THE USE OF PASSIVE DRAG TO INTERPRET VARIATION IN ACTIVE DRAG MEASUREMENTS

This study investigated if a measure of mean passive drag could explain the huge differences in propulsive force required by different swimmers to swim at a similar high velocity. Nineteen elite male and female national freestyle swimmers were subjects. The subject’s mean active and passive drag was measured at each swimmer’s top swimming pace. Stepwise regression analysis was used in the analysis. Passive drag was accepted into the equation to calculate mean propulsive force, prior to velocity being rejected. The correlation coefficient for the relationship between mean propelling force and mean passive drag was 0.77. This was statistically significant at the

Sorting Out Abrasion in a Gypsum Dune Field

Grain size distributions in eolian settings are the result of both sorting and abrasion of grains by saltation. The two are tightly coupled because mobility of particles determines abrasion rate, while abrasion affects the mobility of particles by changing their mass and shape; few field studies have examined this quantitatively. We measured grain size and shape over a 9 km transect downwind of a line sediment source at White Sands National Monument, a gypsum dune field. The sediment source is composed of rodlike (elongate), coarse particles whose shapes appear to reflect the crystalline structure of gypsum. Dispersion in grain size decreases rapidly from the source. Coarse particles gradually become less elongate, while an enrichment of smaller, more elongate grains is observed along the transect. Transport calculations confirm that White Sands is a threshold sand sea in which (1) the predominant particle diameter reflects grains transported in saltation under the dune-forming wind velocity and (2) smaller, elongate grains move in suspension under this dominant wind. Size-selective transport explains first-order trends in grain size; however, abrasion changes the shape of saltating grains and produces elongate, smaller grains that are spallation and breaking products of larger particles. Both shape and size changes saturate 5–6 km downwind of the source. As large particles become more equant, abrasion rates slow down because protruding regions have been removed. Such asymptotic behavior of shape and abrasion rate has been observed in theory and experiment and is likely a generic result of the abrasion process in any environment

Comparison of Methods of Producing Slaughter Weight Steers Using Maximum Quantities of Forage and Minimum Quantities of Grain

The objectives of this study were to compare performance and slaughter characteristics of various production systems by which slaughter steers can be produced in the high desert rangeland of eastern Oregon, which is very similar to the semi-arid rangelands of western South Dakota. Economic analysis and taste panel evaluations are also included

Monsoon-driven biogeochemical processes in the Arabian Sea

Although it is nominally a tropical locale, the semiannual wind reversals associated with the Monsoon system of the Arabian Sea result annually in two distinct periods of elevated biological activity. While in both cases monsoonal forcing drives surface layer nutrient enrichment that supports increased rates of primary productivity, fundamentally different entrainment mechanisms are operating in summer (Southwest) and winter (Northeast) Monsoons. Moreover, the intervening intermonsoon periods, during which the region relaxes toward oligotrophic conditions more typical of tropical environments, provide a stark contrast to the dynamic biogeochemical activity of the monsoons. The resulting spatial and temporal variability is great and provides a significant challenge for ship-based surveys attempting to characterize the physical and biogeochemical environments of the region. This was especially true for expeditions in the pre-satellite era. Here, we present an overview of the dynamical response to seasonal monsoonal forcing and the characteristics of the physical environment that fundamentally drive regional biogeochemical variability. We then review past observations of the biological distributions that provided our initial insights into the pelagic system of the Arabian Sea. These evolved through the 1980s as additional methodologies, in particular the first synoptic ocean color distributions gathered by the Coastal Zone Color Scanner, became available. Through analyses of these observations and the first largescale physical–biogeochemical modeling attempts, a pre-JGOFS understanding of the Arabian Sea emerged. During the 1990s, the in situ and remotely sensed observational databases were significantly extended by regional JGOFS activities and the onset of Sea-viewing Wide Field-of-View Sensor ocean color measurements. Analyses of these new data and coupled physical–biogeochemical models have already advanced our understanding and have led to either an amplification or revision of the pre-JGOFS paradigms. Our understanding of this complex and variable ocean region is still evolving. Nonetheless, we have a much better understanding of time–space variability of biogeochemical properties in the Arabian Sea and much deeper insights about the physical and biological factors that drive them, as well as a number of challenging new directions to pursue

Understanding co-polymerization in amyloid formation by direct observation of mixed oligomers

Although amyloid assembly in vitro is commonly investigated using single protein sequences, fibril formation in vivo can be more heterogeneous, involving co-assembly of proteins of different length, sequence and/or post-translational modifications. Emerging evidence suggests that co-polymerization can alter the rate and/or mechanism of aggregation and can contribute to pathogenicity. Electrospray ionization-ion mobility spectrometry-mass spectrometry (ESI-IMS-MS) is uniquely suited to the study of these heterogeneous ensembles. Here, ESI-IMS-MS combined with analysis of fibrillation rates using thioflavin T (ThT) fluorescence, is used to track the course of aggregation of variants of islet-amyloid polypeptide (IAPP) in isolation and in pairwise mixtures. We identify a sub-population of extended monomers as the key precursors of amyloid assembly, and reveal that the fastest aggregating sequence in peptide mixtures determines the lag time of fibrillation, despite being unable to cross-seed polymerization. The results demonstrate that co-polymerization of IAPP sequences radically alters the rate of amyloid assembly by altering the conformational properties of the mixed oligomers that form

Must naive realists be relationalists?

Relationalism maintains that perceptual experience involves, as part of its nature, a distinctive kind of conscious perceptual relation between a subject of experience and an object of experience. Together with the claim that perceptual experience is presentational, relationalism is widely believed to be a core aspect of the naive realist outlook on perception. This is a mistake. I argue that naive realism about perception can be upheld without a commitment to relationalism

Barchan-Parabolic Dune Pattern Transition From Vegetation Stability Threshold

Many dune fields exhibit a downwind transition from forward-pointing barchan dunes to stabilized, backward-pointing parabolic dunes, accompanied by an increase in vegetation. A recent model predicts this pattern transition occurs when dune surface erosion/deposition rates decrease below a threshold of half the vegetation growth rate. We provide a direct test using a unique data set of repeat topographic surveys across White Sands Dune Field and find strong quantitative support for the model threshold. We also show the threshold hypothesis applied to a barchan dune results naturally in its curvature inversion, as the point of threshold crossing progresses from the horns to the crest. This simple, general threshold framework can be an extremely useful tool for predicting the response of dune landscapes to changes in wind speed, sediment supply, or vegetation growth rate. Near the threshold, a small environmental change could result in a drastic change in dune pattern and activity

Expression of GP73, A Resident Golgi Membrane Protein, in Viral and Nonviral Liver Disease

GP73 is a novel type II Golgi membrane protein of unknown function that is expressed in the hepatocytes of patients with adult giant-cell hepatitis (Gene 2000;249:53-65). Its expression pattern in human liver disease and the regulation of its expression in hepatocytes have not been systematically studied. The aims of the present study were to compare GP73 protein levels in viral and nonviral human liver disease and in normal livers, to identify its cellular sources, and to study the regulation of its expression in hepatoma cells in vitro. GP73 protein levels were quantitated in explant livers of patients with well-defined disease etiologies and compared with the levels in normal donor livers. GP73-expressing cells were identified immunohistochemically. GP73 expression in vitro was studied by Western blotting and immunofluorescence microscopy in HepG2 and SK-Hep-1 cells and in the HepG2-derived, hepatitis B virus (HBV)-transfected HepG2215 and HepG2T14.1 cell lines. Whole organ levels of GP73 were low in normal livers. Significant increases were found in liver disease due to viral causes (HBV, HCV) or nonviral causes (alcohol-induced liver disease, autoimmune hepatitis). In normal livers, GP73 was constitutively expressed by biliary epithelial cells but not by hepatocytes. Hepatocyte expression of GP73 was dramatically up-regulated in diseased livers, regardless of the etiology, whereas biliary epithelial cell expression did not change appreciably. GP73 was present at high levels in HepG2215 cells (a cell line that supports active HBV replication), but was absent in HepG2T14.1 cells (an HBV-transfected cell line that does not support HBV replication) and in HBV-free HepG2 cells. In SK-Hep-1 cells, GP73 expression was increased in response to interferon gamma (IFN-y), and inhibited by tumor necrosis factor x (TNF-x). In conclusion, increased expression of GP73 in hepatocytes appears to be a general feature of advanced liver disease, and may be regulated via distinct pathways that involve hepatotropic viruses or cytokines

Overview of the Aeroelastic Prediction Workshop

The Aeroelastic Prediction Workshop brought together an international community of computational fluid dynamicists as a step in defining the state of the art in computational aeroelasticity. This workshop's technical focus was prediction of unsteady pressure distributions resulting from forced motion, benchmarking the results first using unforced system data. The most challenging aspects of the physics were identified as capturing oscillatory shock behavior, dynamic shock-induced separated flow and tunnel wall boundary layer influences. The majority of the participants used unsteady Reynolds-averaged Navier Stokes codes. These codes were exercised at transonic Mach numbers for three configurations and comparisons were made with existing experimental data. Substantial variations were observed among the computational solutions as well as differences relative to the experimental data. Contributing issues to these differences include wall effects and wall modeling, non-standardized convergence criteria, inclusion of static aeroelastic deflection, methodology for oscillatory solutions, post-processing methods. Contributing issues pertaining principally to the experimental data sets include the position of the model relative to the tunnel wall, splitter plate size, wind tunnel expansion slot configuration, spacing and location of pressure instrumentation, and data processing methods