The problem of desiccation cracks in soils has received increasing attention in the last few years, in both experimental investigations and modeling. Experimental research has been mainly focused on ...the behavior of slurries subjected to drying in plates of different shapes, sizes and thickness. The main objectives of these studies were to learn about the process of crack formation under controlled environmental conditions, and also to understand better the impact of different factors (e.g. soil type, boundary conditions, soil thickness) on the morphology of the crack network. As for the numerical modeling, different approaches have been proposed to describe the behavior of drying cracks in soils. One aspect that it is still difficult to simulate properly is the 3-D crack pattern typically observed in desiccated soils. In this work we present a numerical technique to model the behavior of drying soils. The proposed approach inserts high aspect ratio elements in-between standard elements of a finite element mesh. This mesh fragmentation technique can be easily adapted to standard finite element programs. We used this technique to analyze multiple case studies related to soil desiccation cracks developed under laboratory and field conditions. We focused our attention in some key factors that control the 3-D morphology of the drying cracks network in soils. We show that the proposed technique is able to simulate very satisfactorily the main patterns typically observed in cracked soils.
In this review, general aspects of the combination of the solid phase extraction (SPE) with energy dispersive X-ray fluorescence spectrometry (EDXRF) for multielement determination are presented. ...Derivations of SPE, such as dispersive solid phase extraction (DSPE), dispersive micro-solid phase extraction (DµSPE), and dispersive magnetic micro-solid phase extraction DM-µSPE are also presented, showing the possibility of direct analysis of the solid phase. The sorbents, advantages, disadvantages, and the analytical characteristics of the combination followed by direct determination of analytes retained on the solid phase are discussed. Furthermore, the perspectives of this analytical arrangement are presented.
Hydraulic fracturing is a technique based on the injection of a viscous fluid at high pressure into an engineered well with the intention of initiating and propagating multiple fractures in a rock ...formation containing hydrocarbons to increase well-reservoir connectivity. This work proposes a framework to simulate the initiation and propagation of hydraulically induced fracture based on the Continuum Strong Discontinuity Approach (CSDA) and solid finite elements with high aspect ratio (HAR) in the context of conventional continuum constitutive (stress–strain) relationships (based on damage theory). The porous media considered here are deformable and the hydro-mechanical problem is solved in a fully-coupled manner. Full details about the proposed continuous approach to model hydraulic fractures are presented, including the finite element equations and their approximations. The new approach is validated against analytical and numerical solutions. Moreover, the influence of the dimensions of the HAR interface elements on the results is also investigated.
•A novel continuum approach to model fractures induced by fluid injection in deformable porous media.•Effects of discontinuity surfaces on the displacement and pressure fields represented by standard finite elements with high aspect ratio.•Fracture water-mass-balance equations naturally obtained from the limit case of the standard weak form of the corresponding continuum water-mass-balance equation.•Verification and validation of the proposed technique against analytical and published numerical solutions.•Almost no sensitivity of the numerical solution on the mesh size.
Abstract
The objective of this work is to physically characterize and analyze synthetic carbonate rocks through microtomography and petrography techniques, focusing on a comparative analysis before ...and after degradation with a reactive fluid. For this study, physical characterization analysis with computerized microtomography and petrography on the samples before and after the acidification procedure was performed. The petrographic analysis verified an increase in both intergranular and intragranular porosities after dissolution. The microtomography analysis quantified the maximum increase in porosity, from 11.8 to 41.3% in the two-dimensional analysis and 31.6–52% in the three-dimensional analysis of the porous structures. Furthermore, the pores were quantified according to their area, and data was obtained on the orientation of the pores, providing insight into the preferred paths of fluid flow. It was also observed that the microtomography technique was an effective tool for characterizing fractures in the samples before and after dissolution. Such analyses are crucial for the extraction and injection of fluids at high depths due to the mechanical and physical risks arising from the dissolution of minerals as well as changes in pressure, temperature, and saturation, all of which affect the stress state of the reservoir rock.
Background
Well‐established conventional thyroidectomy has satisfactory outcomes; however, robotic and endoscopic thyroid surgery can avoid visible anterior neck scars. Transoral endoscopic ...thyroidectomy vestibular approach (TOETVA) is the most recent of these techniques.
Methods
This was a retrospective review of 412 patients who underwent TOETVA from 2017 to 2020 in 13 Brazilian centers.
Results
The study included 359 (87.1%) females and 53 (12.9%) males, with a mean age of 40 years. There were 231 (56.1%) total thyroidectomies. The conversion rate was 0.7%. The transient vocal cord palsy rate was 7.6% (30 patients). Temporary and persistent hypocalcemia rates were 4.0% and 0.8%, respectively. There were two cases of infection (0.5%).
Discussion
This is a large multi‐institute TOETVA study, with one of the largest cohorts published to date that; despite its retrospective nature and selection bias, reached outcomes comparable to previously reported series, this study reinforced safeness, feasibility, and nationwide reproducibility for this technique.
In the present work, we developed an experimental class for undergraduate students concerning the linear synthesis of 2-phenylimidazo1,2-αpyridine through mechanochemical techniques. This approach ...aims to conceptualize the green chemistry principles through a safe, robust, atom-economic, energy-efficient, and solvent-free method for preparing these classes of compounds by manual grinding and vortex mixing. The methodology was easily applied in experimental classes for chemistry students and could be easily expanded to other courses such as pharmacy and biotechnology.
The injection of water (or CO2) at high pressure is a common practice to enhance oil production. A crucial component of this activity is the estimation of the maximum pressure at which the fluids can ...be injected without inducing the reactivation of pre-existing faults that may exist in the formation. The damage zones typically formed around the geological faults are highly heterogeneous. The materials involved in the damage zones are characterized by the huge variation of their properties and high uncertainties associated with them. To estimate the maximum allowable injection pressure this paper presents a novel approach based on: a coupled hydro-mechanical formulation (for the numerical analyses); a criterion based on the total plastic work (for the fault reactivation); and the evidence theory (for uncertainty quantification). A case study based on information gathered from an actual field is presented to illustrate the capabilities of the proposed framework.
This review provides an overview and discusses analytical strategies for the preconcentration of trace elements using lignocellulosic sorbents for solid-phase extraction. This procedure is widely ...used for the determination of metals and metalloids in different types of samples due to its simplicity, rapidity, minimal waste generation, reduction of sample matrix effects as well as sorption of the target species on the solid surface. For this purpose, some inorganic, organic, and several natural adsorbents are used. New approaches to obtaining adsorbent materials from natural sources such as agro-industrial residues and composting materials have received attention. The most used lignocellulosic materials as sorbents for solid-phase extraction are bagasse sugarcane, cotton, sisal, palm fiber, coconut, corn cob, soybean straw, jute, and rice. The lignocellulosic materials have been investigated because the presence of functional groups in their structures is made up of lignin and cellulose. These materials have been used in the development of analytical methods with the varied proposal, such as preconcentration or speciation of analytes.
•Preconcentration of trace elements using lignocellulosic sorbents.•Development of sustainable and environmentally friendly analytical methods.•Lignocellulosic biosorbents in solid phase extraction coupled with elemental detection techniques.•Advantages and disadvantages of lignocellulosic materials in the development of preconcentration methods.
PDF
