DETERMINATION OF SPACE GROUP OF PrCo_(12)B_6 COMPOUND BY CONVERGENT BEAM ELECTRON DIFFRACTION

The space group of PrCo_(12)B_6,compound has been determined using the convergent beam elec- tron diffraction method.The space group is found to be R3m.

THE CURVED BEAM ELEMENT AND ITS CONVERGENCE RATE

The quasi-conforming element of the curved beam and shallow curved beam is given in this paper. Numerical examples illustrate that the quasi-conforming elements of the curved beam and shallow curved beam which is used to approximate the curved beam have better accuracy than the straight beam clement. The curved beam element constructed by displacement method can not satisfy rigid body motion condition and the very fine grids have to be used in order to satisfy rigid body motion condition approxtmately.In this paper it is proved that the straight beam element and the quasi-conforming element of the curved beam and shallow curved beam, when element size is reduced infinitely, have convergence rate with the same order O(l2) and when regular elements are used. I is the element length.

STUDY OF MICROSTRUCTURE IN AN Au-Ni-Fe-Cr-In-Zr ALLOY

The mierostructure of an AuNiFeCrlnZr alloy has been studied by means of TEM,CBED. SEM and EDS. The results show that the alloy contains Au-rich solid solution, Ni-rich solid solution, and η- and -ωphases. The η-phase containing 90at%Cr possesses an orlhorhombic .structure with a = 0.448nm. b = 1.40nm and c = 1.21nm, and space group of Pmm2 or Pmmm. The ω-phase is an fee structure with a = 0.682nin and space group of Fm3m. The ω-phase dispersed in the alloy matrix plays an important role in increasing strength and wear resistance of the alloy.

A Study of Quasicrystal Structure Factorsby Using Quantitative CBED

The procedure of simulating convergent beam electron diffraction (CBED) pattern of quasicrystals by dynamical theory is described. The simulated patterns are generally coincide with the experimental patterns. The variations of intensity distribution in CBED pattern with the amplitude and phase of the structure factor of quasicrystal are calculated with dynamical theory. The sensitivity of intensity distribution to the structure factor is investigated.

A Study of Interfacial Reactions and Interface Residual Strains in K_2O·6TiO_(2w)/Al Composite

X-ray energy disperslve analyses sbow that the rati0 of titanium to potassium in the interlayer ismuch higher than that of the whlsker K,o.6TlO,, and that titanium and p0tassium atoms of the whisker arepartly diss0lved into the matrix AI near the whisker. The lnterrace residual strains in the composite are determined in terms of the shifts of HOLZ llnes. To unlqueIy evaluate the Iattlce parameters and the lattice strainsfrom an experimentaI HOLZ line pattern, the pIane stress approximation is employed to reduce the numberof adjustable parameters in the optimization procedure. The results obtained with this method are in goodagreement with other works. The possible expIanations for the high von Mises effective stresses in the matrixnear the whisker are discussed.

Structure Refinement of the Icosahedral AlPdMn Quasicrystal Using Quantitative CBED

The atomic structure of the perfect AlPdMn icosahedral phase has been studied on a single crystal specimen by quantitative convergent beam electron diffraction (QCBED) technique in combination with describing the shape of atomic surface by symmetry\|adapted series of surface harmonics. The spherical model was used as the starting model for the refinement. By fitting the calculated electron diffraction intensities to the experimental line scan profile, the coefficients in the surface harmonics expansion of the boundaries of atomic surface are refined. The refined parameters show that the fluctuations of the external boundary of atomic surface for Pd at n 0 can be as large as 0.2 nm. The boundaries of atomic surfaces for Mn show little fluctuation. In the present model, the number of unphysically short interatomic distances is significantly reduced in comparison with the spherical model.

Gateside packwall design in solid backfill mining-A case study

Based upon characteristic movement features of the overlying strata in solid backfill mining and in-situ observations,an associated model representing a roadway support system has been developed.Based on the Winkler foundation and beam model,the current study presents a static analysis of the model,thus permitting acquisition of a theoretical formula pertaining to roof convergence.Through use of working face 6304-1(Jisan Colliery) as the research setting,the association between roof convergence magnitude and both packwall strength and width have been elucidated.Based upon observed conditions at the working face,realistic packwall parameters have been formulated,with numerical simulation results and field application results indicating that design parameters garnered from the developed formula successfully adapted to local geological movement and deformation.Accordingly,roadway deformation was shown to be within the permissible range,thus satisfying mine production requirements.The proposed method in the current study may give a design basis for pack design in the context of SBM under similar conditions.

52 m/9 Gb/s PAM4 plastic optical fiber-underwater wireless laser transmission convergence with a laser beam reducer

A 52 m/9 Gb/s four-level pulse amplitude modulation（PAM4） plastic optical fiber（POF）-underwater wireless laser transmission（UWLT） convergence with a laser beam reducer is proposed. A 52 m/9 Gb/s PAM4 POFUWLT convergence is practically demonstrated with the application of a laser beam reducer to reduce the collimated beam diameter. A 50 m graded-index（GI）-POF is employed as an underwater extender to efficiently enhance the coverage of UWLT. The performances of PAM4 POF-UWLT convergence in view of bit error rate（BER） and eye diagrams improve with the decrease of the collimated beam diameter because of the small amount of light absorbed by clear ocean water. Competent BER and eye diagrams（three independent eye diagrams） are achieved over a 50 m GI-POF transmission with a 2 m clear ocean water link.

Quantifying the Microstructures of Pure Cu Subjected to Dynamic Plastic Deformation at Cryogenic Temperature

A pure Cu （99.995 wt%） has been subjected to dynamic plastic deformation at cryogenic temperature to a strain of 2.1. Three types of microstructures that are related to dislocation slip, twinning and shear banding have been quantitatively characterized by transmission electron microscopy （TEM） assisted by convergent beam electron diffraction （CBED） analysis. Microstructures originated from dislocation slip inside or outside the shear bands are characterized by low angle boundaries （〈15°） that are spaced in the nanometer scale, whereas most deformation twins are deviated from the perfect ∑3 coincidence （60°/〈111〉） up to the maximum angle of 9°. The quantitative structural characteristics are compared with those in conventionally deformed Cu at low strain rates, and allowed a quantitative analysis of the flow stress-structural parameter relationship.

Experimental Measurement of Valence Electron Concentration of Icosahedral AlPdMn Quasicrystal

The valence charge density distribution for the icosahedral AlPdMn （i-AlPdMn） quasicrystal was obtained with the structure factors of the nine strongest symmetry inequivalent reflections, which were refined by using the quantitative convergent beam electron diffraction （QCBED） technique. It shows that the bonding charge is localized. The enhanced charge density in the middle of the aluminum-transition-metal （Al-TM） bond shown in the valence charge density＇ distribution is the characteristic of covalent bonding. Assuming that the shape of an atom is a sphere with covalent radius, the number of electrons that each atom gains or loses in 55 different pseudo-Mackay clusters （PMCs） was cal- culated based on the obtained valence charge density distribution. It indicates that almost all the atoms lose electrons except a few Pd atoms that are in some particular shells. It also shows that the atoms of an identified element could have different valences because of chemically and/or structurally different local environments in which the atoms situ- ate. Regardless of the topology and chemical occupancy, the number of valence electrons per atom in a cluster is close to 1.69. This strongly suggests that the pseudo-Mackay clusters are stabilized at a certain elec- tron concentration.