中子i_(13/2)组态在A=120—140区超形变态中的作用

A=120—140质量区的超形变带已发现许多事例,一般均认为中子i_((13)/2)轨道的占据是导致超形变带出现的重要原因.本文利用我们提出的改进了的本质量区的Nilsson κμ参数,系统地计算了Z=56—64,N=69—77奇中子核的i_((13)/2)带头能量及形变.所得结果一方面说明νi_((13)/2)轨道的占据,确实有利于原子核趋于超形变;另一方面又指出了从实验上易于发现νi_((13)/2)组态的可能原子核.

Double contrast-enhanced two-dimensional and three-dimensional ultrasonography for evaluation of gastric lesions

AIM： To investigate the value of two-dimensional （2D） and three-dimensional （3D） double contrast-enhanced ultrasonography （DCUS） imaging for evaluation of gas- tric lesions. METHODS： 2D and 3D DCUS imaging with both oral and intravenous administrations of contrast agents was used to assess gastroscopiclly-confirmed gastric lesions in 46 patients with benign and malignant diseases. Initially, liquid-based ultrasound contrast agent （Xinzhang） was given orally at dose of 500-600 mL for conventional ultrasound examination of the gastric lesions, and then a microbubble-based contrast agent （SonoVue） was injected intravenously at dose of 1.2-2.4 mL in bolus fashion to assess the perfusion pattern of the lesions using contrast imaging modes. The parameters derived from time-intensity curves including the arrival time （AT）, time to peak （lq-P）, peak intensity （PI） and en- hanced intensity （EI） were measured on the 2D DCUS imaging. 3D DCUS of the lesions was acquired to dem- onstrate the value of this imaging mode. RESULTS： There were 22 cases with benign lesions including chronic gastritis （n= 5）, gastric ulcer （n = 9）, gastric polyps （n = 3）, gastric stromal tumors （n = 5）, and 24 cases with malignant lesions including gastric cancer （n = 20）, gastric cardia carcinoma （n = 3） and post-operative recurrent gastric cancer （n = 1） in the study, The oral contrast-enhanced ultrasonography （CEUS） imaging of the stomach clearly demonstrated the anatomy of the stomach and morphologic features of gastric lesions, With optimal scanning window and imaging display under oral CEUS, intravenous CEUS clearly showed the perfusion of gastric lesions with various characteristic manifestations. Both 2D and 3D DCUS images clearly demonstrated normal gastric wall as a three-layer structure, from the inside out, hypere- choic mucosa, hypoechoic muscularis and hyperechoic serosa, respectively. There were statistical significant differences of AT （8.68±2.06 vs 10.43 ±2.75, P = 0.017）, PI （34.64 ± 6.63 vs 29.58 ± 8.22, P = 0.023） and EI （29.72 ± 6.69 vs 22.66 ± 7.01, P = 0.001） between malignant lesions and normal gastric wall. However, no differences of AT, PI and EI between benign lesions and normal gastric wall tissue were found. 3D DCUS could intuitively display morphological features and vascularities of the lesions with multiplanar and volume views. 3D DCUS imaging provided comprehen- sive information complementary to 2D imaging. The crater or wellhead appearances and feeding vessels as well as distorted nourishing vasculature of gastric carcinoma were better seen with 3D imaging than 2D imaging. CONCLUSION： DCUS imaging can simultaneouslydisplay the anatomic and perfusion features of gastric lesions. 3D DCUS can provide additional information to 2D DCUS for evaluation of gastric lesions.

Determination of dynamic recrystallization parameter domains of Ni80A superalloy by enhanced processing maps

The determination of intrinsic deformation parameters inducing grain refinement mechanism of dynamic recrystallization (DRX) contributes to the relative forming process design. For Ni80A superalloy, the processing maps were constructed by the derivation of the stress-strain data coming from a series of isothermal compression tests at temperatures of 1273^-1473 K and strain rates of 0.01-10 s^-1. According to the processing maps and microstructural validation, the deformation parameter windows with DRX mechanism were separated in an innovative deformation mechanism map. In addition, the deformation activation energy representing deformation energy barrier was introduced to further optimize such windows. Finally, the enhanced processing maps were constructed and the parameter domains corresponding to DRX mechanism and lower deformation barrier were determined as follows: at ε=0.3, domains: 1296-1350 K, 0.056-0.32 s^-1 and 1350-1375 K, 0.035-0.11 s^-1;at ε=0.5, domains: 1290-1348 K, 0.2-0.5 s^-1 and 1305-1370 K, 0.035-0.2 s^-1;at ε=0.7, domains: 1290-1355 K, 0.042-0.26 s^-1;at ε=0.9, domains: 1298-1348 K, 0.037-0.224 s^-1.

Effect of initial microstructure on superplastic deformation of AZ70 magnesium alloy

The mechanical properties and deformation mechanism of semi-continuously casting and as-extruded AZ70 magnesium alloys in a wide range of grain sizes(from 14 to 103μm)were investigated at 653 K and 1×10-3s -1.It is discovered that with reducing grain size,flow stress is weakened and plasticity is improved and even superplasticity exhibits.SEM and OM were used to clarify the deformation mechanism.It is suggested that dynamic recrystallization(DRX)is the coordination deformation mechanism of grain boundary sliding(GBS)for coarse grain,and cavity and intracrystalline slip are the coordination deformation mechanisms of GBS for fine grain.

极端条件下原子核性质的研究

近几年来，北京大学重离子物理研究所低能核物理理论研究组，对极端条件下原子核性质研究取得了一些成果，其中包括原子核的高自旋态。

An oxygen isotope study of quartz veins within eclogites from the Dabie terrane

The oxygen isotope composition of minerals from quartz veins and host eclogites in the Dabie terrane was measured in order to place geochemical constraints on the origin and transport of metamorphic fluid. The results are discussed together with structural and petrological relationships between quartz vein and wallrock. The quartz veins can be temporally classified into three groups: (1) synmetamorphic vein which would be formed prior to eclogite-facies recrystallization when they were exhumated from mantle depths to deep crustal levels; (2) early retrogressive vein which was formed in the early stage of eclogite exhumation subsequent to the recrystallization, the vein-forming fluid is still relevant to the eclogites; (3) late retrogressive vein which was formed in the late stage of eclogite exhumation from deep crustal to upper crustal levels, oxygen isotope fractionation between vein quartz and host eclogite significantly deviates from equilibrium values and the vein-forming fluid was principally derived from granitic gneiss hosting the eclogites. For the synmetamorphic vein, it appears that local advective transport of fluid is the predominant mechanism in the processes of vein precipitation; the scale of oxygen isotope homogenization within the veins is much larger than that within the associated eclogites. The vein-forming fluid would be derived from the exsolution of dissolved hydroxyls within eclogite minerals due to significant pressure decrease. Fluid flow prior to the eclogite-facies recrystallization and the early retrogression may occur mainly along pressure gradients.

Oblate Superdeformed High-K States in Superheavy Nuclei

Configuration-constrained calculations of potential-energy surfaces for ^292 122 show the occurrence of multiquasiparticle high-K isomeric state at oblate superdeformation. Such state could play a unique role in superheavy nuclei, with possible long life time from enhanced difficulty in fission due to additional barrier at oblate deformation, retardation in a decay due to unpaired nucleons, and hindrance in γ-ray transition due to K forbiddenness.