Search

The seismoelectric (SE) wave at the vadose zone‐aquifer interface, which results from the electrokinetic effect, is a valuable tool for groundwater exploration. We propose a method for imaging aquifer interfaces using SE waves. The common‐receiver SE gather, generated by multiple sources, is analogous to the exploding‐reflector seismic gather, forming the theoretical foundation of this method. To test this method, two 2D aquifer models are designed to simulate the synthetic common‐receiver SE gather, followed by the application of exploding‐reflector migration. The result shows that the aquifer interface is well imaged by the SE waves. Additionally, laboratory experiments successfully recovering the interfaces of the rocks confirm the validity of the SE imaging method, suggesting its feasible use in real groundwater exploration in the future. Plain Language Summary: The seismic wave can generate a seismoelectric (SE) wave at the interface between a vadose zone and an aquifer. We propose a new imaging method for imaging aquifer interfaces using SE waves, based on multiple sources excitation and combined with exploding‐reflector migration. The method is applied to the synthetic SE waves created in the 2D aquifer models, successfully imaging the aquifer interfaces. Laboratory experiments further validated the method, recovering the upper surfaces of the rocks. Our study suggests a useful tool for groundwater exploration in the future. Key Points: Reflected interface seismoelectric waves in a common‐receiver seismoelectric gather preserve the underground interfaceWe propose a method of using seismoelectric waves for imaging the aquifer interfaceThe method is validated using the synthetic seismoelectric data from 2D aquifer models and laboratory experimental data [ABSTRACT FROM AUTHOR]

We propose a frequency-domain finite-element (FDFE) method to model the 2-D P–SV waves propagating in porous media. This specific finite-element method (FEM) is based on the framework of variational principles, which differs from previously widely used FEMs that rely on the weak formulations of the governing equations. By applying the calculus of variations, we establish the equivalence between solving the stress–strain relations, equations of motion and boundary conditions that govern the propagation of P–SV waves, and determining the extremum or stationarity of a properly defined functional. The structured rectangular element is utilized to partition the entire computational region. We validate the FDFE method by conducting a comparison with an analytically-based method for models of a horizontal planar contact of two poroelastic half-spaces, and a poroelastic half-space with a free surface. The excellent agreements between the analytically-based solutions and the FDFE solutions indicate the effectiveness of the FDFE method in modelling the poroelastic waves. Modelling results manifest that both propagative and diffusive natures of the Biot slow P wave can be effectively modelled. The proposed FDFE method simulates wavefields in the frequency domain, allowing for easy incorporation of frequency-dependent parameters and enabling parallel computational capabilities at each frequency point (sample). We further employ the developed FDFE method to model two simplified poroelastic reservoirs, one with gas-saturated sandstone and the other with oil-saturated sandstone. The results suggest that changing the fluid phase of the sandstone reservoir from gas to oil can substantially impact the recorded solid and relative fluid–solid displacements. The modelling suggests that the proposed FDFE algorithm is a useful tool for studying the propagation of poroelastic waves. [ABSTRACT FROM AUTHOR]

We present a frequency-domain finite-element (FDFE) method for simulating PSV -mode seismic waves (including two slow compressional waves) in 2-D double-porosity media. A functional, whose extremum corresponds to the governing equations with boundary conditions for 2-D PSV waves, is constructed. Solving the boundary value problem of the governing equations is thus equivalent to finding the extremum of the associated functional. We use structured rectangular elements to discretize the computational domain and employ perfectly matched layers (PMLs) to absorb the seismic waves. The FDFE method is validated by comparing the results with those from a semi-analytic method. Numerical simulations are conducted to investigate the propagation of seismic waves in double-porosity media. Assuming a non-viscous pore fluid, we simulate the propagation of slow P waves (P 2 and P 3 waves) in a two-layer model consisting of double-porosity media. We observe the reflection and transmission of the P 2 and P 3 waves at the interface. Additionally, we simulate the propagation of seismic waves in a model with irregular interfaces. Seismic signals collected from horizontal and vertical receiver arrays have demonstrated that the P 1 wave experiences higher attenuation in a double-porosity medium. [ABSTRACT FROM AUTHOR]

Abstract Background Treatment for drug-sensitive tuberculosis (TB) is taken for at least 6 months and problems with adherence are common. Therefore, there is substantial interest in the possible use of eHealth interventions to support patients to take their treatment. Electronic medication monitors have been shown to improve adherence to TB medication, but the impact on clinical outcomes is unknown. We aim to evaluate the impact of a medication monitor-based treatment strategy for drug-sensitive TB patients on a composite poor outcome measured over 18 months from start of TB treatment. Methods/design We will conduct an open, pragmatic, cluster randomised superiority trial, with 24 counties/districts in three provinces in China, randomised 1:1 to implement the intervention or standard of care. Adults (aged ≥ 18 years) with a new episode of GeneXpert-positive and rifampicin-sensitive pulmonary TB, who plan to be in the study area for the next 18 months, and will receive daily fixed-dose combination tablets for 6 months of treatment are eligible. The intervention is centred around a medication monitor that holds a 1-month supply of medication and has three key functions: as an audio and visual reminder for patients to take their daily medication; reminds patients of upcoming monthly visit; and records date and time whenever the box is opened. At the monthly follow-up visit, the doctor downloads these data to generate a graphical display of the last month’s adherence record for discussion with the patient and potentially to switch the patient to more intensive management. The primary outcome is a composite poor outcome measured over 18 months from start of TB treatment, defined as either of poor outcome at the end of treatment (death, treatment failure, or loss to follow-up) or subsequent recurrence (culture positive for TB at 12 or 18 months or re-starting TB treatment in the follow-up period). An economic evaluation will also be conducted as part of this study. Discussion This trial will assess whether a medication monitor-based treatment strategy can improve clinical outcomes for TB patients. Several trials of other eHealth interventions for TB treatment are ongoing and are summarised in this paper. This trial will provide an important part of the emerging evidence base for the potential of eHealth to improve TB treatment outcomes. Trial registration This trial was registered with Current Controlled Trials (identifier: ISRCTN35812455). Registered on May 19, 2016.

In this paper, we study a three-species predator-prey model with modified LG-Holling type II with Lévy jumps, and we take the competition among predators into consideration. First, We use an Ornstein-Uhlenbeck process to describe the environmental stochasticity and prove that there is a unique positive solution to the system by mathematical analysis skills such as comparison theorem. Futhermore, the extinction or persistence in the mean of each species under different conditions is obtained. Finally, some numerical simulations are carried out to support our main results. [ABSTRACT FROM AUTHOR]

We propose a frequency-domain finite-element (FDFE) method to simulate the 2-D SHTE mode seismoelectric and electroseismic waves. By neglecting the secondary weak wavefield feedbacks, the SH and TE waves are solved, separately. In a finite plane region, propagations of both SH and TE waves can be described as the Helmholtz equation with boundary conditions, which is proved to be equivalent to the extremum of functional by conducting calculus of variation. The computation region is partitioned into structured rectangular elements with the bilinear interpolation. The proposed FDFE algorithm solves the wavefield in frequency domain and avoids adopting the quasi-static approximation. One advantage of the proposed algorithm is its ability to accurately simulate the seismoelectric and electroseismic responses generated from the free surface. We verify the proposed algorithm based on a layered model beneath a free surface by comparing the waveforms calculated using the FDFE algorithm with those calculated using analytically-based method. The proposed algorithm is applied in feasibility studies of interface seismoelectric and electroseismic responses in exploring the hydrocarbon reservoir and monitoring the time-lapse pollutant within a sand channel. [ABSTRACT FROM AUTHOR]

Analytic solutions are derived for the problem of scattering of obliquely incident plane waves from a rectangular crack in a fluid-saturated porous solid. The propagation direction and polarization direction of the incident waves can be arbitrary. The solutions are based on expanding the crack opening displacements in terms of Chebyshev functions. Explicit expressions for the frequency-dependent stress intensity factors and scattering far fields are obtained. The poroelastic effects play a key role in determining the crack opening mode by changing the effective normal stress applied on the crack surfaces. Consequently, the dynamic responses of the crack can be quite different from those of conventional dry crack in an elastic solid. The effects of scattered slow-P waves as well as wave-induced crack fluid pressure on the dynamic stress intensity factors are clarified, and a corner effect is observed in the scattering patterns for moderately high frequencies. The comparisons of synthetic seismograms with the elastic model show the slow-P waves can cause significant energy loss and waveform change. This study can be used for fracture analysis of porous media and nondestructive testing for individual hydraulic fractures in reservoirs. [ABSTRACT FROM AUTHOR]

Recently, atmospheric perturbations residing over around epicenters of forthcoming earthquakes were remotely sensed by the multiple instruments of the MVP-LAI (Monitoring of Vibrations and Perturbations in Lithosphere, Atmosphere and Ionosphere) system. In this study, we found another way and proposed a theory for the evolution of the perturbations in the atmosphere from the aspect of numerical simulation. We started from the fundamental hydromechanics equations for the perturbations based on the atmospheric dynamics in the cylindrical symmetric coordinate to solve their analytical solution. The solution shows that a persistent vibration at the bottom of the cylindrical symmetric coordinate tends to decay exponentially with along altitude. In other words, a persistent ground vibration in a wide area can rapidly evolve into small-scale perturbations in the atmosphere. The preliminary theoretical model in this study shows the kernel concept for the coupling of geospheres. [ABSTRACT FROM AUTHOR]