62,833 research outputs found
Index to NASA Tech Briefs, 1975
This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs
Accretion, ejection and reprocessing in supermassive black holes
This is a White Paper in support of the mission concept of the Large
Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA mission. We
discuss the potential of LOFT for the study of active galactic nuclei. For a
summary, we refer to the paper.Comment: White Paper in Support of the Mission Concept of the Large
Observatory for X-ray Timin
CleAir monitoring system for particulate matter. A case in the Napoleonic Museum in Rome
Monitoring the air particulate concentration both outdoors and indoors is becoming a more relevant issue in the past few decades. An innovative, fully automatic, monitoring system called CleAir is presented. Such a system wants to go beyond the traditional technique (gravimetric analysis), allowing for a double monitoring approach: the traditional gravimetric analysis as well as the optical spectroscopic analysis of the scattering on the same filters in steady-state conditions. The experimental data are interpreted in terms of light percolation through highly scattering matter by means of the stretched exponential evolution. CleAir has been applied to investigate the daily distribution of particulate matter within the Napoleonic Museum in Rome as a test case
TIR-based dynamic liquid-level and flow-rate sensing and its application on centrifugal microfluidic platforms
For the first time we present a technique for the spatio-temporally resolved localization of liquid-gas interfaces on centrifugal microfluidic platforms based on total internal reflection (TIR) at the channel wall. The simple setup consists of a line laser and a linear image sensor array mounted in a stationary instrument. Apart from identifying the presence of (usually unwanted) gas bubbles, the here described online meniscus detection allows to measure liquid volumes with a high precision of 1.9%. Additionally, flow rates and viscosities (range: 1-10.7 mPa s) can be sensed even during rotation at frequencies up to 30 Hz with a precision of 4.7% and 4.3%, respectively
Pulsed Frequency Shifted Feedback Laser for Accurate Long Distance Measurements: Beat Order Determination
Long-distance measurements (10 m - 1000 m) with an accuracy of 10-7 is a
challenge for many applications. We show that it is achievable with Frequency
Shifted Feedback (FSF) laser interferometry technique, provided that the
determination of the radio frequency beat order be made without ambiguity and
on a time scale compatible with atmospheric applications. Using the pulsed-FSF
laser that we developed for laser guide star application, we propose and test,
up to 240 m, a simple method for measuring the beat order in real time. The
moving-comb and Yatsenko models are also discussed. The first of these models
fails to interpret our long-distance interferometry results. We show that the
accuracy of long-distance measurements depends primarily on the stabilization
of the acoustic frequency of the modulator
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Time-of-flight resolved light field fluctuations reveal deep human tissue physiology.
Red blood cells (RBCs) transport oxygen to tissues and remove carbon dioxide. Diffuse optical flowmetry (DOF) assesses deep tissue RBC dynamics by measuring coherent fluctuations of multiply scattered near-infrared light intensity. While classical DOF measurements empirically correlate with blood flow, they remain far-removed from light scattering physics and difficult to interpret in layered media. To advance DOF measurements closer to the physics, here we introduce an interferometric technique, surmounting challenges of bulk motion to apply it in awake humans. We reveal two measurement dimensions: optical phase, and time-of-flight (TOF), the latter with 22 picosecond resolution. With this multidimensional data, we directly confirm the unordered, or Brownian, nature of optically probed RBC dynamics typically assumed in classical DOF. We illustrate how incorrect absorption assumptions, anisotropic RBC scattering, and layered tissues may confound classical DOF. By comparison, our direct method enables accurate and comprehensive assessment of blood flow dynamics in humans
General Defocusing Particle Tracking: fundamentals and uncertainty assessment
General Defocusing Particle Tracking (GDPT) is a single-camera,
three-dimensional particle tracking method that determines the particle depth
positions from the defocusing patterns of the corresponding particle images.
GDPT relies on a reference set of experimental particle images which is used to
predict the depth position of measured particle images of similar shape. While
several implementations of the method are possible, its accuracy is ultimately
limited by some intrinsic properties of the acquired data, such as the
signal-to-noise ratio, the particle concentration, as well as the
characteristics of the defocusing patterns. GDPT has been applied in different
fields by different research groups, however, a deeper description and analysis
of the method fundamentals has hitherto not been available. In this work, we
first identity the fundamental elements that characterize a GDPT measurement.
Afterwards, we present a standardized framework based on synthetic images to
assess the performance of GDPT implementations in terms of measurement
uncertainty and relative number of measured particles. Finally, we provide
guidelines to assess the uncertainty of experimental GDPT measurements, where
true values are not accessible and additional image aberrations can lead to
bias errors. The data were processed using DefocusTracker, an open-source GDPT
software. The datasets were created using the synthetic image generator
MicroSIG and have been shared in a freely-accessible repository
On-line measurement of heat of combustion
An experimental method for an on-line measurement of heat of combustion of a gaseous hydrocarbon fuel mixture of unknown composition is developed. It involves combustion of a test gas with a known quantity of air to achieve a predetermined oxygen concentration level in the combustion products. This is accomplished by a feedback controller which maintains the gas volumetric flow rate at a level consistent with the desired oxygen concentration in the products. The heat of combustion is determined from a known correlation with the gas volumetric flow rate. An on-line microcomputer accesses the gas volumetric flow data, and displays the heat of combustion values at desired time intervals
Index to NASA Tech Briefs, January - June 1967
Technological innovations for January-June 1967, abstracts and subject inde
The effect of flow oscillations on cavity drag
An experimental investigation of flow over an axisymmetric cavity shows that self-sustained, periodic oscillations of the cavity shear layer are associated with low cavity drag. In this low-drag mode the flow regulates itself to fix the mean-shear-layer stagnation point at the downstream corner. Above a critical value of the cavity width-to-depth ratio there is an abrupt and large increase of drag due to the onset of the ‘wake mode’ of instability. It is also shown by measurement of the momentum balance how the drag of the cavity is related to the state of the shear layer, as defined by the mean momentum transport and the Reynolds stress , and how these are related to the amplifying oscillations in the shear layer. The cavity shear layer is found to be different, in several respects, from a free shear layer
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