10,395 research outputs found
Abradable compressor and turbine seals, volume 1
The application and advantages of abradable coatings as gas-path seals in a general aviation turbine engine were evaluated for use on the high-pressure compressor, the high-pressure turbine, and the low-pressure turbine shrouds. Topics covered include: (1) the initial selection of candidate materials for interim full-scale engine testing; (2) interim engine testing of the initially selected materials and additional candidate materials; (3) the design of the component required to adapt the hardware to permit full-scale engine testing of the most promising materials; (4) finalization of the fabrication methods used in the manufacture of engine test hardware; and (5) the manufacture of the hardware necessary to support the final full-scale engine tests
Abradable compressor and turbine seals, volume 2
The applications and advantages of abradable coatings as gas path seals in a general aviation turbofan engine were investigated. Abradable materials were evaluated for the high pressure radial compressor and the axial high and low pressure turbine shrouds
RHESSI Observations of the Solar Flare Iron-line Feature at 6.7 keV
Analysis of RHESSI 3--10 keV spectra for 27 solar flares is reported. This
energy range includes thermal free--free and free--bound continuum and two line
features, at 6.7keV and 8keV, principally due to highly ionized iron (Fe). We
used the continuum and the flux in the so-called Fe-line feature at 6.7keV to
derive the electron temperature T_e, the emission measure, and the Fe-line
equivalent width as functions of time in each flare. The Fe/H abundance ratio
in each flare is derived from the Fe-line equivalent width as a function of
T_e. To minimize instrumental problems with high count rates and effects
associated with multi-temperature and nonthermal spectral components, spectra
are presented mostly during the flare decay phase, when the emission measure
and temperature were smoothly varying. We found flare Fe/H abundance ratios
that are consistent with the coronal abundance of Fe (i.e. 4 times the
photospheric abundance) to within 20% for at least 17 of the 27 flares; for 7
flares, the Fe/H abundance ratio is possibly higher by up to a factor of 2. We
find evidence that the Fe XXV ion fractions are less than the theoretically
predicted values by up to 60% at T_e=25 MK appear to be displaced from the most
recent theoretical values by between 1 and 3 MK.Comment: To be published, Ap
Connecting the X(5)-, X(5)-, and X(3) models to the shape/phase transition region of the interacting boson model
The parameter independent (up to overall scale factors) predictions of the
X(5)-, X(5)-, and X(3) models, which are variants of the X(5)
critical point symmetry developed within the framework of the geometric
collective model, are compared to two-parameter calculations in the framework
of the interacting boson approximation (IBA) model. The results show that these
geometric models coincide with IBA parameters consistent with the phase/shape
transition region of the IBA for boson numbers of physical interest (close to
10). Nuclei within the rare-earth region and select Os and Pt isotopes are
identified as good examples of X(3), X(5)-, and X(5)-
behavior
Adoption of Collaboration Technologies: Integrating Technology Acceptance and Collaboration Technology Research
This paper integrates the technology acceptance model (TAM) with constructs from collaboration technology research to present a model of collaboration technology use. Specifically, constructs in four sets of characteristics—technology, individual and group, task, and situational—drawn from various media choice theories are presented as determinants of the TAM constructs of perceived usefulness, perceived ease of use, and attitude toward using collaboration technology. The model was tested among 349 short message service (SMS) users in Finland. The model was largely supported, with the most significant findings being the effects of the four technology characteristics—social presence, media richness, immediacy, and concurrency—on the TAM constructs. In addition to making an important contribution by integrating two of the more dominant streams of information systems research, the model presented here is focused on a specific class of technology—i.e., collaboration technology—and, therefore, answers recent calls for developing models that deepen our understanding about the technology artifact
P–C and C–H Bond Cleavages of dppm in the Thermal Reaction of [Ru\u3csub\u3e3\u3c/sub\u3e(CO)\u3csub\u3e10\u3c/sub\u3e(μ-dppm)] with Benzothiophene: X-ray structures of [Ru\u3csub\u3e6\u3c/sub\u3e(μ-CO)(CO)\u3csub\u3e13\u3c/sub\u3e{μ\u3csub\u3e4\u3c/sub\u3e-PhP(C\u3csub\u3e6\u3c/sub\u3eH\u3csub\u3e4\u3c/sub\u3e)PPh}(μ\u3csub\u3e6\u3c/sub\u3e-C)] and [Ru\u3csub\u3e4\u3c/sub\u3e(CO)\u3csub\u3e9\u3c/sub\u3e(μ\u3csub\u3e3\u3c/sub\u3e-η\u3csup\u3e2\u3c/sup\u3e-PhPCH\u3csub\u3e2\u3c/sub\u3ePPh\u3csub\u3e2\u3c/sub\u3e)(μ\u3csub\u3e4\u3c/sub\u3e-η\u3csup\u3e6\u3c/sup\u3e:η\u3csup\u3e1\u3c/sup\u3e:η\u3csup\u3e1\u3c/sup\u3e-C\u3csub\u3e6\u3c/sub\u3eH\u3csub\u3e4\u3c/sub\u3e)(μ-H)]
The thermal reaction of [Ru3(CO)10(μ-dppm)] (1) with benzothiophene in refluxing toluene gives a complex mixture of products. These include the known compounds [Ru2(CO)6{μ-CH2PPh(C6H4)PPh}] (2), [Ru2(CO)6{μ-C6H4PPh(CH2)PPh}] (3), [Ru3(CO)9{μ3-η3-(Ph)PCH2P(Ph)C6H4}] (4) and [Ru3(CO)10{μ-η2-PPh(CH2)(C6H4)PPh}] (6), as well as the new clusters [Ru6(μ-CO)(CO)13{μ3-η2-PhP(C6H4)PPh}(μ6-C)] (5) and [Ru4(CO)9(μ3-η2-PhPCH2PPh2)(μ4-η6:η1:η1-C6H4)(μ-H)] (7). The solid-state molecular structures of 5 and 7 were confirmed by single crystal X-ray analyses. Compound 5 consists of interesting example of a hexaruthenium interstitial carbido cluster having a tetradentate diphosphine ligand derived from the activation of P–C and C–H bonds of the dppm ligand in 1. The tetranuclear compound 7 consists of a unique example of a non-planar spiked triangular metal fragment of ruthenium [Ru(1), Ru(2) and Ru(3)] unit with Ru(4) being bonded to Ru(1). The μ4-η1:η6:η1-benzyne ligand in this compound represents a previously uncharacterized bonding mode for benzyne. Compounds 5 and 7 do not contain any benzothiophene-derived ligand. The reaction of 4 with benzothiophene gives 2, 3, 5 and 6. Thermolysis of 1 in refluxing toluene gives 2, 3 and 4; none of 5 and 7 is detected in reaction mixture
Wigner flow reveals topological order in quantum phase space dynamics
The behaviour of classical mechanical systems is characterised by their phase
portraits, the collections of their trajectories. Heisenberg's uncertainty
principle precludes the existence of sharply defined trajectories, which is why
traditionally only the time evolution of wave functions is studied in quantum
dynamics. These studies are quite insensitive to the underlying structure of
quantum phase space dynamics. We identify the flow that is the quantum analog
of classical particle flow along phase portrait lines. It reveals hidden
features of quantum dynamics and extra complexity. Being constrained by
conserved flow winding numbers, it also reveals fundamental topological order
in quantum dynamics that has so far gone unnoticed.Comment: 6 pages, 6 figure
On the Spatial Distribution of Stellar Populations in the Large Magellanic Cloud
We measure the angular correlation function of stars in a region of the Large
Magellanic Cloud (LMC) that spans 2 degrees by 1.5 degrees. We find that the
correlation functions of stellar populations are represented well by
exponential functions of the angular separation for separations between 2 and
40 arcmin (corresponding to ~ 30 pc and 550 pc for an LMC distance of 50 kpc).
The inner boundary is set by the presence of distinct, highly correlated
structures, which are the more familiar stellar clusters, and the outer
boundary is set by the observed region's size and the presence of two principal
centers of star formation within the region. We also find that the
normalization and scale length of the correlation function changes
systematically with the mean age of the stellar population. The existence of
positive correlation at large separations (~300 pc), even in the youngest
population, argues for large-scale hierarchical structure in current star
formation. The evolution of the angular correlation toward lower normalizations
and longer scale lengths with stellar age argues for the dispersion of stars
with time. We show that a simple, stochastic, self-propagating star formation
model is qualitatively consistent with this behavior of the correlation
function.Comment: 30 pages, 13 Figures. Scheduled for publication in AJ in June 199
Recommended from our members
Paleomagnetic Results from the Cretaceous Dumisseau Formation of Haiti
Paleomagnetic studies of basalts and sediments from the Dumisseau Formation show that: 1) The basalt magnetizations are characterized by very low coercivlty components. The sediments have generally higher but more variable stabilities against alternating field (AF) treatment compared to the basalts. The 200 oe AF mean directions for the Dumlsseau basalt and sediment sites tend to fall near the present geomagnetic dipole field direction corresponding to the Latitude of Haiti. It is suggested that these rocks carry predominantly secondary magnetization of recent origin and there is little evidence for the preservation of remanent magnetization which may correspond to the time of formation of the rock units in the Late Cretaceous. 2) The remanent magnetic properties of the basalts, particularly those from the upper part of the formation in the Dumisseau area, are very similar to those reported for basalts recovered in the Caribbean DSDP Leg 15, Sites 146, 150, 151, 152 and 153, suggesting also similarities in their petrotectonic origin
- …