Shearing box simulations in the Rayleigh unstable regime

We study the stability properties of Rayleigh unstable flows both in the purely hydrodynamic and magnetohydrodynamic (MHD) regimes for two different values of the shear $q=2.1, 4.2$ ($q = - d\ln\Omega / d\ln r$) and compare it with the Keplerian case $q=1.5$. We find that the $q>2$ regime is unstable both in the hydrodynamic and in the MHD limit (with an initially weak magnetic field). In this regime, the velocity fluctuations dominate the magnetic fluctuations. In contrast, in the $q<2$ (magnetorotational instability (MRI)) regime the magnetic fluctuations dominate. This highlights two different paths to MHD turbulence implied by the two regimes, suggesting that in the $q>2$ regime the instability produces primarily velocity fluctuations that cause magnetic fluctuations, with the causality reversed for the $q<2$ MRI unstable regime. We also find that the magnetic field correlation is increasingly localized as the shear is increased in the Rayleigh unstable regime. In calculating the time evolution of spatial averages of different terms in the MHD equations, we find that the $q>2$ regime is dominated by terms which are nonlinear in the fluctuations, whereas for $q<2$, the linear terms play a more significant role.Comment: accepted by MNRAS: 10 pages, 14 figures, 1 table; revised and expande

Development of Standard Criteria to Evaluate the Effectiveness of Helmets at Decreasing the Risk of Concussions

In many sports, such as American football, accumulations of mild traumatic brain injuries have been suggested as a possible link to neurodegeneration and future mental disorders. With head impacts occurring at all levels of competition and in different sports, it is critical to develop an accurate method for quantifying the effects of head impacts and determining the efficacy of helmets. This study examines the derivation of different dimensionless numbers and ascertains the critical factors needed to predict the effects of head impacts, specifically the resulting accelerations from an impact. Given a known force of impact, parameters such as peak translation acceleration and impact duration were collected for a total of 200 impacts at 10 locations around the head. These parameters were used in conjunction with dimensionless numbers to compare various helmet designs across sports. Five input and four output criteria, or π variables, were derived using fundamental variables of total mass, width of neck, and the difference between muscle reaction time and the impact duration. By determining the coefficients of the governing equations for each output π variable, the impulse of impacts had a consistent effect on helmet efficacy, while the masses and radii of helmets contained confounding variables that made it difficult to predict the effectiveness of attenuating the head accelerations

Comparison of X-ray and gamma-ray dose-response curves for pink somatic mutations in Tradescantia clone 02

Microdosimetric data indicate that the mean specific energy,zeta, produced by individual charged particles from X rays and gamma rays is different for the two radiation qualities by nearly a factor of two. In order to test whether this influences the initial, linear component in the dose-effect relations, a comparison was made between dose-response curves for pink somatic mutations inTradescantia clone 02 stamen hairs following X and gamma irradiations. Absorbed doses ranged from 2.66 to 300 rad. The results are in agreement with predictions made on the basis of microdosimetric data. At low doses gamma rays are substantially less effective than X rays. The RBE of gamma rays vs. X rays at low doses was approximately 0.6, a value lower than those usually reported in other experimental systems

Activation of the central nervous system induced by micro-magnetic stimulation

Electrical and transcranial magnetic stimulation have proven to be therapeutically beneficial for patients suffering from neurological disorders. Moreover, these stimulation technologies have provided invaluable tools for investigating nervous system functions. Despite this success, these technologies have technical and practical limitations impeding the maximization of their full clinical and preclinical potential. Recently, micro-magnetic stimulation, which may offer advantages over electrical and transcranial magnetic stimulation, has proven effective in activating the neuronal circuitry of the retina in vitro. Here we demonstrate that this technology is also capable of activating neuronal circuitry on a systems level using an in vivo preparation. Specifically, the application of micro-magnetic fields to the dorsal cochlear nucleus activates inferior colliculus neurons. Additionally, we demonstrate the efficacy and characteristics of activation using different magnetic stimulation parameters. These findings provide a rationale for further exploration of micro-magnetic stimulation as a prospective tool for clinical and preclinical applications

Comparative Analysis of Impact Attenuation Properties from Soccer Headgear

Athletes suffering from long-term neurocognitive deficiency due to subconcussive impacts is a major concern for football and soccer players today. Football players wear helmets that can help reduce injury risks like skull fractures, and these helmets must meet standard criteria that determinines how well a functional helmet should reduce accelerations of the player’s head. Currently no standard exists for testing soccer headgear despite studies demonstrating soccer players experience similar magnitudes of impacts. In this study, a modal impact hammer was used in conjunction with a Hybrid III 50th percentile test dummy head to simulate impacts experienced by soccer players to quantify the effectiveness of headgear in attenuating head acceleration due to direct impacts. The study found one device to be functional, and able to reduce the translational acceleration for an average hit experienced by a soccer player by 20%. Devices need to be developed and common testing standards need to be established to allow for a more widespread implementation of similar devices to protect players from short and long-term injuries due to impacts

Gender score development in the Berlin Aging Study II: A retrospective approach

In addition to biological sex, gender, defined as the sociocultural dimension of being a woman or a man, plays a central role in health. However, there are so far few approaches to quantify gender in a retrospective manner in existing study datasets. We therefore aimed to develop a methodology that can be retrospectively applied to assess gender in existing cohorts. We used baseline data from the Berlin Aging Study II (BASE-II), obtained in 2009-2014 from 1869 participants aged 60 years and older. We identified 13 gender-related variables and used them to construct a gender score by using primary component and logistic regression analyses. Of these, nine variables contributed to a gender score: chronic stress, marital status, risk-taking behaviour, personality attributes: agreeableness, neuroticism, extraversion, loneliness, conscientiousness, and level of education. Females and males differed significantly in the distribution of the gender score, but a significant overlap was also found. Thus, we were able to develop a gender score in a retrospective manner from already collected data that characterized participants in addition to biological sex. This approach will allow researchers to introduce the notion of gender retrospectively into a large number of studies