scholarly journals Gas vs dust radial extent in disks: the importance of their thermal interplay

2017 ◽  
Vol 13 (S332) ◽  
pp. 129-136
Author(s):  
Stefano Facchini
Keyword(s):  
Thermal Structure ◽  
Sharp Decrease ◽  
Outer Edge ◽  
Outer Radius ◽  
Gas Temperature ◽  
Secular Evolution ◽  
Radial Extent ◽  
Grain Size Distributions ◽  
The Difference ◽  
Dust Grain

AbstractA key parameter governing the secular evolution of protoplanetary disks is their outer radius. In this paper, the feedback of realistic dust grain size distributions onto the gas emission is investigated. Models predict that the difference of dust and gas extents as traced by CO is primarily caused by differences in the optical depth of lines vs continuum. The main effect of radial drift is the sharp decrease in the intensity profile at the outer edge. The gas radial extent can easily range within a factor of 2 for models with different turbulence. A combination of grain growth and vertical settling leads to thermal de-coupling between gas and dust at intermediate scale-heights. A proper treatment of the gas thermal structure within dust gaps will be fundamental to disentangle surface density gaps from gas temperature gaps.

scholarly journals Searching for a kinematic signature of the moderately metal-poor stars in the Milky Way bulge using N-body simulations

2018 ◽  
Vol 615 ◽  
pp. A100 ◽  
Author(s):  
A. Gómez ◽  
P. Di Matteo ◽  
M. Schultheis ◽  
F. Fragkoudi ◽  
M. Haywood ◽  
...  
Keyword(s):  
Milky Way ◽  
Thin Disk ◽  
Secular Evolution ◽  
Thick Disc ◽  
Thin Disc ◽  
The Mean ◽  
The Difference ◽  
Different Origins ◽  
Argos Data ◽  
Internal Evolution

Although there is consensus that metal-rich stars in the Milky Way bulge are formed via secular evolution of the thin disc, the origin of their metal-poor counterparts is still under debate. Two different origins have been invoked for metal-poor stars: they might be classical bulge stars or stars formed via internal evolution of a massive thick disc. We use N-body simulations to calculate the kinematic signature given by the difference in the mean Galactocentric radial velocity (ΔVGC) between metal-rich stars ([Fe/H] ≥ 0) and moderately metal-poor stars (–1.0 ≤ [Fe/H] < 0) in two models, one containing a thin disc and a small classical bulge (B/D = 0.1), and the other containing a thin disc and a massive centrally concentrated thick disc. We reasonably assume that thin-disk stars in each model may be considered as a proxy of metal-rich stars. Similarly, bulge stars and thick-disc stars may be considered as a proxy of metal-poor stars. We calculate ΔVGC at different latitudes (b = 0°, − 2°, − 4°, − 6°, − 8° and − 10°) and longitudes (l = 0°, ± 5°, ± 10° and ± 15°) and show that the ΔVGC trends predicted by the two models are different. We compare the predicted results with ARGOS data and APOGEE DR13 data and show that moderately metal-poor stars are well reproduced with the co-spatial stellar discs model, which has a massive thick disc. Our results give more evidence against the scenario that most of the metal-poor stars are classical bulge stars. If classical bulge stars exists, most of them probably have metallicities [Fe/H] < –1 dex, and their contribution to the mass of the bulge should be a small percentage of the total bulge mass.

scholarly journals The Flying Saucer: Tomography of the thermal and density gas structure of an edge-on protoplanetary disk

2017 ◽  
Vol 607 ◽  
pp. A130 ◽  
Author(s):  
A. Dutrey ◽  
S. Guilloteau ◽  
V. Piétu ◽  
E. Chapillon ◽  
V. Wakelam ◽  
...  
Keyword(s):  
Thermal Structure ◽  
Direct Determination ◽  
Molecular Data ◽  
Temperature Structure ◽  
Gas Temperature ◽  
Star Forming ◽  
Star Forming Regions ◽  
Flying Saucer ◽  
Grain Properties

Context. Determining the gas density and temperature structures of protoplanetary disks is a fundamental task in order to constrain planet formation theories. This is a challenging procedure and most determinations are based on model-dependent assumptions. Aims. We attempt a direct determination of the radial and vertical temperature structure of the Flying Saucer disk, thanks to its favorable inclination of 90 degrees. Methods. We present a method based on the tomographic study of an edge-on disk. Using ALMA, we observe at 0.5″ resolution the Flying Saucer in CO J = 2–1 and CS J = 5–4. This edge-on disk appears in silhouette against the CO J = 2–1 emission from background molecular clouds in ρ Oph. The combination of velocity gradients due to the Keplerian rotation of the disk and intensity variations in the CO background as a function of velocity provide a direct measure of the gas temperature as a function of radius and height above the disk mid-plane. Results. The overall thermal structure is consistent with model predictions, with a cold (<12−15 K) CO-depleted mid-plane and a warmer disk atmosphere. However, we find evidence for CO gas along the mid-plane beyond a radius of about 200 au, coincident with a change of grain properties. Such behavior is expected in the case of efficient rise of UV penetration re-heating the disk and thus allowing CO thermal desorption or favoring direct CO photo-desorption. CO is also detected at up to 3–4 scale heights, while CS is confined to around 1 scale height above the mid-plane. The limits of the method due to finite spatial and spectral resolutions are also discussed. Conclusions. This method appears to be a very promising way to determine the gas structure of planet-forming disks, provided that the molecular data have an angular resolution which is high enough, on the order of 0.3−0.1″ at the distance of the nearest star-forming regions.

The Retrieval of Marine Stratiform Cloud Properties from Multiple Observations in the 3.9-µm Window under Conditions of Varying Solar Illumination

1995 ◽  
Vol 34 (7) ◽  
pp. 1512-1524 ◽  
Author(s):  
Thomas J. Kleespies
Keyword(s):  
Climate Modeling ◽  
Thermal Structure ◽  
Cloud Microphysics ◽  
Time Interval ◽  
Short Time Interval ◽  
Cloud Parameters ◽  
Cloud Properties ◽  
Multiple Observations ◽  
Simplifying Assumptions ◽  
The Difference

Abstract Radiometric observations in the 3.9-µm region have been used by a number of investigators for the determination of cloud parameters or sea surface temperature at night. Only a few attempts have been made to perform quantitative assessments of cloud and surface properties during the daytime because of the inability to distinguish between the thermal and solar components of the satellite-sensed radiances. This paper presents a new method of separating the thermal and solar components of upwelling 3.9-µm radiances. Two collocated satellite observations are made under conditions where the solar illumination angle changes but the thermal structure of the cloud and atmosphere, as well as the cloud microphysics change very little. These conditions can easily be met by observing the same cloud from geosynchoronous orbit over a short time interval during the morning hours. When the radiances are differenced under these constraints, the thermal components cancel, and the difference in the radiances is simply the difference in the solar component. With a few simplifying assumptions, a cloud microphysical property, specifically effective radius, can be inferred. This parameter is of particular importance to both climate modeling and global change studies. The methodology developed in this paper is applied to data from the Visible-Infrared Spin Scan Radiometer Atmospheric Sounder onboard the GOES-7 spacecraft for a period in August 1992.

scholarly journals Interrogation tactics with an interpreter

2021 ◽  
Vol 118 ◽  
pp. 03004
Author(s):  
Sergey Vladimirovich Shvets ◽  
Vladimir Dmitrievich Zelensky ◽  
Svetlana Alexandrovna Kuemzhieva ◽  
Anastasiya Plotskaya
Keyword(s):  
Sharp Decrease ◽  
Point Of View ◽  
Theory And Practice ◽  
Criminal Proceedings ◽  
Linguistic Rights ◽  
Information Interaction ◽  
Lack Of Control ◽  
The Difference ◽  
Transfer Of Information ◽  
Investigation Procedure

In holding an investigation in relation to or with the involvement of persons, who do not know or insufficiently know the language of criminal proceedings, it becomes necessary to involve an interpreter in the crime investigation procedure. However, the contemporary investigative theory and practice take into account only one situation, namely the monolingualism of parties to a criminal proceeding. The situation when the investigator and his/her procedural opponent are fluent in different languages is still overlooked by our today’s researchers. The article examines features of the influence of the need to use an interpreter on the interrogation from the point of view of information interaction between the parties. Within the framework of this research, it was substantiated that during the interrogation involving an interpreter, additional tasks, that are not characteristic of interrogation in its classical sense, arise. The groups of communication features of interrogation with the involvement of an interpreter, generated by the difference in the language system, the lack of control on the part of the investigator over the transfer of information between the interpreter and interrogated person, as well as a sharp decrease in the range of tactical techniques suitable for use, were identified. It is proposed to divide tactical techniques during interrogation involving an interpreter into four groups depending on the need to explain the essence of them to the interpreter, as well as the need to prepare an interpreter to participate in their implementation. The article concludes the influence of an interpreter on the tactics of investigative actions, if necessary, to involve him/her to guarantee the linguistic rights of the parties to criminal proceedings, and also offers recommendations for overcoming the tactical difficulties that arise during interrogation.

scholarly journals Analisis Pengaruh High Pressure Compressor Rotor Clearance Terhadap Exhaus Gas Temperature Margin pada CFM56-7

2021 ◽  
Vol 6 (2) ◽  
pp. 50-55
Author(s):  
Wildan Sofary Darga ◽  
Edy K. Alimin ◽  
Endah Yuniarti
Keyword(s):  
High Pressure ◽  
Engine Performance ◽  
Exhaust Gas ◽  
Gas Temperature ◽  
Compressor Rotor ◽  
High Pressure Compressor ◽  
The Difference ◽  
Gas Turbine Exhaust ◽  
Temperature Margin ◽  
Pressure Compressor

Exhaust Gas Temperatue is an parameter where the hot gases’s temperature leave the gas turbine. Exhaust gas temperature margin is the difference between highest temperature at take off phase with redline on indicator (???????????? ???????????????????????? °????=???????????? ????????????????????????????−???????????? ???????????????? ????????????). EGTM is one of any factor to determine engine performance. A good perfomance of an engine when it has a big margin (EGTM), during operation of an engine the EGTM could decrease untill 0 (zero). So many factors could affect EGTM deteroration there are: distress hardware such as airfoil erosion, leak of an airseals, and increase of clearance between tip balde and shroud. Increase of clearance happens in high pressure compressor rotor clearance. In CFM56-7 have 9 stage(s) of high pressure compressor and each stage give the EGT Loses. The calculation of EGT Effect/Losses is actual celarance – minimum clearance x 1000 x EGT Effect °C, where actual clearance define by the substraction of outside diameter’s rotor with inside diameter’s shroud, minimum clearance define in the manual, 1000 is adjustment from mils/microinch to inch, and EGT Effect is temperature that define in the manual. The analysist had done with 6 (six) engine serial number and proceed by corelation that shown linkage between clearance and EGT Effect, the corelation is strong shown the result of corelation (r) is 0.994275999 or nearest 1.

scholarly journals Influence of grain growth on the thermal structure of protoplanetary discs

2020 ◽  
Vol 640 ◽  
pp. A63 ◽  
Author(s):  
Sofia Savvidou ◽  
Bertram Bitsch ◽  
Michiel Lambrechts
Keyword(s):  
Particle Size ◽  
Grain Size ◽  
Grain Growth ◽  
Thermal Structure ◽  
Size Composition ◽  
Size Distributions ◽  
Migration Rates ◽  
Grain Size Distributions ◽  
Hydrodynamical Simulations ◽  
Protoplanetary Discs

The thermal structure of a protoplanetary disc is regulated by the opacity that dust grains provide. However, previous works have often considered simplified prescriptions for the dust opacity in hydrodynamical disc simulations, for example, by considering only a single particle size. In the present work, we perform 2D hydrodynamical simulations of protoplanetary discs where the opacity is self-consistently calculated for the dust population, taking into account the particle size, composition, and abundance. We first compared simulations utilizing single grain sizes to two different multi-grain size distributions at different levels of turbulence strengths, parameterized through the α-viscosity, and different gas surface densities. Assuming a single dust size leads to inaccurate calculations of the thermal structure of discs, because the grain size dominating the opacity increases with orbital radius. Overall the two grain size distributions, one limited by fragmentation only and the other determined from a more complete fragmentation-coagulation equilibrium, give comparable results for the thermal structure. We find that both grain size distributions give less steep opacity gradients that result in less steep aspect ratio gradients, in comparison to discs with only micrometer-sized dust. Moreover, in the discs with a grain size distribution, the innermost (<5 AU) outward migration region is removed and planets embedded in such discs experience lower migration rates. We also investigated the dependency of the water iceline position on the alpha-viscosity (α), the initial gas surface density (Σg,0) at 1 AU and the dust-to-gas ratio (fDG) and find rice ∝ α0.61Σg,00.8fDG0.37 independently of the distribution used in the disc. The inclusion of the feedback loop between grain growth, opacities, and disc thermodynamics allows for more self-consistent simulations of accretion discs and planet formation.

scholarly journals Thermal Characteristics of Positive Leaders under Different Electrode Terminals in a Long Air Gap

Energies ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 4024 ◽  
Author(s):  
Du ◽  
Tang ◽  
Li ◽  
Zou ◽  
Ma ◽  
...  
Keyword(s):  
High Speed ◽  
Thermal Characteristics ◽  
Video Camera ◽  
Air Gap ◽  
Radius Of Curvature ◽  
Gas Temperature ◽  
Gas Density ◽  
Interference Fringes ◽  
High Speed Video Camera ◽  
The Difference

The thermal characteristics of the positive leader discharges occurring under the different electrode terminals in a 1 m rod-plate air gap were studied quantitatively using Mach–Zehnder interferometry and a high-speed video camera. When disturbed by the discharge channel, the interference fringes are distorted because of the change in the refractive index of air, which is related to the gas density. Therefore, the gas temperature and gas density distribution in the leader channel can be retrieved from the offset of the interference fringes. Based on these results, the thermal characteristics of the leader channel were studied under different electrode terminals with a radius of curvature of 2.5 mm and 5 mm for cone electrodes and a diameter of 40 mm for a spherical electrode. The results show that the gas temperature in the leader channel increased while the gas density decreased as the radius of curvature of the electrode terminal decreased. Additionally, a smaller radius of curvature leads to a larger thermal diameter, but the difference in the thermal diameter is not obvious; for the terminals used in this paper, the difference is within 2 mm.

scholarly journals The time evolution of dusty protoplanetary disc radii: observed and physical radii differ

2019 ◽  
Vol 486 (4) ◽  
pp. 4829-4844 ◽  
Author(s):  
Giovanni P Rosotti ◽  
Marco Tazzari ◽  
Richard A Booth ◽  
Leonardo Testi ◽  
Giuseppe Lodato ◽  
...  
Keyword(s):  
Outer Part ◽  
Theoretical Models ◽  
Outer Edge ◽  
Continuum Emission ◽  
Multiple Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
Dust Distribution ◽  
Dust Grain ◽  
Dust Grain Growth

ABSTRACT Protoplanetary disc surveys conducted with Atacama Large Millimetre Array (ALMA) are measuring disc radii in multiple star-forming regions. The disc radius is a fundamental quantity to diagnose whether discs undergo viscous spreading, discriminating between viscosity or angular momentum removal by winds as drivers of disc evolution. Observationally, however, the sub-mm continuum emission is dominated by the dust, which also drifts inwards, complicating the picture. In this paper we investigate, using theoretical models of dust grain growth and radial drift, how the radii of dusty viscous protoplanetary discs evolve with time. Despite the existence of a sharp outer edge in the dust distribution, we find that the radius enclosing most of the dust mass increases with time, closely following the evolution of the gas radius. This behaviour arises because, although dust initially grows and drifts rapidly on to the star, the residual dust retained on Myr time-scales is relatively well coupled to the gas. Observing the expansion of the dust disc requires using definitions based on high fractions of the disc flux (e.g. 95 per cent) and very long integrations with ALMA, because the dust grains in the outer part of the disc are small and have a low sub-mm opacity. We show that existing surveys lack the sensitivity to detect viscous spreading. The disc radii they measure do not trace the mass radius or the sharp outer edge in the dust distribution, but the outer limit of where the grains have significant sub-mm opacity. We predict that these observed radii should shrink with time.

Magnetic Accretion Funnels in Young Stellar Objects: Thermal Structure and Emission Signatures

1997 ◽  
Vol 163 ◽  
pp. 760-760
Author(s):  
Steven C. Martin ◽  
Arieh Königl
Keyword(s):  
Magnetic Field ◽  
Near Infrared ◽  
Thermal Structure ◽  
Line Emission ◽  
Young Stellar Objects ◽  
Rate Equations ◽  
Gas Temperature ◽  
Ionization State ◽  
Object A ◽  
T Tauri

AbstractA self-consistent procedure is outlined for determining the thermal structure of gas inflowing along magnetic field lines of a young stellar object. A young pre-main-sequence star (e.g., a classical T Tauri star) is assumed to possess a dipole magnetic field that disrupts a geometrically thin accretion disk and channels the incoming gas toward the stellar surface, leading to the formation of a pair of accretion funnels that terminate in shocks at high stellar latitudes. The heat equation is solved together with the rate equations for hydrogen, and the main physical processes that heat and cool the gas are identified. In particular, in the case of T Tauri stars, it is found that adiabatic compression is the principal heat source and that the Ca II and Mg II ions act as a powerful thermostat that regulates the gas temperature. The ionization state of the gas in the radiation field of the stellar photosphere and of the accretion shocks is found in this case to be controlled by Balmer continuum photons. The implications of these calculations to the observational signatures of accreting YSOs (e.g., their near-infrared hydrogen and CO overtone line emission) are discussed.

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