Towards performance control on the Grid.

Advances in computational Grid technologies are enabling the development of simulations of complex biological and physical systems. Such simulations can be assembled from separate components--separately deployable computation units of well-defined functionality. Such an assemblage can represent an application composed of interacting simulations or might comprise multiple instances of a simulation executing together, each running with different simulation parameters. However, such assemblages need the ability to cope with heterogeneous and dynamically changing execution environments, particularly where such changes can affect performance. This paper describes the design and implementation of a prototype performance control system (PerCo), which is capable of monitoring the progress of simulations and redeploying them so as to optimize performance. The ability to control performance by redeployment is demonstrated using an assemblage of lattice Boltzmann simulations running with and without control policies. The cost of using PerCo is evaluated and it is shown that PerCo is able to reduce overall execution time.

Comparison of oral and intramuscular preanesthetic medication for pediatric inpatient surgery.

The child's fear of injections coupled with the concern that the psychologic advantage of intramuscular premedication may be all or in part negated by the trauma of injections prompted the authors to seek an oral preanesthetic medication to safely and reliably replace injections. The authors describe the results of a prospective, randomized, double-blind study comparing the pharmacologic effects of oral versus injectable preanesthetic medication in 67 healthy pediatric inpatients older than 1 yr. Children given the oral medication (meperidine 3.0 mg/kg, pentobarbital 4.0 mg/kg) were significantly more drowsy in the holding area (P less than 0.001) and more cooperative at the time of induction of anesthesia (P less than 0.01) than the children given intramuscular medication (morphine 0.1 mg/kg, pentobarbital 4.0 mg/kg). There were no other differences between the two groups. These data demonstrate that oral preanesthetic medication can be as or more effective compared with intramuscular medication in producing the desired effects without adverse side effects. As a result of this study, the benefits of preanesthetic medication can now be achieved in nearly all surgical patients without injections.

Further evidence for local osmotic coupling in the rabbit cornea.

1. The present experiments measure net fluxes of fluid, Cl- and HCO-3 across de-epithelialised rabbit corneas clamped between half chambers and bathed in Ringer solutions. 2. Net fluxes of HCO-3 and fluid occurred together across the cornea from stroma to aqueous when HCO-3 and CO2 were present in the bathing solution. 3. No net trans-corneal C1-flux was found 4. The initiation of fluid flow in the presence of HCO-3 and CO2 cannot be accounted for by bulk-phase osmotic flow across the cornea.

Intercellular spaces in chemically fixed corneal endothelia are related to solute pump activity not to solvent coupling.

1. Stereological analyses of the lateral intercellular spaces in the endothelium of rabbit corneas after chemical fixation were undertaken. 2. Immediately preceding chemical fixation the endothelia were in one of four transport modes: (a) bicarbonate pump activated and no coupled solvent flux, (b) bicarbonate pump activated and, coupled to it, a solvent flux, (c) no fluxes across the endothelia and (d) passive fluid fluxes across the endothelia. 3. In each transport mode, the intercellular spaces were measured after immersion in a series of fixatives in which the concentration of buffer (sodium cacodylate) was increased. 4. Lateral intercellular spaces were a function of buffer concentration in the fixative and activity of the bicarbonate pump. They were not a function of either solvent coupling or passive solvent flow. 5. It is concluded that the characteristic changes of lateral intercellular spaces, when transport is inhibited, do not indicate the site of local osmotic coupling.

Local osmotic coupling to the active trans-endothelial bicarbonate flux in the rabbit cornea.

The present experiments investigate HCO3-, Cl- and fluid fluxes across partially destromalised corneas. Although there is no net flux of Cl-, there is a net flux of HCO-3 across the endothelium from stromal side to aqueous side which is accompanied by a flux of water in the same direction. Bulk phase osmosis cannot account for the initiation of the flux of fluid. Local osmotic coupling between ions and water is postulated to occur in the preparation. The exudate is hypertonic to the bathing Ringer solution.