Dielectric, Switching and System Requirements under Out-of-Phase Conditions, during Synchronisation and under Comparable Stresses

Recent developments in electrical networks can increase the probability of out-of-phase switching and dielectric stresses being applied to open circuit-breakers, due to asynchronous systems at both sides. This report presents a systematic study of TRV-stresses associated with generator separation and system separation. TRV peak values are higher than required in the Standards, even for relatively small out-of-phase angles (75º to 90º), and the dielectric stresses are high with respect to the shortduration power frequency withstand voltages across a circuit-breaker open contacts, especially taking into consideration the external insulation under pollution and ageing processes. To the opinion of the authors, the Standards should be revised to give users clear and adequate guidance on the assessment and specification of TRV-values and dielectric withstand requirements under out-of-phase conditions

COVID-19 and Sepsis Are Associated With Different Abnormalities in Plasma Procoagulant and Fibrinolytic Activity

OBJECTIVE: Coronavirus disease 2019 (COVID-19) is associated with derangement in biomarkers of coagulation and endothelial function and has been likened to the coagulopathy of sepsis. However, clinical laboratory metrics suggest key differences in these pathologies. We sought to determine whether plasma coagulation and fibrinolytic potential in patients with COVID-19 differ compared with healthy donors and critically ill patients with sepsis. Approach and Results: We performed comparative studies on plasmas from a single-center, cross-sectional observational study of 99 hospitalized patients (46 with COVID-19 and 53 with sepsis) and 18 healthy donors. We measured biomarkers of endogenous coagulation and fibrinolytic activity by immunoassays, thrombin, and plasmin generation potential by fluorescence and fibrin formation and lysis by turbidity. Compared with healthy donors, patients with COVID-19 or sepsis both had elevated fibrinogen, d-dimer, soluble TM (thrombomodulin), and plasmin-antiplasmin complexes. Patients with COVID-19 had increased thrombin generation potential despite prophylactic anticoagulation, whereas patients with sepsis did not. Plasma from patients with COVID-19 also had increased endogenous plasmin potential, whereas patients with sepsis showed delayed plasmin generation. The collective perturbations in plasma thrombin and plasmin generation permitted enhanced fibrin formation in both COVID-19 and sepsis. Unexpectedly, the lag times to thrombin, plasmin, and fibrin formation were prolonged with increased disease severity in COVID-19, suggesting a loss of coagulation-initiating mechanisms accompanies severe COVID-19. CONCLUSIONS: Both COVID-19 and sepsis are associated with endogenous activation of coagulation and fibrinolysis, but these diseases differently impact plasma procoagulant and fibrinolytic potential. Dysregulation of procoagulant and fibrinolytic pathways may uniquely contribute to the pathophysiology of COVID-19 and sepsis

Lyapunov-stable discrete-time model reference adaptive control

Discrete-time model reference adaptive control (MRAC) is considered with both least squares and projection algorithm parameter identification. For both cases complete Lyapunov proofs are given for stability and convergence. The results extend the approach of Johansson ( Int. J. Control 1989; 50 (3):859–869) to include Lyapunov stability for MRAC when the normalized projection algorithm is used for parameter identification. Copyright © 2005 John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48767/1/876_ftp.pd

AIRS: the Infrared Spectroscopic Instrument of ESA M4 ARIEL mission

The AIRS spectrometer will be used for Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, which will allow to measure atmospheric signals from the planet at levels of 10-100 part per million (ppm) relative to the star. This will require exquisite control of the full photon to digital codes acquisition chain bias along the long duration observation sequence. The prism-based spectrometer has been specifically designed to use anamorphosis of the prisms for circularizing the PSF of the elliptical primary mirror pupil in order to ensure optimal sampling and SNR. Because of the large dynamics of the stars the detector for the long waveband in the 7.80 µm range will need to be state-of-the-art and to be operated at 40-K. <P /

Shade-tolerant flowering plants in the Southern African flora : morphology, adaptions and horticultural application

Shade plants (sciophytes) may be regarded as stress-tolerant and are classified either as obligate or facultative. Most southern African sciophytes are facultative. Two broad adaptive strategies are employed by shade plants. Optimal use is made of available energy and energy is conserved. Climatic, topographical and ecological factors are inseperable from the presence of shade. Temperature, humidity and nutrient status may even play a more important role in plant adaptation than the presence of shade. There are 1105 plants listed in the database. As might be expected of forest undergrowth in general, many southern African sciophytes are herbaceous perennials. This group forms 23% of the total number. Equivalent in represententatives, are the xerophytic plants (succulents) also 23%. These two groups together thus forms 43% of the shade plants. The second largest group are the woody plants which in total makes up 30% if the shrubs, trees and climbers are combined. The third largest group are the geophytic (bulbous) plants and forms 14% of the shade plants. All other groups make up less than 5% of the total. Many of the attributes encountered in sciophytes occurring in tropical rainforests are also found in the drier, southern African climate. The red undersurface of leaves which has hitherto only been described in herbaceous species, is described here in succulent, southern African sciophytes. The literature relating to anatomical and physiological adaptations of sciophytes is surveyed and discussed. Of particular interest is the phenomenon of sunflecks. Morphological adaptions include heart-shaped leaves, or variations thereof. The arrangements of stems and leaves to maximize the use of available light are architectural adaptations that are also discussed. Sciophytes practice many conservative reproductive strategies. Small and inconspicuous flowers are the norm. Where flowering in the shade does indeed occur, reproductive structures are adapted to local pollinating agents. Hybridisation of both herbaceous and succulent sciophytes is a common, natural phenomenon. Throughout the description of the adaptations, the applications thereof in horticultural terms have been highlighted where possible. The application is printed in bold letters directly following the adaptation described in the text. The practical side of shade gardening is discussed, highlighting and describing several southern African plants from different growth groups and situations. A database has been compiled, listing the southern African shade plants. As much as possible information on each plant concerning the names, distribution, description, uses, growth requirements and other additional general information has been made available in this database. Pre-selected combinations are printed out, for instance plants for specific horticultural uses or certain climatic conditions. Any other selected fields can be retrieved by the user according to his needs and choice directly from the database. The database should also be updated and supplemented with new information on each plant, as well as adding new plants.Dissertation (MSc)--University of Pretoria, 1998.Plant ScienceMScUnrestricte