Electronic structure of Yb/H－Si (111) interface

Photoemission spectra are measured for Yb covered surface of wet-chemically-etched H－Si (111). The results reveal that the lattice structure of the H－Si (111) surface is stable against the deposition of Yb atoms. X-ray photoemission spectra indicate the formation of a polarized (dipole) surface layer, with the silicon negatively charged. Ultraviolet photoemission spectra exhibit the semiconducting property of the interface below one monolayer coverage. Work function variation during the formation of the Yb/H－Si (111) interface is measured by the secondary-electron cutoff in the ultraviolet photoemission spectral line. The largest decrease of work function is ～1.65eV. The contributions of the dipole surface layer and the band bending to the work function change are determined to be ～1.15eV and ～0.5eV, respectively. The work function of metal Yb is determined to be ～2.80±0.05eV.     

A design of novel type superconducting magnet for super—high field functional magnetic resonance imaging by using the harmonic analysis method of magnetic vector potentials

The approach of expanding the magnetic scalar potential in a series of Legendre polynomials is suitable for designing a conventional superconducting magnetic resonance imaging magnet of distributed solenoidal configuration. Whereas the approach of expanding the magnetic vector potential in associated Legendre harmonics is suitable for designing a single-solenoid magnet that has multiple tiers, in which each tier may have multiple layers with different winding lengths. A set of three equations to suppress some of the lowest higher-order harmonics is found. As an example, a 4T single-solenoid magnetic resonance imaging magnet with 4×6 layers of superconducting wires is designed. The degree of homogeneity in the 0.5m diameter sphere volume is better than 5.8 ppm. The same degree of homogeneity is retained after optimal integralization of turns in each correction layer. The ratio B_m/B₀ in the single-solenoid magnet is 30% lower than that in the conventional six-solenoid magnet. This tolerates higher rated superconducting current in the coil. The Lorentz force of the coil in the single-solenoid system is also much lower than in the six-solenoid system. This novel type of magnet possesses significant advantage over conventional magnets, especially when used as a super-high field functional magnetic resonance imaging magnet.     

A polynomial approximation for the scattering wavefunction of an arbitrary spherically symmetric potential

A new variational approach is proposed to calculate scattering phase shifts.In this approach,the variational parameter is contained not explicitly in the trial function but in the boundary conditions that the scattering wavefunction should satisfy.It was found that a high accuracy could be reached.Furthermore,the scattering wavefunction appears as a polynomial of finite orders in the interior region.This expression is convenient for applications.     

Positive Solutions of Fully Nonlinear Elliptic Equations on General Bounded Domains

We prove the refined ABP maximum principle, comparison principle, and related existence and uniqueness theorem for the positive solutions of the Dirichlet problems of second order fully nonlinear elliptic equations on arbitrary bounded domains.     

Interpolation in the unit ball ofC n

A necessary and sufficient condition is given for a discrete multiplicity variety in the unit ballB _n ofC ⁿ to be an interpolating variety for weighted spaces of holomorphic functions inB _n . Partially supported by NSF Grant DMS-9706376.     

Studies on the Valence Band of Ethylene (C2 H4) on Fu ( ) Surface

The ethylene(C2H4)absorbs in molecular state on Ru (1010) surface stably below 200K. The dehydrogenated of ethylene occurs at 200K. The main product of the dehydrogenation of the absorbed ethylene is the acetylene (C2H2). After the dehydrogenation of the absorbed ethylene, the binding energies ofσCCandσCHbond have an increase of 0.5 and 1.1eV respectively. The C-C bonds of both ethylene and acetylene tilt in <0001> azimuth.     

Cr~(4+)在MgCaBa-铝酸盐玻璃中的发射及光学增益

研究了四价铬离子掺杂的MgCaBa 铝酸盐玻璃在近红外区的发射光谱 ,既有源于1E—3 A2 跃迁 ,位于1 1 8μm处的窄带 ,又有源于3 T2 —3 A2 范围在 1 1～ 1 4 μm内的宽带 ,利用ASE(AmplifiedSpontaneousEmis sion)方法研究了其增益特性 ,测量了在 63 2 8nm激发下不同激发长度下的发射光谱 ,得到其光学增益系数在1 1 8μm和 1 2 4 μm处分别为BE=( 0 7± 0 0 4 )mm-1和BT=( 0 0 5± 0 0 0 5)mm-1,并根据这种材料的光谱性质 ,对其作为近红外可调谐激光介质的可能作出评估。     

Characterization of Fibers in an Existing Network for High Speed System (10Gb/s or Greater) Compatibility

With OC-192 communications systems being commercially available and higher bit rate systems in development, prudent telecommunications network administrators are testing their installed fibers to determine if they can be successfully used at 10 Gb/s and higher. Together with New Brunswick Telephone (NBTel), the Fiber Optics Group at UNB have tested various installed fibers and cables in the NBTel network for their losses at wavelengths of 1244, 1310, 1550, and 1625 nm, as well as for strain and polarization mode dispersion (PMD). Weather conditions, age, place of installation, and cable types have also been considered. Aging does not seem to affect the performance of the fibers. Although most fibers are high-speed system compatible when looking at attenuation measurements, about 40% of the fibers tested would not meet the 10 Gb/s OC-192 system manufacturer's design guidelines concerning PMD.     

埋置框架质量检测的探讨

提出了埋置框架的回传射线矩阵法,研究了方波脉冲轴向作用、水平作用和斜向作用下有缺陷埋置框架和无缺陷埋置框架的速度波．结果表明;横向速度波不能识别埋置框架的基桩缺陷,轴向速度波可以识别,而且基桩缺陷信号很强烈;脉冲水平作用不能识别基桩缺陷,轴向或斜向作用可以识别．     

Synthesis of unsymmetrically tetrasubstituted pyrroles and studies of AIEE in pyrrolo[1,2-a]pyrimidine derivatives

Pyrroles are among the most important heterocycles in pharmaceuticals and agrochemicals. Construction of pyrrole scaffolds with different substituents and a free NH group, however, is challenging. Herein, a metal-free method for the synthesis of unsymmetrically tetrasubstituted NH-pyrroles using a consecutive chemoselective double cyanation is reported. The desired pyrroles were obtained with yields up to 99% and good functional group tolerance. Mechanistic studies identified a reaction mechanism that features a subtle sequence of first cyano-addition and migration, followed by cyano-addition and aromatization to afford the pyrrole skeleton. Pyrrolo[1,2-a]pyrimidines are synthesized as the synthetic applications of NH-pyrroles, and these pyrrolo[1,2-a]pyrimidines exhibit unpredicted time-dependent aggregation-induced emission enhancement (AIEE) properties.

A novel method for the challenging synthesis of unsymmetrically tetrasubstituted NH-pyrroles from chalcone derivatives is reported. The pyrrolo[1,2-a]pyrimidine derivatives that were synthesized from NH-pyrroles exhibit AIE and AIEE property.