From cosmological initial conditions to primordial protostellar cloud cores

1999 ◽  
Author(s):  
Michael L. Norman ◽  
Tom Abel ◽  
Greg Bryan
Keyword(s):  
Initial Conditions ◽  
Protostellar Cloud ◽  
Cloud Cores

scholarly journals The Structure of Cold Molecular Cloud Cores

2004 ◽  
Vol 221 ◽  
pp. 43-50
Author(s):  
D. Ward-Thompson ◽  
D. J. Nutter ◽  
J. M. Kirk ◽  
P. André
Keyword(s):  
Molecular Cloud ◽  
Initial Conditions ◽  
Current Knowledge ◽  
Current Debate ◽  
Core Density ◽  
Density Profiles ◽  
Cloud Cores ◽  
Protostellar Collapse ◽  
The Magnetic Field ◽  
Equilibrium Status

A brief summary is presented of our current knowledge of the structure of cold molecular cloud cores that do not contain protostars, sometimes known as starless cores. The most centrally condensed starless cores are known as pre-stellar cores. These cores probably represent observationally the initial conditions for protostellar collapse that must be input into all models of star formation. The current debate over the nature of core density profiles is summarised. A cautionary note is sounded over the use of such profiles to ascertain the equilibrium status of cores. The magnetic field structure of pre-stellar cores is also briefly discussed.

scholarly journals Dust emission from star forming clouds: a progress report

1991 ◽  
Vol 147 ◽  
pp. 245-257
Author(s):  
P. G. Mezger ◽  
A. Sievers ◽  
R. Zylka
Keyword(s):  
Angular Momentum ◽  
Accretion Disks ◽  
Physical State ◽  
Initial Conditions ◽  
Dust Emission ◽  
Progress Report ◽  
Mass Star ◽  
Star Forming ◽  
Low Mass ◽  
Cloud Cores

Model computations of protostellar evolution depend very strongly on the initial conditions: Fragmentation of massive cloud cores or coagulation of substellar condensations, the physical state of gas and dust (e.g. the formation of ice-mantles and grain coagulation), the presence of magnetic fields and its effect on gas and dust, and the formation of accretion disks as a consequence of an initial angular momentum of the protostellar condensation. The MPIfR bolometer group together with the molecular spectroscopists R. Mauersberger and T.L. Wilson have embarked on a program aimed at the exploration of the earliest evolutionary stages of high- and low-mass star formation. Here follows a brief progress report.

scholarly journals Accretion bursts in low-metallicity protostellar disks

2020 ◽  
Vol 641 ◽  
pp. A72
Author(s):  
Eduard I. Vorobyov ◽  
Vardan G. Elbakyan ◽  
Kazuyuki Omukai ◽  
Takashi Hosokawa ◽  
Ryoki Matsukoba ◽  
...  
Keyword(s):  
Initial Conditions ◽  
Gravitational Instability ◽  
Mass Loading ◽  
Protostellar Disks ◽  
Numerical Hydrodynamics ◽  
Accretion Rates ◽  
Solar Metallicity ◽  
Disk Evolution ◽  
Low Metallicity ◽  
Cloud Cores

Aims. The early evolution of protostellar disks with metallicities in the Z = 1.0 − 0.01 Z⊙ range was studied with a particular emphasis on the strength of gravitational instability and the nature of protostellar accretion in low-metallicity systems. Methods. Numerical hydrodynamics simulations in the thin-disk limit were employed that feature separate gas and dust temperatures, and disk mass-loading from the infalling parent cloud cores. Models with cloud cores of similar initial mass and rotation pattern but distinct metallicity were considered to distinguish the effect of metallicity from that of the initial conditions. Results. The early stages of disk evolution in low-metallicity models are characterized by vigorous gravitational instability and fragmentation. Disk instability is sustained by continual mass-loading from the collapsing core. The time period that is covered by this unstable stage is much shorter in the Z = 0.01 Z⊙ models than in their higher metallicity counterparts thanks to the higher rates of mass infall caused by higher gas temperatures (which decouple from lower dust temperatures) in the inner parts of collapsing cores. Protostellar accretion rates are highly variable in the low-metallicity models reflecting the highly dynamic nature of the corresponding protostellar disks. The low-metallicity systems feature short but energetic episodes of mass accretion caused by infall of inward-migrating gaseous clumps that form via gravitational fragmentation of protostellar disks. These bursts seem to be more numerous and last longer in the Z = 0.1 Z⊙ models than in the Z = 0.01 Z⊙ case. Conclusions. Variable protostellar accretion with episodic bursts is not a particular feature of solar metallicity disks. It is also inherent to gravitationally unstable disks with metallicities up to 100 times lower than solar.

scholarly journals Impact of Magnetic Fields on Fragmentation

2001 ◽  
Vol 200 ◽  
pp. 371-380 ◽  
Author(s):  
Alan P. Boss
Keyword(s):  
Magnetic Fields ◽  
Molecular Clouds ◽  
Initial Conditions ◽  
Three Dimensional ◽  
Obvious Effect ◽  
Multiple Stars ◽  
Dense Molecular Cloud ◽  
Three Dimensional Models ◽  
Cloud Cores ◽  
Collapse Phase

Fragmentation is the leading explanation for the formation of binary and multiple stars. However, nearly all three dimensional calculations of the collapse and fragmentation of dense molecular cloud cores have ignored the effects of magnetic fields, whereas magnetic fields are generally regarded to be a dominant force in molecular clouds. Three dimensional models of the collapse of clouds with frozen-in magnetic fields have shown that such clouds cannot fragment for a range of initial conditions. However, calculations that allow for magnetic field loss by am-bipolar diffusion have shown that fragmentation is possible for initially prolate or oblate, rotating, magnetically-supported cloud cores. The latter calculations rely on approximations that should be verified by more detailed, traditional magnetohydrodynamical codes. The most obvious effect of magnetic fields is to delay the onset of the collapse phase, but once collapse begins in earnest, fragmentation proceeds in much the same manner as in nonmagnetic clouds, with initially prolate clouds tending to form binary protostars, and with initially oblate clouds tending to form multiple protostars.

scholarly journals Dust emission from star forming clouds: a progress report

1991 ◽  
Vol 147 ◽  
pp. 245-257 ◽  
Author(s):  
P. G. Mezger ◽  
A. Sievers ◽  
R. Zylka
Keyword(s):  
Angular Momentum ◽  
Accretion Disks ◽  
Physical State ◽  
Initial Conditions ◽  
Dust Emission ◽  
Progress Report ◽  
Mass Star ◽  
Star Forming ◽  
Low Mass ◽  
Cloud Cores

Model computations of protostellar evolution depend very strongly on the initial conditions: Fragmentation of massive cloud cores or coagulation of substellar condensations, the physical state of gas and dust (e.g. the formation of ice-mantles and grain coagulation), the presence of magnetic fields and its effect on gas and dust, and the formation of accretion disks as a consequence of an initial angular momentum of the protostellar condensation. The MPIfR bolometer group together with the molecular spectroscopists R. Mauersberger and T.L. Wilson have embarked on a program aimed at the exploration of the earliest evolutionary stages of high- and low-mass star formation. Here follows a brief progress report.

Sebuah Generalisasi Baru Barisan Fibonacci-Lucas

2019 ◽  
Vol 2 (2) ◽  
Author(s):  
Musraini M Musraini M ◽  
Rustam Efendi ◽  
Rolan Pane ◽  
Endang Lily
Keyword(s):  
Recurrence Relation ◽  
Initial Conditions ◽  
Lucas Sequence ◽  
Binet’S Formula

Barisan Fibonacci dan Lucas telah digeneralisasi dalam banyak cara, beberapa dengan mempertahankan kondisi awal, dan lainnya dengan mempertahankan relasi rekurensi. Makalah ini menyajikan sebuah generalisasi baru barisan Fibonacci-Lucas yang didefinisikan oleh relasi rekurensi B_n=B_(n-1)+B_(n-2),n≥2 , B_0=2b,B_1=s dengan b dan s bilangan bulat  tak negatif. Selanjutnya, beberapa identitas dihasilkan dan diturunkan menggunakan formula Binet dan metode sederhana lainnya. Juga dibahas beberapa identitas dalam bentuk determinan.   The Fibonacci and Lucas sequence has been generalized in many ways, some by preserving the initial conditions, and others by preserving the recurrence relation. In this paper, a new generalization of Fibonacci-Lucas sequence is introduced and defined by the recurrence relation B_n=B_(n-1)+B_(n-2),n≥2, with ,  B_0=2b,B_1=s                          where b and s are non negative integers. Further, some identities are generated and derived by Binet’s formula and other simple methods. Also some determinant identities are discussed.

Meningkatkan Kemampuan Guru dalam Menerapkan Model Pembelajaran Problem Centered Learning Melalui Focus Group Discission di Sekolah Dasar Negeri 187/X Bangun Karya Tahun 2019/2020

2020 ◽  
Vol 10 (1) ◽  
pp. 86
Author(s):  
Mujiem Mujiem
Keyword(s):  
Elementary School ◽  
Action Research ◽  
Focus Group ◽  
Initial Conditions ◽  
Learning Model ◽  
Class Action ◽  
Learning Activities ◽  
Implementation Phase ◽  
The Subject ◽  
Academic Year

This research is a classroom action research that aims to improve the ability of teachers to apply the problem centered learning model of learning in the Elementary School 187/ X Bangun Karya, Academic Year 2019/2020. The subject of this study was a teacher at 187 / X Bangun Karya Elementary School, Rantau Rasau District, Tanjung Jabung Timur District, Jambi Province. This class action research was carried out in two cycles, each cycle consisting of two meetings. The results of the evaluation are converted into a recapitulation table of the results of cycle I. The conversion results state that the research has not yet reached the target, it needs to be continued with cycle II. The results of observers in the implementation phase of the second cycle showed that all parts of the learning activities were going well, so that there were no more parts of the learning activities that needed to be improved. While the results of the second cycle are converted with the results of the recapitulation table states that the study has reached the target limit of completeness criteria in the first cycle that is equal to 50% and an average of 68.7 in the initial conditions of improvement in the second cycle completeness criteria to be 100% and the average namely 91.7 states that the Focus Group Discission can improve the ability of teachers to apply the Problem Centered Learning learning model in learning in 187 / X Public Elementary School Build Work Year 2019/2020.

Dynamics of the macromolecular composition of the biomass of microalgae in the morning under natural light. Model

2020 ◽  
pp. 45-52
Author(s):  
Alexander S. Lelekov ◽  
Anton V. Shiryaev
Keyword(s):  
Biochemical Composition ◽  
Initial Conditions ◽  
Natural Light ◽  
Photoautotrophic Growth ◽  
Structural Part ◽  
Basic Model ◽  
Microalgae Culture ◽  
Simulation Results ◽  
Structural Parts ◽  
Macromolecular Composition

The work is devoted to modeling the growth of optically dense microalgae cultures in natural light. The basic model is based on the idea of the two-stage photoautotrophic growth of microalgae. It is shown that the increase in the intensity of sunlight in the first half of the day can be described by a linear equation. Analytical equations for the growth of biomass of microalgae and its macromolecular components are obtained. As the initial conditions, it is assumed that at the time of sunrise, the concentration of reserve biomass compounds is zero. The simulation results show that after sunrise, the growth of the microalgae culture is due only to an increase in the reserve part of the biomass, while the structural part practically does not change over six hours. Changes in the ratio of the reserve and structural parts of the biomass indicate a change in the biochemical composition of cells.

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