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1.
Abstract: Maintainability problems associated with traditional software systems are exacerbated in rule-based systems. The very nature of that approach — separation of control knowledge and data-driven execution — hampers maintenance. While there are widely accepted techniques for maintaining conventional software, the same is not true for rule-based systems. In most situations, both a knowledge engineer and a domain expert are necessary to update the rules of a rule-based system. This paper presents, first, an overview of the software engineering techniques and object-oriented methods used in maintaining rule-based systems. It then discusses alternate paradigms for expert system development. The benefits of using case-based reasoning (from the maintenance point of view) are illustrated through the implementation of a case-based scheduler. The main value of the scheduler is that its knowledge base can be modified by the expert without the assistance of a knowledge engineer. Since changes in application requirements can be given directly to the system by the expert, the effort of maintaining the knowledge base is greatly reduced. 相似文献
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The photosensitizing properties of p-nitroacetophenone (PNAP), a well-known radiosensitizer, have been studied in near UV region. The mechanism of PNAP photosensitization has been investigated by testing the efficiency of singlet oxygen production using photooxidation of 2,2,6,6-tetramethylpiperidine (TEMP) and photodegradation of guanosine. In both the cases, the enhancement effect of deuterated solvents has been observed. Results of these experiments suggest the significant role of type II mechanisms in PNAP photosensitization. 相似文献
4.
G Bioque D Vargas O Bulbena J Roselló-Catafau Gelpi E 《Canadian Metallurgical Quarterly》1993,38(1-2):38-43
N-phenyllinoleamide (NPLA) has been detected as extraneous compound in adulterated cooking oils associated with a unique epidemic disease known as the Toxic Oil Syndrome (TOS). In this communication we report on the action of NPLA on the endogenous cyclooxygenase and lipoxygenase arachidonate metabolism. Results show that mouse peritoneal macrophages (MPM) exposed to 1 mM NPLA for 2 h undergo significant increases of 6-keto prostaglandin F1a, prostaglandin E2, leukotriene B4, 12- and 15-hydroxyeicosatetraenoic acids. MPM prelabelled with 3H-AA showed an enhanced release when exposed to NPLA. Thus, it is concluded that NPLA potentiates AA release from cell membrane phospholipids and the subsequent cyclooxygenase and lipoxygenase oxidative metabolism of this precursor to various eicosanoids. This is in agreement with the implication of peroxidative process mediated by fatty acids anilides in TOS. 相似文献
5.
AIM: To evaluate a new enzyme immunoassay (EIA) method for detection of Clostridium difficile toxin by comparing it to cytotoxicity assay. To investigate the nature of false negative and false positive EIA results by evaluating clinical and therapeutic parameters. METHODS: 737 consecutive diarrhoeal specimens collected from patients clinically suspected of having C difficile colitis were tested for the presence of C difficile toxin by EIA for toxin A and by cytotoxicity assay. Clinical data were evaluated in all cases positive by either method. RESULTS: With the cytotoxicity assay as a gold standard, the specificity of EIA for toxin detection was 99.3% and the sensitivity was 62.2%. No false negative EIA specimens were obtained from patients already being treated for C difficile colitis. Among patients with cytotoxicity positive specimens, those with EIA positive samples had no clinical features distinguishing them from patients with EIA negative samples. CONCLUSIONS: Although specific, the new EIA method directed against toxin A lacks sensitivity compared to cytotoxicity. False negative EIA tests are not associated with concurrent treatment for C difficile colitis nor with any specific clinical features examined in our study. 相似文献
6.
The author presents highlights from the 7th Annual IEEE Latin American Test Workshop (LATW '06), held in the capital city of Buenos Aires, Argentina, 26-29 March. 相似文献
7.
The phosphorylation of glucose to glucose-6-phosphate, catalyzed by hexokinase, is the first committed step in glucose uptake into skeletal muscle. Two isoforms of hexokinase, HKI and HKII, are expressed in human skeletal muscle, but only HKII expression is regulated by insulin. HKII messenger RNA, protein, and activity are increased after 4 h of insulin infusion; however, glucose uptake is stimulated much more rapidly, occurring within minutes. Studies in rat muscle suggest that changes in the subcellular distribution of HKII may be an important regulatory factor for glucose uptake. The present studies were undertaken to determine if insulin causes an acute redistribution of HKII activity in human skeletal muscle in vivo. Muscle biopsies (vastus lateralis muscle) were performed before and at the end of 30 min insulin infusion, performed using the euglycemic clamp technique. Muscle biopsies were subfractionated into soluble and particulate fractions to determine if insulin acutely changes the subcellular distribution of HKII. Insulin decreased HKII activity in the soluble fraction from 2.20 +/- 0.31 to 1.40 +/- 0.18 pmoles/(min[chempt]micrograms) and increased HKII activity in the particulate fraction from 3.02 +/- 0.46 to 3.45 +/- 0.46 pmoles/(min[chempt]micrograms) (P < 0.01 for both). These changes in HKII activity were correlated with changes in HKII protein, as determined by immunoblot analysis (r = 0.53, P = 0.05). Insulin had no effect on the subcellular distribution of HKII activity, which was primarily restricted to the soluble fraction. These studies are consistent with the conclusion that, in vivo in human skeletal muscle, insulin changes the subcellular distribution of HKII within 30 min. 相似文献
8.
SF Brenière W Morochi MF Bosseno J Ordo?ez T Gutierrez F Vargas N Yaksic F Noireau 《Canadian Metallurgical Quarterly》1998,71(3):269-283
Triatoma sordida is the second species of Triatominae considered of epidemiological significance in Bolivia. Associated with Triatoma infestans in various regions, it is as yet the only triatomine species established in human dwellings in localities of Velasco province, Department of Santa Cruz. This domestication is considered as primary. Flagellate parasites were detected in 16.2% of domiciliary T. sordida and the kDNA-PCR confirmed the presence of Trypanosoma cruzi. Frequencies of T. cruzi clonets 20 and 39, common clonets in Bolivian domestic cycle (T. infestans), were established by their direct detection in feces using PCR and hybridization. These clonets present low frequencies in T. sordida and synanthropic mammals. Forty-six stocks were isolated and analysed by multilocus enzyme electrophoresis (MLEE). The MLEE showed a higher clonal diversity than in T. infestans domestic cycle and the genotypes were clustered in the two principal lineages of T. cruzi. Within each lineage, a broad variability was observed. Mixture of genotypes was mostly observed in mammals. The large diversity of T. cruzi in this cycle should be related to its sylvatic origin. Moreover, the current limited sample of stocks suggests a lineage association with specific hosts. 相似文献
9.
F.J. Medellín‐Rodríguez J.M. Mata‐Padilla B.S. Hsiao M.A. Waldo‐Mendoza E. Ramírez‐Vargas S. Sánchez‐Valdes 《Polymer Engineering and Science》2007,47(11):1889-1897
The influence of organomodified nanoclay (montmorillonite) on the crystallization and melting mechanisms of isotactic polypropylene (iPP) was studied. Films of both neat polymer and clay nanocomposites were prepared after molecular weight optimization through melt extrusion. Products exhibited the tactoidlike morphology since no compatibilizers were used. The effect of introduction of nanoclay within the polymer was studied through isothermal crystallization and linear heating. The results indicated that low nanoclay concentrations induce the formation of the β‐crystalline structure, its formation being inhibited with high nanoclay contents. Dynamic nonisothermal bulk crystallization experiments indicated that nanoclays act as nucleating agents of iPP. Isothermal, bulk crystallization studies indicated that the crystallization process (induction time and crystallization kinetics) is proportionally accelerated by the nanoclay presence. There was also an accelerated formation of secondary crystallization when nanoclays were present in high concentrations. POLYM. ENG. SCI., 47:1889–1897, 2007. © 2007 Society of Plastics Engineers 相似文献
10.
A. Barrera J.A. Montoya M. Viniegra J. Navarrete G. Espinosa A. Vargas P. del Angel G. Prez 《Applied Catalysis A: General》2005,290(1-2):97-109
The catalytic performance of mono- and bimetallic Pd (0.6, 1.0 wt.%)–Pt (0.3 wt.%) catalysts supported on ZrO2 (70, 85 wt.%)–Al2O3 (15, 0 wt.%)–WOx (15 wt.%) prepared by sol–gel was studied in the hydroisomerization of n-hexane. The catalysts were characterized by N2 physisorption, XRD, TPR, XPS, Raman, NMR, and FT-IR of adsorbed pyridine. The preparation of ZrW and ZrAlW mixed oxides by sol–gel favored the high dispersion of WOx and the stabilization of zirconia in the tetragonal phase. The Al incorporation avoided the formation of monoclinic-WO3 bulk phase. The catalysts increased their SBET for about 15% promoted by Al2O3 addition. Various oxidation states of WOx species coexist on the surface of the catalysts after calcination. The structure of the highly dispersed surface WOx species is constituted mainly of isolated monotungstate and two-dimensional mono-oxotungstate species in tetrahedral coordination. The activity of Pd/ZrW catalysts in the hydroisomerization of n-hexane is promoted both with the addition of Al to the ZrW mixed oxide and the addition of Pt to Pd/ZrAlW catalysts. The improvement in the activity of Pd/ZrAlW catalysts is ascribed to a moderated acid strength and acidity, which can be correlated to the coexistence of W6+ and reduced-state WOx species (either W4+ or W0). The addition of Pt to the Pd/ZrAlW catalyst does not modify significantly its acidic character. Selectivity results showed that the catalyst produced 2MP, 3MP and the high octane 2,3-dimethylbutane (2,3-DMB) and 2,2-dimethylbutane (2,2-DMB) isomers. 相似文献