1,630 research outputs found
Producing airpower : the rise and fall of neo-liberalism’s defence agenda
Neo-liberalism stands out as one of the most potent contemporary political philosophies. Neo-liberal governments re-fashioned states’ economies and neo-liberal ideas came to dominate international financial organizations. Perhaps nowhere are the challenges of translating neo-liberal theories into policy more apparent than in defence. The existing institutions and practices whereby states produce military power are often anathema to neo-liberal concepts of efficiency. Bureaucratic armed forces and national champion defence firms, within this context, clash with neo-liberalism’s ideological hostility to hierarchical-bureaucratic systems and belief that market mechanisms generate efficiency. Neo-liberal governments therefore developed policies for applying the philosophy’s economic formulae to defence. Two broad categories of reforms—enhancing inter-firm competition for contracts and outsourcing activities to the private sector—emerged as central to the neo-liberal defence agenda. Surprisingly, in light of neo-liberal policies’ adoption by militarily active states, no study has systematically examined these reforms’ content and impact. My article fills this lacuna by examining the state—the United Kingdom—that most consistently enacted neo-liberal defence reforms. To preview the conclusion, neo-liberalism did not prove the panacea that proponents espoused. This agenda’s internal logic nevertheless drove policymakers, from Prime Minister Margaret Thatcher’s regime (1979-90) onwards, to compensate for the negative externalities generated by one set of neo-liberal reforms by introducing further market mechanisms. Neo-liberal policies’ initially disappointing outcomes thus resulted in further neo-liberal reforms rather than a reassessment of the philosophy’s suitability to this domain. Nevertheless, each of the neo-liberal defence agenda’s two pillars suffered from internal contradictions that ultimately stymied their application.PostprintPeer reviewe
Magnetic-Island Contraction and Particle Acceleration in Simulated Eruptive Solar Flares
The mechanism that accelerates particles to the energies required to produce
the observed high-energy impulsive emission in solar flares is not well
understood. Drake et al. (2006) proposed a mechanism for accelerating electrons
in contracting magnetic islands formed by kinetic reconnection in multi-layered
current sheets. We apply these ideas to sunward-moving flux ropes (2.5D
magnetic islands) formed during fast reconnection in a simulated eruptive
flare. A simple analytic model is used to calculate the energy gain of
particles orbiting the field lines of the contracting magnetic islands in our
ultrahigh-resolution 2.5D numerical simulation. We find that the estimated
energy gains in a single island range up to a factor of five. This is higher
than that found by Drake et al. for islands in the terrestrial magnetosphere
and at the heliopause, due to strong plasma compression that occurs at the
flare current sheet. In order to increase their energy by two orders of
magnitude and plausibly account for the observed high-energy flare emission,
the electrons must visit multiple contracting islands. This mechanism should
produce sporadic emission because island formation is intermittent. Moreover, a
large number of particles could be accelerated in each
magnetohydrodynamic-scale island, which may explain the inferred rates of
energetic-electron production in flares. We conclude that island contraction in
the flare current sheet is a promising candidate for electron acceleration in
solar eruptions.Comment: Accepted for publication in The Astrophysical Journal (2016
Recovery of an initial temperature from discrete sampling
The problem of recovering the initial temperature of a body from discrete temperature measurements made at later times is studied. While this problem has a general formulation, the results of this paper are only given in the simplest setting of a finite (one-dimensional), constant coefficient, linear rod. It is shown that with a judicious placement of a thermometer on this rod, the initial temperature profile of the rod can be completely determined by later time measurements. The paper then studies the number of measurements that are needed to recover the initial profile to a prescribed accuracy and provides an optimal reconstruction algorithm under the assumption that the initial profile is in a Sobolev class
A model for straight and helical solar jets: II. Parametric study of the plasma beta
Jets are dynamic, impulsive, well-collimated plasma events that develop at
many different scales and in different layers of the solar atmosphere.
Jets are believed to be induced by magnetic reconnection, a process central
to many astrophysical phenomena. Within the solar atmosphere, jet-like events
develop in many different environments, e.g., in the vicinity of active regions
as well as in coronal holes, and at various scales, from small photospheric
spicules to large coronal jets. In all these events, signatures of helical
structure and/or twisting/rotating motions are regularly observed. The present
study aims to establish that a single model can generally reproduce the
observed properties of these jet-like events.
In this study, using our state-of-the-art numerical solver ARMS, we present a
parametric study of a numerical tridimensional magnetohydrodynamic (MHD) model
of solar jet-like events. Within the MHD paradigm, we study the impact of
varying the atmospheric plasma on the generation and properties of
solar-like jets.
The parametric study validates our model of jets for plasma ranging
from to , typical of the different layers and magnetic
environments of the solar atmosphere. Our model of jets can robustly explain
the generation of helical solar jet-like events at various . This
study introduces the new result that the plasma modifies the morphology
of the helical jet, explaining the different observed shapes of jets at
different scales and in different layers of the solar atmosphere.
Our results allow us to understand the energisation, triggering, and driving
processes of jet-like events. Our model allows us to make predictions of the
impulsiveness and energetics of jets as determined by the surrounding
environment, as well as the morphological properties of the resulting jets.Comment: Accepted in Astronomy and Astrophysic
Functionals of exponential Brownian motion and divided differences
We provide a surprising new application of classical approximation theory to a fundamental asset-pricing model of mathematical finance. Specifically, we calculate an analytic value for the correlation coefficient between
exponential Brownian motion and its time average, and we find the use of divided differences greatly elucidates formulae, providing a path to several new results. As applications, we find that this correlation coefficient is always at least 1/p2 and, via the Hermite–Genocchi integral relation, demonstrate that all moments of the time average are certain divided differences of the exponential function. We also prove that these moments agree with the somewhat more complex formulae obtained by Oshanin and Yor
- …