Neurulation is critical for the proper development of the central nervous system during embryogenesis. This process requires coordinated morphogenetic movements driven by localized cell movements. The key morphogenetic process responsible for lengthening the neural plate is convergent extension. During convergent extension medially oriented cell polarity, protrusive activity, and motility are thought to generate forces through cell intercalation resulting in stiffer elongating tissues. My research determines that forces that help shape the neural plate arise from morphogenetic movements in the neural tissue and determines PCP signaling regulates tissue stiffness in the neural ectoderm. We have established an experimental system sensitive enough to evaluate the stiffness of Xenopus neural tissue. Stiffness is measured by gluing two fine wires onto neural explants from an early gastrula stage Xenopus laevis embryo. The wires stretch the tissue at a constant strain rate using a real-time image-based feedback system and stiffness is determined by measuring the deflection of one wire. Measurements obtained from control embryos prior to neurulation estimate tissue stiffness at approximately 12.7 ± 0.53 mN/m in both mediolateral and anteroposterior directions. Stiffness measurements double in early neurula embryos (P < 0.05). Mediolateral stiffness, 24.9 ±6.2 mN/m, is significantly greater than anteroposterior stiffness, 21.4 ±5.3 mN/m (P < 0.05). These trends are strengthened in normalized data to reduce clutch-to-clutch variation. Expressions of dominant-negative Wnt11, Fz7, and Dsh constructs successfully disrupt neurulation by interfering with the PCP pathway. Changes in stiffness of the neural plate were measured and show reduced stiffness at early neurula stage in both mediolateral and anteroposterior directions suggesting mechanical forces are generated within the neural plate.

This dissertation primarily documents the quantification of the interfacial behavior of carbon based nanomaterials, which includes two categories, one is the nanofriction properties evaluation of aligned carbon nanotube carpets, few-layer graphene as well as three types of functionalized graphene nanoribbons, the second is the mechanical characterization of individual functionalized carbon nanofibers and the interfacial fracture toughness quantification in carbon nanotube/polymer derived ceramics nanocomposite. The aligned carbon nanotube carpets have a highly anisotropic friction behavior, which means the friction force are lower for transversely aligned CNTs side than for vertically aligned CNTs surface. We can also tune the friction properties of graphene ribbons by grafting different functional groups. In addition, two narrow angular regions with high friction, separated by a wide angular interval with low friction, were identified between graphene and highly oriented pyrolytic graphite. The distance between the two friction peaks is 61◦, which corresponds well with the 60◦ symmetry of individual atomic layers in the graphite lattice. The technique that involves the usage of mcirodevices and nanoidenter was used to conduct tensile tests on pristine, fluorinated and amino-functionalized carbon nanofibers, which were found to exhibit varied load-bearing abilities and unique fracture modes. The technique was also used to perform single fiber pullout experiments to study carbon nanotube/polymer derived ceramic interface.

Neurulation is critical for the proper development of the central nervous system during embryogenesis. This process requires coordinated morphogenetic movements driven by localized cell movements. The key morphogenetic process responsible for lengthening the neural plate is convergent extension. During convergent extension medially oriented cell polarity, protrusive activity, and motility are thought to generate forces through cell intercalation resulting in stiffer elongating tissues. My research determines that forces that help shape the neural plate arise from morphogenetic movements in the neural tissue and determines PCP signaling regulates tissue stiffness in the neural ectoderm. We have established an experimental system sensitive enough to evaluate the stiffness of Xenopus neural tissue. Stiffness is measured by gluing two fine wires onto neural explants from an early gastrula stage Xenopus laevis embryo. The wires stretch the tissue at a constant strain rate using a real-time image-based feedback system and stiffness is determined by measuring the deflection of one wire. Measurements obtained from control embryos prior to neurulation estimate tissue stiffness at approximately 12.7 ± 0.53 mN/m in both mediolateral and anteroposterior directions. Stiffness measurements double in early neurula embryos (P < 0.05). Mediolateral stiffness, 24.9 ±6.2 mN/m, is significantly greater than anteroposterior stiffness, 21.4 ±5.3 mN/m (P < 0.05). These trends are strengthened in normalized data to reduce clutch-to-clutch variation. Expressions of dominant-negative Wnt11, Fz7, and Dsh constructs successfully disrupt neurulation by interfering with the PCP pathway. Changes in stiffness of the neural plate were measured and show reduced stiffness at early neurula stage in both mediolateral and anteroposterior directions suggesting mechanical forces are generated within the neural plate.

Mechanical characterization of four polymer nanocomposite systems and two pure polymer reference systems was performed. Alumina (Al2O3) and magnetite (Fe3O4) nanoparticles were embedded in poly(methyl methacrylate) (PMMA) and polystyrene (PS) matrices. Mechanical testing techniques utilized include tensile testing, dynamic mechanical analysis (DMA), and nanoindentation. Consistent results from the three techniques proved that these nanocomposite systems exhibit worse mechanical properties than their respective pure polymer systems. The interphase, an interfacial area between the nanoparticle filler and the polymer matrix, was investigated using two approaches to explain the mechanical testing results. The first approach utilized data from thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM) to predict the structure and density of the interphase for the four nanocomposite systems. The second approach analyzed the bonding between the polymer and the nanoparticle surfaces using Fourier Transform Infrared Spectroscopy (FT-IR) to calculate the density of the interphase for the two PMMA-based nanocomposite systems. Results from the two approaches were compared to previous studies. The results indicate that Al2O3 nanoparticles are more reactive with the polymer matrix than are Fe3O4 nanoparticles, but neither have strong interaction with the polymer matrix. The poor interaction leads to low density interphase which results in the poor mechanical properties.

Polyethylene terephthalate is one of the most important engineering thermal plastics used for fibers, films and bottles. Despite its wide applications and vast global market, PET has shortcomings, which limits it usage in many areas. PET has a glass transition temperature (Tg) of 80 DEGREE Celsius, this temperature is too low for certain applications. Increase in glass transition temperature, high temperature mechanical properties, and dimensional stability is of great importance to further expand the applications of PET. Significant research efforts have been made toward this goal, using a variety of approaches. In this work, we attempt to improve the properties of PET melt spun filament. Three strategies has been investigated (i) copolymerization of more rigid comonomer, 4, 4' bibenzoate unit into the PET structure, (ii) UV crosslinking of functionalized PET fiber, and (iii) Reinforcing PET matrix with carbon nanofibers.

Cartapip-treated pulps are evaluated for increased strength properties / Thesis (Ph.D.)--Institute of Paper Science and Technology, 1995.

The objective of this work is to investigate the influence of hot rolling process on the mechanical properties of AA 5052 aluminum alloy. Hot-rolled band fabricated by tandem mill (hot-band A) will be compared with that fabricated by reverse mill hot-band C). Optical microscopic observations revealed that hot-band A has a uniform microstructure throughout the thickness, while hot-band C exhibits non-uniform microstructure, fine grains near the surface and coarser grains in the center. Both hot-bands were subjected to cold-rolling and annealing to O-temper. Two annealing processes were used: (a) annealing in 500oC salt bath, which may simulate the high heating rate of continuous annealing line (CAL), and (b) annealing in 320oC conventional air furnace with heating rate of 30oC/h, which may simulate the slow heating rate of batch-type annealing. In general, both materials annealed in 320oC air furnace exhibit higher yield strength than those annealed in 500oC salt bath do, however, both materials exhibit better tensile ductility after annealed in 500oC salt bath as compared with those annealed in 320oC air furnace.TEM examinations indicated that the cold-rolled sheet after annealing in 320oC air furnace contains larger number of precipitates comparing with its 500oC salt bath annealed counterpart. This observation may account for the higher yield strength of cold-rolled sheet annealed in 320oC air furnace. After cold-rolling and annealing in 320oC air furnace, the material C shows higher yield strength than the material A does. However, after annealing in 500oC salt bath, both materials have similar yield strength. XRD pole-figure analysis indicated that hot-band A exhibited stronger texture than hot-band C did. The texture intensity for both materials decreased considerably after cold-rolling and annealing. Orientation image mapping (OIM) obtained by EBSD (electron backscattered diffraction) analysis indicated that the grain boundaries in both materials after cold-rolling and annealing were mainly high angle boundaries, and the 500oC salt bath annealed specimens have more equiaxed grain shape as compared with the 320oC air furnace annealed specimens.

The work aims to manufacture AS-4/PEEK APC-2 nano-composite laminates first. We used the prepreg form of AS-4 Graphite/PEEK laminae to make APC-2 laminates of 2 mm thick with two lay-ups of cross-ply and quasi-isotropic totally 16 plies by a hot press via the modified diaphragm curing. The nano-particles SiO2 with the average diameter of 15¡Ó5 nm were uniformly spread in the specific interfaces of laminate. From mechanical testing it is found that the nanocomposite specimens of spreading 10 plies nanoparticles (3% by wt. of matrix) possesses the highest mechanical properties. we see that in cross-ply specimens the ultimate strength increases 10.91 % and stiffness 6.7 %; while in quasi-isotropic specimens the ultimate strength increases 12.48 % and stiffness 19.93 %. Second, repeat the tensile tests at 50, 75, 100, 125, 150¢J to receive respective stress-strain curve , strength and stiffness. At elevated temperatures the ultimate strength decreases slightly below 75¢J and the elastic modulus reduces slightly below 125¢J, however, both properties degrade highly at 150¢J ( Tg) for two layups generally. Finally, the constant stress amplitude tension-tension cyclic testing was conducted. It is found that both the stress-cycles (S-N) curves are very close below 104 cycles for cross-ply laminates w/wo nanoparticles, and the S-N curve of nano-laminate slightly bent down after 105 cycles. Whilst in quasi-isotropic laminates, the S-N curve of nano-laminate is always slightly below that of APC-2 laminate through the life.

Thesis (M.S.D.)--Indiana University School of Dentistry, 2009. / Title from PDF t. p. (viewed Feb. 9, 2009) Advisor(s): Jeffrey A. Platt, Chair of the Research Committee, Tien-Min Gabriel Chu, Michael A. Cochran, Bruce A. Matis, Burak Taskonak, B. Keith Moore. Curriculum vitae. Includes abstract. Includes bibliographical references (leaves 71-76).

Corroded steel in concrete is a structural issue that plaques concrete structures in coastal regions. Traditionally corroded steel strength is calculated from a distributed area loss due to corrosion over the entire surface of the steel and reducing the capacity accordingly. In reality, corrosion attacks localized regions creating pits and reducing the cross section in a small region which amplifies the effects of corrosion. Stress concentrations at the corrosion pitting damage may further reduce the tensile capacity of the steel. A study of corrosion damage and strength associated with pitting damage can assist in understanding the ultimate tensile capacity of corroded steel strands, better correlations are needed to estimate actual strength of damaged steel. The focus of this thesis is on seven-wire prestress steel strands with various stages of induced corrosion. Each strand has been documented, profiled, and measured in order to correlate physical damage with ultimate capacity.