Study on creep deformation and energy development of underground surrounding rock under four‐dimensional support

There is an urgent need to develop optimal solutions for deformation control of deep high‐stress roadways,one of the critical problems in underground engineering.The previously proposed four‐dimensional support(hereinafter 4D support),as a new support technology,can set the roadway surrounding rock under three‐dimensional pressure in the new balanced structure,and prevent instability of surrounding rock in underground engineering.However,the influence of roadway depth and creep deformation on the surrounding rock supported by 4D support is still unknown.This study investigated the influence of roadway depth and creep deformation time on the instability of surrounding rock by analyzing the energy development.The elastic strain energy was analyzed using the program redeveloped in FLAC3D.The numerical simulation results indicate that the combined support mode of 4D roof supports and conventional side supports is highly applicable to the stability control of surrounding rock with a roadway depth exceeding 520 m.With the increase of roadway depth,4D support can effectively restrain the area and depth of plastic deformation in the surrounding rock.Further,4D support limits the accumulation range and rate of elastic strain energy as the creep deformation time increases.4D support can effectively reduce the plastic deformation of roadway surrounding rock and maintain the stability for a long deformation period of 6 months.As confirmed by in situ monitoring results,4D support is more effective for the long‐term stability control of surrounding rock than conventional support.

Assessment of Myocardial Perfusion and Systolic Function in Patients with Coronary Artery Disease after Coronary Artery Bypass Surgery by Myocardial Contrast Echocardiography and Two-dimensional Strain Echocardiography

The clinically applied value of myocardial perfusion and systolic function in patients with coronary artery disease after coronary artery bypass surgery using real-time myocardial contrast echocardiography （RT-MCE） combined with two-dimensional strain echocardiography was assessed. Twenty patients underwent intravenous RT-MCE by intravenous injections of SonoVue before and after coronary artery bypass surgery. Two-dimensional images were recorded from the left ventricular four-chamber view, two-chamber view and the apical view before, and two weeks and three months after coronary artery bypass surgery, and the peak systolic longitudinal strain was measured. The results showed that myocardial perfusion was significantly increased after coronary artery bypass surgery in about 71.6% segments. In the group that myocardial perfusion was improved, the peak systolic longitu- dinal strain three months after bypass surgery was significantly higher than that before operation [（-15.78±5.91）% vs （-10.45±8.31）%, P〈0.05]. However, the parameters did not change in the group without myocardial perfusion improvement [（-10.33±6.53）% vs （-9.41±6.09）%, P〉0.05]. It was concluded that whether or not the improvement of myocardial perfusion can mirror the recovery trend of regional systolic function, two-dimensional strain echocardiography can observe dynamic change of regional systolic function. The combination of myocardial perfusion with two-dimensional strain echocardiography can more accurately assess the curative effectiveness of coronary artery bypass surgery.

Evaluation of Epirubicin-induced Cardiotoxicity by Two-dimensional Strain Echocardiography in Breast Cancer Patients

The value of two-dimensional strain echocardiography for assessing left ventricular regional systolic function in breast cancer patients who were treated with epirubicin was evaluated. A total of 116 breast cancer patients were divided into 3 groups： Thirty-eight patients in group A were given epirubicin （Epi） of 120-340 mg/m^2, 42 patients in group B received epimbicin of≥ 360 mg/m^2, and 36 patients after surging without chemotherapy served as the control group C. High frame rate two-dimensional images were recorded from apical long-axis view, four-chamber view, two-chamber view of left ventricle. Peak systolic strain of left ventricular subendocardial myocardium was measured using two-dimensional strain software. The conventional echocardiographic parameters were also obtained. Conventional echocardiography showed there was no significant changes in conventional echocardiographic parameters among the three groups （P〉0.05）. Two-dimensional strain echocardiography revealed that the peak systolic strain of left ventricular subendocardial myocardium in group A was reduced in some segments as compared with the controls （P〈0.05）. The peak systolic strain of left ventricular subendocardial myocardium in group B was reduced significantly as com- pared with group C （P〈0.05）, but that was reduced in group B just in some of the segments as compared with group A （P〈0.05）. It was concluded that two-dimensional strain echocardiography could early and sensitively display the effects of epirubicin-induced cardiotoxicity on the systolic function of left ventricular subendocardial myocardium, and early monitor the epirubicin-induced cardiotoxicity.

The Expression of Stress and Strain at the Tip of Three-Dimensional Notch

The singularity of stress and strain at the tip of three-dimensional notch isanalysed by the power expansion method .the eigenquation of the notch is gainedthrough the boundary conditions of the notch, the eigenvalues under different innerangles of the notch are obtained, the expression of stress and strain at the tip of thenotch is finally derived .

Nanoimprint-induced strain engineering of two-dimensional materials

The high stretchability of two-dimensional(2D)materials has facilitated the possibility of using external strain to manipulate their properties.Hence,strain engineering has emerged as a promising technique for tailoring the performance of 2D materials by controlling the applied elastic strain field.Although various types of strain engineering methods have been proposed,deterministic and controllable generation of the strain in 2D materials remains a challenging task.Here,we report a nanoimprint-induced strain engineering(NISE)strategy for introducing controllable periodic strain profiles on 2D materials.A three-dimensional(3D)tunable strain is generated in a molybdenum disulfide(MoS_(2))sheet by pressing and conforming to the topography of an imprint mold.Different strain profiles generated in MoS_(2)are demonstrated and verified by Raman and photoluminescence(PL)spectroscopy.The strain modulation capability of NISE is investigated by changing the imprint pressure and the patterns of the imprint molds,which enables precise control of the strain magnitudes and distributions in MoS_(2).Furthermore,a finite element model is developed to simulate the NISE process and reveal the straining behavior of MoS_(2).This deterministic and effective strain engineering technique can be easily extended to other materials and is also compatible with common semiconductor fabrication processes;therefore,it provides prospects for advances in broad nanoelectronic and optoelectronic devices.

Review of Electronic Speckle Pattern Interferometry(ESPI) for Three Dimensional Displacement Measurement

Three dimensional（3D） displacements, which can be translated further into 3D strain, are key parameters tor design, manufacturing and quality control. Using different optical setups, phase-shift methods, and algorithms, several different 3D electronic speckle pattern interferometry（ESPl） systems for displacement and strain measurements have been achieved and commercialized. This paper provides a review of the recent developments in ESPI systems for 3D displacement and strain measurement. After an overview of the fundamentals of ESP! theory, temporal phase-shift, and spatial phase-shift techniques, 3D deformation measurements by the temporal phase-shift ESPI system, which is suited well for static measurement, and by the spatial phase-shift ESPI system, which is particularly useful for dynamic measurement, are discussed. For each method, the basic theory, a brief derivation and different optical layouts are presented. The state of art application, potential and limitation of the ESPI systems are shown and demonstrated.

Assessment of Regional Left Ventricular Myocardial Function in Rats after Acute Occlusion of Left Anterior Descending Artery by Two-dimensional Speckle Tracking Imaging

This study evaluated the change in regional left ventricular myocardial function in rats following acute occlusion of the left anterior descending coronary artery （LAD） by using two-dimensional speckle tracking imaging （2D-STI）. Sixty Wistar rats were randomly divided into two groups, a myocardial infarction （MI） group, in which 50 rats were subjected to LAD occlusion for 30–45 min, and a sham-operated （SHAM） group that contained 10 rats serving as control. Echo-cardiography was performed at baseline and 1, 4 and 8 week（s） after the operation. High frequency two-dimensional images of left ventricular short axis at papillary muscle level were recorded. Peak systolic radial strain （PRS） and circumferential strain （PCS） were measured in the mid-ventricle in short-axis view by using EchoPAC workstation. Left ventricular internal diameter at diastole （LVIDd） and systole （LVIDs）, fractional shortening （FS）, ejection fraction （EF） and left ventricular mass （LVM） were measured by anatomical M-model echocardiography. Infarct size was measured using triphenyl tetrazolium chloride （TTC） staining 1 week and 8 weeks after the operation. Fibrosis of left ventricu-lar myocardium was displayed using Van Gieson staining 1 week after the infarction. In terms of the TTC staining results, the left ventricle fell into three categories： infarcted, peri-infarcted and remote myocardial regions. Compared with those at baseline and in the SHAM group, （1） PRS and PCS in the infarcted, peri-infarcted and remote myocardial regions were significantly decreased in the MI group within 1 week after the operation （P〈0.05） and the low levels lasted 8 weeks; （2） Compared with those at baseline, LVIDd, LVIDs, FS, EF and LVM in the MI group showed no significant dif-ference 1 week after the operation （P〉0.05）. However, LVIDd, LVIDs and LVM were increased sig-nificantly 4 and 8 weeks after the operation （P〈0.05）, and FS and EF were decreased substantially （P〈0.05）. Van Gieson staining showed that fibrosis developed in all the three myocardial regions to varying degrees. It is concluded that 2D-STI is non-invasive and can be used to assess regional func-tion of myocardium with different blood supply in rats following acute occlusion of the LAD, and can be used as a sensitive and reliable means to follow up the process of left ventricular remodeling.

THE CONSTITUTIVE RELATION OF CRACK-WEAKENED ROCK MASSES UNDER AXIAL-DIMENSIONAL UNLOADING

An accurate and efficient numerical method for solving the crack-crack interaction problem is presented. The method is mainly by means of the dislocation model, stress superposition principle and Chebyshev polynomial expansion of the pseudo-traction. This method can be applied to compute the stress intensity factors of multiple kinked cracks and multiple rows of periodic cracks as well as the overall strains of rock masses containing multiple kinked cracks under complex loads. Many complex computational examples are given. The dependence of the crack-crack interaction on the crack configuration, the geometrical and physical parameters, and loads pattern, is investigated. By comparison with numerical results under confining pressure unloading, it is shown that the crack-crack interaction under axial-dimensional unloading is weaker than those under confining pressure unloading. Numerical results for single faults and crossed faults show that the single faults are more unstable than the crossed faults. It is found from numerical results for different crack lengths and different crack spacing that the interaction among kinked cracks decreases with an increase in length of the kinked cracks and the crack spacing under axial-dimensional unloading.

Analytical Solution for Three-dimensional Forging Taking into Account Bulging of Sides by Mean Yield Criterion

Currently, for some complex plastic deformations, the analytical solution can not be obtained by using Mises yield criterion, because Mises yield criterion is nine dimensions, the velocity field is complex, and the solving methods are not innovative. Corresponding solutions of these problems are that yield criterion is linearized to reduce the variable numbers, and the velocity field and the solving methods are reasonably simplified, respectively. In this paper, a new linear yield criterion--mean yield（MY） criterion and inner-product of strain rate vector are used to analytically solve 3D forging taking into account bugling of sides. The velocity field is expressed as a vector in three dimensions, and rotation and divergence are applied to confirm that the velocity field is kinematically admissible. Then, the corresponding strain rate tensor of the velocity field is transformed into principal one by making the determinant of coefficients of the tensor cubic equation be zero. By using MY criterion, the plastic power is term by term integrated and summed according to inner-product of strain rate vector. An upper bound analytical solution is obtained for the forging, and verified by a pure lead press test. The test result turns out that the total pressure calculated by MY criterion is higher by 2.5%-15% than measuring value. In addition, a measuring formula of bulging parameter （a） is proposed, but the values of a measured by the formula are lower than those optimized by the golden section search. The total pressure calculated by MY criterion is compared with the ones by twin shear, Trasca yield, and Mises yield criterion. The comparing result shows that the total pressure calculated by MY criterion is slightly higher than the mean value of that by twin shear and Trasca yield criterion, and lower than that by Mises yield criterion, but more close to that by Mises yield criterion compared with that by other two. The proposed analytical solving methods can be effectively used to other complex plastic deformation, simplifying the solving process and obtaining the reasonable results.

One-dimensional ZnO nanostructure-based optoelectronic

Semiconductor nanowires, with their unique capability to bridge the nanoscopic and macroscopic worlds, have been demonstrated to have potential applications in energy conversion, electronics, optoelectronics, and biosensing devices. Onedimensional（1D） ZnO nanostructures, with coupled semiconducting and piezoelectric properties, have been extensively investigated and widely used to fabricate nanoscale optoelectronic devices. In this article, we review recent developments in 1D ZnO nanostructure based photodetectors and device performance enhancement by strain engineering piezoelectric polarization and interface modulation. The emphasis is on a fundamental understanding of electrical and optical phenomena, interfacial and contact behaviors, and device characteristics. Finally, the prospects of 1D ZnO nanostructure devices and new challenges are proposed.

High Dimensionality Effects on the Efficient Frontier: A Tri-Nation Study

Markowitz Portfolio theory under-estimates the risk associated with the return of a portfolio in case of high dimensional data. El Karoui mathematically proved this in [1] and suggested improved estimators for unbiased estimation of this risk under specific model assumptions. Norm constrained portfolios have recently been studied to keep the effective dimension low. In this paper we consider three sets of high dimensional data, the stock market prices for three countries, namely US, UK and India. We compare the Markowitz efficient frontier to those obtained by unbiasedness corrections and imposing norm-constraints in these real data scenarios. We also study the out-of-sample performance of the different procedures. We find that the 2-norm constrained portfolio has best overall performance.

超声心动图监测45例法布雷病患者心脏早期受累的特征分析

【目的】分析45例临床确诊的法布雷病(AFD)患者的临床特征,同时应用超声心动图二维斑点追踪技术(2D-STE)评估法布雷病患者应变图像,以期探索法布雷患者心脏早期受累在超声心动图(UCG)上的表现。【方法】本研究为观察性研究。共纳入确诊为AFD的患者45例,根据UCG测量左室壁有无肥厚,分为左室壁肥厚组(17例,室间隔或左室后壁厚度≥12 mm)和无左室壁肥厚组(28例)。收集患者基线资料,并对所有患者进行常规UCG检查及二维斑点追踪超声心动图分析。应用TomTec工作站分析超声心动图图像,比较两组的临床基线资料、UCG常规参数及心肌应变特征。【结果】本研究共纳入45例AFD患者,年龄(32.33±16.11)岁,其中男性27例(60.00%)。左室壁肥厚组17例(37.78%),无左室壁肥厚组28例(62.22%)。45例患者的左室射血分数(LVEF)均正常(>50%)。与无左室壁肥厚组相比,左室壁肥厚组患者的靶器官受累比例明显增加。与无左室壁肥厚组相比,左室壁肥厚组患者的E/A,平均E/E'明显升高(P<0.05);左室壁肥厚组的整体、心肌层、心内膜以及各节段的纵向应变(LS),周向应变(CS)及径向应变(RS)的差异均无统计学意义(P值均>0.05)。AFD患者心肌层的整体和各节段LS、CS的绝对值均低于心内膜的对应值(P值均<0.05)。AFD患者的中间段的LS、RS绝对值较基底段和心尖段高(P值均<0.05)。【结论】早期收缩功能障碍与左室壁厚度无明显关系。2D-STE心肌应变可以早期监测AFD室壁肌层受累较心内膜严重,而中间段受累较心尖段和基底段轻。

一维结构柔性应变传感器在智能纺织服用品中的应用进展

一维结构柔性应变传感器具有优异的可集成性、适形性和灵活的结构变化等特点,在智能纺织服用品的开发与应用方面具有很大潜力。通过对纤维和纱线制备一维结构柔性应变传感器的工艺及其优缺点的介绍,综述近年来纤维型和纱线型一维结构柔性应变传感器在智能纺织服用品设计与应用中的研究进展,分析其在智能可穿戴应用领域中存在的问题。研究表明,一维结构柔性应变传感器在智能纺织服用品中的应用前景广阔,未来研究人员可不断优化和提升传感器的性能和制备工艺,推动一维结构柔性应变传感器在智能纺织服用品的实际应用。

3种方法单独及联合诊断甲状腺微小结节的价值比较

目的 比较二维高频超声、声脉冲辐射力成像(ARFI)-声触诊组织定量(VTQ)技术及应变弹性成像3种方法单独及联合诊断甲状腺微小结节良恶性的价值。方法 回顾性分析2021年6月—2023年6月在陕西省宝鸡市人民医院就诊的99例(107个甲状腺微小实性结节)结节直径≤10.0 mm患者的临床资料,均采用二维高频超声、ARF-VTQ技术及应变弹性成像进行检查,获得超声资料评分及数据,以穿刺活检和手术病理结果为诊断“金标准”,比较3种超声检查方法单独及联合应用对甲状腺微小结节的诊断效能。结果 62例患者(共68个结节)选择FNAB,37例患者(共39个结节)选择手术。107个甲状腺微小结节中,诊断为恶性微小结节45个,良性微小结节62个。恶性微小结节与良性微小结节相比,结节内回声(等回声和高回声、极低回声和低回声)、边界、微钙化、纵横比>1及血供情况和供血动脉阻力指数(RI)比较,差异均有统计学意义(P<0.05)。二维高频超声诊断甲状腺微小结节C-TIRADS积分临界值≥2分(C-TIRADS 4b)时,诊断灵敏度为73.33%,特异度为79.03%,曲线下面积[AUC(95%CI)]为0.762(95%CI:0.670~0.839);ARFI-VTQ技术中,107个甲状腺微小结节SWV测值为0.52~7.55 m/s,平均(2.62±0.61)m/s,其中24个实性结节多次出现×.××m/s,最后测值以7.55 m/s记录。恶性微小结节SWV均值为(5.24±2.23) m/s,高于良性微小结节的(2.11±0.70) m/s,差异有统计学意义(t=10.258,P<0.05);当SWV临界值为3.19 m/s时,诊断灵敏度为77.78%,特异度为80.65%,AUC(95%CI)为0.792(95%CI:0.703~0.865);应变弹性成像检查中,当评分临界值≥3分时,诊断的灵敏度为75.56%,特异度为77.42%,AUC(95%CI)为0.765(95%CI:0.673~0.841)。三者联合应用诊断的阳性微小结节为44个,阴性微小结节63个,诊断灵敏度为93.33%,特异度为96.77%,AUC(95%CI)为0.951(95%CI:0.891~0.983)。三者联合诊断效能与二维高频超声检查、ARFI-VTQ、应变弹性成像单独检测比较,差异均有统计学意义(Z=4.861、4.393、4.842,P<0.05)。结论 二维高频超声联合ARFI-VTQ技术及应变弹性成像可提高甲状腺微小结节良恶性的诊断准确性。

海上风电单柱复合筒型基础复合加载条件下的承载特性

为研究新型海上风电单柱复合筒型基础在二维复合加载条件下的承载特性,利用有限元模型计算,首先得到模型在一维荷载空间下的极限承载力,随后通过施加不同的竖向荷载,得到在V-H、V-M、V-H-M荷载空间下的承载能力包络图,并分析不同二维荷载工况下的单柱复合筒型基础各位置处的土压力分布情况以及筒体底部等效塑性应变区的变化情况。结果表明:对于单柱复合筒型基础,在一定范围内,竖向荷载(0~0.15倍竖向极限承载力)的存在能够增大结构的水平及弯矩承载力;在V-H与V-M荷载空间中,基础各位置处的土压力变化、土体等效塑性应变变化具有一定的相似性,可互相对映参考;基础所承受的最大土压力位置与基础受力倾倒方向一致;随着竖向荷载的增加,结构达到极限承载力时,基础底部土体等效塑性应变区的范围与深度相应扩大。

融入几何先验的圆柱表面三维应变场双目视觉测量方法

针对现有基于双目视觉的圆柱表面三维应变场测量方法从位移场计算应变场效率低下的问题,将圆柱结构几何先验信息融入子域投影法理论,利用圆柱标准坐标变换替代大量冗余的局部切平面最小二乘拟合求解,提出了一种融合圆柱拟合和子域投影的表面三维应变场计算方法;然后采用数值模拟方式,在不同应变区域和位移场噪声条件下,将所提方法与一般曲面子域投影法进行对比分析;最后开展圆柱拉伸实验,分别从单点和全场两个角度将所提方法的应变计算结果与应变片测量结果进行了对比。研究结果表明:在保证计算精度和位移场噪声鲁棒性的同时,所提方法将计算效率提高了约20%,且与应变片实验测量结果吻合较好,验证了该方法能够实现圆柱结构表面三维应变场的高效测量,也为规则结构表面三维应变场的计算提供了新思路。

超声斑点追踪技术在原发性二尖瓣反流评估中的应用

二尖瓣反流是常见的心脏瓣膜疾病之一,重度二尖瓣反流患者及时进行手术干预对改善患者预后至关重要。二维斑点追踪成像(two-dimensional speckle tracking imaging,2D-STI)能够追踪心动周期内心肌的运动轨迹,量化心肌力学功能,与常规超声参数相比,2D-STI能够更早、更准确地反应心肌的真实力学状态并检测到更加细微的功能变化,可以更加有效地指导重度原发性二尖瓣反流患者的手术决策。本文将对2D-STI在原发性二尖瓣反流评估中的应用进行系统性综述,以期为临床的治疗决策提供参考。

三维斑点追踪技术评估非瓣膜性心房颤动患者左房低电压区对左房结构及功能的影响

目的应用三维斑点追踪技术(3D-STI)评估非瓣膜性心房颤动(以下简称房颤)患者不同程度左房低电压区(LVA)对左房结构及功能的影响。方法选取我院拟行射频消融术的非瓣膜性房颤患者66例,术前均行经胸超声心动图检查获得左房收缩末期前后径、左右径、上下径和左室舒张末期内径、左室射血分数、二尖瓣口舒张早期峰值血流速度与二尖瓣环峰值运动速度比值(E/e’);3D-STI获得左房储器期应变(LASr)、管道期应变(LAScd)、泵功能期应变(LASct)及左房射血分数(LAEF)。进行射频消融术时应用三维电解剖标测技术获得LVA,根据LVA面积占左房总面积的百分比定义LVA程度,将患者分为无LVA患者组(Ⅰ组)29例、LVA程度<10%组(Ⅱ组)26例、LVA程度≥10%组(Ⅲ组)11例,比较各组临床资料和超声心动图参数的差异;分析左房应变参数与LVA的相关性。结果Ⅲ组陈旧性脑梗死或一过性脑缺血、持续性房颤占比及CHA_(2)DS_(2)-VASc评分均高于Ⅰ组、Ⅱ组,差异均有统计学意义(均P<0.05)。Ⅰ组与Ⅲ组、Ⅱ组与Ⅲ组E/e’>14者占比比较,差异均有统计学意义(均P<0.05);其余常规超声心动图参数比较,差异均无统计学意义。Ⅲ组LASr、LAScd、LASct、LAEF均低于Ⅰ组、Ⅱ组,差异均有统计学意义(均P<0.05)。相关性分析显示,LASr、LAScd、LASct均与LVA呈负相关(r=-0.538、-0.448、-0.501,均P<0.05)。结论当LVA达到10%时,房颤患者左房结构虽未发生改变,但其功能已经减低;应用3D-STI可以早期发现非瓣膜性房颤患者LVA程度对左房功能的影响。

基于超声分层应变成像技术评价苓桂气化方改善射血分数保留心力衰竭早期大鼠心肌功能的研究

目的基于超声分层应变成像技术评价苓桂气化方改善射血分数保留心力衰竭(heart failure with preserved ejection fraction,HFpEF)早期大鼠心肌功能。方法40只SPF级SHR大鼠随机分为HFpEF模型组、恩格列净组、苓桂气化方低剂量组和苓桂气化方高剂量组,10只WKY大鼠为空白组。采用高盐高脂高糖饮食及腹腔注射链脲佐菌素建立HFpEF早期大鼠模型,各组予相应干预9周后测量左室舒张末期内径、左室舒张末期后壁厚度、舒张早期血液速度/舒张早期二尖瓣环间隔侧组织多普勒频谱、左室射血分数以及左室心内膜下心肌整体纵向应变、中层心肌整体纵向应变、心外膜下心肌整体纵向应变、心内膜下心肌整体圆周应变、中层心肌整体圆周应变和心外膜下心肌整体圆周应变。酶联免疫吸附法测定血清B型脑尿钠肽。马松染色观察心肌组织病理变化。结果与模型组比较,恩格列净组心内膜下心肌整体纵向应变、中层心肌整体纵向应变和心内膜下心肌整体圆周应变明显升高(P<0.05),苓桂气化方低剂量组心内膜下心肌整体纵向应变和中层心肌整体纵向应变明显改善(P<0.05),苓桂气化方高剂量组心内膜下心肌整体纵向应变、中层心肌整体纵向应变和中层心肌整体圆周应变明显提升(P<0.05)。苓桂气化方低剂量组和苓桂气化方高剂量组心肌细胞间隙变窄,胶原纤维沉积减少。结论苓桂气化方能提高HFpEF早期模型大鼠心内膜下心肌整体纵向应变、中层心肌整体纵向应变、中层心肌整体圆周应变,改善左室重构和收缩功能。超声分层应变成像技术可以无创、定量、敏感检测HFpEF早期大鼠左室壁心肌改变。

新型Janus二维材料VSiN_(3)电子结构和电极化特性的理论研究

由于存在本征的电极化和内建电场,Janus二维材料可作为潜在的光催化水分离、太阳能电池和“自旋–谷”电子材料.然而,目前实现Janus二维材料的主要方法为采用同族元素进行表面原子替换,而固有Janus构型的二维材料却鲜有报道.通过第一性原理计算,文章系统地研究了一种新型稳定的Janus二维材料VSiN_(3)的电极化特性和电子特性.它的表面功函数差异可达0.93 eV,估算的内建电场强度为0.21 eV/Å.进一步的电子结构计算表明,VSiN_(3)是本征的间接带隙半导体,其禁带宽度为1.70 eV.研究发现VSiN_(3)的价带顶和导带底存在van Hove反常,可以通过载流子掺杂实现Stoner铁磁相变.通过对VSiN_(3)的电子结构及其应力效应的深入分析,得出VSiN_(3)能够作为优秀的二维电子材料和Stoner铁磁相变材料.