Bar-Ilan University

About: Bar-Ilan University is a education organization based out in Ramat Gan, Israel. It is known for research contribution in the topics: Population & Poison control. The organization has 12835 authors who have published 34964 publications receiving 995648 citations. The organization is also known as: Bar Ilan University & BIU.

On Dynamic Shortest Paths Problems

Abstract: We obtain the following results related to dynamic versions of the shortest-paths problem: Reductions that show that the incremental and decremental single-source shortest-paths problems, for weighted directed or undirected graphs, are, in a strong sense, at least as hard as the static all-pairs shortest-paths problem. We also obtain slightly weaker results for the corresponding unweighted problems. A randomized fully-dynamic algorithm for the all-pairs shortest-paths problem in directed unweighted graphs with an amortized update time of $\tilde {O}(m\sqrt{n})$ (we use $\tilde {O}$ to hide small poly-logarithmic factors) and a worst case query time is O(n3/4). A deterministic O(n2log n) time algorithm for constructing an O(log n)-spanner with O(n) edges for any weighted undirected graph on n vertices. The algorithm uses a simple algorithm for incrementally maintaining single-source shortest-paths tree up to a given distance.

Role of Hydrogen Peroxide in Sperm Capacitation and Acrosome Reaction

Abstract: The generation of reactive oxygen species (ROS) has been implicated in the regulation of sperm capacitation and acrosome reaction; however, the mechanisms underlying this regulation remain unclear. To examine the cellular processes involved, we studied the effect of different concentrations of hydrogen peroxide (H(2)O(2)) on protein tyrosine phosphorylation under various conditions. Treatment of spermatozoa with H(2)O(2) in medium without heparin caused a time- and dose-dependent increase in protein tyrosine phosphorylation of at least six proteins in which maximal effect was seen after 2 h of incubation with 50 microM H(2)O(2). At much higher concentrations of H(2)O(2) (0.5 mM), there is significant reduction in the phosphorylation level, and no protein tyrosine phosphorylation is observed at 5 mM H(2)O(2) after 4 h of incubation. Exogenous NADPH enhanced protein tyrosine phosphorylation similarly to H(2)O(2). These two agents, but not heparin, induced Ca(2+)-dependent tyrosine phosphorylation of an 80-kDa protein. Treatment with H(2)O(2) (50 microM) caused approximately a twofold increase in cAMP, which is comparable to the effect of bicarbonate, a known activator of soluble adenylyl cyclase in sperm. This report suggests that relatively low concentrations of H(2)O(2) are beneficial for sperm capacitation, but that too high a concentration inhibits this process. We also conclude that H(2)O(2) activates adenylyl cyclase to produce cAMP, leading to protein kinase A-dependent protein tyrosine phosphorylation.

The Effect of External Nutrient Resources on the Optical Properties and Photosynthetic Efficiency of Stylophora pistillata

Abstract: Enrichment of the hermatypic Red Sea coral Stylophora pistillata with dissolved inorganic nitrogen, inorganic nitrogen+phosphorus, and feeding on Artemia, all led to increases in areal pigmentation in comparison with control colonies. These increases, unlike photoadaptive ones, resulted from growth in cell numbers ranging from $\times $ 2.75 in the Artemia-fed to $\times $ 4.85 in the N+P-enriched corals. The treated corals absorbed 51-85% of incident light, whereas the controls absorbed only 33%. Areal photosynthesis increased with treatment, although to a lesser degree than absorptivity. This difference resulted in reduced photosynthetic efficiencies in the treated colonies. Photosynthetic rates, calculated on a percell basis, were inversely correlated with algal densities, indicating possible competition among the algae for CO$_{2}$.