Djuth F.T.,Geospace Research Inc. |
DuBois D.F.,Lodestar Research Corporation
Earth, Moon and Planets | Year: 2015
The Arecibo high-power, high-frequency (HF) facility and 430 MHz radar are used to examine the temporal development of the HF-induced Langmuir and ion turbulences from 1 ms to many minutes after the turn-on of the HF beam in the F region. All HF observations begin in a smooth, stratified, stable plasma. “Cold start” HF transmissions are employed to avoid remnant irregularities from prior HF transmissions. HF-excited plasma line (HFPL) and ion line echoes are used to monitor the evolution of the turbulence. In the evening/nighttime the HFPL develops in three reproducible stages. Over time scales of 0 to 10–20 ms (possibly 40 ms), the smooth plasma conditions are maintained, and the results are consistent with theoretical models of the excitation of strong Langmuir turbulence near HF reflection. This entails the initiation of the so-called “caviton production cycle.” The turbulence from the parametric decay instability is detected at lower altitudes where the radar wave vector matches those of the HF-enhanced waves. The data suggests that the two processes coexist in the region in between. After ~40 ms the “overshoot process” begins and consists of a downward extension of the HFPL from the HF reflection region to heights ~1.1 km below followed by a retreat back to the reflection region. The whole overshoot process takes place over a time scale of ~3 s. Thereafter the echo remains near HF reflection for 20–90 s after HF turn-on. The HFPL echo subsequently breaks up into patches because of the formation of large-scale electron density structures in the plasma. New kinetic models indicate that suprathermal electrons excited in the plasma by, for example, caviton burn-out serve to regulate plasma turbulence in the modified ionospheric volume. © 2015 Springer Science+Business Media Dordrecht Source
Zheng F.,University of Southern California |
Li Y.,University of Southern California |
Hsu H.-S.,University of Southern California |
Liu C.,Geospace Research Inc. |
And 4 more authors.
Applied Physics Letters | Year: 2012
A high frequency ultrasonic phased array is shown to be capable of trapping and translating microparticles precisely and efficiently, made possible due to the fact that the acoustic beam produced by a phased array can be both focused and steered. Acoustic manipulation of microparticles by a phased array is advantageous over a single element transducer since there is no mechanical movement required for the array. Experimental results show that 45 μm diameter polystyrene microspheres can be easily and accurately trapped and moved to desired positions by a 64-element 26 MHz phased array. © 2012 American Institute of Physics. Source
Agency: Department of Health and Human Services | Branch: | Program: SBIR | Phase: Phase II | Award Amount: 1.48M | Year: 2006
DESCRIPTION (provided by applicant): The proposed effort focuses on the final development of a high-frequency (100 MHz), broadband ultrasound microsystem designed to image cellular structure/tissue along the gastrointestinal (GI) tract. The unit fits within a standard GI endoscope. It consists of a paraboloid transmitter, a 16 x 16 ultrasound receiver array, a read-out integrated circuit (ROIC), and an interposer layer that links the latter two items. Fourteen-bit digitized data flow from the ROIC to an external computer where three-dimensional images are formed. The nominal sampled volume extends below the GI tract surface to depths in the range 1-3 mm, depending on the proximity of the sensor to the GI wall. The diameter of the probed volume ranges from 0.6 mm to 0.9 mm. The main functions of the imager include: 1) the imaging of pre-cancerous dysplastic mucosa, polyps, and adenomas, 2) real-time grading of dysplasia (pre-cancerous tissue), 3) immediate viewing of cellular structure in tumors (e.g., squamous cell carcinoma and adenocarcinoma, benign growths), 4) as required, guidance for directing fine-needle aspiration biopsies to regions that pose the greatest threat, and 5) the system serves as a patient friendly, pre-cancer diagnostic for severe gastroesophageal reflux disease (Barrett's esophagus). Overall, the suggested imager provides a new opportunity for the detection of pre-cancerous tissue along the GI tract, which at present is usually a chance finding and cannot be recognized endoscopically. The developmental prototype has a novel bistatic architecture aimed at increasing system sensitivity, reducing the time required to obtain an image, and simplifying the receiver system. A new sol-gel PZT (PbZr0.6Ti0.4O3) thick film, invented as part of the preceding NIH program, is used as the transducer material. It is much improved over previous efforts in this area. The PZT thick film density is 89-90% of the full thin film density and the thick film piezoelectric coefficients are very close to those of thin films. The advantage of the new thick film is 1) its patterning and fabrication process is well established and many methods are available, 2) it supports a very large etch selectivity of 15:1, 3) the fabrication/assembly process is straightforward and amenable to large-scale production, and 4) the fabrication process yields very inexpensive transducer arrays. The latter is very important because the transducer array/interposer/ROIC will be used only once and discarded.
Agency: Department of Health and Human Services | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 164.11K | Year: 2004
DESCRIPTION (provided by applicant): The proposed research effort is aimed at advancing the state-of-the-art in high-frequency (200 MHz), broadband ultrasound to provide images of malignant tumor cells and surrounding tissue. The principal types of canc
Agency: NSF | Branch: Continuing grant | Program: | Phase: AERONOMY | Award Amount: 627.21K | Year: 2011
This collaborative project has two primary goals: (1) to resolve a long-standing discrepancy in data/model comparisons of electron energy balance in the mid-latitude F-region ionosphere from ~105-600 km, and (2) to assess potential secular temperature trends associated with global change. Both studies will utilize highly-precise measurements of ionospheric composition and temperature acquired from incoherent scatter radar (ISR) at Arecibo Observatory, Puerto Rico, under both active and quiet solar cycle conditions.