New approach to simulation of radiative-conductive heat transfer in semi-transparent crystals being pulled from a melt

A method is suggested for the solution of multi-dimensional radiative heat transfer problems arising in growing crystals. The basic idea of the approach lies in the construction of a special division of the unit sphere into a set of solid angles (cells) and in the approximation of the radiation intensity in each solid angle by the P₁ approximation. The radiant transport equation is satisfied in the mean over each elementary cell and the system of partial differential equations of the second order relative to the local zeroth-moments of radiation intensity are obtained. It is shown that the solid angle subdivision can be carried out in different ways with respect to specific features of the heat transfer problem under consideration. As a result even a very rough partition permits satisfactory accuracy of the numerical solutions. One of the main advantages of the method consists in using solid angle subdivisions which can be varied from point to point of the spatial domain. The latter gave possibility to simulate the radiative heat transfer in a circular cylinder of finite length with specular side surface. On this basis the calculation of the temperature field in a cylindrical sapphire crystal being pulled from the melt has been carried out without any restriction on the size of the crystal     

Process optimisation of MOVPE growth by numerical modelling of transport phenomena including thermal radiation

A global transport model for the MOVPE of III–V growth based on the finite volume solution of coupled flow, heat and mass transfer, including detailed radiative transfer, multicomponent diffusion and homogeneous and heterogeneous chemical reactions, is presented. For radiative transfer modelling, a combined approach is used of grey-diffuse view-factor based heat flux exchange between the semi-transparent reactor walls through the transparent reactor interior, and a spherical harmonics approximation for the radiative-conductive heat transfer problem in participating massive quartz elements with complex shapes. The described modelling approach is applied to the horizontal multiwafer radial flow Planetary Reactor™, validated experimentally and used for process improvements. The mutual interaction of changing radiation properties at internal solid boundaries due to semiconductor coatings and thermal behaviour in that particular MOVPE reactor is discussed.     

Preparation and characterization of fluorine-containing acrylate copolymers by Co γ-ray radiation co-polymerization

A series of fluorine-containing acrylate copolymers were prepared by ⁶⁰Co γ-ray radiation co-polymerization in a mixed acrylate system, including butyl acrylate, acrylic acid, acrylonitrile, N-hydroxymethyl acrylamide and perfluoroalkylethyl methacrylate (FMA). The yield of the copolymers reached 96% when they were radiated for 34 h with the radiation dose of 1 kGy/h. Moreover, the surface structure and properties of the copolymers were determined by Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and contact angle (CA) analysis. And the glass-transition temperature was measured by dynamic mechanical thermal analysis (DMTA). It was found that the fluoropolymer was of large water static contact angle and fluorine was enriched at the polymer-air interface. The relationship between the copolymer composition, annealed temperature and static contact angle was also discussed in detail. Furthermore, when the FMA content reached 3%, the cotton treated with our products exhibited better oil repellency.     

Radiation resistance and molecular structure of poly(arylene ether sulfone)s

The radiation resistance of a series of aromatic polysulfones comprising alternating units of diphenyl sulfone and various aromatic diols has been investigated by measuring volatile products, soluble fractions and electron spin resonance (ESR) spectra. The yields of radicals at 77 K observed by ESR and of SO₂ at 423 K have indicated that biphenol gives enhanced resistance to Y radiation, and tetramethyl bisphenol-A decreased resistance, relative to bisphenol-A, bisphenol-S and hydroquinone. The protective effect of bisphenol was confirmed by lower scission and crosslinking yields determined from the soluble fractions after high doses.     

Study on polytetrafluoroethylene aqueous dispersion irradiated by gamma ray

Gamma-radiation induced degradation of polytetrafluoroethylene (PTFE) in 60 wt.% dispersion was studied in the dose range of 20-200 kGy and the change in property of PTFE was characterized by differential scanning calorimetry (DSC), photon cross correlation spectroscopy (PCCS), X-ray diffraction (XRD), scanning electron microscopy (SEM), FT-IR spectroscopy and X-ray photoelectron spectroscope (XPS). It was found that the mean particle size of PTFE reduces from 250 nm of the control to 170 nm at 100 kGy, as confirmed by dynamic laser scattering and SEM. The crystallinity degree of PTFE increased at 20 kGy but remained unvaried at higher dose level. G-value of scission, G(s), was determined to be 0.46 μmol/J.     

Dynamics of three-body half collisions: Ultraviolet and visible photodissociation of s-tetrazine

Ultraviolet (266 nm) and visible (532 nm) photodissociation of collision-free s-tetrazine show asymmetric dynamics with production of one translationally cool and one translationally hot HCN molecule. Furthermore, visible and ultraviolet dynamics are nearly identical, arguing that two-photon excitation is necessary for photodissociation in the visible.     

Experimental study of triplet exciton diffusivity in crystalline pyrene at 300 K

Preliminary measurements of the triplet diffusivity tensor in crystalline pyrene at 300 K are reported. Maximum diffusivity occurs along the b axis and D_ab = (1.25 ± 0.3) × 10^?4 cm² s^?1. Diffusion in the ac′ plane is nearly isotropic with D ≈ (0.3 ± 0.1) × 10^?4 cm² s^?1. These results are tentatively interpreted as diffusion dominated by nonlocal scattering.     

Preparation of cation exchange membrane as a separator for the all-vanadium redox flow battery

Chlorosulfonated homogeneous polyethylene (PE) dense film (PE-X) and asymmetric membrane (MH-X) were tested as separators for the all-vanadium redox flow battery. The membranes are prepared by the vapour phase chlorosulfonation of the PE film. The measured lowest resistivites equilibrated in 2 M KCl aqueous solution were 0.27 Ω cm² and 0.96 Ω cm², respectively, for PE-X (with thickness 20 μm) and for MH-X (with PE-layer 20 μm). The area resistivities of the membranes as separators in the all-vanadium redox flow battery were obtained. At a charge-discharge current density 633 A/m², these values were 3.09 Ω cm² and 3.46 Ω cm², respectively, for charge and discharge PE-X, and were 3.26 Ω cm² and 8.30 Ω cm², respectively, for charge and discharge MH-X.     

Study on slow release anti-cancer drugs prepared by radiation induced polymerization

This paper reports the research results which the anticancer drugs Ara-C with controlled slow release were made by radiation induced polymerization of monomers such as methacrylates at room temperature. Our studies showed that not only hydrophilic synthetic polymers but also hydrophobic polymers such as hydrophobic methacrylates (including MMA, EMA, and BMA) could be used to the immobilization. In vitro the rate of drugs release was controlled by the many factors such as the content of drugs, the monomer material, the crosslinking agent, the irradiation dose and the water content, etc.     

186Re/188Re labeled polypeptide microspheres as a potential radiation synovectomy agent

Polypeptide microspheres containing polycysteine crosslinked with polylysine were prepared and radiolabeled with¹⁸⁶Re and¹⁸⁸Re. High labeling yields with the microspheres with both¹⁸⁶Re and¹⁸⁸Re (97%) were obtained, and above 99% retention of radiolabels in water in 24 hours was obtained. Rhenum-186 labeled polycysteine and polylysine microspheres (11 ratio, 20 m as mean diameter) were injected intra-articularly into the rear stifes (knee joints) of normal New Zealand white rabbits. About 87% of injected dose was retained in rabbit stifles and adjacent tissues in 96 hours after injection, while most of the activity lost from the joints was excreted in the urine. Due to its simplicity of preparation and radiolabeling, versatility, and biodegradability, this type of conjugate system may become the therapeutics of choice for radiation synovectomy.