A 2200-yr record of hydrologic variability from Foy Lake, Montana, USA, inferred from diatom and geochemical data

2006 ◽  
Vol 65 (02) ◽  
pp. 264-274 ◽  
Author(s):  
Lora R. Stevens ◽  
Jeffery R. Stone ◽  
Josh Campbell ◽  
Sherilyn C. Fritz
Keyword(s):  
Spectral Analysis ◽  
High Resolution ◽  
High Frequency ◽  
Lake Level ◽  
Low Frequency ◽  
Seasonal Distribution ◽  
Geochemical Data ◽  
Hydrologic Variability ◽  
Moisture Balance ◽  
Hydrologic Balance

AbstractA 2200-yr long, high-resolution (∼5 yr) record of drought variability in northwest Montana is inferred from diatoms and δ18O values of bio-induced carbonate preserved in a varved lacustrine core from Foy Lake. A previously developed model of the diatom response to lake-level fluctuations is used to constrain estimates of paleolake levels derived from the diatom data. High-frequency (decadal) fluctuations in the de-trended δ18O record mirror variations in wet/dry cycles inferred from Banff tree-rings, demonstrating the sensitivity of the oxygen-isotope values to changes in regional moisture balance. Low frequency (multi-centennial) isotopic changes may be associated with shifts in the seasonal distribution of precipitation. From 200 B.C. to A.D. 800, both diatom and isotope records indicate that climate was dry and lake level low, with poor diatom preservation and high organic carbon: nitrogen ratios. Subsequently, lake level rose slightly, although the climate was drier and more stable than modern conditions. At A.D. 1200, lake level increased to approximately 6 m below present elevation, after which the lake fluctuated between this elevation and full stage, with particularly cool and/or wetter conditions after 1700. The hydrologic balance of the lake shifted abruptly at 1894 because of the establishment of a lumber mill at the lake's outlet. Spectral analysis of the δ18O data indicates that severe droughts occurred with multi-decadal (50 to 70 yr) frequency.

Spectral analysis of the EMG and diaphragmatic muscle fatigue during periodic breathing in infants

1985 ◽  
Vol 58 (3) ◽  
pp. 830-833 ◽  
Author(s):  
S. T. Nugent ◽  
J. P. Finley
Keyword(s):  
Spectral Analysis ◽  
Muscle Fatigue ◽  
Preterm Infants ◽  
High Frequency ◽  
Power Spectra ◽  
Low Frequency ◽  
Periodic Breathing ◽  
Full Term ◽  
Diaphragmatic Muscle ◽  
Normal Breathing

Periodic breathing occurs commonly in full-term and preterm infants. The mechanisms which switch breathing on and off within a cycle of periodic breathing are not certain. Since immature infants may experience diaphragmatic muscle fatigue, one potential switching mechanism is fatigue. Power spectra of the electromyogram, uncontaminated by the electrocardiograph artifact, were studied for evidence of diaphragmatic muscle fatigue during spontaneous periodic breathing in infants. A fall in the high-frequency (103–600 Hz) power and an increase in the low-frequency (23–47 Hz) power during periodic as compared with normal breathing would indicate fatigue. This effect was not observed in any of the infants studied. Hence, there is no evidence that periodic breathing is the result of diaphragmatic muscle fatigue. This finding suggests that the effect of drugs such as theophylline in eliminating periodic breathing may be unrelated to the fact that they also reduce fatigue.

The A2Π–X2Σ+ system of MgCl

1987 ◽  
Vol 65 (12) ◽  
pp. 1594-1603 ◽  
Author(s):  
M. Singh ◽  
G. S. Ghodgaonkar ◽  
M. D. Saksena
Keyword(s):  
High Resolution ◽  
Structure Analysis ◽  
Vibrational Level ◽  
High Frequency ◽  
Low Frequency ◽  
Rotational Structure ◽  
Rotational Analysis ◽  
The Common ◽  
Π State

The A2Π–X2Σ+ system of MgCl has been photographed at high resolution and analyzed for the rotational structure. Analysis of the low-frequency sub-bands of the 0–0, 0–1, and 0–2 bands showed that there is a nonzero Λ doubling in the common vibrational level ν′ = 0, thereby indicating that the A2Π state is regular and not inverted as presumed by earlier workers. Spin-doubling has been seen in the ν = 1 and 2 levels of the X2Σ+ state. Rotational analysis of the high-frequency sub-band has also been done for the 0–0 band.

Frequency-dependent baroreflex modulation of blood pressure and heart rate variability in conscious mice

2005 ◽  
Vol 289 (5) ◽  
pp. H1968-H1975 ◽  
Author(s):  
Rubens Fazan ◽  
Mauro de Oliveira ◽  
Valdo José Dias da Silva ◽  
Luis Fernando Joaquim ◽  
Nicola Montano ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Heart Rate Variability ◽  
Spectral Analysis ◽  
High Frequency ◽  
Low Frequency ◽  
Systolic Arterial Pressure ◽  
Pulse Interval ◽  
Sham Surgery ◽  
Cardiac Receptors

The goal of this study was to determine the baroreflex influence on systolic arterial pressure (SAP) and pulse interval (PI) variability in conscious mice. SAP and PI were measured in C57Bl/6J mice subjected to sinoaortic deafferentation (SAD, n = 21) or sham surgery ( n = 20). Average SAP and PI did not differ in SAD or control mice. In contrast, SAP variance was enhanced (21 ± 4 vs. 9.5 ± 1 mmHg2) and PI variance reduced (8.8 ± 2 vs. 26 ± 6 ms2) in SAD vs. control mice. High-frequency (HF: 1–5 Hz) SAP variability quantified by spectral analysis was greater in SAD (8.5 ± 2.0 mmHg2) compared with control (2.5 ± 0.2 mmHg2) mice, whereas low-frequency (LF: 0.1–1 Hz) SAP variability did not differ between the groups. Conversely, LF PI variability was markedly reduced in SAD mice (0.5 ± 0.1 vs. 10.8 ± 3.4 ms2). LF oscillations in SAP and PI were coherent in control mice (coherence = 0.68 ± 0.05), with changes in SAP leading changes in PI (phase = −1.41 ± 0.06 radians), but were not coherent in SAD mice (coherence = 0.08 ± 0.03). Blockade of parasympathetic drive with atropine decreased average PI, PI variance, and LF and HF PI variability in control ( n = 10) but had no effect in SAD ( n = 6) mice. In control mice, blockade of sympathetic cardiac receptors with propranolol increased average PI and decreased PI variance and LF PI variability ( n = 6). In SAD mice, propranolol increased average PI ( n = 6). In conclusion, baroreflex modulation of PI contributes to LF, but not HF PI variability, and is mediated by both sympathetic and parasympathetic drives in conscious mice.

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.

A Complete Computational Model of Ultrasound Vibro-Acoustography

2006 ◽  
Author(s):  
Alison E. Malcolm ◽  
Fernando Reitich ◽  
Jiaqi Yang ◽  
Mostafa Fatemi ◽  
James F. Greenleaf
Keyword(s):  
High Resolution ◽  
Optimal Design ◽  
Computational Model ◽  
High Frequency ◽  
Imaging Modality ◽  
Low Frequency ◽  
High Frequency Ultrasound ◽  
Linear Interaction ◽  
Modeling Simulation ◽  
Frequency Ultrasound

Ultrasound vibro-acoustography is a novel medical imaging modality that combines the high resolution of high-frequency ultrasound with the speckle-free images obtained using low-frequency methods. This imaging modality relies on the non-linear interaction of two high frequency beams at slightly different frequencies. We describe the physics of ultrasound vibro-acoustography and outline a strategy for its modeling, simulation, and optimal design.

scholarly journals Radio Emission from Nearby Galaxies at High Frequencies

1981 ◽  
Vol 94 ◽  
pp. 225-226
Author(s):  
Rainer Beck ◽  
Ulrich Klein
Keyword(s):  
High Resolution ◽  
High Frequency ◽  
Spiral Galaxies ◽  
Low Frequency ◽  
Cosmic Ray ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Frequency Synthesis ◽  
High Frequencies ◽  
Nearby Galaxies

High resolution observations of the radio continuum emission from nearby galaxies at several frequencies provide information about the cosmic ray electrons. Optimum results are expected by combining low-frequency synthesis observations with high-frequency single dish data, e.g. Westerbork 610 MHz / Effelsberg 10.7 GHz (1′ resolution) or Cambridge 150 MHz / Effelsberg 2.7 GHz (4′ resolution). Maps of 15 nearby spiral galaxies at 10.7 GHz have been made with the Effelsberg 100-m telescope. Maps of M31 and M33 are available at 2.7 and 4.8 GHz.

Impact of Changes in Respiratory Frequency and Posture on Power Spectral Analysis of Heart Rate and Systolic Blood Pressure Variability in Normal Subjects and Patients with Heart Failure

1996 ◽  
Vol 91 (1) ◽  
pp. 35-43 ◽  
Author(s):  
John E. Sanderson ◽  
Leata Y. C. Yeung ◽  
Dickens T. K. Yeung ◽  
Richard L. C. Kay ◽  
Brian Tomlinson ◽  
...  
Keyword(s):  
Heart Failure ◽  
Blood Pressure ◽  
Heart Rate ◽  
Spectral Analysis ◽  
High Frequency ◽  
Low Frequency ◽  
Power Spectral Analysis ◽  
Normal Subjects ◽  
Power Spectral ◽  
Patients With Heart Failure

1. Autonomic dysfunction is a major feature of congestive cardiac failure and may have an important role in determining progression and prognosis. The low-frequency/high-frequency ratio derived from power spectral analysis of heart rate variability has been proposed as a non-invasive method to assess sympatho-vagal balance. However, the effects of different respiratory rates or posture are rarely accounted for, but may be relevant in patients with heart failure in whom clinical improvement is accompanied by a fall in respiratory rate and an increased proportion of the day in the upright position. 2. We have assessed the effect of controlled respiration at different rates (10, 15, 20 breaths/min or 0.17, 0.25 and 0.33 Hz), while supine and standing, on power spectral analysis of heart rate and blood pressure variability in 11 patients with heart failure and 10 normal subjects. 3. Heart rate variance and low-frequency power (normalized units) were reduced in patients with heart failure (absent in six). During controlled breathing while supine, the power of the high-frequency component was significantly greater at 10 breaths/min than at 20 breaths/min in patients with heart failure, whether expressed in absolute units (P = 0.005) or percentage of total power (P = 0.03). 4. On standing, controlled breathing in patients with heart failure produced less change in high-frequency power (P = 0.054), but the low-frequency/high-frequency ratio at lower respiratory rates was reduced (P = 0.05). In normal subjects, as expected, respiratory rate had a highly significant effect on high-frequency power. Also, in normal subjects there was the expected increase in heart rate low-frequency power (P = 0.04) moving from supine to standing with an increase in the low-frequency/high-frequency ratio (P = 0.003), while in the patients with heart failure this was absent, reflecting blunted cardiovascular reflexes. 5. Systolic blood pressure low- and high-frequency components and their ratio were significantly affected by respiration (P > 0.03) and change in posture (P > 0.03) in both patients with heart failure and normal subjects, with a significant increase in the low-frequency/high-frequency ratio (P = 0.03) on standing in patients with heart failure, indicating that autonomic modulation of blood pressure is still operating in heart failure. 6. Thus, respiratory rate and changes in posture have a significant effect on measurements derived from spectral analysis of heart rate and blood pressure variability. Studies that use power spectral analysis as a measure of sympatho-vagal balance should control for these variables.

scholarly journals Spectral analysis of heart period variability in anorexia nervosa

2005 ◽  
Vol 62 (1) ◽  
pp. 27-31 ◽  
Author(s):  
Mirjana Platisa ◽  
Vera Gal ◽  
Svetozar Damjanovic
Keyword(s):  
Body Mass Index ◽  
Spectral Analysis ◽  
Anorexia Nervosa ◽  
Body Mass ◽  
High Frequency ◽  
Spectral Power ◽  
Low Frequency ◽  
Heart Period ◽  
Standing Posture ◽  
Total Variability

The aim of this study was to investigate the response of autonomic cardiac control to postural change using spectral analysis, in patients with anorexia nervosa. Spectral components of total variability as well as of low and high frequencies were analyzed for 17 anorexic patients with mean body mass index (14.9 ? 1.9) kg/m2 and for 9 healthy age-matched women with body mass index (20.3 ? 1.7) kg/m2, in supine and standing postures. During standing posture, increased heart rate in all subjects was accompanied by the decrease in total variability and high frequency spectral powers. In supine posture, anorexic patients demonstrated the reduced low frequency spectral power. Compared to control women, during standing posture anorexic patients showed higher heart rate, reduced total variability and high frequency spectral powers. Statistically significant correlation was noticed between body mass index and spectral power of low frequency in both supine and standing posture. Alterations in autonomic cardiac control induced by anorexia nervosa could be estimated by spectral analysis of heart period variability.

Evidence of low- and high-frequency oscillations in human AV interval variability: evaluation with spectral analysis

1994 ◽  
Vol 267 (4) ◽  
pp. H1410-H1418 ◽  
Author(s):  
G. Nollo ◽  
M. Del Greco ◽  
F. Ravelli ◽  
M. Disertori
Keyword(s):  
Spectral Analysis ◽  
High Frequency ◽  
Low Frequency ◽  
Atrial Pacing ◽  
Autonomic Modulation ◽  
High Frequency Oscillations ◽  
Av Conduction ◽  
Relative Standard ◽  
Frequency Domains ◽  
The Mean

The spontaneous beat-to-beat variation of atrioventricular (AV) interval was analyzed in time and frequency domains and compared with atrial cycle length (A-A) variability. The analysis was applied in humans at rest and tilt position during sinus rhythm and atrial pacing. The AV intervals showed spontaneous oscillations of small amplitude with a relative standard deviation of 1.8%. Spectral analysis of AV interval series showed the existence of two main oscillatory components at low frequency (LF; 0.04-0.13 Hz) and at high frequency (HF; 0.17-0.4 Hz), synchronous with those of A-A interval series. The same LF and HF fluctuations were found in AV interval variability during atrial pacing. Tilt maneuver inducing a sympathetic stimulation and vagal withdrawal increased LF power and decreased HF power of A-A interval spectra (P < 0.05). On the contrary, tilt decreased the LF (46%, P < 0.05) and HF power (29%, P = NS) of AV conduction spectra. In parallel, tilt decreased (P < 0.0001) the mean A-A interval, leaving the mean AV interval unchanged. When heart rate was held constant by atrial pacing, tilt reduced the mean AV interval, the LF power (65%, P < 0.05), and HF power (10%, P = NS). These results indicate a direct influence of the autonomic nervous system on the LF and HF oscillations of AV conduction. The decrease of AV interval oscillations during tilt demonstrates a marked reduction of autonomic modulation of AV conduction mainly attributable to parasympathetic withdrawal.

Assessment of autonomic function in humans by heart rate spectral analysis

1985 ◽  
Vol 248 (1) ◽  
pp. H151-H153 ◽  
Author(s):  
B. Pomeranz ◽  
R. J. Macaulay ◽  
M. A. Caudill ◽  
I. Kutz ◽  
D. Adam ◽  
...  
Keyword(s):  
Heart Rate ◽  
Nervous System ◽  
Spectral Analysis ◽  
High Frequency ◽  
Autonomic Function ◽  
Parasympathetic Nervous System ◽  
Low Frequency ◽  
Parasympathetic System ◽  
Heart Rate Fluctuations ◽  
Frequency Fluctuations

Spectral analysis of spontaneous heart rate fluctuations were assessed by use of autonomic blocking agents and changes in posture. Low-frequency fluctuations (below 0.12 Hz) in the supine position are mediated entirely by the parasympathetic nervous system. On standing, the low-frequency fluctuations increase and are jointly mediated by the sympathetic and parasympathetic nervous systems. High-frequency fluctuations, at the respiratory frequency, are decreased by standing and are mediated solely by the parasympathetic system. Heart rate spectral analysis is a powerful noninvasive tool for quantifying autonomic nervous system activity.

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