On Strong Pressure Waves in Cylinders

High power-density devices such as liquid rocket engines and gas turbine power plants often experience combustion instabilities, when the fluid flow ceases to be smooth and begins oscillating. These flow oscillations often have pressure oscillations with negative consequences. Much work has been done in recent years to extend the theories describing these combustion instabilities to cover high-amplitude waves, where the behavior ceases to be linear and energy cascades through the natural modes of the system. However, in cylindrical geometries, a tension exists between the usual model (that energy cascades through natural modes) and the observed phenomena (which usually contains integer harmonics of the primary frequency), as the natural frequencies of circular waves are not harmonics of each other. One old theory describes strong cylindrical waves, predicting that the natural mode shapes will change in the presence of strong nonlinearity. Several recent theories use an assumption that the natural modes do not change in strong waves, and that the nonlinear solution can be expressed in terms of these unchanged natural modes. All the theories shared a lack of strong, direct experimental validation for strong cylindrical waves. An experiment was located which exhibits the properties under consideration, and that experiment was modeled with four different theories. The theories successfully modeled the major behavior of the experiment, with varying degrees of quantitative agreement. Three of the theories did not make the assumption that the linear mode shapes do not change, and were used to evaluate the quality of that assumption. Further, the three theories that permitted it all showed a spatially-distributed, time-independent pressure shift: a DC offset with a radial dependence. This valley-shaped time-independent pressure feature was not found in the literature, though it would have important consequences to engine design and operation if it is real

Melanism as a potential thermal benefit in eastern fox squirrels (Sciurus niger)

Melanistic fox squirrels (Sciurus niger) have expanded westward and increased in frequency in the Omaha, Nebraska, and Council Bluffs, Iowa, metropolitan areas. The selective advantage of melanism is currently unknown, but thermal advantages have been hypothesized, especially in winter. No difference in metabolic response curves were measured between melanistic (black) and rufus (orange) fox squirrels. When exposed to sunny skies, both melanistic and rufus squirrels had higher surface (skin and fur) temperature as ambient temperatures increased. Melanistic squirrel surface temperatures did not differ when squirrels were exposed to sunny or cloudy skies. However, rufus individuals showed significantly lower increases in surface temperatures when under cloudy skies. During fall months, rufus individuals were about 1.5 times more active throughout the day than melanistic individuals. However, in winter, melanistic fox squirrels were approximately 30% more active in the mornings (before 13:00) compared to rufus squirrels. Pre-winter body condition was higher in melanistic (25.5 ± 1.8 g/cm) compared to rufus (20.30 ± 3.6 g/cm) fox squirrels; however, there were no significant differences between melanistic (22.8 ± 1.4 g/cm) and rufus (23.9 ± 0.8 g/cm) fox squirrel post-winter body condition. The results of this study indicate that melanistic fox squirrels may have a slight winter thermal advantage over rufus fox squirrels by maintaining higher skin temperatures

Spatial Models to Account for Variation in Observer Effort in Bird Atlases

To assess the importance of variation in observer effort between and within bird atlas projects and demonstrate the use of relatively simple conditional autoregressive (CAR) models for analyzing grid-based atlas data with varying effort. Pennsylvania and West Virginia, United States of America. We used varying proportions of randomly selected training data to assess whether variations in observer effort can be accounted for using CAR models and whether such models would still be useful for atlases with incomplete data. We then evaluated whether the application of these models influenced our assessment of distribution change between two atlas projects separated by twenty years (Pennsylvania), and tested our modeling methodology on a state bird atlas with incomplete coverage (West Virginia). Conditional Autoregressive models which included observer effort and landscape covariates were able to make robust predictions of species distributions in cases of sparse data coverage. Further, we found that CAR models without landscape covariates performed favorably. These models also account for variation in observer effort between atlas projects and can have a profound effect on the overall assessment of distribution change. Accounting for variation in observer effort in atlas projects is critically important. CAR models provide a useful modeling framework for accounting for variation in observer effort in bird atlas data because they are relatively simple to apply, and quick to run

Visualizing the Past: Tools and Techniques for Understanding Historical Processes

The University of Richmond requests a Level I Digital Humanities Start-Up grant to bring together experts for investigations about how to overcome limitations that prevent most humanities scholars from taking advantage of visualization techniques in their research. The grant will fund a two-day workshop where invited scholars will discuss current work on visualizing historical processes, and together consider: (1) How can we harness emerging cyber-infrastructure tools and interoperability standards to explore, visualize, and analyze spatial and temporal components of distributed digital archives to better understand historical events and processes? (2) How can user-friendly tools or web sites be created to allow scholars and researchers to animate spatial and temporal data housed on different systems across the Internet? The grant will also fund initial experiments toward creating new tools for overcoming obstacles to data visualization work. Results will be presented as a white paper

A Laboratory Investigation of Multiperson Rationality and Presentation Effects

This paper reports the results of laboratory experiments in which subjects were presented with different two-person decision problems in both their extensive and normal forms. All games generated the same equilibrium outcomes. Our results indicate that the presentation of the decision problem significantly affects the strategy chosen. Surprisingly, these presentation effects were most prominent in the simplest games where differences in presentation would seem most transparent. It appears that subjects are much more likely to use (and fear) incredible threats when the problem is presented as a one-stage rather than as a multistage game

Dynamical instabilities of Bose-Einstein condensates at the band-edge in one-dimensional optical lattices

We report on experiments that demonstrate dynamical instability in a Bose-Einstein condensate at the band-edge of a one-dimensional optical lattice. The instability manifests as rapid depletion of the condensate and conversion to a thermal cloud. We consider the collisional processes that can occur in such a system, and perform numerical modeling of the experiments using both a mean-field and beyond mean-field approach. We compare our numerical results to the experimental data, and find that the Gross-Pitaevskii equation is not able to describe this experiment. Our beyond mean-field approach, known as the truncated Wigner method, allows us to make quantitative predictions for the processes of parametric growth and thermalization that are observed in the laboratory, and we find good agreement with the experimental results.Comment: v2: Added several reference

Age-of-acquisition affects word naming in Italian only when stress is irregular.

In Italian, effects of age of acquisition (AoA) have been found in object naming, semantic categorization of words and lexical decision, but not in word naming (reading aloud). The lack of an AoA effect in Italian word naming is replicated in Experiment 1 which involved reading aloud two-syllable words which all have regular spelling-sound correspondences and regular stress patterns. Studies of English word naming have reported stronger effects of AoA for irregular or exception words than for words with regular, consistent spelling-sound correspondences. There are no grapheme-phoneme irregularities in Italian, but words containing three or more syllables can carry either regular stress on the penultimate syllable or irregular stress on the antepenultimate syllable. Experiment 2 found effects of AoA on reading three-syllable words for words with irregular stress. The results are interpreted in terms of the \u27mapping hypothesis\u27 of AoA, with effects arising as a result of a difficulty to generalize earlier-acquired patterns to irregular late-acquired words