Fast integer merging on the EREW PRAM

We investigate the complexity of merging sequences of small integers on the EREW PRAM. Our most surprising result is that two sorted sequences of $n$ bits each can be merged in $O(\log\log n)$ time. More generally, we describe an algorithm to merge two sorted sequences of $n$ integers drawn from the set $\{0,\ldots,m-1\}$ in $O(\log\log n+\log m)$ time using an optimal number of processors. No sublogarithmic merging algorithm for this model of computation was previously known. The algorithm not only produces the merged sequence, but also computes the rank of each input element in the merged sequence. On the other hand, we show a lower bound of $\Omega(\log\min\{n,m\})$ on the time needed to merge two sorted sequences of length $n$ each with elements in the set $\{0,\ldots,m-1\}$, implying that our merging algorithm is as fast as possible for $m=(\log n)^{\Omega(1)}$. If we impose an additional stability condition requiring the ranks of each input sequence to form an increasing sequence, then the time complexity of the problem becomes $\Theta(\log n)$, even for $m=2$. Stable merging is thus harder than nonstable merging

Using mobile relays for ensuring connectivity in sparse networks

Jarosław KutyłowskiPaderborn, Univ., Diss., 200

Application of Topology Optimization to Thighbone/Implant Interaction Modelling

This paper presents an application of topology optimization in the analysis of the thighbone with an inserted endoprosthesis. A variational minimum compliance approach with mass constraints is employed to solve the problem. Changes in the bone structure depending on the implant’s mechanical parameters are studied. Numerical results for mass distribution in the modelled thighbone with an inserted endoprosthesis are analyzed using an original numerical algorithm and a program developed in Matlab. It is numerically proven that owing to the use of an implant with material properties similar to those of the bone no degradation of the latter in the vicinity of the implant occurs. The endoprosthesis will serve longer and the postoperative complications connected with the accelerated degradation of the bone in the neighborhood of the implant will be avoided if the implant has similar material properties as the bone

Fault Jumping Attacks against Shrinking Generator

In this paper we outline two new cryptoanalytic attacks against hardware implementation of the shrinking generator by Coppersmith et al., a classic design in low-cost, simple-design pseudorandom bitstream generator. This is a report on work on progress, since implementation and careful adjusting the attack strategy in order to optimize the atatck is still not completed

07311 Abstracts Collection -- Frontiers of Electronic Voting

From July the 29th to August the 3th, 2007, the Dagstuhl Seminar 07311 ``Frontiers of Electronic Voting\u27\u27 was held in the International Conference and Research Center (IBFI), Schloss Dagstuhl. During the seminar, several participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this paper. The first section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available

Scratch, Click & Vote: E2E voting over the Internet

We present Scratch, Click & Vote voting scheme, which is a modification of the Punchscan and ThreeBallot systems. The scheme is end-to-end veryfiable and allows for voting over the Internet. Security against malicious hardware and software used by a voter %TT is due to the fact that a voter\u27s computer does not get any knowledge about the voter\u27s choice. Moreover, it can change successfully a voter\u27s ballot only with a small probability. As a side result, we present a modification of the ThreeBallot that eliminates Strauss\u27-like attacks on this scheme

Optimizing Segment Based Document Protection (Corrected Version)

In this paper we provide a corrected and generalized version of the scheme presented at SOFSEM\u272012 in our paper ``Optimizing Segment Based Document Protection\u27\u27 (SOFSEM 2012: Theory and Practice of Computer Science, LNCS 7147, pp. 566-575). We develop techniques for protecting documents with restricted access rights. In these documents so called \emph{segments} are encrypted. Different segments may be encrypted with different keys so that different user may be given different \emph{access rights}. Hierarchy of access rights is represented by means of a directed acyclic \emph{access graph}. The segments are encrypted with keys - where each key corresponds to one node in the access graph. The main feature of the access graph is that if there is an arch $\overrightarrow{AB}$ in the graph, then all segments labelled with $B$ can be decrypted with the key corresponding to node $A$. We show how to minimize the space overhead necessary for auxiliary keying information stored in the document. We provide an algorithm based on node disjoint paths in the access graph and key derivation based on one-way functions. Our current solution, based on maximal weighted matchings, provides an optimal solution for creating subdocuments, in case when frequency of creating each subdocument is known

Maintaining communication between an explorer and a base station

Consider a (robotic) explorer starting an exploration of an unknown terrain from its base station. As the explorer has only limited communication radius, it is necessary to maintain a line of robotic relay stations following the explorer, so that consecutive stations are within the communication radius of each other. This line has to start in the base station and to end at the explorer. In the simple scenario considered here we assume an obstacle-free terrain, so that the shortest connection (the one which needs the smallest number of relay stations) is a straight line. We consider an explorer who goes an arbitrary, typically winding way, and define a very simple, intuitive, fully local, distributed strategy for the relay stations – our Go-To-The-Middle strategy – to maintain a line from the base station to the robot as short as possible. Besides the definition of this strategy, we present an analysis of its performance under different assumptions. For the static case we prove a bound on the convergence speed, for the dynamic case we present experimental evaluations that show the quality of our strategy under different types of routes the explorer could use.1st IFIP International Conference on Biologically Inspired Cooperative Computing - CommunicationRed de Universidades con Carreras en Informática (RedUNCI

Gathering Anonymous, Oblivious Robots on a Grid

We consider a swarm of $n$ autonomous mobile robots, distributed on a 2-dimensional grid. A basic task for such a swarm is the gathering process: All robots have to gather at one (not predefined) place. A common local model for extremely simple robots is the following: The robots do not have a common compass, only have a constant viewing radius, are autonomous and indistinguishable, can move at most a constant distance in each step, cannot communicate, are oblivious and do not have flags or states. The only gathering algorithm under this robot model, with known runtime bounds, needs $\mathcal{O}(n^2)$ rounds and works in the Euclidean plane. The underlying time model for the algorithm is the fully synchronous $\mathcal{FSYNC}$ model. On the other side, in the case of the 2-dimensional grid, the only known gathering algorithms for the same time and a similar local model additionally require a constant memory, states and "flags" to communicate these states to neighbors in viewing range. They gather in time $\mathcal{O}(n)$. In this paper we contribute the (to the best of our knowledge) first gathering algorithm on the grid that works under the same simple local model as the above mentioned Euclidean plane strategy, i.e., without memory (oblivious), "flags" and states. We prove its correctness and an $\mathcal{O}(n^2)$ time bound in the fully synchronous $\mathcal{FSYNC}$ time model. This time bound matches the time bound of the best known algorithm for the Euclidean plane mentioned above. We say gathering is done if all robots are located within a $2\times 2$ square, because in $\mathcal{FSYNC}$ such configurations cannot be solved