2,121 research outputs found
Introduction to Focus Issue: Lagrangian Coherent Structures
The topic of Lagrangian coherent structures (LCS) has been a rapidly growing area of research in nonlinear dynamics for almost a decade. It provides a means to rigorously define and detect transport barriers in dynamical systems with arbitrary time dependence and has a wealth of applications, particularly to fluid flow problems. Here, we give a short introduction to the topic of LCS and review the new work presented in this Focus Issue
Excitation and resonant enhancement of axisymmetric internal wave modes
To date, axisymmetric internal wave fields, which have relevance to
atmospheric internal wave fields generated by storm cells and oceanic
near-inertial wave fields generated by surface storms, have been experimentally
realized using an oscillating sphere or torus as the source. Here, we use a
novel wave generator configuration capable of exciting axisymmetric internal
wave fields of arbitrary radial form to generate axisymmetric internal wave
modes. After establishing the theoretical background for axisymmetric mode
propagation, taking into account lateral and vertical confinement, and also
accounting for the effects of weak viscosity, we experimentally generate and
study modes of different order. We characterize the efficiency of the wave
generator through careful measurement of the wave amplitude based upon group
velocity arguments. This established, we investigate the ability of vertical
confinement to induce resonance, identifying a series of experimental resonant
peaks that agree well with theoretical predictions. In the vicinity of
resonance, the wave fields undergo a transition to non-linear behaviour that is
initiated on the central axis of the domain and proceeds to erode the wave
field throughout the domain.Comment: 15 pages, 9 figure
Signatures of multiple stellar populations in unresolved extragalactic globular/ young massive star clusters
We present an investigation of potential signatures of the formation of
multiple stellar populations in recently formed extragalactic star clusters.
All of the Galactic globular clusters for which good samples of individual
stellar abundances are available show evidence for multiple populations. This
appears to require that multiple episodes of star formation and light element
enrichment are the norm in the history of a globular cluster. We show that
there are detectable observational signatures of multiple formation events in
the unresolved spectra of massive, young extragalactic star clusters. We
present the results of a pilot program to search for one of the cleanest
signatures that we identify - the combined presence of emission lines from a
very recently formed population and absorption lines from a somewhat older
population. A possible example of such a system is identified in the Antennae
galaxies. This source's spectrum shows evidence of two stellar populations with
ages of 8 Myr and 80 Myr. Further investigation shows that these populations
are in fact physically separated, but only by a projected distance of 59 pc. We
show that the clusters are consistent with being bound and discuss the
possibility that their coalescence could result in a single globular cluster
hosting multiple stellar populations. While not the prototypical system
proposed by most theories of the formation of multiple populations in clusters,
the detection of this system in a small sample is both encouraging and
interesting. Our investigation suggests that expanded surveys of massive young
star clusters should detect more clusters with such signatures.Comment: 11 pages, 7 figures: accepted for publication in Ap
Limits on [OIII] 5007 emission from NGC4472's globular clusters: constraints on planetary nebulae and ultraluminous black hole X-ray binaries in globular clusters
We have searched for [OIII] 5007 emission in high resolution spectroscopic
data from Flames/Giraffe VLT observations of 174 massive globular clusters
(GCs) in NGC4472. No planetary nebulae (PNe) are observed in these clusters,
constraining the number of PNe per bolometric luminosity,
\alpha<0.8*10^{-7}PN/L_{\odot}. This is significantly lower than the rate
predicted from stellar evolution, if all stars produce PNe. Comparing our
results to populations of PNe in galaxies, we find most galaxies have a higher
\alpha than these GCs (more PNe per bolometric luminosity - though some massive
early-type galaxies do have similarly low \alpha). The low \alpha required in
these GCs suggests that the number of PNe per bolometric luminosity does not
increase strongly with decreasing mass or metallicity of the stellar
population. We find no evidence for correlations between the presence of known
GC PNe and either the presence of low mass X-ray binaries (LMXBs) or the
stellar interaction rates in the GCs. This, and the low \alpha observed,
suggests that the formation of PNe may not be enhanced in tight binary systems.
These data do identify one [OIII] emission feature, this is the (previously
published) broad [OIII] emission from the cluster RZ 2109. This emission is
thought to originate from the LMXB in this cluster, which is accreting at
super-Eddington rates. The absence of any similar [OIII] emission from the
other clusters favors the hypothesis that this source is a black hole LMXB,
rather than a neutron star LMXB with significant geometric beaming of its X-ray
emission.Comment: 10 pages, 3 figures, accepted for publication in Ap
Translation of lines of Euripides by Thomas Love Peacock
Translation by Thomas Love Peacock of the last five lines of Euripides\u27 Alcestis. An addendum by \u27R. Garnett\u27 (presumably Richard Garnett) notes this. A pencilled note on the verso suggests that the manuscript was given by Garnett to \u27J. Everson\u27 in 1902.https://scholarworks.umt.edu/whicker/1012/thumbnail.jp
A study of post-tenure review *policies among Nevada community colleges and the peer institutions of Ccsn
This study carries forward the research of post-tenure review in selected community colleges. Administrators, faculty leadership, and faculty from the four (4) community colleges in Nevada and the seven (7) peer institutions of the Community College of Southern Nevada (CCSN) participated in this research; A descriptive survey instrument was used that was formatted using Likert-type items. The participants were asked to rate the degree to which they agreed or disagreed with the 27 statements; Statements 1--15 were designed to reflect the participant perceptions on how their institutions post-tenure review procedures comported with the AAUP\u27s MINIMUM STANDARDS FOR GOOD PRACTICES IF A FORMAL SYSTEM OF POST TENURE REVIEW IS ESTABLISHED. Statements 16--20 were to provide information from the participant regarding their perceptions of post-tenure review. There were 45 completed instruments returned out of a possible 65 for a response rate of 69 percent; The statements relating to consistency with the AAUP standards found that generally participants felt the following components of their post-tenure review process fell short of consistency with AAUP standards: (1) Participants generally felt that their post-tenure review was only a reevaluation or revalidation of their tenure status. (2) There was a general feeling that the burden of proof was shifted from administration to the individual faculty members to show cause why he/she should be retained. (3) Only one half of the faculty participants felt there were tangible recognition of those faculty members who had actually demonstrated high or improved performance. (4) Generally, administrators felt they could mandate or impose a developmental program. (5) Only 43 percent of the faculty agreed that other possibilities such as mutually agreeable reassignment to other duties were an option to separation; It was clear from this research that generally there is support for post tenure review in a formative context rather than a summative one; Based on the results of this study and reflection on the implications of these findings, suggestions for a model for post-tenure review for CCSN was formulated and presented.*; *This dissertation is compound (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirements: Adobe Acrobat
Computational Analysis of T Cell Receptor Repertoire and Structure
The human adaptive immune system has evolved to provide a sophisticated response to a vast body of pathogenic microbes and toxic substances. The primary mediators of this response are T and B lymphocytes. Antigenic peptides presented at the surface of infected cells by major histocompatibility complex (MHC) molecules are recognised by T cell receptors (TCRs) with exceptional specificity. This specificity arises from the enormous diversity in TCR sequence and structure generated through an imprecise process of somatic gene recombination that takes place during T cell development. Quantification of the TCR repertoire through the analysis of data produced by high-throughput RNA sequencing allows for a characterisation of the immune response to disease over time and between patients, and the development of methods for diagnosis and therapeutic design. The latest version of the software package Decombinator extracts and quantifies the TCR repertoire with improved accuracy and compatibility with complementary experimental protocols and external computational tools. The software has been extended for analysis of fragmented short-read
data from single cells, comparing favourably with two alternative tools. The development of cell-based therapeutics and vaccines is incomplete without an understanding of molecular level interactions. The breadth of TCR diversity and cross-reactivity presents a barrier for comprehensive structural resolution of the repertoire by traditional means. Computational modelling of TCR structures and TCR-pMHC complexes provides an efficient alternative. Four generalpurpose protein-protein docking platforms were compared in their ability to accurately model TCR-pMHC complexes. Each platform was evaluated against an expanded benchmark of docking test cases and in the context of varying additional information about the binding interface.
Continual innovation in structural modelling techniques sets the stage for novel automated tools for TCR design. A prototype platform has been developed, integrating structural modelling and an optimisation routine, to engineer desirable features into TCR and TCR-pMHC complex models
Lagrangian Based Methods for Coherent Structure Detection
There has been a proliferation in the development of Lagrangian analytical methods for detecting coherent structures in fluid flow transport, yielding a variety of qualitatively different approaches. We present a review of four approaches and demonstrate the utility of these methods via their application to the same sample analytic model, the canonical double-gyre flow, highlighting the pros and cons of each approach. Two of the methods, the geometric and probabilistic approaches, are well established and require velocity field data over the time interval of interest to identify particularly important material lines and surfaces, and influential regions, respectively. The other two approaches, implementing tools from cluster and braid theory, seek coherent structures based on limited trajectory data, attempting to partition the flow transport into distinct regions. All four of these approaches share the common trait that they are objective methods, meaning that their results do not depend on the frame of reference used. For each method, we also present a number of example applications ranging from blood flow and chemical reactions to ocean and atmospheric flows. (C) 2015 AIP Publishing LLC.ONR N000141210665Center for Nonlinear Dynamic
Manuscript poem by Thomas Love Peacock
Manuscript poem by Thomas Love Peacock from a letter to Lord Broughton, November 13, 1862, on mourning paper. Cf. Nicholas A. Joukovsky, Letters of Thomas Love Peacock, v. 2, 1828-1866, Oxford: Clarendon Press, 2001. Letter no. 327.https://scholarworks.umt.edu/whicker/1011/thumbnail.jp
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