Scalable Peer-to-Peer Indexing with Constant State

We present a distributed indexing scheme for peer to peer networks. Past work on distributed indexing traded off fast search times with non-constant degree topologies or network-unfriendly behavior such as flooding. In contrast, the scheme we present optimizes all three of these performance measures. That is, we provide logarithmic round searches while maintaining connections to a fixed number of peers and avoiding network flooding. In comparison to the well known scheme Chord, we provide competitive constant factors. Finally, we observe that arbitrary linear speedups are possible and discuss both a general brute force approach and specific economical optimizations

Analysis of Petri Net Models through Stochastic Differential Equations

It is well known, mainly because of the work of Kurtz, that density dependent Markov chains can be approximated by sets of ordinary differential equations (ODEs) when their indexing parameter grows very large. This approximation cannot capture the stochastic nature of the process and, consequently, it can provide an erroneous view of the behavior of the Markov chain if the indexing parameter is not sufficiently high. Important phenomena that cannot be revealed include non-negligible variance and bi-modal population distributions. A less-known approximation proposed by Kurtz applies stochastic differential equations (SDEs) and provides information about the stochastic nature of the process. In this paper we apply and extend this diffusion approximation to study stochastic Petri nets. We identify a class of nets whose underlying stochastic process is a density dependent Markov chain whose indexing parameter is a multiplicative constant which identifies the population level expressed by the initial marking and we provide means to automatically construct the associated set of SDEs. Since the diffusion approximation of Kurtz considers the process only up to the time when it first exits an open interval, we extend the approximation by a machinery that mimics the behavior of the Markov chain at the boundary and allows thus to apply the approach to a wider set of problems. The resulting process is of the jump-diffusion type. We illustrate by examples that the jump-diffusion approximation which extends to bounded domains can be much more informative than that based on ODEs as it can provide accurate quantity distributions even when they are multi-modal and even for relatively small population levels. Moreover, we show that the method is faster than simulating the original Markov chain

Income Tax Incentives to Promote Saving

We examine six alternative plans which might be discussed in an effort to increase consumer savings through the personal income tax system in the United States. These plans attempt to affect savings through an increase in the real rate of return either by direct tax cuts on savings or by indexing tax rates against inflation. The paper presents estimates of static and dynamic resource allocation effects for the six plans, and compares them to results obtained in earlier work on the impacts of more sweeping reforms. A medium-scale numerical general equilibrium model is used which integrates the U. S. tax system with consumer demand behavior by household and producer behavior by industry.

Influence of Ibuprofen on Phospholipid Membranes

Basic understanding of biological membranes is of paramount importance as these membranes comprise the very building blocks of life itself. Cells depend in their function on a range of properties of the membrane, which are important for the stability and function of the cell, information and nutrient transport, waste disposal and finally the admission of drugs into the cell and also the deflection of bacteria and viruses. We have investigated the influence of ibuprofen on the structure and dynamics of L-alpha-phosphatidylcholine (SoyPC) membranes by means of grazing incidence small-angle neutron scattering (GISANS), neutron reflectometry and grazing incidence neutron spin echo spectroscopy (GINSES). From the results of these experiments we were able to determine that ibuprofen induces a two-step structuring behavior in the SoyPC films, where the structure evolves from the purely lamellar phase for pure SoyPC over a superposition of two hexagonal phases to a purely hexago- nal phase at high concentrations. Additionally, introduction of ibuprofen stiffens the membranes. This behavior may be instrumental in explaining the toxic behavior of ibuprofen in long-term application.Comment: -Improved indexing in Fig. 4e) -changed concentrations to mol% -improved arguments, however conclusions stay unchange

An exploratory study of user-centered indexing of published biomedical images

User-centered image indexing—often reported in research on collaborative tagging, social classification, folksonomy, or personal tagging—has received a considerable amount of attention [1-7]. The general themes in more recent studies on this topic include user-centered tagging behavior by types of images, pros and cons of user-created tags as compared to controlled index terms; assessment of the value added by user-generated tags, and comparison of automatic indexing versus human indexing in the context of web digital image collections such as Flickr. For instance, Golbeck\u27s finding restates the importance of indexer experience, order, and type of images [8]. Rorissa has found a significant difference in the number of terms assigned when using Flickr tags or index terms on the same image collection, which might suggest a difference in level of indexing by professional indexers and Flickr taggers [9]. Studies focusing on users and their tagging experiences and user-generated tags suggest ideas to be implemented as part of a personalized, customizable tagging system. Additionally, Stvilia and her colleagues have found that tagger age and image familiarity are negatively related, while indexing and tagging experience were positively associated [10]. A major question for biomedical image indexing is whether the results of the aforementioned studies, all of which dealt with general image collections, are applicable to images in the medical domain. In spite of the importance of visual material in medical education and the prevalence of digitized images in formal medical practice and education, medical students have few opportunities to annotate biomedical images. End-user training could improve the quality of image indexing and so improve retrieval. In a pilot assessment of image indexing and retrieval quality by medical students, this study compared concept completion and retrieval effectiveness of indexing terms generated by medical students on thirty-nine histology images selected from the PubMed Central (PMC) database. Indexing instruction was only given to an intervention group to test its impact on the quality of end-user image indexing

Array operators using multiple dispatch: a design methodology for array implementations in dynamic languages

Arrays are such a rich and fundamental data type that they tend to be built into a language, either in the compiler or in a large low-level library. Defining this functionality at the user level instead provides greater flexibility for application domains not envisioned by the language designer. Only a few languages, such as C++ and Haskell, provide the necessary power to define $n$-dimensional arrays, but these systems rely on compile-time abstraction, sacrificing some flexibility. In contrast, dynamic languages make it straightforward for the user to define any behavior they might want, but at the possible expense of performance. As part of the Julia language project, we have developed an approach that yields a novel trade-off between flexibility and compile-time analysis. The core abstraction we use is multiple dispatch. We have come to believe that while multiple dispatch has not been especially popular in most kinds of programming, technical computing is its killer application. By expressing key functions such as array indexing using multi-method signatures, a surprising range of behaviors can be obtained, in a way that is both relatively easy to write and amenable to compiler analysis. The compact factoring of concerns provided by these methods makes it easier for user-defined types to behave consistently with types in the standard library.Comment: 6 pages, 2 figures, workshop paper for the ARRAY '14 workshop, June 11, 2014, Edinburgh, United Kingdo