Search

Compared with the ring-barrier framework used for ring structures (or phasing plans) in signalized control of intersections in the United States, the Dutch framework has no explicit barriers, but only a requirement to respect pairwise conflicts. This paper describes how ring structures can be modeled with pairwise conflicts as a starting point. Modeling techniques were extended to account for offset constraints such as leading pedestrian intervals in which the start or end of one traffic movement was constrained by the start or end of another one that was otherwise compatible. One practical drawback of the more flexible Dutch framework is that it permits so many more possible ring structures that it can be prohibitive to evaluate them all manually. Therefore, this paper describes VRIGEN, an automated method that overcomes this drawback by identifying and evaluating all possible ring structures. Finally, this paper presents several examples in which barrier-free ring designs allow signals to cycle more quickly and efficiently, with improvements in safety and delay for pedestrians and bicyclists. Most of these examples feature pedestrian phases that are allowed to overlap while their parent vehicular phases are not.

Time within an actuated signal cycle can be decomposed into time that is fully used, which is the saturation headway multiplied by the number of passing vehicles, and time that is wasted or lost. Activity network modeling is used to show the interaction between signal timing events and traffic flow transitions. Seven components of generalized lost time are identified: those associated with start-up, minimum green, parallel queue discharge (for simultaneous gap-out), extension green, parallel extension (for nonsimultaneous gap-out), the passing of the critical gap, and phase end. Simple formulas can be used to estimate all of these components for many practical cases, allowing one to estimate average cycle length without iteration. The modeling framework accounts for the dual-ring structure with minimum green and maximum green constraints and on–off settings for recall and simultaneous gap-out. Experiments with microsimulation software verify the formulas developed. The formulas show the sensitivity of lost time, and therefore average cycle length, to parameters that a designer can control including detector setback, critical gap, gap-out settings, and number of lanes. They also show sensitivity to total demand and to the ratio of noncritical to critical phase volumes.

Transfers cost effort and take time. They reduce the attractiveness and the competitiveness of public transportation. The impedance of transferring should be limited, especially when low-frequency routes are involved. First, this paper shows the effects of planning the offset between the timetable arrival time of the feeder line and the timetable departure time of the connecting line on the transfer waiting time. An optimized buffer time reduces the probability of missing the connection to the point at which a further reduction would cause a still greater disbenefit by making passengers who make their connection wait longer. Second, the paper shows the effects of punctuality control on the routes on the transfer waiting time. If general operational control can reduce the punctuality standard deviations of arrivals and departures, it increases the reliability of the transfer. Third, the paper shows the effects of departure control at the interchange on the transfer waiting time. Holding connecting vehicles prevents missed connections because of early departures and holding just until the connection is made prevents unnecessary delays after passengers have transferred. Example results are derived by the use of a mathematical model.

Heart failure is a major cause of premature death and disability in the United States. Stem cell therapy has attracted great interest for the treatment of myocardial infarction and heart failure. Some tissue-specific adult-derived stem cells demonstrate plasticity in that they are multipotent, react to inductive signals provided by a new micro-environment, and acquire the phenotype of cells endogenous to the new micro-environment. The mechanism through which this phenotype is acquired is unknown. We have demonstrated that a liver-derived clonal stem cell line, WB F344, differentiate into cardiomyocytes in vivo and in vitro. Using a co-culture model of neonatal heart cells and WB F344 cells, we have found that cytosolic communication between the two cell types results in calcium-induced transcription of cardiac transcription factors and appears to usher in the cardiac phenotype. Functional gap junctions and IP3 receptors appear to be required for this process. We propose that the observed low frequency of stem cell differentiation into cardiomyocytes when transplanted into the injured heart is due, in part, to their inability to establish functioning intercellular communications with healthy cardiomyocytes and receive instructive signals needed to activate a cardiac gene program.

To improve reliability, transit routes have time points at which early vehicles are held. Holding reduces waiting time and the amount of time passengers have to budget for a trip. However, it also reduces operating speed and thus increases passenger riding time and, potentially, operating cost. A new approach is presented for quantifying the user costs associated with unreliability. User cost has three components: excess waiting time, potential travel time or buffer time (related to budgeted travel time), and mean riding time, of which the first two are reliability impacts. For long headway service, these costs can be determined from 2-percentile departure times, 95-percentile arrival times, and mean arrival and departure times at stops. With a simple route operations model on a hypothetical route, impacts of scheduling with different numbers of time points and with different levels of running time and cycle time supplements are explored, and optimal running time schedules are determined. For a typical case, the optimal time point schedule offers net benefits equivalent to 4.5 min of riding time per passenger compared with operation without time point control. Optimal route running times are roughly mean plus one standard deviation of uncontrolled running time, and optimal cycle time is roughly mean plus two to three standard deviations of uncontrolled route running time. Surprisingly, it was found that in an optimal schedule, inserting slack at time points does not increase cycle time, because slack time inserted en route simply substitutes for slack time needed in layover.

A control structure shows the sequence of realization of all green phases. Often, control structures designed for fixed-time control are based only on the order of the critical conflict group. When applied to vehicle-actuated control, structures based only on the critical conflict group regularly lead to inefficient control structures. Because of its flexibility, vehicle-actuated control requires a different approach for designing control structures. This paper presents a design method based on combining maximum conflict groups (mutual conflicting streams), resulting in all possible control schemes. Based on volume and saturation flow rate and assuming a uniform arrival process, each control scheme has a specific minimum cycle length. By ordering a control scheme according to its minimum cycle length and its flexibility to adjust green periods to varying traffic demand, the designer is supported in the process of choosing the most appropriate control scheme. This method was recently implemented in the Traffic Control Program Generator design support program and is used for training practitioners. If the minimum cycle length is less than the accepted maximum cycle, volumes can be increased proportionally to find maximum extension green times. In the near future, the Dutch province of South Holland intends to implement this method in a controller to generate online the most suitable control structure and control parameters.

European public transport operators, first in Paris and then in Brussels, Belgium, have developed a framework, a standard, and certification procedures for the management of service quality. Based on Averous's service quality cycle, this framework incorporates both customer satisfaction and performance evaluation with service standards and service indicators that are customer oriented yet objectively measurable. The development of this quality movement is documented, and its implementation in Brussels is used as a case study. There, the management contract provides financial incentives based on the percentage of passengers served by lines whose service quality has been certified, and the organization chart includes several managers responsible for service quality. The process of defining service targets is described with a framework that emphasizes extreme values and specification of both a base level and a level of un-acceptability that demands immediate action. Special attention is given to two methods of performance measurement: automatic processing of archived automatic vehicle location data and “mystery shopper” surveys. Improvements, organizational changes, and new programs developed in response to the quality process are described.

Traditional transit service quality measures separate waiting time from service reliability and thereby underestimate the real cost of waiting and fail to evaluate the effect of unreliability on passengers. This study's analysis of passenger behavior shows that, for short headway service, the cost of waiting involves not only the mean time spent waiting on the platform but also potential waiting time, that is, the additional time that passengers have to budget for waiting. Budgeted waiting time is based on an extreme of the waiting time distribution such as its 95th percentile value, which is extremely sensitive to service reliability. Methods for determining the distribution of passenger waiting time from automatic vehicle location (AVL) data are derived. For long headway service, actual and budgeted waiting times are shown to be related to high and low extremes of the schedule deviation distribution, which can likewise be determined from AVL data. Two other components of long headway waiting, schedule inconvenience and synchronization cost, are also analyzed. Waiting cost functions and waiting time measures that account for both headway and service reliability are developed and are harmonized in a framework that provides a smooth transition from short to long headway waiting. Examples show how service reliability can be measured as a waiting cost and how service reliability improvements can reduce waiting cost as much as a large reduction in headway can.

Alkyne allyl alcohols are readily transformed into β-amino ethyl alkylidene tetrahydrofurans or β-amino ethyl alkylidene pyrrolidines in a Pd-catalyzed cycloisomerization-reductive amination sequence with remarkable chemoselectivity leaving benzyl groups and trisubstituted double bonds intact.

We examined the differentiation potential of an adult liver stem cell line (WB F344) in a cardiac microenvironment, ex vivo. WB F344 cells were established from a single cloned nonparenchymal epithelial cell isolated from a normal male adult rat liver. Genetically modified, WB F344 cells that express β-galactosidase and green fluorescent protein or only β-galactosidase were co-cultured with dissociated rat or mouse neonatal cardiac cells. After 4 to 14 days, WB F344-derived cardiomyocytes expressed cardiac-specific proteins and exhibited myofibrils, sarcomeres, and a nascent sarcoplasmic reticulum. Further, rhythmically beating WB F344-derived cardiomyocytes displayed calcium transients. Fluorescent recovery after photobleaching demonstrated that WB F344-derived cardiomyocytes were coupled with adjacent neonatal cardiomyocytes and other WB F344-derived cardiomyocytes. Fluorescence in situhybridization experiments suggested that fusion between WB F344 cells and neonatal mouse cardiomyocytes did not take place. Collectively, these results support the conclusion that these adult-derived liver stem cells respond to signals generated in a cardiac microenvironment ex vivoacquiring a cardiomyocyte phenotype and function. The identification ex vivoof microenvironmental signals that appear to cross germ layer and species specificities should prove valuable in understanding the molecular basis of adult stem cell differentiation and phenotypic plasticity.

At signalized intersections the red clearance interval has to be long enough to prevent accidents but not longer than necessary to ensure efficient traffic operations and encourage respect for the red indication. Because designers used a variety of methods to calculate clearance times, the association of Dutch traffic control engineers (Contactgroep Ver-keersregeltechnici Nederland) initiated the development of a generally applicable method. The resulting method is based on a driver behavior model that involves five parameters. In contrast to the suggested Institute of Transportation Engineers (ITE) method, it determines red clearance time for each ordered pair of conflicting streams depending on the distance of the entering and exiting streams from the zone in which the two streams' paths overlap. The conflict zone method was calibrated by using field data collected at two intersections and was included in the 1996 Dutch guidelines for traffic controllers. In comparison with the ITE-suggested method, which gives the exiting stream enough time to clear the entire intersection, the new method is sensitive to the sequence in which traffic streams appear in the cycle and tends to call for less clearance time, improving intersection capacity and reducing delay. This approach is especially beneficial in improving efficiency of intersections with actuated control.