Dynamic Decision Support for Regional LTL Carriers

This thesis focuses on decision support for regional LTL carriers. The basic operating characteristics of regional LTL carriers are similar to those of national LTL carriers, i.e., they operate linehaul networks with satellites, breakbulks, and relays to consolidate freight so as to be able to cost-effectively serve their customers. However, there are also key differences. Most importantly, because the area covered by a regional carrier is smaller, a regional carrier handles less freight (sometimes significantly less) and therefore typically has fewer consolidation opportunities, which results in higher handling and transportation costs per unit of freight. Consequently, competing with national carriers on price is difficult. Therefore, to gain or maintain market share, regional carriers have to provide better service. To be able to provide better service, regional carriers have to be more dynamic, e.g., they have to be able to deviate from their load plan when appropriate, which creates challenges for decision makers. Regional carriers deliver about 60% of their shipments within a day and almost all of their shipments within two days. Furthermore, most drivers get back to their domicile at the end of each day. Therefore, the focus of the thesis is the development of effective and efficient decision models supporting daily operations of regional LTL carriers which provide excellent service at low cost. This thesis presents an effective solution approach based on two optimization models: a dynamic load planning model and a driver assignment model. The dynamic load planning model consists of two parts: an integer program to generate the best paths for daily origin-destination freight volumes and an integer program to pack freight into trailers and trailers into loads, and to determine dispatch times for these loads. Techniques to efficiently solve these integer program solution are discussed in detail. The driver assignment model is solved in multiple stages, each stage requiring the solution of a set packing models in which columns represent driver duties. Each stages determines admissible driver duties. The quality and efficiency of the solution approach are demonstrated through a computational study with real-life data from one of the largest regional LTL carriers in the country. An important "technique" for reducing driver requirements is the use of meet-and-turn operations. A basic meet-and-turn operation involves two drivers meeting at a location in between terminals and exchange trucks. A parking lot or a rest area suffices as a meet-and-turn location. This ensures that drivers return to the terminal where they started. More sophisticated meet-and-turn operations also exist, often called drop and hook operations. In this case, drivers do not exchange trucks, but one of their trailers. The motivation in this case is not to get drivers back to their domicile, but to reduce load- miles. The thesis presents analytical results quantifying the maximum benefits of using meet and turn operations and optimization techniques for identifying profitable meet-and-turn opportunities.Ph.D.Committee Co-Chair: Alan L. Erera; Committee Co-Chair: Martin W. P. Savelsbergh; Committee Member: Chelsea C. White, III; Committee Member: Corne Aantjes; Committee Member: Joel Soko

Parental presence during pediatric emergency procedures: finding answers in an Asian context

Objective The practice of allowing parental presence during invasive procedures in children varies depending on setting and individual provider preference. We aim to understand the attitudes, preferences, and practices of physicians and nurses with regard to parental presence during invasive pediatric emergency procedures in an Asian cultural context. Methods We surveyed physicians and nurses in the pediatric emergency department of a large tertiary hospital using separate self-administered questionnaires over three months. The data collected included the demographics and clinical experience of interview respondents. Each provider was asked about their attitude and preference regarding parental presence during specific invasive procedures. Results We surveyed 90 physicians and 107 nurses. Most physicians in our context preferred to perform pediatric emergency procedures without parental presence (82, 91.1%). Forty physicians (44.4%) reported that parental presence slowed down procedures, while 75 (83.3%) felt it increased provider stress. Most physicians made the decision to allow parents into the procedure room based on parental attitude (69, 76.7%) and the child’s level of cooperation (64, 71.1%). Most nurses concurred that parental presence would add to provider stress during procedures (69, 64.5%). We did not find a significant relationship between provider experience (P=0.26) or age (P=0.50) and preference for parental presence. Conclusion In our cultural context, most physicians and nurses prefer to perform procedures for children in the absence of parents. We propose that this can be changed by health professional training with role play and simulation, adequate supervision by experienced physicians, and clear communication with parents

Line-of-sight based formation keeping and attitude control of two spacecraft

We consider coupled attitude and position control of two spacecraft where absolute attitudes are not available. The objective is to attain a formation requiring a desired distance between two spacecraft and alignment of attitudes along the inertial line-of-sight (LOS) direction between the center of masses of the spacecraft. A relative attitude and position control scheme is developed using LOS vectors measured in each spacecraft's body frame. The current work differs from past research in the sense that the relative positions of the two spacecraft are not assumed to be fixed and all control laws are obtained in respective body fixed frames. The state feedback laws put forth in this work guarantee almost semi-global asymptotic stability of the desired closed-loop equilibrium configuration. (C) 2016 IAA. Published by Elsevier Ltd. All rights reserved

Line-of-sight based spacecraft attitude and position tracking control

This paper considers the problem of formation control of three spacecraft consisting of one leader and two followers. The leader spacecraft controls its attitude and position to track a desired attitude and position trajectory in the Earth Centred Inertial (ECI) frame. Each follower spacecraft tracks a desired relative attitude and relative position trajectory with respect to the leader spacecraft. Absolute attitude control law for the leader and relative attitude control laws for the followers are obtained in terms of line-of-sight vectors between the spacecraft. A relative attitude determination scheme using line-of-sight vectors is also proposed. The state feedback laws proposed in this work guarantee almost global asymptotic stability of the desired closed-loop equilibrium. (C) 2016 European Control Association. Published by Elsevier Ltd. All rights reserved

Point-of-care ultrasound identification of pneumatosis intestinalis in pediatric abdominal pain: a case report

10.1186/s13089-017-0057-0Critical Ultrasound Journal91