167 research outputs found
Formal Verification of Industrial Software and Neural Networks
Software ist ein wichtiger Bestandteil unsere heutige Gesellschaft. Da Software vermehrt
in sicherheitskritischen Bereichen angewandt wird, müssen wir uns auf eine korrekte und
sichere Ausführung verlassen können. Besonders eingebettete Software, zum Beispiel in
medizinischen Geräten, Autos oder Flugzeugen, muss gründlich und formal geprüft werden.
Die Software solcher eingebetteten Systeme kann man in zwei Komponenten aufgeteilt.
In klassische (deterministische) Steuerungssoftware und maschinelle Lernverfahren
zum Beispiel für die Bilderkennung oder Kollisionsvermeidung angewandt werden.
Das Ziel dieser Dissertation ist es den Stand der Technik bei der Verifikation von
zwei Hauptkomponenten moderner eingebetteter Systeme zu verbessern: in C/C++
geschriebene Software und neuronalen Netze. Für beide Komponenten wird das Verifikationsproblem
formal definiert und neue Verifikationsansätze werden vorgestellt
Lange Kohärenzzeit optisch gefangener Ensembles
[no abstract
Combining Graph-Based and Deduction-Based Information-Flow Analysis
Information flow control (IFC) is a category of techniques for
ensuring system security by enforcing information flow properties such as
non-interference. Established IFC techniques range from fully automatic
approaches with much over-approximation to approaches with high pre-
cision but potentially laborious user interaction. A noteworthy approach
mitigating the weaknesses of both automatic and interactive IFC tech-
niques is the hybrid approach, developed by Küsters et al., which – how-
ever – is based on program modifications and still requires a significant
amount of user interaction.
In this paper, we present a combined approach that works without any
program modifications. It minimizes potential user interactions by apply-
ing a dependency-graph-based information-flow analysis first. Based on
over-approximations, this step potentially generates false positives. Pre-
cise non-interference proofs are achieved by applying a deductive theorem
prover with a specialized information-flow calculus for checking that no
path from a secret input to a public output exists. Both tools are fully
integrated into a combined approach, which is evaluated on a case study,
demonstrating the feasibility of automatic and precise non-interference
proofs for complex programs
Extended coherence time on the clock transition of optically trapped Rubidium
Optically trapped ensembles are of crucial importance for frequency
measurements and quantum memories, but generally suffer from strong dephasing
due to inhomogeneous density and light shifts. We demonstrate a drastic
increase of the coherence time to 21 s on the magnetic field insensitive clock
transition of Rb-87 by applying the recently discovered spin self-rephasing.
This result confirms the general nature of this new mechanism and thus shows
its applicability in atom clocks and quantum memories. A systematic
investigation of all relevant frequency shifts and noise contributions yields a
stability of 2.4E-11 x tau^(-1/2), where tau is the integration time in
seconds. Based on a set of technical improvements, the presented frequency
standard is predicted to rival the stability of microwave fountain clocks in a
potentially much more compact setup.Comment: 5 pages, 4 figure
Dynamics of Bloch Oscillations in Disordered Lattice Potentials
We present a detailed analysis of the dynamics of Bloch oscillations of
Bose-Einstein condensates in disordered lattice potentials. Due to the disorder
and the interparticle interactions these oscillations undergo a dephasing,
reflected in a damping of the center of mass oscillations, which should be
observable under realistic experimental conditions. The interplay between
interactions and disorder is far from trivial, ranging from an
interaction-enhanced damping due to modulational instability for strong
interactions, to an interaction-reduced damping due to a dynamical screening of
the disorder potential
Anti-alignments in conformance checking: the dark side of process models
Conformance checking techniques asses the suitability of a process model in representing an underlying process, observed through a collection of real executions. These techniques suffer from the wellknown state space explosion problem, hence handling process models exhibiting large or even infinite state spaces remains a challenge. One important metric in conformance checking is to asses the precision of the model with respect to the observed executions, i.e., characterize the ability of the model to produce behavior unrelated to the one observed. By avoiding the computation of the full state space of a model, current techniques only provide estimations of the precision metric, which in some situations tend to be very optimistic, thus hiding real problems a process model may have. In this paper we present the notion of antialignment as a concept to help unveiling traces in the model that may deviate significantly from the observed behavior. Using anti-alignments, current estimations can be improved, e.g., in precision checking. We show how to express the problem of finding anti-alignments as the satisfiability of a Boolean formula, and provide a tool which can deal with large models efficiently.Peer ReviewedPostprint (author's final draft
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