Ecological studies involving large jellyfish have been limited by the inability of oceanographers to measure the abundance and distribution patterns of these highly aggregated animals at local scales. Conventional plankton nets are undesirable in these applications because they cannot sample volumes large enough to accurately determine jellyfish concentration, nor do they have adequate spatial resolution to account for the ubiquitous patchiness of most large jellies. Nets are also notorious for damaging the watery bodies of jellyfish. To overcome these problems, we have developed a video system for use in the in situ study of large jellyfish. The design of our JellyCam is easily replicated since it incorporates commercially available components within a frame designed to hold hydrographic instrumentation available at most marine laboratories. We present data sets from 2 occasions as a demonstration of the utility of the JellyCam. On one occasion, a vertical profile of medusae of Pelagia noctiluca revealed intense layering of these jellyfish at the pronounced halocline/pycnocline. Most jellyfish in this layer were swimming toward the surface, and it was hypothesized that retarded forward-swimming velocity at the halocline, due to salt retention in jellyfish, caused this accumulation. A separate 800 m long horizontal transect of Phyllorhiza punctata medusae revealed distinct concentrated bands of jellyfish associated with increased chlorophyll concentration. Concomitant hydrographic data from the JellyCam showed that accumulation of both jellyfish and chlorophyll was associated with a hydrographic front. These data sets demonstrate that this system is capable of the desired 2 m 3 resolution, which is adequate for the observation and quantification of jellyfish distributions around small-scale physical discontinuities (e.g. fronts and pycnoclines). A series of side-by-side comparisons with a conventional plankton trawl resulted in comparable measurements of large jellyfish (Aurelia aurita) concentrations. Though in situ videography by itself is a powerful tool for investigating jellyfish, its use in conjunction with conventional nets or other technologies, such as acoustics and self-propelled vehicles (e.g. remotely operated vehicles and submersibles), will provide the most comprehensive view of jellyfish distribution in 3 dimensions.
Such is the complex nature of termination that ad hoc methods for its automatic detection in logic programs are giving way to techniques more rmly based on theory. Many of these approaches relate to the early theoretical result 3] which showed that a logic program terminates for bounded goals if and only if it is recurrent. De nitions of recurrency and boundedness are formulated in terms of level mappings which assign natural numbers, or levels, to ground atoms.A predicate is recurrent with respect to some level mapping if the level of its head is greater than the level of each of its body atoms. The termination of bounded goals, whose level cannot increase, then follows from the well-foundedness of the natural numbers.Level mappings are often de ned in terms of norms which measure the size of terms. For example, the norm j:j list-length de ned to measure the length of a list, can be used as the basis for a level mapping for the Delete/3 predicate below. Comparing the size of the second argument in the head of the recursive clause with the size of the second argument in the recursive call, and using list length as a measure for size, we see that the size of this argument decreases by one on each recursive call. Thus the predicate is recurrent with respect to the level mapping j:j de ned by jDelete(t 1 ; t 2 ; t 3 )j = jt 2 j list-length and terminates for all goals bounded with respect to j:j. Note that the predicate is also recurrent with respect to other level mappings and indeed termination can be proved for other goals by choosing a di erent mapping.Delete(x, x|y], y). Delete(x, y|z], y|w]) <-Delete(x, z, w).Deducing termination for programs which are not structurally recursive is more complex, requiring the derivation of inter-argument relationships 2]. Inter-argument relationships express how the sizes of an atom's arguments are related. In the case of Delete/3, for example, the length of the second argument is one plus the length of the third argument. The Perm/2 predicate de ned below is one example where an inter-argument relationship is needed to prove termination.Perm( ], ]). Perm( h|t], a|p]) <-Delete(a, h|t], l) & Perm(l, p).In fact it can be shown that this program is not recurrent and will not terminate for all ground queries { recurrency implies that a program terminates for all computation rules and here there exists a computation rule which selects non-ground Delete/3 goals which lead to in nite derivations. It can be shown however to be acceptable 1], an analogous concept to recurrency for programs executed using a left-to-right computation rule. A key step in the proof is to show that the size of the rst argument in the head of the recursive clause is strictly greater than the size
Abstract. The current state of the art for ensuring finite unfolding of logic programs consists of a number of online techniques where unfolding decisions are made at specialisation time. Introduction of a static termination analysis phase into a partial deduction algorithm permits unfolding decisions to be made offline, before the actual specialisation phase itself. This separation improves specialisation time and facilitates the automatic construction of compilers and compiler generators. The main contribution of this paper is how this separation may be achieved in the context of logic programming, while providing non-trivial support for partially static datastructures. The paper establishes a solid link between the fields of static termination analysis and partial deduction enabling existing termination analyses to be used to ensure finiteness of the unfolding process. This is the first offline technique which allows arbitrarily partially instantiated goals to be sufficiently unfolded to achieve good specialisation results. Furthermore, it is demonstrated that an offline technique such as this one can be implemented very efficiently and, surprisingly, yield even better specialisation than a (pure) online technique. It is also, to our knowledge, the first offline approach which passes the KMP test (i.e., obtaining an efficient Knuth-Morris-Pratt pattern matcher by specialising a naive one).
We present an application of the Java™ programming language to specify and implement reactive real-time systems. We have developed and tested a collection of classes and methods to describe concurrent modules and their asynchronous communication by means of signals. The control structures are closely patterned after those of the synchronous language Esterel, succinctly describing concurrency, sequencing and preemption. We show the user-friendliness and efficiency of the proposed technique by using an example from the automotive domain.
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