2,713 research outputs found
Bounded Refinement Types
We present a notion of bounded quantification for refinement types and show
how it expands the expressiveness of refinement typing by using it to develop
typed combinators for: (1) relational algebra and safe database access, (2)
Floyd-Hoare logic within a state transformer monad equipped with combinators
for branching and looping, and (3) using the above to implement a refined IO
monad that tracks capabilities and resource usage. This leap in expressiveness
comes via a translation to "ghost" functions, which lets us retain the
automated and decidable SMT based checking and inference that makes refinement
typing effective in practice.Comment: 14 pages, International Conference on Functional Programming, ICFP
201
Aspects of M-5 brane world volume dynamics
This paper studies various aspects of the world volume dynamics of the
M-theory five-brane, including: non-BPS solutions and solution generating
symmetries; the scattering properties of world volume solutions; and the
equivalence with probe brane dynamics.Comment: 14 pages, latex. v2: Some additional comments and references adde
A note on the M2-M5 brane system and fuzzy spheres
This note covers various aspects of recent attempts to describe membranes
ending on fivebranes using fuzzy geometry. In particular, we examine the
Basu-Harvey equation and its relation to the Nahm equation as well as the
consequences of using a non-associative algebra for the fuzzy three-sphere.
This produces the tantalising result that the fuzzy funnel solution
corresponding to Q coincident membranes ending on a five-brane has
degrees of freedom.Comment: 17 pages, late
A Calculation of the plane wave string Hamiltonian from N=4 super-Yang-Mills theory
Berenstein, Maldacena, and Nastase have proposed, as a limit of the strong
form of the AdS/CFT correspondence, that string theory in a particular plane
wave background is dual to a certain subset of operators in the N=4
super-Yang-Mills theory. Even though this is a priori a strong/weak coupling
duality, the matrix elements of the string theory Hamiltonian, when expressed
in gauge theory variables, are analytic in the 't Hooft coupling constant. This
allows one to conjecture that, like the masses of excited string states, these
can be recovered using perturbation theory in Yang-Mills theory.
In this paper we identify the difference between the generator of scale
transformations and a particular U(1) R-symmetry generator as the operator dual
to the string theory Hamiltonian for nonvanishing string coupling. We compute
its matrix elements and find that they agree with the string theory prediction
provided that the state-operator map is modified for nonvanishing string
coupling. We construct this map explicitly and calculate the anomalous
dimensions of the new operators. We identify the component arising from the
modification of the state-operator map with the contribution of the string
theory contact terms to the masses of string states.Comment: 38 pages, Latex; v2: Comparison with string theory changed in light
of corrections to string theory results in hep-th/0206073 v3; state-operator
map modified; Physical interpretation and conclusions unchange
Five-brane Calibrations and Fuzzy Funnels
We present a generalisation of the Basu-Harvey equation that describes
membranes ending on intersecting five-brane configurations corresponding to
various calibrated geometries.Comment: 20 pages, latex, v2: typos fixed and refs adde
Large-small dualities between periodic collapsing/expanding branes and brane funnels
We consider space and time dependent fuzzy spheres arising in
intersections in IIB string theory and collapsing D(2p)-branes in
IIA string theory.
In the case of , where the periodic space and time-dependent solutions
can be described by Jacobi elliptic functions, there is a duality of the form
to which relates the space and time dependent solutions.
This duality is related to complex multiplication properties of the Jacobi
elliptic functions. For funnels, the description of the periodic space
and time dependent solutions involves the Jacobi Inversion problem on a
hyper-elliptic Riemann surface of genus 3. Special symmetries of the Riemann
surface allow the reduction of the problem to one involving a product of genus
one surfaces. The symmetries also allow a generalisation of the to duality. Some of these considerations extend to the case of the
fuzzy .Comment: Latex, 50 pages, 2 figures ; v2 : a systematic typographical error
corrected + minor change
Enhancing surgical performance in cardiothoracic surgery with innovations from computer vision and artificial intelligence: a narrative review
\ua9 The Author(s) 2024. When technical requirements are high, and patient outcomes are critical, opportunities for monitoring and improving surgical skills via objective motion analysis feedback may be particularly beneficial. This narrative review synthesises work on technical and non-technical surgical skills, collaborative task performance, and pose estimation to illustrate new opportunities to advance cardiothoracic surgical performance with innovations from computer vision and artificial intelligence. These technological innovations are critically evaluated in terms of the benefits they could offer the cardiothoracic surgical community, and any barriers to the uptake of the technology are elaborated upon. Like some other specialities, cardiothoracic surgery has relatively few opportunities to benefit from tools with data capture technology embedded within them (as is possible with robotic-assisted laparoscopic surgery, for example). In such cases, pose estimation techniques that allow for movement tracking across a conventional operating field without using specialist equipment or markers offer considerable potential. With video data from either simulated or real surgical procedures, these tools can (1) provide insight into the development of expertise and surgical performance over a surgeonâs career, (2) provide feedback to trainee surgeons regarding areas for improvement, (3) provide the opportunity to investigate what aspects of skill may be linked to patient outcomes which can (4) inform the aspects of surgical skill which should be focused on within training or mentoring programmes. Classifier or assessment algorithms that use artificial intelligence to âlearnâ what expertise is from expert surgical evaluators could further assist educators in determining if trainees meet competency thresholds. With collaborative efforts between surgical teams, medical institutions, computer scientists and researchers to ensure this technology is developed with usability and ethics in mind, the developed feedback tools could improve cardiothoracic surgical practice in a data-driven way
Graviton-Scalar Interaction in the PP-Wave Background
We compute the graviton two scalar off-shell interaction vertex at tree level
in Type IIB superstring theory on the pp-wave background using the light-cone
string field theory formalism. We then show that the tree level vertex vanishes
when all particles are on-shell and conservation of p_{+} and p_{-} are
imposed. We reinforce our claim by calculating the same vertex starting from
the corresponding SUGRA action expanded around the pp-wave background in the
light-cone gauge.Comment: 26 pages, harvmac One reference added. A few comments changed in the
introduction. The "cyclic perms." term removed from some equations as
unnecessary and equations (2.38) and (3.19) are corrected accordingl
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Simultaneous mesoscopic and two-photon imaging of neuronal activity in cortical circuits.
Spontaneous and sensory-evoked activity propagates across varying spatial scales in the mammalian cortex, but technical challenges have limited conceptual links between the function of local neuronal circuits and brain-wide network dynamics. We present a method for simultaneous cellular-resolution two-photon calcium imaging of a local microcircuit and mesoscopic widefield calcium imaging of the entire cortical mantle in awake mice. Our multi-scale approach involves a microscope with an orthogonal axis design where the mesoscopic objective is oriented above the brain and the two-photon objective is oriented horizontally, with imaging performed through a microprism. We also introduce a viral transduction method for robust and widespread gene delivery in the mouse brain. These approaches allow us to identify the behavioral state-dependent functional connectivity of pyramidal neurons and vasoactive intestinal peptide-expressing interneurons with long-range cortical networks. Our imaging system provides a powerful strategy for investigating cortical architecture across a wide range of spatial scales
DLCQ String Spectrum from SYM Theory
We study non planar corrections to the spectrum of operators in the
supersymmetric Yang Mills theory which are dual to string
states in the maximally supersymmetric pp-wave background with a {\em compact}
light-cone direction. The existence of a positive definite discrete light-cone
momentum greatly simplifies the operator mixing problem. We give some examples
where the contribution of all orders in non-planar diagrams can be found
analytically. On the string theory side this corresponds to finding the
spectrum of a string state to all orders in string loop corrections.Comment: 35 pages, no figure
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