Bonsai Trees, or How to Delegate a Lattice Basis

We introduce a new lattice-based cryptographic structure called a bonsai tree, and use it to resolve some important open problems in the area. Applications of bonsai trees include an efficient, stateless ‘hash-and-sign’ signature scheme in the standard model (i.e., no random oracles), and the first hierarchical identity-based encryption (HIBE) scheme (also in the standard model) that does not rely on bilinear pairings. Interestingly, the abstract properties of bonsai trees seem to have no known realization in conventional number-theoretic cryptography.     

Biomineralization in diatoms: the role of silacidins

Diatoms are eukaryotic, unicellular algae encased within siliceous cell walls (frustules), which are precisely reproduced generation by generation. The production of this nanostructured silica is under genetic control and the isolation of specific gene products (the proteins silaffins, silacidins) guiding the biomineralization processes, and which are necessary to produce the frustules, has already been described. Under silicon starvation, the amount of silacidins present in the cell walls of Thalassiosira pseudonana increases relative to other proteins. Natsilacidins, the native and highly phosphorylated silacidins are enormously effective in silica precipitation whereas silacidin A', the nonphosphorylated form, is not. This indicates an important role for natsilacidins in the survival of diatoms under silicic acid depleted conditions.     

Concurrent bisimulations in Petri nets

Summary After various attempts, an equivalence relation is defined for labelled Petri nets, on the base of the concurrency semantics of net theory. This relation, called Fully Concurrent bisimulation and abbreviated FC-bisimulation, preserves the level of concurrency of visible operations and, under some conditions, allows to enforce injective labelling on them. Refinements of a visible operation are also defined and we show that, under some conditions, they preserve FC-bisimulation.Research partly supported by ESPRIT Basic Research Action, project 3148: DEMON     

Hypertrophic tonsils as a cause of hypoxia and growth stagnation

A case is reported describing severe hypoxaemia and growth retardation in a child suffering from hypertrophic tonsils. A rapid increase in weight and length was demonstrated postoperatively and on clinical examination one year after tonsillectomy the child shows no signs of obstruction of the airways.     

Some (in)sufficient conditions for secure hybrid encryption

In hybrid public key encryption (PKE), first a key encapsulation mechanism (KEM) is used to fix a random session key that is then fed into a highly efficient data encapsulation mechanism (DEM) to encrypt the actual message. A well-known composition theorem states that if both the KEM and the DEM have a high enough level of security (i.e., security against chosen-ciphertext attacks), then so does the hybrid PKE scheme. It is not known if these strong security requirements on the KEM and DEM are also necessary, nor if such general composition theorems exist for weaker levels of security.Using six different security notions for KEMs, 10 for DEMs, and six for PKE schemes, we completely characterize in this work which combinations lead to a secure hybrid PKE scheme (by proving a composition theorem) and which do not (by providing counterexamples). Furthermore, as an independent result, we revisit and extend prior work on the relations among security notions for KEMs and DEMs.     

Concept-based querying in mediator systems

One approach to overcoming heterogeneity as a part of data integration in mediator systems is the use of metadata in the form of a vocabulary or ontology to represent domain knowledge explicitly. This requires including this meta level during query formulation and processing. In this paper, we address this problem in the context of a mediator that uses a concept-based integration model and an extension of the XQuery language called CQuery. This mediator has been developed as part of a project for integrating data about cultural assets. We describe the language extensions and their semantics as well as the rewriting and evaluation steps. Furthermore, we discuss aspects of caching and keyword-based search in support of an efficient query formulation and processing.Received: 23 December 2002, Accepted: 15 September 2003, Published online: 6 February 2004Edited by: V. Atluri.     

Precracked pipe under waterhammer action

We numerically simulate a full scale test in several computational steps with the finite element method and compare all calculated data with the experimental findings. First, we compute the deflection under static loading and the spectrum of eigenfrequencies of an integer piping, attached to a nuclear reactor pressure vessel (RPV). Then we consider a sudden pipe break at some distance from the vessel, immediately followed by an undamped closure of a check valve close to the break on the RPV side, and calculate the elastic and plastic transient dynamic response of the integer piping part between the RPV and the break. Finally, we consider a circumferential internal surface crack, fairly close to the vessel; after extensive testing of our fracture mechanics calculation procedure we investigate the stress in the crack region under the waterhammer action.