17,448 research outputs found
Design of all electric secondary power system for future advanced MALE UAV
SAvE (Systems for UAV Alternative Energy) is a research project funded in 2007 by Piemonte Regional Government, Italy, and assigned to Politecnico di Torino and Alenia Aeronautica. Aim of the project is the study of new, more efficient, more effective and more environmentally friendly on board systems for future advanced Unmanned Aerial Vehicles (UAV), particularly for future advanced MALE UAVs. The paper deals with the analysis and design of the all electric Secondary Power System of a future advanced MALE UAV, that we consider as "reference aircraft". After a thorough trade-off analysis of different configurations of the Secondary Power System, the hybrid configuration, characterized by generators (or better, starter/generators), fuel cells and traditional and innovative batteries, has been selected as the most promising. Detailed investigations to find the best way to apportion the supply of secondary power, considering the various power sources (generators or starter/generators, batteries and fuel cells) in the different modes of operations, have been performed thanks to an integrated simulation environment, where physical, functional and mission scenario simulations continuously exchange data and results
Optimization method for the determination of material parameters in damaged composite structures
An optimization method to identify the material parameters of composite structures using an inverse method is proposed. This methodology compares experimental results with their numerical reproduction using the finite element method in order to obtain an estimation of the error between the results. This error estimation is then used by an evolutionary optimizer to determine, in an iterative process, the value of the material parameters which result in the best numerical fit. The novelty of the method is in the coupling between the simple genetic algorithm and the mixing theory used to numerically reproduce the composite behavior. The methodology proposed has been validated through a simple example which illustrates the exploitability of the method in relation to the modeling of damaged composite structures.Peer ReviewedPostprint (author’s final draft
Impact of photometric variability on age and mass determination of Young Stellar Objects: A case study on Orion Nebula Cluster
In case of pre-main sequence objects, the only way to determine age and mass
is by fitting theoretical isochrones on color-magnitude (alternatively
luminosity-temperature) diagrams. Since young stellar objects exhibit
photometric variability over wide range in magnitude and colors, the age and
mass determined by fitting isochrones is expected to be inaccurate, if not
erroneous. These in turn will badly affect any study carried out on age spread
and process of star formation. Since we have carried out very extensive
photometric observations of the Orion Nebula Cluster (ONC), we decided to use
our multi-band data to explore the influence of variability in determining mass
and age of cluster members. In this study, we get the amplitudes of the
photometric variability in V, R, and I optical bands of a sample of 346 ONC
members and use it to investigate how the variability affects the inferred
masses and ages and if it alone can take account for the age spread among the
ONC members reported by earlier studies. We find that members that show
periodic and smooth photometric rotational modulation have their masses and
ages unaffected by variability. On other hand, we found that members with
periodic but very scattered photometric rotational modulation and members with
irregular variability have their masses and ages significantly affected.
Moreover, using Hertzsprung-Russell (HR) diagrams we find that the observed I
band photometric variability can take account of only a fraction (about 50%) of
the inferred age spread, whereas the V band photometric variability is large
enough to mask any age spread.Comment: Accepted by MNRAS; 17 pages, 4 Tables, 15 Figure
On the Topology of the Inflaton Field in Minimal Supergravity Models
We consider global issues in minimal supergravity models where a single field
inflaton potential emerges. In a particular case we reproduce the Starobinsky
model and its description dual to a certain formulation of R+R^2 supergravity.
For definiteness we confine our analysis to spaces at constant curvature,
either vanishing or negative. Five distinct models arise, two flat models with
respectively a quadratic and a quartic potential and three based on the
SU(1,1)/U(1) space where its distinct isometries, elliptic, hyperbolic and
parabolic are gauged. Fayet-Iliopoulos terms are introduced in a geometric way
and they turn out to be a crucial ingredient in order to describe the de Sitter
inflationary phase of the Starobinsky model.Comment: 31 pages, LaTex, 7 eps figures, 2 table
Many body exchange effects close to the s-wave Feshbach resonance in two-component Fermi systems: Is a triplet superfluid possible?
We suggest that the exchange fluctuations close to a Feshbach resonance in a
two-component Fermi gas can result in an effective p-wave attractive
interaction. On the BCS side of a Feshbach resonance, the magnitude of this
effective interaction is comparable to the s-wave interaction, therefore
leading to a possible spin-triplet superfluid in the range of temperatures of
actual experiments. We also show that the particle-hole exchange fluctuations
introduce an effective scattering length which does not diverge, as the
standard mean-field one does. Finally, using the effective interaction
quantities we are able to model the molecular binding energy on the BEC side of
the resonance.Comment: 5 pages, 5 figures,revised text version. Replaced with published
versio
Towards active microfluidics: Interface turbulence in thin liquid films with floating molecular machines
Thin liquid films with floating active protein machines are considered.
Cyclic mechanical motions within the machines, representing microscopic
swimmers, lead to molecular propulsion forces applied to the air-liquid
interface. We show that, when the rate of energy supply to the machines exceeds
a threshold, the flat interface becomes linearly unstable. As the result of
this instability, the regime of interface turbulence, characterized by
irregular traveling waves and propagating machine clusters, is established.
Numerical investigations of this nonlinear regime are performed. Conditions for
the experimental observation of the instability are discussed.Comment: 9 pages, 8 figures, RevTeX, submitted to Physical Review
- …