The flow of time can be conceptualized either as a cycle or an arrow. We offer a combined view: a helix. Chronological age (geophysical time reference) is not necessarily identical to biological age (internal time reference), and aging does not necessarily imply senescence. A new scheme of senescence, based on homeodynamics (nonlinear mechanics and nonequilibrium thermodynamics), is introduced as a plausible physical basis for understanding senescence. We propose that energy throughput, initially constructive of forms and functions, becomes destructive once most of the available degrees of freedom have been “frozen out” by the construction. Senescence becomes manifested at that point.

Recently, Y.Q. Bai, M. El Ghami and C. Roos [3] introduced a new class ofso-called eligible kernel functions which are defined by somesimple conditions.The authors designed primal-dual interior-point methods for linear optimization (LO)based on eligible kernel functionsand simplified the analysis of these methods considerably.In this paper we consider the semidefinite optimization (SDO) problemand we generalize the aforementioned results for LO to SDO.The iteration bounds obtained are analogous to the results in [3] for LO.

In formal language theory, many families of languages are defined using either grammars or finite acceptors. For instance, context-sensitive languages are the languages generated by growing grammars, or equivalently those accepted by Turing machines whose work tape's size is proportional to that of their input. A few years ago, a new characterisation of context-sensitive languages as the sets of traces, or path labels, of rational graphs (infinite graphs defined by sets of finite-state transducers) was established. We investigate a similar characterisation in the more general framework of graphs defined by term transducers. In particular, we show that the languages of term-automatic graphs between regular sets of vertices coincide with the languages accepted by alternating linearly bounded Turing machines.
As a technical tool, we also introduce an arborescent variant of tiling systems, which provides yet another characterisation of these languages.

Assume that n tasks must be processed by one machine in a fixed sequence. The processing time, the preferred starting time and the earliness and tardiness costs per time unit are known for each task. The problem is to allocate each task a starting time such that the total cost incurred by the early and tardy tasks is minimum. Garey et al. have proposed a nice O(nlogn) algorithm for the special case of symmetric and task-independent costs. In this paper we first extend that algorithm to the case of asymmetric and task-independent cost without increasing its worst-case complexity. For the general case of asymmetric and task-dependent costs, we propose an O(n3 logn) algorithm based on a strong dominance property that yields to model the scheduling problem as a minimum cost path in a valued directed acyclic graph.

A cooperative game is defined as a set of players and a cost function. The distribution of the whole cost between theplayers can be done using the core concept, that is the set of all undominated cost allocations which prevent playersfrom grouping. In this paper we study a game whose cost function comes from the optimal solution of a linear integercovering problem. We give necessary and sufficient conditions for the core to be nonempty and characterize itsallocations using linear programming duality. We also discuss a special allocation, called the nucleolus. Wecharacterize that allocation and show that it can be computed in polynomial time using a column generation method.

We show that the problem of deciding if there is a scheduleof length three for the multiprocessor scheduling problem on identicalmachines and unit execution time tasks in -complete even for bipartitegraphs, i.e. for precedence graphs of depth one. This complexity resultextends a classical result of Lenstra and Rinnoy Kan [5].