Shock-Induced Damage Mechanism of Perineuronal Nets

The perineuronal net (PNN) region of the brain’s extracellular matrix (ECM) surrounds the neural networks within the brain tissue. The PNN is a protective net-like structure regulating neuronal activity such as neurotransmission, charge balance, and action potential generation. Shock-induced damage of this essential component may lead to neuronal cell death and neurodegenerations. The shock generated during a vehicle accident, fall, or improvised device explosion may produce sufficient energy to damage the structure of the PNN. The goal is to investigate the mechanics of the PNN in reaction to shock loading and to understand the mechanical properties of different PNN components such as glycan, GAG, and protein. In this study, we evaluated the mechanical strength of PNN molecules and the interfacial strength between the PNN components. Afterward, we assessed the PNN molecules’ damage efficiency under various conditions such as shock speed, preexisting bubble, and boundary conditions. The secondary structure altercation of the protein molecules of the PNN was analyzed to evaluate damage intensity under varying shock speeds. At a higher shock speed, damage intensity is more elevated, and hyaluronan (glycan molecule) is most likely to break at the rigid junction. The primary structure of the protein molecules is least likely to fail. Instead, the molecules’ secondary bonds will be altered. Our study suggests that the number of hydrogen bonds during the shock wave propagation is reduced, which leads to the change in protein conformations and damage within the PNN structure. As such, we found a direct connection between shock wave intensity and PNN damage.

Analysis of Type II radio burst relationship with CME driven shocks

Type II radio bursts are known to be the signatures of coronal shocks. In this paper we examine the relationship between 129 type II bursts in the frequency range 35 – 450 MHz observed at Culgooora observatory during May 2002 – October 2015 and the associated CMEs. We apply Newkirk (1961) density model to determine the formation height of type IIs. We find that in 109/129 cases, type II bursts were preceded/ succeeded by CMEs. The CME associated type II events in which the CME height is above the type II burst source are categorized as group I events (91/129 cases). 91% of the bursts in this group are also associated with flares and 58% of these bursts originate during decaying phase of the flare. The correlation between CME speed and type II shock speed for limb events in this group is 0.33.The CME associated type IIs in which the CME height is below the type II source are categorized as group II (18/129 cases). CME driven shock could have been the exciter of these type II bursts.88% of this group events are associated with flares and 62% of these bursts originate during the rising phase of the flare. The correlation between CME speed and type II shock speed for limb events in this group is 0.96. In 20/129 cases of our data set, type II bursts are not associated with CME and are categorized as group III. 90% of the bursts in this group are associated with flares. 77% of the bursts in the group are originating in the decaying phase of flares. Poor temporal association (9/69 cases) between type IIs and flares of X class during this period. Our results suggest that inspite of temporal association with metric type II bursts, majority of the CME driven shocks (84%) are not successful in exciting type II bursts in 35-450 MHz domain. The type II bursts temporally correlated with CMEs and likely to have been excited by CMEs (type II height > CME height) are originating during the rising phase of the flares in majority of the events. In case of type II bursts temporally correlated with CMEs supposedly not excited by the CMEs (type II height < CME height) ,majority of them are originating in the decaying phase of flares.

Size distribution of superbubbles

ABSTRACT We consider the size distribution of superbubbles in a star-forming galaxy. Previous studies have tried to explain the distribution by using adiabatic self-similar evolution of wind-driven bubbles, assuming that bubbles stall when pressure equilibrium is reached. We show, with the help of hydrodynamical numerical simulations, that this assumption is not valid. We also include radiative cooling of shells. In order to take into account non-thermal pressure in the ambient medium, we assume an equivalent higher temperature than implied by thermal pressure alone. Assuming that bubbles stall when the outer shock speed becomes comparable to the ambient sound speed (which includes non-thermal components), we recover the size distribution with a slope of ∼−2.7 for typical values of interstellar medium pressure in Milky Way, which is consistent with observations. Our simulations also allow us to follow the evolution of size distribution in the case of different values of non-thermal pressure, and we show that the size distribution steepens with lower pressure, to slopes intermediate between only-growing and only-stalled cases.

X-ray study of the double radio relic Abell 3376 with Suzaku

We present an X-ray spectral analysis of the nearby double radio relic merging cluster Abell 3376 (z = 0.046), observed with the Suzaku XIS instrument. These deep (∼360 ks) observations cover the entire double relic region in the outskirts of the cluster. These diffuse radio structures are amongst the largest and arc-shaped relics observed in combination with large-scale X-ray shocks in a merging cluster. We confirm the presence of a stronger shock (ℳW = 2.8 ± 0.4) in the western direction at r ∼ 26′, derived from a temperature and surface brightness discontinuity across the radio relic. In the east, we detect a weaker shock (ℳE = 1.5 ± 0.1) at r ∼ 8′, possibly associated with the “notch” of the eastern relic, and a cold front at r ∼ 3′. Based on the shock speed calculated from the Mach numbers, we estimate that the dynamical age of the shock front is ∼0.6 Gyr after core passage, indicating that Abell 3376 is still an evolving merging cluster and that the merger is taking place close to the plane of the sky. These results are consistent with simulations and optical and weak lensing studies from the literature.

An Approach to Obtain the Correct Shock Speed for Euler Equations with Stiff Detonation

Incorrect propagation speed of discontinuities may occur by straightforward application of standard dissipative schemes for problems that contain stiff source terms for underresolved grids even for time steps within the CFL condition. By examining the dissipative discretized counterpart of the Euler equations for a detonation problem that consists of a single reaction, detailed analysis on the spurious wave pattern is presented employing the fractional step method, which utilizes the Strang splitting. With the help of physical arguments, a threshold values method (TVM), which can be extended to more complicated stiff problems, is developed to eliminate the wrong shock speed phenomena. Several single reaction detonations as well as multispecies and multi-reaction detonation test cases with strong stiffness are examined to illustrate the performance of the TVM approach.