The inviscid stability of supersonic flow past a sharp cone

The laminar boundary layer which forms on a sharp cone in a supersonic freestream, where lateral curvature plays a key role in the physics of the problem is considered. This flow is then analyzed from the point of view of linear, temporal, inviscid stability. The basic, non-axisymmetric disturbance equations are derived for general flows of this class, and a so called triply generalized inflexion condition is found for the existence of subsonic neutral modes of instability. This condition is analogous to the well-known generalized inflexion condition found in planar flows, although in the present case the condition depends on both axial and aximuthal wavenumbers. Extensive numerical results are presented for the stability problem at a freestream Mach number of 3.8, for a range of streamwise locations. These results reveal that a new mode of instability may occur, peculiar to flows of this type involving curvature. Additionally, asymptotic analyses valid close to the tip of the cone, far downstream of the cone are presented, and these give a partial (asymptotic) description of this additional mode of instability

Bibliographic Instruction: Two Models Converging in a Common Goal

Introduction This essay will explore research in the undergraduate curriculum by examining the divergent ways research is understood. The debate centers around the ways that the typical student perceives the role of the library in her education at the university. To limit the discussion to the relation between the student and the librarian misses the larger issue at stake. What needs does the average undergraduate have after completion of the B.A., if they have no plans to continue education further? Are research skills necessary only for the graduate student, or is there some truth to the humanistic notion of \u27knowledge for knowledge\u27s sake? There are three key sections to this essay; the first examines the perceived role of the academic library, in an overview fashion, from both the undergraduate and the casual reader of library literature. The second examines what I am calling the \u27BI\u27 (Bibliographic Instruction) model of research; what is usually taught in the one-shot 50 minute sessions about how to hunt down citations and navigate the OPAC and relevant databases. The last examines the \u27humanistic\u27 tradition which posits research as a democratizing tool needed for an effective citizenry. It is argued that the BI model is a tool necessary to have in our cognitive toolbox and the humanistic model is the mindset necessary to see the value in the tool. As an imperfect analogy, consider the frustrated high school freshman forced to learn algebra. Why do I have to learn this, he cries, I\u27ll never have to use the quadratic equation after I leave here! The role of the successful teacher is to show him why he will need the overall mathematical philosophy learned, even if the specific formula will never again surface. So it is with research--although the average student will never have to track citations down with ISI Web of Science, the skillset she learns will be tested and used even without her knowing it. Conclusion We must move out of packaging undergraduate research. Yes it is understood that it a goal we all adopt and that there is real disagreement over whose provenance it is, but this all misses the central point that we have conflated two different conceptions of what research actually is. To the average student, research means the ability to pull up resources her professor will accept as footnotes in an essay. For the educator and librarian, it means a lifelong tool that is the bedrock for civilization; it is the ability to critically assess all possible information sources for relevance and worth. This is of greater and greater import in this wired world, but the recognition of the import of the mission is in danger of being lost. Again, this is all lost if the students do not realize for themselves the benefit they stand to lose by not having this skill. Few undergraduates bother to consider the library as a place that offers classes, can help them with more than \u27the printer is out of toner,\u27 and more importantly can help them beyond this class and this assignment. How is this to be accomplished? Perhaps by recognizing (MacDonald et alia 2000) that we have to build for the future. The libraries have to take the research paradigm beyond the one-shot classes (while not discarding them, mind you) and actively involve the undergraduate, graduate, faculty, staff and community member. Borrow a page from the public library and have classes just for non-campus members, pop-up BI ads on the OPAC, posted signs on the walls and near the computers, hand out slingers as students check out books, take out advertisements in the student papers, mail handouts to student advisors. The list is endless, but so are the needs

Absolute linear instability in laminar and turbulent gas/liquid two-layer channel flow

We study two-phase stratified flow where the bottom layer is a thin laminar liquid and the upper layer is a fully-developed gas flow. The gas flow can be laminar or turbulent. To determine the boundary between convective and absolute instability, we use Orr--Sommerfeld stability theory, and a combination of linear modal analysis and ray analysis. For turbulent gas flow, and for the density ratio r=1000, we find large regions of parameter space that produce absolute instability. These parameter regimes involve viscosity ratios of direct relevance to oil/gas flows. If, instead, the gas layer is laminar, absolute instability persists for the density ratio r=1000, although the convective/absolute stability boundary occurs at a viscosity ratio that is an order of magnitude smaller than in the turbulent case. Two further unstable temporal modes exist in both the laminar and the turbulent cases, one of which can exclude absolute instability. We compare our results with an experimentally-determined flow-regime map, and discuss the potential application of the present method to non-linear analyses.Comment: 33 pages, 20 figure

Effects of the Burrowing Brittlestar, Microphiopholis gracillima (Echinodermata: Ophiuroidea), on the Flux of Lithium, an Inert Tracer, Across the Sediment-Water Interface

Burrowing and ventilation activities of infaunal organisms have been shown to affect geochemical processes in sediments and at the sediment-water interface. Although burrowing brittlestars are dominant in many benthic environments, their role in these processes is poorly known. We tested the effect of the amphiurid brittlestar, Microphiopholis gracillima, on the flux of lithium ion from the sediment to the overlying water by using sediment cores with false bottoms for continuous flow of a Li+1-seawater solution. Brittlestars at densities of 300 and 600 individuals m-2 caused a twofold increase in the rate that Li was transported through the sediment. Density of brittlestars appeared to have no effect on the flux of Li+1 from the sediment, indicating a possible threshold beyond which density increases do not influence fluxes of solute from the sediment

The efficacy of downhill running as a method to enhance running economy in trained distance runners

© 2018 European College of Sport Science Running downhill, in comparison to running on the flat, appears to involve an exaggerated stretch-shortening cycle (SSC) due to greater impact loads and higher vertical velocity on landing, whilst also incurring a lower metabolic cost. Therefore, downhill running could facilitate higher volumes of training at higher speeds whilst performing an exaggerated SSC, potentially inducing favourable adaptations in running mechanics and running economy (RE). This investigation assessed the efficacy of a supplementary 8-week programme of downhill running as a means of enhancing RE in well-trained distance runners. Nineteen athletes completed supplementary downhill (−5% gradient; n = 10) or flat (n = 9) run training twice a week for 8 weeks within their habitual training. Participants trained at a standardised intensity based on the velocity of lactate turnpoint (vLTP), with training volume increased incrementally between weeks. Changes in energy cost of running (E C ) and vLTP were assessed on both flat and downhill gradients, in addition to maximal oxygen uptake (⩒O 2max). No changes in E C were observed during flat running following downhill (1.22 ± 0.09 vs 1.20 ± 0.07 Kcal kg −1  km −1 , P = .41) or flat run training (1.21 ± 0.13 vs 1.19 ± 0.12 Kcal kg −1  km −1 ). Moreover, no changes in E C during downhill running were observed in either condition (P  >  .23). vLTP increased following both downhill (16.5 ± 0.7 vs 16.9 ± 0.6 km h −1 ,P = .05) and flat run training (16.9 ± 0.7 vs 17.2 ± 1.0 km h −1 , P = .05), though no differences in responses were observed between groups (P = .53). Therefore, a short programme of supplementary downhill run training does not appear to enhance RE in already well-trained individuals

Laboratory Method to Estimate Rain-Induced Splitting in Cultivated Blueberries

Preharvest rainfall that occurs when fruit are fully ripe or approaching full ripeness can result in detrimental fruit splitting in rabbiteye and southern highbush blueberries. This study was initiated to develop a laboratory method to model rain-related incidence of splitting in cultivated blueberries with the goal of predicting the incidence of splitting in blueberry cultivars and selections. Multiyear field surveys of rabbiteye and southern highbush cultivars show that the incidence of rain-related splitting is strongly cultivar-dependent. Laboratory values for forced splitting and naturally occurring rain-related field splitting data show a strong correlation indicating that the incidence of fruit splitting can be accurately estimated by this laboratory method. Soaking the berries in distilled water 14 h at room temperature gives a confident determination of splitting tendencies. Blueberry breeders and geneticists can use this method to evaluate new potential blueberry cultivars for splitting tendencies as part of routine screening. This would lead to a long-term goal of reducing splitting susceptible blueberry cultivars in commercial plantings

Excessive Daytime Sleepiness Is Associated with Changes in Salivary Inflammatory Genes Transcripts

Excessive daytime sleepiness (EDS) is a ubiquitous problem that affects public health and safety. A test that can reliably identify individuals that suffer from EDS is needed. In contrast to other methods, salivary biomarkers are an objective, inexpensive, and noninvasive method to identify individuals with inadequate sleep. Although we have previously shown that inflammatory genes are elevated in saliva samples taken from sleep deprived individuals, it is unclear if inflammatory genes will be elevated in clinical populations with EDS. In this study, salivary samples from individuals with sleep apnea were evaluated using the Taqman low density inflammation array. Transcript levels for 3 genes, including prostaglandin-endoperoxide synthase 2 (PTGS2), were elevated in patients with sleep apnea. Interestingly, PTGS2 was also elevated in patients with EDS but who did not have sleep apnea. These data demonstrate the feasibility of using salivary transcript levels to identify individuals that self-report excessive daytime sleepiness

Translation of a minigene in the 5′ leader sequence of the enterohaemorrhagic Escherichia coli LEE1 transcription unit affects expression of the neighbouring downstream gene

The 5′ end of the major RNA transcript of the LEE1 operon of enterohaemorrhagic Escherichia coli contains ~170 bases before the AUG translation start codon of the first recognized gene, ler. This unusually long leader sequence carries three potential alternative AUG start codons. Using a lac fusion expression vector, we confirmed that the ler gene AUG is functional for translation initiation, and we checked for translation initiation at the three alternative AUG codons. Whereas two of the alternative AUG codons appear incompetent for translation initiation, we detected strong initiation at the third AUG, which is followed by one AAA codon and a UAG stop codon. The location of this very short two-codon open reading frame with respect to the ler translation start appears to be critical. Hence mutations that destroy the UAG stop codon, or short deletions between the UAG stop codon and the ler translation initiation region, result in big effects on ler expression. In the context of the full-length LEE1 operon leader sequence, translation of this very short two-codon open reading frame is necessary for optimal expression of the ler gene and for the subsequent interactions of enterohaemorrhagic Escherichia coli with host target cells