Discrete-time queueing models with state-dependent service capacity and arrival process

In dit proefschrift worden wachtlijnsystemen met twee toestanden geanalyseerd. Een wachtlijnsysteem bestaat uit klanten die een bepaalde bediening verwachten van een bedieningsstation (ook wel server genoemd). Wanneer alle bedieningsstations bezig zijn, vormen nieuwe klanten een wachtrij. In veel praktische wachtlijnsystemen varieert de mate waarin nieuwe klanten toekomen, of de mate waarin bedieningsstations beschikbaar zijn. Bijvoorbeeld de grotere drukte en het extra personeel in een luchthaven tijdens piekuren. Door het model op te splitsen in twee toestanden kunnen we zo'n variërend aankomstproces en/of bedieningsproces modelleren. We ontwikkelen een algemene techniek om dergelijke wachtlijnmodellen te analyseren, en bekomen daarbij resultaten in verband met het aantal klanten in het systeem alsook hun totale wachttijd

Delay in a 2-state discrete-time queue with stochastic state-period lengths and state-dependent server availability and arrivals

In this paper, we consider a discrete-time multiserver queueing system with correlation in the arrival process and in the server availability. Specifically, we are interested in the delay characteristics. The system is assumed to be in one of two different system states, and each state is characterized by its own distributions for the number of arrivals and the number of available servers in a slot. Within a state, these numbers are independent and identically distributed random variables. State changes can only occur at slot boundaries and mark the beginnings and ends of state periods. Each state has its own distribution for its period lengths, expressed in the number of slots. The stochastic process that describes the state changes introduces correlation to the system, e.g., long periods with low arrival intensity can be alternated by short periods with high arrival intensity. Using probability generating functions and the theory of the dominant singularity, we find the tail probabilities of the delay

Delay analysis of a discrete-time single-server queue with an occasional extra server

In this work we look at the delay analysis of a customer in a discrete-time queueing system with one permanent server and one occasional extra server. The arrival process is assumed to be general independent, the buffer size infinite and the service times deterministically equal to one slot. The system is assumed to be in one of two different states; during the UP-state 2 servers are available and during the DOWN-state 1 server is available. State changes can only occur at slot boundaries and mark the beginnings and ends of UP-periods and DOWN-periods. The lengths of the UP-periods, expressed in their number of slots, are assumed to follow a geometric distribution, while the lengths of the DOWN-periods follow a general distribution with rational probability generating function. We provide a method to compute the tail characteristics of the delay of an arbitrary customer based on the theory of the dominant singularity. We illustrate the developed method with several numerical examples

Long-Term Quality of Life after Minimally Invasive vs Open Distal Pancreatectomy in the LEOPARD Randomized Trial

BACKGROUND: Minimally invasive distal pancreatectomy (MIDP) shortens time to functional recovery and improves 30-day quality of life (QoL), as compared with open distal pancreatectomy (ODP) for nonmalignant disease. The impact of MIDP on QoL, cosmetic satisfaction, and overall major complications beyond 1-year follow-up is currently unknown. STUDY DESIGN: The Minimally Invasive Versus OpenDistal Pancreatectomy (LEOPARD) trial randomized 108 patients to MIDP (laparoscopic or robotic) or ODP in 14 Dutch centers (April 2015 to March 2017). The primary outcome measure of this study was quality-adjusted life years (QALYs), as assessed with the EQ-5D. QoL was assessed using subscales of the EORTCQLQ-C30, PAN-26, and a body image questionnaire. The latter included a cosmetic satisfaction score (range 3-24), and a body image score (range 5-20). Differences between MIDP and ODP for QALYs, generic, and disease-specific QoL and body image were analyzed. Missing QoL data were imputed using multiple imputation. RESULTS: In total, 84 patients were alive, with amedian follow-up of 44 months; 62 of these patients (74%) completed the questionnaires (27 MIDP, 35 ODP). There was no significant difference in QALYs between the 2 groups (mean score 2.34 vs 2.46 years, p = 0.63), nor on the QoL subscales. Significant overall change in EQ-5D health utilities were found for both groups over time (p < 0.001). Patients in the MIDP group scored higher on cosmetic satisfaction (21 vs 14, p = 0.049). No differences between the 2 groups were observed for clinical outcomes such as major complications, readmissions, and incisional hernias. CONCLUSIONS: More than 3 years after distal pancreatectomy, no improvement in QALYs and overall QoL was seen after MIDP, whereas cosmetic satisfaction was higher after MIDP as compared with ODP

Long-Term Quality of Life after Minimally Invasive vs Open Distal Pancreatectomy in the LEOPARD Randomized Trial

BACKGROUND: Minimally invasive distal pancreatectomy (MIDP) shortens time to functional recovery and improves 30-day quality of life (QoL), as compared with open distal pancreatectomy (ODP) for nonmalignant disease. The impact of MIDP on QoL, cosmetic satisfaction, and overall major complications beyond 1-year follow-up is currently unknown. STUDY DESIGN: The Minimally Invasive Versus Open Distal Pancreatectomy (LEOPARD) trial randomized 108 patients to MIDP (laparoscopic or robotic) or ODP in 14 Dutch centers (April 2015 to March 2017). The primary outcome measure of this study was quality-adjusted life years (QALYs), as assessed with the EQ-5D. QoL was assessed using subscales of the EORTC QLQ-C30, PAN-26, and a body image questionnaire. The latter included a cosmetic satisfaction score (range 3-24), and a body image score (range 5-20). Differences between MIDP and ODP for QALYs, generic, and disease-specific QoL and body image were analyzed. Missing QoL data were imputed using multiple imputation. RESULTS: In total, 84 patients were alive, with a median follow-up of 44 months; 62 of these patients (74%) completed the questionnaires (27 MIDP, 35 ODP). There was no significant difference in QALYs between the 2 groups (mean score 2.34 vs 2.46 years, p = 0.63), nor on the QoL subscales. Significant overall change in EQ-5D health utilities were found for both groups over time (p < 0.001). Patients in the MIDP group scored higher on cosmetic satisfaction (21 vs 14, p = 0.049). No differences between the 2 groups were observed for clinical outcomes such as major complications, readmissions, and incisional hernias. CONCLUSIONS: More than 3 years after distal pancreatectomy, no improvement in QALYs and overall QoL was seen after MIDP, whereas cosmetic satisfaction was higher after MIDP as compared with ODP

Long-Term Quality of Life after Minimally Invasive vs Open Distal Pancreatectomy in the LEOPARD Randomized Trial

Background: Minimally invasive distal pancreatectomy (MIDP) shortens time to functional recovery and improves 30-day quality of life (QoL), as compared with open distal pancreatectomy (ODP) for nonmalignant disease. The impact of MIDP on QoL, cosmetic satisfaction, and overall major complications beyond 1-year follow-up is currently unknown. Study Design: The Minimally Invasive Versus Open Distal Pancreatectomy (LEOPARD) trial randomized 108 patients to MIDP (laparoscopic or robotic) or ODP in 14 Dutch centers (April 2015 to March 2017). The primary outcome measure of this study was quality-adjusted life years (QALYs), as assessed with the EQ-5D. QoL was assessed using subscales of the EORTC QLQ-C30, PAN-26, and a body image questionnaire. The latter included a cosmetic satisfaction score (range 3–24), and a body image score (range 5–20). Differences between MIDP and ODP for QALYs, generic, and disease-specific QoL and body image were analyzed. Missing QoL data were imputed using multiple imputation. Results: In total, 84 patients were alive, with a median follow-up of 44 months; 62 of these patients (74%) completed the questionnaires (27 MIDP, 35 ODP). There was no significant difference in QALYs between the 2 groups (mean score 2.34 vs 2.46 years, p = 0.63), nor on the QoL subscales. Significant overall change in EQ-5D health utilities were found for both groups over time (p < 0.001). Patients in the MIDP group scored higher on cosmetic satisfaction (21 vs 14, p = 0.049). No differences between the 2 groups were observed for clinical outcomes such as major complications, readmissions, and incisional hernias. Conclusions: More than 3 years after distal pancreatectomy, no improvement in QALYs and overall QoL was seen after MIDP, whereas cosmetic satisfaction was higher after MIDP as compared with ODP