Network Model With Reduced Metabolic Rate Predicts Spatial Synchrony of Neuronal Activity

In a cerebral hypometabolic state, cortical neurons exhibit slow synchronous oscillatory activity with sparse firing. How such a synchronization spatially organizes as the cerebral metabolic rate decreases have not been systemically investigated. We developed a network model of leaky integrate-and-fire neurons with an additional dependency on ATP dynamics. Neurons were scattered in a 2D space, and their population activity patterns at varying ATP levels were simulated. The model predicted a decrease in firing activity as the ATP production rate was lowered. Under hypometabolic conditions, an oscillatory firing pattern, that is, an ON-OFF cycle arose through a failure of sustainable firing due to reduced excitatory positive feedback and rebound firing after the slow recovery of ATP concentration. The firing rate oscillation of distant neurons developed at first asynchronously that changed into burst suppression and global synchronization as ATP production further decreased. These changes resembled the experimental data obtained from anesthetized rats, as an example of a metabolically suppressed brain. Together, this study substantiates a novel biophysical mechanism of neuronal network synchronization under limited energy supply conditions.

Experimental Study of Fire Behavior in a Depressurized Aircraft Cargo Compartment

To analyze the fire behavior in the dynamic pressure environment, a series of n-heptane pool fire experiments were conducted in an 8.11m × 4.16m × 1.67m simulated aircraft cargo compartment. The compartment is capable of mimicking flight environment from taking off to landing of the aircraft according to the standards of Federal Aviation Administration (FAA) by a pressure control system. Pool fires with 30cm diameter were tested under the dynamic pressure from 101kPa to 45kPa with various depressurization rates of 10kPa/min, 15kPa/min, 20kPa/min and 25kPa/min. Fire behavior such as burning rate, oscillation frequency and flame temperature were analyzed. The results revealed that the dynamic pressure influences the burning rate not only during the depressurization stage but also after depressurization. The oscillation frequency increases with the pressure decrease but has no relationship with depressurization rate. The flame temperature at different heights shows various tendencies with pressure.

Numerical simulation of the internal flow of swirl atomizer under ambient pressure

This paper presents the simulation study of internal flow of open-end swirl injectors under steady and oscillating ambient pressures. A two-dimensional swirl axisymmetric model based on the volume of fluid method was developed to study the effect of ambient pressure on the internal flow of open-end swirl injectors. The response of injector flow to the ambient pressure oscillation was investigated by superimposing periodical oscillation of ambient pressure at the spout outlet. The results show that the variation of ambient pressure affects the liquid phase volumetric fraction within the gas–liquid shear layer. The spray angle near the wall remains constant independent of the ambient pressure. The velocity distribution on different axial sections rarely varies with ambient pressure. When the ambient pressure oscillated, the ambient pressure oscillation would cause the flow rate oscillation at the spout. The phase delay between the flow rate oscillation at spout and the ambient pressure oscillation is proportional to the oscillation frequency.