555 research outputs found
Large scale optimization of transonic axial compressor rotor blades
[First Paragraphs]
In the present work the Multipoint Approximation Method (MAM) by Toropov et al. (1993) has been applied to
the shape optimization of an existing transonic compressor rotor (NASA rotor 37) as a benchmark case.
Simulations were performed using the Rolls-Royce plc. PADRAM-HYDRA system (Shahpar and Lapworth 2003,
Lapworth and Shahpar 2004) that includes the parameterization of the blade shape, meshing, CFD analysis, postprocessing,
and objective/constraints evaluation. The parameterization approach adopted in this system is very
flexible but can result in a large scale optimization problem.
For this pilot study, a relatively coarse mesh has been used including around 470,000 nodes. The
parameterization was done using 5 engineering blade parameters like axial movement of sections along the engine
axis in mm (XCEN), circumferential movements of sections in degrees (DELT), solid body rotation of sections in
degrees (SKEW), and leading/trailing edge recambering (LEM0/TEMO) in degrees. The design variables were
specified using 6 control points at 0 % (hub), 20%, 40%, 60%, 80%, and 100% (tip) along the span. Thus the total
number of independent design variables N was 30. B-spline interpolation was used through the control points to
generate smooth design perturbations in the radial direction
The use of composite ferrocyanide materials for the treatment of high salinity liquid radioactive wastes rich in cesium isotopes
Several factors affecting the removal of cesium from LRW, namely total salt content, pH
and organic matter content, were also investigated. High concentrations of complexing organic matter
significantly reduced the sorption capacity of ferrocyanide sorbents
Detection Statistics of Pulse Signals at Declinations from to at the Frequency 111 MHz
A search for pulse signals was carried out in a new sky area included in the
monitoring program for the search for pulsars and transients. Processing of
several months data recorded in six frequency channels with a total bandwidth
of 2.5 MHz showed that, on average, 4 pulses per hour are observed in each of
the 24 connected stationary beams. Of these pulses, 18.3% are similar to those
of pulsars. They are visible in one or two neighboring beams and have a
pronounced dispersion shift, that is, they are recorded first at a high and
then at a low frequency, which indicates the possible passage of the signal
through the interstellar medium. Almost 68% of such detected pulses belong to
six known pulsars with dispersion measures from 9 to 141 , and almost
all of the remaining pulses are either noise of an unknown nature or artifacts
of the proposed pulse separation technique. An additional study of the selected
array of 3650 obvious pulsar pulses revealed 13 pulses belonging to four
rotating radio transients (RRATs). Their dispersion measures are in the range
of 17-51 . A search for regular (periodic) RRAT emission was carried
out using power spectra summed over 121 days. Periodic radiation was not
detected, but for two RRATs, upper estimates of the periods were obtained from
measurements of the time intervals between pulses. The upper estimates of the
integrated flux density of the detected RRATs are in the range 2-4 mJy at the
frequency 111 MHz.Comment: published in Astronomy Report, translated by Yandex translator with
correction of scientific lexis, 6 pages, 3 figures, 2 table
Interplay of the exciton and electron-hole plasma recombination on the photoluminescence dynamics in bulk GaAs
We present a systematic study of the exciton/electron-hole plasma
photoluminescence dynamics in bulk GaAs for various lattice temperatures and
excitation densities. The competition between the exciton and electron-hole
pair recombination dominates the onset of the luminescence. We show that the
metal-to-insulator transition, induced by temperature and/or excitation
density, can be directly monitored by the carrier dynamics and the
time-resolved spectral characteristics of the light emission. The dependence on
carrier density of the photoluminescence rise time is strongly modified around
a lattice temperature of 49 K, corresponding to the exciton binding energy (4.2
meV). In a similar way, the rise-time dependence on lattice temperature
undergoes a relatively abrupt change at an excitation density of 120-180x10^15
cm^-3, which is about five times greater than the calculated Mott density in
GaAs taking into account many body corrections.Comment: 15 pages, 7 figures, submitted to Phys. Rev.
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