Surface chemistry of new lubrication systems for high-speed spacecraft bearings

Multialkylated cyclopentane (MAC) and silahydrocarbon (SiHC) are primary candidates for future spacecraft applications due to their high viscosity and good viscosity–temperature profile, low vapor pressure and good lubricating properties. In this work, the friction, wear and associated tribochemistry of these fluids, both unformulated and formulated with 2% aryl phosphate ester (TPP), were investigated. A Plint reciprocating wear rig equipped with an environmental chamber that was filled with dry air or nitrogen was used to produce boundary lubrication conditions. The resulting specimens were examined by X-ray absorption near-edge structure (XANES) spectroscopy in order to gain some understanding of how the base fluid and additive function. Several relationships were discovered among friction, wear and tribochemistry within the wear scar. First, the wear rate in both unformulated and formulated fluids was higher in a dry nitrogen environment than in dry air. Second, when tested in air, unformulated silahydrocarbon acts as its own antiwear additive by decomposing to a silicon oxide glass within the wear track thereby eliminating additive issues such as solubility, evaporation and concentration effects. Third, the antiwear properties of silahydrocarbon oil are hindered by the presence of a phosphate additive. Both the oil and additive form an oxide glass within the wear track and compete for active growth sites. Fourth, the chain length of the polyphosphate glass formed in the wear track controls the antiwear performance of the film. The phosphate additive in multialkylated cyclopentane decomposed to a polyphosphate glass in both dry air to generate a good antiwear film (short to medium chain length polyphosphate) and nitrogen to form a poor antiwear film (long chain length polyphosphate). This revised version was published online in July 2006 with corrections to the Cover Date.     

Constructive Alignment of Interdisciplinary Graduate Curriculum in Engineering and Science: An Analysis of Successful IGERT Proposals

Background Interdisciplinary approaches are critical to solving the most pressing technological challenges. Despite the proliferation of graduate programs to fill this need, there is little archival literature identifying learning outcomes, learning experiences, or benchmarks for evaluating interdisciplinary graduate student learning. Purpose (Hypothesis ) The purpose of this study is to understand how engineering and science academics conceptualize interdisciplinary graduate education in order to identify common practices and recommend improvements. Questions generated by an instructional design framework guided the analysis: what desired outcomes, evidence, and learning experiences are currently associated with interdisciplinary graduate education? To what extent are these components constructively aligned with each other? Design /Method Content analysis was performed on 130 funded proposals from the U.S. National Science Foundation's Integrative Graduate Education and Research Traineeship (IGERT) program. Results Four desired student learning outcomes were identified: contributions to the technical area, broad perspective, teamwork, and interdisciplinary communication skills. Student requirements (educational plans) addressed these outcomes to some extent, but assessment/evidence sections generally targeted program level goals—as opposed to student learning. This lack of constructive alignment between components is a major weakness of graduate curriculum. Conclusions Current practices are promising. Further clarification of interdisciplinary learning outcomes, coupled with closer alignment of outcomes, evidence, and learning experiences will continue to improve interdisciplinary graduate education in engineering and science. Specific recommendations for engineering and science faculty members are: define clear learning objectives, enlist assessment/evaluation expertise, and constructively align all aspects of the curriculum.     

Time-resolved three-dimensional molecular tracking in live cells

We report a method for tracking individual quantum dot (QD) labeled proteins inside of live cells that uses four overlapping confocal volume elements and active feedback once every 5 ms to follow three-dimensional molecular motion. This method has substantial advantages over three-dimensional molecular tracking methods based upon charge-coupled device cameras, including increased Z-tracking range (10 μm demonstrated here), substantially lower excitation powers (15 μW used here), and the ability to perform time-resolved spectroscopy (such as fluorescence lifetime measurements or fluorescence correlation spectroscopy) on the molecules being tracked. In particular, we show for the first time fluorescence photon antibunching of individual QD labeled proteins in live cells and demonstrate the ability to track individual dye-labeled nucleotides (Cy5-dUTP) at biologically relevant transport rates. To demonstrate the power of these methods for exploring the spatiotemporal dynamics of live cells, we follow individual QD-labeled IgE-FcεRI receptors both on and inside rat mast cells. Trajectories of receptors on the plasma membrane reveal three-dimensional, nanoscale features of the cell surface topology. During later stages of the signal transduction cascade, clusters of QD labeled IgE-FcεRI were captured in the act of ligand-mediated endocytosis and tracked during rapid (~950 nm/s) vesicular transit through the cell.     

Transfer-matrix simulations of field emission from a metallic (5,5) carbon nanotube

We present three-dimensional simulations of field emission from an open (5,5) carbon nanotube without adsorption, by using a transfer-matrix methodology. By introducing pseudopotentials for the representation of carbon atoms and by repeating periodically a basic unit of the nanotube, band-structure effects are manifested in the distributions of energies. A representation of the band structure of the (5,5) nanotube is presented. The total-energy distributions of both the incident and field-emitted electrons contain peaks, which are related to discontinuities in the band structure or to standing waves in the carbon nanotube (a total length of 5.657 nm is considered). These peaks move to lower energies when the extraction field is increased. Such peaks should be observable in field-emission experiments.     

Quantitative noninvasive testing for Helicobacter pylori does not predict gastroduodenal ulcer disease

BACKGROUND: Helicobacter pylori is strongly associated with gastric and duodenal ulcer disease. However, the diagnosis of gastroduodenal ulcers requires an endoscopic or radiographic examination. In this study, we attempted to establish a relationship between the magnitude of [13C]urea breath test results or serum H. pylori IgG levels and endoscopic findings in H. pylori-infected individuals. METHODS: Patients who had undergone endoscopy and had a positive [13C]urea breath test and/or positive H. pylori IgG serology were identified. Endoscopic diagnoses included duodenal ulcer, gastric ulcer, nonulcer dyspepsia, and others. Results of 6% or greater on the [13C]urea breath test was defined as positive for H. pylori infection. H. pylori IgG serology was determined by an enzyme linked immunosorbent assay with values of greater than or equal to 1.0 being seropositive. RESULTS: One hundred seventy-five patients were seropositive (mean = 3.01 +/- 1.58). One hundred sixty-eight patients had a positive [13C]urea breath test (mean = 25.43 +/- 16.90). One hundred fifty-five patients were common to both the groups. Statistical analysis did not reveal any relationship between quantitative [13C]urea breath test results or H. pylori IgG values and endoscopic diagnoses. CONCLUSION: The magnitude of [13C]urea breath test or H. pylori IgG serology cannot be used to predict the presence or absence of gastroduodenal ulcer disease.     

Damage-Resistant SiC–AlN Layered Composites with Surface Compressive Stresses

Three-layer samples in the SiC-AlN system with outer layers richer in SiC, as well as monolithic samples of uniform composition, were fabricated by hot-pressing. The strain gage technique, previously described, was used to estimate residual compressive stress in the outer layers developed because of the difference in coefficients of thermal expansion between inner and outer layers. Bar-shaped samples were indented using a Vickers indenter under loads as high as 20 kg (196 N) on outer layers and were fractured in three-point bending. Three-layer samples with outer layers under compression exhibited increased resistance to the contact-induced damage in comparison to the monoclinic samples.     

Effect of standard and high dose ranitidine on [13C]urea breath test results

OBJECTIVE: It has been suggested that standard dose H2 blockers will affect the [14-C]urea breath test. The aim of this study was to evaluate the effect of standard and high dose ranitidine on the [13C]urea breath test in a prospective cross-over study. METHODS: Volunteers found to be positive for H. pylori by IgG serology and [13C]urea breath test were given either ranitidine 150 mg b.i.d. or 300 mg b.i.d. for 14 days. Repeat breath tests were completed on the last day of antisecretory dosing and study patients were immediately crossed over to the other ranitidine dose. The third breath test was performed at 14 days after initiation of the new dose. RESULTS: A total of 20 volunteers were enrolled. Using the established cut-off of 2.4% for the commercial breath test, only one patient developed negative results on H2 blockers. This patient had negative breath tests on both ranitidine doses and remained test-negative off all medications 6 wk after study completion, suggesting either a false positive baseline test or an unexpected bacterial eradication. No specific trend in breath test results was observed for the group (p=NS). On ranitidine 300 mg, six of 19 patients elevated their breath results from 23% to 112% (mean 76%) above baseline. CONCLUSION: Ranitidine at standard or high doses did not generate a reproducible decline in breath test results. Histamine 2 blockers do not need to be discontinued before urea breath testing.     

The role of strong syllables in segmentation for lexical access.

A model of speech segmentation in a stress language is proposed, according to which the occurrence of a strong syllable triggers segmentation of the speech signal, whereas occurrence of a weak syllable does not trigger segmentation. We report experiments in which listeners detected words embedded in nonsense bisyllables more slowly when the bisyllable had two strong syllables than when it had a strong and a weak syllable; mint was detected more slowly in mintayve than in mintesh. According to our proposed model, this result is an effect of segmentation: When the second syllable is strong, it is segmented from the first syllable, and successful detection of the embedded word therefore requires assembly of speech material across a segmentation position. Speech recognition models involving phonemic or syllabic recoding, or based on strictly left-to-right processes, do not predict this result. It is argued that segmentation at strong syllables in continuous speech recognition serves the purpose of detecting the most efficient locations at which to initiate lexical access. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sintering and Characterization of Polycrystalline Monoclinic, Tetragonal, and Cubic Zirconia

Polycrystalline monoclinic ( m ), tetragonal ( t ), and cubic ( c ) ZrO₂, sintered at 1500°C, were annealed in the cubic stability field and rapidly cooled to permit the displacive c → t ' transformation to occur in compositions containing 0–6 mol% Y₂O₃. The bulk fracture toughness of coarse-grained (> 25 μm) m , t ', and c zirconias were compared with conventionally sintered, fine-grained (typically less than 1 μm) materials. The ferroelastic monoclinic and tetragonal zirconias were more than twice as tough as paraelastic cubic zirconia.