15,025 research outputs found
A model for prediction of STOVL ejector dynamics
A semi-empirical control-volume approach to ejector modeling for transient performance prediction is presented. This new approach is motivated by the need for a predictive real-time ejector sub-system simulation for Short Take-Off Verticle Landing (STOVL) integrated flight and propulsion controls design applications. Emphasis is placed on discussion of the approximate characterization of the mixing process central to thrust augmenting ejector operation. The proposed ejector model suggests transient flow predictions are possible with a model based on steady-flow data. A practical test case is presented to illustrate model calibration
STOVL propulsion system volume dynamics approximations
Two approaches to modeling turbofan engine component volume dynamics are explored and compared with a view toward application to real-time simulation of short take-off vertical landing (STOVL) aircraft propulsion systems. The first (and most popular) approach considers only heat and mass balances; the second approach includes a momentum balance and substitutes the heat equation with a complete energy balance. Results for a practical test case are presented and discussed
Detecting Majorana bound states
We propose a set of interferometric methods on how to detect Majorana bound
states induced by a topological insulator. The existence of these states can be
easily determined by the conductance oscillations as function of magnetic flux
and/or electric voltage. We study the system in the presence and absence of
Majorana bound states and observe strikingly different behaviors. Importantly,
we show that the presence of coupled Majorana bound states can induce a
persistent current in absence of any external magnetic field.Comment: 7 pages, 6 figures, 1 table, revised and expanded, accepted for
publication in Phys. Rev.
A Brief History of BioPerl
Large-scale open-source projects face a litany of pitfalls and difficulties. Problems of contribution quality, credit for contributions, project coordination, funding, and mission-creep are ever-present. Of these, long-term funding and project coordination can interact to form a particularly difficult problem for open-source projects in an academic environment.
BioPerl was chosen as an example of a successful academic open-source project. Several of the roadblocks and hurdles encountered and overcome in the development of BioPerl are examined through the telling of the history of the project. Along the way, key points of open-source law are explained, such as license choice and copyright.
The BioPerl project current status is then analyzed, and four different strategies typically employed by traditional open-source projects at this stage are analyzed as future directions. Strategies such as soliciting donations, securing grants, providing dual-licenses to enhance commercial interest, and the paid provision of support have all been employed in various traditional open-source projects with success, but each has drawbacks when applied to the academy. Finally, the construction of a successful long-term strategy for BioPerl, and other academic open-source projects, is proposed so that such projects can navigate the difficulties
Excitations of the static quark-antiquark system in several gauge theories
The spectrum of gluons in the presence of a static quark-antiquark pair is
studied using Monte Carlo simulations on anisotropic space-time lattices. For
very small quark-antiquark separations R, the level orderings and approximate
degeneracies disagree with the expectations from an effective string theory. As
the quark-antiquark separation R increases, a dramatic rearrangement of the
energies occurs, and above 2 fm, all of the levels studied show behavior
consistent with an effective string description. The energy spacings are nearly
pi/R, but a tantalizing fine structure remains. In addition to 4-dimensional
SU(3) gauge theory, results from 3-dimensional SU(2) and compact U(1) gauge
theories are also presented.Comment: 12 pages, 4 figures, talk presented at the International Conference
on Color Confinement and Hadrons in Quantum Chromodynamics (Confinement
2003), RIKEN, July 21-24, 200
The heavy-quark hybrid meson spectrum in lattice QCD
Recent findings on the spectrum of heavy-quark mesons from computer
simulations of quarks and gluons in lattice QCD are summarized, with particular
attention to quark-antiquark states bound by an excited gluon field. The
validity of a Born-Oppenheimer treatment for such systems is discussed. Recent
results on glueball masses, the light-quark 1-+ hybrid meson mass, and the
static three-quark potential are summarized.Comment: 15 pages, 13 figures, talk given at the Workshop on Scalar Mesons: An
Interesting Puzzle for QCD, SUNY Institute of Technology, Utica, NY, May
16-18, 2003, submitted to American Institute of Physics Conference
Proceedings. After publication, it will be found at
http://proceedings.aip.org/proceedings
Indirect Convertibility and Quasi-futures Contracts: Two Non-operational Schemes for Automatic Stabilisation of the Price Level
This paper examines two proposals for automatic stabilization of the price level based on indirect convertibility and something called a 'quasi futures contract'. These two schemes represent attempts to render operational ideas implicit in the Black (1970) Fama (1980) and Hall (1982) vision of the monetary system. Criticisms of the two schemes have been rejected by their exponents. The paper clarifies the analytical issues at stake in this debate and concludes that both schemes do suffer from fundamental flaws which would render them nonoperational. Hence, neither scheme offers an operational basis for a laissez faire banking system or provides a workable alternative to current methods of stabilising the price level.indirect convertibility, quasi-futures contracts
An AD100 implementation of a real-time STOVL aircraft propulsion system
A real-time dynamic model of the propulsion system for a Short Take-Off and Vertical Landing (STOVL) aircraft was developed for the AD100 simulation environment. The dynamic model was adapted from a FORTRAN based simulation using the dynamic programming capabilities of the AD100 ADSIM simulation language. The dynamic model includes an aerothermal representation of a turbofan jet engine, actuator and sensor models, and a multivariable control system. The AD100 model was tested for agreement with the FORTRAN model and real-time execution performance. The propulsion system model was also linked to an airframe dynamic model to provide an overall STOVL aircraft simulation for the purposes of integrated flight and propulsion control studies. An evaluation of the AD100 system for use as an aircraft simulation environment is included
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