scholarly journals Formation and evolution of nuclear star clusters

2014 ◽  
Vol 10 (S312) ◽  
pp. 122-125
Author(s):  
Alessandra Mastrobuono-Battisti ◽  
Hagai B. Perets
Keyword(s):  
Galactic Center ◽  
Stellar Clusters ◽  
Massive Black Hole ◽  
Loss Cone ◽  
A Value ◽  
Free Case ◽  
Formation And Evolution ◽  
Cumulative Constraint ◽  
Age Segregation

AbstractNuclear stellar clusters (NSCs) are dense stellar systems known to exist at the center of most of the galaxies. Some of them host a central massive black hole (MBH). They are though to form through in-situ star formation following the infall of gas to the galactic center and/or because of the infall and merger of several stellar clusters. Here we explore the latter scenario by means of detailed self-consistent N-body simulations, proving that a NSC built by the infall and following merger of stellar clusters shows many of the observed features of the Milky Way NSC. We also explore the possibility that the infalling clusters host intermediate mass black holes (IMBHs). Once decayed to the center, the IMBHs act as massive-perturbers accelerating the relaxation of the NSC, filling the loss-cone and boosting the tidal disruption rate of stars up to a value larger than the observational estimates, therefore providing a cumulative constraint on the existence of IMBHs in NSCs. Studying how the properties of the infalling clusters map to the properties of the resulting NSC, we find that, in the IMBHs-free case, the infall mechanism is able to produce many different observational signatures in the form of age segregation.

scholarly journals MONITORING STELLAR ORBITS AROUND THE MASSIVE BLACK HOLE IN THE GALACTIC CENTER

2009 ◽  
Vol 692 (2) ◽  
pp. 1075-1109 ◽  
Author(s):  
S. Gillessen ◽  
F. Eisenhauer ◽  
S. Trippe ◽  
T. Alexander ◽  
R. Genzel ◽  
...  
Keyword(s):  
Black Hole ◽  
Galactic Center ◽  
Massive Black Hole ◽  
Stellar Orbits

scholarly journals An Atmospheric Origin for HCN-Derived Polymers on Titan

Processes ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 965
Author(s):  
Zoé Perrin ◽  
Nathalie Carrasco ◽  
Audrey Chatain ◽  
Lora Jovanovic ◽  
Ludovic Vettier ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Gas Phase ◽  
Formation Process ◽  
Upper Atmosphere ◽  
Gas Mixture ◽  
Space Probe ◽  
Atmospheric Haze ◽  
Formation And Evolution ◽  
Haze Formation

Titan’s haze is strongly suspected to be an HCN-derived polymer, but despite the first in situ measurements by the ESA-Huygens space probe, its chemical composition and formation process remain largely unknown. To investigate this question, we simulated the atmospheric haze formation process, experimentally. We synthesized analogues of Titan’s haze, named Titan tholins, in an irradiated N2–CH4 gas mixture, mimicking Titan’s upper atmosphere chemistry. HCN was monitored in situ in the gas phase simultaneously with the formation and evolution of the haze particles. We show that HCN is produced as long as the particles are absent, and is then progressively consumed when the particles appear and grow. This work highlights HCN as an effective precursor of Titan’s haze and confirms the HCN-derived polymer nature of the haze.

A Value Focused Thinking Approach to Decommissioning Decision Making

2021 ◽  
Author(s):  
Aaron Tung
Keyword(s):  
Decision Making ◽  
Scientific Evidence ◽  
Analysis Tool ◽  
Stakeholder Values ◽  
A Value ◽  
Value Focused Thinking ◽  
Science Theory ◽  
Past Experiences ◽  
Stakeholder Acceptance

Abstract Values are what stakeholders regard to be important to decisions (Kruglanski & Higgins 2007). How stakeholder prioritize, rank, balance, and trade-off values can have significant influence on their reasoning and evaluation of decommissioning outcomes and decisions. Stakeholder values can vary depending on various factors including religious beliefs, personal interests, and past experiences (Lechner et al., 2017). Value-focused thinking is a decision science theory developed by Keeney (1992) which builds upon the concept of varying stakeholder values. Keeney (1992) argues that the best decision is one that best reflects the actual values of stakeholders. which suggests that the acceptability of decommissioning decisions (full removal, partial removal, leave in-situ, rigs-to-reefs, etc.) by stakeholders will vary depending on the values of stakeholder in that particular context. This paper explores the idea of value-focused thinking and derive implications for decommissioning decision-making. Overall, the research finding suggests that rather than basing a decommissioning decision solely on scientific evidence, there is also a need for the decommissioning decisions to be able to reflect the actual values of stakeholders in that particular context. The criteria and weightage of the adopted multi-criteria decision analysis tool, for example, should accurately represent the actual values of stakeholders, so as to enable the tool to produce outcomes and decisions that has a higher probability of stakeholder acceptance.

In situ thermal-conductivity measurements and morphological characterization of intumescent coatings for fire protection

2018 ◽  
Vol 36 (5) ◽  
pp. 419-437 ◽  
Author(s):  
Jiyuan Kang ◽  
Fumiaki Takahashi ◽  
James S T’ien
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Fire Protection ◽  
Heat Fluxes ◽  
Loss Cone ◽  
Char Layer ◽  
Intumescent Coatings ◽  
Apparent Thermal Conductivity ◽  
Initial Coating

Thermal insulating performance and char-layer properties have been studied for water-based intumescent coatings for structural steel fire protection using a new laboratory-scale mass-loss cone apparatus. A specimen (100 × 100 mm mild steel plate; the initial coating thickness: 0.3–2.0 mm) is placed horizontally and exposed to a constant incident radiant heat flux (25, 50, or 75 kW/m2). The apparent thermal conductivity of the expanding char layer is determined in situ based on real-time measurements of the temperature distribution in the char layer and the heat flux transmitted through the char layer. Three-dimensional morphological observations of the expanded char layer are made using a computed tomographic–based analytical method. The vertical variation of the porosity of the expanded char layer is measured. The measured heat-blocking efficiency is correlated strongly with the incident heat flux, which increases the expanded char-layer thickness, and porosity for sufficiently large initial coating thicknesses (>0.76 mm). For a thin coating (0.30 mm), violent off-gassing disrupts the intumescing processes to form a consistent char layer after abrupt exposure to higher incident heat fluxes, thus resulting in lower heat-blocking efficiency. Therefore, the product application thickness must exceed a proper threshold value to ensure an adequate thermal insulation performance.

Direct visualization of a vast cortical calcium compartment in Paramecium by secondary ion mass spectrometry (SIMS) microscopy: possible involvement in exocytosis

1995 ◽  
Vol 108 (5) ◽  
pp. 1895-1909 ◽  
Author(s):  
N. Stelly ◽  
S. Halpern ◽  
G. Nicolas ◽  
P. Fragu ◽  
A. Adoutte
Keyword(s):  
Mass Spectrometry ◽  
Secondary Ion Mass Spectrometry ◽  
Membrane Vesicles ◽  
Cell Periphery ◽  
A Value ◽  
External Reference ◽  
Ion Mass Spectrometry ◽  
First Time ◽  
Secondary Ion

The plasma membrane of ciliates is underlaid by a vast continuous array of membrane vesicles known as cortical alveoli. Previous work had shown that a purified fraction of these vesicles actively pumps calcium, suggesting that alveoli may constitute a calcium-storage compartment. Here we provide direct confirmation of this hypothesis using in situ visualization of total cell calcium on sections of cryofixed and cryosubstituted cells analyzed by SIMS (secondary ion mass spectrometry) microscopy a method never previously applied to protists. A narrow, continuous, Ca-emitting zone located all along the cell periphery was observed on sections including the cortex. In contrast, Na and K were evenly distributed throughout the cell. Various controls confirmed that emission was from the alveoli, in particular, the emitting zone was still seen in mutants totally lacking trichocysts, the large exocytotic organelles docked at the cell surface, indicating that they make no major direct contribution to the emission. Calcium concentration within alveoli was quantified for the first time in SIMS microscopy using an external reference and was found to be in the range of 3 to 5 mM, a value similar to that for sarcoplasmic reticulum. After massive induction of trichocyst discharge, this concentration was found to decrease by about 50%, suggesting that the alveoli are the main source of the calcium involved in exocytosis.

Counting and Size Classification of Active Soil Bacteria by Fluorescence In Situ Hybridization with an rRNA Oligonucleotide Probe

1999 ◽  
Vol 65 (4) ◽  
pp. 1753-1761 ◽  
Author(s):  
Henrik Christensen ◽  
Michael Hansen ◽  
Jan Sørensen
Keyword(s):  
In Situ Hybridization ◽  
Nucleotide Sequence ◽  
Fluorescence In Situ Hybridization ◽  
Soil Bacteria ◽  
Oligonucleotide Probe ◽  
A Value ◽  
Nonspecific Staining ◽  
Dry Soil ◽  
Active Bacteria

ABSTRACT A fluorescence in situ hybridization (FISH) technique based on binding of a rhodamine-labelled oligonucleotide probe to 16S rRNA was used to estimate the numbers of ribosome-rich bacteria in soil samples. Such bacteria, which have high cellular rRNA contents, were assumed to be active (and growing) in the soil. Hybridization to an rRNA probe, EUB338, for the domain Bacteria was performed with a soil slurry, and this was followed by collection of the bacteria by membrane filtration (pore size, 0.2 μm). A nonsense probe, NONEUB338 (which has a nucleotide sequence complementary to the nucleotide sequence of probe EUB338), was used as a control for nonspecific staining. Counting and size classification into groups of small, medium, and large bacteria were performed by fluorescence microscopy. To compensate for a difference in the relative staining intensities of the probes and for binding by the rhodamine part of the probe, control experiments in which excess unlabelled probe was added were performed. This resulted in lower counts with EUB338 but not with NONEUB338, indicating that nonspecific staining was due to binding of rhodamine to the bacteria. A value of 4.8 × 108 active bacteria per g of dry soil was obtained for bulk soil incubated for 2 days with 0.3% glucose. In comparison, a value of 3.8 × 108 active bacteria per g of dry soil was obtained for soil which had been air dried and subsequently rewetted. In both soils, the majority (68 to 77%) of actively growing bacteria were members of the smallest size class (cell width, 0.25 to 0.5 μm), but the active (and growing) bacteria still represented only approximately 5% of the total bacterial population determined by DAPI (4′,6-diamidino-2-phenylindole) staining. The FISH technique in which slurry hybridization is used holds great promise for use with phylogenetic probes and for automatic counting of soil bacteria.

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