Total Service Time Research Articles

Measuring performance of night-time interfacility transport service

The service reorganization is a part of the healthcare system reform. Some hospitals may not be able to provide all services in a 24-h basis. This evaluation was on all night-time (22 : 00 p.m. to 07 : 00 a.m.) interfacility transport by Alice Ho Miu Ling Hospital emergency department from January 2008 to December 2010, which were in-patients from nonemergency wards. The safety, speed, and performance were analyzed. During the study period, 73 cases were transferred out. Majority of them were having neurosurgical emergency (n=21, 29%) or surgical emergency (n=34, 46%). En-route physiological deteriorations were encountered in 4% (3/73) of cases. The mean acceptance time was 8 min and the team mobilization time was 13 min on average. The total service time ranged from 40 to 115 min. In conclusion, en-route adverse event was not rare. The specialized team can act as a facilitator and coordinator to improve the safety and effectiveness of the whole process.

混雑ピークと運用規模の違いによる岸壁空間利用の生産性への影響

In order to use the quay space efficiently, we address various cases of partitioning arrangement in a given quay space operated by multiple units of one-berth, one unit of multiple-berth, and multiple units of medium and small sizes consisted of one or more berths. In this paper, we investigate the impact of partitioning arrangements and rush-hour traffic on quay space utilization. From the computational results, the arrangements operated by one units of large-size and multiple units of medium-size outperform those done by the others, in most cases. However, it is clear that total service times depend on ship arrival pattern, ship service distribution and rush-hour traffic.

Scheduling of Inbound Trucks at a Cross-Docking Facility

This paper examines the problem of scheduling of inbound trucks to the inbound doors at a cross-docking facility. The authors optimize for two conflicting objectives: minimize the total service time for all the inbound trucks and minimize the delayed completion of service for a subset of the inbound trucks, which are considered as preferential customers. The problem is formulated as a bi-objective and as a bi-level mixed integer problem. Due to the nature of the former and the complexity of the latter formulation, a genetic algorithm and a k-th best based algorithm are proposed as the solution approaches. Computational examples are used to discuss the advantages and drawbacks of each formulation.

Management Insights

Management Insights

Solving a multi-objective interval crew-scheduling problem via Genetic Algorithms

In this paper, a crew-scheduling problem has been formulated considering the daily assignment of a set of crew staff to their round-trips for all the public transports (e.g. train, bus or air bus) that will minimize the waiting times and total service times (including waiting times) of all crews separately. In this approach, the waiting times as well as the service times of crews have been taken as intervals. Here the problem has been formulated as a multi-objective assignment problem using interval arithmetic and the order relations (for the case of pessimistic decision making) that represent the decision maker’s preference between interval times. For this purpose, we have used the existing complete definition of order relations recently developed. Finally, the reformulated problem has been converted to a single objective optimization problem using Global Criterion Method and then solved the same by tournament genetic algorithm. The experimental results of the proposed approach to a crew-scheduling problem have been reported.

Berth allocation planning in Seville inland port by simulation and optimisation

We study the problems associated with allocating berths for containerships in the port of Seville. It is the only inland port in Spain and it is located on the Guadalquivir River. This paper addresses the berth allocation planning problems using simulation and optimisation with Arena software. We propose a mathematical model and develop a heuristic procedure based on genetic algorithm to solve non-linear problems. Allocation planning aims to minimise the total service time for each ship and considers a first-come-first-served allocation strategy. We conduct a large amount of computational experiments which show that the proposed model improves the current berth management strategy.

ANALYSIS OF MULTI-SERVER SINGLE QUEUE

Queuing properties such as expected total service time and its variance and some performance measures like the expected number of phases in the system, expected number of phases in the queue, expected number of customers in the queue, expected waiting time in the queue and in the system as well as the number of customers in the system have been derived for an  M/Ek/s: ( /FCFS) queuing model with k identified stages in series, each with average service time of . Also, numerical illustrations have also been used to illustrate the results.

A Hybrid Ant Colony Optimization Algorithm for the Extended Capacitated Arc Routing Problem

The capacitated arc routing problem (CARP) is representative of numerous practical applications, and in order to widen its scope, we consider an extended version of this problem that entails both total service time and fixed investment costs. We subsequently propose a hybrid ant colony optimization (ACO) algorithm (HACOA) to solve instances of the extended CARP. This approach is characterized by the exploitation of heuristic information, adaptive parameters, and local optimization techniques: Two kinds of heuristic information, arc cluster information and arc priority information, are obtained continuously from the solutions sampled to guide the subsequent optimization process. The adaptive parameters ease the burden of choosing initial values and facilitate improved and more robust results. Finally, local optimization, based on the two-opt heuristic, is employed to improve the overall performance of the proposed algorithm. The resulting HACOA is tested on four sets of benchmark problems containing a total of 87 instances with up to 140 nodes and 380 arcs. In order to evaluate the effectiveness of the proposed method, some existing capacitated arc routing heuristics are extended to cope with the extended version of this problem; the experimental results indicate that the proposed ACO method outperforms these heuristics.

A delay‐oriented prioritization policy based on non‐congestive queuing

AbstractIn this paper, we depart from our previously proposed Non‐Congestive Queuing (NCQ) mechanism and propose a new scheduling discipline that allows for efficient interoperation of dedicated systems (such as sensor and voice networks) with the Internet. More precisely, our approach provides delay guarantees to applications that do not contribute noticeably to congestion because of their tiny packet sizes and low transmission rates. In addition, our approach uses a second level of prioritization that conditionally favors, in terms of delay, applications with slightly longer packets as well. Based on the NCQ concept, Non‐Congestive Queuing Plus (NCQ+) promotes applications that require comparatively small service times, as long as their total service times cause insignificant delays to other packets in the queue. Therefore, we prioritize packets, and in turn corresponding flows, according to their impact on total delay. We evaluate NCQ+ using ns‐2‐based experiments. Results show that whenever prioritization buffer resources are sufficient, NCQ+ can provide non‐detectable delays to sensor applications and conditionally improve the performance of VoIP applications, while maintaining the impact on the performance of the other flows insignificant. Copyright © 2011 John Wiley & Sons, Ltd.

Joint ground and air emergency medical services coverage models: A greedy heuristic solution approach

Aeromedical and ground ambulance services often team up in responding to trauma crashes, especially when the emergency helicopter is unable to land at the crash scene. We propose location-coverage models and a greedy heuristic for their solution to simultaneously locate ground and air ambulances, and landing zones (transfer points). We provide a coverage definition based on both response time and total service time, and consider three coverage options; only ground emergency medical services (EMS) coverage, only air EMS coverage, or joint coverage of ground and air EMS in which the patient is transferred from an ambulance into an emergency helicopter at a transfer point. To analyze this complex coverage situation we develop two sets of models, which are variations of the Location Set Covering Problem (LSCP) and the Maximal Covering Location Problem (MCLP). These models address uncertainty in spatial distribution of motor vehicle crash locations by providing coverage to a given set of both crash nodes and paths. The models also consider unavailability of ground ambulances by drawing upon concepts from backup coverage models. We illustrate our results on a case study that uses crash data from the state of New Mexico. The case study shows that crash node and path coverage percentage values decrease when ground ambulances are utilized only within their own jurisdiction.

An integer-valued model for the problem of minimizing the total servicing time of unit claims with parallel devices with precedences

We describe an integer-valued model of the total service time minimization problem for a partially ordered set of claims with identical servicing times, serviced in parallel by identical devices. We construct a target function over the polyhedron corresponding to the problem. We give results of a numerical experiment that deal with the variance of the total service time and the structure of the schedules' convex hull.

A bi-objective supply chain design problem with uncertainty

We consider the design of a two-echelon production distribution network with multiple manufacturing plants, customers and a set of candidate distribution centers. The main contribution of the study is to extend the existing literature by incorporating the demand uncertainty of customers within the distribution center location and transportation mode allocation decisions, as well as providing a network design satisfying the both economical and service quality objectives of the decision maker within two levels supply network setting. We formulate the problem as two stage integer recourse problem to find a set of optimal network configuration and assignment of transportation modes and the respective flows in order to minimize total cost and total service time, simultaneously. We develop a stochastic optimization model under demand uncertainty, where the inherent risk is modeled by scenarios. Finally, we propose solution methods for our stochastic optimization problem based on L-shaped algorithm within an ∊-optimality framework and present numerical results demonstrating the computational effectiveness.

The Berth-Scheduling Problem

This paper presents a new formulation for the discrete space berth-scheduling problem at marine container terminals. This formulation reflects an environmentally friendly berth-scheduling policy with the objectives of (a) maximizing berth productivity by minimizing the total service time and delayed departures for all vessels and (b) minimizing the total emissions and fuel consumption for all vessels while in transit to their next port of call. A genetic algorithms–based heuristic is presented to solve the resulting problem, and computational examples are presented to evaluate the proposed berth-scheduling policy.

Incorporating congestion in preventive healthcare facility network design

Preventive healthcare aims at reducing the likelihood and severity of potentially life-threatening illnesses by protection and early detection. The level of participation to preventive healthcare programs is a crucial factor in terms of their effectiveness and efficiency. This paper provides a methodology for designing a network of preventive healthcare facilities so as to maximize participation. The number of facilities to be established and the location of each facility are the main determinants of the configuration of a healthcare facility network. We use the total (travel, waiting and service) time required for receiving the preventive service as a proxy for accessibility of a healthcare facility, and assume that each client would seek the services of the facility with minimum expected total time. At each facility, which we model as an M/M/1 queue so as to capture the level of congestion, the expected number of participants from each population zone decreases with the expected total time. In order to ensure service quality, the facilities cannot be operated unless their level of activity exceeds a minimum workload requirement. The arising mathematical formulation is highly nonlinear, and hence we provide a heuristic solution framework for this problem. Four heuristics are compared in terms of accuracy and computational requirements. The most efficient heuristic is utilized in solving a real life problem that involves the breast cancer screening center network in Montreal. In the context of this case, we found out that centralizing the total system capacity at the locations preferred by clients is a more effective strategy than decentralization by the use of a larger number of smaller facilities. We also show that the proposed methodology can be used in making the investment trade-off between expanding the total system capacity and changing the behavior of potential clients toward preventive healthcare programs by advertisement and education.

The CMS-1500 Claim Form

The CMS-1500 Claim Form

Mechanical Properties of G17CrMoV5 – 10 Cast Steel after Regenerative Heat Treatment

The paper presents results of research on the influence of regenerative heat treatment on structure and properties of G17CrMoV5 – 10 cast steel. Investigated material was taken out from a turbine frame serviced for over 250 000 hours (total service time) at the temperature of 535 oC. The cast steel after service revealed degraded bainitic-ferritic structure and was characterized by mechanical properties ranging below norm requirements. It has been proved that high tempering temperature in the case of cast steel with bainitic structure ensures optimum combination of mechanical properties and impact energy. It has also been shown that ferrite has a negative influence on impact energy of the cast steel with bainitic-ferritic structure.

Overall level of service measures for airport passenger terminals

Overall level of service (LOS) measures for airport passenger terminals are presented in this paper. These measures are useful to evaluate the overall LOS in a single scale, according to user perceptions. The procedure consists of observing passengers and collecting several socio-economic and physical variables that might influence the user evaluation of the airport as a whole. A psychometric scaling technique is used to obtain quantitative LOS ratings from survey data. Regression analysis is used to obtain mathematical relationships between the quantitative LOS ratings and global indices (total service time, total walking distance and two orientation indices). The methodology is illustrated with its application at São Paulo/Guarulhos International Airport in Brazil.

The Berth Allocation Problem with Service Time and Delay Time Objectives

This study addresses a two-objective berth allocation problem: ship service quality expressed by the minimisation of delay in ships' departure and berth utilisation expressed by the minimisation of the total service time. In this problem, noninferior solutions are expected to be identified. Two heuristics, which are implemented based on two existing procedures of the subgradient optimisation and genetic algorithm, are proposed for solving this problem. Through numerical experiments, it was found that in most cases the genetic algorithm outperformed the subgradient optimisation. Also the tight time window yielded noninferior solutions.

Child protection in Stockholm: A local cohort study on childhood prevalence of investigations and service delivery

Prevalence figures of child protection investigations and services are dominated by cross-sectional data and annual statistics. So far, no data exist on how many children are investigated or receive services at some time during childhood, from birth to age of majority. This study reports on Child Protection Authorities' (CPA) involvement in a random sample of children born from 1968 to 1975, who resided permanently in Stockholm (Sweden) from birth to age 18 ( N = 2.297). Information is based on reviews of CPA case files, registering information of all referrals, investigations and social services received by those children until the age of 20. In the study population, 12% ( n = 272) were objects of at least one child protection investigation during their childhood and 7% ( n = 162) received social services at least once. When these figures are extrapolated to children who have at any time lived in Stockholm (including those born outside of Stockholm but moving to Stockholm and children born in Stockholm but migrated elsewhere), they increase to point estimates of 19% and 10%. The average total service time was about 5 years. Three out of four children receiving services were at one time or another in out-of-home care. 56% of the service receivers were re-referred to the CPA after terminated services. Implications for the findings are discussed.

Berthing ships at a multi-user container terminal with a limited quay capacity

This paper addresses a variation of the berth allocation problem at multi-user terminals, as ships which would normally be served at the terminal but their expected wait time exceeds the time limit, are assigned to an external terminal. The objective of the problem is to minimize the total service time of ships at the external terminal. A genetic algorithm based heuristic is developed and a wide variety of numerical experiments showed that the heuristic developed performed well in reducing external terminal usage and thus may be helpful in the efficient management of busy ports during extreme peaking conditions.