Permeability and borehole Stoneley waves: Comparison between experiment and theory

Geophysics ◽  
1989 ◽  
Vol 54 (1) ◽  
pp. 66-75 ◽  
Author(s):  
Kenneth W. Winkler ◽  
Hsui‐Lin Liu ◽  
David Linton Johnson
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Theoretical Models ◽  
Oil Field ◽  
Stoneley Wave ◽  
Biot Theory ◽  
Frequency Dependent ◽  
Low Frequencies ◽  
High Frequencies ◽  
Theoretical Predictions

We performed laboratory experiments to evaluate theoretical models of borehole. Stoneley wave propagation in permeable materials. A Berea sandstone and synthetic samples made of cemented glass beads were saturated with silicone oils. We measured both velocity and attenuation over a frequency band from 10 kHz to 90 kHz. Our theoretical modeling incorporated Biot theory and Deresiewicz‐Skalak boundary conditions into a cylindrical geometry and included frequency‐dependent permeability. By varying the viscosity of the saturating pore fluid, we were able to study both low‐frequency and high‐frequency regions of Biot theory, as well as the intermediate transition zone. In both low‐frequency and high‐frequency regions of the theory, we obtained excellent agreement between experimental observations and theoretical predictions. Velocity and attenuation (1/Q) are frequency‐dependent, especially at low frequencies. Also at low frequencies, velocity decreases and attenuation increases with increasing fluid mobility (permeability/viscosity). More complicated behavior is observed at high frequencies. These results support recent observations from the oil field suggesting that Stoneley wave velocity and attenuation may be indicative of formation permeability.

scholarly journals High Frequency Performance of Piezoelectric Diaphragms for Impedance-Based SHM Applications

2020 ◽  
Vol 2 (1) ◽  
pp. 16
Author(s):  
Guilherme Rezende ◽  
Fabricio Baptista
Keyword(s):  
High Frequency ◽  
Structural Damage ◽  
Low Cost ◽  
Low Frequency ◽  
Experimental Tests ◽  
Piezoelectric Transducers ◽  
Low Frequencies ◽  
High Frequencies ◽  
Electromechanical Impedance ◽  
Damage Indices

Piezoelectric transducers are used in a wide variety of applications, including damage detection in structural health monitoring (SHM) applications. Among the various methods for detecting structural damage, the electromechanical impedance (EMI) method is one of the most investigated in recent years. In this method, the transducer is typically excited with low frequency signals up to 500 kHz. However, recent studies have indicated the use of higher frequencies, usually above 1 MHz, for the detection of some types of damage and the monitoring of some structures’ characteristics that are not possible at low frequencies. Therefore, this study investigates the performance of low-cost piezoelectric diaphragms excited with high frequency signals for SHM applications based on the EMI method. Piezoelectric diaphragms have recently been reported in the literature as alternative transducers for the EMI method and, therefore, investigating the performance of these transducers at high frequencies is a relevant subject. Experimental tests were carried out with piezoelectric diaphragms attached to two aluminum bars, obtaining the impedance signatures from diaphragms excited with low and high frequency signals. The analysis was performed using the real part of the impedance signatures and two basic damage indices, one based on the Euclidean norm and the other on the correlation coefficient. The experimental results indicate that piezoelectric diaphragms are usable for the detection of structural damage at high frequencies, although the sensitivity decreases.

Sympathetic stimulation elicits increased or decreased VO2 in the perfused rat hindlimb via alpha 1-adrenoceptors

1997 ◽  
Vol 272 (5) ◽  
pp. H2146-H2153 ◽  
Author(s):  
J. L. Hall ◽  
J. M. Ye ◽  
M. G. Clark ◽  
E. Q. Colquhoun
Keyword(s):  
High Frequency ◽  
Pressor Response ◽  
Low Frequency ◽  
Sympathetic Nerves ◽  
High Frequency Stimulation ◽  
Arterial Infusion ◽  
Low Frequencies ◽  
High Frequencies ◽  
Low Frequency Stimulation ◽  
Frequency Stimulation

The effects of lumbar sympathetic nerve stimulation on oxygen uptake (VO2) in curarized muscle of the perfused rat hindlimb were investigated. Stimulation of sympathetic nerves elicited vasoconstriction at all frequencies. Importantly, this was associated with changes in VO2 that were generally stimulatory at low frequencies (0.5-2 Hz) and inhibitory at high frequencies (5-10 Hz). Both the pressor response and the changes in VO2 were almost completely blocked by the alpha 1/alpha 2-blocker phentolamine (1.0 microM) but were not affected by the beta 1/beta 2-blocker DL-propranolol (2.0 microM). The alpha 2-blocker yohimbine (0.1 microM) did not significantly affect either the pressor or VO2 response. The alpha 1-antagonist prazosin (0.1 microM) abolished the vasoconstriction with low-frequency stimulation and inhibited > 90% of the vasoconstriction with high-frequency stimulation. Intra-arterial infusion of phenylephrine (alpha 1-agonist), but not of UK-14304 (alpha 2-agonist), also elicited a similar biphasic response in VO2 during vasoconstriction. The changes in VO2 at both low- and high-frequency stimulation were fully reversed by prazosin. The vasodilator sodium nitroprusside also showed similar effects to prazosin in blocking both VO2 and vasoconstriction. Thus sympathetic control of VO2 in the perfused rat hindlimb appears to be initiated by activation of predominantly vascular alpha 1-adrenoceptors.

Neural Sensitivity to Interaural Envelope Delays in the Inferior Colliculus of the Guinea Pig

2005 ◽  
Vol 93 (6) ◽  
pp. 3463-3478 ◽  
Author(s):  
Sarah J. Griffin ◽  
Leslie R. Bernstein ◽  
Neil J. Ingham ◽  
David McAlpine
Keyword(s):  
Fine Structure ◽  
Guinea Pig ◽  
Inferior Colliculus ◽  
High Frequency ◽  
Low Frequency ◽  
Nerve Fibers ◽  
Neural Firing ◽  
Low Frequencies ◽  
Interaural Time Differences ◽  
High Frequencies

Interaural time differences (ITDs) are important cues for mammalian sound localization. At high frequencies, sensitivity to ITDs, which are conveyed only by the envelope of the waveforms, has been shown to be poorer than sensitivity to ITDs at low frequencies, which are conveyed primarily by the fine structure of the waveforms. Recently, human psychophysical experiments have demonstrated that sensitivity to envelope-based ITDs in high-frequency transposed tones can be equivalent to low-frequency fine-structure–based ITD sensitivity. Transposed tones are designed to provide high-frequency auditory nerve fibers (ANFs) with similar temporal information to that provided by low-frequency tones. We investigated neural sensitivity to ITDs in high-frequency transposed and sinusoidally amplitude modulated (SAM) tones, in the inferior colliculus of the guinea pig. Neural sensitivity to ITDs in transposed tones was found to be greater than that to ITDs in SAM tones; in response to transposed tones, neural firing rates were more modulated as a function of ITD and discrimination thresholds were found to be lower than those in response to SAM tones. Similar to psychophysical findings, ITD discrimination of single neurons in response to transposed tones for rates of modulation <250 Hz was comparable to neural discrimination of ITDs in low-frequency tones. This suggests that the neural mechanisms that mediate sensitivity to ITDs at high and low frequencies are functionally equivalent, provided that the stimuli result in appropriate temporal patterns of action potentials in ANFs.

Autoregressive recovery of the acoustic impedance

Geophysics ◽  
1983 ◽  
Vol 48 (10) ◽  
pp. 1338-1350 ◽  
Author(s):  
Colin Walker ◽  
Tad J. Ulrych
Keyword(s):  
Frequency Band ◽  
Acoustic Impedance ◽  
High Frequency ◽  
Low Frequency ◽  
Minimum Entropy ◽  
Linear Programming Method ◽  
Low Frequencies ◽  
High Frequencies ◽  
Ar Modeling ◽  
Positive Frequency

This paper presents a method of recovering the acoustic impedance from reflection seismograms using autoregressive (AR) modeling, an approach originally applied to deconvolution by Lines and Clayton (1977). The algorithm which we describe is novel both in the manner in which the missing low‐ and high‐frequency information is predicted, and in the fact that the prediction may be constrained if acoustic impedance information is available. The prediction of the low frequencies treats the missing data as a gap which extends from the low‐frequency cut‐off in the negative frequency band to the corresponding frequency in the positive frequency band. The conjugate symmetry which governs the behavior of the spectrum in the band is taken into account in the prediction. The missing high frequencies are predicted using a modified minimum entropy norm in the frequency domain. Both synthetic and field examples are presented and illustrate the robustness of the new AR algorithm under a variety of conditions. The field example also compares the results obtained using the AR algorithm with the linear programming method of Oldenburg et al (1983). The agreement in results is particularly gratifying in view of the differences in the two inversion schemes.

scholarly journals Rheology of rounded mammalian cells over continuous high-frequencies

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Gotthold Fläschner ◽  
Cosmin I. Roman ◽  
Nico Strohmeyer ◽  
David Martinez-Martin ◽  
Daniel J. Müller
Keyword(s):  
High Frequency ◽  
Mammalian Cells ◽  
Mechanical Response ◽  
Cell Mass ◽  
Low Frequency ◽  
Mass Measurements ◽  
High Frequencies ◽  
Polymer Relaxation ◽  
Continuous Frequency ◽  
Rheological Experiments

AbstractUnderstanding the viscoelastic properties of living cells and their relation to cell state and morphology remains challenging. Low-frequency mechanical perturbations have contributed considerably to the understanding, yet higher frequencies promise to elucidate the link between cellular and molecular properties, such as polymer relaxation and monomer reaction kinetics. Here, we introduce an assay, that uses an actuated microcantilever to confine a single, rounded cell on a second microcantilever, which measures the cell mechanical response across a continuous frequency range ≈ 1–40 kHz. Cell mass measurements and optical microscopy are co-implemented. The fast, high-frequency measurements are applied to rheologically monitor cellular stiffening. We find that the rheology of rounded HeLa cells obeys a cytoskeleton-dependent power-law, similar to spread cells. Cell size and viscoelasticity are uncorrelated, which contrasts an assumption based on the Laplace law. Together with the presented theory of mechanical de-embedding, our assay is generally applicable to other rheological experiments.

scholarly journals Earless toads sense low frequencies but miss the high notes

2017 ◽  
Vol 284 (1864) ◽  
pp. 20171670 ◽  
Author(s):  
Molly C. Womack ◽  
Jakob Christensen-Dalsgaard ◽  
Luis A. Coloma ◽  
Juan C. Chaparro ◽  
Kim L. Hoke
Keyword(s):  
High Frequency ◽  
Species Differences ◽  
Low Frequency ◽  
Auditory Brainstem ◽  
Low Frequencies ◽  
Hearing Sensitivity ◽  
Sensory Pathways ◽  
Airborne Sound ◽  
Vibrational Sensitivity ◽  
Species Specific

Sensory losses or reductions are frequently attributed to relaxed selection. However, anuran species have lost tympanic middle ears many times, despite anurans' use of acoustic communication and the benefit of middle ears for hearing airborne sound. Here we determine whether pre-existing alternative sensory pathways enable anurans lacking tympanic middle ears (termed earless anurans) to hear airborne sound as well as eared species or to better sense vibrations in the environment. We used auditory brainstem recordings to compare hearing and vibrational sensitivity among 10 species (six eared, four earless) within the Neotropical true toad family (Bufonidae). We found that species lacking middle ears are less sensitive to high-frequency sounds, however, low-frequency hearing and vibrational sensitivity are equivalent between eared and earless species. Furthermore, extratympanic hearing sensitivity varies among earless species, highlighting potential species differences in extratympanic hearing mechanisms. We argue that ancestral bufonids may have sufficient extratympanic hearing and vibrational sensitivity such that earless lineages tolerated the loss of high frequency hearing sensitivity by adopting species-specific behavioural strategies to detect conspecifics, predators and prey.

Frequency-Weighted Variable-Length Controllers Using Anytime Control Strategies

2011 ◽  
Author(s):  
Gundula B. Runge ◽  
Al Ferri ◽  
Bonnie Ferri
Keyword(s):  
Time Scale ◽  
Weighting Function ◽  
Control Strategies ◽  
Low Frequency ◽  
Low Frequencies ◽  
High Frequencies ◽  
Frequency Components ◽  
Computational Resources ◽  
Weighted Variable ◽  
Selection Of

This paper considers an anytime strategy to implement controllers that react to changing computational resources. The anytime controllers developed in this paper are suitable for cases when the time scale of switching is in the order of the task execution time, that is, on the time scale found commonly with sporadically missed deadlines. This paper extends the prior work by developing frequency-weighted anytime controllers. The selection of the weighting function is driven by the expectation of the situations that would require anytime operation. For example, if the anytime operation is due to occasional and isolated missed deadlines, then the weighting on high frequencies should be larger than that for low frequencies. Low frequency components will have a smaller change over one sample time, so failing to update these components for one sample period will have less effect than with the high frequency components. An example will be included that applies the anytime control strategy to a model of a DC motor with deadzone and saturation nonlinearities.

Vibration Characteristics of Metamaterial Beams With Periodic Local Resonances

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
M. Nouh ◽  
O. Aldraihem ◽  
A. Baz
Keyword(s):  
Band Gap ◽  
Low Frequency ◽  
Element Model ◽  
Small Mass ◽  
Vibration Characteristics ◽  
Structural Vibrations ◽  
Low Frequencies ◽  
Theoretical Predictions ◽  
Gap Characteristics ◽  
Unique Band

Vibration characteristics of metamaterial beams manufactured of assemblies of periodic cells with built-in local resonances are presented. Each cell consists of a base structure provided with cavities filled by a viscoelastic membrane that supports a small mass to form a source of local resonance. This class of metamaterial structures exhibits unique band gap behavior extending to very low-frequency ranges. A finite element model (FEM) is developed to predict the modal, frequency response, and band gap characteristics of different configurations of the metamaterial beams. The model is exercised to demonstrate the band gap and mechanical filtering capabilities of this class of metamaterial beams. The predictions of the FEM are validated experimentally when the beams are subjected to excitations ranging between 10 and 5000 Hz. It is observed that there is excellent agreement between the theoretical predictions and the experimental results for plain beams, beams with cavities, and beams with cavities provided with local resonant sources. The obtained results emphasize the potential of the metamaterial beams for providing significant vibration attenuation and exhibiting band gaps extending to low frequencies. Such characteristics indicate that metamaterial beams are more effective in attenuating and filtering low-frequency structural vibrations than plain periodic beams of similar size and weight.

scholarly journals The Estimation of Hydrometeor Profiles from Wideband Microwave Observations

2000 ◽  
Vol 39 (10) ◽  
pp. 1645-1656 ◽  
Author(s):  
Gail M. Skofronick-Jackson ◽  
James R. Wang
Keyword(s):  
High Frequency ◽  
Cloud Water ◽  
Tropical Ocean ◽  
Low Frequencies ◽  
High Frequencies ◽  
Atmospheric Research ◽  
Brightness Temperatures ◽  
Microphysical Properties ◽  
Ice Microphysics ◽  
Updraft Region

Abstract Profiles of the microphysical properties of clouds and rain cells are essential in many areas of atmospheric research and operational meteorology. To enhance the understanding of the nonlinear and underconstrained relationships between cloud and hydrometeor microphysical profiles and passive microwave brightness temperatures, estimations of cloud profiles for an anvil region, a convective region, and an updraft region of an oceanic squall were performed. The estimations relied on comparisons between radiative transfer calculations of incrementally estimated microphysical profiles and concurrent dual-altitude wideband brightness temperatures from the 22 February 1993 flight during the Tropical Ocean and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment. The wideband observations (10–220 GHz) are necessary for estimating cloud profiles reaching up to 20 km. The low frequencies enhance the rain and cloud water profiles, and the high frequencies are required to detail the higher-altitude ice microphysics. A microphysical profile was estimated for each of the three regions of the storm. Each of the three estimated profiles produced calculated brightness temperatures within ∼10 K of the observations. A majority of the total iterative adjustments were to the estimated profile’s frozen hydrometeor characteristics and were necessary to match the high-frequency calculations with the observations. This requirement indicates a need to validate cloud-resolving models using high frequencies. Some difficulties matching the 37-GHz observation channels on the DC-8 and ER-2 aircraft with the calculations simulated at the two aircraft heights (∼11 km and 20 km, respectively) were noted, and potential causes were presented.

scholarly journals ANALYSIS OF HIGH-FREQUENCY C-CORE MAGNETIC FLUX LEAKAGES FOR BONE TUMOR WITH INDUCTION HEATING BY USING MULTI-COIL

2019 ◽  
Author(s):  
Metharak Jokpudsa ◽  
Supawat Kotchapradit ◽  
Chanchai Thongsopa ◽  
Thanaset Thosdeekoraphat
Keyword(s):  
Magnetic Field ◽  
High Frequency ◽  
Tumor Tissue ◽  
Low Frequency ◽  
Heat Energy ◽  
High Frequencies ◽  
Frequency Magnetic Field ◽  
High Frequency Magnetic Field ◽  
The Magnetic Field ◽  
Flux Leakage

High-frequency magnetic field has been developed pervasively. The induction of heat from the magnetic field can help to treat tumor tissue to a certain extent. Normally, treatment by the low-frequency magnetic field needed to be combined with magnetic substances. To assist in the induction of magnetic fields and reduce flux leakage. However, there are studies that have found that high frequencies can cause heat to tumor tissue. In this paper present, a new magnetic application will focus on the analysis of the high-frequency magnetic nickel core with multi-coil. In order to focus the heat energy using a high-frequency magnetic field into the tumor tissue. The magnetic coil was excited by 915 MHz signal and the combination of tissues used are muscle, bone, and tumor. The magnetic power on the heating predicted by the analytical model, the power loss density (2.98e-6 w/m3) was analyzed using the CST microwave studio.

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