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

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

8-Bromo-2-methyl­quinoline

In the crystal structure of the title compound, C10H8BrN, the dihedral angle between the two six-membered rings of the quinoline system is 0.49 (16)°. The mol­ecules are packed in a face-to-face arrangement fashion, with a centroid–centroid distance of 3.76 Å between the benzene and pyridine rings of adjacent mol­ecules. No hydrogen bonding is found in the crystal structure

Role of optical coherence tomography angiography in myopic choroidal neovascularization after intravitreal injections of Ranibizumab

AIM: To investigate the change of myopic choroidal neovascularization treated by ranibizumab and evaluate their value in monitoring the effect of anti- vascular endothelial growth factor(VEGF)therapy.METHODS: The study enrolled 30 patients(30 eyes)diagnosed with myopic choroidal neovascularization. All affected eyes were treated with intravitreal ranibizumab 0.05mL(10mg/mL). Best corrected visual acuity(BCVA), non-contact tonometer, ophthalmoscope, fundus fluorescein angiograph(FFA)and OCTA were evaluated monthly until 6mo. The changes of BCVA and central macular thickness(CMT)were compared at 1, 3 and 6mo after treatment.RESULTS: All patients received an average of 1.70±0.65 injections. BCVA was 0.96±0.17(LogMAR)before therapy, and BCVA 1, 3 and 6mo after treatment respectively improved by 0.23±0.09, 0.34±0.07, 0.38±0.11. The differences were significant(t=5.461, 8.191, 8.894; Pt=12.007, 13.360, 9.531; PCONCLUSION: Intravitreal ranibizumab for CNV secondary to pathologic myopia is effective and safe; OCTA is a noninvasive and time-saving new technology, and it also is a promising tool for clinicians to make preliminary diagnosis and assess treatment efficacy in the follow-up visits

Quantum-Hall plateau-plateau transition in top-gated epitaxial graphene grown on SiC (0001)

We investigate the low-temperature magneto-transport properties of monolayer epitaxial graphene films formed on the Si-face of semi-insulating 4H-SiC substrates by a high temperature sublimation process. A high-k top-gate on the epitaxial graphene is realized by inserting a fully oxidized nanometer thin aluminum film as a seeding layer, followed by an atomic layer deposition process. At low temperatures, the devices demonstrate a strong field effect by the top gate with an on/off ratio of ~7 and an electron mobility up to ~3250 cm^2/Vs. After the observation of the half-integer quantum Hall effect for monolayer epitaxial graphene films, detailed magneto-transport measurements have been carried out including varying densities, temperatures, magnetic fields and currents. We study the width of the distinguishable quantum-Hall plateau to plateau transition (Landau level index n=0 to n=1) as temperature (T) and current are varied. For both gate voltage and magnetic field sweeps and T>10 K the transition width goes as T^{-\kappa} with exponent \kappa ~0.42. This universal scaling exponent agrees well with those found in III-V heterojunctions with short range alloy disorders and in exfoliated graphene.Comment: accepted by Journal of Applied Physic