7,070 research outputs found
Flight test pilot evaluation of a delayed flap approach procedure
Using NASA's CV-990 aircraft, a delayed flap approach procedure was demonstrated to nine guest pilots from the air transport industry. Four demonstration flights and 37 approaches were conducted under VFR weather conditions. A limited pilot evaluation of the delayed flap procedure was obtained from pilot comments and from questionaires they completed. Pilot acceptability, pilot workload, and ATC compatibility were quantitatively rated. The delayed flap procedure was shown to be feasible, and suggestions for further development work were obtained
Delayed flap approach procedures for noise abatement and fuel conservation
The NASA/Ames Research Center is currently investigating the delayed flap approach during which pilot actions are determined and prescribed by an onboard digital computer. The onboard digital computer determines the proper timing for the deployment of the landing gear and flaps based on the existing winds and airplane gross weight. Advisory commands are displayed to the pilot. The approach is flown along the conventional ILS glide slope but is initiated at a higher airspeed and in a clean aircraft configuration that allows for low thrust and results in reduced noise and fuel consumption. Topics discussed include operational procedures, pilot acceptability of these procedures, and fuel/noise benefits resulting from flight tests and simulation
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The microstratigraphy of middens: capturing daily routine in rubbish at Neolithic Çatalhöyük, Turkey
Microstratigraphy — the sequencing of detailed biological signals on site — is an important new approach being developed in the Çatalhöyük project. Here the authors show how microscopic recording of the strata and content of widespread middens on the tell are revealing daily activities and the selective employment of plants in houses and as fuel. Here we continue to witness a major advance in the practice of archaeological investigation.</jats:p
Flight tests of IFR landing approach systems for helicopters
Joint NASA/FAA helicopter flight tests were conducted to investigate airborne radar approaches (ARA) and microwave landing system (MLS) approaches. Flight-test results were utilized to prove NASA with a data base to be used as a performance measure for advanced guidance and navigation concepts, and to provide FAA with data for establishment of TERPS criteria. The first flight-test investigation consisted of helicopter IFR approaches to offshore oil rigs in the Gulf of Mexico, using weather/mapping radar, operational pilots, and a Bell 212 helicopter. The second flight-test investigation consisted of IFR MLS approaches at Crows Landing (near Ames Research Center), with a Bell UH-1H helicopter, using NASA, FAA, and operational industry pilots. Tests are described and results discussed
A comparison of two different model checking techniques
Thesis (MSc)--University of Stellenbosch, 2003.ENGLISH ABSTRACT: Model checking is a computer-aided verification technique that is used to verify properties
about the formal description of a system automatically. This technique has been applied
successfully to detect subtle errors in reactive systems. Such errors are extremely difficult to
detect by using traditional testing techniques. The conventional method of applying model
checking is to construct a model manually either before or after the implementation of a
system. Constructing such a model requires time, skill and experience. An alternative method
is to derive a model from an implementation automatically.
In this thesis two techniques of applying model checking to reactive systems are compared,
both of which have problems as well as advantages. Two specific strategies are compared in
the area of protocol development:
1. Structuring a protocol as a transition system, modelling the system, and then deriving
an implementation from the model.
2. Automatically translating implementation code to a verifiable model.
Structuring a reactive system as a transition system makes it possible to verify the control flow
of the system at implementation level-as opposed to verifying the control flow at abstract
level. The result is a closer correspondence between implementation and specification (model).
At the same time testing, which is restricted to small, independent code fragments that
manipulate data, is simplified significantly.
The construction of a model often takes too long; therefore, verification results may no longer
be applicable when they become available. To address this problem, the technique of automated
model extraction was suggested. This technique aims to reduce the time required to
construct a model by minimising manual input during model construction.
A transition system is a low-level formalism and direct execution through interpretation is feasible. However, the overhead of interpretation is the major disadvantage of this technique.
With automated model extraction there are disadvantages too. For example, differences
between the implementation and specification languages-such as constructs present in the
implementation language that cannot be expressed in the modelling language-make the
development of an automated model extraction tool extremely difficult.
In conclusion, the two techniques are compared against a set of software development considerations.
Since a specific technique is not always preferable, guidelines are proposed to help
select the best approach in different circumstances.AFRIKAANSE OPSOMMING: Modeltoetsing is 'n rekenaargebaseerde verifikasietegniek wat gebruik word om eienskappe
rakende 'n formele spesifikasie van 'n stelsel te verifieer. Die tegniek is al suksesvol toegepas
om subtiele foute in reaktiewe stelsels op te spoor. Sulke foute word uiters moeilik opgespoor
as tradisionele toetsings tegnieke gebruik word. Tradisioneel word modeltoetsing toegepas
deur 'n model te bou voor of na die implementasie van 'n stelsel. Om'n model te bou
verg tyd, vernuf en ervaring. 'n Alternatiewe metode is om outomaties 'n model van 'n
implementasie af te lei.
In hierdie tesis word twee toepassingstegnieke van modeltoetsing vergelyk, waar beide tegnieke
beskik oor voordele sowel as nadele. Twee strategieë word vergelyk in die gebied van protokol
ontwikkeling:
1. Om 'n protokol as 'n oorgangsstelsel te struktureer, dit te moduleer en dan 'n implementasie
van die model af te lei.
2. Om outomaties 'n verifieerbare model van 'n implementasie af te lei.
Om 'n reaktiewe stelsel as 'n oorgangsstelsel te struktureer maak dit moontlik om die kontrolevloei
op implementasie vlak te verifieer-in teenstelling met verifikasie van kontrolevloei
op 'n abstrakte vlak. Die resultaat is 'n nouer band wat bestaan tussen die implementasie en
die spesifikasie. Terselfdetyd word toetsing, wat beperk word tot klein, onafhanklike kodesegmente
wat data manupileer, beduidend vereenvoudig.
Die konstruksie van 'n model neem soms te lank; gevolglik, wanneer die verifikasieresultate
beskikbaar word, is dit dalk nie meer toepaslik op die huidige weergawe van 'n implementasie
nie. Om die probleem aan te spreek is 'n tegniek om modelle outomaties van implementasies
af te lei, voorgestel. Die doel van die tegniek is om die tyd wat dit neem om 'n model te bou
te verminder deur handtoevoer tot 'n minimum te beperk. 'n Oorgangsstelsel is 'n laevlak formalisme en direkte uitvoering deur interpretasie is wesenlik.
Die oorhoofse koste van die interpreteerder is egter die grootste nadeel van die tegniek. Daar is
ook nadele wat oorweeg moet word rakende die tegniek om outomaties modelle van implementasies
af te lei. Byvoorbeeld, verskille tussen die implementasietaal en spesifikasietaal=-soos
byvoorbleed konstrukte wat in die implementasietaal gebruik word wat nie in die modeleringstaal
voorgestel kan word nie-vrnaak die ontwikkeling van 'n modelafieier uiters moeilik.
As gevolg word die twee tegnieke vergelyk teen 'n stel van programatuurontwikkelingsoorwegings.
Omdat 'n spesifieke tegniek nie altyd voorkeur kan geniet nie, word riglyne voorgestel
om te help met die keuse om die beste tegniek te kies in verskillende omstandighede
A Smirnov-Bickel-Rosenblatt theorem for compactly-supported wavelets
In nonparametric statistical problems, we wish to find an estimator of an
unknown function f. We can split its error into bias and variance terms;
Smirnov, Bickel and Rosenblatt have shown that, for a histogram or kernel
estimate, the supremum norm of the variance term is asymptotically distributed
as a Gumbel random variable. In the following, we prove a version of this
result for estimators using compactly-supported wavelets, a popular tool in
nonparametric statistics. Our result relies on an assumption on the nature of
the wavelet, which must be verified by provably-good numerical approximations.
We verify our assumption for Daubechies wavelets and symlets, with N = 6, ...,
20 vanishing moments; larger values of N, and other wavelet bases, are easily
checked, and we conjecture that our assumption holds also in those cases
The Voluntary Adjustment of Railroad Obligations
Automatic memory management techniques eliminate many programming errors that are both hard to find and to correct. However, these techniques are not yet used in embedded systems with hard realtime applications. The reason is that current methods for automatic memory management have a number of drawbacks. The two major ones are: (1) not being able to always guarantee short real-time deadlines and (2) using large amounts of extra memory. Memory is usually a scarce resource in embedded applications. In this paper we present a new technique, Real-Time Reference Counting (RTRC) that overcomes the current problems and makes automatic memory management attractive also for hard real-time applications. The main contribution of RTRC is that often all memory can be used to store live objects. This should be compared to a memory overhead of about 500% for garbage collectors based on copying techniques and about 50% for garbage collectors based on mark-and-sweep techniques
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