44,805 research outputs found
A change propagating model transformation language
Model transformations are a key component in Model Driven Development, but most approaches only allow `one shot' transformations to be expressed. Change propagating
model transformations are those which can make suitable updates to models after an initial transformation. In this paper I outline the challenges presented by change prop-
agating model transformations, before presenting a new change propagating model transformation approach
A Change propagating model transformation language.
Model transformations are a key component in Model Driven Development, but most approaches only allow āone shot' transformations to be expressed. Change propagating model transformations are those which can make suitable updates to models after an initial transformation
Model transformations and Tool Integration
Model transformations are increasingly recognised as being of significant importance to many areas of software development and integration. Recent attention on model transformations has particularly focused on the OMGs Queries/Views/Transformations (QVT) Request for Proposals (RFP). In this paper I motivate the need for dedicated approaches to model transformations, particularly for the data involved in tool integration, outline the challenges involved, and then present a number of technologies and techniques which allow the construction of flexible, powerful and practical model transformations
M-Theory Through the Looking Glass: Tachyon Condensation in the E_8 Heterotic String
We study the spacetime decay to nothing in string theory and M-theory. First
we recall a nonsupersymmetric version of heterotic M-theory, in which bubbles
of nothing -- connecting the two E_8 boundaries by a throat -- are expected to
be nucleated. We argue that the fate of this system should be addressed at weak
string coupling, where the nonperturbative instanton instability is expected to
turn into a perturbative tachyonic one. We identify the unique string theory
that could describe this process: The heterotic model with one E_8 gauge group
and a singlet tachyon. We then use worldsheet methods to study the tachyon
condensation in the NSR formulation of this model, and show that it induces a
worldsheet super-Higgs effect. The main theme of our analysis is the
possibility of making meaningful alternative gauge choices for worldsheet
supersymmetry, in place of the conventional superconformal gauge. We show in a
version of unitary gauge how the worldsheet gravitino assimilates the goldstino
and becomes dynamical. This picture clarifies recent results of Hellerman and
Swanson. We also present analogs of R_\xi gauges, and note the importance of
logarithmic CFT in the context of tachyon condensation.Comment: 36 pages, 1 figur
Ground state and edge excitations of quantum Hall liquid at filling factor 2/3
We present a numerical study of fractional quantum Hall liquid at Landau
level filling factor in a microscopic model including long-range
Coulomb interaction and edge confining potential, based on the disc geometry.
We find the ground state is accurately described by the particle-hole conjugate
of a Laughlin state. We also find there are two counter-propagating
edge modes, and the velocity of the forward-propagating mode is larger than the
backward-propagating mode. The velocities have opposite responses to the change
of the background confinement potential. On the other hand changing the
two-body Coulomb potential has qualitatively the same effect on the velocities;
for example we find increasing layer thickness (which softens of the Coulomb
interaction) reduces both the forward mode and the backward mode velocities.Comment: 12 pages, 13 figure
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