On the Improvement From Scheduling a Two-Station Queueing Network in Heavy Traffic

For a two-station multiclass queueing network in heavy traffic, we assess the improvement from scheduling (job release and priority sequencing) that can occur relative to Poisson input and first-come first-served (FCFS) sequencing. In particular, simple upper bounds are derived on the optimal objective function value (found in Wein 1989a) of a Brownian control problem that approximates (via Harrison's 1988 model) a two-station queueing network scheduling problem in heavy traffic. When the system is perfectly balanced, the Brownian analysis predicts that optimal scheduling will reduce the long run expected average number of customers in the network by at least a factor of four relative to the Poisson input, FCFS sequencing policy that achieves the same throughput rate. When the system is not perfectly balanced, the corresponding factor is slightly smaller than two

Performance Bounds for Scheduling Queueing Networks

The goal of this paper is to assess the improvement in performance that might' be achieved by optimally scheduling a multiclass open queueing network. A stochastic process is defined whose steady-state mean value is less than or equal to the mean number of customers in a queueing network under any arbitrary scheduling policy. Thus, this process offers a lower bound on performance when the objective of the queueing network scheduling problem is to minimize the mean number of customers in the network. Since this bound is easily obtained from a computer simulation model of a queueing network, its main use is to aid job-shop schedulers in determining how much further improvement (relative to their proposed policies) might be achievable from scheduling. Through computational examples, we identify some factors that affect the tightness of the bound

The Impact of Processing Time Knowledge on Dynamic Job-Shop Scheduling

The goal of this paper is to determine if the results for dynamic job-shop scheduling problems are affected by the assumptions made with regard to the processing time distributions and the scheduler's knowledge of the processing times. Three dynamic jobshop scheduling problems (including a two station version of Conway et al.'s [2] nine station symmetric shop) are tested under seven different scenarios, one deterministic and six stochastic, using computer simulation. The deterministic scenario, where the processing times are exponential and observed by the scheduler, has been considered in many simulation studies, including Conway et al's. The six stochastic scenarios include the case where the processing times are exponential and only the mean is known to the scheduler, and five different cases where the machines are subject to unpredictable failures. Two policies were tested, the shortest expected processing time (SEPT) rule, and a rule derived from a Brownian analysis of the corresponding queueing network scheduling problem. Although the SEPT rule performed well in the deterministic scenario, it was easily outperformed by the Brownian policies in the six stochastic scenarios for all three problems. Thus, the results from simulation studies of dynamic, deterministic job-shop scheduling problems do not necessarily carry over to the more realistic setting where there is unpredictable variability present

Dynamic Scheduling of a Production/Inventory System with By-Products and Random Yield

Motivated by semiconductor wafer fabrication, we consider a scheduling problem for a single-server multiclass queue. A single workstation fabricates semiconductor wafers according to a variety of different processes, where each process consists of multiple stages of service with a different general service time distribution at each stage. A batch (or lot) of wafers produced according to a particular process randomly yields chips of many different product types, and completed chips of each type enter a finished goods inventory that services exogenous customer demand for that type. The scheduling problem is to dynamically decide whether the server should be idle or working, and in the latter case, to decide which stage of which process type to serve next. The objective is to minimize the long run expected average cost, which includes costs for holding work-in-process inventory(which may differ by process type and service stage) and backordering and holding finished goods inventory (which may differ by product type). We assume the workstation must be busy the great majority of the time in order to satisfy customer demand, and approximate the scheduling problem by a control problem involving Brownian motion. A scheduling policy is derived by interpreting the exact solution to the Brownian control problem in terms of the production/inventory system. The proposed dynamic scheduling policy takes a relatively simple form and appears to be effective in numerical studies

Characteristics of Real Futures Trading Networks

Futures trading is the core of futures business, and it is considered as one of the typical complex systems. To investigate the complexity of futures trading, we employ the analytical method of complex networks. First, we use real trading records from the Shanghai Futures Exchange to construct futures trading networks, in which nodes are trading participants, and two nodes have a common edge if the two corresponding investors appear simultaneously in at least one trading record as a purchaser and a seller respectively. Then, we conduct a comprehensive statistical analysis on the constructed futures trading networks. Empirical results show that the futures trading networks exhibit features such as scale-free behavior with interesting odd-even-degree divergence in low-degree regions, small-world effect, hierarchical organization, power-law betweenness distribution, disassortative mixing, and shrinkage of both the average path length and the diameter as network size increases. To the best of our knowledge, this is the first work that uses real data to study futures trading networks, and we argue that the research results can shed light on the nature of real futures business.Comment: 18 pages, 9 figures. Final version published in Physica

Single cell atlas for 11 non-model mammals, reptiles and birds.

The availability of viral entry factors is a prerequisite for the cross-species transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Large-scale single-cell screening of animal cells could reveal the expression patterns of viral entry genes in different hosts. However, such exploration for SARS-CoV-2 remains limited. Here, we perform single-nucleus RNA sequencing for 11 non-model species, including pets (cat, dog, hamster, and lizard), livestock (goat and rabbit), poultry (duck and pigeon), and wildlife (pangolin, tiger, and deer), and investigated the co-expression of ACE2 and TMPRSS2. Furthermore, cross-species analysis of the lung cell atlas of the studied mammals, reptiles, and birds reveals core developmental programs, critical connectomes, and conserved regulatory circuits among these evolutionarily distant species. Overall, our work provides a compendium of gene expression profiles for non-model animals, which could be employed to identify potential SARS-CoV-2 target cells and putative zoonotic reservoirs

Dynamic scheduling of queueing networks

Thesis (Ph. D.)--Massachusetts Institute of Technology, Sloan School of Management, 1991.Includes bibliographical references (leaves 81-83).Jihong Ou.Ph.D

An analysis of China's position on the Diaoyu/Senkaku islands dispute.

48 p.The Diaoyu/Senkaku Islands dispute is still a sensitive issue between China and Japan. Despite the latter's actual control of the islands, China never gives up its sovereignty claim. Due to this unresolved dispute, their bilateral relationships have experienced ups and downs. In an attempt to settle the dispute, Deng Xiaoping, the then Chinese Vice Premier, proposed a policy of "shelf dispute, develop jointly" in the late 1970s, which since then has become the official attitude of China to tackle the dispute. This paper using a micro-macro linkage approach argues that China's decision to put aside the dispute is a tradeoff between sovereignty and time for the sake of its modernization.Master of Science (International Relations

Routing and scheduling pickup vehicles at a central mail processing facility

Research Paper Series (National University of Singapore. Faculty of Business Administration); 1996-0031-1

PRAYING FOR RAIN: STATE, SOCIETY AND CULTURE IN CHINA 1912-1949

Master'sMASTER OF ARTS (RSH-FASS