Multiple scattering theory for polycrystalline materials with strong grain anisotropy: theoretical fundamentals and applications

This work is a natural extension of the authors previous work, Multiple scattering theory for heterogeneous elastic continua with strong property fluctuation, theoretical fundamentals and applications, which established the foundation for developing multiple scattering model for strongly scattering heterogeneous elastic continua. In this work, the corresponding multiple scattering theory for polycrystalline materials with randomly oriented anisotropic crystallites is developed. As applications in ultrasonic nondestructive evaluation, we calculated the dispersion and attenuation coefficient of one of the most important polycrystalline materials in aeronautics engineering, high temperature titanium alloys. The effects of grain symmetry, grain size, and alloying elements on the dispersion and attenuation behaviors are examined. Key information is obtained which has significant implications for quantitatively evaluating the average grain size, monitoring the phase transition, and even estimating gradual change in chemical composition of titanium components in gas turbine engines. For applications in seismology, the velocities and Q-factors for both hexagonal and cubic polycrystalline iron models for the Earth uppermost inner core are obtained in the whole frequency range. This work provides a universal, quantitative model for characterization of a large variety of polycrystalline materials. It also can be extended to incorporate more complicated microstructures, including ellipsoidal grains with or without textures, and even multiphase polycrystalline materials. The new model demonstrates great potential of applications in ultrasonic nondestructive evaluation and inspection of aerospace and aeronautic structures. It also provides a theoretical framework for quantitative seismic data explanation and inversion for the material composition and structural formations of the Earth inner core.Comment: 37 pages, 16 figure

Parameter interdependence and success of skeletal muscle modelling

In muscle and movement modelling it is almost invariably assumed that force actually exerted is determined by several independent factors. This review considers the fact that length force characteristics are not a relatively fixed property of muscle but should be considered the product of a substantial number of interacting factors. Level of activation and recruitment are influential factors in relation to aspects of muscle architecture. For the level of activation effects of its short term history (potentiation, fatigue in sustained contractions) have to be taken into account and are reviewed on the basis of recent experimental results as well as available literature. History is also an important determinant for the effect of length changes. This concept is introduced on the basis of recent experimental evidence as well as available literature. Regarding effects of muscle architecture, the concepts of primary and secondary distribution of fibre mean sarcomere length are introduced as well as effects of muscle geometry for mono- and bi-articular muscles on those distributions. Implications for motor control are discussed and the need for intramuscular coordination indicated

Muscle force is determined also by muscle relative position: isolated effects

Effects on force of changes of the position of extensor digitorum longus muscle (EDL) relative to surrounding tissues were investigated in rat. Connective tissue at the muscle bellies of tibialis anterior (TA), extensor hallucis longus (EHL) and EDL was left intact, to allow myofascial force transmission. The position of EDL muscle was altered, without changing EDL muscle–tendon complex length, and force exerted at proximal and distal tendons of EDL as well as summed force exerted at the distal tendons of TA and EHL muscles (TA+EHL) were measured. Proximal and distal EDL forces as well as distal TA+EHL force changed significantly on repositioning EDL muscle.\ud \ud These muscle position–force characteristics were assessed at two EDL lengths and two TA+EHL lengths. It was shown that changes of muscle force with length changes of a muscle is the result of the length changes per se, as well as of changes of relative position of parts of the muscle. It is concluded that in addition to length, muscle position relative to its surroundings co-determines isometric muscle force.\ud \ud Keywords: Intermuscular and extramuscular connective tissue; Myofascial force transmission; Rat m. extensor digitorum longus (EDL); Sarcomere length; Muscle relative positio

Spray Techniques And Lung Cancer Chemoprevention

Chemoprevention is a promising approach to decrease the incidence of lung cancer in current and former smokers. Directly delivering drugs to the lung could lead to a high concentration in the target organ with a lower dose compared to other means of administration. The primary advantages of aerosol delivery in treating lung diseases include improving the bioavailability of the drug in the lung, decreasing the medicine dose, rapid action, and reducing the systemic toxicity as well as side effects. Spray techniques are widely used for aerosol delivery. Two spray techniques were evaluated in this study for their applications in lung cancer chemoprevention. One is the spray-drying process which was used to study the inhibitory effects of chemopreventive agents in lung tumorigenesis using the A/J mice model. The other is a twin-head electrospray: THES) to generate chemopreventive agent particles. Six single agents and three combinational agents, both natural and synthetic compounds, were investigated in the first part of this dissertation work. Polyphenon E and Polyphenon E without EGCG, which are mixtures of tea catechins, were studied to investigate the prevention mechanism of the mixture. Resveratrol was delivered in aerosol form to improve its efficacy, because it did not show any inhibitory effects in the dietary form due to its low bioavailability in the lung. Gefitinib and erlotinib were delivered via aerosols to decrease the dose to prevent severe skin toxicities associated with high dosages. The effect of aerosolized budesonide was studied. It was further combined with diet Polyphenon E, diet indole-3-carbinal, or oral pioglitazone in the animal study for the inhibitory effects over lung carcinogenesis. Aerosol characterization and drug concentration in different organs of mice, after exposure to the drug aerosols, were also carried out to facilitate the data interpretation. In the second part of this work, a twin-head electrospray system was developed to be used as an aerosol generator in animal studies of lung cancer chemoprevention. The system consists of two electrospray heads: one producing positively charged particles and the other for negatively charged ones. The coagulation between oppositely charged droplets generated by the THES was verified in three ways. The size evolution due to coagulation was studied for particles from 10 nm to 710 nm. The effect of the initial charge level on the coagulation process was investigated using dual-capillary ES. The residual charges on coagulated particles were measured. The particle transmission efficiency through the THES system was also characterized. The effect of particle mixing on the coagulation process was also investigated. The THES was then used to generate PLGA-based controlled release drug particles. Two drugs, budesonide and pioglitazone, were coated with PLGA using dual-capillary heads in the THES. Particles in various sizes and different drug-to-polymer ratios were prepared. The release profiles of prepared drug particles before and after coagulation were compared to investigate the release characteristics of THES-prepared drug particles. A promising application of the THES, as an electrospray inhaler, was also proposed