Approximating Minimum Feedback Sets and Multicuts in Directed Graphs

This paper deals with approximating feedback sets in directed graphs. We consider two related problems: the weighted feedback vertex set (FVS) problem, and the weighted feedback edge set (FES) problem. In the {FVS} (resp. FES) problem, one is given a directed graph with weights (each of which is at least one) on the vertices (resp. edges), and is asked to find a subset of vertices (resp. edges) with minimum total weight that intersects every directed cycle in the graph. These problems are among the classical NP-hard problems and have many applications. We also consider a generalization of these problems: subset-fvs and subset-fes, in which the feedback set has to intersect only a subset of the directed cycles in the graph. This subset consists of all the cycles that go through a distinguished input subset of vertices and edges, denoted by X . This generalization is also NP-hard even when |X|=2 . We present approximation algorithms for the subset-fvs and subset-fes problems. The first algorithm we present achieves an approximation factor of O(log ² |X|) . The second algorithm achieves an approximation factor of O(min{log τ ^* log log τ ^* , log n log log n)} , where τ ^* is the value of the optimum fractional solution of the problem at hand, and n is the number of vertices in the graph. We also define a multicut problem in a special type of directed networks which we call circular networks, and show that the subset-fes and subset-fvs problems are equivalent to this multicut problem. Another contribution of our paper is a combinatorial algorithm that computes a (1+ɛ) approximation to the fractional optimal feedback vertex set. Computing the approximate solution is much simpler and more efficient than general linear programming methods. All of our algorithms use this approximate solution. Received May 31, 1995; revised June 11, 1996, and October 9, 1996.     

A statistical analysis of interference and effective deployment strategies for facility-specific wireless sensor networks

Sensors are essential to industrial automation as they provide vital links between control systems and the physical world. Recently, wireless sensor networks (WSNs) attract more attention as they become feasible solutions for facility management. Unlike simulated environments, however, there are challenges in developing reliable WSNs for monitoring real facilities, including reduced accuracy, reliability and performance due to unpredictable interferences. This paper investigates deployment of automation facility-specific WSNs, called facility sensor networks (FSNs). First, interferences at multiple sensing nodes are analyzed to see if FSNs are vulnerable to interference. Second, interference sources are identified by applying statistical methods to collected data, in order to find the appropriate FSN configuration. Finally, an interference model is proposed to obtain optimal deployment strategies that minimize influence of interference. The strategy yields the lowest interference level compared to others. The results also suggest the appropriate number of sensors to be deployed.     

Performance evaluation of wireless sensor network protocols for industrial applications

Recently, distributed wireless microsensor systems have provided more flexible leverage to emerging industrial applications. The tiny distributed wireless microsensor network systems, however, should be designed to overcome various constraints such as limited energy, bandwidth limit, and unexpected failure of communication under disturbances. In addition, their network topologies need to be managed with designated communication protocols. Thus, design of microsensor network protocols still needs to be application-specific. It should be also evaluated through designated tools at each level of networking characteristics. This research describes essential factors that affect the performance of sensor network systems in the design of wireless microsensor network protocols, and presents effective time-based network protocol and performance evaluation tool which are applicable for various protocols in industrial applications. The developed network evaluation tool, called TIE/MEMS, also includes functional comparison with recent protocols proposed for wireless microsensor networks, and provides design guidelines for multi-sensor network systems needed for emerging industrial applications.     

A hierarchical non-parametric method for capturing non-rigid deformations

We present a novel approach for measuring image similarity based on the composition of parts. The measure identifies common sub-regions between the images at multiple sizes, and evaluates the amount of deformation required to align the common regions. The scheme allows complex, non-rigid deformation of the images, and penalizes irregular deformations more than coherent shifts of larger sub-parts. The measure is implemented by an algorithm which is a variant of dynamic programming, extended to multi-dimensions, and is using scores measured on a relative scale. The similarity measure is shown to be robust to non-rigid deformations of parts at various positions and scales, and to capture basic characteristics of human similarity judgments.     

Scaling approach to water sorption isotherms of hydrogels and foods

Mechanisms affecting water sorption isotherms of foods, at high water activities, were evaluated by the processes of swelling and shrinking of model systems of uncharged and charged hydrogels. Their water activity was found to be determined by the combined effect of their osmotic pressure and the network pressure of the polymeric network. The scaling approach in polymer science indicates that in an uncharged network the osmotic pressure is affected by the mobility of the polymer segments and thus by the degree of cross-linking. However, in charged gels, which behave in a similar manner to many food systems, the counterions play the dominant role in determining the osmotic pressure. The network pressure may shift from a positive to a negative value during shrinking (dehydration), thus counteracting or co-operating with the osmotic pressure in decreasing the water activity. A scaling sorption isotherm, at high water activity, is formulated for a food system with physically significant parameters.     

Investigations into the occurrence and the antibiotic susceptibility of gram negative anaerobes of the genera Bacteroides, Prevotella, Porphyromonas and Fusobacterium in specimens obtained from diseased animals

From different samples of 247 diseased animals (cattle, sheep, goat, horse, pig, dog, cat, rodent, zoo-animals), 410 strains of gram-negative anaerobes were cultured. 297 isolates (72.4%) could be differentiated to the species level by using cultural-biochemical methods, gaschromatography and cell-wall-lipidanalysis. They belonged to 29 different species. For an additional 113 strains (27.6%) only the genus could be determined. Bacteria belonging to the genus Fusobacterium occurred with the highest isolation rates (36% of all strains) in the samples examined, followed by Bacteroides spp. (26.1%), Prevotella spp. (19.9%) and Prophyromonas spp. (17.8%). Fusobacterium necrophorum was the single species isolated most frequently. Antibiotic susceptibility tests by E-test were performed on 100 strains belonging to the the above mentioned genera. Of these strains 18% were resistant to penicillin and 20% to tetracycline. The resistant strains belonged mainly to the Bacteroides fragilis-group. Resistant rates to most other antimicrobial agents tested were Amoxicillin in combination with clavulanic acid: 1%, Chloramphenicol: 3%, Clindamycin:8%. All 100 selected strains proved to be susceptible to Metronidazol.     

Reading cursive handwriting by alignment of letter prototypes

We describe a new approach to the visual recognition of cursive handwriting. An effort is made to attain human-like performance by using a method based on pictorial alignment and on a model of the process of handwriting. The alignment approach permits recognition of character instances that appear embedded in connected strings. A system embodying this approach has been implemented and tested on five different word sets. The performance was stable both across words and across writers. The system exhibited a substantial ability to interpret cursive connected strings without recourse to lexical knowledge.SU is partially supported by NSF grant IRI-8900267.     

Human fetal pituitary expresses functional growth hormone-releasing peptide receptors

We have demonstrated that transferrin binding protein (TfBP), ferritin, and iron, are specifically localized in Bergmann glia, while the transferrin receptor is confined to Purkinje cells in the chicken cerebellum. The results of this study suggest that Bergmann glia have previously undescribed functions related to iron regulation such as sequestration of iron and the maintenance of iron homeostasis in the cerebellum.