1,134 research outputs found
Complexity Hierarchies and Higher-order Cons-free Term Rewriting
Constructor rewriting systems are said to be cons-free if, roughly,
constructor terms in the right-hand sides of rules are subterms of the
left-hand sides; the computational intuition is that rules cannot build new
data structures. In programming language research, cons-free languages have
been used to characterize hierarchies of computational complexity classes; in
term rewriting, cons-free first-order TRSs have been used to characterize the
class PTIME.
We investigate cons-free higher-order term rewriting systems, the complexity
classes they characterize, and how these depend on the type order of the
systems. We prove that, for every K 1, left-linear cons-free systems
with type order K characterize ETIME if unrestricted evaluation is used
(i.e., the system does not have a fixed reduction strategy).
The main difference with prior work in implicit complexity is that (i) our
results hold for non-orthogonal term rewriting systems with no assumptions on
reduction strategy, (ii) we consequently obtain much larger classes for each
type order (ETIME versus EXPTIME), and (iii) results for cons-free
term rewriting systems have previously only been obtained for K = 1, and with
additional syntactic restrictions besides cons-freeness and left-linearity.
Our results are among the first implicit characterizations of the hierarchy E
= ETIME ETIME ... Our work confirms prior
results that having full non-determinism (via overlapping rules) does not
directly allow for characterization of non-deterministic complexity classes
like NE. We also show that non-determinism makes the classes characterized
highly sensitive to minor syntactic changes like admitting product types or
non-left-linear rules.Comment: extended version of a paper submitted to FSCD 2016. arXiv admin note:
substantial text overlap with arXiv:1604.0893
Complexity Hierarchies and Higher-Order Cons-Free Rewriting
Constructor rewriting systems are said to be cons-free if, roughly,
constructor terms in the right-hand sides of rules are subterms of constructor
terms in the left-hand side; the computational intuition is that rules cannot
build new data structures. It is well-known that cons-free programming
languages can be used to characterize computational complexity classes, and
that cons-free first-order term rewriting can be used to characterize the set
of polynomial-time decidable sets.
We investigate cons-free higher-order term rewriting systems, the complexity
classes they characterize, and how these depend on the order of the types used
in the systems. We prove that, for every k 1, left-linear cons-free
systems with type order k characterize ETIME if arbitrary evaluation is
used (i.e., the system does not have a fixed reduction strategy).
The main difference with prior work in implicit complexity is that (i) our
results hold for non-orthogonal term rewriting systems with possible rule
overlaps with no assumptions about reduction strategy, (ii) results for such
term rewriting systems have previously only been obtained for k = 1, and with
additional syntactic restrictions on top of cons-freeness and left-linearity.
Our results are apparently among the first implicit characterizations of the
hierarchy E = ETIME ETIME .... Our work
confirms prior results that having full non-determinism (via overlaps of rules)
does not directly allow characterization of non-deterministic complexity
classes like NE. We also show that non-determinism makes the classes
characterized highly sensitive to minor syntactic changes such as admitting
product types or non-left-linear rules.Comment: Extended version (with appendices) of a paper published in FSCD 201
Expert operator's associate: A knowledge based system for spacecraft control
The Expert Operator's Associate (EOA) project is presented which studies the applicability of expert systems for day-to-day space operations. A prototype expert system is developed, which operates on-line with an existing spacecraft control system at the European Space Operations Centre, and functions as an 'operator's assistant' in controlling satellites. The prototype is demonstrated using an existing real-time simulation model of the MARECS-B2 telecommunication satellite. By developing a prototype system, the extent to which reliability and effectivens of operations can be enhanced by AI based support is examined. In addition the study examines the questions of acquisition and representation of the 'knowledge' for such systems, and the feasibility of 'migration' of some (currently) ground-based functions into future spaceborne autonomous systems
Evaluation Measures for Relevance and Credibility in Ranked Lists
Recent discussions on alternative facts, fake news, and post truth politics
have motivated research on creating technologies that allow people not only to
access information, but also to assess the credibility of the information
presented to them by information retrieval systems. Whereas technology is in
place for filtering information according to relevance and/or credibility, no
single measure currently exists for evaluating the accuracy or precision (and
more generally effectiveness) of both the relevance and the credibility of
retrieved results. One obvious way of doing so is to measure relevance and
credibility effectiveness separately, and then consolidate the two measures
into one. There at least two problems with such an approach: (I) it is not
certain that the same criteria are applied to the evaluation of both relevance
and credibility (and applying different criteria introduces bias to the
evaluation); (II) many more and richer measures exist for assessing relevance
effectiveness than for assessing credibility effectiveness (hence risking
further bias).
Motivated by the above, we present two novel types of evaluation measures
that are designed to measure the effectiveness of both relevance and
credibility in ranked lists of retrieval results. Experimental evaluation on a
small human-annotated dataset (that we make freely available to the research
community) shows that our measures are expressive and intuitive in their
interpretation
Relationship between water quality, watermilfoil frequency, and weevil distribution in the State of Washington
During the summer of 1997, we surveyed 50 waterbodies
in Washington State to determine the distribution of the
aquatic weevil
Euhrychiopsis lecontei
Dietz. We collected data
on water quality and the frequency of occurrence of watermilfoil
species within selected watermilfoil beds to compare
the waterbodies and determine if they were related to the
distribution
E. lecontei
. We found
E. lecontei
in 14 waterbodies,
most of which were in eastern Washington. Only one lake
with weevils was located in western Washington. Weevils were
associated with both Eurasian (
Myriophyllum spicatum
L.) and
northern watermilfoil (
M. sibiricum
K.). Waterbodies with
E.
lecontei
had significantly higher (
P
< 0.05) pH (8.7
±
0.2)
(mean
±
2SE), specific conductance (0.3
±
0.08 mS cm
-1
) and
total alkalinity (132.4
±
30.8 mg CaCO
3
L
-1
). We also found
that weevil presence was related to surface water temperature
and waterbody location ( = 24.3,
P
≤
0.001) and of all
the models tested, this model provided the best fit (Hosmer-
Lemeshow goodness-of-fit = 4.0,
P
= 0.9). Our results suggest
that in Washington State
E. lecontei
occurs primarily in
eastern Washington in waterbodies with pH
≥
8.2 and specific
conductance
≥
0.2 mS cm
-1
. Furthermore, weevil distribution
appears to be correlated with waterbody location (eastern
versus western Washington) and surface water temperature
Is there something wrong with society, or is it just me? : Social and medical knowledge in a Norwegian anti-discrimination law
What is the current relationship between the social and medical definitions of
disability in Norway? The Norwegian Discrimination and Accessibility Act, which
entered into effect on 1 January 2009, frames its overarching goals in terms of
human rights and equal opportunity and studiously avoids the use of medicodiagnostic
language. Most of the specific provisions of the law are, however,
justified as means of compensation for inherent or pre-existing disadvantage due
to impairment. In order to be effective, they must engage with medical,
impairment-specific knowledge. Social and medical perspectives and explanatory
models that are often seen as conflicting or even mutually exclusive instead
become intertwined in the spaces of negotiation that are opened by the law. Thus,
elements of what has traditionally been termed the medical model become
integrated in a larger framework that is defined by the goals of the social model
Two phenomena: Honji instability, and ringing of offshore structures
AbstractHonji instability and ringing of offshore structrures are two different phenomena. Honji instability occurs at a circular cylinder in transverse periodic finite motion in a water tank. It is superposed on the streaming flow induced by the cylinder's boundary layer. Its oscillation period is half of the period of the cylinder oscillation. Finite volume calculations of the filtered Navier-Stokes equations visualize the three-dimensional instability, where fluid particles transported by the circumferencial roll pairs exhibit a periodic mushroom-like pattern. Force is the same with and without the Honji instability. The large eddy simulation calculations for high Reynolds number support a drag coefficient in accordance with the Stokes-Wang solution below separation and conform with experimental measurements of the damping force on a harmonically oscillating cylinder. Ringing of offshore structures are vibrations which appear at natural frequencies and concern fatigue. It is generated by a higher harmonic force oscillating with frequency being 3–4 times the fundamental wave frequency. Together with a strong inertia load in phase with the incoming wave's acceleration, a secondary load cycle appears in strong seas when the wave crest leaves the structure; this occurs about 1/4 wave period after the main force peak, it starts when the wave crest is about one cylinder radius behind the cylinder, lasts for about 15–20 percent of the wave period and has a magnitude up to 11 % of the peak-to-peak total force. It is a gravity effect and appears in strong irregular seas when kA > 0.18 and um/gD>0.4 (k wavenumber, A amplitude, um maximal wave induced velocity, g acceleration of gravity, D cylinder diameter)
Entropy and Graph Based Modelling of Document Coherence using Discourse Entities: An Application
We present two novel models of document coherence and their application to
information retrieval (IR). Both models approximate document coherence using
discourse entities, e.g. the subject or object of a sentence. Our first model
views text as a Markov process generating sequences of discourse entities
(entity n-grams); we use the entropy of these entity n-grams to approximate the
rate at which new information appears in text, reasoning that as more new words
appear, the topic increasingly drifts and text coherence decreases. Our second
model extends the work of Guinaudeau & Strube [28] that represents text as a
graph of discourse entities, linked by different relations, such as their
distance or adjacency in text. We use several graph topology metrics to
approximate different aspects of the discourse flow that can indicate
coherence, such as the average clustering or betweenness of discourse entities
in text. Experiments with several instantiations of these models show that: (i)
our models perform on a par with two other well-known models of text coherence
even without any parameter tuning, and (ii) reranking retrieval results
according to their coherence scores gives notable performance gains, confirming
a relation between document coherence and relevance. This work contributes two
novel models of document coherence, the application of which to IR complements
recent work in the integration of document cohesiveness or comprehensibility to
ranking [5, 56]
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