Two universality classes for random hyperbranched polymers

We grow AB₂ random hyperbranched polymer structures in different ways and using different simulation methods. In particular we use a method of ad hoc construction of the connectivity matrix and the bond fluctuation model on a 3D lattice. We show that hyperbranched polymers split into two universality classes depending on the growth process. For a “slow growth” (SG) process where monomers are added sequentially to an existing molecule which strictly avoids cluster–cluster aggregation the resulting structures share all characteristic features with regular dendrimers. For a “quick growth” (QG) process which allows for cluster–cluster aggregation we obtain structures which can be identified as random fractals. Without excluded volume interactions the SG model displays a logarithmic growth of the radius of gyration with respect to the degree of polymerization while the QG model displays a power law behavior with an exponent of 1/4. By analyzing the spectral properties of the connectivity matrix we confirm the behavior of dendritic structures for the SG model and the corresponding fractal properties in the QG case. A mean field model is developed which explains the extension of the hyperbranched polymers in an athermal solvent for both cases. While the radius of gyration of the QG model shows a power-law behavior with the exponent value close to 4/5, the corresponding result for the SG model is a mixed logarithmic–power-law behavior. These different behaviors are confirmed by simulations using the bond fluctuation model. Our studies indicate that random sequential growth according to our SG model can be an alternative to the synthesis of perfect dendrimers

Comparison of the effects of intravenous and oral montelukast on airway function: a double blind, placebo controlled, three period, crossover study in asthmatic patients

BACKGROUND—Montelukast, a leukotriene receptor antagonist, improves parameters of asthma control including forced expiratory volume in one second (FEV(1)) when given orally to patients aged six years or older. This study was undertaken to compare the effect on FEV(1) of intravenous and oral montelukast and placebo during the 24hour period following administration.
METHODS—Fifty one asthmatic patients (FEV(1) 40-80% predicted and ⩾15% improvement after inhaled β agonist) were enrolled in a double blind, single dose, three period, crossover study to receive intravenous montelukast (7 mg), oral montelukast (10 mg), or placebo in a randomised fashion. The primary end point was area under the curve (AUC)(0-24 h) of the percentage change from baseline in FEV(1). Additional end points were maximum percentage change in FEV(1) and percentage change at different time points.
RESULTS—Compared with placebo, intravenous and oral montelukast significantly increased the AUC(0-24 h) (means of 20.70%, 15.72%, and 7.75% for intravenous, oral and placebo, respectively; no statistical difference between intravenous and oral). The difference in least square means from placebo for intravenous montelukast was 13.27% (95% CI 7.07 to 19.46), p<0.001 and for oral montelukast was 7.44% (95% CI 1.20 to 13.68), p = 0.020. The maximum percentage change in FEV(1) was not significantly different for intravenous and oral montelukast (difference in least square means 6.78% (95% CI -0.59 to 14.15), p = 0.071). The mean percentage change in FEV(1) for intravenous montelukast was greater than for oral montelukast within the first hour (15.02% vs 4.67% at 15 min, p⩽0.001; 18.43% vs 12.90% at one hour, p<0.001 for intravenous and oral montelukast, respectively (placebo 3.05% at 15 minutes, 7.33% at one hour). Intravenous and oral montelukast were similar to placebo in the frequency of adverse events.
CONCLUSIONS—The onset of action for intravenous montelukast was faster than for oral montelukast and the improvement in airway function lasted over the 24 hour observation period for both treatments. Although not well understood, there was a trend toward a greater improvement in FEV(1) with intravenous than with oral montelukast. These findings suggest that leukotriene receptor antagonists should be investigated as a treatment for acute severe asthma.


A Service Architecture for Context Awareness and Reaction Provisioning

Context awareness has emerged as an important element in distributed computing. It offers mechanisms allowing applications to be aware of their environment and enabling them to adjust their behavior to the current context. In order to keep track of the relevant context information, a flexible service mechanism should be available for the client applications. In this paper we present a service architecture to provide context-awareness capabilities to users and client applications. Moreover, the service is able to react depending on the user’s preferences and context. The conditions for the reaction and the reaction itself are defined in rules the users submit to the service by means of a convenient rule language