4,831 research outputs found
The Long-Baseline Neutrino Experiment: Exploring Fundamental Symmetries of the Universe
The preponderance of matter over antimatter in the early Universe, the
dynamics of the supernova bursts that produced the heavy elements necessary for
life and whether protons eventually decay --- these mysteries at the forefront
of particle physics and astrophysics are key to understanding the early
evolution of our Universe, its current state and its eventual fate. The
Long-Baseline Neutrino Experiment (LBNE) represents an extensively developed
plan for a world-class experiment dedicated to addressing these questions. LBNE
is conceived around three central components: (1) a new, high-intensity
neutrino source generated from a megawatt-class proton accelerator at Fermi
National Accelerator Laboratory, (2) a near neutrino detector just downstream
of the source, and (3) a massive liquid argon time-projection chamber deployed
as a far detector deep underground at the Sanford Underground Research
Facility. This facility, located at the site of the former Homestake Mine in
Lead, South Dakota, is approximately 1,300 km from the neutrino source at
Fermilab -- a distance (baseline) that delivers optimal sensitivity to neutrino
charge-parity symmetry violation and mass ordering effects. This ambitious yet
cost-effective design incorporates scalability and flexibility and can
accommodate a variety of upgrades and contributions. With its exceptional
combination of experimental configuration, technical capabilities, and
potential for transformative discoveries, LBNE promises to be a vital facility
for the field of particle physics worldwide, providing physicists from around
the globe with opportunities to collaborate in a twenty to thirty year program
of exciting science. In this document we provide a comprehensive overview of
LBNE's scientific objectives, its place in the landscape of neutrino physics
worldwide, the technologies it will incorporate and the capabilities it will
possess.Comment: Major update of previous version. This is the reference document for
LBNE science program and current status. Chapters 1, 3, and 9 provide a
comprehensive overview of LBNE's scientific objectives, its place in the
landscape of neutrino physics worldwide, the technologies it will incorporate
and the capabilities it will possess. 288 pages, 116 figure
Proceedings of Sixth International Workshop on Unification
Swiss National Science Foundation; Austrian Federal Ministry of Science and Research; Deutsche Forschungsgemeinschaft (SFB 314); Christ Church, Oxford; Oxford University Computing Laborator
Classification-based phrase structure grammar: an extended revised version of HPSG
This thesis is concerned with a presentation of Classification -based Phrase Structure
Grammar (or cPSG), a grammatical theory that has grown out of extensive revisions
of, and extensions to, HPSG. The fundamental difference between this theory and HPSG
concerns the central role that classification plays in the grammar: the grammar classifies
strings, according to their feature structure descriptions, as being of various types.
Apart from the role of classification, the theory bears a close resemblance to HPSG,
though it is by no means a direct translation, including numerous revisions and extensions.
A central goal in the development of the theory has been its computational
implementation, which is included in the thesis.The presentation may be divided into four parts. In the first, chapters 1 and 2, we
present the grammatical formalism within which the theory is stated. This consists of a
development of the notion of a classificatory system (chapter 1), and the incorporation
of hierarchality into that notion (chapter 2).The second part concerns syntactic issues. Chapter 3 revises the HPSG treatment of
specifiers, complements and adjuncts, incorporating ideas that specifiers and complements
should be distinguished and presenting a treatment of adjuncts whereby the
head is selected for by the adjunct. Chapter 4 presents several options for an account of
unbounded dependencies. The accounts are based loosely on that of GPSG, and a reconstruction
of GPSG's Foot Feature Principle is presented which does not involve a notion
of default. Chapter 5 discusses coordination, employing an extension of Rounds- Kasper
logic to allow a treatment of cross -categorial coordination.In the third part, chapters 6, 7 and 8, we turn to semantic issues. We begin (Chapter 6)
with a discussion of Situation Theory, the background semantic theory, attempting to
establish a precise and coherent version of the theory within which to work. Chapter 7
presents the bulk of the treatment of semantics, and can be seen as an extensive revision
of the HPSG treatment of semantics. The aim is to provide a semantic treatment which
is faithful to the version of Situation Theory presented in Chapter 6. Chapter 8 deals
with quantification, discussing the nature of quantification in Situation Theory before
presenting a treatment of quantification in CPSG. Some residual questions about the
semantics of coordinated noun phrases are also addressed in this chapter.The final part, Chapter 9, concerns the actual computational implementation of the
theory. A parsing algorithm based on hierarchical classification is presented, along with
four strategies that might be adopted given that algorithm. Also discussed are some
implementation details. A concluding chapter summarises the arguments of the thesis
and outlines some avenues for future research
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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