268,945 research outputs found
Computations and interaction
We enhance the notion of a computation of the classical theory of computing with the notion of interaction. In this way, we enhance a Turing machine as a model of computation to a Reactive Turing Machine that is an abstract model of a computer as it is used nowadays, always interacting with the user and the world
A new model of a tidally disrupted star
A new semi-analytical model of a star evolving in a tidal field is proposed.
The model is a generalization of the so-called 'affine' stellar model. In our
model the star is composed of elliptical shells with different parameters and
different orientations, depending on time and on the radial Lagrangian
coordinate of the shell. The evolution equations of this model are derived from
the virial relations under certain assumptions, and the integrals of motion are
identified. It is shown that the evolution equations can be deduced from a
variational principle. The evolution equations are solved numerically and
compared quantitatively with the results of 3D numerical computations of the
tidal interaction of a star with a supermassive black hole. The comparison
shows very good agreement between the main ``integral'' characteristics
describing the tidal interaction event in our model and in the 3D computations.
Our model is effectively a one-dimensional Lagrangian model from the point of
view of numerical computations, and therefore it can be evolved numerically
times faster than the 3D approach allows. This makes our model
well suited for intensive calculations covering the whole parameter space of
the problem.Comment: This version is accepted for publication in ApJ. Stylistic and
grammatical changes, new Appendix adde
Numerical computations of swirling recirculating flow
Swirling, recirculating, nonreacting flows were computed using a 2D elliptic program consisting of three tasks. The computations in Task 1 and 2 were made using an independent analysis for the two coaxial swirling flows. The Task 2 computations were made using the measured profiles of the mixing region. In Task 3, a modified 2D elliptic program was employed to include the effects of interaction between the inner and outer streams
A thread calculus with molecular dynamics
We present a theory of threads, interleaving of threads, and interaction
between threads and services with features of molecular dynamics, a model of
computation that bears on computations in which dynamic data structures are
involved. Threads can interact with services of which the states consist of
structured data objects and computations take place by means of actions which
may change the structure of the data objects. The features introduced include
restriction of the scope of names used in threads to refer to data objects.
Because that feature makes it troublesome to provide a model based on
structural operational semantics and bisimulation, we construct a projective
limit model for the theory.Comment: 47 pages; examples and results added, phrasing improved, references
replace
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A general theory of action languages
We present a general theory of action-based languages as a paradigm, for the description, of those computational
systems which include elements of concurrency and networking, and extend this approach
to describe dist.ributed systems and also t,o describe the interaction of a system, with an environment.
As part of this approach we introduce the Action Language as a common model for the class of nondeterministic
concurrent programming languages and define its intensional and interaction semantics
in terrors of continuous transformation of environment behavior. This semantics i.s specialized for
programs with stores, and extended to describe distributed computations
Casimir interaction between spheres in -dimensional Minkowski spacetime
We consider the Casimir interaction between two spheres in
-dimensional Minkowski spacetime due to the vacuum fluctuations of
scalar fields. We consider combinations of Dirichlet and Neumann boundary
conditions. The TGTG formula of the Casimir interaction energy is derived. The
computations of the T matrices of the two spheres are straightforward. To
compute the two G matrices, known as translation matrices, which relate the
hyper-spherical waves in two spherical coordinate frames differ by a
translation, we generalize the operator approach employed in [IEEE Trans.
Antennas Propag. \textbf{36}, 1078 (1988)]. The result is expressed in terms of
an integral over Gegenbauer polynomials. Using our expression for the Casimir
interaction energy, we derive the large separation and small separation
asymptotic expansions of the Casimir interaction energy. In the large
separation regime, we find that the Casimir interaction energy is of order
, and respectively for Dirichlet-Dirichlet,
Dirichlet-Neumann and Neumann-Neumann boundary conditions, where is the
center-to-center distance of the two spheres. In the small separation regime,
we confirm that the leading term of the Casimir interaction agrees with the
proximity force approximation, which is of order , where
is the distance between the two spheres. Another main result of this work
is the analytic computations of the next-to-leading order term in the small
separation asymptotic expansion. This term is computed using careful order
analysis as well as perturbation method. We find that when is large, the
ratio of the next-to-leading order term to the leading order term is linear in
, indicating a larger correction at higher dimensions.Comment: 23 page
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