210 research outputs found
Clumpy streams in a smooth dark halo: the case of Palomar 5
By means of direct N-body simulations and simplified numerical models, we
study the formation and characteristics of the tidal tails around Palomar 5,
along its orbit in the Milky Way potential. Unlike previous findings, we are
able to reproduce the substructures observed in the stellar streams of this
cluster, without including any lumpiness in the dark matter halo. We show that
overdensities similar to those observed in Palomar 5 can be reproduced by the
epicyclic motion of stars along its tails, i.e. a simple local accumulation of
orbits of stars that escaped from the cluster with very similar positions and
velocities. This process is able to form stellar clumps at distances of several
kiloparsecs from the cluster, so it is not a phenomenon confined to the inner
part of Palomar 5's tails, as previously suggested. Our models can reproduce
the density contrast between the clumps and the surrounding tails found in the
observed streams, without including any lumpiness in the dark halo, suggesting
new upper limits on its granularity.Comment: 6 pages, 7 figures. A&A Letters, accepted. Top panel of Fig. A1
replaced, minor typos corrected. High resolution version available at
http://mygepi.obspm.fr/~paola/Pal5
Are Current Cancer Treatments on Target for Our Ageing Cancer Population?
Worldwide the cancer population is ageing – within a decade almost two-thirds of newly diagnosed patients will be aged 65 years and older. Despite this, the majority of oncology clinical trials continue to recruit patients who are younger and fitter than those typically encountered in clinical practice. As such, there is a lack of clinical data to guide management, particularly in those patients living with frailty and/or comorbidity. Importantly, the lack of older adults in trials also means that the subsequent translational work that underpins biomarker and therapeutic discovery may not be relevant to those we see in clinic. In this commentary, we discuss this challenge and the ways we as an Oncology community can look to address this pressing issue
Are Current Cancer Treatments on Target for Our Ageing Cancer Population?
Worldwide the cancer population is ageing – within a decade almost two-thirds of newly diagnosed patients will be aged 65 years and older. Despite this, the majority of oncology clinical trials continue to recruit patients who are younger and fitter than those typically encountered in clinical practice. As such, there is a lack of clinical data to guide management, particularly in those patients living with frailty and/or comorbidity. Importantly, the lack of older adults in trials also means that the subsequent translational work that underpins biomarker and therapeutic discovery may not be relevant to those we see in clinic. In this commentary, we discuss this challenge and the ways we as an Oncology community can look to address this pressing issue
The distribution of globular clusters in kinematic spaces does not trace the accretion history of the host galaxy
Reconstructing how all the stellar components of the Galaxy formed and
assembled over time, by studying the properties of the stars which make it, is
the aim of Galactic archeology. In these last years, thanks to the launch of
the ESA Gaia astrometric mission, and the development of many spectroscopic
surveys, we are for the first time in the position to delve into the layers of
the past of our galaxy. Globular clusters (GCs) play a fundamental role in this
research field since they are among the oldest stellar systems in the Milky Way
(MW) and so bear witness of its entire past. In the recent years, there have
been several attempts to constrain the nature of clusters (accreted or formed
in the MW itself) through the analysis of kinematic spaces and to reconstruct
from this the properties of the accretions events experienced by the MW through
time. This work aims to test a widely-used assumption about the clustering of
the accreted populations of GCs in the integrals of motions space. We analyze a
set of dissipation-less N-body simulations that reproduce the accretion of one
or two satellites with their GC population on a MW-type galaxy. Our results
demonstrate that a significant overlap between accreted and
"kinematically-heated" in-situ GCs is expected in kinematic spaces, for mergers
with mass ratios of 1:10. In contrast with standard assumptions made in the
literature so far, we find that accreted GCs do not show dynamical coherence,
that is they do not cluster in kinematic spaces. In addition, GCs can also be
found in regions dominated by stars which have a different origin (i.e.
different progenitor). This casts doubt on the association between GCs and
field stars that is generally made in the literature to assign them to a common
origin. Our findings severely question the recovered accretion history of the
MW based on the phase-space clustering of the GC population.Comment: Submitted to A&A, 23 pages, 13 figure
NBSymple, a double parallel, symplectic N-body code running on Graphic Processing Units
We present and discuss the characteristics and performances, both in term of
computational speed and precision, of a numerical code which numerically
integrates the equation of motions of N 'particles' interacting via Newtonian
gravitation and move in an external galactic smooth field. The force evaluation
on every particle is done by mean of direct summation of the contribution of
all the other system's particle, avoiding truncation error. The time
integration is done with second-order and sixth-order symplectic schemes. The
code, NBSymple, has been parallelized twice, by mean of the Computer Unified
Device Architecture to make the all-pair force evaluation as fast as possible
on high-performance Graphic Processing Units NVIDIA TESLA C 1060, while the
O(N) computations are distributed on various CPUs by mean of OpenMP Application
Program. The code works both in single precision floating point arithmetics or
in double precision. The use of single precision allows the use at best of the
GPU performances but, of course, limits the precision of simulation in some
critical situations. We find a good compromise in using a software
reconstruction of double precision for those variables that are most critical
for the overall precision of the code. The code is available on the web site
astrowww.phys.uniroma1.it/dolcetta/nbsymple.htmlComment: Paper composed by 29 pages, including 9 figures. Submitted to New
Astronomy
EUSO-SPB2 Fluorescence Telescope Calibration and Field Tests
The Extreme Universe Space Observatory on a Super Pressure Balloon 2
(EUSO-SPB2), successfully launched from Wanaka, New Zealand on May 13, 2022, is
a precursor for a space-based astroparticle observatory such as the Probe Of
Extreme Multi-Messenger Astrophysics (POEMMA). EUSO-SPB2 flew two custom
telescopes. Both have UV/UV-visible sensitivity and feature Schmidt optics. The
Fluorescence Telescope (FT) measures ultra-high energy cosmic rays by looking
down. The \v{C}erenkov Telescope (CT) searches for neutrino signatures by
looking toward Earth's limb. The two telescopes each have a 1 m diameter
entrance pupil and segmented glass mirrors that collect light from extensive
air showers at the PeV and EeV-scale. Here we describe the FT telescope optics
together with the results of the FT field tests at the Utah Telescope Array
(TA) site from August/September 2022. The FT recorded the night sky background,
lasers, and artificial point sources. The field tests included an absolute
photometric calibration of the FT telescope that is compared to a piece-wise
laboratory calibration
An increase in the levels of middle surface antigen characterizes patients developing HBV-driven liver cancer despite prolonged virological suppression
: Hepatitis B virus (HBV) contains three surface glycoproteins-Large-HBs (L-HBs), Middle-HBs (M-HBs), and Small-HBs (S-HBs), known to contribute to HBV-driven pro-oncogenic properties. Here, we examined the kinetics of HBs-isoforms in virologically-suppressed patients who developed or did not develop hepatocellular carcinoma (HCC). This study enrolled 30 chronically HBV-infected cirrhotic patients under fully-suppressive anti-HBV treatment. Among them, 13 patients developed HCC. Serum samples were collected at enrolment (T0) and at HCC diagnosis or at the last control for non-HCC patients (median (range) follow-up: 38 (12-48) months). Ad-hoc ELISAs were designed to quantify L-HBs, M-HBs and S-HBs (Beacle). At T0, median (IQR) levels of S-HBs, M-HBs and L-HBs were 3140 (457-6995), 220 (31-433) and 0.2 (0-1.7) ng/mL. No significant differences in the fraction of the three HBs-isoforms were noticed between patients who developed or did not develop HCC at T0. On treatment, S-HBs showed a >25% decline or remained stable in a similar proportion of HCC and non-HCC patients (58.3% of HCC- vs. 47.1% of non-HCC patients, p = 0.6; 25% of HCC vs. 29.4% of non-HCC, p = 0.8, respectively). Conversely, M-HBs showed a >25% increase in a higher proportion of HCC compared to non-HCC patients (50% vs. 11.8%, p = 0.02), in line with M-HBs pro-oncogenic role reported in in vitro studies. No difference in L-HBs kinetics was observed in HCC and non-HCC patients. In conclusion, an increase in M-HBs levels characterizes a significant fraction of HCC-patients while under prolonged HBV suppression and stable/reduced total-HBs. The role of M-HBs kinetics in identifying patients at higher HCC risk deserves further investigation
Whole exome HBV DNA integration is independent of the intrahepatic HBV reservoir in HBeAg-negative chronic hepatitis B
The involvement of HBV DNA integration in promoting hepatocarcinogenesis and the extent to which the intrahepatic HBV reservoir modulates liver disease progression remains poorly understood. We examined the intrahepatic HBV reservoir, the occurrence of HBV DNA integration and its impact on the hepatocyte transcriptome in hepatitis B 'e' antigen (HBeAg)-negative chronic hepatitis B (CHB)
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