270 research outputs found
Flow dynamics and structure of solid pellets along the channel of a single screw extruder
Plasticating single screw extrusion involves the progressive compaction and heating of loose solid
pellets that eventually melt, form a relatively homogenous stream and are subsequently pumped through a
shaping tool. Traditional analyses of the solids conveying stage assume the sliding of an elastic solid plug due
to differential wall friction coefficients. However, not only the corresponding predictions may fail
considerably, but it is also well known that, at least in the initial screw turns, pellets are far from compact.
This work follows previous efforts to model the flow of solids in the hopper and initial screw turns using the
Discrete Element Method (DEM). The model considers the development of normal and tangential forces
resulting from the inelastic collisions between the pellets and between them and the neighbouring metallic
surfaces. As an example of the capability of the model to capture detailed features of granular flow, the effect
of pellet size on flow is discussed.Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BPD/39381/2007
Strange filamentary structures ("fireballs") around a merger galaxy in the Coma cluster of galaxies
We found an unusual complex of narrow blue filaments, bright blue knots, and
H-alpha emitting filaments and clouds, which morphologically resembled a
complex of ``fireballs,'' extending up to 80 kpc south from an E+A galaxy RB199
in the Coma cluster. The galaxy has a highly disturbed morphology indicative of
a galaxy--galaxy merger remnant. The narrow blue filaments extend in straight
shapes toward the south from the galaxy, and several bright blue knots are
located at the southern ends of the filaments. The Rc band absolute magnitudes,
half light radii and estimated masses of the bright knots are -12 - -13 mag,
200 - 300 pc and 10^6-7 Msolar, respectively. Long, narrow H-alpha emitting
filaments are connected at the south edge of the knots. The average color of
the fireballs is B - Rc = 0.5, which is bluer than RB199 (B - R = 0.99),
suggesting that most of the stars in the fireballs were formed within several
times 10^8 yr. The narrow blue filaments exhibit almost no H-alpha emission.
Strong H-alpha and UV emission appear in the bright knots. These
characteristics indicate that star formation recently ceased in the blue
filaments and now continues in the bright knots. The gas stripped by some
mechanism from the disk of RB199 may be traveling in the intergalactic space,
forming stars left along its trajectory. The most plausible fireball formation
mechanism is ram pressure stripping by high-speed collision between the galaxy
and the hot intra-cluster medium. The fireballs may be a snapshot of diffuse
intra-cluster population formation, or halo star population formation in a
cluster galaxy.Comment: 13 pages, 14 figures, submitted to Ap
Modelling pellet flow in single extrusion with DEM
Plasticating single-screw extrusion involves the continuous conversion of loose solid
pellets into a pressurized homogeneous melt that is pumped through a shaping tool. Traditional
analyses of the solids conveying stage assume the movement of an elastic solid plug at a fixed
speed. However, not only the corresponding predictions fail considerably, but it is also well
known that, at least in the initial screw turns, the flow of loose individual pellets takes place.
This study follows previous efforts to predict the characteristics of such a flow using the discrete
element method. The model considers the development of normal and tangential forces resulting
from the inelastic collisions between the pellets and between them and the neighbouring metallic
surfaces. The algorithm proposed here is shown to be capable of capturing detailed features of the
granular flow. The predictions of velocities in the cross- and down-channel directions and of the
coordination number are in good agreement with equivalent reported results. The effect of pellet
size on the flow features is also discussed
Derivatives of meromorphic functions of finite order
A result is proved concerning meromorphic functions of finite order in the plane such that all but finitely many zeros of the second derivative are zeros of the first derivative
The influence of CeF₃ on radiation hardness and luminescence properties of Gd₂O₃–B₂O₃ glass scintillator
The effect of CeF3 concentration and γ-irradiation on the physical, optical and luminescence properties of Gd2O3–B2O3–CeF3 glasses were studied in this work. Before irradiation, the addition of CeF3 in glass degraded the network connectivity observed from FTIR and possibly created the non-bridging oxygen (NBO) in glass structure. This NBO caused the reduction of Ce3+/Ce4+ ratio in XANES, the red-shift in transmission spectra and the raise of refractive index with addition of CeF3 content. Such red-shift also was influenced by 4f–5d transition of Ce3+ dopant. This ion generated the strongest photoluminescence (PL) and radioluminescence (RL) in 0.3 mol% CeF3-doped glass with nanoseconds decay time. The irradiation with γ-rays damaged the glass structure, broke the chemical bonds, and created color center in the glass network. The non-bridging oxygen hole center (NBOHC), that absorbed photons in the visible light region, caused the darkening, color change and increment of refractive index. These irradiation effects on glass were mitigated by the addition of CeF3 that the electron donation of Ce3+ decreased the number of NBOHC. The Ce3+/Ce4+ ratio in most glasses after irradiation then reduced compared to them before irradiation, resulting to the decrease in PL and RL intensity. Our results confirm that CeF3 can enhance the radiation hardness of glass and the 0.3 mol% CeF3-doped glass is a promising glass scintillator.Kaewnuam E., Wantana N., Ruangtaweep Y., et al. The influence of CeF₃ on radiation hardness and luminescence properties of Gd₂O₃–B₂O₃ glass scintillator. Scientific Reports 12, 11059 (2022); https://doi.org/10.1038/s41598-022-14833-3
Development and operational experience of magnetic horn system for T2K experiment
A magnetic horn system to be operated at a pulsed current of 320 kA and to
survive high-power proton beam operation at 750 kW was developed for the T2K
experiment. The first set of T2K magnetic horns was operated for over 12
million pulses during the four years of operation from 2010 to 2013, under a
maximum beam power of 230 kW, and protons were exposed to
the production target. No significant damage was observed throughout this
period. This successful operation of the T2K magnetic horns led to the
discovery of the oscillation phenomenon in 2013 by
the T2K experiment. In this paper, details of the design, construction, and
operation experience of the T2K magnetic horns are described.Comment: 22 pages, 40 figures, also submitted to Nuclear Instrument and
Methods in Physics Research,
GPIB ADDRESS CONVERTER
Abstract A GPIB address converter (GAC) has been constructed. This paper reports on the function and test results. The GAC has two GPIB connectors (upper and lower ports). The upper port has a GPIB primary address, and is connected to a GPIB system controller. The lower port acts as a GPIB controller of the lower side GPIB line. The GPIB system controller can access the lower side GPIB devices through the GAC by using an extended two-byte address function. The two-byte address (primary + secondary) is shown in the combination of the GAC address and the address of the lower side device. The GAC converts the secondary address into the primary address of the lower side GPIB device. By using of 30 GACs, the GPIB system controller can access 930 devices assigned only primary addresses
- …