Search results for "Star"

A new general relativistic magnetohydrodynamics code for dynamical spacetimes

2008

We present a new numerical code which solves the general relativistic magneto-hydrodynamics (GRMHD) equations coupled to the Einstein equations for the evolution of a dynamical spacetime within the conformally-flat approximation. This code has been developed with the main objective of studying astrophysical scenarios in which both, high magnetic fields and strong gravitational fields appear, such as the magneto-rotational collapse of stellar cores, the collapsar model of GRBs, and the evolution of neutron stars. The code is based on an existing and thoroughly tested purely hydrodynamics code and on its extension to accommodate weakly magnetized fluids (passive magnetic field approximation).…

Local simulations of the magnetized Kelvin-Helmholtz instability in neutron-star mergers

2010

Context. Global MHD simulations show Kelvin-Helmholtz (KH) instabilities at the contact surface of two merging neutron stars. That region has been identified as the site of efficient amplification of magnetic fields. However, these global simulations, due to numerical limitations, were unable to determine the saturation level of the field strength, and thus the possible back-reaction of the magnetic field onto the flow. Aims. We investigate the amplification of initially weak fields in KH unstable shear flows, and the back-reaction of the field onto the flow. Methods. We use a high-resolution ideal MHD code to perform 2D and 3D local simulations of shear flows. Results. In 2D, the magnetic …

General relativistic simulations of pasive-magneto-rotational core collapse with microphysics

2007

This paper presents results from axisymmetric simulations of magneto-rotational stellar core collapse to neutron stars in general relativity using the passive field approximation for the magnetic field. These simulations are performed using a new general relativistic numerical code specifically designed to study this astrophysical scenario. The code is based on the conformally-flat approximation of Einstein's field equations and conservative formulations of the magneto-hydrodynamics equations. The code has been recently upgraded to incorporate a tabulated, microphysical equation of state and an approximate deleptonization scheme. This allows us to perform the most realistic simulations of m…

Accretion disk coronae of intermediate polar cataclysmic variables

2017

Context. Intermediate polar cataclysmic variables (IPCV) contain a magnetic, rotating white dwarf surrounded by a magnetically truncated accretion disk. To explain their strong flickering X-ray emission, accretion has been successfully taken into account. Nevertheless, observations suggest that accretion phenomena might not be the only process behind it. An intense flaring activity occurring on the surface of the disk may generate a corona, contribute to the thermal X-ray emission, and influence the system stability. Aims. Our purposes are: investigating the formation of an extended corona above the accretion disk, due to an intense flaring activity occurring on the disk surface; studying t…

Accretion disk coronae of Intermediate Polar Cataclysmic Variables: 3D MagnetoHydroDynamic modeling and thermal X-ray emission

Intermediate Polar Cataclysmic Variables (IPCVs), also known as DQ Her stars after their prototype, are cataclysmic variable stars characterized by the presence of an accreting, magnetic, rapidly rotating white dwarf surrounded by an accretion disk magnetically truncated by the inner magnetosphere of the star. These objects exhibit a magnetic field of the order of few MG, able to disrupt the inner part of the disk but not strong enough to inhibit the formation of a disk. These stars show a strong X-ray emission with a stochastic pulsation that in some cases arise in the inner part of the disk. However, the observations of the X-ray luminosity for these objects do not match the expected valu…

Dž. Serla apziņas intencionalitātes un M. Polaņi netiešo zināšanu koncepciju salīdzinošā analīze

2021

Darbs pievērsīsies netiešo zināšanu un intencionalitātes koncepciju salīdzinājumam Maikla Polaņī un Džona Serla darbu kontekstā, parādot dažādās motivācijas un atšķirīgās jēdzienu izpratnes, kas noveda abus domātājus pie līdzīgiem secinājumiem par prāta un ķermeņa attiecībām. Darbā tiks kritiski apskatīta Serla intencionalitātes teorija, kā arī sniegta Polaņī jēdzieniskā ietvara interpretācija, lai pamatotu to, ka Serls pārprot Polaņī, dēvējot viņu par kognitīvistu.

Early impairment of epigenetic pattern in neurodegeneration: Additional mechanisms behind pyrethroid toxicity

2019

Abstract Permethrin is a synthetic pyrethroid extensively used as anti-woodworm agent and for indoor and outdoor pest control. The main route of human exposure is through fruit, vegetable and milk intake. Low dosage exposure to permethrin during neonatal brain development (from postnatal day 6 to postnatal day 21) leads to dopamine decrease in rat striatum nucleus, oxidative stress and behavioural changes linked to the development of Parkinson's like neurodegeneration later in life. The aim of this study was to evaluate the expression of genes involved in the dopaminergic pathway and epigenetic regulatory mechanisms in adolescent rats treated with permethrin during neonatal brain developmen…

Sex Differences in Age-Associated Type 2 Diabetes in Rats—Role of Estrogens and Oxidative Stress

2019

Females live longer than males, and the estrogens are one of the reasons for this difference. We reported some years ago that estrogens are able to protect rats against oxidative stress, by inducing antioxidant genes. Type 2 diabetes is an age-associated disease in which oxidative stress is involved, and moreover, some studies show that the prevalence is higher in men than in women, and therefore there are sex-associated differences. Thus, the aim of this study was to evaluate the role of estrogens in protecting against oxidative stress in type 2 diabetic males and females. For this purpose, we used Goto-Kakizaki rats, which develop type 2 diabetes with age. We found that female diabetic ra…

Involvement of TRPV1 channels in the activity of the cannabinoid WIN 55,212-2 in an acute rat model of temporal lobe epilepsy

2016

The exogenous cannabinoid agonist WIN 55,212-2, (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl) pyrrolo[1,2,3-de]-1,4-benzoxazin-6-Yl]-1-naphthalenylmethanone (WIN), has revealed to play a role on modulating the hyperexcitability phenomena in the hippocampus. Cannabinoid-mediated mechanisms of neuroprotection have recently been found to imply the modulation of transient receptor potential vanilloid 1 (TRPV1), a cationic channel subfamily that regulate synaptic excitation. In our study, we assessed the influence of pharmacological manipulation of TRPV1 function, alone and on WIN antiepileptic activity, in the Maximal Dentate Activation (MDA) acute model of temporal lobe epilepsy. Our r…

Regional differences in mu-opioid receptor-dependent modulation of basal dopamine transmission in rat striatum

2016

Abstract The nigrostriatal dopamine system is implicated in the regulation of reward and motor activity. Dopamine (DA) release in dorsal striatum (DS) is controlled by the firing rate of DA neurons in substantia nigra pars compacta. However, influences at terminal level, such as those involving activation of mu opioid receptors (MORs), can play a key role in determining DA levels in striatum. Nonetheless, published data also suggest that the effect of opioid drugs on DA levels may differ depending on the DS subregion analyzed. In this study, in vivo microdialysis in rats was used to explore this regional dependence. Changes in basal DA levels induced by local retrodialysis application of DA…