7,848 research outputs found
The Phoenix with an Eagleâs wings: an analysis of the Phoenix/Phung Hoang Programme, 1967-1975
The Phoenix/Phung Hoang Programme, a CIA-launched operation in South Vietnam lasting from 1967 to 1975, is a largely misunderstood topic, and no fully comprehensive account of its history has yet been produced. Through the use of primary and secondary source material, and by engaging with various historical and contemporary viewpoints, this thesis provides a contribution to the small yet diverse pool of scholarly debate surrounding the programme, paying particularly attention to disputes over effectiveness and ethical violations. To achieve this, Phoenix/Phung Hoangâs history is examined from inception to conclusion and placed within the context of the broader Vietnam War. Moreover, the goals and impact of key figures, such as Richard Nixon, Robert Komer and William E. Colby, will be discussed throughout the thesis.
This study aims to demonstrate that Phoenix/Phung Hoang developed into a highly effective counterinsurgency programme, yet ultimately failed following the conclusion of American participation in 1972/73. Contrary to the assertions of a number of scholars, the programme made great strides, and had by 1971 taken a heavy toll on the communist political apparatus in South Vietnam. Furthermore, this study challenges the view that Phoenix/Phung Hoang was exceedingly immoral, and contends that most accusations of torture, assassination, corruption and mass arrests were inaccurate or exaggerated. Close attention is paid to the programmeâs role within, and dependence on, the broader Vietnam War, primarily regarding its inability to function capably without American support, guidance, or personnel. Emphasis is placed on the role of a number of factors relating to the broader war in accelerating American disengagement from Phoenix/Phung Hoang, such as US anti-war demonstrations, Nixonâs efforts to attain a second term in office, and Vietnamisation. Additionally, this thesis explores parallels between the programmeâs failure in the political conflict, and the US/South Vietnamese failure in the military conflict as exemplified by the fall of Saigon. As will be seen, both failures were the result of the United Statesâ departure from Vietnam
Uncertainty Quantification for Airfoil Icing using Polynomial Chaos Expansions
The formation and accretion of ice on the leading edge of a wing can be
detrimental to airplane performance. Complicating this reality is the fact that
even a small amount of uncertainty in the shape of the accreted ice may result
in a large amount of uncertainty in aerodynamic performance metrics (e.g.,
stall angle of attack). The main focus of this work concerns using the
techniques of Polynomial Chaos Expansions (PCE) to quantify icing uncertainty
much more quickly than traditional methods (e.g., Monte Carlo). First, we
present a brief survey of the literature concerning the physics of wing icing,
with the intention of giving a certain amount of intuition for the physical
process. Next, we give a brief overview of the background theory of PCE.
Finally, we compare the results of Monte Carlo simulations to PCE-based
uncertainty quantification for several different airfoil icing scenarios. The
results are in good agreement and confirm that PCE methods are much more
efficient for the canonical airfoil icing uncertainty quantification problem
than Monte Carlo methods.Comment: Submitted and under review for the AIAA Journal of Aircraft and 2015
AIAA Conferenc
The V<sub>H</sub> gene repertoire of splenic B cells and somatic hypermutation in systemic lupus erythematosus
In systemic lupus erythematosus (SLE) it has been hypothesized that self-reactive B cells arise from virgin B cells that express low-affinity, nonpathogenic germline V genes that are cross-reactive for self and microbial antigens, which convert to high-affinity autoantibodies via somatic hypermutation. The aim of the present study was to determine whether the V<sub>H</sub> family repertoire and pattern of somatic hypermutation in germinal centre (GC) B cells deviates from normal in SLE. Rearranged immunoglobulin V<sub>H</sub> genes were cloned and sequenced from GCs of a SLE patient's spleen. From these data the GC V gene repertoire and the pattern of somatic mutation during the proliferation of B-cell clones were determined. The results highlighted a bias in V<sub>H</sub>5 gene family usage, previously unreported in SLE, and under-representation of the V<sub>H</sub>1 family, which is expressed in 20â30% of IgM+ B cells of healthy adults and confirmed a defect in negative selection. This is the first study of the splenic GC response in human SLE
Antiamoebic Properties of the Actinomycete Metabolites Echinomycin A and Tirandamycin A
Entamoeba histolytica infects 50 million people per year, causing 100,000 deaths worldwide. The primary treatment for amoebiasis is metronidazole. However, increased pathogen resistance combined with the drugâs toxic side effects encourages a search for alternative therapeutic agents. Secondary metabolites from marine bacteria are a promising resource for antiprotozoan drug discovery. In this study, extracts from a collection of marine-derived actinomycetes were screened for antiamoebic properties, and the activities of antibiotics echinomycin A and tirandamycin A are shown. Both antibiotics inhibited the in vitro growth of a E. histolytica laboratory strain (HM-1:IMSS) and a clinical isolate (Colombia, Col) at 30- to 60-ÎŒM concentrations. EIC50 (estimated inhibitory concentration) values were comparable for both antibiotics (44.3â46.3 ÎŒM) against the E. histolytica clinical isolate
Firewood, food and niche construction : the potential role of Mesolithic hunter-gatherers in actively structuring Scotland's woodlands.
Over the past few decades the potential role of Mesolithic hunterâgatherers in actively constructing their own niches, through the management of wild plants, has frequently been discussed. It is probable that Mesolithic hunterâgatherers systematically exploited specific woodland resources for food and fuel and influenced the ânaturalâ abundance or distribution of particular species within Mesolithic environments. Though there has been considerable discussion of the pollen evidence for potential small-scale human-woodland manipulation in Mesolithic Scotland, the archaeobotanical evidence for anthropogenic firewood and food selection has not been discussed in this context. This paper assesses the evidence for the active role of Mesolithic hunterâgatherer communities in systematically exploiting and managing woodlands for food and fuel in Scotland. While taphonomic factors may have impacted on the frequency of specific species in archaeobotanical assemblages, it is suggested that hunterâgatherers in Mesolithic Scotland were systematically using woodland plants, and in particular hazel and oak, for food and fuel. It is argued that the pollen evidence for woodland management is equivocal, but hints at the role of hunterâgatherers in shaping the structure of their environments, through the maintenance or creation of woodland clearings for settlement or as part of vegetation management strategies. It is proposed that Mesolithic hunterâgatherers may have actively contributed to niche construction and that the systematic use of hazel and oak as a fuel may reflect the deliberate pruning of hazel trees to increase nut-yields and the inadvertent â or perhaps deliberate â coppicing of hazel and oak during greenwood collection
State-space model identification and feedback control of unsteady aerodynamic forces
Unsteady aerodynamic models are necessary to accurately simulate forces and
develop feedback controllers for wings in agile motion; however, these models
are often high dimensional or incompatible with modern control techniques.
Recently, reduced-order unsteady aerodynamic models have been developed for a
pitching and plunging airfoil by linearizing the discretized Navier-Stokes
equation with lift-force output. In this work, we extend these reduced-order
models to include multiple inputs (pitch, plunge, and surge) and explicit
parameterization by the pitch-axis location, inspired by Theodorsen's model.
Next, we investigate the na\"{\i}ve application of system identification
techniques to input--output data and the resulting pitfalls, such as unstable
or inaccurate models. Finally, robust feedback controllers are constructed
based on these low-dimensional state-space models for simulations of a rigid
flat plate at Reynolds number 100. Various controllers are implemented for
models linearized at base angles of attack , and . The resulting control laws are
able to track an aggressive reference lift trajectory while attenuating sensor
noise and compensating for strong nonlinearities.Comment: 20 pages, 13 figure
Large-angle scattering and quasi-elastic barrier distributions
We study in detail the barrier distributions extracted from large-angle
quasi-elastic scattering of heavy ions at energies near the Coulomb barrier.
Using a closed-form expression for scattering from a single barrier, we compare
the quasi-elastic barrier distribution with the corresponding test function for
fusion. We examine the isocentrifugal approximation in coupled-channels
calculations of quasi-elastic scattering and find that for backward angles, it
works well, justifying the concept of a barrier distribution for scattering
processes. This method offers an interesting tool for investigating unstable
nuclei. We illustrate this for the Mg + Pb reaction, where the
quadrupole collectivity of the neutron-rich Mg remains to be clarified
experimentally.Comment: 26 pages, 10 eps figure
Lessons and Prospects from the pMSSM after LHC Run I: Neutralino LSP
We study SUSY signatures at the 7, 8 and 14 TeV LHC employing the
19-parameter, R-Parity conserving p(henomenological)MSSM, in the scenario with
a neutralino LSP. Our results were obtained via a fast Monte Carlo simulation
of the ATLAS SUSY analysis suite. The flexibility of this framework allows us
to study a wide variety of SUSY phenomena simultaneously and to probe for weak
spots in existing SUSY search analyses. We determine the ranges of the
sparticle masses that are either disfavored or allowed after the searches with
the 7 and 8 TeV data sets are combined. We find that natural SUSY models with
light squarks and gluinos remain viable. We extrapolate to 14 TeV with both 300
fb and 3 ab of integrated luminosity and determine the expected
sensitivity of the jets + MET and stop searches to the pMSSM parameter space.
We find that the high-luminosity LHC will be powerful in probing SUSY with
neutralino LSPs and can provide a more definitive statement on the existence of
natural Supersymmetry.Comment: 41 pages, 27 figures. arXiv admin note: substantial text overlap with
arXiv:1307.844
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