Agent-based model of angiogenesis simulates capillary sprout initiation in multicellular networks.

Many biological processes are controlled by both deterministic and stochastic influences. However, efforts to model these systems often rely on either purely stochastic or purely rule-based methods. To better understand the balance between stochasticity and determinism in biological processes a computational approach that incorporates both influences may afford additional insight into underlying biological mechanisms that give rise to emergent system properties. We apply a combined approach to the simulation and study of angiogenesis, the growth of new blood vessels from existing networks. This complex multicellular process begins with selection of an initiating endothelial cell, or tip cell, which sprouts from the parent vessels in response to stimulation by exogenous cues. We have constructed an agent-based model of sprouting angiogenesis to evaluate endothelial cell sprout initiation frequency and location, and we have experimentally validated it using high-resolution time-lapse confocal microscopy. ABM simulations were then compared to a Monte Carlo model, revealing that purely stochastic simulations could not generate sprout locations as accurately as the rule-informed agent-based model. These findings support the use of rule-based approaches for modeling the complex mechanisms underlying sprouting angiogenesis over purely stochastic methods.

Semiconductor-doped-silica saturable-absorber films for solid-state laser mode locking.

We describe a new saturable-absorber materials system for solid-state laser mode locking based on thin, nonepitaxially grown, semiconductor-doped films. We fabricated thin films of InAs semiconductor microcrystalites in silica, using rf sputtering. We could control the linear absorption by varying the film thickness, and the nonlinear absorption saturation cross section and recovery time could be adjusted by use of rapid thermal annealing. The use of 30-nm- thick InAs-doped silica films on sapphire for initiation of Kerr-lens mode locking in a Ti:Al(2)O(3) laser was demonstrated. Pulses as short as 25 fs were generated with a wavelength tuning range from 800 to 880 nm.

Preparing for a JCAHO survey.

With the Joint Commission on Accreditation of Healthcare Organizations' (JCAHO) new Environment of Care (EC) standards now in place, many facilities are struggling to reorganize their programs to meet JCAHO requirements. This document provides practical advice on how to approach a JCAHO survey and what a facilities manager can do to be as fully prepared as possible.

High-resolution transient-double-resonance spectroscopy in SF6.

Four distinct collisionless excitation processes are observed when SF(6) molecules are illuminated simultaneously by "weak" continuously tunable cw probe radiation and by "strong" pulsed-pump radiation. These processes are identified by studying the line shape, frequency, and temporal decay of the change in transmitted probe intensity induced by the pump pulse. The significance of this work for the spectroscopy of high vibrational levels and for collisionless dissociation is discussed briefly.

Blood patch for spinal headache. A recurrence and a complication.

The management of a patient is described who has a blood patch for spinal headache, but who had a recurrence of symptoms 1 day later which was successfully treated by a second patch. A second case is described in which there was a second dural puncture immediately prior to the blood patch and, immediately following the blood patch, the patient complained of severe debilitating 'paralysing' pain in both legs. This pain was of short duration and the blood patch was successful. Some further observations on the use of a blood patch are recorded.