The Odyssey Approach for Optimizing Federated SPARQL Queries

Answering queries over a federation of SPARQL endpoints requires combining data from more than one data source. Optimizing queries in such scenarios is particularly challenging not only because of (i) the large variety of possible query execution plans that correctly answer the query but also because (ii) there is only limited access to statistics about schema and instance data of remote sources. To overcome these challenges, most federated query engines rely on heuristics to reduce the space of possible query execution plans or on dynamic programming strategies to produce optimal plans. Nevertheless, these plans may still exhibit a high number of intermediate results or high execution times because of heuristics and inaccurate cost estimations. In this paper, we present Odyssey, an approach that uses statistics that allow for a more accurate cost estimation for federated queries and therefore enables Odyssey to produce better query execution plans. Our experimental results show that Odyssey produces query execution plans that are better in terms of data transfer and execution time than state-of-the-art optimizers. Our experiments using the FedBench benchmark show execution time gains of at least 25 times on average.Comment: 16 pages, 10 figure

Productivity shocks and real exchange rate: a reappraisal

We reappraise the relationship between productivity and equilibrium real exchange rates using a panel estimation framework that incorporates a large number of countries and importantly, a dataset that allows explicit consideration of the role of non-traded, as well as traded, sector productivity shocks in exchange rate determination. We find evidence of significant correlation between real exchange rates and productivity differentials in both sectors. But our finding of a significant role for the non-traded sector in exchange rate determination, and of a relatively larger correlation between exchange rates and productivity shocks of a given size emanating from this sector, represent clear contradictions of the widely cited Balassa-Samuelson hypothesis. Our findings remain valid in the face of a number of robustness tests, including the exchange rate regime and numéraire currency

Blood lead levels in pregnant women and the neonate

Population studies carried out during the 1980s had shown that the Maltese population was characterized by high blood lead (PbB) levels. These high levels appeared to be a feature at all age groups including neonates. A number of environmental control measures had been initiated to attempt to decrease these PbB levels. The present study reviews PbB levels in pregnant women and newborns. It is shown that mean cord PbB levels decreased significantly in the last decade from a mean of 165.1 + 87.9 ug/I in 1985 to 89.79 + 31.23 ug/I in 1996. This decrease did not correlate with the increasing use of multimineral supplements which include the zinc cation said to be useful to counter the effects of chronic lead intoxication. Placental transfer of lead is also shown to follow closely maternal levels with a correlation coefficient of 0.81. In spite of the apparent decrease in PbB levels, about half of newborns still I have levels which require preventive community measures.peer-reviewe

Numerical simulation of particulateflow in spiral separators (15 % solids)

Spiral separator is a gravity concentration device. It wasinvented by Humphreys in 1941.It is firstly designed anddeveloped based on experience and through many testingof prototypes and modifications. The main objective of thepresent study is simulation of the particulate-flow of morerealistic solids concentration (15% solids by weight) in spiralseparator. The study is based on Eulerian approach and RING K-E turbulence modelin. The results focus on particulate-flow characteristics such as velocity, and distribution and concentration of particulates on the spiral trough.The predicted results are compared with the experimentalin case LD9 coal spiral. Comparisons between numericaland measured data show good agreement

The thickness of the shower disc as observed in showers produced by primaries above 10 (19)eV

The thickness of the shower disk has been measured in showers initiated by primaries of energy to 10 the 19th power eV using the large area water Cerenkov detectors of the Haverah Park array. Results are presented which (1) provide supporting evidence for the accuracy of analysis procedures in giant showers, (2) offer an evaluation of the mini-array technique for the detection of giant showers and (3) extend earlier work on developmental fluctuations above 10 to the 19th power eV

Genetic diversity in the env V1-V2 region of proviral quasispecies from long-term controller MHC-typed cynomolgus macaques infected with SHIVSF162P4cy

Intra-host evolution of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) has been shown by viral RNA analysis in subjects who naturally suppress plasma viremia to low levels, known as controllers. However, little is known about the variability of proviral DNA and the inter-relationships among contained systemic viremia, rate of reservoir reseeding and specific major histocompatibility complex (MHC) genotypes, in controllers. Here, we analysed the proviral DNA quasispecies of the env V1-V2 region, in PBMCs and in anatomical compartments of 13 long-term controller monkeys after 3.2 years of infection with simian/human immunodeficiency virus (SHIV)SF162P4cy. A considerable variation in the genetic diversity of proviral quasispecies was present among animals. Seven monkeys exhibited env V1-V2 proviral populations composed of both clusters of identical ancestral sequences and new variants, whereas the other six monkeys displayed relatively high env V1-V2 genetic diversity with a large proportion of diverse novel sequences. Our results demonstrate that in SHIVSF162P4cy-infected monkeys there exists a disparate pattern of intra-host viral diversity and that reseeding of the proviral reservoir occurs in some animals. Moreover, even though no particular association has been observed between MHC haplotypes and the long-term control of infection, a remarkably similar pattern of intra-host viral diversity and divergence was found within animals carrying the M3 haplotype. This suggests that in animals bearing the same MHC haplotype and infected with the same virus, viral diversity follows a similar pattern with similar outcomes and control of infection

Initial eccentricity fluctuations and their relation to higher-order flow harmonics

Monte Carlo simulations are used to compute the centrality dependence of the participant eccentricities ($\epsilon_{n}$) in Au+Au collisions, for the two primary models currently employed for eccentricity estimates -- the Glauber and the factorized Kharzeev-Levin-Nardi (fKLN) models. They suggest specific testable predictions for the magnitude and centrality dependence of the flow coefficients $v_n$, respectively measured relative to the event planes $\Psi_n$. They also indicate that the ratios of several of these coefficients may provide an additional constraint for distinguishing between the models. Such a constraint could be important for a more precise determination of the specific viscosity of the matter produced in heavy ion collisions.Comment: 6 pages, 6 figures, published versio