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41.
FC Blow KL Barry BJ BootsMiller LA Copeland R McCormick S Visnic 《Canadian Metallurgical Quarterly》1998,32(5):311-319
Within a fungal species, a subset of individuals may have more than the minimal complement of chromosomes. If the extra chromosomes are composed primarily of DNA not found in all representatives of the species, they are most appropriately referred to as supernumerary chromosomes. The patterns of repeated DNA sequences on certain supernumerary chromosomes suggest that they have a different evolutionary history from the essential chromosomes in the same genome. Supernumerary chromosomes can carry functional genes and, in at least two fungal species, genes on such chromosomes play important roles in host-pathogen interactions. Supernumerary chromosomes that confer an adaptive advantage in certain habitats, such as the ability to cause disease on a specific host, may be referred to as "conditionally dispensable" chromosomes in order to reflect their importance in some, but not all, growth conditions. In addition to describing the structural and functional characteristics of known supernumerary chromosomes in fungi, this review discusses the relative merits of the terms that have been used to describe them, and establishes experimental criteria for their identification. 相似文献
42.
GW Gao SH Lin YF Lin LK Diang KC Lu FC Yu SD Shieh 《Canadian Metallurgical Quarterly》1996,57(6):438-442
Despite a general national decline in criminal activities in the 1990s, juvenile criminal offenses continue to increase, (including violent, property, and delinquency acts). In addition increased numbers of children are being held in juvenile jails. It is all but impossible for pediatric health providers to think that "their patients" and "their practices" are immune from the epidemic of crime that affects and is caused by "just kids." 相似文献
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The need to make the contents of the Semantic Web accessible to end-users becomes increasingly pressing as the amount of information stored in ontology-based knowledge bases steadily increases. Natural language interfaces (NLIs) provide a familiar and convenient means of query access to Semantic Web data for casual end-users. While several studies have shown that NLIs can achieve high retrieval performance as well as domain independence, this paper focuses on usability and investigates if NLIs and natural language query languages are useful from an end-user's point of view. To that end, we introduce four interfaces each allowing a different query language and present a usability study benchmarking these interfaces. The results of the study reveal a clear preference for full natural language query sentences with a limited set of sentence beginnings over keywords or formal query languages. NLIs to ontology-based knowledge bases can, therefore, be considered to be useful for casual or occasional end-users. As such, the overarching contribution is one step towards the theoretical vision of the Semantic Web becoming reality. 相似文献
46.
Friesz Terry L. Bernstein David Suo Z. Tobin Roger L. 《Networks and Spatial Economics》2001,1(3-4):319-347
This paper recasts the Friesz et al. (1993) measure theoretic model of dynamic network user equibrium as a controlled variational inequality problem involving Riemann integrals. This restatement is done to make the model and its foundations accessible to a wider audience by removing the need to have a background in functional analysis. Our exposition is dependent on previously unavailable necessary conditions for optimal control problems with state-dependent time lags. These necessary conditions, derived in an Appendix, are employed to show that a particular variational inequality control problem has solutions that are dynamic network user equilibria. Our analysis also shows that use of proper flow propagation constraints obviates the need to explicitly employ the arc exit time functions that have complicated numerical implementations of the Friesz et al. (1993) model heretofore. We close by describing the computational implications of numerically determining dynamic user equilibria from formulations based on state-dependent time lags. 相似文献
47.
A survey of approaches to automatic schema matching 总被引:76,自引:1,他引:75
Erhard Rahm Philip A. Bernstein 《The VLDB Journal The International Journal on Very Large Data Bases》2001,10(4):334-350
Schema matching is a basic problem in many database application domains, such as data integration, E-business, data warehousing,
and semantic query processing. In current implementations, schema matching is typically performed manually, which has significant
limitations. On the other hand, previous research papers have proposed many techniques to achieve a partial automation of
the match operation for specific application domains. We present a taxonomy that covers many of these existing approaches,
and we describe the approaches in some detail. In particular, we distinguish between schema-level and instance-level, element-level
and structure-level, and language-based and constraint-based matchers. Based on our classification we review some previous
match implementations thereby indicating which part of the solution space they cover. We intend our taxonomy and review of
past work to be useful when comparing different approaches to schema matching, when developing a new match algorithm, and
when implementing a schema matching component.
Received: 5 February 2001 / Accepted: 6 September 2001 Published online: 21 November 2001 相似文献
48.
We consider adaptive stabilization for a class of nonlinear second-order systems. Interpreting the system states as position and velocity, the system is assumed to have unknown, nonparametric position-dependent damping and stiffness coefficients. Lyapunov methods are used to prove global convergence of the adaptive controller. Furthermore, the controller is shown to be able to reject constant disturbances and to asymptotically track constant commands. For illustration, the controller is used to stabilize the van der Pol limit cycle, the Duffing oscillator with multiple equilibria, and several other examples 相似文献
49.
C Beretta-Piccoli P Weidmann R de Chatel D Hirsch FC Reubi 《Canadian Metallurgical Quarterly》1977,107(4):104-115
35 patients with benign essential hypertension were treated for 6 weeks with high doses of the mineralocorticoid-antagonist spironolactone (400 mg/day), or with the "loop-diuretic" mefruside (mean maximal dose 110 mg/day). Spironolactone caused greater reductions in blood pressure and blood volume and a more marked increase in plasma renin activity (PRA) than mefruside (p less than 0.05). It appears possible that he weaker antihypertensive effect of mefruside may relate partly to its lesser influence on circulatory volume. With both diuretics, mean decreases in blood pressure were greater in patients with low pre-therapeutic PRA than in patients with normal or high PRA. However, the diuretic-induced changes in blood pressure did not correlate with the associated variations in blood volume or PRA. Thus, the increased blood pressure sensitivity to diuretics in patients with low-renin essential hypertension did not appear to be volume or renin-dependent. Under normal conditions, the maintenance of a constant blood pressure during volume depletion may partly depend on compensatory activation of the sympathetic nervous system. Moreover, patients with low-renin essential hypertension have been found to have decreased adrenergic activity. It seems possible, therefore, that the marked blood pressure sensitivity to diuretic treatment in such patients may be the result of an impaired compensatory sympathetic response to sodium and volume depletion. Analysis of the literature suggests that the diuretic furosemide, a structural relative of mefruside, may also have less blood pressure lowering efficacy in patients with essential hypertension than the distally-acting thiazides, chlorthalidone or spironolactone. Consideration of possible differences in the blood pressure reducing potential of certain diuretics thus appears to be necessary in planning the pharmacotherapy of essential hypertension. 相似文献
50.
As is readily apparent, there is not a consensus regarding the treatment of lateral ligamentous ruptures of the ankle. Certainly, the elimination of functional instability is the goal of treatment. What actually causes this is still open to debate, but from Harrington's work, it appears that degenerative changes can result from mechanical instability. We are all aware that many athletes compete actively with "two-plane" instability of the ankle, but it remains to be seen if they will also suffer the late degenerative changes that Harrington describes. In the meantime, each physician must decide which diagnostic technique to rely upon and which treatment regimen will provide the most consistent results with the least incidence of functional instability. 相似文献