45 research outputs found
Combined ship routing and inventory management in the salmon farming industry
We consider a maritime inventory routing problem for Norway's largest salmon farmer both producing the feed at a production factory and being responsible for fish farms located along the Norwegian coast. The company has bought two new ships to transport the feed from the factory to the fish farms and is responsible for the routing and scheduling of the ships. In addition, the company has to ensure that the feed at the production factory as well as at the fish farms is within the inventory limits. A mathematical model of the problem is presented, and this model is reformulated to improve the efficiency of the branch-and-bound algorithm and tightened with valid inequalities. To derive good solutions quickly, several practical aspects of the problem are utilized and two matheuristics developed. Computational results are reported for instances based on the real problem of the salmon farmer
Long‐term effects of short planning horizons for inventory routing problems
This paper presents a detailed study concerning the importance of the planning horizon when solving inventory routing problems (IRPs). We evaluate the quality of decisions obtained by solving a finite-horizon IRP. We also discuss the relevance of explicitly considering profit maximization models rather than the traditional cost minimization variant. As a means to this end, we describe four classes of the IRP corresponding to different types of markets. Two of them lead to nonlinear models, which are linearized. Furthermore, we provide a deterministic simulator to evaluate the long-term effects arising from using planning horizons of varying lengths when solving the IRP. A computational study is performed on cases generated from benchmark data instances. The results confirm that the long-term performance of the IRP decisions is, in part, contingent on the length of the selected planning horizon. They also show that considering profit maximization instead of cost minimization leads to different decisions, generating considerably more revenue and profits, albeit not nearly as much as suggested by individual solutions to static IRPs with short planning horizons. Keywords: profit maximization, path flow, linearization, end effect, simulatio
Timing of hip hemiarthroplasty and the influence on prosthetic joint infection
Introduction
Previous research suggested that patients have increased risk of infection with increased
time from presentation with a femoral neck fracture to treatment with a hip hemiarthroplasty
(HHA). The purpose of this study was to determine if rates of prosthetic joint infections within
3 months of surgery was affected by the time from patient presentation with a femoral neck
fracture to the time of treatment with HHA.
Materials and methods
Acute hip fractures treated with HHA between 2005 and 2017 at three centres in Norway
were enrolled in the study. Multi-trauma patients were excluded. Univariable analysis was
performed to determine any significant effect of pre-operative waiting time on infection rate.
Two pre-planned analyses dichotomizing pre-operative waiting time cut-offs were performed.
Results
There were 2300 patients with an average age of 82 (range, 48–100) years included of
which 3.4% experienced a prosthetic joint infection within 3 months. The primary analysis
found no significant difference in infection rate depending on time to surgery (OR = 1.06
(95% CI 0.94–1.20, p = 0.33)). The secondary analyses showed no significant differences in
infection rates when comparing pre-operative waiting time of <24 hours vs �24 hours (OR =
0.92 (95% CI 0.58–1.46, p = 0.73)) and <48 hours vs �48 hours (OR = 1.39 (95% CI 0.81–
2.38, p = 0.23)).
Conclusion
Based off of a large retrospective Norwegian database of hip fractures there did not appear
to be a significant difference in infection rate based on pre-operative wait time to surgery