ABSTRACT
PtS2, a member of the group 10 transition metal dichalcogenides (TMDs), has received extensive attention because of its excellent electrical properties and air stability. However, there are few reports on the preparation of single-crystal PtS2 in the literature, and the growth mechanism of single crystal PtS2 is not well elucidated. In this work, we proposed a method of preparation that combines magnetron sputtering and chemical vapor transport to obtain monocrystalline PtS2 on a SiO2/Si substrate. By controlling the growth temperature and time, we have synthesized a single crystalline PtS2 of hexagonal shape and size of 1-2 µm on a silicon substrate. Combining the molecular dynamics simulation, the growth mechanism of single crystal PtS2 was investigated both experimentally and theoretically. The synthesis method has a short production cycle and low cost, which opens the door for the fabrication of other TMDs single crystals.
ABSTRACT
The first asymmetric synthesis of a scillascillin-type homoisoflavonoid was reported. Key reactions for the asymmetric synthesis of benzocyclobutene include catalytic reductive desymmetrization of malonic ester and an intramolecular C-H activation of the methyl group.
ABSTRACT
Stress sensitivity in reservoirs is critical during the exploitation of oil and gas fields. As a deep clastic reservoir under strong tectonic compression, the Ahe Formation in the northern tectonic zone of the Kuqa depression exhibited strong stress sensitivity effect. However, the conventional evaluation method by using permeability damage rate as a constraint restricts the mechanistic understanding of the strong stress sensitivity effect. In this study, morphology of stress sensitivity test curve, coupled with rate change of permeability and extent of irreversible damage in actual sample measurement through micro-CT in-situ scanning, is used to characterize differentially. The strong stress sensitivity effects of the studied intervals can be divided into three types: (1) rapid change in permeability-weak irreversible damage, (2) moderate change in permeability-strong irreversible damage and (3) moderate change in permeability-moderate irreversible damage. The strong stress sensitivity is caused by the micro-pores and micro-fractures, which are widely developed in the studied reservoir. The mechanisms caused by the two types of pore are different. The stress sensitivity effects in micro-fracture-rich reservoirs are characterized by rapid change in permeability and weak irreversible damage. Meanwhile, the stress sensitivity effects in micro-pore-rich reservoirs are manifested as moderate change in permeability and strong irreversible damage. The study shows that the differences in the content of micro-pores and micro-fractures and their reverse mechanisms of stress sensitivity co-create different types of stress sensitivity within the samples. Accordingly, the differences of the stress sensitivity type in macroscopic samples are caused by the competition between the microscopic differences of pore types.
ABSTRACT
Fusing a number of classifiers can generally improve the performance of individual classifiers, and the fuzzy integral, which can clearly express the interaction among the individual classifiers, has been acknowledged as an effective tool of fusion. In order to make the best use of the individual classifiers and their combinations, we propose in this paper a new scheme of classifier fusion based on upper integrals, which differs from all the existing models. Instead of being a fusion operator, the upper integral is used to reasonably arrange the finite resources, and thus to maximize the classification efficiency. By solving an optimization problem of upper integrals, we obtain a scheme for assigning proportions of examples to different individual classifiers and their combinations. According to these proportions, new examples could be classified by different individual classifiers and their combinations, and the combination of classifiers that specific examples should be submitted to depends on their performance. The definition of upper integral guarantees such a conclusion that the classification efficiency of the fused classifier is not less than that of any individual classifier theoretically. Furthermore, numerical simulations demonstrate that most existing fusion methodologies, such as bagging and boosting, can be improved by our upper integral model.
ABSTRACT
The role of atherosclerosis in ischemic stroke has been intensively investigated in recent years, and lipoprotein (a) [Lp(a)] is found to have roles during the process. The aim of this study was to investigate the relationship between acute ischemic stroke (AIS) and serum Lp(a) levels in the Chinese population. All consecutive patients with first-ever acute ischemic stroke during 2011-2012 were recruited to participate in the study. Serum Lp(a) levels and routine tests were examined in both groups. The National Institutes of Health Stroke Scale (NIHSS) score was assessed on admission blinded to Lp(a) levels. In this study, 181 patients with acute ischemic stroke were included. There was a significant difference in median serum Lp(a) levels between acute ischemic stroke patients and control cases (328 [IQR, 173-554] vs. 145 [IQR, 66-254] mg/L, respectively; P = 0.000). Lp(a) levels increased with increasing severity of stroke as defined by the NIHSS score (P = 0.000). For the entire group, when adjusting for other possible risk factors, an elevated Lp(a) level was an independent risk factor for stroke, and a serum Lp(a) level ≥300 mg/L was associated with a 2.23-fold increase in AIS (P = 0.015). In addition, this association was stronger in male than in female patients. High Lp(a) levels are significantly related to stroke, independent from other traditional and emerging risk factors, suggesting that they may play a role in its pathogenesis. It should be considered as a routine risk factor for stroke in the Chinese population.
