scholarly journals Conductivity tomography at two frequencies

Geophysics ◽  
2003 ◽  
Vol 68 (2) ◽  
pp. 516-522 ◽  
Author(s):  
Junxing Cao ◽  
Zhenhua He ◽  
Jieshou Zhu ◽  
Peter K. Fullagar
Keyword(s):  
Single Frequency ◽  
Dual Frequency ◽  
Frequency Range ◽  
Frequency Method ◽  
New Approach ◽  
Electromagnetic Absorption ◽  
Universal Approach ◽  
Approximate Frequency ◽  
Transmitting Antenna

We present a new approach for crosshole radio tomography. Conductivity images of the investigated area are reconstructed from the ratio of the electric field intensities measured at two similar frequencies. The method largely avoids assumptions about the radiation pattern and in‐situ intensity of the transmitting antenna, which introduce errors in conventional single‐frequency crosshole electromagnetic‐absorption tomography. Application of the method to field data achieved an improvement in resolution of anomalies over traditional single‐frequency absorption tomography. The dual‐frequency method is not a universal approach; it is suitable for moderately conductive media (<0.01 S/m) over the approximate frequency range 1–100 MHz.

scholarly journals An Initial Assessment of the Surface Reference Technique Applied to Data from the Dual-Frequency Precipitation Radar (DPR) on the GPM Satellite

2015 ◽  
Vol 32 (12) ◽  
pp. 2281-2296 ◽  
Author(s):  
Robert Meneghini ◽  
Hyokyung Kim ◽  
Liang Liao ◽  
Jeffrey A. Jones ◽  
John M. Kwiatkowski
Keyword(s):  
Cross Section ◽  
Radar Data ◽  
Single Frequency ◽  
Initial Assessment ◽  
Dual Frequency ◽  
Precipitation Radar ◽  
Frequency Method ◽  
Ka Band ◽  
Spaceborne Radar ◽  
Ku Band

AbstractIt has long been recognized that path-integrated attenuation (PIA) can be used to improve precipitation estimates from high-frequency weather radar data. One approach that provides an estimate of this quantity from airborne or spaceborne radar data is the surface reference technique (SRT), which uses measurements of the surface cross section in the presence and absence of precipitation. Measurements from the dual-frequency precipitation radar (DPR) on the Global Precipitation Measurement (GPM) satellite afford the first opportunity to test the method for spaceborne radar data at Ka band as well as for the Ku-band–Ka-band combination.The study begins by reviewing the basis of the single- and dual-frequency SRT. As the performance of the method is closely tied to the behavior of the normalized radar cross section (NRCS or σ0) of the surface, the statistics of σ0 derived from DPR measurements are given as a function of incidence angle and frequency for ocean and land backgrounds over a 1-month period. Several independent estimates of the PIA, formed by means of different surface reference datasets, can be used to test the consistency of the method since, in the absence of error, the estimates should be identical. Along with theoretical considerations, the comparisons provide an initial assessment of the performance of the single- and dual-frequency SRT for the DPR. The study finds that the dual-frequency SRT can provide improvement in the accuracy of path attenuation estimates relative to the single-frequency method, particularly at Ku band.

Dual frequency bioelectrical impedance analysis to estimate hematocrit for prognosis of dengue fever in Indian children

2019 ◽  
Vol 64 (4) ◽  
pp. 459-469 ◽  
Author(s):  
Neelamegam Devarasu ◽  
Gnanou Florence Sudha
Keyword(s):  
Statistical Analysis ◽  
Blood Cells ◽  
Bioelectrical Impedance Analysis ◽  
Bioelectrical Impedance ◽  
Impedance Analysis ◽  
Single Frequency ◽  
Dual Frequency ◽  
Frequency Method ◽  
Indian Children ◽  
Significant Difference

Abstract A noninvasive investigation to ascertain the hematocrit (HCT) or packed cell volume (PCV) was conducted on 44 hospitalized dengue hemorrhagic fever (DHF) subjects, male and female aged between 3 and 14 years using bioelectrical impedance analysis (BIA). Among the 44 subjects, 30 subjects were confirmed to be non-structural protein-1 (NS1) positive at the time of admission, whose blood investigations such as HCT level, platelet (PLT) count, aspartate aminotransferase (AST) level and alanine aminotransferase (ALT) level were taken for the classification of risk as low risk (LR) and high risk (HR) DHF. Electrical conductivity of blood reflects a linear correlation with HCT. To provide a better and more accurate estimate of HCT, a dual frequency method is proposed to calculate the conductivities of plasma and blood cells. The resistance at 100 kHz is used to estimate the conductivity of blood cells and the impedance at 5 kHz to estimate the conductivity of plasma. Statistical analysis reveals that the HCT estimated using the proposed dual frequency method shows a significant difference with a single frequency (50 kHz) estimate of HCT and also shows a good correlation with the blood investigation results. In addition, statistical analysis of the proposed method on different fever subjects indicates a significant difference with DHF.

scholarly journals Retrieval of snowflake microphysical properties from multi-frequency radar observations

2018 ◽  
Author(s):  
Jussi Leinonen ◽  
Matthew D. Lebsock ◽  
Simone Tanelli ◽  
Ousmane O. Sy ◽  
Brenda Dolan ◽  
...  
Keyword(s):  
Single Frequency ◽  
Parameter Estimates ◽  
Dual Frequency ◽  
Snow Density ◽  
Radar Observations ◽  
Microphysical Properties ◽  
Triple Frequency ◽  
Multiple Frequencies ◽  
The Difference

Abstract. We have developed an algorithm that retrieves the microphysical properties of falling snow from multi-frequency radar observations. This work builds on previous studies that have indicated that three-frequency radars can provide information on snow density, potentially improving the accuracy of snow parameter estimates. The algorithm is based on a Bayesian framework, using lookup tables mapping the measurement space to the state space, which allows fast and robust retrieval. In the forward model, we calculate the radar reflectivities using recently published snow scattering databases. We demonstrate the algorithm using multi-frequency airborne radar observations from the OLYMPEX/RADEX field campaign, comparing the retrieval results to hydrometeor identification using ground-based polarimetric radar, and also to collocated in situ observations made using another aircraft. Using these data, we examine how the availability of multiple frequencies affects the retrieval accuracy, and test the sensitivity of the algorithm to the prior assumptions. The results suggest that multi-frequency radars are substantially better than single-frequency radars at retrieving snow microphysical properties. Meanwhile, triple-frequency radars can retrieve wider ranges of snow density than dual-frequency radars, and better locate regions of high-density snow such as graupel, although these benefits are relatively modest compared to the difference in retrieval performance between dual- and single-frequency radars.

In-situ RF diagnostic for PECVD process control

1997 ◽  
Vol 502 ◽  
Author(s):  
S. Raoux ◽  
K. S. Liu ◽  
X. Guo ◽  
D. Silvetti
Keyword(s):  
Process Control ◽  
Gas Flow ◽  
Input Parameter ◽  
Chemical Vapor ◽  
Single Frequency ◽  
Electrode Spacing ◽  
Electrical Characteristics ◽  
Dual Frequency ◽  
Statistical Process

ABSTRACTThe fabrication of advanced integrated circuits requires increased accuracy in process monitoring and active control. As higher production yields are required, the technology is moving from statistical process control to in-situ diagnostic techniques. A set of experiments was conducted to explore the feasibility of using radio frequency (RF) impedance probes to detect deviation of electrical characteristics of process chambers during wafer fabrication. A probe was integrated on a plasma-enhanced chemical vapor deposition (PECVD) chamber to explore the sensitivity of the reactor electrical characteristics on the events of process drift or input parameter variation. We measured RF the voltage, current and harmonics, the phase angle and the impedance magnitude for a capacitively coupled reactor. A single frequency (13.56MHz) process for depositing Si0 2 and a dual frequency (13.56MHz+35OkHz) process for Si3N4 deposition were characterized. We investigated the dependence of the RF signature and process parameters such as RF power, pressure, gas flow and electrode spacing. We observed that there is a correlation between the film properties (especially stress) and the plasma electrical characteristics. Furthermore, RF probes can be used to detect chamber malfunctions such as lost of RF ground or wafer-out-of-pocket events.

scholarly journals Vertical Air Motion Retrieved from Dual-Frequency Profiler Observations

2012 ◽  
Vol 29 (10) ◽  
pp. 1471-1480 ◽  
Author(s):  
Christopher R. Williams
Keyword(s):  
Rayleigh Scattering ◽  
Warm Pool ◽  
Single Frequency ◽  
Doppler Velocity ◽  
Dual Frequency ◽  
Frequency Method ◽  
Bright Band ◽  
Northwest Territory ◽  
Downward Bias ◽  
Air Motion

Abstract The 50-MHz profiler operating near Darwin, Northwest Territory, Australia, is sensitive to both turbulent clear-air (Bragg) and hydrometeor (Rayleigh) scattering processes. Below the radar bright band, the two scattering peaks are observed as two well-separated peaks in the Doppler velocity spectra. The Bragg scattering peak corresponds to the vertical air motion and the Rayleigh scattering peak corresponds to the hydrometeor motion. Within the radar bright band, the Rayleigh scattering peak intensity increases and the downward velocity decreases causing the hydrometeor peak to overlap or merge with the air motion peak. If the overlap of the two peaks is not taken into account, then the vertical air motion estimate will be biased downward. This study describes a filtering procedure that identifies and removes the downward bias in vertical air motions caused by hydrometeor contamination. This procedure uses a second collocated profiler sensitive to hydrometeor motion to identify contamination in the 50-MHz profiler spectra. When applied to four rain events during the Tropical Warm Pool-International Cloud Experiment (TPW-ICE), this dual-frequency filtering method showed that approximately 50% of the single-frequency method vertical air motion estimates within the radar bright band were biased downward due to hydrometeor contamination.

Experimental and Numerical Validation of Digital, Electromechanical, Parametrically Excited Amplifiers

2016 ◽  
Vol 138 (6) ◽  
Author(s):  
Amit Dolev ◽  
Izhak Bucher
Keyword(s):  
Theoretical Model ◽  
Single Frequency ◽  
Nonlinear Feedback ◽  
Dual Frequency ◽  
Detailed Model ◽  
Digital Implementation ◽  
Modeling Uncertainties ◽  
Wide Range ◽  
Sinusoidal Input

A parametric amplifier having a tunable, dual-frequency pumping signal and a controlled cubic stiffness term is realized and investigated experimentally. This device can be tuned to amplify a desired, single frequency weak signal, well below resonance. The transition between a previously described theoretical model and a working prototype requires an additional effort in several areas: modeling, design, calibration, identification, verification, and adjustment of the theoretical model. The present paper describes these necessary steps and analyzes the results. Tunability is achieved here by adding a digitally controlled feedback, driving a linear mechanical oscillator with an electromechanical actuator. The main advantage of the present approach stems from the separation of the controlled parametric and nonlinear feedback terms which are linked to the resonating element. This separation allows for the realization of feedback in an electronic form where a digital implementation adds further advantages as the feedback coefficients can be tuned in situ. This arrangement benefits from the mechanical resonance of a structure and from the ability to set the parametric excitation such that it accommodates sinusoidal input signals over a wide range of frequencies. The importance of an in situ identification phase is made clear in this work, as the precise setting of model and feedback parameters was shown to be crucial for successful application of the amplifier. A detailed model-identification effort is described throughout this paper. It has been shown through identification that the approach is robust despite some modeling uncertainties and imperfections.

INVESTIGATION OF THE DUAL-FREQUENCY METHOD FOR REMOTE SENSING OF SOLID AEROSOLS

2010 ◽  
Vol 69 (13) ◽  
pp. 1205-1219
Author(s):  
O. A. Voitovych ◽  
A. M. Linkova ◽  
G. I. Khlopov
Keyword(s):  
Remote Sensing ◽  
Dual Frequency ◽  
Frequency Method

scholarly journals A Dual Frequency Ultrasonic Cleaning Tank Developed by Transient Dynamic Analysis

2021 ◽  
Vol 11 (2) ◽  
pp. 699
Author(s):  
Worapol Tangsopa ◽  
Jatuporn Thongsri
Keyword(s):  
High Performance ◽  
Acoustic Pressure ◽  
Single Frequency ◽  
Response Analysis ◽  
Dual Frequency ◽  
Transient Dynamic Analysis ◽  
Ultrasonic Cleaning ◽  
Calculational Method ◽  
Successful Design ◽  
Harmonic Response Analysis

At present, development of manufacturer’s ultrasonic cleaning tank (UCT) to match the requirements from consumers usually relies on computer simulation based on harmonic response analysis (HRA). However, this technique can only be used with single-frequency UCT. For dual frequency, the manufacturer used information from empirical experiment alongside trial-and-error methods to develop prototypes, resulting in the UCT that may not be fully efficient. Thus, lack of such a proper calculational method to develop the dual frequency UCT was a problem that greatly impacted the manufacturers and consumers. To resolve this problem, we proposed a new model of simulation using transient dynamics analysis (TDA) which was successfully applied to develop the prototype of dual frequency UCT, 400 W, 18 L in capacity, eight horn transducers, 28 and 40 kHz frequencies for manufacturing. The TDA can indicate the acoustic pressure at all positions inside the UCT in transient states from the start to the states ready for proper cleaning. The calculation also reveals the correlation between the positions of acoustic pressure and the placement positions of transducers and frequencies. In comparison with the HRA at 28 kHz UCT, this TDA yielded the results more accurately than the HRA simulation, comparing to the experiments. Furthermore, the TDA can also be applied to the multifrequency UCTs as well. In this article, the step-by-step development of methodology was reported. Finally, this simulation can lead to the successful design of the high-performance dual frequencies UCT for the manufacturers.

scholarly journals Neuroimmune Response Mediated by Cytokines in Natural Scrapie after Chronic Dexamethasone Treatment

Biomolecules ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 204
Author(s):  
Isabel M. Guijarro ◽  
Moisés Garcés ◽  
Pol Andrés-Benito ◽  
Belén Marín ◽  
Alicia Otero ◽  
...  
Keyword(s):  
Prion Diseases ◽  
Global Approach ◽  
Profile Data ◽  
Dexamethasone Treatment ◽  
New Approach ◽  
Complex Interactions ◽  
Natural Scrapie ◽  
Anti Inflammatory

The actual role of prion protein-induced glial activation and subsequent cytokine secretion during prion diseases is still incompletely understood. The overall aim of this study is to assess the effect of an anti-inflammatory treatment with dexamethasone on different cytokines released by neuroglial cells that are potentially related to neuroinflammation in natural scrapie. This study emphasizes the complex interactions existent among several pleiotropic neuromodulator peptides and provides a global approach to clarify neuroinflammatory processes in prion diseases. Additionally, an impairment of communication between microglial and astroglial populations mediated by cytokines, mainly IL-1, is suggested. The main novelty of this study is that it is the first one assessing in situ neuroinflammatory activity in relation to chronic anti-inflammatory therapy, gaining relevance because it is based on a natural model. The cytokine profile data would suggest the activation of some neurotoxicity-associated route. Consequently, targeting such a pathway might be a new approach to modify the damaging effects of neuroinflammation.

Sign in / Sign up

Export Citation Format

Share Document