Phase pure and well crystalline Cr2AlB2 powders are synthesized by heating the mixtures of CrB and Al powders at 900~℃.Cr2AlB2 exhibits nanolaminated morphology which transforms from flake-like crystallite to needle-...Phase pure and well crystalline Cr2AlB2 powders are synthesized by heating the mixtures of CrB and Al powders at 900~℃.Cr2AlB2 exhibits nanolaminated morphology which transforms from flake-like crystallite to needle-like grain with the increase of holding time.The morphology-structure relationships of Cr2AlB2 are delicately discussed.Meanwhile,as the precursor for fabrication of Cr2AlB2,high purity CrB powders are also prepared by high-temperature reaction of B and Cr elemental powders at 1800℃.CrB grains grow into regular plate-like morphology.Through Rietveld structure refinement,new sets of diffraction data are presented for both CrB and Cr2AlB2 and overlapped peak positions and intensities are revealed which make up for the deficiency of the existing data in ICDD PDF#32-0277(CrB)and ICDD PDF#72-1847(Cr2AlB2).Moreover,since MAB phases are precursors for preparing MBenes,2D-CrBnanosheets are successfully prepared by completely etching out Al atomic layers from Cr2AlB2.2D-CrB crystalizes in CrB structure with two-dimensional lamellar morphology.Simultaneously the formation mechanism of 2D-CrB is vividly depicted.A system of materials preparation from CrB to Cr2AlB2 and then to 2D-CrB is well established.展开更多
In this communication, the possibility for the preparation of two-dimensional MBene CrB from MAB phase Cr2AlB2 is demonstrated for the first time. Herein M is a transition metal, A is a group IIIAor IVA element and B ...In this communication, the possibility for the preparation of two-dimensional MBene CrB from MAB phase Cr2AlB2 is demonstrated for the first time. Herein M is a transition metal, A is a group IIIAor IVA element and B is boron; MAB phases are layered transition metal ternary borides, MBene is used to emphasize the loss of A group element from the parent MAB phases and to highlight the 2 D nature. The possible 2 D CrB nano sheets are prepared by selectively etching out Al layers from Cr2AlB-2 by immersing the Cr2AlB2 powders in dilute HCl solution at room temperature. The as-prepared 2 D CrB nano sheets are examined using X-ray diffraction and scanning electron microscopy and energy dispersive X-ray spectroscopy（EDS）. In addition, different structure models are built to explain the observed phenomena.The discovery in this work opens a door to the synthesis of a large number of new 2 D MBenes from MAB phases.展开更多
二维相控阵利用多个小天线单元在空间中信号合成,实现对信号的定向和聚焦,从而提高发射和接收增益。二维相控阵天线具有高灵活性、高可靠性、高精度指向性,以及波束扫描速度快等特性。因此相控阵天线技术在雷达、通信等领域有较广泛的应...二维相控阵利用多个小天线单元在空间中信号合成,实现对信号的定向和聚焦,从而提高发射和接收增益。二维相控阵天线具有高灵活性、高可靠性、高精度指向性,以及波束扫描速度快等特性。因此相控阵天线技术在雷达、通信等领域有较广泛的应用,其中波束指向延时量快速计算是其核心关键技术之一。随着二维相控阵阵元越来越多,对实现波束指向快速形成的运算要求越来越高。为提高波束形成效率,简化传统常规解算算法,提出了一种方位俯仰量分离、阵元分割结合泰勒级数展开与放大移位近似计算延时量的简化算法。该算法可将基于坐标旋转数字计算方法(Coordinate Rotation Digital Computer, CORDIC)的依次计算法时间大幅缩短,且该算法随着计算阵元的增多呈现的效果越明显。并且由于方位俯仰方向延时量的计算分离、存储分置,还可实现方位俯仰两个维度指向的独立控制,提高了设备的灵活性和可靠性。该算法已在FPGA上得到验证。展开更多
The Moho interface provides critical evidence for crustal thickness and the mode of oceanic crust accretion. The seismic Moho interface has not been identified yet at the magma-rich segments （46°-52°E） of ...The Moho interface provides critical evidence for crustal thickness and the mode of oceanic crust accretion. The seismic Moho interface has not been identified yet at the magma-rich segments （46°-52°E） of the ultra- slow spreading Southwestern Indian Ridge （SWIR）. This paper firstly deduces the characteristics and do- mains of seismic phases based on a theoretical oceanic crust model. Then, topographic correction is carried out for the OBS record sections along Profile Y3Y4 using the latest OBS data acquired from the detailed 3D seismic survey at the SWIR in 2010. Seismic phases are identified and analyzed, especially for the reflected and refracted seismic phases from the Moho. A 2D crustal model is finally established using the ray tracing and travel-time simulation method. The presence of reflected seismic phases at Segment 28 shows that the crustal rocks have been separated from the mantle by cooling and the Moho interface has already formed at zero age. The 2D seismic velocity structure across the axis of Segment 28 indicates that detachment faults play a key role during the processes of asymmetric oceanic crust accretion.展开更多
After developing the mathematical means for the correspondence of classical phase-space function to quantum-mechanical operators with symmetrical ordering of the basic canonical operators in the sense of Weyl the appr...After developing the mathematical means for the correspondence of classical phase-space function to quantum-mechanical operators with symmetrical ordering of the basic canonical operators in the sense of Weyl the approach is applied to an infinite series of classical monomial functions of the canonical variables. These include as well as pure powers of the amplitude as also basic periodic functions of the phase φwith their quantum-mechanical correspondence. In the representation by number states, all the considered operators involve the Jacobi polynomials as the essential formative element. Whereas the quantity in normal ordering due to its indeterminacy leads to the introduction of the notions of sub- and super-Poissonian statistics the analogous quantity in (Weyl) symmetrical orderingis positive definite and satisfies an inequality. The notions of sub- and super-Poissonian statistics are problematic when they are used for the definition of nonclassicality of states since the mentioned measure in normal ordering does not determine the Poisson statistics in their middle in unique way but determines only a large set of statistics which may be very far in the sense of the Hilbert-Schmidt distance from a Poisson statistics that is discussed.展开更多
基金financial supports from the National Natural Science Foundation of China under grant No. 51672064, No. U1435206 and No. 61271049
文摘Phase pure and well crystalline Cr2AlB2 powders are synthesized by heating the mixtures of CrB and Al powders at 900~℃.Cr2AlB2 exhibits nanolaminated morphology which transforms from flake-like crystallite to needle-like grain with the increase of holding time.The morphology-structure relationships of Cr2AlB2 are delicately discussed.Meanwhile,as the precursor for fabrication of Cr2AlB2,high purity CrB powders are also prepared by high-temperature reaction of B and Cr elemental powders at 1800℃.CrB grains grow into regular plate-like morphology.Through Rietveld structure refinement,new sets of diffraction data are presented for both CrB and Cr2AlB2 and overlapped peak positions and intensities are revealed which make up for the deficiency of the existing data in ICDD PDF#32-0277(CrB)and ICDD PDF#72-1847(Cr2AlB2).Moreover,since MAB phases are precursors for preparing MBenes,2D-CrBnanosheets are successfully prepared by completely etching out Al atomic layers from Cr2AlB2.2D-CrB crystalizes in CrB structure with two-dimensional lamellar morphology.Simultaneously the formation mechanism of 2D-CrB is vividly depicted.A system of materials preparation from CrB to Cr2AlB2 and then to 2D-CrB is well established.
基金supports from the National Natural Science Foundation of China under grant No. 51672064 and No. U1435206the Beijing Municipal Science & Technology Commission under grant No. Z151100003315012 and No. D161100002416001
文摘In this communication, the possibility for the preparation of two-dimensional MBene CrB from MAB phase Cr2AlB2 is demonstrated for the first time. Herein M is a transition metal, A is a group IIIAor IVA element and B is boron; MAB phases are layered transition metal ternary borides, MBene is used to emphasize the loss of A group element from the parent MAB phases and to highlight the 2 D nature. The possible 2 D CrB nano sheets are prepared by selectively etching out Al layers from Cr2AlB-2 by immersing the Cr2AlB2 powders in dilute HCl solution at room temperature. The as-prepared 2 D CrB nano sheets are examined using X-ray diffraction and scanning electron microscopy and energy dispersive X-ray spectroscopy（EDS）. In addition, different structure models are built to explain the observed phenomena.The discovery in this work opens a door to the synthesis of a large number of new 2 D MBenes from MAB phases.
文摘目的探讨二维相位对比(2D phase contrast,2D PC)磁共振成像(magnetic resonance imaging,MRI)序列在定量分析髂静脉压迫综合征(iliac vein compression syndrome,IVCS)患者静脉管腔内血液平均流速(mean blood flow velocity,MV)的应用价值。材料与方法前瞻性招募2023年12月到2024年7月在本院经数字减影血管造影(digital subtraction angiography,DSA)诊断明确为IVCS且需要血管腔内介入治疗的患者30例(试验组)及10名健康志愿者(对照组),收集患者临床资料并行1.5 T飞利浦超导MRI检查,在自由稳态进动(balance fast field echo,B-FFE)序列图像基础上分别在下腔静脉、双侧髂外静脉的冠状位、矢状位及轴位图上垂直扫描2D PC MRI序列,使用定量流量(quantitative flow,Q_FLOW)后处理软件得到血管垂直横切面感兴趣区(region of interest,ROI)内MV值。所有2D PC MRI检查进行两次,通过分析两次扫描结果的一致性(Bland-Altman图)来验证序列稳定性;分别比较IVCS试验组与对照组双侧髂外静脉MV值,评估IVCS患者髂总静脉受压对远端血流的影响;比较IVCS试验组(健侧髂外MV-患侧髂外MV)与对照组(右侧髂外MV-左侧髂外MV)髂外静脉MV差值,分析流速差诊断IVCS的效能;术中通过中心静脉导管(central venous catheter,CVC)测量IVCS患者组髂-下腔静脉压力梯度,并与患侧髂外静脉MV值进行相关性分析。结果两次2D PC MRI扫描结果一致性良好(P均<0.001);试验组患侧髂外静脉血液流速低于健侧(P<0.001),对照组双侧髂外静脉MV值差异没有统计学意义(P=0.518);使用双侧髂外静脉MV差值诊断IVCS效能高,AUC为0.939(95%CI:0.887~0.991),敏感度为81.7%,特异度为100.0%;术中CVC测量压力梯度结果与狭窄静脉远心端MV呈负相关(r=-0.951,P<0.001)。结论2D PC MRI定量分析IVCS患者静脉血液流速结果稳定、可靠,双侧髂外静脉MV差值诊断IVCS特异性高,IVCS患者髂外静脉MV值与髂-下腔静脉压力梯度符合伯努利原理,2D PC MRI可作为一种无创诊断IVCS及间接评估静脉血流压力的工具,为IVCS患者血管腔内介入治疗的手术指征提供重要参考。
文摘二维相控阵利用多个小天线单元在空间中信号合成,实现对信号的定向和聚焦,从而提高发射和接收增益。二维相控阵天线具有高灵活性、高可靠性、高精度指向性,以及波束扫描速度快等特性。因此相控阵天线技术在雷达、通信等领域有较广泛的应用,其中波束指向延时量快速计算是其核心关键技术之一。随着二维相控阵阵元越来越多,对实现波束指向快速形成的运算要求越来越高。为提高波束形成效率,简化传统常规解算算法,提出了一种方位俯仰量分离、阵元分割结合泰勒级数展开与放大移位近似计算延时量的简化算法。该算法可将基于坐标旋转数字计算方法(Coordinate Rotation Digital Computer, CORDIC)的依次计算法时间大幅缩短,且该算法随着计算阵元的增多呈现的效果越明显。并且由于方位俯仰方向延时量的计算分离、存储分置,还可实现方位俯仰两个维度指向的独立控制,提高了设备的灵活性和可靠性。该算法已在FPGA上得到验证。
基金The National Natural Science Foundation of China under contract Nos 41176053,41076029,91028002 and 41176046Dayang 115 under contract No.DYXM-115-02-3-01
文摘The Moho interface provides critical evidence for crustal thickness and the mode of oceanic crust accretion. The seismic Moho interface has not been identified yet at the magma-rich segments （46°-52°E） of the ultra- slow spreading Southwestern Indian Ridge （SWIR）. This paper firstly deduces the characteristics and do- mains of seismic phases based on a theoretical oceanic crust model. Then, topographic correction is carried out for the OBS record sections along Profile Y3Y4 using the latest OBS data acquired from the detailed 3D seismic survey at the SWIR in 2010. Seismic phases are identified and analyzed, especially for the reflected and refracted seismic phases from the Moho. A 2D crustal model is finally established using the ray tracing and travel-time simulation method. The presence of reflected seismic phases at Segment 28 shows that the crustal rocks have been separated from the mantle by cooling and the Moho interface has already formed at zero age. The 2D seismic velocity structure across the axis of Segment 28 indicates that detachment faults play a key role during the processes of asymmetric oceanic crust accretion.
文摘After developing the mathematical means for the correspondence of classical phase-space function to quantum-mechanical operators with symmetrical ordering of the basic canonical operators in the sense of Weyl the approach is applied to an infinite series of classical monomial functions of the canonical variables. These include as well as pure powers of the amplitude as also basic periodic functions of the phase φwith their quantum-mechanical correspondence. In the representation by number states, all the considered operators involve the Jacobi polynomials as the essential formative element. Whereas the quantity in normal ordering due to its indeterminacy leads to the introduction of the notions of sub- and super-Poissonian statistics the analogous quantity in (Weyl) symmetrical orderingis positive definite and satisfies an inequality. The notions of sub- and super-Poissonian statistics are problematic when they are used for the definition of nonclassicality of states since the mentioned measure in normal ordering does not determine the Poisson statistics in their middle in unique way but determines only a large set of statistics which may be very far in the sense of the Hilbert-Schmidt distance from a Poisson statistics that is discussed.
