Mechanical behavior of hydrate‐bearing sediments is critical for well stability, reservoir deformation, and sea floor settlement during gas production. Current understanding on the mechanism of ...hydrate strengthening hosting sediments relies on conceptual models based on idealistic pore‐scale assumptions. Yet pore‐scale study is rare and limited to hydrate‐bearing sediments formed with surrogate guest molecules rather than methane. We present for the first time pore‐scale triaxial test results of methane hydrate‐bearing sediments. Besides the traditional stress‐strain relationship, we further explored (1) sand particle crushing and (2) pressure‐temperature dependent strength variations and (3) creep of hydrate‐bearing sediments. Results show that as hydrate enables the sand skeleton to bear additional loads, the potential of sand crushing upon hydrate dissociation also increases. Strength of hydrate‐bearing sediments decreases as pressure‐temperature condition approaches hydrate phase boundary. Hydrate‐bearing sediments creep and heal with time. The new observations suggest additional complications to be considered during gas production.
Plain Language Summary
The presence of solid hydrate in sediment pores is known to enhance the strength of hosting sediments, similar to the effect of ice in frozen sediments. However, our understanding on the mechanism of increased strength still relies on simplified conceptual models based on idealistic pore‐scale assumptions. Direct visualization of pore‐scale hydrate behavior can greatly advance our knowledge on this issue, yet studies are rare and conducted with surrogate gas hydrates due to challenges (1) to maintain the stability of hydrate under high pressure and low temperature, (2) to visualize the specimen with high resolution while the specimen is housed inside high‐pressure core holders, and (3) to distinguish methane hydrate from other pore constituents in CT images. We overcome these issues and conducted three experiments on specimens with different hydrate saturations. Our results highlight that the presence of hydrate strengthens the sediments by (1) providing supports for the original sediment skeleton and (2) forming hydrate skeletons to directly bear the load, especially when the hydrate saturation is high. In addition, our results show massive sand crushing, temperature‐pressure‐dependent specimen strength, creeping, and healing of hydrate‐bearing sediments.
Key Points
Higher hydrate saturation increases the load‐bearing capacity of sediments, hence the potential of sand crushing
Hydrate‐bearing sediments degrade gradually as the pressure‐temperature approaches hydrate phase boundary and can fail catastrophically
Hydrate‐bearing sediments creep, therefore induce reservoir deformation with time and meanwhile heal to partially regain strength
X‐ray computed tomography (CT) has become a critical technique in the study of porous media. It has attracted growing attention for analyzing hydrate‐bearing sediment, but this has been done using ...surrogates (Xe/Kr) only due to difficulties in distinguishing methane hydrate from water. This study presents the successful imaging of methane hydrate coexisting with pore liquid, gas, and sediments. We used potassium iodide (KI) solutions and in‐line propagation‐based phase‐contrast CT analysis of X‐ray attenuation and diffraction to distinguish the four materials. Thus, consideration for CT‐related X‐ray physics was necessary to optimize KI concentrations, improve material separation with X‐ray propagation, and properly interpret artifacts within the images. The images clearly show methane hydrate in the pore space of sand (~250 μm) coexisting with KI solution and gas. Following this, X‐ray CT can now be used to visualize pore habits of natural methane hydrate in sediment cores.
Plain Language Summary
Methane hydrate has great potential as an energy resource. Thus, the behavior of methane hydrate in reservoirs is the current focus of research for gas production and environmental impacts. It is critical to know how hydrate is distributed in sediment pores and how it interacts with sediments in order to understand the potentially dynamic physical and chemical properties of hydrate‐bearing sediments. This study develops an X‐ray computed tomography technique to gain 3‐D insight into sediment pores with resolution down to micron level, while maintaining high pressure and low temperature during the scan to keep methane hydrate stable. This technique takes advantages of both the attenuation and interference of X‐ray waves. Attenuation characteristics of materials of interest are manipulated with enhancing agents to achieve optimum contrasts. X‐ray wave interference is utilized to enhance edge detection between different materials. Our results establish the ability of the proposed techniques to discern methane hydrate from its hosting environment. The proper interpretation of results relies on the fundamental understanding of X‐ray physics so that artifacts induced by X‐ray wave interference can be discerned from real features of interest on material surfaces. The technique can be utilized for various aspects of geomaterial characterization.
Key Points
Methane‐hydrate coexisting with pore liquid, gas, and sediment are 3‐D visualized at pore scale
Image contrasts among different materials are enhanced via optimizing X‐ray attenuation and diffraction
Brighter‐darker pair pattern resulted from X‐ray diffraction could lead to erroneous interpretation
Nanocomposites, multiphase solid materials with at least one nanoscaled component, have been attracting ever‐increasing attention because of their unique properties. Graphene is an ideal filler for ...high‐performance multifunctional nanocomposites in light of its superior mechanical, electrical, thermal, and optical properties. However, the 2D nature of graphene usually gives rise to highly anisotropic features, which brings new opportunities to tailor nanocomposites by making full use of its excellent in‐plane properties. Here, recent progress on graphene/polymer nanocomposites is summarized with emphasis on strengthening/toughening, electrical conduction, thermal transportation, and photothermal energy conversion. The influence of the graphene configuration, including layer number, defects, and lateral size, on its intrinsic properties and the properties of graphene/polymer nanocomposites is systematically analyzed. Meanwhile, the role of the interfacial interaction between graphene and polymer in affecting the properties of nanocomposites is also explored. The correlation between the graphene distribution in the matrix and the properties of the nanocomposite is discussed in detail. The key challenges and possible solutions are also addressed. This review may provide a constructive guidance for preparing high‐performance graphene/polymer nanocomposite in the future.
Recent progress on graphene/polymer nanocomposites is reviewed, with emphasis on strengthening and toughening, electrical conduction, thermal transportation, and photothermal conversion. The roles of graphene configuration, interfacial interaction, and distribution of graphene in the polymer to determine the properties of the nanocomposites are systematically explored. This may provide constructive guidance to develop high‐performance nanocomposites in the future.
The exploration of ultra-wideband electromagnetic shielding materials is still a huge challenge in the elimination of electromagnetic interference from electronic devices of various frequencies in ...military and civil fields. Herein, a free-standing graphene oxide/silver nanowire (GO/Ag-7L) film with a dense sandwich-like structure is fabricated
via
vacuum-assisted self-assembly. Compared with the random distribution of physical mixed films, silver nanowires are woven into a 3D conductive network in the multilayer GO/Ag-7L film, which provides a superb electrical conductivity (2255.8 S cm
−1
). Benefitting from the multilayer structure with multiple absorptions of the GO layer and multiple reflections of the silver nanowire network, the electromagnetic interference shielding effectiveness (EMI SE) is up to 62 dB when the thickness is merely 8 μm in the ultra-wideband of 8-40 GHz (covering the X-band, Ku-band, K-band, and Ka-band). The corresponding specific SE (EMI SE/
t
) is as high as 77 500 dB cm
−1
. After inserting the GO layer, the GO/Ag-7L film exhibits outstanding flexibility and anti-corrosion properties. Considering practical application, it can be employed as a novel strain sensor with high sensitivity and a quick strain response in the robotics field, which satisfies the requirement for both electromagnetic interference protection and real-time motion monitoring. Thus, it has promising potential applications in sophisticated electronic equipment.
A free-standing graphene oxide/Ag nanowire film with a dense sandwich-like structure was fabricated
via
vacuum-assisted self-assembly. The EMI SE is up to 62 dB when the thickness is merely 8 μm in 8-40 GHz. The corresponding specific SE (EMI SE/t) is up to 77 500 dB cm
−1
.
Gas hydrate, as a solid pore constituent, can potentially share external load with sediment matrix, and critically impact geological evolution of its hosting sediments, well integration and sediment ...settlement during gas production depending on its contribution to support external loading. We aim to address the question of whether hydrate shares the load with the soil skeleton through isotropic consolidation experiments. Our results highlight the formation of methane hydrate does not affect the integrity of sediment skeletons if the effective stress previously applied on the skeleton remains constant, which indicates that methane hydrate would not actively support the load. Subsequent external load applied to the sediments after hydrate formation can be supported by hydrate. Secondly, hydrate as well as hydrate-bearing sediments exhibit creep behavior. As hydrate creeps, the load transfers to the sediment skeleton with time and hydrate gradually retreats from the status of load-bearing. When hydrate saturation is low and the coexisting pore fluid can percolate through sediments, the local deformation of hydrate due to sediment consolidation induces excess pore pressure, which dissipates by pushing out the pore fluid. When the coexisting pore fluid is enclosed in hydrate mass in high hydrate saturation environments, the dissipation of excess pore pressure relies on the viscous flow of hydrate. This pressure dissipation could last for millions of years according to analytical analysis based on Terzaghi's consolidation theory, during which hydrate cannot completely escape the status of load-bearing. These observations conclude that load-bearing is a dynamic status rather than a stagnant pore habit, countering conventional thinking that load-bearing joins grain-coating, cementing and pore-filling as a pore habit of gas hydrate.
•Newly-formed methane hydrate in sandy sediments does not alter the initial sediment skeleton or take load.•Methane hydrate shares external loads applied after its formation but gradually passes the loads to sediment skeleton.•The dissipation of excess-pressure in methane hydrate can take geologic time when hydrate saturation is high.
As the black cesium lead iodide (CsPbI
) tends to transit into a yellow δ-phase at ambient, it is imperative to develop a stabilized black phase for photovoltaic applications. Herein, we report a ...distorted black CsPbI
film by exploiting the synergistic effect of hydroiodic acid (HI) and phenylethylammonium iodide (PEAI) additives. It is found that the HI induces formation of hydrogen lead iodide (HPbI
), an intermediate to the distorted black phase with appropriate band gap of 1.69 eV; while PEAI provides nucleation for optimized crystallization. More importantly, it stabilizes the distorted black phase by hindering phase transition via its steric effects. Upon optimization, we have attained solar cell efficiency as high as 15.07%. Specifically, the bare cell without any encapsulation shows negligible efficiency loss after 300 h of light soaking. The device keeps 92% of its initial cell efficiency after being stored for 2 months under ambient conditions.
Infrared (IR) small target detection under low signal-to-clutter ratio (SCR) is a fundamental and important problem in some critical missions like IR search and tracking (IRST). Though there exist a ...lot of works using local contrast measure (LCM) to detect the target, their performance are still unsatisfying due to the imperfect knowledge of target structure. In this letter, a novel IR small target detection method utilizing halo structure prior (HSP)-based LCM (HSPLCM) is proposed, which adequately considers the structure characteristic of the target. Specifically, through weighting the raw IR image via image structure tensor, we put forward a simple but useful image prior (named as HSP) which reflects the unique structural feature of the target to distinguish the real target and other background clutters. Afterward, based on this prior an effective LCM method is constructed to detect the IR small target, which can enhance the target and suppress the background clutters simultaneously. Furthermore, we extend the proposed algorithm to its multiscale version to solve the target scale uncertainty issues. Extensive experimental results have demonstrated that our proposed method favorably outperforms the state-of-the-arts.
AIM To investigate the relationship between autophagy and perineural invasion(PNI), clinical features, and prognosis in patients with pancreatic cancer. METHODS Clinical and pathological data were ...retrospectively collected from 109 patients with pancreatic ductal adenocarcinoma who underwent radical resection at the First Affiliated Hospital of Zhengzhou University from January 2011 to August 2016. Expression levels of the autophagy-related protein microtubuleassociated protein 1 A/1 B-light chain 3(LC3) and PNI marker ubiquitin carboxy-terminal hydrolase(UCH) in pancreatic cancer tissues were detected by immunohistochemistry. The correlations among LC3 expression, PNI, and clinical pathological features in pancreatic cancer were analyzed. The patients were followed for further survival analysis. RESULTS In 109 cases of pancreatic cancer, 68.8%(75/109) had evidence of PNI and 61.5%(67/109) had high LC3 expression. PNI was associated with lymph node metastasis, pancreatitis, and CA19-9 levels(P < 0.05). LC3 expression was related to lymph node metastasis(P < 0.05) and was positively correlated with neural invasion(P < 0.05, r = 0.227). Multivariate logistic regression analysis indicated that LC3 expression, lymph node metastasis, pancreatitis, and CA19-9 level were factors that influenced neural invasion, whereas only neural invasion itself was an independent factor for high LC3 expression. Univariate analysis showed that LC3 expression, neural invasion, and CA19-9 level were related to the overall survival of pancreatic cancer patients(P < 0.05). Multivariate COX regression analysis indicated that PNI and LC3 expression were independent risk factors for poor prognosis in pancreatic cancer(P < 0.05). CONCLUSION PNI in patients with pancreatic cancer is positively related to autophagy. Neural invasion and LC3 expression are independent risk factors for pancreatic cancer with a poor prognosis.
Abstract
Background
Ovarian cancer (OC) is the most lethal gynaecological tumor. Changes in glycolysis have been proven to play an important role in OC progression. We aimed to identify a novel ...glycolysis-related gene signature to better predict the prognosis of patients with OC.
Methods
mRNA and clinical data were obtained from The Cancer Genome Atlas (TCGA), International Cancer Genome Consortium (ICGC) and Genotype Tissue Expression (GTEx) database. The “limma” R package was used to identify glycolysis-related differentially expressed genes (DEGs). Then, a multivariate Cox proportional regression model and survival analysis were used to develop a glycolysis-related gene signature. Furthermore, the TCGA training set was divided into two internal test sets for validation, while the ICGC dataset was used as an external test set. A nomogram was constructed in the training set, and the relative proportions of 22 types of tumor-infiltrating immune cells were evaluated using the “CIBERSORT” R package. The enriched Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were determined by single-sample gene set enrichment analysis (ssGSEA) with the “GSVA” R package. Finally, the expression and function of the unreported signature genes ISG20 and SEH1L were explored using immunohistochemistry, western blotting, qRT-PCR, proliferation, migration, invasion and xenograft tumor assays.
Results
A five-gene signature comprising ANGPTL4, PYGB, ISG20, SEH1L and IRS2 was constructed. This signature could predict prognosis independent of clinical factors. A nomogram incorporating the signature and three clinical features was constructed, and the calibration plot suggested that the nomogram could accurately predict the survival rate. According to ssGSEA, the signature was associated with KEGG pathways related to axon guidance, mTOR signalling, tight junctions, etc. The proportions of tumor-infiltrating immune cells differed significantly between the high-risk group and the low-risk group. The expression levels of ISG20 and SEH1L were lower in tumor tissues than in normal tissues. Overexpression of ISG20 or SEH1L suppressed the proliferation, migration and invasion of Caov3 cells in vitro and the growth of xenograft tumors in vivo.
Conclusion
Five glycolysis-related genes were identified and incorporated into a novel risk signature that can effectively assess the prognosis and guide the treatment of OC patients.
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