256 research outputs found
Prediction of jet engine parameters for control design using genetic programming
The simulation of a jet engine behavior is widely used in many different aspects of the engine development and maintenance. Achieving high quality jet engine control systems requires the iterative use of these simulations to virtually test the performance of the engine avoiding any possible damage on the real engine. Jet engine simulations involve the use of mathematical models which are complex and may not always be available. This paper introduces an approach based on Genetic Programming (GP) to model different parameters of a small engine for control design such as the Exhaust Gas Temperature (EGT). The GP approach has no knowledge of the characteristics of the engine. Instead, the model is found by the evolution of models based on past measurements of parameters such as the pump voltage. Once the model is obtained, it is used to predict the behaviour of the jet engine one step ahead. The proposed approach is successfully applied for the simulation of a Behotec j66 jet engine and the results are presented
Data Integration Driven Ontology Design, Case Study Smart City
Methods to design of formal ontologies have been in focus of research since the early nineties when their importance and conceivable practical application in engineering sciences had been understood. However, often significant customization of generic methodologies is required when they are applied in tangible scenarios. In this paper, we present a methodology for ontology design developed in the context of data integration. In this scenario, a targeting ontology is applied as a mediator for distinct schemas of individual data sources and, furthermore, as a reference schema for federated data queries. The methodology has been used and evaluated in a case study aiming at integration of buildings' energy and carbon emission related data. We claim that we have made the design process much more efficient and that there is a high potential to reuse the methodology
HIV-Positive Inmates Released from Nevada’s Prisons in 2001: Results from Matching Health Division and Corrections’ Databases
It is estimated that about one quarter of all HIV-infected individuals in the United States are released from a correctional facility each year. To better understand the needs of inmates with HIV exiting the prison system, a partnership with the Nevada State Health Division (NSHD), the Nevada Department of Corrections (DOC), and the University of Nevada, Reno School of Public Health was formed to examine this population using information contained in existing databases. An analysis of DOC data matched with the data from the HIV/AIDS Reporting System (HARS) maintained by the NSHD identified 2,802 HIV-negative inmates (2,451 males and 350 females) and 44 HIV-positive inmates (33 males and 11 females) who exited prison in 2001. Results showed that HIV-positive inmates released in Nevada were more likely than HIV negative inmates to be African American, have a prior felony, and be re-incarcerated in a three-year follow-up period. For male and female participants living with AIDS, almost one-third had never received antiretroviral therapy. The cyclical pattern of re-incarceration among HIV-positive inmates in Nevada provides an opportunity to reach this population with medical care, infectious disease prevention, and social services. Future analyses with more complete data hold even more promise for understanding the needs of incarcerated individuals living with HIV in Nevada and directing public health interventions
Structural and magnetic deconvolution of FePt/FeOx-nanoparticles using x-ray magnetic circular dichroism
Recently, magnetite nanoparticles have attracted much attention, due to their technological potential based on different optic, magnetic and catalytic sections. In particular, the magnetic properties of hybrid nanocrystals can be tailored by the combination of complementary magnetic materials like for example magnetite and FePt. In order to analyse the related magnetic and structural properties of the resulting bi-component systems, we present x-ray absorption and x-ray magnetic circular dichroism studies at the Fe L2,3 edges simultaneously performed in total electron yield and transmission mode, done at room and low temperatures. This provides in particular the separation of volume- and surface-related properties. The investigated system was made up of FePt/FeOx hybrid nanocrystals, which could be uniquely tuned in size and volume ratios. These measurements have been combined with magnetometry and high-resolution transmission electron microscopy studies. The separation between surface and bulk has been done by a deconvolution of the absorption spectra in terms of a linear superposition of reference spectra. With this universally applicable technique we are able to experimentally determine that the outer FeOx shell fraction at the surface has a strongly reduced magnetization and is of maghemite character, while the inner part is more magnetite like. So the technique shown here can be used to characterize nanoparticular systems and determine their structural and magnetic properties
Collective Particle Flow through Random Media
A simple model for the nonlinear collective transport of interacting
particles in a random medium with strong disorder is introduced and analyzed. A
finite threshold for the driving force divides the behavior into two regimes
characterized by the presence or absence of a steady-state particle current.
Below this threshold, transient motion is found in response to an increase in
the force, while above threshold the flow approaches a steady state with motion
only on a network of channels which is sparse near threshold. Some of the
critical behavior near threshold is analyzed via mean field theory, and
analytic results on the statistics of the moving phase are derived. Many of the
results should apply, at least qualitatively, to the motion of magnetic bubble
arrays and to the driven motion of vortices in thin film superconductors when
the randomness is strong enough to destroy the tendencies to lattice order even
on short length scales. Various history dependent phenomena are also discussed.Comment: 63 preprint pages plus 6 figures. Submitted to Phys Rev
Stochastic Growth Equations and Reparametrization Invariance
It is shown that, by imposing reparametrization invariance, one may derive a
variety of stochastic equations describing the dynamics of surface growth and
identify the physical processes responsible for the various terms. This
approach provides a particularly transparent way to obtain continuum growth
equations for interfaces. It is straightforward to derive equations which
describe the coarse grained evolution of discrete lattice models and analyze
their small gradient expansion. In this way, the authors identify the basic
mechanisms which lead to the most commonly used growth equations. The
advantages of this formulation of growth processes is that it allows one to go
beyond the frequently used no-overhang approximation. The reparametrization
invariant form also displays explicitly the conservation laws for the specific
process and all the symmetries with respect to space-time transformations which
are usually lost in the small gradient expansion. Finally, it is observed, that
the knowledge of the full equation of motion, beyond the lowest order gradient
expansion, might be relevant in problems where the usual perturbative
renormalization methods fail.Comment: 42 pages, Revtex, no figures. To appear in Rev. of Mod. Phy
Heterotic domain wall solutions and SU(3) structure manifolds
We examine compactifications of heterotic string theory on manifolds with
SU(3) structure. In particular, we study N = 1/2 domain wall solutions which
correspond to the perturbative vacua of the 4D, N =1 supersymmetric theories
associated to these compactifications. We extend work which has appeared
previously in the literature in two important regards. Firstly, we include two
additional fluxes which have been, heretofore, omitted in the general analysis
of this situation. This allows for solutions with more general torsion classes
than have previously been found. Secondly, we provide explicit solutions for
the fluxes as a function of the torsion classes. These solutions are
particularly useful in deciding whether equations such as the Bianchi
identities can be solved, in addition to the Killing spinor equations
themselves. Our work can be used to straightforwardly decide whether any given
SU(3) structure on a six-dimensional manifold is associated with a solution to
heterotic string theory. To illustrate how to use these results, we discuss a
number of examples taken from the literature.Comment: 34 pages, minor corrections in second versio
Static and Dynamic Properties of Inhomogeneous Elastic Media on Disordered Substrate
The pinning of an inhomogeneous elastic medium by a disordered substrate is
studied analytically and numerically. The static and dynamic properties of a
-dimensional system are shown to be equivalent to those of the well known
problem of a -dimensional random manifold embedded in -dimensions.
The analogy is found to be very robust, applicable to a wide range of elastic
media, including those which are amorphous or nearly-periodic, with local or
nonlocal elasticity. Also demonstrated explicitly is the equivalence between
the dynamic depinning transition obtained at a constant driving force, and the
self-organized, near-critical behavior obtained by a (small) constant velocity
drive.Comment: 20 pages, RevTeX. Related (p)reprints also available at
http://matisse.ucsd.edu/~hwa/pub.htm
Scaling properties of driven interfaces in disordered media
We perform a systematic study of several models that have been proposed for
the purpose of understanding the motion of driven interfaces in disordered
media. We identify two distinct universality classes: (i) One of these,
referred to as directed percolation depinning (DPD), can be described by a
Langevin equation similar to the Kardar-Parisi-Zhang equation, but with
quenched disorder. (ii) The other, referred to as quenched Edwards-Wilkinson
(QEW), can be described by a Langevin equation similar to the Edwards-Wilkinson
equation but with quenched disorder. We find that for the DPD universality
class the coefficient of the nonlinear term diverges at the depinning
transition, while for the QEW universality class either or
as the depinning transition is approached. The identification
of the two universality classes allows us to better understand many of the
results previously obtained experimentally and numerically. However, we find
that some results cannot be understood in terms of the exponents obtained for
the two universality classes {\it at\/} the depinning transition. In order to
understand these remaining disagreements, we investigate the scaling properties
of models in each of the two universality classes {\it above\/} the depinning
transition. For the DPD universality class, we find for the roughness exponent
for the pinned phase, and
for the moving phase. For the growth exponent, we find for the pinned phase, and for the moving phase.
Furthermore, we find an anomalous scaling of the prefactor of the width on the
driving force. A new exponent , characterizing the
scaling of this prefactor, is shown to relate the values of the roughnessComment: Latex manuscript, Revtex 3.0, 15 pages, and 15 figures also available
via anonymous ftp from ftp://jhilad.bu.edu/pub/abms/ (128.197.42.52
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