17,268 research outputs found
Experimentally determined flutter from two- and three-bladed model bearingless rotors in hover
A series of experiments was performed on a 1.8-m-diam model rotor in hover for the principal purpose of investigating the lead-lag stability of isolated bearingless rotors. Incidental to those tests, at least three types of pitch-flap flutter were encountered. Type 1 flutter occurred approximately at the second flap-mode frequency on both two-and three-bladed rotors for both small and large pitch angles and appeared to be a classic pitch-flap flutter. Type 2 flutter showed mostly torsional motion and was seen on both two- and three-bladed rotors. Type 3 flutter was a regressing flap flutter that occurred for only the three-bladed rotor configurations and appears to be a wake excited flutter. Although flutter occurred on a number of different configurations, no rotor parameters were identified that were clearly stabilizing or destabilizing
QCD: Challenges for the Future
Despite many experimental verifications of the correctness of our basic
understanding of QCD, there remain numerous open questions in strong
interaction physics and we focus on the role of future colliders in addressing
these questions. We discuss possible advances in the measurement of ,
in the study of parton distribution functions, and in the understanding of low
physics at present colliders and potential new facilities. We also touch
briefly on the role of spin physics in advancing our understanding of QCD.Comment: 12 pages, LATEX2e with snow2e, epsfig and 2 figures. Also available
at http://penguin.phy.bnl.gov/~dawson/qcdsnow.ps . QCD working group summary
at DPF/DPB Summer Study on New Directions for High Energy Physics, Snowmass,
CO, June 25- July 12, 199
Automated patient monitoring system
Radio-linked patient monitoring system collects several channels of physiological data from as many as 64 hospital patients and transmits the data in digital form to a central control station. The system consists of a central control station and battery-operated patient units comprising small strap-on electronics packages
Mechanism of enhanced light output in InGaN-based microlight emitting diodes
Micro-light emitting diode (LED) arrays with diameters of 4 to 20 mum have been fabricated and were found to be much more efficient light emitters compared to their broad-area counterparts, with up to five times enhancement in optical power densities. The possible mechanisms responsible for the improvement in performance were investigated. Strain relaxation in the microstructures as measured by Raman spectroscopy was not observed, arguing against theories of an increase in internal quantum efficiency due to a reduction of the piezoelectric field put forward by other groups. Optical microscope images show intense light emission at the periphery of the devices, as a result of light scattering off the etched sidewalls. This increases the extraction efficiency relative to broad area devices and boosts the forward optical output. In addition, spectra of the forward emitted light reveal the presence of resonant cavity modes [whispering gallery (WG) modes in particular] which appear to play a role in enhancing the optical output
Systematic characterization of thermodynamic and dynamical phase behavior in systems with short-ranged attraction
In this paper we demonstrate the feasibility and utility of an augmented
version of the Gibbs ensemble Monte Carlo method for computing the phase
behavior of systems with strong, extremely short-ranged attractions. For
generic potential shapes, this approach allows for the investigation of
narrower attractive widths than those previously reported. Direct comparison to
previous self-consistent Ornstein-Zernike approximation calculations are made.
A preliminary investigation of out-of-equilibrium behavior is also performed.
Our results suggest that the recent observations of stable cluster phases in
systems without long-ranged repulsions are intimately related to gas-crystal
and metastable gas-liquid phase separation.Comment: 10 pages, 8 figure
Characterizing and correcting for the effect of sensor noise in the dynamic mode decomposition
Dynamic mode decomposition (DMD) provides a practical means of extracting
insightful dynamical information from fluids datasets. Like any data processing
technique, DMD's usefulness is limited by its ability to extract real and
accurate dynamical features from noise-corrupted data. Here we show
analytically that DMD is biased to sensor noise, and quantify how this bias
depends on the size and noise level of the data. We present three modifications
to DMD that can be used to remove this bias: (i) a direct correction of the
identified bias using known noise properties, (ii) combining the results of
performing DMD forwards and backwards in time, and (iii) a total
least-squares-inspired algorithm. We discuss the relative merits of each
algorithm, and demonstrate the performance of these modifications on a range of
synthetic, numerical, and experimental datasets. We further compare our
modified DMD algorithms with other variants proposed in recent literature
InGaN nano-ring structures for high-efficiency light emitting diodes
A technique based on the Fresnel diffraction effect for the fabrication of nano-scale site-controlled ring structures in InGaN/GaN multi-quantum well structures has been demonstrated. The ring structures have an internal diameter of 500 nm and a wall width of 300 nm. A 1 cm-1 Raman shift has been measured, signifying substantial strain relaxation from the fabricated structure. The 9 nm blueshift observed in the cathodoluminescence spectra can be attributed to band filling and/or screening of the piezoelectric field. A light emitting diode based on this geometry has been demonstrated
Low Mass Dark Matter and Invisible Higgs Width In Darkon Models
The Standard Model (SM) plus a real gauge-singlet scalar field dubbed darkon
(SM+D) is the simplest model possessing a weakly interacting massive particle
(WIMP) dark-matter candidate. In this model, the parameters are constrained
from dark matter relic density and direct searches. The fact that interaction
between darkon and SM particles is only mediated by Higgs boson exchange may
lead to significant modifications to the Higgs boson properties. If the dark
matter mass is smaller than a half of the Higgs boson mass, the Higgs boson can
decay into a pair of darkons resulting in a large invisible branching ratio.
The Higgs boson will be searched for at the LHC and may well be discovered in
the near future. If a Higgs boson with a small invisible decay width will be
found, the SM+D model with small dark matter mass will be in trouble. We find
that by extending the SM+D to a two-Higgs-doublet model plus a darkon (THDM+D)
it is possible to have a Higgs boson with a small invisible branching ratio and
at the same time the dark matter can have a low mass. We also comment on other
implications of this model.Comment: RevTeX, 15 pages, 11 figures. A few typos corrected and some
references adde
Estimates of production rates of SUSY particles in ultra-relativistic heavy-ion collisions
We estimate the production rates of supersymmetric particles in central
heavy-ion collisions at LHC. The parton cascade model is used to seek for
possible collective phenomena which enlarge the production probability of very
heavy particles. Even if there is some indication of such cooperative effects,
higher energy and higher luminosity of proton beams at LHC disfavor heavy-ion
reactions in the search for supersymmetric particles.Comment: 19 pages including 10 EPS figure
Higgs Radiation off Top Quarks at the Tevatron and the LHC
Higgs bosons can be searched for in the channels
at the Tevatron and the LHC. We have calculated the QCD corrections to these
processes in the Standard Model at next-to-leading order. The higher-order
corrections reduce the renormalization and factorization scale dependence
considerably and stabilize the theoretical predictions for the cross sections.
At the central scale the properly defined factors are
slightly below unity for the Tevatron () and slightly above unity
for the LHC ().Comment: 5 pages, latex, 2 figure
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