This paper reports a detailed evaluation of the effectiveness of a system that has been developed for the identification and
retrieval of morphological variants in searches of Latin text databases. A user of the retrieval system enters the principal
parts of the search term (two parts for a noun or adjective, three parts for a deponent verb, and four parts for other verbs),
this enabling the identification of the type of word that is to be processed and of the rules that are to be followed in determining
the morphological variants that should be retrieved. Two different search algorithms are described. The algorithms are applied
to the Latin portion of the Hartlib Papers Collection and to a range of classical, vulgar and medieval Latin texts drawn from
the Patrologia Latina and from the PHI Disk 5.3 datasets. The effectiveness of these searches demonstrates the effectiveness
of our procedures in providing access to the full range of classical and post-classical Latin text databases.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
This paper is concerned with computing an L2-optimal reduced-order model for a given stable multivariable linear system in the presence of input and output frequency weightings. By parametrizing a class of reduced-order models in terms of an orthogonal projection and using manifold techniques as tools, both continuous and iterative algorithms are derived and their convergence properties are established. As an application, we show that an L2 optimal reduced-order filter in the closed-loop sense can be computed using these algorithms. 相似文献
The pervasive use of computers in work settings implies that an increased number of workers, with varying levels of skills and abilities, will be performing computerbased tasks. This study investigated the impact of age, cognitive abilities, and computer experience on the performance of a real world data entry task. One hundred and ten subjects, ranging in age from 20 - 75 years, performed the task for nine hours following task training. The results indicated that abilities such as visuo-spatial skills, motor skills and processing speed had a significant impact on performance as did age and prior computer experience. With respect to age, the older participants completed less work than the younger and middle-aged subjects. Age differences in psychomotor skills and processing speed appeared to be important factors underlying age effects. In fact, the data indicated that after controlling for differences in these abilities age was no longer a significant predictor of work output. Further, after controlling for differences in work output the older people made fewer errors than the younger people. Overall the data suggest that older people will be at a disadvantage in the performance of computer-based data entry work to the extent to which speed of responding is emphasized. However, if speed of responding is not a critical element of performance they will be able to achieve comparable levels of performance to that of younger people. 相似文献
This paper describes a new approach to mobile robot position estimation, based on principal component analysis of laser range data. An eigenspace is constructed from the principal components of a large number of range data sets. The structure of an environment, as seen by a range sensor, is represented as a family of surfaces in this space. Subsequent range data sets from the environment project as a point in this space. Associating this point to the family of surfaces gives a set of candidate positions and orientations (poses) for the sensor. These candidate poses correspond to positions and orientations in the environment which have similar range profiles. A Kalman filter can be used to select the most likely candidate pose based on coherence with small movements.
The first part of this paper describes how a relatively small number of depth profiles of an environment can be used to generate a complete eigenspace. This space is used to build a representation of the range scan profiles obtained from a regular grid of positions and orientations (poses). This representation has the form of a family of surface (a manifold). This representation converts the problem of associating a range profile to possible positions and orientations into a table lookup. As a side benefit, the method provides a simple means to detect obstacles in a range profile. The final section of the paper reviews the use of estimation theory to determine the correct pose hypothesis by tracking. 相似文献
Software engineering education has a 30-year history. It is a story of academics struggling to fulfill industry needs with almost no support from computer science curriculum designers. It is a story of industry finally winning over some of academia to teach software engineering rather than vanilla computer science. It is a story of a discipline still incomplete, but having made great strides in the last decade. This paper discusses the succeeding eras of software engineering education, from lone teachers to master's curricula to undergraduate degree programs. Even though the maturity of the discipline is as yet unattained, it will achieve adult status through practice, not by waiting for academia to glacially catch up. 相似文献
In this paper we present a general framework for synthesizing state feedback controllers to achieve any desired closed loop
dissipative behavior. Special cases include positive real andH∞ controller synthesis. We show that the solution to this dissipative controller synthesis problem is equivalent to the existence
of a solution to a partial differential inequality (nonlinear systems case) or an algebraic Riccati inequality (linear systems
case). Stability results can be obtained under appropriate detectability assumptions, and a generalization of the strict bounded
real lemma is given. We also present an application of the results to a robust stabilization problem.
This work was supported by the Cooperative Research Centre for Robert and Adaptive Systems (CRASys), Australia. 相似文献
A path-method is used as a mechanism in object-oriented databases (OODBs) to retrieve or to update information relevant to one class that
is not stored with that class but with some other class. A path-method is a method which traverses from one class through
a chain of connections between classes and accesses information at another class. However, it is a difficult task for a casual
user or even an application programmer to write path-methods to facilitate queries. This is because it might require comprehensive
knowledge of many classes of the conceptual schema that are not directly involved in the query, and therefore may not even
be included in a user's (incomplete) view about the contents of the database. We have developed a system, called path-method generator (PMG), which generates path-methods automatically according to a user's database-manipulating requests. The PMG offers the
user one of the possible path-methods and the user verifies from his knowledge of the intended purpose of the request whether
that path-method is the desired one. If the path method is rejected, then the user can utilize his now increased knowledge
about the database to request (with additional parameters given) another offer from the PMG. The PMG is based on access weights attached to the connections between classes and precomputed access relevance between every pair of classes of the OODB. Specific rules for access weight assignment and algorithms for computing access
relevance appeared in our previous papers [MGPF92, MGPF93, MGPF96]. In this paper, we present a variety of traversal algorithms
based on access weights and precomputed access relevance. Experiments identify some of these algorithms as very successful
in generating most desired path-methods. The PMG system utilizes these successful algorithms and is thus an efficient tool
for aiding the user with the difficult task of querying and updating a large OODB.
Received July 19, 1993 / Accepted May 16, 1997 相似文献
Summary. We set out a modal logic for reasoning about multilevel security of probabilistic systems. This logic contains expressions
for time, probability, and knowledge. Making use of the Halpern-Tuttle framework for reasoning about knowledge and probability,
we give a semantics for our logic and prove it is sound. We give two syntactic definitions of perfect multilevel security
and show that their semantic interpretations are equivalent to earlier, independently motivated characterizations. We also
discuss the relation between these characterizations of security and between their usefulness in security analysis. 相似文献
This article discusses the definition of cyberterrorism and its potential, and suggests an approach to minimizing its dangers. The definition of cyberterrorism used in this article combines the United States Department of State's definition of terrorism as politically motivated acts of violence against non-combatants with a definition of cyberspace as the computers, networks, programs and data which make up the information infrastructure. The conclusion is that by limiting the physical capabilities of the information infrastructure, we can limit its potential for physical destruction. 相似文献
The robust H∞ control problem for discrete-time uncertain systems is investigated in this paper. The uncertain systems are modelled as
a polytopic type with linear fractional uncertainty in the vertices. A new linear matrix inequality (LMI) characterization
of the H∞ performance for discrete systems is given by introducing a matrix slack variable which decouples the matrix of a Lyapunov
function candidate and the parametric matrices of the system. This feature enables one to derive sufficient conditions for
discrete uncertain systems by using parameter-dependent Lyapunov functions with less conservativeness. Based on the result,
H∞ performance analysis and controller design are carried out. A numerical example is included to demonstrate the effectiveness
of the proposed results.
This work was partially supported by RGC Grant 7103/01P and the open project of the state key Laboratory of intelligent and
Systems, Tsinghua University (No.0406). 相似文献