48 research outputs found
Incremental polynomial time dualization of quadratic functions and a subclass of degree-k functions
Cataloged from PDF version of article.We consider the problem of dualizing a Boolean function f represented by
a DNF. In its most general form, this problem is commonly believed not to be solvable
by a quasi-polynomial total time algorithm.We show that if the input DNF is quadratic or is
a special degree-k DNF, then dualization turns out to be equivalent to hypergraph dualization
in hypergraphs of bounded degree and hence it can be achieved in incremental polynomial
time
Cost and emission impacts of virtual power plant formation in plug-in hybrid electric vehicle penetrated networks
Cataloged from PDF version of article.With increasing interest in alternative energy resources and technologies, mass penetration of PHEVs
(plug-in hybrid vehicles) into the electricity grid and widespread utilization of DERs (distributed energy
resources) are anticipated in the near future. As an aggregation unit, the VPP (virtual power plant) is
introduced for load management and resource scheduling. In this article, we develop an energy management
model for VPPs and analyze the cost and emission impacts of VPP formation and PHEV
penetration. We conduct a case study for the state of California using real-world data from official resources.
An average of 29.5% cost reduction and 79% CO2 and 83% NOx emission reductions are attained as
shared benefits of consumers in the case study. Results are illustrative of opportunities that VPP formation
can provide for the community. Sensitivity of the results to the DER costs and capacities, battery
and gasoline prices are also analyzed. In addition, we prove that charging and discharging do not
simultaneously occur in the solutions, which leads to a simplification in traditional energy management
models.
2013 Elsevier Ltd. All rights reserved
Regenerator Location Problem and survivable extensions: A hub covering location perspective
Cataloged from PDF version of article.In a telecommunications network the reach of an optical signal is the maximum distance it can traverse before its quality degrades. Regenerators are devices to extend the optical reach. The regenerator placement problem seeks to place the minimum number of regenerators in an optical network so as to facilitate the communication of a signal between any node pair. In this study, the Regenerator Location Problem is revisited from the hub location perspective directing our focus to applications arising in transportation settings. Two new dimensions involving the challenges of survivability are introduced to the problem. Under partial survivability, our designs hedge against failures in the regeneration equipment only, whereas under full survivability failures on any of the network nodes are accounted for by the utilization of extra regeneration equipment. All three variations of the problem are studied in a unifying framework involving the introduction of individual flow-based compact formulations as well as cut formulations and the implementation of branch and cut algorithms based on the cut formulations. Extensive computational experiments are conducted in order to evaluate the performance of the proposed solution methodologies and to gain insights from realistic instances. (C) 2014 Elsevier Ltd. All rights reserved
Minimum cost path problem for Plug-in Hybrid Electric Vehicles
Cataloged from PDF version of article.We introduce a practically important and theoretically challenging problem: finding
the minimum cost path for plug-in hybrid electric vehicles (PHEVs) in a network
with refueling and battery switching stations, considering electricity and
gasoline as sources of energy with different cost structures and limitations. We
show that this problem is NP-complete even though its electric vehicle and conventional
vehicle special cases are polynomially solvable. We propose three solution
techniques: (1) a mixed integer quadratically constrained program that incorporates
non-fuel costs such as vehicle depreciation, battery degradation and stopping,
(2) a dynamic programming based heuristic and (3) a shortest path heuristic. We
conduct extensive computational experiments using both real world road network
data and artificially generated road networks of various sizes and provide signifi-
cant insights about the effects of driver preferences and the availability of battery
switching stations on the PHEV economics. In particular, our findings show that
increasing the number of battery switching stations may not be enough to overcome
the range anxiety of the drivers
TCP flow aware adaptive path switching in diffserv enabled MPLS networks
Cataloged from PDF version of article.We propose an adaptive flow-level multi-path routing-based traffic engineering solution for an IP backbone network
carrying TCP/IP traffic. Incoming TCP flows are switched between two explicitly routed paths, namely the primary and
secondary paths (PP and SP), for resilience and potential goodput improvement at the TCP layer. In the proposed
architecture, PPs receive a preferential treatment over SPs using differentiated services mechanisms. The reason for this
choice is not for service differentiation but for coping with the detrimental knock-on effect stemming from the use of longer
SP that is well known for conventional network load balancing algorithms. Moreover, both paths are congestion-controlled
using Explicit Congestion Notification marking at the core and Additive Increase Multiplicative Decrease rate adjustment
at the ingress nodes. The delay difference between PP and SP is estimated using two per-egress rate-controlling buffers
maintained at the ingress nodes for each path, and this delay difference is used to determine the path over which a new TCP
flow will be routed. We perform extensive simulations using ns-2 in order to demonstrate the viability of the proposed
distributed adaptive multi-path routing method in terms of per-flow TCP goodput. The proposed solution consistently
outperforms the single-path routing policy and provides substantial per-flow goodput gains under poor PP conditions.
Moreover, highest goodput improvements under the proposed scheme are achieved by flows that receive the lowest
goodputs with single-path routing, while the performance of the flows with high goodputs with single-path routing does not
deteriorate with the proposed path switching technique. Copyright # 2011 John Wiley & Sons, Ltd
Impacts of battery characteristics, driver preferences and road network features on travel costs of a plug-in hybrid electric vehicle (PHEV) for long-distance trips
Cataloged from PDF version of article.In a road network with refueling and fast charging stations, the minimum-cost driving path of a plug-in hybrid electric vehicle (PHEV) depends on factors such as location and availability of refueling/fast charging stations, capacity and cost of PHEV batteries, and driver tolerance towards extra mileage or additional stopping. In this paper, our focus is long-distance trips of PHEVs. We analyze the impacts of battery characteristics, often-overlooked driver preferences and road network features on PHEV travel costs for long-distance trips and compare the results with hybrid electric and conventional vehicles. We investigate the significance of these factors and derive critical managerial insights for shaping the future investment decisions about PHEVs and their infrastructure. In particular, our findings suggest that with a certain level of deployment of fast charging stations, well established cost and emission benefits of PHEVs for the short range trips can be extended to long distance. Drivers׳ stopping intolerance may hamper these benefits; however, increasing battery capacity may help overcome the adverse effects of this intolerance
An analysis of cyclic scheduling problems in robot centered cells
Cataloged from PDF version of article.The focus of this study is a robot centered cell consisting of m computer numerical control (CNC)
machines producing identical parts. Two pure cycles are singled out and further investigated as
prominent cycles in minimizing the cycle time. It has been shown that these two cycles jointly
dominate the rest of the pure cycles for a wide range of processing time values. For the remaining
region, the worst case performances of these pure cycles are established. The special case of 3-machines
is studied extensively in order to provide further insight for the more general case. The situation where
the processing times are controllable is analyzed. The proposed pure cycles also dominate the rest when
the cycle time and total manufacturing cost objectives are considered simultaneously from a bicriteria
optimization point of view. Moreover, they also dominate all of the pure cycles in in-line robotic cells.
Finally, the efficient frontier of the 3-machine case with controllable processing times is depicted as an
example
Survivability in hierarchical telecommunications networks under dual homing
Cataloged from PDF version of article.The motivation behind this study is the essential need for survivability in the telecommunications networks.
An optical signal should find its destination even if the network experiences an occasional fiber cut. We consider
the design of a two-level survivable telecommunications network. Terminals compiling the access layer
communicate through hubs forming the backbone layer. To hedge against single link failures in the network,
we require the backbone subgraph to be two-edge connected and the terminal nodes to connect to the backbone
layer in a dual-homed fashion, i.e., at two distinct hubs. The underlying design problem partitions a given
set of nodes into hubs and terminals, chooses a set of connections between the hubs such that the resulting
backbone network is two-edge connected, and for each terminal chooses two hubs to provide the dual-homing
backbone access. All of these decisions are jointly made based on some cost considerations. We give alternative
formulations using cut inequalities, compare these formulations, provide a polyhedral analysis of the smallsized
formulation, describe valid inequalities, study the associated separation problems, and design variable
fixing rules. All of these findings are then utilized in devising an efficient branch-and-cut algorithm to solve
this network design problem
The design of single allocation incomplete hub networks
Cataloged from PDF version of article.The hub location problem deals with finding the location of hub facilities and allocating the
demand nodes to these hub facilities so as to effectively route the demand between any
origin–destination pair. In the extensive literature on this challenging network design
problem, it has widely been assumed that the subgraph induced by the hub nodes is complete.
Relaxation of this basic assumption constitutes the starting point of the present
work. In this study, we provide a uniform modeling treatment to all the single allocation
variants of the existing hub location problems, under the incomplete hub network design.
No network structure other than connectivity is imposed on the induced hub network.
Within this context, the single allocation incomplete p-hub median, the incomplete hub
location with fixed costs, the incomplete hub covering, and the incomplete p-hub center
network design problems are defined, and efficient mathematical formulations for these
problems with Oðn3Þ variables are introduced. Computational analyses with these formulations
are presented on the various instances of the CAB data set and on the Turkish
network.
2009 Elsevier Ltd. All rights reserved
Release Time Scheduling and Hub Location for Next-Day Delivery
Cataloged from PDF version of article.Inspired by a real-life problem faced by one of the largest ground-based cargo companies of Turkey, the current study
introduces a new facet to the hub location literature. The release time scheduling and hub location problem aims to select a
specified number of hubs from a fixed set of demand centers, to allocate each demand center to a hub, and to decide on the
release times of trucks from each demand center in such a way that the total amount of cargo guaranteed to be delivered
to every potential destination by the next day is not below a threshold and the total routing cost is minimized. The paper
introduces integer programming models to solve this problem in the special cases when the cargo uniformly arrives to each
demand center during the day and the more realistic pattern of when the cargo arrivals exhibit a piecewise linear form.
Several classes of valid inequalities are proposed to strengthen the formulations. Extensions with multiple service levels
and discrete sets for release times are also discussed. Computational results show the computational viability of the models
under realistic scenarios as well as the validity of the proposed problems in answering several interesting questions from
the cargo sector’s perspective