Molecular dynamics calculation of mean square displacement in alkali metals and rare gas solids and comparison with lattice dynamics

Molec ul ar dynamics calculations of the mean sq ua re displacement have been carried out for the alkali metals Na, K and Cs and for an fcc nearest neighbour Lennard-Jones model applicable to rare gas solids. The computations for the alkalis were done for several temperatures for temperature vol ume a swell as for the the ze r 0 pressure ze ro zero pressure volume corresponding to each temperature. In the fcc case, results were obtained for a wide range of both the temperature and density. Lattice dynamics calculations of the harmonic and the lowe s t order anharmonic (cubic and quartic) contributions to the mean square displacement were performed for the same potential models as in the molecular dynamics calculations. The Brillouin zone sums arising in the harmonic and the quartic terms were computed for very large numbers of points in q-space, and were extrapolated to obtain results ful converged with respect to the number of points in the Brillouin zone.An excellent agreement between the lattice dynamics results was observed molecular dynamics and in the case of all the alkali metals, e~ept for the zero pressure case of CSt where the difference is about 15 % near the melting temperature. It was concluded that for the alkalis, the lowest order perturbation theory works well even at temperat ures close to the melting temperat ure. For the fcc nearest neighbour model it was found that the number of particles (256) used for the molecular dynamics calculations, produces a result which is somewhere between 10 and 20 % smaller than the value converged with respect to the number of particles. However, the general temperature dependence of the mean square displacement is the same in molecular dynamics and lattice dynamics for all temperatures at the highest densities examined, while at higher volumes and high temperatures the results diverge. This indicates the importance of the higher order (eg. ~* ) perturbation theory contributions in these cases

Measurements or Static Analysis or Both?

To date, measurement-based WCET analysis and static analysis have largely been seen as being at odds with each other. We argue that instead they should be considered complementary, and that the combination of both represents a promising approach that provides benefits over either individual approach. In this paper we discuss in some detail how we aim to improve on our probabilistic measurement-based technique by adding static cache analysis. Specifically we are planning to make use of recent advances within the functional languages research community. The objective of this paper is not to present finished or almost finished work. Instead we hope to trigger discussion and solicit feedback from the community in order to avoid pitfalls experienced by others and to help focus our research

Components + Security = OS Extensibility

Component-based programming systems have shown themselves to be a natural way of constructing extensible software. Well-defined interfaces, encapsulation, late binding and polymorphism promote extensibility, yet despite this synergy, components have not been widely employed at the systems level. This is primarily due to the failure of existing component technologies to provide the protection and performance required of systems software. In this paper we identify the requirements for a component system to support secure extensions, and describe the design of such a system on the Mungi OS

Measurements or static analysis or both?

To date, measurement-based WCET analysis and static analysis have largely been seen as being at odds with each other. We argue that instead they should be considered complementary, and that the combination of both represents a promising approach that provides benefits over either individual approach. In this paper we discuss in some detail how we aim to improve on our probabilistic measurement-based technique by adding static cache analysis. Specifically we are planning to make use of recent advances within the functional languages research community. The objective of this paper is not to present finished or almost finished work. Instead we hope to trigger discussion and solicit feedback from the community in order to avoid pitfalls experienced by others and to help focus our research

A Survey of Microarchitectural Timing Attacks and Countermeasures on Contemporary Hardware

Microarchitectural timing channels expose hidden hardware states though timing. We survey recent attacks that exploit microarchitectural features in shared hardware, especially as they are relevant for cloud computing. We classify types of attacks according to a taxonomy of the shared resources leveraged for such attacks. Moreover, we take a detailed look at attacks used against shared caches. We survey existing countermeasures. We finally discuss trends in attacks, challenges to combating them, and future directions, especially with respect to hardware support

Proving the Absence of Microarchitectural Timing Channels

Microarchitectural timing channels are a major threat to computer security. A set of OS mechanisms called time protection was recently proposed as a principled way of preventing information leakage through such channels and prototyped in the seL4 microkernel. We formalise time protection and the underlying hardware mechanisms in a way that allows linking them to the information-flow proofs that showed the absence of storage channels in seL4.Comment: Scott Buckley and Robert Sison were joint lead author