The role of flexural slip in the development of chevron folds

Chevron folds are characterized by straight limbs and narrow hinge zones. One of the conceptual models to initiate and develop chevron folds involves flexural slip during folding. While some kinematical models show the necessity for slip to initiate during chevron folding, recent numerical modeling studies of visco-elastic effective single layer buckle folding have shown that flexural slip does not result in chevron folds. In this study, several 2D finite element analysis models are run, distinguished by 1) geometry of the initial perturbation (sinusoidal and white noise), 2) varying thewavelength of the initial perturbation (10%, 50%, and 100% of the dominant wavelength) and 3) variation of the friction coefficient (high and low friction coefficient between interlayers). All numerical simulations apply 60% of shortening, in order to achieve inter-limb angles of 60 to 70 degrees. The results show that for sinusoidal initial perturbations, systematic and symmetric chevron folds are reproduced when 10% of the dominant wavelength is used for the initial perturbation. Using 50% or 100% of the dominant wavelength results in circular and sinusoidal folds, respectively. Low friction coefficient models result in larger amplitudes and sharper inter-limb angles compared to high friction coefficient models. For white noise initial perturbations, isolated and asymmetric chevron folds are developed when the friction coefficient is low. High friction coefficient models reproduce the dominant wavelength without chevron folds and low friction coefficient models result in a different dominant wavelength. In all chevron folds models, slip initiates at the early stages of folding (i.e. 1% to 5% of shortening) --Abstract, page iii

Feature Adversarial Distillation for Point Cloud Classification

Due to the point cloud's irregular and unordered geometry structure, conventional knowledge distillation technology lost a lot of information when directly used on point cloud tasks. In this paper, we propose Feature Adversarial Distillation (FAD) method, a generic adversarial loss function in point cloud distillation, to reduce loss during knowledge transfer. In the feature extraction stage, the features extracted by the teacher are used as the discriminator, and the students continuously generate new features in the training stage. The feature of the student is obtained by attacking the feedback from the teacher and getting a score to judge whether the student has learned the knowledge well or not. In experiments on standard point cloud classification on ModelNet40 and ScanObjectNN datasets, our method reduced the information loss of knowledge transfer in distillation in 40x model compression while maintaining competitive performance.Comment: Accepted to ICIP202

Characterization of the mud displacement in an enlarged wellbore: An integrated rock-fluid model

Cement-mud displacement plays a crucial role in the sealability of cement sheaths. Irregular geometric features of a wellbore due to washout can have a negative impact on mud and cement mobilization. An unstable interface between two fluids always leads to mud channeling, interfluid mixing, and cement contamination, degrading the cement quality. Many factors, such as mechanical and rheological properties of fluids, annulus geometry, flow pattern, and flow rate, significantly influence the displacement efficiency. This study investigates the characterization of the mud displacement in an irregular horizontal well using a 3D computational fluid dynamics (CFD) model. Mud is displaced in an enlarged wellbore by geopolymer and neat class G cement. The wellbore geometry is developed based on the caliper log data from an unconventional shale well in the Tuscaloosa Marine Shale (TMS) lithology. The effects of pump rate, density difference, and mud contamination are evaluated by numerical simulations. The results present those residual muds mainly exist in the upper annulus of the enlarged section. Geopolymer has a better sealing performance and can resist more water-based mud (WBM) contaminations than neat class G cement. The scenario with a low mud-cement density difference and high cement injection rate results in a high cement volume fraction, mitigating the gas migration.publishedVersio

Investigation of Hydraulic and Mechanical Cement Integrity: An Advanced Computational Study

Cement sheath is a significant barrier to maintain the zonal isolation of wells, preventing severe consequences such as kick (or influx) accidents, environmental contaminations, and safety threats. Many previous investigations have assessed the performance of cement via experimental and analytical studies based on several setups. However, further advanced studies should be conducted to solve the severe challenges posed by the increased exploration activities in harsh operational environments and advanced stimulation in long lateral wells. To achieve this goal, mechanical and hydraulic cement integrity considerations should be involved during the analysis. Mechanical considerations should satisfy the requirements of structural failure prevention in the cement under different wellbore conditions, such as high-temperature high-pressure (HTHP). Hydraulic integrity needs quality evaluations of cement slurry. This dissertation aims to evaluate cement quality by analyzing the mechanical stresses around the set cement and the fluid mechanics in the cement displacement processes using a numerical approach. The specific objectives are to (i) investigate the performance of cement under various designs, operations, and loading conditions, (ii) identify the influencing parameters which affect the cement performance, and (iii) evaluate the influence of enlarged wellbore on the mud displacement efficiency via a numerical approach. Diametric compression simulation indicates that cement sheath is likely to fail at the casing interface before the formation interface. Along with the casing-cement interface, failure would initiate at the location parallel to the direction of applied load (θ = 0°). High hoop stresses exceeding the limiting strength are the primary cause of the cement failure. HTHP wellbore conditions have a significant influence on cement integrity due to high thermal loads. Heat flow direction away from the wellbore (ΔT >0) generates approximately 65% higher magnitudes of radial and hoop stresses in the cement sheath compared to heat flow direction toward the wellbore (ΔT 0), there is no precise predictor of stresses in cement. Radial stress primarily depends on temperature difference and internal casing pressure, followed by the cement’s Young’s modulus and in-situ stresses. On the other hand, Hoop stress mainly depends on the cement’s Young’s modulus and Poisson’s ratio, followed by temperature difference and in-situ stress. For the cement hydraulic integrity study, an incomplete mud removal has a high risk of occurring at the top of the annulus. Technical novel information of this research is to (i) investigate the performance of different cement under subsurface conditions by an experimentally validated finite element analysis (FEA) model, (ii) use the casing-cement-formation system to represent a more realistic wellbore condition, and (iii) study the influence of fluid dynamics during mud removal

Two hAT transposon genes were transferred from Brassicaceae to broomrapes and are actively expressed in some recipients

A growing body of evidence is pointing to an important role of horizontal gene transfer (HGT) in the evolution of higher plants. However, reports of HGTs of transposable elements (TEs) in plants are still scarce, and only one case is known of a class II transposon horizontally transferred between grasses. To investigate possible TE transfers in dicots, we performed transcriptome screening in the obligate root parasite Phelipanche aegyptiaca (Orobanchaceae), data-mining in the draft genome assemblies of four other Orobanchaceae, gene cloning, gene annotation in species with genomic information, and a molecular phylogenetic analysis. We discovered that the broomrape genera Phelipanche and Orobanche acquired two related nuclear genes (christened BO transposase genes), a new group of the hAT superfamily of class II transposons, from Asian Sisymbrieae or a closely related tribe of Brassicaceae, by HGT. The collinearity of the flanking genes, lack of a classic border structure, and low expression levels suggest that BO transposase genes cannot transpose in Brassicaceae, whereas they are highly expressed in P. aegyptiaca

Extremely large magnetoresistance in topologically trivial semimetal α\alpha-WP2_2

Extremely large magnetoresistance (XMR) was recently discovered in many non-magnetic materials, while its underlying mechanism remains poorly understood due to the complex electronic structure of these materials. Here, we report an investigation of the $\alpha$-phase WP$_2$, a topologically trivial semimetal with monoclinic crystal structure (C2/m), which contrasts to the recently discovered robust type-II Weyl semimetal phase in $\beta$-WP$_2$. We found that $\alpha$-WP$_2$ exhibits almost all the characteristics of XMR materials: the near-quadratic field dependence of MR, a field-induced up-turn in resistivity following by a plateau at low temperature, which can be understood by the compensation effect, and high mobility of carriers confirmed by our Hall effect measurements. It was also found that the normalized MRs under different magnetic fields has the same temperature dependence in $\alpha$-WP$_2$, the Kohler scaling law can describe the MR data in a wide temperature range, and there is no obvious change in the anisotropic parameter $\gamma$ value with temperature. The resistance polar diagram has a peanut shape when field is rotated in $\textit{ac}$ plane, which can be understood by the anisotropy of Fermi surface. These results indicate that both field-induced-gap and temperature-induced Lifshitz transition are not the origin of up-turn in resistivity in the $\alpha$-WP$_2$ semimetal. Our findings establish $\alpha$-WP$_2$ as a new reference material for exploring the XMR phenomena.Comment: 18 pages, 12 figure