3,481 research outputs found
Comparison of blade loads of fixed and free yawing wind turbine
The self regulating composite bearingless wind turbine utilizes an automatic pitch control concept and a completely unrestrained yawing degree of freedom. Aerodynamic moments caused by skewed flow provide the control to align the wind turbine with the wind. Model tests demonstrated the feasibility of the concept and analytical studies showed the free system to experience lower blade loads compared to the fixed system
Nominal Logic Programming
Nominal logic is an extension of first-order logic which provides a simple
foundation for formalizing and reasoning about abstract syntax modulo
consistent renaming of bound names (that is, alpha-equivalence). This article
investigates logic programming based on nominal logic. We describe some typical
nominal logic programs, and develop the model-theoretic, proof-theoretic, and
operational semantics of such programs. Besides being of interest for ensuring
the correct behavior of implementations, these results provide a rigorous
foundation for techniques for analysis and reasoning about nominal logic
programs, as we illustrate via examples.Comment: 46 pages; 19 page appendix; 13 figures. Revised journal submission as
of July 23, 200
A social history of Somerville, Massachusetts 1630-1842
Thesis (Ed.M.)--Boston University, 1949. This item was digitized by the Internet Archive
Alien Registration- Cheney, Ivy M. (Monticello, Aroostook County)
https://digitalmaine.com/alien_docs/33926/thumbnail.jp
Investigation of a bearingless helicopter rotor concept having a composite primary structure
Experimental and analytical investigations were conducted to evaluate a bearingless helicopter rotor concept (CBR) made possible through the use of the specialized nonisotropic properties of composite materials. The investigation was focused on four principal areas which were expected to answer important questions regarding the feasibility of this concept. First, an examination of material properties was made to establish moduli, ultimate strength, and fatigue characteristics of unidirectional graphite/epoxy, the composite material selected for this application. The results confirmed the high bending modulus and strengths and low shear modulus expected of this material, and demonstrated fatigue properties in torsion which make this material ideally suited for the CBR application. Second, a dynamically scaled model was fabricated and tested in the low speed wind tunnel to explore the aeroelastic characteristics of the CBR and to explore various concepts relative to the method of blade pitch control. Two basic control configurations were tested, one in which pitch flap coupling could occur and another which eliminated all coupling. It was found that both systems could be operated successfully at simulated speeds of 180 knots; however, the configuration with coupling present revealed a potential for undesirable aeroelastic response. The uncoupled configuration behaved generally as a conventional hingeless rotor and was stable for all conditions tested
Fitting theories of nuclear binding energies
In developing theories of nuclear binding energy such as density-functional
theory, the effort required to make a fit can be daunting due to the large
number of parameters that may be in the theory and the large number of nuclei
in the mass table. For theories based on the Skyrme interaction, the effort can
be reduced considerably by using the singular value decomposition to reduce the
size of the parameter space. We find that the sensitive parameters define a
space of dimension four or so, and within this space a linear refit is adequate
for a number of Skyrme parameters sets from the literature. We do not find
marked differences in the quality of the fit between the SLy4, the Bky4 and SkP
parameter sets. The r.m.s. residual error in even-even nuclei is about 1.5 MeV,
half the value of the liquid drop model. We also discuss an alternative norm
for evaluating mass fits, the Chebyshev norm. It focuses attention on the cases
with the largest discrepancies between theory and experiment. We show how it
works with the liquid drop model and make some applications to models based on
Skyrme energy functionals. The Chebyshev norm seems to be more sensitive to new
experimental data than the root-mean-square norm. The method also has the
advantage that candidate improvements to the theories can be assessed with
computations on smaller sets of nuclei.Comment: 17 pages and 4 figures--version encorporates referee's comment
Students Voicing Collegiate Recovery
Young adults increasingly enter college with substance use addiction. Some may achieve recovery before setting their foot on a college campus whereas others during their college years. These students often struggle to maintain sobriety as they act out their daily lives because they find themselves in abstinence-hostile environments (Bugbee et al., 2016; Harris et al., 2008). This presentation will discuss students’ collegiate recovery experiences and will report on a photovoice project documenting students’ recovery experience and recovery management and support needs. Photovoice is a participatory social action method that uses photography to answer research questions (Wang, 2006); a photovoice exhibit, involving a gallery of participants’ photographs and linked narrative text to explicate the photos’ meaning, disseminates the findings. The presentation will focus on the narratives of students in recovery and attendees will obtain an in-depth understanding of recovery students’ experiences of stigma, shame and isolation, and marginalized social positions, which are intimately tied to their addiction histories. Students in recovery represent an invisible student group that struggles to access resources and needed healthcare services. The photovoice method can act as a powerful tool to empower marginalized students to share their recovery experiences and articulate their needs; ultimately providing a vehicle for structural-level and systemic change
It Could Not Be Seen Because It Could Not Be Believed on June 30, 2013
Nineteen Prescott Fire Department, Granite Mountain Hot Shot
(GMHS) wildland firefighters (WF) perished in Arizona in June 2013 Yarnell Hill
Fire, an inexplicable wildland fire disaster. In complex wildland fires, sudden,
dynamic changes in human factors and fire conditions can occur, thus mistakes can
be unfortunately fatal. Individual and organizational faults regarding the predictable,
puzzling, human failures that will result in future WF deaths are
addressed. The GMHS were individually, then collectively fixated with abandoning
their Safety Zone to reengage, committing themselves at the worst possible
time, to relocate to another Safety Zone - a form of collective tunnel vision. Our
goal is to provoke meaningful discussion toward improved wildland firefighter
safety with practical solutions derived from a long-established wildland firefighter
expertise/performance in a fatality-prone profession. Wildfire fatalities are
unavoidable, hence these proposals, applied to ongoing training, can significantly
contribute to other well-thought-out and validated measures to reduce them
Book Reviews
Book Reviews of: G. de Bertier de Sauvigny, La France et les français vus par les voyageurs américains, 1814-1948 (Flammarion, 1982-1985) Mary Midgley, Wickedness: A Philosophical Essay (Routledge & Kegan Paul, 1984) Jerome Bruner, Actual Minds, Possible Worlds (Harvard University Press, 1986
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