1,234 research outputs found
The impact of metallicity and dynamics on the evolution of young star clusters
The early evolution of a dense young star cluster (YSC) depends on the
intricate connection between stellar evolution and dynamical processes. Thus,
N-body simulations of YSCs must account for both aspects. We discuss N-body
simulations of YSCs with three different metallicities (Z=0.01, 0.1 and 1
Zsun), including metallicity-dependent stellar evolution recipes and
metallicity-dependent prescriptions for stellar winds and remnant formation. We
show that mass-loss by stellar winds influences the reversal of core collapse.
In particular, the post-collapse expansion of the core is faster in metal-rich
YSCs than in metal-poor YSCs, because the former lose more mass (through
stellar winds) than the latter. As a consequence, the half-mass radius expands
more in metal-poor YSCs. We also discuss how these findings depend on the total
mass and on the virial radius of the YSC. These results give us a clue to
understand the early evolution of YSCs with different metallicity.Comment: to appear in "Massive Young Star Clusters Near and Far: From the
Milky Way to Reionization", 2013 Guillermo Haro Conference, Eds. Y. D. Mayya,
D. Rosa-Gonzalez & E. Terlevich, INAOE and AMC. 4 pages, 2 figure
Forming circumnuclear disks and rings in galactic nuclei: a competition between supermassive black hole and nuclear star cluster
We investigate the formation of circumnuclear gas structures from the tidal
disruption of molecular clouds in galactic nuclei, by means of smoothed
particle hydrodynamics simulations. We model galactic nuclei as composed of a
supermassive black hole (SMBH) and a nuclear star cluster (NSC) and consider
different mass ratios between the two components. We find that the relative
masses of the SMBH and the NSC have a deep impact on the morphology of the
circumnuclear gas. Extended disks form only inside the sphere of influence of
the SMBH. In contrast, compact rings naturally form outside the SMBH's sphere
of influence, where the gravity is dominated by the NSC. This result is in
agreement with the properties of the Milky Way's circumnuclear ring, which
orbits outside the SMBH sphere of influence. Our results indicate that compact
circumnuclear rings can naturally form outside the SMBH sphere of influence.Comment: Accepted for publication in ApJ. 12 pages, 6 figures, 3 tables.
Comments welcom
Runway exit designs for capacity improvement demonstrations. Phase 2: Computer model development
The development is described of a computer simulation/optimization model to: (1) estimate the optimal locations of existing and proposed runway turnoffs; and (2) estimate the geometric design requirements associated with newly developed high speed turnoffs. The model described, named REDIM 2.0, represents a stand alone application to be used by airport planners, designers, and researchers alike to estimate optimal turnoff locations. The main procedures are described in detail which are implemented in the software package and possible applications are illustrated when using 6 major runway scenarios. The main output of the computer program is the estimation of the weighted average runway occupancy time for a user defined aircraft population. Also, the location and geometric characteristics of each turnoff are provided to the user
Runway Exit Designs for Capacity Improvement Demonstrations. Phase 1: Algorithm Development
A description and results are presented of a study to locate and design rapid runway exits under realistic airport conditions. The study developed a PC-based computer simulation-optimization program called REDIM (runway exit design interactive model) to help future airport designers and planners to locate optimal exits under various airport conditions. The model addresses three sets of problems typically arising during runway exit design evaluations. These are the evaluations of existing runway configurations, addition of new rapid runway turnoffs, and the design of new runway facilities. The model is highly interactive and allows a quick estimation of the expected value of runway occupancy time. Aircraft populations and airport environmental conditions are among the multiple inputs to the model to execute a viable runway location and geometric design solution. The results presented suggest that possible reductions on runway occupancy time (ROT) can be achieved with the use of optimally tailored rapid runway designs for a given aircraft population. Reductions of up to 9 to 6 seconds are possible with the implementation of 30 m/sec variable geometry exits
The ominous fate of exomoons around hot Jupiters in the high-eccentricity migration scenario
All the giant planets in the Solar system host a large number of natural satellites. Moons in extrasolar systems are difficult to detect, but a Neptune-sized exomoon candidate has been recently found around a Jupiter-sized planet in the Kepler-1625b system. Due to their relative ease of detection, hot Jupiters (HJs), which reside in close orbits around their host stars with a period of a few days, may be very good candidates to search for exomoons. It is still unknown whether the HJ population can host (or may have hosted) exomoons. One suggested formation channel for HJs is high-eccentricity migration induced by a stellar binary companion combined with tidal dissipation. Here, we investigate under which circumstances an exomoon can prevent or allow high-eccentricity migration of a HJ, and in the latter case, if the exomoon can survive the migration process. We use both semi-analytic arguments, as well as direct N-body simulations including tidal interactions. Our results show that massive exomoons are efficient at preventing high-eccentricity migration. If an exomoon does instead allow for planetary migration, it is unlikely that the HJ formed can host exomoons since the moon will either spiral on to the planet or escape from it during the migration process. A few escaped exomoons can become stable planets after the Jupiter has migrated, or by tidally migrating themselves. The majority of the exomoons end up being ejected from the system or colliding with the primary star and the host planet. Such collisions might none the less leave observable features, such as a debris disc around the primary star or exorings around the close-in giant
Short communication: Relationships between milk quality and acidification in the production of table Mozzarella without starters.
The effect of some quality parameters of the milk (refrigeration time, pH, protein, and fat/protein ratio) on the extent of acidification in the production technology of table Mozzarella without starters was investigated. A screening phase carried out at the laboratory level demonstrated that variations of the milk characteristics require different levels of acidification to keep constant the quality of the cheese. The elaboration of the data collected throughout the successive experimentation on industrial scale allowed us to find a mathematical model to describe the relationships between the pH of the curd at stretching time and the milk characteristics, of which the protein concentration and the refrigeration time play the main roles
Constraining the binarity of black hole candidates: a proof-of-concept study of Gaia BH1 and Gaia BH2
Nearly a hundred of binary black holes (BBHs) have been discovered with
gravitational-wave signals emitted at their merging events. Thus, it is quite
natural to expect that significantly more abundant BBHs with wider separations
remain undetected in the universe, or even in our Galaxy. We consider a
possibility that star-BH binary candidates may indeed host an inner BBH,
instead of a single BH. We present a detailed feasibility study of constraining
the binarity of the currently available two targets, Gaia BH1 and Gaia BH2.
Specifically, we examine three types of radial velocity (RV) modulations of a
tertiary star in star-BBH triple systems; short-term RV modulations induced by
the inner BBH, long-term RV modulations induced by the nodal precession, and
long-term RV modulations induced by the von Zeipel-Kozai-Lidov oscillations.
Direct three-body simulations combined with approximate analytic models reveal
that Gaia BH1 system may exhibit observable signatures of the hidden inner BBH
if it exists at all. The methodology that we examine here is quite generic, and
is expected to be readily applicable to future star-BH binary candidates in a
straightforward manner.Comment: 19 pages, 10 figures, 1 table, submitted to Ap
Heterogeneous response to immunotherapy in a patient with tonsillar squamous cell carcinoma assessed by18f-fdg pet/ct
Tonsillar carcinoma is the second most common malignancy of the head and neck region, with Squamous Cell Carcinoma (TSCC) as the most common histological type (>90%). For the advanced stage of TSCC, radiotherapy with or without platinum-based chemotherapy is the only therapeutic option. Immuno-checkpoint inhibitors (ICIs), in particular Nivolumab, considerably improves clinical management of these patients, but the response can be unpredictable. Difficulties can be encountered in evaluating response to immunotherapy, especially with morphological imaging, which can show an atypical response, such as pseudo-progression, leading to a premature discontinuation. Conversely, metabolic imaging can guide a more properly therapeutic decision. We present a case of a 71-year-old man affected by TSCC, treated with chemotherapy, radiotherapy, and Nivolumab as the last line of treatment. Pre-and post-immunotherapy18F-FDG PET/CT showed an impressive response, avoiding early drug discontinuation and ensuring better management of this patient
Gender, difference and urban change: implications for promotion of well-being?
This article examines the impacts of urban change on the well-being of women and men, and girls and boys, living in cities, and explores how gender intersects with other social relations to differentiate these impacts. It then considers the implications of intersectionality for organisations aiming to promote the interests of specific social groups (such as women, or people with disabilities) vis-a-vis urban change by looking at the experience of Leonard Cheshire’s Asha project, working with girls and boys with disabilities in Mumbai. It concludes that organisations working to promote the interest of identity based constituents should (a) base their strategies around research that recognises the intersectional nature of social identities and (b) develop agendas for change that build agendas for social justice that unite, rather than fragment, identity based claims
Extreme eccentricities of triple systems: Analytic results
Triple stars and compact objects are ubiquitously observed in nature. Their
long-term evolution is complex; in particular, the von-Zeipel-Lidov-Kozai (ZLK)
mechanism can potentially lead to highly eccentric encounters of the inner
binary. Such encounters can lead to a plethora of interacting binary phenomena,
as well as stellar and compact-object mergers. Here we find explicit analytical
formulae for the maximal eccentricity, , of the inner binary
undergoing ZLK oscillations, where both the test particle limit (parametrised
by the inner-to-outer angular momentum ratio ) and the double-averaging
approximation (parametrised by the period ratio, ) are
relaxed, for circular outer orbits. We recover known results in both limiting
cases (either or ) and verify the validity of
our model using numerical simulations. We test our results with two accurate
numerical N-body codes, for Newtonian dynamics and
for general-relativistic (GR) dynamics, and find excellent
correspondence. We discuss the implications of our results for stellar triples
and both stellar and supermassive triple black hole mergers
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