Optimal Positive Capital Taxes at Interior Steady States

We generalize recent results of Bassetto and Benhabib (2006) and Straub and Werning (2019) in a neoclassical model with endogenous labor-leisure choice where all agents are allowed to save and accumulate capital. We provide a sufficient condition under which optimal redistributive capital taxes remain at their allowed upper bound forever, even if the resulting equilibrium trajectory converges to a unique steady state with positive and finite consumption, capital, and labor. We then provide an interpretation of our sufficient condition. Using recent evidence on wealth distribution in the United States, we argue that our sufficient condition is empirically plausible. (JEL D31, E21, H21, H23, H25, J22)

Effects of Air Humidity on Properties of JO-9159 Explosive by Molecular Dynamics Simulation

To explore effects of air humidity on properties of JO-9159 explosive, the amorphous model of six components was constructed by Materials Studio software, periodic molecular dynamics simulation was conducted at seven kinds of relative humidity ranging from 10% to 70% for (001), (010), (100) crystal planes of JO-9159 explosive in COMPASS force field and NVT ensemble. Mechanical properties, sensitivity and detonation properties of JO-9159 explosive were researched basing on equilibrium trajectory of model. The results show that with the increasing of relative humidity, the total adsorption energy increases. The adsorption capacity of JO-9159 explosive for H2O is much stronger than O2 and N2; The breaking strength has a decreasing trend with the humidity increases and the stiffness and hardness of JO-9159 explosive are smaller at 30% and 40% relative humidity; At 30% relative humidity, the sensitivity of JO-9159 explosive is highest and detonation properties are weakest, while the detonation properties are strongest at 20% relative humidity.

Are Complex Control Signals Required for Human Arm Movement?

Gribble, Paul L., David J. Ostry, Vittorio Sanguineti, and Rafael Laboissière. Are complex control signals required for human arm movement? J. Neurophysiol. 79: 1409–1424, 1998. It has been proposed that the control signals underlying voluntary human arm movement have a “complex” nonmonotonic time-varying form, and a number of empirical findings have been offered in support of this idea. In this paper, we address three such findings using a model of two-joint arm motion based on the λ version of the equilibrium-point hypothesis. The model includes six one- and two-joint muscles, reflexes, modeled control signals, muscle properties, and limb dynamics. First, we address the claim that “complex” equilibrium trajectories are required to account for nonmonotonic joint impedance patterns observed during multijoint movement. Using constant-rate shifts in the neurally specified equilibrium of the limb and constant cocontraction commands, we obtain patterns of predicted joint stiffness during simulated multijoint movements that match the nonmonotonic patterns reported empirically. We then use the algorithm proposed by Gomi and Kawato to compute a hypothetical equilibrium trajectory from simulated stiffness, viscosity, and limb kinematics. Like that reported by Gomi and Kawato, the resulting trajectory was nonmonotonic, first leading then lagging the position of the limb. Second, we address the claim that high levels of stiffness are required to generate rapid single-joint movements when simple equilibrium shifts are used. We compare empirical measurements of stiffness during rapid single-joint movements with the predicted stiffness of movements generated using constant-rate equilibrium shifts and constant cocontraction commands. Single-joint movements are simulated at a number of speeds, and the procedure used by Bennett to estimate stiffness is followed. We show that when the magnitude of the cocontraction command is scaled in proportion to movement speed, simulated joint stiffness varies with movement speed in a manner comparable with that reported by Bennett. Third, we address the related claim that nonmonotonic equilibrium shifts are required to generate rapid single-joint movements. Using constant-rate equilibrium shifts and constant cocontraction commands, rapid single-joint movements are simulated in the presence of external torques. We use the procedure reported by Latash and Gottlieb to compute hypothetical equilibrium trajectories from simulated torque and angle measurements during movement. As in Latash and Gottlieb, a nonmonotonic function is obtained even though the control signals used in the simulations are constant-rate changes in the equilibrium position of the limb. Differences between the “simple” equilibrium trajectory proposed in the present paper and those that are derived from the procedures used by Gomi and Kawato and Latash and Gottlieb arise from their use of simplified models of force generation.