Multi-Commodity Network Flow Based Approaches for the Railroad Crew Scheduling Problem

In this paper, we study one of the most important railroad optimization problems, the crew scheduling problem, in the context of North American railroads. Crew scheduling for North American railroads is very different from that of European railroads, which has been well studied. The crew scheduling problem is to assign crew (train operators) to scheduled trains over a time horizon (generally a week) at minimal cost while honoring several operational and contractual requirements. Each North American Class I railroad spends at least a billion dollars in crew costs annually and does not have any decision support system available that can assist it in all levels of decision making: tactical, planning, and strategy. Indeed, all decisions related to crew are made manually, thereby leaving sufficient room for improvement. We have developed a network-flow based crew-optimization model that has applications in all levels of decision making in crew scheduling: tactical, planning, and strategy. Our network-flow model maps the assignment of crew to trains as the flow of crew on an underlying network where different crew types are modeled as different commodities in this network. We formulate the crew assignment problem as an integer-programming problem on this network, which allows this problem to be solved to optimality. We also develop several highly efficient algorithms using problem decomposition and relaxation techniques, where we use the special structure of the underlying network model to obtain significant speed-ups. We present very promising computational results of our algorithms on the data provided by a major North American railroad. Our network flow model is likely to form a backbone for a decision-support system for crew scheduling

Synthesis, characterization, and binding of [Cr(naphen)(H<SUB>2</SUB>O)<SUB>2</SUB>]<SUP>+</SUP> with DNA: experimental and modeling study

A chromium(III) complex of naphen, where naphen denotes 1,2-bis(naphthylideneamino)ethane having the basic salen structure, with an extended aromatic system, has been synthesized and characterized using UV–visible, infrared and ESI mass spectra. Absorption titration and thermal denaturation studies revealed that [Cr(naphen)( H2O)2]+ binds to DNA with moderate strength. Relative viscosity measurements clearly indicate that it binds to DNA by an intercalative mode. This observation is in contrast to an observation with the parent complex, [Cr(salen)( H2O)2]+, which prefers groove binding. Intercalation of the complex results in a change in the helicity of CT DNA, which is reflected in the CD spectrum of DNA in the presence of [Cr(naphen)( H2O)2]+. The binding constant of the complex to CT DNA has been estimated to be (0.51 ± 0.07)×104 M-1 (1 M = mol dm-3), which is lower than the values reported for classical intercalators. Modeling studies with the dodecamer d(GCGCAATTGCGC) 2 show that as a result of the intercalation of [Cr(naphen)( H2O)2]+ the vertical separation of the bases increases by 2.67 Å in one strand and by 1.89 Å in the other

Real-life locomotive planning: New formulations and computational results

In this paper, the authors develop new formulations for the locomotive planning problem (LPP) which is one of the most important railroad optimization problems. The objective of the LPP is to assign a consist (a set of locomotives) to each train in a pre-planned train schedule so as to provide sufficient power to pull the trains from their origins to their respective destinations at minimal cost. This assignment plan should be repeatable every week. In an earlier paper, the authors developed a formulation for locomotive planning and proposed a novel two-phase solution approach using linear, integer, and network programming. However, that formulation did not incorporate all the real-world constraints needed to generate a fully implementable solution. In this paper, the authors extend that approach on several dimensions by adding new constraints to the planning problem desired by locomotive directors, and by developing additional formulations necessary to transition solutions of their models to practice. The authors propose two formulations for this generalized LPP: consist formulation, and hybrid formulation. Finally, the authors present detailed computational tests that demonstrate the efficacy of models and conduct case studies on a number of instances to obtain several insights

Real-life locomotive planning: New formulations and computational results

In this paper, we develop new formulations for the locomotive planning problem (LPP) which is one of the most important railroad optimization problems. The objective of the LPP is to assign a consist (a set of locomotives) to each train in a pre-planned train schedule so as to provide sufficient power to pull the trains from their origins to their respective destinations at minimal cost. This assignment plan should be repeatable every week. In an earlier paper, we developed a formulation for locomotive planning and proposed a novel two-phase solution approach using linear, integer, and network programming. However, that formulation did not incorporate all the real-world constraints needed to generate a fully implementable solution. In this paper, we extend that approach on several dimensions by adding new constraints to the planning problem desired by locomotive directors, and by developing additional formulations necessary to transition solutions of our models to practice. We propose two formulations for this generalized LPP: consist formulation, and hybrid formulation. Finally, we present detailed computational tests that demonstrate the efficacy of models and conduct case studies on a number of instances to obtain several insights.

Investigation of nuclease, proteolytic and antiproliferative effects of copper(II) complexes of thiophenylmethanamine derivatives

Four coordinate copper(II) complexes 1, 2 and 3 of ligands based on thiophenemethylamine containing imidazole, benzimidazole and pyridine moiety have been synthesized and characterized. Complex 1 has also been crystallographically characterized. The three complexes bind to DNA non-intercalatively, though partial intercalation in the case of complex 2 cannot be ruled out. All the three complexes bring about hydroxyl radical mediated DNA cleavage in the presence of H2O2. Binding of the three copper(II) complexes to BSA lead to changes in the helicity of the protein. Among the three complexes, 2 and 3 are more effective in inhibiting the growth of cancerous MG63 cells than normal NIH3T3 cells. These two complexes promote apoptosis in MG 63 cells

Dedicated pediatric cardiac intensive care unit in a developing country: Does it improve the outcome?

Introduction and Aim : Focussed cardiac intensive care is known to produce better outcomes. We have evaluated the benefits of a dedicated Pediatric Cardiac Intensive Care Unit (PCICU) in the early postoperative outcomes of patients undergoing surgery for congenital heart disease. Methods : Prospectively collected data of 634 consecutive patients who underwent congenital heart surgery from September 2008 to September 2009 were analyzed. Midway through this period a dedicated PCICU was started. The patients who were treated in this new PCICU formed the study group (Group B, n = 318). The patients who were treated in a common postoperative cardiac surgery ICU formed the control group (Group A, n = 316). Early postoperative outcomes between the two groups were compared. Results : The two groups were comparable with respect to demographic data and intraoperative variables. The duration of mechanical ventilation in the dedicated pediatric cardiac ICU group (32.22 ± 52.02 hours) was lower when compared with the combined adult and pediatric surgery ICU group (42.92 ± 74.24 hours, P= 0.04). There was a shorter duration of ICU stay in the dedicated pediatric cardiac ICU group (2.69 ± 2.9 days vs. 3.43 ± 3.80 days, P = 0.001). The study group also showed a shorter duration of inotropic support and duration of invasive lines. The incidence of blood stream infections was also lower in the dedicated pediatric ICU group (5.03 vs. 9.18%, P = 0.04). A subgroup analysis of neonates and infants <1 year showed that the advantages of a dedicated pediatric intensive care unit were more pronounced in this group of patients. Conclusions : Establishment of a dedicated pediatric cardiac intensive care unit has shown better outcomes in terms of earlier extubation, de-intensification, and discharge from the ICU. Blood stream infections were also reduced

Stage one Norwood procedure in an emerging economy:Initial experience in a single center

Objective: The evolution of surgical skills and advances in pediatric cardiac intensive care has resulted in Norwood procedure being increasingly performed in emerging economies. We reviewed the feasibility and logistics of performing stage one Norwood operation in a limited-resource environment based on a retrospective analysis of patients who underwent this procedure in our institution. Methods : Retrospective review of medical records of seven neonates who underwent Norwood procedure at our institute from October 2010 to August 2012. Results: The median age at surgery was 9 days (range 5-16 days). All cases were done under deep hypothermic cardiopulmonary bypass and selective antegrade cerebral perfusion. The median cardiopulmonary bypass (CPB) time was 240 min (range 193-439 min) and aortic cross-clamp time was 130 min (range 99-159 min). A modified Blalock-Taussig (BT) shunt was used to provide pulmonary blood flow in all cases. There were two deaths, one in the early postoperative period. The median duration of mechanical ventilation was 117 h (range 71-243 h) and the median intensive care unit (ICU) stay was 12 days (range 5-16 days). Median hospital stay was 30.5 days (range 10-36 days). Blood stream sepsis was reported in four patients. Two patients had preoperative sepsis. One patient required laparotomy for intestinal obstruction. Conclusions:Stage one Norwood is feasible in a limited-resource environment if supported by a dedicated postoperative intensive care and protocolized nursing management. Preoperative optimization and prevention of infections are major challenges in addition to preventing early circulatory collapse