Search results for "ACOUSTIC"
showing 10 items of 1590 documents
Objective Amplitude of Accommodation Computed from Optical Quality Metrics Applied to Wavefront Outcomes
2009
Purpose: We studied the accuracy and precision of 32 objective wavefront methods for finding the amplitude of accommodation obtained in 180 eyes. Methods: Ocular accommodation was stimulated with 0.5 D steps in target vergence spanning the full range of accommodation for each subject. Subjective monocular amplitude of accommodation was measured using two clinical methods, using negative lenses and with a custom Badal optometer. Results: Both subjective methods gave similar results. Results obtained from the Badal optometer where used to test the accuracy of the objective methods. All objective methods showed lower amplitude of accommodation that the subjective ones by an amount that varied …
Measurement of acoustic attenuation in South Pole ice
2010
Using the South Pole Acoustic Test Setup (SPATS) and a retrievable transmitter deployed in holes drilled for the IceCube experiment, we have measured the attenuation of acoustic signals by South Pole ice at depths between 190 m and 500 m. Three data sets, using different acoustic sources, have been analyzed and give consistent results. The method with the smallest systematic uncertainties yields an amplitude attenuation coefficient alpha = 3.20 \pm 0.57 km^(-1) between 10 and 30 kHz, considerably larger than previous theoretical estimates. Expressed as an attenuation length, the analyses give a consistent result for lambda = 1/alpha of ~1/300 m with 20% uncertainty. No significant depth or …
Acoustic characterization of the ancient theatre at Syracuse
2008
The ancient theatre at Syracuse, the largest open air theatre in Sicily, experienced many structural changes along its history. Today its very renowned drama festival attracts visitors from all the world that fill the entire cavea: customized seats accomodation and a prominent stage play an important role in the theatre acoustics. Because no data were available in literature on its acoustical perfomance a measurement session was carried out by our team in the framework of a wide research project on ancient theatres acoustics in the modern use. From data recorded "room criteria" parameters have been evaluated together with spectral analysis in order to gain a deeper information on the acoust…
Acoustic doppler velocity profiler for velocity and turbulence measurements in a large amplitude meandering flume
2008
Flow over deformed bed of a meandering laboratory channel is experimentally investigated. The velocity components have been obtained using an Ultrasonic Doppler Profiler (DOP2000) that measures the instantaneous flow velocity profile along the probe direction. In this work, some results obtained in peculiar sections along the channel are reported. A refined mesh of the measurement points has been used for each considered cross-section. The analysis of the collected data essentially confirms that when the aspect ratio is small the secondary circulation assumes great importance and, in accordance with previous findings, a second counter-rotating secondary circulation cell appears near the fre…
Reflexionsakustische Lagebestimmung von Trachealkanülen
1997
Non-invasive acoustic airway monitoring was evaluated in an experimental study. Recording amplitude and travel time of acoustic pulse response, an area-distance function of the cross sectional dimensions of the endotracheal tube and the adjacent airway was calculated to obtain an acoustic pattern of the airway. Measurements on models and excised human cadaver lungs were performed to discover whether displacement or obstruction of the artificial airway can be detected in the acoustic equivalent. Regression analysis revealed a close correlation between displacement of tracheostomy tubes and the shifting of the acoustic area-distance function (corr. coeff. 0.97-1). Dispersion analysis confirme…
Review of Advanced Acoustical Imaging Techniques for Nondestructive Evaluation of Art Objects
2006
Proper preventative diagnosis of different art objects, including wooden, bronze and marble sculptures, frescoes, and paintings (on canvas, wood, metal, and glass), is very important for conservation purposes. Various advanced ultrasonic imaging methods for analysis and assessment of art objects can bring about drastic changes in the regular evaluation and inventory carried out by museums and can bring advanced, powerful, and new techniques for objective assessment of physical conditions of museum resplendence. Using these methods, it will be possible to plan ad hoc repair works on art objects, and, as a result, we will preserve our heritage. The goal of this review is to introduce recent a…
Wooden panel paintings investigation: An air-coupled ultrasonic imaging approach
2007
In this paper, a method for the study of wooden panel paintings using air-coupled acoustical imaging is presented. In order to evaluate the advantages of the technique, several samples were made to mimic panel paintings along with their typical defects. These specimens were tested by means of both single-sided and through-transmission techniques using planar transducers. Image data were processed by means of a two-dimensional (2-D)-fast Fourier transform-based algorithm to increase the S/N ratio and 2-D representations (C-scans) were generated. The simulated defects were imaged using both configurations. Investigations were undertaken on four antique paintings from a private collection. The…
Air-Coupled Imaging Method Applied to the Study and Conservation of Paintings
2007
An air-coupled acoustical imaging method for the study of wooden panel paintings is presented. After a brief overview of the state of the art, an introduction is given regarding the production technique of the art object under investigation. The technology employed is described in detail, as well as the proposed method. After a feasibility campaign of experiments, real ancient paintings have been investigated by means of a through-transmission and a single-sided lay-out. Defects were imaged in all the objects examined and in both the configurations adopted
Femtosecond up-conversion technique for probing the charge transfer in a P3HT : PCBM blend via photoluminescence quenching
2009
We report on an experimental study of the charge transfer dynamics in a P3HT : PCBM blend by means of a femtosecond fluorescence up-conversion technique. Using two-photon excitation we probe the exciton dynamics in P3HT and a P3HT : PCBM blend with a weight ratio of 1 : 1 at excitation densities of up to 6 × 1018 cm−3. In both samples we find strongly nonexponential decay traces compatible with (i) diffusion-limited exciton–exciton annihilation and (ii) diffusion-limited donor–acceptor charge transfer in the polymer blend. Additionally, our results indicate that in the P3HT : PCBM blend about 50% of the photogenerated excitons undergo a prompt charge transfer process on a time scale of abou…
Calculations of high-power production target and beamdump for the GSI future Super-FRS for a fast extraction scheme at the FAIR Facility
2005
A superconducting fragment separator (Super-FRS) is being designed for the production and separation of radioactive isotopes at the future FAIR (Facility for Antiprotons and Ion Research) facility at Darmstadt. This paper discusses various aspects and requirements for the high-power production target that will be used in the Super-FRS experiments. The production target must survive over an extended period of time as it will be used during the course of many experiments. The specific power deposited by the high intensity beam that will be generated at the future FAIR facility will be high enough to destroy the target in most of the cases as a result of a single shot from the new heavy ion sy…