Paper

We are dealing with friction from the viewpoint of granular material research, where heaps can maintain their shape only in the presence of Coulomb friction.

The libpcap is the foundation of many different tools for monitoring, diagnosing and protecting networks. A bug in the implementation of the analysis of VLANs (802.1q) leads to these programs not receiving important network traffic. This is the written summary of this lecture.

There is a variety of tools to filter packets from a network. One of the most popular ones is the Berkeley Packet Filter (BPF). All such filters are based on static descriptions, e.g., fixed source ports or fixed subnets of IP addresses. These methods work well for most types of network traffic, but there are cases in which a wider variety of applications may be appropriate. In this paper we will introduce a new analysis tool which will allow us to do a time-dependent analysis.

Buffer overflows are among the most common security vulnerabilities in current IT systems. An attempt is made to describe how they occur, how to suppress the direct consequences and what measures can be taken to protect the overall system. This is the written summary of this lecture.

We study the averaged macroscopic strain tensor for a sand pile consisting of soft convex polygonal particles numerically, using the discrete-element method (DEM). First, we construct two types of “sand piles” by two different pouring protocols. Afterwards, we deform the sand piles, relaxing them under a 10% reduction of gravity. Four different types of methods, three best-fit strains and a derivative strain, are adopted for determining the strain distribution under a sand pile. The results of four different versions of strains obtained from DEM simulation are compared with each other.

We numerically investigate the effective material properties of aggregates consisting of soft convex polygonal particles, using the discrete element method. First, we construct two types of “sand piles” by two different procedures. Then we measure the averaged stress and strain, the latter via imposing a 10% reduction of gravity, as well as the fabric tensor. Furthermore, we compare the vertical normal strain tensor between sand piles qualitatively and show how the construction history of the piles affects their strain distribution as well as the stress distribution.

The averaged stress and strain response functions of granular aggregates are investigated numerically. We use the discrete-element method (DEM) to generate granular packings consisting of soft convex polygonal particles, i.e., the simulation geometry is two-dimensional. Packings are prepared in a rectangular container. To determine the stress response of a packing, we apply an external load to a single grain from the top layer of the assembly, with a force small enough not to cause structural rearrangements.

We investigate numerically the micro and macro mechanical behaviour of non-cohesive granular materials, especially in the static limit. To achieve this goal we performed numerical simulations generating twodimensional “sand piles” from several thousands of convex polygonal particles with varying shapes, sizes and corner numbers, using a discrete element approach based on soft particles. We emphasize that the displacement (strain) fields inside sand piles have not been measured in experiments on sand piles.

The discrete element method allows the simulation of complex behavior of granular materials without constitutive laws. While in two dimensions shape-effects are well established, in three dimensions there is no universally applicable simulation algorithm for non-spherical particles. We will first present a force model for convex polyhedral particles, using the “overlap” of non-deformed polyhedra as a “measure” of the elastic force and explain the overlap computation algorithm.

The pressure distribution under heaps has found to be dependent on the building history of the heap both in experiments and in simulations. Up to now, theoretical models and analysis assume that the packing of the heap is homogeneous. We show new experimental and simulational results which indicate that the packing is inhomogeneous and that this packing property is likely causing the pressure minimum under the heap.