Narrow Results

To ensure the safe operation of many safety critical structures such as nuclear plants, aircraft and oil pipelines, non-destructive imaging is employed using piezoelectric ultrasonic transducers. These sensors typically operate at a single frequency due to the restrictions imposed on their resonant behavior by the use of a single length scale in the design. To allow these transducers to transmit and receive more complex signals it would seem logical to use a range of length scales in the design so that a wide range of resonating frequencies will result. In this paper, we derive a mathematical model to predict the dynamics of an ultrasound transducer that achieves this range of length scales by adopting a fractal architecture. In fact, the device is modeled as a graph where the nodes represent segments of the piezoelectric and polymer materials. The electrical and mechanical fields that are contained within this graph are then expressed in terms of a finite element basis. The structure of the resulting discretized equations yields to a renormalization methodology which is used to derive expressions for the non-dimensionalized electrical impedance and the transmission and reception sensitivities. A comparison with a standard design shows some benefits of these fractal designs.

Vinylidene fluoride-trifluoroethylene copolymer films of molar ratio 70/30 with thickness of about 1 $\mu$m have been deposited from solution in ethyl methyl ketone to a glass substrate with an aluminum electrode by spin coating. The solution has been filtrated through a PTFE membrane filter with pore size 0.2 $\mu$m directly before spin coating or it has been used as is (unfiltrated). After deposition of a top electrode, the samples have been polarized by hysteresis loops with an electric field amplitude of about 100 V/$\mu$m. In samples, annealed at temperature 145${}^{\circ }$C for 3 h, a high remanent polarization of about 7.5 $\mu$C/cm² has been achieved, without significant differences between samples fabricated of filtrated or unfiltrated solution. Spherulitic lamella are growing in films fabricated of filtrated solution when they are heated above the melting temperature to 159${}^{\circ }$C for 3 min before the further annealing process at 145${}^{\circ }$C. These films show substantially lower remanent polarization below 4 $\mu$C/cm². Pyroelectric images recorded with a pyroelectric laser scanning microscope show that the spherulites have very small pyroelectric activity, i.e., the spherulites consist of flat-on lamella. In contrast, no spherulitic lamella are growing in films fabricated of unfiltrated solution heated above the melting temperature, melted and annealed under the same conditions. An explanation for this observation is that filtrating changes the structure of the copolymer in solution from polymer coil to rod. Copolymer rods deposited on a substrate will crystallize in flat-on lamella when heated above the melting temperature, in contrast to copolymer coils which crystallize in edge-on lamella.

The probability density for the area A enclosed by a polymer loop in crossed electric-magnetic fields is evaluated using the Hida-Streit formulation. In this approach, the many possible conformations of the polymer, x(v) and y(v), are represented by paths and are parametrized in terms Brownian motion. When the magnetic field is switched off, results agree with the works of Khandekar and Wiegel⁵

Mechanisms of plasma-surface interaction are required to understand in order to control the reactions precisely. Recent progress in atmospheric pressure plasma provides to apply as a tool of sterilization of contaminated foodstuffs. To use the plasma with safety and optimization, the real time in situ detection of free radicals - in particular dangling bonds by using the electron-spin-resonance (ESR) technique has been developed because the free radical plays important roles for dominantly biological reactions. First, the kinetic analysis of free radicals on biological specimens such as fungal spores of Penicillium digitatum interacted with atomic oxygen generated plasma electric discharge. We have obtained information that the in situ real time ESR signal from the spores was observed and assignable to semiquinone radical with a g-value of around 2.004 and a line width of approximately 5G. The decay of the signal was correlated with a link to the inactivation of the fungal spore. Second, we have studied to detect chemical modification of edible meat after the irradiation. Using matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF-MS) and ESR, signals give qualification results for chemical changes on edible liver meat. The in situ real-time measurements have proven to be a useful method to elucidate plasma-induced surface reactions on biological specimens.

The scaling expression for fractional Brownian modeled linear polymer chains was obtained both theoretically and numerically. Through the probability distribution of fractional Brownian paths, the scaling was found out to be 〈R²〉 ~ N^2H, where R is the end-to-end distance of the polymer chain, N is the number of monomer units and H is the Hurst parameter. Numerical data was generated through the use of Monte Carlo simulation implementing the Metropolis algorithm. Results show good agreement between numerical and theoretical scaling constants after some parameter optimization. The probability distribution confirmed the Gaussian nature of fractional Brownian motion and the behavior is not affected by varying values of the Hurst parameter and of the number of monomer units.

Chemical approaches to creating new drug delivery systems and biomaterials are discussed. These delivery systems have been used to study how blood vessels grow and how different molecules affecting the brain behave. They have also been used in treatments ranging from schizophrenia to brain cancer.

By synthesizing new polymeric materials and combining them with growth factors or cells, new tissues and organs can potentially be created for use in drug testing-thereby potentially reducing animal and human testing- and to treat disease. Examples discussed include blood vessels, heart muscle, spinal cord repair, artifi cial skin, cartilage, and pancreas.

Immunotherapy has offered an alternative therapy method for cancer patients with metastatic tumors or who are not suitable for surgical resection. Different from traditional surgery, radiotherapy and chemotherapy, immunotherapy mainly restores the activity of the body’s own immune cells silenced in the tumor microenvironment to achieve anticancer therapy. Gene therapy which corrects abnormal expression of immune cells in tumor microenvironment by delivering exogenous genes to specific immune cells, is the most widely studied immunotherapy. Although most available gene delivery vectors are still viral vectors, the further application of viral vectors is still limited by the immunogenicity and mutagenesis. Based on this, cationic polymeric gene vectors with high flexibility, high feasibility, low cost and high safety have been widely used in gene delivery. The structural variability of polymers allows specific chemical modifications to be incorporated into polymer scaffolds to improve their physicochemical properties for more stable loading of genes or more targeted delivery to specific cells. In this review, we have summarized the structural characteristics and application potential in cancer immunotherapy of these polymeric gene vectors based on poly(L-lysine), poly(lactic-co-glycolic acid), polyethyleneimine, poly(amidoamine) and hydrogel system.