Intermediate Destinations Research Articles

Hop-Congestion Trade-Offs for High-Speed Networks

Message transmission in ATM networks is via virtual paths. Packets are routed along virtual paths by maintaining a routing field whose subfields determine the intermediate destinations of the packet. In such a network it is important to construct path layouts that minimize the hop number (i.e. the number of virtual paths used to travel between any two nodes) as a function of edge-congestion (i.e. the number of virtual paths passing through a link). In this paper we construct asymptotically optimal virtual path layouts for chains and meshes.

Comprehensive Planning Model for Ferry Ridership Forecasting Analysis in Puget Sound Region

The methods used to develop a travel forecasting model for the Washington State Ferries (WSF) are described. The model is being used to develop ridership forecasts for the WSF Long-Range System Plan and other project planning efforts. The WSF model covers a 12-county ferry system service area, including the four counties within the central Puget Sound region. The model was designed to be sensitive to policy variables and to produce detailed ridership forecasts on each ferry route by ( a) boarding methods, ( b) mode of access and egress combinations for walk-on passengers, and ( c) vehicle occupancy for those persons boarding by vehicle. The model is fully incremental and uses observed travel patterns from a comprehensive on-board origin-destination survey of ferry riders conducted in 1993 for the afternoon peak period. Choice of terminal is an intermediate destination choice for walk-on ferry riders and is a prime example of trip chaining between an origin and destination. A new method involving matrix algebra has been used to formulate choice of terminal in terms of matrix products. This method estimates demand matrices corresponding to individual legs of the trip chain for each access and egress mode combination. The modeling system was validated for replication of ridership on each route by boarding methods and by mode of access and egress combinations.

When is double rounding innocuous?

Double rounding is the phenomenon that occurs when the result of an operation is rounded to fit some intermediate destination, and then again when delivered to its final destination. This can be a common occurrence when using some floating-point arithmetic engines which lack single precision registers: results of operations are typically rounded to fit in a register, whose width may be double precision or wider, before being stored in some memory location possibly in a format narrower than that of the registers. Examples of such floating-point arithmetic engines include Intel's x87 series and IBM's POWER architecture. (Implementations of the latter are found in some IBM workstations.)

Transport of a lysosomally targeted Rous sarcoma virus envelope glycoprotein involvestransient expression on the cell surface

The details of intracellular transport pathways for glycosylated proteins remain incompletely described. We previouslydescribed a mutant Rous sarcoma virus envelope glycoprotein (gp), μ26, with an altered membrane-spanning domain that was targeted to Iysosomes after traversing the trans-Golgi. This mutant protein was not detectable on the cell surface by immunofluorescence, but its pathway for degradation remained unclear. To investigate this we have employed a second env mutation, S19, that results in a protein which is defective for normal cleavage/activation by intracellular enzymes, but remains susceptible to cleavage by extracellular proteases. Cleavage/activation of the double mutant by trypsin, which could only occur if it was exposed on the cell surface, was observed, indicating that the plasma membrane is an intermediate destination in the transport of this mutant protein. To substantiate these results, cells expressing the μ26 glycoprotein were incubated with an antibody specific for the native protein in the presence of chloroquine. The specific accumulation of this antibody/gp complex in vesicles, as detected by internal immunofluorescence, confirmed the trypsin cleavage results. We conclude that this rapidly degraded mutant protein is transported from the trans-Golgi to the cell surface, where it is only transiently exposed, and then rapidly endocytosed and lysosomally degraded. The relevance of these results to the targeting of lysosomal proteins is discussed.

New bounds on the reliability of augmented shuffle-exchange networks

The reliability resulting from two forms of redundancy, spatial and temporal, in multistage interconnection networks is examined. The extra-stage shuffle-exchange network (SEN+) which is an example of the former is investigated here. The SEN+ is decomposed into two subnetworks connected by two extreme stages. Given k random faults in one subnetwork, our problem reduces to estimating the maximum and minimum number of switches in the other subnetwork that must be operational for full access, i.e., connection between every input (processor) and output (memory) pair. This investigation results in obtaining analytical estimates for the upper and lower bounds on its reliability which are a substantial improvement over existing ones. We next examine the effect of wrap-around connections from each output node to its corresponding input node. This may provide a path between a source-destination pair under faults by diverting a given packet through one or more intermediate destinations. The reliability offered by this scheme that provides temporal redundancy is also estimated and compared with the scheme employing hardware redundancy. >

Determining intermediate origin-destination matrices for the analysis of composite mode trips

We consider in this paper the problem of determining intermediate origin-destination matrices for composite mode trips that involve a trip by private car to a parking facility and the continuation of the trip to the destination either by walking or by a transit mode. The intermediate origin-destination matrices relate to each component of the composite mode trip: a matrix from the trip origins to intermediate destinations which are parking lots and a matrix from the parking lots to the final destinations. The approach that we propose to solve this problem is to modify the entropy based trip distribution models to consider inequality constraints related to parking lot capacities. Such models may be easily calibrated by using well known calibration methods or generalization of these methods and may be easily solved by applying a primal feasible direction method of nonlinear programming.