44 research outputs found
Assessment of prescribing pattern and cost analysis of topical steroids for skin disorders in dermatological outpatient department of a tertiary care hospital
Background: Topical steroid is most commonly prescribed in non-infective dermatological conditions. Periodical Prescription audit is mandatory for the effective management. Hence the present study is designed to assess the prescribing pattern and cost analysis of topical steroids for various skin disorders in the dermatology OPD of a teaching hospital.Methods: This is a prospective observational study conducted in dermatology OPD of a teaching hospital from Jan-Mar 2019 in patients prescribed with topical steroids in all age groups after obtaining IEC approval. Data was analyzed for prescription pattern and cost analysis using descriptive statistics and expressed in percentage.Results: A total of 90 prescriptions were analyzed among which males were 45% and females were 55%, the common indications were eczema-27.7%, atopic dermatitis-25.5%, psoriasis-16.6%, dermatoses-13.3%, lichen planus-7.77% etc. Topical steroids commonly prescribed were super potent (Clobetasol 34.4% and Halobetasol 22.2%). Cream and ointment formulation were commonly used. Common adverse reactions were skin atrophy, hypopigmentation, acne. In prescribing pattern, specification of strength and quantity were lacking whereas instructions regarding area of application-44.4%, route of administration-83.3%, frequency and duration-91% were noted. In cost analysis, comparison is made between similar potency and clinical outcome. Of which, Clobetasol 0.05% and Betamethasone 0.01% is found to be cost effective compared to Halobetasol 0.05% and Mometasone 0.1% respectively.Conclusions: This study provides a limelight on prescribing pattern of topical steroids and emphasize periodic audit to rationalize the prescription with cost effectiveness
Dust retention in protoplanetary disks
Context: Protoplanetary disks are observed to remain dust-rich for up to
several million years. Theoretical modeling, on the other hand, raises several
questions. Firstly, dust coagulation occurs so rapidly, that if the small dust
grains are not replenished by collisional fragmentation of dust aggregates,
most disks should be observed to be dust poor, which is not the case. Secondly,
if dust aggregates grow to sizes of the order of centimeters to meters, they
drift so fast inwards, that they are quickly lost.
Aims: We attempt to verify if collisional fragmentation of dust aggregates is
effective enough to keep disks 'dusty' by replenishing the population of small
grains and by preventing excessive radial drift.
Methods: With a new and sophisticated implicitly integrated coagulation and
fragmentation modeling code, we solve the combined problem of coagulation,
fragmentation, turbulent mixing and radial drift and at the same time solve for
the 1-D viscous gas disk evolution.
Results: We find that for a critical collision velocity of 1 m/s, as
suggested by laboratory experiments, the fragmentation is so effective, that at
all times the dust is in the form of relatively small particles. This means
that radial drift is small and that large amounts of small dust particles
remain present for a few million years, as observed. For a critical velocity of
10 m/s, we find that particles grow about two orders of magnitude larger, which
leads again to significant dust loss since larger particles are more strongly
affected by radial drift.Comment: Letter accepted 3 July 2009, included comments of language edito
Planetesimal Formation In Self-Gravitating Discs
We study particle dynamics in local two-dimensional simulations of
self-gravitating accretion discs with a simple cooling law. It is well known
that the structure which arises in the gaseous component of the disc due to a
gravitational instability can have a significant effect on the evolution of
dust particles. Previous results using global simulations indicate that spiral
density waves are highly efficient at collecting dust particles, creating
significant local over-densities which may be able to undergo gravitational
collapse. We expand on these findings, using a range of cooling times to mimic
the conditions at a large range of radii within the disc. Here we use the
Pencil Code to solve the 2D local shearing sheet equations for gas on a fixed
grid together with the equations of motion for solids coupled to the gas solely
through aerodynamic drag force. We find that spiral density waves can create
significant enhancements in the surface density of solids, equivalent to 1-10cm
sized particles in a disc following the profiles of Clarke (2009) around a
solar mass star, causing it to reach concentrations several orders of magnitude
larger than the particles mean surface density. We also study the velocity
dispersion of the particles, finding that the spiral structure can result in
the particle velocities becoming highly ordered, having a narrow velocity
dispersion. This implies low relative velocities between particles, which in
turn suggests that collisions are typically low energy, lessening the
likelihood of grain destruction. Both these findings suggest that the density
waves that arise due to gravitational instabilities in the early stages of star
formation provide excellent sites for the formation of large,
planetesimal-sized objects.Comment: 11 pages, 8 figures, accepted for publication in MNRA
Possible planet-forming regions on submillimetre images
Submillimetre images of transition discs are expected to reflect the
distribution of the optically thin dust. Former observation of three transition
discs LkHa330, SR21N, and HD1353444B at submillimetre wavelengths revealed
images which cannot be modelled by a simple axisymmetric disc. We show that a
large-scale anticyclonic vortex that develops where the viscosity has a large
gradient (e.g., at the edge of the disc dead zone), might be accountable for
these large-scale asymmetries. We modelled the long-term evolution of vortices
being triggered by the Rossby wave instability. We found that a
horseshoe-shaped (azimuthal wavenumber m=1) large-scale vortex forms by
coalescing of smaller vortices within 5x10^4 yr, and can survive on the disc
life-time (~5x10^6 yr), depending on the magnitude of global viscosity and the
thickness of the viscosity gradient. The two-dimensional grid-based global disc
simulations with local isothermal approximation and compressible-gas model have
been done by the GPU version of hydrodynamic code FARGO (GFARGO). To calculate
the dust continuum image at submillimetre wavelengths, we combined our
hydrodynamical results with a 3D radiative transfer code. By the striking
similarities of the calculated and observed submillimetre images, we suggest
that the three transition discs can be modelled by a disc possessing a
large-scale vortex formed near the disc dead zone edge. Since the larger dust
grains (larger than mm in size) are collected in these vortices, the
non-axisymmetric submillimetre images of the above transition discs might be
interpreted as active planet and planetesimal forming regions situated far (>
50 AU) from the central stars.Comment: 13 pages, 14 figures, accepted for publication in MNRA
Planetary population synthesis
In stellar astrophysics, the technique of population synthesis has been
successfully used for several decades. For planets, it is in contrast still a
young method which only became important in recent years because of the rapid
increase of the number of known extrasolar planets, and the associated growth
of statistical observational constraints. With planetary population synthesis,
the theory of planet formation and evolution can be put to the test against
these constraints. In this review of planetary population synthesis, we first
briefly list key observational constraints. Then, the work flow in the method
and its two main components are presented, namely global end-to-end models that
predict planetary system properties directly from protoplanetary disk
properties and probability distributions for these initial conditions. An
overview of various population synthesis models in the literature is given. The
sub-models for the physical processes considered in global models are
described: the evolution of the protoplanetary disk, the planets' accretion of
solids and gas, orbital migration, and N-body interactions among concurrently
growing protoplanets. Next, typical population synthesis results are
illustrated in the form of new syntheses obtained with the latest generation of
the Bern model. Planetary formation tracks, the distribution of planets in the
mass-distance and radius-distance plane, the planetary mass function, and the
distributions of planetary radii, semimajor axes, and luminosities are shown,
linked to underlying physical processes, and compared with their observational
counterparts. We finish by highlighting the most important predictions made by
population synthesis models and discuss the lessons learned from these
predictions - both those later observationally confirmed and those rejected.Comment: 47 pages, 12 figures. Invited review accepted for publication in the
'Handbook of Exoplanets', planet formation section, section editor: Ralph
Pudritz, Springer reference works, Juan Antonio Belmonte and Hans Deeg, Ed
The Gaia-ESO Survey::the present-day radial metallicity distribution of the Galactic disc probed by pre-main-sequence clusters
Context. The radial metallicity distribution in the Galactic thin disc represents a crucial constraint for modelling disc formation and evolution. Open star clusters allow us to derive both the radial metallicity distribution and its evolution over time.
Aims. In this paper we perform the first investigation of the present-day radial metallicity distribution based on [Fe/H] determinations in late type members of pre-main-sequence clusters. Because of their youth, these clusters are therefore essential for tracing the current interstellar medium metallicity.
Methods. We used the products of the Gaia-ESO Survey analysis of 12 young regions (age < 100 Myr), covering Galactocentric distances from 6.67 to 8.70 kpc. For the first time, we derived the metal content of star forming regions farther than 500 pc from the Sun. Median metallicities were determined through samples of reliable cluster members. For ten clusters the membership analysis is discussed in the present paper, while for other two clusters (i.e. Chamaeleon I and Gamma Velorum) we adopted the members identified in our previous works.
Results. All the pre-main-sequence clusters considered in this paper have close-to-solar or slightly sub-solar metallicities. The radial metallicity distribution traced by these clusters is almost flat, with the innermost star forming regions having [Fe/H] values that are 0.10−0.15 dex lower than the majority of the older clusters located at similar Galactocentric radii.
Conclusions. This homogeneous study of the present-day radial metallicity distribution in the Galactic thin disc favours models that predict a flattening of the radial gradient over time. On the other hand, the decrease of the average [Fe/H] at young ages is not easily explained by the models. Our results reveal a complex interplay of several processes (e.g. star formation activity, initial mass function, supernova yields, gas flows) that controlled the recent evolution of the Milky Way
Connecting Planetary Composition with Formation
The rapid advances in observations of the different populations of
exoplanets, the characterization of their host stars and the links to the
properties of their planetary systems, the detailed studies of protoplanetary
disks, and the experimental study of the interiors and composition of the
massive planets in our solar system provide a firm basis for the next big
question in planet formation theory. How do the elemental and chemical
compositions of planets connect with their formation? The answer to this
requires that the various pieces of planet formation theory be linked together
in an end-to-end picture that is capable of addressing these large data sets.
In this review, we discuss the critical elements of such a picture and how they
affect the chemical and elemental make up of forming planets. Important issues
here include the initial state of forming and evolving disks, chemical and dust
processes within them, the migration of planets and the importance of planet
traps, the nature of angular momentum transport processes involving turbulence
and/or MHD disk winds, planet formation theory, and advanced treatments of disk
astrochemistry. All of these issues affect, and are affected by the chemistry
of disks which is driven by X-ray ionization of the host stars. We discuss how
these processes lead to a coherent end-to-end model and how this may address
the basic question.Comment: Invited review, accepted for publication in the 'Handbook of
Exoplanets', eds. H.J. Deeg and J.A. Belmonte, Springer (2018). 46 pages, 10
figure
Planetary Migration in Protoplanetary Disks
The known exoplanet population displays a great diversity of orbital architectures, and explaining the origin of this is a major challenge for planet formation theories. The gravitational interaction between young planets and their protoplanetary disks provides one way in which planetary orbits can be shaped during the formation epoch. Disk-planet interactions are strongly influenced by the structure and physical processes that drive the evolution of the protoplanetary disk. In this review we focus on how disk-planet interactions drive the migration of planets when different assumptions are made about the physics of angular momentum transport, and how it drives accretion flows in protoplanetary disk models. In particular, we consider migration in discs where: (i) accretion flows arise because turbulence diffusively transports angular momentum; (ii) laminar accretion flows are confined to thin, ionised layers near disk surfaces and are driven by the launching of magneto-centrifugal winds, with the midplane being completely inert; (iii) laminar accretion flows pervade the full column density of the disc, and are driven by a combination of large scale horizontal and vertical magnetic fields
Disk Weather
Recent years have shown that accretion disks around young stars have extended regions,
which are too low ionized to couple to magnetic fields and thus the nature of the
underlying turbulence cannot be exclusively magnetic. We also found that disks have in
general a baroclinic density and temperature structure which means that a typical disk is
radially buoyant and has a vertical velocity gradient also known as thermal wind. Here we
show that the expected entropy gradients in observed accretion disks around young stars
are in fact steep enough and that the thermal relaxation times are sufficiently short to
allow for efficient amplification of vortices