Scaling of granular temperature in a vibrated granular bed

Granular temperature underpins the kinetic theory of granular flows as well as models for heat transfer, segregation, erosion, attrition, and aggregation in various granular systems. It is generally thought that granular temperature in vibrated granular systems scales with the square of the peak vibrational velocity. However, careful diffusing wave spectroscopy experiments and statistical analysis of data obtained from these for a three-dimensional vibrated bed of monodisperse glass particles reveals that the granular temperature is also significantly correlated with other vibrational parameters. Reexamination of previously published data obtained by others using alternative methods further supports our thus far unremarked upon observation reported here.

A viscoelastic biomechanical model of the cornea describing the effect of viscosity and elasticity on hysteresis

PURPOSE

To develop a method for evaluating viscosity and elasticity of the cornea and to examine the effect that both properties have on hysteresis.

METHODS

A three-component spring and dashpot model was created in Simulink in Matlab to represent the purely elastic and viscoelastic behavior of the cornea during a measurement using device called an ocular response analyzer (ORA). Values for elasticity and viscosity were varied while sinusoidal stress was applied to the model. The simulated stresses were used to determine how hysteresis is affected by the individual components of elasticity, viscosity, and maximum stress. To validate the model, high-speed photography was used to measure induced strain in a corneal phantom during ORA measurement. This measured strain was compared with the strains simulated by the model.

RESULTS

When the spring in the viscoelastic portion of the model was stiffened, hysteresis decreased. When the spring in the purely elastic element was stiffened, hysteresis increased. If both springs were stiffened together, hysteresis peaked strongly as a function of the viscosity of the viscoelastic element. Below the peak value, lower elasticity was associated with higher hysteresis. Above the peak value, higher elasticity was associated with higher hysteresis. In addition, hysteresis increased as the air maximum pressure was increased. Measurements from phantom corresponded to predictions from the model.

CONCLUSIONS

A viscoelastic model is presented to illustrate how changing viscosity and elasticity may affect hysteresis. Low hysteresis can be associated with either high elasticity or low elasticity, depending on the viscosity, a finding consistent with clinical reports.

Amobarbital sodium and the effects of reward and nonreward in the Amsel double runway

Rats received 60 trials (Condition I) with 6 pellets reward at the second goal of a double runway and either 6 ( n = 12) or 0 ( n = 12) at the first goal, followed by, for all Ss, 24 trials (Condition II) with 0 reward at the first goal, then 36 trials (Condition III) with 50% reward at the first goal. Half of each reward group received amobarbital sodium (20 mg/kg, IP) and half saline prior to the 6 daily trials. Neither excitatory nor inhibitory effects of the reward shift occurred in Condition II. In Condition III inhibitory effects were observed to occur anticipatory to the first goal; these were reduced in magnitude by the drug. Excitatory effects of nonreward occurred after the goal if this effect is defined as increased speed relative to that in Condition II or greater speed on nonreward trials relative to reward trials in Condition III. These differences were not reduced by the drug. Problems concerning the possible “demotivating” effects of reward were raised which are not yet completely resolved.