This paper studies the global (in time) regularity and large time behavior of solutions to the 2D micropolar equations with only angular viscosity dissipation. Micropolar equations model a class of ...fluids with nonsymmetric stress tensor such as fluids consisting of particles suspended in a viscous medium. When there is no kinematic viscosity in the momentum equation, the global regularity problem is not easy due to the lack of suitable bounds on the derivatives. The idea here is to fully exploit the structure of the system and control the vorticity via the evolution equation of a combined quantity of the vorticity and the micro-rotation angular velocity. To understand the large time behavior, we overcome two main difficulties, the lack of kinematic viscosity and the presence of linear terms. Classical tools such as the Fourier splitting method of Schonbek and Kato's approach for the decay of small solutions do not apply here. We introduce a diagonalization process to eliminate the linear terms and rely on the uniform bounds for the first derivatives of the solutions to generate suitable decay rates.
New classes of two-dimensional (2D) materials beyond graphene, including layered and non-layered, and their heterostructures, are currently attracting increasing interest due to their promising ...applications in nanoelectronics, optoelectronics and clean energy, where thermal transport is a fundamental physical parameter. In this paper, we systematically investigated the phonon transport properties of the 2D orthorhombic group IV-VI compounds of GeS, GeSe, SnS and SnSe by solving the Boltzmann transport equation (BTE) based on first-principles calculations. Despite their similar puckered (hinge-like) structure along the armchair direction as phosphorene, the four monolayer compounds possess diverse anisotropic properties in many aspects, such as phonon group velocity, Young's modulus and lattice thermal conductivity (
κ
),
etc
. Especially, the
κ
along the zigzag and armchair directions of monolayer GeS shows the strongest anisotropy while monolayer SnS and SnSe show almost isotropy in phonon transport. The origin of the diverse anisotropy is fully studied and the underlying mechanism is discussed in details. With limited size, the
κ
could be effectively lowered, and the anisotropy could be effectively modulated by nanostructuring, which would extend the applications to nanoscale thermoelectrics and thermal management. Our study offers fundamental understanding of the anisotropic phonon transport properties of 2D materials, and would be of significance for further study, modulation and applications in emerging technologies.
The four monolayer group IV-VI compounds (GeS, GeSe, SnS and SnSe), although possessing similar hinge-like structure along the armchair direction, show diverse anisotropic properties in phonon transport.
Summary
Phosphoglycerate kinase (PGK) is a highly conserved reversible enzyme that participates in both glycolysis and photosynthesis. In Arabidopsis thaliana, one cytosolic PGK (PGKc) and two ...plastidial PGKs (PGKp) are known. It remains debatable whether the two PGKp isozymes are functionally redundant or specialized in plastidial carbon metabolism and fixation. Here, using a pooled clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR‐associated protein 9 (Cas9) strategy, we found that plants with single mutations in pgkp1 or pgkp2 were not significantly affected, whereas a pgkp1pgkp2 double mutation was lethal due to retarded carbon fixation, suggesting that PGKp isozymes play redundant functional roles. Metabolomic analysis demonstrated that the sugar‐deficient pgkp1pgkp2 double mutation was partially complemented by exogenous sugar, although respiration intermediates were not rescued. Chloroplast development was defective in pgkp1pgkp2, due to a deficiency in glycolysis‐dependent galactoglycerolipid biosynthesis. Ectopic expression of a plastid targeting PGKc did not reverse the pgkp1pgkp2 double‐mutant phenotypes. Therefore, PGKp1 and PGKp2 play redundant roles in carbon fixation and metabolism, whereas the molecular function of PGKc is more divergent. Our study demonstrated the functional conservation and divergence of glycolytic enzymes.
Significance Statement
There have been debates on whether different plastidial PGK isoforms play specialized or redundant roles in plastidial glycolysis and the Calvin cycle. Utilizing CRISPR/Cas9 and biochemical, metabolomic and lipidomic approaches, we found that Arabidopsis PGKp isozymes serve redundant, but essential, functions in carbon fixation, metabolism and galactoglycerolipids biosynthesis in chloroplasts.
Lithium-sulfur batteries have high cathode theoretical energy density, but the poor conductivity of sulfur and polysulfide shuttling result in serious polarization and low sulfur utilization. ...Moreover, the addition of insulating binder in the electrode increases the internal resistance, reducing specific capacity and rate performance. Herein, we develop a composite binder with higher electronic conductivity, superior mechanical property and strong adsorption of polysulfides that imparts it some electrocatalytic activity. The reduced graphene oxide- polyacrylic acid (GOPAA) binder is prepared via a simple solution process. At constant loading fraction of 10wt%, using GOPAA binder induces a 30% enhancement in the cathode capacity, better cycle life and rate capability compared to using PAA binder, reducing both the local charge-transfer resistance and the global electronic resistance before and after cycling. These are attributed to the enhanced binding strength and synergistic effect of reduced graphene oxide and PAA forming well-dispersed conductive bridges to promote rapid electron transfer. Additionally, GOPAA provides active sites for adsorption of lithium polysulfides and electrocatalytic activity, shifting redox peaks in cyclic voltammetry and improving roundtrip efficiency.
Display omitted
•A conductive composite binder with high electric conductivity and strong adhesion was obtained by a simple solution process.•The conductive composite binder could trap lithium polysulfides by a chemical absorption.•Lithium-sulfur batteries using the conductive composite binder exhibit excellent electrochemical performance.
In order to raise the accuracy of the circular gratings angle-measuring system, a comprehensive error model is established, and a novel compensation method is proposed. Firstly, many error sources, ...including the rotary errors of axis system, the installation eccentricity and the inclination of the circular grating disc, the graduation line error of the circular grating disc, and the installation error of the multiple readingheads of the high precision circular gratings angle-measuring system are comprehensively taken into consideration. Secondly, the position and attitude errors are propagated to the angular position outputs, thus the mathematical relationships between error sources and the angular position error are established. Aiming at multiple readingheads system, the mechanism of influence of the error sources on the angular position error is unveiled, and the mechanical error identification and reduction method is proposed. After that, a checking system with a 23-mirrored polygon and an autocollimator is set up, and the complete combinatorial method of separating the angular position errors from the readouts of the autocollimator precisely is used. Finally, the angular position error compositions are separated by the harmonic analysis method, and the concerned error coefficients are compensated. The experimental results show that the nominal indication interval value of the angular position errors is reduced to 0.23" by the mechanical error reduction method, and then the nominal indication interval value of the angular position errors is reduced to 0.12" by software measurement method. And the two sets’ repeatability of the separated biases of the 23-mirrored polygon before and after compensating is 95%.
Display omitted
•An error model designed includes all error sources in angle-measuring system.•Radial error, eccentricity errors and indicating grating installing errors can be reduced.•Mechanical compensation method and software compensation method are combined to further improve angle measurement system accuracy.•Consistency of polygon separated biases in different initial angular position validates the effectiveness.•Proposed method is suitable for any angle measurement system.
Hydroxyapatites (HAP m -T) of varying molar Ca/P ratios m (1.58–1.69) and calcination temperatures T (360–700 °C) were prepared and comprehensively characterized by nitrogen adsorption, TG, XPS, XRD, ...CO2-TPD, and NH3-TPD and were employed to catalyze the gas-phase dehydration of lactic acid (LA) to produce acrylic acid (AA). While the texture and crystallinity of the HAP m -T sample were affected little by variation of m, its surface acidity decreased but basicity increased with the increase in m. The HAP m -T sample with a higher T showed a higher crystallinity but lower surface area, acidity, and basicity. The conversion of LA decreased with increasing either m or T of the HAP m -T catalyst; the selectivity for AA maximized at m = 1.62 but decreased steadily with the T increase. The HAP1.62-360 sample (m = 1.62, T = 360 °C) was identified as the most efficient catalyst, offering an AA yield as high as 50–62% for longer than 8 h (AA selectivity: 71–74 mol %) under optimized reaction conditions (360 °C, WHSVLA= 1.4–2.1 h–1). Correlating the catalyst performance with its surface acidity and basicity disclosed that the LA consumption rate increased linearly with the acidity/basicity ratio, but volcano-type dependence appeared between the AA production rate and the acidity/basicity ratio, which reveals a kind of cooperative acid–base catalysis for selective AA production. The HAP m -T catalysts became more or less deactivated after reaction, but the reacted ones could be fully regenerated by in situ treatment with flowing air.
Background The 2019 Bosniak classification (version 2019) of cystic renal masses (CRMs) provides a systematic update to the currently used 2005 Bosniak classification (version 2005). Further ...validation is required before widespread application. Purpose To evaluate the interobserver agreement of MRI criteria, the impact of readers' experience, and the diagnostic performance between version 2019 and version 2005. Materials and Methods From January 2009 to December 2018, consecutive patients with CRM who had undergone renal MRI and surgical-pathologic examination were included in this retrospective study. On the basis of version 2019 and version 2005, all CRMs were independently classified by eight radiologists with different levels of experience. By using multirater κ statistics, interobserver agreement was evaluated with comparisons between classifications and between senior and junior radiologists. Diagnostic performance between classifications by dichotomizing classes I-IV into lower (I-IIF) and higher (III-IV) classes was compared by using the McNemar test.
< .05 was considered to indicate a statistically significant difference. Results A total of 207 patients (mean age ± standard deviation, 49 years ± 12; 139 male and 68 female patients) with CRMs were included. Overall, interobserver agreement was higher with version 2019 than version 2005 (weighted κ = 0.64 vs 0.50, respectively;
< .001). Interobserver agreement between senior and junior radiologists did not differ between version 2019 (weighted κ = 0.65 vs 0.64, respectively;
= .71) and version 2005 (weighted κ = 0.54 vs 0.46;
< .001). Diagnostic specificity for malignancy was higher with version 2019 than with version 2005 (83% 92 of 111 vs 68% 75 of 111, respectively;
< .001), without any difference in sensitivity (89% 85 of 96 vs 84% 81 of 96;
= .34). Conclusion In the updated Bosniak classification, interobserver agreement improved and was unaffected by observers' experience. The diagnostic performance with version 2019 was superior to that with version 2005, with higher specificity. Published under a CC BY 4.0 license.
See also the editorial by Choyke in this issue.
Abstract
This article establishes the global existence and regularity for a system of the two-dimensional (2D) magnetohydrodynamic (MHD) equations with only directional hyper-resistivity. More ...precisely, the equation of $b_1$ (the horizontal component of the magnetic field) involves only vertical hyperdiffusion (given by $\Lambda_2^{2\beta} b_1$) while the equation of $b_2$ (the vertical component) has only horizontal hyperdiffusion (given by $\Lambda_1^{2\beta} b_2$), where $\Lambda_1$ and $\Lambda_2$ are directional Fourier multiplier operators with the symbols being $|\xi_1|$ and $|\xi_2|$, respectively. We prove that, for $\beta>1$, this system always possesses a unique global-in-time classical solution when the initial data is sufficiently smooth. The model concerned here is rooted in the MHD equations with only magnetic diffusion, which play a significant role in the study of magnetic reconnection and magnetic turbulence. In certain physical regimes and under suitable scaling, the magnetic diffusion becomes partial (given by part of the Laplacian operator). There have been considerable recent developments on the fundamental issue of whether classical solutions of these equations remain smooth for all time. The papers of Cao–Wu–Yuan 8 and of Jiu–Zhao 26 obtained the global regularity when the magnetic diffusion is given by the full fractional Laplacian $(-\Delta)^\beta$ with $\beta>1$. The main result presented in this article requires only directional fractional diffusion and yet we prove the regularization in all directions. The proof makes use of a key observation on the structure of the nonlinearity in the MHD equations and technical tools on Fourier multiplier operators such as the Hörmander–Mikhlin multiplier theorem. The result presented here appears to be the sharpest for the 2D MHD equations with partial magnetic diffusion.
This paper focuses on a system of the 2D magnetohydrodynamic (MHD) equations with the kinematic dissipation given by the fractional operator
(
-
Δ
)
α
and the magnetic diffusion by partial Laplacian. ...We are able to show that this system with any
α
>
0
always possesses a unique global smooth solution when the initial data is sufficiently smooth. In addition, we make a detailed study on the large-time behavior of these smooth solutions and obtain optimal large-time decay rates. Since the magnetic diffusion is only partial here, some classical tools such as the maximal regularity property for the 2D heat operator can no longer be applied. A key observation on the structure of the MHD equations allows us to get around the difficulties due to the lack of full Laplacian magnetic diffusion. The results presented here are the sharpest on the global regularity problem for the 2D MHD equations with only partial magnetic diffusion.
Inspired by the successful synthesis of Fe/Cu-5,5′-bis(4-pyridyl)(2,2′-bipirimidine) (PBP), a family of two-dimensional (2D) metal-organic frameworks (MOFs) with the Shastry-Sutherland lattice,
i.e.
..., transition metal (TM)-PBP (TM = Cr, Mn, Fe, Co, Ni, Cu, Zn) has been systematically investigated by means of first-principles density functional theory calculations and Monte Carlo simulations. Mn-PBP is discovered to be the first ferromagnetic 2D MOF with the Shastry-Sutherland lattice and the Curie temperature is predicted to be about 105 K, while Fe-PBP, TM-PBP (TM = Cr, Co, Ni) and TM-PBP (TM = Cu, Zn) are found to be stripe-order antiferromagnetic, magnetic-dimerized and nonmagnetic, respectively. The electronic structure calculations reveal that TM-PBP MOFs are semiconductors with band gaps ranging from 0.12 eV to 0.85 eV, which could be easily modulated by various methods. Particularly, Mn-PBP would exhibit half-metallic behavior under compressive strain or appropriate electron/hole doping and a Mn-PBP based spintronic device has been proposed. This study not only improves the understanding of the geometric, electronic and magnetic properties of the 2D TM-PBP MOF family, but also provides a novel spin lattice playground for the research of 2D magnetic systems, which has diverse modulating possibilities and rich potential applications.
Mn-PBP is discovered to be the first ferromagnetic 2D MOF with the Shastry-Sutherland lattice and the predicted Curie temperature is 105 K.
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