Parallel plate model for trabecular bone exhibits volume fraction-dependent bias

Unbiased stereological methods were used in conjunction with microcomputed tomographic (micro-CT) scans of human and animal bone to investigate errors created when the parallel plate model was used to calculate morphometric parameters. Bone samples were obtained from the human proximal tibia, canine distal femur, rat tail, and pig spine and scanned in a micro-CT scanner. Trabecular thickness, trabecular spacing, and trabecular number were calculated using the parallel plate model. Direct thickness, and spacing and connectivity density were calculated using unbiased three-dimensional methods. Both thickness and spacing calculated using the plate model were well correlated to the direct three-dimensional measures (r(2) = 0. 77-0.92). The correlation between trabecular number and connectivity density varied greatly (r(2) = 0.41-0.94). Whereas trabecular thickness was consistently underestimated using the plate model, trabecular spacing was underestimated at low volume fractions and overestimated at high volume fractions. Use of the plate model resulted in a volume-dependent bias in measures of thickness and spacing (p < 0.001). This was a result of the fact that samples of low volume fraction were much more "rod-like" than those of the higher volume fraction. Our findings indicate that the plate model provides biased results, especially when populations with different volume fractions are compared. Therefore, we recommend direct thickness measures when three-dimensional data sets are available

Responses of Southern Ocean seafloor habitats and communities to global and local drivers of change

Knowledge of life on the Southern Ocean seafloor has substantially grown since the beginning of this century with increasing ship-based surveys and regular monitoring sites, new technologies and greatly enhanced data sharing. However, seafloor habitats and their communities exhibit high spatial variability and heterogeneity that challenges the way in which we assess the state of the Southern Ocean benthos on larger scales. The Antarctic shelf is rich in diversity compared with deeper water areas, important for storing carbon (“blue carbon”) and provides habitat for commercial fish species. In this paper, we focus on the seafloor habitats of the Antarctic shelf, which are vulnerable to drivers of change including increasing ocean temperatures, iceberg scour, sea ice melt, ocean acidification, fishing pressures, pollution and non-indigenous species. Some of the most vulnerable areas include the West Antarctic Peninsula, which is experiencing rapid regional warming and increased iceberg-scouring, subantarctic islands and tourist destinations where human activities and environmental conditions increase the potential for the establishment of non-indigenous species and active fishing areas around South Georgia, Heard and MacDonald Islands. Vulnerable species include those in areas of regional warming with low thermal tolerance, calcifying species susceptible to increasing ocean acidity as well as slow-growing habitat-forming species that can be damaged by fishing gears e.g., sponges, bryozoan, and coral species. Management regimes can protect seafloor habitats and key species from fishing activities; some areas will need more protection than others, accounting for specific traits that make species vulnerable, slow growing and long-lived species, restricted locations with optimum physiological conditions and available food, and restricted distributions of rare species. Ecosystem-based management practices and long-term, highly protected areas may be the most effective tools in the preservation of vulnerable seafloor habitats. Here, we focus on outlining seafloor responses to drivers of change observed to date and projections for the future. We discuss the need for action to preserve seafloor habitats under climate change, fishing pressures and other anthropogenic impacts

Hedonism and the experience machine

Money isn’t everything, so what is? Many government leaders, social policy theorists, and members of the general public have a ready answer: happiness. This paper examines an opposing view due to Robert Nozick, which centres on his experience-machine thought experiment. Despite the example's influence among philosophers, the argument behind it is riddled with difficulties. Dropping the example allows us to re-version Nozick's argument in a way that makes it far more forceful - and less dependent on people's often divergent intutions about the experience machine

A Geophysical and Geological Investigation of Potentially Favorable Areas for Petroleum Exploration in Southeastern Arizona

The objective of this study has been to determine areas potentially favorable for oil and gas exploration in southeastern Arizona. Surface geological investigations in the mountain ranges indicate that a thick sequence of marine sedimentary Paleozoic and Mesozoic (Cretaceous) rocks was deposited in the Pedregosa basin in southeastern Cochise County and adjacent shelf areas. According to Wengerd (1962), Kottlowski (1971), Greenwood (1969), and Greenwood and Kottlowski {1974), these marine strata deposited in this basin are similar in many aspects to those in petroleum-productive areas in southeast New Mexico and west Texas. They contain organic-rich basin facies of rocks that were probable sources for oil and gas. The margins of the Pedregosa basin offer structural, stratigraphic, unconformity, and paleogeomorphic traps. However, such adverse factors as the wide thickness variance of Cenozoic valley fill (100 feet or less to almost 12,000 feet), very little information as to the absence or presence of potentially petroleum-productive undeformed Paleozoic and Mesozoic rocks beneath Cenozoic rocks in the valleys, and extensive evidence in the mountains that the area has had an extremely complex geologic history, have discouraged exploration in the past.Originally published in 1974 as OGCC Report of Investigation RI-3.Documents in the AZGS Document Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]

A Study of Regional Geophysical Data in the Holbrook Area, Arizona

An analysis of the available geophysical data in the Holbrook basin area of north central Arizona in Coconino, Navajo and Apache Counties has been made. This study has been supported by a contract with the Arizona Oil and Gas Conservation Commission, John Bannister, executive secretary, and the Four Corners Regional Commission. The primary objectives of the analysis were to determine: (1) thicknesses and lithology of sedimentary column overlying Precambrian basement; (2) structural configuration of basement surface, faults in basement and sedimentary rocks; and (3) anomalous conditions within the sedimentary rocks potentially favorable for entrapment of hydrocarbons.Originally published as OGCC Report of Investigation RI-2 in 1972Documents in the AZGS Document Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]

Residual Aeromagnetic Map of Arizona

Residual magnetic intensity values are given in gammas. The original total field data were corrected for diurnal variation as observed at the Tucson Magnetic Observatory during the flight period.Published online courtesy of the University of Arizona Geophysical Society.Documents in the AZGS Document Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]