Large-Area Near-Infrared Emission Enhancement on Single Upconversion Nanoparticles by Metal Nanohole Array.

Single lanthanide (Ln) ion doped upconversion nanoparticles (UCNPs) exhibit great potential for biomolecule sensing and counting. Plasmonic structures can improve the emission efficiency of single UCNPs by modulating the energy transferring process. Yet, achieving robust and large-area single UCNP emission modulation remains a challenge, which obstructs investigation and application of single UCNPs. Here, we present a strategy using metal nanohole arrays (NHAs) to achieve energy-transfer modulation on single UCNPs simultaneously within large-area plasmonic structures. By coupling surface plasmon polaritons (SPPs) with higher-intermediate state (1D2 → 3F3, 1D2 → 3H4) transitions, we achieved a remarkable up to 10-fold enhancement in 800 nm emission, surpassing the conventional approach of coupling SPPs with an intermediate ground state (3H4 → 3H6). We numerically simulate the electrical field distribution and reveal that luminescent enhancement is robust and insensitive to the exact location of particles. It is anticipated that the strategy provides a platform for widely exploring applications in single-particle quantitative biosensing.

Electronic Flat Band in Distorted Colouring Triangle Lattice.

Dispersionless flat bands (FBs) in momentum space, given rise to electron destructive interference in frustrated lattices, offer opportunities to enhance electronic correlations and host exotic many-body phenomena, such as Wigner crystal, fractional quantum hall state, and superconductivity. Despite successes in theory, great challenges remain in experimentally realizing FBs in frustrated lattices due to thermodynamically structural instability. Here, the observation of electronic FB in a potassium distorted colouring triangle (DCT) lattice is reported, which is supported on a blue phosphorene-gold network. It is verified that the interaction between potassium and the underlayer dominates and stabilizes the frustrated structures. Two-dimensional electron gas is modulated by the DCT lattice, and in turn results in a FB dispersion due to destructive quantum interferences. The FB exhibits suppressed bandwidth with high density of states, which is directly observed by scanning tunneling microscopy and confirmed by the first-principles calculation. This work demonstrates that DCT lattice is a promising platform to study FB physics and explore exotic phenomena of correlation and topological matters.

Development and validation of a radiomics-based nomogram for the preoperative prediction of microsatellite instability in colorectal cancer.

BACKGROUND: Preoperative prediction of microsatellite instability (MSI) status in colorectal cancer (CRC) patients is of great significance for clinicians to perform further treatment strategies and prognostic evaluation. Our aims were to develop and validate a non-invasive, cost-effective reproducible and individualized clinic-radiomics nomogram method for preoperative MSI status prediction based on contrast-enhanced CT (CECT)images. METHODS: A total of 76 MSI CRC patients and 200 microsatellite stability (MSS) CRC patients with pathologically confirmed (194 in the training set and 82 in the validation set) were identified and enrolled in our retrospective study. We included six significant clinical risk factors and four qualitative imaging data extracted from CECT images to build the clinics model. We applied the intra-and inter-class correlation coefficient (ICC), minimal-redundancy-maximal-relevance (mRMR) and the least absolute shrinkage and selection operator (LASSO) for feature reduction and selection. The selected independent prediction clinical risk factors, qualitative imaging data and radiomics features were performed to develop a predictive nomogram model for MSI status on the basis of multivariable logistic regression by tenfold cross-validation. The area under the receiver operating characteristic (ROC) curve (AUC), calibration plots and Hosmer-Lemeshow test were performed to assess the nomogram model. Finally, decision curve analysis (DCA) was performed to determine the clinical utility of the nomogram model by quantifying the net benefits of threshold probabilities. RESULTS: Twelve top-ranked radiomics features, three clinical risk factors (location, WBC and histological grade) and CT-reported IFS were finally selected to construct the radiomics, clinics and combined clinic-radiomics nomogram model. The clinic-radiomics nomogram model with the highest AUC value of 0.87 (95% CI, 0.81-0.93) and 0.90 (95% CI, 0.83-0.96), as well as good calibration and clinical utility observed using the calibration plots and DCA in the training and validation sets respectively, was regarded as the candidate model for identification of MSI status in CRC patients. CONCLUSION: The proposed clinic-radiomics nomogram model with a combination of clinical risk factors, qualitative imaging data and radiomics features can potentially be effective in the individualized preoperative prediction of MSI status in CRC patients and may help performing further treatment strategies.

Strain Dependence of Energetics and Kinetics of Vacancy in Tungsten.

We investigate the influence of hydrostatic/biaxial strain on the formation, migration, and clustering of vacancy in tungsten (W) using a first-principles method, and show that the vacancy behaviors are strongly dependent on the strain. Both a monovacancy formation energy and a divacancy binding energy decrease with the increasing of compressive hydrostatic/biaxial strain, but increase with the increasing of tensile strain. Specifically, the binding energy of divacancy changes from negative to positive when the hydrostatic (biaxial) tensile strain is larger than 1.5% (2%). These results indicate that the compressive strain will facilitate the formation of monovacancy in W, while the tensile strain will enhance the attraction between vacancies. This can be attributed to the redistribution of electronic states of W atoms surrounding vacancy. Furthermore, although the migration energy of the monovacancy also exhibits a monotonic linear dependence on the hydrostatic strain, it shows a parabola with an opening down under the biaxial strain. Namely, the vacancy mobility will always be promoted by biaxial strain in W, almost independent of the sign of strain. Such unexpected anisotropic strain-enhanced vacancy mobility originates from the Poisson effect. On the basis of the first-principles results, the nucleation of vacancy clusters in strained W is further determined with the object kinetic Monte Carlo simulations. It is found that the formation time of tri-vacancy decrease significantly with the increasing of tensile strain, while the vacancy clusters are not observed in compressively strained W, indicating that the tensile strain can enhance the formation of voids. Our results provide a good reference for understanding the vacancy behaviors in W.

COVID-19 with acute cholecystitis: a case report.

BACKGROUND: The 2019 novel coronavirus (COVID-19) presents a major threat to public health and has rapidly spread worldwide since the outbreak in Wuhan, Hubei Province, China in 2019. To date, there have been few reports of the varying degrees of illness caused by the COVID-19. CASE PRESENTATION: A case of 68-year-old female with COVID-19 pneumonia who had constant pain in the right upper quadrant of her abdomen during her hospitalization that was finally diagnosed as acute cholecystitis. Ultrasound-guided percutaneous transhepatic gallbladder drainage (PTGD) was performed, and the real-time fluorescence polymerase chain reaction (RT-PCR) COVID-19 nucleic acid assay of the bile was found to be negative. PTGD, antibacterial and anti-virus combined with interferon inhalation treatment were successful. CONCLUSION: The time course of chest CT findings is typical for COVID-19 pneumonia. PTGD is useful for acute cholecystitis in COVID-19 patients. Acute cholecystitis is likely to be caused by COVID-19 .

Twin and dislocation mechanisms in tensile W single crystal with temperature change: a molecular dynamics study.

Molecular dynamics simulations are performed to investigate the orientation and temperature dependence of tensile response in single crystal W. It is found that W single crystal exhibits distinct temperature-dependent deformation behaviors along different orientations. With increasing temperature, the yield strain in the [001] orientation increases, while those in [110] and [111] orientations first increase and then decrease. The tensile deformations along orientations close to [001] are found to be dominated by twinning; the nucleation and growth of twins are accomplished through the nucleation and glide of ⅙111 partial dislocations on {112} planes. In contrast, the deformations along orientations close to [110] and [111] are found to be dominated by the slip of ½111 full dislocations, which move in a stay-and-go fashion. Moreover, intermediate deformation behaviors, which may become unstable at high temperatures, are observed for some intervening orientations. The distinct deformation behaviors of W along different orientations are rationalized based on the twinning-antitwinning asymmetry of ⅙111 partial dislocations on {112} planes.

Halogen-Adatom Mediated Phase Transition of Two-Dimensional Molecular Self-Assembly on a Metal Surface.

Construction of tunable and robust two-dimensional (2D) molecular arrays with desirable lattices and functionalities over a macroscopic scale relies on spontaneous and reversible noncovalent interactions between suitable molecules as building blocks. Halogen bonding, with active tunability of direction, strength, and length, is ideal for tailoring supramolecular structures. Herein, by combining low-temperature scanning tunneling microscopy and systematic first-principles calculations, we demonstrate novel halogen bonding involving single halogen atoms and phase engineering in 2D molecular self-assembly. On the Au(111) surface, we observed catalyzed dehalogenation of hexabromobenzene (HBB) molecules, during which negatively charged bromine adatoms (Brδ-) were generated and participated in assembly via unique C-Brδ+···Brδ- interaction, drastically different from HBB assembly on a chemically inert graphene substrate. We successfully mapped out different phases of the assembled superstructure, including densely packed hexagonal, tetragonal, dimer chain, and expanded hexagonal lattices at room temperature, 60 °C, 90 °C, and 110 °C, respectively, and the critical role of Brδ- in regulating lattice characteristics was highlighted. Our results show promise for manipulating the interplay between noncovalent interactions and catalytic reactions for future development of molecular nanoelectronics and 2D crystal engineering.

Embedded-atom method potential for modeling hydrogen and hydrogen-defect interaction in tungsten.

An embedded-atom method potential has been developed for modeling hydrogen in body-centered-cubic (bcc) tungsten by fitting to an extensive database of density functional theory (DFT) calculations. Comprehensive evaluations of the new potential are conducted by comparing various hydrogen properties with DFT calculations and available experimental data, as well as all the other tungsten-hydrogen potentials. The new potential accurately reproduces the point defect properties of hydrogen, the interaction among hydrogen atoms, the interplay between hydrogen and a monovacancy, and the thermal diffusion of hydrogen in tungsten. The successful validation of the new potential confirms its good reliability and transferability, which enables large-scale atomistic simulations of tungsten-hydrogen system. The new potential is afterward employed to investigate the interplay between hydrogen and other defects, including [1 1 1] self-interstitial atoms (SIAs) and vacancy clusters in tungsten. It is found that both the [1 1 1] SIAs and the vacancy clusters exhibit considerable attraction for hydrogen. Hydrogen solution and diffusion in strained tungsten are also studied using the present potential, which demonstrates that tensile (compressive) stress facilitates (impedes) hydrogen solution, and isotropic tensile (compressive) stress impedes (facilitates) hydrogen diffusion while anisotropic tensile (compressive) stress facilitates (impedes) hydrogen diffusion.

Energetics of vacancy segregation to [100] symmetric tilt grain boundaries in bcc tungsten.

The harsh irradiation environment poses serious threat to the structural integrity of leading candidate for plasma-facing materials, tungsten (W), in future nuclear fusion reactors. It is thus essential to understand the radiation-induced segregation of native defects and impurities to defect sinks, such as grain boundaries (GBs), by quantifying the segregation energetics. In this work, molecular statics simulations of a range of equilibrium and metastable [100] symmetric tilt GBs are carried out to explore the energetics of vacancy segregation. We show that the low-angle GBs have larger absorption length scales over their high-angle counterparts. Vacancy sites that are energetically unfavorable for segregation are found in all GBs. The magnitudes of minimum segregation energies for the equilibrium GBs vary from -2.61 eV to -0.76 eV depending on the GB character, while those for the metastable GB states tend to be much lower. The significance of vacancy delocalization in decreasing the vacancy segregation energies and facilitating GB migration has been discussed. Metrics such as GB energy and local stress are used to interpret the simulation results, and correlations between them have been established. This study contributes to the possible application of polycrystalline W under irradiation in advanced nuclear fusion reactors.

Energetic and kinetic dataset on interaction of the vacancy and self-interstitial atom with the grain boundary in α-iron.

We provide the dataset of the vacancy (interstitial) formation energy, segregation energy, diffusion barrier, vacancy-interstitial annihilation barrier near the grain boundary (GB) in bcc-iron and also the corresponding interactive range. The vacancy-interstitial annihilation mechanisms in the bulk, near the GB and at the GB at across scales were given.

Shear-coupled grain boundary migration assisted by unusual atomic shuffling.

Shear-coupled grain boundary (GB) migration can be an efficacious mechanism to accommodate plastic deformation when the grain size of polycrystalline materials goes small. Nevertheless, how this kind of GB motion comes into play at the atomic level has not been fully revealed. Here, we have investigated the shear-coupled migration (SCM) of typical [100] group symmetrical tilt GBs in bcc W using atomistic simulations. Depending on GB character, the SCM is found to proceed via dislocation slipping in the 〈100〉 or 〈110〉 mode with striking shear strength difference between them. We demonstrate that there exists an unusual atomic shuffling along the tilt axis, which greatly assists SCM to operate in the easier 〈110〉 mode instead of the 〈100〉 one. The present results highlight the significant role of GB character in the atomistic SCM process and contribute to the future design and fabrication of high-performance materials in GB engineering.

Interplay between intrinsic point defects and low-angle grain boundary in bcc tungsten: effects of local stress field.

We have used molecular statics in conjunction with an embedded atom method to explore the interplay between native point defects (vacancies and self-interstitials (SIAs)) and a low-angle grain boundary (GB) in bcc tungsten. The low-angle GB has biased absorption of SIAs over vacancies. We emphasize the significance of phenomena such as vacancy delocalization and SIA instant absorption around the GB dislocation cores in stabilizing the defect structures. Interstitial loading into the GB can dramatically enhance the interaction strength between the point defects and the GB due to SIA clustering (SIA cloud formation) or SIA vacancy recombination. We propose that the 'maximum atom displacement' can complement the 'vacancy formation energy' in evaluating unstable vacancy sites. Calculations of point defect migration barriers in the vicinity of GB dislocation cores show that vacancies and SIAs preferentially migrate along the pathways in the planes immediately above and below the core, respectively.

Critical concentration for hydrogen bubble formation in metals.

Employing a thermodynamic model with previously calculated first-principle energetics as inputs, we determined the hydrogen (H) concentration at the interstitial and monovacancy as well as its dependence on temperature and pressure in tungsten and molybdenum. Based on this, we predicted the critical H concentration for H bubble formation at different temperatures. The critical concentration, defined as the value when the concentration of H at a certain mH-vacancy complex first became equal to that of H at the interstitial, was 24 ppm/7.3 GPa and 410 ppm/4.7 GPa at 600 K in tungsten and molybdenum in the case of a monovacancy. Beyond the critical H concentration, numerous H atoms accumulated in the monovacancy, leading to the formation and rapid growth of H-vacancy complexes, which was considered the preliminary stage of H bubble formation. We expect that the proposed approach will be generally used to determine the critical H concentration for H bubble formation in metals.

Characterization of iron ferromagnetism by the local atomic volume: from three-dimensional structures to isolated atoms.

We present a comprehensive study of the relationship between the ferromagnetism and the structural properties of Fe systems from three-dimensional ones to isolated atoms based on the spin-density functional theory. We have found a relation between the magnetic moment and the volume of the Voronoi polyhedron, determining, in most cases, the value of the total magnetic moment as a function of this volume with an average accuracy of ±0.28 µ(B) and of the 3d magnetic moment with an average accuracy of ±0.07 µ(B) when the atomic volume is larger than 22 ų. It is demonstrated that this approach is applicable for many three-dimensional systems, including high-symmetry structures of perfect body-centered cubic (bcc), face-centered cubic (fcc), hexagonal close-packed (hcp), double hexagonal close-packed (dhcp), and simple cubic (sc) crystals, as well as for lower-symmetry ones, for example atoms near a grain boundary (GB) or a surface, around a vacancy or in a linear chain (for low-dimensional cases, we provide a generalized definition of the Voronoi polyhedron). Also, we extend the validity of the Stoner model to low-dimensional structures, such as atomic chains, free-standing monolayers and surfaces, determining the Stoner parameter for these systems. The ratio of the 3d-exchange splitting to the magnetic moment, corresponding to the Stoner parameter, is found to be I(3d) = (0.998 ± 0.006) eV /µ(B) for magnetic moments up to 3.0 µ(B). Further, the 3d exchange splitting changes nearly linearly in the region of higher magnetic moments (3.0-4.0 µ(B)) and the corresponding Stoner exchange parameter equals I(h)(3d) = (0.272 ± 0.006) eV /µ(B). The existence of these two regions reflects the fact that, with increasing Voronoi volume, the 3d bands separate first and, consequently, the 3d magnetic moment increases. When the Voronoi volume is sufficiently large (≥22 ų), the separation of the 3d bands is complete and the magnetic moment reaches a value of 3.0 µ(B). Then, when the volume further increases, the 4s bands start to separate, increasing thus the 4s magnetic moment. Surprisingly, in the region of higher magnetic moments (≥3.0 µ(B)), there is also a linear relationship between the 4s exchange splitting and the total magnetic moment with a slope of I(h)(4s) = (1.053 ± 0.016) eV /µ(B), which is nearly identical to I(3d) for magnetic moments up to 3.0 µB. These linear relations can be considered as an extension of the Stoner model for low-dimensional systems.

Structure and stability of He and He-vacancy clusters at a Σ5(310)/[001] grain boundary in bcc Fe from first-principles.

We have studied the atomic structure and energetic stability of helium (He) and He-vacancy clusters in an iron (Fe) Σ5(310)/[001] grain boundary (GB) using a first-principles method. The He and He-vacancy clusters in the Fe GB are shown to exhibit high-symmetry structures. The equilibrium He-He distance in the clusters is ~1.70 Å, much smaller than 2.80 Å in the vacuum or 2.94 Å in a face centred cubic (fcc) crystal, indicating the attractive interaction between the He atoms due to the presence of Fe. The charge density surrounding He is demonstrated to decrease with an increasing number of He atoms in the clusters, leading to a positive binding energy of a He atom to the clusters. This suggests He and He-vacancy clusters can energetically trap more He atoms, which is responsible for the growth of the He-related clusters (He and He-vacancy clusters) and thus the He bubbles in the GB. The binding energy of an interstitial He atom to the He-related clusters is found generally lower in the GB than in a bcc crystal. Besides, the binding strengths of small He clusters to the GB and to a vacancy in a bcc matrix are compared, and the latter shows greater trapping strength to an interstitial He and a He(2) cluster. The magnetism of the Fe atoms near the GB as well as its variation caused by the He-related clusters is also investigated. The local magnetic moment variation of the Fe atoms in the system is enhanced to a different extent, depending on the size of the He-related clusters.

Anisotropic strain enhanced hydrogen solubility in bcc metals: the independence on the sign of strain.

When an impurity is doped in a solid, it inevitably induces a local stress, tending to expand or contract the lattice. Consequently, strain can be applied to change the solubility of impurity in a solid. Generally, the solubility responds to strain "monotonically," increasing (decreasing) with the tensile (compressive) strain if the impurity induces a compressive stress or vice versa. Using first-principles calculations, however, we discovered that the H solubility can be enhanced by anisotropic strain in some bcc metals, almost independent of the sign of strain. This anomalous behavior is found to be caused by a continuous change of H location induced by anisotropic strain. Our finding suggests a cascading effect of H bubble formation in bcc metals: the H solution leads to H bubble formation that induces anisotropic strain that in turn enhances H solubility to further facilitate bubble growth.

Effects of O in a binary-phase TiAl-Ti3Al alloy: from site occupancy to interfacial energetics.

We have investigated site occupancy and interfacial energetics of a TiAl-Ti(3)Al binary-phase system with O using a first-principles method. Oxygen is shown to energetically occupy the Ti-rich octahedral interstitial site, because O prefers to bond with Ti rather than Al. The occupancy tendency of O in TiAl alloy from high to low is α(2)-Ti(3)Al to the γ-α(2) interface and γ-TiAl. We demonstrate that O can largely affect the mechanical properties of the TiAl-Ti(3)Al system. Oxygen at the TiAl-Ti(3)Al interface reduces both the cleavage energy and the interface energy, and thus weakens the interface strength but strongly stabilizes the TiAl/Ti(3)Al interface with the O(2) molecule as a reference. Consequently, the mechanical property variation of TiAl alloy due to the presence of O not only depends on the number of TiAl/Ti(3)Al interfaces but also is related to the O concentration in the alloy.

Dissolution, diffusion and permeation behavior of hydrogen in vanadium: a first-principles investigation.

Employing a first-principles method, we have studied the stability, diffusivity, and permeation properties of hydrogen (H) and its isotopes in bcc vanadium (V). A single H atom is found to favor the tetrahedral interstitial site (TIS) in V. The charge density distribution exhibits a strong interaction between H and its neighbor V atoms. Analysis of DOS and Bader charge reveals that the occupation number of H-induced low energy states is directly associated with the stability of H in V. Further, H is shown to diffuse between the neighboring TISs with a diffusion barrier of 0.07 eV. Diffusion coefficients and permeabilities of H isotopes in V are estimated with empirical theory. At a typical temperature of 800 K, the diffusion coefficient and the permeability of H are 2.48 × 10(-4) cm(2) s(-1) and 2.19 × 10(-9) mol m(-1) s(-1) Pa(- 1/2), respectively.

Energy investigation of effects of O on mechanical properties of NiAl intermetallics.

We have investigated effects of O on mechanical properties of NiAl by calculating the cleavage energy (γ(C)) and the unstable stacking fault energy (γ(us)) using a first-principles method. O is shown to reduce γ(C)/γ(us) for the [001](110) and [100](001) slip systems, indicating that the presence of O should be associated with the ductility reduction of NiAl. Further, γ(C)/γ(us) of the NiAl-O system can be increased by Cr, suggesting the possibility to suppress the negative effect of O via alloying elements.

First-principles study of He effects in a bcc Fe grain boundary: site preference, segregation and theoretical tensile strength.

We perform a first-principles calculation to investigate the effects of He in an Fe Σ5(310)/[001] grain boundary (GB) with the SIESTA code, for which the reliability of the pseudopotential and the basis set are systematically tested. We calculate the formation and segregation energies for different substitutional and interstitial cases in order to determine the site preference and the segregation properties of He in the Fe GB. It is demonstrated that the He segregation either breaks (substitution) or weakens (interstitial) the surrounding interfacial Fe-Fe bonds, leading to the GB tensile strength reduction.