9,413 research outputs found
Frequency vs. Association for Constraint Selection in Usage-Based Construction Grammar
A usage-based Construction Grammar (CxG) posits that slot-constraints
generalize from common exemplar constructions. But what is the best model of
constraint generalization? This paper evaluates competing frequency-based and
association-based models across eight languages using a metric derived from the
Minimum Description Length paradigm. The experiments show that
association-based models produce better generalizations across all languages by
a significant margin
Spacetime states and covariant quantum theory
In it's usual presentation, classical mechanics appears to give time a very
special role. But it is well known that mechanics can be formulated so as to
treat the time variable on the same footing as the other variables in the
extended configuration space. Such covariant formulations are natural for
relativistic gravitational systems, where general covariance conflicts with the
notion of a preferred physical-time variable. The standard presentation of
quantum mechanics, in turns, gives again time a very special role, raising well
known difficulties for quantum gravity. Is there a covariant form of
(canonical) quantum mechanics? We observe that the preferred role of time in
quantum theory is the consequence of an idealization: that measurements are
instantaneous. Canonical quantum theory can be given a covariant form by
dropping this idealization. States prepared by non-instantaneous measurements
are described by "spacetime smeared states". The theory can be formulated in
terms of these states, without making any reference to a special time variable.
The quantum dynamics is expressed in terms of the propagator, an object
covariantly defined on the extended configuration space.Comment: 20 pages, no figures. Revision: minor corrections and references
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Army-NASA aircrew/aircraft integration program (A3I) software detailed design document, phase 3
The capabilities and design approach of the MIDAS (Man-machine Integration Design and Analysis System) computer-aided engineering (CAE) workstation under development by the Army-NASA Aircrew/Aircraft Integration Program is detailed. This workstation uses graphic, symbolic, and numeric prototyping tools and human performance models as part of an integrated design/analysis environment for crewstation human engineering. Developed incrementally, the requirements and design for Phase 3 (Dec. 1987 to Jun. 1989) are described. Software tools/models developed or significantly modified during this phase included: an interactive 3-D graphic cockpit design editor; multiple-perspective graphic views to observe simulation scenarios; symbolic methods to model the mission decomposition, equipment functions, pilot tasking and loading, as well as control the simulation; a 3-D dynamic anthropometric model; an intermachine communications package; and a training assessment component. These components were successfully used during Phase 3 to demonstrate the complex interactions and human engineering findings involved with a proposed cockpit communications design change in a simulated AH-64A Apache helicopter/mission that maps to empirical data from a similar study and AH-1 Cobra flight test
Some Physical Aspects of Liouville String Dynamics
We discuss some physical aspects of our Liouville approach to non-critical
strings, including the emergence of a microscopic arrow of time, effective
field theories as classical ``pointer'' states in theory space, violation
and the possible apparent non-conservation of angular momentum. We also review
the application of a phenomenological parametrization of this formalism to the
neutral kaon system.Comment: CERN-TH.7269/94, 37 pages, 2 figures (not included), latex. Direct
inquiries to: [email protected]
On Role Logic
We present role logic, a notation for describing properties of relational
structures in shape analysis, databases, and knowledge bases. We construct role
logic using the ideas of de Bruijn's notation for lambda calculus, an encoding
of first-order logic in lambda calculus, and a simple rule for implicit
arguments of unary and binary predicates. The unrestricted version of role
logic has the expressive power of first-order logic with transitive closure.
Using a syntactic restriction on role logic formulas, we identify a natural
fragment RL^2 of role logic. We show that the RL^2 fragment has the same
expressive power as two-variable logic with counting C^2 and is therefore
decidable. We present a translation of an imperative language into the
decidable fragment RL^2, which allows compositional verification of programs
that manipulate relational structures. In addition, we show how RL^2 encodes
boolean shape analysis constraints and an expressive description logic.Comment: 20 pages. Our later SAS 2004 result builds on this wor
Survey on Combinatorial Register Allocation and Instruction Scheduling
Register allocation (mapping variables to processor registers or memory) and
instruction scheduling (reordering instructions to increase instruction-level
parallelism) are essential tasks for generating efficient assembly code in a
compiler. In the last three decades, combinatorial optimization has emerged as
an alternative to traditional, heuristic algorithms for these two tasks.
Combinatorial optimization approaches can deliver optimal solutions according
to a model, can precisely capture trade-offs between conflicting decisions, and
are more flexible at the expense of increased compilation time.
This paper provides an exhaustive literature review and a classification of
combinatorial optimization approaches to register allocation and instruction
scheduling, with a focus on the techniques that are most applied in this
context: integer programming, constraint programming, partitioned Boolean
quadratic programming, and enumeration. Researchers in compilers and
combinatorial optimization can benefit from identifying developments, trends,
and challenges in the area; compiler practitioners may discern opportunities
and grasp the potential benefit of applying combinatorial optimization
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