Eddy current inspection of graphite fiber components

The recognition of defects in materials properties still presents a number of problems for nondestructive testing in aerospace systems. This project attempts to utilize current capabilities in eddy current instrumentation, artificial intelligence, and robotics in order to provide insight into defining geometrical aspects of flaws in composite materials which are capable of being evaluated using eddy current inspection techniques. The unique capabilities of E-probes and horseshoe probes for inspecting probes for inspecting graphite fiber materials were evaluated and appear to hold great promise once the technology development matures. The initial results are described of modeling eddy current interactions with certain flaws in graphite fiber samples

Improved navigation by combining VOR/DME information with air or inertial data

The improvement was determined in navigational accuracy obtainable by combining VOR/DME information (from one or two stations) with air data (airspeed and heading) or with data from an inertial navigation system (INS) by means of a maximum-likelihood filter. It was found that the addition of air data to the information from one VOR/DME station reduces the RMS position error by a factor of about 2, whereas the addition of inertial data from a low-quality INS reduces the RMS position error by a factor of about 3. The use of information from two VOR/DME stations with air or inertial data yields large factors of improvement in RMS position accuracy over the use of a single VOR/DME station, roughly 15 to 20 for the air-data case and 25 to 35 for the inertial-data case. As far as position accuracy is concerned, at most one VOR station need be used. When continuously updating an INS with VOR/DME information, the use of a high-quality INS (0.01 deg/hr gyro drift) instead of a low-quality INS (1.0 deg/hr gyro drift) does not substantially improve position accuracy

Controlling the Assembly of Nanoparticles in Polymer Blends

While many novel methods have been devised for directing the assembly of nanoparticles in block copolymers, the topic has not reached the same level of sophistication for polymer blends. The assembly of particles at the interface between phase-separated domains can serve as a means to compatibilize polymer blends, reducing domain sizes and enhancing interdomain adhesion by impeding coalescence and decreasing interfacial tension. Compatibilization optimizes the performance of blended materials in applications where the properties of both components must be expressed synergistically, such as in plastics requiring both high strength and high toughness and in photovoltaic films. Thus, approaches to robustly control particle location in blends, especially those generating interfacial adsorption, are a much sought-after goal. This dissertation is a discussion of such approaches. Recognizing that Janus particles present a promising route to achieving interfacial adsorption of particles in an immiscible blend, we attempted the synthesis of several types of Janus particles with the goal of producing one that could kinetically stabilize a bicontinuous morphology in a blend during spinodal decomposition. Using ternary blends of polystyrene (PS), poly(methyl methacrylate) (PMMA), and Janus particles (JPs) with symmetric PS and PMMA hemispheres, we demonstrated the stabilization of dispersed and bicontinuous phase-separated morphologies by the interfacial adsorption of Janus particles during demixing upon solvent evaporation. The resulting blend morphology was varied by changing the blend composition and JP loading. Increasing particle loading decreased the size of phase-separated domains, while altering the mixing ratio of the PS/PMMA homopolymers produced morphologies ranging from PMMA droplets in a PS matrix to PS droplets in a PMMA matrix. Notably, bicontinuous morphologies were obtained at intermediate blend compositions, marking the first report of highly continuous domains obtained through demixing in a blend compatibilized by Janus particles. The JPs were found to assemble in a densely packed monolayer at the interface, thus largely preventing coalescence of domains in films annealed above the glass transition temperature. The rate of solvent evaporation from the drop-cast films and the molecular weights of the homopolymers were found to greatly affect blend morphology. In another approach, we used specific interactions to direct the localization of nanoparticles both within each phase and to the interface in a polymer blend. Using hydrogenbond- accepting nanoparticles, gold nanoparticles with poly(styrene-r-2-vinyl pyridine) (P(S-r- 2VP)) ligands, and two copolymers featuring competitive hydrogen-bond donation, poly(styrene-r-hydroxy styrene) (P(S-r-HS)) and poly(methyl methacrylate-r-2-hydroxyethyl methacrylate) (P(MMA-r-HEMA)), we demonstrated that the particles exhibit a distribution of locations strongly favoring the phase in which the total hydrogen-bonding interaction strength is greater. When HEMA/HS interactions were balanced, the particles displayed interfacial adsorption. This apparent balance occurs at a consistent ratio of HEMA/HS across several HEMA compositions. Annealing above the glass transition temperature generally induced adsorption at the interface between the two copolymers. Favorable hydrogen bonding interactions between phases increase the compatibility of the copolymers and can induce miscibility; the lower prevalence of hydrogen bonding at elevated temperatures is thus associated with increased interfacial tension, providing a greater driving force for the interfacial adsorption of 5 particles. This work marks one of the few reports regarding stimuli-responsive relocation of nanoparticles in a polymer blend, and could have fundamental application in gaining better understanding of the effect of particle location on the rheology and structural development of blends

A terminal guidance scheme for lifting body entry vehicles

Perturbation feedback guidance for terminal phase of lifting body entry vehicl

Do Job Security Guarantees Work?

We investigate the effect of employer job security guarantees on employee perceptions of job security. Using linked employer-employee data from the 1998 British Workplace Employee Relations Survey, we find job security guarantees reduce employee perceptions of job insecurity. This finding is robust to endogenous selection of job security guarantees by employers engaging in organisational change and workforce reductions. Furthermore, there is no evidence that increased job security through job guarantees results in greater work intensification, stress, or lower job satisfaction

Integrating modes of policy analysis and strategic management practice : requisite elements and dilemmas

There is a need to bring methods to bear on public problems that are inclusive, analytic, and quick. This paper describes the efforts of three pairs of academics working from three different though complementary theoretical foundations and intervention backgrounds (i.e., ways of working) who set out together to meet this challenge. Each of the three pairs had conducted dozens of interventions that had been regarded as successful or very successful by the client groups in dealing with complex policy and strategic problems. One approach focused on leadership issues and stakeholders, another on negotiating competitive strategic intent with attention to stakeholder responses, and the third on analysis of feedback ramifications in developing policies. This paper describes the 10 year longitudinal research project designed to address the above challenge. The important outcomes are reported: the requisite elements of a general integrated approach and the enduring puzzles and tensions that arose from seeking to design a wide-ranging multi-method approach