31,707 research outputs found
Actuator participation in a bending mode identification system
A hydraulic actuator designed for a thrust vector control system used as a shaker for a vehicle to determine the bending mode frequencies is described. The actuator is used as the prime mover and the frequency sensor for the flexible vehicle in a test tower. Advantages in using the actuator piston position with respect to a commanded position to obtain the bending mode frequencies are shown
Documenting helicopter operations from an energy standpoint
Results are presented of a study of the relative and absolute energy consumption of helicopters, including limited comparisons with fixed-wing aircraft, and selected surface transportation vehicles. Additional comparisons were made to determine the level of reduction in energy consumption expected from the application of advanced technologies to the helicopter design and sizing process. It was found that improvements in helicopter consumption characteristics can be accomplished through the utilization of advanced technology to reduce drag, structures weight, and powerplant fuel consumption
Demand Under Product Differentiation: An Empirical Analysis of the US Wine Market
Oversupply has posed a number of problems for the Australian wine industry in recent times. When disaggregated from the industry level, however, the problem can be better described as a range of attribute-specific disequilibria. To date, solutions to this problem have predominantly revolved around reducing output through crop thinning or vine pulling. This paper proposes a different approach by suggesting that disequilibria may be reduced by gaining a better understanding of the demand for Australian wine. A discrete choice model of product differentiation is used to estimate the demand for wine in the United States, Australia's second largest export market. Implications of the analysis are explored.oversupply, demand for wine, product differentiation, nested logit, Demand and Price Analysis,
The Quantum Cosmological Wavefunction at Very Early Times for a Quadratic Gravity Theory
The quantum cosmological wavefunction for a quadratic gravity theory derived
from the heterotic string effective action is obtained near the inflationary
epoch and during the initial Planck era. Neglecting derivatives with respect to
the scalar field, the wavefunction would satisfy a third-order differential
equation near the inflationary epoch which has a solution that is singular in
the scale factor limit . When scalar field derivatives are included,
a sixth-order differential equation is obtained for the wavefunction and the
solution by Mellin transform is regular in the limit. It follows that
inclusion of the scalar field in the quadratic gravity action is necessary for
consistency of the quantum cosmology of the theory at very early times.Comment: Tex, 13 page
Magnetoresistance in the superconducting state at the (111) LaAlO/SrTiO interface
Condensed matter systems that simultaneously exhibit superconductivity and
ferromagnetism are rare due the antagonistic relationship between conventional
spin-singlet superconductivity and ferromagnetic order. In materials in which
superconductivity and magnetic order is known to coexist (such as some
heavy-fermion materials), the superconductivity is thought to be of an
unconventional nature. Recently, the conducting gas that lives at the interface
between the perovskite band insulators LaAlO (LAO) and SrTiO (STO) has
also been shown to host both superconductivity and magnetism. Most previous
research has focused on LAO/STO samples in which the interface is in the (001)
crystal plane. Relatively little work has focused on the (111) crystal
orientation, which has hexagonal symmetry at the interface, and has been
predicted to have potentially interesting topological properties, including
unconventional superconducting pairing states. Here we report measurements of
the magnetoresistance of (111) LAO/STO heterostructures at temperatures at
which they are also superconducting. As with the (001) structures, the
magnetoresistance is hysteretic, indicating the coexistence of magnetism and
superconductivity, but in addition, we find that this magnetoresistance is
anisotropic. Such an anisotropic response is completely unexpected in the
superconducting state, and suggests that (111) LAO/STO heterostructures may
support unconventional superconductivity.Comment: 6 Pages 4 figure
Anisotropic, multi-carrier transport at the (111) LaAlO/SrTiO interface
The conducting gas that forms at the interface between LaAlO and
SrTiO has proven to be a fertile playground for a wide variety of physical
phenomena. The bulk of previous research has focused on the (001) and (110)
crystal orientations. Here we report detailed measurements of the
low-temperature electrical properties of (111) LAO/STO interface samples. We
find that the low-temperature electrical transport properties are highly
anisotropic, in that they differ significantly along two mutually orthogonal
crystal orientations at the interface. While anisotropy in the resistivity has
been reported in some (001) samples and in (110) samples, the anisotropy in the
(111) samples reported here is much stronger, and also manifests itself in the
Hall coefficient as well as the capacitance. In addition, the anisotropy is not
present at room temperature and at liquid nitrogen temperatures, but only at
liquid helium temperatures and below. The anisotropy is accentuated by exposure
to ultraviolet light, which disproportionately affects transport along one
surface crystal direction. Furthermore, analysis of the low-temperature Hall
coefficient and the capacitance as a function of back gate voltage indicates
that in addition to electrons, holes contribute to the electrical transport.Comment: 11 pages, 9 figure
Superconductivity and Frozen Electronic States at the (111) LaAlO/SrTiO Interface
In spite of Anderson's theorem, disorder is known to affect superconductivity
in conventional s-wave superconductors. In most superconductors, the degree of
disorder is fixed during sample preparation. Here we report measurements of the
superconducting properties of the two-dimensional gas that forms at the
interface between LaAlO (LAO) and SrTiO (STO) in the (111) crystal
orientation, a system that permits \emph{in situ} tuning of carrier density and
disorder by means of a back gate voltage . Like the (001) oriented LAO/STO
interface, superconductivity at the (111) LAO/STO interface can be tuned by
. In contrast to the (001) interface, superconductivity in these (111)
samples is anisotropic, being different along different interface crystal
directions, consistent with the strong anisotropy already observed other
transport properties at the (111) LAO/STO interface. In addition, we find that
the (111) interface samples "remember" the backgate voltage at which they
are cooled at temperatures near the superconducting transition temperature
, even if is subsequently changed at lower temperatures. The low
energy scale and other characteristics of this memory effect ( K)
distinguish it from charge-trapping effects previously observed in (001)
interface samples.Comment: 6 pages, 5 Figure
Design and Scale-Up of Production Scale Stirred Tank Fermentors
In the bio/pharmaceutical industry, fermentation is extremely important in pharmaceutical development, and in microbial research. However, new fermentor designs are needed to improve production and reduce costs of complex systems such as cultivation of mammalian cells and genetically engineered micro-organisms. Traditionally, stirred tank design is driven by the oxygen transfer capability needed to achieve cell growth. However, design methodologies available for stirred tank fermentors are insufficient and many times contain errors. The aim of this research is to improve the design of production scale stirred tank fermentors through the development of dimensionless correlations and by providing information on aspects of fermentor tanks that can aid in oxygen mass transfer. This was accomplished through four key areas. Empirical studies were used to quantify the mass transfer capabilities of several different reactors. Computational fluid dynamics (CFD) was used to assess the impact of certain baffle and impeller geometries. Correction schemes were developed and applied to the experimental data. Dimensionless correlations were created from corrected experimental data to act as a guide for future production scale fermentor design. The methods for correcting experimental data developed in this research have proven to be accurate and useful. Furthermore, the correlations found from the corrected experimental data in this study are of great benefit in the design of production scale stirred tank fermentors. However, when designing a stirred tank fermentor of a different size, further experimentation should be performed to refine the correlations presented
Building a More Robust Qualitative Methodology in the Study of Digital Communities in Virtual Worlds: Revisiting the Case Study Approach
This paper addresses methodological challenges of research in the increasingly complex arena of virtual worlds and virtual reality. Case studies can be a valuable research tool, yet traditional approaches do not take into consideration the nuances of virtual experiences. Addressing what appears to be a growing body of evidence that points to a lack of rigor in research methodology in this field, specifically as evidenced by inconsistent research methods and analysis, this paper proposes an adaptation of the traditional multimethod qualitative case study method to address the affordances of virtual worlds and VR. It extends Yin’s (2009) traditional sources of evidence necessary to create a robust case study to virtual environments including digital/virtual forms of: documents, archival records, interviews, direct observation, participantobservation, and physical artifacts
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