University of Akron

About: University of Akron is a education organization based out in Akron, Ohio, United States. It is known for research contribution in the topics: Polymer & Polymerization. The organization has 17401 authors who have published 29127 publications receiving 702386 citations. The organization is also known as: The University of Akron.

Developments in implicit leadership theory and cognitive science: Applications to improving measurement and understanding alternatives to hierarchical leadership

Abstract: After reviewing key findings regarding leadership categorization theory, we develop new perspectives regarding the design of behavioral measures of leadership and the implications of shared leadership and complex adaptive leadership conceptualizations of leadership. In particular, by applying recent developments in cognitive science, we explain how an understanding of symbolic, connectionist, and embodied representations of knowledge can benefit behavioral measures of leadership. Additionally, we address some practical issues associated with the measurement of leadership and argue that ratings which tap episodic memory at the event level may be more meaningful than ratings based on semantic memory. Finally, we discuss how notions of shared leadership and of leaders as catalysts for complexity can create unique complications for leadership perceptions, coordinated behavior within a group, and the measurement of leadership.

DNA fibers by electrospinning

Abstract: Thin fibers of calf thymus Na-DNA were electrospun from aqueous solutions with concentrations from 0.3% to 1.5%. In electrospinning, a high voltage is used to create an electrically charged jet of liquid solution, which dries to leave a polymer fiber. The electrospun DNA fibers have diameters around 50 to 80 nm. The diameter of the electrospun fibers is an order of magnitude or more smaller than that of previously reported fibers. The DNA fibers were observed by optical microscopy, scanning electron microscopy, and transmission electron microscopy. Bead-like structures were observed on many of the fibers. During electrospinning a process called splaying causes the jet to split longitudinally into two smaller jets, which split again, repeatedly, until the very small diameter fibers are formed. The small-diameter fibers are transparent in ordinary 100 kV electron microscopes. Fibers can be spun from samples of DNA as small as 1 mg.

Gradient nanostructure and residual stresses induced by Ultrasonic Nano-crystal Surface Modification in 304 austenitic stainless steel for high strength and high ductility

Abstract: In this study, the effects of Ultrasonic Nano-crystal Surface Modification (UNSM) on residual stresses, microstructure changes and mechanical properties of austenitic stainless steel 304 were investigated. The dynamic impacts induced by UNSM leads to surface nanocrystallization, martensite formation, and the generation of high magnitude of surface compressive residual stresses (−1400 MPa) and hardening. Highly dense deformation twins were generated in material subsurface to a depth of 100 µm. These deformation twins significantly improve material work-hardening capacity by acting both as dislocation blockers and dislocation emission sources. Furthermore, the gradually changing martensite volume fraction ensures strong interfacial strength between the ductile interior and the two nanocrystalline surface layers and thus prevents early necking. The microstructure with two strong surface layers and a compliant interior embedded with dense nanoscale deformation twins and dislocations leads to both high strength and high ductility. The work-hardened surface layers (3.5 times the original hardness) and high magnitude of compressive residual stresses lead to significant improvement in fatigue performance; the fatigue endurance limit was increased by 100 MPa. The results have demonstrated that UNSM is a powerful surface engineering technique that can improve component mechanical properties and performance.

Failure Processes in Elastomers at or Near a Rigid Spherical Inclusion

Abstract: A systematic experimental study has been carried out of two distinct failure phenomena, cavitation and debonding, in an elastomer containing a rigid spherical inclusion. Several elastomers were employed containing glass beads of various diameters, ranging from 60 to 5000 μm, and with chemically different surfaces. The critical stress for cavitation was found to depend upon both Young's modulus, E, of the elastomer and the diameter of the bead. By extrapolation, it was found that the stress for cavitation near an infinitelylarge bead is given by 5E/12, as predicted by theory. In contrast, the critical stress for debonding decreased somewhat with increasing Young's modulus of the elastomer. This is attributed to a concomitant decrease in the strength of adhesion between the elastomer and the bead surface, due to rheological effects. The stresses for both cavitation and for debonding were found to vary approximately with the negative half-power of the bead diameter. This suggests that a similar Griffith mechanism governs both failure processes when the bead size is small. A study of cavitation and debonding in the presence of two glass beads was also carried out. As predicted from theoretical considerations, both stresses were found to decrease as the distance between the two beads was decreased, irrespective of the diameter of the bead and Young's modulus of the elastomer. At higher strains, however, a second cavitation process was found to take place at a point midway between the beads. Tensile fracture of the specimen resulted from the unrestrained lateral growth of the second cavity.

Self‐Reinforced melt processible polymer composites: Extrusion, compression, and injection molding

Abstract: Rheological properties, extrusion, fiber spinning, compression, and injection molding of blends of polycarbonate and two thermotropic liquid crystal polymers based on wholly aromatic copolyesters have been studied. Blends were prepared using an internal Banbury mixer and static Koch mixer. Based upon differential scanning calorimetry and dynamic mechanical measurements, these blends have been shown to be incompatible in the entire range of concentrations. During extrusion and injection molding at high strain rates, it has been observed that thermotropic liquid crystal polymer at concentrations 2.5, 5, and 10 percent by weight in situ forms high modulus and high strength fibers within the polycarbonate matrix leading to self-reinforced polymer composites. The tensile strength of the composite containing 10 percent of liquid crystal polymer exceeds that of the pure components. In addition, anisotropy of properties of the injection molded parts has been found to substantially reduce in a comparison with that of liquid crystal polymer. The processing conditions and technique for the production of self-reinforced polymer composite during processing of the blends have been identified. This has been done by measurements of mechanical properties, direct observation of morphology, and by theoretical calculation using simplified composite theory for the unidirectional continuous fiber-reinforced composites. At the high concentrations, 25 and 50 percent by weight, thermotropic liquid crystal polymer forms large spherical droplets inside polycarbonate leading to highly brittle material. This is in distinction from the fibrous, high modulus tough composites formed at the lower concentrations.