Fabrication of composite fan blades using PMR A-type polyimide resin and graphite fiber reinforcement

PMR polyimides are safe, easy to handle, can be processed with relatively wide process controls, and offer excellent mechanical properties, with thermo-oxidative stability. Procedures, staging and cure schedules fully dense, crackfree, dimensionally controlled, complex structure: high tip speed fan blades 1.27 cm (0.5 in) thick

PMR polyimide/graphite fiber composite fan blades

Ultrahigh speed fan blades, designed in accordance with the requirements of an ultrahigh tip speed blade axial flow compressor, were fabricated from a high strength graphite fiber tow and a PMR polyimide resin. The PMR matrix was prepared by combining three monomeric reactants in methyl alcohol, and the solution was applied directly to the reinforcing fiber for subsequent in situ polymerization. Some of the molded blades were completely finished by secondary bonding of root pressure pads and an electroformed nickel leading edge sheath prior to final machining. The results of the spin testing of nine PMR fan blades are given. Prior to blade fabrication, heat resin tensile properties of the PMR resin were examined at four formulated molecular weight levels. Additionally, three formulated molecular weight levels were investigated in composite form with both a high modulus and a high strength fiber, both as-molded and postcured, in room temperature and 232 C transverse tensile, flexure and short beam shear. Mixed fiber orientation panels simulating potential blade constructions were also evaluated. Flexure tests, short beam shear tests, and tensile tests were conducted on these angle-plied laminates

Poverty impacts of a WTO agreement : synthesis and overview

This paper reports on the findings from a major international research project investigating the poverty impacts of a potential Doha Development Agenda (DDA). It combines in a novel way the results from several strands of research. Intensive analysis of the DDA Framework Agreement pays particularly close attention to potential reforms in agriculture. The scenarios are built up using newly available tariff line data and their implications for world markets are established using a global modeling framework. These world trade impacts, in turn, form the basis for 12 country case studies of the national poverty impacts of these DDA scenarios. The focus countries include Bangladesh, Brazil (two studies), Cameroon, China (two studies), Indonesia, Mexico, Mozambique, the Philippines, Russia, and Zambia. The diversity of approaches taken in these studies allows the paper to reflect local conditions and priorities and illustrates many important facets of the trade and poverty link. It does, however, limit the ability to draw broader conclusions. Thus an additional study provides a 15-country cross-section analysis, and a global analysis provides estimates for the world as a whole.Rural Poverty Reduction,Poverty Assessment,Free Trade,Economic Theory&Research,Achieving Shared Growth

Fiber reinforced PMR polyimide composites

Commercially obtained PMR-15 polyimide prepregs with S-glass and graphite fiber reinforcements were evaluated along with in-house prepared glass and graphite cloth PMR 2 materials. A novel autoclave approach was conceived and used to demonstrate that both the PMR systems respond to 1.4 MPa (200 psi) autoclave pressures to produce void free composites equivalent to die molded laminates. Isothermal gravimetric analysis and subsequent mechanical property tests indicated that the PMR 2 system was significantly superior in thermo-oxidative stability, and that S-glass reinforcements may contribute to the accelerated degradation of composites at 316 C (600 F) when compared to graphite fiber reinforced composites. Fully reversed bending fatigue experiments were conducted with a type of fixture unused for organic matrix composites. These studies indicated that the graphite fiber composites were clearly superior in fatigue resistance to the glass fiber reinforced material and that PMR matrix composite systems yield performance of the same order as composite materials employing other families of matrices

Composite impact strength improvement through a fiber/matrix interphase

Research was conducted to improve the impact strength and toughness of fiber/resin composites by means of a fiber coating interphase. Graphite fiber/epoxy resin composites were fabricated with four different fiber coating systems introduced in a matrix-fiber interphase. Two graphite fibers, a high strength and a high modulus type, were studied with the following coating systems: chemical vapor deposited boron, electroless nickel, a polyamide-imide resin and a thermoplastic polysulfone resin. Evaluation methods included the following tests: Izod, flexure, shear fracture toughness, longitudinal and transverse tensile, and transverse and longitudinal compression. No desirable changes could be effected with the high strength fiber, but significant improvements in impact performance were observed with the polyamide-imide resin coated high modulus fiber with no loss in composite modulus

Revenue Estimates for Eliminating Sales Tax Exemptions and Adding Services to the Sales Tax Base

This report provides revenue estimates for alternative combinations of eliminating sales tax exemptions and adding services to the sales tax base. FRC Report 17

Distributional effects of WTO agricultural reforms in rich and poor countries

Rich countries'agricultural trade policies are the battleground on which the future of the WTO's troubled Doha Round will be determined. Subject to widespread criticism, they nonetheless appear to be almost immune to serious reform, and one of their most common defenses is that they protect poor farmers. The authors'findings reject this claim. The analysis uses detailed data on farm incomes to show that major commodity programs are highly regressive in the United States, and that theonly serious losses under trade reform are among large, wealthy farmers in a few heavily protected subsectors. In contrast, analysis using household data from 15 developing countries indicates that reforming rich countries'agricultural trade policies would lift large numbers of developing country farm households out of poverty. In the majority of cases these gains are not outweighed by the poverty-increasing effects of higher food prices among other households. Agricultural reforms that appear feasible, even under an ambitious Doha Round, achieve only a fraction of the benefits for developing countries that full liberalization promises, but protect U.S. large farms from most of the rigors of adjustment. Finally, the analysis indicates that maximal trade-led poverty reductions occur when developing countries participate more fully in agricultural trade liberalization.Rural Poverty Reduction,Economic Theory&Research,Population Policies,Achieving Shared Growth

Analysis of nanopore detector measurements using Machine-Learning methods, with application to single-molecule kinetic analysis

<p>Abstract</p> <p>Background</p> <p>A nanopore detector has a nanometer-scale trans-membrane channel across which a potential difference is established, resulting in an ionic current through the channel in the pA-nA range. A distinctive channel current blockade signal is created as individually "captured" DNA molecules interact with the channel and modulate the channel's ionic current. The nanopore detector is sensitive enough that nearly identical DNA molecules can be classified with very high accuracy using machine learning techniques such as Hidden Markov Models (HMMs) and Support Vector Machines (SVMs).</p> <p>Results</p> <p>A non-standard implementation of an HMM, emission inversion, is used for improved classification. Additional features are considered for the feature vector employed by the SVM for classification as well: The addition of a single feature representing spike density is shown to notably improve classification results. Another, much larger, feature set expansion was studied (2500 additional features instead of 1), deriving from including all the HMM's transition probabilities. The expanded features can introduce redundant, noisy information (as well as diagnostic information) into the current feature set, and thus degrade classification performance. A hybrid Adaptive Boosting approach was used for feature selection to alleviate this problem.</p> <p>Conclusion</p> <p>The methods shown here, for more informed feature extraction, improve both classification and provide biologists and chemists with tools for obtaining a better understanding of the kinetic properties of molecules of interest.</p

Fishes of Morrow Creek, a Lower Ouachita River Tributary, in Southern Arkansas

The fishes of Moro Creek, a fifth order stream tributary of the lower Ouachita River in southern Arkansas, were sampled from 1972-1977. Field collections, literature records and museum records revealed a total of 63 species representing 14 families. An undescribed cyprinid, the bluehead shiner, is reported from Moro Creek for the first time. In general, longitudinal zonation of fish species was apparent as species diversity increased downstream. Stream inhabitants were typical Coastal Plain fishes of the lower Ouachita River system