Combined free-stream disturbance measurements and receptivity studies in hypersonic wind tunnels by means of a slender wedge probe and direct numerical simulation

Combined free-stream disturbance measurements and receptivity studies in hypersonic wind tunnels were conducted by means of a slender wedge probe and direct numerical simulation. The study comprises comparative tunnel noise measurements at Mach 3, 6 and 7.4 in two Ludwieg tube facilities and a shock tunnel. Surface pressure fluctuations were measured over a wide range of frequencies and test conditions including harsh test environments not accessible to measurement techniques such as Pitot probes and hot-wire anemometry. A good agreement was found between normalized Pitot pressure fluctuations converted into normalized static pressure fluctuations and the wedge probe readings. Quantitative results of the tunnel noise are provided in frequency ranges relevant for hypersonic boundary-layer transition. Complementary numerical simulations of the leading-edge receptivity to fast and slow acoustic waves were performed for the applied wedge probe at conditions corresponding to the experimental free-stream conditions. The receptivity to fast acoustic waves was found to be characterized by an early amplification of the induced fast mode. For slow acoustic waves an initial decay was found close to the leading edge. At all Mach numbers, and for all considered frequencies, the leading-edge receptivity to fast acoustic waves was found to be higher than the receptivity to slow acoustic waves. Further, the effect of inclination angles of the acoustic wave with respect to the flow direction was investigated. An inclination angle was found to increase the response on the wave-facing surface of the probe and decrease the response on the opposite surface for fast acoustic waves. A frequency-dependent response was found for slow acoustic waves. The combined numerical and experimental approach in the present study confirmed the previous suggestion that the slow acoustic wave is the dominant acoustic mode in noisy hypersonic wind tunnels.The present study was supported by an ESA funded Technology Research Project (ESA-Contract number $4200022793/09/NL/CP$).Published versio

Urine tests for Down's syndrome screening

Background Down's syndrome occurs when a person has three copies of chromosome 21, or the specific area of chromosome 21 implicated in causing Down's syndrome, rather than two. It is the commonest congenital cause of mental disability and also leads to numerous metabolic and structural problems. It can be life-threatening, or lead to considerable ill health, although some individuals have only mild problems and can lead relatively normal lives. Having a baby with Down's syndrome is likely to have a significant impact on family life. The risk of a Down's syndrome affected pregnancy increases with advancing maternal age. Noninvasive screening based on biochemical analysis of maternal serum or urine, or fetal ultrasound measurements, allows estimates of the risk of a pregnancy being affected and provides information to guide decisions about definitive testing. Before agreeing to screening tests, parents need to be fully informed about the risks, benefits and possible consequences of such a test. This includes subsequent choices for further tests they may face, and the implications of both false positive and false negative screening tests (i.e. invasive diagnostic testing, and the possibility that a miscarried fetus may be chromosomally normal). The decisions that may be faced by expectant parents inevitably engender a high level of anxiety at all stages of the screening process, and the outcomes of screening can be associated with considerable physical and psychological morbidity. No screening test can predict the severity of problems a person with Down's syndrome will have. Objectives To estimate and compare the accuracy of first and second trimester urine markers for the detection of Down's syndrome. Search methods We carried out a sensitive and comprehensive literature search of MEDLINE (1980 to 25 August 2011), EMBASE (1980 to 25 August 2011), BIOSIS via EDINA (1985 to 25 August 2011), CINAHL via OVID (1982 to 25 August 2011), The Database of Abstracts of Reviews of Effectiveness (The Cochrane Library 2011, Issue 7), MEDION (25 August 2011), The Database of Systematic Reviews and Meta-Analyses in Laboratory Medicine (25 August 2011), The National Research Register (archived 2007), Health Services Research Projects in Progress database (25 August 2011). We studied reference lists and published review articles. Selection criteria Studies evaluating tests of maternal urine in women up to 24 weeks of gestation for Down's syndrome, compared with a reference standard, either chromosomal verification or macroscopic postnatal inspection. Data collection and analysis We extracted data as test positive or test negative results for Down's and non-Down's pregnancies allowing estimation of detection rates (sensitivity) and false positive rates (1-specificity). We performed quality assessment according to QUADAS (Quality Assessment of Diagnostic Accuracy Studies) criteria. We used hierarchical summary ROC (receiver operating characteristic) meta-analytical methods to analyse test performance and compare test accuracy. We performed analysis of studies allowing direct comparison between tests. We investigated the impact of maternal age on test performance in subgroup analyses. Main results We included 19 studies involving 18,013 pregnancies (including 527 with Down's syndrome). Studies were generally of high quality, although differential verification was common with invasive testing of only high-risk pregnancies. Twenty-four test combinations were evaluated formed from combinations of the following seven different markers with and without maternal age: AFP (alpha-fetoprotein), ITA (invasive trophoblast antigen), ß-core fragment, free ßhCG (beta human chorionic gonadotrophin), total hCG, oestriol, gonadotropin peptide and various marker ratios. The strategies evaluated included three double tests and seven single tests in combination with maternal age, and one triple test, two double tests and 11 single tests without maternal age. Twelve of the 19 studies only evaluated the performance of a single test strategy while the remaining seven evaluated at least two test strategies. Two marker combinations were evaluated in more than four studies; second trimester ß-core fragment (six studies), and second trimester ß-core fragment with maternal age (five studies). In direct test comparisons, for a 5% false positive rate (FPR), the diagnostic accuracy of the double marker second trimester ß-core fragment and oestriol with maternal age test combination was significantly better (ratio of diagnostic odds ratio (RDOR): 2.2 (95% confidence interval (CI) 1.1 to 4.5), P = 0.02) (summary sensitivity of 73% (CI 57 to 85) at a cut-point of 5% FPR) than that of the single marker test strategy of second trimester ß-core fragment and maternal age (summary sensitivity of 56% (CI 45 to 66) at a cut-point of 5% FPR), but was not significantly better (RDOR: 1.5 (0.8 to 2.8), P = 0.21) than that of the second trimester ß-core fragment to oestriol ratio and maternal age test strategy (summary sensitivity of 71% (CI 51 to 86) at a cut-point of 5% FPR). Authors' conclusions Tests involving second trimester ß-core fragment and oestriol with maternal age are significantly more sensitive than the single marker second trimester ß-core fragment and maternal age, however, there were few studies. There is a paucity of evidence available to support the use of urine testing for Down's syndrome screening in clinical practice where alternatives are available

Die Messung von Anströmungsstörungen in hypersonischen Windkanälen mit intrusiven und nicht-intrusiven Messtechniken

Der laminar-turbulente Grenzschichtumschlag wird stark von Störungen in der freien Anströmung beeinflusst. Um die Vorhersagen von Windkanalexperimenten zu verbessern sind genaue Kenntnisse dieser Anströmungsstörungen in Versuchsanlagen erforderlich. Hierzu wurde am Deutschen Zentrum für Luft- und Raumfahrt (DLR) eine schlanke Keilsonde entwickelt, die mit geringem Aufwand in verschiedenen Windkanälen einsetzbar ist. Im Rahmen dieser Arbeit wurden mit dieser Sonde Messungen am Ludwiegrohr (HLB) der Technischen Universität Braunschweig geplant und durchgeführt. Die Auswertung erfolgte im Vergleich mit vorherigen Messungen am Hochenthalpiekanal (HEG) und Rohrwindkanal (RWG) am DLR-Standort in Göttingen. Aufgrund von fehlenden Messgrößen, ist die Messung auf der Keilsonde allein jedoch nicht ausreichend, um die Anströmungsstörungen vollständig zu beschreiben. Mit dem Ziel die Keilsonde zu ergänzen wurden verschiedener Messtechniken eingehend untersucht. Ein Fokussiertes Laser Differential Interferometer (FLDI) erschien am geeignetsten. Zur Entwicklung eines FLDI für den Einsatz am HEG wurde zusätzlich ein kleinskaliger Laboraufbau dieses Interferometers aufgebaut und erfolgreich getested. Hiervon ausgehend wurde ein weiterer, optimierter FLDI-Test-Aufbau konzipiert und aufgebaut, der anhand des zur Verfügungs stehenden Raumes am HEG dimensioniert wurde. Die vollständige Ausrichtung dieses Aufbaus konnte im Rahmen dieser Arbeit jedoch nicht abgeschlossen werden

Messung von Anströmungsstörungen in Hypersonischen Windkanälen - Motiviert durch Transitionsuntersuchungen am HEG

Die Kenntnis von Anströmungsstörungen ist für die Untersuchung des laminar-turbulenten Grenz-schichtumschlages unerlässlich. Für die Messung von Anströmungsstörungen in hypersonischen Stoßrohrwindkanälen sind übliche Messtechniken wie Pitot-Sonden oder Hitzdraht-Anemometer jedoch nicht geeignet. Daher wurde am DLR in Göttingen eine schlanke keilförmige Sonde konstruiert, in deren Oberfläche Druck- und Wärmestromsensoren eingelassen sind. Da eine weite Bandbreite im Spektrum der Anströmungsstörungen den Umschlagsprozess beeinflusst, ist es notwendig dieses Spektrum bis zu hohen Frequenzen zu vermessen. In dem vorliegenden Beitrag wird die messtechnische Auslegung dieser Keilsonde vorgestellt und diskutiert, sowie erste Ergebnisse gezeigt

Messung von Anströmungsstörungen in Hypersonischen Windkanälen

Die Kenntnis von Anströmungsstörungen ist für die Untersuchung des laminar-turbulenten Grenz-schichtumschlages unerlässlich. Für die Messung von Anströmungsstörungen in hypersonischen Stoßrohrwindkanälen sind übliche Messtechniken wie Pitot-Sonden oder Hitzdraht-Anemometer jedoch nicht geeignet. Daher wurde am DLR in Göttingen eine schlanke keilförmige Sonde konstruiert, in deren Oberfläche Druck- und Wärmestromsensoren eingelassen sind. Da eine weite Bandbreite im Spektrum der Anströmungsstörungen den Umschlagsprozess beeinflusst, ist es notwendig dieses Spektrum bis zu hohen Frequenzen zu vermessen. Dazu werden hochempfindliche PCB-Druck-sensoren eingesetzt, die allerdings auch gegenüber Beschleunigungen sensitiv sind. Während der Überströmung der Sonde im Versuch werden so mechanische Schwingungen auf die Sonde übertragen, die die Messung der Anströmungsstörungen unmöglich macht. In dem vorliegenden Beitrag werden verschiedene Optimierungen hinsichtlich der Halterung der Sonde und des Einbaus der Sensoren vorgestellt, mit deren Hilfe die mechanischen Schwingungen gedämpft werden und der Einsatz in hypersonischen Stoßrohrwindkanälen ermöglicht wird

Wayfinding and restructuring in a novel city: an insight problem solving task

Navigating in a novel environment can serve as an applied insight problem solving task, since many people gain a sudden, clear understanding (Aha-moment) of the spatial relations after being lost. With a unique design, we transformed the city center of a medieval German city into a virtual maze. The aim of the study was to test whether a spatial decision making task simulating real navigation would be feasible for investigating insight problem solving. Participants learned two pathways which they subsequently had to restructure to find their way to the navigation targets. We found evidence for the restructuring of participants’ prior knowledge during the solution attempts. 73% of all problem solvers reported an Aha-moment and there was an error drop at the critical intersection by those who had insight. The slope of the learning curve was established as a measurement of insightful experiences

Quantitative Auswertung von Hochgeschwindigkeitsschlierenaufnahmen der hypersonischen Grenzschichtinstabilität am Hochenthalpiekanal Göttingen

For the first time the influence of ultrasonically absorptive carbon-carbon material on hypersonic laminar to turbulent boundary-layer transition was investigated experimentally. A 7° half-angle blunted cone with a nose radius of 2.5 mm and a total length of 1077 mm was tested at zero angle of attack in the High Enthalpy Shock Tunnel Göttingen (HEG) of the German Aerospace Center (DLR) at Mach 7.5. One third of the model surface in circumferential direction was equipped with a in-house manufactured ultrasonically absorptive carbon-carbon material with random microstructure for passive transition control. The remaining model surface consisted of polished steel and served as reference surface. The study revealed a clear damping of the second-mode instabilities and a delay of boundary layer transition along the ultrasonically absorptive carbon-carbon insert

High Frequency Free-Stream Disturbance Measurements in Hypersonic Wind Tunnels by Means of a Slender Wedge Probe

Experimental investigations of the free-stream disturbance spectrum by means of a slender wedge probe were conducted in the DLR High Enthalpy Shock Tunnel Göttingen (HEG) at Mach 7.4, the DNW Ludwieg tube (RWG) at Mach 3 and Mach 6 as well as in the TU Braunschweig Ludwieg tube (HLB) at Mach 6. The identical measurement chain, including the probe, the amplifier and the type of transducer were used in all facilities. A wide range of fast response pressure, temperature and heat flux transducers were used to measure the corresponding fluctuations on the probe surface behind the oblique shock. Quantitative results were obtained as function of frequency taking into account the limitations imposed by each transducer. The wedge probe was shown to be a robust and easy to implement probe particularly suited for use in harsh test environments which do not allow the application of hot wire techniques or flush mounted transducers in a Pitot probe configuration