Time-averaged and time-resolved laser optical temperature measurements in water with Filtered Brillouin Scattering combined with LDV

A laser measuring system was developed and built that allows to optically measure temperature in water using the method of Filtered Brillouin Scattering (FBS). First time-resolved optical temperature measurements were demonstrated. Furthermore, the FBS-system was combined with an LDV to enable simultaneous measurement of flow velocity and therefore the system is also capable to measure the heat flow. Time-averaged temperature values were determined with good accuracy and, as a special highlight, also timeresolved temperature measurements have been demonstrated with temporal resolution in the order of approximately 10 ms, validated by comparison with fast thermocouple measurements. The overarching goal of the research project was to prepare the market introduction of a laser-optical measuring system for spatially point-based and time-resolved measurement of the heat flow in liquids, especially in water. In order to realize this, it was necessary to measure the local velocity and the local temperature in a liquid. The optical measurement of the local velocity has long been possible using the established method of laser Doppler velocimetry (LDV). Therefore, the heat flow measurement method to be developed should be based on this technology. Until now, there was no suitable optical method for measuring the temperature. In recent years, however, the physical phenomenon of Brillouin scattering has become one focus of measurement technology development. If a small volume of liquid is irradiated with light, the molecules in the liquid scatter back part of the light, which is known as Brillouin scattering. The spectrum of the scattered light depends on the local temperature in the liquid; and it turns out that this physical relationship can be exploited to develop a highly accurate, fast, and non-contact method for measuring temperature. In this paper, we explain the Filtered Brillouin Scattering (FBS) method, show a setup for measuring temperature and velocity in water flows and thus a method for determining the heat flow, and demonstrate the measurement accuracy using a calibration test bench. The temperature measurement accuracy achieved is in the order of 1 K

Laseroptische Temperaturmessung in Flüssigkeiten mittels gefilterter Brillouin-Streuung

In diesem Beitrag wird ein neuartiges, laserbasiertes Messverfahren zur Erfassung der Temperatur von Flüssigkeiten vorgestellt. Das Verfahren basiert auf der temperaturabhängigen Brillouin-Streuung von Laserlicht kombiniert mit einem optischen Filter in Form molekularen Joddampfes. Das Verfahren kann beispielsweise zur örtlich und zeitlich aufgelösten Erfassung des Temperaturprofils einer Rohrströmung eingesetzt werden. Der nichtinvasive Charakter laseroptischer Messverfahren verhindert dabei die Beeinflussung des Strömungsprofils durch Sensoreinbauten. Der vorliegende Beitrag führt kurz die physikalischen Grundlagen aus, beschreibt den Einsatz eines Molekularfilters und stellt die verschiedenen Teilkomponenten des Messsystems vor. Anschließend wird mit ausgewählten Messergebnissen für stationäre und dynamische Temperaturzustände die grundsätzliche Funktionsfähigkeit des Messprinzips nachgewiesen

Cognitive Trajectories in Preclinical and Prodromal Alzheimer's Disease Related to Amyloid Status and Brain Atrophy:A Bayesian Approach

Background: Cognitive decline is a key outcome of clinical studies in Alzheimer’s disease (AD). Objective: To determine effects of global amyloid load as well as hippocampus and basal forebrain volumes on longitudinal rates and practice effects from repeated testing of domain specific cognitive change in the AD spectrum, considering non-linear effects and heterogeneity across cohorts. Methods: We included 1,514 cases from three cohorts, ADNI, AIBL, and DELCODE, spanning the range from cognitively normal people to people with subjective cognitive decline and mild cognitive impairment (MCI). We used generalized Bayesian mixed effects analysis of linear and polynomial models of amyloid and volume effects in time. Robustness of effects across cohorts was determined using Bayesian random effects meta-analysis. Results: We found a consistent effect of amyloid and hippocampus volume, but not of basal forebrain volume, on rates of memory change across the three cohorts in the meta-analysis. Effects for amyloid and volumetric markers on executive function were more heterogeneous. We found practice effects in memory and executive performance in amyloid negative cognitively normal controls and MCI cases, but only to a smaller degree in amyloid positive controls and not at all in amyloid positive MCI cases. Conclusions: We found heterogeneity between cohorts, particularly in effects on executive functions. Initial increases in cognitive performance in amyloid negative, but not in amyloid positive MCI cases and controls may reflect practice effects from repeated testing that are lost with higher levels of cerebral amyloid

Relevance of Minor Neuropsychological Deficits in Patients With Subjective Cognitive Decline

peer reviewed[en] BACKGROUND AND OBJECTIVES: To determine the relevance of minor neuropsychological deficits (MNPD) in patients with subjective cognitive decline (SCD) with regard to CSF levels of Alzheimer disease (AD) biomarkers, cognitive decline, and clinical progression to mild cognitive impairment (MCI). METHODS: This study included patients with clinical SCD and SCD-free, healthy control (HC) participants with available baseline CSF and/or longitudinal cognitive data from the observational DZNE Longitudinal Cognitive Impairment and Dementia study. We defined MNPD as a performance of at least 0.5SD below the mean on a demographically adjusted total score derived from the Consortium to Establish a Registry for Alzheimer's Disease neuropsychological assessment battery. We compared SCD patients with MNPD and those without MNPD with regard to CSF amyloid-β (Aβ)42/Aβ40, phosphorylated tau (p-tau181), total tau and Aβ42/p-tau181 levels, longitudinal cognitive composite trajectories, and risk of clinical progression to incident MCI (follow-up M ± SD: 40.6 ± 23.7 months). In addition, we explored group differences between SCD and HC in those without MNPD. RESULTS: In our sample (N = 672, mean age: 70.7 ± 5.9 years, 50% female), SCD patients with MNPD (n = 55, 12.5% of SCD group) showed significantly more abnormal CSF biomarker levels, increased cognitive decline, and a higher risk of progression to incident MCI (HR: 4.07, 95% CI 2.46-6.74) compared with SCD patients without MNPD (n = 384). MNPD had a positive predictive value of 57.0% (95% CI 38.5-75.4) and a negative predictive value of 86.0% (95% CI 81.9-90.1) for the progression of SCD to MCI within 3 years. SCD patients without MNPD showed increased cognitive decline and a higher risk of incident MCI compared with HC participants without MNPD (n = 215; HR: 4.09, 95% CI 2.07-8.09), while AD biomarker levels did not differ significantly between these groups. DISCUSSION: Our results suggest that MNPD are a risk factor for AD-related clinical progression in cognitively normal patients seeking medical counseling because of SCD. As such, the assessment of MNPD could be useful for individual clinical prediction and for AD risk stratification in clinical trials. However, SCD remains a risk factor for future cognitive decline even in the absence of MNPD

Relevance of Minor Neuropsychological Deficits in Patients With Subjective Cognitive Decline

Background and ObjectivesTo determine the relevance of minor neuropsychological deficits (MNPD) in patients with subjective cognitive decline (SCD) with regard to CSF levels of Alzheimer disease (AD) biomarkers, cognitive decline, and clinical progression to mild cognitive impairment (MCI).MethodsThis study included patients with clinical SCD and SCD-free, healthy control (HC) participants with available baseline CSF and/or longitudinal cognitive data from the observational DZNE Longitudinal Cognitive Impairment and Dementia study. We defined MNPD as a performance of at least 0.5SD below the mean on a demographically adjusted total score derived from the Consortium to Establish a Registry for Alzheimer's Disease neuropsychological assessment battery. We compared SCD patients with MNPD and those without MNPD with regard to CSF amyloid-beta (A beta)42/A beta 40, phosphorylated tau (p-tau181), total tau and A beta 42/p-tau181 levels, longitudinal cognitive composite trajectories, and risk of clinical progression to incident MCI (follow-up M +/- SD: 40.6 +/- 23.7 months). In addition, we explored group differences between SCD and HC in those without MNPD.ResultsIn our sample (N = 672, mean age: 70.7 +/- 5.9 years, 50% female), SCD patients with MNPD (n = 55, 12.5% of SCD group) showed significantly more abnormal CSF biomarker levels, increased cognitive decline, and a higher risk of progression to incident MCI (HR: 4.07, 95% CI 2.46-6.74) compared with SCD patients without MNPD (n = 384). MNPD had a positive predictive value of 57.0% (95% CI 38.5-75.4) and a negative predictive value of 86.0% (95% CI 81.9-90.1) for the progression of SCD to MCI within 3 years. SCD patients without MNPD showed increased cognitive decline and a higher risk of incident MCI compared with HC participants without MNPD (n = 215;HR: 4.09, 95% CI 2.07-8.09), while AD biomarker levels did not differ significantly between these groups.DiscussionOur results suggest that MNPD are a risk factor for AD-related clinical progression in cognitively normal patients seeking medical counseling because of SCD. As such, the assessment of MNPD could be useful for individual clinical prediction and for AD risk stratification in clinical trials. However, SCD remains a risk factor for future cognitive decline even in the absence of MNPD

Charakterisierung des Strömungsfelds eines Ranque-Hilsch-Wirbelrohrs mittels gefilterter Rayleigh Streuung

Das mittlere Strömungsfeld eines Ranque-Hilsch-Wirbelrohrs wurde mittels des laserbasier-ten optischen Messverfahrens der gefilterten Rayleigh-Streuung, erweitert um die Frequenz-scan-Methode, charakterisiert. Es wurden Verteilungen der Temperatur, der axialen und der Umfangsgeschwindigkeit für den gesamten mittleren Rohrquerschnitt gewonnen. In den Ver-teilungen dieser Geschwindigkeitskomponenten wurde eine Strömungsstruktur identifiziert, die an eine angefachte Oszillation erinnert. Diese Strömungsstruktur deutet darauf hin, dass eine starke Kopplung des Strömungsfelds mit dem akustischen Feld des Wirbelrohrs besteht

Development of laser-optical measurement techniques on the vortex tube: Taking PIV to its limits

The Ranque-Hilsch vortex tube (RHVT) is referred to as one of the unsolved problems in physics: consisting of a cylindrical tube with several tangential inlet nozzles only, the expanded gas forms a complex internal flow field, resulting in a unique temperature separation effect. Since the vortex tube’s invention by Ranque (1933) and Hilsch (1947) it has been used for decentralized cooling and gas cleaning purposes. While so far it has been investigated by means of conventional probes as well as laser-optical techniques such as FRS, L2F and LDA, this contribution targets on planar two-component PIV measurements. While the usual configuration features one outlet on each end of the tube, it will be shown that the major internal flow phenomena occur in a similar manner on a uni-flow configuration with only one outlet opposite to the inlet. The focus however is not on the temperature separation. Instead the RHVT is introduced as a development platform for laser-optical methods: it will be shown that the RHVT’s complex flow topology is pushing the PIV technique to its limits; challenges and possible solutions are discussed. Especially the high tangential velocity component results in a strong projection error in the observed axial and radial velocities: to address this issue stereoscopic PIV will be deployed for the purpose of mapping the RHVT

Methods to improve pressure, temperature and velocity accuracies of filtered Rayleigh scattering measurements in gaseous flows

Frequency scanning filtered Rayleigh scattering is able to simultaneously provide time-averaged measurements of pressure, temperature and velocity in gaseous flows. By extending the underlying mathematical model, a robust alternative to existing approaches is introduced. Present and proposed model functions are then characterized during a detailed uncertainty analysis. Deviations between the analytical solution of a jet flow experiment and measured results could be related to laser-induced background radiation as well as the Rayleigh scattering’s spectral distribution. In applying a background correction method and by replacing the standard lineshape model by an empirical formulation, detrimental effects on pressure, temperature and velocity accuracies could be reduced below 15 hPa, 2.5 K and 2.7 m/s

The flow field inside a Ranque-Hilsch vortex tube part I: Experimental analysis using planar filtered Rayleigh scattering

The flow field of a Ranque-Hilsch vortex tube is characterized experimentally. Firstly conventional probe based technology is used in order to measure inlet and outlet temperatures as well as to acquire temporally resolved wall pressure data over a wide range of operating conditions. Secondly the filtered Rayleigh scattering technique is employed in order to gather detailed temporally averaged planar information on the vortex tube’s flow topology. These measurements form the basis of a detailed numerical study in part II of this contribution

Current activities on frequency modulated Filtered Rayleigh Scattering (fm-FRS)

Der Schwerpunkt des Vortrages wird auf der Darstellung aktueller Aktivitäten zum Einsatz der gefilterten Rayleigh-Streuung (FRS) mit Frequenzmodulation liegen. Diese Erweiterung der gefilterten Rayleigh-Streuung soll instationäre Punktmessungen ermöglichen. Damit ergeben sich neue Anwendungsmöglichkeiten in Flugzeugen (in-flight diagnostic), in Turbomaschinen, Windkanälen und am Brennkammeraustritt. Während des Fluges könnten Messgrößen wie Temperatur, Geschwindigkeit und Druck künftig außerhalb des Flugzeuges berührungslos erfasst werden. Im Vortrag werden messtechnische Aspekte besprochen und eingeordnet