The sol/gel contribution to the behavior of γ-irradiated poly(vinylidene fluoride)

Poly(vinylidene fluoride) films were γ-irradiated in the dose range of 1–20 Mrad, resulting in up to 74% gel. The irradiated polymer undergoes both crosslinking and chain scission, about 5 : 3 events, respectively. Swelling measurements indicate an increasing crosslink density with the gel content, already at the lower doses. Thermal analysis of the gel fraction and the unextracted irradiated samples shows that although crosslinking affects the crystallization, degree of crystallinity, and the melting characteristics, the behavior of the crosslinked material is predominantly controlled by the extractable sol fraction which consists of the more mobile original chains, branched chains, and degraded ones. The crosslinks, already at low density, retard the development of ordinary crystalline polymer morphology.     

Structure and properties of molded polyblends containing liquid crystalline polymers

The relationship between the microstructure developed during injection molding of liquid crystalline polymers (LCPs) containing blends and their mechanical properties, was studied. A wholly aromatic copolyester LCP was melt blended in various levels with polycarbonate (PC), poly(butylene terephthalate) (PBT), Nylon 6 (N-6), and amorphous nylon (AN). In all cases the LCP was the minor component. The resulting injection molded structure had a distinct skin core morphology, where elongated fibrous LCP particles comprised the skin layer and spherical and ellipsoidal ones composed the core section. The highest elongation and the finest diameter LCP fibrils were obtained with AN/LCP system, followed by PC/LCP. PBT/LCP blends showed a coarser morphology, while N-6/LCP system did not correlate with the tensile moduli of the injection molded specimens. AN/LCP blends demonstrated the highest moduli values, consistent with the highest orientations observed using electron microscopy, followed by PC/LCP, PBT/LCP, and N-6/LCP. Finally, tensile strength levels were correlated with both orientation levels and interfacial adhesion between the polyblend components. AN/LCP that exhibited the highest orientation and good adhesion appearance gave the highest tensile strength values followed by PC/LCP, PBT/LCP, and N-6/LCP polyblends.     

Quantum key distribution by a free-space MIMO system

Quantum key distribution (QKD) systems for use in future free-space optical communication links restrict communication to a low bit rate. In this paper, increasing the QKD bit rate using a communication system that includes a multiple-input-multiple-output quantum key distribution (MQKD) is proposed. Such a system can enable a number of receivers to communicate simultaneously with a number of transmitter elements, which consequently increases the overall QKD bit rate. However, due to scattering and turbulence in the atmospheric channel, this method may introduce interference effects when a photon transmitted from one transmitter element reaches the wrong detector element in the receiver. These interference effects reduce the system bit rate and increase the quantum bit error rate. A novel mathematical model for analyzing the effect of crosstalk and interference on the MQKD system performance is derived. The results of the analysis indicate that atmospheric effects impair performance. In order to mitigate the atmospheric effect, using several wavelengths simultaneously is suggested. Criteria to define the number of wavelengths that are required to achieve a given performance are also provided.     

Potential of MRI and Ultrasound Radiation Force in Elastography: Applications to Diagnosis and Therapy

Elastography has many exciting new areas of application in the domains of diagnosis and therapy. We present in this overview the current gold standard given by MR elastography, which uses a full three-dimensional approach to solve locally for the unknown complex shear modulus at one frequency. Clinical results for benign and malignant breast lesions are shown. Less rigorous in terms of data completeness, but significantly faster and easier to apply, we introduce the ultrasound-based supersonic shear imaging technique, which uses acoustic radiation force to generate inside the medium planar shear waves. Subsequent ultrafast imaging of the propagating shear wave allows one to recuperate detailed time-of-flight maps of in-vivo breast lesions. Lastly, we present initial results for using magnetic resonance imaging and acoustic radiation force together for high-intensity focused ultrasound interventions.     

Evaluation of an in situ sampling probe for its accuracy in determining particle size distributions from flames

An in situ sampling probe for flames is evaluated for any biases with respect to size distributions in a given size and concentration range. Ultrafine metal particles (Pd, Pt) suspended in argon gas are added to a laminar diffusion flame, burning with argon-diluted methane. Samples of combustion aerosol are extracted from the flame via a small orifice and immediately quenched with nitrogen. The size distribution of the metal particles, recorded at various sampling positions in the flame, is found to be but little affected by the flame and the sampling procedure. The distribution of carbonaceous soot particles from an unseeded flame at a fixed sampling position is not shifted upon seeding but coexists next to the peak from the metallic flame additive. It is concluded that droplets of volatile combustion products, formed in the sampling system through homogeneous nucleation, do not significantly contribute to the soot particle signal. An investigation of the photoelectric yield of the samples implies significant changes of the surface properties of the metal particles during the combustion process. This seeding method offers a new path to study chemical processes in the flame, especially heterogeneous and catalytic reactions of flame gases with particles.     

Properties of type K expansive cement of pure components I. Hydration of unrestrained paste of expansive component — Results

A mixture of $\text{C}{}_4\text{A}{}_3\text{S}\text{, C}\text{S}\text{H}{}_2\text{and CH}$, in stoichiometric ratio to form ettringite only was paste hydrated at temperatures between 20–50°C. Unrestrained specimens were tested for expansion, porosity, strength and hydration at different times. Expansions started at a critical degree of hydration α_cr, at which total porosity was minimum and strength was maximum. Raising curing temperature reduced α_cr and enhanced expansion and total porosity. Mercury intrusion porosimetry revealed a bimodal pore size distribution.