PD-MORL: Preference-Driven Multi-Objective Reinforcement Learning Algorithm

Multi-objective reinforcement learning (MORL) approaches have emerged to tackle many real-world problems with multiple conflicting objectives by maximizing a joint objective function weighted by a preference vector. These approaches find fixed customized policies corresponding to preference vectors specified during training. However, the design constraints and objectives typically change dynamically in real-life scenarios. Furthermore, storing a policy for each potential preference is not scalable. Hence, obtaining a set of Pareto front solutions for the entire preference space in a given domain with a single training is critical. To this end, we propose a novel MORL algorithm that trains a single universal network to cover the entire preference space scalable to continuous robotic tasks. The proposed approach, Preference-Driven MORL (PD-MORL), utilizes the preferences as guidance to update the network parameters. It also employs a novel parallelization approach to increase sample efficiency. We show that PD-MORL achieves up to 25% larger hypervolume for challenging continuous control tasks and uses an order of magnitude fewer trainable parameters compared to prior approaches.Comment: 24 pages, 8 Figures, 9 Tables, Published as a conference paper at ICLR 2023, https://openreview.net/forum?id=zS9sRyaPFl

BhCG as a Rupture Marker in Ectopic Pregnancy: A Retrospective Study

Objective:To find effective criteria in determining the risk of ectopic pregnancy rupture in patients with ectopic pregnancy.Method:The data of 101 patients who were hospitalized with the diagnosis of ectopic pregnancy in the tertiary center between January 2018 and January 2021 were analyzed retrospectively. Demographic data of the patients, the month of admission, the patients’ beta-human corionic gonadotropin (BhCG) values at the time of admission, blood type, endometrial thickness measured with transvaginal ultrasound, presence of adnexal mass suggestive of ectopic pregnancy and treatments applied to the patients were recorded. These data were compared between patients who had surgery for ectopic pregnancy rupture and those whose treatment was completed without it.Results:In the statistical analysis of the data, ectopic pregnancy rupture was found significantly more frequent for a threshold value of BhCG >4000 IU/L. Other data were not statistically significant.Conclusion:In cases of ectopic pregnancy, if the BhCG value at the time of admission exceeds the threshold value, the possibility of surgical approach increases. Medical treatment may be more successful at lower BhCG levels

10’DAN GERİYE SAYMA TEKNİKLERİ

Hakan Urgancı’nın 10’dan Geriye Say adlı yapıtında anlatım tekniklerinin “ölüm” olgusunun aktarılmasındaki işlevi nasıl değerlendirilebilir

A parametric study on optimization of ring inserted heat exchanger tube

This study presents a parametric optimization of ring inserted heat exchanger tube according toNusselt number and friction factor. The heat exchanger tube was heated with constant heat flux and flowconditions is turbulent corresponding to Reynolds number of 25,000. Inner diameter, thickness and pitchlengths of the rings were considered as factors and each factor is composed of five various levels. The studywas carried out by using a computational fluid dynamics program that is Ansys-Fluent 18.0. Realizable kepsilon turbulence model is employed to simulate the turbulent flow condition. The results showed thatinner diameter, thickness and pitch length of the rings increases, the Nusselt number and the friction factortend to decrease. The configuration of the ring inserted heat exchanger tube provides the highest Nusseltnumber which is the inner diameter of 17mm, the thickness of 4 mm and the pitch length of 50 mm. On theother hand, the configuration of the ring inserted heat exchanger tube provides the lowest friction factorwhich is the inner diameter of 25 mm, the thickness of 10 mm and the pitch length of 250 mm. When theresults are simultaneously optimized according to both the Nusselt number and the friction factor, it wasfound that the best configuration is the inner diameter of 25 mm, the thickness of 2 mm and the pitch lengthof 50 mm.&nbsp;</p

Numerical investigation of battery thermal management by using different phase change materials under extreme working conditions

Owing to increasing globally interest on electrical vehicles, battery thermal management (BTM) issue has critically importance in increasing the life time and safety, decreasing the charging time and cost and weight of the electrical vehicles. Li-ion cells are preferred due to high energy density and lo self-discharge rate, long cycle life. BTM by using phase change materials (PCMs) is sensible due to the melting temperature of PCM is in the range of desired temperature of Li-ion cells. This study aims to compare the performance of different PCMs such as paraffin and n-octadecane to cool a Li-ion cell which are used in electrical vehicles. Time dependent numerical analyzes were conducted to show the performance of PCMs on the BTM at cycle time of 20,000. Boundary condition for the numerical analyzes were considered as different discharging time such as 1C, 3C and 5C. As a result, paraffin appears to undergo a phase change longer than n-octadecane. This is because the paraffin has a higher latent heat value compared to n-octadecane. According to the results, it was able to keep cell temperature between 258-313K by using paraffin at a discharge rate of 1C and 3C. However, n-octadecane was not able to keep the temperature of the cell at desired range at discharge rate of 3C. At 5C discharge rate, neither paraffin nor octadecane could provide the desired cell temperatures. On the other hand, both paraffin and n-octadecane ensured that the temperature difference in the cell remained below 2.5K at all discharge rates.</p