5,549 research outputs found
Modal Logics with Hard Diamond-free Fragments
We investigate the complexity of modal satisfiability for certain
combinations of modal logics. In particular we examine four examples of
multimodal logics with dependencies and demonstrate that even if we restrict
our inputs to diamond-free formulas (in negation normal form), these logics
still have a high complexity. This result illustrates that having D as one or
more of the combined logics, as well as the interdependencies among logics can
be important sources of complexity even in the absence of diamonds and even
when at the same time in our formulas we allow only one propositional variable.
We then further investigate and characterize the complexity of the
diamond-free, 1-variable fragments of multimodal logics in a general setting.Comment: New version: improvements and corrections according to reviewers'
comments. Accepted at LFCS 201
Vertex Operators in 2K Dimensions
A formula is proposed which expresses free fermion fields in 2K dimensions in
terms of the Cartan currents of the free fermion current algebra. This leads,
in an obvious manner, to a vertex operator construction of nonabelian free
fermion current algebras in arbitrary even dimension. It is conjectured that
these ideas may generalize to a wide class of conformal field theories.Comment: Minor change in notation. Change in references
Instabilities in droplets spreading on gels
We report a novel surface-tension driven instability observed for droplets
spreading on a compliant substrate. When a droplet is released on the surface
of an agar gel, it forms arms/cracks when the ratio of surface tension gradient
to gel strength is sufficiently large. We explore a range of gel strengths and
droplet surface tensions and find that the onset of the instability and the
number of arms depend on the ratio of surface tension to gel strength. However,
the arm length grows with an apparently universal law L ~ t^{3/4}
General Solution of the non-abelian Gauss law and non-abelian analogs of the Hodge decomposition
General solution of the non-abelian Gauss law in terms of covariant curls and
gradients is presented. Also two non-abelian analogs of the Hodge decomposition
in three dimensions are addressed. i) Decomposition of an isotriplet vector
field as sum of covariant curl and gradient with respect to an
arbitrary background Yang-Mills potential is obtained. ii) A decomposition of
the form which involves non-abelian
magnetic field of a new Yang-Mills potential C is also presented. These results
are relevant for duality transformation for non-abelian gauge fields.Comment: 6 pages, no figures, revte
Supergrassmannian and large N limit of quantum field theory with bosons and fermions
We study a large N_{c} limit of a two-dimensional Yang-Mills theory coupled
to bosons and fermions in the fundamental representation. Extending an approach
due to Rajeev we show that the limiting theory can be described as a classical
Hamiltonian system whose phase space is an infinite-dimensional
supergrassmannian. The linear approximation to the equations of motion and the
constraint yields the 't Hooft equations for the mesonic spectrum. Two other
approximation schemes to the exact equations are discussed.Comment: 24 pages, Latex; v.3 appendix added, typos corrected, to appear in
JM
An informed thought experiment exploring the potential for a paradigm shift in aquatic food production
The Neolithic Revolution began c. 10000 years ago and is characterised by the
ultimate, near complete transition from hunting and gathering to agricultural
food production on land. The Neolithic Revolution is thought to have been
catalysed by a combination of local population pressure, cultural diffusion,
property rights and climate change. We undertake a thought experiment that
examines trends in these key hypothesised catalysts and patters of today to
explore whether society could be on a path towards another paradigm shift in
food production: away from hunting of wild fish towards a transition to mostly
fish farming. We find similar environmental and cultural pressures have driven
the rapid rise of aquaculture, during a period that has now been coined the
Blue Revolution, providing impetus for such a transition in coming decades to
centuries. We also highlight the interacting and often mutually reinforcing
impacts of 1)technological and scientific advancement, 2)environmental
awareness and collective action and 3)globalisation and trade influencing the
trajectory and momentum of the Blue Revolution. We present two qualitative
narratives that broadly fall within two future trajectories: 1)a ubiquitous
aquaculture transition and 20commercial aquaculture and fisheries coexistence.
This scenarios approach aims to encourage logical, forward thinking, and
innovative solutions to complex systems dynamics. Scenario-based thought
experiments are useful to explore large scale questions, increase the
accessibility to a wider readership and ideally catalyse discussion around
proactive governance mechanisms. We argue the future is not fixed and society
now has greater foresight and capacity to choose the workable balance between
fisheries sand aquaculture that supports economic, environmental, cultural and
social objectives through combined planning, policies and management
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