Narrow associated quasi-stellar object absorbers: clustering, outflows and the line-of-sight proximity effect

Using data from the Sloan Digital Sky Survey data release 3 (SDSS DR3), we investigate how narrow (<700 km s⁻¹) C  iv and Mg  ii quasar absorption-line systems are distributed around quasars. The C  iv absorbers lie in the redshift range 1.6 < z < 4 and the Mg  ii absorbers in the range 0.4 < z < 2.2. By correlating absorbers with quasars on different but neighbouring lines of sight, we measure the clustering of absorbers around quasars on comoving scales between 4 and 30 Mpc. The observed comoving correlation lengths are   r _o∼ 5 h ⁻¹Mpc  , similar to those observed for bright galaxies at these redshifts. Comparing correlations between absorbers and the quasars, in whose spectra they are identified, then implies: (i) that quasars destroy absorbers to comoving distances of ∼300 kpc (C  iv ) and ∼800 kpc (Mg  ii ) along their lines of sight; (ii) that ≳40 per cent of C  iv absorbers within 3000 km s⁻¹ of the quasi-stellar object are not a result of large-scale clustering but rather are directly associated with the quasar itself; (iii) that this intrinsic absorber population extends to outflow velocities of the order of 12 000 km s⁻¹; (iv) that this outflow component is present in both radio-loud and radio-quiet quasars and (v) that a small high-velocity outflow component is also observed in the Mg  ii population. We also find an indication that absorption systems within 3000 km s⁻¹ are more abundant for radio-loud quasars than for radio-quiet quasars. This suggests either that radio-loud objects live in more massive haloes, or that their radio activity generates an additional low-velocity outflow, or both.     

Black ordinary chondrites: An analysis of abundance and fall frequency

Abstract— Black ordinary chondrite meteorites sample the spectral effects of shock on ordinary chondrite material in the space environment. Since shock is an important regolith process, these meteorites may provide insight into the spectral properties of the regoliths on ordinary chondrite parent bodies. To determine how common black chondrites are in the meteorite collection and, by analogy, the frequency of shock-alteration in ordinary chondrites, several of the world's major meteorite collections were examined to identify black chondrites. Over 80% of all catalogued ordinary chondrites were examined and, using an optical definition, 61 black chondrites were identified. Black chondrites account for approximately 13.7% of ordinary chondrite falls. If the optically altered gas-rich ordinary chondrites are included, the proportion of falls that exhibit some form of altered spectral properties increases to 16.7%. This suggests that optical alteration of asteroidal material in the space environment is a relatively common process.     

Testing and calibrating parametric wave transformation models on natural beaches

To provide coastal engineers and scientists with a detailed inter-comparison of widely used parametric wave transformation models, several models are tested and calibrated with extensive observations from six field experiments on barred and unbarred beaches. Using previously calibrated (“default”) values of a free parameter γ, all models predict the observations reasonably well (median root-mean-square wave height errors are between 10% and 20%) at all field sites. Model errors can be reduced by roughly 50% by tuning γ for each data record. No tuned or default model provides the best predictions for all data records or at all experiments. Tuned γ differ for the different models and experiments, but in all cases γ increases as the hyperbolic tangent of the deep-water wave height, H_o. Data from two experiments are used to estimate empirical, universal curves for γ based on H_o. Using the new parameterization, all models have similar accuracy, and usually show increased skill relative to using default γ.     

Simulated asteroid materials based on carbonaceous chondrite mineralogies

A set of high‐fidelity simulated asteroid materials, or simulants, was developed based on the mineralogy of carbonaceous chondrite meteorites. Three varieties of simulant were developed based on CI1 chondrites (typified by Orgueil), CM2 chondrites (typified by Murchison), and CR2/3 chondrites (multiple samples). The simulants were designed to replicate the mineralogy and physical properties of the corresponding meteorites and anticipated asteroid surface materials as closely as is reasonably possible for bulk amounts. The simulants can be made in different physical forms ranging from larger cobbles to fine‐grained regolith. We analyzed simulant prototypes using scanning electron microscopy, X‐ray fluorescence, reflectance spectroscopy at ambient conditions and in vacuum, thermal emission spectroscopy in a simulated asteroid environment chamber, and combined thermogravimetry and evolved gas analysis. Most measured properties compare favorably to the reference meteorites and therefore to predicted volatile‐rich asteroid surface materials, including boulders, cobbles, and fine‐grained soils. However, there were also discrepancies, and mistakes were made in the original mineral formulations that will be updated in the future. The asteroid simulants are available to the community from the nonprofit Exolith Lab at UCF, and the mineral recipes are freely published for other groups to reproduce and modify as they see fit.     

The morphology and surface processes of Comet 19/P Borrelly

The flyby of the nucleus of the Comet 19P/Borrelly by the Deep Space 1 spacecraft produced the best views to date of the surface of these interesting objects. It transformed Borrelly from an astronomical object shrouded in coma of gas and dust into a geological object with complex surface processes and a rich history of erosion and landform evolution. Based on analysis of the highest resolution images, stereo images, photometry, and albedo we have mapped four major morphological units and four terrain features. The morphological units are named dark spots, mottled terrain, mesas, and smooth terrain. The features are named ridges, troughs, pits, and hills. In strong contrast to asteroids, unambiguous impact craters were not observed on Borrelly's surface. Because of the relatively short period of this comet, surface erosion by volatile sublimation is, in geologic terms, a very active process. The formation and the morphologies of units and features appear to be driven by differential rates of sublimation erosion. Erosional rates across the comet are probably controlled by solar energy input and the location of the subsolar point during perihelion. Differences in energy input may produce different varieties of sublimation erosional landforms. The terrains on Borrelly suggest that solar energy input could map directly into erosional processes and landforms.     

Analysis of systematic error in “bead method” measurements of meteorite bulk volume and density

The Archimedean glass bead method for determining meteorite bulk density has become widely applied. We used well characterized, zero-porosity quartz and topaz samples to determine the systematic error in the glass bead method to support bulk density measurements of meteorites for our ongoing meteorite survey. Systematic error varies according to bead size, container size and settling method, but in all cases is less than 3%, and generally less than 2%. While measurements using larger containers (above 150 cm³) exhibit no discernible systematic error but much reduced precision, higher precision measurements with smaller containers do exhibit systematic error. For a 77 cm³ container using 40-80 μm diameter beads, the systematic error is effectively eliminated within measurement uncertainties when a “secured shake” settling method is employed in which the container is held securely to the shake platform during a 5 s period of vigorous shaking. For larger 700-800 μm diameter beads using the same method, bulk volumes are uniformly overestimated by 2%. Other settling methods exhibit sample-volume-dependent biases. For all methods, reliability of measurement is severely reduced for samples below ∼5 cm³ (10-15 g for typical meteorites), providing a lower-limit selection criterion for measurement of meteoritical samples.     

Incompletely compacted equilibrated ordinary chondrites

Abstract— We document the size distributions and locations of voids present within five highly porous equilibrated ordinary chondrites using high‐resolution synchrotron X‐ray microtomography (μCT) and helium pycnometry. We found total porosities ranging from ～10 to 20% within these chondrites, and with μCT we show that up to 64% of the void space is located within intergranular voids within the rock. Given the low (S1‐S2) shock stages of the samples and the large voids between mineral grains, we conclude that these samples experienced unusually low amounts of compaction and shock loading throughout their entire post accretionary history. With Fe metal and FeS metal abundances and grain size distributions, we show that these chondrites formed naturally with greater than average porosities prior to parent body metamorphism. These materials were not “fluffed” on their parent body by impact‐related regolith gardening or events caused by seismic vibrations. Samples of all three chemical types of ordinary chondrites (LL, L, H) are represented in this study and we conclude that incomplete compaction is common within the asteroid belt.     

Small‐scale experimental simulation of talus evolution

We investigated a small‐scale laboratory model of a talus slope evolution. Five different size classes of basaltic rock were selected and marked with different colours. Homogenized mixtures of grains of different sizes were dropped from a fixed height onto a tilted experimental board covered with a loose granular layer. This was conducted in a series of regular sequences, and the resulting distribution on the board was studied after each sequence. At the beginning of the experiment, the grains developed a longitudinal gradation similar to natural talus slopes, where small grains settle at the top while the large ones roll down to the distal part. However, after a transient period dominated by single‐particle dynamics on the inert granular medium, the evolution proved to be more variable than expected. Due to the continuous shower of falling grains, the shear stress at the bottom of the upper granular layer increased. This resulted initially in a slow creep down slope that finally collapsed in large avalanches homogenizing the material. The slides occurred at the boundary between a weaker layer created by migration of small grains through the interstices, and marked by a vertical transition between small and large grains. We compare the experimental findings with observations from natural talus slopes, and suggest that similar experiments may be helpful in understanding the evolution of taluses. Copyright © 2009 John Wiley & Sons, Ltd.     

Controls of Wellbore Flow Regimes on Pump Effluent Composition

Where well water and formation water are compositionally different or heterogeneous, pump effluent composition will vary due to partial mixing and transport induced by pumping. Investigating influences of purging and sampling methodology on composition variability requires quantification of wellbore flow regimes and mixing. As a basis for this quantification, analytical models simulating Poiseuille flow were developed to calculate flow paths and travel times. Finite element modeling was used to incorporate influences of mixing. Parabolic velocity distributions within the screened interval accelerate with cumulative inflow approaching the pump intake while an annulus of inflowing formation water contracts uniformly to displace an axial cylinder of pre‐pumping well water as pumping proceeds. Increased dispersive mixing forms a more diffuse formation water annulus and the contribution of formation water to pump effluent increases more rapidly. Models incorporating viscous flow and diffusion scale mixing show that initially pump effluent is predominantly pre‐pumping well water and compositions vary most rapidly. After two screen volumes of pumping, 94% of pump effluent is inflowing formation water. Where the composition of formation water and pre‐pumping well water are likely to be similar, pump effluent compositions will not vary significantly and may be collected during early purging or with passive sampling. However, where these compositions are expected to be considerably different or heterogeneous, compositions would be most variable during early pumping, that is, when samples are collected during low‐flow sampling. Purging of two screen volumes would be required to stabilize the content and collect a sample consisting of 94% formation water.