Optimization Approaches for Solving Large-Scale Personnel Scheduling Problems

Personnel scheduling is one of the most critical components in logistical planning for many practical areas, particularly in transportation, public services, and clinical operations. Because manpower is both an expensive and scarce resource, even a tiny improvement in utilization can provide huge expense savings for businesses. Additionally, a slightly better assignment schedule of the involved professionals can significantly increase their work satisfaction, which can in turn greatly improve the quality of the services customers or patients receive. However, practical personnel scheduling problems (PSPs) are hard to solve because modeling all of the complicated and nuanced requirements and rules is challenging. Moreover, since an iterative construction process may be necessary for handling the multiple-criteria or ill-defined objective nature of many PSPs, the model is expected to be solved in a short time while providing high-quality solutions, despite its large size and complexity. In this dissertation, we propose new models and solution approaches to address these challenges. We study in total three real-world PSPs. We first consider the crew pairing construction for a cargo airline. Each crew pairing is a sequence of flights assigned to a specific line/bid crew to operate in practice. Unlike traditional passenger aviation, due to the cargo airline's underlying network, each crew pairing will specify a complete flying schedule for the assigned crew over the entire planning horizon. Consequently, an extra and unique set of requirements must be incorporated into the construction process. We solve the problem using a delayed column generation framework. We develop a restricted shortest path model to incorporate the entire set of complicated requirements simultaneously and solve it using a labeling algorithm accelerated by a handful of proposed strategies. Computational experiments show that our approach can solve the crew pairing problem in a short time, while almost always delivering an optimal solution. Second, we consider an extension of the previous cargo crew scheduling problem, where a "break" is allowed to take place in the "middle" of each crew pairing. This break feature, working as a special type of conventional deadheading, is expected to significantly increase the flight coverage for practical deployment. However, incorporating this feature will result in an extremely dense underlying network, which introduces new computational challenges. To address this issue, we propose a bidirectional labeling based arc selection approach, which only needs to work on a tiny sub-network each time but can still guarantee the exactness of the delayed column generation process. We demonstrate through real-world instances that our proposed approach can solve this relaxed problem extension in a very short time and the resulting flight coverage will increase by over 30%. Finally, we study a medical resident annual block scheduling problem. We need to assign residents to perform services at different clinical units during each time period across the academic year so that the residents receive appropriate training while the hospital gets staffed sufficiently. We propose a two-stage partial fixing solution framework to address the long runtime issue caused by traditional approaches. A network-based model is also developed to provide a high-quality service selection to initiate this two-stage framework. Experiments using inputs from our clinical collaborator show that our approach can speed up the schedule construction at least 5 times for all instances and even over 100 times for some huge-size ones compared to a widely-used traditional approach.PHDIndustrial & Operations EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/169758/1/jhguo_1.pd

Research on Conflict Point Delay of Left-turning Vehicles at Two Phases Signal Control Intersection

AbstractAnalysis of intersection delay is important for intersection signal timing. Based on the gap acceptance theory, the conflict point delay of left-turning vehicles crossing opposing flow in mixed traffic at two phases signal control intersections is set up with probability theory. Observed values of conflict point delay of left-turning vehicles are compared with the calculated values from the model by choosing some certain intersections in Nanjing. Relationships among conflict point delay of left- turning vehicles, volume of opposing flow and composition of left-turning vehicles has been analyzed. The result shows that the model accords with the actual traffic flow condition at a two phases signal control intersection

What is the Connection Between Issues, Bugs, and Enhancements? (Lessons Learned from 800+ Software Projects)

Agile teams juggle multiple tasks so professionals are often assigned to multiple projects, especially in service organizations that monitor and maintain a large suite of software for a large user base. If we could predict changes in project conditions changes, then managers could better adjust the staff allocated to those projects.This paper builds such a predictor using data from 832 open source and proprietary applications. Using a time series analysis of the last 4 months of issues, we can forecast how many bug reports and enhancement requests will be generated next month. The forecasts made in this way only require a frequency count of this issue reports (and do not require an historical record of bugs found in the project). That is, this kind of predictive model is very easy to deploy within a project. We hence strongly recommend this method for forecasting future issues, enhancements, and bugs in a project.Comment: Accepted to 2018 International Conference on Software Engineering, at the software engineering in practice track. 10 pages, 10 figure

Ginkgo Biloba Extract EGB761 Protects against Aging-Associated Diastolic Dysfunction in Cardiomyocytes of D-Galactose-Induced Aging Rat

The aim of the present study was to make use of the artificially induced aging model cardiomyocytes to further investigate potential anti-aging-associated cellular diastolic dysfunction effects of EGB761 and explore underlying molecular mechanisms. Cultured rat primary cardiomyocytes were treated with either D-galactose or D-galactose combined with EGB761 for 48 h. After treatment, the percentage of cells positive for SA-β-gal, AGEs production, cardiac sarcoplasmic reticulum calcium pump (SERCA) activity, the myocardial sarcoplasmic reticulum calcium uptake, and relative protein levels were measured. Our results demonstrated that in vitro stimulation with D-galactose induced AGEs production. The addition of EGB761 significantly decreased the number of cells positive for SA-β-gal. Furthermore, decreased diastolic [Ca2+]i, curtailment of the time from the maximum concentration of Ca2+ to the baseline level and increased reuptake of Ca2+ stores in the SR were also observed. In addition, the level of p-Ser16-PLN protein as well as SERCA was markedly increased. The study indicated that EGb761 alleviates formation of AGEs products on SERCA2a in order to mitigate myocardial stiffness on one hand; on other hand, improve SERCA2a function through increase the amount of Ser16 sites PLN phosphorylation, which two hands finally led to ameliorate diastolic dysfunction of aging cardiomyocytes

How Extreme Events in China Would Be Affected by Global Warming-Insights From a Bias-Corrected CMIP6 Ensemble

In recent years, concurrent climate extreme conditions (i.e., hot-dry, cold-dry, hot-wet, and cold-wet) have led to various unprecedented natural disasters (e.g., floods, landslide, wildfire, droughts, etc.), causing significant damages to human societies and ecosystems. This is especially true for China where many unprecedented natural disasters have been reported due to the recent warming in local climate. In this paper, we focus on the issue of ultra-extreme events (1‰ threshold) and address how future global warming would affect the climate extreme conditions in China. Specifically, to reduce the uncertainties from models, we use a downscaled and bias-corrected CMIP6 ensemble under two continuously-warming scenarios to evaluate the impact of global warming on ultra-extreme events over China. The results show that, under both SSP245 and SSP585 scenarios, extreme hot conditions would become dominant in most regions of China and some regions are likely to experience over 50 extreme hot days at future warming levels. The frequency of extreme cold events is projected to be small. More frequent extreme hot-wet events with concurrence in the same month and year would be expected for China under the continuously-warming scenarios. This is particularly obvious for the west where more than 6 hot-wet months are likely to take place under future warming scenarios. This may imply that more extreme heat waves and flooding events would coincide in the same month or year for China in the future. For univariate ultra-extreme events, both extreme hot events and extreme wet events would drop by above 25% from 2.0°C to 1.5°C global warming level, particularly under the SSP245 scenario. When the global mean temperature is limited to 1.5°C rather than 2°C, the avoided impacts of hot-wet and cold-wet extremes concurring in the same month will be larger than those of dry-related compound extremes. Overall, the results suggest that slowing down global warming can reduce the frequency of concurrent climate extreme conditions in China, highlighting the importance of immediate action toward carbon emission reduction

Evaluation and projection of precipitation extremes under 1.5 degrees C and 2.0 degrees C GWLs over China using bias-corrected CMIP6 models

China is facing an increasing challenge from severe precipitation-related extremes with accelerating global warming. In this study, using a bias-corrected CMIP6 ensemble, future responses of precipitation extreme indices at 1.5°C and 2.0°C global warming levels (GWLs) under the SSP245, SSP370 and SSP585 scenarios are investigated. Despite different change magnitudes, extreme precipitation events will be more frequent and more intense over China as a whole under higher emissions and GWLs. The increase in annual total precipitation could attribute to a sharp increase in the intensity and days of very heavy precipitation in future global warming scenarios. Limiting global warming to 1.5°C and low emission pathways (i.e., SSP245) instead of 2°C and high emission pathways (i.e., SSP585) would have substantial benefits for China in terms of reducing occurrences of extreme precipitation events

Structure, expression differentiation and evolution of duplicated fiber developmental genes in Gossypium barbadense and G. hirsutum

<p>Abstract</p> <p>Background</p> <p>Both <it>Gossypium hirsutum </it>and <it>G. barbadense </it>probably originated from a common ancestor, but they have very different agronomic and fiber quality characters. Here we selected 17 fiber development-related genes to study their structures, tree topologies, chromosomal location and expression patterns to better understand the interspecific divergence of fiber development genes in the two cultivated tetraploid species.</p> <p>Results</p> <p>The sequence and structure of 70.59% genes were conserved with the same exon length and numbers in different species, while 29.41% genes showed diversity. There were 15 genes showing independent evolution between the A- and D-subgenomes after polyploid formation, while two evolved via different degrees of colonization. Chromosomal location showed that 22 duplicate genes were located in which at least one fiber quality QTL was detected. The molecular evolutionary rates suggested that the D-subgenome of the allotetraploid underwent rapid evolutionary differentiation, and selection had acted at the tetraploid level. Expression profiles at fiber initiation and early elongation showed that the transcripts levels of most genes were higher in Hai7124 than in TM-1. During the primary-secondary transition period, expression of most genes peaked earlier in TM-1 than in Hai7124. Homeolog expression profile showed that A-subgenome, or the combination of A- and D-subgenomes, played critical roles in fiber quality divergence of <it>G. hirsutum </it>and <it>G. barbadense</it>. However, the expression of D-subgenome alone also played an important role.</p> <p>Conclusion</p> <p>Integrating analysis of the structure and expression to fiber development genes, suggests selective breeding for certain desirable fiber qualities played an important role in divergence of <it>G. hirsutum </it>and <it>G. barbadense</it>.</p