STURGEONS (Acipenseridae) - RELICTS OF THE PREHISTORIC ICHTIOFAUNA

U radu se prikazuju sistematika, biologija, areal rasprostranjenosti i mjere zaštita vrste riba iz porodice Acipenseridae. Posebno se iznose problemi i mogućnosti uzgoja pojedinih vrsta jesetri u akvakulturi. Dosadašnjim rezultatima uzgoja jesetri u češkoj akvakulturi utvrđeno je da najveći problemi nastaju u početnoj fazi uzgoja mlađa, nakon prelaska ličinki na egzogenu prehranu, te, poslije, kad jednogodišnji mlađ prelazi s prirodne na industrijsku hranu. Na početku uzgoja gubitci su veći od 50%. Gubitci se smanjuju kad mlađ postigne individualnu masu od 1 g, a minimalni su kad se mlađ adaptira na granuliranu, industrijsku hranu. Vrijeme ovisnosti mlađa o prirodnoj hrani različito je kod različitih vrsta jesetri i kreće se od velićine 2-3 cm (sibirska jesetra) do 10-12 cm (moruna). U akvakulturi se u jesen postže masa riba 250-450 g (veslonos), 450-500 g (moruna), 550-650 g (sibirska jesetra). Dosadašnjim je rezultatima istraživanja utvrđeno da dobra prilagodljivost i zahtjevnost okolišnih uvjeta, kao i brzi rast uz uporabu industrijske hrane, daje velike mogućnosti za uzgoj jesetri u različitim akvakulturnim sustavima.The work presents systematic, biology, areal diffusion and measures for prevention of the fish species from the family of sturgeons (Acipenseridae). Problems and possibilities of cultivating some sturgeon species in aquaculture are stressed. Based on the past results of sturgeon cultivation in the aquaculture of the Check Republik one has come to the conclusion that the major problems occur in the initial phase of fry cultivation, after the larvae turn to exogene feeding and later when one-year fry turn form natural to industrial food. At the beginning of the cultivation the losses are higher than 50 per cent. The reduction of losses occurs when the fry acquires an individual mass of 1 g, and when the fry adapts to granulated industrial food the losses are minimal. The duration of fry addiction to natural food depends on the respective sturgeon species and varies from the size of 2 to 3 cm (Siberian sturgeon) to 10 to 12 cm (beluga). In autumn in aquaculture the fish-mass of 250 to 450 g (američki veslonos), 450 to 500 g (beluga) and 530 to 650 g (Siberian sturgeon) can acquired. Up to now the research results have shown that a good adaptability and demanding surroundings conditions as well as a quick growth and application of industrial food provide great possibilities for sturgeon cultivation in different aquaculture structures

LOCALIZATION ANALYSIS OF DAMAGE FOR ONE-DIMENSIONAL PERIDYNAMIC MODEL

Peridynamics is a recently developed extension of continuum mechanics, which replaces the traditional concept of stress by force interactions between material points at a finite distance. The peridynamic continuum is thus intrinsically nonlocal. In this contribution, a bond-based peridynamic model with elastic-brittle interactions is considered and the critical strain is defined for each bond as a function of its length. Various forms of length functions are employed to achieve a variety of macroscopic responses. A detailed study of three different localization mechanisms is performed for a one-dimensional periodic unit cell. Furthermore, a convergence study of the adopted finite element discretization of the peridynamic model is provided and an effective event-driven numerical algorithm is described

A stochastic flow rule for granular materials

There have been many attempts to derive continuum models for dense granular flow, but a general theory is still lacking. Here, we start with Mohr-Coulomb plasticity for quasi-2D granular materials to calculate (average) stresses and slip planes, but we propose a "stochastic flow rule" (SFR) to replace the principle of coaxiality in classical plasticity. The SFR takes into account two crucial features of granular materials - discreteness and randomness - via diffusing "spots" of local fluidization, which act as carriers of plasticity. We postulate that spots perform random walks biased along slip-lines with a drift direction determined by the stress imbalance upon a local switch from static to dynamic friction. In the continuum limit (based on a Fokker-Planck equation for the spot concentration), this simple model is able to predict a variety of granular flow profiles in flat-bottom silos, annular Couette cells, flowing heaps, and plate-dragging experiments -- with essentially no fitting parameters -- although it is only expected to function where material is at incipient failure and slip-lines are inadmissible. For special cases of admissible slip-lines, such as plate dragging under a heavy load or flow down an inclined plane, we postulate a transition to rate-dependent Bagnold rheology, where flow occurs by sliding shear planes. With different yield criteria, the SFR provides a general framework for multiscale modeling of plasticity in amorphous materials, cycling between continuum limit-state stress calculations, meso-scale spot random walks, and microscopic particle relaxation

Quotient Complexity of Regular Languages

The past research on the state complexity of operations on regular languages is examined, and a new approach based on an old method (derivatives of regular expressions) is presented. Since state complexity is a property of a language, it is appropriate to define it in formal-language terms as the number of distinct quotients of the language, and to call it "quotient complexity". The problem of finding the quotient complexity of a language f(K,L) is considered, where K and L are regular languages and f is a regular operation, for example, union or concatenation. Since quotients can be represented by derivatives, one can find a formula for the typical quotient of f(K,L) in terms of the quotients of K and L. To obtain an upper bound on the number of quotients of f(K,L) all one has to do is count how many such quotients are possible, and this makes automaton constructions unnecessary. The advantages of this point of view are illustrated by many examples. Moreover, new general observations are presented to help in the estimation of the upper bounds on quotient complexity of regular operations

The Magic Number Problem for Subregular Language Families

We investigate the magic number problem, that is, the question whether there exists a minimal n-state nondeterministic finite automaton (NFA) whose equivalent minimal deterministic finite automaton (DFA) has alpha states, for all n and alpha satisfying n less or equal to alpha less or equal to exp(2,n). A number alpha not satisfying this condition is called a magic number (for n). It was shown in [11] that no magic numbers exist for general regular languages, while in [5] trivial and non-trivial magic numbers for unary regular languages were identified. We obtain similar results for automata accepting subregular languages like, for example, combinational languages, star-free, prefix-, suffix-, and infix-closed languages, and prefix-, suffix-, and infix-free languages, showing that there are only trivial magic numbers, when they exist. For finite languages we obtain some partial results showing that certain numbers are non-magic.Comment: In Proceedings DCFS 2010, arXiv:1008.127