5,856 research outputs found
Aerial Search Optimization Model (ASOM) for UAVs in Special Operations
We construct an optimization model that assists commanders, operators, and planners to effectively deploy and employ unmanned aerial vehicles (UAVs) in special operations missions. Specifically, we consider situations where targets (e.g., insurgents) operate in a region of interest and a small special operations team is assigned to search and detect these targets. The special operations team is equipped with short-range surveillance UAVs. We combine intelligence regarding the targets with availability and capability of UAVs in an integer linear programming model. The goal is to detect the largest possible number of targets with the given resources. The model prescribes optimal deployment locations for the ground units and optimal time-phased search areas for the UAVs. The model has been implemented successfully in four field experiments. Preliminary empirical evidence indicates that the model provides 50% increase in detection opportunities compared with a plan manually generated by experienced commanders
Hydrodynamic and magnetohydrodynamic computations inside a rotating sphere
Numerical solutions of the incompressible magnetohydrodynamic (MHD) equations
are reported for the interior of a rotating, perfectly-conducting, rigid
spherical shell that is insulator-coated on the inside. A previously-reported
spectral method is used which relies on a Galerkin expansion in
Chandrasekhar-Kendall vector eigenfunctions of the curl. The new ingredient in
this set of computations is the rigid rotation of the sphere. After a few
purely hydrodynamic examples are sampled (spin down, Ekman pumping, inertial
waves), attention is focused on selective decay and the MHD dynamo problem. In
dynamo runs, prescribed mechanical forcing excites a persistent velocity field,
usually turbulent at modest Reynolds numbers, which in turn amplifies a small
seed magnetic field that is introduced. A wide variety of dynamo activity is
observed, all at unit magnetic Prandtl number. The code lacks the resolution to
probe high Reynolds numbers, but nevertheless interesting dynamo regimes turn
out to be plentiful in those parts of parameter space in which the code is
accurate. The key control parameters seem to be mechanical and magnetic
Reynolds numbers, the Rossby and Ekman numbers (which in our computations are
varied mostly by varying the rate of rotation of the sphere) and the amount of
mechanical helicity injected. Magnetic energy levels and magnetic dipole
behavior are exhibited which fluctuate strongly on a time scale of a few eddy
turnover times. These seem to stabilize as the rotation rate is increased until
the limit of the code resolution is reached.Comment: 26 pages, 17 figures, submitted to New Journal of Physic
Reading Videogames as (authorless) Literature
This article presents the outcomes of research, funded by the Arts and Humanities Research Council in England and informed by work in the fields of new literacy research, gaming studies and the socio-cultural framing of education, for which the videogame L.A. Noire (Rockstar Games, 2011) was studied within the orthodox framing of the English Literature curriculum at A Level (pre-University) and Undergraduate (degree level). There is a plethora of published research into the kinds of literacy practices evident in videogame play, virtual world engagement and related forms of digital reading and writing (Gee, 2003; Juul, 2005; Merchant, Gillen, Marsh and Davies, 2012; Apperley and Walsh, 2012; Bazalgette and Buckingham, 2012) as well as the implications of such for home / school learning (Dowdall, 2006; Jenkins, 2006; Potter, 2012) and for teachers’ own digital lives (Graham, 2012). Such studies have tended to focus on younger children and this research is also distinct from such work in the field in its exploration of the potential for certain kinds of videogame to be understood as 'digital transformations' of conventional ‘schooled’ literature. The outcomes of this project raise implications of such a conception for a further implementation of a ‘reframed’ literacy (Marsh, 2007) within the contemporary curriculum of a traditional and conservative ‘subject’. A mixed methods approach was adopted. Firstly, students contributing to a gamplay blog requiring them to discuss their in-game experience through the ‘language game’ of English Literature, culminating in answering a question constructed with the idioms of the subject’s set text ‘final examination’. Secondly, students taught their teachers to play L.A. Noire, with free choice over the context for this collaboration. Thirdly, participants returned to traditional roles in order to work through a set of study materials provided, designed to reproduce the conventions of the ‘study guide’ for literature education. Interviews were conducted after each phase and the outcomes informed a redrafting of the study materials which are now available online for teachers – this being the ‘practical’ outcome of the research (Berger and McDougall, 2012). In the act of inserting the study of L.A. Noire into the English Literature curriculum as currently framed, this research moves, through a practical ‘implementation’ beyond longstanding debates around narratology and ludology (Frasca, 2003; Juul, 2005) in the field of game studies (Leaning, 2012) through a direct connection to new literacy studies and raises epistemological questions about ‘subject identity’, informed by Bernstein (1996) and Bourdieu (1986) and the implications for digital transformations of texts for both ideas about cultural value in schooled literacy (Kendall and McDougall, 2011) and the politics of ‘expertise’ in pedagogic relations (Ranciere, 2009, Bennett, Kendall and McDougall, 2012a)
The LKB1-salt-inducible kinase pathway functions as a key gluconeogenic suppressor in the liver
LKB1 is a master kinase that regulates metabolism and growth through adenosine monophosphate-activated protein kinase (AMPK) and 12 other closely related kinases. Liver-specific ablation of LKB1 causes increased glucose production in hepatocytes in vitro and hyperglycaemia in fasting mice in vivo. Here we report that the salt-inducible kinases (SIK1, 2 and 3), members of the AMPK-related kinase family, play a key role as gluconeogenic suppressors downstream of LKB1 in the liver. The selective SIK inhibitor HG-9-91-01 promotes dephosphorylation of transcriptional co-activators CRTC2/3 resulting in enhanced gluconeogenic gene expression and glucose production in hepatocytes, an effect that is abolished when an HG-9-91-01-insensitive mutant SIK is introduced or LKB1 is ablated. Although SIK2 was proposed as a key regulator of insulin-mediated suppression of gluconeogenesis, we provide genetic evidence that liver-specific ablation of SIK2 alone has no effect on gluconeogenesis and insulin does not modulate SIK2 phosphorylation or activity. Collectively, we demonstrate that the LKB1-SIK pathway functions as a key gluconeogenic gatekeeper in the liver
The Role of the Environment in Chaotic Quantum Dynamics
We study how the interaction with an external incoherent environment induces
a crossover from quantum to classical behavior for a particle whose classical
motion is chaotic. Posing the problem in the semiclassical regime, we find that
noise produced by the bath coupling rather than dissipation is primarily
responsible for the dephasing that results in the ``classicalization'' of the
particle. We find that the bath directly alters the phase space structures that
signal the onset of classical chaos. This dephasing is shown to have a
semiclassical interpretation: the noise renders the interfering paths
indistinguishable and therefore incoherent. The noise is also shown to
contribute to the quantum inhibition of mixing by creating new paths that
interfere coherently.Comment: 10 pages RevTex. Three figures in Postscript as a uuencoded
compressed tar file have been submitted as wel
Electronic structure and the minimum conductance of a graphene layer on SiO2 from density-functional methods.
The effect of the SiO substrate on a graphene film is investigated using
realistic but computationally convenient energy-optimized models of the
substrate supporting a layer of graphene. The electronic bands are calculated
using density-functional methods for several model substrates. This provides an
estimate of the substrate-charge effects on the behaviour of the bands near
, as well as a variation of the equilibrium distance of the graphene
sheet. A model of a wavy graphene layer is examined as a possible candidate for
understanding the nature of the minimally conducting states in graphene.Comment: 6 pages, 5 figure
Ab initio optical properties of Si(100)
We compute the linear optical properties of different reconstructions of the
clean and hydrogenated Si(100) surface within DFT-LDA, using norm-conserving
pseudopotentials. The equilibrium atomic geometries of the surfaces, determined
from self-consistent total energy calculations within the Car-Parrinello
scheme, strongly influence Reflectance Anisotropy Spectra (RAS), showing
differences between the p(2x2) and c(4x2)reconstructions. The Differential
Reflectivity spectrum for the c(4x2) reconstruction shows a positive peak at
energies < 1 eV, in agreement with experimental results.Comment: fig. 2 correcte
Origin of volatiles in the Main Belt
We propose a scenario for the formation of the Main Belt in which asteroids
incorporated icy particles formed in the outer Solar Nebula. We calculate the
composition of icy planetesimals formed beyond a heliocentric distance of 5 AU
in the nebula by assuming that the abundances of all elements, in particular
that of oxygen, are solar. As a result, we show that ices formed in the outer
Solar Nebula are composed of a mix of clathrate hydrates, hydrates formed above
50 K and pure condensates produced at lower temperatures. We then consider the
inward migration of solids initially produced in the outer Solar Nebula and
show that a significant fraction may have drifted to the current position of
the Main Belt without encountering temperature and pressure conditions high
enough to vaporize the ices they contain. We propose that, through the
detection and identification of initially buried ices revealed by recent
impacts on the surfaces of asteroids, it could be possible to infer the
thermodynamic conditions that were present within the Solar Nebula during the
accretion of these bodies, and during the inward migration of icy
planetesimals. We also investigate the potential influence that the
incorporation of ices in asteroids may have on their porosities and densities.
In particular, we show how the presence of ices reduces the value of the bulk
density of a given body, and consequently modifies its macro-porosity from that
which would be expected from a given taxonomic type.Comment: Accepted for publication in MNRA
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