Problem-solving models and search strategies for pattern recognition

Noting the major limitations of multivariate statistical classification and syntactic pattern recognition models, this paper presents an overview of some recent work using alternate representations for multistage and nearest neighbor multiclass classification, and for structural analysis and feature extraction. These alternate representations are based on generalizations of state-space and AND/OR graph models and search strategies developed in artificial intelligence (AI). The paper also briefly touches on other current interactions and differences between artificial intelligence and pattern recognition.     

Parallel algorithm on inversion for adjacent pentadiagonal matrices with MPI

In this work, the method based on the work of Huang and McColl on analytical inversion of general tridiagonal matrices is parallelized with MPI. The proposed method is not only capable of finding inverses of full pentadiagonal matrices, but also of those with pentadiagonal envelope, such as tridiagonal matrices. The method is modified to generate an MPI algorithm. The speed-up performance of the parallelized algorithm is also analyzed on different cases.     

Reversible ischemia determined by xenon-enhanced CT after 90 minutes of complete basilar artery occlusion

Intraarterial thrombolytic therapy decreases mortality in the treatment of acute basilar artery occlusion. An acute decrease in cerebral blood flow (CBF) (<12 mL/100 g per minute) has been reported to invariably result in infarction. We report a case of acute basilar artery occlusion, recanalized within 90 minutes, with reversal of CBF of less than 6 mL/100 g per minute. After reperfusion, areas with persistent CBF of 6 mL/100 g per minute resulted in infarctions on subsequent CT studies. Parenchymal viability is possible after 90 minutes of posterior CBF of 6 mL/100 g per minute.     

Knapsack packing networks

A knapsack packing neural network of 4n units with both low-order and conjunctive asymmetric synapses is derived from a non-Hamiltonian energy function. Parallel simulations of randomly generated problems of size n in {5, 10, 20} are used to compare network solutions with those of simple greedy fast parallel enumerative algorithms.     

Problem reduction representation for the linguistic analysis of waveforms

This paper shows how the nondirectional structural analysis of pattern data can be performed by matching a problem reduction representation (PRR) of pattern structure with sample data, using a best-first state space search algorithm called SSS*. The end result of the matching algorithm is a tree whose nodes represent recognized structures in the data. Tip nodes of the tree structure correspond to primitives which are recognized in the raw data by curve fitting routines. The operators of the algorithm allow the tree to be constructed with a combination of top-down or bottom-up steps. The matching of the structure tree to waveform segments need not be done in a left-right sequence. Moreover ambiguous matches are pursued in a best first order by using state space search with partial parse trees as states. A software system called WAPSYS (for waveform parsing system) is described, which implements this structural analysis paradigm. Experience using WAPSYS to analyze carotid pulse waves is also discussed.     

Hybrid Error Control Using Retransmission and Generalized Burst-Trapping Codes

On most real channels hybrid error control schemes are expected to provide a throughput higher than that of automatic repeatrequest (ARQ) systems and a reliability better than forward error correction (FEC) systems. On compound channels, channels with a mixture of random and burst errors, generalized burst-trapping (GBT) codes seem to be quite effective for FEC. In this paper, a hybrid scheme with Go BackNARQ as the retransmission component and GBT code as the FEC component, is described. Its performance is analyzed in terms of throughput efficiency and undetected error probability and is compared with that of a forward-acting GBT code. Numerical calculations of the parameters are presented to illustrate the performance.     

A mechanistic view of the non-ideal osmotic and motional behavior of intracellular water

It is commonly assumed that essentially all of the water in cells has the same ideal motional and colligative properties as does water in bulk liquid state. This assumption is used in studies of volume regulation, transmembrane movement of solutes and electrical potentials, solute and solution motion, solute solubility and other phenomena. To get at the extent and the source of non-ideally behaved water (an operational term dependent on the measurement method), we studied the motional and colligative properties of water in cells, in solutions of amino acids and glycine peptides whose surface characteristics are known, and in solution of bovine serum albumin, hemoglobin and some synthetic polypeptides. Solutions of individual amino acids with progressively larger hydrophobic side chains showed one perturbed water molecule (structured-slowed in motion) per nine square angstroms of hydrophobic surface area. Water molecules adjacent to hydrophobic surfaces form pentagonal structural arrays, as shown by X-ray diffraction studies, that are reported to be disrupted by heat, electric field, hydrostatic pressure and phosphorylation state. Hydrophilic amino acids demonstrated water destructuring (increased motion) that was attributed to dielectric realignment of dipolar water molecules in the electric field between charge groups. In solutions of proteins, several methods indicate the equivalent of 2-8 layers of structured water molecules extending beyond the protein surface, and we have recently demonstrated that induced protein conformational change modifies the extent of non-ideally behaved water. Water self-diffusion rate as measured in three different cell types was about half that of bulk water, indicating that most of the water in these cells was slower in motion than bulk water. In different cell types the extent of osmotically perturbed water ranged from less that half to almost all of the intracellular water. The assumption that essentially all intracellular water has ideal osmotic and motional behavior is not supported by the experimental findings. The non-ideally of cell water is an operational term. Therefore, the amount of non-ideally behaving water is dependent on the characteristics of water targeted, i.e. the measurement method, and a large fraction of it is explainable in mechanistic terms at a molecular level based on solute-solvent interactions.     

Discussion of Cheeseman's An inquiry into computer understanding

We discuss some points on which we agree, and others on which we disagree, with Cheeseman's target article. Particular agreements include the need for an eclectic approach; disagreements include the misleading distinction between probabilistic and logical reasoning regarding the notion of truth, and also some matters of nonmonotonicity.     

On the asymptotic performance of IDA*

Since best‐first search algorithms such as A* require large amounts of memory, they sometimes cannot run to completion, even on problem instances of moderate size. This problem has led to the development of limited‐memory search algorithms, of which the best known is IDA*. This paper presents the following results about IDA* and related algorithms: 1) The analysis of asymptotic optimality for IDA* in [R.E. Korf, Optimal path finding algorithms, in: Search in Artificial Intelligence, eds. L. Kanal and V. Kumar (Springer‐Verlag, 1988) pp. 200-222] is incorrect. There are trees satisfying the asymptotic optimality conditions given in [R.E. Korf, Optimal path finding algorithms, in: Search in Artificial Intelligence, eds. L. Kanal and V. Kumar (Springer‐Verlag, 1988) pp. 200-222] for which IDA* is not asymptotically optimal. 2) To correct the above problem, we state and prove necessary and sufficient conditions for asymptotic optimality of IDA* on trees. On trees not satisfying our conditions, we show that no best‐first limited‐memory search algorithm can be asymptotically optimal. 3) On graphs, IDA* can perform quite poorly. In particular, there are graphs on which IDA* does Ω(2^2N) node expansions where N is the number of nodes expanded by A*. This revised version was published online in June 2006 with corrections to the Cover Date.     

Aneurysm clips: evaluation of MR imaging artifacts at 1.5 T

PURPOSE: Endothelin-1 (ET-1), a peptide produced by the vascular endothelium, causes profound renal vasoconstriction by binding to ET-A receptors. The present study examined the renal actions of ET-1 after ET-A receptors were blocked by BE-18257B to unmask the functions of ET-B receptors. MATERIALS AND METHODS: Renal hemodynamics and clearance measurements were obtained in anesthetized dogs after intrarenal infusion of BE-18257B at 100 ng./kg./min. (Group 1), after intrarenal infusion of ET-1 at 2 ng./kg./min. (Group 2), or after intrarenal infusion of ET-1 superimposed on BE-18257B (Group 3). RESULTS: In Group 1, BE-18257B infusion did not alter arterial pressure, renal blood flow (RBF), GFR or tubular function. In Group 2, ET-1 infusion led to a significant decrease in RBF and GFR (37 and 40%, respectively) without altering arterial pressure. Urinary volume and sodium excretion were not changed but osmolality decreased significantly. In Group 3, BE-18257B infusion significantly attenuated the decrease in RBF caused by ET-1 and increased GFR by 40% without altering arterial pressure, associated with significant diuresis and natriuresis. CONCLUSION: Renal vasoconstriction caused by ET-1 is attenuated by ET-A receptor blockade with BE-18257B, which unmasks the hemodynamic and tubular actions of ET-B receptors. As a result, it limits the ET-1 induced decrease in RBF and raises GFR, and leads to a diuresis and natriuresis.