Abstract Planning of operations, such as routing of vehicles, is often performed repetitively in rea-world settings, either by humans or algorithms solving mathematical problems. While humans build experience over multiple executions of such planning tasks and are able to recognize common patterns in different problem instances, classical optimization algorithms solve every instance independently. Machine learning (ML) can be seen as a computational counterpart to the human ability to recognize patterns based on experience. We consider variants of the classical Vehicle Routing Problem with Time Windows and Capacitated Vehicle Routing Problem, which are based on the assumption that problem instances follow specific common patterns. For this problem, we propose a ML-based branch and price framework which explicitly utilizes those patterns. In this context, the ML models are used in two ways: (a) to predict the value of binary decision variables in the optimal solution and (b) to predict branching scores for fractional variables based on full strong branching. The prediction of decision variables is then integrated in a node selection policy, while a predicted branching score is used within a variable selection policy. These ML-based approaches for node and variable selection are integrated in a reliability-based branching algorithm that assesses their quality and allows for replacing ML approaches by other (classical) better performing approaches at the level of specific variables in each specific instance. Computational results show that our algorithms outperform benchmark branching strategies. Further, we demonstrate that our approach is robust with respect to small changes in instance sizes.
Archival data storage plays a critical role in data preservation as almost all current data will eventually be archived. In addition, the demands placed on archival storage tiers are growing because of large regularly-scheduled backups. Archival storage tiers usually consist of tape-based devices with a large storage capacity, but limited I/O performance for retrieving data, especially when multiple retrieval requests are made simultaneously. The cost of disk-based devices continues to decrease while the capacity of individual disks increases so that disk-based systems are a realistic option for enterprise archival storage tiers. Optimization approaches can design archival storage systems with the best mix of small, low-cost machines and larger, expensive machines, but only if various metrics of the candidate machines are well-understood. This paper investigates the measurement of different classes of enterprise servers when utilized by a distributed file system. Our study primarily concerns the possible use of these servers within a disk-based archival storage system and produces measurements suitable for immediate use in the optimization-driven design of archival storage. Observing patterns from these measurements also enables us to predict metrics for other enterprise servers and then incorporate these alternative servers in the design process. We combine our measurements and predictions with an optimization engine to discover an ideal building block for a 500TB archival storage system.
Little is known about tibial bone remodeling with TKA and its clinical relevance. We performed a randomized clinical trial to compare tibial bone density changes in cemented components with different bearing designs. Bone density changes were assessed using quantitative computed tomography (qCT)-assisted osteodensitometry. Twenty-eight rotating-platform and 26 fixed-platform cemented TKAs were included. The nonoperated contralateral side was used as a control. CT scans were performed postoperatively and 1 year and 2 years after the index operation. Cancellous bone density loss (up to 12.6% at 2 years) was observed in all proximal tibial regions in both cohorts. In contrast, we found lower cortical bone density loss (up to 3.6% at 2 years). We found no differences in bone loss between fixed- and rotating-platform implants. The decrease of cancellous bone density after TKA suggests stress transfer to the cortical bone.
Background: Current trends in the treatment of idiopathic clubfoot have shifted from extensive surgical release to more conservative techniques. The purpose of the present study was to prospectively compare the results of the Ponseti method with those of surgical releases for the correction of clubfoot deformity. Methods: We prospectively compared patients who had idiopathic clubfoot deformities that were treated at a single institution either with the Ponseti method or with below-the-knee casting followed by surgical release. The clinical records of the patients with a minimum duration of follow-up of two years were reviewed. All scheduled and completed operative interventions and associated complications were recorded. Results: Fifty-five patients with eighty-six clubfeet were treated; forty feet were included in the group that was treated with the Ponseti method, and forty-six feet were included in the group that was treated with below-the-knee casts followed by surgery (with three of these feet requiring casting only). There was no difference between the groups in terms of sex, ethnicity, age at the time of first casting, pretreatment Pirani score (average, 5.2 in both groups), or family history. The average number of casts was six in the Ponseti group and thirteen in the surgical group. Of the feet that were treated with below-the-knee casts, forty-three underwent surgery, with forty-two undergoing major surgery (posterior release [eleven] or posteromedial release [thirty-one]). In the Ponseti group, fourteen feet required fifteen operative interventions for recurrences, with only one foot requiring revision surgery. Four of these fifteen were major (necessitating posterior [one] or posteromedial release [three]) while eleven were minor. Thirteen feet in the surgical group required fourteen surgical revisions. Two postoperative complications were seen in each group. Conclusions: While both cohorts had a relatively high recurrence rate, the Ponseti cohort was managed with significantly less operative intervention and required less revision surgery. The Ponseti method has now been adopted as the primary treatment for clubfoot at our institution. Level of Evidence: Therapeutic Level II. See Instructions to Authors for a complete description of levels of evidence.
Background: Nonoperative treatment of idiopathic clubfoot has become increasingly accepted worldwide as the initial standard of care. The Ponseti method has become particularly popular as a result of published short and long-term success rates in North America. The purpose of the current study was to examine the early rate of clubfoot recurrence following the use of the Ponseti treatment method in a New Zealand population and to analyze patient characteristics to identify factors predictive of recurrence. Methods: Fifty-one consecutive babies with a total of seventy-three clubfeet treated by the Ponseti technique were followed prospectively for a minimum of two years from the start of treatment. Recurrence, defined as the need for any subsequent operative treatment, was analyzed with respect to the severity at presentation, the time of presentation, the number of casts needed to obtain the initial correction, any family history of clubfoot, ethnicity, and the compliance with postcorrection abduction bracing. Recurrence was classified as minor, defined as requiring a tendon transfer or an Achilles tendon lengthening, or major, defined as requiring a full posterior or posteromedial surgical release to achieve a corrected plantigrade foot. Results: Twenty-one (41%) of the fifty-one patients had a recurrence, which was major in twelve of them and minor in nine. The parents of twenty-six babies (51%) complied with the abduction bracing protocol, and only three of these children had a major recurrence. Compliance with abduction bracing was associated with the greatest risk reduction for recurrence (odds ratio, 0.2; p = 0.009). When the parents had not complied with the bracing protocol, the patient had a five times greater chance of having a recurrence. With the numbers studied, no significant relationships were found between recurrence and the severity at presentation, the time of presentation, the number of casts needed to obtain correction, ethnicity, or a family history of clubfoot. Conclusions: Compliance with the postcorrection abduction bracing protocol is crucial to avoid recurrence of a clubfoot deformity treated with the Ponseti method. When the parents comply with the bracing protocol, the Ponseti method is very effective at maintaining a correction, although minor recurrences are still common. When the parents do not comply with the bracing protocol, many major and minor recurrences should be expected. Level of Evidence: Prognostic Level II. See Instructions to Authors for a complete description of levels of evidence.
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