Long-range communications at extremely low frequencies

1974 ◽  
Vol 62 (3) ◽  
pp. 292-312 ◽  
Author(s):  
S.L. Bernstein ◽  
M.L. Burrows ◽  
J.E. Evans ◽  
A.S. Griffiths ◽  
D.A. McNeill ◽  
...  
Keyword(s):  
Long Range ◽  
Low Frequencies

Long-range detection and identification of underwater mines using very low frequencies (1 to 10 kHz)

1998 ◽  
Author(s):  
Timothy J. Yoder ◽  
Joseph A. Bucaro ◽  
Brian H. Houston ◽  
Harry J. Simpson
Keyword(s):  
Long Range ◽  
Low Frequencies ◽  
Detection And Identification

The Long-range Navigation of Civil Aircraft

1964 ◽  
Vol 17 (2) ◽  
pp. 167-182 ◽  
Author(s):  
D. E. Hampton ◽  
J. R. Mills
Keyword(s):  
Long Range ◽  
Failure Rate ◽  
Ground Level ◽  
Single System ◽  
Basic System ◽  
Reliable System ◽  
Low Frequencies ◽  
Navigation Computer ◽  
Civil Aircraft ◽  
Navigation Information

This paper, which was presented at an Ordinary Meeting of the Institute held in London on 15 November 1963, sets out to comment on certain aspects of the long-range navigation of civil aircraft. It concentrates on three areas where there seems to be room for improvement: reliability (a failure rate of 1 : 10 is suggested); the integration of navigation information into a single system and display; standardization of navigation facilities so that all aircraft can use the same basic system.It is concluded that a reliable system is required down to ground level, an indication of reliability should be presented to the pilot, that high reliabilities can be obtained by comparison of ground-based and self-contained aids, that a navigation computer is necessary to reduce the information to a presentable form, and that the use of very low frequencies seems to be the most promising way of developing an aid along these lines.

scholarly journals Prestimulus frontal-parietal coherence predicts auditory detection performance in rats

2014 ◽  
Vol 111 (10) ◽  
pp. 1986-2000 ◽  
Author(s):  
Linnea Herzog ◽  
Kia Salehi ◽  
Kaitlin S. Bohon ◽  
Michael C. Wiest
Keyword(s):  
Long Range ◽  
Parietal Cortex ◽  
Low Frequency ◽  
Detection Performance ◽  
Beta Band ◽  
Low Frequencies ◽  
Auditory Detection ◽  
Local Synchronization ◽  
Motivational Changes ◽  
External Stimuli

Electrophysiology in primates has implicated long-range neural coherence as a potential mechanism for enhancing sensory detection. To test whether local synchronization and long-range neural coherence support detection performance in rats, we recorded local field potentials (LFPs) in frontal and parietal cortex while rats performed an auditory detection task. We observed significantly elevated power at multiple low frequencies (<15 Hz) preceding the target beep when the animal failed to respond to the signal (misses), in both frontal and parietal cortex. In terms of long-range coherence, we observed significantly more frontal-parietal coherence in the beta band (15–30 Hz) before the signal on misses compared with hits. This effect persisted after regressing away linear trends in the coherence values during a session, showing that the excess frontal-parietal beta coherence prior to misses cannot be explained by slow motivational changes during a session. In addition, a trend toward higher low-frequency (<15 Hz) coherence prior to miss trials compared with hits became highly significant when we rereferenced the LFPs to the mean voltage on each recording array, suggesting that the results are specific to our frontal and parietal areas. These results do not support a role for long-range frontal-parietal coherence or local synchronization in facilitating the detection of external stimuli. Rather, they extend to long-range frontal-parietal coherence previous findings that correlate local synchronization of low-frequency (<15 Hz) oscillations with inattention to external stimuli and synchronization of beta rhythms (15–30 Hz) with voluntary or involuntary prolongation of the current cognitive or motor state.

Long-Range Acoustic Scattering by Surface Inhomogeneities Beneath a Turbulent Boundary Layer

1984 ◽  
Vol 106 (3) ◽  
pp. 376-382 ◽  
Author(s):  
D. G. Crighton
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Long Range ◽  
Fluid Layer ◽  
Acoustic Scattering ◽  
Acoustic Power ◽  
Coupling Mechanism ◽  
Fluid Loading ◽  
Low Frequencies ◽  
Homogeneous Surface

Low-frequency turbulent boundary layer eddies inject a power Ps into the elastic structure over which the boundary layer is formed which generally greatly exceeds the acoustic power Pa directly radiated by the eddies (acoustically equivalent to quadrupoles). The power Ps remains trapped in the surface and an adjacent fluid layer and propagates in subsonic surface wave modes until it encounters a rib, or edge, or other surface inhomogeneity, from which a power Pe is scattered to the far field. While Pe is again small compared with Ps, it may nonetheless greatly exceed Pa, and in that case the dominant acoustic mechanism is associated with the long-range coupling between the quadrupole eddy and the remote inhomogeneity via subsonic surface waves. That interaction, and the acoustic fields produced by it, are examined in detail in this paper for the inhomogeneities represented by a simple line support rib, a simple point support rib, and an edge to a plane elastic plate, either with or without an adjacent rigid baffle, and with a range of edge conditions. Under conditions of “light” fluid loading, the long-range coupling mechanism seems unlikely to be of importance, but at low frequencies and under “heavy” fluid loading it appears that, even for large separations between an eddy and an inhomogeneity, the long-range coupling generates an acoustic field far in excess of that radiated by the same boundary layer turbulence over a homogeneous surface.

The S-SH Confusion Test and the Effects of Frequency Lowering

2019 ◽  
Vol 62 (5) ◽  
pp. 1486-1505
Author(s):  
Joshua M. Alexander
Keyword(s):  
Cognitive Processing ◽  
Hearing Aids ◽  
Response Times ◽  
Nonlinear Frequency ◽  
Low Frequencies ◽  
Frequency Compression ◽  
Negative Side ◽  
Minimal Word ◽  
Low Pass ◽  
Negative Side Effects

PurposeFrequency lowering in hearing aids can cause listeners to perceive [s] as [ʃ]. The S-SH Confusion Test, which consists of 66 minimal word pairs spoken by 6 female talkers, was designed to help clinicians and researchers document these negative side effects. This study's purpose was to use this new test to evaluate the hypothesis that these confusions will increase to the extent that low frequencies are altered.MethodTwenty-one listeners with normal hearing were each tested on 7 conditions. Three were control conditions that were low-pass filtered at 3.3, 5.0, and 9.1 kHz. Four conditions were processed with nonlinear frequency compression (NFC): 2 had a 3.3-kHz maximum audible output frequency (MAOF), with a start frequency (SF) of 1.6 or 2.2 kHz; 2 had a 5.0-kHz MAOF, with an SF of 1.6 or 4.0 kHz. Listeners' responses were analyzed using concepts from signal detection theory. Response times were also collected as a measure of cognitive processing.ResultsOverall, [s] for [ʃ] confusions were minimal. As predicted, [ʃ] for [s] confusions increased for NFC conditions with a lower versus higher MAOF and with a lower versus higher SF. Response times for trials with correct [s] responses were shortest for the 9.1-kHz control and increased for the 5.0- and 3.3-kHz controls. NFC response times were also significantly longer as MAOF and SF decreased. The NFC condition with the highest MAOF and SF had statistically shorter response times than its control condition, indicating that, under some circumstances, NFC may ease cognitive processing.ConclusionsLarge differences in the S-SH Confusion Test across frequency-lowering conditions show that it can be used to document a major negative side effect associated with frequency lowering. Smaller but significant differences in response times for correct [s] trials indicate that NFC can help or hinder cognitive processing, depending on its settings.

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