The rapid growth in the performance of graphics hardware, coupled with recent improvements in its programmability has lead to its adoption in many non-graphics applications, including a wide variety of scientific computing fields. At the same time, a number of important dynamic optimal policy problems in economics are athirst of computing power to help overcome dual curses of complexity and dimensionality. We investigate if computational economics may benefit from new tools on a case study of imperfect information dynamic programming problem with learning and experimentation trade-off, that is, a choice between controlling the policy target and learning system parameters. Specifically, we use a model of active learning and control of a linear autoregression with the unknown slope that appeared in a variety of macroeconomic policy and other contexts. The endogeneity of posterior beliefs makes the problem difficult in that the value function need not be convex and the policy function need not be continuous. This complication makes the problem a suitable target for massively-parallel computation using graphics processors (GPUs). Our findings are cautiously optimistic in that the new tools let us easily achieve a factor of 15 performance gain relative to an implementation targeting single-core processors. Further gains up to a factor of 26 are also achievable but lie behind a learning and experimentation barrier of their own. Drawing upon experience with CUDA programming architecture and GPUs provides general lessons on how to best exploit future trends in parallel computation in economics. 相似文献
The GIT-32 current generator was developed for experiments with current carrying pulsed plasma. The main parts of the generator are capacitor bank, multichannel multigap spark switches, low inductive current driving lines, and central load part. The generator consists of four identical sections, connected in parallel to one load. The capacitor bank is assembled from 32 IEK-100-0.17 (0.17 microF, 40 nH, 100 kV) capacitors, connected in parallel. It stores approximately 18 kJ at 80 kV charging voltage. Each two capacitors are commuted to a load by a multigap spark switch with eight parallel channels. Switches operate in ambient air at atmospheric pressure. The GIT-32 generator was tested with 10, 15, and 20 nH inductive loads. At 10 nH load and 80 kV of charging voltage it provides 1 MA of current amplitude and 490 ns rise time with 0.8 Omega damping resistors in discharge circuit of each capacitor and 1.34 MA530 ns without resistors. The net generator inductance without a load was optimized to be as low as 12 nH, which results in extremely low self-impedance of the generator ( approximately 0.05 Omega). It ensures effective energy coupling with low impedance loads like Z pinch. The generator operates reliably without any adjustments in 40-80 kV range of charging voltage. Maximum jitter (relative to a triggering pulse) at 40 kV charging voltage is about 7 ns and lower at higher charging voltages. Operation and handling are very simple, because no oil and no purified gases are required for the generator. The GIT-32 generator has dimensions of 3200 x 3200 x 400 mm(3) and total weight of about 2500 kg, thus manifesting itself as a simple, robust, and cost effective apparatus. 相似文献
Solvent‐free protocols for Miyaura borylation and the one‐pot, two‐step homocoupling of aryl halides are reported for the first time. Bis(dibenzylideneacetone)palladium(0) [Pd(dba)2] is an optimal source of palladium for Miyaura borylation, while for one‐pot two‐step homocoupling palladium(II) acetate [Pd(OAc)2] gives highest yields. Aryl bromides are coupled most efficiently using the DPEphos ligand. Chlorides are coupled using XPhos. The developed protocols are robust, versatile and easily reproducible on a large scale.
Recent evidence suggests that fibrotic liver injury in patients with chronic hepatitis C correlates with cellular senescence in damaged liver tissue. However, it is still unclear how senescence can affect replication of the hepatitis C virus (HCV). In this work, we report that an inhibitor of cyclin-dependent kinases 4/6, palbociclib, not only induced in hepatoma cells a pre-senescent cellular phenotype, including G1 arrest in the cell cycle, but also accelerated viral replicon multiplication. Importantly, suppression of HCV replication by direct acting antivirals (DAAs) was barely affected by pre-senescence induction, and vice versa, the antiviral activities of host-targeting agents (HTAs), such as inhibitors of human histone deacetylases (HDACi), produced a wide range of reactions—from a dramatic reduction to a noticeable increase. It is very likely that under conditions of the G1 arrest in the cell cycle, HDACi exhibit their actual antiviral potency, since their inherent anticancer activity that complicates the interpretation of test results is minimized. 相似文献
