Closed-loop two-echelon repairable item systems

In this paper we consider closed loop two-echelon repairable item systems with repair facilities both at a number of local service centers (called bases) and at a central location (the depot). The goal of the system is to maintain a number of production facilities (one at each base) in optimal operational condition. Each production facility consists of a number of identical machines which may fail incidentally. Each repair facility may be considered to be a multi-server station, while any transport from the depot to the bases is modeled as an ample server. At all bases as well as at the depot, ready-for-use spare parts (machines) are kept in stock. Once a machine in the production cell of a certain base fails, it is replaced by a ready-for-use machine from that base's stock, if available. The failed machine is either repaired at the base or repaired at the central repair facility. In the case of local repair, the machine is added to the local spare parts stock as a ready-for-use machine after repair. If a repair at the depot is needed, the base orders a machine from the central spare parts stock to replenish its local stock, while the failed machine is added to the central stock after repair. Orders are satisfied on a first-come-first-served basis while any requirement that cannot be satisfied immediately either at the bases or at the depot is backlogged. In case of a backlog at a certain base, that base's production cell performs worse. To determine the steady state probabilities of the system, we develop a slightly aggregated system model and propose a special near-product-form solution that provides excellent approximations of relevant performance measures. The depot repair shop is modeled as a server with state-dependent service rates, of which the parameters follow from an application of Norton's theorem for Closed Queuing Networks. A special adaptation to a general Multi-Class MDA algorithm is proposed, on which the approximations are based. All relevant performance measures can be calculated with errors which are generally less than one percent, when compared to simulation results. \u

Analytical models to determine room requirements in outpatient clinics

Outpatient clinics traditionally organize processes such that the doctor remains in a consultation room while patients visit for consultation, we call this the Patient-to-Doctor policy (PtD-policy). A different approach is the Doctor-to-Patient policy (DtP-policy), whereby the doctor travels between multiple consultation rooms, in which patients prepare for their consultation. In the latter approach, the doctor saves time by consulting fully prepared patients. We use a queueing theoretic and a discrete-event simulation approach to provide generic models that enable performance evaluations of the two policies for different parameter settings. These models can be used by managers of outpatient clinics to compare the two policies and choose a particular policy when redesigning the patient process.We use the models to analytically show that the DtP-policy is superior to the PtD-policy under the condition that the doctor’s travel time between rooms is lower than the patient’s preparation time. In addition, to calculate the required number of consultation rooms in the DtP-policy, we provide an expression for the fraction of consultations that are in immediate succession; or, in other words, the fraction of time the next patient is prepared and ready, immediately after a doctor finishes a consultation. We apply our methods for a range of distributions and parameters and to a case study in a medium-sized general hospital that inspired this research

Congestion and residential moving behaviour

In this paper we study how congestion and residential movingbehaviour are interrelated using a two-region job search model. Workerschoose optimally between interregional commuting and residential movingto live closer to the place of work. This choice affects the external costs ofcommuting due to congestion. The welfare maximizing road tax is derived.We demonstrate that road pricing may not only reduce congestion but alsoincrease total residential moving costs in the economy. One of the mainconsequences is that the road tax does not necessarily increase welfare

Risk factors for non-closure of an intended temporary defunctioning stoma after emergency resection of left-sided obstructive colon cancer

Purpose: A substantial part (21–35%) of defunctioning stomas created during resection for colorectal cancer will never be reversed. Known risk factors for non-closure are age, peri- or postoperative complications, comorbidity, and tumor stage. However, studies performed to identify these risk factors mostly focus on rectal cancer and include both preoperative and postoperative factors. This study aims to identify preoperative risk factors for non-reversal of intended temporary stomas created during acute resection of left-sided obstructive colon cancer (LSOCC) with primary anastomosis. Methods: All patients who underwent emergency resection for LSOCC with primary anastomosis and a defunctioning stoma between 2009 and 2016 were selected from the Dutch ColoRectal Audit, and additional data were collected in the local centers. Multivariable analysis was performed to identify independent preoperative factors for non-closure of the stoma. Results: A total of 155 patients underwent acute resection for LSOCC with primary anastomosis and a defunctioning stoma. Of these, 51 patients (32.9%) did not have their stoma reversed after a median of 53 (range 7–104) months of follow-up. In multivariable analysis, hemoglobin &lt; 7.5 mmol/L (odds ratio (OR) 4.79, 95% confidence interval (95% CI) 1.60–14.38, p = 0.005), estimated glomerular filtration rate (eGFR) ≤ 45 mL/min/1.73 m2 (OR 4.64, 95% CI 1.41–15.10, p = 0.011), and metastatic disease (OR 6.12, 95% CI 2.35–15.94, p &lt; 0.001) revealed to be independent predictors of non-closure. Conclusions: Anemia, impaired renal function, and metastatic disease at presentation were found to be independent predictors for non-reversal of intended temporary stomas in patients who underwent acute resection for LSOCC. In patients who have an increased risk of non-reversal, the surgeon should consider a Hartmann’s procedure.</p

Marketing patterns of agricultural commodities in an upland area of Central Java

ABSTRACT In the uplands of Central Java a wide variety of dry cultivated crops are produced for subsistence as well as for cash. The marketing channels for these crops are also diverse. The producers can choose between selling at the market place or at their farmseither to consumers or tradersor they can sell their products to wholesalers in the towns. However, this freedom of choice is not absolute and is determined by the quantity of the merchandise. Farmers/who can sell large amounts of produce are able to bypass some steps in the hierarchical order of market places or traders. Thus, producers with relatively large farmlands can sell their commodities in more profitable ways compared to those with /smaller farms. Moreover, the latter are often forced to sell their produce below market value to traders who provided them with advance or who bought the crop before harvest (tebasan), because of their need for cash key word: farming, agricultu

If You Could Only Choose Five Psychotropic Medicines: Updating the Interagency Emergency Health Kit

Mark van Ommeren and colleagues describe how they chose five psychotropic medicines to add to the Interagency Emergency Health Kit, which is a box with medicines and medical supplies designed to help people in major humanitarian emergencies