Healthcare queueing models.

Healthcare systems differ intrinsically from manufacturing systems. As such, they require a distinct modeling approach. In this article, we show how to construct a queueing model of a general class of healthcare systems. We develop new expressions to assess the impact of service outages and use the resulting model to approximate patient flow times and to evaluate a number of practical applications. We illustrate the devastating impact of service interruptions on patient flow times and show the potential gains obtained by pooling hospital resources. In addition, we present an optimization model to determine the optimal number of patients to be treated during a service session.Operations research; Health care evaluation mechanisms; Organizational efficiency; Management decision support systems; Time management; Queueing theory;

A Policy Switching Approach to Consolidating Load Shedding and Islanding Protection Schemes

In recent years there have been many improvements in the reliability of critical infrastructure systems. Despite these improvements, the power systems industry has seen relatively small advances in this regard. For instance, power quality deficiencies, a high number of localized contingencies, and large cascading outages are still too widespread. Though progress has been made in improving generation, transmission, and distribution infrastructure, remedial action schemes (RAS) remain non-standardized and are often not uniformly implemented across different utilities, ISOs, and RTOs. Traditionally, load shedding and islanding have been successful protection measures in restraining propagation of contingencies and large cascading outages. This paper proposes a novel, algorithmic approach to selecting RAS policies to optimize the operation of the power network during and after a contingency. Specifically, we use policy-switching to consolidate traditional load shedding and islanding schemes. In order to model and simulate the functionality of the proposed power systems protection algorithm, we conduct Monte-Carlo, time-domain simulations using Siemens PSS/E. The algorithm is tested via experiments on the IEEE-39 topology to demonstrate that the proposed approach achieves optimal power system performance during emergency situations, given a specific set of RAS policies.Comment: Full Paper Accepted to PSCC 2014 - IEEE Co-Sponsored Conference. 7 Pages, 2 Figures, 2 Table

Data Analysis of Transmission Line Restoration Times

The world is highly dependent on electricity, and any service interruptions can be contagious sometimes leading to devastating blackouts. This in turn have severe impacts on customers. Large service interruption can impact an entire region. Therefore, reliability is an integral part of the system operations for utilities. On an interruption of power supply caused by a transmission or distribution failure, measures taken to restore the service highly depend on the interruption duration of normal supply paths. This thesis is a systematic study of transmission line restoration times with statistics obtained from a utility’s data. The empirical probability distribution of transmission line restoration times is obtained from 14 years of field data. The distribution of restoration times has a heavy tail that indicates that long restoration times, although less frequent, routinely occur. The heavy tail differs from the convenient assumption of exponentially distributed restoration times, impacts power system resilience, and makes estimates of the mean time to repair highly variable. The mean restoration time of the heavy tailed distribution and its confidence interval is estimated using special bootstrap methods and its implications are outlined. The heavy tail in transmission line restoration times is one factor to be considered in assessing power system resilience

Modeling a healthcare system as a queueing network:The case of a Belgian hospital.

The performance of health care systems in terms of patient flow times and utilization of critical resources can be assessed through queueing and simulation models. We model the orthopaedic department of the Middelheim hospital (Antwerpen, Belgium) focusing on the impact of outages (preemptive and nonpreemptive outages) on the effective utilization of resources and on the flowtime of patients. Several queueing network solution procedures are developed such as the decomposition and Brownian motion approaches. Simulation is used as a validation tool. We present new approaches to model outages. The model offers a valuable tool to study the trade-off between the capacity structure, sources of variability and patient flow times.Belgium; Brownian motion; Capacity management; Decomposition; Health care; Healthcare; Impact; Model; Models; Performance; Performance measurement; Queueing; Queueing theory; Simulation; Stochastic processes; Structure; Studies; Systems; Time; Tool; Validation; Variability;

On the Verge of One Petabyte - the Story Behind the BaBar Database System

The BaBar database has pioneered the use of a commercial ODBMS within the HEP community. The unique object-oriented architecture of Objectivity/DB has made it possible to manage over 700 terabytes of production data generated since May'99, making the BaBar database the world's largest known database. The ongoing development includes new features, addressing the ever-increasing luminosity of the detector as well as other changing physics requirements. Significant efforts are focused on reducing space requirements and operational costs. The paper discusses our experience with developing a large scale database system, emphasizing universal aspects which may be applied to any large scale system, independently of underlying technology used.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics (CHEP03), La Jolla, Ca, USA, March 2003, 6 pages. PSN MOKT01

Distribution substation reliability assessment

Currently, reliability assessment methods have been developed to accommodate distribution systems. These methods can compute a customer\u27s reliability based on the system topology and component characteristics. The reliability assessment gives the utility an idea of where the problem areas are in a system. However, most of these methods lack a detailed representation of distribution substations, modeling only a small part of the substation, such as a transformer, or a transformer and a breaker. They fail to represent the rest of the substation like the switchgear and bus topology configurations. Without modeling the entire substation, the reliability calculation will suffer in accuracy and could give engineers misleading results. In addition, most reliability assessment methods do not take into account the degradation of component failure rates. The failure rates or hazard rates are treated as constant under exponential recovery models. The historical field data collected by utilities in the recent past has shown the contrary. Most power system components including lines, transformers, capacitors and protection equipment, exhibit failure rates that change with time. New component failure rates need to be integrated into the reliability models to resemble these time-varying effects. The objective of this research is to develop a reliability assessment method, which is relevant to all distribution substation configurations for a typical utility\u27s system. The new method will account for the degradation of component failure rates and give a detailed representation of substation equipment. In addition, the interruption impact to the customers will be assessed to determine the influence of time-dependent failure rates

Reliability Analysis of Dual-Purpose (Power and Water) Production Station, Volume I

This thesis presents the outcome of applying reliability engineering analysis techniques to a thermal dual-purpose (power&water) production station. The thermal cycle of the station is a fossil fueled steam boiler, condensing-extraction steam turbine, a generator, and a multi-stage flash evaporator