Search

Phosphorus‐nitrogen (PN) adamantanoid cages are valuable precursors for materials chemistry, but their syntheses are based on harsh methods that sometimes require access to restricted reagents. We report a new and scalable synthesis of PN adamantanoid compounds by chlorosilane elimination between bis‐silylated amines and phosphorus trichloride. We further study the mechanism of the recently‐reported four‐fold oxidation of such cages with Me3SiN3 to yield tetravalent tetrahedral connectors for materials chemistry. Reaction monitoring and kinetic modelling revealed the key rate‐limiting step, but attempts to accelerate this using Lewis acid additives were unsuccessful. Nevertheless, a new four‐fold oxidized PN‐adamantanoid cage has been prepared and structurally characterized. [ABSTRACT FROM AUTHOR]

In this work, an effective and fast finite element numerical method with high‐order accuracy is discussed for solving a nonlinear time fractional diffusion equation. A two‐level linearized finite element scheme is constructed and a temporal–spatial error splitting argument is established to split the error into two parts, that is, the temporal error and the spatial error. Based on the regularity of the time discrete system, the temporal error estimate is derived. Using the property of the Ritz projection operator, the spatial error is deduced. Unconditional superclose result in H1‐norm is obtained, with no additional regularity assumption about the exact solution of the problem considered. Then the global superconvergence error estimate is obtained through the interpolated postprocessing technique. In order to reduce storage and computation time, a fast finite element method evaluation scheme for solving the nonlinear time fractional diffusion equation is developed. To confirm the theoretical error analysis, some numerical results are provided. [ABSTRACT FROM AUTHOR]

AbstractThe geological environment of marine methane hydrate-bearing sediments (MHBS) is highly complex. Mastering the mechanical behavior of MHBS is crucial for analyzing geomechanical hazards and evaluating its stability. The marine sediment in the South China Sea (SCS) contains a significant amount of porous foraminifera shells, which serve as the primary storage space for natural gas hydrates and differ significantly from other sea areas. In the laboratory, porous carbonate sand (CS) and cohesion-less silt were utilized to prepare host sand of methane hydrate. In this paper, based on the analysis of experimental data, a bounding surface model was proposed to describe the mechanical behavior of artificial MHBS. The effect of methane hydrates on the elastic strain, normal consolidation and critical state of host sand is discussed, and corresponding equations for the model parameters are established, taking into consideration the cementing mechanism of hydrates. These equations are defined as functions of hydrate saturation, carbonate sand content (CSC), and initial void ratio. The increase in hydrate saturation significantly reduces the compressibility of the host sand and improves its strength. The proposed model is applied to predict the results of isotropic consolidation and drained triaxial tests on MHBS, demonstrating satisfactory performance. [ABSTRACT FROM AUTHOR]

The superconvergence for a nonconforming mixed finite element approximation of the Navier-Stokes equations is analyzed in this article. The velocity field is approximated by the constrained nonconforming rotated Q1 (CNR Q1) element, and the pressure is approximated by the piecewise constant functions. Under some regularity assumptions, the superconvergence estimates for both the velocity in broken H1-norm and the pressure in L2-norm are obtained. Some numerical examples are presented to demonstrate our theoretical results. © 2015 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 32: 646-660, 2016 [ABSTRACT FROM AUTHOR]

An effective finite difference scheme for solving the nonlinear Fermi-Pasta-Ulam (FPU) problem is derived. The most important feature of the scheme inherits energy conservation property from the nonlinear FPU problem. The unique solvability and the convergence of the difference scheme are proved by the energy method. The convergence order is [ABSTRACT FROM AUTHOR]

Objective: This study aimed to validate the Chinese version of the Somatic Symptom Disorder-B Criteria Scale (SSD-12) in an outpatient sample from Chinese general hospitals and to determine the diagnostic performance of the SSD-12 as a screening tool for somatic symptom disorder (SSD)., Methods: The Chinese version of the SSD-12 was completed by 699 outpatients from nine general hospitals during a 16-month period (2016-2018). The SSD section of the Structured Clinical Interview for DSM Disorders, Fifth Edition, Research Version, was used to determine diagnostic accuracy (criterion validity). The construct validity of the SSD-12 was evaluated by examining correlations with the Whiteley Index-7, Patient Health Questionnaire-15, Patient Health Questionnaire-9, General Anxiety Disorder-7, World Health Organization Disability Assessment Schedule, and Medical Outcome Study 12-item Short Form Health Survey (SF-12)., Results: The SSD-12 had excellent internal consistency in this sample (Cronbach α = .95). Confirmatory factor analyses replicated a three-factor structure that reflects the cognitive, affective, and behavioral aspects (Comparative Fit Index = 0.963, Tucker-Lewis Index = 0.952, root mean square error of approximation = 0.08, 90% confidence interval = 0.08-0.09), but was also consistent with a general one-factor model of the SSD-12 (Comparative Fit Index = 0.957, Tucker-Lewis Index = 0.948, root mean square error of approximation = 0.09, 90% confidence interval = 0.08-0.10). The optimal cutoff point for the Structured Clinical Interview for DSM Disorders-based diagnosis of SSD was 16 (sensitivity = 0.76, specificity = 0.80). The SSD-12 sum score was significantly associated with somatic symptom burden (Patient Health Questionnaire-15: r = 0.52, p < .001), health anxiety (Whiteley Index-7: r = 0.82, p < .001), depressive symptoms (Patient Health Questionnaire-9: r = 0.63, p < .001), general anxiety (General Anxiety Disorder-7: r = 0.64, p < .001), health-related quality of life (physical component score of SF-12: r = -0.49, p < .001; mental component score of SF-12: r = -0.61, p < .001), and health-related disabilities (World Health Organization Disability Assessment Schedule: r = 0.56, p < .001)., Conclusions: Initial assessment indicates that the Chinese version of the SSD-12 has sufficient reliability and validity to warrant further testing in both research and clinical settings.