线阵扫描超声相关合成成像方法与实验

本文讨论了改进的医用B超线阵扫描探头在工业无损检测中的应用．在合成孔径聚焦技术（SAFT）基础上提出了改进方法，在探元响应带宽较窄的情况下可获得较高信噪比的成像结果．文中介绍了成像系统，实验方法，并给出了一些实验结果．     

Surface atomic imaging of La2CuO4 and superconducting Tl2Ba2Ca2Cu3O10

Surface structures of the high T_c oxide superconductors Tl₂Ba₂Ca₂Cu₃O₁₀ and La₂CuO₄ have been studied by high resolution electron microscopy. In addition to the single atomic layer of La on the (113) surface observed previously, several atomic layers of the C-form of La₂O₃ were found to coat the (001) surfaces of La₂CuO₄. Surface reconstruction with the incorporation of excess Ba on the (110) surface of Tl₂Ba₂Ca₂Cu₃O₁₀ has been observed together with a stepped (11l) surface produced by a combination of the (110) and (001) planes. The (001) surface of Tl₂Ba₂Ca₂Cu₃O₁₀ was also found to terminate with a Ba-O layer. Possible mechanisms for the formation of these surface structures are discussed.     

Temperature dependence of the magnetic penetration depth in YBa2Cu3O6.95

We report precision transverse fieldSR measurements of the internal field distribution in the vortex state of crystalline YBa₂Cu₃O_6.95. A novel low background apparatus was used to study a mosaic sample of three high quality single crystals (T_c=93.3K). The observed frequency spectra in magnetic fields of 5kG and 15 kG applied along the c-axis have the characteristic features expected for a regular vortex lattice with some additional broadening. From a preliminary analysis we find that [(0)/(T)]² has a linear temperature coefficient forT<30 K. Such a term is inconsistent with simple s-wave pairing in the superconducting state. These results support recent microwave measurements of(T) on similar crystals in zero applied field but differ significantly from previousSR reports on sintered powders and crystals with lower T_c.This research was supported by the Natural Sciences and Engineering Research Council of Canada.     

视界和温度格林函数的生成泛函

在平衡态条件下,利用格林函数的欧氏生成泛函讨论了具有视界的Rindler时空和黑洞时空中量子场温度的几何来源。在Minkowski时空到Rindler时空的变换下,绝对零度格林函数欧氏生成泛函的路径积分表示变换为有限温度量子场的相应表示,说明Minkowski真空态和Rindler时空中的一量子混合态性质相同,导出了这个态的温度格林函数及各热力学格林函数。对于Schwarzschild,Reissner-Nordstrom和Kerr黑洞,得到了类似的结果,并获得了描写量子混合态的统计算符的具体形式。 关键词：     

布鲁塞尔子的球对称结构

本文利用分支点理论详细地计算了布鲁塞尔子的球对称解。结果表明,它不仅具有空间和时间耗散结构,而且其空间耗散结构还具有新的特点,即在球的中心有一个高浓度区。这对于了解生物、生物化学等现象中的核型结构可能有所帮助。 关键词：     

Study of Intramolecular Cyclization of N-styryl-oxo-cinnamides (Ⅱ)

lnthepreviouspaper',wereportedtheintramolecularcyclizationsofamide4anditscis-eneisomerinanattempttosynthesizehomoclausenamideandzetaclausenamide2.Inordertostudytherelationshipbetweenthestereochemistryandtheilltramolecularcyclizationofthisseriesofcompounds,theamides5(cis-oxirane,trans-ene)and8(cis-oxirane,cis-ene)wereprepared,andtheirintramolecularcyclizationswerereportedinthispaper.Theamide5withm.p.152.O-l54.O"CwasobtainedfromDarzen'scondensationofcompound3withPhCHOinMeOHatl5-2OoCwithMeO…     

Pointwise Stabilization for a Chain of Coupled Vibrating Strings

For the system representing a chain of coupled vibrating strings,we show that the associated semigroup satisfies the assumptionof spectrum-determined growth, and hence obtain conditions forenergy to decay strongly or exponentially. We examine in detailthe three-string case, and our results include those obtainedby others for the two-string case. Permanent address: Beijing Institute of Information and Control,Beijing, China.     

The Perturbation of the Interface of the Two-dimensional Diffraction Problem and an Approximating Muskat Modal

ln this paper, a new transformation is found out to straighten the interface Γ_2 x = f(y), f ∈ C^{2+a}([0, a]), f_y|_y =0, δ < f < l-δ,δ > 0,δ,l=constants and a perturbation of the interface is considered for a two dimensional diffraction problem. And the existence, uniqueness and regularity of an appeoximating Muskat model are proved.     

团簇Aun+1-1、AunCr-1 (n=1-10)吸附CO的密度泛函理论研究

采用密度泛函理论对CO在阴离子团簇Aun+1-1、AunCr-1(n=1-10))表面的吸附做了系统研究.结果表明,团簇Aun+1CO-1、AunCrCO-1的基态结构是在团簇Aun+1-1、AunCr-1最低能量结构的基础上吸附CO形成; 吸附后的CO键长变长,振动频率减小,表明CO分子被活化;取值相同时,AunCrCO-1的平均结合能高,表明团簇Aun+1CO-1掺杂Cr后稳定性升高.HOMO-LOMO能隙结果表明Aun+1CO-1替代掺杂Cr原子后团簇的化学活性得到了提升,AunCrCO-1、Aun+1CO-1团簇能隙具有奇偶振荡的现象;轨道电荷分析表明CO与团簇相互作用实质是C原子与成键Au原子或Cr原子间转移电荷,CO在与团簇相互作用过程中O原子轨道电荷分布几乎没有发生变化.     

Some Properties for the Euclidean Distance Matrix and Positive Semidefinite Matrix Completion Problems

The Euclidean distance matrix (EDM) completion problem and the positive semidefinite (PSD) matrix completion problem are considered in this paper. Approaches to determine the location of a point in a linear manifold are studied, which are based on a referential coordinate set and a distance vector whose components indicate the distances from the point to other points in the set. For a given referential coordinate set and a corresponding distance vector, sufficient and necessary conditions are presented for the existence of such a point that the distance vector can be realized. The location of the point (if it exists) given by the approaches in a linear manifold is independent of the coordinate system, and is only related to the referential coordinate set and the corresponding distance vector. An interesting phenomenon about the complexity of the EDM completion problem is described. Some properties about the uniqueness and the rigidity of the conformation for solutions to the EDM and PSD completion problems are presented.