3,033 research outputs found
Rotating pressure measurement system using an on board calibration standard
A computer-controlled multichannel pressure measurement system was developed to acquire detailed flow field measurements on board the Large Low Speed Centrifugal Compressor Research Facility at the NASA Lewis Research Center. A pneumatic slip ring seal assembly is used to transfer calibration pressures to a reference standard transducer on board the compressor rotor in order to measure very low differential pressures with the high accuracy required. A unique data acquisition system was designed and built to convert the analog signal from the reference transducer to the variable frequency required by the multichannel pressure measurement system and also to provide an output for temperature control of the reference transducer. The system also monitors changes in test cell barometric pressure and rotating seal leakage and provides an on screen warning to the operator if limits are exceeded. The methods used for the selection and testing of the the reference transducer are discussed, and the data acquisition system hardware and software design are described. The calculated and experimental data for the system measurement accuracy are also presented
Risk Parity Optimality
A poster summarizing some of the results of research by Gregg S. Fisher, Philip Z. Maymin, Zakhar G. Maymin that was published in Journal of Portfolio Management (2015), 41:2, 42-56 under the title "Risk Parity Optimality"
Comparison between measured and computed magnetic flux density distribution of simulated transformer core joints assembled from grain oriented and non-oriented electrical steel
The flux distribution in an overlapped linear joint constructed in the central region of an Epstein Square was
studied experimentally and results compared with those obtained using a computational magnetic field
solver. High permeability grain-oriented (GO) and low permeability non-oriented (NO) electrical steels
were compared at a nominal core flux density of 1.60 T at 50 Hz. It was found that the experimental results
only agreed well at flux densities at which the reluctance of different paths of the flux are similar. Also it
was revealed that the flux becomes more uniform when the working point of the electrical steel is close to
the knee point of the B-H curve of the steel
When Can You Pick Up Fallen Fruit?
A poster discussing applying ideas from the Talmud to business
Behavioral Despair in the Talmud
We solve two "unsolvable" (teyku) problems from the Talmud that had remained unsolved for about 1,500 years. The Talmudic problems concern the implied decision-making of farmers who have left some scattered fruit behind, and the alleged impossibility of knowing whether they would return for given amounts of fruit over given amounts of land area if we aware of their behavior at exactly one point. We solve the problems by formalizing the Talmudic discussion and expressing five natural economic and mathematical assumptions
312-fs pulse generation from a passive C-band InAs/InP quantum dot mode-locked laser.
For the first time, we report femtosecond pulses from a passive single-section InAs/InP quantum-dot (QD) mode-locked laser (MLL) with the active length of 456 microm and ridge width of 2.5 microm at the C-band wavelength range. Without any external pulse compression, the transform-limited Gaussian-pulses are generated at the 92 GHz repetition rate with the 312 fs pulse duration, which is the shortest pulse from any directly electric-pumping semiconductor MLLs to our best knowledge. The lasing threshold injection current and external differential quantum efficiency are 17.2 mA and 38%, respectively. We have also investigated the working principles of the proposed QD MLLs
Variability in the Thermal Emission from Accreting Neutron Star Transients
The composition of the outer 100 m of a neutron star sets the heat flux that
flows outwards from the core. For an accreting neutron star in an X-ray
transient, the thermal quiescent flux depends sensitively on the amount of
hydrogen and helium remaining on the surface after an accretion outburst and on
the composition of the underlying ashes of previous H/He burning. Because H/He
has a higher thermal conductivity, a larger mass of H/He implies a shallower
thermal gradient through the low density envelope and hence a higher effective
temperature for a given core temperature. The mass of residual H and He varies
from outburst to outburst, so the thermal quiescent flux is variable even
though the core temperature is constant for timescales < 10 000 yr. Heavy
elements settle from a H/He envelope in a few hours; we therefore model the
quiescent envelope as two distinct layers, H/He over heavier elements, and
treat the mass of H/He as a free parameter. We find that the emergent thermal
quiescent flux can vary by a factor of 2 to 3 between different quiescent
epochs. The variation is more pronounced at lower interior temperatures, making
systems with low quiescent luminosities and frequent outbursts, such as SAX
J1808.4-3658, ideal candidates from which to observe this effect. We compute,
for different ash compositions, the interior temperatures of Cen X-4, Aql X-1,
and SAX J1808.4-3658. In the case of Aql X-1, the inferred high interior
temperature suggests that neutrino cooling contributes to the neutron star's
thermal balance.Comment: 14 pages, 5 figures, uses emulateapj5 and psnfss fonts. To be
published in The Astrophysical Journa
A Survey of Local Group Galaxies Currently Forming Stars. I. UBVRI Photometry of Stars in M31 and M33
We present UBVRI photometry obtained from Mosaic images of M31 and M33 using
the KPNO 4-m telescope. The survey covers 2.2 sq degrees of M31, and 0.8 sq
degrees of M33, chosen so as to include all of the regions currently active in
forming massive stars. The catalog contains 371,781 and 146,622 stars in M31
and M33, respectively, where every star has a counterpart (at least) in B, V,
and R. We compare our photometry to previous studies. We provide cross
references to the stars confirmed as members by spectroscopy, and compare the
location of these to the complete set in color-magnitude diagrams. While
follow-up spectroscopy is needed for many projects, we demonstrate the success
of our photometry in being able to distinguish M31/M33 members from foreground
Galactic stars. We also present the results of newly obtained spectroscopy,
which identifies 34 newly confirmed members, including B-A supergiants, the
earliest O star known in M31, and two new Luminous Blue Variable candidates
whose spectra are similar to that of P Cygni.Comment: Accepted by the Astronomical Journal. A version with higher
resolution figures can be found at:
http://www.lowell.edu/users/massey/M3133.pdf.g
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