664 research outputs found
Anisotropic intrinsic lattice thermal conductivity of phosphorene from first principles
Phosphorene, the single layer counterpart of black phosphorus, is a novel
two-dimensional semiconductor with high carrier mobility and a large
fundamental direct band gap, which has attracted tremendous interest recently.
Its potential applications in nano-electronics and thermoelectrics call for a
fundamental study of the phonon transport. Here, we calculate the intrinsic
lattice thermal conductivity of phosphorene by solving the phonon Boltzmann
transport equation (BTE) based on first-principles calculations. The thermal
conductivity of phosphorene at is
(zigzag) and
(armchair), showing an obvious anisotropy along different directions. The
calculated thermal conductivity fits perfectly to the inverse relation with
temperature when the temperature is higher than Debye temperature (). In comparison to graphene, the minor contribution around
of the ZA mode is responsible for the low thermal conductivity of
phosphorene. In addition, the representative mean free path (MFP), a critical
size for phonon transport, is also obtained.Comment: 5 pages and 6 figures, Supplemental Material available as
http://www.rsc.org/suppdata/cp/c4/c4cp04858j/c4cp04858j1.pd
Diverse anisotropy of phonon transport in two-dimensional IV-VI compounds: A comparative study
New classes 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 property is one of
the fundamental physical parameters. In this paper, we systematically
investigated the phonon transport properties of 2D orthorhombic group IV-VI
compounds of , , and by solving the Boltzmann transport
equation (BTE) based on first-principles calculations. Despite the 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 (), etc. Especially, the along the zigzag and
armchair directions of monolayer shows the strongest anisotropy while
monolayer and shows an almost isotropy in phonon transport. The
origin of the diverse anisotropy is fully studied and the underlying mechanism
is discussed in detail. With limited size, the could be effectively
lowered, and the anisotropy could be effectively modulated by nanostructuring,
which would extend the applications in 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 aplications in emerging technologies.Comment: 14 pages, 8 figures, 2 table
Topological superconductor candidates PdBiTe and PdBiTe from a generic ab initio strategy
Superconducting topological metals (SCTMs) have recently emerged as a
promising platform of topological superconductivity (TSC) and Majorana zero
modes(MZMs) for quantum computation. Despite their importance in both
fundamental research and applications, SCTMs are very rare in nature. In
addition, some superconductors with topological electronic structures have been
reported recently, but a feasible program to determine their TSC properties is
still lacking. Here, we propose a new strategy to design SCTMs by intercalating
the superconducting units into the topological insulators. A program that
characterizes the superconducting BdG Chern number of 2D BdG Hamiltonian from
ab initio calculations is also developed. Following this strategy,
PdBiTe and PdBiTe are found to be experimentally synthesizable
and ideal SCTMs. Chiral TSC could be realized in such SCTMs by incorporating
topological surface states with Zeeman effect, which can be realized by an
external magnetic field or in proximity to ferromagnetic (FM) insulator. Our
strategy provides a new method for identifying the SCTMs and TSC candidates,
and the program makes it possible to design and modulate the TSC candidates
from ab initio calculations
Numerical Simulation of Soil Water Movement under Subsurface Irrigation
By constructing a radial basis function collocation method combined with a difference method, a two-dimensional mathematical model with boundary conditions of soil water movement under irrigation is proposed. The nonlinear term is dealt with a difference method and the equation is solved using an implicit scheme. In addition, the existence and uniqueness of the solution to the soil water movement equation are proven. Numerical results show that the proposed method has high precision and is easier to use than traditional methods. Moreover, the selection of parameter c plays an important role in guaranteeing calculation precision. It lays the foundation for the numerical solutions to high-dimensional soil water movement equations
Clinical Value of Spectral Imaging Combined with MAR for CTA after Embolization of Intracranial Aneurysms
Objective: To evaluate the application value of combining spectral imaging and metal artifact reduction (MAR) in head and neck CTA after the embolization of intracranial aneurysms. Methods: We collected 37 patients who experienced embolization of intracranial aneurysms then received spectral imaging of head and neck CTA. Monochromatic images with energy ranging from 70~140 keV, 120 kVp-like mixed energic images, 70~140 keV MAR images, and 120 kVp-like MAR images were generated. The region of interest was placed on the area near the coil and with the most serious metal artifact. CT attenuation and standard deviation were measured, and artifact index (AI) and signal-noise ratio (SNR) were calculated. Two radiologists independently subjectively evaluated the metal artifact and the display of surrounding vessels using Likert 5 scales. The subjective scores and objective parameters between MAR and non-MAR images were compared. The Wilcoxon ranking test, paired sample t test, and independent sample t test were utilized to compare parameters between the groups. Results: MAR images had significantly lower AI than did non-MAR images for all eight monochromatic energies. When energies ranged from 80~110 keV, SNR was higher for MAR images than for non-MAR images, and the difference was statistically significant. With same energies, MAR images had higher artifact and vessel display scores than did non-MAR images. For non-MAR images, the different coil diameters did not make a statistical difference in AI and vessel display scores. For MAR images, a larger coil diameter (>8.79 mm) led to higher AI and lower vessel display scores than did normal diameters (≤8.79 mm). Conclusion: The combination of spectral imaging and MAR could effectively reduce the metal artifact of implants for the embolization of intracranial aneurysms and improve the surrounding vessel display. Moreover, the metal artifact reduction effect was more significant for the coils with smaller diameters
ECOLOGICAL CHARACTERISTICS AND SUITABILITY EVALUATION OF FRITILLARIA CIRRHOSA D. DON BASED ON MAXENT MODEL
Background: As a rare and endangered medicinal plant growing in plateaus, Fritillaria cirrhosa D. Don is a scant resource in terms of quantity and planting regions. However, there is limited knowledge on predicting the potential ecological suitability of regions for the species with the climate factors. This paper evaluates the ecological suitability of F. cirrhosa D. Don on a global scale using Maxent.
Materials and Methods: The ecologically suitable regions for F. cirrhosa D. Don around the world were evaluated using the maximum entropy model (Maxent), based on 127 known occurrence records and specific environmental predictor variables.
Results: The Maxent model was highly accurate, with a statistically significant Area Under the Receiving Operator Curve (AUC) value of 0.993, and the most suitable areas and the suitable areas for F. cirrhosa D. Don were approximately 450,000 and 700,000 sq. km., respectively, including China, Pakistan, Nepal, and Bhutan. A quantitative study of the climatic characteristics of F. cirrhosa D. Don indicated that the period from May to October was critical for plant growth and development. Thus, the stable precipitation-temperature ratios (0.59 to 2.42) during this period could serve as a feature indicator for the geographical distribution of the plant.
Conclusion: This work should be beneficial for the introduction and resource protection of F. cirrhosa D. Don, meanwhile, the analytical method could be expanded to predict the potential distribution of other medicinal plants
Sedimentation and geomorphology of the Ruoergai Basin outlet reach at the source of the Yellow River: Response to the late quaternary glacial debris flow damming events
Fluvial terraces in the source of the Yellow River suggest that Ruoergai Basin was connected with the lower reach after ∼10 ka, much younger than the uplift chronology of the Tibetan Plateau. In this study, the geomorphology and sedimentation of the Cairima–Ningmute River at the exit of the Ruoergai Basin were investigated. Combined with the optically stimulated luminescence dating of the sediments, the reconstructed fluvial geomorphology processes are as follows: During ∼50–20 ka, coarse debris such as moraines and glacial mudflows from the Anyemaqen Shan and Xiqing Shan were unloaded to the Maqu valley in the bottleneck reach of the Ruoergai Basin outflow, causing river blockage and lake formation in the upper Ruoergai Basin; during ∼20–12 ka, the headward erosion of the river accelerated from the downstream to the upstream and the barrier dam eroded, forming terraces; since ∼12 ka, the Yellow River has cut through the Ruoergai Basin and has developed two levels of terraces based on lacustrine sediments. Our results suggest that glacial debris flow from the Anyemaqen Shan extensively accumulated at the basin-canyon bottleneck during the last glacial period, and when the amount of sediment accumulation exceeded the amount of river erosion, damming events occurred. The glacial-interglacial cycles during the Quaternary might generate repeated damming and cut-through of the Ruoergai Basin. The Ruoergai Basin should be connected with the lower reach before ∼50 ka
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