5,516 research outputs found
Ranking Functions for Size-Change Termination II
Size-Change Termination is an increasingly-popular technique for verifying
program termination. These termination proofs are deduced from an abstract
representation of the program in the form of "size-change graphs".
We present algorithms that, for certain classes of size-change graphs, deduce
a global ranking function: an expression that ranks program states, and
decreases on every transition. A ranking function serves as a witness for a
termination proof, and is therefore interesting for program certification. The
particular form of the ranking expressions that represent SCT termination
proofs sheds light on the scope of the proof method. The complexity of the
expressions is also interesting, both practicaly and theoretically.
While deducing ranking functions from size-change graphs has already been
shown possible, the constructions in this paper are simpler and more
transparent than previously known. They improve the upper bound on the size of
the ranking expression from triply exponential down to singly exponential (for
certain classes of instances). We claim that this result is, in some sense,
optimal. To this end, we introduce a framework for lower bounds on the
complexity of ranking expressions and prove exponential lower bounds.Comment: 29 pages
Lifetime of Surface Features and Stellar Rotation: A Wavelet Time-Frequency Approach
We explore subtle variations in disk-integrated measurements spanning
\lsim 18 years of stellar surface magnetism by using a newly developed
time-frequency gapped wavelet algorithm.
We present results based on analysis of the Mount Wilson
Ca II H and K emission fluxes in four, magnetically-active stars (HD 1835
[G2V], 82885 [G8IV-V], 149661 [K0V] and 190007 [K4V]) and sensitivity tests
using artificial data.
When the wavelet basis is appropriately modified (i.e., when the
time-frequency resolution is optimized), the results are consistent with the
existence of spatially localized and long-lived
Ca II features (assumed here as activity regions that tend to recur in
narrowly-confined latitude bands), especially in HD 1835 and 82885.
This interpretation is based on the observed persistence of relatively
localized Ca II wavelet power at a narrow range of rotational time scales,
enduring as long as \gsim 10 years.Comment: to appear in THE ASTROPHYSICAL JOURNAL LETTER
BRST extension of the Faddeev model
The Faddeev model is a second class constrained system. Here we construct its
nilpotent BRST operator and derive the ensuing manifestly BRST invariant
Lagrangian. Our construction employs the structure of Stuckelberg fields in a
nontrivial fashion.Comment: 4 pages, new references adde
CS 801: Advanced Database Systems
Introduction of current trends and research issues in database systems
BRST invariance and de Rham-type cohomology of 't Hooft-Polyakov monopole
We exploit the 't Hooft-Polyakov monopole to define closed algebra of the
quantum field operators and the BRST charge . In the first-class
configuration of the Dirac quantization, by including the -exact
gauge fixing term and the Faddeev-Popov ghost term, we find the BRST invariant
Hamiltonian to investigate the de Rham-type cohomology group structure for the
monopole system. The Bogomol'nyi bound is also discussed in terms of the
first-class topological charge defined on the extended internal 2-sphere.Comment: 8 page
CS 405/605: Introduction to Database Management Systems
Survey of logical and physical aspects of database management systems. Entity Relationship, relational, object-oriented models for databases are presented. Physical implementation methods are discussed
CS 801: Advanced Database Systems
Introduction of current trends and research issues in database systems
CEG 820-01: Computer Architecture II
Continuation of CEG 720 with more details on multiprocessor systems, parallel processing, and performance analysis
CS 701: Database Systems and Design
Introduction of DB design concepts and operating principles of database systems
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