34,007 research outputs found
The UH-1H helicopter icing flight test program: An overview
An ongoing joint NASA/Army program to study the effects of ice accretion on unprotected helicopter rotor aerodynamic performance is discussed. This program integrates flight testing, wind tunnel testing, and analytical modeling. Results are discussed for helicopter flight testing in the Canadian NRC hover spray rig facility to measure rotor aero performance degradation and document rotor ice accretion characteristics. The results of dry wind tunnel testing of airfoil sections with artificial ice accretions and predictions of rotor performance degradation using available rotor performance codes and the wind tunnel data are presented. An alternative approach to conducting future helicopter icing flight programs is discussed
Determining the parameters in a social welfare function using stated preference data: an application to health
One way in which economists might determine how best to balance the competing objectives of efficiency and equity is to specify a social welfare function (SWF). This paper looks at how the stated preferences of a sample of the general public can be used to estimate the shape of the SWF in the domain of health benefits. The results suggest that it is possible to determine the parameters in a social welfare function from stated preference data, but show that people are sensitive to what inequalities exist and to the groups across which those inequalities exist
Design of experiment for the optimisation of deep reactive ion etching of silicon inserts for micro-fabrication
The following paper describes a design of experiments investigation of the deep reactive of pillar structures on a silicon wafer. The etched wafers would subsequently be used as masters for the fabrication of nickel mould inserts for microinjection moulding. Undercuts occur when the pillar base has a smaller cross-section than the apex of the pillar. They therefore affect tolerances of the subsequent nickel mould, its strength and its de-mouldability from the silicon form. The response measured in these experiments was the degree of undercut of micro-scale (10 Ī¼m x 10 Ī¼m x 40 Ī¼m, 5 Ī¼m x 5 Ī¼m x 40 Ī¼m and 2 Ī¼m x 2 Ī¼m x 40 Ī¼m) The literature suggests that gas pressure, platen power, gas flow rate, phase switching times and mask size can all affect the degree of undercut. After examination of this literature, and of manufacturers guidelines, three parameters were selected for experimental testing: platen power, C 4F 8 gas flow rate during the passivation phase and switching times. Switching times was found to be the only statistically significant parameter for both 10x10 Ī¼m and 5x5 Ī¼m pillars. The 2x2 Ī¼m pillars were not successfully replicated and could therefore not undergo statistical evaluation
Contrasts between Equilibrium and Non-equilibrium Steady States: Computer Aided Discoveries in Simple Lattice Gases
A century ago, the foundations of equilibrium statistical mechanics were
laid. For a system in equilibrium with a thermal bath, much is understood
through the Boltzmann factor, exp{-H[C]/kT}, for the probability of finding the
system in any microscopic configuration C. In contrast, apart from some special
cases, little is known about the corresponding probabilities, if the same
system is in contact with more than one reservoir of energy, so that, even in
stationary states, there is a constant energy flux through our system. These
non-equilibrium steady states display many surprising properties. In
particular, even the simplest generalization of the Ising model offers a wealth
of unexpected phenomena. Mostly discovered through Monte Carlo simulations,
some of the novel properties are understood while many remain unexplained. A
brief review and some recent results will be presented, highlighting the sharp
contrasts between the equilibrium Ising system and this non-equilibrium
counterpart.Comment: 9 pages, 3 figure
Kinetics of non-equilibrium quasiparticle tunneling in superconducting charge qubits
We directly observe low-temperature non-equilibrium quasiparticle tunneling
in a pair of charge qubits based on the single Cooper-pair box. We measure
even- and odd-state dwell time distributions as a function of temperature, and
interpret these results using a kinetic theory. While the even-state lifetime
is exponentially distributed, the odd-state distribution is more heavily
weighted to short times, implying that odd-to-even tunnel events are not
described by a homogenous Poisson process. The mean odd-state dwell time
increases sharply at low temperature, which is consistent with quasiparticles
tunneling out of the island before reaching thermal equilibrium.Comment: Replaced Figure 1 with color version, corrected more typos. Version
submitted to PR
Laser Interferometer Gravitational-Wave Observatory beam tube component and module leak testing
Laser Interferometer Gravitational-Wave Observatory (LIGO) is a joint project of the California Institute of Technology and the Massachusetts Institute of Technology funded by the National Science Foundation. The project is designed to detect gravitational waves from astrophysical sources such as supernova and black holes. The LIGO project constructed observatories at two sites in the U.S. Each site includes two beam tubes (each 4 km long) joined to form an "L" shape. The beam tube is a 1.25 m diam 304 L stainless steel, ultrahigh vacuum tube that will operate at 1Ć10^ā9 Torr or better. The beam tube was manufactured using a custom spiral weld tube mill from material processed to reduce the outgassing rate in order to minimize pumping costs. The integrity of the beam tube was assured by helium mass spectrometer leak testing each component of the beam tube system prior to installation. Each 2 km long, isolatable beam tube module was then leak tested after completion
V. problem presentation and advice-giving on a home birth helpline
The rate of home births in the UK is very low (around 2%) and many women who would like to give birth at home find it impossible to get midwifery cover or are advised of medical contraindications. The Home Birth Helpline offers support and expertise for women in this situation. Based on the analysis of 80 recorded calls, this article uses conversation analysis (CA) to explore how callers present their reason for calling the helpline, and what this shows about the culturally shared medicalized culture of birth. This research is an example of feminist CA in that it contributes both to the study of childbirth as a key women's health issue and to the study of helpline interaction from a conversation analytic perspectiv
The application of the scanning electron microscope to studies of current multiplication, avalanche breakdown and thermal runaway. Part 1 - General physical basis
Scanning electron microscope applications in study of current multiplication, avalanche breakdown, and thermal runaway - Physical basi
Surf zone currents and influence on surfability
Surfing headlands are shallow and exposed coastal features that provide a specific form of breaking wave allowing a board-rider to ride on the unbroken wave face. The seabed shape and refraction of the waves in relation to depth contours provide the greatest influence on the quality of the surf break. The large scale and orientation of the Raglan headland allows only the low frequency swells to refract around the headland to create seven different surfing breaks. Each represents a compartmentalization of the shoreline along the headland. This creates variability in wave and current characteristics depending on the orientation and bathymetry at different locations. This provides not only potential access points through the surf-zone (ie: smaller currents), but greater surfability in a range of conditions that is not possible on small scale headlands.
Headlands with surfing waves can be classified as mis-aligned sections of the coast, where the higher oblique angle of the breaking surf generates strong wave-driven currents. These currents are far greater than that found on coastlines in equilibrium with the dominant swell direction, where comparatively insignificant longshore drift is found. The strength and direction of wave-driven currents in the surf zone can influence the surfability of a break. At a surfing headland strong currents flowing downdrift along the shoreline make it difficult for a paddling surfer to get to the "take-off" location of the break, or maintain position in the line-up. In comparison currents flowing updrift along headlands makes getting "out the back" relatively easy, although surfers can be taken out to sea past the "take-off" point by a fast flowing current.
Field experiments at Raglan, on the west coast of New Zealand have been conducted to measure current speed and direction during a large swell event. Observations of surfers attempting to paddle through the breaking-wave zone, confirms the strength of the wave-driven currents with surfers being swept rapidly down the headland. Results from the experiments at Raglan, have shown strong currents in the inshore breaking wave zone with burst-averaged velocities attaining 0.8 ms-1, and maximum bed orbital velocities of up to 2.0 ms-1. Interestingly, further offshore the currents have been found to flow in a re-circulating gyre back up the headland. Comparisons are made from observations of waves and currents found at other surfing headlands around the world. The effect that strong currents may have on the surfability of artificial surfing reefs needs to be considered in the design process, if the surfing amenity is to be maximised for large surf conditions
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