Broad-band acoustic low frequency collimated beam for ultrasonic imaging

2013 ◽  
Author(s):  
Cristian Pantea ◽  
Dipen Sinha
Keyword(s):  
Broad Band ◽  
Ultrasonic Imaging ◽  
Low Frequency ◽  
Collimated Beam

scholarly journals The Low-Frequency Array (LOFAR): Opening a New Window on the Universe

2002 ◽  
Vol 199 ◽  
pp. 474-483
Author(s):  
Namir E. Kassim ◽  
T. Joseph W. Lazio ◽  
William C. Erickson ◽  
Patrick C. Crane ◽  
R. A. Perley ◽  
...  
Keyword(s):  
Angular Resolution ◽  
Broad Band ◽  
Low Frequency ◽  
Electromagnetic Spectrum ◽  
Interferometric Imaging ◽  
Very Large Array ◽  
Long Wavelength ◽  
Calibration Techniques ◽  
Long Baselines ◽  
The Universe

Decametric wavelength imaging has been largely neglected in the quest for higher angular resolution because ionospheric structure limited interferometric imaging to short (< 5 km) baselines. The long wavelength (LW, 2—20 m or 15—150 MHz) portion of the electromagnetic spectrum thus remains poorly explored. The NRL-NRAO 74 MHz Very Large Array has demonstrated that self-calibration techniques can remove ionospheric distortions over arbitrarily long baselines. This has inspired the Low Frequency Array (LOFAR)—-a fully electronic, broad-band (15—150 MHz)antenna array which will provide an improvement of 2—3 orders of magnitude in resolution and sensitivity over the state of the art.

scholarly journals The challenging SED of AP Librae

2011 ◽  
Vol 7 (S284) ◽  
pp. 411-413 ◽  
Author(s):  
David Sanchez ◽  
Berrie Giebels ◽  
Pascal Fortin ◽  
Keyword(s):  
Spectral Energy Distribution ◽  
Broad Band ◽  
Low Frequency ◽  
Theoretical Models ◽  
Intermediate Frequency ◽  
High Energy ◽  
Spectral Energy ◽  
Broad Band Emission ◽  
Band Emission ◽  
Bl Lac

AbstractMatching the broad-band emission of active galaxies with the predictions of theoretical models can be used to derive constraints on the properties of the emitting region and to probe the physical processes involved. AP Librae is the third low frequency peaked BL Lac (LBL) detected at very high energy (VHE, E>100GeV) by an Atmospheric Cherenkov Telescope; most VHE BL Lacs (34 out of 39) belong to the high-frequency and intermediate-frequency BL Lac classes (HBL and IBL). LBL objects tend to have a higher luminosity with lower peak frequencies than HBLs or IBLs. The characterization of their time-averaged spectral energy distribution is challenging for emission models such as synchrotron self-Compton (SSC) models.

Processing of frequency-modulated sounds in the cat's anterior auditory field

1994 ◽  
Vol 71 (5) ◽  
pp. 1959-1975 ◽  
Author(s):  
B. Tian ◽  
J. P. Rauschecker
Keyword(s):  
Pure Tone ◽  
Frequency Tuning ◽  
Broad Band ◽  
Low Frequency ◽  
Sweep Rate ◽  
Direction Selectivity ◽  
Neuron Activity ◽  
Complex Sounds ◽  
Range Rate ◽  
Auditory Field

1. Single-neuron activity was recorded from the anterior auditory field (AAF) in the cortex of gas-anesthetized cats. 2. Tone bursts and broad-band complex sounds were used for auditory stimulation. Responses to frequency-modulated (FM) sounds, in particular, were studied systematically. 3. Linear FM sweeps were centered around the best frequency (BF) of a neuron and had an excursion large enough to cover its whole frequency tuning range. Rate and direction of change of the FM sweeps were varied. 4. In 69% of the FM responses, a peak was found at an instantaneous frequency that corresponded to the BF in the pure-tone response. Thirty-three percent of the units had multiple maxima in their FM response. These secondary maxima were not always reflected in the pure-tone response of the same neurons. 5. The vast majority of AAF neurons showed one of two types of selectivity for FM rate. Depending on the criterion, almost half of the cells (46%) preferred fast changes of > 200 Hz/ms (high-pass) in both FM directions. Forty-eight percent of all neurons showed band-pass behavior with a clear preference in the middle range of FM rates in one or both directions. Low-pass or all-pass neurons made up only a small proportion (4 and 1%, respectively) of AAF neurons. 6. When both directions of an FM sweep (low-to-high and high-to-low-frequency) were tested, 66% of the neurons clearly were selective for one direction. This selectivity was not present necessarily at the preferred FM rate. In general, FM direction selectivity was most pronounced at slower FM rates. 7. The selectivity of AAF neurons for the rate and direction of FM sounds makes these neurons suitable for the detection and analysis of communication sounds, which often contain FM components with a particular sweep rate and direction.

scholarly journals Solitary potential structures observed in the magnetosheath by the Cluster spacecraft

2003 ◽  
Vol 10 (1/2) ◽  
pp. 3-11 ◽  
Author(s):  
J. S. Pickett ◽  
J. D. Menietti ◽  
D. A. Gurnett ◽  
B. Tsurutani ◽  
P. M. Kintner ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Time Series Data ◽  
Broad Band ◽  
Low Frequency ◽  
Bow Shock ◽  
Local Magnetic Field ◽  
Series Data ◽  
The Individual ◽  
Almost All ◽  
The Magnetic Field

Abstract. Bipolar pulses of ~ 25-100 µs in duration have been observed in the wave electric field data obtained by the Wideband plasma wave instrument on the Cluster spacecraft in the dayside magnetosheath. These pulses are similar in almost all respects to those observed on several spacecraft over the last few years. They represent solitary potential structures, and in this case, electron phase space holes. When the time series data containing the bipolar pulses on Cluster are transformed to the frequency domain by a windowed FFT, the pulses appear as typical broad-band features, extending from the low-frequency cutoff of the bandpass filter, ~ 1 kHz, up to as great as 20-40 kHz in some cases, with decreasing intensity as the frequency increases. The upper frequency cutoff of the broad band is an indication of the individual pulse durations (1/f). The solitary potential structures are detected when the local magnetic field is contained primarily in the spin plane, indicating that they propagate along the magnetic field. Their frequency extent and intensity seem to increase as the angle between the directions of the magnetic field and the plasma flow decreases from 90°. Of major significance is the finding that the overall profile of the broad-band features observed simultaneously by two Cluster spacecraft, separated by a distance of over 750 km, are strikingly similar in terms of onset times, frequency extent, intensity, and termination. This implies that the generation region of the solitary potential structures observed in the magnetosheath near the bow shock is very large and may be located at or near the bow shock, or be connected with the bow shock in some way.

Optimal ventilation waveforms for estimating low-frequency respiratory impedance

1993 ◽  
Vol 75 (1) ◽  
pp. 478-488 ◽  
Author(s):  
K. R. Lutchen ◽  
K. Yang ◽  
D. W. Kaczka ◽  
B. Suki
Keyword(s):  
Broad Band ◽  
Viscoelastic Model ◽  
Harmonic Distortion ◽  
Low Frequency ◽  
Amplitude Dependence ◽  
Asthmatic Subject ◽  
Healthy Humans ◽  
Before And After ◽  
Airway Opening ◽  
Nonlinear Viscoelastic Model

We present a broad-band optimal ventilator waveform (OVW), the concept of which was to create a computer-driven ventilator waveform containing increased energy at specific frequencies (f). Values of f were chosen such that nonlinear harmonic distortion and intermodulation were minimized. The phases at each f were then optimized such that the resulting flow waveform delivered sufficient volume to maintain gas exchange while minimizing peak-to-peak airway opening pressure. Simulations with a linear anatomically consistent branching airway model and a nonlinear viscoelastic model showed that respiratory resistance (Rrs) and elastance (Ers) estimates at 0.1–2 Hz from the OVW are far superior to those from a standard step ventilator waveform (SVW) during healthy and obstructed conditions and that the OVW reduces the influences of harmonic interactions. Using a servo-controlled oscillator, we applied individual sine waves, an OVW containing energy at 0.15625–2.4 Hz, and an SVW to healthy humans and one symptomatic asthmatic subject before and after bronchodilation. The OVW was markedly superior to the SVW and always provided smooth estimates of Rrs and Ers. Before bronchodilation in the asthmatic subject Rrs was highly elevated and Ers was markedly increased with f; after bronchodilation the level of Rrs and the f dependence of Ers decreased. Although based on results from only one asthmatic subject, these data suggest a dominant influence of airway constriction and lung inhomogeneities during asthmatic bronchoconstriction that is alleviated by bronchodilators. These and other results indicate that the OVW approach has high potential for simultaneously probing f and amplitude dependence in the mechanical properties of clinical subjects during physiological breathing conditions and perhaps during dynamic bronchoconstriction.

An infrared and Raman spectroscopic study of some Group 1B halide complexes containing an M4X4 core

1978 ◽  
Vol 31 (10) ◽  
pp. 2137 ◽  
Author(s):  
GA Bowmaker ◽  
RJ Knappstein ◽  
SF Tham
Keyword(s):  
Raman Spectra ◽  
Broad Band ◽  
Low Frequency ◽  
Far Infrared ◽  
Infrared And Raman Spectra ◽  
Intense Band ◽  
Raman Spectroscopic ◽  
Raman Spectroscopic Study ◽  
Halide Complexes ◽  
Far Infrared Spectra

The infrared and Raman spectra of [Et3PcuI]4 and [Et3AsCuI]4 have been measured, and bands have been assigned to vibrations of the ligand and of the Td Cu4I4 core. The far-infrared spectra show two strong T2 v(CuI) bands at about 90 and 140 cm-1, the higher frequency member of which has a Raman counterpart which shows possible longitudinal-transverse splitting. The Raman spectra also show an intense band at about 50 cm-1. Similar features have been observed in the low-frequency vibrational spectra of [Et2S]3 [CuI]4, [C5H5NcuI]4, [C5H11NAgI]4, [Et3PAgBr]4 and [Et3PagCl]4, although the last two compounds gave only a single broad band in the v(MX) region.

scholarly journals Multi-cavity locally resonant structure with the low frequency and broad band-gaps

AIP Advances ◽  
2016 ◽  
Vol 6 (11) ◽  
pp. 115024 ◽  
Author(s):  
Jiulong Jiang ◽  
Hong Yao ◽  
Jun Du ◽  
Jinbo Zhao
Keyword(s):  
Broad Band ◽  
Low Frequency ◽  
Band Gaps ◽  
Resonant Structure
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