Optical gain signal-to-noise ratio transfer efficiency as an index for ranking of phosphor- photodetector combinations used in X-ray medical imaging

Phosphor materials are used in medical imaging combined with radiographic film or other photodetectors. A parameter for choosing a phosphor material is the number of light photons produced per absorbed X-ray energy E, i.e. phosphor gain. Traditionally, a parameter for choosing the best photodetector for a phosphor material is the spectral matching factor, which denotes the percentage of the optical photons detected by the photodetector. However, this factor does not account for the phosphor gain neither in terms of signal strength nor in terms of noise. In this paper a new factor is introduced which evaluates phosphor-photodetector combinations in terms of optical gain signal-to-noise ratio matching. The proposed factor was implemented to some phosphor-photodetector combinations. It was found that for the narrow band emitting phosphors studied the results of the new factor and the matching factor were numerically the same. However, when not narrow bandwidth emitting phosphors were considered the results were numerically different. Additionally, for the case of CsI:Na phosphor different results were obtained in combinations ranking. PACS 78.65; 42.80     

An asymptotic result and a stability criterion for linear nonautonomous delay difference equations

Linear delay difference equations with variable coefficients and constant delays are considered. By the use of an appropriate solution of the so called generalized characteristic equation, an asymptotic result is obtained and a stability criterion is established.     

Micelles of poly(isoprene-b-2-vinylpyridine-b-ethylene oxide) terpolymers in aqueous media and their interaction with surfactants

Well-defined poly(isoprene-b-2-vinylpyridine-b-ethylene oxide) (PI-P2VP-PEO) triblock terpolymers were synthesized by anionic polymerization high-vacuum techniques. The terpolymers formed spherical three-layer (onion-type) micelles in neutral and acidic pH aqueous media as evidenced by static and dynamic light scattering. In pure water, kinetically frozen micelles with a core composed of a soft PI inner part and a hard P2VP outer shell and protected by a neutral PEO corona were formed. In acidic media the core was formed by the soft PI hydrophobic segment, whereas the corona consisted of an inner cationic polyelectrolyte P2VPH⁺ part and an outer PEO shell. The aggregation numbers were found to be high in all cases, due to the high hydrophobicity of the core-forming blocks. In the latter case an increase in size was observed due to the electrostatic repulsions between the P2VPH⁺ chains in the inner part of the corona, which is also responsible for the lower aggregation numbers observed in the acidic solutions. The interaction of these onion-type micelles with cationic (DTMAB) and anionic (SDS) surfactants led to the formation of mixed polymer/surfactant aggregates. Their structural characteristics could be varied by combining changes in surfactant type and concentration, solution pH and type of electrostatic interaction, leading to interesting, block-copolymer-based, environmentally responsive colloidal systems.     

Mössbauer study of 1% <Superscript>57</Superscript>Fe doped ferromagnetic insulator La<Subscript>0.825</Subscript>Ca<Subscript>0.175</Subscript>MnO<Subscript>3</Subscript>

We have employed magnetization measurements, M?ssbauer and ESR spectroscopic techniques, in order to study the ferromagnetic insulating (FMI) compound La_1-xCa_xMnO₃ (x=0.175) doped with 1% ⁵⁷Fe. We have used two samples; one prepared in air which has cation vacancies and a second in inert atmosphere, which is stoichiometric. An abrupt change of the experimental results is obtained, by all techniques, in the ferromagnetic insulating regime, in the temperature region of T_O/O//≈60 K, where an orbital rearrangement is suggested to occur. An analysis of these findings points to an orbital rearrangement transformation. Ferromagnetic resonance reveals considerable differences between stoichiometric and cation deficient samples, indicating anisotropy of the exchange interactions in the former sample with significant temperature dependence, most pronounced in the vicinity of T_O/O//     

Hysteretic Θ(S) Curve Prediction: Comparison of Two Models

The prediction of the first-order wetting and drying scanning curves is attempted by two different methods. These are: Mualem model II and Poulovassilis and Kargas (P–K). Model II by Mualem was chosen deliberately as the most appropriate. Experimental gr" align="BASELINE" BORDER="0"> (S) data obtained in the laboratory for a sand mixture and a real soil were used for the comparison. Moreover, data presented originally by Poulovassilis (1970) were also used for the same purpose. It is shown that the P–K method gives better results than Mualems model II. Some remarks on Mualems model are also included.     

A Generalization of the Poincaré--Bendixson Theorem for Compact 3-manifolds

It is shown that compressible cylindrical ends in compact foliated 3-manifolds spiral onto toral leaves.Mathematics Subject Classification (2000).57R30, 57M99.     

Congruences of Fluids in a Finslerian Anisotropic Space-Time

We derive the generalized Raychauduri equation concepts of expansion, shear and vorticity. We give the Ricci tensor of a constant-curvature Randers–Finsler space metric whose first term is the Robertson–Walker metric.Dedicated to the memory of Professor Nikolaos Danikas.     

Three dimensional divisorial extremal neighborhoods

In this paper we study divisorial extremal neighborhoods such that 0 ∈ X is a cA_n type threefold terminal singularity, and Γ=f(E) is a smooth curve, where E is the f-exceptional divisor. We view a divisorial extremal neighborhood as a one parameter smoothing of certain surface singularities, and based on this we give a classification of such neighborhoods.     

alpha-(Phenylazo)-4-nitrobenzyl cyanide, a new acid-base indicator

A new acid-base indicator, alpha-(phenylazo)-4-nitrobenzyl cyanide, is proposed. The indicator changes colour from yellow to violet in the presence of alkali owing to the formation of a nitronic acid structure. This indicator is applicable for the titration of weak acids in acetone and ethanol media or in a mixture of these organic solvents and water, with 0.1M aqueous sodium hydroxide as titrant. The absorption spectra have been recorded for the indicator in 25%, 50% and 75% aqueous ethanol and acetone. By means of the spectra the dissociation constants in these media have been determined. The pK value of alpha-(phenylazo)-4-nitrobenzyl cyanide is 12.10 in water, and is decreased considerably in acetone but only slightly in ethanol. This behaviour is similar to that of positively charged weak acids and irregular for a weak acid carrying no charge or a negative charge.