2,860 research outputs found
Rotorcraft convertible engine study
The objective of the Rotorcraft Convertible Engine Study was to define future research and technology effort required for commercial development by 1988 of convertible fan/shaft gas turbine engines for unconventional rotorcraft transports. Two rotorcraft and their respective missions were defined: a Fold Tilt Rotor aircraft and an Advancing Blade Concept (ABC) rotorcraft. Sensitivity studies were conducted with these rotorcraft to determine parametrically the influence of propulsion characteristics on aircraft size, mission fuel requirements, and direct operating costs (DOC). The two rotorcraft were flown with conventional propulsion systems (separate lift/cruise engines) and with convertible propulsion systems to determine the benefits to be derived from convertible engines. Trade-off studies were conducted to determine the optimum engine cycle and staging arrangement for a convertible engine. Advanced technology options applicable to convertible engines were studied. Research and technology programs were identified which would ensure technology readiness for commercial development of convertible engines by 1988
An effective approach to improve the performance of PC-based superplasticizer in alkali-activated slag
The lack of workability has hindered the industriallisation of alkali-activated slag
(AAS) - a novel, low carbon cementitious building material. In order to address this main barrier,
adding superplasticiser (SP) is essential. The main reason causing the dysfunction of current
commercial SP in AAS has been identified as competitive adsorption between the SPs and the
activators. The separate SP addition methods (adding SP and activator separately) offers the
potentials to tackle the above issue. In this paper, the effects of separate addition methods of
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lignosulfonate superplasticiser (LS) in AAS activated by NaOH were investigated. The adsorption
between the LS and the slag was examined to understand the interaction between the SP and the
slag. The workability and rheological properties of fresh NaOH-activated slag and the compressive
strength of hardened NaOH-activated slag were also investigated. The results indicated that the
separate addition methods reduced the competitive adsorption between the SPs and the NaOH
activator, leading to a higher adsorption of the SPs on the slag. Consequently, the workability and
rheological properties of NaOH-activated slag was enhanced by separate addition methods without
reducing the compressive strength of hardened NaOH-activated slag
Bostonia. Volume 6
Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs
Homotopy types of stabilizers and orbits of Morse functions on surfaces
Let be a smooth compact surface, orientable or not, with boundary or
without it, either the real line or the circle , and
the group of diffeomorphisms of acting on by the rule
, where and .
Let be a Morse function and be the orbit of under this
action. We prove that for , and
except for few cases. In particular, is aspherical, provided so is .
Moreover, is an extension of a finitely generated free abelian
group with a (finite) subgroup of the group of automorphisms of the Reeb graph
of .
We also give a complete proof of the fact that the orbit is tame
Frechet submanifold of of finite codimension, and that the
projection is a principal locally trivial -fibration.Comment: 49 pages, 8 figures. This version includes the proof of the fact that
the orbits of a finite codimension of tame action of tame Lie group on tame
Frechet manifold is a tame Frechet manifold itsel
Z-Spec: A MM-Wave Spectrometer For Measuring Redshifts Of Submillimeter Galaxies
We are building a background-limited, broadband millimeter-wave spectrometer (Z-Spec) for observations of CO rotational transitions from high-redshift dusty galaxies. The large instantaneous bandwidth (195 to 310 GHz) will enable redshifts of dust obscured galaxies to be unambiguously measured. Z-Spec uses a waveguide-coupled grating architecture in which the light propagation is confined within a parallel-plate waveguide. The grating is extremely compact compared to a classical free-space system. An array of silicon nitride bolometers cooled to 100 mK will provide background-limited performance. Z-Spec serves as a technology demonstration for a future space-borne far-infrared grating spectrometer
PNF 2.0? Initial evidence that gamification can increase the efficacy of brief, web-based personalized normative feedback alcohol interventions
Gamified interventions exploit the motivational characteristics of a game in order to provide prevention information and promote behavior change. Despite the modest effect sizes observed in increasingly popular web-based personalized normative feedback (PNF) alcohol interventions for college students, previous research has yet to consider how gamification might be used to enhance efficacy. This study examines whether a novel, gamified PNF intervention format, which includes a point-based reward system, the element of chance, and personal icons to visually represent users, is more effective in reducing short-term alcohol use than the standard web-based style of PNF currently used on college campuses. Two-hundred and thirty-seven college students were randomly assigned to receive either a standard brief, web-based PNF alcohol intervention or the same alcohol intervention components delivered within a Facebook-connected social game called CampusGANDR (Gamified Alcohol Norm Discovery and Readjustment). In both study conditions participants answered identical questions about their perceptions of peer drinking norms and own drinking and then received the same PNF slides. Two weeks following PNF delivery, participants again reported their perceptions of peers\u27 alcohol use and own drinking. Students in the CampusGANDR condition reported significantly reduced peer drinking norms and alcohol use at the two-week follow-up relative to students who received identical PNF delivered by standard online survey. Further, a mediation model demonstrated that this effect was driven by larger reductions in perceived drinking norms among participants assigned to receive CampusGANDR, relative to control. As web-based PNF is becoming an increasingly universal prevention strategy, findings from this study suggest gamification may represent one method by which intervention efficacy could be substantially improved. The potential methodological and economic benefits associated with gamified PNF interventions are emphasized and directions for future research are discussed
The 1995-1996 Decline of R Coronae Borealis - High Resolution Optical Spectroscopy
A set of high-resolution optical spectra of RCrB acquired before, during, and
after its 1995-1996 decline is discussed. All of the components reported from
earlier declines are seen. This novel dataset provides new information on these
components including several aspects not previously seen in declines of RCrB
and other RCBs. In the latter category is the discovery that the decline's
onset is marked by distortions of absorption lines of high-excitation lines,
and quickly followed by emission in these and in low excitation lines. This
'photospheric trigger' implies that dust causing the decline is formed close to
the star. These emission lines fade quickly. After 1995 November 2, low
excitation narrow (FWHM ~12 km s-1) emission lines remain. These appear to be a
permanent feature, slightly blue-shifted from the systemic velocity, and
unaffected by the decline except for a late and slight decrease of flux at
minimum light. The location of the warm, dense gas providing these lines is
uncertain. Absorption lines unaffected by overlying sharp emission are greatly
broadened, weakened, and red-shifted at the faintest magnitudes when scattered
light from the star is a greater contributor than direct light transmitted
through the fresh soot cloud. A few broad lines are seen at and near minimum
light with approxiamately constant flux: prominent among these are the He I
triplet series, Na I D, and [N II] lines. These lines are blue-shifted by about
30 km s(-1) relative to the systemic velocity with no change in velocity over
the several months for whicht he lines were seen. It is suggested that these
lines, especially the He I lines, arise from an accretion disk around an unseen
compact companion, which may be a low-mass white dwarf. If so, R CrB is similar
to the unusual post-AGB star 89 Her.Comment: 31 pages, 26 figure
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