Optimal Service Time Windows

Because customers must usually arrange their schedules to be present for home services, they desire an accurate estimate of when the service will take place. However, even when firms quote large service time windows, they are often missed, leading to customer dissatisfaction. Wide time windows and frequent failures occur because time windows must be communicated to customers in the face of several uncertainties: future customer requests are unknown, final service plans are not yet determined, and when fulfillment is outsourced to a third party, the firm has limited control over routing procedures. Even when routing is performed in-house, time windows typically do not receive explicit consideration. In this paper, we show how companies can communicate reliable and narrow time windows to customers in the face of arrival time uncertainty. Under mild assumptions, our main result characterizes the optimal policy, identifying structure that reduces a high-dimensional stochastic non-linear optimization problem to a root-finding problem in one dimension. The result inspires a practice-ready heuristic for the more general case. Relative to the industry standard of communicating uniform time windows to all customers, and to other policies applied in practice, our method of quoting customer-specific time windows yields a substantial increase in customer convenience without sacrificing reliability of service, providing results that nearly achieve the lower bound on the optimal solution. Our results show that (i) time windows should be tailored to individual customers, (ii) time window sizes should be proportional to the service level, (iii) larger time windows should be assigned to earlier requests and smaller time windows to later requests, (iv) larger time windows should be assigned to customers further from the depot of operation and smaller time windows to closer customers, and (v) two time windows for one customer are helpful in some cases

Dynamic Orienteering on a Network of Queues

Abstract We propose a stochastic orienteering problem on a network of queues with time windows at customers. While this problem is of wide applicability, we study it in the context of routing and scheduling a textbook salesperson who visits professors on campus to gain textbook adoptions. The salesperson must determine which professors to visit and how long to wait in queues at each professor. We model the problem as a Markov decision process (MDP) with the objective of maximizing expected sales. We investigate the existence of optimal control limits and examine conditions under which certain actions cannot be optimal. To solve the problem, we propose an approximate dynamic programming approach based on rollout algorithms. The method introduces a two-stage heuristic estimation that we refer to as compound rollout. In the first stage, the algorithm decides whether to stay at the current professor or go to another professor. If departing the current professor, it chooses the professor to whom to go in the second stage. We demonstrate the value of our modeling and solution approaches by comparing the dynamic policies to a-priori-route solutions with recourse actions

Key ethical issues discussed at CDC-sponsored international, regional meetings to explore cultural perspectives and contexts on pandemic influenza preparedness and response

Background: Recognizing the importance of having a broad exploration of how cultural perspectives may shape thinking about ethical considerations, the Centers for Disease Control and Prevention (CDC) funded four regional meetings in Africa, Asia, Latin America, and the Eastern Mediterranean to explore these perspectives relevant to pandemic influenza preparedness and response. The meetings were attended by 168 health professionals, scientists, academics, ethicists, religious leaders, and other community members representing 40 countries in these regions. Methods: We reviewed the meeting reports, notes and stories and mapped outcomes to the key ethical challenges for pandemic influenza response described in the World Health Organization’s (WHO’s) guidance, Ethical Considerations in Developing a Public Health Response to Pandemic Influenza: transparency and public engagement, allocation of resources, social distancing, obligations to and of healthcare workers, and international collaboration. Results: The important role of transparency and public engagement were widely accepted among participants. However, there was general agreement that no “one size fits all” approach to allocating resources can address the variety of economic, cultural and other contextual factors that must be taken into account. The importance of social distancing as a tool to limit disease transmission was also recognized, but the difficulties associated with this measure were acknowledged. There was agreement that healthcare workers often have competing obligations and that government has a responsibility to assist healthcare workers in doing their job by providing appropriate training and equipment. Finally, there was agreement about the importance of international collaboration for combating global health threats. Conclusion: Although some cultural differences in the values that frame pandemic preparedness and response efforts were observed, participants generally agreed on the key ethical principles discussed in the WHO’s guidance. Most significantly the input gathered from these regional meetings pointed to the important role that procedural ethics can play in bringing people and countries together to respond to the shared health threat posed by a pandemic influenza despite the existence of cultural differences

Spin Foam Models of Riemannian Quantum Gravity

Using numerical calculations, we compare three versions of the Barrett-Crane model of 4-dimensional Riemannian quantum gravity. In the version with face and edge amplitudes as described by De Pietri, Freidel, Krasnov, and Rovelli, we show the partition function diverges very rapidly for many triangulated 4-manifolds. In the version with modified face and edge amplitudes due to Perez and Rovelli, we show the partition function converges so rapidly that the sum is dominated by spin foams where all the spins labelling faces are zero except for small, widely separated islands of higher spin. We also describe a new version which appears to have a convergent partition function without drastic spin-zero dominance. Finally, after a general discussion of how to extract physics from spin foam models, we discuss the implications of convergence or divergence of the partition function for other aspects of a spin foam model.Comment: 23 pages LaTeX; this version to appear in Classical and Quantum Gravit

Commuting Simplicity and Closure Constraints for 4D Spin Foam Models

Spin Foam Models are supposed to be discretised path integrals for quantum gravity constructed from the Plebanski-Holst action. The reason for there being several models currently under consideration is that no consensus has been reached for how to implement the simplicity constraints. Indeed, none of these models strictly follows from the original path integral with commuting B fields, rather, by some non standard manipulations one always ends up with non commuting B fields and the simplicity constraints become in fact anomalous which is the source for there being several inequivalent strategies to circumvent the associated problems. In this article, we construct a new Euclidian Spin Foam Model which is constructed by standard methods from the Plebanski-Holst path integral with commuting B fields discretised on a 4D simplicial complex. The resulting model differs from the current ones in several aspects, one of them being that the closure constraint needs special care. Only when dropping the closure constraint by hand and only in the large spin limit can the vertex amplitudes of this model be related to those of the FK Model but even then the face and edge amplitude differ. Curiously, an ad hoc non-commutative deformation of the $B^{IJ}$ variables leads from our new model to the Barrett-Crane Model in the case of Barbero-Immirzi parameter goes to infinity.Comment: 41 pages, 4 figure

Listening to the New Student Voice: How They Learn

In 2003 it was forecasted that medical students’preclinical learning would mostly consist of large portions of educational training and instruction provided on the internet and other technology tools, while the traditional lecture format would become more infrequent. Five years later many medical schools have adapted to this new technological-enhanced learning environment. No one can argue that today’s millennial generation of medical students is more familiar with technology than their predecessors. However, does this technology savvy generation report that these new tools are indeed superior when compared to the traditional tools of facilitating learning and understanding in the preclinical years? Additionally, is there a difference in usefulness of learning techniques for students in year one as compared to year two of medical school? This study examines the learning tools in basic science courses to determine how the millennial generation of students report they are learning best. Tools from our blended learning curriculum were investigated within and across preclinical years one and two. Presented at the AAMC (Association of American Colleges) Annual Meeting, RIME (Research in Medical Education) Program, November 2008

Spin Structures on Kleinian Manifolds

We derive the topological obstruction to spin-Klein cobordism. This result has implications for signature change in general relativity, and for the $N=2$ superstring.Comment: 8 page