Simulation of incoherent radiation of fast particles in an oriented crystal

Incoherent bremsstrahlung of high-energy electrons in a crystal is due to the thermal spread of atoms with respect to their equilibrium positions in the lattice. In this paper, an incoherent-radiation simulation procedure based on semiclassical formulas of bremsstrahlung theory is developed. A significant orientation dependence of the intensity of hard incoherent radiation is demonstrated for angles of electron incidence on a densely packed crystallographic axis (plane) that are close to the critical axial (plane) channeling angle. The simulation results are in good agreement with the experimental data.     

Crystallization and dielectric properties of low temperature dielectrics containing Li2O filler

Crystallization and dielectric properties of typical low temperature co-fired ceramics (LTCC) consisting of calcium zinc aluminoborosilicate glass and Al₂O₃ filler were investigated by substituting the Al₂O₃ filler partially with Li₂O at the levels of 2-10 wt%. Depending on the content of Li₂O, densification was found significantly affected by early crystallization that resulted from the formation of unexpected crystalline phases including LiAlSiO₄, Ca₂SiO₄, LiAlO₂, and LiAlSi₃O₈. The effect of hindering sintering via earlier crystallization became enormous regardless of firing temperature when >5 wt% Li₂O substitution occurred. It was observed that the substitution of 2 wt% Li₂O for Al₂O₃ was beneficial in producing promising performance at the low temperature of 750 °C, which can be highlighted with k ∼ 8.7 and tan δ ∼ 0.009 at 1 MHz.     

Plant Coumarins. 3. (+)-PTeryxin from <Emphasis Type="Italic">Peucedanum terebinthaceum</Emphasis>

The potentially medically valuable pyranocoumarin (+)-pteryxin was isolated for the first time from Peucedanum terebinthaceum Fischer et Turcz. The structure of (+)-pteryxin was rigorously proved using mass spectrometry, NMR, IR, and UV spectroscopy and comparison of the spectral characteristics of this compound and its basic hydrolysis products (+)-cis- and (−)-trans-khellactone and angelic and acetic acids. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 468–470, September-October, 2008.     

Relativistic-electron scattering on an atomic string of a crystal at ultrasmall angles of particle incidence on a string

The classical and quantum scattering of fast electrons on an atomic string of a crystal is considered at angles of particle incidence on the string that are much smaller than the critical angle of axial channeling. The investigation was performed within the simplest approximation of the continuous atomic-string potential in the form of a cutoff Coulomb potential. For this case, the azimuthal scattering of particles at an angle exceeding 180° in the plane orthogonal to the string axis is shown to be possible for all impact-parameter values. It is demonstrated that, in particle scattering on a string, an effect can occur that is similar to the Ramsauer-Townsend effect, which consists in a considerable reduction of the total cross section for slow-electron scattering on atoms.     

Crystalline fullerene deuteride C60D24: Spectral investigation

X-ray diffraction patterns, infrared and x-ray photoelectron spectra, and electron energy-loss spectra are obtained for fullerene deuteride C₆₀D₂₄ prepared by treating solid C₆₀ with D₂ gas. It is established that the deuteride is a polycrystalline powder with an fcc lattice (a ₀=14.55 Å). The product of thermal decomposition of the deuteride consists mainly of fullerene molecules separated by a distance much greater than in the initial fullerite.     

Water sorption and activation energy in polyimide thin films

The water sorption behavior and the activation energy were investigated for various chemical structure polyimide thin films; BPDA‐PDA, BPDA‐ODA, PMDA‐ODA, and 6FDA‐ODA. The activation energy for the water diffusion varied in the range of 5.53 to 9.27kcal/mol, and was in the increasing order: BPDA‐PDA < BPDA‐ODA < PMDA‐ODA < 6FDA‐ODA. BPDA‐PDA and BPDA‐ODA polyimide films showed relatively well‐ordered morphological structure, which results in relatively low diffusion coefficient and high activation energy. It was found that the diffusion coefficient and the activation energy are significantly related to the in‐plane orientation, crystallinity, and packing order in the polyimide thin films. The morphological structure was predominant factors for the water diffusion coefficient and activation energy in the polyimide thin films. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2714–2720, 2000     

Results of the Experiments on the Crystallization of a Ge–Si–Sb Solid Solution under the Conditions of Microgravity on the Soyuz–Apollo Spacecraft

Physics of the Solid State - Objective factors that allow the experiment on growing crystals of a Ge–Si–Sb solid solution on the Soyuz–Apollo spacecraft to take a special place...     

The new composites,polyacetylene-carbon nanotubes: Electrochemical properties

Polyacetylene- and carbon-nanotube-based composite materials are prepared by the method of polymerization filling for the first time. It is shown that the acetylene polymerization mainly occurs at catalytic centers attached to the carbon nanotubes. It follows from TEM data that in the case of single-wall nanotubes the polyacetylene fibriles are wound up onto the nanotubes. In the case of multi-wall nanotubes, polyacetylene can form separate bodies that are connected to the multi-wall nanotubes. The specific electrochemical capacity of the novel composite materials is nearly twice as large as compared with that of the composite prepared by mechanical mixing; it is by two orders of magnitude larger than the pure polyacetylene capacity. The reversibility of the Li⁺ intercalation-deintercalation electrode reaction appears significantly improved at the polyacetylene-carbon nanotubes composites.