39 research outputs found
Gaps, Rings, and Non-Axisymmetric Structures in Protoplanetary Disks - From Simulations to ALMA Observations
Recent observations by the Atacama Large Millimeter/submillimeter Array
(ALMA) of disks around young stars revealed distinct asymmetries in the dust
continuum emission. In this work we want to study axisymmetric and
non-axisymmetric structures, evocated by the magneto-rotational instability in
the outer regions of protoplanetary disks. We combine the results of
state-of-the-art numerical simulations with post-processing radiative transfer
(RT) to generate synthetic maps and predictions for ALMA. We performed
non-ideal global 3D MHD stratified simulations of the dead-zone outer edge
using the FARGO MHD code PLUTO. The stellar and disk parameters are taken from
a parameterized disk model applied for fitting high-angular resolution
multi-wavelength observations of circumstellar disks. The 2D temperature and
density profiles are calculated consistently from a given surface density
profile and Monte-Carlo radiative transfer. The 2D Ohmic resistivity profile is
calculated using a dust chemistry model. The magnetic field is a vertical net
flux field. The resulting dust reemission provides the basis for the simulation
of observations with ALMA. The fiducial model develops a large gap followed by
a jump in surface density located at the dead-zone outer edge. The jump in
density and pressure is strong enough to stop the radial drift of particles. In
addition, we observe the generation of vortices by the Rossby wave instability
(RWI) at the jumps location close to 60 AU. The vortices are steadily generated
and destroyed at a cycle of 40 local orbits. The RT results and simulated ALMA
observations predict the feasibility to observe such large scale structures
appearing in magnetized disks without having a planet.Comment: Language update, added comments, added citations, in press. (A&A
Synthetic route optimization of Sumepirin antiepileptic drug candidate
In this work we describe the transformation of synthetic route of the antiepileptic drug candidate Sumepirin starting from discovery stage. Initial method included six step process requiring two steps of purification using colon chromatography and has poor overall yield of target compound. The process developed is convenient, scalable, technological and meet the most of conditions of green chemistry. The overall yield was increased up to 62.5% in four steps without colon chromatography purification which allows to obtain the target compound with purity of 99.5+% which is especially important for the active ingredient
SYNTHETIC ROUTE OPTIMIZATION OF SUMEPIRIN ANTIEPILEPTIC DRUG CANDIDATE
Epilepsy is one of the most common chronic diseases of the nervous system in the world, which affects both children and adults. 30% of patients with epilepsy are pharmacoresistant. Sumepirin 1 is a novel antiepileptic drug candidate developed in the Scientific and Educational Center of Pharmaceutics of the Kazan Federal University and having pronounced antiseizure effect and improved safety profile. This compound is pyridoxine-based molecule with residue of methanesulfonic acid in the 6th position of pyridoxine ring.This work was supported by subsidy allocated to Kazan Federal University for the state assignment in the sphere of scientificactivities (project number 0671-2020-0053
A high-order Godunov scheme for global 3D MHD accretion disks simulations. I. The linear growth regime of the magneto-rotational instability
We employ the PLUTO code for computational astrophysics to assess and compare
the validity of different numerical algorithms on simulations of the
magneto-rotational instability in 3D accretion disks. In particular we stress
on the importance of using a consistent upwind reconstruction of the
electro-motive force (EMF) when using the constrained transport (CT) method to
avoid the onset of numerical instabilities. We show that the electro-motive
force (EMF) reconstruction in the classical constrained transport (CT) method
for Godunov schemes drives a numerical instability. The well-studied linear
growth of magneto-rotational instability (MRI) is used as a benchmark for an
inter-code comparison of PLUTO and ZeusMP. We reproduce the analytical results
for linear MRI growth in 3D global MHD simulations and present a robust and
accurate Godunov code which can be used for 3D accretion disk simulations in
curvilinear coordinate systems
Turbulence and Steady Flows in 3D Global Stratified MHD Simulations of Accretion Disks
We present full 2 Pi global 3-D stratified MHD simulations of accretion
disks. We interpret our results in the context of proto-planetary disks. We
investigate the turbulence driven by the magneto-rotational instability (MRI)
using the PLUTO Godunov code in spherical coordinates with the accurate and
robust HLLD Riemann solver. We follow the turbulence for more than 1500 orbits
at the innermost radius of the domain to measure the overall strength of
turbulent motions and the detailed accretion flow pattern. We find that regions
within two scale heights of the midplane have a turbulent Mach number of about
0.1 and a magnetic pressure two to three orders of magnitude less than the gas
pressure, while outside three scale heights the magnetic pressure equals or
exceeds the gas pressure and the turbulence is transonic, leading to large
density fluctuations. The strongest large-scale density disturbances are spiral
density waves, and the strongest of these waves has m=5. No clear meridional
circulation appears in the calculations because fluctuating radial pressure
gradients lead to changes in the orbital frequency, comparable in importance to
the stress gradients that drive the meridional flows in viscous models. The net
mass flow rate is well-reproduced by a viscous model using the mean stress
distribution taken from the MHD calculation. The strength of the mean turbulent
magnetic field is inversely proportional to the radius, so the fields are
approximately force-free on the largest scales. Consequently the accretion
stress falls off as the inverse square of the radius.Comment: Accepted for publication in Ap
Trapping Solids at the Inner Edge of the Dead Zone: 3-D Global MHD Simulations
The poorly-ionized interior of the protoplanetary disk is the location where
dust coagulation processes may be most efficient. However even here,
planetesimal formation may be limited by the loss of solid material through
radial drift, and by collisional fragmentation of the particles. Our aim is to
investigate the possibility that solid particles are trapped at local pressure
maxima in the dynamically evolving disk. We perform the first 3-D global
non-ideal MHD calculations of the disk treating the turbulence driven by the
magneto-rotational instability. The domain contains an inner MRI-active region
near the young star and an outer midplane dead zone, with the transition
between the two modeled by a sharp increase in the magnetic diffusivity. The
azimuthal magnetic fields generated in the active zone oscillate over time,
changing sign about every 150 years. We thus observe the radial structure of
the `butterfly pattern' seen previously in local shearing-box simulations. The
mean magnetic field diffuses from the active zone into the dead zone, where the
Reynolds stress nevertheless dominates. The greater total accretion stress in
the active zone leads to a net reduction in the surface density, so that after
800 years an approximate steady state is reached in which a local radial
maximum in the midplane pressure lies near the transition radius. We also
observe the formation of density ridges within the active zone. The dead zone
in our models possesses a mean magnetic field, significant Reynolds stresses
and a steady local pressure maximum at the inner edge, where the outward
migration of planetary embryos and the efficient trapping of solid material are
possible.Comment: 17 pages, 30 *.ps files for figures. Accepted 16 November 2009 in A&
The dynamics of inner dead-zone boundaries in protoplanetary disks
In protoplanetary disks, the inner radial boundary between the MRI turbulent
(`active') and MRI quiescent (`dead') zones plays an important role in models
of the disk evolution and in some planet formation scenarios. In reality, this
boundary is not well-defined: thermal heating from the star in a passive disk
yields a transition radius close to the star (<0.1 au), whereas if the disk is
already MRI active, it can self-consistently maintain the requisite
temperatures out to a transition radius of roughly 1 au. Moreover, the
interface may not be static; it may be highly fluctuating or else unstable. In
this paper, we study a reduced model of the dynamics of the active/dead zone
interface that mimics several important aspects of a real disk system. We find
that MRI-transition fronts propagate inward (a `dead front' suppressing the
MRI) if they are initially at the larger transition radius, or propagate
outward (an `active front' igniting the MRI) if starting from the smaller
transition radius. In both cases, the front stalls at a well-defined
intermediate radius, where it remains in a quasi-static equilibrium. We propose
that it is this new, intermediate stalling radius that functions as the true
boundary between the active and dead zones in protoplanetary disks. These
dynamics are likely implicated in observations of variable accretion, such as
FU Ori outbursts, as well as in those planet formation theories that require
the accumulation of solid material at the dead/active interface.Comment: 16 pages, 10 figures; MNRAS accepted; v3 final correction
Large Scale Azimuthal Structures Of Turbulence In Accretion Disks - Dynamo triggered variability of accretion
We investigate the significance of large scale azimuthal, magnetic and
velocity modes for the MRI turbulence in accretion disks. We perform 3D global
ideal MHD simulations of global stratified proto-planetary disk models. Our
domains span azimuthal angles of \pi/4, \pi/2, \pi and 2\pi. We observe up to
100% stronger magnetic fields and stronger turbulence for the restricted
azimuthal domain models \pi/2 and \pi/4 compared to the full 2\pi model. We
show that for those models, the Maxwell Stress is larger due to strong
axisymmetric magnetic fields, generated by the \alpha \Omega dynamo. Large
radial extended axisymmetric toroidal fields trigger temporal magnification of
accretion stress. All models display a positive dynamo-\alpha in the northern
hemisphere (upper disk). The parity is distinct in each model and changes on
timescales of 40 local orbits. In model 2\pi, the toroidal field is mostly
antisymmetric in respect to the midplane. The eddies of the MRI turbulence are
highly anisotropic. The major wavelengths of the turbulent velocity and
magnetic fields are between one and two disk scale heights. At the midplane, we
find magnetic tilt angles around 8-9 degree increasing up to 12-13 degree in
the corona. We conclude that an azimuthal extent of \pi is sufficient to
reproduce most turbulent properties in 3D global stratified simulations of
magnetised accretion disks.Comment: accepted for publication in Ap
Pyridoxine dipharmacophore derivatives as potent glucokinase activators for the treatment of type 2 diabetes mellitus
© 2017 The Author(s). Glucokinase is one of the promising targets for glucose-lowering agents, and the development of GK activators are now considered as one of the most promising strategies for the treatment of type 2 diabetes mellitus. In this work, a series of novel symmetric molecular constructs, in which two pyridoxine moieties are connected via sulfur-containing linkers, have been synthesized and tested in vitro for glucokinase activation potential. The enzyme activation rates by two most active compounds at 100 μM (~150% and 130%) were comparable to that of the reference agent PF-04937319 (~154%). Both leading compounds demonstrated low cytotoxicity and excellent safety profile in acute toxicity experiment in rats after oral administration with LD 50 exceeding 2000 mg/kg of body weight. Binding mode of the active compounds in comparison with the reference agent was studied using molecular docking. The leading compounds represent viable preclinical candidates for the treatment of type 2 diabetes mellitus, as well as a promising starting point for the design of structural analogs with improved activity
Circumstellar disks and planets. Science cases for next-generation optical/infrared long-baseline interferometers
We present a review of the interplay between the evolution of circumstellar
disks and the formation of planets, both from the perspective of theoretical
models and dedicated observations. Based on this, we identify and discuss
fundamental questions concerning the formation and evolution of circumstellar
disks and planets which can be addressed in the near future with optical and
infrared long-baseline interferometers. Furthermore, the importance of
complementary observations with long-baseline (sub)millimeter interferometers
and high-sensitivity infrared observatories is outlined.Comment: 83 pages; Accepted for publication in "Astronomy and Astrophysics
Review"; The final publication is available at http://www.springerlink.co