Fast Measurements (fast + measurement)

Distribution by Scientific Domains

Selected Abstracts

Towards Fast Measurement of the Electron Temperature in the SOL of ASDEX Upgrade Using Swept Langmuir Probes

H.W. Müller
Abstract On ASDEX Upgrade first experiments were made using single probes with a voltage sweep frequency up to 100kHz. Possibilities and limitations using fast swept probes with a standard diagnostic and analysis tools are discussed. A good agreement between the data derived from fast swept single probe characteristics and floating as well as saturation current measurements was found. In a stationary (non ELMing) plasma the data of the fast swept probe are compared to standard slow swept probes (kHz range) showing an improvement of the measurement by faster sweeping. While ELM filaments already could be resolved the access of electron temperature fluctuations in small scale turbulence still has to be improved. Further comparisons are done in ELMy H-mode with combined ball-pen probe/floating potential measurements which can deliver electron temperatures with 25 , s time resolution at reduced spatial resolution compared to pin probes. During ELMs the electron temperatures derived from the ball-pen probe and fast swept single probes agreed (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Fast measurement of intracardiac pressure differences with 2D breath-hold phase-contrast MRI,

Richard B. Thompson
Abstract Intracardiovascular blood pressure differences can be derived from velocity images acquired with phase-contrast (PC) MRI by evaluating the Navier-Stokes equations. Pressure differences within a slice of interest can be calculated using only the in-plane velocity components from that slice. This rapid exam is proposed as an alternative to the lengthy 3D velocity imaging exams. Despite their good spatial coverage, the 3D exams are prone to artifacts and errors from respiratory motion and insufficient temporal resolution, and are unattractive in the clinical setting due to their excessive scan times (>10 min of free breathing). The proposed single-slice approach requires only one or two breath-holds of acquisition time, and the velocity data can be processed for the calculation of pressure differences online with immediate feedback. The impact of reducing the pressure difference calculation to two dimensions is quantified by comparison with 3D data sets for the case of blood flow within the cardiac chambers. The calculated pressure differences are validated using high-fidelity pressure transducers both in a pulsatile flow phantom and in vivo in a dog model. There was excellent agreement between the transducer and PC-MRI results in all of the studies. Magn Reson Med 49:1056,1066, 2003. Published 2003 Wiley-Liss, Inc. [source]

Fast measurements of photoreflectance spectra by using multi-channel detector

R. Kudrawiec
Abstract Photoreflectance (PR) measurements were performed on GaAs- and GaN-based structures in the so called ,bright configuration' where the sample was illuminated by white light (probing beam) instead of monochromatic light as it takes place in the standard configuration, i.e., so-called ,dark configuration'. Within this concept the whole PR spectrum can be measured/processed at the same time using a multi-channel detector (i.e., CCD camera) instead the phase sensitive lock-in detection system with the one-channel detector. In this work PR spectra for Si ,-doped GaAs structure have been measured using both the CCD detector system as well as the standard lock-in technique with the one-channel detector system. GaAs-related Franz,Keldysh oscillations, which are typical of Si ,-doped GaAs structure, have been clearly observed in PR spectra measured by using the two detection systems. In addition, the PR system with the CCD detector has been used to measure PR spectra in the UV spectral region for an InGaN/GaN/Al2O3 structure. In this case, PR resonances related to InGaN and GaN band gap absorption have been clearly observed. Using the PR system with CCD detector the time of PR measurements was reduced to few seconds for both GaAs- and GaN-based structures. It shows that the bright configuration of PR set-up with multi-channel detection system is very promising and perspective in the fast diagnostic of semiconductor structures. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Angle-resolved Mueller polarimeter using a microscope objective

S. Ben Hatit
Abstract A new Mueller polarimeter based on liquid crystals and a microscope objective is presented for the characterization of diffraction gratings in a conical diffraction mounting. Fast measurements of complete Mueller matrices over a range of polar angles , (0,60°) and azimuthal angles , (0,360°) are achieved without mechanical movements. The polarization states generator and analyzer are based on nematic liquid crystals. The angular range is achieved through focalization of light over the measured sample with a microscope objective of high numerical aperture and imaging of the objective's back Fourier plane on a CCD. Results on isotropic samples and diffraction gratings are shown. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]