Dual-coupling-guided epitaxial growth of wafer-scale single-crystal WS2 monolayer on vicinal a-plane sapphire

The growth of wafer-scale single-crystal two-dimensional transition metal dichalcogenides (TMDs) on insulating substrates is critically important for a variety of high-end applications^1-4. Although the epitaxial growth of wafer-scale graphene and hexagonal boron nitride on metal surfaces has been reported^5-8, these techniques are not applicable for growing TMDs on insulating substrates because of substantial differences in growth kinetics. Thus, despite great efforts^9-20, the direct growth of wafer-scale single-crystal TMDs on insulating substrates is yet to be realized. Here we report the successful epitaxial growth of two-inch single-crystal WS₂ monolayer films on vicinal a-plane sapphire surfaces. In-depth characterizations and theoretical calculations reveal that the epitaxy is driven by a dual-coupling-guided mechanism, where the sapphire plane-WS₂ interaction leads to two preferred antiparallel orientations of the WS₂ crystal, and sapphire step edge-WS₂ interaction breaks the symmetry of the antiparallel orientations. These two interactions result in the unidirectional alignment of nearly all the WS₂ islands. The unidirectional alignment and seamless stitching of WS₂ islands are illustrated via multiscale characterization techniques; the high quality of WS₂ monolayers is further evidenced by a photoluminescent circular helicity of ~55%, comparable to that of exfoliated WS₂ flakes. Our findings offer the opportunity to boost the production of wafer-scale single crystals of a broad range of two-dimensional materials on insulators, paving the way to applications in integrated devices.

Application of deep learning to auto-delineation of target volumes and organs at risk in radiotherapy

The technological advancement heralded the arrival of precision radiotherapy (RT), thereby increasing the therapeutic ratio and decreasing the side effects from treatment. Contour of target volumes (TV) and organs at risk (OARs) in RT is a complicated process. In recent years, automatic contouring of TV and OARs has rapidly developed due to the advances in deep learning (DL). This technology has the potential to save time and to reduce intra- or inter-observer variability. In this paper, the authors provide an overview of RT, introduce the concept of DL, summarize the data characteristics of the included literature, summarize the possible challenges for DL in the future, and discuss the possible research directions.

J-shaped relationship between admission diastolic blood pressure and 2-year cardiovascular mortality in elderly patients with acute coronary syndrome

Objective

To investigate the relationship between admission diastolic blood pressure (DBP) and subsequent cardiovascular and all-cause mortality in elderly patients with acute coronary syndrome (ACS).

Methods

This is a retrospective observational study. Consecutive patients ≥65 years of age admitted for ACS at a 2,300-bed tertiary hospital from December 2012 to July 2019 were included. The association between admission DBP and cardiovascular and all-cause mortality during hospitalization and over the follow-up period among this population were analyzed using multivariate COX regression model. Results were presented according to DBP quartiles: Q1, less than 67 mm Hg; Q2, from 67 to 72 mm Hg; Q3, from 73 to 80 mm Hg; and Q4, above 80 mm Hg.

Results

A total of 6 785 patients were included in this cohort study. Mean (SD) patient age was 74.0 (6.5) years, and 47.6% were women. Mean (SD) follow-up time was 2.54 (1.82) years. A non-linear relation was observed between DBP at admission and cardiovascular and all-cause mortality during hospitalization and over the follow-up period using restricted cubic splines. After adjustment for potential confounders, patients in Q3 or Q2 had lower risk for 2-year cardiovascular death by Cox proportional hazard model compared with patients in Q4 (hazard ratio [HR] 0.66; 95% confidence interval [CI], 0.48–0.90, P=0.010, for Q3 vs Q4; and HR 0.72; 95% CI, 0.53–0.99, P=0.041, for Q2vs Q4), while patients in Q1 had similar risk for cardiovascular death with that of patients in Q4. Meanwhile, when compared with patients in Q1, patients in Q3 had lower risk for 2-year cardiovascular death (HR, 0.72; 95% CI, 0.53–0.97, P=0.033). However, lower or higher admission DBP was not an independent predictor of 2-year all-cause mortality in this population.

Conclusion

Among patients aged ≥65 years admitted for ACS, there is a J-curve relationship between supine admission DBP and risk for 2-year cardiovascular death, with a nadir at 73–80 mm Hg.

Funding Acknowledgement

Type of funding sources: Other. Main funding source(s): the Beijing Municipal Administration of Hospitals Clinical Medicine Development of Special Funding Support Study population and selectionAdjusted multivariate COX regression

Is Heuristic Sampling Necessary in Training Deep Object Detectors?

To train accurate deep object detectors under the extreme foreground-background imbalance, heuristic sampling methods are always necessary, which either re-sample a subset of all training samples (hard sampling methods, e.g. biased sampling, OHEM), or use all training samples but re-weight them discriminatively (soft sampling methods, e.g. Focal Loss, GHM). In this paper, we challenge the necessity of such hard/soft sampling methods for training accurate deep object detectors. While previous studies have shown that training detectors without heuristic sampling methods would significantly degrade accuracy, we reveal that this degradation comes from an unreasonable classification gradient magnitude caused by the imbalance, rather than a lack of re-sampling/re-weighting. Motivated by our discovery, we propose a simple yet effective Sampling-Free mechanism to achieve a reasonable classification gradient magnitude by initialization and loss scaling. Unlike heuristic sampling methods with multiple hyperparameters, our Sampling-Free mechanism is fully data diagnostic, without laborious hyperparameters searching. We verify the effectiveness of our method in training anchor-based and anchor-free object detectors, where our method always achieves higher detection accuracy than heuristic sampling methods on COCO and PASCAL VOC datasets. Our Sampling-Free mechanism provides a new perspective to address the foreground-background imbalance. Our code is released at https://github.com/ChenJoya/sampling-free.

A generalized l 2,p-norm regression based feature selection algorithm

Feature selection is an important data dimension reduction method, and it has been used widely in applications involving high-dimensional data such as genetic data analysis and image processing. In order to achieve robust feature selection, the latest works apply the l 2 , 1 or l 2 , p -norm of matrix to the loss function and regularization terms in regression, and have achieved encouraging results. However, these existing works rigidly set the matrix norms used in the loss function and the regularization terms to the same l 2 , 1 or l 2 , p -norm, which limit their applications. In addition, the algorithms for solutions they present either have high computational complexity and are not suitable for large data sets, or cannot provide satisfying performance due to the approximate calculation. To address these problems, we present a generalized l 2 , p -norm regression based feature selection ( l 2 , p -RFS) method based on a new optimization criterion. The criterion extends the optimization criterion of ( l 2 , p -RFS) when the loss function and the regularization terms in regression use different matrix norms. We cast the new optimization criterion in a regression framework without regularization. In this framework, the new optimization criterion can be solved using an iterative re-weighted least squares (IRLS) procedure in which the least squares problem can be solved efficiently by using the least square QR decomposition (LSQR) algorithm. We have conducted extensive experiments to evaluate the proposed algorithm on various well-known data sets of both gene expression and image data sets, and compare it with other related feature selection methods.

Three Novel Structural Variations at MHC and IL12B Predisposing to Psoriasis

BACKGROUND

Structural variations (SVs, defined as DNA variants ≥50 bp) have been associated with various complex human diseases. However, research to screen the whole genome for SVs predisposing to psoriasis is still lacking.

OBJECTIVES

This study aimed to investigate the association of SVs and psoriasis.

METHODS

We performed a genome-wide screen on SVs using an imputation method on 5 independent cohorts with 45,386 subjects from the Chinese Han population. Fine mapping analysis, genetic interaction analysis and RNA expression analysis were conducted to explore the mechanism of SVs.

RESULTS

We obtained 4,535 SVs in total and identified 2 novel deletions (esv3608550, OR=2.73, P<2.00×10^-308 ; esv3608542, OR=0.47, P=7.40×10^-28 ) at 6q21.33 (MHC), 1 novel Alu element insertion (esv3607339, OR=1.22, P=1.18×10^-35 ) at 5q33.3 (IL12B), and confirmed 1 previously reported deletion (esv3587563, OR=1.30, P=9.52×10^-60 ) at 1q21.2 (LCE) for psoriasis. Fine mapping analysis including SNPs and small Insertions/Deletions (InDels) revealed that esv3608550 and esv3608542 were independently associated with psoriasis, and a novel independent SNP (rs9378188, OR=1.65, P=3.46×10^-38 ) was identified at 6q21.33. By genetic interaction analysis and RNA expression analysis, we speculate that the association of 2 deletions at 6q21.33 with psoriasis might relate to their influence on the expression of HLA-C.

CONCLUSIONS

Our study constructed the most comprehensive SV map for psoriasis thus far and enriched the genetic architecture and pathogenesis of psoriasis as well as highlighted the nonnegligible impact of SVs on complex diseases.

Giant All-Optical Modulation of Second-Harmonic Generation Mediated by Dark Excitons

All-optical control of nonlinear photonic processes in nanomaterials is of significant interest from a fundamental viewpoint and with regard to applications ranging from ultrafast data processing to spectroscopy and quantum technology. However, these applications rely on a high degree of control over the nonlinear response, which still remains elusive. Here, we demonstrate giant and broadband all-optical ultrafast modulation of second-harmonic generation (SHG) in monolayer transition-metal dichalcogenides mediated by the modified excitonic oscillation strength produced upon optical pumping. We reveal a dominant role of dark excitons to enhance SHG by up to a factor of ∼386 at room temperature, 2 orders of magnitude larger than the current state-of-the-art all-optical modulation results. The amplitude and sign of the observed SHG modulation can be adjusted over a broad spectral range spanning a few electronvolts with ultrafast response down to the sub-picosecond scale via different carrier dynamics. Our results not only introduce an efficient method to study intriguing exciton dynamics, but also reveal a new mechanism involving dark excitons to regulate all-optical nonlinear photonics.

Manipulating Ferromagnetism in Few-Layered Cr2 Ge2 Te6

The discovery of magnetism in 2D materials offers new opportunities for exploring novel quantum states and developing spintronic devices. In this work, using field-effect transistors with solid ion conductors as the gate dielectric (SIC-FETs), we have observed a significant enhancement of ferromagnetism associated with magnetic easy-axis switching in few-layered Cr₂ Ge₂ Te₆ . The easy axis of the magnetization, inferred from the anisotropic magnetoresistance, can be uniformly tuned from the out-of-plane direction to an in-plane direction by electric field in the few-layered Cr₂ Ge₂ Te₆ . Additionally, the Curie temperature, obtained from both the Hall resistance and magnetoresistance measurements, increases from 65 to 180 K in the few-layered sample by electric gating. Moreover, the surface of the sample is fully exposed in the SIC-FET device configuration, making further heterostructure-engineering possible. This work offers an excellent platform for realizing electrically controlled quantum phenomena in a single device.

Accuracy of Bolton's Analysis among Different Malocclusion Patients Plaster Models and Digital Models Obtained by Ex Vivo Scanning with iTero Scanner in Chinese Han Population

Aim

This investigation aimed to compare the accuracy of Bolton's analysis on plaster models of various malocclusion groups by utilizing digital calipers and iTero scanner.

Materials and Methods

The data consisted maxillary and mandibular plaster study casts of 61 patients (Class I-20, Class II-20, Class III-21) there were 31 males and 30 females. iTero®element scanner was utilized to scan the models and Bolton's analysis was performed on digital models. Also, the Digital caliper was utilized to perform the Manual measurements. Mesiodistal tooth widths, Anterior and Overall Bolton ratio was measured utilizing OrthoCAD™ software on digital models and plaster models with digital calipers. Statistical analysis was performed utilizing One-way ANOVA and independent T-test.

Results

Results revealed anterior and overall Bolton ratios showed significant differences (P < 0.05) for the measurements performed utilizing digital models. Anterior ratio for (Group 1) iTero measurements depicted the statistical significant value (P < 0.03) and overall ratio for (Group 2) digital caliper measurements depicted the statistical significant value (P < 0.02).

Conclusion

With the introduction of intra-oral laser scanners it has become more convenient for the practitioner to perform the intra-oral digital scanning and carry out the model analysis digitally and iTero scanner can also be utilized extra-orally to perform the scanning and model analysis. Our study concludes that intra-oral laser scanner like iTero is more convenient for an orthodontist, and can be utilized for extra-oral scanning of orthodontic dental models as the measurements obtained on digital models was as accurate as the conventional method.

[PI3K/Akt signaling pathway mediates the protective effect of endomorphin-1 postconditioning against myocardial ischemia-reperfusion injury in rats]

OBJECTIVE

To investigate the role of PI3K/Akt signaling pathway in mediating the protective effect of endomorphin-1 against myocardial ischemia-reperfusion (IR) injury.

OBJECTIVE

Fifty SD male rats were randomly divided into sham operation group, myocardial IR group, endomorphin-1 post-treatment group (EM50 group), endomorphin-1+wortmannin (a PI3K/Akt signaling pathway inhibitor) treatment group (EM50+Wort group), and wortmannin treatment group (Wort group). Rat models of myocardial IR injury were established by ligation of the left anterior descending coronary artery for 30 min followed by reperfusion for 120 min. The heart rate and mean arterial pressure were monitored during the experiment. Plasma levels of LDH, CK-MB, cTnI, IL-6, TNF-α, SOD and MDA were measured after reperfusion. The mRNA expression of Bax and Bcl-2 was detected using RT-PCR, and the expression of apoptosis-related protein cleaved caspase-3, phosphorylated Akt protein and total Akt protein in myocardial tissue was detected using Western blotting.

OBJECTIVE

Myocardial IR injury significantly decreased heart rate and blood pressure of the rats in comparison with the sham operation (P < 0.05). Compared with those in the IR group, the rats in EM50 group showed significantly increased heart rate and blood pressure (P < 0.05) with decreased plasma LDH, CK-MB, cTnI, IL-6, TNF-α and MDA levels (P < 0.05), increased SOD activity (P < 0.05), increased expression of p-Akt protein and Bcl-2 mRNA (P < 0.05), and decreased expression of Bax mRNA and cleaved caspase-3 protein (P < 0.05). In EM50+Wort group, the heart rate and blood pressure were significantly lowered (P < 0.05), plasma LDH, CK-MB, cTnI, IL-6, TNF-α and MDA levels increased (P < 0.05), SOD activity decreased (P < 0.05), the expression of p-Akt protein and Bcl-2 mRNA was reduced (P < 0.05), and the expression of Bax mRNA and cleaved caspase-3 protein increased (P < 0.05) as compared with those in EM50 group.

OBJECTIVE

EM-1 postconditioning can regulate cardiac myocyte apoptosis and reduce myocardial IR injury in rats. The PI3K/Akt signaling pathway may play a role in mediating the myocardial protective effects of EM-1 postconditioning.

Peta-electron volt gamma-ray emission from the Crab Nebula

The Crab Nebula is a bright source of gamma rays powered by the Crab Pulsar's rotational energy through the formation and termination of a relativistic electron-positron wind. We report the detection of gamma rays from this source with energies from 5 × 10^-4 to 1.1 peta-electron volts with a spectrum showing gradual steepening over three energy decades. The ultrahigh-energy photons imply the presence of a peta-electron volt electron accelerator (a pevatron) in the nebula, with an acceleration rate exceeding 15% of the theoretical limit. We constrain the pevatron's size between 0.025 and 0.1 parsecs and the magnetic field to ≈110 microgauss. The production rate of peta-electron volt electrons, 2.5 × 10³⁶ ergs per second, constitutes 0.5% of the pulsar spin-down luminosity, although we cannot exclude a contribution of peta-electron volt protons to the production of the highest-energy gamma rays.

Probing the Chiral Domains and Excitonic States in Individual WS2 Tubes by Second-Harmonic Generation

Distinct from carbon nanotubes, transition-metal dichalcogenide (TMD) nanotubes are noncentrosymmetric and polar and can exhibit some intriguing phenomena such as nonreciprocal superconductivity, chiral shift current, bulk photovoltaic effect, and exciton-polaritons. However, basic characterizations of individual TMD nanotubes are still quite limited, and much remains unclear about their structural chirality and electronic properties. Here we report an optical second-harmonic generation (SHG) study on multiwalled WS₂ nanotubes on a single-tube level. As it is highly sensitive to the crystallographic symmetry, SHG microscopy unveiled multiple structural domains within a single WS₂ nanotube, which are otherwise hidden under conventional white-light optical microscopy. Moreover, the polarization-resolved SHG anisotropy patterns revealed that different domains on the same tube can be of different chirality. In addition, we observed the excitonic states of individual WS₂ nanotubes via SHG excitation spectroscopy, which were otherwise difficult to acquire due to the indirect band gap of the material.