2458859
Impossibility of distributed consensus with one faulty process
The consensus problem involves an asynchronous system of processes, some of which may be unreliable. The problem is for the reliable processes to agree on a binary value. We show that every protocol for this problem has the possibility of nontermination, even with only one faulty process. By way of contrast, solutions are known for the synchronous case, the "Byzantine Generals" problem.
207660233
Impossibility of distributed consensus with one faulty process
The consensus problem involves an asynchronous system of processes, some of which may be unreliable. The problem is for the reliable processes to agree on a binary value. In this paper, it is shown that every protocol for this problem has the possibility of nontermination, even with only one faulty process. By way of contrast, solutions are known for the synchronous case, the “Byzantine Generals” problem.
15236721
Bounds on secret key exchange using a random deal of cards
We present a general model for communication among a “team” of players overheard by a passive eavesdropper, Eve, in which all players including Eve are given private inputs that may be correlated. We define and explore secret key exchange in this model. Our secrecy requirements are information-theoretic and hold even if Eve is computationally unlimited. In particular, we consider the situation in which the team players are dealt hands of cards of prespecified sizes from a known deck of distinct cards. We explore when the team players can use the information contained in their hands to determine a value that each team player knows exactly but Eve cannot guess.
201632
CULTURE AND INDIGENOUS KNOWLEDGE SYSTEMS: EMERGENT ORDER AND THE INTERNAL REGULATION OF SHARED SYMBOLIC SYSTEMS
ABSTRACT I explore the relationship between culture, knowledge and behaviour in a context of change, comparing scientific with cultural knowledge. I argue that applications (or instantiations) of scientific knowledge are not the same as science, and undergo a process that has properties not unlike those described by Ellen and Harris for ‘Indigenous Knowledge’ (IK). This process uses knowledge that is not derived from the system represented, but nevertheless is necessary for the system to operate in a contingent world even though this knowledge was not in the original subset of knowledge being applied. This consideration of knowledge about what contexts must be instantiated to enable domain knowledge to be instantiated builds on Ellen's concept of prehension, which in part includes the anticipatory knowledge a subject brings to a situation. I suggest the operative principles in IK have similar properties.
9204420
Partitioned neighborhood spanners of minimal outdegree
A geometric spanner with vertex set P IRD is a sparse approximation of the complete Euclidean graph determined by P. We introduce the notion of partitioned neighborhood graphs (PNGs), unifying and generalizing most constructions of spanners treated in literature. Two important parameters characterizing their properties are the outdegree k IN and the stretch factor f 1 describing the ‘quality’ of approximation. PNGs have been thuroughly investigated with respect to small values of f . We, on the other hand, present in this work results about feasable values of k — so to say the other extreme. The aim of minimizing this parameter rather than the first one arises from two observations: a) It determines the amount of space required for storing PNGs. b) Many algorithms employing a (previously constructed) spanner have running times depending on its outdegree. Our results include, for fixed dimensions D as well as asymptotically, upper and lower bounds on this optimal value of k. The upper bounds are constructive and yield efficient algorithms for actually computing the corresponding graphs. 1Partially supported by EU ESPRIT Long Term Research Project 20244 (ALCOM-IT) and DFG Grants Me872/7-1 and Me872/4-1
7656106
Geometric Searching in Walkthrough Animations with Weak Spanners in Real Time
We study algorithmic aspects in the management of geometric scenes in interactive walkthrough animations. We consider arbitrarily large scenes consisting of unit size balls. For a smooth navigation in the scene we have to fulfill hard real time requirements. Therefore, we need algorithms whose running time is independent of the total number of objects in the scene and that use as small space as possible. In this work we focus on one of the basic operations in our walkthrough system: reporting the objects around the visitor within a certain distance. 
 
Previously a randomized data structure was presented that supports reporting the balls around the visitor in an output sensitive time and allows insertion and deletion of objects nearly as fast as searching. These results were achieved by exploiting the fact that the visitor moves "slowly" through the scene. A serious disadvantage of the aforementioned data structure is a big space overhead and the use of randomization. 
 
Our first result is a construction of weak spanners that leads to an improvement of the space requirement of the previously known data structures. Then we develop a deterministic data structure for the searching problem in which insertion of objects are allowed. Our incremental data structure supports O(1+k) reporting time, where k is a certain quantity close to the number of reported objects. The insertion time is similar to the reporting time and the space is linear to the total number of objects.
14681345
The randomized sample tree: a data structure for interactive walkthroughs in externally stored virtual environments
We present a new data structure for rendering highly complex virtual environments of arbitrary topology. The special feature of our approach is that it allows an interactive navigation in very large scenes (30 GB/400 million polygons in our benchmark scenes) that cannot be stored in main memory, but only on a local or remote hard disk. Furthermore, it allows interactive rendering of substantially more complex scenes by instantiating objects.For the computation of an approximate image of the scene, a sampling technique is used. In the preprocessing, a so-called sample tree is built whose nodes contain randomly selected polygons from the scene. This tree only uses space that is linear in the number of polygons. In order to produce an image of the scene, the tree is traversed and polygons stored in the visited nodes are rendered. During the interactive walkthrough, parts of the sample tree are loaded from local or remote hard disk.We implemented our algorithm in a prototypical walkthrough system. Analysis and experiments show that the quality of our images is comparable to images computed by the conventional z-buffer algorithm regardless of the scene topology.
16340460
Bi-directional Coupling of Simulation Tools with a Walkthrough-System
Visualising is amethod used to help experiencing a nd understanding causal cohesions in simulation processes. For this purpose, tools for visualising are already implemented in prevalent simulation systems. The user creates his imulation model and generates a 3-dimensional (2,5-dimensional) visualising by means of the simulation system. This helps examining the process which makes it easier for the viewer to “understand” it. Simulatio n tools usually only provide the opportunity for a unidirectional visualising. In a 3-dimensional surr ounding the viewer can not implement an interaction with the simulation while the system is running. Though an interaction during the simulation run enables the user to gain a better un derstanding of causal cohesions. Solutions via HLA are sophisticated and therefore rather suited f or extensive projects. We present a distributed system consisting of a com mercial manufacturing simulation tool, a coupling module and a walkthrough system. The distr ibuted system in conjunctions with the coupling module guarantees generality and a wide field of applications of the walkthrough system. Further it guarantees flexibility and selection of the specialized graphics hardware for the walkthrough system. A further contribution of this paper is the solution of the time synchronisation problem caused by simulation tool and walkthrough s ystem.