73 research outputs found
On the Newtonian Anisotropic Configurations
In this paper we are concerned with the effects of anisotropic pressure on
the boundary conditions of anisotropic Lane-Emden equation and homology
theorem. Some new exact solutions of this equation are derived. Then some of
the theorems governing the Newtonian perfect fluid star are extended taking the
anisotropic pressure into account
Kinematics of galaxies from [CII] line emission
We study the kinematical properties of galaxies in the Epoch of Reionization
via the [CII] 158m line emission. The line profile provides information on
the kinematics as well as structural properties such as the presence of a disk
and satellites. To understand how these properties are encoded in the line
profile, first we develop analytical models from which we identify disk
inclination and gas turbulent motions as the key parameters affecting the line
profile. To gain further insights, we use "Althaea", a highly-resolved () simulated prototypical Lyman Break Galaxy, in the redshift range , when the galaxy is in a very active assembling phase. Based on
morphology, we select three main dynamical stages: I) Merger , II) Spiral Disk,
and III) Disturbed Disk. We identify spectral signatures of merger events,
spiral arms, and extra-planar flows in I), II), and III), respectively. We
derive a generalised dynamical mass vs. [CII]-line FWHM relation. If precise
information on the galaxy inclination is (not) available, the returned mass
estimate is accurate within a factor (). A Tully-Fisher relation is
found for the observed high- galaxies, i.e. for which we provide a simple, physically-based
interpretation. Finally, we perform mock ALMA simulations to check the
detectability of [CII]. When seen face-on, Althaea is always detected at ; in the edge-on case it remains undetected because the larger
intrinsic FWHM pushes the line peak flux below detection limit. This suggests
that some of the reported non-detections might be due to inclination effects.Comment: 14 pages, 12 figures, accepted for publication in MNRA
Quantitative model for efficient temporal targeting of tumor cells and neovasculature
The combination of cytotoxic therapies and anti-angiogenic agents is emerging
as a most promising strategy in the treatment of malignant tumors. However, the
timing and sequencing of these treatments seem to play essential roles in
achieving a synergic outcome. Using a mathematical modeling approach that is
grounded on available experimental data, we investigate the spatial and
temporal targeting of tumor cells and neovasculature with a nanoscale delivery
system. Our model suggests that the experimental success of the nanoscale
delivery system depends crucially on the trapping of chemotherapeutic agents
within the tumor tissue. The numerical results also indicate that substantial
further improvements in the efficiency of the nanoscale delivery system can be
achieved through an adjustment of the temporal targeting mechanism.Comment: 17 pages, 5 figure
Deep into the structure of the first galaxies: SERRA views
We study the formation and evolution of a sample of Lyman Break Galaxies in
the Epoch of Reionization by using high-resolution (),
cosmological zoom-in simulations part of the SERRA suite. In SERRA, we follow
the interstellar medium (ISM) thermo-chemical non-equilibrium evolution, and
perform on-the-fly radiative transfer of the interstellar radiation field
(ISRF). The simulation outputs are post-processed to compute the emission of
far infrared lines ([CII], [NII], and [OIII]). At , the most massive
galaxy, `Freesia', has an age , stellar mass
, and a star formation rate
, due to a recent burst.
Freesia has two stellar components (A and B) separated by ; other 11 galaxies are found within . The
mean ISRF in the Habing band is and is spatially uniform; in
contrast, the ionisation parameter is , and
has a patchy distribution peaked at the location of star-forming sites. The
resulting ionising escape fraction from Freesia is .
While [CII] emission is extended (radius 1.54 kpc), [OIII] is concentrated in
Freesia-A (0.85 kpc), where the ratio . As many high- galaxies, Freesia lies below the local [CII]-SFR
relation. We show that this is the general consequence of a starburst phase
(pushing the galaxy above the Kennicutt-Schmidt relation) which
disrupts/photodissociates the emitting molecular clouds around star-forming
sites. Metallicity has a sub-dominant impact on the amplitude of [CII]-SFR
deviations.Comment: 22 pages, 14 figures, accepted by MNRA
Denoising Diffusion Restoration Tackles Forward and Inverse Problems for the Laplace Operator
Diffusion models have emerged as a promising class of generative models that
map noisy inputs to realistic images. More recently, they have been employed to
generate solutions to partial differential equations (PDEs). However, they
still struggle with inverse problems in the Laplacian operator, for instance,
the Poisson equation, because the eigenvalues that are large in magnitude
amplify the measurement noise. This paper presents a novel approach for the
inverse and forward solution of PDEs through the use of denoising diffusion
restoration models (DDRM). DDRMs were used in linear inverse problems to
restore original clean signals by exploiting the singular value decomposition
(SVD) of the linear operator. Equivalently, we present an approach to restore
the solution and the parameters in the Poisson equation by exploiting the
eigenvalues and the eigenfunctions of the Laplacian operator. Our results show
that using denoising diffusion restoration significantly improves the
estimation of the solution and parameters. Our research, as a result, pioneers
the integration of diffusion models with the principles of underlying physics
to solve PDEs.Comment: 29 page
Hard-core Yukawa model for charge-stabilized colloids
The hypernetted chain approximation is used to study the phase diagram of a simple hardcore Yukawa model of a charge-stabilized colloids. We calculate the static structure factor, the pair distribution function, and the collective mode energies over a wide range of parameters, and the results are used for studying the freezing transition of the system. The resulting phase diagram is in good agreement with the known estimates and the Monte Carlo simulations. ©2000 The American Physical Society
Dynamical characterization of galaxies up to
The characterization of the dynamical state of galaxies up to z~7 is crucial
for constraining the mechanisms driving the mass assembly in the early
Universe. However, it is unclear whether the data quality of current and future
observations is sufficient to perform a solid dynamical analysis. This paper
defines the angular resolution and S/N required for a robust characterization
of the dynamical state of galaxies up to the EoR. The final aim is to help
design spatially-resolved surveys targeting emission lines of primeval
galaxies. We investigate the [CII]-158um emission from z~6-7 LBGs from the
SERRA cosmological simulation, covering a range of dynamical states: from disks
to major mergers. We create ALMA mock observations with various data quality
and apply the kinematic classification methods used in the literature. These
tests allow us to quantify the performances of such methods as a function of
angular resolution and S/N. We find that barely-resolved observations do not
allow the correct dynamical characterization of a galaxy, resulting in the
misclassification of all disks in our sample. However, even when using
spatially-resolved observations with data quality typical of high-z galaxies,
the standard kinematic classification methods, based on the analysis of the
moment maps, fail to distinguish a merger from a disk. The high angular
resolution and S/N needed to apply these standard methods successfully can be
achieved with current data only for a handful of bright galaxies. We propose a
new classification method, called PVsplit, that quantifies the asymmetries and
morphological features in position-velocity diagrams using three empirical
parameters. We test PVsplit on our mock data concluding that it can predict
whether a galaxy is a disk or a merger provided that S/N , and the
major axis is covered by independent resolution elements.Comment: Submitted to Astronomy and Astrophysics (A&A) Journal. Comments are
welcom
Early galaxy growth: mergers or gravitational instability?
We investigate the spatially-resolved morphology of galaxies in the early
Universe. We consider a typical redshift z = 6 Lyman Break galaxy, "Althaea"
from the SERRA hydrodynamical simulations. We create mock rest-frame
ultraviolet, optical, and far-infrared observations, and perform a
two-dimensional morphological analysis to de-blend the galaxy disk from
substructures (merging satellites or star-forming regions). We find that the
[CII]158um emitting region has an effective radius 1.5 - 2.5 times larger than
the optical one, consistent with recent observations. This [CII] halo in our
simulated galaxy arises as the joint effect of stellar outflows and carbon
photoionization by the galaxy UV field, rather than from the emission of
unresolved nearby satellites. At the typical angular resolution of current
observations (> 0.15") only merging satellites can be detected; detection of
star-forming regions requires resolutions of < 0.05". The [CII]-detected
satellite has a 2.5 kpc projected distance from the galaxy disk, whereas the
star-forming regions are embedded in the disk itself (distance < 1 kpc). This
suggests that multi-component systems reported in the literature, which have
separations > 2 kpc, are merging satellites, rather than galactic
substructures. Finally, the star-forming regions found in our mock maps follow
the local L[CII] - SFR_UV relation of galaxy disks, although sampling the
low-luminosity, low-SFR tail of the distribution. We show that future JWST
observations, bridging UV and [CII] datasets, will be exceptionally suited to
characterize galaxy substructures thanks to their exquisite spatial resolution
and sensitivity to both low-metallicity and dust-obscured regions that are
bright at infrared wavelengths.Comment: Accepted for publication in MNRAS; 17 pages (plus appendix), 7
figures, 4 table
Instability and Fluctuations of Flux Lines with Point Impurities in a Parallel Current
A parallel current can destabilize a single flux line (FL), or an array of
FLs. We consider the effects of pinning by point impurities on this
instability. The presence of impurities destroys the long-range order of a flux
lattice, leading to the so called Bragg glass (BrG) phase. We first show that
the long-range topological order of the BrG is also destroyed by a parallel
current. Nonetheless, some degree of short-range order should remain, whose
destruction by thermal and impurity fluctuations, as well as the current, is
studied here. To this end, we employ a cage model for a single FL in the
presence of impurities and current, and study it analytically (by replica
variational methods), and numerically (using a transfer matrix technique). The
results are in good agreement, and in conjunction with a Lindemann criterion,
provide the boundary in the magnetic field--temperature plane for destruction
of short-range order. In all cases, we find that the addition of impurities or
current (singly or in combination) leads to further increase in equilibrium FL
fluctuations. Thus pinning to point impurities does not stabilize FLs in a
parallel current , although the onset of this instability is much delayed
due to large potential barriers that diverge as .Comment: 10 pages, 6 figure
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