Plasma echo theory is revisited and reviewed to apply it to a semi-bounded plasma. Spatial echoes in a semibounded plasma are investigated by calculating the electric field produced by external charges and satisfying the boundary conditions at the interface. We show that echoes can occur at various spots. The diversity of echo occurrence spots is due to the boundary terms.

Dolphins that emit whistle signals (except for sperm whales) project short broadband biosonar clicks containing about 5 to 7 cycles with exponential decaying envelope and Q (center frequency over bandwidth) between 2 and 3. The broadband nature of the biosonar clicks allow for good temporal resolution of echo highlights which in turn allows for the discriminations of different targets including...

1. Introduction The most popular principle of diffusion measurements by NMR is the attenuation of spin echoes due to incomplete refocusing of coherences as a consequence of incoherent molecular displacements in the diffusion interval of the pulse sequence [0-Fehler! Verweisquelle konnte nicht gefunden werden.]. Attenuation of echoes on these grounds arises in the presence of pulsed or steady gr...

In the present work, the Plexiglas cylinders used in our Couette geometry were sand-blasted in order to provide a roughness of about 1 μm which leads to significant scattering of the incident ultrasonic pulses. This results in spurious fixed echoes in the raw ultrasonic data that get mixed with the echoes backscattered by the moving particles. Such fixed echoes appear as vertical lines in the s...

The generation mechanism for naturally enhanced ion-acoustic echoes is still debated. One important issue is how these enhancements are related to auroral activity. All events of enhanced ion-acoustic echoes observed simultaneously with the EISCAT Svalbard Radar (ESR) and with high-resolution narrow field-of-view auroral imagers have been collected and studied. Characteristic of all the events ...

Light echoes are interesting because of the wealth of information they offer about their progenitors and the reflecting dust. Due to their faint surface brightnesses, difference imaging is necessary to separate most light echoes from the sky background. However, difference images reveal only the relative fluxes between two epochs. Obtaining absolute fluxes for individual epochs has traditionall...

To elucidate the mechanism of regional hemostasis in the left ventricular (LV) cavity during myocardial infarction, the blood pathway in LV cavity was examined with contrast echocardiography injected from the left atrium before and after coronary ligation in nine canines. Before coronary ligation, contrast echoes spread over LV cavity with one rush. After ligation, smokelike echoes indicating h...

A new approach to spin-echo imaging is presented in which the 180 degrees RF pulse refocuses two or more spin-echoes at different positions in the readout period. When simultaneous echo refocusing (SER) is implemented using multiple 180 degrees pulses, an undesirable mixing of stimulated echoes and primary echoes from different slices can occur. A novel periodic gradient spoiler scheme eliminat...

Chemical shift based methods are often used to achieve uniform water-fat separation that is insensitive to Bo inhomogeneities. Many spin-echo (SE) or fast SE (FSE) approaches acquire three echoes shifted symmetrically about the SE, creating time-dependent phase shifts caused by water-fat chemical shift. This work demonstrates that symmetrically acquired echoes cause artifacts that degrade image...

not advocate the use in this country of some of the blatant methods that have been tried in America, but far more might be done by use of the Press and the Poster in teaching the public some of the elementary rules of health. There is a great distinction between ' false publicity' that aims mainly at personal advertising and the true publicity that aims at arousing interest and educates the pub...