Study on the Diffraction Patterns of α"-Fe_(16)N_2 with Jack-1 and Jack-2 Structural Parameters

Two body centered tetragonal (bet) crystal structures of α'-Fe_(16)N_2 with x=0.25, z=0.3125 (Jack-1) and x=0.222, z=0.306 (Jack-2) respectively, were analyzed theoretically with EMS software package. The simulation of diffraction patterns indicates that both diffraction patterns of the same axis in these two structures obey bcc extinction rule. The conclusion is also obtained from the analyses of the diffracted waves. α'-Fe_(16)N_2 precipitates in the diffusion layer of ion-nitrided α-iron have been studied with transmission electron microscope (TEM). We have distinctly observed the electron diffraction patterns of α'-Fe_(16)N_2 in [100], [111], [110], [011], [210], [021], [311], [113], [331] and [133] zone axes with perfect symmetry, which indicate the parallel orientation relationship with α matrix:<001>α'//<001>α'// {100}.α'// {100}ｔα. The analyses of diffraction patterns, which obey bcc extinction rule, verify the bct structure of α'-Fe_(16)N_2 discovered by X-ray diffraction.

Optically induced atomic lattice with tunable near-field and far-field diffraction patterns

Conventional periodic structures usually have nontunable refractive indices and thus lead to immutable photonic bandgaps. A periodic structure created in an ultracold atoms ensemble by externally controlled light can overcome this disadvantage and enable lots of promising applications. Here, two novel types of optically induced square lattices, i.e., the amplitude and phase lattices, are proposed in an ultracold atoms ensemble by interfering four ordinary plane waves under different parameter conditions. We demonstrate that in the far-field regime, the atomic amplitude lattice with high transmissivity behaves similarly to an ideal pure sinusoidal amplitude lattice, whereas the atomic phase lattices capable of producing phase excursion across a weak probe beam along with high transmissivity remains equally ideal. Moreover, we identify that the quality of Talbot imaging about a phase lattice is greatly improved when compared with an amplitude lattice. Such an atomic lattice could find applications in alloptical switching at the few photons level and paves the way for imaging ultracold atoms or molecules both in the near-field and in the far-field with a nondestructive and lensless approach.

CRYSTAL STRUCTURE OF A LONG－PERIOD ORDERED PHASE IN Fe－C MARTENSITE AND COMPUTER SIMULATION OF ITS ELECTRON DIFFRACTION PATTERNS

Different structure models of a long-period ordered phase in Fe-C martenstie formed during aging have been checked by computer simulation of electron diffraction(ED) patterns based on these models.The results showed that the simulated ED pattern of γ'-FexC(Ⅱ) model proposed by the present authors is in good agreement with experimentally observed ED pattern.It was also confirmed that the incommensurate superperiod stems from the coexistence of several γ'-Fe_xC(H) phases with different superperiods.The Fe(144)C(24)(Fe6C) model proposed by Uwakweh et al.generated ED patterns remarkably different from the experimental ones.

X-ray Powder Diffraction Pattern of Bi_4(SiO_4)_3

In cooperation with figure-of-merits the Rietveld analysis can appraise both angular and intensity data of powder diffraction. In this work, X-ray diffraction pattern of Bi4(SiO4)3 was redetermined with intensity figure-of-merits, which qualify agreement between observed and calculated relative intensities. F30 is 158.90 (0.0059, 32), intensity figure of merit Rint is 8.7, I20(17), 8.0. The values of figure-of-merits show that the data of JCPDS cards are distorted. Both the experimental and calculated peak positions and heights are listed in detail.

IDENTIFICATION AND SIMULATION OF X-RAY POWDER DIFFRACTION PATTERN

A new method for pattern identification and simulation of X-ray powder diffraction data is described, which can give definite phase composition of the unknown rapidly and correctly. The method is implemented in Microsoft Fortran 77 for the IBM PC/XT/AT personal computer or their compatibles.

Structural and Piezoelectric Properties of Sr_(0.6)Ba_(0.4)Nb_2O_6 Micro-rods Synthesized by Molten-Salt Method

Sr0.6 Ba0.4 Nb2 O6 micro-rods are prepared by the molten-salt method with K2 SO4,KCl-K2 SO4,and KCl as fluxes.It reveals that the Sr0.6 Ba0.4 Nb2 O6 synthesized with KCl as a flux exhibits a single phase with tetragonal tungsten bronze structure.The measurement of X-ray diffraction indicates that the Sr0.6 Ba0.4 Nb2 O6 micro-rods synthesized at 1 300℃are anisotropic.The morphology of the powers is examined by transmission electron microscope.It reveals that the length-diameter ratio of Sr0.6 Ba0.4 Nb2 O6 micro-rods increases with increasing annealing temperature from 900℃to 1 300℃.At 1 300℃,the rod possesses a large length-diameter ratio of 8∶1.Moreover,the analysis of the piezoelectric properties of single micro-rods using apiezo-response force microscope indicates that the domains of the material are arranged along its radial direction.

Characteristics of La-Pr-Nd Electrodes for Nickel-Metal Hydride Batteries

The effects of replacement of lanthanum by neodymium and praseodymium on the electrode characteristics were studied. The result indicated that the discharge capacity and cycle life are closely related with the alloy structure decided by alloy composition. The electrode with praseodymium have higher discharge capacity than that with neodymium. The replacement of lanthanum by both neodymium and praseodymium gave the electrodes higher discharge capacity and longer cycle life. The selected area diffraction pattern from the interface between two particles after 120 charge discharge cycles showed that the polycrystalline diffraction rings created from oxides and hydroxides can be observed and X ray diffraction analysis verified this conclusion.

Comments on Quasicrystals

The discoveries of so-called quasicrystals have broken through the theoretic foundation set up by the classical crystallographic group theory since 1891 and proposed new topics for study of solid structures. Electron diffraction patterns (EDP' s) and high-resolution microscopic (HREM) images have proved invaluable tools of studying the structures of crystals. The recognition and determination of EDP's and HREM images of a real-structure play a key role for understanding the structure. This paper will introduce some new developments about crystallographic group theory and new image processing methods on EDP's and HREM images. Contrary to popular beliefs, the research shows that quasicrystals can be understood (perturbed) complex periodic structures.

Image Analysis in Microbiology: A Review

This review is focused on using computer image analysis as a means of objective and quantitative characterizing optical images of the macroscopic (e.g. microbial colonies) and the microscopic (e.g. single cell) objects in the microbiological research. This is the way of making many visual inspection assays more objective and less time and labor consuming. Also, it can provide new visually inaccessible information on relation between some optical parameters and various biological features of the microbial cul-tures. Of special interest is application of image analysis in fluorescence microscopy as it opens new ways of using fluorescence based methodology for single microbial cell studies. Examples of using image analysis in the studies of both the macroscopic and the microscopic microbiological objects obtained by various imaging techniques are presented and discussed.

Design of refractive/diffractive hybrid optical elements for beam shaping with large diffraction pattern

Diffractive optics is an important technique for beam shaping with high light efficiency and strong diffraction pattern flexibility. Since the diffraction angle is limited by the unit size of the diffractive optical element （DOE）, the size of the required diffraction pattern is always rather small. In this Letter, refractive/diffractive hybrid optical elements （RDHOEs） consisting of a DOE and a lens are used to realize beam shaping for a large diffraction pattern. The lens, as the component of the RDHOEs, can not only be concave but also convex, and the double sampling Fresnel diffraction algorithm is developed for the design of these two types of RDHOEs. The simulation and experimental results provide solid evidence to demonstrate the proposed method with the pure phase spatial light modulator.

High-contrast imaging for weakly diffracting specimens in coherent diffraction imaging

Coherent diffraction imaging （CDI） and ptychography techniques bypass the difficulty of having high- quality optics in X-ray microscopy by using a numerical reconstruction of the image that is obtained by inverting the diffracted intensity recorded by a charge-coupled device array. However, the reconstruction of the image from the intensity data obtained from a weakly diffracting specimen is known to be difficult because of the obvious reduction in signal-to-noise ratio （SNR）. In this case, the specimen only slightly modifies the probe diffraction pattern~ resulting in difficulty in the identification of the detailed structure of the specimen from the reconstructed image because of the poor contrast and sharpness of the image. To address this situation, a modification in the image retrieval algorithms used in the iterative reconstruction of the image is suggested. This modification should double the presence of high spatial frequencies in the diffraction pattern to enhance the contrast and edge detection in existing imaging techniques.

Effects of Multiple Strengthening Treatments on Mechanical Properties and Stability of Nanoscale Precipitated Phases in an Aluminum-Copper-Lithium Alloy

Effects of multiple strengthening treatments （i.e. ag mechanical properties and stability of nanoscale prec in this research. Various tests such as hardness, tensi ng either at three or four consecutive temperatures） on pitated phases in an AA2090 alloy have been evaluated e, electrical resistance, differential scanning calorimetric （DSC）, and transmission electron microscopy （TEM） have been performed. The results show that the ultimate tensile strength （UTS） and the yield strength of the samples aged at four consecutive temperatures （i.e. natural aging＋190℃＋150℃＋100℃） can be increased approximately to 660 and 610 MPa, respectively. It is also found that precipitation of T1 phase occurs during multiple aging process of the alloy and the higher amounts of enthalpies shown in DSC charts are linked to higher volume fraction of this precipitate. Furthermore, TEM observations reveal that T1 phase has plate shape morphology and its crystal structure is in the form of hcp with lattice parameters of a=0.467 nm and c=0.878 nm.

Preparation,mechanical,and thermal properties of a promising thermal barrier material:Y_(4)Al_(2)O_(9)

In our previous work,anisotropic chemical bonding,low shear deformation resistance,damage tolerance ability,low thermal conductivity,and moderate thermal expansion coefficient of Y_(4)Al_(2)O_(9)(YAM)were predicted.In this work,phase-pure YAM powders were synthesized by solid-state reaction between Y2O3 and Al_(2)O_(3)and bulk YAM ceramics were prepared by hot-pressing method.Lattice parameters and a new set of X-ray powder diffraction data were obtained by Rietveld refinement.The mechanical and thermal properties of dense YAM ceramics were investigated.The measured elastic moduli are close to the theoretical predicted values and the stiffness can be maintained up to 1400℃.The flexural strength and fracture toughness are 252.1±7.3 MPa and 3.36±0.20 MPa·m^(1/2),respectively.Damage tolerance of YAM was also experimentally proved.The measured average linear thermal expansion coefficient(TEC)of YAM is 7.37×10^(-6)K^(-1),which is very close to the theoretical predicted value.Using high-temperature X-ray diffraction(XRD)analysis,volumetric TEC is determined(23.37±1.61)×10^(-6)K^(-1)and the anisotropic TEC areaa=7.34×10^(-6)K^(-1),ab=7.54×10^(-6)K^(-1),andac=7.61×10^(-6)K^(-1).

Relationship between luminescence and matrices in the system Al_2O_3-B_2O_3-C_2O_3

The system Al-2O-3-B-2O-3-Ce-2O-3, with Al/B ratio varying from 4.5 to 2 and Ce/(Al+B)=0.02, has been prepared at the temperature from 1 200 to 1 400℃. Relationship between luminescence and matrices in the system Al-2O-3-B-2O-3-Ce-2O-3 was investigated. It was found that some changes of the matrices occurred with Al/B ratio varying from 4.5 to 2. These results lead to a great change in luminescence properties, indicating variation of Ce-surroundings of crystal field. With the decrease of the ratio from 3 to 2, the excitation and emission peaks shift to shorter wavelengths. It was also found that a new type of rare earth luminescent materials was obtained with appropriate Al/B ratio.