scholarly journals Path length variations due to changes in tropospheric refraction

1979 ◽  
Vol 89 ◽  
pp. 157-162 ◽  
Author(s):  
Allen Joel Anderson
Keyword(s):  
Spectral Analysis ◽  
Gravitational Radiation ◽  
Path Length ◽  
Low Frequency ◽  
Length Variation ◽  
Deep Space ◽  
Very Low Frequency ◽  
Tropospheric Refraction ◽  
Detection Capabilities

An experiment is described in which microwave Doppler is used to determine very small changes in path length to spacecraft tracked by the Deep Space Tracking Network (DSN). The experiment was carried out to test the detection capabilities of the DSN system to gravitational radiation of very low frequency (10−2–10−4 Hz). In this work spectral analysis of Doppler variations were performed for periods over 4 hours and more.These results indicated that one of major sources of noise was due to rapid variations in tropospheric refraction. The results obtained a differential path length variation, ΔL/L, of 1 part in 1014 for periods between 100 and 1 000 seconds.Doppler spectra are shown and a general discussion of the experiment is given.

Continuous, on-line, real-time spectral analysis of SAP signals during cardiopulmonary bypass

1995 ◽  
Vol 268 (6) ◽  
pp. H2329-H2335
Author(s):  
M. W. Yang ◽  
T. B. Kuo ◽  
S. M. Lin ◽  
K. H. Chan ◽  
S. H. Chan
Keyword(s):  
Spectral Analysis ◽  
Cardiopulmonary Bypass ◽  
Blood Vessels ◽  
Real Time ◽  
Low Frequency ◽  
Frequency Component ◽  
Very Low Frequency ◽  
Frequency Components ◽  
On Line ◽  
Very High

We communicated the application of continuous, on-line, real-time power spectral analysis of systemic arterial pressure (SAP) signals during cardiopulmonary bypass when the heart was functionally but reversibly disconnected from the blood vessels. Based on observations from 15 cases of successfully completed coronary artery bypass grafting procedures, we found that the very low (0.00-0.08 Hz), low (0.08-0.15 Hz)-, high (0.15-0.25 Hz)-, and very high (0.80-1.60 Hz) frequency components of SAP signals exhibited differential changes before, during, and after cardiopulmonary bypass. In particular, the very low-frequency component, which purportedly represents the contribution of vasomotor activity to SAP, presented only a mild decrease in power during hypothermic cardioplegia. Interestingly, the total peripheral resistance also manifested only a slight reduction during the same period. On the other hand, the low-, high-, and very high frequency components were essentially eliminated. These results unveiled an active role for the blood vessels in the maintenance of SAP during cardiopulmonary bypass, possibly as a result of a maintained vasomotor tone as reflected by the sustained very low frequency component of the SAP signals.

scholarly journals A Spaceborne Multi-Arm Interferometer for VLF Gravitational Wave Detection. (The SMILE Project)

1988 ◽  
Vol 129 ◽  
pp. 321-322
Author(s):  
Allen Joel Anderson
Keyword(s):  
Gravitational Wave ◽  
Gravitational Waves ◽  
Low Frequency ◽  
Deep Space ◽  
Detection Capability ◽  
Gravitational Wave Detection ◽  
Very Low Frequency ◽  
Wave Detection ◽  
Designed Experiment ◽  
Spacecraft Tracking

This project would be the next step in our ability to detect very low frequency (VLF) gravitational waves and the first committed spaceborne designed experiment. Present Deep Space spacecraft tracking experiments are severely limited in their detection capability. It is proposed to construct a spaceborne multi-arm microwave interferometer using current elements of design applicable for the detection of VLF gravitational waves. The elements are outlined with particular emphasis placed on the utilization of small inexpensive get away special (GAS) modules currently under development at JPL for launch in the 1990's.

scholarly journals Predictive value of very low frequency at spectral analysis among patients with unexplained syncope assessed by head-up tilt testing

2018 ◽  
Vol 111 (2) ◽  
pp. 95-100 ◽  
Author(s):  
Michela Anna Pia Ciliberti ◽  
Francesco Santoro ◽  
Luigi Flavio Massimiliano Di Martino ◽  
Antonio Cosimo Rinaldi ◽  
Giuseppe Salvemini ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Predictive Value ◽  
Low Frequency ◽  
Tilt Testing ◽  
Very Low Frequency ◽  
Head Up Tilt ◽  
Unexplained Syncope

Coarse-graining spectral analysis: new method for studying heart rate variability

1991 ◽  
Vol 71 (3) ◽  
pp. 1143-1150 ◽  
Author(s):  
Y. Yamamoto ◽  
R. L. Hughson
Keyword(s):  
Heart Rate ◽  
Time Series ◽  
Heart Rate Variability ◽  
Spectral Analysis ◽  
High Frequency ◽  
Low Frequency ◽  
Scale Invariant ◽  
Very Low Frequency ◽  
Frequency Components ◽  
Harmonic Components

Heart rate variability (HRV) spectra are typically analyzed for the components related to low- (less than 0.15 Hz) and high- (greater than 0.15 Hz) frequency variations. However, there are very-low-frequency components with periods up to hours in HRV signals, which might smear short-term spectra. We developed a method of spectral analysis suitable for selectively extracting very-low-frequency components, leaving intact the low- and high-frequency components of interest in HRV spectral analysis. Computer simulations showed that those low-frequency components were well characterized by fractional Brownian motions (FBMs). If the scale invariant, or self-similar, property of FBMs is considered a new time series (x′) was constructed by sampling only every other point (course graining) of the original time series (x). Evaluation of the cross-power spectra between these two (Sxx′) showed that the power of the FBM components was preserved, whereas that of the harmonic components vanished. Subtraction of magnitude of Sxx from the autopower spectra of the original sequence emphasized only the harmonic components. Application of this method to HRV spectral analyses indicated that it might enable one to observe more clearly the low- and high-frequency components characteristic of autonomic control of heart rate.

Low-frequency renal sympathetic nerve activity, arterial BP, stationary “1/f noise,” and the baroreflex

1999 ◽  
Vol 277 (3) ◽  
pp. R894-R903 ◽  
Author(s):  
Don E. Burgess ◽  
Tabitha A. Zimmerman ◽  
Marshall T. Wise ◽  
Sheng-Gang Li ◽  
David C. Randall ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Low Frequency ◽  
Stationary Time Series ◽  
Nerve Activity ◽  
Renal Sympathetic Nerve Activity ◽  
Very Low Frequency ◽  
Renal Sympathetic Nerve ◽  
Renal Sympathetic

The object of this study is to quantify the very low frequency (i.e., <0.1 Hz) interactions between renal sympathetic nerve activity (SNA) and arterial blood pressure (ABP). Six rats were instrumented for chronic recordings of SNA and ABP. Data were collected 24 h after surgery at 10 kHz for 2–5 h and subsequently compressed to a 1-kHz signal. The power spectra and ordinary coherence were calculated from data epochs up to 1 h in length. The very low frequency spectra for both variables were fitted to a constant times f −β. The peak magnitude squared of the coherence near 0.4 Hz was 0.82 ± 0.08, but the apparent linear coherence fell off quickly at lower frequencies so that it was close to zero for frequencies <0.1 Hz. Moreover, at these low frequencies β, as computed by a coarse grain spectral analysis, was significantly ( P < 0.01) different for SNA (0.66 ± 0.12) and ABP (1.12 ± 0.14). Assuming that SNA and ABP are stationary time series, the results of our classical spectral analysis would indicate that SNA and ABP are not linearly correlated at frequencies with a period more than ∼10 s. Accordingly, we tested for stationarity by computing the spectral coherence and found that SNA and ABP are not stationary “1/ f noise” within the frequency range from 0.02 to 2.0 Hz. Rather the SNA exerts control over the cardiovascular system through intermittent bursts of activity. Such intermittent behavior can be modeled by nonlinear dynamics.

Role of sinoaortic afferents in modulating BP and pulse-interval spectral characteristics in unanesthetized cats

1991 ◽  
Vol 261 (6) ◽  
pp. H1811-H1818 ◽  
Author(s):  
M. Di Rienzo ◽  
G. Parati ◽  
P. Castiglioni ◽  
S. Omboni ◽  
A. U. Ferrari ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
High Frequency ◽  
Spectral Characteristics ◽  
Low Frequency ◽  
Pulse Interval ◽  
Very Low Frequency ◽  
Variability Pattern ◽  
Spectral Components ◽  
Related Increase

Sinoaortic denervation (SAD) is accompanied by an increase in blood pressure (BP) and a reduction in pulse-interval (PI) variance. Little is known, however, about the effect of SAD on the complex BP and PI variability pattern, which is identified by spectral analysis. In nine unanesthetized cats in which intra-arterial BP was monitored before and 7-10 days after SAD, spectral powers (estimated by fast Fourier transform) were calculated for the low frequency (LF, 0.025-0.07 Hz), midfrequency (MF, 0.07-0.14 Hz), and high frequency (HF, 0.14-0.60 Hz) band. The very low frequency (VLF) BP and PI components (VLF less than 0.025 Hz) were also estimated. SAD increased systolic BP variance and decreased PI variance. The reduction of PI variance was paralleled by significant and marked reductions in all PI powers including the VLF components. In contrast, the increase in systolic BP variance was accompanied by a marked increase in LF power, a decrease in MF power, and no change in HF power. The VLF BP components increased after SAD for frequencies between 0.025 and 0.0012 Hz, whereas a sudden marked reduction was observed below 0.0012 Hz. Similar results were obtained for diastolic BP powers. Thus the reduction in PI variance induced by SAD is paralleled by a reduction in all PI fluctuations identified by spectral analysis. This is not the case for the SAD-related increase in BP variance, which is accompanied by an increase, no change, or even a reduction in the different BP spectral components.(ABSTRACT TRUNCATED AT 250 WORDS)

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