Instruction Caches in Static WCET Analysis of Artificially Diversified Software

Artificial Software Diversity is a well-established method to increase security of computer systems by thwarting code-reuse attacks, which is particularly beneficial in safety-critical real-time systems. However, static worst-case execution time (WCET) analysis on complex hardware involving caches only delivers sound results for single versions of the program, as it relies on absolute addresses for all instructions. To overcome this problem, we present an abstract interpretation based instruction cache analysis that provides a safe yet precise upper bound for the execution of all variants of a program. We achieve this by integrating uncertainties in the absolute and relative positioning of code fragments when updating the abstract cache state during the analysis. We demonstrate the effectiveness of our approach in an in-depth evaluation and provide an overview of the impact of different diversity techniques on the WCET estimations

Model checking SystemC designs using timed automata

SystemC is widely used for modeling and simulation in hard-ware/software co-design. Due to the lack of a complete for-mal semantics, it is not possible to verify SystemC designs. In this paper, we present an approach to overcome this prob-lem by defining the semantics of SystemC by a mapping from SystemC designs into the well-defined semantics of Uppaal timed automata. The informally defined behavior and the structure of SystemC designs are completely preserved in the generated Uppaal models. The resulting Uppaal models allow us to use the Uppaal model checker and the Uppaal tool suite, including simulation and visualization tools. The model checker can be used to verify important properties such as liveness, deadlock freedom or compliance with tim-ing constraints. We have implemented the presented trans-formation, applied it to two examples and verified liveness, safety and timing properties by model checking, thus show-ing the applicability of our approach in practice

Primary thermometry in the intermediate Coulomb blockade regime

We investigate Coulomb blockade thermometers (CBT) in an intermediate temperature regime, where measurements with enhanced accuracy are possible due to the increased magnitude of the differential conductance dip. Previous theoretical results show that corrections to the half width and to the depth of the measured conductance dip of a sensor are needed, when leaving the regime of weak Coulomb blockade towards lower temperatures. In the present work, we demonstrate experimentally that the temperature range of a CBT sensor can be extended by employing these corrections without compromising the primary nature or the accuracy of the thermometer.Comment: 8 pages, 4 figure

Progress towards an accurate determination of the Boltzmann constant by Doppler spectroscopy

In this paper, we present significant progress performed on an experiment dedicated to the determination of the Boltzmann constant, k, by accurately measuring the Doppler absorption profile of a line in a gas of ammonia at thermal equilibrium. This optical method based on the first principles of statistical mechanics is an alternative to the acoustical method which has led to the unique determination of k published by the CODATA with a relative accuracy of 1.7 ppm. We report on the first measurement of the Boltzmann constant by laser spectroscopy with a statistical uncertainty below 10 ppm, more specifically 6.4 ppm. This progress results from improvements in the detection method and in the statistical treatment of the data. In addition, we have recorded the hyperfine structure of the probed saQ(6,3) rovibrational line of ammonia by saturation spectroscopy and thus determine very precisely the induced 4.36 (2) ppm broadening of the absorption linewidth. We also show that, in our well chosen experimental conditions, saturation effects have a negligible impact on the linewidth. Finally, we draw the route to future developments for an absolute determination of with an accuracy of a few ppm.Comment: 22 pages, 11 figure

Theory and applications of atomic and ionic polarizabilities

Atomic polarization phenomena impinge upon a number of areas and processes in physics. The dielectric constant and refractive index of any gas are examples of macroscopic properties that are largely determined by the dipole polarizability. When it comes to microscopic phenomena, the existence of alkaline-earth anions and the recently discovered ability of positrons to bind to many atoms are predominantly due to the polarization interaction. An imperfect knowledge of atomic polarizabilities is presently looming as the largest source of uncertainty in the new generation of optical frequency standards. Accurate polarizabilities for the group I and II atoms and ions of the periodic table have recently become available by a variety of techniques. These include refined many-body perturbation theory and coupled-cluster calculations sometimes combined with precise experimental data for selected transitions, microwave spectroscopy of Rydberg atoms and ions, refractive index measurements in microwave cavities, ab initio calculations of atomic structures using explicitly correlated wave functions, interferometry with atom beams, and velocity changes of laser cooled atoms induced by an electric field. This review examines existing theoretical methods of determining atomic and ionic polarizabilities, and discusses their relevance to various applications with particular emphasis on cold-atom physics and the metrology of atomic frequency standards.Comment: Review paper, 44 page