Total Service Capacity Research Articles

Line balancing of aircraft IDG part maintenance process line balance using line balancing and promodel

Aircraft have thousands of components that must be maintained to remain functional. Components on aircraft have a high enough price that maintenance is required. The power source on an airplane can be divided into 2 types, namely AC and DC. One source of AC electricity is the Integrated Drive Generator (IDG) which is one of the important components of an aircraft that functions as a generator of electricity. If IDG experiences a problem, it will disrupt aircraft operations. For this purpose, IDG must receive good care with effective services. The processing time for maintenance services takes 42.8 hours for one IDG part unit. This study aims to balance the trajectory. The IDG part maintenance process is carried out by Pro-model simulation. The results of the IDG maintenance simulation are the maintenance time in operation (Average time in Operation) which is 42.61 hours and the IDG parts handled are 11 IDG parts. The results of this simulation scenario can estimate the possible number of IDG parts that will occur annually and can estimate the total service capacity that handles the planned number of incoming entities. The best scenario results when the capacity of 1 service group per unit will result in the number of IDG maintenance services of 11 units per year, by increasing the service capacity to 2 service groups per unit will result in the number of IDG maintenance services of 23 units per year. And by increasing the service capacity to 4 service groups per unit, the number of maintenance services will be 46 units per year.

Capturing twenty years of change in ecosystem services provided by coastal Massachusetts habitats

Accounting for ecosystem services across expansive and diverse landscapes presents unique challenges to managers tasked with navigating and synthesizing the social-ecological dynamics of varied stakeholder interests and ecological functions. One approach to this challenge is through expert based matrices that provide valuations for specific service-habitat combinations. In this study, we combine a literature review with local expert input to build an ecosystem service capacity matrix for the Massachusetts Bays National Estuary Partnership (MassBays). We then apply this matrix to a custom conglomerate land cover data set and a habitat connectivity analysis to assess the spatial and temporal dynamics in select ecosystem services of coastal habitats across MassBays from 1996 to 2016. In 1996, saltmarsh was the primary provider of coastal ecosystem services, representing roughly 60% of the total service capacity. More specifically, high elevation saltmarsh was top-ranked, followed by tidal flats, seagrass, low elevation saltmarsh and unclassified saltmarsh. This distribution of service provisioning varied considerably among the five regions of MassBays, reflecting the unique habitat mixes and local expert valuations of each. Although saltmarsh dominated the overall production of services, seagrass and tidal flats drove 97% of the service changes that occurred from one year to the next. From 1996 to 2016, MassBays lost 50% of its seagrass cover and gained 20% more tidal flats, resulting in a 5% overall loss in ecosystem services. Again, this varied among the five regions, with Cape Cod losing as much as 12% of a given service while the Upper North Shore gained 4% in services overall. We bootstrapped the analysis to provide a range of probable outcomes. We also mapped the changes in service production for each of the sixty-eight embayments. This analysis will aid local managers in accounting for ecosystem services as they develop management plans for their represented stakeholders.

Evaluation of the Effectiveness of Brazilian Community Restaurants for the Dimension of Low-Income People Access to Food.

This study aimed to evaluate the effectiveness of community restaurants (CRs), managed by the Government of the State of Bahia/Brazil, for the dimension of access to food. The study used secondary data obtained from the public opinion survey Profile of users of community restaurants in Salvador. The nutritional information was accessed through the analysis of CRs’ menus. Adequate effectiveness of access to food was considered when the CR served meals to 50% to 70% of the users considered the target audience (individuals served by the two CRs located in the city of Salvador/Bahia/Brazil). The participants (n = 1464; 778 as low-income individuals) were adult CR users from Salvador/Brazil. Most of the respondents were male, 40 to 54 years old, not white, had up to 9 years of formal education, without a partner, and living in the municipality of Salvador. The evaluated CRs are effective in serving 53.1% of the target population in their total service capacity. Meal provision only reached an estimated 0.7% of the socially vulnerable community in the district. The average energy value of the meal served by the CR units was 853.05 kcal/meal, with a mean energy density composition classified as average (1.15 kcal/g). The effectiveness of the evaluated community restaurants showed that these instruments were minimally effective in promoting access to food for the low-income population within their total daily service capacity, and the current quantity of these facilities was insufficient. However, these instruments stand out in the fundamental role of promoting the daily distribution of meals to the Brazilian population with the highest social vulnerability levels.

Optimization and analysis of a tandem queueing system with parallel channel at second station

We consider a tandem queue consisting of two stations. We demonstrate that customer numbers and waiting times at both stations are independent of each other in the steady-state. As an optimal design, in the second station, We consider that there is a single channel that has the total service capacity of two parallel channels instead of two identical channels. Then, we indicate that the optimal system works faster than the tandem queue system with parallel channels at the second station. Also, when the total service capacity is limited, the mean waiting time in the system has been minimized in the optimal system obtained the mean waiting time lower limit. We compared it to those found through a numerical example.

Service capacity procurement of logistics service supply chain with demand updating and loss-averse preference

This paper studies the impacts of loss-averse preference on the service capacity procurement decisions with demand updating in a logistics service supply chain, which consists of one logistics service integrator and one functional logistics service provider. It starts from a basic two-stage Stackelberg game model, then, extends to three scenarios where either the integrator or the provider or neither of them has loss-averse preference. The impact of loss-averse preference on the decisions of supply chain members is discussed by comparing the four models. Our results reveal, first, the loss-averse preferences do not always affect the decisions of supply chain members. If certain conditions are satisfied, the logistics service integrator can benefit from its loss-averse preference. Second, the increased service level can affect the logistics service integrator's procurement strategy and the functional logistics service provider's pricing strategy. This effect is only related to the loss-averse preference of the functional logistics service provider. Last, under certain conditions, the total service capacity decreases with the increased service level, regardless of whether or not the supply chain members have loss-averse preferences.

An analysis of nonstationary coupled queues

We consider a two dimensional time varying tandem queue with coupled processors. We assume that jobs arrive to the first station as a non-homogeneous Poisson process. When each queue is non-empty, jobs are processed separately like an ordinary tandem queue. However, if one of the processors is empty, then the total service capacity is given to the other processor. This problem has been analyzed in the constant rate case by leveraging Riemann Hilbert theory and two dimensional generating functions. Since we are considering time varying arrival rates, generating functions cannot be used as easily. Thus, we choose to exploit the functional Kolmogorov forward equations (FKFE) for the two dimensional queueing process. In order to leverage the FKFE, it is necessary to approximate the queueing distribution in order to compute the relevant expectations and covariance terms. To this end, we expand our two dimensional Markovian queueing process in terms of a two dimensional polynomial chaos expansion using the Hermite polynomials as basis elements. Truncating the polynomial chaos expansion at a finite order induces an approximate distribution that is close to the original stochastic process. Using this truncated expansion as a surrogate distribution, we can accurately estimate probabilistic quantities of the two dimensional queueing process such as the mean, variance, and probability that each queue is empty.

Routing and Staffing in Large-Scale Service Systems: The Case of Homogeneous Impatient Customers and Heterogeneous Servers

Motivated by call centers, we study large-scale service systems with homogeneous impatient customers and heterogeneous servers; the servers differ with respect to their speed of service. For this model, we propose staffing and routing rules that are jointly asymptotically optimal in the heavy-traffic many-server QED, ED, and ED + QED regimes, respectively. For the QED regime, our proposed routing rule is FSF, that assigns customers to the fastest server available first. In the ED and ED + QED regimes, all work-conserving policies perform (asymptotically) equally well. In all these regimes, the form of the asymptotically optimal staffing is consistent with the asymptotically optimal staffing in the same regimes in the single-pool case, respectively. In particular, the total service capacity is (asymptotically) equal to a term that is proportional to the arrival rate plus, possibly, a term that is proportional to the square-root of the arrival rate, with both terms being regime dependent. Our specific proposed approximation for the optimal staffing vector is obtained via a straightforward solution to a deterministic optimization problem subject to a linear feasible region.

Using aggregation to construct periodic policies for routing jobs to parallel servers with deterministic service times

The problem of routing deterministic arriving jobs to parallel servers with deterministic service times, when the job arrival rate equals the total service capacity, requires finding a periodic routing policy. Because there exist no efficient exact procedures to minimize the long-run average waiting time of arriving jobs, heuristics to construct periodic policies have been proposed. This paper presents an aggregation approach that combines servers with the same service rate, constructs a policy for the aggregated system, and then disaggregates this policy into a feasible policy for the original system. Computational experiments show that using aggregation not only reduces average waiting time but also reduces computational effort.

A Tandem Queue with Coupled Processors: Computational Issues

In Resing and Örmeci [16] it is shown that the two-stage tandem queue with coupled processors can be solved using the theory of boundary value problems. In this paper we consider the issues that arise when calculating performance measures like the mean queue length and the fraction of time a station is empty. It is assumed that jobs arrive at the first station according to a Poisson process and require service at both stations before leaving the system. The amount of work that a job requires at each of the stations is an independent, exponentially distributed random variable. When both stations are nonempty, the total service capacity is shared among the stations according to fixed proportions. When one of the stations becomes empty, the total service capacity is given to the nonempty station. We study the two-dimensional Markov process representing the numbers of jobs at the two stations. The problem of finding the generating function of the stationary distribution can be reduced to two different Riemann-Hilbert boundary value problems, where both problems yield a complete analytical solution. We discuss the similarities and differences between the two problems, and relate them to the computational aspects of obtaining performance measures.

Routing Jobs to Servers with Deterministic Service Times

In this paper we consider the problem of routing deterministic arriving jobs to parallel servers with deterministic (distinct) service times, where we assume that the arrival rate of the jobs is equal to the total service capacity of the servers. Our goal is to find routing policies that minimize the long-run average waiting time of the arriving jobs. We give lower and upper bounds for the minimal long-run average waiting time, and we present results on the structure of optimal policies. We derive mathematical programming problems that can be solved to obtain optimal routing policies, and for a single queue we have results on routing according to a regular sequence to that queue. Finally, we discuss several algorithms to obtain within reasonable time good but generally not optimal deterministic routing policies.

Waiting time distributions for M/M/N processor sharing queues

We consider a multiple server queue in which arrivals form a Poisson process and each customer's service demand is exponentially distributed. The servers work according to the processor sharing discipline. If there are fewer customers than servers in the system, each customer is served by a single processor, the other servers remaining idle. Otherwise each customer's demand is reduced in proportion to the total service capacity. We calculate implicit representations for the Laplace–Stieltjes transform of conditioned waiting time distributions. In particular we compute the mean and variance of the waiting time of a tagged customer conditioned on the number of customers in the system and the corresponding moments of the equilibrium waiting time. Numerical results are presented

On queueing systems with variable service capacities

AbstractIn some queueing systems the total service capacity utilized at any given time is a variable under the control of a decision maker. Management doctrines are examined which prescribe the actual service capacity as a function of the queue length and the recent history of the system. Steady state probabilities, expected queue lengths and frequencies of change in capacity are evaluated for a wide class of possible control schemes. Optimization procedures are outlined.