivalve and crab species in its diet in relation to live abundance, while at the same time exercising an element of selectivity, as some species were actively avoided. Comparison of litter remains from the northern-most range of O. dofleini with those published for British Columbia show that diet breadth was similar, but the identity of major hard-bodied prey species was very different for Alaskan octopuses.     

Infrared Polarimetry and the Torus

Polarimetry at near-infrared wavelengths is shown to be an important tool in understanding the properties of the obscuring torus in NGC1068. We present evidence for the existence of aligned grains in the torus, which produce polarized flux through dichroism, and show how the torus itself can be observed in silhouette in polarized flux images. This revised version was published online in July 2006 with corrections to the Cover Date.