In this paper, we introduce a new concept of semi-preemptive scheduling and we show how it can be used to derive a maximum‡ow based lower bound for the P=rj=Lmax which dominates the well-known preemptive lower bound. We show that, in some cases the proposed bound strictly dominates the preemptive one while having the same complexity.

introduction: several mehods have been proposed to alleviate pain after hysterectomy. pre-emptive analgesia has been used to relieve pain following abdominal hysterectomy with conflicting results. this study was performed to evaluate the efficacy of pre-incision skin infiltration of lidocaine in relieving postoperative pain in patients undergoing abdominal hysterectomy.  methods: 60 patients wi...

Background and Objective: Post-operative nausea and vomiting (PONV) is a common adverse effect of the anesthesia in laparoscopic surgery. Ondansetron has been used for prevention and treatment of the PONV. The purpose of the present study was to compare the effects of preemptive and preventive intravenous ondansetron on PONV in patients undergoing diagnostic gynecologic laparoscopy. Materials &...

We investigate the problem of scheduling the maintenance of edges in a network, motivated by the goal of minimizing outages in transportation or telecommunication networks. We focus on maintaining connectivity between two nodes over time; for the special case of path networks, this is related to the problem of minimizing the busy time of machines. We show that the problem can be solved in polyn...

In the recent years, constraint programming has been applied to a wide variety of academic and industrial non-preemptive scheduling problems, i.e., problems in which activities cannot be interrupted. In comparison, preemptive scheduling problems have received almost no attention from both the Operations Research and the Artificial Intelligence community (see, for example, (Demeulemeester, 1992)...

BACKGROUND Information to guide the timing of a second kidney transplantation is limited. METHODS We compared outcomes of 3509 preemptive and 14,075 nonpreemptive second kidney transplant recipients in the U.S. Renal Data System between 1995 and 2007. RESULTS Preemptive recipients had less acute rejection (12% vs. 16%; P<0.0001) and delayed graft function (8% vs. 23%; P<0.0001). Preemptive ...

We design an algorithm of the best possible competitive ratio for preemptive and non-preemptive scheduling of unit size jobs with rejection on three identical machines. The algorithm does not use preemption even for the preemptive variant, and it has the interesting feature that one of its parameters is not fixed in advance, and it is defined based on the properties of the first input job havin...