Using Branch-and-Price to Find High Quality Solutions Quickly

We develop an exact solution approach for integer programs that produces high- quality solutions quickly by solving well-chosen restrictions of the problem. Column generation is used both for generating these problem restrictions and for producing bounds on the value of an optimal solution to the problem. Obtaining primal solutions by solving problem restrictions also provides an easy way to search for improved solutions in the neighborhood of the current best solution. The overall approach is parallelized and computational experiments demonstrate its efficacy. An application to inventory routing is presented

Planning Strategies for Home Health Care Delivery

In home health care, continuity of care, wherein a patient is always visited by the same nurse, can be just as important as cost, as it is closely correlated to quality of care. While a patient typically receives care for two to three months, such that assigning a nurse to a patient impacts operations for lengthy periods of time, previous research focusing on continuity of care uses planning horizons that are often a week or shorter. This paper computationally demonstrates that considering a long planning horizon in this setting has significant potential for savings. Initially, a deterministic setting is considered, with all patient requests during the planning horizon known a priori, and the routing cost of planning for two to three months is compared with the cost when planning is done on a weekly basis. With inherent uncertainty in planning for such a long time horizon, a methodology is presented that anticipates future patient requests that are unknown at the time of planning. Computational evidence shows that its use is superior to planning on a weekly basis under uncertainty

Enabling Greater Access to Home Meal Delivery

Non-profit organizations like the Meals on Wheels (MOW) association of America prepare and deliver meals, typically daily, to approximately one million homebound citizens in the United States alone. However, many MOW agencies are facing a steadily increasing number of clients requesting meal service without an increase in resources (either financial or human). One strategy for accommodating these requests is to deliver multiple (frozen) meals at a time and thus make fewer delivers. However, many of the stakeholders (funders, volunteers, meal recipients) value the relationships that are developed by having a client receive daily deliveries from the same volunteer. Further, meal recipients may be concerned with the quality of the food delivered through a frozen meal. In this paper, we develop a method for introducing consolidation into home meal delivery while minimizing operational disruptions and maintaining client satisfaction. With an extensive computational study, the savings associated with various levels and types of disruptions are detailed

Not quite cooking on gas: Understanding biogas plant failure and abandonment in Northern Tanzania

The potential for biogas to fulfil an integral role in promoting sustainable energy solutions, particularly in the Global South, is evident, and especially pertinent in the Sustainable Development Goal era. Internationally, multiple initiatives driven by private, public and third sectors have resulted in a significant growth in the numbers of biogas plants constructed. These processes are highly visible in Tanzania which has witnessed considerable investment across the sector in recent decades leading to a proliferation of biogas systems. However, research suggests that many of these plants experience failures which can lead to the ultimate abandonment of the systems, eroding the potential benefits of widespread biogas adoption. This research explores some of the main drivers of biogas plant failure and abandonment in the northern Tanzania through a rapid review of the literature identifying current sector best practice and a series of semi-structed interviews with key stakeholders including biogas plant owners, operators, constructors, government officials and private enterprises. Our analysis reveals a range of clear and, at points, interrelated themes associated with biogas failure which can be largely grouped under the following banners; poor construction and installation, sub-optimal feeding practices, operation and maintenance issues, and training provision and knowledge erosion. By illuminating the subtleties surrounding each challenge, this paper is designed to stimulate a re-evaluation of how long-term, sustained and successful use of biogas plants can be fostered through a reduction in failure and/or abandonment. This is particularly important given that the biogas sector continues to evolve and expand across the globe. Response to Reviewers: We thank all the editors and reviewers for their comments, please see the "detailed response to reviewers" for our specific and individual responses. Thanks you for helping significantly increase the quality of this paper

Hybrid life-cycle assessment for robust, best-practice carbon accounting

In order to meet internationally agreed targets for avoiding dangerous anthropogenic climate change, an absolute priority for global society is to rapidly stabilise and then reduce carbon dioxide emissions into the atmosphere. Any entity, be it individual, company, or nation state, is more able to reduce its carbon dioxide (and other greenhouse gas) emissions if these can be quantified and attributed and the effects of interventions estimated. The current state of product and supply chain carbon accounting methods does not consistently meet the standards required to tackle this global challenge. This study therefore aims to identify key methodological practices affecting the accuracy of carbon accounting models and in particular to assess the effects of the system boundaries they employ. Models currently available for estimating carbon emissions are either input-output based (using macro-economic analysis), process-based (using specific carbon emissions attributes through the life-cycle of a product, service or event), or a hybrid of the two. Here, a detailed comparison has been made between various input-output and process-based models and the results compared with those from a hybrid model that was taken to represent ‘best practice’ in carbon accounting. Key factors affecting accuracy were found to lie in: the detail of methodological decisions for input-output models, the economic region or regions upon which the model is based, and the quality, disaggregation and, especially for price-volatile products, the temporal alignment of the data. The relative significance of these factors is explored. For copper wire, a system boundary gap analysis was conducted on an industry-leading process-based model (GREET.net) compared with a complete system as described by the best performing input-output model. GREET.net was found to suffer a 60% truncation error. The copper wire example demonstrates the practicality of substituting process-based analysis into input-output based supply chain emissions assessments

Finance and the improved cookstove sector in East Africa: barriers and opportunities for value-chain actors

Despite a long history of diverse approaches designed to increase the adoption of improved cookstoves (ICS), multiple barriers continue to exist which stunt their uptake in many developing countries. This paper focuses specifically on the financial barriers facing actors within the ICS value chain, such as manufacturers, suppliers and distributors. Examining data from interviews with twenty nine ICS enterprises in Kenya and Uganda, this paper finds that limited access to credit services is a substantial barrier to increasing the capacity of businesses within the ICS value chain. In addition, data from twenty-seven financial providers including banks, microfinance institutions and savings and credit co-operatives (SACCOs) viewed the ICS market as relatively underserved and believed greater integration could be mutually beneficial. This paper explores the way in which this relationship plays out in current market conditions and how connections between the two sectors can be strengthened, with the objective of overcoming these financial challenges and expanding the capacity of ICS businesses as a mechanism to facilitate ICS uptake by local populations