Regenerative process

Abstract: During hematoma formation following injury, an inflammatory reaction ensues as an initial step in the healing process. As granulation tissue matures, revascularization is a prerequisite for successful healing. The hypothesis of this study was that scarless tissue reconstitution in the regenerative bone healing process is dependent on a balanced immune reaction that initiates revasculatory steps. To test this hypothesis, cellular composition and expression profiles of a bone hematoma (regenerative, scarless) was compared with a muscle soft tissue hematoma (healing with a scar) in a sheep model. Upregulation of regulatory T helper cells and anti-inflammatory cytokine expression (IL-10) coincided with an upregulation of angiogenic factors (HIF1α and HIF1α regulated genes) in the regenerative bone hematoma but not in the soft tissue hematoma. These results indicate that the timely termination of inflammation and early onset of revascularization are interdependent and essential for a regenerative healing process. Prolonged pro-inflammatory signaling occurring in a delayed bone-healing model supports the finding that timely termination of inflammation furthers the regenerative process. Differing cellular compositions are due to different cell sources invading the hematoma, determining the ensuing cytokine expression profile and thus paving the path for regenerative healing in bone or the formation of scar tissue in muscle injury.

Abstract: Liver regeneration after partial hepatectomy is the only example of a regenerative process in mammals in which the organ/body weight ratio returns to 100% of the original when the process is complete. The adjustment of liver weight to the needs of the body suggests a complicated set of control points, a ‘hepatostat’. There has been much progress in elucidation of mechanisms involved in initiation of liver regeneration. More recent studies have focused on termination pathways, because these may be the underlying controls of the hepatostat and their elimination may be relevant to hepatic neoplasia. When the standard regenerative process is thwarted due to failure of either hepatocytes or biliary epithelial cells to proliferate, each of the two epithelial compartments can function as a source of facultative stem cells for the other.

Abstract: Using some well-known and some recently proved asymptotic properties of regenerative processes, we present a new proof in a general regenerative setting of the equivalence of the limiting distributions of a stochastic process at an arbitrary point in time and at the time of an event from an associated Poisson process. From the same asymptotic properties, several conservation equations are derived that hold for a wide class of GI/G/1 priority queues. Finally, focussing our attention on the alternating-priority queue with Poisson arrivals, we use both types of result to give a new, simple derivation of the expected steady-state delay in the queue in each class.

Abstract: In this paper the author continues his study of the regenerative method for analyzing simulations of stable stochastic systems. The principal concern is to estimate the quantiles of the stationary distribution of a regenerative process. Markov chains in discrete or continuous time and multiple server queues in light traffic provide concrete examples of regenerative processes to which this technique applies. Approximate confidence intervals for these quantiles are derived from appropriate central limit theorems. The method has been applied to three stochastic simulations, and the numerical results are presented.