Differences between FRP bond behavior in cracked and uncracked regions

Based on an analysis of the experimental results of a proposed bond test method, significant differences are shown to exist between the local FRP bond stress-slip relationships in the uncracked anchorage regions and in the regions between cracks. The proposed method simulates the bond behavior between the flexural cracks and anchorage regions of a flexurally FRP-strengthened RC beam. The boundary conditions, including the presence of cracks and steel, are shown to have significant effects on the local bond stress-slip models. The results showed that, at the same force, the bond stresses in the regions between cracks were lower than in regions outside the cracks, so the debonding formed in the anchorage regions. The local bond stress-slip models in the anchorage regions can be obtained from the conventional bond test methods but these do not mimic the conditions between the cracks.

Mechanical and chemical bonding properties of ground state BeH2

The crystal structure, mechanical properties and electronic structure of ground state BeH2 are calculated employing the first-principles methods based on the density functional theory. Our calculated structural parameters at equilibrium volume are well consistent with experimental results. Elastic constants, which well obey the mechanical stability criteria, are firstly theoretically acquired. The bulk modulus B, Shear modulus G, Young's modulus E, and Poisson's ratio upsilon are deduced from the elastic constants. The bonding nature in BeH2 is fully interpreted by combining characteristics in band structure, density of states, and charge distribution. The ionicity in the Be-H bond is mainly featured by charge transfer from Be 2s to H 1s atomic orbitals while its covalency is dominated by the hybridization of H 1s and Be 2p states. The Bader analysis of BeH2 and MgH2 are performed to describe the ionic/covalent character quantitatively and we find that about 1.61 (1.6) electrons transfer from each Be (Mg) atom to H atoms.

ON THE DANGLING-BOND RELAXATION PROBLEM IN HYDROGENATED AMORPHOUS-SILICON

The influence of pulsed bias light excitation on the absorption in the defect region of undoped a-Si:H film has been investigated. Ac constant photocurrent method has been used to measure the absorption spectrum. The absorption in the defect region increases with the light pulse duration.The analysis of obtained results does not support the existence of a long time relaxation process of dangling-bond states in a-Si:H.

Nondestructive measurements of stoichiometry in undoped semi-insulating gallium arsenide by x-ray bond method

The influences of microdefects and dislocations on the lattice parameters of undoped semi-insulating GaAs single crystals were analyzed, and a novel nondestructive method for measuring stoichiometry in undoped semi-insulating GaAs was established in this letter. The comparison of this method with coulometric titration indicates that the method of nondestructive measurements is indeed convenient and reliable. (C) 1996 American Institute of Physics.

半绝缘GaAs单晶化学配比的X射线双晶衍射Bond方法测量

利用X射线双晶衍射Bond方法，精确测量了各种条件下生长的半绝缘GaAs的晶格参数。建立了过量As在晶体中存在的间隙原子对模型，在理论上找到了影响半绝缘GaAs晶格参数的根本原因。并建立了半绝缘GaAs晶格参数与化学配比的关系，实现了化学配比的无损测量。这对于GaAs单晶的制备和相关光电子器件的研究具有重要意义。

Light-induced change of Si-H bond absorption in hydrogenated amorphous silicon

Device-quality a-Si:H films were prepared by glow discharge CVD with pure or H-diluted silane as well as by hot-wire CVD. The hydrogen content was varied from similar to 2 to 15 at. %. The Si-H bond absorption and its light-soaking-induced changes were studied by IR and differential IR absorption spectroscopes. The results indicate that the more stable sample exhibits an increase of the absorption at wave number similar to 2000 cm(-1), and the less stable one exhibits a decrease at similar to 2040 cm(-1) and an increase at similar to 1880 cm(-1).