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Purpose -Blast-induced traumatic brain injury (TBI) is a signature injury of the current military conflicts. Among the different types of TBI, diffuse axonal injury (DAI) plays an important role since it can lead to devastating effects in the inflicted military personnel. To better understand the potential causes associated with DAI, this paper aims to investigate a transient non-linear dynamics finite element simulation of the response of the brain white matter to shock loading. Design/methodology/approach -Brain white matter is considered to be a heterogeneous material consisting of fiber-like axons and a structure-less extracellular matrix (ECM). The brain white matter microstructure in the investigated corpus callosum region of the brain is idealized using a regular hexagonal arrangement of aligned equal-size axons. Deviatoric stress response of the axon and the ECM is modeled using a linear isotropic viscoelastic formulation while the hydrostatic stress response is modeled using a shock-type equation of state. To account for the stochastic character of the brain white matter microstructure and shock loading, a parametric study is carried out involving a factorial variation of the key microstructural and waveform parameters. Findings -The results obtained show that the extent of axon undulations and the strength of axon/ECM bonding profoundly affect the spatial distribution and magnitude of the axonal axial normal and shear stresses (the stresses which can cause diffuse axonal injury). Originality/value -The present approach enables a more accurate determination of the mechanical behavior of brain white matter when subjected to a shock.

A pulsating heat pipe (PHP), also known as an oscillating heat pipe (OHP), is a passive thermal transport device which consists of a single meandering microchannel making multiple passes each through an evaporator and condenser. With a sufficient number of such passes, intermittent boiling of liquid slugs within each evaporator pass perturbs flow in adjacent channels leaving the device in a perpetually unstable state of oscillation. A PHP is thus distinguished operationally from a loop thermosyphon by having a motive force other than buoyancy and the ability to operate in all gravitational orientations. The most successful PHP models to date track liquid slug motion, sensible heating of the slugs, and mass transfer between liquid slugs and vapor plugs due to evaporation and condensation. However, the predictive capabilities of PHP models remain poor and the numbers assigned to evaporation and condensation heat transfer coefficients are generally not well justified by any realistic physical process. The current study applies methods consistent with state of the art prediction methods in microchannel boiling, to obtain results which predict the PHP’s heat transfer performance and the effect of gravitational orientation on performance.

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