176 research outputs found
Relaxation of spherical systems with long-range interactions: a numerical investigation
The process of relaxation of a system of particles interacting with
long-range forces is relevant to many areas of Physics. For obvious reasons, in
Stellar Dynamics much attention has been paid to the case of 1/r^2 force law.
However, recently the interest in alternative gravities emerged, and
significant differences with respect to Newtonian gravity have been found in
relaxation phenomena. Here we begin to explore this matter further, by using a
numerical model of spherical shells interacting with an 1/r^alpha force law
obeying the superposition principle. We find that the virialization and
phase-mixing times depend on the exponent alpha, with small values of alpha
corresponding to longer relaxation times, similarly to what happens when
comparing for N-body simulations in classical gravity and in Modified Newtonian
Dynamics.Comment: 6 pages, 3 figures, accepted in the International Journal of
Bifurcation and Chao
Testing Feedback-Modified Dark Matter Haloes with Galaxy Rotation Curves: Estimation of Halo Parameters and Consistency with CDM
Cosmological -body simulations predict dark matter (DM) haloes with steep
central cusps (e.g. NFW, Navarro et al. 1996). This contradicts observations of
gas kinematics in low-mass galaxies that imply the existence of shallow DM
cores. Baryonic processes such as adiabatic contraction and gas outflows can,
in principle, alter the initial DM density profile, yet their relative
contributions to the halo transformation remain uncertain. Recent high
resolution, cosmological hydrodynamic simulations (Di Cintio et al. 2014, DC14)
predict that inner density profiles depend systematically on the ratio of
stellar to DM mass (M/M). Using a Markov Chain Monte Carlo
approach, we test the NFW and the M/M-dependent DC14 halo
models against a sample of 147 galaxy rotation curves from the new {\it
Spitzer} Photometry and Accurate Rotation Curves (SPARC) data set. These
galaxies all have extended H{\small I} rotation curves from radio
interferometry as well as accurate stellar mass density profiles from
near-infrared photometry. The DC14 halo profile provides markedly better fits
to the data compared to the NFW profile. Unlike NFW, the DC14 halo parameters
found in our rotation curve fits naturally fall within two standard deviations
of the mass-concentration relation predicted by CDM and the stellar
mass-halo mass relation inferred from abundance matching with few outliers.
Halo profiles modified by baryonic processes are therefore more consistent with
expectations from cold dark matter (CDM) cosmology and
provide better fits to galaxy rotation curves across a wide range of galaxy
properties than do halo models that neglect baryonic physics. Our results offer
a solution to the decade long cusp-core discrepancy.Comment: 23 Pages, 18 Figures, MNRAS Accepte
Successful Surgical Treatment of Two Patients with Restenosis after Previous Stenting of the Carotid Artery
A rumble in the dark: signatures of self-interacting dark matter in supermassive black hole dynamics and galaxy density profiles
We explore for the first time the effect of self-interacting dark matter (SIDM) on the dark matter (DM) and baryonic distribution in massive galaxies formed in hydrodynamical cosmological simulations, including explicit baryonic physics treatment. A novel implementation of supermassive black hole (SMBH) formation and evolution is used, as in Tremmel et al., allowing us to explicitly follow the SMBH dynamics at the centre of galaxies. A high SIDM constant cross-section is chosen, σ = 10 cm2gr−1, to amplify differences from CDM models. Milky Way-like galaxies form a shallower DM density profile in SIDM than they do in cold dark matter (CDM), with differences already at 20 kpc scales. This demonstrates that even for the most massive spirals, the effect of SIDM dominates over the adiabatic contraction due to baryons. Strikingly, the dynamics of SMBHs differs in the SIDM and reference CDM case. SMBHs in massive spirals have sunk to the centre of their host galaxy in both the SIDM and CDM run, while in less massive galaxies about 80 per cent of the SMBH population is off-centred in the SIDM case, as opposed to the CDM case in which ∼ 90 per cent of SMBHs have reached their host’s centre. SMBHs are found as far as ∼9 kpc away from the centre of their host SIDM galaxy. This difference is due to the increased dynamical friction time-scale caused by the lower DM density in SIDM galaxies compared to CDM, resulting in core stalling. This pilot work highlights the importance of simulating in a full hydrodynamical context different DM models combined to the SMBH physics to study their influence on galaxy formation
Spectroscopic characterisation of the stellar content of ultra diffuse galaxies
Understanding the peculiar properties of Ultra Diffuse Galaxies (UDGs) via
spectroscopic analysis is a challenging task requiring very deep observations
and exquisite data reduction. In this work we perform one of the most complete
characterisations of the stellar component of UDGs to date using deep optical
spectroscopic data from OSIRIS at GTC. We measure radial and rotation
velocities, star formation histories (SFH) and mean population parameters, such
as ages and metallicities, for a sample of five UDG candidates in the Coma
cluster. From the radial velocities, we confirm the Coma membership of these
galaxies. We find that their rotation properties, if detected at all, are
compatible with dwarf-like galaxies. The SFHs of the UDG are dominated by old
(~ 7 Gyr), metal-poor ([M/H] ~ -1.1) and alpha-enhanced ([Mg/Fe] ~ 0.4)
populations followed by a smooth or episodic decline which halted ~ 2 Gyr ago,
possibly a sign of cluster-induced quenching. We find no obvious correlation
between individual SFH shapes and any UDG morphological properties. The
recovered stellar properties for UDGs are similar to those found for DDO44, a
local UDG analogue resolved into stars. We conclude that the UDGs in our sample
are extended dwarfs whose properties are likely the outcome of both internal
processes, such as bursty SFHs and/or high-spin haloes, as well as
environmental effects within the Coma cluster.Comment: Accepted for publication in MNRA
Self-interacting dark matter and the delay of supermassive black hole growth
Using cosmological hydrodynamic simulations with physically motivated models of supermassive black hole (SMBH) formation and growth, we compare the assembly of Milky Way-mass (Mvir ≈ 7 × 1011 M⊙ at z = 0) galaxies in cold dark matter (CDM) and self-interacting dark matter (SIDM) models. Our SIDM model adopts a constant cross-section of 1 cm2 g−1. We find that SMBH formation is suppressed in the early Universe due to SIDM interactions. SMBH–SMBH mergers are also suppressed in SIDM as a consequence of the lower number of SMBHs formed. Lack of initial merger-driven SMBH growth in turn delays SMBH growth by billions of years in SIDM compared to CDM. Further, we find that this delayed growth suppresses SMBH accretion in the largest progenitors of the main SIDM galaxies during the first 5 Gyr of their evolution. Nonetheless, by z = 0.8 the CDM and SIDM SMBH masses differ only by around 0.2 dex, so that both remain compatible with the MBH–M* relation. We show that the reduced accretion causes the SIDM SMBHs to less aggressively regulate star formation in their host galaxies than their CDM counterparts, resulting in a factor of 3 or more stars being produced over the lifetime of the SIDM galaxies compared to the CDM galaxies. Our results highlight a new way in which SIDM can affect the growth and merger history of SMBHs and ultimately give rise to very different galaxy evolution compared to the classic CDM model
Ruolo della chirurgia endovascolare nelle rotture aortiche del politraumatizzato con lesioni polidistrettuali di pertinenza chirurgica
Nel politraumatizzato con gravi lesioni polidistrettuali di interesse chirurgico il trattamento endovascolare (TEV) della rottura posttraumatica dell’ aorta toracica (RPAT) rappresenta oggi una valida alternativa terapeutica al trattamento chirurgico convenzionale.
Nella nostra esperienza (ottobre 2001-novembre 2004) abbiamo
osservato 5 casi di RPAT (3 rotture istmiche, 2 rotture aorta toracica
discendente) in gravi politraumatizzati, tutti di sesso maschile, di etÃ
compresa fra i 23 ed i 42 anni (media 32,4), trattate con successo con
TEV. Il Glasgow Coma Score (GCS) era compreso fra 5 e 13. Tutti i
pazienti sono stati sottoposti, dopo adeguata stabilizzazione del quadro clinico-emodinamico, ad angio-TC total body al fine di valutare
la lesione aortica ed identificare le altre lesioni associate. In 4 casi erano coinvolti più distretti corporei di pertinenza chirurgica (3 casi:
trauma osseo, addominale e neurochirurgico; 1 caso: trauma osseo, addominale, neurochirurgico e toracico). Il TEV è stato eseguito sempre
in sala operatoria previa arteriografia digitale. La durata media della
procedura angio-radiologica è stata di 105 minuti (range 80 - 125).
Non si è verificata nessuna complicanza né immediata né a distanza
(follow-up = medio 24 mesi; range 12-36).
In conclusione il TEV delle RPAT offre in pazienti ‘critici’ una valida opzione terapeutica alla chirurgia tradizionale in grado di stabilizzare il quadro clinico e trattare successivamente ‘in sicurezza’ le altre gravi lesioni chirurgiche associate
Article a new epigenetic model to stratify glioma patients according to their immunosuppressive state
Gliomas are the most common primary neoplasm of the central nervous system. A promising frontier in the definition of glioma prognosis and treatment is represented by epigenetics. Further-more, in this study, we developed a machine learning classification model based on epigenetic data (CpG probes) to separate patients according to their state of immunosuppression. We considered 573 cases of low-grade glioma (LGG) and glioblastoma (GBM) from The Cancer Genome Atlas (TCGA). First, from gene expression data, we derived a novel binary indicator to flag patients with a favorable immune state. Then, based on previous studies, we selected the genes related to the immune state of tumor microenvironment. After, we improved the selection with a data-driven procedure, based on Boruta. Finally, we tuned, trained, and evaluated both random forest and neural network classifiers on the resulting dataset. We found that a multi-layer perceptron network fed by the 338 probes selected by applying both expert choice and Boruta results in the best performance, achieving an out-of-sample accuracy of 82.8%, a Matthews correlation coefficient of 0.657, and an area under the ROC curve of 0.9. Based on the proposed model, we provided a method to stratify glioma patients according to their epigenomic state
The distribution of mass components in simulated disc galaxies
Using 22 hydrodynamical simulated galaxies in a LCDM cosmological context we
recover not only the observed baryonic Tully-Fisher relation, but also the
observed "mass discrepancy--acceleration" relation, which reflects the
distribution of the main components of the galaxies throughout their disks.
This implies that the simulations, which span the range 52 < V <
222 km/s where V is the circular velocity at the flat part of the
rotation curve, and match galaxy scaling relations, are able to recover the
observed relations between the distributions of stars, gas and dark matter over
the radial range for which we have observational rotation curve data.
Furthermore, we explicitly match the observed baryonic to halo mass relation
for the first time with simulated galaxies. We discuss our results in the
context of the baryon cycle that is inherent in these simulations, and with
regards to the effect of baryonic processes on the distribution of dark matter.Comment: 8 pages, 7 pdf figures. Accepted for publication in MNRAS on 2015
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