Assigning buses to schedules in a metropolitan area

The problem of scheduling a fleet of buses to a given set of trips is encountered by large bus companies performing thousands of trips per day. The time-tables for those trips are planned separately and reflect the passengers demand for transportation. These time-tables are inputs for the bus scheduling procedures. The scheduling problem is difficult due to its size and due to many operational constraints which are imposed. A mathematical formulation of the problem is presented and an efficient algorithm is developed. This paper presents results and computational experience that were obtained from implementing the model in a large bus company.     

Occam algorithms for computing visual motion

The standard approach to computing motion relies on pixel correspondence. Computational schemes impose additional constraints, such as smoothness and continuity of the motion vector even though these are not directly related to pixel correspondence. This paper proposes an alternative to the multiple constraints approach. By drawing analogy with machine learning, motion is computed as a function that accurately predicts frames. The Occam-Razor principle suggests that among all functions that accurately predict the second frame from the first frame, the best predictor is the “simplest,” and simplicity can be rigorously defined in terms of encoding length. An implementation of a practical algorithm is described. Experiments with real video sequences verify the algorithm assumptions by showing that motion in typical sequences can be accurately described in terms of a few parameters. Our particular choice of predictors produces results that compare very favorably with other image flow algorithms in terms of accuracy and compactness. It may, however, be too constrained to enable accurate recovery of 3D motion and structure     

Adhesion of mature polyploid megakaryocytes to fibronectin is mediated by beta 1 integrins and leads to cell damage

Human CD34+ bone marrow cells were committed to the megakaryocytic lineage in serum-free liquid cultures by the following cytokines: thrombopoietin, erythropoietin, and IL-6. Megakaryocyte maturation has been described as being regulated by the extracellular matrix. These cells express receptors for laminin, collagen, and vitronectin, but they selectively adhere to and spread on fibronectin, a major component of the bone marrow environment. Function-perturbing antibodies against beta 1 integrins totally abolished the adhesion of megakaryocytes on fibronectin, whereas antibodies to beta 3 did not, suggesting that beta 1 integrins were responsible for the adhesive phenotype of these polyploid cells. beta 1-positive clusters were visualized in close contact with the extremities of stress fibers at the cell surface. In the course of cell spreading, we observed morphological modifications such as the disorganization of the compact nuclei structure and the appearance of holes in the cytoplasm leading to the release of alpha IIb beta 3-positive cellular fragments. This process appeared to be a specific feature of megakaryocytes and is correlated neither to apoptosis nor to integrin signaling.     

Acquisition and extended retention of a conditioned taste aversion in preweanling rats.

Four experiments employed a taste aversion conditioning procedure appropriate for both neonatal and adult rats to investigate the ontogeny of extended retention. In Exp I, 200 outbred albino rats trained at 1, 10, 20, or 60 days of age were tested for retention of the taste aversion 25 days later. At testing, only those Ss conditioned when 20 or 60 days old demonstrated significant taste aversions. Exps II and III, with 190 Ss, established that Ss 14–25 days old and older were able to retain significant taste aversions following a 25-day retention interval. 80 younger Ss did, however, acquire and retain the aversion for several days and showed a gradual retention loss over progressively longer retention intervals (Exp IV). Findings suggest that preweanling rats demonstrate initial consolidation, storage, and retrieval of conditioned taste aversions. It is only after this initial period that retention deficits become evident. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Optimization of road networks using evolutionary strategies

A road network usually has to fulfill two requirements: (i) it should as far as possible provide direct connections between nodes to avoid large detours; and (ii) the costs for road construction and maintenance, which are assumed proportional to the total length of the roads, should be low. The optimal solution is a compromise between these contradictory demands, which in our model can be weighted by a parameter. The road optimization problem belongs to the class of frustrated optimization problems. In this paper, a special class of evolutionary strategies, such as the Boltzmann and Darwin and mixed strategies, are applied to find differently optimized solutions (graphs of varying density) for the road network, depending on the degree of frustration. We show that the optimization process occurs on two different time scales. In the asymptotic limit, a fixed relation between the mean connection distance (detour) and the total length (costs) of the network exists that defines a range of possible compromises. Furthermore, we investigate the density of states, which describes the number of solutions with a certain fitness value in the stationary regime. We find that the network problem belongs to a class of optimization problems in which more effort in optimization certainly yields better solutions. An analytical approximation for the relation between effort and improvement is derived.