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51.
52.
RH Peters EF Wever RN Hauer EO Robles de Medina 《Canadian Metallurgical Quarterly》1998,19(7):1070-1074
AIMS: The aetiology of ventricular fibrillation in patients without identifiable structural heart disease is unknown. Recently, high prevalence of silent ischaemia due to coronary artery spasm has been reported in such patients. However, in at least one report, all patients had non-critical coronary artery lesions. Identification of coronary artery spasm as the underlying aetiology of ventricular fibrillation has important therapeutic implications. METHODS AND RESULTS: We performed ergonovine provocation tests in 18 patients (14 males, and four females; mean age, 36 years) with documented ventricular fibrillation in the absence of identifiable structural heart disease who had undergone aborted sudden death. In group I (n = 7) ergonovine provocation tests were performed at a mean interval of 31 months (range 21-42 months) after the index episode. These patients had already received an implantable cardioverter defibrillator, after failed electrophysiologically guided antiarrhythmic therapy. In group II (n = 11) the ergonovine provocation test was performed prospectively as part of the diagnostic evaluation. All patients were off antiarrhythmic drugs, calcium entry or beta-adrenoceptor blockers at the time of the ergonovine provocation test. Ergonovine was administered intravenously as a bolus injection, beginning with 0.05 mg followed every 3 min by incremental doses up to a cumulative maximum dose of 0.45 mg. Predefined end-points were (1) recording of ischaemic ST segment shifts of > or = 1 mm in at least two corresponding leads of the 12-lead electrocardiogram; (2) induction of ventricular tachycardia or ventricular fibrillation; and (3) administration of a cumulative dose of 0.45 mg. A positive response to ergonovine was seen in only one patient (5%) in group I in whom there developed ST segment elevation without angina and a short burst of rapid ventricular tachycardia. CONCLUSIONS: This study found a low prevalence of coronary artery spasm in patients with aborted sudden death resulting from documented ventricular fibrillation and non-apparent underlying heart disease. All patients had normal coronary angiograms and a negative history for spontaneous episodes of chest pain. The mechanism of arrhythmogenesis in such patients remains largely unknown. 相似文献
53.
Barranco A Alonso-Salces RM Crespo I Berrueta LA Gallo B Vicente F Sarobe M 《Journal of food protection》2004,67(12):2786-2791
The levels of polycyclic aromatic hydrocarbons (PAHs) were determined by reversed-phase high-performance liquid chromatography with fluorescence detection in different fatty foods from a Spanish market. The average concentration of the sum of total PAHs in edible vegetable oils was below 25 ng/g, whereas the sum of heavy PAHs did not surpass 5 ng/g. Olive pomace oils obtained before the summer of 2001 were an exception because they were highly contaminated. The effects of different technological processes, such as bleaching, deodorization, and hydrogenation, on PAH concentration in edible oils have been studied. The PAH profiles, as well as the influence of cooking procedures, of other fatty foods (margarine, mayonnaise, and oils from canned fishes) have been examined. 相似文献
54.
Short-Channel Effect Limitations on High-Frequency Operation of AlGaN/GaN HEMTs for T-Gate Devices 总被引:4,自引:0,他引:4
Jessen G.H. Fitch R.C. Gillespie J.K. Via G. Crespo A. Langley D. Denninghoff D.J. Trejo M. Heller E.R. 《Electron Devices, IEEE Transactions on》2007,54(10):2589-2597
AlGaN/GaN high-electron mobility transistors (HEMTs) were fabricated on SiC substrates with epitaxial layers grown by multiple suppliers and methods. Devices with gate lengths varying from 0.50 to 0.09 mum were fabricated on each sample. We demonstrate the impact of varying the gate lengths and show that the unity current gain frequency response (fT) is limited by short-channel effects for all samples measured. We present an empirically based physical model that can predict the expected extrinsic fT for many combinations of gate length and commonly used barrier layer thickness (tbar) on silicon nitride passivated T-gated AlGaN/GaN HEMTs. The result is that even typical high-aspect-ratio (gate length to barrier thickness) devices show device performance limitations due to short-channel effects. We present the design tradeoffs and show the parameter space required to achieve optimal frequency performance for GaN technology. These design rules differ from the traditional GaAs technology by requiring a significantly higher aspect ratio to mitigate the short-channel effects. 相似文献
55.
M.J. Escalona M. Urbieta G. Rossi J.A. Garcia-Garcia E. Robles Luna 《Journal of Systems and Software》2013
Web requirements engineering is an essential phase in the software project life cycle for the project results. This phase covers different activities and tasks that in many situations, depending on the analyst's experience or intuition, help getting accurate specifications. One of these tasks is the conciliation of requirements in projects with different groups of users. This article presents an approach for the systematic conciliation of requirements in big projects dealing with a model-based approach. The article presents a possible implementation of the approach in the context of the NDT (Navigational Development Techniques) Methodology and shows the empirical evaluation in a real project by analysing the improvements obtained with our approach. The paper presents interesting results that demonstrate that we can get a reduction in the time required to find conflicts between requirements, which implies a reduction in the global development costs. 相似文献
56.
Eloy Garcia Yongcan Cao Han Yu Panos Antsaklis David Casbeer 《International journal of control》2013,86(9):1479-1488
This note studies event-triggered control of Multi-Agent Systems (MAS) with first-order integrator dynamics. It extends previous work on event-triggered consensus by considering limited communication capabilities through strict peer-to-peer non-continuous information exchange. The approach provides both a decentralised control law and a decentralised communication policy. Communication events require no global information and are based only on local state errors; agents do not require a global sampling period or synchronous broadcasting as in sampled-data approaches. The proposed decentralised event-triggered control technique guarantees that the inter-event times for each agent are strictly positive. Finally, the ideas in this note are used to consider the practical scenario where agents are able to exchange only quantised measurements of their states. 相似文献
57.
Luciana Katty Figueiredo Sanches Edmea Lodovici Leticia Cristina Cidreira Boaro Leonardo Eloy Rodrigues-Filho 《Journal of Adhesion Science and Technology》2013,27(12):1386-1394
The durability of adhesive interfaces is still a problem in adhesive restorations in dentistry. Laboratorial ageing methods have been proposed to predict the performance of materials, but they still require standardization. The objective of this study was to evaluate the resin-dentin microtensile bond strength of composite restorations subjected to pH cycling and different levels of mechanical loading. Resin blocks were built over a flat superficial dentin of bovine incisors (n = 40), using a three-step adhesive system. Half of the specimens were submitted to 10 cycles of pH cycling, followed by mechanical loading (0, 500,000; 1,000,000; 2,000,000 cycles – 98 N, 4 Hz). The other half was directly subjected to mechanical loading. After ageing, all groups were subjected to a microtensile bond test. Data were analyzed using two-way ANOVA and Tukey’s test (α = 0.05). The frequency of the early de-bonding was compared using the Chi-square test (α = 0.05). The statistical analysis revealed that the cross-product interaction ‘pH cycling’ vs. ‘number of mechanical loading cycles’ (p = 0.72) as well as the main factor ‘pH cycling’ (p = 0.49) was not statistically significant, and they were not able to reduce the resin–dentin bond strength values. Regarding the number of mechanical loading cycles, the groups subjected to 2,000,000 cycles showed lower bond strength values than the others (p = 0.003). The frequency of debonded specimens increased with mechanical loading. Therefore, it can be concluded that in this restorative model, at least 2,000,000 mechanical cycles are need to decrease the microtensile strength and simulate the ageing of the interface. 相似文献
58.
A comparison of different isolation techniques and culture media for detection of filamentous fungi and yeasts in the aquatic environment revealed that the use of membrane filtration with the media dichloran rose bengal chloramphenicol (DRBC) optimized fungi detection in terms of abundance and variety in three untreated water sources with very different characteristics (surface water, spring water, and groundwater). The diversity of the fungi population captured by direct DNA extraction of fungi collected by membrane filtration was compared with the isolates obtained after selective growth using different culture media through amplification of the internal transcribed spacer gene and denaturing gradient gel electrophoresis (DGGE). The Czapek-Dox agar, Sabouraud dextrose agar, and DRBC media showed closer similarities to those obtained by the uncultured biomass for the different water sources. Based on these data and the best enumeration results, DRBC is recommended for the assessment of fungi in water sources using culture-based methods. DGGE was also used to monitor temporal variations in the fungal population structure and showed that each water matrix possessed a distinct population profile as well as that changes in the fungal community can be expected in the different matrices throughout the year. 相似文献
59.
Claudia F. Galinha Gilda Carvalho Carla A. M. Portugal Giuseppe Guglielmi Maria A. M. Reis João G. Crespo 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2011,86(7):985-992
BACKGROUND: The use of two‐dimensional (2D) fluorescence for monitoring complex biological systems requires careful assessment of the effect of chemical species present, which may be fluorescent and/or may interfere with the fluorescence response of target fluorophores. Given the complexity of fluorescence data (excitation emission matrices—EEMs), the challenge is how to recover the information embedded into those EEMs that can be related quantitatively with the observed performance of the biological processes under study. RESULTS: This work shows clearly that interference effects (such as quenching and inner filter effects) occur due to the presence of multiple species in complex biological media, such as natural water matrices, wastewaters and activated sludge. A statistical multivariate analysis is proposed to recover quantitative information from 2D fluorescence data, correlating EEMs with the observed performance. A selected case study is discussed, where 2D fluorescence spectra obtained from the effluent of a membrane bioreactor were compressed using PARAFAC and successfully correlated with the effluent chemical oxygen demand, using projection to latent structures modelling. CONCLUSION: This study demonstrates the potential of using 2D fluorescence spectroscopy as a status fingerprint. Additionally, it is shown how statistical multivariate data analysis can be used to correlate EEMs with selected performance parameters for monitoring of biological systems. Copyright © 2011 Society of Chemical Industry 相似文献
60.
María J. Martín de Vidales José Robles‐Molina Juan C. Domínguez‐Romero Pablo Cañizares Cristina Sáez Antonio Molina‐Díaz Manuel A. Rodrigo 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2012,87(10):1441-1449
BACKGROUND: Sulfamethoxazole (SMX, used as a model bacteriostatic antibiotic) is persistent to conventional biological treatments of wastewaters. In this work, conductive‐diamond electrochemical oxidation (CDEO) was found to be an effective technology for its removal from the effluents of conventional wastewater treatment plants. RESULTS: The use of CDEO has been evaluated for the removal of the antibiotic SMX from water and wastewaters. The results show that CDEO can reduce the concentration of this organic pollutant to values below 0.1 µg dm?3. The variation of the SMX concentration during electrolysis shows a complex shape with a plateau zone that increases in size with the initial concentration of SMX. This complex trend is not observed in the changes of TOC, which seems to indicate that the CDEO of SMX solutions does not lead directly to the generation of carbon dioxide as a final product. A tentative reaction pathway has been proposed based on a thorough analysis of the reaction mixture, in which the main intermediate products were identified. The use of liquid chromatography time‐of‐flight mass spectrometry (LC‐TOFMS) allowed the identification of nine organic intermediates (with Mw 98, 108, 172, 173, 197, 203, 227, 269 and 287) during the electrolysis and the concentration of these compounds depends on the initial SMX concentration and on the current density applied. CONCLUSIONS: CDEO is able to reduce the concentration of the organic pollutant below 0.1 mg dm?3. SMX removal is faster than that of TOC. This fact indicates the formation of reaction intermediates. Analytical techniques show that nine reaction intermediates are generated in the system, and that their concentration depends on the initial SMX concentration and on the current density used. Copyright © 2012 Society of Chemical Industry 相似文献