Using density functional theory combined with a semiempirical van der Waals dispersion correction, we have investigated the stability of lattice defects including boron vacancy, substitutional and ...interstitial X (X = H, C, B, N, O), and Σ5 tilt grain boundaries in borophene and their influence on the anisotropic mechanical properties of this two-dimensional system. The pristine borophene has significant in-plane Young’s moduli and Poisson’s ratio anisotropy due to its strong and highly coordinated B–B bonds. The concentration of B vacancy and Σ5 grain boundaries could be rather high given that their formation energies are as low as 0.10 and 0.06 eV/Å, respectively. In addition, our results also suggest that borophene can react easily with H2, O2, and N2 when exposed to these molecules. We find that the mechanical strength of borophene is remarkably reduced by these defects. The anisotropy in Poisson’s ratio, however, can be tuned by some of them. Furthermore, the adsorbed H or substitutional C may induce negative Poisson’s ratio in borophene, and the substitutional C or N can significantly increase the Poisson’s ratio by constrast.
Native point defects in few-layer phosphorene Wang, V.; Kawazoe, Y.; Geng, W. T.
Physical review. B, Condensed matter and materials physics,
01/2015, Letnik:
91, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Using hybrid density functional theory combined with a semiempirical van der Waals dispersion correction, we have investigated the structural and electronic properties of vacancies and ...self-interstitials in defective few-layer phosphorene. We find that both a vacancy and a self-interstitial defect are more stable in the outer layer than in the inner layer. The formation energy and transition energy of both a vacancy and a self-interstitial P defect decrease with increasing film thickness, mainly due to the upward shift of the host valence band maximum in reference to the vacuum level. Consequently, both vacancies and self-interstitials could act as shallow acceptors, and this well explains the experimentally observed p-type conductivity in few-layer phosphorene. On the other hand, since these native point defects have moderate formation energies and are stable in negatively charged states, they could also serve as electron compensating centers in n-type few-layer phosphorene.
Background
Health‐related quality of life (HRQL) is an important outcome measure in studies of cancer therapy. This study aimed to investigate HRQL and survival in patients with small hepatocellular ...carcinoma (HCC) treated with either surgical resection or percutaneous radiofrequency ablation (RFA).
Methods
Between January 2006 and June 2009, patients with newly diagnosed solitary, small (3 cm or less) HCC were invited to participate in this non‐randomized prospective parallel cohort study. The Functional Assessment of Cancer Therapy – Hepatobiliary (FACT‐Hep) instrument was used for assessing HRQL. HRQL and survival were compared between the two treatment groups.
Results
A total of 389 patients were enrolled. Questionnaires were completed fully by 99·7 per cent of invited participants (388 of 389) at baseline, 98·7 per cent (383 of 388) at 3 months, 99·0 per cent (379 of 383) at 6 months, 98·4 per cent (365 of 371) at 1 year, 96·6 per cent (336 of 348) at 2 years and 95·1 per cent (289 of 304) at 3 years. There were no significant differences in disease‐free and overall survival between the two groups. Patients treated with percutaneous RFA had significantly better HRQL total scores after 3, 6, 12, 24 and 36 months than those who had surgical resection (P < 0·001, P < 0·001, P = 0·001, P = 0·003 and P = 0·025 respectively). On multivariable analysis, the presence of concomitant disease, cirrhosis and surgical resection were significant risk factors associated with a worse HRQL score after treatment.
Conclusion
Percutaneous RFA produced better post‐treatment HRQL than surgical resection for patients with solitary small (no more than 3 cm) HCC.
Radiofrequency ablation is a good alternative for surgery
Hydrogen-Enhanced Vacancy Diffusion in Metals Du, Jun-Ping; Geng, W. T; Arakawa, Kazuto ...
The journal of physical chemistry letters,
09/2020, Letnik:
11, Številka:
17
Journal Article
Recenzirano
Odprti dostop
Vacancy diffusion is fundamental to materials science. Hydrogen atoms bind strongly to vacancies and are often believed to retard vacancy diffusion. Here, we use a potential-of-mean-force method to ...study the diffusion of vacancies in Cu and Pd. We find H atoms, instead of dragging, enhance the diffusivity of vacancies due to a positive hydrogen Gibbs excess at the saddle-point: that is, the migration saddle attracts more H than the vacancy ground state, characterized by an activation excess ΓH m ≈ 1 H, together with also-positive migration activation volume Ωm and activation entropy S m. Thus, according to the Gibbs adsorption isotherm generalized to the activation path, a higher μH significantly lowers the migration free-energy barrier. This is verified by ab initio grand canonical Monte Carlo simulations and direct molecular dynamics simulations. This trend is believed to be generic for migrating dislocations, grain boundaries, and so on that also have a higher capacity for attracting H atoms due to a positive activation volume at the migration saddles.
A topological meron features a non-coplanar structure, whose order parameters in the core region are perpendicular to those near the perimeter. A meron is half of a skyrmion, and both have potential ...applications for information carrying and storage. Although merons and skyrmions in ferromagnetic materials can be readily obtained via inter-spin interactions, their behaviour and even existence in ferroelectric materials are still elusive. Here we observe using electron microscopy not only the atomic morphology of merons with a topological charge of 1/2, but also a periodic meron lattice in ultrathin PbTiO
films under tensile epitaxial strain on a SmScO
substrate. Phase-field simulations rationalize the formation of merons for which an epitaxial strain, as a single alterable parameter, plays a critical role in the coupling of lattice and charge. This study suggests that by engineering strain at the nanoscale it should be possible to fabricate topological polar textures, which in turn could facilitate the development of nanoscale ferroelectric devices.
To have a fully first-principles description of the moiré pattern in transition-metal dichalcogenide heterobilayers, we have carried out density functional theory calculations on a MoTe2(9 × ...9)/MoS2(10 × 10) stacking, which has a superlattice larger than an exciton yet not large enough to justify a continuum model treatment. Lattice corrugation is found to be significant in both monolayers, yet its effect on the electronic properties is marginal. We reveal that the variation of the average local potential near Mo atoms in both MoTe2 and MoS2 layers displays a conspicuous moiré pattern. They are the intralayer moiré potentials correlating closely with the spatial variation of the valence band maximum and conduction band minimum. The interlayer moiré potential, defined as the difference between the two intralayer moiré potentials, changes roughly in proportion to the band gap variation in the moiré cell. This finding might be instructive in chemical engineering of van der Waals bilayers.
We report a first-principles density functional theory study on the role of grain boundary and dislocation loop in H blistering in W. At low temperature, the Σ3(111) tilt grain boundary can trap up ...to six H atoms per (1×1) unit in (111) plane before significant sliding occurs. This amount of H weakens greatly the cohesion across the boundary. At room temperature, when only three H can be trapped, this effect can be still significant. A dislocation loop in (100) plane can trap four H per (1×1) unit even at room temperature, whose detrimental effect is strong enough to break the crystal. Our numerical results demonstrate unambiguously the grain boundaries and dislocation loops can serve as precursors of H blistering. In addition, we find no H2 molecules can be formed in either environment before fracture of W bonds starts, well explaining the H blistering in the absence of voids during non-damaging irradiation.
We report a first-principles study on the initial deposition of Li2O2 on three rutile oxide surfaces, RuO2(110)-(1×1)-O, TiO2(110), and SnO2(110). The intermediate discharge product in a Li–air ...battery, LiO2, is found to be less stable on all rutile surfaces and will be further reduced to Li2O2 through disproportionation reaction. For the first and second layers of deposited Li2O2, the adsorption energy is comparable to the cohesive energy of bulk Li2O2, suggesting Li2O2 will likely wet the oxide surfaces and grow into thin films rather than particles. Electronic structure analyses of interfaces demonstrate Li2O2/TiO2(110) is metallic and Li2O2/SnO2(110) is semiconducting with a bandgap of 0.2 eV, substantially smaller than in bulk Li2O2. The large lattice mismatch at these interfaces could create amorphousness of Li2O2 and grain boundaries might form abundantly thereafter, both of which can provide charge and ion transport channels needed for oxygen reduction and evolution reactions in Li–air batteries. Therefore, coating nanostructured carbon cathode with thin films of TiO2 or employing mesoporous TiO2 nanostructures as cathode could possibly lead to the formation of low-resistance Li2O2 thin films and thereby enhance the rate capacity of Li–air batteries.
Genetic polymorphisms of CYP2C9 significantly influence the pharmacokinetics and pharmacodynamics of some drugs, which might result in adverse drug effects and therapeutic failure. Several studies ...have been performed on CYP2C9 genetic polymorphisms in Han Chinese populations. However, these studies only focused on two commonly investigated alleles, *2 and *3, in relatively small sample sizes. To scale up the gene-scanning region and determine relatively precise data on the genetic distribution pattern in Chinese populations, unrelated healthy Han Chinese volunteers from Zhejiang Province (n=1127) and Hebei (n=1000) Province were recruited as subjects for the direct sequencing of all exons of CYP2C9. As a result, 14 previously reported alleles were detected in this work, and 8 of these alleles (*14, *16, *19, *23, *27, *29, *33 and *34) were described for the first time in Chinese populations. In addition, 37 novel mutations were also detected, of which 22 variants were non-synonymous, and 21 new alleles, *36-*56, were designated by the Human CYP Allele Nomenclature Committee. In vitro functional analysis of these 22 novel CYP2C9 variants revealed that 17 mutations had a significant influence on the protein's catalytic activity. Our study provides the most accurate data on CYP2C9 polymorphisms in Han Chinese populations and detects the largest number of novel allelic variants existing to date. These new alleles will greatly enrich the current knowledge of naturally occurring CYP2C9 variants in Chinese populations.
In order to find good candidate materials for degradable fracturing ball applications, the microstructure, mechanical behavior and corrosion properties of as‐cast Mg‐17Al‐3Zn‐xCu alloys were ...investigated using optical microscope, scanning electronic microscope equipped with energy dispersive spectroscope, compression tests, electrochemical measurements, and immersion tests. The results show that Cu addition affects not only the amount but also the morphology and distribution of T‐phases. The distribution of Al also has a large dependence on Cu concentration. These modifications of the microstructures accordingly affect the mechanical and corrosion properties of the investigated alloys. Mg‐17Al‐3Zn‐5Cu alloy can be used as degradable fracturing ball.
PDF
