Strong reduction of thermal conductivity of WSe2with introduction of atomic defects.

The thermal conductivities of pristine and defective single-layer tungsten diselenide (WSe2) are investigated by using equilibrium molecular dynamics method. The thermal conductivity of WSe2increases dramatically with size below a characteristic of ~5 nm and levels off for broader samples and reaches a constant value of ~2 W/mK. By introducing atomic vacancies, we discovered that the thermal conductivity of WSe2is significantly reduced. In particular, the W vacancy has a greater impact on thermal conductivity reduction than Se vacancies: the thermal conductivity of pristine WSe2is reduced by ~60% and ~70% with the adding of ~1% of Se and W vacancies, respectively. The reduction of thermal conductivity is found to be related to the decrease of mean free path (MFP) of phonons in the defective WSe2. The MFP of WSe2decreases from ~4.2 nm for perfect WSe2to ~2.2 nm with the addition of 0.9% Se vacancies. More sophisticated types of point defects, such as vacancy clusters and anti-site defects, are explored in addition to single vacancies and are found to dramatically renormalize the phonons. The reconstruction of the bonds leads to localized phonons in the forbidden gap in the phonon density of states which leads to a drop in thermal conduction. This work demonstrates the influence of different defects on the thermal conductivity of single-layer WSe2, providing insight into the process of defect-induced phonon transport as well as ways to improve heat dissipation in WSe2-based electronic devices.

Electronic and optical properties of Janus black arsenic-phosphorus AsP quantum dots under magnetic field.

By utilizing the tight-binding method, the electronic spectrum and states distribution of square Janus monolayer black arsenic phosphorus (b-AsP) quantum dots (QDs) in the presence of a perpendicular magnetic field are explored. Strong in-gap states of b-AsP QDs, whose probability densities are distributed on the armchair boundary (armchair edge states) appear in the energy gap of host perfect two-dimensional b-AsP. The corresponding energy levels of the armchair edge states can degenerate to the Landu energy levels upon applying a perpendicular magnetic field. When an in-plane polarized light is introduced, due to the presence of armchair edge states, the edge-to-edge transitions are mainly induced from the armchair edge (hole) states to zigzag edge (electron) states. The optical absorption undergoes blue shift as a function of the magnetic field. Our work suggests tunable optical properties via modulating the armchair edge states of a b-AsP QD and provides a theoretical basis for the design of b-AsP-based optoelectronic devices.

Promoted Electronic Coupling of Acoustic Phonon Modes in Doped Semimetallic MoTe2.

As a prototype of the Weyl superconductor, layered molybdenum ditelluride (MoTe2) encompasses two semimetallic phases (1T' and Td) which differentiate from each other via a slight tilting of the out-of-plane lattice. Both phases are subjected to serious phase mixing, which complicates the analysis of its origin of superconductivity. Herein, we explore the electron-phonon coupling (EPC) of the monolayer semimetallic MoTe2, without phase ambiguity under this thickness limit. Apart from the hardening or softening of the phonon modes, the strength of the EPC can be strongly modulated by doping. Specifically, longitudinal and out-of-plane acoustic modes are significantly activated for electron doped MoTe2. This is ascribed to the presence of rich valley states and equispaced nesting bands, which are dynamically populated under charge doping. Through comparing the monolayer and bilayer MoTe2, the strength of EPC is found to be less likely to depend on thickness for neutral samples but clearly promoted for thinner samples with electron doping, while for hole doping, the strength alters more significantly with the thickness than doping. Our work explains the issue of the doping sensitivity of the superconductivity in semimetallic MoTe2 and establishes the critical role of activating acoustic phonons in such low-dimensional materials.

Surface asymmetry induced turn-overed lifetime of acoustic phonons in monolayer MoSSe.

Recent successful growth of asymmetric transition metal dichalcogenides via accurate manipulation of different chalcogen atoms in top and bottom surfaces demonstrates exotic electronic and chemical properties in such Janus systems. Within the framework of density functional perturbation theory, anharmonic phonon properties of monolayer Janus MoSSe sheet are explored. By considering three-phonons scattering, out-of-plane flexural acoustic (ZA) mode tends to undergo a stronger phonon scattering than transverse acoustic (TA) mode and the longitudinal acoustic (LA) mode with phonon lifetime of ZA (1.0 ps) < LA (23.8 ps) < TA (25.8 ps). This is sharply different from the symmetric MoS2 where flexural ZA mode has the weakest anharmonicity and is least scattered. Moreover, utilizing non-equilibrium Green function method, ballistic thermal conductance at room temperature is found to be around 0.11 nWK-1nm-2, lower than that of MoS2. Our work highlights intriguing phononic properties of such MoSSe Janus layers associated with asymmetric surfaces.

A living biobank of matched pairs of patient-derived xenografts and organoids for cancer pharmacology.

Patient-derived tumor xenograft (PDX)/organoid (PDO), driven by cancer stem cells (CSC), are considered the most predictive models for translational oncology. Large PDX collections reflective of patient populations have been created and used extensively to test various investigational therapies, including population-trials as surrogate subjects in vivo. PDOs are recognized as in vitro surrogates for patients amenable for high-throughput screening (HTS). We have built a biobank of carcinoma PDX-derived organoids (PDXOs) by converting an existing PDX library and confirmed high degree of similarities between PDXOs and parental PDXs in genomics, histopathology and pharmacology, suggesting "biological equivalence or interchangeability" between the two. Here we demonstrate the applications of PDXO biobank for HTS "matrix" screening for both lead compounds and indications, immune cell co-cultures for immune-therapies and engineering enables in vitro/in vivo imaging. This large biobank of >550 matched pairs of PDXs/PDXOs across different cancers could become powerful tools for the future cancer drug discovery.

Multifactor effects on the N2O emissions and yield of potato fields based on the DNDC model.

Maintaining or increasing grain yields while also reducing the emissions of field agricultural greenhouse gases is an important objective. To explore the multifactor effects of nitrogen fertilizer on nitrous oxide (N2O) emissions and the yield of potato fields and to verify the applicability of the denitrification-decomposition (DNDC) model when used to project the N2O emission load and yield, this research chooses a potato field in Shenyang northeast China from 2017 to 2019 as the experiment site. The experiment includes four nitrogen levels observing the emission of N2O by static chamber/gas chromatograph techniques. The results of this study are as follows: (1) DNDC has a good performance regarding the projection of N2O emissions and yields. The model efficiency index EFs were 0.45 ~ 0.88 for N2O emissions and 0.91, 0.85, and 0.85 for yields from 2017 to 2019. (2) The annual precipitation, soil organic carbon, and soil bulk density had the most significant influence on the accumulated N2O emissions during the growth period of potatoes. The annual precipitation, annual average temperature, and CO2 mass concentration had the most significant influences on yield. (3) Under the premise of a normal water supply, sowing potatoes within 5 days after the 5-day sliding average temperature in this area exceeds 10℃ can ensure the temperature required for the normal growth of potatoes and achieve the purpose of maintaining and increasing yield. (4) The application of 94.5 kg·hm-2 nitrogen and 15 mm irrigation represented the best results for reducing N2O emissions while also maintaining the yield in potato fields.

Quantitative and qualitative analyses of orthodontic-related videos on YouTube.

OBJECTIVES: To investigate content of orthodontic-related videos on YouTube to improve the understanding of orthodontic patients' perceptions and treatment experiences. MATERIALS AND METHODS: A systematic search was conducted on YouTube on March 20, 2018, and updated on August 4, 2019, to identify all relevant videos using search terms "orthodontic," "orthodontics," "braces," and "orthodontic braces." The data set was captured from YouTube Data API (Application Programming Interface) and stored in an Excel database using a query function written in Python. All videos captured were viewed and categorized by three independent dental investigators using thematic analysis. The top 100 videos (by view count) related to patients' treatment experience were further analyzed using discourse analysis. RESULTS: A total of 600 orthodontic videos were screened, and 546 were included in the study. Six main themes were identified: (1) individual review of orthodontic treatment (45.8%, n = 250), (2) entertainment (19.8%, n = 108), (3) education (18.3%, n = 100), (4) advertisements (6.6%, n = 36), (5) time lapse of orthodontic treatment (5.3%, n = 29), and (6) do-it-yourself orthodontics (4.2%, n = 23). Of the top 100 videos related to patient's individual review of treatment, patients' main focuses were on pain (24%), problems with chewing and swallowing (12%), and adhesive removal (10%). CONCLUSIONS: Orthodontic-related YouTube videos are diverse in nature. The most common video category was video providing an individual review of orthodontic treatment experience. Other popular video categories included entertainment, education, and advertisements. A range of do-it-yourself YouTube videos were also identified. YouTube may provide an opportunity for orthodontic professionals to disseminate health information.

Replication Study: The microRNA miR-34a inhibits prostate cancer stem cells and metastasis by directly repressing CD44.

As part of the Reproducibility Project: Cancer Biology, we published a Registered Report (Li et al., 2015), that described how we intended to replicate selected experiments from the paper 'The microRNA miR-34a inhibits prostate cancer stem cells and metastasis by directly repressing CD44' (Liu et al., 2011). Here we report the results. We found the microRNA, miR-34a, was expressed at twice the level in CD44+ prostate cancer cells purified from xenograft tumors (LAPC4 cells) compared to CD44- LAPC4 cells, whereas the original study reported miR-34a was underexpressed in CD44+ LAPC4 cells (Figure 1B; Liu et al., 2011). When LAPC4 cells engineered to express miR-34a were injected into mice, we did not observe changes in tumor growth or CD44 expression; however, unexpectedly miR-34a expression was lost in vivo. In the original study, LAPC4 cells expressing miR-34a had a statistically significant reduction in tumor regeneration and reduced CD44 expression compared to control (Figure 4A and Supplemental Figures 4A,B and 5C; Liu et al., 2011). Furthermore, when we tested if miR-34a regulated CD44 through binding sites in the 3'UTR we did not find a statistically significant difference, whereas the original study reported miR-34a decreased CD44 expression that was partially abrogated by mutation of the binding sites in the CD44 3'UTR (Figure 4D; Liu et al., 2011). Finally, where possible, we report meta-analyses for each result.

The Smaller the Leaf Is, the Faster the Leaf Water Loses in a Temperate Forest.

Leaf size (i.e., leaf surface area and leaf dry mass) profoundly affects a variety of biological carbon, water and energy processes. Therefore, the remarkable variability in individual leaf size and its trade-off with total leaf number in a plant have particularly important implications for understanding the adaption strategy of plants to environmental changes. The various leaf sizes of plants growing in the same habitat are expected to have distinct abilities of thermal regulation influencing leaf water loss and shedding heat. Here, we sampled 16 tree species co-occurring in a temperate forest in northeastern China to quantify the variation of leaf, stomata and twigs traits, and to determine the relationships of leaf size with leaf number and leaf water loss. We examined the right-skewed distributions of leaf size, leafing intensity, stomatal size and stomatal density across species. Leafing intensity was significantly negatively correlated with leaf size, accounting for 4 and 12% of variation in leaf area and leaf mass, respectively. Species was the most important factor in explaining the variation in leaf size (conditional R 2 of 0.92 for leaf area and 0.82 for leaf mass). Leaf area and mass significantly increased with increasing diameter of twigs. Leaf water loss was strongly negatively correlated with leaf area and leaf mass during the first four hours of the measurement. Leaf area and leaf mass accounted for 38 and 30% of variation in total leaf water loss, respectively. Leaf water loss rate (k) was significantly different among tree species and markedly linearly decreased with increasing leaf area and leaf mass for simple-leaved tree species. In conclusion, the existence of a cross-species trade-off between the size of individual leaves and the number of leaves per yearly twig unit was confirmed in that temperate forest. There was strongly negative correlation between leaf water loss and leaf size across tree species, which provides evidences for leaf size in leaf temperature regulation in dry environment with strong radiation. The size-dependent leaf water relation is of central importance to recognize the functional role of leaf size in a changing climate including rapid changes in air temperature and rainfall.

Gambogic acid grafted low molecular weight heparin micelles for targeted treatment in a hepatocellular carcinoma model with an enhanced anti-angiogenesis effect.

Gambogic acid (GA) is a potential anti-cancer agent with poor water-solubility, whereas heparin has anti-angiogenesis effects with good hydrophilicity. In this study, GA grafted low molecular weight heparin (GA-LMWH) was prepared and self-assembled into micelles in aqueous solution to improve the solubility and antitumor effects against hepatocellular carcinoma. The substitution of GA-LMWH is 27.5±0.2%. The micelles had a mean size of 190.4±10.8nm, a low critical micelle concentration of 2.4±0.2µgmL-1, and the highest area under the concentration-time curve and mean retention time in the liver compared to the heart, spleen, lung and kidney (p<0.05). The targeting efficiency of micelles to the liver is 2.1-times higher than that of the GA solution. GA-LMWH micelles were administered intravenously and significantly improved liver function, decreased cell lesions in hepatic tissue, inhibited the expression of CD105 and prolonged survival time of hepatocellular carcinoma model compared with groups treated with normal saline or GA solution. These results suggest that GA-LMWH micelles may improve anti-cancer effects by targeting the delivery of GA to the liver and enhancing the anti-angiogenesis effect.

[Seed flows of restoration succession series communities in alkaline meadow of Northeast China Songnen Plain].

After compared the source seed bank, soil seed bank, and seedling bank of the dominant species in four communities of restoration succession series in alkaline meadow of Songnen Plain, the model of seed flows was established. At early succession stage, the density of dominant source seed bank in Choris virgata community arrived its maximal value 446,182 +/- 180,455 seeds x m(-2) being 7.2 times of that in Puccinellia tenuiflora community at intermediate succession stage, 11.4 times of that in P. tenuiflora + Leymus chinensis community at later succession stage, and 164.8 times of that in L. chinensis community at climax succession stage. The densities of soil seed bank and seedling bank were all the maximal in C. virgata community, which were 63,650 +/- 14,541 seeds x m(-2) and 39,160 +/- 15,192 seedlings x m(-2), while the minimal in L. chinensis community, being 14,310 +/- 7,686 seeds x m(-2) and 790 +/- 745 seedlings x m(-2), respectively, representing a decreasing trend with the restoration. In the seedling banks of all communities in the restoration succession series, C. virgata was dominant, with its percentage ranged from 79.8% to 100%. In the seed flows, the input from dominant source seed banks to soil seed banks was only 10%-35%, while the output differed significantly at different succession stages, being the highest (62.3%) in C. virgata community and none in P. tenuiflora and L. chinensis communities.