The effects of aeroelastic deformation on the unaugmented stopped-rotor dynamics of an X-Wing aircraft

A new design concept in the development of VTOL aircraft with high forward flight speed capability is that of the X-Wing, a stiff, bearingless helicopter rotor system which can be stopped in flight and the blades used as two forward-swept and two aft-swept wings. Because of the usual configuration in the fixed-wing mode, there is a high potential for aeroelastic divergence or flutter and coupling of blade vibration modes with rigid-body modes. An aeroelastic stability analysis of an X-Wing configuration aircraft was undertaken to determine if these problems could exist. This paper reports on the results of dynamic stability analyses in the lateral and longitudinal directions including the vehicle rigid-body and flexible modes. A static aeroelastic analysis using the normal vibration mode equations of motion was performed to determine the cause of a loss of longitudinal static margin with increasing airspeed. This loss of static margin was found to be due to aeroelastic washin of the forward-swept blades and washout of the aft-swept blades moving the aircraft aerodynamic center forward of the center of gravity. This phenomenon is likely to be generic to X-Wing aircraft

NC's Anti-Predatory Lending Law: Doing What It's Supposed To Do: A Reply

We reply to criticisms of our recent study about North Carolina's Anti-Predatory Lending Law reducing predatory loan terms and preserving access to credit (NC's Anti-Predatory Lending Law: Doing What it's Supposed to Do). To examine whether the decline in overall subprime lending in North Carolina, following passage of the predatory lending law, was due to a decline in loans with legitimate terms or to a reduction in loans with abusive terms, we examined specific market segments and market practices using loan level data from the Loan Performance Asset Backed Securities (ABS) database. Our study revealed that, although the total volume of subprime originations in North Carolina declined, the number of home purchase loans was unaffected by the law. Given the robustness of the LP data, we are baffled by the criticism and disappointed by confusion that has arisen over mistaken data interpretation. For reasons discussed in this paper, we stand by our descriptive study and will continue to use LP data in our future work.Technology and Industry, Regulatory Reform

High efficiency pump for space helium transfer

A centrifugal pump was developed for the efficient and reliable transfer of liquid helium in space. The pump can be used to refill cryostats on orbiting satellites which use liquid helium for refrigeration at extremely low temperatures. The pump meets the head and flow requirements of on-orbit helium transfer: a flow rate of 800 L/hr at a head of 128 J/kg. The overall pump efficiency at the design point is 0.45. The design head and flow requirements are met with zero net positive suction head, which is the condition in an orbiting helium supply Dewar. The mass transfer efficiency calculated for a space transfer operation is 0.99. Steel ball bearings are used with gas fiber-reinforced teflon retainers to provide solid lubrication. These bearings have demonstrated the longest life in liquid helium endurance tests under simulated pumping conditions. Technology developed in the project also has application for liquid helium circulation in terrestrial facilities and for transfer of cryogenic rocket propellants in space

Excessive Strand End Slip in Prestressed Piles

This paper presents the results of a research project that investigated excessive strand end slip observed recently in some prestressed piles. From measurements taken in the field, it is apparent that the problem o excessive initial strand slip is independent of pile shape and size. Strand end slip is evident in piles of different manufacturers in different states in the Southeast. Excessive strand end slip was found in both the top and bottom of the cross section of the piles, although the top portion of the cross section generally exhibited much higher initial slip. Several preventive measures can be adopted to reduce the excessive strand end slip. These preventive measures include: a) proper concrete mixture proportioning to reduce top bar effect; b) use of higher-strength concrete with the lowest possible slump and setting time; c) assessment of the condition of the strands prior to installation to insure excellent bond characteristics; d) gradual release of prestress, with an optimal release sequence; and e) use of adequate vibration to ensure consolidation. The strand end slip measured at five prestressing plants in the Southeast is considerably higher than the allowable end slip and is expected to affect the pile performance. If the strand slip theory is adopted, the strand development length increases substantially due to the excessive strand end slip. A top bar effect factor similar to the one used in reinforced concrete design is recommended. To maintain the excellent quality of precast and prestressed concrete products, manufacturers should adopt a dynamic quality control process that follows the rapid changes in the industry. More tests are necessary to ensure excellent quality, such as the Moustafa or an equivalent test, to assess the bond capabilities of the strands, end slip measurements, and direct measurement of the transfer length. Installation of piles should proceed in a manner to alleviate the top bar effects by placing piles alternately in their best and worst directions

pH-Independent, 520 mV Open-Circuit Voltages of Si/Methyl Viologen^(2+/+) Contacts Through Use of Radial n^+p-Si Junction Microwire Array Photoelectrodes

The effects of introducing an n^+-doped emitter layer have been evaluated for both planar Si photoelectrodes and for radial junction Si microwire-array photoelectrodes. In contact with the pH-independent, one-electron, outer-sphere, methyl viologen redox system (denoted MV^(2+/+)), both planar and wire array p-Si photoelectrodes yielded open-circuit voltages, V_(oc), that varied with the pH of the solution. The highest V_(oc) values were obtained at pH = 2.9, with V_(oc) = 0.53 V for planar p-Si electrodes and V_(oc) = 0.42 V for vapor−liquid−solid catalyzed p-Si microwire array samples, under 60 mW cm^(−2) of 808 nm illumination. Increases in the pH of the electrolyte produced a decrease in V_(oc) by approximately −44 mV/pH unit for planar electrodes, with similar trends observed for the Si microwire array electrodes. In contrast, introduction of a highly doped, n^+ emitter layer produced V_(oc) = 0.56 V for planar Si electrodes and V_(oc) = 0.52 V for Si microwire array electrodes, with the photoelectrode properties in each system being essentially independent of pH over six pH units (3 < pH < 9). Hence, formation of an n^+ emitter layer not only produced nearly identical photovoltages for planar and Si microwire array photoelectrodes, but decoupled the band energetics of the semiconductor (and hence the obtainable photovoltage) from the value of the redox potential of the solution. The formation of radial junctions on Si microwire arrays thus provides an approach to obtaining Si-based photoelectrodes with high-photovoltages that can be used for a variety of photoelectrochemical processes, including potentially the hydrogen evolution reaction, under various pH conditions, regardless of the intrinsic barrier height and flat-band properties of the Si/liquid contact

La boîte à outils géotechniques de demain: EN 1997-1: 202x Règles générales

This paper describes the development of the final Project Team (PT) draft of the next generation of Eurocode 7 Part 1 (EN 1997-1:202x). The use of Nationally Determined Parameters and the drive for ease-of-use is highlighted. Key changes from the previous version of EN 1997-1 are explained, including the introduction of the Geotechnical Design Model; revision of the Geotechnical Categories and their application; the implementation of Consequence Classes and Geotechnical Complexity Classes in achieving the reliability required by the Eurocodes; elaboration on the use of numerical methods within Eurocode 7; the treatment of rock on an equal basis with soil; and greater emphasis on the Observational Method.Postprint (published version

Solar Water Splitting Cells

No abstract

Probing the Earth's interior with a large-volume liquid scintillator detector

A future large-volume liquid scintillator detector would provide a high-statistics measurement of terrestrial antineutrinos originating from $\beta$-decays of the uranium and thorium chains. In addition, the forward displacement of the neutron in the detection reaction $\bar\nu_e+p\to n+e^+$ provides directional information. We investigate the requirements on such detectors to distinguish between certain geophysical models on the basis of the angular dependence of the geoneutrino flux. Our analysis is based on a Monte-Carlo simulation with different levels of light yield, considering both unloaded and gadolinium-loaded scintillators. We find that a 50 kt detector such as the proposed LENA (Low Energy Neutrino Astronomy) will detect deviations from isotropy of the geoneutrino flux significantly. However, with an unloaded scintillator the time needed for a useful discrimination between different geophysical models is too large if one uses the directional information alone. A Gd-loaded scintillator improves the situation considerably, although a 50 kt detector would still need several decades to distinguish between a geophysical reference model and one with a large neutrino source in the Earth's core. However, a high-statistics measurement of the total geoneutrino flux and its spectrum still provides an extremely useful glance at the Earth's interior.Comment: 21 pages, 9 figures. Minor changes, version accepted for publication in Astroparticle Physic