Analysis of an ancient bronze statue by external beam pixe

A quantitative analysis of an ancient Buddha statue was performed by external beam Proton Induced X-ray Emission for the purpose of identifying its originality. It is shown how the PIXE method can be applied for archeological study. The elemental composition of the statue is compared with that of several samples with definite ages. The experiment was performed by extracting 2.4 MeV proton beam through a 2 mm diameter collimator and 7.6 m kapton foil to the He atmosphere. X-rays were measured by a Si(Li) detector. The analysed elements were Fe, Cu, Ag, Au and Hg for gold coating and Fe, Ni, Cu, Zn, As, Ag, Sn, Au, Pb and Bi for bronze body.     

Stacking sequence effect of aramid–UHMPE hybrid composites by flexural test method: MATERIAL PROPERTIES

Aramid fibre–ultra-high modulus polyethylene (UHMPE) fibre interply hybrid composites were fabricated with changes in the stacking sequence. The flexural strength and modulus of hybrid composites were measured in order to investigate the effect of stacking sequence. Scanning electron microscopy (SEM) was used to examine the fracture surface of interply hybrid composites. When aramid fibre was at the compressive side and dispersion extent of fibers was small, the higher flexural strength and positive hybrid effect were observed. In addition, the different stacking sequence resulted in a change in flexural failure mechanism which had an effect on the flexural strength. As the dispersion extent of fibers decreased, the introduction of cohesive failure in aramid–aramid interface and PE–PE interface improved the flexural strength of hybrid composites.     

The measurement of rates of initiation in the thermal polymerization of styrene

The thermal initiation of the polymerization of styrene has been studied at temperatures from 60–140°C using DPPH as a free radical scavenger. Rates of free radical formation, measured by the decrease in absorbance at 525 nm, are about seven times greater than those obtained from inhibition period measurements. The difference is probably due to the much greater reactivity of trinitrobenzene derivatives towards diradicals from styrene than towards styryl monoradicals. This view is supported by the different behaviour of the AIBN initiated polymerization of styrene in the presence of DPPH. The thermal initiation process has a low efficiency of initiation and the activation energy is 121 kJ/mole. The results strongly support the diradical mechanism for the thermal initiation of styrene polymerization.     

DNA-templated self-assembly of protein and nanoparticle linear arrays

Self-assembling DNA tiling lattices represent a versatile system for nanoscale construction. Self-assembled DNA arrays provide an excellent template for spatially positioning other molecules with increased relative precision and programmability. Here we report an experiment using a linear array of DNA triple crossover tiles to controllably template the self-assembly of single-layer or double-layer linear arrays of streptavidin molecules and streptavidin-conjugated nanogold particles through biotin-streptavidin interaction. The organization of streptavidin and its conjugated gold nanoparticles into periodic arrays was visualized by atomic force microscopy and scanning electron microscopy.     

Imidazole-based excited-state intramolecular proton-transfer materials: synthesis and amplified spontaneous emission from a large single crystal

We have synthesized a novel class of imidazole-based excited-state intramolecular proton-transfer (ESIPT) materials, i.e., hydroxy-substituted tetraphenylimidazole (HPI) and its derivative HPI-Ac, which formed large single crystals exhibiting intense blue fluorescence and amplified spontaneous emission (ASE). Transparent, clear, and well-defined fluorescent single crystals of HPI-Ac as large as 20 mm x 25 mm x 5 mm were easily grown from its dilute solution. From the X-ray crystallographic analysis and semiempirical molecular orbital calculation, it was deduced that the four phenyl groups substituted into the imidazole ring of HPI and HPI-Ac allowed the crystals free from concentration quenching of fluorescence by limiting the excessive tight-stacking responsible for intermolecular vibrational coupling and relevant nonradiative relaxation. Fluorescence spectral narrowing and efficient ASE were observed in the HPI-Ac single crystal even at low excitation levels attributed to the intrinsic four-level ESIPT photocycle.     

Characterization and epitope mapping of two monoclonal antibodies against human CD99

CD99 plays a critical role in the diapedesis of monocytes, T cell differentiation, and the transport of MHC molecules. Engagement of CD99 by agonistic monoclonal antibodies has been reported to trigger multifactorial events including T cell activation as well as cell-cell adhesion during hematopoietic cell differentiation. In this study, to identify the functional domains participating in the cellular events, we mapped the epitopes of CD99, which are recognized by two agonistic CD99 monoclonal antibodies, DN16 and YG32. Using recombinant fusion proteins of GST with whole or parts of CD99, we found that both antibodies interact with CD99 molecules independently of sugar moieties. DN16 mAb detected a linear epitope located in the amino terminal region of CD99 while YG32 mAb bound another linear epitope in the center of the extracellular domain. To confirm that the identified epitopes of CD99 are actually recognized by the two mAbs, we showed the presence of physical interaction between the mAbs and the fusion proteins or synthetic peptides containing the corresponding epitopes using surface plasmon resonance analyses. The dissociation constants of DN16 and YG32 mAbs for the antigen were calculated as 1.27 x 10(-7) and 7.08 x 10(-9) M, respectively. These studies will help understand the functional domains and the subsequent signaling mechanism of CD99.     

PIAD — A computer code for peak identification and activity determination

A Peak Identification and Activity Determination (PIAD) computer program has been developed. A new concept of peak significance is introduced and a great change has been made to the currently used associated gamma lines technique in calculating the confidence index; confidence factor is also given to the gamma line of a nuclide that is not seen in the spectrum. The program is written in Fortran IV under the operating system of RSX-11M.     

Status of activation analysis and its applications in Korea

Brief history and current status of activation analysis in Korea are described. About 120 papers have been published since the first paper was reported in 1960. They are sorted out into 5 consecutive periods according to the publication year, and typical feature of each period is described.     

Defect Energetics and Nonstoichiometry in Lanthanum Magnesium Hexaaluminate

Computer-based atomistic simulation methods are applied to address quantitatively the defect energetics and crystal chemistry of lanthanum magnesium hexaaluminate (LMA). The tetrahedral site preference of Mg in the magnetoplumbite structure is determined by calculating lattice energies for different Mg ion distributions. It is revealed that the intrinsic and extrinsic disorders are much influenced by the distribution of Mg in the structure. Our calculations show that oxygen Frenkel disorder is the dominant defect mode to be expected, even though Schottky disorder may also exist. Several feasible defect processes in nonstoichiometric LMA are determined from the enthalpies of the quasi-chemical reactions for the processes with simple point defect energies. We have also modeled some defect complexes in the mirror plane regions. It is found that the Mg ions positioned in the tetrahedral sites suppress the formation of cation vacancies in the mirror plane, through hindering the relaxation of the 12kAl ions by which the vacancies are stabilized. In Mg-deficient nonstoichiometric LMA, however, it is expected that the defect complex [V_La+V_Al+2(V_Al+Al_i)] will be formed in the interspinel layer. Our calculations also indicate that the O_Ladefect is improbable in LMA not only as a simple point defect but also as a member of a defect complex.     

Diffusion of additives and plasticizers in poly(vinyl chloride)—II: The self-diffusion of the stabilizers dibutyltin dilaurate and dibutyltin bismonobutylmaleate in plasticized poly(vinyl chloride)

The self-diffusion coefficient, D, of dibutyltin dilaurate and dibutyltin bismonobutylmaleate have been obtained at 35, 45 and 55° in samples of poly(vinyl chloride) plasticized with 34, 60 and 100 phr of di(2-ethylhexyl)phthalate. D at 2 phr of the laurate is 3–5 times larger than for the smaller maleate molecule. In all cases, D increases with increasing plasticizer concentration, an effect interpreted in terms of the free volume theory of diffusion. D for the laurate increases by a factor of about 2.7 when the laurate diffusant concentration is increased from 0 to 4 phr. The activation energies for diffusion, E_D, lie between 50 and 90 kJ mol^?1. They increase with increasing plasticizer concentration but become constant at higher plasticizer concentrations (60–100 phr). It is impossible to correlate all the known data on diffusion in plasticized PVC with an equation of the form log D₀ = C₁ + C₂ E_D/RT