Threshold nets and cell-assemblies

Motivated by the cell-assemblies theory of the brain, we propose a new formal model of threshold nets (TN). TN are patterned after Petri nets, with a very different firing rule, which removes all tokens upon firing of a transition. The generative power of threshold nets, with and without inhibition, is compared with traditional families of languages. Excitatory TN languages are included by the noncounting regular languages and form an infinite hierarchy for increasing values of threshold. Inhibitory nets are included by the context-sensitive languages. Two new net operators, motivated by the phenomena of growth, learning and brain damage are introduced and compared with Boolean operators

JIST: just-in-time scheduling translation for parallel processors

The application fields of bytecode virtual machines and VLIW processors overlap in the area of embedded and mobile systems, where the two technologies offer different benefits, namely high code portability, low power consumption and reduced hardware cost. Dynamic compilation makes it possible to bridge the gap between the two technologies, but special attention must be paid to software instruction scheduling, a must for the VLIW architectures. We have implemented JIST, a Virtual Machine and JIT compiler for Java Bytecode targeted to a VLIW processor. We show the impact of various optimizations on the performance of code compiled with JIST through the experimental study on a set of benchmark programs. We report significant speedups, and increments in the number of instructions issued per cycle up to 50% with respect to the non-scheduling version of the JITcompiler. Further optimizations are discussed

The PAPAGENO Parallel-Parser Generator

The increasing use of multicore processors has deeply transformed computing paradigms and applications. The wide availability of multicore systems had an impact also in the field of compiler technology, although the research on deterministic parsing did not prove to be effective in exploiting the architectural advantages, the main impediment being the inherent sequential nature of traditional LL and LR algorithms. We present PAPAGENO, an automated parser generator relying on operator precedence grammars. We complemented the PAPAGENO-generated parallel parsers with parallel lexing techniques, obtaining near-linear speedups on multicore machines, and the same speed as Bison parsers on sequential execution

Применение метода контрольных возмущений для определения характерных узлов присоединения комплексной нагрузки при расчетах динамической устойчивости

Рассматривается влияние способа замещения комплексной нагрузки на характер электромеханических переходных процессов в электрических системах (ЭС) от действия больших возмущений. Показано, что установить общие рекомендации относительно способа замещения нагрузки в сложных ЭС затруднительно. Предлагается для опреде­ления характерных узлов нагрузки, оказывающих существенное влияние на характер динамического перехода, применять известный метод контрольных возмущений. Приводятся результаты сравнительных расчетов с использованием предлагаемой методики

Deterministic dequeue automata abd LL(1) parsing of breadth-depth grammars

Breadth-depth grammars [3] extend the context-free ones by allowing breadth-first derivations. Breadth-depth languages include the context-free ones and are recognized by monostatic (one-state) automata having a double-ended queue (dequeue) as their memory. Examples of breadth-depth grammars for compilation and scheduling problems are included to argue for their applicability. We define deterministic monostatic dequeue automata and investigate their languages. Main results are their incomparability with context-free deterministic languages and linear-time recognizability. We introduce the LL(1) grammars, as an extension of the classical top-down deterministically parsable context-free grammars, and we present a recursive descent parsing algorithm using a FIFO queue. Work supported by ESPRIT Basic Research Actions ASMICS and by Ministero dell'Università e della Ricerca Scientifica e Tecnologica MURST 60%

Multi-push-down languages and grammars

A new class of languages, called multi-push-down (mpd), that generalize the classical context-free (cf, or Chomsky type 2) ones is introduced. These languages preserve some important properties of cf languages: a generalization of the Chomsky-Schützenberger homomorphic characterization theorem, the Parikh theorem and a “pumping lemma” are proved. Multi-push-down languages are an AFL. Their recognizers are automata equipped with a multi-push-down tape. Multi-push-down languages form a hierarchy based on the number of push-down tapes

Le pietre naturali rinvenute nello scavo del Parco Novi Sad

Analisi dei materiali lapidei archeologici rinvenuti nello scavo del Parco Novi Sad a Modena