21 research outputs found
Orbit classification in the meridional plane of a disk galaxy model with a spherical nucleus
We investigate the regular or chaotic nature of star orbits moving in the
meridional plane of an axially symmetric galactic model with a disk and a
spherical nucleus. We study the influence of some important parameters of the
dynamical system, such as the mass and the scale length of the nucleus, the
angular momentum or the energy, by computing in each case the percentage of
chaotic orbits, as well as the percentages of orbits of the main regular
resonant families. Some heuristic arguments to explain and justify the
numerically derived outcomes are also given. Furthermore, we present a new
method to find the threshold between chaos and regularity for both Lyapunov
Characteristic Numbers and SALI, by using them simultaneously.Comment: Published in Celestial Mechanics & Dynamical Astronomy (CMDA) journa
On a possible origin for the lack of old star clusters in the Small Magellanic Cloud
We model the dynamical interaction between the Small and Large Magellanic
Clouds and their corresponding stellar cluster populations. Our goal is to
explore whether the lack of old clusters ( Gyr) in the Small
Magellanic Cloud (SMC) can be the result of the capture of clusters by the
Large Magellanic Cloud (LMC), as well as their ejection due to the tidal
interaction between the two galaxies. For this purpose we perform a suite of
numerical simulations probing a wide range of parameters for the orbit of the
SMC about the LMC. We find that, for orbital eccentricities ,
approximately 15 per cent of the SMC clusters are captured by the LMC. In
addition, another 20 to 50 per cent of its clusters are ejected into the
intergalactic medium. In general, the clusters lost by the SMC are the less
tightly bound cluster population. The final LMC cluster distribution shows a
spatial segregation between clusters that originally belonged to the LMC and
those that were captured from the SMC. Clusters that originally belonged to the
SMC are more likely to be found in the outskirts of the LMC. Within this
scenario it is possible to interpret the difference observed between the star
field and cluster SMC Age-Metallicity Relationships for ages Gyr.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter
On the correct computation of all Lyapunov exponents in Hamiltonian dynamical systems
The Lyapunov Characteristic Exponents are a useful indicator of chaos in
astronomical dynamical systems. They are usually computed through a standard,
very efficient and neat algorithm published in 1980. However, for Hamiltonian
systems the expected result of pairs of opposite exponents is not always
obtained with enough precision. We find here why in these cases the initial
order of the deviation vectors matters, and how to sort them in order to obtain
a correct result.Comment: 8 pages, 3 figure
And yet it moves: The dangers of artificially fixing the Milky Way center of mass in the presence of a massive Large Magellanic Cloud
Motivated by recent studies suggesting that the Large Magellanic Cloud (LMC)
could be significantly more massive than previously thought, we explore whether
the approximation of an inertial Galactocentric reference frame is still valid
in the presence of such a massive LMC. We find that previous estimates of the
LMC's orbital period and apocentric distance derived assuming a fixed Milky Way
are significantly shortened for models where the Milky Way is allowed to move
freely in response to the gravitational pull of the LMC. Holding other
parameters fixed, the fraction of models favoring first infall is reduced. Due
to this interaction, the Milky Way center of mass within the inner 50 kpc can
be significantly displaced in phase-space in a very short period of time that
ranges from 0.3 to 0.5 Gyr by as much as 30 kpc and 75 km/s. Furthermore, we
show that the gravitational pull of the LMC and response of the Milky Way are
likely to significantly affect the orbit and phase space distribution of tidal
debris from the Sagittarius dwarf galaxy (Sgr). Such effects are larger than
previous estimates based on the torque of the LMC alone. As a result, Sgr
deposits debris in regions of the sky that are not aligned with the present-day
Sgr orbital plane. In addition, we find that properly accounting for the
movement of the Milky Way around its common center of mass with the LMC
significantly modifies the angular distance between apocenters and tilts its
orbital pole, alleviating tensions between previous models and observations.
While these models are preliminary in nature, they highlight the central
importance of accounting for the mutual gravitational interaction between the
MW and LMC when modeling the kinematics of objects in the Milky Way and Local
Group.Comment: Accepted for publication in ApJ; 16 pages, 11 figure
Dose-Ranging Effect of Adjunctive Oral Cannabidiol vs Placebo on Convulsive Seizure Frequency in Dravet Syndrome A Randomized Clinical Trial
Question Is adjunctive cannabidiol at doses of 10 and 20 mg/kg/d
superior to placebo in reducing convulsive seizure frequency in
patients with Dravet syndrome?
Findings This double-blind clinical trial randomized 199 children
with Dravet syndrome to cannabidiol (10 or 20 mg/kg/d) or
matched placebo for 14 weeks. Convulsive seizure frequency
compared with baseline was reduced by 48.7% in the 10-mg/kg/d
cannabidiol group and 45.7% in the 20-mg/kg/d cannabidiol
group vs 26.9% in the placebo group.
Meaning Both doses of adjunctive cannabidiol were similarly
efficacious in reducing convulsive seizures associated with Dravet
syndrome
Clonal chromosomal mosaicism and loss of chromosome Y in elderly men increase vulnerability for SARS-CoV-2
The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, COVID-19) had an estimated overall case fatality ratio of 1.38% (pre-vaccination), being 53% higher in males and increasing exponentially with age. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, we found 133 cases (1.42%) with detectable clonal mosaicism for chromosome alterations (mCA) and 226 males (5.08%) with acquired loss of chromosome Y (LOY). Individuals with clonal mosaic events (mCA and/or LOY) showed a 54% increase in the risk of COVID-19 lethality. LOY is associated with transcriptomic biomarkers of immune dysfunction, pro-coagulation activity and cardiovascular risk. Interferon-induced genes involved in the initial immune response to SARS-CoV-2 are also down-regulated in LOY. Thus, mCA and LOY underlie at least part of the sex-biased severity and mortality of COVID-19 in aging patients. Given its potential therapeutic and prognostic relevance, evaluation of clonal mosaicism should be implemented as biomarker of COVID-19 severity in elderly people. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, individuals with clonal mosaic events (clonal mosaicism for chromosome alterations and/or loss of chromosome Y) showed an increased risk of COVID-19 lethality
Effects of chaos on the detectability of stellar streams
Observations show that stellar streams originating in satellite dwarf galaxies are frequent in the Universe. While such events are predicted by theory, it is not clear how many of the streams that are generated are washed out afterwards to the point in which it is impossible to detect them. Here, we study how these diffusion times are affected by the fact that typical gravitational potentials of the host galaxies can sustain chaotic orbits. We do this by comparing the behaviour of simulated stellar streams that reside in chaotic or non-chaotic regions of the phase space. We find that chaos does reduce the time interval in which streams can be detected. By analysing detectability criteria in configuration and velocity space, we find that the impact of these results on the observations depends on the quality of both the data and the underlying stellar halo model. For all the stellar streams, we obtain a similar upper limit to the detectable mass
Smart: A program to automatically compute accelerations and variational equations
Modern astronomical potentials modeling galaxies or stellar systems can be
rather involved, and deriving their first derivatives (accelerations) and
second derivatives (variational equations) in order to compute orbits and their
chaoticity may be a formidable task. We present here a fully automated routine,
dubbed Smart, with which the accelerations and the variational equations of an
arbitrary potential that has been written in the Fortran 77 language can be
computed. Almost any Fortran 77 statement is admitted in the potential, and the
output are standard Fortran 77 routines ready to use. We validate our algorithm
with a set of potentials including time-dependent, velocity-dependent and very
complex potentials that even involve auxiliary routines. We also describe with
some detail a realistic seven-component Galactic potential, MilkyWayHydra,
which yields very involved derivatives, thus being a good test bed for Smart.Comment: 37 pages, 5 figures. To be published in Astronomy and Computing, in
pres
Dose-Ranging Effect of Adjunctive Oral Cannabidiol vs Placebo on Convulsive Seizure Frequency in Dravet Syndrome A Randomized Clinical Trial
Question Is adjunctive cannabidiol at doses of 10 and 20 mg/kg/d
superior to placebo in reducing convulsive seizure frequency in
patients with Dravet syndrome?
Findings This double-blind clinical trial randomized 199 children
with Dravet syndrome to cannabidiol (10 or 20 mg/kg/d) or
matched placebo for 14 weeks. Convulsive seizure frequency
compared with baseline was reduced by 48.7% in the 10-mg/kg/d
cannabidiol group and 45.7% in the 20-mg/kg/d cannabidiol
group vs 26.9% in the placebo group.
Meaning Both doses of adjunctive cannabidiol were similarly
efficacious in reducing convulsive seizures associated with Dravet
syndrome
Add-on cannabidiol in patients with Dravet syndrome: Results of a long-term open-label extension trial
Objective: Add-on cannabidiol (CBD) reduced seizures associated with Dravet
syndrome (DS) in two randomized, double-blind, placebo-controlled trials:
GWPCARE1 Part B (NCT02091375) and GWPCARE2 (NCT02224703). Patients
whocompletedGWPCARE1 PartA(NCT02091206)orPartB,orGWPCARE2,were
enrolled in a long-term open-label extension trial, GWPCARE5 (NCT02224573).
We present an interim analysis of the safety, efficacy, and patient-reported outcomes from GWPCARE5.
Methods: Patientsreceived a pharmaceutical formulation of highly purified CBD
in oral solution (100 mg/ml), titrated from 2.5 to 20 mg/kg/day over a 2-week period, added to their existing medications. Based on response and tolerance, CBD
could be reduced or increased to 30 mg/kg/day.
Results: Of the 330 patients who completed the original randomized trials, 315
(95%) enrolled in this open-label extension. Median treatment duration was
444 days (range = 18–1535), with a mean modal dose of 22 mg/kg/day; patients
received a median of three concomitant antiseizure medications. Adverse events
(AEs)occurredin97%patients(mild,23%;moderate,50%;severe,25%).Commonly
reported AEs were diarrhea (43%), pyrexia (39%), decreased appetite (31%), and
somnolence (28%). Twenty-eight (9%) patients discontinued due to AEs. Sixtynine (22%) patients had liver transaminase elevations >3 × upper limit of normal;
84% were on concomitant valproic acid. In patients from GWPCARE1 Part B and
GWPCARE2, the median reduction from baseline in monthly seizure frequency
assessed in 12-week periods up to Week 156 was 45%–74% for convulsive seizures
and 49%–84% for total seizures. Across all visit windows, ≥83% patients/caregivers completing a Subject/Caregiver Global Impression of Change scale reported
improvement in overall condition.
Significance: We show that long-term CBD treatment had an acceptable safety
profile and led to sustained, clinically meaningful reductionsin seizure frequency
in patients with treatment-resistant DS