6,397 research outputs found
Artificial intelligence: opportunities and implications for the future of decision making
Artificial intelligence has arrived. In the online world it is already a part of everyday life, sitting invisibly behind a wide range of search engines and online commerce sites. It offers huge potential to enable more efficient and effective business and government but the use of artificial intelligence brings with it important questions about governance, accountability and ethics. Realising the full potential of artificial intelligence and avoiding possible adverse consequences requires societies to find satisfactory answers to these questions. This report sets out some possible approaches, and describes some of the ways government is already engaging with these issues
Black Hole Lightning from the Peculiar Gamma-Ray Loud Active Galactic Nucleus IC 310
The nearby active galaxy IC 310, located in the outskirts of the Perseus
cluster of galaxies is a bright and variable multi-wavelength emitter from the
radio regime up to very high gamma-ray energies above 100 GeV. Originally, the
nucleus of IC 310 has been classified as a radio galaxy. However, studies of
the multi-wavelength emission showed several properties similarly to those
found from blazars as well as radio galaxies. In late 2012, we have organized
the first contemporaneous multi-wavelength campaign including radio, optical,
X-ray and gamma-ray instruments. During this campaign an exceptionally bright
flare of IC 310 was detected with the MAGIC telescopes in November 2012
reaching an averaged flux level in the night of up to one Crab above 1 TeV with
a hard spectrum over two decades in energy. The intra-night light curve showed
a series of strong outbursts with flux-doubling time scales as fast as a few
minutes. The fast variability constrains the size of the gamma-ray emission
regime to be smaller than 20% of the gravitational radius of its central black
hole. This challenges the shock acceleration models, commonly used to explain
gamma-ray radiation from active galaxies. Here, we will present more details on
the MAGIC data and discuss several possible alternative emission models.Comment: 8 pages, 5 figures, Proceedings of the 34th International Cosmic Ray
Conference, 30 July - 6 August, 2015, The Hague, The Netherland
Insights into the particle acceleration of a peculiar gamma -ray radio galaxy IC 310
IC 310 has recently been identified as a gamma-ray emitter based on
observations at GeV energies with Fermi-LAT and at very high energies (VHE, E >
100 GeV) with the MAGIC telescopes. Despite IC 310 having been classified as a
radio galaxy with the jet observed at an angle > 10 degrees, it exhibits a
mixture of multiwavelength properties of a radio galaxy and a blazar, possibly
making it a transitional object. On the night of 12/13th of November 2012 the
MAGIC telescopes observed a series of violent outbursts from the direction of
IC 310 with flux-doubling time scales faster than 5 min and a peculiar spectrum
spreading over 2 orders of magnitude. Such fast variability constrains the size
of the emission region to be smaller than 20% of the gravitational radius of
its central black hole, challenging the shock acceleration models, commonly
used in explanation of gamma-ray radiation from active galaxies. Here we will
show that this emission can be associated with pulsar-like particle
acceleration by the electric field across a magnetospheric gap at the base of
the jet.Comment: 2014 Fermi Symposium proceedings - eConf C14102.
Kondo effect in a one dimensional d-wave superconductor
We derive a solvable resonant-level type model, to describe an impurity spin
coupled to zero-energy bound states localized at the edge of a one dimensional
d-wave superconductor. This results in a two-channel Kondo effect with a quite
unusual low-temperature thermodynamics. For instance, the local impurity
susceptibility yields a finite maximum at zero temperature (but no
logarithmic-divergence) due to the splitting of the impurity in two Majorana
fermions. Moreover, we make comparisons with the Kondo effect occurring in a
two dimensional d-wave superconductor.Comment: 9 pages, final version; To be published in Europhysics Letter
Renormalization of Hamiltonian Field Theory; a non-perturbative and non-unitarity approach
Renormalization of Hamiltonian field theory is usually a rather painful
algebraic or numerical exercise. By combining a method based on the coupled
cluster method, analysed in detail by Suzuki and Okamoto, with a Wilsonian
approach to renormalization, we show that a powerful and elegant method exist
to solve such problems. The method is in principle non-perturbative, and is not
necessarily unitary.Comment: 16 pages, version shortened and improved, references added. To appear
in JHE
Generating Function for Particle-Number Probability Distribution in Directed Percolation
We derive a generic expression for the generating function (GF) of the
particle-number probability distribution (PNPD) for a simple reaction diffusion
model that belongs to the directed percolation universality class. Starting
with a single particle on a lattice, we show that the GF of the PNPD can be
written as an infinite series of cumulants taken at zero momentum. This series
can be summed up into a complete form at the level of a mean-field
approximation. Using the renormalization group techniques, we determine
logarithmic corrections for the GF at the upper critical dimension. We also
find the critical scaling form for the PNPD and check its universality
numerically in one dimension. The critical scaling function is found to be
universal up to two non-universal metric factors.Comment: (v1,2) 8 pages, 5 figures; one-loop calculation corrected in response
to criticism received from Hans-Karl Janssen, (v3) content as publishe
Third World gap year projects: Youth transitions and the mediation of risk
This is the post-print version of the final published article. The definitive, peer-reviewed and edited version of this article is available from the link below. Copyright @ 2008 Pion.In recent years in the UK there has been a great expansion in the number of young people travelling to Third World countries between school and university in order to participate as volunteers on structured gap year projects. Travel to such places is commonly perceived as âriskyâ, and takes young people outside the protective cocoon of UK health and safety legislation. One of the functions played by the providers of gap year projects is to mediate risk. On the basis of analysis of promotional literature, interviews with organisers of gap year projects, and focus groups of returned volunteers, in this paper I argue that the various strategies of risk mediation undertaken by gap year providers serve to reconcile modernising tendencies in UK society toward risk control and structure with postmodern inclinations towards individualisation and uncertainty
Enhanced electrical resistivity before N\'eel order in the metals, RCuAs (R= Sm, Gd, Tb and Dy
We report an unusual temperature (T) dependent electrical resistivity()
behavior in a class of ternary intermetallic compounds of the type RCuAs
(R= Rare-earths). For some rare-earths (Sm, Gd, Tb and Dy) with negligible
4f-hybridization, there is a pronounced minimum in (T) far above
respective N\'eel temperatures (T). However, for the rare-earths which are
more prone to exhibit such a (T) minimum due to 4f-covalent mixing and
the Kondo effect, this minimum is depressed. These findings, difficult to
explain within the hither-to-known concepts, present an interesting scenario in
magnetism.Comment: Physical Review Letters (accepted for publication
Landau-Ginzburg Description of Boundary Critical Phenomena in Two Dimensions
The Virasoro minimal models with boundary are described in the
Landau-Ginzburg theory by introducing a boundary potential, function of the
boundary field value. The ground state field configurations become non-trivial
and are found to obey the soliton equations. The conformal invariant boundary
conditions are characterized by the reparametrization-invariant data of the
boundary potential, that are the number and degeneracies of the stationary
points. The boundary renormalization group flows are obtained by varying the
boundary potential while keeping the bulk critical: they satisfy new selection
rules and correspond to real deformations of the Arnold simple singularities of
A_k type. The description of conformal boundary conditions in terms of boundary
potential and associated ground state solitons is extended to the N=2
supersymmetric case, finding agreement with the analysis of A-type boundaries
by Hori, Iqbal and Vafa.Comment: 42 pages, 13 figure
Theoretical Overview Quark Matter '04
The much wider transverse-momentum range accessible in heavy-ion collisions
at RHIC and at the LHC allows us to disentangle the dynamics of partonic
equilibration from the dynamics of delayed hadronization. This provides a novel
tool for testing the equilibration mechanisms underlying QCD thermodynamics.
Here, I argue, on the basis of simple formation-time arguments, why this is so,
and I review recent theoretical developments in this context.Comment: 12 pages, Latex, 3 eps figures, invited introductory talk at Quark
Matter 2004, Oakland, January 11-17, 200
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