Asymptotic independence of regenerative processes with a special dependence structure

Queueing Systems - We identify some conditions under which regenerative processes with a certain dependence structure among them are asymptotically independent. The result is applied to various...     

Nystatin—dextran conjugates: Synthesis and characterization

The coupling of nystatin (Nys), a water-insoluble antifungal agent, to dextran via an imine or amine bond was systematically investigated. Dextran was first oxidized to dialdehyde dextran using potassium periodate, purified from the oxidizing agent, and reacted with Nys to form the Schiff base. The Schiff base was reduced to the amine using borohydride. All reactions took place in water. The purification of the oxidized dextran from the oxidizing agent was essential to prevent oxidative degradation of Nys at the coupling step. The effects on the coupling yield of the following factors: dextran molecular weight, degree of oxidation (aldehyde content), Nys to dextran ratio, temperature, and reaction pH were studied. A 95% coupling yield was obtained at the optimized coupling conditions: pH 8.9 ± 0.1, 50% degree of oxidation, and initial ratio of Nys to dialdehyde dextran 1:2.5. In all experiments, dextran was decreased in molecular weight during the oxidation step. Both imine and amine forms of Nys-dextran conjugates were soluble in water and exhibited improved stability in aqueous solutions as compared to the unbound drug. The conjugates showed comparable minimum inhibitory concentration (MIC) values against Candida albicans and Cryptococcus neoformans. The conjugates were about 25 times less toxic than free Nys after a single injection in mice. © 1996 John Wiley & Sons, Inc.     

Limited sensitivity to analyticity: a manifestation of quantum chaos

Classical Hamiltonian systems generally exhibit an intricate mixture of regular and chaotic motions on all scales of phase space. As a nonintegrability parameter K (the “strength of chaos”) is gradually increased, the analyticity domains of functions describing regular-motion components [e.g., Kolmogorov-Arnol’d-Moser (KAM) tori] usually shrink and vanish at the onset of global chaos (breakup of all KAM tori). It is shown that these phenomena have quantum-dynamical analogs in simple but representative classes of model systems, the kicked rotors and the two-sided kicked rotors. Namely, as K is gradually increased, the analyticity domain ℛ_QE of the quantum-dynamical eigenstates decreases monotonically, and the width of ℛ_QE in the global-chaos regime vanishes in the semiclassical limit. These phenomena are presented as particular aspects of a more general scenario: As K is increased, ℛ_QE gradually becomes less sensitive to an increase in the analyticity domain of the system.     

Empirical extraction of mechanisms underlying real world network generation

The generation mechanisms of real world networks have been described using multiple models. The mathematical features of these models are usually extrapolated from statistical properties of a snapshot of these networks. We here propose an alternative method based on direct measurement of a sequence of consecutive snapshots to uncover the dynamics underlying real world generation. We assume that the probability of adding a node or an edge depends only on local features surrounding the newly added node/edge, and directly measure the contribution of these features to the node/edge addition probability. These measurements are performed using newly defined N-node local structures. Each N-node local structure represents the configuration of edges surrounding a newly added edge. The N-node local structure measurements reproduce for some networks the now classical addition of edges between high degree node mechanisms. It also provides quantitative estimates of more complex mechanisms driving other networks’ evolution, such as the effect of common first and second neighbors. This new methodology reveals the relative importance of different generation mechanisms. We show, for example, that the main mechanism driving hyperlink addition between two websites is the existence of a third website linking to both the source and the target of the new hyperlink.     

Regulation of a single-server queue with customers who dynamically choose their service durations

Queueing Systems - In recent years, there is a growing attention towards queueing models with customers who choose their service durations. The model assumptions in the existing literature imply...