Dosimetric characteristic of a new 125I brachytherapy source

A new brachytherapy (125)I source has been investigated at Iranian Agricultural, Medical and Industrial Research School. Dosimetric characteristics [dose-rate constant Λ, radial dose function g(l)(r) and anisotropy function F(r,)] of IRA-(125)I were theoretically determined in terms of the updated AAPM task group 43 (TG-43U1) recommendations. Versions 5 and 4C of the Monte Carlo radiation transport code were used to calculate the dosimetry parameters around the source. The Monte Carlo calculated dose-rate constant of the (125)I source in water was found to be 92×10(-4) Gy h(-1) U(-1) with an approximate uncertainty of ±3 %. Brachytherapy seed model, 6711-(125)I, carrying (125)I radionuclides, was modelled and benchmarked against previously published values. Finally, the calculated results were compared with the published results of those of other source manufacturers.     

A density-based fuzzy clustering technique for non-destructive detection of defects in materials

In non-destructive testing and evaluation of materials, defects contain visible aggregations of similar levels of brightness with large scale of correlation between them. In most cases, these brightnesses have no notable contrast relative to non-defect counterparts. However, the density and the size of the defect are visually the most notable features. In this paper, we have utilized human conception for classifying defects by the fusion of fuzzy clustering method and fuzzy logic rules based on the density and the size of the defect. The probability of detection and the probability of error are compared with the Bayes classifier. The proposed approach shows that there is less dependency between the variation of density and size of a defect and variations of noise density and distribution. Experimental images from eddy current, ultrasonic and radiography techniques are investigated. It is shown that the new approach reduces the noise and drift, leading to a better detection of defects.     

The effect of initiator‐to‐monomer ratio on the properties of the polybutadiene‐ol synthesized by free radical solution polymerization of 1,3‐butadiene

Polybutadiene‐ol was synthesized by solution radical polymerization of 1,3‐butadiene in the presence of hydrogen peroxide as initiator and 2‐propanol as solvent. The ratio of initiator to monomer molar concentration, [I₀]/[M₀], was varied while temperature, reaction time and the type and amount of solvent were kept constant. The effects on the M_n; M_w; M_v; PDI, OH‐number and functionality of the synthesized polyols were studied. By taking several samples during a polymerization batch and analyzing them, the time of reaction was chosen as 100 min, after which the PDI changed dramatically. M_n decreased exponentially with increasing [I₀]/[M₀] according to the relationship M_n = 565.55 ([I₀]/[M₀])^?0.7553. The decrease observed in M_w gradually levelled off with increasing [I₀]/[M₀] and molecular weight distribution broadened at larger values of [I₀]/[M₀]. The OH‐number increases with [I₀]/[M₀]. In addition to the number‐average molecular weight, functionality is dependent on the number of hydroxyl‐terminated chain radicals in the reaction medium. Copyright © 2003 Society of Chemical Industry     

A modified segment-based nonrandom two-liquid model for the calculation of vapor-liquid equilibrium of aqueous polymer-salt solutions

A new model for representation of the excess Gibbs energy of polymer-electrolyte solutions is proposed. The excess Gibbs energy of a polymer-electrolyte solution is expressed as a sum of contributions of a combinatorial, a long-range and a short-range excess Gibbs energy term. The Flory-Huggins expression and the Pitzer's extension of Debye-Hückel function are used, respectively, as a combinatorial and a long-range contribution to the excess Gibbs energy. A new expression based on the local composition concept, which is the modified nonrandom two-liquid (NRTL) model, is developed to account for the short-range contribution to the excess Gibbs energy. The model provides a versatile and flexible thermodynamic framework for both correlating and predicting the phase equilibrium of electrolyte solutions, polymer solutions and complex systems containing both electrolytes and polymers. The utility of the model is demonstrated with successful representation of vapor-liquid equilibrium of several PEG or PPG-salt-H₂O systems at different polymer molar masses. Results are compared with those obtained from the NRTL model.     

An optimal proportional-plus-integral/tracking control law for aircraft applications

An optimal proportional-plus-integral/tracking control law is formulated. The control law has a command augmentation system configuration suitable for implementation on a digital computer on-board an aircraft. The proposed configuration offers the flexibility for choosing a feedforward matrix incorporating a set of additional control elements and for shaping the transient response without affecting the steady-state tracking property. Assuming the system is open-loop stable, then in the presence of a "jam" the disengaged system will maintain the steady-state tracking property which is desirable for aircraft continuing their mission.     

An analogue approach to surface definition

This note describes a method for producing cubic curves made up from Bézier functions on an oscilloscope screen using simple analogue techniques. Ruled surface patches are illustrated in a simple extension of the method. It also indicates how generalized Bézier patches could be produced.     

Study of crystal structure of (polyvinylidene fluoride/clay) nanocomposite films: Effect of process conditions and clay type

Three Polyvinylidene fluoride (PVDF) different in molecular structure were used to produce nanocomposities films by cast extrusion with a particular emphasis on maximizing the β crystal phase content. The PVDF/clay compounding followed by cast film production was carried out through melt extrusion using a twin screw extruder equipped with a slit die. X‐ray diffraction (XRD) results showed that clay melt intercalation is almost similar for all three PVDFs. The XRD results also revealed that nanocomposite films from PVDF with branched chain structure (PVDFB) generated the greatest amount of β phase. FTIR spectroscopy measurements confirmed the XRD results but also revealed that significant stretching of the melt films at the die or rapid cooling would adversely affect the formation of β phase. The amount of β phase obtained based on nanoclay compounding was compared with that obtained from conventional method: stretching of molded PVDF film with initial α phase. Stretching of PVDF film at 60°C yielded pure β phase that means complete transformation of α to β. From mechanical properties, tensile tests were carried out on PVDF nanocomposite films to evaluate mechanical strength. PVDF with low molecular weight exhibited a very low strain at break while branched PVDF and high molecular weight PVDF could sustain more strain. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers