29,453 research outputs found
Low cost fabrication development for oxide dispersion strengthened alloy vanes
Viable processes were developed for secondary working of oxide dispersion strengthened (ODS) alloys to near-net shapes (NNS) for aircraft turbine vanes. These processes were shown capable of producing required microstructure and properties for vane applications. Material cost savings of 40 to 50% are projected for the NNS process over the current procedures which involve machining from rectangular bar. Additional machining cost savings are projected. Of three secondary working processes evaluated, directional forging and plate bending were determined to be viable NNS processes for ODS vanes. Directional forging was deemed most applicable to high pressure turbine (HPT) vanes with their large thickness variations while plate bending was determined to be most cost effective for low pressure turbine (LPT) vanes because of their limited thickness variations. Since the F101 LPT vane was selected for study in this program, development of plate bending was carried through to establishment of a preliminary process. Preparation of ODS alloy plate for bending was found to be a straight forward process using currently available bar stock, providing that the capability for reheating between roll passes is available. Advanced ODS-NiCrAl and ODS-FeCrAl alloys were utilized on this program. Workability of all alloys was adequate for directional forging and plate bending, but only the ODS-FeCrAl had adequate workability for shaped preform extrustion
Static-pressure contours in the blade passage at the tip of several high Mach number rotors
Static pressure contours of turbine rotor blade tips at high Mach number
Fast C-V method to mitigate effects of deep levels in CIGS doping profiles
In this work, methods to determine more accurate doping profiles in
semiconductors is explored where trap-induced artifacts such as hysteresis and
doping artifacts are observed. Specifically in CIGS, it is shown that this fast
capacitance-voltage (C-V) approach presented here allows for accurate doping
profile measurement even at room temperature, which is typically not possible
due to the large ratio of trap concentration to doping. Using deep level
transient spectroscopy (DLTS) measurement, the deep trap responsible for the
abnormal C-V measurement above 200 K is identified. Importantly, this fast C-V
can be used for fast evaluation on the production line to monitor the true
doping concentration, and even estimate the trap concentration. Additionally,
the influence of high conductance on the apparent doping profile at different
temperature is investigated
Problem-based Learning: A Critical Rationalist Perspective
Although problem-based learning is being adopted by many institutions around the world as an effective model of learning in higher education, there is a surprising lack of critique in the problem-based learning literature in relation to its philosophical characteristics. This paper explores epistemology as a starting point for investigating the theoretical underpinnings of problem-based learning as a learning model. Criticisms of empiricism are analysed in terms of the perceived learning outcomes of learners undertaking a problem-based learning curriculum. It is argued that models of empiricism theorised by philosophers such as Bacon, Locke and Hume cannot fully account for the learning model found in problem-based learning curricula. It is proposed that an alternative epistemological approach is needed. The work of Karl Popper is discussed, whose critical rationalist epistemology emphasises the generation of bold conjectures and criticism. Popper's work shows a positive contribution to the demands of higher education, characterised by learners who are serious about making professional progress. The paper concludes by critically analysing the tensions and contradictions of problem-based learning in light of Popper's epistemological theory of critical rationalism. It is argued that a critical rationalist perspective has educational benefits for students as it creates an environment rich in critical thinking, reading and writing and values disjunction and challenge
Ks band secondary eclipses of WASP-19b and WASP-43b with the Anglo-Australian Telescope
We report new Ks band secondary eclipse observations for the hot-Jupiters
WASP-19b and WASP-43b. Using the IRIS2 infrared camera on the Anglo-Australian
Telescope (AAT), we measured significant secondary eclipses for both planets,
with depths of 0.287 -0.020/+0.020% and 0.181 -0.027/+0.027% for WASP-19b and
WASP-43b respectively. We compare the observations to atmosphere models from
the VSTAR line-by-line radiative transfer code, and examine the effect of C/O
abundance, top layer haze, and metallicities on the observed spectra. We
performed a series of signal injection and recovery exercises on the observed
light curves to explore the detection thresholds of the AAT+IRIS2 facility. We
find that the optimal photometric precision is achieved for targets brighter
than Kmag = 9, for which eclipses as shallow as 0.05% are detectable at >5
sigma significance.Comment: Accepted for publication in MNRAS, 13 pages, 10 figure
Failure assessment of lightly reinforced floor slabs. I: Experimental investigation
This paper is concerned with the ultimate behavior of lightly reinforced concrete floor slabs under extreme loading conditions. Particular emphasis is given to examining the failure conditions of idealized composite slabs which become lightly reinforced in a fire situation as a result of the early loss of the steel deck. An experimental study is described which focuses on the response of two-way spanning floor slabs with various materials and geometric configurations. The tests enable direct assessment of the influence of a number of key parameters such as the reinforcement type, properties, and ratio on the ultimate response. The results also permit the development of simplified expressions that capture the influence of salient factors such as bond characteristics and reinforcement properties for predicting the ductility of lightly reinforced floor slabs. The companion paper complements the experimental observations with detailed numerical assessments of the ultimate response and proposes analytical models that predict failure of slab members by either reinforcement fracture or compressive crushing of concrete. © 2011 American Society of Civil Engineers
Analysis and application of digital spectral warping in analog and mixed-signal testing
Spectral warping is a digital signal processing transform which shifts the frequencies contained within a signal along the frequency axis. The Fourier transform coefficients of a warped signal correspond to frequency-domain 'samples' of the original signal which are unevenly spaced along the frequency axis. This property allows the technique to be efficiently used for DSP-based analog and mixed-signal testing. The analysis and application of spectral warping for test signal generation, response analysis, filter design, frequency response evaluation, etc. are discussed in this paper along with examples of the software and hardware implementation
Systems study for an Integrated Digital-Electric Aircraft (IDEA)
The results of the Integrated Digital/Electric Aircraft (IDEA) Study are presented. Airplanes with advanced systems were, defined and evaluated, as a means of identifying potential high payoff research tasks. A baseline airplane was defined for comparison, typical of a 1990's airplane with advanced active controls, propulsion, aerodynamics, and structures technology. Trade studies led to definition of an IDEA airplane, with extensive digital systems and electric secondary power distribution. This airplane showed an improvement of 3% in fuel use and 1.8% in DOC relative to the baseline configuration. An alternate configuration, an advanced technology turboprop, was also evaluated, with greater improvement supported by digital electric systems. Recommended research programs were defined for high risk, high payoff areas appropriate for implementation under NASA leadership
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