Frequent Path Research Articles

A Stable Routing Protocol to Support ITS Services in VANET Networks

There are numerous research challenges that need to be addressed until a wide deployment of vehicular ad hoc networks (VANETs) becomes possible. One of the critical issues consists of the design of scalable routing algorithms that are robust to frequent path disruptions caused by vehicles' mobility. This paper argues the use of information on vehicles' movement information (e.g., position, direction, speed, and digital mapping of roads) to predict a possible link-breakage event prior to its occurrence. Vehicles are grouped according to their velocity vectors. This kind of grouping ensures that vehicles, belonging to the same group, are more likely to establish stable single and multihop paths as they are moving together. Setting up routes that involve only vehicles from the same group guarantees a high level of stable communication in VANETs. The scheme presented in this paper also reduces the overall traffic in highly mobile VANET networks. The frequency of flood requests is reduced by elongating the link duration of the selected paths. To prevent broadcast storms that may be intrigued during path discovery operation, another scheme is also introduced. The basic concept behind the proposed scheme is to broadcast only specific and well-defined packets, referred to as ldquobest packetsrdquo in this paper. The performance of the scheme is evaluated through computer simulations. Simulation results indicate the benefits of the proposed routing strategy in terms of increasing link duration, reducing the number of link-breakage events and increasing the end-to-end throughput.

Efficient algorithms for incremental Web log mining with dynamic thresholds

With the fast increase in Web activities, Web data mining has recently become an important research topic and is receiving a significant amount of interest from both academic and industrial environments. While existing methods are efficient for the mining of frequent path traversal patterns from the access information contained in a log file, these approaches are likely to over evaluate associations. Explicitly, most previous studies of mining path traversal patterns are based on the model of a uniform support threshold, where a single support threshold is used to determine frequent traversal patterns without taking into consideration such important factors as the length of a pattern, the positions of Web pages, and the importance of a particular pattern, etc. As a result, a low support threshold will lead to lots of uninteresting patterns derived whereas a high support threshold may cause some interesting patterns with lower supports to be ignored. In view of this, this paper broadens the horizon of frequent path traversal pattern mining by introducing a flexible model of mining Web traversal patterns with dynamic thresholds. Specifically, we study and apply the Markov chain model to provide the determination of support threshold of Web documents; and further, by properly employing some effective techniques devised for joining reference sequences, the proposed algorithm dynamic threshold miner (DTM) not only possesses the capability of mining with dynamic thresholds, but also significantly improves the execution efficiency as well as contributes to the incremental mining of Web traversal patterns. Performance of algorithm DTM and the extension of existing methods is comparatively analyzed with synthetic and real Web logs. It is shown that the option of algorithm DTM is very advantageous in reducing the number of unnecessary rules produced and leads to prominent performance improvement.

A preferred link based routing protocol for wireless ad hoc networks

Routing protocols in wireless ad hoc networks experience high control overhead due to frequent path breaks that occur due to mobility of nodes, which leads to flooding of control packets throughout the network. We propose a preferred link based routing protocol that reduces flooding of control packets by selectively allowing some nodes to forward the packets using a preferred list. We propose two algorithms to compute the preferred list. The first algorithm computes the preferred list based on neighbor's degree. The second algorithm computes the preferred list based on stability information. Simulation results illustrate their performance and demonstrate their good behavior compared to other protocols. They also show that the stability based algorithm finds more stable paths while the neighbor's degree based algorithm has least control overhead.

Recommender Systems Based on User Navigational Behavior in the Internet

Starting from data available about (anonymous) visitors of a website, possibilities of extracting information as well as enriching pure browsing patterns with the help of business measures (e-metrics) and detecting possibly negative effects of web robots are sketched as prerequisites for interpretation purposes of the navigational behavior of internet users. Problems with the reconstruction of user navigation paths are explained and different heuristics for path completion are discussed. Additionally, several kinds of features of user navigation paths (e.g., sets, sequences, path fragments) have to be mentioned to prepare for an adequate theoretical background concerning recommender systems that can be used for tasks as different as site personalization, cross-/up-selling, and navigation assistance. A vocabulary to describe different kinds of recommender systems and generic quality measures for system evaluation are formulated. Then, specific recommender systems, especially systems based on frequent path features, are defined and evaluated in a final experiment. In an outlook directions for future research on recommender systems are given.

PGI11: CHARACTERIZATION AND MARKOV MODELING OF GASTROESOPHAGEAL REFLUX DISEASE STATES IN A LARGE HEALTH CARE PLAN

OBJECTIVES: The objective was to describe the disease state (DS) transition patterns of gastroesophageal reflux disease (GERD) by applying a multi-state model assuming a Markov process. METHODS: This retrospective study utilized administrative claims for subjects with GERD from a large Midwest USA health care plan. Subjects were tracked for six, six-month time periods (baseline and five followups). Within each time period, ICD-9 diagnosis codes were used to categorize subjects' GERD into four DS plus a non-symptomatic state: DS0 {no GERD diagnosis}, DS1 {mild esophagitis}, DS2 {reflux esophagitis}, DS3 {esophageal ulceration}, and DS4 {strictures and complications}. GERD transition probabilities and patterns were analyzed in a five-state Markov framework. Disease regressions and progressions were allowed. The effects of patient and provider covariables on transition probabilities were modeled using logistic regression techniques. RESULTS: A total of 7575 subjects with GERD were analyzed. In the five followup periods combined, 79% of the subjects were in GERD DS0, 6% in DS1, 8% in DS2, 2% in DS3, and 5% in DS4. For all initial DS, the most frequent transition path was to regress to DS0 (becoming non-symptomatic) and the second most common was to stay in the initial disease state. For subjects ending a time period in DS1, 89% regressed to DS0 in the next time period, while 6% stayed in DS1, 3% progressed to DS2, 1% progressed to DS3, and 1% progressed to DS4. Multivariate modeling of risk factors influencing transitions showed that progressing from DS1 is associated with age> 70, a proton pump inhibitor prescription, and absence of a diagnostic procedure. CONCLUSIONS: The Markov analysis showed that subjects with GERD commonly have their symptoms regress, with only a small percent progressing. The Markov model is a useful methodology to research disease states in a retrospective database setting within a health care plan.

Intracranial extension of acquired aural cholesteatoma.

Cholesteatoma of the petrous bone extending into the intracranial region is an unusual occurrence. Most cases have been attributed to secondary extension of a primary epidermal blastomatous malformation of the temporal bone into the middle or posterior fossae. Within the past two and a half decades, intracranial extension of acquired aural cholesteatoma has been recognized as a likely alternative to this mechanism. Recent literature has rejoined this observation by considering both primary and secondary cholesteatoma of the petrous bone as a single group, petrosal cholesteatoma. The present study is presented to analyze the clinical presentation, imaging findings, and surgical treatment of six patients with acquired aural cholesteatoma extending into the intracranial region. Findings in this study are compared with the extant literature on congenital and acquired cholesteatoma of the petrous bone. This study proposes that petrosal cholesteatoma is a valid anatomical construct; however, the pathogenesis of petrosal cholesteatoma is still important in understanding the clinical presentation and management of cholesteatoma that extends beyond the usual confines of the middle ear and mastoid. Retrospective case review conducted at a tertiary referral center. From 1985 to 1999, 477 patients were surgically treated for acquired aural cholesteatoma. Patients with intracranial extension of cholesteatoma were studied. Clinical presentation, imaging studies, operative findings, surgical treatment, and postoperative results were evaluated. Six cases in a series of 477 patients with acquired aural cholesteatoma had intracranial extension of disease. In this series, the most frequent pathway for intracranial extension was supralabyrinthine through the supratubal recess into the middle cranial fossa. A less frequent pathway was via the retrofacial air cells into the posterior cranial fossa. Surgical access for removal of intracranial cholesteatoma was accomplished through several approaches including translabyrinthine, transcochlear, retrolabyrinthine, and middle cranial fossa. In two patients who had reoperation for possible residual disease, one was free of residual disease and one was found to have residual cholesteatoma in the region of the horizontal facial nerve. Acquired aural cholesteatoma can extend into either the middle or posterior cranial fossae. In this study, cholesteatoma extended into the middle fossa through the supratubal recess along the labyrinthine facial nerve and into or above the internal auditory canal. A less frequent path is through the retrofacial air cells into the posterior fossa. Intracranial acquired cholesteatoma is generally small and presents with complaints related to underlying otitis media rather than the neurological deficits that are often associated with primary petrous bone cholesteatoma. While computed tomography and magnetic resonance imaging are both required to differentiate congenital petrous cholesteatoma from other lesions of the petrous bone, computed tomography of the temporal bone is usually sufficient to diagnosis and define intracranial extension of acquired aural cholesteatoma. These lesions can be completely excised rather than exteriorized.

On overestimation of displacements in numerical calculation of zoned dams

AbstractOverestimation of displacements in numerical calculations can occur if some requirements are not met by the constitutive relations. Along with consideration for small strain behaviour of soils1 the stiffening effects of unloading in shear should be taken into account. The latter problem is analysed in the paper using embankment dams as a typical example. Strain and stress paths in their cores and shells were derived from field measurement results and frequent path direction changes during seemingly monotonic loading process were discovered. Proportional loading test results of isotropically and anisotropically consolidated sand allowed interpretation of the in situ paths by the incremental theory of plasticity and distinction between the sections where unloading and reloading in shear develop. Furthermore, the analysis of these tests showed a marked stiffening of the soil due to unloading as well as neutral loading in shear. The strain redistribution due to material inhomogeneity, either inherent or introduced by the loading process, was identified as a common reason for the frequent occurrence of this phenomenon. Consequently, overestimations in displacement calculations can be brought about by neglecting this important effect by the constitutive model used. Accordingly, the unit response envelopes of some typical constitutive laws have been checked from this special point of view, and the models properly describing this phenomenon selected.