83,568 research outputs found
Wheel/Rail Contact Isolation Due to Track Contamination
An experimental study has been carried out to
investigate the effect of sanding on the electrical
isolation of a wheel/rail contact. Sand is applied to the
wheel/rail interface to increase adhesion in both braking
and traction. Train detection, for signalling purposes,
can be by means of track circuits. Signalling block
occupancy is triggered by the wheelset of the train
‘shorting out’ the track circuit. Sand in the wheel/rail
interface means that contact between the wheelsets and
the track may be compromised, inhibiting train
identification.
Static tests were performed using sections cut
from wheels and rail and dynamic tests on a twin disc
machine where rail and wheel steel discs are loaded
together and driven under controlled conditions of
rolling and slip. The electrical circuit used was a
simplified simulation of the TI21 track circuit.
The application of sand was carried out under a
range of mild and severe test conditions. The results
indicated that a transition exists in the amount of sand
applied, below which there is a measurable, but not
severe, change in voltage, but above which the contact
conductance decreases by an order of magnitude. A
model of electrical isolation has been developed
assuming either full disc separation by a sand layer or
partial disc contact with some sand present.
Idealisations inherent in both test methods mean
that they represent a severe case. Given these
limitations, it is likely that the test methods, at their
present stage of development, should be used as a
means to qualitatively assess the relative effects on
electrical isolation of different contaminants
Design overview of fiber-reinforced superalloy composites for the Space Shuttle main engine
This preliminary design study evaluated the potential of fiber-reinforced superalloys (FRS) for hot-section components of Space Shuttle Main Engine turbopumps. Emphasis was placed on uncooled turbine blades, with a more limited evaluation of FRS turbine stator vanes. The study included FRS properties evaluation, current structural design capability, and preliminary design and structural analysis. In addition, key technology needs were identified, and a plan was generated to develop operational hardware for advanced versions of the SSME. Based on projections of design properties for FRS composites comprising 50 volume percent of W-4Re-0.38Hf-0.02C wire filaments in a ductile superalloy matrix, it was concluded that FRS turbine blades offer the potential of significant improved operating life and higher temperature capability over the MAR-M-246(Hf) (DS) blades currently used in the SSME
Portable electron beam weld chamber
Development and characteristics of portable vacuum chamber for skate type electron beam welding are discussed. Construction and operational details of equipment are presented. Illustrations of equipment are provided
CINDA - Chrysler Improved Numerical Differencing Analyzer computer program
Dimensionless multioption systems compiler computer program constructs and analyzes a mathematical model of any arbitrary one, two, or three dimensional lumped parameter representation of a physical system. It automatically optimizes the utilization of computer core space and is more general and versatile than BETA
Status of Chiral-Scale Perturbation Theory
Chiral-scale perturbation theory PT has been proposed as an
alternative to chiral perturbation theory which
explains the rule for kaon decays. It is based on a low-energy
expansion about an infrared fixed point in three-flavor QCD. In
PT, quark condensation induces nine Nambu-Goldstone bosons: and a QCD dilaton
which we identify with the resonance. Partial conservation
of the dilatation and chiral currents constrains low-energy constants which
enter the effective Lagrangian of PT. These constraints allow us
to obtain new phenomenological bounds on the dilaton decay constant via the
coupling of to pions, whose value is known precisely from
dispersive analyses of scattering. Improved predictions for and the coupling are also noted. To test
PT for kaon decays, we revive a 1985 proposal for lattice
methods to be applied to on-shell.Comment: 10 pages, 1 figure. Presented at the 8th International Workshop on
Chiral Dynamics, 29 June 2015 - 03 July 2015, Pisa, Italy. Revision:
references and comment adde
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Thermal tides in an assimilation of three years of Thermal Emission Spectromenter data from Mars Global Surveyor
Introduction. Thermal tides are particularly prominent in the Mars atmosphere with the result that temperature and wind fields have a strong dependence on local solar time (LT). Tides include westward propagating migrating (sun-synchronous) waves driven in response to solar heating and additional nonmigrating waves resulting from zonal variations in the thermotidal forcing. Zonal modulation of forcing can arise from longitudinal variations of the boundary (topography and surface thermal inertia) and radiatively active aerosols (dust and water ice clouds). Nonmigrating tides appear as diurnally varying upslope/ downslope circulations within the near-surface boundary layer that, like their migrating counterparts, are also able to propagate vertically to aerobraking altitudes in the lower thermosphere. The Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) has yielded atmospheric temperature profiles with unprecedented latitude and longitude coverage that has provided the basis for characterizing the seasonal evolution of tides and stationary waves [1]. However, the twice-daily observations (2 am and 2 pm LT) are insufficient to unambiguously resolve the sunsynchronous tides. Recently the technique of data assimilation has been sufficiently developed for Mars to yield a dynamically consistent set of thermal and dynamic fields suitable for detailed investigations of various aspects of the martian circulations system [2,3,4,5]. We will refer to this data set an the TES Reanalysis, which represents the current best estimate of the evolving state of the martian atmosphere during the MGS mission. The assimilated thermal and dynamical fields provide a means of assessing circulation variability and transport capability reflecting the variability of the actual Mars atmosphere
Urban and regional land use analysis: CARETS and Census Cities experiment package
There are no author-identified significant results in this report
Crystallization and preliminary X-ray analysis of the sporulation factor SpoIIAA in its native and phosphorylated forms
Sporulation in Bacillus begins with an asymmetric cell division producing two progeny with identical chromosomes but different developmental fates. As such, it is a simple example of cellular differentiation. The establishment of cell type is controlled by a series of alternate RNA polymerase sigma subunits. The first compartment-specific sigma factor is sigma (F), whose activity is controlled by SpoIIAB, an anti-sigma factor, and SpoIIAA, an anti-sigma factor antagonist which is phosphorylated by the kinase activity of SpoIIAB. Here, the preliminary crystallographic analysis of SpoIIAA and phosphorylated SpoIIAA from B. sphaericus in forms suitable for high-resolution structure determination are reported
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