19,135 research outputs found
Decision-making for unmanned aerial vehicle operation in icing conditions
With the increased use of unmanned aerial systems
(UAS) for civil and commercial applications, there is
a strong demand for new regulations and technology that
will eventually permit for the integration of UAS in
unsegregated airspace. This requires new technology to
ensure sufficient safety and a smooth integration process.
The absence of a pilot on board a vehicle introduces new
problems that do not arise in manned flight. One challenging
and safety-critical issue is flight in known icing
conditions. Whereas in manned flight, dealing with icing is
left to the pilot and his appraisal of the situation at hand; in
unmanned flight, this is no longer an option and new
solutions are required. To address this, an icing-related
decision-making system (IRDMS) is proposed. The system
quantifies in-flight icing based on changes in aircraft performance
and measurements of environmental properties,
and evaluates what the effects on the aircraft are. Based on
this, it determines whether the aircraft can proceed, and
whether and which available icing protection systems should be activated. In this way, advice on an appropriate
response is given to the operator on the ground, to ensure
safe continuation of the flight and avoid possible accidents
Study of thermal insulation for airborne liquid hydrogen fuel tanks
A concept for a fail-safe thermal protection system was developed. From screening tests, approximately 30 foams, adhesives, and reinforcing fibers using 0.3-meter square liquid nitrogen cold plate, CPR 452 and Stafoam AA1602, both reinforced with 10 percent by weight of 1/16 inch milled OCF Style 701 Fiberglas, were selected for further tests. Cyclic tests with these materials in 2-inch thicknesses bonded on a 0.6-meter square cold plate with Crest 7410 adhesive systems, were successful. Zero permeability gas barriers were identified and found to be compatible with the insulating concept
Earth-like sand fluxes on Mars
Strong and sustained winds on Mars have been considered rare, on the basis of surface meteorology measurements and global circulation models, raising the question of whether the abundant dunes and evidence for wind erosion seen on the planet are a current process. Recent studies showed sand activity, but could not determine whether entire dunes were moving—implying large sand fluxes—or whether more localized and surficial changes had occurred. Here we present measurements of the migration rate of sand ripples and dune lee fronts at the Nili Patera dune field. We show that the dunes are near steady state, with their entire volumes composed of mobile sand. The dunes have unexpectedly high sand fluxes, similar, for example, to those in Victoria Valley, Antarctica, implying that rates of landscape modification on Mars and Earth are similar
Use of Logical Models for Proving Operational Termination in General Logics
The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-319-44802-2_2[EN] A declarative programming language is based on some logic L and its operational semantics is given by a proof calculus which is often presented in a natural deduction style by means of inference rules. Declarative programs are theories S of L and executing a program is proving goals ϕ in the inference system I(S) associated to S as a particulariza-tion of the inference system of the logic. The usual soundness assumption for L implies that every model A of S also satisfies ϕ. In this setting, the operational termination of a declarative program is quite naturally defined as the absence of infinite proof trees in the inference system I(S). Proving operational termination of declarative programs often involves two main ingredients: (i) the generation of logical models A to abstract the program execution (i.e., the provability of specific goals in I(S)), and (ii) the use of well-founded relations to guarantee the absence of infinite branches in proof trees and hence of infinite proof trees, possibly taking into account the information about provability encoded by A. In this paper we show how to deal with (i) and (ii) in a uniform way. The main point is the synthesis of logical models where well-foundedness is a side requirement for some specific predicate symbols.Partially supported by the EU (FEDER), Spanish MINECO TIN 2013-45732-C4-1-P and TIN2015-69175-C4-1-R, and GV PROMETEOII/2015/013.Lucas Alba, S. (2016). Use of Logical Models for Proving Operational Termination in General Logics. Lecture Notes in Computer Science. 9942:26-46. https://doi.org/10.1007/978-3-319-44802-2S2646994
Mass media destabilizes the cultural homogeneous regime in Axelrod's model
An important feature of Axelrod's model for culture dissemination or social
influence is the emergence of many multicultural absorbing states, despite the
fact that the local rules that specify the agents interactions are explicitly
designed to decrease the cultural differences between agents. Here we
re-examine the problem of introducing an external, global interaction -- the
mass media -- in the rules of Axelrod's model: in addition to their
nearest-neighbors, each agent has a certain probability to interact with a
virtual neighbor whose cultural features are fixed from the outset. Most
surprisingly, this apparently homogenizing effect actually increases the
cultural diversity of the population. We show that, contrary to previous claims
in the literature, even a vanishingly small value of is sufficient to
destabilize the homogeneous regime for very large lattice sizes
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