Queueing Approaches to Appointment System Design

We develop useful queueing models to analyze appointment-based service systems. There are many factors that make appointment scheduling in service systems extremely complex. For example, scheduled customers may not arrive on time or show up at all, customers with different priorities may have conflict of service access, service may last shorter or longer than expected, and so on. These kinds of uncertainties make stochastic modeling a perfect tool to be used to analyze and improve the performance of such systems. The objective of our research is to identify appointment scheduling policies that balance the utilization of expensive service resources and customer waiting. We specifically consider two problems that have been commonly observed in practice but received little attention from the past appointment-scheduling literature. The first problem is how to schedule appointments when scheduled services may be interrupted by service requests with higher priority. We generate the optimal scheduling policies under various scenarios: finite and infinite time horizon, equally spaced and non-equally spaced scheduling, constant and time-dependent interruption rate, and preemptive and non-preemptive service interruptions. In the second problem, we consider the appointment system as two queues in tandem: the appointment queue followed by the service queue. The customers join the appointment queue when they call for an appointment, stay there (not physically) until the appointment time comes, and then leave the appointment queue and physically join the service queue, and wait there until served. We explicitly capture the dependence between these two queues and derive important performance measures of interest, such as service utilization and customer long-run average waiting times in both queues.Doctor of Philosoph

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Active-Sensing Epidermal Stretchable Bioelectronic Patch for Noninvasive, Conformal, and Wireless Tendon Monitoring

Sensors capable of monitoring dynamic mechanics of tendons throughout a body in real time could bring systematic information about a human body’s physical condition, which is beneficial for avoiding muscle injury, checking hereditary muscle atrophy, and so on. However, the development of such sensors has been hindered by the requirement of superior portability, high resolution, and superb conformability. Here, we present a wearable and stretchable bioelectronic patch for detecting tendon activities. It is made up of a piezoelectric material, systematically optimized from architectures and mechanics, and exhibits a high resolution of 5.8×10−5 N with a linearity parameter of R2=0.999. Additionally, a tendon real-time monitoring and healthcare system is established by integrating the patch with a micro controller unit (MCU), which is able to process collected data and deliver feedback for exercise evaluation. Specifically, through the patch on the ankle, we measured the maximum force on the Achilles tendon during jumping which is about 16312 N, which is much higher than that during normal walking (3208 N) and running (5909 N). This work not only provides a strategy for facile monitoring of the variation of the tendon throughout the body but also throws light on the profound comprehension of human activities