202 research outputs found
Experimental and numerical analysis of hovering multicopter performance in low-Reynolds number conditions
Unmanned Aircraft Systems (UAS) are state of the art in the aerospace industry and are involved in
many operations. Although initially developed for military purposes, commercial applications of small-
scale UAS, such as multicopters, are abundant today. Accurate engineering tools are required to assess
the performance of these vehicles and optimize power consumption. The thrust and power curves of
the rotors used by small-scale UAS are essential elements in designing efficient aircraft. The scarcity of
experimental data and sufficiently accurate prediction models to evaluate rotor aerodynamic performance
in the flight envelope are primary limitations in UAS science. In addition, for small-scale rotors at usual
rotation rates, chord-based Reynolds numbers are typically smaller than 100,000, a flow regime in which
performance tends to degrade. In this paper, experimental data on small-scale multicopter propulsion
systems are presented and combined with a Computational Fluid Dynamics (CFD) model to describe the
aerodynamics of these vehicles in low Reynolds numbers conditions. We use the STAR-CCM+ software to
perform CFD simulations adopting both a dynamic-grid, time-accurate analysis and a static-grid, steady-
state technique that solves the Navier-Stokes equations in a suitable framework. Comparing numerical
simulation results on a conventional UAS propeller with related experimental data suggests that the
proposed approach can correctly describe the thrust and torque coefficients in the range of Reynolds
numbers characterizing the UAS flight envelope
A segmented Hybrid Photon Detector with integrated auto-triggering front-end electronics for a PET scanner
We describe the design, fabrication and test results of a segmented Hybrid Photon Detector with integrated auto-triggering front-end electronics. Both the photodetector and its VLSI readout electronics are custom designed and have been tailored to the requirements of a recently proposed novel geometrical concept of a Positron Emission Tomograph. Emphasis is put on the PET specific features of the device. The detector has been fabricated in the photocathode facility at CERN
Multilayer aerogel for compact RICH detectors
This paper covers some of the latest achievements in the testing of multi–index silica aerogel. Optical bench measurements and preliminary results from a recently performed charged particle beam test are presented. This work is part of an effort aimed at assessing the potential of multilayer aerogel as a radiator for compact, proximity focused ring imaging Cherenkov detectors
Beam-helicity asymmetries for single-hadron production in semi-inclusive deep-inelastic scattering from unpolarized hydrogen and deuterium targets
A measurement of beam-helicity asymmetries for single-hadron production in
deep-inelastic scattering is presented. Data from the scattering of 27.6 GeV
electrons and positrons off gaseous hydrogen and deuterium targets were
collected by the HERMES experiment. The asymmetries are presented separately as
a function of the Bjorken scaling variable, the hadron transverse momentum, and
the fractional energy for charged pions and kaons as well as for protons and
anti-protons. These asymmetries are also presented as a function of the three
aforementioned kinematic variables simultaneously
Transverse-target-spin asymmetry in exclusive -meson electroproduction
Hard exclusive electroproduction of mesons is studied with the
HERMES spectrometer at the DESY laboratory by scattering 27.6 GeV positron and
electron beams off a transversely polarized hydrogen target. The amplitudes of
five azimuthal modulations of the single-spin asymmetry of the cross section
with respect to the transverse proton polarization are measured. They are
determined in the entire kinematic region as well as for two bins in photon
virtuality and momentum transfer to the nucleon. Also, a separation of
asymmetry amplitudes into longitudinal and transverse components is done. These
results are compared to a phenomenological model that includes the pion pole
contribution. Within this model, the data favor a positive
transition form factor.Comment: DESY Report 15-14
Measurement of pretzelosity asymmetry of charged pion production in Semi-Inclusive Deep Inelastic Scattering on a polarized He target
An experiment to measure single-spin asymmetries in semi-inclusive production
of charged pions in deep-inelastic scattering on a transversely polarized
He target was performed at Jefferson Lab in the kinematic region of
and . The pretzelosity asymmetries on
He, which can be expressed as the convolution of the
transverse momentum dependent distribution functions and the Collins
fragmentation functions in the leading order, were measured for the first time.
Using the effective polarization approximation, we extracted the corresponding
neutron asymmetries from the measured He asymmetries and cross-section
ratios between the proton and He. Our results show that for both
on He and on the neutron the pretzelosity asymmetries are
consistent with zero within experimental uncertainties.Comment: 6 pages, 3 figures; enlarged the legends in Fig.3; added 3 citation
Longitudinal double-spin asymmetries in semi-inclusive deep-inelastic scattering of electrons and positrons by protons and deuterons
A comprehensive collection of results on longitudinal double-spin asymmetries is presented for charged pions and kaons produced in semi-inclusive deep-inelastic scattering of electrons and positrons on the proton and deuteron, based on the full HERMES data set. The dependence of the asymmetries on hadron transverse momentum and azimuthal angle extends the sensitivity to the flavor structure of the nucleon beyond the distribution functions accessible in the collinear framework. No strong dependence on those variables is observed. In addition, the hadron charge-difference asymmetry is presented, which under certain model assumptions provides access to the helicity distributions of valence quarks
Single Spin Asymmetries of Inclusive Hadrons Produced in Electron Scattering from a Transversely Polarized He Target
We report the first measurement of target single-spin asymmetries (A) in
the inclusive hadron production reaction,
+, using a transversely polarized
He target. The experiment was conducted at Jefferson Lab in Hall A using a
5.9-GeV electron beam. Three types of hadrons (,
and proton) were detected in the transverse hadron momentum range 0.54
0.74 GeV/c. The range of for pions was -0.29 -0.23 and for kaons
-0.25 -0.18. The observed asymmetry strongly depends on the type of
hadron. A positive asymmetry is observed for and . A
negative asymmetry is observed for . The magnitudes of the asymmetries
follow . The K and proton
asymmetries are consistent with zero within the experimental uncertainties. The
and asymmetries measured for the He target and
extracted for neutrons are opposite in sign with a small increase observed as a
function of .Comment: Updated version, submitted to Phys. Rev.
Double Spin Asymmetries of Inclusive Hadron Electroproductions from a Transversely Polarized Target
We report the measurement of beam-target double-spin asymmetries
() in the inclusive production of identified hadrons,
+, using a longitudinally
polarized 5.9 GeV electron beam and a transversely polarized
target. Hadrons (, and proton) were detected at
16 with an average momentum =2.35 GeV/c and a transverse
momentum () coverage from 0.60 to 0.68 GeV/c. Asymmetries from the
target were observed to be non-zero for production
when the target was polarized transversely in the horizontal plane. The
and asymmetries have opposite signs, analogous to the
behavior of in semi-inclusive deep-inelastic scattering.Comment: Published in PRC (92.015207), nuclear experiment, high-energy
experimen
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