Geoelectrical monitoring of dissolution and precipitation reactions in a saturated calcareous porous medium

Precipitation and dissolution are prime processes in carbonate rocks and being able to monitor them is a major deal of reservoir exploitation for geo-resources (water, gas) or geological storage (CO2, H2, waste). Geophysics can be used to monitor these processes non-intrusively and at low cost. Among the existing techniques, we used two electrical methods to monitor the reactivity of a synthetic calcareous porous medium: self-potential (SP) and spectral induced polarization (SIP). SP is a passive technique that consists in measuring the electrical field as it is affected by water fluxes and concentration gradients through electrokinetic and electrochemical couplings. SIP is an active method that provides the electrical conductivity and the chargeability of a porous medium in a low frequency range (mHz to kHz). We carried out a two months laboratory experiment to monitor the geoelectrical signals generated by chemical variations in a synthetic medium composed of pure calcite grains. Three different solutions were injected to alternatively dissolve or precipitate calcite in the sample. The sample is equipped with four aligned non-polarizable Ag/AgCl electrodes in order to geoelectrically monitor the fluid percolation and the ionic concentration gradients changes through the medium. Moreover, we conducted chemical analyses of the downstream fluid to monitor its ionic composition. We made a 1D reactive-transport simulation with the software CrunchFlow to get the concentration gradients of all dissolved ions along the column. Following a theoretical framework, we used a physically based analytical model to relate our electrical signals to ionic concentrations of a multicomponent electrolyte. We find that dissolution and precipitation generate measurable geoelectrical signals because of chemical reactions and ions substitutions. These findings open the possibility to better understand geoelectrical signals in natural media and possibly use them to monitor in situ reactivity.

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Patients in intensive care unit for COVID-19 pneumonia: the lung ultrasound patterns at admission and discharge. An observational pilot study

The Ultrasound Journal ◽

10.1186/s13089-021-00213-x ◽

2021 ◽

Vol 13 (1) ◽

Author(s):

Persona Paolo ◽

Valeri Ilaria ◽

Zarantonello Francesco ◽

Forin Edoardo ◽

Sella Nicolò ◽

...

Keyword(s):

Intensive Care ◽

Lung Ultrasound ◽

Low Cost ◽

Low Frequency ◽

Specific Pattern ◽

University Hospital ◽

Left Hemithorax ◽

Significant Difference ◽

The Right ◽

B Lines

Abstract Background During COVID-19 pandemic, optimization of the diagnostic resources is essential. Lung Ultrasound (LUS) is a rapid, easy-to-perform, low cost tool which allows bedside investigation of patients with COVID-19 pneumonia. We aimed to investigate the typical ultrasound patterns of COVID-19 pneumonia and their evolution at different stages of the disease. Methods We performed LUS in twenty-eight consecutive COVID-19 patients at both admission to and discharge from one of the Padua University Hospital Intensive Care Units (ICU). LUS was performed using a low frequency probe on six different areas per each hemithorax. A specific pattern for each area was assigned, depending on the prevalence of A-lines (A), non-coalescent B-lines (B1), coalescent B-lines (B2), consolidations (C). A LUS score (LUSS) was calculated after assigning to each area a defined pattern. Results Out of 28 patients, 18 survived, were stabilized and then referred to other units. The prevalence of C pattern was 58.9% on admission and 61.3% at discharge. Type B2 (19.3%) and B1 (6.5%) patterns were found in 25.8% of the videos recorded on admission and 27.1% (17.3% B2; 9.8% B1) on discharge. The A pattern was prevalent in the anterosuperior regions and was present in 15.2% of videos on admission and 11.6% at discharge. The median LUSS on admission was 27.5 [21–32.25], while on discharge was 31 [17.5–32.75] and 30.5 [27–32.75] in respectively survived and non-survived patients. On admission the median LUSS was equally distributed on the right hemithorax (13; 10.75–16) and the left hemithorax (15; 10.75–17). Conclusions LUS collected in COVID-19 patients with acute respiratory failure at ICU admission and discharge appears to be characterized by predominantly lateral and posterior non-translobar C pattern and B2 pattern. The calculated LUSS remained elevated at discharge without significant difference from admission in both groups of survived and non-survived patients.

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Numerical simulation of seismic waves in porous media components

Eurasian Journal of Mathematical and Computer Applications ◽

10.32523/2306-6172-2021-9-1-4-30 ◽

2021 ◽

Vol 9 (1) ◽

pp. 4-30

Author(s):

M. Azeredo ◽

◽

V. Priimenko ◽

Keyword(s):

Numerical Simulation ◽

Porous Medium ◽

High Frequency ◽

Seismic Waves ◽

Computational Algorithm ◽

Low Frequency ◽

Physical Parameters ◽

Mathematical Algorithm ◽

Biot Equations ◽

Attenuation And Dispersion

This work presents a mathematical algorithm for modeling the propagation of poroelastic waves. We have shown how the classical Biot equations can be put into Ursin’s form in a plane-layered 3D porous medium. Using this form, we have derived explicit for- mulas that can be used as the basis of an efficient computational algorithm. To validate the algorithm, numerical simulations were performed using both the poroelastic and equivalent elastic models. The results obtained confirmed the proposed algorithm’s reliability, identify- ing the main wave events in both low-frequency and high-frequency regimes in the reservoir and laboratory scales, respectively. We have also illustrated the influence of some physical parameters on the attenuation and dispersion of the slow wave.

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An EEG Experimental Study Evaluating the Performance of Texas Instruments ADS1299

Sensors ◽

10.3390/s18113721 ◽

2018 ◽

Vol 18 (11) ◽

pp. 3721 ◽

Cited By ~ 17

Author(s):

Usman Rashid ◽

Imran Niazi ◽

Nada Signal ◽

Denise Taylor

Keyword(s):

Experimental Study ◽

Mixed Models ◽

Signal To Noise Ratio ◽

Low Cost ◽

Low Frequency ◽

Low Power Consumption ◽

Motor Tasks ◽

Negative Peak ◽

Eeg Data ◽

Healthy Participants

Texas Instruments ADS1299 is an attractive choice for low cost electroencephalography (EEG) devices owing to its low power consumption and low input referred noise. To date, there have been no rigorous evaluations of its performance. In this EEG experimental study we evaluated the performance of the ADS1299 against a high quality laboratory-based system. Two self-paced lower limb motor tasks were performed by 22 healthy participants. Recorded power across delta, theta, alpha, and beta EEG bands, the power ratio across the motor tasks, pre-movement noise, and signal-to-noise ratio were obtained for evaluation. The amplitude and time of the negative peak in the movement-related cortical potentials (MRCPs) extracted from the EEG data were also obtained. Using linear mixed models, no statistically significant differences (p > 0.05) were found in any of these measures across the two systems. These findings were further supported by evaluation of cosine similarity, waveform differences, and topographic maps. There were statistically significant differences in MRCPs across the motor tasks in both systems. We conclude that the performance of the ADS1299 in combination with wet Ag/AgCl electrodes is analogous to that of a laboratory-based system in a low frequency (<40 Hz) EEG recording.

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Review on the Millimeter-Wave Generation Techniques Based on Photon Assisted for the RoF Network System

Advances in Condensed Matter Physics ◽

10.1155/2020/6692941 ◽

2020 ◽

Vol 2020 ◽

pp. 1-14

Author(s):

Jiangnan Xiao ◽

Chuang Zhao ◽

Xingxing Feng ◽

Xu Dong ◽

Jiangli Zuo ◽

...

Keyword(s):

High Frequency ◽

Low Cost ◽

Electronic Devices ◽

Low Frequency ◽

Digital Signal ◽

Development Trend ◽

Wave Generation ◽

Communication Link ◽

Network System ◽

High Frequency Microwave

With the development trend of wireless and broadband in the communication link and even the whole information industry, the demand of high-frequency microwave bandwidth has been increasing. The RoF network system solves the problem of spectrum congestion in low-frequency band by providing an effective technology for the distribution of high-frequency microwave signals over optical fiber links. However, the traditional mm-wave generation technique is limited by the bandwidth of electronic devices. It is difficult to generate high-frequency and low-phase noise mm-wave signals with pure electrical components. The mm-wave communication technology based on photon assisted can overcome the bandwidth bottleneck of electronic devices and provide the potential for developing the low-cost infrastructure demand of broadband mobile services. This paper will briefly explain the characteristics of the RoF network system and the advantages of high-frequency mm-wave. Then we, respectively, introduce the modulation schemes of RoF mm-wave generation based on photon assisted including directly modulated laser (DML), external modulation, and optical heterodyne. The review mainly focuses on a variety of different mm-wave generation technologies including multifrequency vector mm-wave. Furthermore, we list several approaches to realize the large capacity data transmission techniques and describe the digital signal processing (DSP) algorithm flow in the receiver. In the end, we summarize the RoF network system and look forward to the future.

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The origin of the observed low-frequency electrical polarization in sandstones

Geophysics ◽

10.1190/1.2258092 ◽

2006 ◽

Vol 71 (5) ◽

pp. G235-G238 ◽

Cited By ~ 23

Author(s):

Julian B. Scott

Keyword(s):

Double Layer ◽

Electrical Double Layer ◽

Ionic Composition ◽

Low Frequency ◽

Ionic Mobility ◽

Electrical Measurements ◽

Pore Throat ◽

Polarization Model ◽

Electrical Relaxation ◽

Water Saturated

There has been an increasing debate regarding the mechanism controlling the low-frequency polarization (megahertz to kilohertz) in sandstones. The polarization and related electrical relaxation are extremely important because they can be used to provide a significant amount of information on length scales within the sandstone. Complex electrical measurements, in the mHz to kHz range, were made on gel-filled samples. This gel decreases the ionic mobility in the bulk pore fluid while keeping the ionic composition similar to that in a water-saturated sample. The presence of the gel was shown to have little effect on the electrical relaxation. This adds to the argument that the electrical double layer close to the grain surface is where the polarization originates. The correlation between pore-throat size and the relaxation time is consistent with the polarization mechanism of ion diffusion within the electrical double layer. The membrane-type polarization model, used previously to explain the polarization in pore-throat regions, is likely to be incorrect because of the relative thinness of the electrical double layer.

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A time-lapse seismic repeatability test using the P-Cable high-resolution 3D marine acquisition system

The Leading Edge ◽

10.1190/tle39070480.1 ◽

2020 ◽

Vol 39 (7) ◽

pp. 480-487

Author(s):

Patrick Smith ◽

Brandon Mattox

Keyword(s):

High Resolution ◽

Seismic Data ◽

Low Cost ◽

Low Frequency ◽

Time Lapse ◽

Seismic Signal ◽

Residual Energy ◽

Acquisition System ◽

Positioning Errors ◽

Seismic Surveying

The P-Cable high-resolution 3D marine acquisition system tows many short, closely separated streamers behind a small source. It can provide 3D seismic data of very high temporal and spatial resolution. Since the system is containerized and has small dimensions, it can be deployed at short notice and relatively low cost, making it attractive for time-lapse seismic reservoir monitoring. During acquisition of a 3D high-resolution survey in the Gulf of Mexico in 2014, a pair of sail lines were repeated to form a time-lapse seismic test. We processed these in 2019 to evaluate their geometric and seismic repeatability. Geometric repetition accuracy was excellent, with source repositioning errors below 10 m and bin-based receiver positioning errors below 6.25 m. Seismic data comparisons showed normalized root-mean-square difference values below 10% between 40 and 150 Hz. Refinements to the acquisition system since 2014 are expected to further improve repeatability of the low-frequency components. Residual energy on 4D difference seismic data was low, and timing stability was good. We conclude that the acquisition system is well suited to time-lapse seismic surveying in areas where the reservoir and time-lapse seismic signal can be adequately imaged by small-source, short-offset, low-fold data.

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Low-frequency lattice phonons in halide perovskites explain high defect tolerance toward electron-hole recombination

Science Advances ◽

10.1126/sciadv.aaw7453 ◽

2020 ◽

Vol 6 (7) ◽

pp. eaaw7453 ◽

Cited By ~ 14

Author(s):

Weibin Chu ◽

Qijing Zheng ◽

Oleg V. Prezhdo ◽

Jin Zhao ◽

Wissam A. Saidi

Keyword(s):

Low Cost ◽

Low Frequency ◽

Nonradiative Recombination ◽

Defect Tolerance ◽

Electron Hole ◽

Surface Hopping ◽

Recombination Processes ◽

Halide Perovskites ◽

Electron And Hole States ◽

Hole Recombination

Low-cost solution-based synthesis of metal halide perovskites (MHPs) invariably introduces defects in the system, which could form Shockley-Read-Hall (SRH) electron-hole recombination centers detrimental to solar conversion efficiency. Here, we investigate the nonradiative recombination processes due to native point defects in methylammonium lead halide (MAPbI3) perovskites using ab initio nonadiabatic molecular dynamics within surface-hopping framework. Regardless of whether the defects introduce a shallow or deep band state, we find that charge recombination in MAPbI3 is not enhanced, contrary to predictions from SRH theory. We demonstrate that this strong tolerance against defects, and hence the breakdown of SRH, arises because the photogenerated carriers are only coupled with low-frequency phonons and electron and hole states overlap weakly. Both factors appreciably decrease the nonadiabatic coupling. We argue that the soft nature of the inorganic lattice with small bulk modulus is key for defect tolerance, and hence, the findings are general to other MHPs.

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A low-cost multichannel NIRS oximeter for monitoring systemic low-frequency oscillations

Neural Computing and Applications ◽

10.1007/s00521-020-04897-5 ◽

2020 ◽

Vol 32 (19) ◽

pp. 15629-15641

Author(s):

Yingwei Li ◽

Yunfei Ma ◽

Shaoqing Ma ◽

Lia Maria Hocke ◽

Yunjie Tong ◽

...

Keyword(s):

Low Cost ◽

Low Frequency ◽

Low Frequency Oscillations

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Ostracodes as Hydrologic Indicators in Springs, Streams and Wetlands: A Tool for Environmental and Paleoenvironmental Assessment

The Paleontological Society Papers ◽

10.1017/s1089332600002217 ◽

2003 ◽

Vol 9 ◽

pp. 203-222 ◽

Cited By ~ 7

Author(s):

Alison J. Smith ◽

Jesse W. Davis ◽

Donald F. Palmer ◽

Richard M. Forester ◽

B. Brandon Curry

Keyword(s):

Ionic Composition ◽

The United States ◽

Ionic Concentration ◽

Climate Data ◽

Large Database ◽

Chemical Parameters ◽

Hydrologic Indicators ◽

Components Analysis ◽

Physical And Chemical ◽

Total Ionic Concentration

Although the majority of publications on extant nonmarine ostracode species in North America are concerned with lacustrine settings, many species that are potentially valuable as indicators of water quality changes live in non-lacustrine settings. Ostracode distributions in 157 springs, wetlands and streams in the United States are examined here in order to assess 1) species richness, 2) association with physical and chemical parameters of their habitats and 3) the presence of potentially useful biomonitors and environmental sentinels. The 157 non-lacustrine sites are a subset of a large database (North American Non-marine Ostracode Database: NANODe version 1) consisting of 611 mostly lacustrine sites with ostracode species, presence-absence data, hydrochemistry and climate data (Forester et al., in review). Of the 89 species represented in NANODe version 1, 51 species are found in springs, 59 species are found in wetlands and only 15 species are found in streams. Many species are found in at least two of these habitats and some in all three. Principal Components Analysis of these 157 sites indicates that 71% of the variance is explained by salinity (total ionic concentration), alkalinity and temperature, a result consistent with previously published analyses of natural water. Cluster analysis shows that spring species are most strongly tied to temperature, whereas wetlands and streams are most strongly tied to ionic composition. Three species are found to be potentially valuable biomonitors: Cavernocypris wardi in springs, Fabaeformiscandona rawsoni in wetlands and Physocypria globula in streams.

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A Miniaturized 878 MHz Slotted Meander Line Monopole Antenna

Indonesian Journal of Electrical Engineering and Computer Science ◽

10.11591/ijeecs.v7.i1.pp170-177 ◽

2017 ◽

Vol 7 (1) ◽

pp. 170

Author(s):

Nabilah Ripin ◽

Ahmad Asari Sulaiman ◽

Nur Emileen Abd Rashid ◽

Mohamad Fahmi Hussin ◽

Nor Najwa Ismail

Keyword(s):

Simple Structure ◽

Low Cost ◽

Low Frequency ◽

Monopole Antenna ◽

Impedance Bandwidth ◽

Antenna Size ◽

Printed Monopole Antenna ◽

Printed Monopole ◽

Small Antenna ◽

Meander Line

A slotted meander line printed monopole antenna for low frequency applications at 878 MHz is presented. The operating frequency of the conventional printed monopole antenna was greatly reduced by the presence of the slots and meander line which lead to the reduction of the antenna size. The size reduction up to 70% compared to the conventional reference antenna is achieved in this study. The antenna has a simple structure and small antenna size of 46.8 mm x 74 mm or 0.137𝝀0 x 0.217𝝀0. The antenna has been fabricated on the low-cost FR4 substrate and measured to validate the simulation performances. Measured results display that the proposed antenna produces omnidirectional radiation pattern of impedance bandwidth of 48.83 MHz and the maximum gain of -1.18 dBi.

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