Thermomechanical Properties of Transition Metal Dichalcogenides Predicted by a Machine Learning Parameterized Force Field.

The mechanical and thermal properties of transition metal dichalcogenides (TMDs) are directly relevant to their applications in electronics, thermoelectric devices, and heat management systems. In this study, we use a machine learning (ML) approach to parametrize molecular dynamics (MD) force fields to predict the mechanical and thermal transport properties of a library of monolayered TMDs (MoS2, MoTe2, WSe2, WS2, and ReS2). The ML-trained force fields were then employed in equilibrium MD simulations to calculate the lattice thermal conductivities of the foregoing TMDs and to investigate how they are affected by small and large mechanical strains. Furthermore, using nonequilibrium MD, we studied thermal transport across grain boundaries. The presented approach provides a fast albeit accurate methodology to compute both mechanical and thermal properties of TMDs, especially for relatively large systems and spatially complex structures, where density functional theory computational cost is prohibitive.

Comparison of sequential and mixture injections of opioids and hyperbaric bupivacaine for subarachnoid block for lower segment caesarean section: a randomised controlled study.

INTRODUCTION: Opioids are commonly added to local anaesthetic for subarachnoid block for caesarean section due to their synergistic effects. The physiochemical characteristics of opioids suggest premixing with hyperbaric bupivacaine may limit their distribution within the CSF. We studied the effect of a separate injection with a combination of bupivacaine, morphine and fentanyl on block characteristics, haemodynamic changes, postoperative pain and patient satisfaction. METHOD: Following ethical approval and informed consent, a prospective double-blinded randomised controlled trial was performed in a university hospital. A total of 126 patients undergoing caesarean section were randomised to two groups. In group M, the premixed group, patients received 12 mg of hyperbaric bupivacaine, 20 mcg of fentanyl and 100 mcg of morphine injected as a single mixture. In group S, the separate injection group, patients received the same drugs in separate injections. Measurements included haemodynamics, block distribution, intra- and postoperative pain, as well as patient satisfaction. RESULTS: Patients in both groups had similar block height, time to maximum sensory block, time to block regression and motor block. However, haemodynamics were different between the groups. The proportion of systolic hypotension episodes was greater in group S [159/1320 (12.05%)] than group M [113/1452 (7.78%)], with P = 0.0002. Moreover, a greater amount of ephedrine was administered in group S than group M, with values 12.09 (8.1) and 9.09 (8.5) mg respectively (P = 0.001). Additionally, postoperative pain, as measured by the Visual Analogue Scale (VAS), was greater in group M, with a VAS of 4.6 (1.7), vs. group S, which recorded a VAS of 3.8 (2.0) (P = 0.017). CONCLUSION: Sequential injection of intrathecal opioids and hyperbaric bupivacaine resulted in greater early haemodynamic instability and slightly better postoperative analgesia without any difference in block height or patient satisfaction. CLINICAL TRIAL REGISTRATION: NCT04403724.