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Yayın Medical device maintenance strategy for post pandemic: case on ventilators(IEOM Society International, 2022-06) Aksezer, Sezgin ÇağlarEquipment-demand of healthcare providing institutions increased drastically during the Covid-19 pandemic. While majority of the demand (also the most publicized) has been occurring for disposable products such as masks, gloves, gowns, sterilizers, and test kits; the demand for electronic devices also increased during the initial waves of the pandemic but dropped afterwards as it was satisfied by the manufacturers. Since devices like vital monitors, dialysis systems, and ventilators are not single use products, handling of such systems after acquisition has become an issue of operations management for healthcare professionals. Utilization of such devices seem to have a cyclic behavior correlated with pandemic waves (as the hospitalizations peak so the usage and vice versa) and tend to have a longterm decreasing trend as the Covid-19 pandemic transforms to epidemic. Ventilators have found extensive usage in the treatment of Covid-19 related patients for ICU and emergency admissions. Medical ventilator device provides mechanically simulated air into the lungs of patients who are completely unable to breathe by themselves or breathes but insufficient to carry the necessary oxygen. So, the total functionality is crucial and service readiness is imminent. Number of active ventilators in Turkey increased to 22.000 units by the first year of the pandemic. However, utilization ratio of ventilators dropped to 29.6% (as of March 17, 2022) from the heights of 55% observed in the winter of 2021. Because of such decline, devices have become idle or operational times have dropped significantly. Health institution under investigation is a full-service government hospital operating in the city of Istanbul, Turkey. There are currently 142 ventilators in the hospital with less than 35% utilization. Maintenance task is only carried out by manufacturer approved service providers and parts are supplied from abroad. Since the operator of devices is a non-profit government hospital, maintenance outsourcing is done by bidding with strict budget and usually under the pressure of currency exchange rates even after the maintenance contract is signed. Failure analyses indicate mean time to failure of devices has not changed significantly with respect to pre-pandemic operation. Periodic maintenance strategy that has long been adopted for such devices has been modified to consider cyclic operation, extended standby durations, and lead time of spare parts. Further proposals are under consideration for group maintenance involving multiple healthcare institutions.Yayın Infrequent rebalancing, risk deferral, and equity returns at the turn of the month(Elsevier Ltd, 2026-03-13) Kayaçetin, Nuri VolkanWe examine equity returns at the turn of the month using return data from thirty countries over the thirty-year period from January 1, 1994, to December 31, 2023. Our analysis reveals that the mean daily return on trading days surrounding the end of the month is significantly larger at 10 bps across the markets examined as compared to 0 bps on other days, with a narrow window bracketing month-ends accounting for all or nearly all positive mean return in each of the countries examined. Linking this pattern to the interaction between slow moving institutional capital and market frictions, we provide evidence in line with the idea that the observed pattern might be sustained by a dual-channel mechanism. First, the effect appears to be amplified hierarchically due to overlapping rebalancing mandates, peaking at lower frequencies due to the synchronization of a larger number of rebalancing schedules. Second, and more importantly, the effect also seems to be conditioned by the deferral of risky investments to structured rebalancing nodes during periods of market distress. Consistent with this mechanism, its magnitude is significantly larger after periods of market turbulence and during recessions, when investors are likely to store more cash in safe assets. Our findings thus provide a robust economic framework for understanding the enduring presence of the turn-of-the-month effect, suggesting that it may emerge as a joint consequence of infrequent rebalancing and risk deferral.
