Helicopter far-field acoustic levels as a function of reduced main-rotor advancing blade-tip Mach number

During the design of a helicopter, the weight, engine, rotor speed, and rotor geometry are given significant attention when considering the specific operations for which the helicopter will be used. However, the noise radiated from the helicopter and its relationship to the design variables is currently not well modeled with only a limited set of full-scale field test data to study. In general, limited field data have shown that reduced main-rotor advancing blade-tip Mach numbers result in reduced far-field noise levels. The status of a recent helicopter noise research project is reviewed. It is designed to provide flight experimental data which may be used to further understand helicopter main-rotor advancing blade-tip Mach number effects on far-field acoustic levels. Preliminary results are presented relative to tests conducted with a Sikorsky S-76A helicopter operating with both the rotor speed and the flight speed as the control variable. The rotor speed was operated within the range of 107 to 90 percent NR at nominal forward speeds of 35, 100, and 155 knots

Localized, Non-Harmonic Active Flap Motions for Low Frequency In-Plane Rotor Noise Reduction

A first-of-its-kind demonstration of the use of localized, non-harmonic active flap motions, for suppressing low frequency, in-plane rotor noise, is reported in this paper. Operational feasibility is verified via testing of the full-scale AATD/Sikorsky/UTRC active flap demonstration rotor in the NFAC's 40- by 80-Foot anechoic wind tunnel. Effectiveness of using localized, non-harmonic active flap motions are compared to conventional four-per-rev harmonic flap motions, and also active flap motions derived from closed-loop acoustics implementations. All three approaches resulted in approximately the same noise reductions over an in-plane three-by-three microphone array installed forward and near in-plane of the rotor in the nearfield. It is also reported that using an active flap in this localized, non-harmonic manner, resulted in no more that 2% rotor performance penalty, but had the tendency to incur higher hub vibration levels

Power efficiency of outer hair cell somatic electromotility

© 2009 Rabbitt et al. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in PLoS Computational Biology 5 (2009): e1000444, doi:10.1371/journal.pcbi.1000444.Cochlear outer hair cells (OHCs) are fast biological motors that serve to enhance the vibration of the organ of Corti and increase the sensitivity of the inner ear to sound. Exactly how OHCs produce useful mechanical power at auditory frequencies, given their intrinsic biophysical properties, has been a subject of considerable debate. To address this we formulated a mathematical model of the OHC based on first principles and analyzed the power conversion efficiency in the frequency domain. The model includes a mixture-composite constitutive model of the active lateral wall and spatially distributed electro-mechanical fields. The analysis predicts that: 1) the peak power efficiency is likely to be tuned to a specific frequency, dependent upon OHC length, and this tuning may contribute to the place principle and frequency selectivity in the cochlea; 2) the OHC power output can be detuned and attenuated by increasing the basal conductance of the cell, a parameter likely controlled by the brain via the efferent system; and 3) power output efficiency is limited by mechanical properties of the load, thus suggesting that impedance of the organ of Corti may be matched regionally to the OHC. The high power efficiency, tuning, and efferent control of outer hair cells are the direct result of biophysical properties of the cells, thus providing the physical basis for the remarkable sensitivity and selectivity of hearing.This work was supported by NIDCD R01 DC04928 (Rabbitt), NIDCD R01 DC00384 (Brownell) and NASA Ames GSRA56000135 (Breneman)

Mantle plumes and Antarctica-New Zealand rifting: evidence from mid-Cretaceous mafic dykes

Ocean floor magnetic anomalies show that New Zealand was the last continental fragment to separate from Antarctica during Gondwana break-up, drifting from Marie Byrd Land, West Antarctica, about 84 Ma ago. Prior to continental drift, a voluminous suite of mafic dykes (dated by Ar–Ar laser stepped heating at 107 ± 5 Ma) and anorogenic silicic rocks, including syenites and peralkaline granitoids (95–102 Ma), were emplaced in Marie Byrd Land during a rifting event. The mafic dyke suite includes both high- and low-Ti basalts. Trace element and Sr and Nd isotope compositions of the mafic dykes may be modelled by mixing between tholeiitic OIB (asthenosphere-derived) and alkaline high- to low-Ti alkaline magmas (lithospheric mantle derived). Pb isotopes indicate that the OIB component had a HIMU composition. We suggest that the rift-related magmatism was generated in the vicinity of a mantle plume. The plume helped to control the position of continental separation within the very wide region of continental extension that developed when the Pacific–Phoenix spreading ridge approached the subduction zone. Separation of New Zealand from Antarctica occurred when the Pacific–Phoenix spreading centre propagated into the Antarctic continent. Sea floor spreading in the region of the mantle plume may have caused an outburst of volcanism along the spreading ridge generating an oceanic plateau, now represented by the 10–15 km thick Hikurangi Plateau situated alongside the Chatham Rise, New Zealand. The plateau consists of tholeiitic OIB-MORB basalt, regarded as Cretaceous in age, and similar in composition to the putative tholeiitic end-member in the Marie Byrd Land dykes. The mantle plume is proposed to now underlie the western Ross Sea, centred beneath Mount Erebus, where it was largely responsible for the very voluminous, intraplate, alkaline McMurdo Volcanic Group. A second mantle plume beneath Marie Byrd Land formed the Cenozoic alkaline volcanic province

Probing the interaction of lipids with the non-annular binding sites of the potassium channel KcsA by magic-angle spinning NMR

The activity of the potassium channel, KcsA is tightly regulated through the interactions of anionic lipids with high-affinity non-annular lipid binding sites located at the interface between the channel's subunits. Here we present solid-state phosphorous NMR studies that resolve the negatively charged lipid phosphatidylglycerol within the non-annular lipid-binding site. Perturbations in chemical shift observed upon the binding of phosphatidylglycerol are indicative of the interaction of positively charged sidechains within the non-annular binding site and the negatively charged lipid headgroup. Site directed mutagenesis studies have attributed these charge interactions to R64 and R89. Functionally the removal of the positive charges from R64 and R89 appears to act synergistically to reduce the probability of channel openin

The Selectivity of K+ Ion Channels: Testing the Hypotheses

How K+ channels are able to conduct certain cations yet not others remains an important but unresolved question. The recent elucidation of the structure of NaK, an ion channel that conducts both Na+ and K+ ions, offers an opportunity to test the various hypotheses that have been put forward to explain the selectivity of K+ ion channels. We test the snug-fit, field-strength, and over-coordination hypotheses by comparing their predictions to the results of classical molecular dynamics simulations of the K+ selective channel KcsA and the less selective channel NaK embedded in lipid bilayers. Our results are incompatible with the so-called strong variant of the snug-fit hypothesis but are consistent with the over-coordination hypothesis and neither confirm nor refute the field-strength hypothesis. We also find that the ions and waters in the NaK selectivity filter unexpectedly move to a new conformation in seven K+ simulations: the two K+ ions rapidly move from site S4 to S2 and from the cavity to S4. At the same time, the selectivity filter narrows around sites S1 and S2 and the carbonyl oxygen atoms rotate 20°−40° inwards toward the ion. These motions diminish the large structural differences between the crystallographic structures of the selectivity filters of NaK and KcsA and appear to allow the binding of ions to S2 of NaK at physiological temperature