Nikola Marković

Evasive flow capture: A multi-period stochastic facility location problem with independent demand

We introduce the problem of locating facilities over a finite time horizon with the goal of intercepting stochastic traffic flows that exhibit evasive behavior, which arises when locating weigh-in-motion systems, tollbooths, vehicle inspection stations, or other fixed flow-capturing facilities used for law enforcement. The problem can be formulated as a multi-stage, mixed-integer stochastic program; however, under certain independence assumptions, this can be reformulated as a large two-stage stochastic program, enabling us to solve much larger instances. We additionally propose an algorithm based on Lagrangian relaxation that separates the reformulated stochastic program into a variant of a deterministic knapsack problem and a sum of time-decoupled single-period stochastic programs that can be solved independently. The model and algorithm are tested on instances involving road networks of Nevada and Vermont. A comparison with the previously studied single-period stochastic programming approach shows that the newly proposed multi-period model substantially reduces the expected cost.

Planning Dial-a-Ride Services: Statistical and Meta-Modeling Approach

Accessibility of public transit is an important political and social objective for transit agencies across the world. To meet this objective, many transit agencies provide a specialized door-to-door transportation service, called “dial-a-ride” (DAR), for the elderly and disabled. Annual DAR ridership growth exceeding 5% is reported in many cities in the United States, and this trend is expected to continue because of the aging population. In response to increased ridership, DAR services have become the fastest growing fraction of many transit agency budgets. These trends motivate the development of models that support decision making in the planning of new DAR systems or expansion of existing systems. Several statistical models have been developed in the past decade that can be used to determine the necessary DAR system capacity. These models focus on peak period analyses and provide good fit when applied to simulated case studies. This study aimed to demonstrate the importance of considering the entire day of operations rather than only the peak period. Several factors were identified that have been omitted in the literature, and comprehensive statistical and meta-models were developed for determining DAR system capacity. The performance of two proposed models was assessed with real-world data from a DAR service. The proposed models are available to the general public through a web system that provides free decision support to practitioners involved in designing DAR systems.

Scheduling Under Uncertainty for Single-Hub Intermodal Freight System

This paper examines the optimization of an intermodal system with freight transfers at a single hub by determining when departures should be scheduled on outbound routes, given information about the probabilistic arrivals of vehicles on inbound routes. The intermodal system is modeled with stochastic programming, and the schedule of outbound vehicles is optimized with a genetic algorithm. The model is designed to minimize the expected total cost of operating an intermodal system while considering all capacity constraints arising in the real world. This model allows the system performance to be computed numerically, without the approximations of alternative methods such as simulation. Although the model can be applied to the most general case, the model seems to be especially suitable for analyzing systems with a relatively small number of arrivals on inbound routes. In particular, the model can be successfully applied to situations where statistical or queuing analyses are not applicable because of the small number of events (vehicle arrivals). The authors specifically analyze an intermodal system consisting of multiple inbound truck routes and multiple outbound airline routes. However, the mathematical model developed in this paper is applicable to other combinations of transportation modes.

Nuclear envelope laminopathies: evidence for developmentally inappropriate chromatin-nuclear envelope interactions

Background During terminal differentiation of cells, there is typically a transition of the nuclear envelope from the Lamin B protein to Lamin A/C proteins. This is commensurate with exit from the cell cycle, and maintenance of the transcriptional programs associated with the terminally differentiated cells. Dominant missense mutations in Lamin A/C cause a broad spectrum of human genetic disorders, where specific point mutations are associated with defects in specific organs or tissues. We have previously presented a model where Lamin A/C mutations disrupt developmentally appropriate interactions between chromatin and the nuclear envelope and lead to poor coordination of E2F cell cycle pathways and terminal differentiation pathways [1]. One of the phenotypes caused by Lamin A/C mutations is Emery Dreifuss Muscular Dystrophy (EDMD). An X-linked recessive phenocopy of EDMD is caused by loss of function of emerin – ab inding partner to Lamin A/C at the nuclear envelope. Here, we tested the hypothesis that emerin plays a role in chromatin remodeling via stabilizing nuclear lamina-heterochromatin interactions necessary for appropriate and time dependent muscle differentiation. Material and methods We used WT and emerin null mouse myogenic stem cells to study transcriptional and epigenetic changes during in vitro exit from the cell cycle and differentiation to the myogenic lineage. Specific cell cycle (E2F) and myogenic genes were analyzed by qPCR and ChlP-qPCR to determine mRNA timing and H3K9me3 enrichment on gene promoters. Nuclear lamina-chromatin colocalization was determined and quantified by confocal imaging and Matlab. Results