Theoretical Wood Densitometry: I Mass Attenuation Equations and Wood Density Models

Theoretical linear and mass attenuation equations that model X-ray attenuation processes of both monoatomic and polyatomic absorbers with homogeneous or heterogeneous structures have been derived. The reaction mechanisms of photons to atoms, as well as relevant atomic parameters, have been used in the development of parametric expressions that relate attenuation coefficients to important radiation parameters—including X-ray energy, absorber thickness, incident angle, and absorber density. To better understand the physical process to be modeled, systematic analyses and critical comparisons of attenuation equations of different X-ray sources and various absorbers are reported in simple physical and mathematical contexts. To address the wood densitometric problems that we encounter, theoretical formulas for transmission probabilities and wood density calculation have also been developed. Examples are provided to demonstrate uses of these theoretical models in calculating (1) atomic mass attenuation coefficients for major elements as well as minor ash elements in wood, (2) mass attenuation coefficients of coniferous wood, (3) transmission probabilities under various combinations of radiation parameters, and (4) wood density of pine heartwood. Throughout this mathematical treatment, emphases have been placed on the microscopic point of view for modeling and the parametric formulation for describing X-ray transmission experiments

Theoretical Wood Densitometry: II. Optimal X-ray Energy For Wood Density Measurement

Using a comparable approach, we extended the theoretical X-ray wood densitometric models to a case encountered in practice. Optimal X-ray energy was treated as the photon energy of the X-radiation which produced the maximum radiation resolution, as measured by differential transmission probabilities detected in a densitometric experiment. Parametric representation of radiation resolutions revealed that the maximum resolution of a specific densitometric procedure is governed by the range of densities in a given wood. The maximum radiation resolution obtainable in a particular wood densitometric experiment can be calculated readily from two equations derived in this study. Examples show that under "good architecture" conditions (1) transmission probabilities for a given wood densitometric experiment increase their magnitudes as the X-ray becomes more energetic, yet the maximum radiation resolution remains constant for a given set of parametric values; (2) optimal X-ray energies, for nine types of coniferous wood, are in the range of 5.13-5.69 keV for 1.0-mm-thick samples; (3) wood with a broader density range results in higher maximum resolution when irradiated by the theoretically optimal X-ray energy; and (4) accurate wood density measurements could be achieved only if the radiation energy used was near the optimal level. Regarding the architecture of a radiation detection system, the advantage of using a monochromator to reduce the X-ray energy continuum so as to increase the accuracy of wood density measurements was examined

Relativistic nucleon optical potentials with isospin dependence in Dirac Brueckner Hartree-Fock approach

The relativistic optical model potential (OMP) for nucleon-nucleus scattering is investigated in the framework of Dirac-Brueckner-Hartree-Fock (DBHF) approach using the Bonn-B One-Boson- Exchange potential for the bare nucleon-nucleon interaction. Both real and imaginary parts of isospin-dependent nucleon self-energies in nuclear medium are derived from the DBHF approach based on the projection techniques within the subtracted T -matrix representation. The Dirac potentials as well as the corresponding Schrodinger equivalent potentials are evaluated. An improved local density approximation is employed in this analysis, where a range parameter is included to account for a finite-range correction of the nucleon-nucleon interaction. As an example the total cross sections, differential elastic scattering cross sections, analyzing powers for n, p + 27Al at incident energy 100 keV < E < 250 MeV are calculated. The results derived from this microscopic approach of the OMP are compared to the experimental data, as well as the results obtained with a phenomenological OMP. A good agreement between the theoretical results and the measurements can be achieved for all incident energies using a constant value for the range parameter.Comment: 10 pages, 16 figure

Production of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) from excess activated sludge as a promising substitute of pure culture

通讯作者地址: Wang, YPThis study aimed to investigate the feasibility and technology to harvest poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) by mixed culture. Copolymer PHBHHx, usually fermented by pure strains, was reported to be synthesized from activated sludge for the first time. Sodium laurate was used as the sole carbon substrate for sludge acclimation and PHBHHx accumulation. Batch experiments were designed to look into the impact of the carbon, nitrogen, phosphorus and oxygen supply on PHBHHx production. The results showed that the acclimated excess sludge was able to produce PHBHHx, and the maximum output (505.6 mg/L PHBHHx containing 6.34 mol% HHx) was achieved with conditions of the continuous aeration, nitrogen and phosphorus limitation, and adequate carbon source implemented by pulse feeding 0.5 g/L sodium laurate every 4 h. Moreover, composition and structure of the PHBHHx from sludge were found similar to that from pure culture, according to literature, FTIR and NMR spectra. Finally, high-throughput sequencing technique characterized that phylum Chlorobi and genus Leadbetterella should be critical groups for PHBHHx synthesis in the sludge community.National Basic Research Program of China 2013CB733505 National Natural Science Foundation of China 21206143 41271260 Program for New Century Excellent Talents in University NCET-12-0326 Development and Reform Commission of Fujian Province, China 2011-159

Theoretical calculations and analysis for n + 6

R-matrix theory is an important methodology for applications on light, medium and heavy mass nuclides nuclear reaction in the resonance energy range. Full R-matrix formalism contains the diagonal elements of the energy levels matrix and it is a rigorous theory. Because of different assumptions and approximations, many kinds of R-matrix derived methods are obtained. The new R-matrix code FDRR is presented and includes 4 kinds of R-matrix applications. It can be used for calculating integral cross sections and angular distributions of 2-bodies reactions. The cross sections and angular distributions of n+ 6Li reaction are calculated and analyzed by FDRR code. The results are in good agreement with experimental data below 20 MeV

Theoretical calculations and analysis for n +

R-matrix theory is an important methodology for applications on light, medium and heavy mass nuclides nuclear reaction in the resonance energy range. Full R-matrix formalism contains the diagonal elements of the energy levels matrix and it is a rigorous theory. Because of different assumptions and approximations, many kinds of R-matrix derived methods are obtained. The new R-matrix code FDRR is presented and includes 4 kinds of R-matrix applications. It can be used for calculating integral cross sections and angular distributions of 2-bodies reactions. The cross sections and angular distributions of n+ 6Li reaction are calculated and analyzed by FDRR code. The results are in good agreement with experimental data below 20 MeV

Theoretical calculations and analysis for n + 6Li reaction

R-matrix theory is an important methodology for applications on light, medium and heavy mass nuclides nuclear reaction in the resonance energy range. Full R-matrix formalism contains the diagonal elements of the energy levels matrix and it is a rigorous theory. Because of different assumptions and approximations, many kinds of R-matrix derived methods are obtained. The new R-matrix code FDRR is presented and includes 4 kinds of R-matrix applications. It can be used for calculating integral cross sections and angular distributions of 2-bodies reactions. The cross sections and angular distributions of n+ 6Li reaction are calculated and analyzed by FDRR code. The results are in good agreement with experimental data below 20 MeV

The nucleon microscopic optical potential based on the Skyrme interaction

The nucleon microscopic optical potential based on the conventional and extended Skyrme interactions are achieved by the single-particle Green function method through nuclear matter approximation and local density approximation. The nucleon-nucleon scattering observables are calculated by the obtained microscopic optical potential and the results are compared with the corresponding experimental data. Good agreement is generally obtained between them

The nucleon microscopic optical potential based on the Skyrme interaction

The nucleon microscopic optical potential based on the conventional and extended Skyrme interactions are achieved by the single-particle Green function method through nuclear matter approximation and local density approximation. The nucleon-nucleon scattering observables are calculated by the obtained microscopic optical potential and the results are compared with the corresponding experimental data. Good agreement is generally obtained between them

Microscopic optical potentials for Li isotopes

The microscopic optical potentials for Li isotopes (A=6,7) without free parameter are obtained by folding the microscopic optical potentials of their internal nucleons with density distributions generated from corresponding internal wave functions of Li isotopes. An isospin-dependent nucleon microscopic optical potential based on the Skyrme nucleon-nucleon effective interaction is used as the nucleon optical potential. Shell model is employed to construct the internal wave functions of Li isotopes and derive their density distributions of internal nucleons. The Li microscopic optical potentials are used to calculate the elastic-scattering angular distributions and reaction cross sections. The results reproduce experimental data well and are comparable to those calculated by phenomenological optical model potentials in many cases