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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Zeitschrift für angewandte Mathematik und Physik 41 (1990), S. 889-899 
    ISSN: 1420-9039
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik , Physik
    Notizen: Abstract Crack-plane stresses and the stress intensity factor were determined in an orthotropic double-cantilever-beam configuration. The DCB fracture specimen was modeled as an infinite strip containing a semi-infinite crack at its midplane. Concentrated loads acted upon the crack surfaces, whereas the strip surfaces were traction free. Constitutive equations of an orthotropic body involving four independent material constants were considered. Fourier transforms and the Wiener-Hopf technique were utilized for an analytical solution within the context of the two-dimensional, linear theory of elasticity.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    ISSN: 0942-0940
    Schlagwort(e): Neuroanaesthesia ; sitting position ; complications ; paradoxical air embolism monitoring ; transoesophageal echocardiography
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary This prospective study investigates the frequency of patent foramen ovale (PFO), venous air embolism (VAE) and paradoxical air embolism (PAE) by transoesophageal echocardiography (TOE) in neurosurgical patients operated on in the sitting position. The risk of PAE after exclusion of PFO is assessed. A PFO was identified by pre-operative TOE and VAE and PAE by continuous intra-operative TOE. Sixty-two patients were divided into two groups, 22 patients were studied in group 1 (posterior fossa surgery) and group 2 (cervical surgery) contained 40 patients. Pre-operative TOE demonstrated a PFO in 5 of the 22 patients in group 1 (23%). Patients with proven PFO were excluded from the sitting position. Two further patients of this group (12% of 17 patients), in whom a PFO had been excluded pre-operatively, nevertheless had PAE, air occurring in all cavities of the heart. In group 2 the incidence of PFO was 4 out of 40 patients (10%). No PAE was observed in this group. Three morphological types of VAE with different haemodynamic and ventilation changes were demonstrated. VAE was observed in 76% of all posterior fossa operations and in 25% of cervical laminectomies. We conclude that a pre-operative search for PFO is mandatory considering its incidence of 23% in group 1 and of 10% in group 2, and the risk of PAE. If a PFO is detected, the sitting position should be avoided. A residual risk for PAE remains despite exclusion of PFO because the reliability of TOE is limited. TOE is the method of choice for detecting VAE and PAE.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Der Anaesthesist 43 (1994), S. 441-446 
    ISSN: 1432-055X
    Schlagwort(e): Schlüsselwörter: Nichtinvasive Blutdruckmessung – Oszillometrie – Neonaten – Simulator – Geräteprüfung ; Key words: Blood pressure measurement – Oscillometric method – Neonates – Simulator – Performance test
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Abstract. Non-invasive blood pressure measurements by the auscultatory method do not provide reliable, reproducible blood pressure values in many neonates because the Korottkoff sounds are often very difficult to detect. This resulted in the development of many alternative indirect methods. Devices utilizing the Doppler ultrasound technique have not found wide acceptance. Since the introduction of automated oscillometric blood pressure monitors, arterial blood pressure has been increasingly brought into discussion as an indicator of the circulatory state. This is the first study to investigate the similarity and reproducibility of the data obtained with five oscillometric devices for measurement of blood pressure in neonates. Materials and methods. Since investigations on the technical performance are not practical in the clinical setting of a neonatal or pediatric ward, we used two simulators, the CuffLink (Dynatech, Nevada, USA) and a device developed by the PTB (Physikalisch-Technische Bundesanstalt). While the latter uses oscillations originally obtained from neonates, the CuffLink uses artificial and therefore ideal signals for the blood pressure monitors. The signals used for the PTB simulator were obtained from three neonates with an average age of 2 months and a weight of 3.5 kg, 4.4 kg, and 7.8 kg. The following blood pressure monitors were studied: Hoyer/Colin, BP-1001; Datex, Cardiocap II; SpaceLabs, model no. 90426; Hewlett-Packard, NBP M1008A; Critikon, Dinamap 1846. Before the measurements were started, the cuff pressure display of each monitor was checked according to a verification procedure. Although the 4 mm Hg margin of error was not exceeded, the results were corrected. Results. The results of the measurements show significant differences between the blood pressure monitors from the various manufacturers, with the differences for the ideal signals of the CuffLink-Simulator being less pronounced than those for the PTB simulator. Direct comparison of results is therefore often impossible. The standard deviation, taken from 20 measurements per monitor and simulation, is below 4 mm Hg for both simulators. We can therefore conclude that the reproducibility of data is satisfactory and the emerging trend is reliable. Discussion. The difference between the results of the PTB simulator and the CuffLink are probably due to the method of evaluation and the identification of artifacts of each blood pressure monitor. This is also confirmed by the studies of Mieke et al. The manufacturers should provide devices that display comparative results and improve the algorithms for detection of artefacts, increasing the accuracy of their blood pressure monitors. This could be done with the help of simulators. Considering the pathophysiological characteristics of neonates and infants, the systematic differences between the five monitors have to be regarded as serious.
    Notizen: Zusammenfassung. Mit Hilfe zweier Simulatoren wurde das Meßverhalten von fünf automatischen Blutdruckmeßgeräten für Neugeborene (Hoyer/Colin, BP-1001; Datex, Cardiocap II; SpaceLabs, Modul 90426; Hewlett-Packard, NBP M1008A; Critikon, Dinamap 1846) auf Vergleichbarkeit und Reproduzierbarkeit der Ergebnisse untersucht. Die an den Simulatoren durchgeführten Messungen zeigen deutliche Unterschiede zwischen den Geräten verschiedener Hersteller. Da die Standardabweichung, ermittelt aus jeweils 20 Wiederholungsmessungen meist unter 4 mm Hg liegt, kann bei diesen Geräten von einer guten bis befriedigenden Reproduzierbarkeit der Messungen gesprochen und der Trend somit relativ sicher ermittelt werden. Angesichts der pathophysiologischen Besonderheiten beim Neugeborenen sind die systematischen Unterschiede zwischen den einzelnen Geräten als gravierend einzustufen. Die Industrie wird aufgefordert, die Vergleichbarkeit der Geräte verschiedener Hersteller zu erreichen.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    ISSN: 1432-055X
    Schlagwort(e): Schlüsselwörter: Offenes Foramen ovale – Transösophageale Echokardiographie – Transthorakale Echokardiographie ; Key words: Patent foramen ovale – Transoesophageal echocardiography – Transthoracic echocardiography
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Abstract. Preoperative detection of a patent foramen ovale (PFO) may be achieved employing either transthoracic echocardiography (TTE) with the Valsalva manoeuvre in the awake patient or trans-oesophageal echocardiography (TEE) in the anaesthesised patient. Our study was undertaken to validate these methods with regard to their efficacy in identifying patients at risk for paradoxical air embolism (PAE). Methods. In 67 patients ranging from 28 to 70 years of age, TEE was performed utilising the Valsalva manoeuvre prior to surgery. The patients were informed about all procedures and agreed to take part in the study. After induction of anaesthesia the patients were evaluated with TEE in the supine and sitting positions. At end-inspiration 10 ml agitated gelatine solution (Gelafundin) was injected through a central venous catheter into the right atrium after airway pressure of 20 cm H2O had been maintained for 5 s. The injected bolus was observed throughout the ventilatory cycle, with special attention being given to early expiration and systole. A right-to-left shunt was assumed if five echo targets were observed in the left atrium. Results. The prevalence of PFO detected by TTE/Valsalva was 9%. The diagnosis was confirmed by TEE in 2 patients in the supine and 1 in the sitting position. An echocardiogram in these patients showed bulging of the septum to the left, which was not seen in those patients in whom PFO was detected only by TTE. Discussion. The reason for the lower incidence of PFO detected by TEE during airway pressure 20 cm H2O may have been an insufficient increase of pressure in the right atrium with a negative right-to-left atrial pressure gradient. A standardised ventilation manoeuvre with supra-atmospheric airway pressure of 20 cm H2O is not sufficient. Bulging of the intra-atrial septum from right to left during airway pressure is a possible indication of the efficacy of the manoeuvre, regardless of the influence of the breathing pattern.
    Notizen: Zusammenfassung. In einer offenen prospektiven Untersuchung wurde die Wertigkeit der transösophagealen Echokardiographie (TEE) zum intraoperativen Nachweis eines funktionell offenen Foramen ovale (PFO) untersucht. Die Untersuchungen auf das Vorliegen eines PFO erfolgten präoperativ durch die transthorakale Echokardiographie (TTE) mit Hilfe des Valsalvamanövers, intraoperativ mittels TEE unter Durchführung eines Ventilationsmanövers (Atemwegsdruck von 20 cm H2O). Dabei wurde als Kontrastmittel Gelatinelösung (Gelafundin®) injiziert. Bei sechs von 67 Patienten konnte durch die TTE ein PFO mit Rechts-links-Shunt nachgewiesen werden. Nur drei dieser sechs Patienten zeigten mit der TEE (Ventilationsmanöver) einen positiven Befund. Echokardiographisch zeigte sich eine linkskonvexe Verlagerung des interatrialen Septums. Dies war nicht der Fall bei den Patienten mit nur durch TTE nachgewiesenen PFO. Als Ursache für die geringere Sensitivität der TEE unter Provokationsmanöver mit Atemdruck von 20 cm H2O kommt eine nicht ausreichende Druckerhöhung im rechten Vorhof mit negativem rechts/linksatrialen Druckgradienten in Frage. Aufgrund unserer Ergebnisse und Literaturangaben erscheint uns ein standardisiertes Ventilationsmanöver mit Atemwegsdruck von 20 cm H2O zum Nachweis eines PFO mit Rechts-links-Shunt nicht ausreichend. Die transiente linksgerichtete Verlagerung des interatrialen Septums während eines Manövers bei beatmeten Patienten kann möglicherweise als Hinweis auf eine effektive Provokation angesehen werden.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 5
    ISSN: 1432-0428
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Communications in mathematical physics 151 (1993), S. 467-479 
    ISSN: 1432-0916
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik , Physik
    Notizen: Abstract Irreducible sigma models, i.e. those for which the partition function does not factorise, are defined on Riemannian spaces with irreducible holonomy groups. These special geometries are characterised by the existence of covariantly constant forms which in turn give rise to symmetries of the supersymmetric sigma model actions. The Poisson bracket algebra of the corresponding currents is aW-algebra. Extended supersymmetries arise as special cases.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Experiments in fluids 15 (1993), S. 459-461 
    ISSN: 1432-1114
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 4 Summary A simple hot-wire sensor positioning technique is presented. The technique is easily integrated with a personal computer to achieve a completely automated system. A single initial calibration of the system outside of the test section is all that is necessary and no subsequent manual re-positioning is required during experimentation. This gives the capability of performing multiple measurements of near-wall velocity at different locations on a wall surface without the need of cumbersome and extensive alignment of the traverse system with respect to the wall surface. Preliminary tests indicate that the technique is viable for near-wall velocity measurements.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Experiments in fluids 14 (1993), S. 213-216 
    ISSN: 1432-1114
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Summary The secondary flow due to the growth of the streamwise vortices near the side walls serves to diminish the spanwise uniformity of the time-mean flow properties. In the region adjacent to the side walls, momentum mixing is enhanced due to the existence of the secondary flow and the separated shear layer spreads faster. There is a corresponding increase in the non-coherent turbulence in this region near the side walls. The increased spreading rates and overall turbulence in the shear layer, in turn, tend to suppress the rolling-up of the separated shear layer into organized structures. This effect is rapidly carried into the core two-dimensional flow region as the streamwise vortex grows under the influence of the adverse pressure gradient. The surface visualizations provide further evidence of the existence of secondary flows near the side walls.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 9
    ISSN: 1432-1106
    Schlagwort(e): Somatostatin ; Visual deprivation ; Cortical areas 17, 18, 18a ; Transience ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The distribution of somatostatin (SRIF)-immunoreactive neurons in the visual cortical areas 17, 18 and 18a of Wistar rats from birth to adulthood was followed in both normal and dark-reared animals. The SRIF neurons show difference in distribution amongst the three cortical areas studied as early as the first postnatal week. Area 17 was distinguished by fewer SRIF cells in the upper layers (I–III), which results in a lower overall density. The SRIF neurons in all areas appeared to increase in numbers up to about 3 weeks and then decline dramatically to adult levels, which were 14–19% of the peak levels. Although this decline was still obvious, it moderated to 25–31% in dark-reared animals. The greatest effect was seen in area 18 where, at 60 days of age, there were twice as many SRIF cells in darkreared as in normal controls. It is suggested that, under conditions of dark rearing, the overall pattern of development of SRIF neurons, being uninfluenced by extrinsic factors, reveals the cells' genetic potential.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 26 (1991), S. 569-578 
    ISSN: 1573-4803
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The crack propagation in PCBA (Lexan)-PMMA (Plexiglas) sandwich plates has been studied by means of the high-speed photography together with a dynamic caustics method. Various phenomena were observed in these experiments: the time lag between the two cracks propagating into the two phases of the sandwich, the time coincidence of the two propagating cracks and phenomena of acceleration, deceleration and bifurcation of the propagating cracks. More precisely, the initial crack begins to propagate first into the brittle (PMMA) phase while a second crack begins to propagate later into the ductile (PCBA) phase of the sandwich plate. The time lag and the time coincidence depend on the nature and the degree of compatibility of the two phases of the sandwich plate.
    Materialart: Digitale Medien
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