6,486 research outputs found
Numerical and Experimental Study on the Addition of Surface Roughness to Micro-Propellers
Micro aerial vehicles are making a large impact in applications such as
search-and-rescue, package delivery, and recreation. Unfortunately, these
diminutive drones are currently constrained to carrying small payloads, in
large part because they use propellers optimized for larger aircraft and
inviscid flow regimes. Fully realizing the potential of emerging microflyers
requires next-generation propellers that are specifically designed for
low-Reynolds number conditions and that include new features advantageous in
highly viscous flows. One aspect that has received limited attention in the
literature is the addition of roughness to propeller blades as a method of
reducing drag and increasing thrust. To investigate this possibility, we used
large eddy simulation to conduct a numerical investigation of smooth and rough
propellers. Our results indicate that roughness produces a 2% increase in
thrust and a 5% decrease in power relative to a baseline smooth propeller
operating at the same Reynolds number of Rec = 6500, held constant by
rotational speed. We corroborated our numerical findings using
thrust-stand-based experiments of 3D-printed propellers identical to those of
the numerical simulations. Our study confirms that surface roughness is an
additional parameter within the design space for micro-propellers that will
lead to unprecedented drone efficiencies and payloads.Comment: 23 Pages, 9 Figure
Extracting the late-time kinetic Sunyaev-Zel'dovich effect
We propose a novel technique to separate the late-time, post-reionization component of the kinetic Sunyaev Zeldovich (kSZ) effect from the contribution to it from a (poorly understood and probably patchy) reionization history. The kSZ effect is one of the most promising probe of the missing baryons in the Universe. We study the possibility of reconstructing it in three dimensions (3D), using future spectroscopic surveys such as the Euclid survey. By reconstructing a 3D template from galaxy density and peculiar velocity fields from spectroscopic surveys we cross-correlate the estimator against CMB maps. The resulting cross-correlation can help us to map out the kSZ contribution to CMB in 3D as a function of redshift thereby extending previous results which use tomographic reconstruction. This allows the separation of the late-time effect from the contribution owing to reionization. By construction, it avoids contamination from foregrounds, primary CMB, tSZ effect as well as from star-forming galaxies. Due to a high number density of galaxies the signal-to-noise ratio (S/N) for such cross-correlational studies is higher, compared to the studies involving CMB power-spectrum analysis. Using a spherical Bessel–Fourier (sFB) transform we introduce a pair of 3D power spectra: C⊥ℓ(k) and C⊥ℓ(k) that can be used for this purpose. We find that in a future spectroscopic survey with near all-sky coverage and a survey depth of z ≈ 1, reconstruction of C⊥ℓ(k) can be achieved in a few radial wave bands k ≈ (0.01–0.5 h−1 Mpc) with a S/N ratio of up to O(10) for angular harmonics in the range = (200–2000)
Transformation of spin information into large electrical signals via carbon nanotubes
Spin electronics (spintronics) exploits the magnetic nature of the electron,
and is commercially exploited in the spin valves of disc-drive read heads.
There is currently widespread interest in using industrially relevant
semiconductors in new types of spintronic devices based on the manipulation of
spins injected into a semiconducting channel between a spin-polarized source
and drain. However, the transformation of spin information into large
electrical signals is limited by spin relaxation such that the magnetoresistive
signals are below 1%. We overcome this long standing problem in spintronics by
demonstrating large magnetoresistance effects of 61% at 5 K in devices where
the non-magnetic channel is a multiwall carbon nanotube that spans a 1.5 micron
gap between epitaxial electrodes of the highly spin polarized manganite
La0.7Sr0.3MnO3. This improvement arises because the spin lifetime in nanotubes
is long due the small spin-orbit coupling of carbon, because the high nanotube
Fermi velocity permits the carrier dwell time to not significantly exceed this
spin lifetime, because the manganite remains highly spin polarized up to the
manganite-nanotube interface, and because the interfacial barrier is of an
appropriate height. We support these latter statements regarding the interface
using density functional theory calculations. The success of our experiments
with such chemically and geometrically different materials should inspire
adventure in materials selection for some future spintronicsComment: Content highly modified. New title, text, conclusions, figures and
references. New author include
Nucleon-Gold Collisions at 200 AGeV Using Tagged d+Au Interactions in PHOBOS
Forward calorimetry in the PHOBOS detector has been used to study charged
hadron production in d+Au, p+Au and n+Au collisions at sqrt(s_nn) = 200 GeV.
The forward proton calorimeter detectors are described and a procedure for
determining collision centrality with these detectors is detailed. The
deposition of energy by deuteron spectator nucleons in the forward calorimeters
is used to identify p+Au and n+Au collisions in the data. A weighted
combination of the yield of p+Au and n+Au is constructed to build a reference
for Au+Au collisions that better matches the isospin composition of the gold
nucleus. The p_T and centrality dependence of the yield of this improved
reference system is found to match that of d+Au. The shape of the charged
particle transverse momentum distribution is observed to extrapolate smoothly
from pbar+p to central d+Au as a function of the charged particle
pseudorapidity density. The asymmetry of positively- and negatively-charged
hadron production in p+Au is compared to that of n+Au. No significant asymmetry
is observed at mid-rapidity. These studies augment recent results from
experiments at the LHC and RHIC facilities to give a more complete description
of particle production in p+A and d+A collisions, essential for the
understanding the medium produced in high energy nucleus-nucleus collisions.Comment: 17 pages, 18 figure
Centrality dependence of charged hadron transverse momentum spectra in d+Au collisions at sqrt(s_NN) = 200 GeV
We have measured transverse momentum distributions of charged hadrons
produced in d+Au collisions at sqrt(s_NN) = 200 GeV. The spectra were obtained
for transverse momenta 0.25 < p_T < 6.0 GeV/c, in a pseudorapidity range of 0.2
< eta < 1.4 in the deuteron direction. The evolution of the spectra with
collision centrality is presented in comparison to p+pbarcollisions at the same
collision energy. With increasing centrality, the yield at high transverse
momenta increases more rapidly than the overall particle density, leading to a
strong modification of the spectral shape. This change in spectral shape is
qualitatively different from observations in Au+Au collisions at the same
energy. The results provide important information for discriminating between
different models for the suppression of high-p_T hadrons observed in Au+Au
collisions.Comment: 5 pages, 4 figures, submitted to PR
Centrality dependence of charged antiparticle to particle ratios near mid-rapidity in d+Au collisions at sqrt(s_NN)=200 GeV
The ratios of the yields of charged antiparticles to particles have been
obtained for pions, kaons, and protons near mid-rapidity for d+Au collisions at
sqrt(s_NN) = 200 GeV as a function of centrality. The reported values represent
the ratio of the yields averaged over the rapidity range of 0.1<y_pi<1.3 and
0<y_(K,p)<0.8, where positive rapidity is in the deuteron direction, and for
transverse momenta 0.1<p_(T)^(pi,K)<1.0 GeV/c and 0.3<p_(T)^(p)<1.0 GeV/c.
Within the uncertainties, a lack of centrality dependence is observed in all
three ratios. The data are compared to results from other systems and model
calculations.Comment: 6 pages, 4 figures, submitted to PR
Charged antiparticle to particle ratios near midrapidity in p+p collisions at sqrt(s_NN)=200 GeV
The ratios of the yields of primary charged antiparticles to particles have
been obtained for pions, kaons, and protons near midrapidity for p+p collisions
at sqrt(s_NN) = 200 GeV. Ratios of =1.000 +/- 0.012 (stat.) +/- 0.019
(syst.), =0.93 +/- 0.05 (stat.) +/- 0.03 (syst.), and =0.85 +/-
0.04 (stat.) +/- 0.03 (syst.) have been measured. The reported values represent
the ratio of the yields averaged over the rapidity range of 0.1<y_{pi}<1.3 and
0<y_{K,p}<0.8, and for transverse momenta of 0.1<p_T^{pi,K}<1.0 GeV/c and
0.3<p_T^{p}<1.0 GeV/c. Within the uncertainties, all three ratios are
consistent with the values measured in d+Au collisions at the same energy. The
data are compared to results from other collision systems and energies.Comment: 3 pages, 2 figures, 1 table, submitted to Phys. Rev.
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