3,417 research outputs found
Slow axial drift in three-dimensional granular tumbler flow
Models of monodisperse particle flow in partially filled three-dimensional
tumblers often assume that flow along the axis of rotation is negligible. We
test this assumption, for spherical and double cone tumblers, using experiments
and discrete element method simulations. Cross sections through the particle
bed of a spherical tumbler show that, after a few rotations, a colored band of
particles initially perpendicular to the axis of rotation deforms: particles
near the surface drift toward the pole, while particles deeper in the flowing
layer drift toward the equator. Tracking of mm-sized surface particles in
tumblers with diameters of 8-14 cm shows particle axial displacements of one to
two particle diameters, corresponding to axial drift that is 1-3% of the
tumbler diameter, per pass through the flowing layer. The surface axial drift
in both double cone and spherical tumblers is zero at the equator, increases
moving away from the equator, and then decreases near the poles. Comparing
results for the two tumbler geometries shows that wall slope causes axial
drift, while drift speed increases with equatorial diameter. The dependence of
axial drift on axial position for each tumbler geometry is similar when both
are normalized by their respective maximum values
Wideband digital phase comparator for high current shunts
A wideband phase comparator for precise measurements of phase difference of
high current shunts has been developed at INRIM. The two-input digital phase
detector is realized with a precision wideband digitizer connected through a
pair of symmetric active guarded transformers to the outputs of the shunts
under comparison. Data are first acquired asynchronously, and then transferred
from on-board memory to host memory. Because of the large amount of data
collected the filtering process and the analysis algorithms are performed
outside the acquisition routine. Most of the systematic errors can be
compensated by a proper inversion procedure.
The system is suitable for comparing shunts in a wide range of currents, from
several hundred of milliampere up to 100 A, and frequencies ranging between 500
Hz and 100 kHz. Expanded uncertainty (k=2) less than 0.05 mrad, for frequency
up to 100 kHz, is obtained in the measurement of the phase difference of a
group of 10 A shunts, provided by some European NMIs, using a digitizer with
sampling frequency up to 1 MHz. An enhanced version of the phase comparator
employs a new digital phase detector with higher sampling frequency and
vertical resolution. This permits to decrease the contribution to the
uncertainty budget of the phase detector of a factor two from 20 kHz to 100
kHz. Theories and experiments show that the phase difference between two high
precision wideband digitizers, coupled as phase detector, depends on multiple
factors derived from both analog and digital imprint of each sampling system.Comment: 20 pages, 9 figure
MESA and NuGrid simulations of classical novae: CO and ONe nova nucleosynthesis
Classical novae are the result of thermonuclear flashes of hydrogen accreted
by CO or ONe white dwarfs, leading eventually to the dynamic ejection of the
surface layers. These are observationally known to be enriched in heavy
elements, such as C, O and Ne that must originate in layers below the H-flash
convection zone. Building on our previous work, we now present stellar
evolution simulations of ONe novae and provide a comprehensive comparison of
our models with published ones. Some of our models include exponential
convective boundary mixing to account for the observed enrichment of the nova
ejecta even when accreted material has a solar abundance distribution. Our
models produce maximum temperature evolution profiles and nucleosynthesis
yields in good agreement with models that generate enriched ejecta by assuming
that the accreted material was pre-mixed. We confirm for ONe novae the result
we reported previously, i.e.\ we found that He could be produced {\it in
situ} in solar-composition envelopes accreted with slow rates (\dot{M} <
10^{-10}\,M_\odot/\mbox{yr}) by cold ( K) CO WDs, and that
convection was triggered by He burning before the nova outburst in that
case. In addition, we now find that the interplay between the He production
and destruction in the solar-composition envelope accreted with an intermediate
rate, e.g.\ \dot{M} = 10^{-10}\,M_\odot/\mbox{yr}, by the ONe
WD with a relatively high initial central temperature, e.g.\ K, leads to the formation of a thick radiative buffer zone that
separates the bottom of the convective envelope from the WD surface. (Abridged)Comment: 19 pages, 23 figures, 2 tables, accepted to publication by MNRA
A New Method for the Solution and Solid Phase Synthesis of Chiral b-Sulfonopeptides Under Mild Conditions.
High-Fidelity Simulation and Novel Data Analysis of the Bubble Creation and Sound Generation Processes in Breaking Waves
Recent increases in computing power have enabled the numerical simulation of
many complex flow problems that are of practical and strategic interest for
naval applications. A noticeable area of advancement is the computation of
turbulent, two-phase flows resulting from wave breaking and other multiphase
flow processes such as cavitation that can generate underwater sound and
entrain bubbles in ship wakes, among other effects. Although advanced flow
solvers are sophisticated and are capable of simulating high Reynolds number
flows on large numbers of grid points, challenges in data analysis remain.
Specifically, there is a critical need to transform highly resolved flow fields
described on fine grids at discrete time steps into physically resolved
features for which the flow dynamics can be understood and utilized in naval
applications. This paper presents our recent efforts in this field. In previous
works, we developed a novel algorithm to track bubbles in breaking wave
simulations and to interpret their dynamical behavior over time (Gao et al.,
2021a). We also discovered a new physical mechanism driving bubble production
within breaking wave crests (Gao et al., 2021b) and developed a model to relate
bubble behaviors to underwater sound generation (Gao et al., 2021c). In this
work, we applied our bubble tracking algorithm to the breaking waves
simulations and investigated the bubble trajectories, bubble creation
mechanisms, and bubble acoustics based on our previous works.Comment: conferenc
Efficiency of dispersive wave generation in dual concentric core microstructured fiber
We describe the generation of powerful dispersive waves that are observed
when pumping a dual concentric core microstructured fiber by means of a
sub-nanosecond laser emitting at the wavelength of~1064 nm. The presence of
three zeros in the dispersion curve, their spectral separation from the pump
wavelength, and the complex dynamics of solitons originated by the pump pulse
break-up, all contribute to boost the amplitude of the dispersive wave on the
long-wavelength side of the pump. The measured conversion efficiency towards
the dispersive wave at 1548 nm is as high as 50%. Our experimental analysis of
the output spectra is completed by the acquisition of the time delays of the
different spectral components. Numerical simulations and an analytical
perturbative analysis identify the central wavelength of the red-shifted pump
solitons and the dispersion profile of the fiber as the key parameters for
determining the efficiency of the dispersive wave generation process.Comment: 11 pages, 12 figure
Impact of preoperative fractional flow reserve on arterial bypass graft anastomotic function:the IMPAG trial
- …